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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.

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. Source

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. Source

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. Source

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. Source

Yazdani Sarvestani H.,Sharif University of Technology | Yazdani Sarvestani M.,University of Tehran
International Journal of Mechanical Sciences | Year: 2011

In this study, based on the reduced from of elasticity displacement field for a long laminate, an analytical method is established to exactly obtain the interlaminar stresses near the free edges of generally laminated composite plates under the extension and bending. The constant parameters, which describe the global deformation of a laminate, are properly computed by means of the improved first-order shear deformation theory. Reddys layerwise theory is subsequently utilized for analytical and numerical examinations of the boundary layer stresses within arbitrary laminated composite plates. A variety of numerical results are obtained for the interlaminar normal and shear stresses along the interfaces and through the thickness of laminates near the free edges. Finally the effects of end conditions of laminates on the boundary-layer stress are examined. © 2011 Elsevier Ltd. Source

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. Source

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. Source

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. Source

Memarzadeh L.,Sharif University of Technology | Macchiavello C.,University of Pavia | Mancini S.,University of Camerino
New Journal of Physics | Year: 2011

We investigate the possibility of correcting errors occurring on a multipartite system through a feedback mechanism that acquires information through partial access to the environment. A partial control scheme of this type might be useful in dealing with correlated errors. In fact, in such a case, it could be enough to gather local information to decide what kind of global recovery to perform. Then, we apply this scheme to the depolarizing and correlated errors and quantify its performance by means of entanglement fidelity. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Source

Barzegar Gerdroodbary M.,Babol Noshirvani University of Technology | Jahanian O.,Babol Noshirvani University of Technology | Mokhtari M.,Sharif University of Technology
International Journal of Hydrogen Energy | Year: 2015

A three-dimensional numerical study has been performed to investigate the influence of angle of shock waves on sonic transverse Hydrogen micro-jets subjected to a supersonic crossflow. This study focuses on mixing of the Hydrogen jet in a Mach 4.0 crossflow with a global equivalence ratio of 0.5. Flow structure and fuel/air mixing mechanism were investigated numerically. Parametric studies were conducted on the angle of shock wave by using the Reynolds-averaged Navier-Stokes equations with Menter's Shear Stress Transport turbulence model. Complex jet interactions were found in the downstream region with a variety of flow features depending upon the angle of shock incident. These flow features were found to have subtle effects on the mixing of Hydrogen jets. Results indicate a different flow structure than for a typical micro jet, with the development of shock angle to the flow of the Hydrogen jet. According to the results, without oblique shock, mixing occurs at a low rate. When the intersection of incident shock and the lower surface is at a low angle (15°) of shock incident; significant reduction (up to 30%) occurs in the maximum concentration of the Hydrogen jet at downstream. Moreover, when the angle of shock incident increases, Hydrogen-air mixing rate increase and the concentration of the Hydrogen micro jet is uniformly distributed. Consequently, an enhanced mixing zone occurs downstream of the injection slots which leads to flame-holding. © 2015 Hydrogen Energy Publications, LLC. Source

Siahkali H.,Islamic Azad University at South Tehran | Vakilian M.,Sharif University of Technology
Electric Power Systems Research | Year: 2011

Wind power is a promising source of electric power generation since it has tremendous environmental and social benefits. The generation scheduling (GS) problem encounters several uncertainties in terms of the system's parameters such as load, reserve and available wind power generation. The modeling of those uncertainties is an important issue in power system scheduling. A fuzzy based modeling approach can be used to develop the generation schedule under an uncertain environment. In this paper, the type-2 fuzzy membership function (MF) is implemented to model the linguistic uncertainty of type-1 MF of available wind power generation which stems from opinions of different experts. The proposed approach is applied to two test systems (six and twenty-six conventional generating units both with two wind farms) and the results of generation scheduling using both fuzzy modeling type-1, and type-2 are presented. These results demonstrate that the advantage of using the type-2 fuzzy to model the linguistic uncertainty of the type-1 MF. This paper demonstrates how unit scheduling in an uncertain environment of type-1 fuzzy MF modeling can be performed just by using a single type-2 fuzzy MF when all type-1 MF were in the footprint of uncertainty (FOU) of type-2 MF. © 2011 Elsevier B.V. All rights reserved. Source

Karimi H.,Sharif University of Technology | Yazdani A.,University of Western Ontario | Iravani R.,University of Toronto
IEEE Transactions on Power Delivery | Year: 2011

This paper proposes a control strategy for the autonomous (islanded) operation of a four-wire, electronically-coupled distributed generation (DG) unit which can feed a highly unbalanced load, e.g., due to the presence of single-phase loads. In the grid-connected mode, the power-electronic interface of the DG unit enables the exchange of real and reactive power with the distribution network, based on the conventional dq-frame current control strategy. The current control scheme is disabled subsequent to the detection of an islanding event, and the proposed controller is activated. The proposed control strategy utilizes: i) an internal oscillator to maintain the island frequency and ii) a feedback control system to regulate the island voltage. The proposed control strategy provides a set of balanced three-phase voltages for the load, despite the load imbalance and parameters uncertainties. The proposed control strategy also guarantees robust stability, fast dynamic response to disturbances, and zero steady-state error. A stability analysis is also carried out to determine the robust stability margin of the closed-loop islanded system. Effectiveness of the proposed control strategy is evaluated based on time-domain simulation studies in the PSCAD/EMTDC software environment and verified based on laboratory experiments. © 2010 IEEE. Source

Bahrani B.,Ecole Polytechnique Federale de Lausanne | Karimi H.,Sharif University of Technology | Iravani R.,University of Toronto
IEEE Transactions on Power Delivery | Year: 2011

This paper analytically determines the nondetection zone (NDZ) of an active islanding detection method, and proposes a solution to obviate the NDZ. The method actively injects a negative-sequence current through the interface voltage-sourced converter (VSC) of a distributed generation (DG) unit, as a disturbance signal for islanding detection. The estimated magnitude of the corresponding negative-sequence voltage at the PCC is used as the islanding detection signal. In this paper, based on a laboratory test system, the performance of the islanding detection method under UL1741 anti-islanding test conditions is evaluated. Then, determining the NDZ of the method and proposing the countermeasure, the existence of the NDZ and the performance of the modified method to eliminate the NDZ is verified based on simulation results in PSCAD/EMTDC software environment and experimental tests. © 2010 IEEE. Source

Bagheri G.A.,Sharif University of Technology
Journal of Alloys and Compounds | Year: 2016

In this research, copper matrix composites reinforced with different amounts of titanium carbide particles were produced by mechanical milling and in-situ formation of reinforcements. Morphology and size of milled powders were inspected by scanning electron microscopy (SEM) several times during milling process. Changes in lattice parameter, crystallite size, lattice strain, dislocation density and Gibbs free energy changes (due to increasing in dislocation densities and grain boundaries) in different samples (with different TiC particles contents) were studied by X-Ray Diffraction technique with Cu-kα radiation and using Nelson-Riley method and Williamson-Hall equation. Microstructure of samples after sintering was investigated by FESEM. Finally, densitometry, hardness, determination of electrical resistance and pin on disk wear test were performed and effect of reinforcement percentages on the physical and mechanical properties of composites was studied. Results show incredible improvement in mechanical properties with increasing in TiC value, even though, electrical conductivity dropped off considerably. © 2016 Elsevier B.V. All rights reserved. Source

