Tehran, Iran

Sharif University of Technology is a public research university in Tehran, Iran known traditionally to be first choice of top ranked Iranian high school and university students in engineering and physical science. The university is located in the Tarasht neighborhood of Tehran within close proximity of Azadi Square, and also has an international campus in Kish, a resort island in the Persian Gulf.Established in 1966, it was formerly named the Aryamehr University of Technology and for a short period after the 1979 revolution, the university was called Tehran University of Technology. Following the revolution the university was named after Majid Sharif Vaghefi, a former student who was killed in 1975.Today, the university provides both undergraduate and graduate programs in 15 main departments. The student body consists of about 6,000 undergraduate students and 4,700 graduate students from all the 30 provinces of Iran. Funding for Sharif University is provided by the government and through private funding. Undergraduate admission to Sharif is limited to the top 1 percent of students who pass the national entrance examination administered annually by the Iranian Ministry of Science, Research and Technology.In the 2013 Academic Ranking of World Universities Engineering/Technology and Computer science rankings, SUT is ranked 5th in the Middle East. It is in the top 251-275 universities in the world and 37th in Asia in the 2014 Times Higher Education World University Rankings. SUT also ranked 1st in the Middle East, 6th in Asia, and 27th in the world in Times Higher Education's top 100 universities under 50. Wikipedia.


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Hariri A.,Sharif University of Technology | Babaie-Zadeh M.,Sharif University of Technology
Signal Processing | Year: 2017

The main motivation behind compressive sensing is to reduce the sampling rate at the input of a digital signal processing system. However, if for processing the sensed signal one requires to reconstruct the corresponding Nyquist samples, then the data rate will be again high in the processing stages of the overall system. Therefore, it is preferred that the desired processing task is done directly on the compressive measurements, without the need for the reconstruction of the Nyquist samples. This paper addresses the case in which the processing task is “detection” (the existence) of a sparse signal in additive white Gaussian noise, with applications e.g. in radar systems. Moreover, we will propose two estimators for estimating the degree of sparsity of the detected signal. We will show that one of the estimators attains the Cramér–Rao lower bound of the problem. © 2016 Elsevier B.V.


Hadi M.,Sharif University of Technology | Pakravan M.R.,Sharif University of Technology
IEEE Photonics Journal | Year: 2017

Spectrum conversion can improve the performance of orthogonal frequency division multiplexing (OFDM)-based elastic optical networks (EONs) by relaxing the continuity constraint and consequently reducing connection request blocking probability during routing and spectrum assignment process. We propose three different architectures for including spectrum conversion capability in bandwidth-variable wavelength cross-connects (BVWXCs). To compare the capability of the introduced architectures, we develop an analytical method for computing average connection request blocking probability in a spectrum-convertible OFDM-based EON in which all, part, or none of the BVWXCs can convert the spectrum. An algorithm for distributing a limited number of spectrum-convertible bandwidth-variable wavelength cross-connects (SCBVWXCs) in an OFDM-based EON is also proposed. Finally, we use simulation results to evaluate the accuracy of the proposed method for calculating connection request blocking probability and the capability of the introduced algorithm for SCBVWXC placement. © 2017 IEEE.


Alizadeh A.,Sharif University of Technology | Medi A.,Sharif University of Technology
IEEE Transactions on Microwave Theory and Techniques | Year: 2017

This paper presents the design and implementation of a distributed class-J power amplifier (DJPA) in a 0.25-μm AlGaAs-InGaAs pHEMT technology. Class-J mode of operation is introduced in design of distributed power amplifiers (DPAs) to achieve high power added efficiencies (PAEs) over wide frequency ranges. Extensive load-pull (LP) and source-pull (SP) simulations are performed to show that class-J PAs are less sensitive to proper termination of higher order harmonics, and high PAE and output power can be obtained even if the second, third, fourth, and fifth harmonics comprise a real impedance. This is essential in DPAs as the higher order harmonics of the frequencies at lower side of the band may fall in the desired bandwidth. Based on LP and SP observations, a proof-of-concept 1.5-10-GHz monolithic microwave integrated circuit DJPA is designed and fabricated. Chip dimensions are 2.15 × 2.15 mm2, and 29-30.7-dBm output power with 33-44% PAE is achieved over the frequency range. The large-signal power gain is greater than 10 dB while the PA maintains an average small-signal gain of 13 dB over the bandwidth. © 2016 IEEE.


Darbandi M.,Sharif University of Technology | Ghafourizadeh M.,Sharif University of Technology
Journal of Heat Transfer | Year: 2017

This work numerically studies the effects of inlet air and fuel turbulators on the thermal behavior of a combustor burning the jet propulsion (JP) (kerosene-surrogate) fuel and its resulting pollutants emission including the nanoparticulate soot aerosols and aromatic compounds. To model the soot formation, the method employs a semi-empirical two-equation model, in which the transport equations for soot mass fraction and soot number density are solved considering soot nanoparticles evolutionary process. The soot nucleation is described using the phenyl route in which the soot is formed from the polycyclic aromatic hydrocarbons. Incorporating a detailed chemical mechanism described by 200 species and 6907 elementary reactions, the flamelets and their lookup table library are precomputed and used in the context of steady laminar flamelet model (SLFM). Thus, the current finite-volume method solves the transport equations for the mean mixture fraction and its variance and considers the chemistry-turbulence interaction using the presumed-shape probability density functions (PDFs). To validate the utilized models, a benchmark combustor is first simulated, and the results are compared with the measurements. Second, the numerical method is used to investigate the effects of embedding different inflow turbulators on the resulting flame structure and the combustor pollutants emission. The chosen turbulators produce mild to severe turbulence intensity (TI) effects at the air and fuel inlets. Generally, the results of current study indicate that the use of suitable turbulators can considerably affect the thermal behavior of a JP-fueled combustor. Additionally, it also reduces the combustor polycyclic aromatic hydrocarbon (PAH) pollutants emission. Copyright © 2017 by ASME.


Shodja H.M.,Sharif University of Technology | Alemi B.,Sharif University of Technology
Composites Part B: Engineering | Year: 2017

Nowadays, by adding a small amount (about 0.5–5% by weight) of a desired nanomaterial to a matrix having certain properties one may design a multifunctional nanocomposites with a remarkably improved macroscopic properties of interest. The capability of conventional continuum theories in treating the problems of embedded ultra-small inhomogeneity with any of its dimensions comparable to the characteristic lengths of the involved constituent phases is questioned, mainly, on the grounds of the accuracy and the size effect. The micromechanical framework based on the Eshelby's ellipsoidal inclusion theory [1] which has been widely used to estimate the overall behavior of composites falls under the same category, as is size insensitive. In this work, effort is directed at the prediction of the macroscopic shear modulus of composites consisting of nano-/micro-size fibers of elliptic cross-sections via couple stress theory, a physically realistic theory that encompasses the size effect. To this end, the fundamental equations of couple stress elasticity in elliptic coordinates are derived and several fundamental elliptic inhomogeneity problems in plane couple stress elasticity are solved analytically. For the purpose of the application of these results to the study of the effective properties of the composites of interest, Mori and Tanaka theory [2] is first reformulated in the mathematical framework of couple stress theory. Subsequently, the overall shear modulus of solids reinforced by aligned as well as randomly oriented elliptic nanofibers will be predicted. The influences of the size, shape, orientation, rigidity, and intrinsic length of the reinforcing nanofibers as well as the effects of the characteristic length of the matrix on the effective shear modulus of the composite are addressed. © 2017 Elsevier Ltd


Feizabadi M.,Sharif University of Technology | Jahromi A.E.,Sharif University of Technology
Reliability Engineering and System Safety | Year: 2017

In discussions related to reliability optimization using redundancy allocation, one of the structures that has attracted the attention of many researchers, is series-parallel structure. In models previously presented for reliability optimization of series-parallel systems, there is a restricting assumption based on which all components of a subsystem must be homogeneous. This constraint limits system designers in selecting components and prevents achieving higher levels of reliability. In this paper, a new model is proposed for reliability optimization of series-parallel systems, which makes possible the use of non-homogeneous components in each subsystem. As a result of this flexibility, the process of supplying system components will be easier. To solve the proposed model, since the redundancy allocation problem (RAP) belongs to the NP-hard class of optimization problems, a genetic algorithm (GA) is developed. The computational results of the designed GA are indicative of high performance of the proposed model in increasing system reliability and decreasing costs. © 2016 Elsevier Ltd


Sahabmanesh A.,Sharif University of Technology | Saboohi Y.,Sharif University of Technology
Energy Policy | Year: 2017

Sustainable economic growth and improvement of the social welfare depend upon the sufficient supply of energy resources, while the utilization of energy resources is one of the main factors of environmental degradation. This research is involved with development of a sustainable energy system model and a new method for sustainability assessment. This model represents the flow of energy from primary resources through processing, conversion, and end-use technologies in an optimization framework where the useful energy demand in various social and economic sectors is met. The impact of energy supply and consumption chain on the environment at each level of energy system is also embedded in the model structure. A multi-criteria analysis of changes is then applied and sustainable development indices of the whole system are concluded. Finally, effects of the energy subsidy policy and high economic growth rate on sustainability of the energy system in three scenarios are analyzed. Results demonstrate that energy subsidy decelerates the improvement rate of the total sustainability index. Also, when a high economic growth is accompanied with the energy subsidy this index reduces considerably. Results show that how penetration of renewable energy potentials changes the sustainability situation of energy systems. © 2017


Abam M.A.,Sharif University of Technology
Algorithmica | Year: 2017

Let (Formula presented.) be a set of n points inside a polygonal domain (Formula presented.). A polygonal domain with h holes (or obstacles) consists of h disjoint polygonal obstacles surrounded by a simple polygon which itself acts as an obstacle. We first study t-spanners for the set (Formula presented.) with respect to the geodesic distance function (Formula presented.) where for any two points p and q, (Formula presented.) is equal to the Euclidean length of the shortest path from p to q that avoids the obstacles interiors. For a case where the polygonal domain is a simple polygon (i.e., (Formula presented.)), we construct a ((Formula presented.))-spanner that has (Formula presented.) edges. For a case where there are h holes, our construction gives a ((Formula presented.))-spanner with the size of (Formula presented.). Moreover, we study t-spanners for the visibility graph of (Formula presented.) ((Formula presented.), for short) with respect to a hole-free polygonal domain (Formula presented.). The graph (Formula presented.) is not necessarily a complete graph or even connected. In this case, we propose an algorithm that constructs a ((Formula presented.))-spanner of size (Formula presented.) for some (Formula presented.). In addition, we show that there is a set (Formula presented.) of n points such that any (Formula presented.)-spanner of (Formula presented.) must contain (Formula presented.) edges. © 2017 Springer Science+Business Media New York


Beigi S.,Institute for Research in Fundamental Sciences | Etesami O.,Institute for Research in Fundamental Sciences | Gohari A.,Sharif University of Technology
SIAM Journal on Computing | Year: 2017

A Santha-Vazirani (SV) source is a sequence of random bits where the conditional distribution of each bit, given the previous bits, can be partially controlled by an adversary. Santha and Vazirani show that deterministic randomness extraction from these sources is impossible. In this paper, we study the generalization of SV sources for nonbinary sequences. We show that unlike the binary setup of Santha and Vazirani, deterministic randomness extraction in the generalized case is sometimes possible. In particular, if the adversary has access to s "nondegenerate" dice that are c-sided and can choose one die to throw based on the previous realizations of the dice, then deterministic randomness extraction is possible if s < c. We present a necessary condition and a sufficient condition for the possibility of deterministic randomness extraction. These two conditions complement each other in the nondegenerate cases. Next, we turn to a distributed setting. In this setting the SV source consists of a random sequence of pairs (a1; b1); (a2; b2),... distributed between two parties, where the first party receives ai's and the second one receives bi's. The goal of the two parties is to extract common randomness without communication. Using the notion of maximal correlation, we prove a necessary condition and a sufficient condition for the possibility of common randomness extraction from these sources. Based on these two conditions, the problem of common randomness extraction essentially reduces to the problem of randomness extraction from (nondistributed) SV sources. This result generalizes results of Gács and Körner, and Witsenhausen about common randomness extraction from independently and identically distributed sources to adversarial sources. © 2017 Society for Industrial and Applied Mathematics.


Mohammad Hasany R.,Sharif University of Technology | Shafahi Y.,Sharif University of Technology
Computers and Industrial Engineering | Year: 2017

The railroad blocking problem is classified in the tactical level of freight rail transportation problems. The objective of this problem is to determine the optimal paths for each shipment such that the railway limitations are satisfied. In this problem, the quantities of both demand and supply resource indicators are often assumed to be certain and known, but because a blocking solution is designed for a relatively long period of time, this assumption is not reasonable. In this paper, we have developed a two-stage stochastic program for this problem to consider the uncertainty inherent in demand and supply resource indicators. Due to the size and complexity of the stochastic program and the impossibility of using commercial software in even the simplest instances, two solution methods have been proposed. The first method developed is based on the L-Shaped method, and the second method is a modification of the first one that uses a new initial solution (which is obtained by adapting a side optimization model) together with the L-Shaped method. Extensive experiments on test networks show that the two methods outperform the commercial software and that the second method is superior to the first one. We finally present the application of the uncertain model and the computational results of the second method for the Railways of Iran as a real-size example, and we show that the application of the stochastic model could reduce total cost by more than 12 million dollars per three-month horizon compared with the deterministic solution. © 2017


Mehri M.,Sharif University of Technology | Asadi H.,University of Alberta | Asadi H.,Amirkabir University of Technology | Kouchakzadeh M.A.,Sharif University of Technology
Computer Methods in Applied Mechanics and Engineering | Year: 2017

As a first endeavor, the aeroelastic responses of functionally graded carbon nanotube reinforced composite (FG-CNTRC) truncated conical curved panels subjected to aerodynamic load and axial compression are investigated. The nonlinear dynamic equations of FG-CNTRC conical curved panels are derived according to Green's strains and the Novozhilov nonlinear shell theory. The aerodynamic load is estimated in accordance with the quasi-steady Krumhaar's modified supersonic piston theory by taking into account the effect of the panel curvature. Matrix transform method along with the harmonic differential quadrature method (HDQM) are employed to solve the nonlinear equations of motion of the FG-CNTRC truncated conical curved panel. The advantage of the matrix transform method is that we only need to discretize the meridional direction. Effects of semi-vertex angle of the cone, subtended angle of the panel, boundary conditions, geometrical parameters, volume fraction and distribution of CNT, and Mach number on the aeroelastic characteristics of the FG-CNTRC conical curved panel are put into evidence via a set of parametric studies and pertinent conclusions are outlined. The results prove that the panels with different FG distributions have different critical dynamic pressure. It is found that the semi-vertex and subtended angles play a pivotal role in changing the critical circumferential mode number of the flutter instability. Besides, the research shows that the superb efficiency of proposed method with few grid points, which requires less CPU time, are attributed to the matrix transform method and the higher-order harmonic approximation function in the HDQM. © 2017 Elsevier B.V.


Zargarnezhad H.,Sharif University of Technology | Dolati A.,Sharif University of Technology
Electrochimica Acta | Year: 2017

A 3D continuum code coupled with a kinetic Monte Carlo module has been developed for the simulation of Ni electrocrystallization in the initial stages of nucleation and growth. Mass transfer in solution was controlled by a finite-difference code which is distributed over an irregular nanoscale grid system in vertical direction to the substrate. Deposition events such as surface diffusion, chemisorption and crystallization in the system were considered in a KMC module that processes the output of a diffusion-controlled scheme in probability functions to model electrodeposition process on surface. Electrochemical data of this simulation was simultaneously generated according to analytical electrochemical equations to study nucleation and growth mechanism. In spite of minor dissimilarities at current transient coordinates, a reasonable agreement could be noticed between electroanalytical simulation data and experimental results, both of which showed that under presumed conditions nickel electrodeposition is prone to a progressive nucleation mechanism at initial seconds. A similar result has been achieved from the juxtaposition of experimental morphological studies and simulated snapshots. It was found that a balance between surface diffusion and charge transfer reaction rate is a critical factor in dominant nucleation mechanism and deviation from the equilibrium could remarkably alter the nucleation regime and also nanostructure of the deposit. © 2017


Naseri N.,Sharif University of Technology
Journal of Alloys and Compounds | Year: 2017

Providing solar hydrogen as a clean energy resource is one of the human challenges for future. Controlling oxygen vacancies as well as surface morphology in metal oxide semiconductors enables developing PEC H2 production in some understood ways. Here, the influence of simple change in annealing atmosphere, air and pure oxygen, on photoresponse of nanocrystalline WO3 has been studied completely. Results revealed that such slight change in annealing procedure increases effective surface interface and donor density by 77 and 72%, respectively. These effects and also retarding recombination of photogenerated electro-hole pair resulted in photocurrent enhancement under solar like illumination more than three times. © 2016 Elsevier B.V.


FERDOWSI A.,Sharif University of Technology | YOOZBASHIZADEH H.,Sharif University of Technology
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2017

The leaching of rare earth elements (REEs) including cerium, lanthanum and neodymium from apatite concentrate obtained from iron ore wastes by nitric acid was studied. The effects of nitric acid concentration, solid to liquid ratio and leaching time on the recoveries of Ce, La and Nd were investigated using response surface methodology. The results showed that the acid concentration and solid to liquid ratio have significant effect on the leaching recoveries while the time has a little effect. The maximum REE leaching recoveries of 66.1%, 56.8% and 51.7% for Ce, La and Nd, respectively were achieved at the optimum leaching condition with 18% nitric acid concentration, 0.06 solid to liquid ratio and 38 min leaching time. The kinetics of cerium leaching was investigated using shrinking core model. It was observed that the leaching is composed of two stages. In the first stage a sharp increase in cerium leaching recovery was observed and at the longer time the leaching became slower. It was found that in the first stage the diffusion of reactants from ash layer is the rate controlling mechanism with an apparent activation energy of 6.54 kJ/mol, while in the second stage the mass transfer in the solution is the controlling mechanism. © 2017 The Nonferrous Metals Society of China


Mirabedin S.M.,Sharif University of Technology | Farhadi F.,Sharif University of Technology
International Journal of Refrigeration | Year: 2017

According to some experimental observations, water droplet with high initial temperature freezes faster than a cold one. There are some explanations to this problem such as sub-cooling, evaporation and radiation. In this work, solidification process of single droplets with and without the effect of evaporation is numerically investigated for three different drop diameters and initial temperatures. It seems that evaporation itself is able to explain why hot water freezes faster than cold water. © 2016 Elsevier Ltd and IIR


Soltani N.,Sharif University of Technology | Gholami M.R.,Sharif University of Technology
ChemPhysChem | Year: 2017

Fibrillation of amyloid beta (Aβ) peptide is the hallmark of Alzheimer's disease. Given that interactions at the bio–nano interface affect the fibrillation tendency of this peptide, an understanding of the interactions at Aβ peptide–inorganic surfaces on the microscopic level can help to determine the possible neurotoxicity of nanoparticles. Here, the interactions between a fibril-forming peptide, Aβ25–35, and (111) and (100) facets of gold and silver surfaces have been studied by conducting atomistic molecular dynamics simulations. The obtained results indicate that the adsorption onto gold and silver surfaces force the peptide into the β-sheet-rich conformations, which is prone to aggregation, suggesting a new mechanism for the acceleration of fibril formation upon interaction with nanoparticles. To quantify the β-sheet content for a single peptide, a new metrics based on the Ramachandran probability distribution is introduced. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim


Mohebbi M.S.,University of Qom | Akbarzadeh A.,Sharif University of Technology
International Journal of Plasticity | Year: 2017

Strain rate sensitivity (m-value) of ultrafine grain (UFG) AA 1050 and AA 5052 sheets processed by accumulative roll-bonding is investigated versus strain rate by stress relaxation (SR) test at ambient temperature. The results show a weak viscous nature of deformation for AA 5052 specimens as compared to AA 1050 ones. So that much less stress relaxation and negligible strain rate sensitivity are obtained for this material due to dislocation and grain boundary mobility limitation caused by Mg solute atoms. In order to formulate strain rate sensitivity of UFG aluminum as a function of strain rate, three phenomenological and two empirical models are developed and assessed by the experimental results. It is shown that since thermally activated dislocation glide is not the single governing phenomenon, the model developed based on this mechanism of deformation fails to predict the variation of m-value by strain rate. Contribution of grain boundary sliding (GBS) can result in a model fitted on the experimental results at lower strain rates, yet not suitable for higher strain rates. However, the third phenomenological model in which dislocation annihilation was taken into account besides the mentioned phenomena can well predict the trend of m-value at full range of the strain rate. Since this is a parametric model formulated by independent variable of time and with no analytical solution, two empirical equations are presented as more simple and straightforward models. It is shown that these models give useful formulas for estimation and extrapolation of the m-value at relatively high strain rates of common deformation processes where a monotonic variation by the strain rate is expected. © 2017 Elsevier Ltd.


Hejranfar K.,Sharif University of Technology | Hajihassanpour M.,Sharif University of Technology
Computers and Fluids | Year: 2017

In this work, the Chebyshev collocation spectral lattice Boltzmann method is implemented in the generalized curvilinear coordinates to provide an accurate and efficient low-speed LB-based flow solver to be capable of handling curved geometries with non-uniform grids. The low-speed form of the D2Q9 and D3Q19 lattice Boltzmann equations is transformed into the generalized curvilinear coordinates and then the spatial derivatives in the resulting equations are discretized by using the Chebyshev collocation spectral method and the temporal term is discretized with the fourth-order Runge–Kutta scheme to provide an accurate and efficient low-speed flow solver. All boundary conditions are implemented based on the solution of the governing equations in the generalized curvilinear coordinates. The accuracy and robustness of the solution methodology presented are demonstrated by computing different benchmark and practical low-speed flow problems that are 2D Couette flow between concentric moving cylinders, 2D flow in a gradual expansion duct, 2D regularized trapezoidal cavity flow, and 3D flow in curved ducts of rectangular cross-sections. Results obtained for these test cases are in good agreement with the existing analytical and numerical results. The computational efficiency of the proposed solution methodology based on the Chebyshev collocation spectral lattice Boltzmann method implemented in the generalized curvilinear coordinates is also examined by comparison with the developed second-order finite-difference lattice Boltzmann method that indicates the proposed method provides more accurate and efficient solutions in terms of the CPU time and memory usage. The study shows the present solution methodology is robust and accurate for solving 2D and 3D low-speed flows over practical geometries. Indications are that the solution algorithm based on the CCSLBM in the generalized curvilinear coordinates does not need any filtering or numerical dissipation for stability considerations and thus high accuracy solutions obtained by applying the CCSLBM can be used as benchmark solutions for the evaluation of other LBM-based flow solvers. © 2017 Elsevier Ltd


Hashemi M.,Sharif University of Technology | Shojaei A.,Sharif University of Technology
Polymer International | Year: 2017

Unsaturated polyester/styrene (UP) resin was filled with nanodiamonds (NDs) containing carboxyl and methacrylate functionalities using mechanical mixing. Field emission SEM exhibited a uniform dispersion of tightly bound aggregates of nanosized spherical NDs with good interfacial interaction. Rheological measurements exhibited a step increment in the shear viscosity of a UP/ND suspension at 0.6 wt% ND resembling a percolation state at this loading. Shear viscosity data supported by dynamic mechanical analysis results suggested the development of effective ND particles in which ND aggregates were covered by only polyester macromolecules. Accordingly, the morphology of UP/ND composites approached a quasi-percolation state at 0.6 wt% in which effective ND particles were connected thoroughly, instead of direct ND-ND contact, forming a co-continuous polyester phase covering the ND particles. Based on such morphology, DSC and Fourier transform infrared analysis suggested the development of heterogeneous microgels in cured UP resin containing NDs which in turn governed the overall mechanical properties of the composites. © 2017 Society of Chemical Industry.


Safdarian A.,Sharif University of Technology | Farajollahi M.,Sharif University of Technology | Fotuhi-Firuzabad M.,Sharif University of Technology
IEEE Transactions on Power Systems | Year: 2017

Remote control switches (RCSs) are often assumed to be fully reliable in reliability and cost/worth analyses. This assumption, however, overestimates their merits, thereby misguiding network owners about their optimal implementation. This letter extends the current reliability evaluation procedure to incorporate probability of RCS malfunctions. Then, the extended procedure is applied to a network equipped with a few RCSs. The numerical studies reveal that RCS malfunctions degrade their worth, which may even affect their optimal number and locations. © 1969-2012 IEEE.


KHANI MOGHANAKI S.,Sharif University of Technology | KAZEMINEZHAD M.,Sharif University of Technology
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2017

Microstructure and mechanical properties of AA2024 after severe plastic deformation (SPD) and non-isothermal annealing were investigated. The non-isothermal treatment was carried out on the severely deformed AA2024, and the interaction between restoration and precipitation phenomena was investigated. Differential scanning calorimetry, hardness and shear punch tests illustrate that static recovery and dissolution of GPB zones/Cu–Mg co-clusters occur concurrently through non-isothermal annealing. Scanning electron microscope and electron backscatter diffraction illustrate that non-isothermal annealing of deformed AA2024 up to 250 °C promotes the particle-free regions and also particle stimulated nucleation. Results show that through heating with the rate of 10 °C/min up to 250 °C, the ultimate shear strength and the hardness are maximum due to the presence of S'/S phases which have been detected during non-isothermal differential scanning calorimetry experiment. Also, recrystallization phenomenon occurs in temperature range which includes the dissolution of S'/S phases. The concurrent recrystallization and dissolution of S'/S phase at 380 °C have been verified by differential scanning calorimetry, mechanical properties, and optical microscope. © 2017 The Nonferrous Metals Society of China


Delavar Z.,Sharif University of Technology | Shojaei A.,Sharif University of Technology
Carbohydrate Polymers | Year: 2017

Polymer composite films based on chitosan (CS) and nanodimaond (ND) were prepared using solution casting method. ND with variable contents of carboxylic functional group was prepared using thermal oxidation at temperature of 420 °C under air atmosphere at various durations of 1.5 and 4.5 h. The interfacial interaction between NDs and CS and morphological evolution of CS in presence of NDs were investigated by Fourier transform infrared (FTIR), differential scanning calorimeter (DSC) and X-ray diffraction (XRD) analyses. A significant improvement in tensile strength (∼85%) and tensile modulus (∼125%) of CS was achieved by oxidized ND (OND) obtained at higher oxidation time of 4.5 at low concentrations (below 1.5 wt%). Theoretical analyses based on micromechanical models showed that the ND with higher degree of carboxylic functionality provided thicker and stronger interphase region which was reflected in higher mechanical properties. The equilibrium water uptake of CS decreased by incorporating ND and increasing its degree of carboxyl functionality. © 2017


Bahrami A.,Sharif University of Technology | Faez R.,Sharif University of Technology
Applied Physics A: Materials Science and Processing | Year: 2017

A novel organic–inorganic hybrid tandem solar cell with inverted structure is proposed. This efficient double-junction hybrid tandem solar cell consists of a single-junction hydrogenated amorphous silicon (a-Si:H) subcell with n-i-p structure as front cell and a P3HT:PCBM organic subcell with inverted structure as back cell. In order to optimize the hybrid tandem cell, we have performed a simulation based on transfer matrix method. We have compared the characteristics of this novel structure with a conventional structure. As a result, a power conversion efficiency (PCE) of 6.1 and 24% improvement compared to the conventional hybrid tandem cell was achieved. We also discuss the high potential of this novel structure for realizing high-stability organic–inorganic hybrid photovoltaic devices. © 2017, Springer-Verlag Berlin Heidelberg.


Moghaddam M.A.K.,Sharif University of Technology | Ahmadi-Boroujeni M.,Sharif University of Technology
Optics Express | Year: 2017

The effect of dielectric cladding on the waveguiding characteristics of an array of metallic pillars on a metal plane in the sub-terahertz band is explored. Firstly, a 2D structure made up of a metallic grating of infinite lateral width with various dielectric overlays is analytically studied to get more insight into the problem. Then the ideas inferred from the 2D structure are applied to the realistic 3D structure that has a finite lateral width. It is shown that by proper design of the dielectric medium surrounding the metallic structure the modal field confinement can be enhanced in a broad frequency band resulting in a low bending loss. Especially, by integrating the pillars into a silicon channel of finite size and evacuating the spaces between them a highly confined spoof surface plasmon is supported and a considerable reduction in the bending loss over a broad bandwidth is observed. Due to small cross-sectional size, low bending loss and ease of fabrication, the proposed waveguide is a promising choice for millimeter-wave and terahertz integrated circuits; particularly those based on the silicon technology. © 2017 Optical Society of America.


Zeibi Shirejini S.,Sharif University of Technology | Mohammadi A.,Sharif University of Technology
Organic Process Research and Development | Year: 2017

A telescoped approach was developed for the efficient synthesis of methoxybenzene through the generation of an unstable intermediate reagent, based on the Br-Li exchange reaction of p-bromoanisole and n-BuLi, followed by its reaction with water. In the first stage, p-methoxyphenyllithium was synthesized and consumed immediately in the second stage. For this purpose, an integrated glass microfluidic device was fabricated using laser ablation followed by the thermal fusion bonding method. The impact of various parameters, including solvent, reaction time, molar ratio, concentration of reagents, and flow rates were investigated to achieve the highest yield of the desired product, leading to an optimized condition for the synthetic approach. It was found that the yield varies significantly with change in solvent composition. While p-bromoanisole does not react with n-BuLi in pure n-hexane, the existence of a small amount of THF (or 2-MeTHF) in n-hexane facilitates p-bromoanisole reaction with n-BuLi. Moreover, the reaction is complete within 1 s by the yield of 95% using the microfluidic device, whereas in a batch system, the best result is obtained in 1 min by the yield of 49%. In addition, the optimal molar ratio of n-BuLi to p-bromoanisole was found to be 1.2. Furthermore, the higher flow rates of the reagents result in a higher yield of the desired product. Finally, under the optimized condition, the generated p-methoxyphenyllithium, by the Br-Li exchange reaction of p-bromoanisole and n-BuLi, was reacted with various electrophiles using the microfluidic device. © 2017 American Chemical Society.


Falsafi A.,Sharif University of Technology | Pishkenari H.N.,Sharif University of Technology
Journal of Physical Chemistry C | Year: 2016

Capillary driven motion of fluids is responsible for many natural phenomena and effective on several industrial applications. By way of illustration, consider water remediation and oil recovery, as well as the operation of some laboratory equipment such as trolling mode atomic force microscopy. Experimental study of formation of meniscus layer as a capillary driven motion in scales smaller than micro is extremely difficult and exceedingly costly. Consequently, computational models seem to be appropriate to study the capillary driven motion in nanoscale. In the present work, we have utilized the MARTINI coarse graining method to investigate the establishment of meniscus layer around a cylindrical nanoneedle. We have demonstrated that growth of meniscus layer height is a function of square root of time, which shows agreement with Lucas-Washburn relation for capillary penetration pace. Accordingly, consistency of the utilized model with the physics of the phenomenon can be concluded. Also the effect of variation of nonbonded solid-fluid interaction potential parameters as well as needle diameter is investigated on the meniscus geometry, capillary force, and radial distribution function. Moreover, it is observed that a nondimensional comparison with the nearest available experimental data demonstrates a reasonable agreement. (Figure Presented). © 2016 American Chemical Society.


Asgari Moghaddam H.,Sharif University of Technology | Mohammadi M.R.,Sharif University of Technology
Journal of the American Ceramic Society | Year: 2017

Different compositions of TiO2-BaTiO3 nanocomposites are synthesized with various weight ratios for dye-sensitized solar cell (DSSC) applications. TiO2 and BaTiO3 nanoparticles (NPs) are synthesized by sol-gel and solvothermal methods, respectively and are employed as the photoanode electrodes. BaTiO3 NPs have pure cubic perovskite crystal structure with an average size of 20-40 nm, while TiO2 NPs show pure anatase phase with 15-30 nm size. The power conversion efficiency (PCE) enhancement of the cells is first attained by controlling the thickness of the films for light harvesting improvement. The fabricated DSSC composed of pure BaTiO3 NPs with an optimal thickness of 25 μm shows efficiency of 6.83%, whereas that made of pure TiO2 NPs with 14 μm thickness has cell efficiency of 7.24%. Further improvement of cell efficiency is achieved by preparation of binary oxide nanocomposites using TiO2 and BaTiO3 NPs with various weight ratios. The highest PCE of 9.40% is obtained for the nanocomposite with TiO2:BaTiO3=85:15 (wt%). The enhancement is assigned to less recombination of photo-generated electrons and higher incident photon to current conversion yield as a result of rapid charge collection and higher dye sensitization. © 2017 American Ceramic Society.


Pourjavadi A.,Sharif University of Technology | Tehrani Z.M.,Sharif University of Technology
International Journal of Polymeric Materials and Polymeric Biomaterials | Year: 2017

In this research a novel controlled anticancer drug delivery system with dual pH and thermal responses was designed based on magnetic mesoporous silica nanoparticles that were anchored by β-cyclodextrin and coated by poly(N-isopropylacrylamide) (PNIPAM). Results demonstrated that the behavior of doxorubicin (anticancer drug) release depended on pH and temperature conditions. At endosomal pH (pH 5.5) the amount of drug release enhanced because the cap was removed from the pores. Furthermore, PNIPAM shell collapsed above the lower critical solution temperature and the releasing of drug increased. Thus, this nanocarrier would have the potential to be applied in the tumor therapy. © 2017 Taylor & Francis.


Zarei S.F.,Sharif University of Technology | Parniani M.,Sharif University of Technology
IEEE Transactions on Power Delivery | Year: 2017

Microgrid (MG) protection is one of the main challenges in proliferation of microgrids. Due to limited fault current feeding of inverter-based distributed generations (DGs), in islanded operation of MG, protection problems become more complicated; and, therefore, conventional protection strategies cannot be applied. Hence, new protection methods that are applicable in islanded and grid-connected modes of operation are necessary. In this paper, a comprehensive digital-relay based protection is introduced for the protection of MGs. The proposed method includes protection of lines, distributed generations, and the point of common coupling. The structure and graphical schematic of the proposed digital relays are also presented. The proposed method is independent of the MG operation mode and benefits from single-phase tripping. In this method, due to fault isolation from both sides of a line, downstream loads and DGs can operate after fault clearance. To demonstrate the effectiveness of the proposed protection method, numerous simulations are carried out on an MG test system in the PSCAD/EMTDC environment. © 2016 IEEE.


Kavehvash Z.,Sharif University of Technology
Scientia Iranica | Year: 2016

In this paper, intelligent traffic surveillance system as an important part of a smart resilient city is reviewed. The smart traffic control system is very important in improving the lifestyle by decreasing the traffic saturation and air pollution. Still, multi-camera vision is more helpful in implementing different automatic traffic surveillance systems. Apart from their superior features, existing multi-camera surveillance systems suffer from computational complexity and degraded accuracy. The main reason for these shortcomings arises from image processing errors. These errors depend on the image content and thus are not predictable. To overcome this shortage, three-dimensional (3D) optical techniques for improved fusing of the multi-camera images and thus extracting 3D vehicle locations is proposed in this paper. In fact, the proposed multi-camera visionary system is a combination of image processing based and geometrical optics based methods. The result of 3D image reconstruction through the proposed technique shows its dominance in providing the 3D image information. © 2016 Sharif University of Technology. All rights reserved.


Khorasani S.,Sharif University of Technology
Scientia Iranica | Year: 2016

The Differential Transfer Matrix Method is extended to the complex plane, which allows dealing with singularities at turning points. The results for real-valued systems are simplified and a pair of basis functions are found. These bases are a bit less accurate than WKB solutions but much easier to work with because of their algebraic form. Furthermore, these bases exactly satisfy the initial conditions and may go over the turning points without the divergent behavior of WKB solutions. The findings of this paper allow explicit evaluation of eigenvalues of confined modes with high precision, as demonstrated by few examples. © 2016 Sharif University of Technology. All rights reserved.


Sayyaadi H.,Sharif University of Technology
Scientia Iranica | Year: 2016

This paper attempts to give a perspective on decentralized formation control of multiple car-like mobile robots using local information and formation changes in a dynamic environment having several obstacles. In addition, for every mobile robot, it takes physical dimensions, mass, moment of inertia, movement constraints, and saturation of actuators into account. This study makes use of Input/Output Feedback Linearization Method to control each robot. Hence, hierarchical leader-follower based algorithm is employed to control the group formation. To avoid collision between robots and obstacles, and of robots with each other, local artificial potential fields are addressed. The group can change formation with respect to obstacles in the environment. Finally, simulation results of seven individual robots formation are presented to show the performance of the proposed control system. © 2016 Sharif University of Technology. All rights reserved.


Zarrinmehr A.,Sharif University of Technology | Shafahi Y.,Sharif University of Technology
Scientia Iranica | Year: 2016

Transportation Discrete Network Design Problem (TDNDP) aims at choosing a subset of proposed projects to minimize the users' total travel time with respect to a budget constraint. Because TDNDP is a hard combinatorial problem, recent research has widely addressed heuristic approaches and ignored the exact solution. This paper explores how application of parallel computation can affect the performance of an exact algorithm in TDNDP. First, we show that the Branch-and-Bound (B&B) algorithm, proposed by LeBlanc, is well adapted to a parallel design with synchronized Master-Slave (MS) paradigm. Then, we develop a parallel B&B algorithm and implement it with two search strategies of Depth-First-Search (DFS) and Best-First-Search (BFS). Detailed results over up to 16 processing cores are reported and discussed in an illustrative example of the Chicago Sketch network. The results suggest an almost linear speedup for both strategies, which slightly drops as more processing cores are added. When using 16 processing cores, the speedup values of 11.80 and 12.20 are achieved for DFS and BFS strategies, respectively. Furthermore, the BFS strategy reveals a very fast parallel performance by finding the optimal solution via the minimum computational effort. © 2016 Sharif University of Technology. All rights reserved.


Haeri S.M.,Sharif University of Technology
Scientia Iranica | Year: 2016

Geotechnical engineering is a fundamental subject in civil and environmental engineering that engineers are required to refer to when any type of retrofitting, design or construction of projects and developments are encountered in a city or in a rural area. Indeed in many projects like geotechnical structures, such as earth dams, geotechnical engineering is the main subject. In this paper, the role of geotechnical engineering in sustainable and resilient cities is elaborated mainly through a series of questions and answers. Also, some related geotechnical engineering research, that is in hands in Civil Engineering Department of Sharif University, is discussed in this paper. A unique geotechnical engineering project that is designed and supervised in the city of Tehran by the author is also introduced herein to indicate how an accurate design and construction of a geotechnical structure can result in a sustainable and resilient condition. However, due to the variety of the subjects involved under the title of the paper, some of the subjects are touched briefly. © 2016 Sharif University of Technology. All rights reserved.


Mahsuli M.,Sharif University of Technology
Scientia Iranica | Year: 2016

This paper puts forward a framework for optimal mitigation of regional risk to enhance the resilience of civil infrastructure. To meet this objective, probabilistic models, methods, and software are developed and applied. The work is conducted within a new reliability-based approach, in which reliability methods compute risk. This contrasts several contemporary approaches for risk analysis. Risk, in this context, denotes the probability of exceeding monetary loss. Evaluating such probabilities requires probabilistic models for hazards, response, damage, and loss. This motivates the following contributions in this paper. First, a new computer program is developed that is tailored to conduct reliability analysis with many interconnected probabilistic models. It orchestrates the interaction of models through an object-oriented architecture. Second, a library of probabilistic models for regional seismic risk analysis is developed. The library includes new models for earthquake location and magnitude and building response, damage, and loss. Third, probabilistic methods for multi-hazard risk analysis are developed and applied in a large-scale regional analysis. The results are cost exceedance probabilities and insights into the seismic risk of the region. Finally, sensitivity measures are developed to identify the buildings whose retrofit yields the most reduction in regional risk, i.e. the most resilience of the region. © 2016 Sharif University of Technology. All rights reserved.


Faegh M.,Sharif University of Technology | Shafii M.B.,Sharif University of Technology
Desalination | Year: 2017

In this study, a novel idea of storing the latent heat of condensing vapor in solar stills by means of phase change materials (PCMs) as a thermal storage is experimentally investigated. During the daytime, the generated water vapor by the solar energy, is conducted to an external condenser filled with PCM to be condensed. The wasted latent heat is absorbed by PCM and thereby stored. It is worth noting that there is no direct contact between the saline water and the PCM, therefore, the solar energy is not directly stored in the PCM. In the evening, the energy stored in the PCM is transferred as heat to the saline water by heat pipes and enables the desalination process to continue. Several tests were run to investigate the performance of the system. The results revealed that the presence of an external condenser filled with PCM and equipped with heat pipes in a solar still with evacuated tube collectors, makes the desalination process continue after the sunset without causing a decrease in the yield during the daytime. The yield increases by 86% as compared to the yield of the system without PCM and reaches to 6.555 kg/m2 day with the efficiency of 50%. © 2017 Elsevier B.V.


Kervee S.E.,Sharif University of Technology | Mohammadi M.R.,Sharif University of Technology
Journal of Photochemistry and Photobiology A: Chemistry | Year: 2017

In this work the influence of different particulate gels on morphology and photoelectric performance of TiO2 dye-sensitized solar cells (DSCs) is studied. Two coagulant and flocculant agents are used to convert a TiO2 particulate sol into the gels using double layer compression and charge neutralization mechanisms. One more TiO2 particulate gel is also prepared by changing the pH of the sol using acid: alkoxide molar ratio higher than the critical ratio to obtain an unstable sol. Based on X-ray diffraction (XRD) analysis, the films contain primary nanoparticles with average crystallite size of 13–15 nm. Field emission scanning electron microscopy (FE-SEM) images show uniform, nanostructured and porous microstructure of the films. For acid- coagulated condition the deposited films show large spherical particles (140–260 nm) containing small nanoparticles, while for base-coagulated condition the films contain 20–40 nm nanoparticles. Photovoltaic measurements reveal that DSCs made of basic particulate gel show higher cell efficiency (i.e., 7.68%) than those prepared by acidic particulate gel (i.e., 6.02% and 7.08%). Such enhancement of efficiency is attributed to the small particle size of the films leading to large surface area for high dye adsorption and good interconnectivity of the nanoparticles for electron transport improvement. © 2017 Elsevier B.V.


Fazlollahtabar H.,Sharif University of Technology | Niaki S.T.A.,Sharif University of Technology
Quality and Reliability Engineering International | Year: 2017

Availability of a system is a crucial factor for planning and optimization. The concept is more challenging for modern systems such as robots and autonomous systems consisting of a complex configuration of components. In this paper, a reliability evaluation framework is developed for a system of binary state autonomous robots in an automated manufacturing environment. In this framework, the concepts in functional block diagram, table of truth, and sum of state are employed simultaneously to develop a binary state reliability model. Due to inefficacy of the method for larger number of components involved in complex systems, an extension of the Bernoulli trials is proposed. In an implementation study, the effectiveness and computational efficiency of the proposed method are illustrated. In addition, an analysis on the failure rate using the maximum likelihood estimation and confidence interval is reported. © 2017 John Wiley & Sons, Ltd.