Haghjou N.,Sharif University of Technology
Pharmaceutical research | Year: 2013

To determine the outward permeability of retina-choroid-sclera (RCS) layer for different ophthalmic drugs and to develop correlations between drug physicochemical properties and RCS permeability. A finite volume model was developed to simulate pharmacokinetics in the eye following drug administration by intravitreal injection. The RCS permeability was determined for 32 compounds by best fitting the drug concentration-time profile obtained by simulation with previously reported experimental data. Multiple linear regression was then used to develop correlations between best fit RCS permeability and drugs physicochemical properties. The RCS drug permeabilities had values that ranged over 3 × 10(-6) m/s. Regression analysis for hydrophilic compounds showed that more than 92% of the variation in permeability values can be explained by correlative models of drug properties that include logarithm of the octanol-water partition coefficient (LogP), protein binding (PB), number of hydrogen bond acceptors (HBA), hydrogen bond donors (HBD), polar surface area (PSA) and dissociation constant (pKa) as independent variables. Regression analysis for lipophilic compounds showed that no significant correlation can be found between just physicochemical properties and RCS permeability. Using the RCS permeability obtained from this study for different drugs, one can predict pharmacokinetics of intravitreal drug delivery systems such as solid implants or colloidal systems. Furthermore, the developed correlations between RCS permeability and physicochemical properties of drugs are useful in early drug development by predicting RCS permeability and drug concentration in the vitreous without experimental data. Source

Anani Y.,Sharif University of Technology | Alizadeh Y.,Amirkabir University of Technology
Materials and Design | Year: 2011

This paper proposes a new visco-hyperelastic constitutive law for modeling the finite-deformation strain rate-dependent behavior of foams as compressible elastomers. The proposed model is based on a phenomenological Zener model, which consists of a hyperelastic equilibrium spring and a Maxwell element parallel to it. The hyperelastic equilibrium spring describes the steady state response. The Maxwell element, which captures the rate-dependency behavior, consists of a nonlinear viscous damper connected in series to a hyperelastic intermediate spring. The nonlinear damper controls the rate-dependency of the Maxwell element. Some strain energy potential functions are proposed for the two hyperelastic springs. compressibility effect in strain energy is described by entering the third invariant of deformation gradient tensor into strain energy functions. A history integral method has been used to develop a constitutive equation for modeling the behavior of the foams. The applied history integral method is based on the Kaye-BKZ theory. The material constant parameters, appeared in the formulation, have been determined with the aid of available uniaxial tensile experimental tests for a specific material. © 2010 Elsevier Ltd. Source

Seyyed Fakhrabadi M.M.,Islamic Azad University at Karaj | Rastgoo A.,University of Tehran | Taghi Ahmadian M.,Sharif University of Technology
International Journal of Mechanical Sciences | Year: 2014

In this paper, the classical and nonlocal elasticity are applied to investigate the deflection and instability of electrostatically actuated carbon nanotubes. The results are presented for different geometries and boundary conditions. They reveal that increasing radius and gap and decreasing length confine to increasing pull-in voltages of the carbon nanotubes. The results prove that application of the nonlocal elasticity theorem leads to stiffer structures with higher pull-in voltages. Thus, in order to obtain more accurate results about the mechanical and electromechanical behaviors of the carbon nanotubes, one should apply the nonclassical elasticity theories such as that applied in this paper. © 2014 Elsevier Ltd. Source

Hamidinejad S.M.,Islamic Azad University at Eghlid | Kolahan F.,Ferdowsi University of Mashhad | Kokabi A.H.,Sharif University of Technology
Materials and Design | Year: 2012

In this study, the resistance spot welding (RSW) process of the galvanized interstitial free (IF) steel sheets and galvanized bake hardenable (BH) steel sheets, used in the manufacturing of car bodies, has been modeled and optimized. The quality measure of a resistance spot welding joint is estimated from the tensile-shear strength. Furthermore, four important process parameters, namely welding current (WC), welding time (WT), electrode force (EF), and holding time (HT) are considered as the factors influencing the quality of the joints. In order to develop an accurate relationship between the process inputs (4-component vectors) and the response output (tensile-shears strength) at first a linear regression model was utilized but the residuals analysis revealed a non-linear behavior. Therefore, an artificial neural network (ANN) was proposed because the ANNs are capable of mapping the non-linear systems. A back propagation neural network model was developed to analyze RSW process and the interaction effects of the parameters. In the second phase of this research, Genetic Algorithm with the fitness function based on an ANN model was employed as an optimization procedure for determining a set of process parameters; as a result, the maximum joint strength was obtained. Optimization results showed high compatibility with the actual experimental data. © 2011 Elsevier Ltd. Source

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. Source

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. Source

Abdzadeh-Ziabari H.,Urmia University | Shayesteh M.G.,Urmia University | Shayesteh M.G.,Sharif University of Technology
IEEE Transactions on Vehicular Technology | Year: 2011

This paper deals with timing and frequency synchronization in orthogonal frequency-division multiplexing (OFDM) systems. A robust multistage scheme that works in the time domain, independent of the preamble structure, is proposed. After coarse-timing estimation, joint timing and integer frequency synchronization is performed. Then, fractional frequency correction is carried out, and finally, fine-timing estimation completes the synchronization process. The new timing estimation method is flexible and can be adjusted according to the degree of channel distortion. Furthermore, frequency synchronization is efficiently accomplished with an estimation range that is as large as the bandwidth of the OFDM signal. The performance of the proposed method is evaluated in terms of the mean square error. The results indicate that the new method significantly improves performance compared with the previous methods. © 2011 IEEE. Source

Maleki S.,Sharif University of Technology | Tabbakhha M.,Ecole Centrale Paris
Journal of Constructional Steel Research | Year: 2012

Reduced Beam Section (RBS) and Slotted Beam Web (SBW) are two types of seismic resistant moment connections that were introduced after the 1994 Northridge earthquake. These connections have been tested under cyclic loading and have had acceptable performance. In this paper, a new hybrid connection is introduced that is composed of RBS and SBW and is named Slotted-Web-Reduced- Flange (SWRF). Nonlinear finite element analyses are performed on SWRF under cyclic loading. It is shown that the new connection in some cases performs better than its RBS and SBW predecessors. The effects of panel zone strength, continuity plates and slot length are also investigated. © 2011 Elsevier Ltd. All rights reserved. Source

Madhkhan M.,Isfahan University of Technology | Azizkhani R.,Isfahan University of Technology | Torki Harchegani M.E.,Sharif University of Technology
Construction and Building Materials | Year: 2012

Effects of pozzolans and fibers on mechanical properties of RCC are addressed. The mechanical properties were evaluated using optimum moisture with different amounts of pozzolans, steel and polypropylene fibers. Using pozzolans, maximum increase in compressive strength was observed to occur between 28 and 90 days of age, rupture modulus was found to decrease; but toughness indices did not change considerably. The influence of steel fibers on compressive strength was often more significant than that of PP fibers; but neither steel nor PP fibers did contribute to increase in the rupture modulus independently from pozzolans. Also, the toughness indices increased when steel fibers were used. © 2011 Elsevier Ltd. All rights reserved. Source

Khavasi A.,Sharif University of Technology
Journal of the Optical Society of America B: Optical Physics | Year: 2015

I propose a novel method for designing a broadband THz absorber by using periodic arrays of graphene ribbons on a Salisbury-screen-like structure. The recently proposed analytical circuit model of graphene arrays is used for obtaining analytical expressions for the input admittance of the proposed device. The input admittance is then adjusted to be closely matched to the free space in a wide frequency range. Consequently, it is demonstrated that a bandwidth of 90% absorption can be extended up to 100% of the central frequency with only one layer of patterned graphene. © 2015 Optical Society of America. Source

Jahani Yekta M.M.,Sharif University of Technology
Digital Signal Processing: A Review Journal | Year: 2011

One of the most important properties of the maximally flat (MF) FIR fractional delay (FD) filter is its equivalence with the Lagrange interpolator for uniformly sampled signals. In this article, to provide the required background for the reader, we first propose a straightforward algebraic proof for this equivalence. This proof is given by simply demonstrating that the system of linear equations governing the maximally flatness property of this filter is the same as the one from which the coefficients of the Lagrange interpolator are computed. We then present the main contribution of the paper, which is a frequency domain proof for the same equivalence. In contrast with its classic counterparts which typically deploy the system of equations characterizing the maximally flatness property of the MFFD filter, the proof presented here is just based on the definition of this property. The aim of the article is to shed more light on the important equivalence it discusses by revisiting it from a new perspective. © 2010 Elsevier Inc. All rights reserved. Source