Mahmoudi N.,Sharif University of Technology | Simchi A.,Sharif University of Technology
Materials Science and Engineering C | Year: 2017

Nanofibrous structures that mimic the native extracellular matrix and promote cell adhesion have attracted considerable interest for biomedical applications. In this study, GO-modified nanofibrous biopolymers (GO) were prepared by electrospinning blended solutions of chitosan (80 vol%), polyvinyl pyrrolidone (15 vol%), polyethylene oxide (5 vol%) containing GO nanosheets (0–2 wt%). It is shown that GO nanosheets significantly change the conductivity and viscosity of highly concentrated chitosan solutions, so that ultrafine and uniform fibers with an average diameter of 60 nm are spinnable. The GO-reinforced nanofibers with controlled pore structure exhibit enhanced elastic modulus and tensile strength (150–300%) with a controllable water permeability to meet the required properties of natural skins. Potential use of the GO-modified biocomposites for tissue engineering is demonstrated in mesenchymal stem cell lines extracted from rat's bone marrow. The biocompatibility assay and SEM imaging reveal that the nanofibrous structure promotes the attachment and maintained characteristic cell morphology and viability up to 72 h. In-vivo evaluations in rats show that a faster and more efficient wound closure rate (about 33%) are attained for the 1.5% GO nanofibrous membrane as compared with control (sterile gauze sponges). © 2016 Elsevier B.V.


Hassani A.H.,Sharif University of Technology | Ghazanfari M.H.,Sharif University of Technology
Journal of Natural Gas Science and Engineering | Year: 2017

Application of the colloidal gas aphrons (CGAs) in minimizing formation damage by plugging pore mechanism is now wildly accepted due to numerous successful field experience. One of the pivotal factors which affects the pore blockage ability of micro-bubbles is their stability. This experimental study tries to investigate the possible synergistic effect of nanoparticles on improving the stability and other properties of non-aqueous CGA drilling fluids, in both bulk and porous media. In particular, two types of hydrophobic nanoparticles including silicon dioxide nanopowder coated with 2 wt% Silane and nanoclay, in presence of a treated version of bentonite (Bentone 34) as a stabilizer and sorbitane monooleate as a non-ionic surfactant are utilized for the formulation of kerosene-based CGA fluids. Results of measuring static drainage rate, API filtration loss, and return permeability in a special designed radial flooding sandpack showed that presence of nanoparticles enhances the stability, filtration loss properties, and the pore blockage ability of non-aqueous CGA drilling fluids. Compared to hydrophobic SiO2, hydrophobic nanoclay was more effective in increasing the stability and plugging performance of non-aqueous CGAs, at an optimum concentration. Also, rheological analysis indicated that nanoparticle addition increases the low shear rate viscosity of non-aqueous CGA fluids and boosts their cutting transport capacity. Optimum concentrations of stabilizer and surfactant were observed to be 3.5 gr in 100 cc kerosene and 1.8 wt%, respectively. Obtained results may provide a better background for the physico-chemical characterization of non-aqueous CGA fluids, especially in presence of nanoparticles. © 2017 Elsevier B.V.


Rabbani A.,Sharif University of Technology | Salehi S.,University of Oklahoma
Journal of Natural Gas Science and Engineering | Year: 2017

In the present paper, a dynamic modeling is presented for deposition of the mud solid particles over and through the porous sandstones during permeability plugging experiments. Scanning electron microscopy (SEM) coupled with image processing are utilized to find the porosity and pore size distribution of the mud cake. The structure of the porous rock as well as the mud cake are modeled via bundle of the curved tubes approach and deposition probability of the solid particles has been taken into the account through filtration theories. Four different sandstones in addition to four mud samples were utilized to measure and predict the volume of the expelled fluid during the 30 min of filtration through thin sections of the rock samples. The presented model is successful to predict the amount of expelled fluid with about 9.2% of relative error. The novelty of the present study, is quantitative utilization of the SEM images by applying the watershed segmentation algorithm to detect and measure the size of the mud cake pore spaces. © 2017 Elsevier B.V.


Hosseini S.A.,Sharif University of Technology | Afrakoti I.E.P.,University of Mazandaran
Annals of Nuclear Energy | Year: 2017

The neutron noise is defined as the stationary fluctuation of the neutron flux around its mean value due to the induced perturbation in the reactor core. The neutron noise analysis may be useful in many applications like noise source reconstruction. To identify the noise source, calculated neutron noise distribution of the detectors is used as input data by the considered unfolding algorithm. The neutron noise distribution of the VVER-1000 reactor core is calculated using the developed computational code based on Galerkin Finite Element Method (GFEM). The noise source of type absorber of variable strength is considered in the calculation. The computational code developed based on An Adaptive Neuro-Fuzzy Inference System (ANFIS) is used to unfold the neutron noise source. Complex neutron noise distribution (real and imaginary parts) in the detectors is considered as input data onto the developed computational code based on the ANFIS algorithm. All the characteristics of the neutron noise source, including strength, frequency and position (X and Y coordinates) are unfolded with excellent accuracy using the developed computational code. © 2017 Elsevier Ltd


Abam M.A.,Sharif University of Technology | De Berg M.,TU Eindhoven | Seraji M.J.R.,Sharif University of Technology
Proceedings of the Annual ACM-SIAM Symposium on Discrete Algorithms | Year: 2017

Let S be a set S of n points on a polyhedral terrain T in R3, and let ϵ > 0 be a fixed constant. We prove that S admits a (2 + ϵ)-spanner with O(n log n) edges with respect to the geodesic distance. This is the first spanner with constant spanning ratio and a near-linear number of edges for points on a terrain. On our way to this result, we prove that any set of n weighted points in Rd admits an additively weighted (2 + ϵ)-spanner with O(n) edges; this improves the previously best known bound on the spanning ratio (which was 5 + ϵ), and almost matches the lower bound. Copyright © by SIAM.


"ARC's team executed another strong quarter, which included advancing construction of the Dawson Phase III gas processing and liquids-handling facility, for which we expect to initiate commissioning activities in the second quarter of 2017," stated Myron Stadnyk, President and CEO. "In addition to the capital investment at Dawson, our development activities in the first quarter of 2017 allowed us to further our understanding of the Lower Montney, which adds development inventory to support future project expansions across our Montney land base. Our current balance sheet strength increases our ability to execute multi-year development projects at Dawson, Parkland/Tower, and Sunrise, and to enter into long-term marketing contracts as we reinvest the proceeds received from the sale of our Saskatchewan assets in late 2016. ARC remains committed to running a profitable business, and with our low-cost Montney businesses, we will be able to maximize the value we continue to create for our shareholders." ARC achieved first quarter 2017 production of 115,129 boe per day, which was two per cent lower than the fourth quarter of 2016. The lower production was a result of the divestment of ARC's Saskatchewan assets in late 2016, which was partially offset by production returning from third-party pipeline restrictions at Dawson in the previous quarter, and production from new wells and optimization activities at Ante Creek. First quarter 2017 natural gas production was 496 MMcf per day and crude oil and liquids production was 32,427 barrels per day. As planned, ARC's second quarter 2017 production will be lower than the first quarter by a few per cent due to planned maintenance activities and anticipated spring break-up impacts to production and field operations. As commissioning activities for the Dawson Phase III gas processing and liquids-handling facility are initiated in the second quarter of 2017, ARC expects production levels at Dawson to increase through the second half of the year. Full-year 2017 annual production is expected to be in the range of 118,000 to 124,000 boe per day, and ARC anticipates its 2017 exit rate to be in excess of 130,000 boe per day. ARC continued to deliver strong financial performance in the first quarter of 2017 with net income of $142.5 million ($0.40 per share). Strengthened commodity prices mitigated the slight decrease in production volumes in the period and resulted in funds from operations of $177.2 million ($0.50 per share) in the first quarter of 2017. Profitability remains a key measure of performance at ARC, and strong full-cycle economics across our portfolio of assets enable us to efficiently convert our resources into earnings for shareholders. ARC's marketing strategy focuses on both natural gas takeaway in western Canada and managing a market diversification strategy. The effectiveness of this strategy is evidenced by minimal impacts to production from pipeline restrictions and strong price realizations due to a diversified sales strategy. Over the quarter, ARC continued to pursue natural gas takeaway with participation in TransCanada Pipeline's ("TCPL") North Montney Mainline Project, and additional diversification with participation in TCPL's Mainline open season. In addition to ARC's physical diversification strategy, ARC's financial hedging program continues to provide greater certainty of cash flows and support of long-term business plans, with first quarter 2017 realized cash gains of $24.4 million. The fair value of ARC's risk management contracts at March 31, 2017 was a net asset of $264.4 million. First quarter 2017 capital expenditures, before land and net property acquisitions and dispositions, of $255.2 million were focused on infrastructure investment at Dawson Phase III and Parkland/Tower Phase III, drilling and completions activities throughout the Montney and the Cardium, and development activities directed at the Lower Montney. With a planned 2017 capital program of $750 million, the first quarter was expected to be the most capital-intensive quarter of the year. The 2017 capital program will allow ARC to sustain its base businesses, carry out drilling rig schedule optimization, complete and bring Dawson Phase III on-stream, and pre-drill wells to bring on production in 2018. As part of the proactive planning of our capital programs, rigs and services have been secured through 2017 to support our budgeted capital plans. ARC drilled 46 operated wells (29 crude oil wells, 15 liquids-rich natural gas wells, and two natural gas wells) in the first quarter of 2017, many of which will be brought on production late in the second quarter of 2017. The following table outlines first quarter activity by ARC's key operating areas. First quarter 2017 operating expenses of $69.9 million ($6.74 per boe) were relatively unchanged from the fourth quarter of 2016. ARC expects full-year 2017 operating expenses to trend towards guidance as the year progresses and fall within the guided range of $6.30 to $6.70 per boe. ARC closed the first quarter with a strong balance sheet with $501.4 million of net debt outstanding at March 31, 2017, and had additional cash and credit capacity of approximately $1.7 billion, taking into account ARC's working capital surplus. The net debt to annualized funds from operations ratio was 0.7 times and net debt was approximately seven per cent of ARC's total capitalization at the end of the first quarter of 2017. ARC expects to outspend its cash flows over the course of the next two to three years and return to target debt levels of between one and 1.5 times annualized funds from operations. The proceeds from the fourth quarter 2016 Saskatchewan asset disposition will be reinvested into profitable projects in the Montney. ARC's low debt levels allow greater certainty around the funding required to execute on our long-term business plans. The following economic, financial, and operational reviews provide further details to the above highlights. For additional commentary on ARC's first quarter 2017 financial and operating results, please view the following videos: "Myron's Minute", "Q1 2017 Financial Review", and "Q1 2017 Operations Review" available on ARC's website at www.arcresources.com. ARC is pleased to announce the following appointment: Mr. Armin Jahangiri has been promoted to the officer position of Vice President, Operations, and is responsible for overseeing the facilities, drilling and completions, health and safety, and environmental and regulatory teams at ARC. Prior to joining ARC in 2014 as a Manager of Operations, Mr. Jahangiri held positions with a major Canadian oil and gas producer and a global oilfield services company. He holds a Bachelor of Science in Mechanical Engineering from the Sharif University of Technology and a Master in Reservoir Engineering from the University of Calgary, and is a member of the Association of Professional Engineers and Geoscientists of Alberta. ARC congratulates Mr. Jahangiri and welcomes him to the executive team. ARC's first quarter 2017 financial and operating results were impacted by commodity prices and foreign exchange rates which are outlined in the following table. Global crude oil prices strengthened in the first quarter of 2017 as data signaled that compliance, by both OPEC and non-OPEC members, with the previously agreed-upon production cuts was higher than originally anticipated. This compliance helped to stabilize the global supply/demand imbalance. The WTI benchmark price averaged five per cent higher than the fourth quarter of 2016. ARC's crude oil price is primarily referenced to the mixed sweet crude stream price at Edmonton, which increased three per cent in the first quarter of 2017 compared to the fourth quarter of 2016. The differential between WTI and the mixed sweet crude stream price at Edmonton widened to average a discount of US$3.56 in the first quarter of 2017, 14 per cent more than the fourth quarter of 2016. US natural gas prices, referenced by the average NYMEX Henry Hub Last Day Settlement price, increased 11 per cent relative to the fourth quarter of 2016. Prices were driven higher by a tight supply/demand balance caused by a combination of rising base load demand and unchanged US production. ARC's realized natural gas price is diversified to multiple sales points including AECO, Station 2, and Chicago hubs. The AECO hub price increased five per cent in the first quarter of 2017 relative to the fourth quarter of 2016. Despite strong local demand, AECO basis differentials remain wide due to the high marginal transportation costs of alleviating the Western Canadian Sedimentary Basin of its excess supply. The Canadian dollar remained range-bound relative to the US dollar during the first quarter of 2017, averaging Cdn$/US$1.32 (US$/Cdn$0.76). The mild strengthening in the Canadian dollar relative to the US dollar in the first quarter of 2017 compared to the fourth quarter of 2016 was partially driven by higher commodity prices. ARC recorded net income of $142.5 million ($0.40 per share) in the first quarter of 2017 compared to net income of $167.0 million ($0.47 per share) in the fourth quarter of 2016. The disposition of certain non-core assets, including ARC's Saskatchewan position in the fourth quarter of 2016, resulted in the reversal of previously-recorded impairment charges totaling $63.1 million, as well as the recognition of a gain on disposal of petroleum and natural gas properties of $196.0 million in the prior period. In the first quarter of 2017, reduced operating netbacks of $18.2 million, driven primarily by lower crude oil production volumes, also served to decrease net income in the first quarter of 2017 relative to the fourth quarter of 2016. Partially offsetting these decreases to net income were increased gains of $201.0 million recognized on ARC's risk management contracts, an increase in foreign exchange gains of $31.8 million, and reduced income taxes of $18.9 million. First quarter 2017 net income of $142.5 million ($0.40 per share) was $78.4 million higher than first quarter 2016 net income. Increased operating netbacks of $69.4 million, driven primarily by improved commodity prices, as well as increased gains on risk management contracts of $73.4 million served to improve earnings over the prior period. Reduced general and administrative ("G&A") expenses of $20.1 million due to recoveries recorded on ARC's share-based compensation plans also contributed to the year-over-year increase in net income. These increases to earnings were partially offset by reduced foreign exchange gains of $58.9 million, and higher income taxes of $49.5 million resulting from improved commodity prices and lost income tax pools. ARC's first quarter 2017 funds from operations of $177.2 million ($0.50 per share) decreased six per cent from fourth quarter 2016 funds from operations of $188.5 million ($0.53 per share). The most significant drivers in the quarter-over-quarter decrease in funds from operations were lower crude oil production and reduced realized gains on hedging contracts. These factors were partially offset by lower current income taxes, higher crude oil prices, lower operating expenses, and lower G&A expenses driven primarily by recoveries recorded on ARC's share-based compensation plans due to the decrease in ARC's share price. First quarter 2017 funds from operations of $177.2 million ($0.50 per share) was 18 per cent higher than first quarter 2016 funds from operations. Improved commodity prices and reduced G&A expenses increased funds from operations relative to the prior year. These items were partially offset by decreased crude oil production and lower realized gains on ARC's risk management contracts. Increased current income taxes and higher royalty expenses also served to decrease funds from operations. The following table details the change in funds from operations for the first quarter of 2017 relative to the fourth quarter of 2016 and to the first quarter of 2016. ARC's first quarter 2017 operating netbacks, before hedging, of $17.98 per boe decreased four per cent relative to the fourth quarter of 2016, and first quarter 2017 operating netbacks, after hedging, of $20.34 per boe decreased seven per cent relative to the fourth quarter of 2016. Lower operating netbacks were predominantly due to an increase in natural gas production as a percentage of total corporate production, resulting in a lower average realized commodity price. ARC's first quarter 2017 operating netbacks, before hedging, of $17.98 per boe increased 72 per cent from the first quarter of 2016, and first quarter 2017 operating netbacks, after hedging, of $20.34 per boe increased 23 per cent relative to the first quarter of 2016. Higher operating netbacks were predominantly due to strengthening crude oil and natural gas prices. ARC's first quarter 2017 total corporate royalty rate of 8.4 per cent ($2.49 per boe) increased slightly from 8.0 per cent ($2.47 per boe) in the fourth quarter of 2016 and 7.9 per cent ($1.62 per boe) in the first quarter of 2016, reflecting the effect of increased commodity prices on royalty rates. First quarter 2017 royalty expenses on an absolute basis were $25.8 million. First quarter 2017 transportation expenses of $2.42 per boe increased four per cent from the fourth quarter of 2016 and increased 10 per cent relative to the first quarter of 2016 as a result of an aggregate increase in tolls for natural gas on third-party pipelines. First quarter 2017 transportation expenses on an absolute basis were $25.0 million. First quarter 2017 operating expenses of $6.74 per boe were relatively unchanged from the fourth quarter of 2016, and increased 10 per cent relative to the first quarter of 2016 due to accelerated maintenance and workover activities in advance of spring break-up. First quarter 2017 operating expenses on an absolute basis were $69.9 million. ARC realized cash gains on natural gas hedging contracts of $25.4 million during the first quarter of 2017. Approximately 30 per cent of natural gas production was hedged at NYMEX Henry Hub with an average floor price of US$4.00 per MMBtu during the first quarter of 2017, while market prices averaged US$3.32 per MMBtu. Approximately 10 per cent of natural gas production was hedged at AECO with an average swap price of Cdn$2.64 per GJ during the first quarter of 2017, while market prices averaged Cdn$2.79 per GJ. ARC has hedged approximately 234,600 MMBtu per day of natural gas production for 2017 and a portion of natural gas production is hedged for the period 2018 through 2021. ARC's natural gas hedging portfolio also includes AECO basis swap contracts which fix the AECO price received relative to the NYMEX Henry Hub price on a portion of its natural gas volumes for 2017 through 2021. ARC's natural gas hedges support long-term development economics for ARC's significant natural gas resource base. Details relating to ARC's natural gas hedged volumes and prices for the period 2017 through 2021 are outlined in the table that follows. ARC incurred cash losses of $0.5 million on crude oil hedging contracts during the first quarter of 2017. ARC currently has 14,000 barrels per day of crude oil production hedged with collars and swaps for 2017 and has additional crude oil production hedged for 2018 and 2019. ARC's crude oil hedging portfolio also includes MSW basis swap contracts for 2017 and 2018, fixing the discount between WTI and the mixed sweet crude stream price at Edmonton. Details relating to ARC's crude oil hedged volumes and prices for the period 2017 through 2019 are outlined in the table that follows. ARC has hedge contracts in place, at levels that support ARC's long-term business plans, to protect prices on a portion of natural gas volumes for 2017 through 2021 and crude oil volumes for 2017 through 2019. ARC will continue to take positions in natural gas, crude oil, foreign exchange rates, power and interest rates, as appropriate, to provide greater certainty over future cash flows. For a complete listing and terms of ARC's hedging contracts as at March 31, 2017, see Note 9 "Financial Instruments and Market Risk Management" in ARC's financial statements for the three months ended March 31, 2017. ARC invested $255.2 million of capital, before land and net property acquisitions and dispositions, in the first quarter of 2017, including drilling 46 operated wells (29 crude oil wells, 15 liquids-rich natural gas wells, and two natural gas wells). Capital expenditures in the period included infrastructure investment at Dawson Phase III and Parkland/Tower Phase III, drilling and completions activities throughout the Montney and the Cardium, and development activities directed at the continued evaluation of the Lower Montney. Approximately 85 per cent of capital investment in the first quarter was invested in ARC's low-cost, high-value Montney assets. First quarter 2017 production was 115,129 boe per day, with natural gas production of 496 MMcf per day (72 per cent of total production) and crude oil and liquids production of 32,427 barrels per day (28 per cent of total production). First quarter 2017 average daily production was two per cent lower relative to the fourth quarter of 2016, primarily driven by the disposition of ARC's Saskatchewan assets in late 2016. This was partially offset by an increase in production at Dawson due to production returning from third-party pipeline outages experienced in the fourth quarter, as well as an increase in production at Ante Creek from new wells that came on-stream late in 2016 and from optimization activities performed in the period. ARC continues to safely shut in offset pads when nearby completion activities are taking place. First quarter 2017 production was seven per cent lower than the first quarter of 2016 primarily due to the 8,800 boe per day of production that was divested throughout 2016 as part of ARC's portfolio rationalization efforts. ARC currently has a land position of approximately 1,200 net Montney sections, and Montney production represented approximately 85 per cent of corporate production in the first quarter of 2017. Excellent operating and capital efficiencies are supported by operating our own facilities, allowing ARC greater control over costs and pace of development. We continue to optimize well designs and maximize well value, pursue new technologies, and partner with service providers to preserve our low cost structure. ARC actively monitors market conditions and maintains a marketing strategy that diversifies ARC's sales portfolio and ensures that production gets to market at optimal pricing. ARC has been de-risking future development projects with appraisal and development drilling, as well as geologic and engineering studies to create optionality in future project selection across all of our Montney and Cardium land base. ARC's land position in the multi-layer Montney has considerable future delineation opportunities and development potential. The Lower Montney zone is currently being de-risked across ARC's Montney acreage as we progress our understanding of the zone and the potential for future commercial development. At Dawson, the Lower Montney zone has shown high liquids yields, with wells currently producing an average of approximately 40 barrels per MMcf of free condensate. This liquids content is driving strong economics and is indicating significant upside across ARC's Dawson lands. In addition to Dawson, appraisal of the Lower Montney has been a focus at Parkland/Tower, Sunrise, and Pouce Coupe. Future development potential has also been identified at Attachie. ARC's 2017 capital program includes the drilling of 12 Lower Montney wells across ARC's Montney acreage. Evaluation and monitoring of production results will be ongoing as ARC optimizes well designs. The long-term growth opportunities from the Lower Montney zone will provide ARC with strategic optionality in the future, and increases the overall depth of ARC's portfolio. The Dawson Montney play is the foundation of ARC's low-cost natural gas business, where ARC has a land position of 137 net Montney sections. Dawson production averaged 178 MMcf per day of natural gas and 1,300 barrels per day of condensate and liquids during the first quarter of 2017, an increase of eight per cent from the fourth quarter of 2016. The increase in production was the result of production returning from line pressure issues experienced on third-party pipelines in the prior quarter, partially offset by the safe shut-in of offset pads due to nearby completion activities. The Dawson play delivers strong economics and significant cash flow at current natural gas prices, due to excellent capital efficiencies, exceptional well results, and low operating expenses. ARC invested $78 million at Dawson in the first quarter of 2017. Capital investment was directed to construction of Dawson Phase III and associated infrastructure, drilling eight liquids-rich natural gas wells and two natural gas wells, and completing nine wells. Two of the wells drilled in the quarter targeted the Lower Montney zone, furthering ARC's broader evaluation of the zone's potential across our Montney acreage. Drilling efficiencies continue to be realized at Dawson, with ARC reducing the average number of drilling days per well by approximately 50 per cent since 2015 to an average of eight days. Physical construction of the Dawson Phase III gas processing and liquids-handling facility continues with the majority of mechanical work now complete. Over 80 kilometers of pipe was installed in the first quarter of 2017, including the gas gathering systems for the facility and the sales lines that will allow for dual-connectivity to third-party pipeline infrastructure and provide increased takeaway optionality. Construction of the facility continues as ARC prepares for upcoming commissioning activities. The first stage of Dawson Phase III is designed to process 90 MMcf per day of natural gas and handle up to 7,500 barrels per day of liquids (approximately 50 per cent condensate-handling). The wells that will be required to initially fill the plant have been drilled and completions of these wells are underway. ARC expects production levels at Dawson to increase through the second half of 2017. ARC has incorporated extra liquids-handling capacity in the Phase III design to be able to handle free liquids and a richer gas production from the Lower Montney in the future. Regulatory approval has been received for a Phase IV Dawson facility expansion, for which pre-planning has commenced. ARC's Parkland/Tower property, located in the Montney play in northeast British Columbia, consists of 57 net Montney sections at Tower, which produce predominantly light crude oil and condensate with liquids-rich associated gas; and 37 net Montney sections at Parkland, which produce liquids-rich natural gas and dry gas. With contiguous lands, these areas share ARC-operated infrastructure and processing capacity. Parkland/Tower first quarter 2017 production averaged 25,200 boe per day (35 per cent crude oil and liquids and 65 per cent natural gas), unchanged from the fourth quarter of 2016. Capital investment at Parkland/Tower was approximately $80 million in the first quarter of 2017 and included the drilling of 15 crude oil wells and four liquids-rich natural gas wells, completion of six wells, and initial investments for the Parkland/Tower Phase III facility expansion. The evaluation of a Phase III expansion of the Parkland/Tower gas processing and liquids-handling facility is now underway. The facility expansion has received regulatory approval and is able to come on-stream in late 2018. Long-term takeaway capacity for production associated with the facility expansion has been secured. ARC continues to evaluate and progress its understanding of the Parkland/Tower area, with a focus on reducing development costs and refining well designs for optimized efficiency. Gas lifts have been installed on producing wells across the field in order to improve production. Well performance at Tower continues to be exceptional, ranking amongst the top oil wells in western Canada. ARC will continue to optimize well designs in the area to ensure best-in-class capital efficiencies and that the optimal exploitation strategy is achieved. ARC plans to ramp up Parkland/Tower production to current facility capacity through 2017. ARC has a land position of 32 net Montney sections at Sunrise, a dry natural gas Montney play in northeast British Columbia with multi-layer development. With a significant natural gas resource base, high well deliverability, low capital requirements, and low operating expenses, Sunrise continues to create significant value and superior full-cycle economics. First quarter 2017 Sunrise production was approximately 136 MMcf per day of natural gas, unchanged from the fourth quarter of 2016, as ARC continues to see strong well performance and longer stabilized production across the area. ARC invested approximately $1 million on capital activities at Sunrise in the first quarter of 2017, directed at front-end engineering and design work for the second stage of the existing Sunrise gas processing facility. The facility expansion, which includes the repatriation of production currently flowing through a third-party facility, is expected to come on-stream mid-year 2019. With increased control of ARC's Sunrise production volumes, operating costs in the area will be significantly reduced once the facility comes on-stream. Long-term takeaway capacity for production associated with the facility expansion has been secured. With strong well performance, ARC expects to maintain production at current facility capacity at Sunrise throughout 2017, and has plans to drill five Lower Montney wells in 2017 to maintain Sunrise facility capacities in 2018. ARC's Attachie property is a highly prospective, Montney crude oil and liquids-rich natural gas exploration play located in northeast British Columbia, where ARC has a land position of 286 net Montney sections. ARC invested approximately $15 million on pilot activities on the west side of Attachie in the first quarter of 2017, including the drilling and completion of two liquids-rich natural gas wells. ARC will continue to build on the success of existing pilots in the area over the course of 2017, and will optimize and monitor production results in the area. ARC is currently producing through third-party infrastructure while long-term infrastructure requirements are being assessed. ARC has a land position of 381 net sections at Ante Creek, a Montney crude oil play in northern Alberta that provides significant cash flow and has substantial future development potential. First quarter 2017 Ante Creek production averaged 17,400 boe per day (approximately 45 per cent crude oil and liquids), an eight per cent increase from the fourth quarter of 2016. Increased production in the area is attributed to new wells that came on-stream late in the fourth quarter of 2016, as well as from optimization activities performed in the period. ARC invested approximately $29 million in the first quarter of 2017, including drilling six crude oil wells and completing four wells. Alongside increased capital activity in 2017, ARC will continue to evaluate and optimize recent changes in well design. Base production continues to perform well at Ante Creek, demonstrating the effectiveness of ARC's ongoing optimization activities and the overall strength of the asset base. ARC's Pembina Cardium assets provide high-quality light oil production, generate strong operating netbacks, and feature favourable half-cycle economics, with required infrastructure already in place. ARC has a land position of 217 net Cardium sections in Pembina, where production averaged approximately 11,000 boe per day (approximately 80 per cent light oil and liquids) in the first quarter of 2017, unchanged from the fourth quarter of 2016. The addition of new production from recent development activities in the area has temporarily been restricted in order to perform pipeline integrity reviews. ARC invested approximately $27 million in capital activities in the first quarter of 2017, including drilling eight crude oil wells and completing 12 wells. ARC continues to focus on capital and operating efficiencies with its drilling and completion designs in Pembina, driving an increase in overall profitability for the area. Optimizing production, converting horizontal injectors, and waterflood management continue to be a core component of operations at Pembina. ARC's Redwater region in Alberta produces high-quality crude oil. First quarter 2017 production averaged approximately 3,100 boe per day of light oil, unchanged from the fourth quarter of 2016. Capital investment for the first quarter of 2017 at Redwater was approximately $2 million. As a dividend-paying corporation, ARC declares monthly dividends to its shareholders. ARC continually assesses dividend levels in light of commodity prices, capital expenditure programs, and production volumes to ensure that dividends are in line with ARC's long-term strategy and objectives. ARC declared dividends totaling $0.15 per share for the first quarter of 2017. The Board of Directors previously confirmed a dividend of $0.05 per share for April 2017, payable on May 15, 2017, and has conditionally declared a monthly dividend of $0.05 per share for May 2017 through August 2017, payable as follows: On February 8, 2017, ARC's Board of Directors approved the elimination of the Dividend Reinvestment Plan ("DRIP") and Stock Dividend Program ("SDP"), which came into effect for the March 2017 dividend. Shareholders that were enrolled in either program now automatically receive dividend payments in the form of cash. During the first quarter of 2017, ARC declared dividends of $53.1 million, of which $0.4 million was issued in the form of common shares under the SDP and $2.6 million was reinvested into ARC shares through the DRIP. Prior to elimination, the DRIP and SDP were a source of funding for ARC's capital programs. The dividends have been designated as eligible dividends under the Income Tax Act (Canada). The declaration of the dividends is conditional upon confirmation by news release and is subject to any further resolution of the Board of Directors. Dividends are subject to change in accordance with ARC's dividend policy depending on a variety of factors and conditions existing from time-to-time, including fluctuations in commodity prices, production levels, capital expenditure requirements, debt service requirements, operating expenses, royalty burdens, foreign exchange rates and the satisfaction of solvency tests imposed by the Business Corporations Act (Alberta) for the declaration and payment of dividends. Shareholders, wherever resident, are encouraged to consult their own tax advisors regarding the tax consequences to them of receiving cash dividends. ARC plans to file a Form 15F with the United States Securities and Exchange Commission (the "Commission" or "SEC") to voluntarily terminate the registration of its securities and its reporting obligations under Section 13(a) and Section 15(d) of the United States Securities Exchange Act of 1934, as amended ("Exchange Act"). ARC's Exchange Act reporting obligations will be immediately suspended upon filing the Form 15F. The termination of ARC's registration and of its reporting obligations under Section 13(a) and Section 15(d) of the Exchange Act is expected to be effective 90 days after filing. ARC is current with all of its reporting requirements under the Exchange Act and is not listed on any US exchange. In determining to deregister, ARC's Board of Directors considered the administrative burden and costs associated with being a US reporting company and believe that the costs outweigh the benefits. ARC will continue to comply with its Canadian continuous disclosure obligations and its common shares will continue to trade on the Toronto Stock Exchange. The foundation of ARC's business strategy is risk-managed value creation. High-quality assets, operational excellence, financial strength, and top talent are the key principles underpinning ARC's business strategy. ARC's goal is to create shareholder value in the form of regular dividends and anticipated capital appreciation relating to profitable future growth. ARC's Board of Directors has approved a $750 million capital program for 2017 that focuses on long-term value creation through the development of ARC's crude oil, liquids-rich natural gas, and natural gas Montney assets and ARC's crude oil Cardium assets. The planned budget includes infrastructure investment at Dawson, Parkland/Tower, and Sunrise, as well as strategic investment in the Lower Montney. The capital plan will allow ARC to sustain its base businesses and optimize capital and operating efficiencies across ARC's focused asset base. As planned, ARC's second quarter 2017 production will be lower than the first quarter by a few per cent due to planned maintenance activities and anticipated spring break-up impacts to production and field operations. As commissioning activities for the Dawson Phase III gas processing and liquids-handling facility are initiated in the second quarter of 2017, ARC expects production levels at Dawson to increase through the second half of the year. Full-year 2017 annual production is expected to be in the range of 118,000 to 124,000 boe per day, and ARC anticipates its 2017 exit rate to be in excess of 130,000 boe per day. Ongoing commodity price volatility may affect ARC's funds from operations and over the long term, profitability of capital programs. As continued volatility is expected, ARC will continue to take steps to mitigate these risks, including managing an active hedging program, focusing on capital and operating efficiencies, and protecting its strong financial position, with a targeted net debt to annualized funds from operations ratio of between one and 1.5 times. ARC will continue to screen projects for profitability in a disciplined manner and will adjust spending and the pace of development, if required, to ensure balance sheet strength is protected. The 2017 capital budget excludes land purchases and property acquisitions or dispositions. ARC will continue to consolidate its land position and grow its presence in key areas through land purchases and property acquisitions. ARC evaluates its asset portfolio on a continuous basis with a view to selling assets that do not meet ARC's investment guidelines. Through the normal course of business, acquisitions and dispositions may occur that would impact the expected production for the year. ARC's 2017 guidance is based on full-year 2017 estimates; certain variances exist between 2017 year-to-date actual results and 2017 full-year guidance estimates due to the cyclical and seasonal nature of operations. ARC expects full-year 2017 actual results to closely approximate guidance. On a per boe basis, ARC's first quarter 2017 operating expenses were slightly above the 2017 guidance range due to accelerated maintenance and workover activities in advance of spring break-up. ARC expects full-year operating expenses to trend towards guidance as the year progresses as additional volumes with lower relative costs to operate are brought on-stream in the second half of the year. ARC's first quarter 2017 G&A expenses before share-based compensation were above the 2017 guidance range due primarily to an increase in compensation expenses associated with reducing the size of ARC's workforce. G&A expenses relating to share-based compensation plans were below the 2017 guidance range due to recoveries recorded on ARC's share-based plans due to the decrease in ARC's share price. ARC expects full-year 2017 G&A expenses before share-based compensation to trend towards guidance as the year progresses. ARC's full-year 2017 guidance estimates and a review of 2017 year-to-date actual results are outlined in the following table. This news release contains certain forward-looking information and statements within the meaning of applicable securities laws. The use of any of the words "expect," "anticipate," "continue," "estimate," "objective," "ongoing," "may," "will," "project," "should," "believe," "plans," "intends," "strategy" and similar expressions are intended to identify forward-looking information or statements. In particular, but without limiting the foregoing, this news release contains forward-looking information and statements pertaining to the following: guidance as to the capital expenditure plans of ARC in 2017 and its 2017 production, and operating expenses under the heading "Financial and Operating Highlights", as to its views on future commodity prices under the heading "Economic Environment", as to its risk management plans for 2017 and beyond under the heading "Risk Management", as to its production, exploration and development plans, and capital expenditures for 2017 and beyond under the heading "Operational Review", as to its plans in relation to future dividend levels under the heading "Dividends", as to termination of ARC's Exchange Act reporting obligations under the heading "United States Securities and Exchange Commission Deregistration", and all matters in respect of 2017 guidance under the heading "Outlook". The forward-looking information and statements contained in this news release reflect material factors and expectations and assumptions of ARC including, without limitation: that ARC will continue to conduct its operations in a manner consistent with past operations; the general continuance of current industry conditions; the continuance of existing (and in certain circumstances, the implementation of proposed) tax, royalty and regulatory regimes; the accuracy of the estimates of ARC's reserves and resource volumes; certain commodity price and other cost assumptions; and the continued availability of adequate debt and equity financing, funds from operations to fund its planned expenditures, and that the United States Securities and Exchange Commission will not object to ARC's termination of its Exchange Act reporting obligations. ARC believes the material factors, expectations and assumptions reflected in the forward-looking information and statements are reasonable but no assurance can be given that these factors, expectations and assumptions will prove to be correct. The forward-looking information and statements included in this news release are not guarantees of future performance and should not be unduly relied upon. Such information and statements involve known and unknown risks, uncertainties and other factors that may cause actual results or events to differ materially from those anticipated in such forward-looking information or statements including, without limitation: changes in commodity prices; changes in the demand for or supply of ARC's products; changes to government regulations including royalty rates, taxes, and environmental and climate change regulation; market access constraints or transportation interruptions, unanticipated operating results, or production declines; changes in development plans of ARC or by third-party operators of ARC's properties, increased debt levels or debt service requirements; inaccurate estimation of ARC's oil and gas reserve and resource volumes; limited, unfavorable or a lack of access to capital markets; increased costs; a lack of adequate insurance coverage; the impact of competitors; the risk that the United States Securities and Exchange Commission will object to ARC's termination of its Exchange Act reporting obligations; and certain other risks detailed from time-to-time in ARC's public disclosure documents (including, without limitation, those risks identified in this news release and in ARC's Annual Information Form). The internal projections, expectations or beliefs are based on the 2017 capital budget which is subject to change in light of ongoing results, prevailing economic circumstances, commodity prices and industry conditions and regulations. Accordingly, readers are cautioned that events or circumstances could cause results to differ materially from those predicted. The forward-looking information and statements contained in this news release speak only as of the date of this news release, and none of ARC or its subsidiaries assumes any obligation to publicly update or revise them to reflect new events or circumstances, except as may be required pursuant to applicable laws. ARC has adopted the standard 6 Mcf : 1 barrel when converting natural gas to boe. Boe may misleading, particularly if used in isolation. A boe conversion ratio of 6 Mcf : 1 barrel is based on an energy equivalency conversion method primarily applicable at the burner tip and does not represent a value equivalency at the wellhead. Given that the value ratio based on the current price of crude oil as compared to natural gas is significantly different than the energy equivalency of the 6:1 conversion ratio, utilizing the 6:1 conversion ratio may be misleading as an indication of value. ARC Resources Ltd. is one of Canada's largest conventional oil and gas companies with an enterprise value (1) of approximately $6.6 billion. ARC's common shares trade on the TSX under the symbol ARX.


Mao H.Y.,National University of Singapore | Laurent S.,University of Mons | Chen W.,National University of Singapore | Chen W.,University of Illinois at Urbana - Champaign | And 5 more authors.
Chemical Reviews | Year: 2013

Graphene, a two-dimensional (2D) sheet of sp2-hybridized carbon atoms packed into a honeycomb lattice, has led to an explosion of interest in the field of materials science, physics, chemistry, and biotechnology since the few-layers graphene (FLG) flakes were isolated from graphite in 2004. For an extended search, derivatives of nanomedicine such as biosensing, biomedical, antibacterial, diagnosis, cancer and photothermal therapy, drug delivery, stem cell, tissue engineering, imaging, protein interaction, DNA, RNA, toxicity, and so on were also added. Since carbon nanotubes are normally described as rolled-up cylinders of graphene sheets and the controllable synthesis of nanotubes is well developed, longitudinally unzipping carbon nanotubes represents a novel strategy to obtain graphene nanoribbons (GNRs) of precise dimensions.


Jenab A.,University of Windsor | Karimi Taheri A.,Sharif University of Technology
International Journal of Mechanical Sciences | Year: 2014

The hot deformation characteristics of 7075 aluminum alloy (AA7075) are investigated by means of hot compression tests carried out in the temperature range of 200-450 C and strain rate range of 0.0003-1 s-1. Two novel processing maps based on flow localization parameter and enhanced DMM are developed and compared with conventional DMM results. It is observed that processing maps based on flow localization parameter can be used successfully to predict AA7075 thermomechanical behavior. Also, the comparison of the DMM results indicates that the new approach to calculate DMM power dissipation efficiency and instability criteria corresponds better with experimental observations. The occurrence of dynamic recrystallization is probable in the temperature range of 400-450 C and strain rates of lower than 0.001 s -1. Moreover, the alloy demonstrated a wide range of flow instabilities at temperatures lower than 300 C and all strain rates tested where the occurrence of dynamic strain ageing is suggested at this domain. However, the most efficient temperature range to deform the alloy is suggested as 300-350 C at strain rates lower than 0.001 s-1. © 2013 Elsevier Ltd. All rights reserved.


Gholizadeh Vayghan A.,Alaodoleh Semnani Institute of Higher Education | Khaloo A.R.,Sharif University of Technology | Rajabipour F.,Pennsylvania State University
Cement and Concrete Composites | Year: 2013

This paper investigates the effects of acid normality (0.01-6 N HCl) and combustion retention time (0.25- 16 hours) on the pozzolanic properties of pre-combustion acid-treated rice husk ash. The pozzolanic reactivity was quantified by adding ground ash to saturated Ca(OH)2 solutions and monitoring the time-dependent electrical conductivity and pH of the solutions. Also, the strength activity of ashes from different processes was measured by testing the compressive strength of mortars. It was observed that acid treatment results in ashes with higher SiO2 content, lower alkali and unburned carbon content, better grindability, and smaller particle size, in comparison with ash from non-acid treated husks. Acid leaching increased the lime reactivity of the ashes and decreased their sensitivity to prolonged combustion times. Further, acid treatment with 0.01 N HCl was found to be sufficient, as the use of stronger acids did not considerably improve the pozzolanic reactivity of rice husk ash. © 2013 Elsevier Ltd. All rights reserved.


Aien M.,Kerman Graduate University of Technology | Fotuhi-Firuzabad M.,Sharif University of Technology | Rashidinejad M.,Shahid Bahonar University of Kerman
IEEE Transactions on Smart Grid | Year: 2014

As a matter of course, the unprecedented ascending penetration of distributed energy resources (DERs), mainly harvesting renewable energies (REs), is concomitant with environmentally friendly concerns. This type of energy resources are innately uncertain and bring about more uncertainties in the power system, consequently, necessitates probabilistic analyses of the system performance. Moreover, the uncertain parameters may have a considerable level of correlation to each other, in addition to their uncertainties. The two point estimation method (2PEM) is recognized as an appropriate probabilistic method in small scale or even medium scale problems. This paper develops a new methodology for probabilistic optimal power flow (P-OPF) studies for such problems by modifying the 2PEM. The original 2PEM cannot handle correlated uncertain variables but the proposed method has been equipped with this ability. In order to justify the impressiveness of the method, two case studies namely the Wood & Woollenberg 6-bus and the Mathpower 30-bus test systems are examined using the proposed method, then, the obtained results are compared against the Monte Carlo simulation (MCS) results. Comparison of the results justifies the effectiveness of the method in the respected area with regards to both accuracy and execution time criteria. © 2013 IEEE.


Jalali M.A.,Sharif University of Technology | Jalali M.A.,Institute for Advanced Study | Tremaine S.,Institute for Advanced Study
Monthly Notices of the Royal Astronomical Society | Year: 2012

We study the linear perturbations of collisionless near-Keplerian discs. Such systems are models for debris discs around stars and the stellar discs surrounding supermassive black holes at the centres of galaxies. Using a finite-element method, we solve the linearized collisionless Boltzmann equation and Poisson's equation for a wide range of disc masses and rms orbital eccentricities to obtain the eigenfrequencies and shapes of normal modes. We find that these discs can support large-scale 'slow' modes, in which the frequency is proportional to the disc mass. Slow modes are present for arbitrarily small disc mass so long as the self-gravity of the disc is the dominant source of apsidal precession. We find that slow modes are of two general types: parent modes and hybrid child modes, the latter arising from resonant interactions between parent modes and singular van Kampen modes. The most prominent slow modes have azimuthal wavenumbers m= 1 and m= 2. We illustrate how slow modes in debris discs are excited during a fly-by of a neighbouring star. Many of the non-axisymmetric features seen in debris discs (clumps, eccentricity, spiral waves) that are commonly attributed to planets could instead arise from slow modes; the two hypotheses can be distinguished by long-term measurements of the pattern speed of the features. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Ahmadi P.,Sharif University of Technology | Hajabdollahi H.,Iran University of Science and Technology | Dincer I.,University of Ontario Institute of Technology
Journal of Heat Transfer | Year: 2011

In the present work, a thermal modeling is conducted for optimal design of compact heat exchangers in order to minimize cost and entropy generation. In this regard, an εNTU method is applied for estimation of the heat exchanger pressure drop, as well as effectiveness. Fin pitch, fin height, fin offset length, cold stream flow length, no-flow length, and hot stream flow length are considered as six decision variables. Fast and elitist nondominated sorting genetic algorithm (i.e., nondominated sorting genetic algorithm II) is applied to minimize the entropy generation units and the total annual cost (sum of initial investment and operating and maintenance costs) simultaneously. The results for Pareto-optimal front clearly reveal the conflict between two objective functions, the number of entropy generation units and the total annual cost. It reveals that any geometrical changes, which decrease the number of entropy generation units, lead to an increase in the total annual cost and vice versa. Moreover, for prediction of the optimal design of the plate fin heat exchanger, an equation for the number of entropy generation units versus the total annual cost is derived for the Pareto curve. In addition, optimization of heat exchangers based on considering exergy destruction revealed that irreversibilities, such as pressure drop and high temperature difference between cold and hot streams, play a key issue in exergy destruction. Thus, more efficient heat exchanger leads to have a heat exchanger with higher total cost rate. Finally, the sensitivity analysis of change in the optimum number of entropy generation units and the total annual cost with change in the decision variables of the plate fin heat exchanger is also performed, and the results are reported. © 2011 American Society of Mechanical Engineers.


Kamyab G.-R.,Islamic Azad University at Tehran | Fotuhi-Firuzabad M.,Sharif University of Technology | Rashidinejad M.,Shahid Bahonar University of Kerman
International Journal of Electrical Power and Energy Systems | Year: 2014

This paper presents a particle swarm optimization (PSO) based approach to solve the multi-stage transmission expansion planning problem in a competitive pool-based electricity market. It is a large-scale non-linear combinatorial problem. We have considered some aspects in our modeling including a multi-year time horizon, a number of scenarios based on the future demands of system, investment and operating costs, the N - 1 reliability criterion, and the continuous non-linear functions of market-driven generator offers and demand bids. Also the optimal expansion plan to maximize the cumulative social welfare among the multi-year horizon is searched. Our proposed PSO based approach, namely modified PSO (MPSO), uses a diversity controlled PSO to overcome the problem of premature convergence in basic PSO (BPSO) plus an initial high diversity swarm to cover the search space efficiently. The MPSO model is applied to the Garver six-bus system and to the IEEE 24-bus test system and compared to the BPSO model and a genetic algorithm based model. © 2013 Elsevier Ltd. All rights reserved.


Feizollahi M.J.,Sharif University of Technology | Modarres M.,Sharif University of Technology
IEEE Transactions on Reliability | Year: 2012

We propose a robust deviation framework to deal with uncertain component reliabilities in the constrained redundancy optimization problem (CROP) in series-parallel reliability systems. The proposed model is based on a linearized binary version of standard nonlinear integer programming formulations of this problem. We extend the linearized model to address uncertainty by assuming that the component reliabilities belong to an interval uncertainty set, where only upper and lower bounds are known for each component reliability, and develop a Min-Max regret model to handle data uncertainty. A key challenge is that, because the deterministic model involves nonlinear functions of the uncertain data, classical robust deviation approaches cannot be applied directly to find robust solutions. We exploit problem structures to develop four exact solution methods, and present computational results demonstrating their performance. © 2012 IEEE.


Bigdeli M.,Islamic Azad University at Zanjan | Vakilian M.,Sharif University of Technology | Rahimpour E.,ABB
IET Electric Power Applications | Year: 2012

This study presents an intelligent fault classification method for identification of transformer winding fault through transfer function (TF) analysis. For this analysis support vector machine (SVM) is used. The required data for training and testing of SVM are obtained by measurement on two groups of transformers (one is a classic 20 kV transformer and the other is a model transformer) under intact condition and under different fault conditions (axial displacement, radial deformation, disc space variation and short circuit of winding). Two different features extracted from the measured TFs are then used as the inputs to SVM classifier for fault classification. The accuracy of proposed method is compared with the accuracy of past well-known works. This comparison indicates that the proposed method can be used as a reliable method for transformer winding fault recognition. © 2012 The Institution of Engineering and Technology.


Shakourian-Fard M.,Sharif University of Technology | Kamath G.,University of Missouri
Journal of Physical Chemistry C | Year: 2014

The adsorption of ionic liquids (ILs) on the hexagonal boron-nitride (h-BN) surface was studied at the M06-2X/cc-pVDZ level of theory. Three types of ionic liquids based on 1-butyl-3-methylimidazolium [Bmim]+, 1-butylpyridinium [Bpy]+, and butyltrimethylammonium [Btma]+ cations, paired with tetrafluoroborate [BF4]-, hexafluorophosphate [PF6]-, and bis(trifluoromethylsilfonyl)imide [Tf2N]- anions were chosen as the adsorbates to better understand the trends in adsorption behavior of ILs on the h-BN surface. We have identified the various stable configurations of the h-BN-ionic liquid (h-BN···IL) complexes based on their binding energies and investigated the effect of charge transfer behavior and noncovalent interactions on the adsorption of ILs. ChelpG analysis indicated that, upon adsorption of ionic liquids on the h-BN surface, the overall charge on the cation, anion, and h-BN surface changes and the transfer (CT) between ILs and h-BN surface occurs. The order for the magnitude of charge transfer between different ILs and the h-BN surface is as follows: [Bmim][Tf2N] (-0.059e) > [Btma][PF6] (0.036e) > [Bpy][Tf2N] (0.028e) > [Btma][Tf2N] (0.021e) > [Bmim][PF6] (0.009e) > [Bpy][BF4] (0.007e) > [Bpy][PF6] (-0.006e) > [Btma][BF4] (-0.003e) > [Bmim][BF4] (-0.001e), respectively. Orbital energy and density of states (DOSs) calculations also show that the HOMO-LUMO energy gap of ILs decreases upon adsorption on the h-BN surface. The order of the HOMO-LUMO gap energy changes of ILs upon adsorption on the h-BN surface is as follows: [Btma][PF6] (3.25 eV) > [Btma][BF4] (2.84 eV) > [Bpy][PF6] (2.41 eV) > [Bpy][BF4] (2.29 eV) > [Bmim][BF4] (1.76 eV) > [Bmim][PF6] (1.54 eV) > [Btma][Tf2N] (1.26 eV) > [Bmim][Tf2N] (1.19 eV) > [Bpy][Tf2N] (0.86 eV), respectively. The binding energies based on QTAIM analysis indicate that the [BF4]-, [PF6]-, and [Tf2N]- anions in the ILs have a stronger interaction with the h-BN surface than [Bmim]+, [Bpy]+, and [Btma]+ cations. The role of cooperative PI ···, C-H···, and X··· (X = N, O, F atoms from anions) interactions on the adsorption of ILs on the h-BN surface was elucidated by analyzing the noncovalent interactions between ILs and the h-BN surface. Energy decomposition analysis (EDA) carried out for the h-BN···IL complexes indicates that the contribution of the Edisp component in each complex is also more than electrostatic (Eelect) and orbital (Eorb) components (Edisp > Eelect> Eorb), with the exception of the h-BN[Btma][BF4] complex whose Edisp and Eelect components are almost equal. For the complexes with the same cations, dispersion interaction increases by increasing size of anion from [BF4]- to [PF6]- and [Tf2N]-. This is confirmed by more favorable enthalpy of adsorption for ILs on the h-BN surface. The thermochemical analysis also indicates that the free energy of adsorption (Gads) of ILs on the h-BN surface is negative, and thus, the adsorption occurs spontaneously. Our first-principles study offers fundamental insights into the nature of the physisorption and solvation behavior of ionic liquids on h-BN. © 2014 American Chemical Society.


News Article | September 22, 2016
Site: www.sciencenews.org

It’s a problem that sounds simple, but the best minds in mathematics have puzzled over it for generations: A salesman wants to hawk his wares in several cities and return home when he’s done. If he’s only visiting a handful of places, it’s easy for him to schedule his visits to create the shortest round-trip route. But the task rapidly becomes unwieldy as the number of destinations increases, ballooning the number of possible routes. Theoretical computer scientist Shayan Oveis Gharan, an assistant professor at the University of Washington in Seattle, has made record-breaking advances on this puzzle, known as the traveling salesman problem. The problem is famous in mathematical circles for being deceptively easy to describe but difficult to solve. But Oveis Gharan has persisted. “He is relentless,” says Amin Saberi of Stanford University, Oveis Gharan’s former Ph.D. adviser. “He just doesn’t give up.” Oveis Gharan’s unwavering focus has enabled him to identify connections between seemingly unrelated areas of mathematics and computer science. He scrutinizes the work of the fields’ most brilliant minds and adapts those techniques to fit his purposes. This strategy — bringing new tools to old problems — is the basis for leaps he has made on two varieties of the traveling salesman problem. “If you want to build a house, you need to have a sledgehammer and a level, a wrench, tape measure,” he says. “You need to have a lot of tools and use them one after another.” Oveis Gharan, age 30, stocks his toolkit with the latest advances in fields with obscure-sounding names, including spectral graph theory, polyhedral theory and geometry of polynomials. And in a twist that only Oveis Gharan saw coming, a recent solution to a long-standing problem originating in quantum mechanics turned out to be the missing piece to one aspect of the salesman’s puzzle. For a salesman’s tour of five cities, there are just 12 possible routes; it’s easy enough to pick the one that will save the most gas. But for 20 cities, there are 60 quadrillion possibilities, and for 80 cities, there are more routes than the number of atoms in the observable universe. Relying on brute force — calculating the distances of all the possible routes — is intractable for all but the easiest cases. Yet no one has found a simple method that can quickly find the shortest path for any number and arrangement of cities. The quandary has real-world importance: Companies like Amazon and Uber, for example, want to ferry goods and people to many destinations in the most efficient way possible. Growing up in his home country of Iran, Oveis Gharan discovered a natural appreciation for challenging puzzles. In middle school, he acquired a book of problems from mathematics Olympiad competitions in the Soviet Union. As a student, “I tend to be one of the slower ones,” Oveis Gharan says, noting that he was usually not the first to grasp a new theorem. But within a few years, he had doggedly plowed through the 200-page book. The effort also provided Oveis Gharan with his first taste of tool collecting, through collaboration with classmates who joined him in working through the math problems. Oveis Gharan found that solutions come easier when many minds contribute. “Each person thinks and solves problems differently,” he says. “Once someone is exposed to many different ideas and ways of thinking on a problem, that will help a lot to increase the breadth of problem-attacking directions.” Oveis Gharan attended Sharif University of Technology in Tehran before making his first breakthroughs on the traveling salesman problem as a graduate student at Stanford University. He spent over a year cracking just one thorny facet, before moving on to a postdoctoral fellowship at the University of California, Berkeley. Rather than attacking the problem head-on, Oveis Gharan works on approximate solutions — routes that are slightly longer than the optimal path but can be calculated in a reasonable amount of time. Since the 1970s, computer scientists have known of a strategy for quickly finding a route that is at most 50 percent longer than the shortest possible path. That record held for decades, until Oveis Gharan tackled it along with Saberi and Mohit Singh, then of McGill University in Montreal. In a paper published in 2011, the team made what might sound like an infinitesimal improvement, shrinking the 50-percent figure by four hundredths of a trillionth of a trillionth of a trillionth of a trillionth of a percentage point. “People make fun of our paper because of that small improvement,” says Oveis Gharan, “but the thing is that in our area, the actual number is not the major question.” Instead, the goal is to develop new ideas that can begin to crack the problem open, says Luca Trevisan, a computer scientist at Berkeley. “What’s so important is not the specific algorithm that he has devised, but that there is a whole new set of techniques that can potentially be applied to other problems.” Following the advance, other scientists revisited the traveling salesman problem, and decreased the number significantly; the selected route is now at most 40 percent longer than optimal. To make his breakthroughs, Oveis Gharan keeps tabs on the scientific literature across a variety of mathematical fields. “Every time new papers or new techniques come out, he’s one of the first people who will pick up the paper and read it,” says Saberi. To discover tools outside his areas of expertise, Oveis Gharan poses pieces of the problem to researchers in other fields. In 2015, Oveis Gharan and computer scientist Nima Anari, then at Berkeley, made further progress on an approximate solution for a more general, and more challenging, version of the traveling salesman problem. In this version, the distance to go from point A to point B might not be the same as going the opposite direction — a plausible situation in cities with many one-way streets. Researchers had a way to estimate the optimum tour length, but they didn’t understand how good the estimate was. Oveis Gharan and Anari showed it was exponentially better than known previously. To make this advance, Oveis Gharan teased out connections to a seemingly unrelated problem in mathematics and quantum mechanics, known as the Kadison-Singer problem. “That was really surprising,” says computer scientist Daniel Spielman of Yale University, part of a team that solved the Kadison-Singer problem in 2013. “There was no obvious connection,” he says. “Shayan is incredibly brilliant and incredibly creative.” Oveis Gharan is now focused on a furtherconquest of this version of the traveling salesman problem. Though his new advance helps approximate the optimal tour length, it can’t identify the corresponding route. Next, Oveis Gharan would like to produce an algorithm that can navigate the correct course. You can bet he’ll continue to add to his tool collection by sampling from related mathematical and computational fields. “The grand plan is: Try to better understand how these different areas are connected to one another,” Oveis Gharan says. “There are many big open problems lying in this intersection.”


News Article | October 27, 2016
Site: news.mit.edu

The School of Engineering will welcome 13 new faculty members to its departments, institutes, labs, and centers during the 2016-17 academic year. With research and teaching activities ranging from nuclear fusion to computational complexity theory, they are poised to make vast contributions to new directions across the school and to a range of labs and centers across the Institute. “We are pleased to welcome such a talented group of faculty to engineering at MIT this year,” says Ian A. Waitz, dean of the School of Engineering. “Every year we broaden the scope and the scale of what we can do, and of how we think about engineering. Our new faculty are often the ones who show us the way forward.” The new School of Engineering faculty members are: Adam Belay will join the Department of Electrical Engineering and Computer Science as an assistant professor in July 2017. He holds a PhD in computer science from Stanford University, where he was a member of the secure computer systems group and the multiscale architecture and systems team. Previously, he worked on storage virtualization at VMware Inc. and contributed substantial power-management code to the Linux Kernel project. Belay’s research area is operating systems and networking. Much of his work has focused on restructuring computer systems so that developers can more easily reach the full performance potential of hardware. He received a Stanford graduate fellowship, a VMware graduate fellowship, and an OSDI Jay Lepreau best paper award. Matteo Bucci will join the Department of Nuclear Science and Engineering (NSE) faculty as an assistant professor in the fall of 2016. He received his PhD in nuclear engineering from the University of Pisa in Italy in 2009. A research scientist in NSE since 2015, Bucci was previously at Commissariat à l’énergie atomique in France, where he led several research projects in experimental and computational thermal-hydraulics for light water reactors and sodium fast reactors. His research will focus in two main areas: heat transfer nanoengineering innovations to improve the safety and economic competitiveness of nuclear reactors, and advanced diagnostics and intelligent systems to improve situational awareness, fault detection and diagnostics, and anticipated failures in nuclear power plants. Bucci is an active member of the Consortium for Advanced Nuclear Energy Systems, one of the MIT’s eight Low-Carbon Energy Centers. Tal Cohen will join the Department of Civil and Environmental Engineering as an assistant professor in November 2016. After she received her PhD in aerospace engineering in 2013 from Technion University in Israel, she came to MIT for a two-year postdoctoral position in the Department of Mechanical Engineering. She is currently a postdoc at the School of Engineering and Applied Sciences at Harvard University. Cohen works in mechanics, especially the mechanics of structures subjected to extreme loading conditions and shock wave propagation. Her work on the mechanics of stretchable materials that can undergo extreme deformations up to loss of stability, and on the mechanics of growth in both biology and engineering, exploits analogies with related fields. By employing complex nonlinear material models, Cohen’s research group will focus on deriving theoretical models that can significantly affect our understanding of observed phenomena but are still simple enough to be applied in design or characterization of materials. Zachary Hartwig will join the Department of Nuclear Science and Engineering in January 2017 as an assistant professor. He will also receive a co-appointment at the MIT Plasma Science and Fusion Center (PSFC). He received his PhD from MIT in 2014 for the development of a novel accelerator-based technique that advanced the ability to study the dynamic interaction of confined plasmas and the surrounding solid materials — known as plasma-material interactions — in fusion devices. Since 2014, he has been a postdoc at the PSFC, continuing to develop diagnostic techniques for plasma-material interactions, leading the establishment of a new laboratory for accelerator-based nuclear science, and leading the design of high-magnetic field net energy gain fusion devices that leverage new superconducting magnet technology. Hartwig’s research will focus on the development and application of particle accelerators, radiation detectors, and computational radiation transport simulations to magnetic fusion energy, nuclear security, and radiation damage in nuclear materials. He presently holds a U.S. Department of Energy ORISE Fellowship in the fusion energy sciences and is the recipient of the Del Favero doctoral thesis prize. Ali Jadbabaie joined the MIT faculty as a full professor with dual appointments in the Department of Civil and Environmental Engineering and the Institute for Data, Systems, and Society in July 2016. He is currently the JR East Professor of Engineering, the director of the Sociotechnical Systems Research Center, and the associate director of the Institute for Data, Systems, and Society at MIT. He is also a principal investigator in the Laboratory for Information and Decision Systems. Jadbabaie received his BS from Sharif University of Technology in Tehran, Iran, his MS in electrical and computer engineering from the University of New Mexico, and his PhD in control and dynamical systems from Caltech. After a year as a postdoc at Yale University, he joined the faculty at University of Pennsylvania in July 2002. At Penn he was named an associate professor with tenure in 2008, a full professor in 2011, and the Alfred Fitler Moore Professor of Network Science in 2013. He also held appointments in computer and information science and operations as well as information and decisions in the Wharton School of Business. Jadbabaie is the inaugural editor-in-chief of IEEE Transactions on Network Science and Engineering, an interdisciplinary journal sponsored by several IEEE societies. He is a recipient of a National Science Foundation Career Award, an Office of Naval Research Young Investigator Award. In 2015, he received the Vannevar Bush Fellowship (formerly known as National Security Science and an Engineering Faculty Fellowship) from the office of Secretary of Defense. Jadbabaie’s students have won and been finalists of numerous best paper awards at various ACC and CDC conferences. He is also an IEEE fellow. He has made foundational contributions to the field of collective autonomy and opinion dynamics, and his current research interests include the interplay of dynamic systems and networks with specific emphasis on multi-agent coordination and control, distributed optimization, network science, and network economics. Carmen Guerra-Garcia will join the Department of Aeronautics and Astronautics as an assistant professor in the fall of 2017. Graduating from the Universidad Politecnica de Madrid with an aeronautical engineering degree in 2007, Guerra-Garcia then matriculated in the Space Propulsion Laboratory at MIT. She completed her PhD with a concentration in plasma physics and propulsion and a minor in numerical methods in 2014. Following a one-year postdoctoral position with Professor Paulo Lozano, Guerra-Garcia relocated to Boeing Madrid for a year. Her research will focus on the study of plasmas for aerospace applications, including plasma-assisted combustion, space propulsion, and lightning strikes on aircraft. Stefanie Mueller will join the Department of Electrical Engineering and Computer Science as an assistant professor in January 2017. She received her PhD in human-computer interaction (HCI) from the Hasso Plattner Institute in 2016, where she also received an MS in IT-systems engineering. In her research, Mueller develops novel interactive hardware and software systems that advance personal fabrication technologies. Her work has been published at the most selective HCI venues — Association for Computing Machinery (ACM), the Conference for Human Factors in Computing Systems (CHI), and User Interface Software and Technology (UIST) — and received a best paper award and two best-paper nominees. Mueller is an associate chair of the program committees at ACM, CHI, and UIST, and is a general co-chair for the ACM SIGGRAPH Symposium on Computational Fabrication that will take place at MIT in June 2017. She has been an invited speaker at MIT, Stanford, the University of California at Berkeley, Harvard, Carnegie Mellon University, Cornell University, Microsoft Research, Disney Research, Adobe Research, and others. In addition, her work has been covered widely in New Scientist, BBC, The Atlantic, and The Guardian. Mueller will head the HCI engineering group at MIT's Computer Science and Artificial Intelligence Laboratory, which works at the intersection of human-computer interaction, computer graphics, computer vision, and robotics. Jennifer Rupp will join the Department of Materials Science and Engineering as an assistant professor in January 2017. She studied at the University of Vienna before receiving a PhD in Materials at ETH Zurich. Rupp is a French and German native and is currently an assistant professor of electrochemical materials at ETH Zurich in Switzerland. She was a researcher at the National Institute of Materials Science in Tsukuba, Japan, in 2011, and previously collaborated with MIT professors Tuller and Yildiz. Her research is primarily in solid-state information memory systems, energy storage, and energy harvesting devices. She has worked on new material architectures and ionic transport-structure relations for solid-state ionic conductor thin films, electrochemistry and system aspects for memristors, solid-state batteries, solar-to-fuel conversion, and micro-fuel cells. Rupp’s awards include “top 40 scientist speaker under the age of 40” at the World Economic Forum, Spark Award for most innovative and economic invention by ETH Zurich, and Kepler Award for New Energy Materials by the European Academy of Science. Max Shulaker joined the Department of Electrical Engineering and Computer Science as an assistant professor in July. He received his BS, master’s, and PhD in electrical engineering at Stanford, where he was a Fannie and John Hertz Fellow and a Stanford Graduate Fellow. Shulaker’s research focuses on the broad area of nanosystems. His Novel Electronic Systems Group aims to understand and optimize multidisciplinary interactions across the entire computing stack — from low-level synthesis of nanomaterials, to fabrication processes and circuit design for emerging nanotechnologies, up to new architectures — to enable the next generation of high performance and energy-efficient computing systems. Zachary P. Smith will join the Department of Chemical Engineering as an assistant professor in January, 2017. Smith earned his bachelor’s degree in chemical engineering from Pennsylvania State’s Schreyer Honors College, and completed his PhD in chemical engineering at the University of Texas at Austin, where he worked under the guidance of Benny Freeman and Don Paul. While at UT Austin, Smith developed structure/property relationships for gas diffusion and sorption in polymer membranes. His postdoctoral training with Jeffrey Long at the UC Berkeley examined the design of coordination solid (i.e. metal-organic frameworks) for selective adsorption based separations. His research focuses on the molecular-level design, synthesis, and characterization of polymers and inorganic materials for applications in membrane and adsorption-based separations. These efforts are promising for gas-phase separations critical to the energy industry and to the environment, such as the purification of olefins and the capture of CO from flue stacks at coal-fired power plants. Smith has co-authored over 20 peer-reviewed papers and been recognized with several awards, including the DoE Office of Science Graduate Fellowship. He was also selected as a U.S. delegate to the Lindau Nobel Laureate meeting on Chemistry in 2013. David Sontag will join the Department of Electrical Engineering and Computer Science in January 2017 as an assistant professor, and he will be part of the Institute for Medical Engineering (IMES) and Science and the Computer Science and Artificial Intelligence Laboratory. He has been an assistant professor in computer science and data science at New York University’s Courant Institute of Mathematical Sciences since 2011. Previously, he was a postdoc at Microsoft Research New England. Sontag’s research interests are in machine learning and artificial intelligence with a recent focus on unsupervised learning, a problem of discovering hidden variables from data, and causal inference, which seeks to estimate the effect of interventions from observational data. As part of IMES, he will lead a research group that aims to transform health care through the use of machine learning. Sontag received the Sprowls award for his PhD thesis at MIT in 2010, best paper awards at the conferences EMNLP, UAI, and NIPS, and a National Science Foundation Early Career award in 2014. Ryan Williams will join MIT as an associate professor (with tenure) in the Department of Electrical Engineering and Computer Science in January 2017, pending the approval of his tenure case by the Executive Committee. He received an BA in computer science and mathematics from Cornell, and a PhD in computer science from Carnegie Mellon. Following postdoctoral appointments at the Institute for Advanced Study (Princeton) and IBM Almaden, he was an assistant professor of computer science at Stanford for five years. Williams’s research interests are in the theoretical design and analysis of efficient algorithms and in computational complexity theory, focusing mainly on new connections (and consequences) forged between algorithm design and logical circuit complexity. Along with some best paper awards, Williams has received a Sloan Fellowship, an NSF CAREER Award, a Microsoft Research Faculty Fellowship, and was an invited speaker at the 2014 International Congress of Mathematicians. Virginia Vassilevska Williams will join electrical engineering and computer science as an associate professor in January 2017, pending the approval of her case by Academic Council. She received a BS in mathematics and engineering and applied science from Caltech and a PhD in computer science from Carnegie Mellon. She was a postdoctoral fellow at the Institute for Advanced Study (Princeton), UC Berkeley, and Stanford. Prior to joining MIT, she spent three and a half years as an assistant professor at Stanford. Her research interests are broadly in theoretical computer science, focusing on the design and analysis of algorithms and fine-grained complexity. Her work on matrix multiplication algorithms was covered by the press and is the most cited paper in algorithms and complexity in the last five years.


News Article | October 23, 2015
Site: news.mit.edu

Twelve new faculty members have been invited to join the ranks of the School of Engineering at MIT. Drawn from institutions and industry around the world, and ranging from distinguished senior researchers to promising young investigators, they will contribute to the research and educational activities of six academic departments in the school and a range of other labs and centers across the Institute. “This year we are welcoming another exceptionally strong group of new faculty to engineering,” says Ian A. Waitz, Dean of the School of Engineering. “They are remarkably accomplished, and their research spans some of the most important and pressing challenges in the world. I can’t wait to see what they do.” The new School of Engineering faculty members are: Mohammad Alizadeh will join the faculty as an assistant professor in the Department of Electrical Engineering and Computer Science in September 2015. He was a principal engineer at Cisco, which he joined through the acquisition of Insieme Networks in 2013. Alizadeh completed his undergraduate degree in electrical engineering at Sharif University of Technology and received his PhD in electrical engineering in 2013 from Stanford University, where he was advised by Balaji Prabhakar. His research interests are broadly in the areas of networked systems, data-center networking, and cloud computing. His dissertation focused on designing high-performance packet-transport mechanisms for data centers. His research has garnered significant industry interest: The Data Center TCP congestion control algorithm has been integrated into the Windows Server 2012 operating system; the QCN algorithm has been standardized as the IEEE 802.1Qau standard; and most recently, the CONGA adaptive load-balancing mechanism has been implemented in Cisco’s new flagship Application Centric Infrastructure products. Alizadeh is a recipient of a SIGCOMM best-paper award, a Stanford Electrical Engineering Departmental Fellowship, the Caroline and Fabian Pease Stanford Graduate Fellowship, and the Numerical Technologies Inc. Prize and Fellowship. Tamara Broderick will start as an assistant professor in electrical engineering and computer science in January 2015. She received a BA in mathematics from Princeton in 2007, a master of advanced study for completion of Part III of the Mathematical Tripos from the University of Cambridge in 2008, an MPhil in physics from the University of Cambridge in 2009, and an MS in computer science and a PhD in statistics from the University of California at Berkeley in 2013 and 2014, respectively. Her recent research has focused on developing and analyzing models for scalable, unsupervised learning using Bayesian nonparametrics. She has been awarded the Evelyn Fix Memorial Medal and Citation (for the PhD student on the Berkeley campus showing the greatest promise in statistical research), the Berkeley Fellowship, a National Science Foundation Graduate Research Fellowship, and a Marshall Scholarship. Michael Carbin will join the Department of Electrical Engineering and Computer Science as an assistant professor in January 2016. His research interests include the theory, design, and implementation of programming systems, including languages, program logics, static and dynamic program analyses, run-time systems, and mechanized verifiers. His recent research has focused on the design and implementation of programming systems that deliver improved performance and resilience by incorporating approximate computing and self-healing. Carbin’s research on verifying the reliability of programs that execute on unreliable hardware received a best-paper award at a leading programming languages conference (OOPSLA 2013). His undergraduate research at Stanford received the Wegbreit Prize for Best Computer Science Undergraduate Honors Thesis. As a graduate student at MIT, he received the MIT-Lemelson Presidential and Microsoft Research Graduate Fellowships. James Collins joined the faculty in the Department of Biological Engineering and as a core member of the Institute for Medical Engineering and Science. Collins received a PhD in mechanical engineering from the University of Oxford and was formerly the William F. Warren Distinguished Professor, university professor, professor of biomedical engineering, and director of the Center of Synthetic Biology at Boston University. He is a world leader in bringing together engineering principles and fundamental biology to make new discoveries and invent systems that can improve the human condition. Collins is among the founders of the field of synthetic biology. Otto X. Cordero will join the Department of Civil and Environmental Engineering as an assistant professor. He received a BS in computer and electrical engineering from the Polytechnic University of Ecuador, and an MS in artificial intelligence and PhD in theoretical biology from Utrecht University. For his dissertation, Cordero worked with Paulien Hogeweg on the scaling laws that govern the evolution of genome size in microbes. While a Netherlands Organization for Scientific Research Postdoctoral Fellow working with Martin Polz, he pursued a study of ecological and social interactions in wild populations of bacteria, and demonstrated the importance of these interactions in generating patterns of diversity and sustaining ecological function. In 2013 Cordero was awarded the European Research Council Starting Grant, the most prestigious career award in Europe, to reconstruct and model networks of ecological interactions that form between heterotrophic microbes in the ocean. Since November 2013, he has been an assistant professor at the Swiss Federal Institute of Technology in Zurich. The main goal of Cordero’s lab is to develop the study of natural microbial communities as dynamical systems, using a combination of experimental and computational approaches. Areg Danagoulian joined the faculty in the Department of Nuclear Science and Engineering (NSE) as an assistant professor in July 2014. He received a BS in physics from MIT and a PhD in experimental nuclear physics from the University of Illinois at Urbana-Champaign. He was a postdoctoral associate at the Los Alamos National Laboratory and subsequently worked as a senior scientist at Passport Systems Inc. Danagoulian’s research interests are focused in nuclear security. He works on problems in the areas of nuclear nonproliferation, technologies for arms-control treaty verification, nuclear safeguards, and nuclear-cargo security. Specific projects include the development of zero-knowledge detection concepts for weapon authentication, and research on monochromatic, tunable sources that can be applied to active interrogation of cargoes. Other areas of research include nuclear forensics and the development of new detection concepts. Danagoulian’s research and teaching will contribute to NSE’s growing program in nuclear security. Ruonan Han joined the electrical engineering and computer science faculty in September as an assistant professor. He is also a core member of the Microsystems Technology Laboratories. He earned his BS from Fudan University in 2007, an MS in electrical engineering from the University of Florida in 2009, and his PhD in electrical and computer engineering from Cornell University in 2014. Han’s research group aims to explore microelectronic-circuit and system technologies to bridge the terahertz gap between microwave and infrared domains. They focus on high-power generation, sensitive detection and energy-efficient systems. Han is the recipient of the Electrical Computing and Engineering Director’s Best Thesis Research Award and Innovation Award from Cornell, the Solid-State Circuits Society Pre-Doctoral Achievement Award and Microwave Theory Techniques Society Graduate Fellowship Award from IEEE, as well as the Best Student Paper Award from IEEE Radio-Frequency Integrated Circuits Symposium. Juejun (JJ) Hu joined the faculty in the Department of Materials Science and Engineering in January 2015 as an assistant professor and as the Merton C. Flemings Career Development Professor of Materials Science and Engineering. He comes to MIT from the University of Delaware, where he was a tenure-track assistant professor. Previously, he was a postdoc in MIT’s Microphotonics Center. As the Francis Alison Young Professor, Hu initiated and led research projects involving environmental monitoring, renewable energy, biological sensing, and optical communications. He received the 2013 Gerard J. Mangone Young Scholars Award, which recognizes promising and accomplished young faculty and is the University of Delaware’s highest faculty honor. His research is in three main areas: substrate-blind multifunctional photonic integration, mid-infrared integrated photonics, and 3-D photonic integrated circuits. Hu’s group has applied photonic technologies to address emerging application needs in environmental monitoring, renewable energy harvesting, communications, and biotechnology. He earned a BS in materials science and engineering from Tsinghua University, and a PhD from MIT. Rafael Jaramillo will join the materials science and engineering faculty as an assistant professor and the Toyota Career Development Professor in Materials Science and Engineering in the summer of 2015. He has a BS summa cum laude and an MEng, both in applied and engineering physics, from Cornell University. He also holds a PhD in physics from the University of Chicago. Jaramillo is currently a senior postdoctoral fellow at MIT in the Laboratory of Manufacturing and Productivity (LMP). His interests in renewable energy and accomplishments in developing materials systems and techniques for energy applications led to him receiving the Energy Efficiency and Renewable Energy Postdoctoral Research Fellowship from the U.S. Department of Energy. Prior to his appointment in LMP, Jaramillo was a postdoctoral fellow at the Harvard University Center for the Environment. His research interests lie at the intersection of solid-state physics, materials science, and renewable energy technologies. Stefanie Jegelka joined the faculty in the electrical engineering and computer science in January 2015. Formerly a postdoctoral researcher in the Department of Electrical Engineering and Computer Science at the University of California at Berkeley, she received a PhD in computer science from the Swiss Federal Institute of Technology in Zurich (in collaboration with the Max Planck Institute for Intelligent Systems in Tuebingen, Germany), and a diploma in bioinformatics with distinction from the University of Tuebingen in Germany. During her studies, she was also a research assistant at the Max Planck Institute for Biological Cybernetics and spent a year at the University of Texas at Austin. She conducted research visits to Georgetown University, the University of Washington, the University of Tokyo, the French Institute for Research in Computer Science and Automation, and Microsoft Research. She has been a fellow of the German National Academic Foundation and its College for Life Sciences, and has received a Google Anita Borg Fellowship, a Fellowship of the Klee Foundation, and a Best Paper Award at the International Conference on Machine Learning. Jegelka organized several workshops on discrete optimization in machine learning, and has held three tutorials on submodularity in machine learning at international conferences. Her research interests lie in algorithmic machine learning. In particular, she is interested in modeling and efficiently solving machine-learning problems that involve discrete structure. She has also worked on distributed machine learning, kernel methods, clustering, and applications in computer vision. Aleksander Madry is a former assistant professor in the Swiss Federal Institute of Technology in Lausanne (EPFL) School of Computer and Communication Sciences and started as an assistant professor in electrical engineering and computer science in February 2015. His research centers on tackling fundamental algorithmic problems that are motivated by real-world optimization. Most of his work is concerned with developing new ideas and tools for algorithmic graph theory, with a particular focus on approaching central questions in that area with a mix of combinatorial and linear-algebraic techniques. He is also interested in understanding uncertainty in the context of optimization — how to model it and cope with its presence. Madry received his PhD in computer science from MIT in 2011 and, prior to joining EPFL, spent a year as a postdoctoral researcher at Microsoft Research New England. His work was recognized with a variety of awards, including the Association for Computing Machinery Doctoral Dissertation Award Honorable Mention, the George M. Sprowls Doctoral Dissertation Award, and a number of best paper awards at Foundations of Computer Science, Symposium on Discrete Algorithms, and Symposium on Theory of Computing meetings. Xuanhe Zhao joined the Department of Mechanical Engineering faculty in September 2014 as an assistant professor. Before joining MIT, he was an assistant professor in the Department of Mechanical Engineering and Materials Science at Duke University. He earned his PhD at Harvard University in 2009. Zhao conducts research on the interfaces between solid mechanics, soft materials, and bio-inspired design. His current research goal is to understand and design new soft materials with unprecedented properties for impactful applications. His current research projects are centered on three bio-inspired themes: artificial muscle (dielectric polymers and electromechanics), tough cartilage (tough and bioactive hydrogels and biomechanics), and transformative skin (functional surface instabilities and thin-film mechanics). Zhao’s discovery of new failure mechanisms of dielectric polymers in 2011 and 2012 can potentially enhance electric energy densities of dielectric elastomers and gels by a factor of 10. In 2012, he designed a new synthetic biocompatible hydrogel with hybrid crosslinking, which achieved fracture toughness multiple times higher than articular cartilage — unprecedented by previous synthetic gels. With fiber reinforcements, Zhao further controlled the modulus of the tough hydrogel over a wide range from a few kilopascals to over 10 megapascals in 2013 and 2014. By harnessing surface instabilities such as wrinkles and creases in 2014, he dynamically varied both surface textures and colors of an electro-mechano-chemically responsive elastomers to achieve the dynamic-camouflage function of cephalopods. This work was highlighted by Nature News, reported by the The Washington Post, and featured on the MIT homepage: “How to hide like an octopus.” Xuanhe is a recipient of the National Science Foundation CAREER Award, Office of Naval Research Young Investigator Program Award, and the Early Career Researchers Award from AVS Biomaterial Interfaces Division.


News Article | October 28, 2015
Site: www.nature.com

The Islamic civilization lays claim to the world's oldest continually operational university. The University of Qarawiyyin was founded in Fes, Morocco, in ad 859, at the beginning of an Islamic Golden Age. Despite such auspicious beginnings, universities in the region are now in dire straits, as demonstrated by a report we have authored, released this week (see go.nature.com/korli3). The 57 countries of the Muslim world — those with a Muslim-majority population, and part of the Organisation of Islamic Cooperation (OIC) — are home to nearly 25% of the world's people. But as of 2012, they had contributed only 1.6% of the world's patents, 6% of its academic publications, and 2.4% of the global research expenditure1, 2 (see 'Quarter deck'). There have been only three Nobel laureates in the sciences from OIC countries; today these nations host fewer than a dozen universities in the top 400 of the many world rankings, and none in the top 100. To assess this situation, for the past two years we have led an international non-governmental and non-partisan task force of experts, formed by the Muslim World Science Initiative. The task force was chaired by Zakri Abdul Hamid, science adviser to the prime minister of Malaysia. It included a dozen experts and scholars — including policymakers, vice-chancellors, professors, and science communicators — from around the world. Our work confirmed many widely known problems, as highlighted by reports such as the Royal Society's 2014 Atlas of Islamic World Science and Innovation2. For example, OIC countries on average invest less than 0.5% of their gross domestic product (GDP) on research and development (R&D). Only Malaysia spends slightly more than 1% (the world average is 1.78%; most advanced countries spend 2–3%). Students in the Muslim world who participate in standardized international science tests lag well behind their peers worldwide, and the situation seems to be worsening3, 4. Our report highlights an even more problematic situation. University science programmes are using narrow content and outdated teaching methods. In most OIC countries, students are channelled into science or non-science streams around the age of 14, and their education thereafter is completely binary: science and technology students receive little in the way of humanities, social-science, language or arts education, and vice versa. Only one university in the region offers a programme in 'science and technology studies': the University of Malaya in Kuala Lumpur. To become beacons in society, OIC universities need to revitalize their teaching methods and meld science with liberal arts such as history and philosophy. For universities to become truly meritocratic, they must develop new ways of assessing faculty members to reward valuable research, teaching and outreach. And for this to happen, governments must give universities more autonomy. Our task force gathered data on science production for the 20 OIC countries that together have represented more than 90% of OIC scientific productivity over the past two decades. From the period 1996–2005 to 2006–15, most countries doubled or tripled their production of science papers. Qatar's output rocketed by a factor of 7.7, and Iran's by 7.6. But the number of scientific papers produced remains below the average of countries with similar GDP per capita. We found an average of 4.2 papers per dollar of GDP per capita for our OIC sample in the most recent decade, compared to an average of 8.6 for a group of 4 peer countries such as Brazil, Spain, South Korea, South Africa and Israel (see Supplementary Information). Papers from these OIC countries are cited less frequently than those from other nations. The average was 5.7 citations per paper for 2006–15, compared with 9.7 for South Africa and 13.8 for Israel, countries with a comparable GDP per capita. A list of the 100 most-cited papers since 1900 has none with a lead author from a Muslim-majority nation (see Nature 514, 550–553; 2014). Scientific research must be relevant and responsive to society's intellectual and practical needs. This dual goal seems to be out of sight — and often out of consideration — for most academic institutions in the region. For scientists and engineers to be creative, innovative and able to engage with questions of ethics, religion and the wider social purpose of research, students must receive a broad, liberal-arts-style education5. A few institutions attempt to relate their students' learning to their cultural backgrounds and contemporary knowledge. In the early 1970s, Tehran's Sharif University of Technology began a rich programme melding Islamic history, philosophy and culture with science and engineering. Its graduate programme in the philosophy of science remains the only one in the OIC that we are aware of. It is perhaps no coincidence that the most recent Times Higher Education world university rankings named Sharif University as the top Iranian university and number eight in the OIC. In recent years, US-style liberal-arts establishments have been set up in the region, modelled on the long-running and respected American University of Beirut and the American University in Cairo. One such is the American University of Sharjah (AUS) in the United Arab Emirates (UAE), which this year ranked seventh in the QS Rankings of universities in the 22 Arab countries. Fully home-grown and self-funded and with no formal affiliation with a US institution, the AUS requires science and engineering students to take roughly one-third of their required 40 or so courses in humanities, social sciences, language and communication. Habib University, founded last year in Karachi, Pakistan, also follows this model. Here, science and engineering students must take courses such as 'Understanding Modernity' and 'Hikma 1 & 2' — a two-course sequence that translates as 'traditional wisdom' — as well as many others that seek to create rounded rather than narrow engineering and science professionals. Other educational establishments should follow suit. Science classes themselves have serious problems. The textbooks used in OIC universities are often imported from the United States or Europe. Although the content is of a high standard, they assume a Western experience and use English or French as the language of instruction. This disadvantages many students, and creates a disconnect between their education and culture. To encourage the production of higher-quality, local textbooks and other academic material, universities need to reward staff for producing these at least as much as they do for research publication. Some basic facts are seen as controversial, and marginalized. Evolution, for example, is usually taught only to biology students, often as “a theory”, and is rarely connected to the rest of the body of knowledge. One ongoing study has found, for example, that most Malaysian physicians and medical students reject evolution (see go.nature.com/38cswo). Evolution needs to be taught widely and shown to be compatible with Islam and its culture6. Teaching the philosophy and history of science would help, too. The global consensus is that enquiry-based science education fosters the deepest understanding of scientific concepts and laws. But in most OIC universities, lecture-based teaching still prevails. Exceptions are rare. One is the Petroleum Institute, an engineering university in Abu Dhabi, UAE, where the faculty has created a hands-on experience with positive results on student interest and enrolment, particularly of women. Another problem is that faculty members rarely — if ever — receive any training or evaluation in pedagogy. This is true elsewhere in the world, but change is harder in many OIC nations. In most, curriculum changes, faculty appointments and promotions are set by ministry rules and decided by centralized commissions and bureaucracies. This leaves little room for universities to innovate. Universities in OIC nations need to be granted more autonomy to transform themselves into meritocracies that strive for scientific excellence and then lead rather than follow the winds of change towards greater transparency and meritocracy within their societies. Universities need to promote the right metrics, so that they do not inadvertently encourage plagiarism and junk science through pressure to publish. The region needs consistent data on science student and faculty profiles, curricula, pedagogy, language of instruction and so on, akin to what the Institute of Statistics of the United Nations Educational, Scientific and Cultural Organization collects — but at a fine-grained, university level. This is a task that must be undertaken by national or transnational bodies, such as the Islamic World Academy of Sciences (IAS) or the Islamic Educational, Scientific and Cultural Organization (ISESCO). We also call for reform of science curricula and pedagogy. Universities need to deliver more multidisciplinary, exploratory science education. A good start would be training for university teachers, with workshops on new tools and approaches. Barriers need to be broken between departments and colleges and new programmes constructed. Professors need to be free to teach topics that are not tightly regulated by ministries. There are grassroots efforts across the Muslim world to stimulate curiosity about science among students of all ages, operating without much government support. Ahmed Djebbar, an emeritus science historian at the University of Lille in France, has constructed an online, pre-university-level course called 'The Discoveries in Islamic Countries' available in three languages7, which relates science concepts to great discoveries and stories from the Islamic Golden Age. Such courses should be scaled up and shared by many institutions. Universities will need to implement reforms individually. We hope that the inspiration from a few islands of excellence will, in time, turn the tide of public and political opinion. There is precedent. In Pakistan, two private universities established in the 1980s — the Aga Khan University and Hospital in Karachi and Lahore University of Management Sciences — revolutionized medical and business education within a decade of their creation. Students elsewhere began demanding the standard set by these educational pioneers. The same can be done for science. Our task force is putting out an open call for universities across the Muslim world to join a voluntary Network of Excellence of Universities for Science (NEXUS), to be launched early next year. This peer group will be managed by the task force and housed in science adviser Zakri's office. We plan for NEXUS to run summer schools for university administrators, to monitor the progress of reforms at participating universities, and to issue a peer report card that will assess the performance of the universities in meeting milestones, thus recognizing and inspiring further improvements. True transformation will require much broader action from ministries, regulators and funding agencies, and these may be the most resistant to change. Without tough reforms, the dream of a scientific revival in the Muslim world will remain just that.