Dabirian A.,Technical University of Delft | Dabirian A.,Sharif University of Technology | Van De Krol R.,Technical University of Delft | Van De Krol R.,Helmholtz Center Berlin
Applied Physics Letters | Year: 2013

In this study, we explore resonance-enhanced optical absorption in Ta 3N5 photoanodes for water splitting. By using a reflecting Pt back-contact and appropriate Ta3N5 film thickness, the resonance frequency can be tuned to energies just above the bandgap, where the optical absorption is normally weak. The resonance results in a significant improvement in the photoanode's incident photon-to-current efficiency. The Ta3N5 films are made by high-temperature nitridation of Ta2O5. The nitridation time is found to be critical, as extended nitridation result in the formation of nitrogen vacancies through thermal reduction. These insights give important clues for the development of efficient (oxy)nitride-based photoelectrodes. © 2013 American Institute of Physics. Source

Fazlollahtabar H.,Mazandaran University of Science and Technology | Mahdavi-Amiri N.,Sharif University of Technology
International Journal of Advanced Manufacturing Technology | Year: 2013

Here, an approach for finding an optimal path in a flexible jobshop manufacturing system considering two criteria of time and cost is proposed. A network is configured in which the nodes are considered to be the shops with arcs representing the paths among the shops. An automated guided vehicle functions as a material handling device through the manufacturing network. To account for uncertainty, time is considered to be a triangular fuzzy number and apply an expert system to infer the cost. The expert system based on fuzzy rule backpropagation network to configure the rules for estimating the cost under uncertainty is proposed. A multiple linear regression model is applied to analyze the rules and find the effective rules for cost estimation. The objective is to find a path minimizing an aggregate weighted unscaled time and cost criteria. A fuzzy dynamic programming approach is presented for computing a shortest path in the network. Then, a comprehensive economic and reliability analysis is worked out on the obtained paths to find the optimal producer's behavior. Finally, an application of the model is illustrated by a numerical example. The results show the effectiveness of our approach for finding an optimal path in a manufacturing system under uncertainty. © 2012 Springer-Verlag London Limited. Source

Akhshik M.,Sharif University of Technology
Journal of Cosmology and Astroparticle Physics | Year: 2015

In solid inflation the single field non-Gaussianity consistency condition is violated. As a result, the long tenor perturbation induces observable clustering fossils in the form of quadrupole anisotropy in large scale structure power spectrum. In this work we revisit the bispectrum analysis for the scalar-scalar-scalar and tensor-scalar-scalar bispectrum for the general parameter space of solid. We consider the parameter space of the model in which the level of non-Gaussianity generated is consistent with the Planck constraints. Specializing to this allowed range of model parameter we calculate the quadrupole anisotropy induced from the long tensor perturbations on the power spectrum of the scalar perturbations. We argue that the imprints of clustering fossil from primordial gravitational waves on large scale structures can be detected from the future galaxy surveys. © 2015 IOP Publishing Ltd and Sissa Medialab srl. Source

Pepper B.,University of California at Santa Barbara | Ghobadi R.,University of Calgary | Ghobadi R.,Sharif University of Technology | Jeffrey E.,Leiden University | And 3 more authors.
Physical Review Letters | Year: 2012

We present a scheme for achieving macroscopic quantum superpositions in optomechanical systems by using single photon postselection and detecting them with nested interferometers. This method relieves many of the challenges associated with previous optical schemes for measuring macroscopic superpositions and only requires the devices to be in the weak coupling regime. It requires only small improvements on currently achievable device parameters and allows the observation of decoherence on a time scale unconstrained by the system's optical decay time. Prospects for observing novel decoherence mechanisms are discussed. © 2012 American Physical Society. Source

Paz-Silva G.A.,University of Southern California | Rezakhani A.T.,University of Southern California | Rezakhani A.T.,Sharif University of Technology | Dominy J.M.,University of Southern California | Lidar D.A.,University of Southern California
Physical Review Letters | Year: 2012

It is well known that the quantum Zeno effect can protect specific quantum states from decoherence by using projective measurements. Here we combine the theory of weak measurements with stabilizer quantum error correction and detection codes. We derive rigorous performance bounds which demonstrate that the Zeno effect can be used to protect appropriately encoded arbitrary states to arbitrary accuracy while at the same time allowing for universal quantum computation or quantum control. © 2012 American Physical Society. Source

Ghotboddini M.M.,University of Tehran | Rabbani M.,University of Tehran | Rahimian H.,Sharif University of Technology
Expert Systems with Applications | Year: 2011

This paper is seeking to design a dynamic cellular manufacturing system (DCMS). Area of multi-objective optimization is attractive not only for offering new opportunities for defining problem, but it helps us to extend and solve the anonymous problem. So a new multi-objective mixed integer model is presented for DCMS. The proposed model considers some real-world critical conditions in lean production which are neglected in similar studies in the literature. This model solves the part and machine grouping simultaneously with labor assignment to minimize the cost of various terms like reassignment cost of human resource, over time cost of equipments and labors, and maximize utilization rate of human resource. The model is linearized and validated with GAMS 22.1Cplex. Because the Benders' decomposition approach has not been applied to solve multi-objective CMS problems so far, we use this method to solve our model. The results are presented at the end. © 2010 Elsevier Ltd. All rights reserved. Source

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. Source

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. Source

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. Source

Ansari K.,Chemical Engineering Gachsaran Gas and Oil Production Company GS NISOC | Goodarznia I.,Sharif University of Technology
Journal of Supercritical Fluids | Year: 2012

In this study, the essential oil of aerial parts species of a plant called Spearmint was extracted by CO 2 to optimize the results of the supercritical extraction process. In order to achieve maximum total yield extraction and SF-CO 2 concentration, tests were done in a laboratorial pilot considering the Taguchi method under following condition: pressure. 90,100,140,170 bar, temperature. of 35, 40, 45, 50 °C, mean particles size: 250,500,710,1000 μm, flow rate 1,3,5,8 ml/s and dynamic time 30,50,90,120 min. The optimizing conditions for SCE and SF-CO 2 concentration are: 90 bar, 45 °C, 500 μm, 5 ml/s, 120 min and 90 bar, 35 °C, 250 μm, 1 ml/s, 30 min. SCE total yield and CO 2 concentration are 2.032% and 0.033 mg/ml. In similar and optimal conditions of extraction, supplementary tests were done so resulted and experimental amount of the calculated sum are in accordance with total yield extraction and SF-CO 2 concentration. This is the first report announcing optimization of spearmint SCE by use of Taguchi method. © 2012 Published by Elsevier B.V. Source

Mohammadi M.R.,Sharif University of Technology | Mohammadi M.R.,University of Cambridge | Fray D.J.,University of Cambridge
Sensors and Actuators, B: Chemical | Year: 2010

Nanostructured TiO2-CeO2 thin films and powders were prepared by a straightforward aqueous particulate sol-gel route. Titanium (IV) isopropoxide and cerium chloride were used as precursors, and hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the specific surface area. The effect of Ce:Ti molar ratio was studied on the crystallisation behaviour of the products. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders crystallised at the low temperature of 500 °C, containing anatase-TiO2, rutile-TiO2 and cubic-CeO2 phases, as well as Ti 8O15, Ti3O5 and Ce 11O20 depending on annealing temperature and Ce:Ti molar ratio. Furthermore, it was found that CeO2 retarded the anatase to rutile transformation up to 700 °C. The activation energy of crystallite growth was calculated in the range 1.92-8.79 kJ/mol. Transmission electron microscope (TEM) image showed that one of the smallest crystallite sizes was obtained for TiO2-CeO2 binary mixed oxide, being 3 nm at 500 °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 17-28 nm at 500 °C. Thin films produced under optimised conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO gas at low operating temperature of 200 °C, resulting in increased thermal stability of sensing films as well as a decrease in their power consumption. Furthermore, calibration curves revealed that TiO 2-CeO2 sensors follow the power law, S = A[gas] B (where S is sensor response, coefficients A and B are constants and [gas] is the gas concentration) for the two types of gases, and they have excellent capability for the detection of low gas concentrations. © 2010 Elsevier B.V. Source