Heidaryan E.,Kermanshah University of Technology | Jarrahian A.,Sharif University of Technology
Canadian Journal of Chemical Engineering | Year: 2013

Accurate value determination of natural gas viscosity plays a key role in its management as it is one of the most important parameters in natural gas engineering calculations. In this study, a comprehensive model is suggested for prediction of natural gas viscosity in a wide range of pressures, temperatures, densities and compositions. The new model can be applicable for gases containing heptane plus and non-hydrocarbon components. It is validated by the 2011 viscosity data from 18 different gas mixtures. Compared to existing similar models and correlations, its results are quite satisfactory. © 2012 Canadian Society for Chemical Engineering.


Jarrahian A.,Sharif University of Technology | Heidaryan E.,Kermanshah University of Technology
Journal of Supercritical Fluids | Year: 2012

In this paper, a new correlation to calculate the thermal conductivity of supercritical carbon dioxide based on 668 data points from the literature is introduced. The proposed correlation is valid in temperature range from 310 to 960 K, and pressures range between 7.4 and 210 MPa. The average absolute error of the model was found to be 2.7 and 2.4% in the comparison with the literature and NIST data respectively, which demonstrates superiority of the model over other methods. © 2012 Elsevier B.V. All rights reserved.


Motahari A.S.,Sharif University of Technology | Oveis-Gharan S.,Ciena | Maddah-Ali M.-A.,Alcatel - Lucent | Khandani A.K.,University of Waterloo
IEEE Transactions on Information Theory | Year: 2014

In this paper, we develop the machinery of real interference alignment. This machinery is extremely powerful in achieving the sum degrees of freedom (DoF) of single antenna systems. The scheme of real interference alignment is based on designing single-layer and multilayer constellations used for modulating information messages at the transmitters. We show that constellations can be aligned in a similar fashion as that of vectors in multiple antenna systems and space can be broken up into fractional dimensions. The performance analysis of the signaling scheme makes use of a recent result in the field of Diophantine approximation, which states that the convergence part of the Khintchine-Groshev theorem holds for points on nondegenerate manifolds. Using real interference alignment, we obtain the sum DoF of two model channels, namely the Gaussian interference channel (IC) and the X channel. It is proved that the sum DoF of the K -user IC is (K/2) for almost all channel parameters. We also prove that the sum DoF of the X -channel with K transmitters and M receivers is (KM/K+M-1) for almost all channel parameters. © 2014 IEEE.


Rahaeifard M.,Golpayegan University of Technology | Ahmadian M.T.,Sharif University of Technology
International Journal of Engineering Science | Year: 2015

In this paper the static deflection and pull-in instability of electrostatically actuated microcantilevers is investigated based on the strain gradient theory. The equation of motion and boundary conditions are derived using Hamilton's principle and solved numerically. It is shown that the strain gradient theory predicts size dependent normalized static deflection and pull-in voltage for the microbeam while according to the classical theory the normalized behavior of the microbeam is independent of its size. The results of strain gradient theory are compared with those of classical and modified couple stress theories and also experimental observations. According to this comparison, the classical theory underestimates the stiffness of the microbeam and there is a gap between the results predicted by the classical theory and those observed in experiment. It is demonstrated that this gap can be reduced when utilizing the strain gradient theory. © 2014 Elsevier Ltd.


Tohidi S.,Sharif University of Technology | Oraee H.,Sharif University of Technology | Zolghadri M.R.,Sharif University of Technology | Shao S.,University of Cambridge | Tavner P.,Durham University
IEEE Transactions on Industrial Electronics | Year: 2013

This paper discusses the dynamic behavior of the brushless doubly fed induction generator during the grid faults which lead to a decrease in the generator's terminal voltage. The variation of the fluxes, back EMFs, and currents are analyzed during and after the voltage dip. Furthermore, two alternative approaches are proposed to improve the generator ride-through capability using crowbar and series dynamic resistor circuits. Appropriate values for their resistances are calculated analytically. Finally, the coupled circuit model and the generator's speed and reactive power controllers are simulated to validate the theoretical results and the effectiveness of the proposed solutions. Moreover, experiments are performed to validate the coupled circuit model used. © 2012 IEEE.


Alaghemandi M.,University of Duisburg - Essen | Gharib-Zahedi M.R.,Sharif University of Technology | Spohr E.,University of Duisburg - Essen | Bohm M.C.,TU Darmstadt
Journal of Physical Chemistry C | Year: 2012

The thermal conductivity (λ) of nanoconfined polyamide-6,6 (PA) oligomers in polymer-graphene nanocomposites has been investigated by reverse nonequilibrium molecular dynamics (RNEMD) simulations. The preferential alignment of the PA chains parallel to the graphene plane as well as their elongation implies that λ of the polymer in nanocomposites is larger than that in the neat polymer system. The ordering of the polymer phase is enhanced in an arrangement of charged graphene surfaces made of one layer with a charge deficit and one with a charge excess. The consequence of the enhanced polymer ordering as well as the denser packing is an increase in λ in the polymer network. Differences in the thermal conductivity for an armchair and zigzag arrangement of the graphene sheets in the direction of the heat transfer are almost negligible. In contrast with this insensitivity, the present RNEMD simulations predict the largest value of λ for composites with the smallest number of PA chains between adjacent graphene sheets. The modifications in the polymer thermal conductivity are rationalized via several structural parameters such as PA bond orientation relative to the graphene sheets, end-to-end distance of polymer chains, and density profiles. © 2012 American Chemical Society.


Arabian-Hoseynabadi H.,Sharif University of Technology | Oraee H.,Sharif University of Technology | Tavner P.J.,Durham University
Renewable Energy | Year: 2010

This paper proposes a reliability model for the electrical subassemblies of geared wind turbine systems with induction generators. The model is derived considering the failure of main subassemblies and their parameters are calculated. A productivity comparison is performed between the selected wind turbine systems including reliability issues. Two methods of modification for variable-speed wind turbines with Doubly Fed Induction Generators (DFIG) to improve their availability are finally suggested. © 2009 Elsevier Ltd. All rights reserved.


Arabian-Hoseynabadi H.,Sharif University of Technology | Oraee H.,Sharif University of Technology | Tavner P.J.,Durham University
International Journal of Electrical Power and Energy Systems | Year: 2010

The Failure Modes and Effects Analysis (FMEA) method has been used to study the reliability of many different power generation systems. This paper now applies that method to a wind turbine (WT) system using a proprietary software reliability analysis tool. Comparison is made between the quantitative results of an FMEA and reliability field data from real wind turbine systems and their assemblies. These results are discussed to establish relationships which are useful for future wind turbine designs. The main system studied is an existing design 2 MW wind turbine with a Doubly Fed Induction Generator (DFIG), which is then compared with a hypothetical wind turbine system using the Brushless Doubly Fed Generator (BDFG) of the same rating. The software reliability analysis tool used for these studies was Relex Reliability Studio 2007 Version 2. © 2010 Elsevier Ltd. All rights reserved.


Saeedi H.,Tarbiat Modares University | Saeedi H.,Sharif University of Technology | Banihashemi A.H.,Carleton University
IEEE Transactions on Information Theory | Year: 2010

In this paper, new sequences (λn,ρn) of capacity achieving low-density parity-check (LDPC) code ensembles over the binary erasure channel (BEC) is introduced. These sequences include the existing sequences by Shokrollahi as a special case. For a fixed code rate R, in the set of proposed sequences, Shokrollahi's sequences are superior to the rest of the set in that for any given value of n, their threshold is closer to the capacity upper bound 1 - R. For any given δ, 0 < δ < 1 - R, however, there are infinitely many sequences in the set that are superior to Shokrollahi's sequences in that for each of them, there exists an integer number n0, such that for any n > n0, the sequence (λn, ρn) requires a smaller maximum variable node degree as well as a smaller number of constituent variable node degrees to achieve a threshold within δ-neighborhood of the capacity upper bound 1-R. Moreover, it is proven that the check-regular subset of the proposed sequences are asymptotically quasi-optimal, i.e., their decoding complexity increases only logarithmically with the relative increase of the threshold. A stronger result on asymptotic optimality of some of the proposed sequences is also established. © 2006 IEEE.


News Article | September 20, 2016
Site: www.nanotech-now.com

Home > News > Iran to hold intl. school on application of nanomaterials in medicine Iran to hold intl. school on application of nanomaterials in medicine Abstract: The International School on Applications of Nanomaterials in Medicine is due to be held at Sharif University of Technology early November, INIC announced Sat. Story: According to Iran Nanotechnology Initiative Council (INIC), the International School on Applications of Nanomaterials in Medicine will be held at Sharif University of Technology on 2-4 November 2016. The Third Physics of Advanced Materials (PAM) International School will be held to introduce the applications of nanomaterials in medicine, engineering and basic sciences to university lecturers, researchers and students in medicine, create an environment for cooperation between researchers in technical and engineering fields with medical researchers, introduce medical sciences with an approach to nanomaterials engineering, transfer know-how and technology in the field of medicine and nanotechnology and understand the importance of correctly selecting nanomaterials based on the required characteristics. Therefore, Iranian and international researchers active in the field of nanosciences and medical sciences have been invited to present their newest achievements in the School. Key speakers of the event include: Mohammad Reza Abidian, Biomedical Eng. Dept, Univ. of Houston, US; K.M. Krishnan, Washington University, Seattle, US; M. Angelakeris, Dept. of Phys., Univ. of Thessaloniki-Greece; Shirin Majd, Biomedical Eng. Dept., Univ. of Houston, US; and Hashem Rafii-Tabar, Shahid Beheshti Univ., Tehran, Iran. The scopes of the School include: Orthopedic and dental nanomaterials; Diagnosis and imaging; Drug delivery and gene therapy; Bio-printing of artificial organs; Stem cells; Toxicity of nanomaterials, standardization, and ethics in nanomedicine; and Wound healing and skin regeneration.


Nayyeri M.J.,Islamic Azad University at Tehran | Khomamizadeh F.,Sharif University of Technology
Journal of Alloys and Compounds | Year: 2011

In the present article, the effect of Rare Earth elements on the microstructural development of as cast and semisolid Mg-4Al alloy produced by SIMA process is studied. Investigation conducted by metallographic observation, scanning electron microscope and quantitative metallographic methods. Results showed that alloy's dendrites turn into larger fully dendritic shape with sharp and narrow arms from equiaxed rosette type as the amount of RE elements increased from 0 through 4%. The effect of RE elements on the microstructure of the treated-alloys was detectable through elimination of vast number of intragranular liquid droplets as well as by decreasing kinetic of microstructural changes. It was shown that the trend of grain coarsening decreased drastically by addition of RE elements to the Mg-4Al alloy during partial remelting at 610 °C. Moreover, the effect of REs on the other parameters such as fraction of liquid, shape factor and particle size was studied. © 2010 Elsevier B.V. All rights reserved.


Kalantari M.,Iran National Institute of Genetic Engineering and Biotechnology | Kalantari M.,Sharif University of Technology | Kazemeini M.,Sharif University of Technology | Tabandeh F.,Iran National Institute of Genetic Engineering and Biotechnology | Arpanaei A.,Iran National Institute of Genetic Engineering and Biotechnology
Journal of Materials Chemistry | Year: 2012

Uniformly sized superparamagnetic single-shell nonporous (S1) and double-shell mesoporous silica nanocomposite particles with ∼130 nm magnetite cluster cores are synthesised in this study. Mesoporous particles are prepared with two BJH pore sizes (2.44 and 3.76 nm, designated as S2 and S3 particles, respectively). Once the lipase was immobilised on particles, our results showed that the enzyme loading capacities of mesoporous structures, i.e. S2 and S3, are higher than that for nonporous particles (S1). Hydrolytic activity tests reveal that immobilised lipases retain about 90% of the free enzyme's activity. Furthermore, comparing to the free enzyme, the thermal stability of immobilised enzymes is considerably enhanced, regardless of the silica matrix structure. Also, our results indicate that the rate of the enzymatic reaction is not influenced by the type of silica matrix used for lipase immobilisation, but immobilisation results in lower enzymatic reaction rates for the immobilised enzymes compared to the free enzyme. Finally, in examining the reusability, the immobilised lipases retained more than 76% of their initial activities after 5 times' reuse. © The Royal Society of Chemistry 2012.


Nasiri S.H.,Islamic Azad University at Tehran | Moravvej-Farshi M.K.,Tarbiat Modares University | Faez R.,Sharif University of Technology
IEEE Electron Device Letters | Year: 2010

We present a Nyquist stability criterion based on transmission line modeling for graphene nanoribbon (GNR) interconnects. This is the first instance that such an analysis has been presented for GNR, so far. In this analysis, the dependence of the degree of relative stability for multilayer GNR (MLGNR) interconnects on the geometry of each ribbon has been acquired. It is shown that, increasing the length and width, MLGNR interconnects become more stable. © 2006 IEEE.


Mondali M.,Islamic Azad University at Tehran | Abedian A.,Sharif University of Technology
International Journal of Non-Linear Mechanics | Year: 2013

The creep deformation behavior of short fiber composites has been studied by an approximate analytical model. A perfect fiber/matrix interfacial bond is assumed and a power law function is considered for describing the steady state creep behavior of the matrix material. The results obtained from the proposed analytical solution satisfy the equilibrium and constitutive creep equations. Also, a parametric study was undertaken to define the effects of geometric parameters on the steady state creep strain rate of short fiber composites. The present model is then validated using the results of finite element method. The predicted strain rate and stress components by the proposed analytical approach exhibit good agreement with the finite element results. © 2013 Elsevier Ltd.


Mousavi Anzehaee M.,Islamic Azad University at Tehran | Haeri M.,Sharif University of Technology
Journal of Process Control | Year: 2012

It is proposed to employ melting rate, heat input, and detaching droplet diameter as controlled variables to control heat and mass transfer to work piece in a gas metal arc welding process. A two-layer architecture with cascade configuration of PI and MPC controllers is implemented to incorporate existing constraints on the process variables, improve transient behavior of the closed-loop responses and reduce interaction level. Computer simulation results are presented to indicate usefulness of the proposed controlled variables selection and applying two-layer control architecture to control heat and mass transfer to work piece. © 2012 Elsevier Ltd.


Sadreddini S.,Islamic Azad University at Tehran | Afshar A.,Sharif University of Technology
Applied Surface Science | Year: 2014

In this study, the influences of different concentrations of SiO 2 nano sized particles in the bath on deposition rate, surface morphology and corrosion behavior of Ni-P-SiO2 Composite coatings were investigated. The deposition rate of coating was influenced by incorporation of SiO2 particles. The microstructure was investigated with field emission scanning electron microscopy (FESEM). The amount of SiO 2 was examined by Energy Dispersive Analysis of X-Ray (EDX) and amount of SiO2 nanoparticles co-deposited reached a maximum value at 4.5 %wt. Corrosion behavior of coated aluminum was evaluated by electrochemical impedance spectroscopy (EIS) and polarization techniques. The results illustrated that the corrosion rate decreases (6.5-0.6 μA/cm2) and the corrosion potential increases (-0.64 to -0.3) with increasing the quantity of the SiO2 nanoparticles in the bath. Moreover, Ni-p-SiO2 nano-composite coating possesses less porosity than that in Ni-P coating, resulting in improving corrosion resistance. © 2014 Elsevier B.V.


Gholami R.M.,Islamic Azad University at Tehran | Borghei S.M.,Sharif University of Technology | Mousavi S.M.,Tarbiat Modares University
Hydrometallurgy | Year: 2011

A spent processing catalyst from an Iranian oil refinery was initially characterized physically and chemically. Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans were used to mobilize Al, Co, Mo and Ni from the spent catalysts under optimized conditions in batch cultures. The characteristics of the bioleach solution (pH, Eh, cell concentration and Fe(II)/Fe(III) concentration) were determined along with the concentration of metal values extracted from the catalyst. The results showed that after bioleaching using A. ferrooxidans in the presence of ferrous sulfate, maximum extractions of 63% Al, 96% Co, 84% Mo and 99% Ni were achieved after 30 days at pH 1.8-2.0. However, the highest extractions using A. thiooxidans in the presence of sulfur were 2.4% Al, 83% Co, 95% Mo and 16% Ni after 30 days at pH 3.9-4.4. The recovery of these metals decreases the environmental impact of the waste catalyst and the recycled product can be further used for industrial purposes. © 2010 Elsevier B.V.


Mahmoudi N.,Sharif University of Technology | Kaflou A.,Iranian Research Organization for Science and Technology | Simchi A.,Sharif University of Technology
Journal of Power Sources | Year: 2011

In the present work, high-energy mechanical alloying (MA) was employed to synthesize a nanostructured magnesium-based composite for hydrogen storage. The preparation of the composite material with composition of MgH2-5 at% (TiCr1.2Fe0.6) was performed by co-milling of commercial available MgH2 powder with the body-centered cubic (bcc) alloy either in the form of Ti-Cr-Fe powder mixture with the proper mass fraction (sample A) or prealloyed TiCr1.2Fe0.6 powder (sample B). The prealloyed powder with an average crystallite size of 14 nm and particle size of 384 nm was prepared by the mechanical alloying process. It is shown that the addition of the Ti-based bcc alloy to magnesium hydride yields a finer particle size and grain structure after mechanical alloying. As a result, the desorption temperature of mechanically activated MgH2 for 4 h decreased from 327 °C to 262 °C for sample A and 241 °C for sample B. A high dehydrogenation capacity (∼5 wt%) at 300 °C is also obtained. The effect of the Ti-based alloy on improvement of the dehydrogenation is discussed. © 2011 Elsevier B.V. All rights reserved.


Asgharzadeh H.,Sharif University of Technology | Simchi A.,Sharif University of Technology | Kim H.S.,Pohang University of Science and Technology
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2011

The microstructure and mechanical properties of the ultra-fine grained (UFG) Al6063 alloy reinforced with nanometric aluminum oxide nanoparticles (25 nm) were investigated and compared with the coarse-grained (CG) Al6063 alloy (∼2 μm). The UFG materials were prepared by mechanical alloying (MA) under high-purity Ar and Ar-5 vol pct O2 atmospheres followed by hot powder extrusion (HPE). The CG alloy was produced by HPE of the gas-atomized Al6063 powder without applying MA. Electron backscatter diffraction under scanning electron microscopy together with transmission electron microscopy studies revealed that the microstructure of the milled powders after HPE consisted of ultra-fine grains (>100 nm) surrounded by nanostructured grains (<100 nm), revealing the formation of a bimodal grain structure. The grain size distribution was in the range of 20 to 850 nm with an average of 360 and 300 nm for Ar and Ar-5 pct O2 atmospheres, respectively. The amount of oxide particles formed by reactive mechanical alloying under the Ar/O 2 atmosphere was ∼0.8 vol pct, whereas the particles were almost uniformly distributed throughout the aluminum matrix. The UFG materials exhibited significant improvement in the hardness and yield strength with an absence of strain hardening behavior compared with CG material. The fracture surfaces showed a ductile fracture mode for both CG and UFG Al6063, in which the dimple size was related to the grain structure. A mixture of ductile-brittle fracture mode was observed for the UFG alloy containing 0.8 vol pct Al 2O3 particles. The tensile behavior was described based on the formation of nonequilibrium grain boundaries with high internal stress and dislocation-based models. © 2010 The Minerals, Metals & Materials Society and ASM International.


Sadeghi J.,Islamic Azad University at Qazvin | Sadeghi S.,Islamic Azad University at Tehran | Niaki S.T.A.,Sharif University of Technology
Computers and Operations Research | Year: 2014

In this research, a bi-objective vendor managed inventory model in a supply chain with one vendor (producer) and several retailers is developed, in which determination of the optimal numbers of different machines that work in series to produce a single item is considered. While the demand rates of the retailers are deterministic and known, the constraints are the total budget, required storage space, vendor's total replenishment frequencies, and average inventory. In addition to production and holding costs of the vendor along with the ordering and holding costs of the retailers, the transportation cost of delivering the item to the retailers is also considered in the total chain cost. The aim is to find the order size, the replenishment frequency of the retailers, the optimal traveling tour from the vendor to retailers, and the number of machines so as the total chain cost is minimized while the system reliability of producing the item is maximized. Since the developed model of the problem is NP-hard, the multi-objective meta-heuristic optimization algorithm of non-dominated sorting genetic algorithm-II (NSGA-II) is proposed to solve the problem. Besides, since no benchmark is available in the literature to verify and validate the results obtained, a non-dominated ranking genetic algorithm (NRGA) is suggested to solve the problem as well. The parameters of both algorithms are first calibrated using the Taguchi approach. Then, the performances of the two algorithms are compared in terms of some multi-objective performance measures. Moreover, a local searcher, named simulated annealing (SA), is used to improve NSGA-II. For further validation, the Pareto fronts are compared to lower and upper bounds obtained using a genetic algorithm employed to solve two single-objective problems separately. © 2013 Elsevier Ltd.


Torshizian M.R.,Islamic Azad University at Tehran | Kargarnovin M.H.,Sharif University of Technology
Theoretical and Applied Fracture Mechanics | Year: 2010

An internal crack located within a functionally graded material (FGM) strip bonded with two dissimilar half-planes and under an anti-plane load is considered. The crack is oriented in an arbitrary direction. The material properties of strip are assumed to vary exponentially in the thickness direction and two half-planes are assumed to be isotropic. Governing differential equations are derived and to reduce the difficulty of the problem dealing with solution of a system of singular integral equations Fourier integral transform is employed. Semi closed form solution for the stress distribution in the medium is obtained and mode III stress intensity factor (SIF), at the crack tip is calculated and its validity was verified. Finally, the effects of nonhomogeneous material parameter and crack orientation on the stress intensity factor are studied. © 2010 Elsevier Ltd.


Ehyaei M.A.,Islamic Azad University at Tehran | Mozafari A.,Sharif University of Technology
Energy and Buildings | Year: 2010

This paper studies the optimization of micro turbine application to meet the electrical, heating and cooling loads of a building by energy, economics and environmental analysis. In this study following three cases are considered: 1: A simple micro gas turbine to meet the electrical power of the building. 2: A simple micro gas turbine to meet the electrical power of the building as well as the power required by heat pump and mechanical refrigerator needed for heating, cooling and domestic hot water (DHW) systems. 3: A CHP micro gas turbine to meet the electrical power of the building as well as part of the power required by heat pump and mechanical refrigerator needed for heating, cooling and DHW systems. The remaining part of the power for heat pump and mechanical refrigerator is provided by the exhaust gases. The research shows that the initial investment is a considerable portion of electricity cost. For an annual interest rate of 10% this portion ranges from 31 to 40% depending on system design configurations, and the lower interest rates results in the smaller portions. It is also concluded that the number of turbine units and electricity cost are highly depended on electricity consumption management. © 2009 Elsevier B.V. All rights reserved.


Alagheband M.R.,Islamic Azad University at Tehran | Aref M.R.,Sharif University of Technology
Security and Communication Networks | Year: 2013

Ubiquitousness of Radio Frequency Identification (RFID) systems with inherent weaknesses has been a cause of concern about their privacy and security. Therefore, secure protocols are essentially necessary for the RFID tags to guarantee privacy and authentication among them and the reader. This paper inspects privacy in the RFID systems. First, we survey four new-found RFID authentication protocols, and then, their weaknesses in formal privacy model are analyzed. Although the authors of the schemes claimed that their protocols completely resist privacy attacks, we formally prove that all of them suffer from the family of traceability attacks. Furthermore, not only are the four improved protocols proposed to prevent the aforementioned attacks, but also we provide formal analysis to guarantee the security and privacy of the proposed enhancements © 2012 John Wiley & Sons, Ltd.


Mamandi A.,Islamic Azad University at Tehran | Kargarnovin M.H.,Sharif University of Technology
Acta Mechanica | Year: 2011

In the first part of this paper, the nonlinear coupled governing partial differential equations of vibrations by including the bending rotation of cross section, longitudinal and transverse displacements of an inclined pinned-pinned Timoshenko beam made of linear, homogenous and isotropic material with a constant cross section and finite length subjected to a traveling mass/force with constant velocity are derived. To do this, the energy method (Hamilton's principle) based on the large deflection theory in conjuncture with the von-Karman strain-displacement relations is used. These equations are solved using the Galerkin's approach via numerical integration methods to obtain dynamic responses of the beam under act of a moving mass/force. In the second part, the nonlinear coupled vibrations of the beam traveled by an arbitrary number of successive moving masses/forces are investigated. To do a thorough study on the subject at hand, a parametric sensitivity analysis by taking into account the effects of the magnitude of the traveling mass or equivalent concentrated force, the velocity of the traveling mass/force, beam's inclination angle, length of the beam, height of the beam and spacing between successive moving masses/forces are carried out. Furthermore, the dynamic magnification factor and normalized time histories of the mid-point of the beam are obtained for various load velocity ratios, and the results are illustrated and compared to the results obtained from traditional linear solution. The influence of the large deflections caused by a stretching effect due to the beam's immovable end supports is captured. It is seen that the existence of quadratic-cubic nonlinear terms in the coupled governing PDEs of motion renders stiffening (hardening) behavior of the dynamic responses of the beam under the action of a moving mass/force. © 2010 Springer-Verlag.


Sadeghi J.,Islamic Azad University at Qazvin | Sadeghi S.,Islamic Azad University at Tehran | Niaki S.T.A.,Sharif University of Technology
Information Sciences | Year: 2014

Vendor-managed inventory (VMI) is a popular policy in supply chain management (SCM) to decrease bullwhip effect. Since the transportation cost plays an important role in VMI and because the demands are often fuzzy, this paper develops a VMI model in a multi-retailer single-vendor SCM under the consignment stock policy. The aim is to find optimal retailers' order quantities so that the total inventory and transportation cost are minimized while several constraints are satisfied. Because of the NP-hardness of the problem, an algorithm based on particle swarm optimization (PSO) is proposed to find a near optimum solution, where the centroid defuzzification method is employed for defuzzification. Since there is no benchmark available in the literature, another meta-heuristic, namely genetic algorithm (GA), is presented in order to verify the solution obtained by PSO. Besides, to make PSO faster in finding a solution, it is improved by a local search. The parameters of both algorithms are calibrated using the Taguchi method to have better quality solutions. At the end, conclusions are made and future research is recommended. © 2014 Elsevier Inc. All rights reserved.


Hemmati M.,Islamic Azad University at Tehran | Amjady N.,Semnan University | Ehsan M.,Sharif University of Technology
International Journal of Electrical Power and Energy Systems | Year: 2014

This paper presents a comprehensive operation model for micro-grids (MG) operating in the islanded mode. Various energy sources of a MG including diesel engine generator, micro-turbine, wind turbine and photovoltaic cell as well as battery storage and AC/DC rectifier/inverter are modeled in the proposed framework. Fuel costs, emission costs, and operation and maintenance (O&M) costs of these sources as well as their operating limits and characteristics are considered in the model. Furthermore, a new multi-cross learning-based chaotic differential evolution (MLCDE) algorithm is presented to solve the optimization problem of MG operation. The numerical results obtained from the proposed solution approach for three MG test cases with real-world data are compared with the results of several other recently published optimization methods. These comparisons confirm the validity of the developed approach. © 2013 Elsevier Ltd. All rights reserved.


Ahmadi M.A.,Petroleum University of Technology of Iran | Ebadi M.,Islamic Azad University at Tehran | Shokrollahi A.,Sharif University of Technology | Javad Majidi S.M.,Sharif University of Technology
Applied Soft Computing Journal | Year: 2013

Multiphase flow meters (MPFMs) are utilized to provide quick and accurate well test data in numerous numbers of oil production applications like those in remote or unmanned locations topside exploitations that minimize platform space and subsea applications. Flow rates of phases (oil, gas and water) are most important parameter which is detected by MPFMs. Conventional MPFM data collecting is done in long periods; because of radioactive sources usage as detector and unmanned location due to wells far distance. In this paper, based on a real case of MPFM, a new method for oil rate prediction of wells base on Fuzzy logic, Artificial Neural Networks (ANN) and Imperialist Competitive Algorithm is presented. Temperatures and pressures of lines have been set as input variable of network and oil flow rate as output. In this case a 1600 data set of 50 wells in one of the northern Persian Gulf oil fields of Iran were used to build a database. ICA-ANN can be used as a reliable alternative way without personal and environmental problems. The performance of the ICA-ANN model has also been compared with ANN model and Fuzzy model. The results prove the effectiveness, robustness and compatibility of the ICA-ANN model. © 2012 Elsevier B.V. All rights reserved.


Esmi Jahromi M.,Islamic Azad University at Tehran | Ehsan M.,Sharif University of Technology | Fattahi Meyabadi A.,Hamadan University of Technology
International Journal of Electrical Power and Energy Systems | Year: 2012

This paper presents a dynamic multi objective model for distribution network expansion, considering the distributed generators (DGs) and network reinforcements. The proposed model simultaneously optimizes three objective functions namely, total cost, emission cost and technical satisfaction (voltage profile) by finding the optimal schemes of timing, sizing, placement and DG technologies in a long term planning period (dynamic planning). The importance of each objective function can be changed in the interactive steps. The calculation algorithm is based on Chaotic Local Search with Modified Honey Bee Mating Optimization (CLSMHBMO). The effectiveness of the proposed model and the calculation method are demonstrated through different studies and comparative analysis on an actual distribution network. © 2012 Elsevier Ltd. All rights reserved.


Ghorbani A.,Islamic Azad University at Tehran | Mozafari B.,Islamic Azad University at Tehran | Ranjbar A.M.,Sharif University of Technology
International Journal of Electrical Power and Energy Systems | Year: 2012

In this paper the impact of Static Synchronous Series Compensator (SSSC) on the impedance calculated by distance relay is investigated. Analytical results are presented and verified by detailed simulations. Six different phase to phase and phase to ground measuring units of the distance relay are simulated to resemble the behavior of the relay. It is shown in this paper that zero sequence of the injected voltage by 48 pulse SSSC converter has the most impact on the apparent impedance seen by the phase to ground fault measuring unit and cause under reaching of distance relay. It can be concluded from the results that SSSC located in the middle of the transmission line cause to divide trip characteristics of distance relay into two separate parts. It is also shown that the over-reaching operation of distance relay might happen in some cases in the presence of SSSC. All the detailed simulations are carried out in MATLAB/Simulink environment. © 2012 Elsevier Ltd. All rights reserved.


Karimipour V.,Sharif University of Technology | Rad M.S.,Sharif University of Technology | Asoudeh M.,Islamic Azad University at Tehran
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We introduce a scheme for perfect state transfer in regular two- and three-dimensional structures. The interactions on the lattices are of the XX spin type with uniform couplings. In two dimensions, the structure is a hexagonal lattice, and in three dimensions, it consists of hexagonal planes joined to each other at arbitrary points. We will show that compared to other schemes, much less control is needed for routing, the algebra of global control is quite simple, and the same kind of control can upload and download qubit states to or from built-in read-write heads. © 2012 American Physical Society.


Asgharzadeh H.,University of Tabriz | Kim H.S.,Pohang University of Science and Technology | Simchi A.,Sharif University of Technology
Materials Characterization | Year: 2012

An ultrafine-grained Al6063/Al 2O 3 (0.8vol.%, 25nm) nanocomposite was prepared via powder metallurgy route through reactive mechanical alloying and hot powder extrusion. Scanning electron microcopy, transmission electron microscopy, and back scattered electron diffraction analysis showed that the grain structure of the nanocomposite is trimodal and composed of nano-size grains (<0.1μm), ultrafine grains (0.1-1μm), and micron-size grains (>1μm) with random orientations. Evaluation of the mechanical properties of the nanocomposite based on the strengthening-mechanism models revealed that the yield strength of the ultrafine-grained nanocomposite is mainly controlled by the high-angle grain boundaries rather than nanometric alumina particles. Hot deformation behavior of the material at different temperatures and strain rates was studied by compression test and compared to coarse-grained Al6063 alloy. The activation energy of the hot deformation process for the nanocomposite was determined to be 291kJmol -1, which is about 64% higher than that of the coarse-grained alloy. Detailed microstructural analysis revealed that dynamic recrystallization is responsible for the observed deformation softening in the ultrafine-grained nanocomposite. © 2012 Elsevier Inc.


Akhavan O.,Sharif University of Technology | Ghaderi E.,Nanobiotechnology Research Laboratory | Hashemi E.,Iran National Institute of Genetic Engineering and Biotechnology | Rahighi R.,Sharif University of Technology
Nanoscale | Year: 2014

Graphene oxide nanoplatelets (GONPs) with extremely sharp edges (lateral dimensions ∼20-200 nm and thicknesses <2 nm) were applied in extraction of the overexpressed guanine synthesized in the cytoplasm of leukemia cells. The blood serums containing the extracted guanine were used in differential pulse voltammetry (DPV) with reduced graphene oxide nanowall (rGONW) electrodes to develop fast and ultra-sensitive electrochemical detection of leukemia cells at leukemia fractions (LFs) of ∼10-11 (as the lower detection limit). The stability of the DPV signals obtained by oxidation of the extracted guanine on the rGONWs was studied after 20 cycles. Without the guanine extraction, the DPV peaks relating to guanine oxidation of normal and abnormal cells overlapped at LFs <10-9, and consequently, the performance of rGONWs alone was limited at this level. As a benchmark, the DPV using glassy carbon electrodes was able to detect only LFs ∼ 10-2. The ultra-sensitivity obtained by this combination method (guanine extraction by GONPs and then guanine oxidation by rGONWs) is five orders of magnitude better than the sensitivity of the best current technologies (e.g., specific mutations by polymerase chain reaction) which not only are expensive, but also require a few days for diagnosis. This journal is © The Royal Society of Chemistry.


Mousavi Anzehaee M.,Islamic Azad University at Tehran | Haeri M.,Sharif University of Technology
Control Engineering Practice | Year: 2011

A predictive functional controller based on ARMarkov model structure has been designed to control welding current and arc voltage in a GMAW process. The closed loop system performance is investigated through computer simulations and is compared by those achieved from implementing two commonly used controllers i.e. PI and feedback linearization based PID. The local stability of the closed loop system is analyzed in the presence of uncertainties in the linearized model of the process as well as the control parameters. Finally it is shown that the proposed controller performs like a PI controller along with a pre-filter compensator. © 2011 Elsevier Ltd.


Azadi M.,Sharif University of Technology | Azadi M.,Irankhodro Powertrian Company IPCo.
International Journal of Fatigue | Year: 2013

In this paper, effects of strain rate and mean strain on the cyclic behavior and the lifetime of aluminum-silicon alloys are investigated under thermo-mechanical and isothermal fatigue loadings. To achieve these goals, low cycle fatigue tests are accomplished at evaluated temperatures under various strain rates (by changing the loading frequency) and different strain ratios (minimum to maximum strain). Thermo-mechanical fatigue experiments are performed in an out-of-phase condition where the temperature varies between 50 and 250 °C. Various heating/cooling rates are taken into account to assess the strain rate effect and different starting temperatures are considered to study the mean strain effect. © 2012 Elsevier Ltd. All rights reserved.


Friedrich R.,University of Munster | Peinke J.,Carl von Ossietzky University | Sahimi M.,University of Southern California | Reza Rahimi Tabar M.,Carl von Ossietzky University | And 2 more authors.
Physics Reports | Year: 2011

This review addresses a central question in the field of complex systems: given a fluctuating (in time or space), sequentially measured set of experimental data, how should one analyze the data, assess their underlying trends, and discover the characteristics of the fluctuations that generate the experimental traces? In recent years, significant progress has been made in addressing this question for a class of stochastic processes that can be modeled by Langevin equations, including additive as well as multiplicative fluctuations or noise. Important results have emerged from the analysis of temporal data for such diverse fields as neuroscience, cardiology, finance, economy, surface science, turbulence, seismic time series and epileptic brain dynamics, to name but a few. Furthermore, it has been recognized that a similar approach can be applied to the data that depend on a length scale, such as velocity increments in fully developed turbulent flow, or height increments that characterize rough surfaces. A basic ingredient of the approach to the analysis of fluctuating data is the presence of a Markovian property, which can be detected in real systems above a certain time or length scale. This scale is referred to as the Markov-Einstein (ME) scale, and has turned out to be a useful characteristic of complex systems. We provide a review of the operational methods that have been developed for analyzing stochastic data in time and scale. We address in detail the following issues: (i) reconstruction of stochastic evolution equations from data in terms of the Langevin equations or the corresponding Fokker-Planck equations and (ii) intermittency, cascades, and multiscale correlation functions. © 2011 Elsevier B.V.


News Article | December 21, 2016
Site: www.prweb.com

SAE International announces that Kasra Ghahremani, PhD, Structural Diagnostics Engineer with Walter P. Moore, is winner of the Henry O. Fuchs Student Award. Established in 1991, this award recognizes a graduate or recently graduated student (i.e. post doctorate or new professor) that is working in the field of fatigue research and applications. The purpose of this award is to promote the education of engineering students in the area of fatigue technology. This award honors the memory of Professor Henry O. Fuchs. Professor Fuchs participated in the SAE Fatigue Design & Evaluation Committee's research projects, was a member of the faculty who founded the SAE Fatigue Concepts in Design short course, published extensively in SAE and elsewhere in the technical community, and actively participated in the Surface Enhancement Division of the Committee which is responsible for many standards relating to surface treatments of metals for withstanding fatigue damage. Dr. Ghahremani’s research during his graduate studies was primarily focused on the fatigue performance, assessment, and retrofitting of metal structures in the long-life regime. His research outcomes have been published in co-authorship with his scientific advisers and other collaborators in 20 journal and conference research papers. Prior to joining Walter P Moore, Dr. Ghahremani was a Post-Doctoral Research Fellow at George Mason University conducting research on detecting structural damage in 3D point clouds. He has received several national and institutional awards and scholarships including the prestigious Natural Sciences and Engineering Research Council of Canada (NSERC) Scholarship. Dr. Ghahremani received his PhD and MASc degrees in Structural Engineering from the University of Waterloo and BSc in Civil Engineering from Sharif University of Technology. SAE International is a global association committed to being the ultimate knowledge source for the engineering profession. By uniting more than 127,000 engineers and technical experts, we drive knowledge and expertise across a broad spectrum of industries. We act on two priorities: encouraging a lifetime of learning for mobility engineering professionals and setting the standards for industry engineering. We strive for a better world through the work of our philanthropic SAE Foundation, including programs like A World in Motion® and the Collegiate Design Series™.


Fallah A.,Amirkabir University of Technology | Fallah A.,Sharif University of Technology | Aghdam M.M.,Amirkabir University of Technology
European Journal of Mechanics, A/Solids | Year: 2011

In this study, simple analytical expressions are presented for large amplitude free vibration and post-buckling analysis of functionally graded beams rest on nonlinear elastic foundation subjected to axial force. Euler-Bernoulli assumptions together with Von Karman's strain-displacement relation are employed to derive the governing partial differential equation of motion. Furthermore, the elastic foundation contains shearing layer and cubic nonlinearity. He's variational method is employed to obtain the approximate closed form solution of the nonlinear governing equation. Comparison between results of the present work and those available in literature shows the accuracy of this method. Some new results for the nonlinear natural frequencies and buckling load of the FG beams such as the effect of vibration amplitude, elastic coefficients of foundation, axial force, and material inhomogenity are presented for future references. © 2011 Elsevier Masson SAS. All rights reserved.


Mostajeran A.,Sharif University of Technology | Mostajeran A.,Cornell University | Bakhtiar M.S.,Sharif University of Technology | Afshari E.,Cornell University
Digest of Technical Papers - IEEE International Solid-State Circuits Conference | Year: 2015

For the last few decades, phase-noise (PN) improvement of VCOs has been an intriguing problem and remains as one of the challenges in transceiver design. PN in CMOS VCOs, especially close-in PN, greatly suffers from flicker noise. The flicker noise can even degrade the PN at higher offset frequencies (∼1MHz). The close-in PN is important in many communication applications. For instance, IEEE 802.11a/b/g requires a very low PN at 10kHz offset frequency [1] and the PN performance at 100kHz is critical in cellular and Wi-Fi MIMO applications. In addition to the PN performance, oscillators with lower power consumption and smaller area are always on demand. © 2015 IEEE.


Malvandi A.,Amirkabir University of Technology | Moshizi S.A.,Amirkabir University of Technology | Soltani E.G.,Sharif University of Technology | Ganji D.D.,Babol Noshirvani University of Technology
Computers and Fluids | Year: 2014

This paper deals with the mixed convective heat transfer of nanofluids through a concentric vertical annulus. Because of the non-adherence of the fluid-solid interface in the presence of nanoparticle migrations, known as slip condition, the Navier's slip boundary condition was considered at the pipe walls. The employed model for nanofluid includes the modified two-component four-equation non-homogeneous equilibrium model that fully accounts for the effects of nanoparticles volume fraction distribution. Assuming the fully developed flow and heat transfer, the basic partial differential equations including continuity, momentum, and energy equations have been reduced to two-point ordinary boundary value differential equations and solved numerically. Two cases including constant heat flux at the outer wall and insulated inner wall (Case A) and constant heat flux at the inner wall with insulated outer wall (Case B) have been considered. Results indicate that the buoyancy has negative effects on the efficiency of the system; however, slip velocity at the surface enhances both the heat transfer rate and the efficiency. © 2013 Elsevier Ltd.