Seyf H.R.,Islamic Azad University at Karaj | Feizbakhshi M.,Sharif University of Technology
International Journal of Thermal Sciences | Year: 2012

Numerical investigation on the application of nanofluids in Micro-Pin-Fin Heat Sinks (MPFHSs) has been presented in this paper. To investigate flow and heat transfer behavior in MPFHS the three-dimensional steady Navier-Stokes and energy equations were discretized using a finite volume approach and have been solved iteratively, using the SIMPLE algorithm. DI-water is used as a base coolant fluid while the nanoparticles used in the present study are CuO nanoparticles with mean diameters of 28.6 and 29 nm and Al 2O 3 nanoparticles with mean diameters of 38.4 and 47 nm. The results show that (i) a significant enhancement of heat transfer in the MPFHS due to suspension of CuO orAl 2O 3 nanoparticles in the base fluid in comparison with pure water, (ii) enhancement of heat transfer is intensified with increasing volume fraction of nanoparticles and Reynolds number, (iii) increasing volume fraction of nanoparticles which is responsible for higher heat transfer performance leads to higher pressure drop or Euler number in MPFHS but the enhancements are small, especially for lower particle volume fractions, (iv) with decreasing particle diameters the Nusselt number increases for Al 2O 3-water nanofluid while the trend is reverse for CuO-water nanofluid. © 2012 Elsevier Masson SAS. All rights reserved. Source

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. Source

Khaleghi S.,Pennsylvania State University | Pakravan M.R.,Sharif University of Technology
Journal of Optical Communications and Networking | Year: 2010

An enhanced media access control (MAC) layer protocol that uses the signaling method benefits of the physical layer in order to provide different levels of quality to different users in optical code-division multiple-access (OCDMA) packet networks is presented. In the proposed network architecture the users are categorized into two classes of service, one having a higher quality level and the other having a lower quality level. Users of each class transmit at the same power level and different from the other classes users. Also, the MAC of each user estimates the amount of interference on the channel and adjusts the packet transmissions time to improve network performance. Through simulation it is shown that the combination of appropriate power assignment to users and proper MAC algorithm parameters can provide various quality of service (QoS) metric levels on metrics such as normalized throughput and packet error rate. This is achieved by dividing the available resources of the OCDMA network between the users of each class. To make the QoS provider method more practical in data communication networks, we have studied the fairness issue by defining two parameters related to the normalized throughput of each class. © 2010 Optical Society of America. Source

Davoodi-Dehaghani F.,University of Tehran | Vosoughi M.,Sharif University of Technology | Ziaee A.A.,University of Tehran
Bioresource Technology | Year: 2010

A new dibenzothiophene (DBT) desulfurizing bacterium was isolated from oil-contaminated soils in Iran. HPLC analysis and PCR-based detection of the presence of the DBT desulfurization genes (dszA, dszB and dszC) indicate that this strain converts DBT to 2-hydroxybiphenyl (2-HBP) via the 4S pathway. The strain, identified as Rhodococcus erythropolis SHT87, can utilize DBT, dibenzothiophene sulfone, thiophene, 2-methylthiophene and dimethylsulfoxide as a sole sulfur source for growth at 30 °C. The maximum specific desulfurization activity of strain SHT87 resting cells in aqueous and biphasic organic-aqueous systems at 30 °C was determined to be 0.36 and 0.47 μmol 2-HBP min-1 (g dry cell)-1, respectively. Three mM DBT was completely metabolized by SHT87 resting cells in the aqueous and biphasic systems within 10 h. The rate and the extent of the desulfurization reaction by strain SHT87 suggest that this strain can be used for the biodesulfurization of diesel oils. © 2009. Source

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. Source

Paredes J.M.,TU Darmstadt | Khalaj B.H.,Sharif University of Technology | Gershman A.B.,TU Darmstadt
IEEE Transactions on Signal Processing | Year: 2010

To achieve the available performance gains in half-duplex wireless relay networks, several cooperative schemes have been earlier proposed using either distributed space-time coding or distributed beamforming for the transmitter without and with channel state information (CSI), respectively. However, these schemes typically have rather high implementation and/or decoding complexities, especially when the number of relays is high. In this paper, we propose a simple low-rate feedback-based approach to achieve maximum diversity with a low decoding and implementation complexity. To further improve the performance of the proposed scheme, the knowledge of the second-order channel statistics is exploited to design long-term power loading through maximizing the receiver signal-to-noise ratio (SNR) with appropriate constraints. This maximization problem is approximated by a convex feasibility problem whose solution is shown to be close to the optimal one in terms of the error probability. Subsequently, to provide robustness against feedback errors and further decrease the feedback rate, an extended version of the distributed Alamouti code is proposed. It is also shown that our scheme can be generalized to the differential transmission case, where it can be applied to wireless relay networks with no CSI available at the receiver. © 2010 IEEE. Source

Tavazoei M.S.,Sharif University of Technology
Journal of Process Control | Year: 2012

In this paper, a sufficient condition for existence of an overshoot in the step response of fractional-order systems is presented. Based on this condition, it can be shown that the existence of an overshoot in the step responses of some classes of fractional-order systems (for example, the class of fractional-order systems having commensurate orders between 1 and 2) is unavoidable. To show the usefulness of the obtained condition, this condition is applied to prove some results on the time response analysis of fractional-order control systems. © 2011 Elsevier Ltd. All Rights Reserved. Source

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. Source

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. Source

Jalili M.,Sharif University of Technology
Simulation | Year: 2013

Social networks are inevitable parts of daily life and there has been an increasing interest in analyzing social phenomena on networked structures. Evolution of opinion formation is one of the topics that has attracted many scholars in the field. In this work we consider the influence of leaders and social power in the evolution of opinion formation. A number of central nodes with specific properties (e.g. nodes with highest degree, betweenness or vulnerability values) are taken as leaders whose opinions are kept unchanged, that is, not influenced by other agents. The leaders try to coordinate the opinions of other agents where the connection structure is considered to be preferential attachment scale-free, Watts-Strogatz small-world or Erdos-Rényi random networks. Numerical simulations show that scale-free networks provide faster consensus compared with other networks. We also study the effects of social power on the consensus time. The social power of a node is considered to be a function of its centrality. Having leaders in the network, we show that the consensus time could be significantly decreased by introducing social power. For scale-free networks, there is an optimal degree of social power in which the consensus time is minimal. These results show the appropriateness of scale-free topology in hierarchal organizations where leaders posit influence on peripheral agents. © 2013 The Society for Modeling and Simulation International. Source

Nobakhti A.,Sharif University of Technology
Cognitive Computation | Year: 2010

Nature has always been a source of great inspiration for engineers and mathematicians. Evolutionary Algorithms are the latest in a line of natural-based innovations which have had a profound effect on the application of optimization in science and engineering. Although based on nature, Evolutionary Algorithms are nonetheless distinctly different from natural evolution in several areas. This paper outlines early and recent developments of Evolutionary Algorithms while covering those areas of difference. Practical issues related to the use of Evolutionary Algorithms, key parameters that affect the quality of the search and impact of user choices in problem formulation are also covered in this paper. © Springer Science+Business Media, LLC 2010. Source

Joudaki A.,Sharif University of Technology
PloS one | Year: 2012

Functional connectivity in human brain can be represented as a network using electroencephalography (EEG) signals. These networks--whose nodes can vary from tens to hundreds--are characterized by neurobiologically meaningful graph theory metrics. This study investigates the degree to which various graph metrics depend upon the network size. To this end, EEGs from 32 normal subjects were recorded and functional networks of three different sizes were extracted. A state-space based method was used to calculate cross-correlation matrices between different brain regions. These correlation matrices were used to construct binary adjacency connectomes, which were assessed with regards to a number of graph metrics such as clustering coefficient, modularity, efficiency, economic efficiency, and assortativity. We showed that the estimates of these metrics significantly differ depending on the network size. Larger networks had higher efficiency, higher assortativity and lower modularity compared to those with smaller size and the same density. These findings indicate that the network size should be considered in any comparison of networks across studies. Source