Adeli M.,Lorestan University | Adeli M.,Sharif University of Technology | Soleyman R.,Research Institute of Petroleum Industry RIPI | Beiranvand Z.,Lorestan University | Madani F.,Lorestan University
Chemical Society Reviews | Year: 2013

Despite the great potential of carbon nanotubes (CNTs) in various areas of biomedicine, concerns regarding their carcinogenicity, inefficient dispersion in aqueous solutions and biological activity in vivo still remain. One important and feasible route to overcome these barriers is modification of CNTs with polymers, which are widely studied and play a vital role in biological and biomedical fields, especially in drug delivery. This comprehensive review focuses on the achievements of our and other groups in currently used methods to functionalize the surface of CNTs with polymers to produce anticancer drug delivery systems. We have intensively studied covalent and noncovalent interactions between CNTs and linear, dendritic and hyperbranched biocompatible polymers as well as biomacromolecules interactions which are very crucial to diminish the toxicity of CNTs via changing their conformations. © 2013 The Royal Society of Chemistry.


Mahmoudi M.,Pasteur Institute of Iran | Mahmoudi M.,Tehran University of Medical Sciences | Hosseinkhani H.,National Yang Ming University | Hosseinkhani M.,Mount Sinai School of Medicine | And 6 more authors.
Chemical Reviews | Year: 2011

Fetal stem cells, which can be isolated from the organs of fetuses, differentiate along multiple lineages. Their advantages over their adult counterparts include better intrinsic homing and engraftment and lower immunogenicity, and they are less ethically contentious. It is noteworthy that Mesenchymal Stem Cells (MSC) can be activated and mobilized at the site of damaged tissue. Since vascular delivery suffers from a pulmonary first pass effect, direct or systemic injection of MSCs into the damaged tissue is preferred, particularly in the case of versatile tissue ischemia. Ultrasound applies acoustic energy with a frequency above human hearing (20 kHz). Ultrasound imaging or sonography scanners operate between 2 and 13 MHz. The frequency determines the image's spatial resolution and the penetration depth into the examined patient.


Nejati A.,Sharif University of Technology | Hosseini Jenab S.M.,Amirkabir University of Technology
Scientometrics | Year: 2010

The quantity and quality of scientific output of the topmost 50 countries in the four basic sciences (agricultural & biological sciences, chemistry, mathematics, and physics & astronomy) are studied in the period of the recent 12 years (1996-2007). In order to rank the countries, a novel two-dimensional method is proposed, which is inspired by the H-index and other methods based on quality and quantity measures. The countries data are represented in a "quantity-quality diagram", and partitioned by a conventional statistical algorithm into three clusters, members of which are rather the same in all of the basic sciences. The results offer a new perspective on the global positions of countries with regards to their scientific output. © 2009 Akadémiai Kiadó, Budapest, Hungary.


Forsati R.,Shahid Beheshti University | Mahdavi M.,Sharif University of Technology | Shamsfard M.,Shahid Beheshti University | Reza Meybodi M.,Amirkabir University of Technology | Reza Meybodi M.,Institute for Studies in Theoretical Physics and Mathematics IPM
Information Sciences | Year: 2013

Clustering has become an increasingly important and highly complicated research area for targeting useful and relevant information in modern application domains such as the World Wide Web. Recent studies have shown that the most commonly used partitioning-based clustering algorithm, the K-means algorithm, is more suitable for large datasets. However, the K-means algorithm may generate a local optimal clustering. In this paper, we present novel document clustering algorithms based on the Harmony Search (HS) optimization method. By modeling clustering as an optimization problem, we first propose a pure HS based clustering algorithm that finds near-optimal clusters within a reasonable time. Then, harmony clustering is integrated with the K-means algorithm in three ways to achieve better clustering by combining the explorative power of HS with the refining power of the K-means. Contrary to the localized searching property of K-means algorithm, the proposed algorithms perform a globalized search in the entire solution space. Additionally, the proposed algorithms improve K-means by making it less dependent on the initial parameters such as randomly chosen initial cluster centers, therefore, making it more stable. The behavior of the proposed algorithm is theoretically analyzed by modeling its population variance as a Markov chain. We also conduct an empirical study to determine the impacts of various parameters on the quality of clusters and convergence behavior of the algorithms. In the experiments, we apply the proposed algorithms along with K-means and a Genetic Algorithm (GA) based clustering algorithm on five different document datasets. Experimental results reveal that the proposed algorithms can find better clusters and the quality of clusters is comparable based on F-measure, Entropy, Purity, and Average Distance of Documents to the Cluster Centroid (ADDC). © 2012 Elsevier Inc. All rights reserved.


Pourjavadi A.,Sharif University of Technology | Hosseini S.H.,Sharif University of Technology | Soleyman R.,Research Institute of Petroleum Industry RIPI
Journal of Molecular Catalysis A: Chemical | Year: 2012

A dual acidic heterogeneous organocatalyst was synthesized by copolymerization of acidic ionic liquid monomer (vinyl-3-(3-sulfopropyl) imidazolium hydrogen sulfate [VSim][HSO 4]) and ionic liquid crosslinker (1,4-butanediyl-3,3′-bis-l-vinyl imidazolium dihydrogen sulfate). The resulting ionic heterogeneous catalyst is shown to be an efficient dual acidic organocatalyst for synthesis of dihydropyrimidines using the Biginelli synthetic route under mild reaction conditions in high yields. Since monomers make the catalyst bed, crosslinked poly(ionic liquid) will have high loading level of acidic groups comparing to other heterogeneous acid catalysts. Despite of conventional heterogeneous ionic liquid catalysts, present poly(ionic liquid) catalyst shows good thermal stability and good reusability. The crosslinked poly(ionic liquid) organocatalyst represents a novel class of high loaded heterogeneous catalyst which are particularly attractive in green chemistry. © 2012 Elsevier B.V.


Mardani A.,Sharif University of Technology | Tabejamaat S.,Amirkabir University of Technology | Hassanpour S.,Amirkabir University of Technology
Combustion and Flame | Year: 2013

Reduction of air pollutants formation from hydrocarbon combustion process requires improvements in combustion systems. The moderate and intense low oxygen dilution (MILD) combustion technique is an opportunity to achieve such a goal. MILD combustion is a combustion regime which can be attained by high temperature preheating and high level dilution. In this paper, the mechanism of CO and CO2 formation for a CH4/H2 fuel mixture is studied under MILD combustion condition of a jet in hot coflow (JHC) burner. This investigation is done using the computational fluid dynamics (CFD) and also zero dimensional well-stirred reactor (WSR) analysis. The RANS equations with modified k-ε equations are solved in an axisymmetric 2D computational domain. The DRM-22 reduced mechanism is considered to represent the chemical reactions. The effects of oxidizer oxygen concentration and fuel hydrogen content are studied on methane oxidation pathways. Results show that the higher hydrocarbon oxidation pathways are effective on CO and CO2 formation under MILD condition. In the methane oxidation mechanism, the ratio between the main route and ethane route is the main reason of CO increment at higher O2 level under MILD condition in JHC laboratory burner. The WSR analysis illustrates that a decrease of O2 concentration in oxidizer does not necessarily lead to lower production of CO and CO2. © 2013 The Combustion Institute.


Khorsandi A.,Amirkabir University of Technology | Hosseinian S.H.,Amirkabir University of Technology | Ghazanfari A.,Sharif University of Technology
Electric Power Systems Research | Year: 2013

This paper presents a fuzzy based modified artificial bee colony (MABC) algorithm to solve discrete optimal power flow (OPF) problem that has both discrete and continuous variables considering valve point effects. The OPF problem is formulated as a multi-objective mixed-integer nonlinear problem, where optimal settings of the OPF control variables for simultaneous minimization of total fuel cost of thermal units, total emission, total real power losses, and voltage deviation are obtained. The proposed approach is applied to the OPF problem on IEEE 30-bus and IEEE 118-bus test systems. The performance and operation of the proposed approach is compared with the conventional methods. The simulation results verify the effectiveness of the proposed method. © 2012 Elsevier B.V. All rights reserved.


Naderi M.,Louisiana State University | Hoseini S.H.,Sharif University of Technology | Khonsari M.M.,Louisiana State University
International Journal of Plasticity | Year: 2013

A three-dimensional (3D) finite element model (FEM) is developed to predict the progressive fatigue damage with provision for stochastic distribution of material properties. Fatigue damage model for low and high cycle fatigue considering plastic deformation is implemented in the FEM and the results are presented for Al 6061-T6, Al 7075-T6, Ti 6Al-4V and SS 316. Comparisons of the numerical and experimental results of stress-life reveal the validity of the approach. Also presented is the result of an investigation showing the effect of element types, element size, variation of material properties, and initial flaws on the randomness of fatigue life. The present fatigue damage simulation allows determining the scatter lifespan of mechanical components subjected to low and high cycle fatigue loading. © 2012 Elsevier Ltd. All rights reserved.


Beigy H.,Sharif University of Technology | Meybodi M.R.,Amirkabir University of Technology
Computers and Electrical Engineering | Year: 2011

In this paper, we first propose two learning automata based decentralized dynamic guard channel algorithms for cellular mobile networks. These algorithms use learning automata to adjust the number of guard channels to be assigned to cells of network. Then, we introduce a new model for nonstationary environments under which the proposed algorithms work and study their steady state behavior when they use LR-I learning algorithm. It is also shown that a learning automaton operating under the proposed nonstationary environment equalizes its penalty strengths. Computer simulations have been conducted to show the effectiveness of the proposed algorithms. The simulation results show that the performances of the proposed algorithms are close to the performance of guard channel algorithm that knows all the traffic parameters. © 2011 Elsevier Ltd. All rights reserved.


Azizi S.,University of Tehran | Gharehpetian G.B.,Amirkabir University of Technology | Dobakhshari A.S.,Sharif University of Technology
IEEE Transactions on Smart Grid | Year: 2013

This paper presents an integer linear programming (ILP) framework for the optimal placement of phasor measurement units (PMUs), in the presence of conventional measurements. Furthermore, by the proposed method, the power system remains completely observable during all possible single contingencies for lines and measurement devices. In doing so, the potential of circuit equations associated with both PMUs and conventional measurements as well as the network topology are fully utilized by a system of equations to reach the minimum possible numbers of required PMUs. The limitation of communication channels is also taken into account in the proposed ILP-based framework. The method is implemented on several IEEE test systems which have already been equipped with conventional measurements. The comparison between obtained results of the proposed method and those of other methods reveals its superiority in the modeling of robust PMU placement problem (OPP) in the presence of conventional measurements. As such, a smooth transition from the SCADA-based monitoring system to the PMU-dominated WAMS is ensured. Moreover, this method is successfully applied on three large-scale test systems, which demonstrates it can effectively be employed for robust OPP in realistic power systems. © 2010-2012 IEEE.


Niazadeh R.,Cornell University | Babaie-Zadeh M.,Sharif University of Technology | Jutten C.,CNRS GIPSA Laboratory | Jutten C.,Institut Universitaire de France
IEEE Transactions on Signal Processing | Year: 2012

Recently, it has been proved in Babadi [B. Babadi, N. Kalouptsidis, and V. Tarokh, "Asymptotic achievability of the Cramér-Rao bound for noisy compressive sampling", IEEE Trans. Signal Process., vol. 57, no. 3, pp. 1233-1236, 2009] that in noisy compressed sensing, a joint typical estimator can asymptotically achieve the Cramér-Rao lower bound of the problem. To prove this result, Babadi used a lemma, which is provided in Akçakaya and Tarokh [M. Akçakaya and V. Trarokh, "Shannon theoretic limits on noisy compressive sampling", IEEE Trans. Inf. Theory, vol. 56, no. 1, pp. 492-504, 2010] that comprises the main building block of the proof. This lemma is based on the assumption of Gaussianity of the measurement matrix and its randomness in the domain of noise. In this correspondence, we generalize the results obtained in Babadi by dropping the Gaussianity assumption on the measurement matrix. In fact, by considering the measurement matrix as a deterministic matrix in our analysis, we find a theorem similar to the main theorem of Babadi for a family of randomly generated (but deterministic in the noise domain) measurement matrices that satisfy a generalized condition known as "the concentration of measures inequality". By this, we finally show that under our generalized assumptions, the Cramér-Rao bound of the estimation is achievable by using the typical estimator introduced in Babadi © 2006 IEEE.


Maali Y.,University of Technology, Sydney | Mahdavi-Amiri N.,Sharif University of Technology
Information Sciences | Year: 2014

We consider a multi-objective linear programming model with type-2 fuzzy objectives. The considered model has the flexibility for the user to specify the more general membership functions for objectives to reflect the inherent fuzziness, while being simple and practical. We develop two solution strategies with reasonable computing costs. The additional cost, as compared to the type-1 fuzzy model, is indeed insignificant. These two algorithms compute Pareto optimal solutions of the type-2 problems, one being based on a maxmin approach and the other on aggregating the objectives. Finally, applying the proposed algorithms, we work out two illustrative examples. © 2014 Elsevier Inc. All rights reserved.


Hajmohammadi M.R.,Amirkabir University of Technology | Alizadeh Abianeh V.,Arak University | Moezzinajafabadi M.,Sharif University of Technology | Daneshi M.,University of Saskatchewan
Applied Thermal Engineering | Year: 2013

In engineering practice, the space occupied by high conductivity materials together with the cost are the two elements of major concern. Therefore, seeking for more efficient designs of high conductivity pathways ('inserts'), embedded into a heat generating body constitutes a formidable challenge. The main idea of this paper is to introduce new patterns for the highly conductive pathways, called 'fork-shaped' configurations. Essentially, two types of fork-shaped pathways, 'F1' and 'F2' are introduced. Numerical results demonstrate that, these two configurations of highly conductive pathways, remarkably surpass the latest configurations reported in the literature, with the same amount of high conductivity materials. It is further confirmed that the 'peak' temperature can be reduced by 41% and 46% by using fork-shaped pathways of 'F1' type, and 'F2' type, respectively, when compared with the base X-shaped inserts. To highlight the discovery found in this paper, it is proved that if only about one third of the high conductivity material used for an X-shaped insert are used for the fork-shaped insert, the heat generating body operates at the same level of peak temperature associated with the new configurations. © 2013 Elsevier Ltd. All rights reserved.


Beigy H.,Sharif University of Technology | Meybodi M.R.,Amirkabir University of Technology
IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics | Year: 2010

The cellular learning automaton (CLA), which is a combination of cellular automaton (CA) and learning automaton (LA), is introduced recently. This model is superior to CA because of its ability to learn and is also superior to single LA because it is a collection of LAs which can interact with each other. The basic idea of CLA is to use LA to adjust the state transition probability of stochastic CA. Recently, various types of CLA such as synchronous, asynchronous, and open CLAs have been introduced. In some applications such as cellular networks, we need to have a model of CLA for which multiple LAs reside in each cell. In this paper, we study a CLA model for which each cell has several LAs. It is shown that, for a class of rules called commutative rules, the CLA model converges to a stable and compatible configuration. Two applications of this new model such as channel assignment in cellular mobile networks and function optimization are also given. For both applications, it has been shown through computer simulations that CLA-based solutions produce better results. © 2009 IEEE.


Nezhadhaghighi M.G.,Sharif University of Technology | Nezhadhaghighi M.G.,University of Potsdam | Rajabpour M.A.,University of Sao Paulo
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We study different aspects of quantum von Neumann and Rényi entanglement entropy of one-dimensional long-range harmonic oscillators that can be described by well-defined nonlocal field theories. We show that the entanglement entropy of one interval with respect to the rest changes logarithmically with the number of oscillators inside the subsystem. This is true also in the presence of different boundary conditions. We show that the coefficients of the logarithms coming from different boundary conditions can be reduced to just two different universal coefficients. We also study the effect of the mass and temperature on the entanglement entropy of the system in different situations. The universality of our results is also confirmed by changing different parameters in the coupled harmonic oscillators. We also show that more general interactions coming from general singular Toeplitz matrices can be decomposed to our long-range harmonic oscillators. Despite the long-range nature of the couplings, we show that the area law is valid in two dimensions and the universal logarithmic terms appear if we consider subregions with sharp corners. Finally, we study analytically different aspects of the mutual information such as its logarithmic dependence to the subsystem, effect of mass, and influence of the boundary. We also generalize our results in this case to general singular Toeplitz matrices and higher dimensions. © 2013 American Physical Society.


Karami A.,Amirkabir University of Technology | Salehi V.,Sharif University of Technology
Journal of Catalysis | Year: 2012

A series of Cr-substituted Fe-Ti compounds were prepared by the co-precipitation method and were systematically investigated as catalysts for the selective catalytic reduction (SCR) of NO by NH 3. A variety of analytical techniques revealed that the Cr substitution amount affects the N 2 selectivity, SCR activity, redox behavior of NH 3/NO x, adsorption ability, and structure of catalysts in terms of surface properties, porosity, mobility of lattice oxygen, oxidative ability of Cr species, ratio of Bronsted acid sites and Lewis acid sites, NO x adsorption capacity, and structural disorder and distortion. In a series of Fe aCr 1-aTiO x (a = 1, 0.75, 0.5, 0.2, 0) catalysts, Fe 0.5Cr 0.5TiO x showed the highest activity because of the optimized interactions of Fe, Cr, and Ti species in this catalyst. © 2012 Elsevier Ltd. All rights reserved.


Taleizadeh A.A.,Iran University of Science and Technology | Niaki S.T.A.,Sharif University of Technology | Nikousokhan R.,University of Tehran
Applied Soft Computing Journal | Year: 2011

An uncertain economic order quantity (UEOQ) model with payment in advance is developed to purchase high-price raw materials. A joint policy of replenishments and pre-payments is employed to supply the materials. The rate of demand is considered LR-fuzzy variables, lead-time is taken to be constant, and it is assumed that shortage does not occur in the cycles. The cycle is divided into three parts; the first part is the time between the previous replenishment-time to the next order-time (t0), the second part is the period between t0 to a payment-time (tk), and the third part is the period between tk to the next replenishment-time. At the start of the second part (t0), α% of the purchasing cost is paid. The (1 - α)% remaining purchasing cost is paid at the start of the third part (tk). The cost of the model is purchasing under incremental discount for each order with rough cost per unit, clearance cost, fixed-order cost, transportation cost, holding, and capital cost. Holding cost is for on-hand inventory and capital cost is for the capital that is paid for the next order. The constraints of the problem are space, budget, and the number of orders per year. Further, lead-time is considered less than a cycle time. We show that the model of this problem is a fuzzy integer-nonlinear-programming type and in order to solve it, a hybrid method of harmony search, fuzzy simulation, and rough simulation is proposed. In order to validate the results and examine the performance of the proposed method, a genetic algorithm, as well as a particle swarm optimization method is also employed. The results of a numerical example show that the proposed procedure has the best performance in terms of the mean of the objective function in different simulation runs. At the end, a case study along with a sensitivity analysis is given to demonstrate the applicability of the proposed methodology in real world inventory control problems and to provide some managerial insights. © 2011 Elsevier B.V. All rights reserved.


Memarzadeh L.,Sharif University of Technology | Mancini S.,University of Camerino | Mancini S.,National Institute of Nuclear Physics, Italy
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We provide an analytical investigation of the entanglement dynamics for a system composed of an arbitrary number of qubits dissipating into a common environment. Specifically, we consider product initial states with a given number of excitations whose evolution remains confined on low-dimensional subspaces of the operators space. We then find for which pairs of qubits entanglement can be generated and can persist at a steady state. Finally, we determine the stationary distribution of entanglement as well as its scaling versus the total number of qubits in the system. © 2013 American Physical Society.


Taleizadeh A.A.,Iran University of Science and Technology | Niaki S.T.A.,Sharif University of Technology | Makui A.,Iran University of Science and Technology
Expert Systems with Applications | Year: 2012

In this paper, a multi-product multi-chance constraint joint single-vendor multi-buyers inventory problem is considered in which the demand follows a uniform distribution, the lead-time is assumed to vary linearly with respect to the lot size, and the shortage in combination of backorder and lost-sale is assumed. Furthermore, the orders are placed in multiple of packets, there is a limited space available for the vendor, there are chance constraints on the vendor service rate to supply the products, and there is a limited budget for each buyer to purchase the products. While the elements of the buyers' cost function are holding, shortage, order and transportation costs, the set up and holding costs are assumed for the vendor. The goal is to determine the re-order point and the order quantity of each product for each buyer such that the chain total cost is minimized. We show the model of this problem to be a mixed integer nonlinear programming type and in order to solve it a particle swarm optimization (PSO) approach is used. To justify the results of the proposed PSO algorithm, a genetic algorithm (GA) is applied as well to solve the problem. Then, the quality of the results and the CPU times of reaching the solution are compared through three numerical examples that are given to demonstrate the applicability of the proposed methodology in real world inventory control problems. The comparison results show the PSO approach has better performances than the GA method. © 2011 Elsevier Ltd. All rights reserved.


Benatti F.,University of Trieste | Benatti F.,National Institute of Nuclear Physics, Italy | Alipour S.,Sharif University of Technology | Rezakhani A.T.,Sharif University of Technology
New Journal of Physics | Year: 2014

Estimation of physical parameters is essential in almost any part of science and technology. The enhancement of performance in this task (e.g. beating the standard classical shot-noise limit) using available physical resources is a major goal in metrology. Quantum metrology in closed systems has indicated that entanglement in such systems may be a useful resource. However, whether in open quantum systems such enhancements may still show up is not yet fully understood. Here, we consider a dissipative (open) quantum system of identical particles in which a parameter of the open dynamics itself is to be estimated. We employ a recently developed dissipative quantum metrology framework, and investigate whether the entanglement produced in the course of the dissipative dynamics may help the estimation task. Specifically, we show that, even in a Markovian dynamics in which states become less distinguishable in time, at small enough times the entanglement generated by the dynamics may offer some advantage over the classical shot-noise limit. © 2014 IOP Publishing and Deutsche Physikalische Gesellschaft.


Soroudi A.,Islamic Azad University at Damavand | Ehsan M.,Sharif University of Technology
IEEE Transactions on Smart Grid | Year: 2013

This paper presents the application of information gap decision theory (IGDT) to help the distribution network operators (DNOs) in choosing the supplying resources for meeting the demand of their customers. The three main energy resources are pool market, distributed generations (DGs), and the bilateral contracts. In deregulated environment, the DNO is faced with many uncertainties associated to the mentioned resources which may not have enough information about their nature and behaviors. In such cases, the classical methods like probabilistic methods or fuzzy methods are not applicable for uncertainty modeling because they need some information about the uncertainty behaviors like probability distribution function (PDF) or their membership functions. In this paper, a decision making framework is proposed based on IGDT model to solve this problem. The uncertain parameters considered here, are as follows: price of electricity in pool market and demand of each bus. The robust strategy of DNO is determined to hedge him against the risk of increasing the total cost beyond what it is willing to pay. The effectiveness of the proposed tool is assessed and demonstrated by applying it on a large distribution network. © 2010-2012 IEEE.


Bayati M.R.,Iran University of Science and Technology | Golestani-Fard F.,Iran University of Science and Technology | Moshfegh A.Z.,Sharif University of Technology
Applied Catalysis A: General | Year: 2010

WO3-TiO2 nano porous layers were synthesized by micro arc oxidation (MAO) process under different applied voltages in electrolytes containing sodium tungstate and phosphate salts with various concentrations. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDS) techniques were employed to study phase structure and chemical composition of the layers. According to our data analysis, the nano porous layers consisted of anatase, rutile, and tungsten oxide phases with a varying fraction depending on the voltage and electrolyte concentration. Moreover, it was found that WO3 not only dispersed in the TiO2 matrix, but also doped into the TiO2 lattice. Morphological and topographical investigations, carried out by scanning electron microscopy (SEM) and atomic force microscopy (AFM), revealed a porous structure with a rough surface. The pore size and the surface roughness of the layers increased with the applied voltage or the electrolyte concentration. The absorption edge of the layers, measured by a UV-Vis spectrophotometer, was observed to shift toward longer wavelengths when WO3 was introduced to the TiO2 layers. The band gap energy was determined as 3.21 eV and 2.88 eV for the MAO-grown TiO2 and WO3-TiO2 systems, respectively. Furthermore, photocatalytic activity of the layers was also examined by measuring the decomposition rate of methylene blue under both ultraviolet and visible photo irradiations. It was observed that the composite layers were more photoactive as compared to MAO-synthesized pure TiO2 layers. A possible growth mechanism was also proposed for the formation of WO3-TiO2 films via MAO process with emphasis on the electrochemical bases for the first time. © 2010 Elsevier B.V. All rights reserved.


Bayati M.R.,Iran University of Science and Technology | Moshfegh A.Z.,Sharif University of Technology | Golestani-Fard F.,Iran University of Science and Technology
Electrochimica Acta | Year: 2010

Micro-arc oxidation process was used to synthesize V2O5-TiO2 porous layers for the first time. Surface morphology and topography of the layers were investigated by scanning electron microscope (SEM) and atomic force microscope (AFM). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques were also employed to evaluate phase structure and chemical composition of the layers. It was found that the V2O5-TiO2 layers consisted of anatase, rutile, and vanadium pentoxide phases fraction of which varied with the applied voltage and the electrolyte concentration. It was also revealed that pore size and surface roughness increased with the applied voltage and the electrolyte concentration. Optical properties of the layers were studied by a UV-vis spectrophotometer, and the band gap energies of the MAO-grown pure TiO2 and V2O5-TiO2 layers were respectively calculated as 3.21 and 2.56 eV. Furthermore, the composite layers exhibited a significantly enhanced photo-activity when compared to pure TiO2 layers. The photocatalytic reaction rate constants of degradation of methylene blue on the surface of the V2O5-TiO2 layers under ultraviolet and visible irradiations were measured as 0.0228 and 0.0117 min-1, respectively. As a consequence, micro-arc oxidation was deduced to be an appropriate and efficient method for synthesis of V2O5-TiO2 porous layers. © 2010 Elsevier Ltd. All rights reserved.


Bayati M.R.,Iran University of Science and Technology | Moshfegh A.Z.,Sharif University of Technology | Golestani-Fard F.,Iran University of Science and Technology
Electrochimica Acta | Year: 2010

TiO2 layers were grown via pulse type microarc oxidation process under different applied voltages, frequencies, and duty cycles. Surface chemical composition and phase structure of the synthesized layers were studied utilizing X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Furthermore, scanning electron microscope (SEM) and atomic force microscope (AFM) were employed to investigate surface morphology and topography of the layers. It was revealed that the layers had a porous structure with both anatase and rutile phases. The anatase relative content in the layers increased with the applied frequency; meanwhile, it decreased with duty cycle at low applied voltages, but increased with duty cycle at high applied voltages. The topographical evaluations showed that the surface of the layers is rough with an average roughness of about 1.8-9.9 nm. It was also found that the pore size decreased with the current frequency and increased with duty cycle at a fixed applied voltage. Photocatalytic performance of the layers was also examined by measuring the decomposition rate of methylene blue solution under ultraviolet irradiation of the surface. It was also found that about 94% of methylene blue solution was decomposed on the synthesized catalysts after 160 min UV irradiation of the surface. © 2009 Elsevier Ltd. All rights reserved.


Bayati M.R.,Iran University of Science and Technology | Moshfegh A.Z.,Sharif University of Technology | Golestani-Fard F.,Iran University of Science and Technology
Applied Catalysis A: General | Year: 2010

Sulfur doped TiO2 layers containing nano/micro-sized pores were synthesized by micro-arc oxidation process. Effect of the applied voltage and the electrolyte composition on physical and chemical properties of the layers was investigated using SEM, AFM, XRD, XPS, and EDS techniques. A UV-vis spectrophotometer was also used to study optical properties of the layers. It was found that the doped layers were porous with a pore size of 40-170 nm. They consisted of anatase and rutile phases with varying fraction depending on the applied voltage and electrolyte concentration. Our XPS investigations revealed the existence of sulfur in the forms of S4+ and S6+ states which substituted Ti4+ in the titania lattice. The sulfur concentration in the layers also increased with the voltage and the electrolyte concentration. Furthermore, the absorption edge of the doped layers shifted significantly toward longer wavelengths as compared to the pure TiO2 layers. The band gap energy was calculated as 2.29 eV for sulfur doped TiO 2 layers, respectively. Finally, photocatalytic activity of the layers was studied by measuring the degradation rate of methylene blue on their surface under UV and visible illuminations. The doped layers showed a slightly enhanced photoactivity than the pure layers under UV-irradiation, while their photocatalytic performance was much higher than that of pure layers under visible-irradiation. It was measured that about 92% and 66% of methylene blue was decomposed over doped layers under UV and visible irradiations, respectively. © 2010 Elsevier B.V. All rights reserved.


Ranjbar-Sahraei B.,Shiraz University | Ranjbar-Sahraei B.,Maastricht University | Shabaninia F.,Shiraz University | Nemati A.,Sharif University of Technology | Stan S.-D.,Technical University of Cluj Napoca
IEEE Transactions on Industrial Electronics | Year: 2012

In this paper, a novel decentralized adaptive control scheme for multiagent formation control is proposed based on an integration of artificial potential functions with robust control techniques. Fully actuated mobile agents with partially unknown models are considered, where an adaptive fuzzy logic system is used to approximate the unknown system dynamics. The robust performance criterion is used to attenuate the adaptive fuzzy approximation error and external disturbances to a prescribed level. The advantages of the proposed controller can be listed as robustness to input nonlinearity, external disturbances, and model uncertainties, and applicability on a large diversity of autonomous systems. A Lyapunov-function-based proof is given of robust stability, which shows the robustness of the controller with respect to disturbances and system uncertainties. Simulation results are demonstrated for a swarm formation problem of a group of six holonomic robots, illustrating the effective attenuation of approximation errors and external disturbances, even in the case of agent failure. Moreover, experimental results confirm the validity of the presented approach and are included to verify the applicability of the scheme for a swarm of six real holonomic robots. © 2012 IEEE.


Azadi M.,Sharif University of Technology | Azadi M.,Irankhodro Powertrain Company IPCo. | Shirazabad M.M.,Iran University of Science and Technology
Materials and Design | Year: 2013

In the present paper, the heat treatment effect on A356.0, a cast aluminum alloy which has been widely used in diesel engine cylinder heads, is investigated under out-of-phase thermo-mechanical fatigue and low cycle fatigue (at different temperatures) loadings. A typical heat treatment is applied to the material including 8. h solution at 535 °C, water quench and 3. h ageing at 180 °C. The experimental fatigue results show that the heat treatment process has considerable influence on mechanical and low cycle fatigue behaviors, especially at room temperature, but its effect on thermo-mechanical fatigue lifetime is not significant. The improvement in the strength can be explained by the dislocation theory. Under thermo-mechanical fatigue loadings, the difference between the fatigue lifetime of A356.0 alloy and A356.0-T6 alloy decreases when the temperature range increases. In this condition, plastic strain increases severely during the fatigue cycles in A356.0-T6 alloy due to over-ageing phenomenon and therefore, the amount of cyclic softening in heat treated alloy is more. © 2012 Elsevier Ltd.


Rahmati A.,Sharif University of Technology | Ghaemi A.,Iran University of Science and Technology | Samadfam M.,Sharif University of Technology
Annals of Nuclear Energy | Year: 2012

Thermodynamic and kinetic studies have been carried out on the adsorption of uranium(VI) by Amberlite IRA-910 resin. The adsorption process has been investigated as a function of adsorbate concentration, solution acidity, contact time, adsorbent dosage, and temperature. The experiments were preformed in batch mode, where uranium initial concentration on the solution samples were 185.5, 277.6 and 456.8 (mg/lit), sulfuric acid concentration range was 0.02-9 (mol/lit) and sorbent dosages were 0.2, 0.3 and 0.5 g. Equilibrium isotherm data were analyzed using Freundlich and Dubinin-Radushkevich isotherm models. The results showed that the adsorption process was well described by Freundlich isotherm model. The kinetic data were analyzed using first-order and pseudo-second order kinetic models. The results indicated that adsorption fitted well with the pseudo-second order kinetic model. The thermodynamic parameters were determined at six (15, 30, 45, 45, 60 and 75 °C) different temperatures by plotting ln K L versus 1/T. The ΔH° and ΔG° values of uranium(VI) adsorption on Amberlite IRA-910 show endothermic heat of adsorption; higher temperatures favor the process. © 2011 Elsevier Ltd. All rights reserved.


Amraee T.,K. N. Toosi University of Technology | Soroudi A.,Islamic Azad University at Damavand | Ranjbar A.M.,Sharif University of Technology
IET Generation, Transmission and Distribution | Year: 2012

Owing to the local nature of voltage and reactive power control, the voltage control is managed in a zonal or regional basis. A new comprehensive scheme for optimal selection of pilot points is proposed in this study. The uncertainties of operational and topological disturbances of the power system are included to provide the robustness of the pilot node set. To reduce the huge number of probable states (i.e. combined states of load and topological changes), a scenario reduction technique is used. The resulted optimal control problem is solved using a new immune-based genetic algorithm. The performance of the proposed method is verified over IEEE 118-bus and realistic Iranian 1274-bus national transmission grids. © 2012 The Institution of Engineering and Technology.


Mohammadi-ivatloo B.,Sharif University of Technology | Rabiee A.,Islamic Azad University at Abhar | Soroudi A.,Islamic Azad University at Damavand | Ehsan M.,Sharif University of Technology
Energy | Year: 2012

Dynamic economic dispatch (DED) aims to schedule the committed generating units' output active power economically over a certain period of time, satisfying operating constraints and load demand in each interval. Valve-point effect, the ramp rate limits, prohibited operation zones (POZs), and transmission losses make the DED a complicated, non-linear constrained problem. Hence, in this paper, imperialist competitive algorithm (ICA) is proposed to solve such complicated problem. The feasibility of the proposed method is validated on five and ten units test system for a 24 h time interval. The results obtained by the ICA are compared with other techniques of the literature. These results substantiate the applicability of the proposed method for solving the constrained DED with non-smooth cost functions. Besides, to examine the applicability of the proposed ICA on large power systems, a test case with 54 units is studied. The results confirm the suitability of the ICA for large-scale DED problem. © 2012 Elsevier Ltd.


Mohammadi-Ivatloo B.,Sharif University of Technology | Rabiee A.,Sharif University of Technology | Soroudi A.,Islamic Azad University at Damavand | Ehsan M.,Sharif University of Technology
International Journal of Electrical Power and Energy Systems | Year: 2012

This paper presents a novel heuristic algorithm for solving economic dispatch (ED) problems, by employing iteration particle swarm optimization with time varying acceleration coefficients (IPSO-TVAC) method. Due to the effect of valve-points and prohibited operation zones (POZs) in the generating units' cost functions, ED problem is a non-linear and non-convex optimization problem. The problem even may be more complicated if transmission losses are taken into account. The effectiveness of the proposed method is examined and validated by carrying out extensive tests on three different test systems. Valve-point effects, POZs, ramp-rate constraints and transmission losses are modeled. Numerical results show that the IPSO-TVAC method has a good convergence property. Furthermore, the generation costs of the IPSO-TVAC method are lower than other optimization algorithms reported in recent literature. © 2012 Elsevier Ltd. All rights reserved.


Rahmati-Rostami M.,Sharif University of Technology | Behzadi B.,Iran University of Science and Technology | Ghotbi C.,Sharif University of Technology
Fluid Phase Equilibria | Year: 2011

Equations of state based on the statistical associating fluid theory for potentials of variable range (SAFT-VR) and the perturbed chain statistical associating fluid theory (PC-SAFT) have been used to model the PVT behavior of ionic liquids and the solubility of H2S in six imidazolium-based ionic liquids. The studied systems included [bmim][PF6], [hmim][PF6], [bmim][BF4], [hmim][BF4], [bmim][NTF2] and [hmim][NTF2] at various temperatures and pressures.For pure components, parameters of the models have been obtained by fitting the models to experimental data on liquid densities; the average relative deviation between the calculated and experimental densities for ionic liquids is less than 2.42% in the PC-SAFT model and 5.44% in the SAFT-VR approach, the latter which incorporates the square-well potential for short-range interactions. In both models an additional term has been added to account for dipole-dipole interactions between solute molecules resulting from the permanent charges on the chain molecules of the solvents. The model parameters have also been correlated as functions of the molecular weight of the solvents. For binary mixtures of ionic liquids and H2S, the association interactions between H2S molecules and between the ionic liquids and H2S molecules have also been taken into account in both approaches, using binary interaction coefficients. The results show an average deviation of less than 5% in the calculation of the mole fraction of H2S in the ionic liquids. The effect of inclusion of the polar term has been studied for binary systems in both models. © 2011 Elsevier B.V.


Roozbeh Nia A.,Islamic Azad University at Qazvin | Hemmati Far M.,Islamic Azad University at Qazvin | Akhavan Niaki S.T.,Sharif University of Technology
International Journal of Production Economics | Year: 2014

In this study, a multi-item economic order quantity model with shortage under vendor managed inventory policy in a single vendor single buyer supply chain is developed. This model explicitly includes warehouse capacity and delivery constraints, bounds order quantity, and limits the number of pallets. Not only the demands are considered imprecise, but also resources such as available storage and total order quantity of all items can be vaguely defined in different ways. An ant colony optimization is employed to find a near-optimum solution of the fuzzy nonlinear integer-programming problem with the objective of minimizing the total cost of the supply chain. Since no benchmark is available in the literature, a genetic algorithm and a differential evolution are developed as well to validate the result obtained. Furthermore, the applicability of the proposed methodology along with a sensitivity analysis on its parameter is demonstrated using five numerical examples containing different numbers of items. © 2014 Elsevier B.V. All rights reserved.


Pasandideh S.H.R.,Kharazmi University | Niaki S.T.A.,Sharif University of Technology | Niknamfar A.H.,Islamic Azad University at Qazvin
Knowledge-Based Systems | Year: 2014

Simultaneous reductions in inventory of raw materials, work-in-process, and finished items have recently become a major focus in supply chain management. Vendor-managed inventory is a well-known practice in supply chain collaborations, in which manufacturer manages inventory at the retailer and decides about the time and replenishment. In this paper, an integrated vendor-managed inventory model is presented for a two-level supply chain structured as a single capacitated manufacturer at the first level and multiple retailers at the second level. Manufacturer produces different products where demands are assumed decreasing functions of retail prices. In this chain, both the manufacturer and retailers contribute to determine their own decision variables in order to maximize their benefits. While previous research on this topic mainly included a single objective optimization model where the objective was either to minimize total supply chain costs or to maximize total supply chain benefits, in this research a fair profit contract is designed for the manufacturer and the retailers. The problem is first formulated into a bi-objective non-linear mathematical model and then the lexicographic max-min approach is utilized to obtain a fair non-dominated solution. Finally, different test problems are investigated in order to demonstrate the applicability of the proposed methodology and to evaluate the solution obtained. © 2014 Elsevier B.V. All rights reserved.


Hadadzadeh A.,University of Waterloo | Ghaznavi M.M.,Sharif University of Technology | Kokabi A.H.,Sharif University of Technology
Materials and Design | Year: 2014

The heat affected zone (HAZ) softening behavior of strain-hardened Al-6.7Mg alloy welded by gas tungsten arc welding (GTAW) process was investigated. Increasing the heat input during welding led to formation of a wider HAZ. Moreover, the size of the precipitates was increased at higher heat inputs. Consequently, by increasing the heat input, lower strength was obtained for the welding joints. At the second stage of the study, pulsed-GTAW (PGTAW) process was employed to improve the strength of the joints. It was observed that the overall strength of the welding joints was improved and the fracture during tensile test was moved from the HAZ to the fusion zone. Moreover, the effect of duration ratio and pulse frequency was studied. For the current study, the duration ratio did not have a significant effect on the strength and microstructure of the weld, but increasing the frequency led to higher strength of the weld and finer microstructure. © 2013 Elsevier Ltd.


Moffat J.W.,Perimeter Institute for Theoretical Physics | Moffat J.W.,University of Waterloo | Rahvar S.,Perimeter Institute for Theoretical Physics | Rahvar S.,Sharif University of Technology
Monthly Notices of the Royal Astronomical Society | Year: 2013

As an alternative to dark matter models, Modified Gravity (MOG) theory is a covariant modification of Einstein gravity. The theory introduces two additional scalar fields and one vector field. The aim is to explain the dynamics of astronomical systems based only on their baryonic matter. The effect of the vector field in the theory resembles a Lorentz force where each particle has a charge proportional to its inertial mass. The weak field approximation of MOG is derived by perturbing the metric and the fields around Minkowski space-time. We obtain an effective gravitational potential which yields the Newtonian attractive force plus a repulsive Yukawa force. This potential, in addition to the Newtonian gravitational constant, GN, has two additional constant parameters α and μ. We use The HI Nearby Galaxy Survey catalogue of galaxies and fix the two parameters α and μ of the theory to be α = 8.89 ± 0.34 and μ = 0.042 ± 0.004 kpc-1. We then apply the effective potential with the fixed universal parameters to the Ursa Major catalogue of galaxies and obtain good fits to galaxy rotation curve data with an average value of χ2 = 1.07. In the fitting process, only the stellar massto- light ratio (M/L) of the galaxies is a free parameter. As predictions of MOG, our derived M/L is shown to be correlated with the colour of galaxies.We also fit the Tully-Fisher relation for galaxies. As an alternative to dark matter, introducing an effective weak field potential for MOG opens a new window to the astrophysical applications of the theory. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Sangpour P.,Sharif University of Technology | Sangpour P.,Material and Energy Research Center | Hashemi F.,Sharif University of Technology | Moshfegh A.Z.,Sharif University of Technology
Journal of Physical Chemistry C | Year: 2010

Titania thin film system containing noble metallic nanoparticles such as Au, Ag, and Cu have been prepared by utilizing radio frequency reactive magnetron cosputtering method. The structural and morphological properties of the thin films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). Surface chemical composition of the films was determined by X-ray photoelectron spectroscopy (XPS). Optical properties of the TiO 2 annealed films containing Au, Ag, and Cu metallic nanoparticles were investigated by UV-visible spectrophotometry showing surface plasmon resonance of the metals. The photocatalytic activity of all synthesized samples annealed at 600 °C in an Ar + H2(80 + 20%) environment was evaluated by measuring the rate of photodegradation reaction of methylene blue (MB) under similar conditions in the presence of UV and visible light irradiation. The Au:TiO2 and Cu:TiO2 thin film systems significantly enhanced photodecomposition of MB resulting in 80 and 90% of its initial concentration after 200 min photoirradiation, respectively. The increase in the surface roughness measured by AFM observation and the presence of the Ti3+ oxygen vacancy in the photoirradiated thin films were found responsible for the enhancement of the MB photodegradation reaction. The photoenhancement of the studied was determined in the following order: Cu:TiO2 > Au:TiO2 > Ag:TiO2 > TiO 2. © 2010 American Chemical Society.


Pasandideh S.H.R.,Islamic Azad University at Qazvin | Niaki S.T.A.,Sharif University of Technology | Nia A.R.,Islamic Azad University at Qazvin
Expert Systems with Applications | Year: 2011

In this research, an economic order quantity (EOQ) model is first developed for a two-level supply chain system consisting of several products, one supplier and one-retailer, in which shortages are backordered, the supplier's warehouse has limited capacity and there is an upper bound on the number of orders. In this system, the supplier utilizes the retailer's information in decision making on the replenishments and supplies orders to the retailer according to the well known (R, Q) policy. Since the model of the problem is of a non-linear integer-programming type, a genetic algorithm is then proposed to find the order quantities and the maximum backorder levels such that the total inventory cost of the supply chain is minimized. At the end, a numerical example is given to demonstrate the applicability of the proposed methodology and to evaluate and compare its performances to the ones of a penalty policy approach that is taken to evaluate the fitness function of the genetic algorithm. © 2010 Elsevier Ltd. All rights reserved.


Jarrahian A.,Sharif University of Technology | Heidaryan E.,Shiraz University
Fuel | Year: 2014

In this paper, the Heidaryan and Jarrahian equation of state (Heidaryan and Jarrahian, 2013) has been adapted as a first worldwide cubic EOS to calculate the density of dry natural gases, wet natural gases, and single-phase gas condensates "sweet and sour mixtures" (up to 73.85, 97.63 and 38.37 mol percent of H2S, CO2, and N2 respectively) even when the gas composition is unknown, through new gas specific gravity correlation equations. Correction terms of water content as high as 10 mol percent of H2O and hythane (natural gas + hydrogen) as high as 74.9 mol percent of H2 were obtained. The equation of state was validated with 8985 experimental compressibility factor data points from 308 different mixtures in a range of atmospheric pressures up to 1570 bar and temperatures from -94 to 210 °C. © 2014 Elsevier Ltd. All rights reserved.


Jarrahian A.,Sharif University of Technology | Heidaryan E.,Shiraz University
Journal of Natural Gas Science and Engineering | Year: 2014

A general investigation of the thermal conductivity of natural gas as a function of temperature, pressure and composition was carried out to develop a generalized correlation. The model obtained was based on 731 data points of 42 binary mixtures in wide ranges of pressures (0.1-300MPa), temperatures (220-425K) and specific gravities (0.626-1.434). Correction terms for non-hydrocarbons of carbon dioxide and nitrogen were up to 87.8 and 82.8 of mole percent, respectively. The arithmetic average of the model's absolute error was found to be 5.69%, which is acceptable in engineering calculations. © 2014 Elsevier B.V.


Karimi M.,University of Waterloo | Nasiri-Kenari M.,Sharif University of Technology
Journal of Lightwave Technology | Year: 2011

Fading and path loss are the major challenges in practical deployment of free space optical communication systems. In this paper, a cooperative free space communication via an optical amplify-and-forward relay is considered to deal with these challenges. We use photon counting approach to investigate the system bit error probability (BEP) performance and study the effects of atmospheric turbulence, background light, amplified spontaneous emission, and receiver thermal noise on the system performance. We compare the results with those of the multiple-transmitter (MT) system. The results indicate that the performance of the relay-assisted system is much better than that of the MT system in different cases considered. We show that there is an optimum place for the relay from the BEP point of view. © 2010 IEEE.


Sadeghi J.,Islamic Azad University at Qazvin | Niaki S.T.A.,Sharif University of Technology
Applied Soft Computing Journal | Year: 2015

This paper presents a bi-objective vendor managed inventory (BOVMI) model for a supply chain problem with a single vendor and multiple retailers, in which the demand is fuzzy and the vendor manages the retailers' inventory in a central warehouse. The vendor confronts two constraints: number of orders and available budget. In this model, the fuzzy demand is formulated using trapezoidal fuzzy number (TrFN) where the centroid defuzzification method is employed to defuzzify fuzzy output functions. Minimizing both the total inventory cost and the warehouse space are the two objectives of the model. Since the proposed model is formulated into a bi-objective integer nonlinear programming (INLP) problem, the multi-objective evolutionary algorithm (MOEA) of non-dominated sorting genetic algorithm-II (NSGA-II) is developed to find Pareto front solutions. Besides, since there is no benchmark available in the literature to validate the solutions obtained, another MOEA, namely the non-dominated ranking genetic algorithms (NRGA), is developed to solve the problem as well. To improve the performances of both algorithms, their parameters are calibrated using the Taguchi method. Finally, conclusions are made and future research works are recommended. © 2015 Elsevier B.V. All rights reserved.


Sadeghi J.,Islamic Azad University at Qazvin | Mousavi S.M.,Islamic Azad University at Qazvin | Niaki S.T.A.,Sharif University of Technology | Sadeghi S.,Islamic Azad University at South Tehran
Knowledge-Based Systems | Year: 2013

The vendor-managed inventory (VMI) is a common policy in supply chain management (SCM) to reduce bullwhip effects. Although different applications of VMI have been proposed in the literature, the multi-vendor multi-retailer single-warehouse (MV-MR-SW) case has not been investigated yet. This paper develops a constrained MV-MR-SW supply chain, in which both the space and the annual number of orders of the central warehouse are limited. The goal is to find the order quantities along with the number of shipments received by retailers and vendors such that the total inventory cost of the chain is minimized. Since the problem is formulated into an integer nonlinear programming model, the meta-heuristic algorithm of particle swarm optimization (PSO) is presented to find an approximate optimum solution of the problem. In the proposed PSO algorithm, a genetic algorithm (GA) with an improved operator, namely the boundary operator, is employed as a local searcher to turn it to a hybrid PSO. In addition, since no benchmark is available in the literature, the GA with the boundary operator is proposed as well to solve the problem and to verify the solution. After employing the Taguchi method to calibrate the parameters of both algorithms, their performances in solving some test problems are compared in terms of the solution quality. © 2013 Elsevier B.V. All rights reserved.


Taleizadeh A.A.,University of Tehran | Niaki S.T.A.,Sharif University of Technology | Wee H.-M.,Chung Yuan Christian University
Knowledge-Based Systems | Year: 2013

This study solves a chance-constraint supply chain problem with stochastic demand which follows a uniform distribution. Fuzzy delay times (moving, waiting and setup time) are assumed to be lot size dependent and shortage is partially backordered. The buyer is responsible for the costs incurred in ordering, holding, shortage and transportation, while the vendor is responsible for setup and holding costs. The service rate of each product has a chance constraint and the buyer has a budget constraint. Our objective is to determine the re-order point and the order quantity of the products such that the total cost is minimized. Since the problem is uncertain integer-nonlinear, two hybrid procedures of Artificial Bee Colony (ABC) and Particle Swarm Optimization (PSO) with fuzzy simulation and approximate simulation methods are developed to solve the problems. Three numerical case examples are given to demonstrate the applicability of the proposed methodologies in a real world supply chain problem. © 2013 Elsevier B.V. All rights reserved.


Pasandideh S.H.R.,Islamic Azad University at Qazvin | Niaki S.T.A.,Sharif University of Technology | Hajipour V.,Islamic Azad University at Qazvin
Journal of Intelligent Manufacturing | Year: 2013

Many research works in mathematical modeling of the facility location problem have been carried out in discrete and continuous optimization area to obtain the optimum number of required facilities along with the relevant allocation processes. This paper proposes a new multi-objective facility-location problem within the batch arrival queuing framework. Three objective functions are considered: (I) minimizing the weighted sum of the waiting and the traveling times, (II) minimizing the maximum idle time pertinent to each facility, and (III) minimizing the total cost associated with the opened facilities. In this way, the best combination of the facilities is determined in the sense of economical, equilibrium, and enhancing service quality viewpoints. As the model is shown strongly NP-hard, two meta-heuristic algorithms, namely genetic algorithm (GA) and simulated annealing (SA) are proposed to solve the model. Not only new coding is developed in these solution algorithms, but also a random search algorithm is proposed to justify the efficiency of both algorithms. Since the solution-quality of all meta-heuristic algorithms severely depends on their parameters, design of experiments and response surface methodologies have been utilized to calibrate the parameters of both algorithms. Finally, computational results obtained by implementing both algorithms on several problems of different sizes demonstrate the performances of the proposed methodology. © 2011 Springer Science+Business Media, LLC.


Ghavam K.,University of Waterloo | Naghdabadi R.,Sharif University of Technology
International Journal of Plasticity | Year: 2011

In this paper, a constitutive model with a temperature and strain rate dependent flow stress (Bergstrom hardening rule) and modified Armstrong-Frederick kinematic evolution equation for elastoplastic hardening materials is introduced. Based on the multiplicative decomposition of the deformation gradient,new kinematic relations for the elastic and plastic left stretch tensors as well as the plastic deformation-dependent spin tensor are proposed. Also, a closed-form solution has been obtained for the elastic and plastic left stretch tensors for the simple shear problem.To evaluate model validity, results are compared with known experimental data for SUS 304 stainless steel, which shows a good agreement with the results of the proposed theoretical model.Finally, the stress-deformation curve, as predicted by the model, is plotted for the simple shear problem at room and elevated temperatures using the same material properties for AA5754-O aluminium alloy.© 2011 Elsevier Ltd. All rights reserved.


Rahmati S.H.A.,Islamic Azad University at Qazvin | Hajipour V.,Islamic Azad University at Qazvin | Niaki S.T.A.,Sharif University of Technology
Applied Soft Computing Journal | Year: 2013

In this paper, a novel multi-objective location model within multi-server queuing framework is proposed, in which facilities behave as M/M/m queues. In the developed model of the problem, the constraints of selecting the nearest-facility along with the service level restriction are considered to bring the model closer to reality. Three objective functions are also considered including minimizing (I) sum of the aggregate travel and waiting times, (II) maximum idle time of all facilities, and (III) the budget required to cover the costs of establishing the selected facilities plus server staffing costs. Since the developed model of the problem is of an NP-hard type and inexact solutions are more probable to be obtained, soft computing techniques, specifically evolutionary computations, are generally used to cope with the lack of precision. From different terms of evolutionary computations, this paper proposes a Pareto-based meta-heuristic algorithm called multi-objective harmony search (MOHS) to solve the problem. To validate the results obtained, two popular algorithms including non-dominated sorting genetic algorithm (NSGA-II) and non-dominated ranking genetic algorithm (NRGA) are utilized as well. In order to demonstrate the proposed methodology and to compare the performances in terms of Pareto-based solution measures, the Taguchi approach is first utilized to tune the parameters of the proposed algorithms, where a new response metric named multi-objective coefficient of variation (MOCV) is introduced. Then, the results of implementing the algorithms on some test problems show that the proposed MOHS outperforms the other two algorithms in terms of computational time. © 2012 Elsevier B.V.


Zolghadr A.,Shiraz University | Escrochi M.,Shiraz University | Ayatollahi S.,Shiraz University | Ayatollahi S.,Sharif University of Technology
Journal of Chemical and Engineering Data | Year: 2013

Crude oil reservoirs have different temperatures, compositions, and pressures, therefore oil recovery performance by CO2 injection varies from one case to another. Furthermore, it is predicted that lower interfacial tension between injected CO2 and reservoir fluid results in more oil recovery. In this study, we investigate the effect of temperature on the equilibrium interfacial tension between CO2 and three different oil fluids at different pressures. Also minimum miscible pressure (MMP) is measured by the vanishing interfacial tension (VIT) technique to determine the temperature effect on the CO2 miscible gas injection. The results on different pure and mixtures of hydrocarbon fluids show that for pressures up to 5.2 MPa, the higher the temperature was, the lower was the interfacial tension (IFT) measured. However, for the cases with pressure higher than 5.2 MPa, as the temperature was increased, the IFT increased too. In addition the VIT technique is used to measure the MMP of CO2 and pure paraffin; the heavier paraffin was, the higher was the MMP noticed. Also, we have learned that paraffin groups have an important effect on multicomponent interfacial tension behavior. © 2013 American Chemical Society.


Heidaryan E.,Shiraz University | Jarrahian A.,Sharif University of Technology
Journal of Supercritical Fluids | Year: 2013

A new simple and explicit reduced temperature and reduced pressure function has been proposed in the present study for modifying Redlich-Kwong equation of state (EoS) to calculate the density of carbon dioxide in the supercritical region. The average absolute error of the model was found to be 1.63 and 2.07% in the comparison with the literature and NIST density data respectively, which demonstrates superiority of the model over other EoSs. © 2013 Elsevier B.V. All rights reserved.


Hassani S.H.,ETH Zurich | Alishahi K.,Sharif University of Technology | Urbanke R.L.,Ecole Polytechnique Federale de Lausanne
IEEE Transactions on Information Theory | Year: 2014

Consider a binary-input memoryless outputsymmetric channel W. Such a channel has a capacity, call it I (W), and for any R < I (W) and strictly positive constant Pewe know that we can construct a coding scheme that allows transmission at rate R with an error probability not exceeding Pe. Assume now that we let the rate R tend to I (W) and we ask how we have to scale the blocklength N in order to keep the error probability fixed to Pe. We refer to this as the finite-length scaling behavior. This question was addressed by Strassen as well as Polyanskiy, Poor, and Verdu, and the result is that N must grow at least as the square of the reciprocal of I (W)- R. Polar codes are optimal in the sense that they achieve capacity. In this paper, we are asking to what degree they are also optimal in terms of their finite-length behavior. Since the exact scaling behavior depends on the choice of the channel, our objective is to provide scaling laws that hold universally for all binary-input memoryless output-symmetric channels. Our approach is based on analyzing the dynamics of the un-polarized channels. More precisely, we provide bounds on (the exponent of) the number of subchannels whose Bhattacharyya constant falls in a fixed interval [a, b]. Mathematically, this can be stated as bounding the sequence {1/n log Pr(Zn∞ [a, b])}n∞N, where Znis the Bhattacharyya process. We then use these bounds to derive tradeoffs between the rate and the block-length. The main results of this paper can be summarized as follows. Consider the sum of Bhattacharyya parameters of subchannels chosen (by the polar coding scheme) to transmit information. If we require this sum to be smaller than a given value Pe> 0, then the required block-length N scales in terms of the rate R < I (W) as N ≥ α/(I (W) - R)μ, where α is a positive constant that depends on Peand I (W). We show that μ = 3.579 is a valid choice, and we conjecture that indeed the value of μ can be improved to μ = 3.627, the parameter for the binary erasure channel. Also, we show that with the same requirement on the sum of Bhattacharyya parameters, the blocklength scales in terms of the rate like N ≤ β/(I (W) - R)μ, where β is a constant that depends on Peand I (W), and μ = 6. © 2014 IEEE.


Saberi R.-S.,Sharif University of Technology | Shahrokhian S.,Sharif University of Technology | Marrazza G.,University of Florence
Electroanalysis | Year: 2013

In this work, an electrochemical DNA biosensor, based on a dual signal amplified strategy by employing a polyaniline film and gold nanoparticles as a sensor platform and enzyme-linked as a label, for sensitive detection is presented. Firstly, polyaniline film and gold nanoparticles were progressively grown on graphite screen-printed electrode surface via electropolymerization and electrochemical deposition, respectively. The sensor was characterized by scanning electron microscopy (SEM), cyclic voltammetry and impedance measurements. The polyaniline-gold nanocomposite modified electrodes were firstly modified with a mixed monolayer of a 17-mer thiol-tethered DNA probe and a spacer thiol, 6-mercapto-1-hexanol (MCH). An enzyme-amplified detection scheme, based on the coupling of a streptavidin-alkaline phosphatase conjugate and biotinylated target sequences was then applied. The enzyme catalyzed the hydrolysis of the electroinactive α-naphthyl phosphate to α-naphthol; this product is electroactive and has been detected by means of differential pulse voltammetry. In this way, the sensor coupled the unique electrical properties of polyaniline and gold nanoparticles (high surface area, fast heterogeneous electron transfer, chemical stability, and ease of miniaturisation) and enzymatic amplification. A linear response was obtained over a concentration range (0.2-10nM). A detection limit of 0.1nM was achieved. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Naderi B.,Islamic Azad University at Qazvin | Salmasi N.,Sharif University of Technology
European Journal of Industrial Engineering | Year: 2012

This paper focuses on the flow shop sequence dependent group scheduling (FSDGS) problem with minimisation of total completion time as the criterion (Fm|f mls, prmu, S plk|ΣC j). The research problem is formulated in form of two different mixed integer linear programming (MILP) models. Comparing with the latest MILP model for the proposed problem in the literature, the complexity size of the proposed models are significantly reduced. One of the proposed mathematical models is so effective that even medium-sized instances (problems up to 60 jobs in all groups) are solved to optimality in a reasonable amount of time. Moreover, a metaheuristic hybridising genetic and simulated annealing algorithm, called GSA, is proposed to solve the problems heuristically. All the results and analyses show the high performance of the proposed mathematical models as well as the proposed metaheuristic algorithm compared to the available ones in literature. Copyright © 2012 Inderscience Enterprises Ltd.


News Article | December 16, 2016
Site: www.chromatographytechniques.com

Researchers from the University of Waterloo have developed a method that will detect roughly 10 black holes per year, doubling the number currently known within two years, and it will likely unlock the history of black holes in a little more than a decade. Avery Broderick, a professor in the Department of Physics and Astronomy at the University of Waterloo, and Mansour Karami, a PhD student also from the Faculty of Science, worked with colleagues in the United States and Iran to come up with the method that has implications for the emerging field of gravitational wave astronomy and the way in which we search for black holes and other dark objects in space. It was published this week in The Astrophysical Journal. “Within the next 10 years, there will be sufficient accumulated data on enough black holes that researchers can statistically analyze their properties as a population,” said Broderick, also an associate faculty member at the Perimeter Institute for Theoretical Physics. “This information will allow us to study stellar mass black holes at various stages that often extend billions of years.” Black holes absorb all light and matter and emit zero radiation, making them impossible to image, let alone detect against the black background of space. Although very little is known about the inner workings of black holes, we do know they play an integral part in the lifecycle of stars and regulate the growth of galaxies. The first direct proof of their existence was announced earlier this year by the Laser Interferometer Gravitational-Wave Observatory (LIGO) when it detected gravitational waves from the collision of two black holes merging into one. “We don’t yet know how rare these events are and how many black holes are generally distributed across the galaxy,” said Broderick. “For the first time we’ll be placing all the amazing dynamical physics that LIGO sees into a larger astronomical context.” Broderick and his colleagues propose a bolder approach to detecting and studying black holes, not as single entities, but in large numbers as a system by combining two standard astrophysical tools in use today: microlensing and radio wave interferometry. Gravitational microlensing occurs when a dark object such as a black hole passes between us and another light source, such as a star. The star’s light bends around the object’s gravitational field to reach Earth, making the background star appear much brighter, not darker as in an eclipse. Even the largest telescopes that observe microlensing events in visible light have a limited resolution, telling astronomers very little about the object that passed by. Instead of using visible light, Broderick and his team propose using radio waves to take multiple snapshots of the microlensing event in real time. “When you look at the same event using a radio telescope – interferometry – you can actually resolve more than one image. That’s what gives us the power to extract all kinds of parameters, like the object’s mass, distance and velocity,” said Karami, a doctoral student in astrophysics at Waterloo. Taking a series of radio images over time and turning them into a movie of the event will allow them to extract another level of information about the black hole itself. A Natural Sciences and Engineering Research Council Discovery Grant partially funded the project. Co-authors on the paper include Sohrab Rahvar of the Perimeter Institute for Theoretical Physics and the Sharif University of Technology in Iran and Mark Reid of the Harvard-Smithsonian Center for Astrophysics.


News Article | December 15, 2016
Site: www.eurekalert.org

Researchers from the University of Waterloo have developed a method that will detect roughly 10 black holes per year, doubling the number currently known within two years, and it will likely unlock the history of black holes in a little more than a decade. Avery Broderick, a professor in the Department of Physics and Astronomy at the University of Waterloo, and Mansour Karami, a PhD student also from the Faculty of Science, worked with colleagues in the United States and Iran to come up with the method that has implications for the emerging field of gravitational wave astronomy and the way in which we search for black holes and other dark objects in space. It was published this week in The Astrophysical Journal. "Within the next 10 years, there will be sufficient accumulated data on enough black holes that researchers can statistically analyze their properties as a population," said Broderick, also an associate faculty member at the Perimeter Institute for Theoretical Physics. "This information will allow us to study stellar mass black holes at various stages that often extend billions of years." Black holes absorb all light and matter and emit zero radiation, making them impossible to image, let alone detect against the black background of space. Although very little is known about the inner workings of black holes, we do know they play an integral part in the lifecycle of stars and regulate the growth of galaxies. The first direct proof of their existence was announced earlier this year by the Laser Interferometer Gravitational-Wave Observatory (LIGO) when it detected gravitational waves from the collision of two black holes merging into one. "We don't yet know how rare these events are and how many black holes are generally distributed across the galaxy," said Broderick. "For the first time we'll be placing all the amazing dynamical physics that LIGO sees into a larger astronomical context." Broderick and his colleagues propose a bolder approach to detecting and studying black holes, not as single entities, but in large numbers as a system by combining two standard astrophysical tools in use today: microlensing and radio wave interferometry. Gravitational microlensing occurs when a dark object such as a black hole passes between us and another light source, such as a star. The star's light bends around the object's gravitational field to reach Earth, making the background star appear much brighter, not darker as in an eclipse. Even the largest telescopes that observe microlensing events in visible light have a limited resolution, telling astronomers very little about the object that passed by. Instead of using visible light, Broderick and his team propose using radio waves to take multiple snapshots of the microlensing event in real time. "When you look at the same event using a radio telescope - interferometry - you can actually resolve more than one image. That's what gives us the power to extract all kinds of parameters, like the object's mass, distance and velocity," said Karami, a doctoral student in astrophysics at Waterloo. Taking a series of radio images over time and turning them into a movie of the event will allow them to extract another level of information about the black hole itself. A Natural Sciences and Engineering Research Council Discovery Grant partially funded the project. Co-authors on the paper include Sohrab Rahvar of the Perimeter Institute for Theoretical Physics and the Sharif University of Technology in Iran and Mark Reid of the Harvard-Smithsonian Center for Astrophysics.


Shokri A.,University of Minnesota | Abedin A.,Sharif University of Technology | Fattahi A.,Sharif University of Technology | Kass S.R.,University of Minnesota
Journal of the American Chemical Society | Year: 2012

The pK a of an acyclic aliphatic heptaol ((HOCH 2CH 2CH(OH)CH 2) 3COH) was measured in DMSO, and its gas-phase acidity is reported as well. This tertiary alcohol was found to be 10 21 times more acidic than tert-butyl alcohol in DMSO and an order of magnitude more acidic than acetic acid (i.e., pK a = 11.4 vs 12.3). This can be attributed to a 21.9 kcal mol -1 stabilization of the charged oxygen center in the conjugate base by three hydrogen bonds and another 6.3 kcal mol -1 stabilization resulting from an additional three hydrogen bonds between the uncharged primary and secondary hydroxyl groups. Charge delocalization by both the first and second solvation shells may be used to facilitate enzymatic reactions. Acidity constants of a series of polyols were also computed, and the combination of hydrogen-bonding and electron-withdrawing substituents was found to afford acids that are predicted to be extremely acidic in DMSO (i.e., pK a < 0). These hydrogen bond enhanced acids represent an attractive class of Brønsted acid catalysts. © 2012 American Chemical Society.


Abolhasani A.A.,Sharif University of Technology | Abolhasani A.A.,Institute for Research in Fundamental Sciences | Firouzjahi H.,Institute for Research in Fundamental Sciences | Namjoo M.H.,Institute for Research in Fundamental Sciences
Classical and Quantum Gravity | Year: 2011

We consider a variant of hybrid inflation where the waterfall phase transition occurs during inflation. By adjusting the parameters associated with the mass of the waterfall field, we can achieve a phase transition that is not sharp, thus inflation can proceed for about 50-60 e-folds after the waterfall phase transition. We show that one can work within the limit where the quantum back-reactions are subdominant compared to the classical back-reactions. It is shown that a significant amount of large scale curvature perturbations are induced from the entropy perturbations. The curvature perturbation spectral index is either blue or red depending on whether the mode of interest leaves the horizon before the phase transition or after the phase transition. This can have interesting observational consequences on CMB. The non-Gaussianity parameter fNL is calculated to be ≲ 1 but much bigger than the slow-roll parameters. © 2011 IOP Publishing Ltd.


Compere G.,Solvay Group | Hajian K.,Institute for Research in Fundamental Sciences | Hajian K.,Sharif University of Technology | Seraj A.,Institute for Research in Fundamental Sciences | Sheikh-Jabbari M.M.,Institute for Research in Fundamental Sciences
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

We construct the NHEG phase space, the classical phase space of Near-Horizon Extremal Geometries with fixed angular momenta and entropy, and with the largest symmetry algebra. We focus on vacuum solutions to d dimensional Einstein gravity. Each element in the phase space is a geometry with SL(2,R)×U(1)d-3 isometries which has vanishing SL(2,R) and constant U(1) charges. We construct an on-shell vanishing symplectic structure, which leads to an infinite set of symplectic symmetries. In four spacetime dimensions, the phase space is unique and the symmetry algebra consists of the familiar Virasoro algebra, while in d> 4 dimensions the symmetry algebra, the NHEG algebra, contains infinitely many Virasoro subalgebras. The nontrivial central term of the algebra is proportional to the black hole entropy. The conserved charges are given by the Fourier decomposition of a Liouville-type stress-tensor which depends upon a single periodic function of d- 3 angular variables associated with the U(1) isometries. This phase space and in particular its symmetries can serve as a basis for a semiclassical description of extremal rotating black hole microstates. © 2015 The Authors.


Moeinifar S.,Islamic Azad University at Shoshtar | Kokabi A.H.,Sharif University of Technology | Hosseini H.R.M.,Sharif University of Technology
Journal of Materials Processing Technology | Year: 2011

The influence of thermal cycles on the properties of the coarse grained heat affected zone in X80 microalloyed steel has been investigated. The thermal simulated involved heating the X80 steel specimens to the peak temperature of 1400 °C, with different cooling rates. The four-wire tandem submerged arc welding process, with different heat input values, was used to generate a welded microstructure. The martensite/austenite constituent appeared in the microstructure of the heat affected zone region for all the specimens along the prior-austenite grain boundaries and between the bainitic ferrite laths. The blocky-like and stringer martensite/austenite morphology were observed in the heat affected zone region. The fractional area of M/A particles due to different cooling rate was the main factor in increasing of the hardness values in the coarse grained heat affected zone. The Charpy absorbed energy of specimens was assessed using Charpy impact testing at -50 °C. The martensite/austenite constituent's size such as mean diameter and length are important factors influencing Charpy impact properties of coarse grained heat affected zone. The micro crack nucleation may occur from M/A particles at the intersection of prior-austenite grain boundaries. Similar crack initiation sites and growth mechanism were investigated for specimens welded with different heat input values. © 2010 Elsevier B.V. All rights reserved.


Fallah F.,Aerospace Research Institute | Nosier A.,Sharif University of Technology
Composite Structures | Year: 2012

The equilibrium equations of the first-order nonlinear von Karman theory for FG circular plates under asymmetric transverse loading and heat conduction through the plate thickness are reformulated into those describing the interior and edge-zone problems of the plate. A two parameter perturbation technique, in conjunction with Fourier series method is used to obtain analytical solutions for nonlinear behavior of functionally graded circular plates with various clamped and simply-supported boundary conditions. The material properties are graded through the plate thickness according to a power-law distribution of the volume fraction of the constituents. The results are verified with known results in the literature. The load-deflection curves for different loadings, boundary conditions, and material constant in a solid circular plate are studied and discussed. It is shown that the behavior of FG plates with clamped or simply-supported boundary conditions are completely different. Under thermo-mechanical loading, snap-through buckling behavior is observed in simply-supported FG plates which are immovable in radial direction. Moreover, it is found that linear theory is inadequate for analyzing FG and also homogenous plates with immovable boundary supports in radial direction and subjected to thermal loading, even for deflections that are normally considered small. © 2012 Elsevier Ltd.


Arjomand M.,Sharif University of Technology | Sarbazi-Azad H.,Institute for Research in Fundamental Sciences
Proceedings of the IEEE International Conference on VLSI Design | Year: 2010

Network-on-Chip combined with Globally Asynchronous Locally Synchronous paradigm is a promising architecture for easy IP integration and utilization with multiple voltage levels. For power reduction, multiple voltage-frequency levels are successfully applied to 2-D NoCs, but never with a generic approach to 3-D counterparts; in which low heat conductivity of insulator layers makes high dense temperature distribution at layers away from heat sink. In this paper, a thermal-aware methodology for regular 3-D NoCs based on multiple voltage levels is proposed. Given an application task graph, this methodology determines an efficient mapping of tasks onto network tiles, considering inherent computation and communication requirements of the tasks and thermal resistance from any silicon layer to the ambient. Then, a heuristic approach is utilized to determine voltage and frequency specifications of all IP cores, such that total power is reduced, dissipated heat is properly conducted to the layers close to the heat sink, and application requirements (in terms of deadline) are satisfied. The experiments confirm a significant saving in total power while performance of the running application is guaranteed. © 2010 IEEE.


Hojabri H.,Sharif University of Technology | Mokhtari H.,Sharif University of Technology | Chang L.,University of New Brunswick
IEEE Transactions on Industrial Electronics | Year: 2011

In this paper, a new simple and complete technique of modeling and analysis of a matrix converter is presented based on the singular value decomposition (SVD) of modulation matrix. The proposed modeling method yields a new limitation between the matrix converter gain and its input power factor, which is more relaxed as compared to the limits reported so far in the literature. The SVD of the modulation matrix leads to a unified modulation technique which achieves the full capability of a matrix converter. It is shown that this approach is general and all other modulation methods established for a matrix converter are specific cases of this technique. The proposed modulation method can be used to obtain the maximum reactive power in the input of a matrix converter in applications such as wind turbine and microturbine generators, where the input reactive power control is necessary. © 2010 IEEE.


Fayazbakhsh Sh.,Institute for Research in Fundamental Sciences | Sadooghi N.,Sharif University of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

The directional weak decay constants of neutral pions are determined at finite temperature T, chemical potential μ and in the presence of a constant magnetic field B. To do this, we first derive the energy dispersion relation of neutral pions from the corresponding effective action of a two-flavor, hot and magnetized Nambu-Jona-Lasinio model. Using this dispersion relation, including nontrivial directional refraction indices, we then generalize the partially conserved axial vector current relation of neutral pions and derive the Goldberger-Treiman as well as the Gell-Mann-Oakes-Renner relations consisting of the directional quark-pion coupling constant gqqπ0(μ) and the weak decay constant fπ0(μ) of neutral pions. The temperature dependence of gqqπ0(μ) and fπ0(μ) are then determined for fixed chemical potential and various constant background magnetic fields. The Goldberger-Treiman and Gell-Mann-Oakes-Renner relations are also verified at finite T, μ and eB. It is shown that, because of the explicit breaking of the Lorentz invariance by the magnetic field, the directional quark-pion coupling and decay constants of neutral pions in the longitudinal and transverse directions with respect to the direction of the external magnetic field are different, i.e., gqqπ0â̂¥≠gqqπ0⊥ and fπ0â̂¥≠fπ0⊥. As it turns out, for fixed T, μ and B, gqqπ0â̂¥>gqqπ0⊥ and fπ0â̂¥


Mahmoudi M.,Pasteur Institute of Iran | Mahmoudi M.,Tehran University of Medical Sciences | Lynch I.,University College Dublin | Ejtehadi M.R.,Sharif University of Technology | And 3 more authors.
Chemical Reviews | Year: 2011

The significant role of protein nanoparticle interactions in nanomedicine and nanotoxicity is emerging recently through the identification of the nanoparticles (NP) protein (biomolecule) corona. The dynamic layer of proteins and/or other biomolecules adsorbed to the nanoparticle surface determines how a NP interacts with living systems and thereby modifies the cellular responses to the NP. Ehrenberg and co-workers used cultured endothelium cells as a model for vascular transport of polystyrene NP with various functional groups, which showed that the capacity of the various NP surfaces to adsorb proteins was indicative of their tendency to associate with cells. The quantification of the adsorbed proteins showed that high-binding NP were maximally coated within seconds to minutes, indicating that proteins on the surface of NP could mediate cell association over much longer time scales. The adsorption or covalent binding of a protein onto a NP's surface can strongly alter the physio-chemical and structural properties of both of them.


Astaneh A.F.,Sharif University of Technology | Astaneh A.F.,Institute for Research in Fundamental Sciences | Patrushev A.,University of Tours | Solodukhin S.N.,University of Tours
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

In this note we address the discrepancy found by Hung, Myers and Smolkin between the holographic calculation of entanglement entropy (using the Jacobson-Myers functional for the holographic minimal surface) and the CFT trace anomaly calculation if one uses the Wald prescription to compute the entropy in six dimensions. As anticipated in our previous work [1] the discrepancy originates entirely from a total derivative term present in the trace anomaly in six dimensions. © 2015 The Authors.


Pasandideh S.H.R.,Kharazmi University | Niaki S.T.A.,Sharif University of Technology
Journal of Intelligent Manufacturing | Year: 2012

In many service and industrial applications of the facility location problem, the number of required facilities along with allocation of the customers to the facilities are the two major questions that need to be answered. In this paper, a facility location problem with stochastic customer demand and immobile servers is studied. Two objectives considered in this problem are: (1) minimizing the average customer waiting time and (2) minimizing the average facility idletime percentage. We formulate this problem using queuing theory and solve the model by a genetic algorithm within the desirability function framework. Several examples are presented to demonstrate the applications of the proposed methodology. © Springer Science+Business Media, LLC 2010.


Beigi S.,Institute for Research in Fundamental Sciences | Gohari A.,Sharif University of Technology
IEEE Transactions on Information Theory | Year: 2014

In this paper, we provide a simple framework for deriving one-shot achievable bounds for some problems in quantum information theory. Our framework is based on the joint convexity of the exponential of the collision relative entropy and is a (partial) quantum generalization of the technique of Yassaee et al. from classical information theory. Based on this framework, we derive one-shot achievable bounds for the problems of communication over classical-quantum channels, quantum hypothesis testing, and classical data compression with quantum side information. We argue that our one-shot achievable bounds are strong enough to give the asymptotic achievable rates of these problems even up to the second order. © 1963-2012 IEEE.


Fayazbakhsh S.,Institute for Research in Fundamental Sciences | Sadeghian S.,Alzahra University | Sadooghi N.,Sharif University of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

The properties of noninteracting σ and π0 mesons are studied at finite temperature, chemical potential, and in the presence of a constant magnetic field. To do this, the energy dispersion relations of these particles, including nontrivial form factors, are derived using a derivative expansion of the effective action of a two-flavor, hot and magnetized Nambu-Jona-Lasinio model up to second order. The temperature dependence of the pole and screening masses as well as the directional refraction indices of magnetized neutral mesons are explored for fixed magnetic fields and chemical potentials. It is shown that, because of the explicit breaking of the Lorentz invariance by the magnetic field, the refraction index and the screening mass of neutral mesons exhibit a certain anisotropy in the transverse and longitudinal directions with respect to the direction of the external magnetic field. In contrast to their longitudinal refraction indices, the transverse indices of the neutral mesons are larger than unity. © 2012 American Physical Society.


Mahmoudi M.,Tehran University of Medical Sciences | Kalhor H.R.,Sharif University of Technology | Laurent S.,University of Mons | Lynch I.,University College Dublin
Nanoscale | Year: 2013

Due to their ultra-small size, nanoparticles (NPs) have distinct properties compared with the bulk form of the same materials. These properties are rapidly revolutionizing many areas of medicine and technology. NPs are recognized as promising and powerful tools to fight against the human brain diseases such as multiple sclerosis or Alzheimer's disease. In this review, after an introductory part on the nature of protein fibrillation and the existing approaches for its investigations, the effects of NPs on the fibrillation process have been considered. More specifically, the role of biophysicochemical properties of NPs, which define their affinity for protein monomers, unfolded monomers, oligomers, critical nuclei, and other prefibrillar states, together with their influence on protein fibrillation kinetics has been described in detail. In addition, current and possible-future strategies for controlling the desired effect of NPs and their corresponding effects on the conformational changes of the proteins, which have significant roles in the fibrillation process, have been presented. © The Royal Society of Chemistry 2013.


Akhavan O.,Sharif University of Technology | Azimirad R.,Malek-Ashtar University of Technology | Safa S.,Science and Technology Research Institute | Larijani M.M.,Science and Technology Research Institute
Journal of Materials Chemistry | Year: 2010

Carbon nanotube (CNT)-doped TiO2 thin films with various CNT contents were synthesized by sol-gel method for visible light photoinactivation of Escherichia coli bacteria. Post annealing of the CNT-doped TiO2 thin films at 450 °C resulted in anatase TiO2 and formation of Ti-C and Ti-O-C carbonaceous bonds in the film. By increasing the CNT content, the thin films could further inactivate the bacteria in the dark. Meanwhile, as the CNT content increased from zero to 40 wt% the effective optical band gap energy of the CNT-doped TiO2 thin films annealed at 450 °C decreased from 3.2-3.3 to less than ∼2.8 eV providing light absorption in the visible region. Concerning this, visible light photoinactivation of the bacteria on the surface of the films was found to be optimum for 20 wt% CNT content. The CNT-doped TiO2 thin films annealed at 450 °C showed a further improved photoinactivation of bacteria than the films annealed at 100 °C. The improvement in the visible light photocatalytic performance was assigned to the charge transfer through the carbonaceous bonds formed between the TiO2 and the CNT content of the films annealed at 450 °C, in contrast to the thin films annealed at 100 °C which contained no such effective bonds. © 2010 The Royal Society of Chemistry.


Hojabri H.,Sharif University of Technology | Mokhtari H.,Sharif University of Technology | Chang L.,University of New Brunswick
IEEE Transactions on Power Delivery | Year: 2013

In this paper, the reactive power control of a variable-speed permanent-magnet synchronous wind generator with a matrix converter at the grid side is improved. A generalized modulation technique based on singular value decomposition of the modulation matrix is used to model different modulation techniques and investigate their corresponding input reactive power capability. Based on this modulation technique, a new control method is proposed for the matrix converter which uses active and reactive parts of the generator current to increase the control capability of the grid-side reactive current compared to conventional modulation methods. A new control structure is also proposed which can control the matrix converter and generator reactive current to improve the grid-side maximum achievable reactive power for all wind speeds and power conditions. Simulation results prove the performance of the proposed system for different generator output powers. © 1986-2012 IEEE.


Farzan Y.,Institute for Research in Fundamental Sciences | Akbarieh A.R.,Institute for Research in Fundamental Sciences | Akbarieh A.R.,Sharif University of Technology
Journal of Cosmology and Astroparticle Physics | Year: 2014

We present a Vector Dark Matter (VDM) model that explains the 3.5 keV line recently observed in the XMM-Newton observatory data from galaxy clusters. In this model, dark matter is composed of two vector bosons, V and V', which couple to the photon through an effective generalized Chern-Simons coupling, gV. V' is slightly heavier than V with a mass splitting mV' - mV 3.5 keV. The decay of V' to V and a photon gives rise to the 3.5 keV line. The production of V and V' takes place in the early universe within the freeze-in framework through the effective gV coupling when mV' < T < Λ, Λ being the cut-off above which the effective gV coupling is not valid. We introduce a high energy model that gives rise to the gV coupling at low energies. To do this, V and V' are promoted to gauge bosons of spontaneously broken new U(1)V and U(1)V' gauge symmetries, respectively. The high energy sector includes milli-charged chiral fermions that lead to the gV coupling at low energy via triangle diagrams.


Jafari S.A.,Sharif University of Technology | Jafari S.A.,Institute for Research in Fundamental Sciences
Journal of Physics Condensed Matter | Year: 2012

We present a formulation for the nonlinear optical response in gapped graphene, where the low-energy single-particle spectrum is modeled by massive Dirac theory. As a representative example of the formulation presented here, we obtain a closed form formula for the third harmonic generation in gapped graphene. It turns out that the covariant form of the low-energy theory gives rise to peculiar logarithmic singularities in the nonlinear optical spectra. The universal functional dependence of the response function on dimensionless quantities indicates that the optical nonlinearity can be largely enhanced by tuning the gap to smaller values. © 2012 IOP Publishing Ltd.


Azizi S.,University of Tehran | Dobakhshari A.S.,Sharif University of Technology | Nezam Sarmadi S.A.,Washington State University | Ranjbar A.M.,Sharif University of Technology
IEEE Transactions on Smart Grid | Year: 2012

Observability of bulk power transmission network by means of minimum number of phasor measurement units (PMUs), with the aid of the network topology, is a great challenge. This paper presents a novel equivalent integer linear programming method (EILPM) for the exhaustive search-based PMU placement. The state estimation implemented based on such a placement is completely linear, thereby eliminating drawbacks of the conventional SCADA-based state estimation. Additional constraints for observability preservation following single PMU or line outages can easily be implemented in the proposed EILPM. Furthermore, the limitation of communication channels is dealt with by translation of nonlinear terms into linear ones. Optimal PMU placement is carried out on the IEEE 118-bus test system in different scenarios. The comparison between obtained results of EILPM and those of other methods reveals optimality of the solutions. Moreover, the proposed method is successfully applied on the Iranian National Grid, which demonstrates it can effectively be employed for practical power networks. © 2011 IEEE.


Neyshabur B.,Sharif University of Technology | Khadem A.,Sharif University of Technology | Hashemifar S.,University of Tehran | Arab S.S.,Tarbiat Modares University | Arab S.S.,Institute for Research in Fundamental Sciences
Bioinformatics | Year: 2013

Motivation: The interactions among proteins and the resulting networks of such interactions have a central role in cell biology. Aligning these networks gives us important information, such as conserved complexes and evolutionary relationships. Although there have been several publications on the global alignment of protein networks; however, none of proposed methods are able to produce a highly conserved and meaningful alignment. Moreover, time complexity of current algorithms makes them impossible to use for multiple alignment of several large networks together.Results: We present a novel algorithm for the global alignment of protein-protein interaction networks. It uses a greedy method, based on the alignment scoring matrix, which is derived from both biological and topological information of input networks to find the best global network alignment. NETAL outperforms other global alignment methods in terms of several measurements, such as Edge Correctness, Largest Common Connected Subgraphs and the number of common Gene Ontology terms between aligned proteins. As the running time of NETAL is much less than other available methods, NETAL can be easily expanded to multiple alignment algorithm. Furthermore, NETAL overpowers all other existing algorithms in term of performance so that the short running time of NETAL allowed us to implement it as the first server for global alignment of protein-protein interaction networks. © The Author 2013.


Goodarzi B.,Sharif University of Technology | Sarbazi-Azad H.,Institute for Research in Fundamental Sciences
Proceedings - 19th International Euromicro Conference on Parallel, Distributed, and Network-Based Processing, PDP 2011 | Year: 2011

Processor allocation in todays many core MPSoCs is a challenging task, especially since the order and requirements of incoming applications are unknown during design stage. To improve network performance, balance the workload across processing cores, or mitigate the effect of hot processing elements in thermal management methodologies, task migration is a method which has attracted much attention in recent years. Runtime task migration was first proposed in multicomputer with load balancing as the major objective. However, specific NoC properties such as limited amount of communication buffers, more sensitivity to implementation complexity, and tight latency and power consumption constraints bring new challenges in using task migration mechanisms in NoCs. As a consequence, the efficiency and applicability of traditional migration mechanisms (developed for multicomputers) are under question. Due to the limited resource budget in NoC-based MPSoCs as well as tight performance constraints of running applications, in this paper, we propose an efficient methodology based on virtual point-to-point (VIP for short) connections. These dedicated VIP connections provide low-latency and low-power paths for heavy communication flows created by task migration mechanisms. Analyzing the results show that the proposed scheme reduces message latency by 13 and migration latency by 14, while 10 power savings can be achieved compared to the previously proposed task migration strategy (known as Gathering-Rout-Scattering) for mesh multiprocessors. © 2011 IEEE.