Noshad M.,Sharif University of Technology | Jamshidi K.,University of Applied Sciences of Leipzig
Journal of Optical Communications and Networking | Year: 2010

A novel family of codes for modified spectral-amplitude-coding optical code division multiple access (SAC-OCDMA) is introduced. The proposed codes exist for more processing gains than the previously reported codes do. In the network using these codes, the number of users can be extended without any essential changes in the previous transmitters. In this study, we propose a construction method for these codes and compare their performance with previously reported codes. © 2009 OSA. Source

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. Source

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. Source

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. Source

Sheikhzadeh M.,Sharif University of Technology | Elahi E.,University of Massachusetts Boston
International Journal of Production Economics | Year: 2013

Bundling has been extensively studied in the literature and its benefits have been manifested through three perspectives of achieving better price discrimination, helping to save costs, and preserving the power for deterring a potential entrant. In this study, we examine two aspects of bundling which have not been studied before. We examine the impact of product heterogeneity on bundling decisions. We also address risk considerations in a bundling problem. Specifically, we consider a retailer who has the option of selling a bundle of two products (pure bundling policy), or selling the products separately (no-bundling policy). The retailer could also face a product selection problem for which we consider three scenarios of choosing two products with perfectly positively correlated, perfectly negatively correlated or independent reservation prices. We use a Mean-Variance approach to include retailer's risk through her profit variability when maximizing the expected value of profit. We characterize the conditions under which a policy or scenario performs better than the others under the influence of product heterogeneity and/or retailer's risk aversion. Among other findings, we show that optimal bundling price chosen by a risk-averse decision maker cannot be larger than the one chosen by a risk neutral decision maker. © 2013 Elsevier B.V. All rights reserved. Source

Moslemi Naeni L.,Sharif University of Technology | Salehipour A.,Islamic Azad University at South Tehran
Expert Systems with Applications | Year: 2011

The earned value technique is an essential technique in analyzing and controlling the performance of a project by providing a more accurate measurement of both project performance and project progress. This paper presents an approach to deal with fuzzy earned value indices. This includes developing new indices under fuzzy circumstances and evaluating them using alpha cut method. The model improves the applicability of the earned value techniques under real-life and uncertain conditions. A small example illustrates how the new model can be implemented in reality. © 2011 Elsevier Ltd. All rights reserved. Source

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. Source

Noori-Darvish S.,Allame Mohaddes Noori University | Mahdavi I.,Mazandaran University of Science and Technology | Mahdavi-Amiri N.,Sharif University of Technology
Applied Soft Computing Journal | Year: 2012

We are concerned with an open shop scheduling problem having sequence-dependent setup times. A novel bi-objective possibilistic mixed-integer linear programming model is presented. Sequence-dependent setup times, fuzzy processing times and fuzzy due dates with triangular possibility distributions are the main constraints of this model. An open shop scheduling problem with these considerations is close to the real production scheduling conditions. The objective functions are to minimize total weighted tardiness and total weighted completion times. To solve small-sized instances for Pareto-optimal solutions, an interactive fuzzy multi-objective decision making (FMODM) approach, called TH method proposed by Torabi and Hassini, is applied. Using this method, an equivalent auxiliary single-objective crisp model is obtained and solved optimally by the Lingo software. For medium to large size examples, a multi-objective particle swarm optimization (MOPSO) algorithm is proposed. This algorithm consists of a decoding procedure using a permutation list to reduce the search area in the solution space. Also, a local search algorithm is applied to generate good initial particle positions. Finally, to evaluate the effectiveness of the MOPSO algorithm, the results are compared with the ones obtained by the well-known SPEA-II, using design of experiments (DOE) based on some performance metrics. © 2011 Elsevier B.V. All rights reserved. Source

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. Source

Hashemi R.,University of Tehran | Abrinia K.,University of Tehran | Assempour A.,Sharif University of Technology
Journal of Manufacturing Processes | Year: 2013

A stress-based forming limit diagram for necking prediction which is based on the strain gradient theory of plasticity in conjunction with the M-K model has been represented and used in tube hydroforming. In this study, the finite element model for bulge forming of straight tube has been constructed and verified with published experimental data. The adaptive simulation technique is based on the ability to detect the onset and growth of defects (e.g., wrinkling, and bursting) and to promptly readjust the loading paths. Thus, a suitable load path has been obtained by applying Adaptive Simulation Method in ANSYS Parametric Design Language (APDL). © 2012 The Society of Manufacturing Engineers. Source

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. Source

Shamloo A.,Sharif University of Technology
Cytoskeleton | Year: 2014

This study investigates the role of cell-cell and cell-ligand interactions in cytoskeleton organization of endothelial cells (ECs) and their directional migration within a microfluidic device. The migration of ECs in response to a biochemical factor was studied. Mathematical analysis of the cell migration pathways and cellular cytoskeleton revealed that directional migration, migration persistence length, migration speed, and cytoskeletal stress fiber alignment can be mediated by the level of cell contacts as well as the presence or absence of a biochemical polarizing factor. It was shown that in the presence of a biochemical polarizing factor, higher cell density and more frequent cell contacts has a reinforcing effect on collective cell chemotaxis. In contrast, in the absence of a polarizing factor, high cell density can decrease or suppress the ability of the cells to migrate. Also, the correlation of actin stress fiber organization and alignment with directional migration of ECs was investigated. It was shown that in the presence of a biochemical polarizing factor, stress fibers within the cytoskeleton of ECs can be significantly aligned parallel to the gradient direction when the cells have higher level of contacts. The results also show that the organization and alignment of actin stress fibers is mediated by cell adhesion junctions during collective cell migration and introduce cell-cell interactions as a key factor during collective cell chemotaxis. © 2014 Wiley Periodicals, Inc. Source

Masoudi Nejad R.,Sharif University of Technology
Engineering Failure Analysis | Year: 2014

One of the most important issues in railway wheels is residual stresses. It is desirable to produce less residual stresses when possible and to decrease the remaining residual stresses in the wheels. The objective of this paper is to provide an estimation of the residual stresses in the rail wheel caused by the stress field from heat treatment process of a railway wheel. A three-dimensional nonlinear stress analysis model has been applied to estimate stress fields of the railway mono-block wheel in heat treatment process. After forging or casting, railway wheels are heat-treated to induce the desirable circumferential compressive residual stress in the upper rim. Finite element analysis model is presented applying the elastic-plastic finite element analysis for the rail wheel under variable thermal loads. Calculative analysis applying a finite element method (FEM) has been used to predict residual stresses. The quenching and annealing segments of the wheel manufacturing process are simulated using a decoupled heat transfer and stress analysis. Three-dimensional finite element analysis results obtained show good agreement with those achieved in field measurements. © 2014 Elsevier Ltd. Source

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. Source

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 effects of the second-order filter on the very small scales. Several numerical experiments are carried out and the accuracy of the nonlinear filter with the proposed sensor is examined. In addition, some comparisons with other filters and sensors are made. © 2010 Elsevier Inc. Source

Mafi Gholami R.,Islamic Azad University at Ahvaz | Mousavi S.M.,Tarbiat Modares University | Borghei S.M.,Sharif University of Technology
Journal of Industrial and Engineering Chemistry | Year: 2012

The present study examines the biorecovery of heavy metals from a spent refinery catalyst obtained from one of the oil refineries in Iran using Aspergillus niger. Bioleaching experiments were carried out in batch cultures using A. niger in the one-step process to mobilize Co, Mo and Ni from hazardous spent catalysts. Response surface methodology (RSM) was applied for the design and analysis of experiments with the optimization of pH, temperature, inoculum percentage, pulp density and rotation speed during the bioleaching of the metals. Experiments were designed as per the central composite design (CCD) technique. Three cubic mathematical models were derived for prediction of the responses. In process optimization, maximal values of Co, Mo and Ni recoveries were achieved as 71%, 69% and 46%, respectively, with a pH of 5.0, a temperature of 31°C, a pulp density of 2. g/L, a rotation speed of 115. rpm, and using a 12% inoculum. © 2011 The Korean Society of Industrial and Engineering Chemistry. Source