Mosqueda G.,State University of New York at Buffalo | Ahmadizadeh M.,Sharif University of Technology
Earthquake Engineering and Structural Dynamics | Year: 2011

A fully implicit iterative integration procedure is presented for local and geographically distributed hybrid simulation of the seismic response of complex structural systems with distributed nonlinear behavior. The purpose of this procedure is to seamlessly incorporate experimental elements in simulations using existing fully implicit integration algorithms designed for pure numerical simulations. The difficulties of implementing implicit integrators in a hybrid simulation are addressed at the element level by introducing a safe iteration strategy and using an efficient procedure for online estimation of the experimental tangent stiffness matrix. In order to avoid physical application of iterative displacements, the required experimental restoring force at each iteration is estimated from polynomial curve fitting of recent experimental measurements. The experimental tangent stiffness matrix is estimated by using readily available experimental measurements and by a classical diagonalization approach that reduces the number of unknowns in the matrix. Numerical and hybrid simulations are used to demonstrate that the proposed procedure provides an efficient method for implementation of fully implicit numerical integration in hybrid simulations of complex nonlinear structures. The hybrid simulations presented include distributed nonlinear behavior in both the numerical and experimental substructures. © 2010 John Wiley & Sons, Ltd.


Razavi S.,Institute for Research in Fundamental Sciences | Sarbazi-Azad H.,Sharif University of Technology
Information Sciences | Year: 2010

In this paper, a new topology for multicomputer interconnection networks, based on triangular mesh, is proposed. The new network, referred to as the triangular pyramid (or tripy for short), has L levels of triangular mesh. We study some basic important properties of the proposed network as well as introduce a routing algorithm for the tripy network based on the routing of triangular meshes. We prove that this form of pyramidal network is Hamiltonian, Hamiltonian-connected, and pancyclic. We also prove that the proposed network is 6-colorable and conduct a brief comparison of the tripy and its traditional pyramid counterpart. Our results show that the proposed network has higher scalability, connectivity, and total network bandwidth while preserving the important properties of the traditional pyramid network. © 2010 Elsevier Inc. All rights reserved.


Delgosha P.,Institute for Research in Fundamental Sciences | Delgosha P.,Sharif University of Technology | Beigi S.,Institute for Research in Fundamental Sciences
Communications in Mathematical Physics | Year: 2014

Local state transformation is the problem of transforming an arbitrary number of copies of a bipartite resource state to a bipartite target state under local operations. That is, given two bipartite states, is it possible to transform an arbitrary number of copies of one of them into one copy of the other state under local operations only? This problem is a hard one in general since we assume that the number of copies of the resource state is arbitrarily large. In this paper we prove some bounds on this problem using the hypercontractivity properties of some super-operators corresponding to bipartite states. We measure hypercontractivity in terms of both the usual super-operator norms as well as completely bounded norms. © 2014 Springer-Verlag Berlin Heidelberg.


Lohrasebi A.,University of Isfehan | Neek-Amal M.,Institute for Research in Fundamental Sciences | Ejtehadi M.R.,Sharif University of Technology
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

Nonequilibrium molecular dynamics simulations are used to study the motion of a C60 molecule on a graphene sheet subjected to a temperature gradient. The C60 molecule is actuated and moves along the system while it just randomly dances along the perpendicular direction. Increasing the temperature gradient increases the directed velocity of C60. It is found that the free energy decreases as the C60 molecule moves toward the cold end. The driving mechanism based on the temperature gradient suggests the construction of nanoscale graphene-based motors. © 2011 American Physical Society.


Akhavan O.,Sharif University of Technology | Ghaderi E.,Nanobiotechnology Research Laboratory
Journal of Materials Chemistry B | Year: 2014

An effective and self-organized differentiation of human neural stem cells (hNSCs) into neurons was developed by the pulsed laser stimulation of the cells on graphene films (prepared by drop-casting a GO suspension onto quartz substrates). The effects of graphene oxide (GO) and hydrazine-reduced graphene oxide (rGO) sheets on the proliferation of hNSCs were examined. The higher proliferation of the cells on the GO was assigned to its better hydrophilicity. On the other hand, the rGO sheets, which have significantly better electrical conductivity than GO, exhibited more differentiation of the cells into neurons. The pulsed laser stimulation not only resulted in an accelerated differentiation of hNSCs into neurons (rather than glia), but also caused the self-organization of a radial neuronal network on the surface of the rGO sheets, due to the radial stress induced by the surface thermal gradient originating from the center of the laser spot. The higher thermal conductivity of the rGO sheets (compared to the GO sheets and the quartz substrate) provided better outward heat flow from the center of the laser spot, and consequently, prevented extra local heating at the position of the laser spot. These results can encourage further investigations into the advantages of graphene in the self-organized differentiation of hNSCs using pulsed laser stimulation. This journal is © the Partner Organisations 2014.


Alishahiha M.,Institute for Research in Fundamental Sciences | Faraji Astaneh A.,Sharif University of Technology | Faraji Astaneh A.,Institute for Research in Fundamental Sciences | Mohammadi Mozaffar M.R.,Institute for Research in Fundamental Sciences
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We study holographic entanglement entropy for certain logarithmic conformal field theories by making use of their gravity descriptions. The corresponding gravity descriptions are provided by higher-derivative gravity at critical points where the equations of motion degenerate leading to a log gravity. When a central charge of the dual theory is zero, the entanglement entropy has a new divergent term whose coefficient is given by the "new anomaly" of the logarithmic conformal field theory. © 2014 American Physical Society.


Farzan Y.,Institute for Research in Fundamental Sciences | Akbarieh A.R.,Sharif University of Technology
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

We present a dark matter model for explaining the observed 130 GeV photon line from the galaxy center. The dark matter candidate is a vector boson of mass mV with a dimensionless coupling to the photon and Z boson. The model predicts a double line photon spectrum at energies equal to mV and mV(1-mZ2/4mV2) originating from the dark matter annihilation. The same coupling leads to a mono-photon plus missing energy signal at the LHC. The entire perturbative parameter space can be probed by the 14 TeV LHC run. The model has also a good prospect of being probed by direct dark matter searches as well as the measurement of the rates of h→γγ and h→Zγ at the LHC. © 2013 Elsevier B.V.


Fayazbakhsh S.,Institute for Research in Fundamental Sciences | Sadooghi N.,Sharif University of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

The effect of the anomalous magnetic moment of quarks on thermodynamic properties of the chiral condensate is studied, using a two-flavor Nambu-Jona-Lasinio model at finite temperature T, chemical potential μ, and in the presence of a uniform magnetic field eB. To this purpose, the Schwinger linear-in-B ansatz for the anomalous magnetic moment of quarks is considered in terms of the nonperturbative Bohr magneton. In a two-dimensional flavor space, it leads to the correction TSch=κQeB in the energy dispersion relation of quarks. Here, Q is the quark charge matrix. We consider three different sets for κ, and numerically determine the dependence of the constituent quark mass on T,μ, and eB for fixed κ. By exploring the complete phase portrait of this model in T-μ, μ-eB, and T-eB phase spaces for various fixed eB, T, μ, and κ, we observe that inverse magnetic catalysis occurs for large enough κ. Moreover, in the regime of weak magnetic fields, the phenomenon of reentrance of chiral symmetry broken and restored phases occurs for T-, μ-, and eB-dependent κ. © 2014 American Physical Society.


Alishahiha M.,Institute for Research in Fundamental Sciences | Faraji Astaneh A.,Sharif University of Technology | Faraji Astaneh A.,Institute for Research in Fundamental Sciences | Mohammadi Mozaffar M.R.,Institute for Research in Fundamental Sciences
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We present an analytic solution of a Vaidya-charged black hole with a hyperscaling violating factor in an Einstein-Maxwell-dilaton model, where the scalar potential plays a key role in the existence of the solution. By making use of this result, we study the process of thermalization after a global quench in a theory which its gravitational description is provided by the resultant solution in the case of zero charge. In particular, we probe the system by entanglement entropy and show that it exhibits certain scaling behaviors during the process. © 2014 American Physical Society.


Akhavan A.,Institute for Research in Fundamental Sciences | Akhavan A.,Sharif University of Technology | Alishahiha M.,Institute for Research in Fundamental Sciences
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

Using a five-dimensional anti-de Sitter (AdS) soliton in an Einstein-Yang-Mills theory with SU(2) gauge group, we study p-wave holographic insulator/superconductor phase transition. To explore the phase structure of the model, we consider the system in the probe limit as well as fully back-reacted solutions. We will also study the zero temperature limit of the p-wave holographic superconductor in four dimensions. © 2011 American Physical Society.


Alishahiha M.,Institute for Research in Fundamental Sciences | Naseh A.,Institute for Research in Fundamental Sciences | Naseh A.,Sharif University of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

We study holographic renormalization for three-dimensional new massive gravity. By studying the general falloff conditions for the metric allowed by the model at infinity, we show that at the critical point where the central charges of the dual conformal field theory (CFT) are zero, it contains a leading logarithmic behavior. In the context of AdS/CFT correspondence it can be identified as a source for an irrelevant operator in the dual CFT. The presence of the logarithmic falloff may be interpreted as the fact that the dual CFT would be a logarithmic conformal field theory. © 2010 The American Physical Society.


Abolhasani A.A.,Sharif University of Technology | Abolhasani A.A.,Institute for Research in Fundamental Sciences | Firouzjahi H.,Institute for Research in Fundamental Sciences
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

In this paper the possibility of generating large scale curvature perturbations induced from the entropic perturbations during the waterfall phase transition of the standard hybrid inflation model is studied. We show that whether or not appreciable amounts of large scale curvature perturbations are produced during the waterfall phase transition depends crucially on the competition between the classical and the quantum mechanical backreactions to terminate inflation. If one considers only the classical evolution of the system, we show that the highly blue-tilted entropy perturbations induce highly blue-tilted large scale curvature perturbations during the waterfall phase transition which dominate over the original adiabatic curvature perturbations. However, we show that the quantum backreactions of the waterfall field inhomogeneities produced during the phase transition dominate completely over the classical backreactions. The cumulative quantum backreactions of very small scale tachyonic modes terminate inflation very efficiently and shut off the curvature perturbation evolution during the waterfall phase transition. This indicates that the standard hybrid inflation model is safe under large scale curvature perturbations during the waterfall phase transition. © 2011 American Physical Society.


Esmaili A.,Sharif University of Technology | Esmaili A.,Institute for Research in Fundamental Sciences
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

Within the "pseudo-Dirac" scenario for massive neutrinos the existence of sterile neutrinos which are almost degenerate in mass with the active ones is hypothesized. The presence of these sterile neutrinos can affect the flavor composition of cosmic neutrinos arriving at Earth after traveling large distances from astrophysical objects. We examine the prospects of neutrino telescopes such as IceCube to probe the very tiny mass squared differences 10-12eV2>Δm2>10-19eV2, by analyzing the ratio of μ-track events to showerlike events. Considering various sources of uncertainties which enter this analysis, we examine the capability of neutrino telescopes to verify the validity of the pseudo-Dirac neutrino scenario and especially to discriminate it from the conventional scenario with no sterile neutrino. We also discuss the robustness of our results with respect to the uncertainties in the initial flavor ratio of neutrinos at the source. © 2010 The American Physical Society.


Shodja H.M.,Sharif University of Technology | Zaheri A.,Princeton University | Tehranchi A.,Sharif University of Technology
Mechanics of Materials | Year: 2013

Incorporation of the first gradient of strain, in addition to the strain itself, into the strain energy density of an elastic solid leads to Mindlin's first strain gradient theory, which is useful for examination of size effect as well as other mechanical phenomena at the nano-scale. For isotropic elastic solids, the first strain gradient theory, in addition to the two independent Lamé constants, gives rise to five new material constants which in turn reduce to two material parameters, ℓ1 and ℓ2 with dimension of length. The evaluation of these parameters, however, has posed serious challenges, both experimentally and theoretically. In this work ab initio method is used to compute the characteristic lengths for several fcc and bcc metal crystals. It will be seen that the elements of the Hessian matrix, obtained by taking the second derivatives of the total energy with respect to the atomic positions, are linked to the strain gradient material constants. © 2013 Elsevier Ltd. All rights reserved.


Sajadian S.,Institute for Research in Fundamental Sciences | Rahvar S.,Sharif University of Technology
Monthly Notices of the Royal Astronomical Society | Year: 2015

Gravitational microlensing can be used as a unique astrophysical tool to study the atmospheres of stars thousands of parsec away from us. This capability results from the bending of light rays in the gravitational field of a lens that can magnify the light of a background source star during the lensing. Moreover, one of the consequences of this light bending is that the circular symmetry of the source is broken because distorted images are produced at either side of the lens position. This property makes it possible to observe polarization, and also the light centroid shift of images. Assigning vectors for these two parameters, they are perpendicular to each other in simple and binary microlensing events, except in fold singularities. In this work, we investigate the advantages of polarimetric and astrometric observations during microlensing events (i) for studying the surface of the source star and spots on it and (ii) for obtaining extra information to determine the trajectory of source stars with respect to the lens. Finally, we analyse the largest sample of microlensing events from the Optical Gravitational Lensing Experiment (OGLE) catalogue and showthat, for almost~4.3 per cent of events in the direction of the Galactic bulge, the polarization signals would be observable with large telescopes. © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Ozmaian M.,Sharif University of Technology | Naghdabadi R.,Sharif University of Technology
Physical Chemistry Chemical Physics | Year: 2014

The perfluorinated sulfonic acid membrane (Nafion) shows among ionomers high water uptake and cationic conductivity. These properties allow Nafion to be used in nanocomposite actuators, sensors and fuel cells. In situ experiments have shown that there is a water gradient within the Nafion membrane. The water gradient causes the alteration of other physical properties within the thickness of the membrane and has a drastic impact on the performance of the devices made of the Nafion membrane. Deriving closed-form equations and using molecular dynamics (MD) simulation results, we bridge Nafion properties at the atomic scale and the macroscopic behavior of the membrane within a hierarchical multi-scale model. Multiple discrete simulation cells are selected across the thickness of the membrane with a wide range of water contents as representative volume elements (RVEs). The present framework is able to quantitatively predict the macroscopic properties of Nafion with the nanometric resolution regarding the water gradient across the membrane. This journal is © the Owner Societies 2014.


Taherpour A.,Sharif University of Technology | Nasiri-Kenari M.,Sharif University of Technology | Gazor S.,Queen's University
IEEE Transactions on Wireless Communications | Year: 2010

In this paper, we consider the problem of spectrum sensing by using multiple antenna in cognitive radios when the noise and the primary user signal are assumed as independent complex zero-mean Gaussian random signals. The optimal multiple antenna spectrum sensing detector needs to know the channel gains, noise variance, and primary user signal variance. In practice some or all of these parameters may be unknown, so we derive the Generalized Likelihood Ratio (GLR) detectors under these circumstances. The proposed GLR detector, in which all the parameters are unknown, is a blind and invariant detector with a low computational complexity. We also analytically compute the missed detection and false alarm probabilities for the proposed GLR detectors. The simulation results provide the available traded-off in using multiple antenna techniques for spectrum sensing and illustrates the robustness of the proposed GLR detectors compared to the traditional energy detector when there is some uncertainty in the given noise variance. © 2010 IEEE.


Mohammadi M.,Sharif University of Technology | Ghorbani M.,Sharif University of Technology
Journal of Coatings Technology Research | Year: 2011

This study focuses on the effect of co-deposition of PTFE and/or MoS 2 particles on the morphology, wear, and corrosion properties of electroless nickel coating. The composite coating of EN-PTFE-MoS 2 was heat treated at different temperatures for hardness investigations. The surface morphology of coatings was characterized by scanning electron microscopy. Pin-on-disk and potentiodynamic polarization tests were used to study the tribological and corrosion properties of the coatings, respectively. Results of hardness analysis revealed that the hardness of electroless nickel coatings was increased by the heat treatment, and its maximum was gained at 400°C. Wear investigations showed that simultaneous co-deposition of the PTFE and MoS 2 particles into the nickel coating increased the wear resistance of the coating by about 30% and reduced the average value of friction coefficient to 0.25 from 0.65. Corrosion studies illustrated that simultaneous co-deposition of the PTFE and MoS 2 particles led to reduction in corrosion resistance by 10 and 5 times that of EN coating in brine and acidic solution, respectively. © 2011 ACA and OCCA.


Dalvand P.,Sharif University of Technology | Mohammadi M.R.,Sharif University of Technology
Journal of Nanoparticle Research | Year: 2011

Cadmium sulfide (CdS) with different morphologies was successfully prepared by solvothermal process by controlling the processing parameters, including nature of precursor and solvent, reaction temperature and process time. X-ray diffraction patterns revealed that, in all cases highly pure and crystallized CdS with hexagonal structure were obtained. In addition, it was found that the processing parameters influence on preferable growth direction of CdS nanostructures. Field emission scanning electron microscope analysis showed that CdS nanowires with different aspect ratios were obtained (depending upon the reaction temperature and process time) in presence of sulfur powder and ethylenediamine, whereas CdS nanoparticles were produced by sulfur powder and ethanolamine. Moreover, CdS nanorods were prepared using thiourea and ethylenediamine. Transmission electron microscope image confirmed that CdS nanowire with one of the highest aspect ratio reported in the literature (i.e., 255) was achieved using sulfur powder and ethylenediamine at 200 °C reaction temperature for 72 h process time. UV-Vis absorption spectra of CdS nanostructures prepared under different conditions displayed a blue shift relative to that of bulk CdS due to the quantum size effect. © Springer Science+Business Media B.V. 2010.


Bagheri H.,Sharif University of Technology | Aghakhani A.,Sharif University of Technology
Analytical Methods | Year: 2011

Novel unbreakable solid phase microextraction (SPME) fiber coatings were fabricated by electrospinning method in which the polymeric solution was converted to nanofibers using high voltages. Four different polymers, polyurethane (PU), polycarbonate (PC), polyamide (PA) and polyvinyl chloride (PVC) were prepared as the fiber coatings on thin stainless steel wires. The extraction efficiencies of new coatings were investigated by headspace solid-phase microextraction (HS-SPME) of some environmentally important chlorobenzenes from aqueous samples followed by gas chromatography-mass spectrometry (GC-MS) analysis. Among them, PU showed a prominent efficiency. Effects of coating time and polymer concentration on the PU fiber capability were also optimized. The scanning electron microscopy (SEM) images of the PU coating showed a diameter range of 150-600 nm with a homogeneous and porous surface structure. Effects of different parameters influencing the extraction efficiency including the extraction temperature, extraction time, ionic strength, desorption temperature and time were investigated and optimized. The limits of detection and quantification of the method under optimized conditions were 10 and 50 ng L-1, respectively. The relative standard deviations (RSD) at a concentration level of 0.5 ng mL-1 were obtained between 3 and 8% (n = 3). The calibration curves of CBs showed linearity from 50 to1000 ng L-1. The proposed method was successfully applied to the extraction of CBs from real water samples and relative recoveries were between 94 and 102%. © 2011 The Royal Society of Chemistry.


Kouchakzadeh M.A.,Sharif University of Technology | Shakouri M.,Sharif University of Technology
International Journal of Mechanical Sciences | Year: 2014

The present study deals with vibrational behavior of two joined cross-ply laminated conical shells. The natural frequencies and mode shapes are investigated. The joined conical shells can be considered as the general case for joined cylindrical-conical shells, joined cylinder-plates or cone-plates, cylindrical and conical shells with stepped thicknesses and also annular plates. Governing equations are obtained using thin-walled shallow shell theory of Donnell type and Hamilton's principle. The appropriate expressions among stress resultants and deformations are extracted as continuity conditions at the joining section of the cones. The equations are solved assuming trigonometric response in circumferential and series solution in meridional directions. All combinations of boundary conditions can be assumed in this method. The results are compared and validated with the available results in other investigations. The effects of semi-vertex angles, meridional lengths and shell thicknesses on the natural frequency and circumferential wave number of joined shells are investigated. © 2013 Elsevier Ltd.


Ashiri R.,Sharif University of Technology | Ashiri R.,Isfahan University of Technology | Ashiri R.,Islamic Azad University at Dezful
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2014

In the present work, an improved method is developed for preparing highly pure ultrathin barium titanate nanostructured films with desired structural and morphological characteristics. In contrast to other approaches, our method can be carried out at a relatively lower temperature to obtain barium titanate ultrathin films free from secondary phases, impurities, and cracks. To reach an in-depth understanding of scientific basis of the proposed process, and in order to disclose the mechanism of formation and growth of barium titanate ultrathin film, in-detail analysis is carried out using XRD, SEM, FE-SEM, and AFM techniques aided by theoretical calculations. The effects of calcining temperature on the nanoscale structure development, phase transition, morphology evolution, and growth mechanism of the ultrathin barium titanate nanostructured films are studied. XRD results indicate that the reaction leading to the formation of the barium titanate initiates at about 873 K (600 °C) and completes at about 1073 K (800 °C). Moreover, secondary phases are not detected in the XRD patterns of the ultrathin films which this observation ensures the phase purity of the ultrathin films. The results show that the ultrathin films are nanothickness and nanostructured leading to the enhancement of rate of diffusion by activating short-circuit diffusion mechanisms. The high rate of the diffusion enhances the rate of the formation of barium titanate and also prevents from the formation of the secondary phases in the final products. SEM and AFM results indicate that the deposited ultrathin films are crack-free exhibiting a dense nanogranular structure. The results indicate that the root-mean square (RMS) roughness of the ultrathin films is in the range of 1.66 to 6.71 nm indicating the surface of the ultrathin films is smooth. RMS roughness also increases with an increase in the calcining temperature which this observation seems to be related to the grain growth process. Finally, based on the observed results, the mechanism of the formation and growth of the ultrathin barium titanate nanostructured films is deeply disclosed. © The Minerals, Metals & Materials Society and ASM International 2014.


Aminzadeh S.,Sharif University of Technology | Ejlali A.,Sharif University of Technology
IEEE Transactions on Computers | Year: 2011

Low energy consumption and fault tolerance are often key objectives in the design of real-time embedded systems. However, these objectives are at odds, and there is a trade-off between them. Real-time systems usually use system level energy reduction methods, i.e., dynamic voltage scaling (DVS) and dynamic power management (DPM). Also hard real-time systems often use replication to achieve fault tolerance. In this paper, we investigate the impact of system level energy reduction methods on both the reliability and energy consumption of hard real-time systems which use replication for fault tolerance. In this analysis, we have considered four various existing energy management methods: 1) Classic DPM, 2) Classic DVS, 3) Postponement method: a variation of DPM which is only applicable to replicated systems, and 4) Hybrid method: a combination of Postponement and DVS. Based on the comparative study, we have provided guidelines so that a designer can decide which energy management method is more suitable for a given application. For example, we have shown that when reliability is the main concern, the postponement method is the most preferable. However, when the energy consumption is the primary concern, the hybrid method may be more appropriate. © 2006 IEEE.


Atrianfar H.,Sharif University of Technology | Haeri M.,Sharif University of Technology
ISA Transactions | Year: 2012

This paper deals with the average consensus problem in a multi-agent system with switching interaction topology modeled as a weighted digraph. The convergence analysis is performed in both discrete-time and continuous-time dynamics based on the theory of infinite matrix products. Conditions for system convergence to average consensus are derived in the form of constraints on direct and reverse graphs and the structure of adjacency elements among the agents. Furthermore, a sufficient condition is provided for convergence to average consensus in systems in which the interaction topology is balanced over infinite contiguous non-overlapping time intervals instead of being balanced continuously. Numerical simulations are given to demonstrate the effectiveness of the theoretical results.© 2012 ISA. Published by Elsevier Ltd. All rights reserved.


Seyed Salehi M.,Sharif University of Technology | Serajzadeh S.,Sharif University of Technology
Computational Materials Science | Year: 2012

A coupled cellular automata and finite element model has been proposed to evaluate static recrystallization kinetics during non-isothermal annealing of cold deformed low carbon steels. The effects of various factors including heating rate, annealing temperature, and initial microstructures have been considered in the model to accurately predict the static recrystallization kinetics and the final microstructures. In order to examine the employed algorithm, the predicted results have been compared with the experimental observations and a good agreement was found between the two sets of results. © 2011 Elsevier B.V. All rights reserved.


Hasani-Marzooni M.,Niroo Research Institute | Hosseini S.H.,Sharif University of Technology
Energy Policy | Year: 2013

This paper develops a system dynamics model to analyze the impacts of different kinds of capacity payment as investment incentive mechanisms in Iranian electricity market. Since it is aimed that the incurred capital and operating costs of generation technologies be recovered in Iranian electricity pool, the noncompetitive capacity payment mechanism has been introduced for this purpose in order to encourage new investments in electric power generation system. In the current mechanism, the capacity payments are designated to the generating units in the whole country electricity market. An annual base value of capacity payment is proposed based on recovering the capital cost of a benchmark generation technology. This value is altered according to the operational reserve in the day-ahead electricity market. This supporting policy is simulated and analyzed in the proposed dynamic framework in order to track the trend of new investments in the Iranian electricity market. The feasibility study of implementing the regional capacity assignment is the main focus of this paper. Different possible regulating policies such as floating rates for capacity payment and electricity price cap, the multiple capacity payments to various technologies, and the regional electricity market with territorial capacity allocation are examined in order to investigate the consequences and performances of different decisions and policies in the capacity investment of Iranian electricity market. © 2012 Elsevier Ltd.


Mossa Hosseini S.,University of Tehran | Ataie-Ashtiani B.,Sharif University of Technology | Kholghi M.,University of Tehran
Desalination | Year: 2011

In this work the application of a modified surface nano zero valent iron (NZVI) as bimetallic Fe/Cu particles to remove high concentration of NO3--N through packed sand column has been studied. Dispersed nano-Fe/Cu particles has been synthesized in water mixed ethanol solvent system (1:4v/v) and described by XRD pattern, TEM and SEM images and BET analyze. Batch experiments have been conducted to investigate the effect of percentage coating of Fe0 by Cu on the nitrate removal. Research on packed sand column (120cm length, 6.5cm inner diameter) has been done under conditions of Nano-Fe/Cu concentration (2, 5, and 8gl-1 of solution), high initial NO3--N concentration (100, 200, and 300mgl-1) and pore water velocity through sand (0.125, 0.250, and 0.375mms-1) in seven sets. Results of batch experiments indicated the efficient coating percentage of Fe0 by Cu in NO3--N reduction was 2.5% (w/w). In addition, increase of pore velocity of water through packed sand has negative effect on the nitrate reduction rate. In contrast, increasing the injected mass of nano particles and the influent NO3--N concentration would increase the rate of NO3--N reduction. The best condition to reduce NO3--N has been observed at end of sand column as 75% of influent concentration when nano-Fe/Cu concentration=8gl-1, high initial NO3--N concentration=100mgl-1 and pore water velocity through sand=0.125mms-1. © 2011 Elsevier B.V.


Gharagheizi F.,Saman Energy Giti Company | Mirkhani S.A.,Sharif University of Technology | Tofangchi Mahyari A.-R.,Sharif University of Technology
Energy and Fuels | Year: 2011

The artificial neural network-group contribution (ANN-GC) method is applied to estimate the standard enthalpy of combustion of pure chemical compounds. A total of 4590 pure compounds from various chemical families are investigated to propose a comprehensive and predictive model. The obtained results show the squared correlation coefficient (R 2) of 0.999 99, root mean square error of 12.57 kJ/mol, and average absolute deviation lower than 0.16% for the estimated properties from existing experimental values. © 2011 American Chemical Society.


Yousefi V.,Sharif University of Technology | Kariminia H.-R.,Sharif University of Technology
International Biodeterioration and Biodegradation | Year: 2010

Enzymatic decolorization of the monoazo dye, acid orange 7 (AO7) by the fungal peroxidase from Coprinus cinereus NBRC 30628 is a complex system, which is greatly affected by temperature, pH, enzyme activity and the concentrations of H2O2 and dye concentration. The study of these factors and investigating the combined interactions between them by applying one-factor-at-a-time (OFAT) method and two other statistical methods including 2-factorial method and response surface methodology (RSM) were aimed in this work. Through OFAT analysis the optimized conditions were a temperature of 25 °C, pH 9.0 with H2O2 concentration of about 3.9 mM and AO7 concentration of 40 mg/l. A complete decolorization attained under such conditions in only 1 min. For statistical optimization, 2-factorial design method was applied first, and three factors of temperature, pH and initial dye concentration were recognized as significant factors. Then, response surface analysis was conducted through central composite design and a second-order polynomial model (R2 = 0.9718) was generated. ANOVA analysis of this model indicated that the temperature, pH and their interaction were the most significant in decolorization of AO7. The optimum condition through RSM was found to be the temperature of 25 °C, pH value of 9.0 and 50 mg/l of AO7 initial concentration, for the maximum decolorization of 100%. © 2010 Elsevier Ltd. All rights reserved.


Shahrokhian S.,Sharif University of Technology | Rastgar S.,Sharif University of Technology
Electrochimica Acta | Year: 2011

A modified glassy carbon electrode, prepared by potentiostatic electrodeposition of platinum-ruthenium nanoparticles (Pt-RuNPs) onto a multi-walled carbon nanotube (MWCNT) layer, offers dramatic improvements in the stability and sensitivity of voltammetric responses toward methyldopa (m-dopa) compared to glassy carbon electrodes individually coated with MWCNT or Pt-RuNPs. The surface morphology and nature of the hybrid film (Pt-RuNPs/MWCNT) deposited on glassy carbon electrodes was characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. A remarkable enhancement in the microscopic area of the electrode together with the catalytic role of the composite modifier resulted in a considerable increase in the peak current (110 times) and a negative shift (-200 mV) in the oxidation peak potential of m-dopa. The mechanism of the electrocatalytic process on the surface of the modified electrode was analyzed via cyclic voltammograms at various potential sweep rates and pHs of the buffer solutions. Differential pulse voltammetry was applied and shown to provide a very sensitive analytical method for the determination of sub-micromolar amounts of m-dopa, for which a linear dynamic range of 0.05-40 μM and a detection limit of 10 nM was obtained. The modified electrode was successfully used for accurate determination of trace amounts of m-dopa in pharmaceutical and clinical preparations. © 2011 Elsevier Ltd. All rights reserved.


Mohammadi M.R.,Sharif University of Technology
Materials Science in Semiconductor Processing | Year: 2014

Nanostructured TiO2-Al2O3 films and powders were prepared by a straightforward aqueous particulate sol-gel route. Titanium (IV) isopropoxide and aluminum chloride were used as precursors, and hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the porosity. The effect of Al:Ti molar ratio was studied on the crystallization behavior of the products. X-ray diffraction (XRD) revealed that the powders crystallized at 800°C, containing anatase-TiO2, rutile-TiO2 and cubic-Al2O3 phases. Furthermore, it was found that Al2O3 retarded the anatase to rutile transformation. Transmission electron microscope (TEM) image showed that one of the smallest crystallite sizes was obtained for TiO2-Al2O3 binary mixed oxide, being 3 nm at 600°C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had nanostructured morphology with the average grain size in the range 20-70 nm at 800°C depending on Al:Ti molar ratio. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO gas at operating temperature of 400°C. © 2014 Elsevier Ltd. All rights reserved.


Haghshenas H.,Sharif University of Technology | Vaziri M.,Sharif University of Technology
Ecological Indicators | Year: 2012

Transportation has significant and long lasting economical, social and environmental impacts, and so is an important dimension of urban sustainability. Some attempts have been made to develop sustainable transport indicators, STI. A few studies actually apply STI to compare sustainability among various world cities. In this paper various world cities ranked in terms of urban sustainable transport composite index. The study database is created from UITP databank: "Millennium cities database for sustainable mobility" or MCDST. Firstly sustainable transportation indicators were selected by reviewing past researches. Some indicators are edited or redefined. Consequently 9 STI were developed, 3 indicators in each 3 groups of environmental, economical and social. Then composite index was also suggested by combination of 9 standardized indicators. According to composite index various cities were compared. Finally some important factors affecting urban transportation sustainability were determined by using correlation analyses between composite index and cities characterizes. © 2011 Elsevier Ltd. All rights reserved.


Mazaheri M.,Sharif University of Technology | Akhavan M.,Sharif University of Technology
Journal of Magnetism and Magnetic Materials | Year: 2010

We present a study of the structural and electrical behavior of nano-polycrystalline mixed barium and alkali substituted lanthanum-based manganite, (La1-yKy)0.7Ba0.3MnO 3 with y=0.00.3. The samples were synthesized by the polymerization complex solgel method. The powder X-ray diffraction (XRD) data of the samples show a single-phase character with R3c space group. The magnetic and electrical transport properties of the nano-polycrystalline samples have been investigated in the temperature range 50300 K and a magnetic field up to 10 kOe. The metalinsulator transition temperature Tp of all the samples decreased with potassium doping, and also, it increased slightly with the application of magnetic field. The low field magnetoresistance, which is absent in the single-crystalline perovskite, was observed and increased with decreasing temperature. Comparing the experimental resistivity data with the theoretical models shows that the high temperature electrical behavior of these samples is in accordance with the adiabatic small polaron-hopping model. In the metal-ferromagnetic region the resistivity is found to be quite well described by ρ=ρ0ρ2T2ρ4.5T4.5. © 2010 Elsevier B.V. All rights reserved.


Ordikhani F.,Sharif University of Technology | Simchi A.,Sharif University of Technology
Applied Surface Science | Year: 2014

Composite coatings with bone-bioactivity and drug-eluting capacity are considered as promising materials for titanium bone implants. In this work, drug-eluting chitosan-bioactive glass coatings were fabricated by a single-step electrophoretic deposition technique. Drug-loading and -releasing capacity of the composite coatings were carried out using the vancomycin antibiotic. Uniform coatings with a thickness of ∼55 μm containing 23.7 wt% bioactive glass particles and various amounts of the antibiotic (380-630 μg/cm2) were produced. The coatings were bioactive in terms of apatite-forming ability in simulated body fluid and showed favorable cell adhesion and growth. In vitro biological tests also indicated that the composite coatings had better cellular affinity than pristine chitosan coatings. The in vitro elution kinetics of the composite coating revealed an initial burst release of around 40% of the drug within the first elution step of 1 h and following by a continuous eluting over 4 weeks, revealing long-term drug-delivering potential. Antibacterial tests using survival assay against Gram-positive Staphylococcus aureus bacteria determined the effect of vancomycin release on reduction of infection risk. Almost no bacteria were survived on the coatings prepared from the EPD suspension containing ≥0.5 g/l vancomycin. The developed chitosan-based composite coatings with bone bioactivity and long-term drug-delivery ability may be potentially useful for metallic implants to reduce infection risk. © 2014 Elsevier B.V. All rights reserved.


Jalili M.,Sharif University of Technology
Journal of Informetrics | Year: 2011

Complex networks may undergo random and/or systematic failures in some of their components, i.e. nodes and edges. These failures may influence various network properties. In this article, for a number of real-world as well as Watts-Strogatz model networks, we investigated the profile of the network small-worldness as random failures, i.e. errors, or systematic failures, i.e. attacks, occurred in the nodes. In errors nodes are randomly removed along with all their tipping edges, while in attacks the nodes with highest degrees are removed from the network. Interestingly, in many cases, the small-worldness of violated networks increased as more nodes underwent an attack. This indicates an important role of the hub nodes in controlling the small-worldness of Watts-Strogatz networks. The profile of changes in the small-worldness as a result of errors/attacks was independent of network size, while it was influenced by average degree and rewiring probability of Watts-Strogatz model. We also found that the pattern of the changes of the small-worldness in real-world networks is completely different than that of the Watts-Strogatz networks. Therefore, although Watts-Strogatz model is often used for constructing networks with small-world property, the resulting networks have different properties compared to real-world ones in terms of robustness in the small-worldness index against errors/attacks. © 2011 Elsevier Ltd.


Fatehi R.,Sharif University of Technology | Manzari M.T.,Sharif University of Technology
Computers and Mathematics with Applications | Year: 2011

Several schemes for discretization of first and second derivatives are available in Smoothed Particle Hydrodynamics (SPH). Here, four schemes for approximation of the first derivative and three schemes for the second derivative are examined using a theoretical analysis based on Taylor series expansion both for regular and irregular particle distributions. Estimation of terms in the truncation errors shows that only the renormalized (the first-order consistent) scheme has acceptable convergence properties to approximate the first derivative. None of the second derivative schemes has the first-order consistency. Therefore, they converge only when the particle spacing decreases much faster than the smoothing length of the kernel function. In addition, using a modified renormalization tensor, a new SPH scheme is presented for approximating second derivatives that has the property of first-order consistency. To assess the computational performance of the proposed scheme, it is compared with the best available schemes when applied to a 2D heat equation. The numerical results show at least one order of magnitude improvement in accuracy when the new scheme is used. In addition, the new scheme has higher-order convergence rate on regular particle arrangements even for the case of only four particles in the neighborhood of each particle. © 2010 Elsevier Ltd. All rights reserved.


Rezaei A.,Sharif University of Technology | Mohammadi M.R.,Sharif University of Technology
Materials Science and Engineering C | Year: 2013

Hydroxyapatite (HA) is the most substantial mineral constituent of a bone which has been extensively used in medicine as implantable materials, owing to its good biocompatibility, bioactivity high osteoconductive, and/or osteoinductive properties. Nevertheless, its mechanical property is not utmost appropriate for a bone substitution. Therefore, a composite consist of HA and a biodegradable polymer is usually prepared to generate an apt bone scaffold. In the present work polycaprolactone (PCL), a newly remarkable biocompatible and biodegradable polymer, was employed as a matrix and hydroxyapatite nanoparticles were used as a reinforcement element of the composite. HA/PCL nanocomposites were synthesized by a new in situ sol-gel process using calcium hydroxide and phosphoric acid precursors in the presence of Tetrahydrofuran (THF) as a solvent. Chemical and physical characteristics of the nanocomposite were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FTIR) analyses. The results indicated that pure HA nanoparticles were well-incorporated and homogenously dispersed in the PCL matrix. It was found that the mechanical property of PCL was improved by addition of 20 wt.% HA nanoparticles. Furthermore, the biological property of nanocomposites was investigated under in vitro condition. For this purpose, HA/PCL scaffolds were prepared through a salt leaching process and immersed in a saturated simulated body fluid (SBF) after 3 and 7 days. It was found that a uniform layer of biomimetic HA could be deposited on the surface of HA/PCL scaffolds. Therefore, the prepared HA/PCL scaffolds showed good potential for bone tissue engineering and could be used for many clinical applications in orthopedic and maxillofacial surgery. © 2012 Elsevier B.V.


Khodaygan S.,Sharif University of Technology
International Journal of Computer Integrated Manufacturing | Year: 2014

Inaccuracies in workpiece location lead to errors in position and orientation of machined features on the workpiece, and strongly affect the assemblability and the quality of the product. The accurate positioning of workpiece on a fixture is influenced by rigid body displacements and rotations of the workpiece due to several errors (e.g. geometric radial and position errors in locators and manufacturing tolerances of the workpiece). In this paper, an efficient approach is introduced for analysis and compensation errors in the workpiece-fixture-cutting tool system. A new mathematical formulation of workpiece-fixture modelling is proposed to establish the relationship between the locating errors and their sources. Based on the proposed method, the locating errors of the workpiece can be accurately estimated by relating them to the specific geometric errors or tolerances of the workpiece and the related locators. Then, to eliminate the effects of the locating errors and the cutting tool wear on the machined features, the location and orientation of the cutting tool in the cutter location data are corrected. The proposed method is proper for error analysis and compensation based on worst case analysis approach. The application of the presented method is illustrated through presenting an example and the computational results are compared to the results of simulation of the case study in a computer aided design and manufacturing (CAD/CAM) system. © 2014 © 2014 Taylor & Francis.


Firouzjaee J.T.,Sharif University of Technology | Firouzjaee J.T.,Pennsylvania State University
International Journal of Modern Physics D | Year: 2012

The spherical symmetry black holes are considered in expanding background. The singularity line and the marginally trapped tube surface behavior are discussed. In particular, we address the conditions whether dynamical horizon forms for these cosmological black holes. We also discuss about the cosmological constant effect on these black hole and the redshift of the light which comes from the marginally trapped tube surface. © 2012 World Scientific Publishing Company.


Pishkenari H.N.,Sharif University of Technology | Meghdari A.,Sharif University of Technology
Ultramicroscopy | Year: 2011

This paper focuses on the influences of the tip mass ratio (the ratio of the tip mass to the cantilever mass), on the excitation of higher oscillation eigenmodes and also on the tip-sample interaction forces in tapping mode atomic force microscopy (TM-AFM). A precise model for the cantilever dynamics capable of accurate simulations is essential for the investigation of the tip mass effects on the interaction forces. In the present work, the finite element method (FEM) is used for modeling the AFM cantilever to consider the oscillations of higher eigenmodes oscillations. In addition, molecular dynamics (MD) is used to calculate precise data for the tip-sample force as a function of tip vertical position with respect to the sample. The results demonstrate that in the presence of nonlinear tip-sample interaction forces, the tip mass ratio plays a significant role in the excitations of higher eigenmodes and also in the normal force applied on the surface. Furthermore, it has been shown that the difference between responses of the FEM and point-mass models in different system operational conditions is highly affected by the tip mass ratio. © 2011 Elsevier B.V.


Eslami P.,Sharif University of Technology | Taheri A.K.,Sharif University of Technology
Materials Letters | Year: 2011

A new method for production of bimetallic rods, utilizing the equal channel angular extrusion (ECAE) process has been introduced before by previous researchers, but no attempt has been made to assess the effect of different temperatures and holding times in order to achieve a diffusional bond between the mating surfaces. In present research copper sheathed aluminum rods have been ECAEed at room temperature and subsequently held at a constant ECAE pressure, at different temperatures and holding times to produce a diffusional bond between the copper sheath and the aluminum core. The bonding quality of the joints was examined by shear strength test and a sound bonding interface was achieved. Based on the results, a bonding temperature of 200 °C and holding time of 60-80 min yielded the highest shear strength value. © 2011 Elsevier B.V. All rights reserved.


Zangiabadi A.,Sharif University of Technology | Kazeminezhad M.,Sharif University of Technology
Materials Science and Engineering A | Year: 2011

A new severe plastic deformation (SPD) method entitled Tube Channel Pressing (TCP) is proposed. In this study, the ability of TCP on strength improvement and grain refinement is assessed. This method is based on pressing a tube through a tubular channel die with a neck zone. Utilization of a mandrel fitted inside the tube prevents the crumpling of tube and preserves its initial dimension. Due to the symmetric design, after one pass, the die is rotated upside down and the second pass is applied by pressing the tube in inverse direction. Ultimate strength of a commercial purity aluminum tube after 5 successful passes is improved to 2 times of the initial strength. Analytical calculations and simulation of this process accompanied by commercial finite element code ABAQUS/Explicit demonstrate that the total average equivalent strain of 1.2 is imposed in each pass. Furthermore, hardness distribution through tube thickness is assessed. Then, ability of TCP in grain refinement of tubular samples after each pass is determined. © 2011 Elsevier B.V.