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. Source

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. Source

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. Source

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. Source

Memarzadeh L.,Sharif University of Technology | Mancini S.,University of Camerino
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

We investigate the possibility of chaining qubits by letting pairs of nearest-neighbor qubits dissipate into common environments. We then study entanglement dynamics within the chain and show that steady-state entanglement can be achieved. © 2011 American Physical Society. Source

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. Source

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. Source

Shalchi-Tabrizi A.,Sharif University of Technology | Seyf H.R.,Islamic Azad University at Karaj
International Journal of Heat and Mass Transfer | Year: 2012

Effect of using Al 2O 3-water nanofluids with different volume fractions and particle diameters on generated entropy, hydrodynamic performance and heat transfer characteristics of a tangential micro-heat sink (TMHS) was numerically investigated in this research. Results indicated that considerable heat transfer enhancement is possible when using Al 2O 3-water nanofluids as coolant and clearly the enhancement improves with increasing particles concentration and decreasing particles size. However, using nanofluid has also induced drastic effects on the pumping power that increases with particles volume fraction and Reynolds number. Finally, it was found that generated total entropy decreases with increasing volume fraction and Reynolds number and decreasing particles size. © 2012 Elsevier Ltd. All rights reserved. Source

Azadi M.,Iran Khodro Powertrain Company IPCO | Farrahi G.H.,Sharif University of Technology | Winter G.,University of Leoben | Eichlseder W.,University of Leoben
Materials and Design | Year: 2014

In the present paper, thermo-mechanical fatigue (TMF) and low cycle fatigue (LCF) or isothermal fatigue (IF) lifetimes of a cast magnesium alloy (the AZ91 alloy) were studied. In addition to a heat treatment process (T6), several rare elements were added to the alloy to improve the material strength in the first step. Then, the cyclic behavior of the AZ91 was investigated. For this objective, strain-controlled tension-compression fatigue tests were carried out. The temperature varied between 50 and 200. °C in the out-of-phase (OP) TMF tests. The constraint factor which was defined as the ratio of the mechanical strain to the thermal strain, was set to 75%, 100% and 125%. For LCF tests, mechanical strain amplitudes of 0.20%, 0.25% and 0.30% were considered at constant temperatures of 25 and 200. °C. Experimental fatigue results showed that the cyclic hardening behavior occurred at the room temperature in the AZ91 alloy. At higher temperatures, this alloy had a brittle fracture. But also, it was not significantly clear that the cyclic hardening or the cyclic softening behavior would be occurred in the material. Then, the high temperature LCF lifetime was more than that at the room temperature. The OP-TMF lifetime was the least value in comparison to that of LCF tests. At the end of this article, two energy-based models were applied to predict the fatigue lifetime of this magnesium alloy. © 2013 Elsevier Ltd. Source

Tavazoei M.S.,Sharif University of Technology
Automatica | Year: 2010

In this paper, it is shown that the fractional-order derivatives of a periodic function with a specific period cannot be a periodic function with the same period. The fractional-order derivative considered here can be obtained based on each of the well-known definitions Grunwald-Letnikov definition, Riemann-Liouville definition and Caputo definition. This concluded point confirms the result of a recently published work proving the non-existence of periodic solutions in a class of fractional-order models. Also, based on this point it can be easily proved the absence of periodic responses in a wider class of fractional-order models. Finally, some examples are presented to show the applicability of the paper achievements in the solution analysis of fractional-order systems. © 2010 Elsevier Ltd. All rights reserved. Source

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. Source

Gholami M.,Sharif University of Technology
Circuits, Systems, and Signal Processing | Year: 2013

This paper presents a novel DLL-based frequency synthesizer architecture to generate fractional multiples of reference frequency and reduce the power consumption of the frequency synthesis block. The architecture is adopted for French VHF application as an example. The DLL architecture allows for minimal area, while consuming low power. The proposed circuit can operate at a substantially low supply voltage. The circuit level and system level designs are presented. It was shown that for the mentioned standard, a mere 27 delay stages for VCDL are sufficient to cover French VHF band. Simulation results confirm the analytical predictions. The proposed DLL-based frequency synthesizer is implemented in a 0.13 μm CMOS technology. This fractional DLL-based frequency synthesizer is adopted for 176 MHz to 216 MHz with maximum power consumption of 2.62 mW and RMS jitter of 10 ps @ 216 MHz. © 2012 Springer Science+Business Media, LLC. Source

Ghojavand M.,Sharif University of Technology
Quantum Information Processing | Year: 2011

For technological purposes and theoretical curiosity, it is very interesting to have a building block that produces a considerable amount of entanglement between on-demand sites through a simple control of a few sites. Here, we consider permanently- coupled spin networks and study entanglement generation between qubit pairs to find low-complexity structures capable of generating considerable entanglement between various qubit pairs.We find that in axially symmetric networks the generated entanglement between some qubit pairs is rather larger than generic networks. We show that in uniformly-coupled spin rings each pair can be considerably entangled through controlling suitable vertices. To set the location of controlling-vertices, we observe that the symmetry has to be broken for a definite time. To achieve this, a magnetic flux can be applied to break symmetry via Aharonov-Bohm effect. Such a set up can serve as an efficient entanglement distributor bus in which each vertex-pair can be efficiently entangled through exciting only one fixed vertex and controlling the evolution time. The low-complexity of this scheme makes it attractive for use in nanoscale quantum information processors. © Springer Science+Business Media, LLC 2010. Source

Mirkhani S.A.,Sharif University of Technology | Gharagheizi F.,Saman Energy Giti Co. | Sattari M.,Saman Energy Giti Co.
Chemosphere | Year: 2012

Evaluation of diffusion coefficients of pure compounds in air is of great interest for many diverse industrial and air quality control applications. In this communication, a QSPR method is applied to predict the molecular diffusivity of chemical compounds in air at 298.15. K and atmospheric pressure. Four thousand five hundred and seventy nine organic compounds from broad spectrum of chemical families have been investigated to propose a comprehensive and predictive model. The final model is derived by Genetic Function Approximation (GFA) and contains five descriptors. Using this dedicated model, we obtain satisfactory results quantified by the following statistical results: Squared Correlation Coefficient = 0.9723, Standard Deviation Error = 0.003 and Average Absolute Relative Deviation = 0.3% for the predicted properties from existing experimental values. © 2011 Elsevier Ltd. Source

Shahbeyk S.,Tarbiat Modares University | Hosseini M.,Tarbiat Modares University | Yaghoobi M.,Sharif University of Technology
Computational Materials Science | Year: 2011

The present paper studies the failure of concrete from the mesoscopic point of view. Biphasic cubic concrete samples containing spherical aggregates embedded in a homogenized mortar have been simulated using standard finite element method. Linear elasticity and damage-plasticity hypotheses are considered for the aggregates and mortar, respectively. Various triaxial loading conditions are assumed for each sample to generate adequate discrete failure points within the stress space. In the next step, the approximated failure surfaces of specimens are constructed using the Delaunay triangulation technique. The effects of mesostructural features such as aggregate grading curve, aggregate volumetric share, and more importantly the controlling parameters of mortars damage-plasticity constitutive model have been investigated. Finally, the failure modes of some selected samples have been reported and discussed. © 2011 Elsevier B.V. All rights reserved. Source

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. Source

Ghobadi R.,University of Calgary | Ghobadi R.,Sharif University of Technology | Lvovsky A.,University of Calgary | Simon C.,University of Calgary
Physical Review Letters | Year: 2013

We propose a scheme for the observation of micro-macro entanglement in photon number based on amplifying and deamplifying a single-photon entangled state in combination with homodyne quantum state tomography. The created micro-macro entangled state, which exists between the amplification and deamplification steps, is a superposition of two components with mean photon numbers that differ by approximately a factor of three. We show that for reasonable values of photon loss it should be possible to detect micro-macro photon-number entanglement where the macrosystem has a mean number of one hundred photons or more. © 2013 American Physical Society. Source