Salmasi N.,Sharif University of Technology | Logendran R.,Oregon State University | Skandari M.R.,Sharif University of Technology
Computers and Operations Research | Year: 2010

We have developed a mathematical programming model for minimizing total flow time of the flow shop sequence dependent group scheduling (FSDGS) problem, typically classified as Fm|fmls, Splk, prmu|∑Cj. As the problem is shown to be strongly NP-hard, a tabu search (TS) algorithm as well as a hybrid ant colony optimization (HACO) algorithm have been developed to heuristically solve the problem. A lower bounding (LB) method based on the Branch-and-Price algorithm is also developed to evaluate the quality of the metaheuristic algorithms. In order to compare the performance of metaheuristic algorithms, random test problems, ranging in size from small, medium, to large are created and solved by both the TS and the HACO algorithms. A comparison shows that the HACO algorithm has a better performance than the TS algorithm. The results of the heuristic algorithms are also compared with the results of the LB method to evaluate the quality of the solutions. The LB method presented in this paper can be generalized to solve the FSDGS problem with other objective functions. © 2009 Elsevier Ltd. All rights reserved.


Mesbahi A.,Sharif University of Technology | Haeri M.,Sharif University of Technology
Journal of Process Control | Year: 2014

A fractional order PID controller is designed to stabilize fractional delay systems with commensurate orders and multiple commensurate delays, where the time delays in the system may belong to several distinct intervals. Moreover, the controller parameters should belong to given intervals. In order to stabilize the system, the D-subdivision method is employed to choose the stabilizing set of the controller parameters from their available values. Furthermore, the nearest values of the obtained stabilizing set to their mean values are selected as the controller parameters so that a non-fragile controller is concluded. Two numerical examples evaluate the proposed control design method. © 2014 Elsevier Ltd.


Amerimehr M.H.,Sharif University of Technology | Ashtiani F.,Sharif University of Technology
IEEE Transactions on Wireless Communications | Year: 2014

This paper presents an analytical study of average delay and throughput in a two-way relay network exploiting network coding to exchange source packets, where arrival and departure of packets are stochastic. In this case, a fundamental problem for the relay node is whether to wait in order to obtain a coding opportunity, leading to reduction of the number of transmissions, or sending a packet (coded/uncoded) whenever it has a transmission opportunity, leading to reduction of the packet delay. In order to address the fundamental trade-off between packet delay and transmission power, we develop three network coding schemes based on power-delay constraint of the application. We devise a theoretical framework to compute the average delay and stability region for each proposed scheme and compare the performance of network coding and traditional routing. Our results reveal that network coding may deliver packets with either larger or lower delay compared to traditional routing, depending on the selected scheme. Unlike the previous works in this area, in order to include channel loss due to noise, interference, etc., we consider probabilistic transmission for all packets. The transmission probabilities depend on the nature (coded/uncoded) and destination of packets, which are generally different for coded and uncoded packets. We carry out simulations to confirm our theoretical analysis. © 2014 IEEE.


Karimi H.,Sharif University of Technology | Davison E.J.,University of Toronto | Iravani R.,University of Toronto
IEEE Transactions on Power Systems | Year: 2010

A linear time-invariant (LTI) robust servomechanism controller for islanded (autonomous) operation of a distributed generation (DG) unit and its local load is proposed. The DG unit utilizes a voltage-sourced converter (VSC) as the interface medium. The controller design is obtained by introducing a new optimal controller design procedure, in conjunction with a proposed non-conservative robustness constraint. The proposed controller utilizes 1) an internal oscillator for frequency control and 2) a robust servomechanism controller (RSC) to regulate the island voltage. Despite uncertainty of the load parameters, the proposed controller guarantees robust stability and pre-specified performance criteria, e.g., fast transient response and zero steady-state error. The theoretical aspects of the proposed robust servomechanism controller including the existence conditions, design of the controller, and robust stability analysis of the closed-loop system are studied. Moreover, the performance of the robust servomechanism controller based on 1) simulation studies in the MATLAB software environment, and 2) experiments in a laboratory-scale setup, is presented in this paper. In particular, reference signal tracking and robustness of the closed-loop system with respect to the load parameter uncertainty are investigated. Both computer simulation studies and experimental results confirm that the proposed robust controller provides the specified performance characteristics of the closed-loop system. © 2010 IEEE.


Pishkenari H.N.,Sharif University of Technology | Meghdari A.,Sharif University of Technology
Ultramicroscopy | Year: 2011

The finite element method and molecular dynamics simulations are used for modeling the AFM microcantilever dynamics and the tip-sample interaction forces, respectively. Molecular dynamics simulations are conducted to calculate the tip-sample force data as a function of tip height at different lateral positions of the tip with respect to the sample. The results demonstrate that in the presence of nonlinear interaction forces, higher eigenmodes of the microcantilever are excited and play a significant role in the tip and sample elastic deformations. Using comparisons between the results of FEM and lumped models, how some aspects of the system behavior can be hidden when the point-mass model is used is illustrated. © 2010 Elsevier B.V.


Tavakoli-Kakhki M.,K. N. Toosi University of Technology | Tavazoei M.S.,Sharif University of Technology
Journal of Process Control | Year: 2014

This paper deals with proportional stabilization and closed-loop step response identification of the fractional order counterparts of the unstable first order plus dead time (FOPDT) processes. At first, the necessary and sufficient condition for stabilizability of such processes by proportional controllers is found. Then, by assuming that a process of this kind has been stabilized by a proportional controller and the step response data of the closed-loop system is available, an algorithm is proposed for estimating the order and the parameters of an unstable fractional order model by using the mentioned data. © 2014 Elsevier Ltd.


Asghari M.,Sharif University of Technology | Ahmadian M.T.,Sharif University of Technology | Kahrobaiyan M.H.,Sharif University of Technology | Rahaeifard M.,Sharif University of Technology
Materials and Design | Year: 2010

In this paper, the size-dependent static and vibration behavior of micro-beams made of functionally graded materials (FGMs) are analytically investigated on the basis of the modified couple stress theory in the elastic range. Functionally graded beams can be considered as inhomogeneous composite structures, with continuously compositional variation from usually a ceramic at the bottom to a metal at the top. The governing equations of motion and boundary conditions are derived on the basis of Hamilton principle. Closed-form solutions for the normalized static deflection and natural frequencies are obtained as a function of the ratio of the beam characteristic size to the internal material length scale parameter and FGM distribution functions of properties. The results show that the static deflection and natural frequencies developed by the modified couple stress theory have a significant difference with those obtained by the classical beam theory when the ratio of the beam characteristic size to the internal material length scale parameter is small. © 2009 Elsevier Ltd. All rights reserved.


Riahi H.T.,Sharif University of Technology | Estekanchi H.E.,Sharif University of Technology
Journal of Constructional Steel Research | Year: 2010

In the endurance time (ET) method, structures are subjected to a specially designed intensifying ground acceleration function and their performance is judged based on their response at various excitation levels. A range of equivalent intensities can be covered in a single numerical or experimental simulation, thus significantly reducing the computational demand as compared to full nonlinear response-history analyses. The applied excitation intensity at various times has been correlated with those of the scaled ground motions. Response spectra of seven ground motions on stiff soil were used to produce intensifying acceleration functions that at each time window produce a response spectrum that is compatible with the template spectrum and proportionally scale up with time. The drift ratios and plastic hinge rotations compare well with those from ground motions in steel frames with various numbers of stories and bays. The locations of plastic hinges are also predicted quite satisfactorily by ET analysis. The sensitivity of the results to the selection of a particular set of ground motions is also studied. © 2009 Elsevier Ltd. All rights reserved.


Kazeminezhad M.,Sharif University of Technology | Hosseini E.,Sharif University of Technology
Materials and Design | Year: 2010

In this paper, considering the problems of common finite element (FE) codes that consider simple constitutive equations, a developed FE code that considers a new constitutive model is used to simulate the behavior of copper sheets under severe plastic deformation (SPD). The new proposed constitutive model, that considers dislocation densities in cell interiors and cell walls of material as true internal state variables, can investigate all stages of flow stress evolution of material during large plastic deformations and also can explain the effects of strain rate magnitude on the mechanical response of material, during room temperature SPD. The proposed FE analysis is used to investigate the effects of die design on the property of SPDed sheets by groove pressing (GP) processes. To do so, the GP processes through existent designations of dies are simulated and a good agreement between the modeling results and experimental data is obtained. In addition, a new die design is proposed that can eliminate the problems of the existent designations of dies and can produce the sheets with higher strength and more uniform hardness. © 2009 Elsevier Ltd. All rights reserved.


Kouchakzadeh M.A.,Sharif University of Technology | Rasekh M.,Tafresh University | Haddadpour H.,Sharif University of Technology
Composite Structures | Year: 2010

The problem of nonlinear aeroelasticity of a general laminated composite plate in supersonic air flow is examined. The classical plate theory along with the von-Karman nonlinear strains is used for structural modeling, and linear piston theory is used for aerodynamic modeling. The coupled partial differential equations of motion are derived by use of Hamilton's principle and Galerkin's method is used to reduce the governing equations to a system of nonlinear ordinary differential equations in time, which are then solved by a direct numerical integration method. Effects of in-plane force, static pressure differential, fiber orientation and aerodynamic damping on the nonlinear aeroelastic behavior of the plate are studied. Results show that the fiber orientation has significant effect on dynamic behavior of the plate and the asymmetric properties, changes the behavior of the limit cycle oscillation. © 2010 Elsevier Ltd.


Sadeghi M.,Sharif University of Technology | Parsafar G.A.,Sharif University of Technology
Journal of Physical Chemistry B | Year: 2012

Water inside carbon nanotubes as an example of nanoconfined water has gained noticeable attention, in both theoretical and applied aspects. Molecular simulation has played a major role in the studies in this field. Yet, there is a need for systematic study of simulation results and compilation of scientifically reliable predictive relations. Here we present Monte Carlo simulations of water inside carbon nanotubes with different radii. An equation of state which was derived on the basis of the extended Lennard-Jones (12,6,3) as the effective pair potential is chosen for the system of water inside the carbon nanotubes. The equation of state is modified to take the effects of anisotropic pressure tensor into account. Using the simulation results, the applicability of this equation of state for water inside the carbon nanotubes is studied and the parameters of the equation of state for this system are obtained. © 2012 American Chemical Society.


Asghari M.,Sharif University of Technology | Ghafoori E.,Sharif University of Technology
Composite Structures | Year: 2010

A semi-analytical three-dimensional elasticity solution for rotating functionally graded disks for both of hollow and solid disks is presented. The aim is to generalize an available two-dimensional plane-stress solution to a three-dimensional one. Although for the thin disks problems the two-dimensional solution provides appropriate results, for the thick disks, a three-dimensional elasticity solution should be considered to avoid poor results. It is shown that although the plane-stress solution satisfies all the governing three-dimensional equations of motion and boundary conditions, it fails to give a compatible three-dimensional strain field. A valid three-dimensional solution has been introduced by modifying the plane-stress solution. © 2009 Elsevier Ltd. All rights reserved.


Motamedi P.,Sharif University of Technology | Bagheri R.,Sharif University of Technology
Materials and Design | Year: 2010

This work aims to investigate the structure-property relationship in ternary nanocomposites consisting of polypropylene as the matrix, nanoclay as the reinforcement and polyamide 6 as the intermediate phase. In this regard, composites of polypropylene/organoclay, polyamide/organoclay, blends of polypropylene/polyamide, and ternary nanocomposites of polypropylene/polyamide/layered silicate with and without compatibilizer were produced via melt compounding. Nanostructure was investigated by wide-angle X-ray diffraction and transmission electron microscopy. Scanning electron microscopy was employed to study the microstructure. Modulus of elasticity and yield strength were measured by uniaxial tensile test. Results show that silicate layers can only be observed inside polyamide particles. Moreover, polypropylene was unable to intercalate the grade of organoclay used in this study. While polyamide/organoclay system exhibited an exfoliated structure, the nanostructure of ternary nanocomposites was chiefly intercalated, due to the high concentration of silicate layers inside polyamide particles. Incorporation of organoclay into the polypropylene/polyamide system was seen to have a noticeable effect on the shape and size of polyamide particles. In addition, elastic modulus and yield strength were observed to be directly affected by incorporation of nanoclay and compatibilizer into the polypropylene matrix, respectively. The simultaneous presence of the two constituents in the system resulted in samples with superior mechanical properties in the elastic as well as the plastic deformation regime. © 2009 Elsevier Ltd. All rights reserved.


Anjabin N.,Sharif University of Technology | Karimi Taheri A.,Sharif University of Technology
Materials and Design | Year: 2010

A mathematical model based on Kocks-Mecking-Bergstrom model, has been proposed to predict the flow behavior of age hardenable aluminum alloys, under different conditions of solution heat treatment and hot deformation. Considering the published literature, most researchers have taken into account the precipitation and solution strengthening contribution to the flow stress by a constant and some others have ignored these effects. So these available descriptions cannot be applicable directly to different conditions of solution heat treatment. In order to enable these constitutive descriptions to take into account the effects of soaking time and temperature, we introduce in this research a relative volume fraction of precipitation into the flow stress by using the appropriate relationships. The GA-based optimization technique is used to evaluate the material constants within the equations from the uniaxial tensile test data of AA6082 reported by previous researchers. © 2009 Elsevier Ltd. All rights reserved.


Baniasadi H.,Sharif University of Technology | Ramazani S.A. A.,Sharif University of Technology | Javan Nikkhah S.,Sharif University of Technology
Materials and Design | Year: 2010

The morphological, physical and mechanical properties of polypropylene/clay nanocomposites (PPCNs) were prepared by in situ polymerization are investigated. Non-modified scmectite type clay (e.g. bentonite) was used to prepare bi-supported Ziegler-Natta catalyst of TiCl4/Mg(OEt)2/clay. Exfoliated PPCNs were obtained by in situ intercalative polymerization of propylene using produced bi-supported catalyst. X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) micrograph were used to assess the clay morphology and dispersion of clay. The crystalline structures of PPCNs were characterized by differential scanning calorimetry (DSC). The mechanical properties of PPCNs were studied by tensile and impact tests. thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis DMTA were used to characterize the thermal and dynamic mechanical properties, respectively. The thermo-mechanical properties of prepared nanocomposites were considerably improved by introducing small amount of clay, which indicated that the clay most be significantly intercalated or exfoliated in the prepared nanocomposite preparation process. In addition, morphology and some of the mechanical and thermal properties of in situ PPCNs were compared with those of PPCNs prepared by melt blending method in this study and some presented reported results in literatures. © 2009 Elsevier Ltd. All rights reserved.


Gharekhanlou B.,Sharif University of Technology | Khorasani S.,Sharif University of Technology
IEEE Transactions on Electron Devices | Year: 2010

In contrast to graphene, which is a gapless semiconductor, graphane, the hydrogenated graphene, is a semiconductor with an energy gap. Together with the 2-D geometry, unique transport features of graphene, and the possibility of doping graphane, p and n regions can be defined so that 2-D p-n junctions become feasible with small reverse currents. This paper introduces a basic analysis to obtain the current-voltage characteristics of such a 2-D p-n junction based on graphane. As we show, within the approximation of Shockley's law of junctions, an ideal I-V characteristic for this p-n junction is to be expected. © 2009 IEEE.


Yavari A.,Georgia Institute of Technology | Khezrzadeh H.,Sharif University of Technology
Engineering Fracture Mechanics | Year: 2010

In this paper we first obtain the order of stress singularity for a dynamically propagating self-affine fractal crack. We then show that there is always an upper bound to roughness, i.e. a propagating fractal crack reaches a terminal roughness. We then study the phenomenon of reaching a terminal velocity. Assuming that propagation of a fractal crack is discrete, we predict its terminal velocity using an asymptotic energy balance argument. In particular, we show that the limiting crack speed is a material-dependent fraction of the corresponding Rayleigh wave speed. © 2010 Elsevier Ltd.


Rahvar S.,Sharif University of Technology
Astrophysical Journal | Year: 2016

The detection of signals from a possible extrasolar technological civilization is one of the most challenging efforts of science. In this work, we propose using natural telescopes made of single or binary gravitational lensing systems to magnify leakage of electromagnetic signals from a remote planet that harbors Extraterrestrial Intelligent (ETI) technology. Currently, gravitational microlensing surveys are monitoring a large area of the Galactic bulge to search for microlensing events, finding more than 2000 events per year. These lenses are capable of playing the role of natural telescopes, and, in some instances, they can magnify radio band signals from planets orbiting around the source stars in gravitational microlensing systems. Assuming that the frequency of electromagnetic waves used for telecommunication in ETIs is similar to ours, we propose follow-up observation of microlensing events with radio telescopes such as the Square Kilometre Array (SKA), the Low Frequency Demonstrators, and the Mileura Wide-Field Array. Amplifying signals from the leakage of broadcasting by an Earth-like civilization will allow us to detect them as far as the center of the Milky Way galaxy. Our analysis shows that in binary microlensing systems, the probability of amplification of signals from ETIs is more than that in single microlensing events. Finally, we propose the use of the target of opportunity mode for follow-up observations of binary microlensing events with SKA as a new observational program for searching ETIs. Using optimistic values for the factors of the Drake equation provides detection of about one event per year. © 2016. The American Astronomical Society. All rights reserved.


Mousavi Abarghouie S.M.R.,Sharif University of Technology | Reihani S.M.S.,Sharif University of Technology
Materials and Design | Year: 2010

In the present research work the 2024 aluminum alloy was reinforced with SiC particles via powder metallurgy method. The effect of heat treatment conditions on artificial aging kinetics was investigated. The solution treatment of the composite sample and the unreinforced alloy was carried out at 495 °C for 1, 2 and 3 h followed by aging at 191 °C for various aging times between 1 and 10 h. The existence of SiC particles led to increasing the peak hardness of the alloy. The peak hardness of the composite sample took place at shorter times than that of the unreinforced alloy for the samples solution treated for 2 and 3 h, but took place at longer times for the samples solution treated for 1 h. The suitable solution treating time was about 2 h for both the composite and the unreinforced alloy that led to the fastest aging kinetics and the maximum hardness. At the solution treating time shorter than 2 h due to incomplete dissolution of precipitates, the aging kinetics decelerated and the hardness values decreased. X-ray diffraction studies indicated the presence of precipitation phases such as CuAl2 and CuMgAl2 in the composite in both as-extruded and solutionized conditions. For the samples solution treated more than 2 h, hardness values decreased due to the grain growth of matrix but no change occurred in the aging kinetics. © 2009 Elsevier Ltd. All rights reserved.


Mousavi Abarghouie S.M.R.,Sharif University of Technology | Seyed Reihani S.M.,Sharif University of Technology
Journal of Alloys and Compounds | Year: 2010

Friction and wear behaviors of artificially aged 2024 Al and 2024 Al/20 vol.% SiC composite prepared by powder metallurgy method were investigated in the temperature range 20250 °C. Dry sliding wear tests were conducted at a constant sliding velocity of 0.5 m/s, an applied load of 20 N, and a sliding distance of 2500m using a pin-on-disc apparatus. Worn surfaces and wear debris were also examined by using SEM and EDS techniques. All specimens showed a transition from mild-to-severe wear above a critical temperature. In the mild wear regime, the wear rate and the friction coefficient of the composite specimen were higher than those of the unreinforced alloy. The SiC particles led to an increase in the critical transition temperature and in the severe wear regime, they caused a considerable improvement in the wear resistance. Analysis of worn surfaces and wear debris indicated that dominant wear mechanisms of the unreinforced alloy were microploughing and slight adhesion in the mild wear regime, whereas the composite specimen showed microcutting and oxidation mechanisms in the same regime. The dominant wear mechanisms shifted to severe adhesion for all specimens in the severe wear regime. © 2009 Elsevier B.V. All rights reserved.


Solhjoo S.,Sharif University of Technology
Materials and Design | Year: 2010

Using the work hardening rate-strain curves, an effective mathematical model has been developed to predict the stress-strain curves of alloy steel during hot deformation up to the peak stress regardless of the level of the strain, weather smaller or larger than the critical strain. This model is expressed in terms of peak stress, peak strain and one temperature-sensitive parameter, S. In addition, one new model, which is a function of peak strain, was proposed to predict the critical strain for the initiation of dynamic recrystallization using the second derivative of work hardening rate with respect to stress. Besides the theoretical study, the analysis is used to determine the stress-strain curves and critical strain of 304 austenitic stainless steel. The predicted results were found to be in accord with the experimental data. © 2009 Elsevier Ltd. All rights reserved.


Ghafoori E.,Ecole Polytechnique Federale de Lausanne | Asghari M.,Sharif University of Technology
Composite Structures | Year: 2010

The dynamic response of angle-ply laminated composite plates traversed by a moving mass or a moving force is investigated. For this purpose, a finite element method based on the first-order shear deformation theory is used. Stationary and adaptive mesh techniques have been applied as two different meshing schemes. The adaptive mesh strategy is then used to avoid off-nodal position of moving mass. In this manner, the finite element mesh is continuously adapted to follow and comply with the path of moving mass. A Newmark direct integration method is employed to solve the equations of motion. Parametric study is directed to find out how different parameters like mass of the moving object as well as the type of the angle-ply laminated composite plates affect the dynamic response. Numerical results show the significant effects of the stacking order on the dynamic responses of the composite structures under a moving mass. It is found that although [30/-60/-60/30] lamination shows the highest maximum vertical deflection but [-45/45/45/-45] lamination has the highest value of the dynamic amplification factor. The dynamic amplification factor for different stacking orders and mass velocities is less than 1.25. © 2010 Elsevier Ltd.


Shidpour R.,Sharif University of Technology | Manteghian M.,Tarbiat Modares University
Nanoscale | Year: 2010

In this study a low-width MoS2 ribbon has been used for probing the electronic structure and local magnetic moment near vacancies. A theoretical study with the full-potential Density Functional Theory (DFT) approach (Wien2K code) have shown that when the dimension of MoS2 is reduced from 2-D to 1-D the nonmagnetic semi-conductor MoS2 becomes a magnetic conductor. Our study has shown that a vacancy on the S-edge with 50% coverage intensifies the magnetization of the edge of the MoS2 nanoribbon but such a vacancy on S-edge with 100% coverage causes this magnetic property to disappear. It is concluded that in both of them, there are positive or negative strong gradients of local magnetic moment near the vacancy. This may explain why lattice defects are essential for catalysis processes. © 2010 The Royal Society of Chemistry.


Mahsuli M.,Sharif University of Technology | Haukaas T.,University of British Columbia
Reliability Engineering and System Safety | Year: 2013

This paper presents a new set of reliability sensitivity measures. The purpose is to identify the optimal manner in which to mitigate risk to civil infrastructure, and reduce model uncertainty in order to improve risk estimates. Three measures are presented. One identifies the infrastructure components that should be prioritized for retrofit. Another measure identifies the infrastructure that should be prioritized for more refined modeling. The third measure identifies the models that should be prioritized in research to improve models, for example by gathering new data. The developments are presented in the context of a region with 622 buildings that are subjected to seismicity from several sources. A comprehensive seismic risk analysis of this region is conducted, with over 300 random variables, 30 model types, and 4000 model instances. All models are probabilistic and emphasis is placed on the explicit characterization of epistemic uncertainty. For the considered region, the buildings that should first be retrofitted are found to be pre-code unreinforced masonry buildings. Conversely, concrete shear wall buildings rank highest on the list of buildings that should be subjected to more detailed modeling. The ground shaking intensity model for shallow crustal earthquakes and the concrete shear wall structural response model rank highest on the list of models that should be prioritized by research to improve engineering analysis models. © 2013 Elsevier Ltd. All rights reserved.


Mahsuli M.,Sharif University of Technology | Haukaas T.,University of British Columbia
Structural Safety | Year: 2013

Reliability methods are employed in this paper to analyze the seismic risk to the Vancouver metropolitan region in Canada. The use of reliability methods contrasts with several contemporary approaches for risk analysis. In this paper, two analysis approaches are presented and implemented in a new computer program. One utilizes the first-order and second-order reliability methods together with a hazard combination technique. The other is a sampling-based method that repeatedly generates damage scenarios in the time period of interest. Both strategies employ the same collection of probabilistic models for seismic risk analysis. While the models are presented in the companion paper, this paper presents the analysis options and a comprehensive application that comprises 559 random variables and 3227 model objects. The primary result is the loss curve, which exposes seismic loss probabilities and serves as a basis for risk mitigation decisions. It is found that the probability of loss in excess of $100 billion in the next 50 years is 5.6%. By-products of the analysis provide further insight; the most vulnerable municipalities and the most influential hazard sources are identified. © 2013 Elsevier Ltd.


Nili-Ahmadabadi M.,Isfahan University of Technology | Poursadegh F.,Sharif University of Technology
Journal of Mechanical Science and Technology | Year: 2013

This paper is concerned with a quasi-3D design method for the radial and axial diffusers of a centrifugal compressor on the meridional plane. The method integrates a novel inverse design algorithm, called ball-spine algorithm (BSA), and a quasi-3D analysis code. The Euler equation is solved on the meridional plane for a numerical domain, of which unknown boundaries (hub and shroud) are iteratively modified under the BSA until a prescribed pressure distribution is reached. In BSA, unknown walls are composed of a set of virtual balls that move freely along specified directions called spines. The difference between target and current pressure distributions causes the flexible boundary to deform at each modification step. In validating the quasi-3D analysis code, a full 3D Navier-Stokes code is used to analyze the existing and designed compressors numerically. Comparison of the quasi-3D analysis results with full 3D analysis results shows viable agreement. The 3D numerical analysis of the current compressor shows a huge total pressure loss on the 90° bend between the radial and axial diffusers. Geometric modification of the meridional plane causes the efficiency to improve by about 10%. © 2013 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.


Elyasi A.,Sharif University of Technology | Salmasi N.,Sharif University of Technology
International Journal of Production Research | Year: 2013

This paper considers two different due date assignment and sequencing problems in single machine where the processing times of jobs are random variables. The first problem is to minimise the maximum due date so that all jobs are stochastically on time. It is shown that sequencing the jobs in decreasing service level (DSL) order optimally solves the problem. The results are then extended for two special cases of flow shop problem. The other problem is to minimise a total cost function which is a linear combination of three penalties: penalty on job earliness, penalty on job tardiness, and penalty associated with long due date assignment. The assignment of a common due date and distinct due dates are investigated for this problem. It is shown that the optimal sequence for the case of common due date is V-shaped. © 2013 Taylor & Francis Group, LLC.


Sadighi-Bonabi R.,Sharif University of Technology | Moshkelgosha M.,Sharif University of Technology
Laser and Particle Beams | Year: 2011

This work is devoted to improving relativistic self-focusing of intense laser beam in underdense unmagnetized plasma. New density profiles are introduced to achieve beam width parameter up to the wavelength of the propagating laser. By investigating variations of the beam width parameter in presence of different density profiles it is found that the beam width parameter is considerably decreased for the introduced density ramp comparing with uniform density and earlier introduced density ramp profiles. By using this new density profile high intensity laser pulses are guided over several Rayleigh lengths with extremely small beam width parameter. © Copyright Cambridge University Press 2011.


Gheidi H.,Sharif University of Technology | Banai A.,Sharif University of Technology
IEEE Transactions on Microwave Theory and Techniques | Year: 2011

A new broadband frequency discriminator is introduced for demodulating the frequency modulated signals in the microwave frequency range. Direct demodulation with no need for tuning the center frequency of the resonance circuits is the most important advantage of the proposed technique. This technique uses the in-phase/quadrature demodulation, in some manner, without using any additional local oscillator for down conversion. Simulation of the proposed demodulator has been done with Advanced Design System software to evaluate and predict the system behavior. A setup based on the proposed method was designed and implemented in order to verify the accuracy of the theory. We tested the proposed frequency discriminator for FM signals at different microwave frequencies with various waveforms of the modulating signal. We also measured the bit error rate of the demodulator when the modulating signal is pseudorandom binary sequences for some data rates. To the best of our knowledge, this structure demonstrates the widest bandwidth direct demodulator without any tuning circuits among published FM demodulators to date. © 2011 IEEE.


Moghadam M.A.G.,Sharif University of Technology | Tahami F.,Sharif University of Technology
IEEE Transactions on Power Electronics | Year: 2013

Position sensorless control of ac machines at zero and low speed is possible using high-frequency carrier injection methods. These methods utilize anisotropic properties of rotor. Therefore, they may lose their efficiency for nonsalient machines or machines with small rotor saliency. In these machines, measurement noise and offset, existing delays, as well as model uncertainties may lead to inaccurate estimation of rotor position. Stator resistance which is usually neglected in these methods may also lead to a considerable error especially in machines with small rotor saliency. In this paper, a new position estimation method is presented, and it is shown that in comparison to conventional methods, the proposed scheme minimizes the estimation error caused by disturbances like stator resistance and delays of the system. © 2012 IEEE.


Mesbahi A.,Sharif University of Technology | Haeri M.,Sharif University of Technology
Automatica | Year: 2013

This paper presents a new method for assessing the bounded input bounded output stability of a class of fractional delay systems with commensurate orders and multiple commensurate delays of retarded type. In the proposed method, first, by mapping the principal sheet of the Riemann surface and a pseudo-delay transformation, an auxiliary polynomial is generated. Then, this auxiliary polynomial is employed to find roots of the characteristic equation on the imaginary axis. The properties of the root path close to these roots are used to identify intervals of delay values, in which the system is stable. The obtained results are illustrated via some numerical examples. © 2013 Elsevier Ltd. All rights reserved.


Mahsuli M.,Sharif University of Technology | Haukaas T.,University of British Columbia
Structural Safety | Year: 2013

A library of probabilistic models for prediction of seismic risk is presented. The models are specifically intended for use with reliability methods to compute event probabilities, such as seismic loss probabilities. Several models are presented here for the first time. In particular, new and generic models are proposed for earthquake location, regional loss, building response, building damage, and building loss. Each model is presented with an explanation of its development and a discussion of its predictions. In addition, models from the literature are " smoothed" to make them amenable to reliability analysis. The models are implemented in a new computer program that is tailored for reliability and optimization analysis with many probabilistic models. The models and the computer program are employed in the companion paper to assess the seismic risk to the Vancouver metropolitan region in Canada. © 2013 Elsevier Ltd.


Kahrobaiyan M.H.,Sharif University of Technology | Asghari M.,Sharif University of Technology | Ahmadian M.T.,Sharif University of Technology
International Journal of Engineering Science | Year: 2013

In this paper, the strain gradient theory, a non-classical continuum theory capable of capturing the size effect observed in micro-scale structures, is employed in order to investigate the size-dependent mechanical behavior of microbars. For a strain gradient bar, the governing equation of motion and classical and non-classical boundary conditions are derived using Hamilton's principle. Closed form solutions have been analytically obtained for static deformation, natural frequencies and mode shapes of strain gradient bars. The static deformation and natural frequencies of a clamped-clamped microbar subjected to a uniform axial distributed force are derived analytically and the results are depicted in some figures. The results indicate that contrary to the classical bars, strain gradient bars show size-dependent and stiffer mechanical behavior. In addition, a size-dependent strain gradient bar element has been developed in order to enable the finite element method (FEM) to numerically deal with the size-dependent problems in micro-scale structures where the attempts of the classical FEM have been in vain. The shape functions as well as the mass and the stiffness matrices are derived analytically based on Galerkin's method. During some examples, it is indicated that how the new element can be used in a problem and the results are compared to the analytical strain gradient results as well as the classical FEM and analytical results. A good agreement is observed between the strain gradient FEM and analytical results whereas the error of using the classical bar element is considerable. © 2013 Elsevier Ltd. All rights reserved.


Khavasi A.,Sharif University of Technology | Mehrany K.,Sharif University of Technology
IEEE Journal of Quantum Electronics | Year: 2011

A circuit model is proposed for periodic 1-D array of metallic strips in the sub-wavelength regime. The parameters of the proposed circuit and their dependence on frequency are all explicitly given by closed form expressions. The necessity of using numerical simulation to extract model parameters is thus sidestepped. It is demonstrated that the proposed model is valid at different incident angles and for arbitrary surrounding mediums given that there is only one propagating diffracted order outside the grating and only one guided mode supported by the slits. Both major polarizations are studied in this paper. © 2011 IEEE.


Tavazoei M.S.,Sharif University of Technology
Automatica | Year: 2013

In this note, the type number concept is defined for fractional-order systems. Based on this definition, it is shown that fractional-order systems having type numbers more than 1 can not track some classes of reference inputs without any overshoot. © 2012 Elsevier Ltd. All rights reserved.


Farahi M.,Sharif University of Technology | Mofid M.,Sharif University of Technology
Engineering Structures | Year: 2013

As a matter of fact, it is necessary to have the values of Response Modification Factor R, Over-strength Factor Ω0, and Deflection Amplification Factor Cd in order to design seismic-force-resisting systems according to design and loading codes. This study is intended to evaluate these factors for a structural lateral bracing system called Chevron Knee Bracing (CKB). In this type of bracing, the knee elements assist the system to dissipate energy through the formation of plastic flexural and/or shear hinges within the presented bracing system. The approach utilized in this study is according to FEMA P695 based on low probability of structural collapse and involves nonlinear static and dynamic analyses. Over-strength and ductility of this type of bracing is investigated through performing nonlinear static analyses. Conducting Incremental Dynamic Analyses (IDA), Collapse Margin Ratios (CMRs) of the defined archetypes model are achieved and modified to obtain an Adjusted Collapse Margin Ratio, ACMR for each archetype. The values of calculated ACMRs are compared with the accepted values proposed by FEMA P695 in which the total system collapse uncertainty is considered to prove the validity of presumed seismic performance factors of CKB systems. © 2012 Elsevier Ltd.


Pahlevani L.,Sharif University of Technology | Shodja H.M.,Sharif University of Technology
Journal of Applied Mechanics, Transactions ASME | Year: 2011

The effect of surface and interface elasticity in the analysis of the Saint-Venant torsion problem of an eccentrically two-phase fcc circular nanorod is considered; description of the behavior of such a small structure via usual classical theories cease to hold. In this work, the problem is formulated in the context of the surface/interface elasticity. For a rigorous solution of the proposed problem, conformal mapping with a Laurent series expansion are employed together. The numerical results well illustrate that the torsional rigidity and stress distribution corresponding to such nanosized structural elements are significantly affected by the size. In order to employ surface and interface elasticity, several key properties such as surface energy, surface stresses, and surface elastic constants of several fcc materials as well as interface properties of the noncoherent fcc bicrystals are derived in terms of Rafii-Tabar and Sutton interatomic potential function. For determination of the surface/interface parameters a molecular dynamics program, which uses the above-mentioned potential function, is developed. The calculated surface and interface properties are in reasonable agreement with the corresponding results in literature. Some applications of the given results can be contemplated in the design of micro-/nano-electromechanical systems. © 2011 American Society of Mechanical Engineers.


Karimi J.,Sharif University of Technology | Pourtakdoust S.H.,Sharif University of Technology
Aerospace Science and Technology | Year: 2013

Motion planning is a key factor in enhancing the autonomy level of unmanned flying vehicles. A new dynamic hybrid algorithm is developed to solve the motion planning problem in real-time using a heuristic optimization approach. The proposed algorithm effectively combines desired features such as rapid convergence to an optimal path with reduced computational effort. In addition to the terrain obstacles, the proposed algorithm is able to avoid random threats that may arise sporadically in the terrain. Using the maneuver automaton concept, nonlinear dynamic model and performance constraints are also considered in the process of motion planning to further ensure feasible trajectories. Evaluation of the proposed algorithm against several simulated scenarios has effectively demonstrated its potential for generating optimal contour-matching trajectories that succeed in avoiding stochastic obstacles. © 2012 Published by Elsevier Masson SAS.


Akhavan O.,Sharif University of Technology
Applied Surface Science | Year: 2010

The effect of thickness of TiO2 coating on synergistic photocatalytic activity of TiO2 (anatase)/α-Fe 2O3/glass thin films as photocatalysts for degradation of Escherichia coli bacteria in a low-concentration H2O2 solution and under visible light irradiation was investigated. Nanograined α-Fe2O3 films with optical band-gap of 2.06 eV were fabricated by post-annealing of thermal evaporated iron oxide thin films at 400 °C in air. Increase in thickness of the Fe2O3 thin film (here, up to 200 nm) resulted in a slight reduction of the optical band-gap energy and an increase in the photoinactivation of the bacteria. Sol-gel TiO2 coatings were deposited on the α-Fe2O 3 (200 nm)/glass films, and then, they were annealed at 400 °C in air for crystallization of the TiO2 and formation of TiO 2/Fe2O3 heterojunction. For the TiO2 coatings with thicknesses ≤50 nm, the antibacterial activity of the TiO 2/α-Fe2O3 (200 nm) was found to be better than the activity of the bare α-Fe2O3 film. The optimum thickness of the TiO2 coating was found to be 10 nm, resulting in about 70 and 250% improvement in visible light photo-induced antibacterial activity of the TiO2/α-Fe2O 3 thin film as compared to the corresponding activity of the bare α-Fe2O3 and TiO2 thin films, respectively. The improvement in the photoinactivation of bacteria on surface of TiO2/α-Fe2O3 was assigned to formation of Ti-O-Fe bond at the interface. © 2010 Elsevier B.V. All rights reserved.


Bahadormanesh B.,Sharif University of Technology | Dolati A.,Sharif University of Technology
Journal of Alloys and Compounds | Year: 2010

Ni-Co/SiC composite coatings with various contents of SiC particles were electrodeposited in a modified Watt's type of Ni-Co bath containing suspended 20 nm SiC particles. Deposition parameters including current density, bath SiC concentration and magnetic stirring rate were optimized for the highest amount of the SiC codeposition: the current density of 4 A/dm2, 40 g/dm 3 SiC concentration and 480 rpm stirring rate. In order to study the SiC particles codeposition, the Guglielmi's model of codeposition was modified for high volume percentages of the second phase and the modified model was employed to explain the effects of deposition parameters on the kinetics of the particles codeposition. Moreover, the influence of suspended SiC particles on the anomalous electrodeposition of Ni2+ and Co2+ ions was studied. In the presence of these particulates, anomalous electrodeposition of Ni2+ and Co2+ ions was enhanced. © 2010 Elsevier B.V. All rights reserved.


Simchi A.,Sharif University of Technology | Tamjid E.,Sharif University of Technology | Pishbin F.,Imperial College London | Boccaccini A.R.,Imperial College London | Boccaccini A.R.,Friedrich - Alexander - University, Erlangen - Nuremberg
Nanomedicine: Nanotechnology, Biology, and Medicine | Year: 2011

This review covers the most recent developments of inorganic and organic-inorganic composite coatings for orthopedic implants, providing the interface with living tissue and with potential for drug delivery to combat infections. Conventional systemic delivery of drugs is an inefficient procedure that may cause toxicity and may require a patient's hospitalization for monitoring. Local delivery of antibiotics and other bioactive molecules maximizes their effect where they are required, reduces potential systemic toxicity and increases timeliness and cost efficiency. In addition, local delivery has broad applications in combating infection-related diseases. Polymeric coatings may present some disadvantages. These disadvantages include limited chemical stability, local inflammatory reactions, uncontrolled drug-release kinetics, late thrombosis and restenosis. As a result, embedding of bioactive compounds and biomolecules within inorganic coatings (bioceramics, bioactive glasses) is attracting significant attention. Recently nanoceramics have attracted interest because surface nanostructuring allows for improved cellular adhesion, enhances osteoblast proliferation and differentiation, and increases biomineralization. Organic-inorganic composite coatings, which combine biopolymers and bioactive ceramics that mimick bone structure to induce biomineralization, with the addition of biomolecules, represent alternative systems and ideal materials for "smart" implants. In this review, emphasis is placed on materials and processing techniques developed to advance the therapeutic use of biomolecules-eluting coatings, based on nanostructured ceramics. One part of this report is dedicated to inorganic and composite coatings with antibacterial functionality. From the Clinical Editor: Inorganic and composite nanotechnology-based coating methods have recently been developed for orthopedic applications, with the main goal to provide bactericide and other enhanced properties, which may result in reduced need for pharmaceutical interventions and overall more cost effective orthopedic procedures. This review discusses key aspects of the above developments. © 2011 Elsevier Inc.


Tavazoei M.S.,Sharif University of Technology | Tavakoli-Kakhki M.,K. N. Toosi University of Technology
IET Control Theory and Applications | Year: 2014

This study deals with a generalised version of lead/lag compensators known as fractional-order lead/lag compensators. Exact and simple formulas are found for designing this introduced type of fractional-order compensators in order to provide the required magnitude and phase at a given frequency. Also, the region in the phase-magnitude plane, which is accessible by these compensators, is analytically found. Moreover, numerical examples and experimental results are presented to show the applicability of the achievements of this study in control system design. © The Institution of Engineering and Technology 2014.


Hadavandi E.,Sharif University of Technology | Shavandi H.,Sharif University of Technology | Ghanbari A.,University of Tehran
Knowledge-Based Systems | Year: 2010

Stock market prediction is regarded as a challenging task in financial time-series forecasting. The central idea to successful stock market prediction is achieving best results using minimum required input data and the least complex stock market model. To achieve these purposes this article presents an integrated approach based on genetic fuzzy systems (GFS) and artificial neural networks (ANN) for constructing a stock price forecasting expert system. At first, we use stepwise regression analysis (SRA) to determine factors which have most influence on stock prices. At the next stage we divide our raw data into k clusters by means of self-organizing map (SOM) neural networks. Finally, all clusters will be fed into independent GFS models with the ability of rule base extraction and data base tuning. We evaluate capability of the proposed approach by applying it on stock price data gathered from IT and Airlines sectors, and compare the outcomes with previous stock price forecasting methods using mean absolute percentage error (MAPE). Results show that the proposed approach outperforms all previous methods, so it can be considered as a suitable tool for stock price forecasting problems. © 2010 Elsevier B.V. All rights reserved.


Fotouhi M.M.,Sharif University of Technology | Firouz-Abadi R.D.,Sharif University of Technology | Haddadpour H.,Sharif University of Technology
International Journal of Engineering Science | Year: 2013

The effect of elastic foundation on the free vibration characteristics of embedded nanocones is investigated in this paper. The nanocone is modeled as a thin shell and the nonlocal elasticity theory is used to derive the governing equations of motion. Also the elastic medium is simulated using Winkler and Pasternak foundation models. Based on the modal analysis technique and applying the Galerkin method the governing equations are solved to obtain the natural frequencies. The drawn results emphasis the effects of geometry and small-scale parameter on the natural frequencies of nanocone. Also the effect of elastic foundation modulus on the resonance frequencies of the nanocones are studied and some conclusions are outlined.© 2013 Elsevier Ltd. All rights reserved.


Mahmoodi Darian H.,University of Tehran | Esfahanian V.,University of Tehran | Hejranfar K.,Sharif University of Technology
Journal of Computational Physics | Year: 2011

A new shock-detecting sensor for properly switching between a second-order and a higher-order filter is developed and assessed. The sensor is designed based on an order analysis. The nonlinear filter with the proposed sensor ensures damping of the high-frequency waves in smooth regions and at the same time removes the Gibbs oscillations around the discontinuities when using high-order compact finite difference schemes. In addition, a suitable scaling is proposed to have dissipation proportional to the shock strength and also to minimize the effe