Tavazoei M.S.,Sharif University of Technology
Journal of Computational and Nonlinear Dynamics | Year: 2014

Finding the oscillatory region in the order space is one of the most challenging problems in nonlinear fractional-order systems. This paper proposes a method to find the possible oscillatory region in the order space for a nonlinear fractional-order system. The effectiveness of the proposed method in finding the oscillatory region and special order sets placed in its boundary is confirmed by presenting some examples. © 2014 by ASME. Source

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. Source

Kiani K.,Sharif University of Technology
International Journal of Mechanical Sciences | Year: 2010

A single-walled nanotube structure embedded in an elastic matrix is simulated by the nonlocal EulerBernoulli, Timoshenko, and higher order beams. The beams are assumed to be elastically supported and attached to continuous lateral and rotational springs to take into account the effects of the surrounding matrix. The discrete equations of motion associated with free transverse vibration of each model are established in the context of the nonlocal continuum mechanics of Eringen using Hamilton's principle and an efficient meshless method. The effects of slenderness ratio of the nanotube, small scale effect parameter, initial axial force and the stiffness of the surrounding matrix on the natural frequencies of various beam models are investigated for different boundary conditions. The capabilities of the proposed nonlocal beam models in capturing the natural frequencies of the nanotube are also addressed. © 2010 Elsevier Ltd. All rights reserved. Source

Tavazoei M.S.,Sharif University of Technology
Signal Processing | Year: 2015

In this paper, an effective way is proposed for reduction of oscillations in the response of dynamical systems. In this regard, it is analytically shown that the undesirable oscillations in the response of dynamical systems can be reduced using a simple input shaping fractional order filter. The effectiveness of the proposed fractional calculus based technique is numerically verified in reduction of oscillations in a mass-spring-damper system, a low-pass Chebyshev filter, and a PI-controlled two-mass drive system. © 2014 Elsevier B.V. All rights reserved. Source

Kiani K.,Sharif University of Technology
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2010

The free longitudinal vibration of tapered nanowires is investigated in the context of nonlocal continuum theory. The problem is studied for the nanowires with linearly varied radii under fixedfixed and fixedfree boundary conditions. In order to assess the problem in a more general form, a perturbation technique is proposed based on the Fredholm alternative theorem. The natural frequencies, corresponding mode shapes, and phase velocities of the tapered nanowires are derived analytically up to the second-order perturbation for different boundary conditions. The predicted results by the perturbation technique are successfully verified with those of the exact solution. The obtained results reveal that the proposed methodology is a capable one in capturing the free longitudinal dynamic response of tapered nanowires with different boundary conditions. However, the differences of the results of the perturbation technique and those of the exact solution increase with the rate of radii change. In a special case, the obtained results are also compared with those of other researchers and a reasonably good agreement is achieved. It is also observed that for higher values of the small scale effect parameter, the variation of the rate of radii change has a more effect on the variation of the natural frequencies and phase velocities, irrespective of the boundary conditions of the tapered nanowire. Additionally, a scrutiny of the presented dispersion curves indicates that for a constant wavenumber, the value of the phase velocity decreases with the small scale effect parameter, particularly for higher wavenumbers. Source

Asadi H.,Sharif University of Technology | Tahoori M.B.,Karlsruhe Institute of Technology
Microelectronics Journal | Year: 2010

Soft errors due to cosmic radiations are the main reliability threat during lifetime operation of digital systems. Fast and accurate estimation of soft error rate (SER) is essential in obtaining the reliability parameters of a digital system in order to balance reliability, performance, and cost of the system. Previous techniques for SER estimation are mainly based on fault injection and random simulations. In this paper, we present an analytical SER modeling technique for ASIC designs that can significantly reduce SER estimation time while achieving very high accuracy. This technique can be used for both combinational and sequential circuits. We also present an approach to obtain uncertainty bounds on estimated error propagation probability (EPP) values used in our SER modeling framework. Comparison of this method with the Monte-Carlo fault injection and simulation approach confirms the accuracy and speed-up of the presented technique for both the computed EPP values and uncertainty bounds. Based on our SER estimation framework, we also present efficient soft error hardening techniques based on selective gate resizing to maximize soft error suppression for the entire logic-level design while minimizing area and delay penalties. Experimental results confirm that these techniques are able to significantly reduce soft error rate with modest area and delay overhead. © 2009 Elsevier Ltd. All rights reserved. Source

Khavasi A.,Sharif University of Technology
Optics Letters | Year: 2013

Li's Fourier factorization rules [J. Opt. Soc. Am. A 13, 1870 (1996)] should be applied to achieve a fast convergence rate in the analysis of diffraction gratings with the Fourier modal method. I show, however, that Li's inverse rule cannot be applied for periodic patterns of graphene when the conventional boundary condition is used. I derive an approximate boundary condition in which a nonzero but sufficiently small height is assumed for the boundary. The proposed boundary condition enables us to apply the inverse rule, leading to a significantly improved convergence rate. A periodic array of graphene ribbons is in fact a special type of finite-conductivity strip grating, and thus the proposed approach is also applicable to these kinds of structures. © 2013 Optical Society of America. Source

Barak S.,Islamic Azad University | Modarres M.,Sharif University of Technology
Expert Systems with Applications | Year: 2014

In this research, a novel approach is developed to predict stocks return and risks. In this three stage method, through a comprehensive investigation all possible features which can be effective on stocks risk and return are identified. Then, in the next stage risk and return are predicted by applying data mining techniques for the given features. Finally, we develop a hybrid algorithm, on the basis of filter and function-based clustering; the important features in risk and return prediction are selected then risk and return re-predicted. The results show that the proposed hybrid model is a proper tool for effective feature selection and these features are good indicators for the prediction of risk and return. To illustrate the approach as well as to train data and test, we apply it to Tehran Stock Exchange (TSE) data from 2002 to 2011. © 2014 Elsevier B.V. All rights reserved. Source

Koochakie M.M.R.,Sharif University of Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

Recently it has been shown that projected entangled-pair states can be considered as a (physically motivated) resource state for measurement-based quantum computation. Here we elaborate on how to construct a deterministic measurement-based quantum computation model on projected entangled-pair states. In particular, we use this scheme to build a four-level many-body model for universal quantum computation on qubits. We also derive a 3-local parent Hamiltonian for this model, whose ground state is nondegenerate. © 2014 American Physical Society. Source

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. Source

Mohammadi M.R.,Sharif University of Technology | Fray D.J.,University of Cambridge
Sensors and Actuators, B: Chemical | Year: 2011

Nanostructured TiO2-ZrO2 thin films and powders were prepared by a straightforward aqueous particulate sol-gel route. Titanium (IV) isopropoxide and zirconium (IV) acetate hydrate were used as precursors, and hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the specific surface area. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy revealed that the powder were crystallised at the low temperature of 500 °C, containing anatase-TiO 2 and tetragonal-ZrO2 phases. Furthermore, it was found that ZrO2 retarded the anatase-to-rutile transformation up to 900 °C. The activation energies for crystallite growth of TiO2 and ZrO2 components in the binary system were calculated 10.16 and 3.12 kJ/mol, respectively. Transmission electron microscope (TEM) image showed that one of the smallest crystallite sizes was obtained for TiO2-ZrO 2 binary mixed oxide, being 5 nm at 500 °C. Field emission scanning electron microscope (FESEM) analysis revealed that the deposited thin films had nanostructured morphology with the average grain size of 20 nm at 500 °C and 36 nm at 900 °C. Thin films produced under optimised conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO and NO 2 gases at low operating temperature of 150 °C, resulted in an increase of thermal stability of sensing films as well as a decrease in the power consumption. Furthermore, calibration curves revealed that TiO 2-ZrO2 sensor follows the power law, S = A[gas] B (where S is sensor response, coefficients A and B are constants and [gas] is gas concentration) for the two types of gases, and it has excellent capability for the detection of low gas concentrations. © 2011 Elsevier B.V. All rights reserved. Source

Golnabi H.,Sharif University of Technology
Optics and Lasers in Engineering | Year: 2010

In this study surface profiling is performed by using a scanning system and an opto-pair fiber design. In this method one fiber transmits the laser light to the target and the second one transmits back the light reflected off the target to a photodetector. The monitoring of the reflected light signal from a surface is accomplished by converting the photon light into an electric signal and measuring by a digital multimeter. By scanning an object mounted on a XYZ-translational stage the reflection signal profiles are obtained for plane and curved surfaces. Output reflection signal variations in the X-, Y-, and Z-directions are measured for different plane and cylindrical surfaces and compared. Reflecting signals can provide information about the structure of the surface and in particular, can provide information about the shape of surface under study. It is noted that the fiber arrangement and the position of the object surface in respect to fibers are important in reflecting signal measurements. The convex surface of the same quality reflecting material has a reflection lower than that of the plane/concave surface. For a brass half-cylindrical shell when the fiber arrangement is vertical but the half-cylinder is horizontal the reflected signal power is lower than for the case that both fibers and cylinder are either horizontal or vertical. The reported opto-mechanical system can also be used to investigate surfaces made from different materials and different final finishes. As a result, the proposed system provides a simple and accurate means for the object shape study and determination of different surface structures through the reflection analysis. © 2009 Elsevier Ltd. All rights reserved. Source

Derakhshani M.,McGill University | Le-Ngoc T.,McGill University | Nasiri-Kenari M.,Sharif University of Technology
IEEE Transactions on Wireless Communications | Year: 2011

This paper proposes efficient cooperative cyclostationary spectrum sensing schemes in which each secondary-user (SU) performs single-cycle (SC) cyclostationary detection for fast and simple implementation, while collaboration between SUs in final decision on the presence or absence of the primary-user (PU) is explored to improve its performance. As the SUs simultaneously measure the spectral correlation functions at different cycle-frequencies (CF) and exchange their information regarding the measured results, a sufficient number of CFs are effectively examined with parallel searching, which makes the proposed cooperative spectrum sensing more reliable. This paper presents another look at performance evaluation of cyclostationary detectors in terms of deflection coefficients. Outage probability of deflection coefficient is defined as a measure to compare the performance of different cyclostationary detectors in a fading channel. Furthermore, performance of the proposed schemes in terms of false-alarm and detection probabilities is evaluated by analysis and simulation in AWGN and fading channels. Illustrative and analytical results show that the proposed schemes outperform both SC and multi-cycle (MC) cyclostationary detectors, especially in fading channels. © 2006 IEEE. Source

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

It is well known that the polarization signal in microlensing events of hot stars is larger than that of main-sequence stars. Most hot stars rotate rapidly around their stellar axes. The stellar rotation creates ellipticity and gravity-darkening effects that break the spherical symmetry of the source's shape and the circular symmetry of the source's surface brightness respectively. Hence, it causes a net polarization signal for the source star. This polarization signal should be considered in polarimetric microlensing of fast rotating stars. For moderately rotating stars, lensing can magnify or even characterize small polarization signals due to the stellar rotation through polarimetric observations. The gravity-darkening effect due to a rotating source star creates asymmetric perturbations in polarimetric and photometric microlensing curves whose maximum occurs when the lens trajectory crosses the projected position of the rotation pole on the sky plane. The stellar ellipticity creates a time shift (i) in the position of the second peak of the polarimetric curves in transit microlensing events and (ii) in the peak position of the polarimetric curves with respect to the photometric peak position in bypass microlensing events. By measuring this time shift via polarimetric observations of microlensing events, we can evaluate the ellipticity of the projected source surface on the sky plane. Given the characterizations of the FOcal Reducer and low dispersion Spectrograph (FORS2) polarimeter at the Very Large Telescope, the probability of observing this time shift is very small. The more accurate polarimeters of the next generation may well measure these time shifts and evaluate the ellipticity of microlensing source stars. © 2016. The American Astronomical Society. All rights reserved. Source

Abbasi B.,RMIT University | Mahlooji H.,Sharif University of Technology
Expert Systems with Applications | Year: 2012

Response surface methodology (RSM) explores the relationships between several explanatory variables and one or more response variables. The main idea of RSM is to use a set of designed experiments to obtain an optimal response. RSM tries to simplify the original problem through some polynomial estimation over small sections of the feasible area, elaborating on optimum provision through a well known optimization technique, say Gradient Method. As the real world problems are usually very complicated, polynomial estimation may not perform well in providing a good representation of the objective function. Also, the main problem of the Gradient Method, getting trapped in local minimum (maximum), makes RSM at a disadvantage, while defining sub-sections of the feasible area is also a problem faced by analyst. In this article, neural networks are used as a means to improve the estimation in the RSM context. This approach leads to reducing the calculations. Furthermore, it is proposed to use simulated annealing in maximizing the estimated objective function in reaching a suitable point. Three examples of different complexities are solved to shed light on the merits of the proposed method. The comparison results indicate that the proposed algorithm outperforms the classical method. © 2011 Elsevier Ltd. All rights reserved. Source

Simchi A.,Sharif University of Technology | Petzoldt F.,Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2010

Sintering response and phase formation during sintering of WC-Co/316L stainless steel composites produced by assembling of powder injection molding (PIM) parts were studied. It is shown that during cosintering a significant mismatch strain (>4 pct) is developed in the temperature range of 1080 °C to 1350 °C. This mismatch strain induces biaxial stresses at the interface, leading to interface delamination. Experimental results revealed that sintering at a heating rate of 20 K/min could be used to decrease the mismatch strain to <2 pct. Meanwhile, WC is decomposed at the contact area and the diffusion of C and Co into the iron lattice results in the formation of a liquid and MC and M6C carbides at 1220 °C. Spreading of the liquid accelerates the reaction, affecting the dimensional stability of the PIM parts. To prevent the reaction, surface oxidation of the cemented carbide followed by hydrogen reduction during sintering was examined. Although the amount of mismatch strain increased, formation of a metallic interface consisting of a W-Co alloy (45 to 50 at. pct Co) and a Co-rich iron alloy (18 at. pct Co) prevented the decomposition of WC and melt formation. It is also shown that the deposition of a thin Ni layer after thermal debinding decreases the mismatch stresses through melt formation, although interlayer diffusion causes pore-band formation close to the steel part. © 2009 The Minerals, Metals & Materials Society and ASM International. Source

Jalili M.,Sharif University of Technology
Physica A: Statistical Mechanics and its Applications | Year: 2013

In this paper we investigate the effects of social power on the evolution of opinions in model networks as well as in a number of real social networks. A continuous opinion formation model is considered and the analysis is performed through numerical simulation. Social power is given to a proportion of agents selected either randomly or based on their degrees. As artificial network structures, we consider scale-free networks constructed through preferential attachment and Watts-Strogatz networks. Numerical simulations show that scale-free networks with degree-based social power on the hub nodes have an optimal case where the largest number of the nodes reaches a consensus. However, given power to a random selection of nodes could not improve consensus properties. Introducing social power in Watts-Strogatz networks could not significantly change the consensus profile. © 2012 Elsevier B.V. All rights reserved. Source

Evazi M.,Sharif University of Technology | Mahani H.,Royal Dutch Shell
SPE Journal | Year: 2010

Reservoir flow simulation involves subdivision of the physical domain into a number of gridblocks. This is best accomplished with optimized gridpoint density and a minimized number of gridblocks, especially for coarse-grid generation from a fine-grid geological model. In any coarse-grid generation, proper distribution of gridpoints, which form the basis of numerical gridblocks, is a challenging task. We show that this can be achieved effectively by a novel grid-generation approach based on a background grid that stores gridpoint spacing parameters. Spacing parameter (L) can be described by Poisson's equation (▽2L = G), where the local density of gridpoints is controlled by a variable source term (G); see Eq. 1. This source term can be based on different gridpoint density indicators, such as permeability variations, fluid velocity, or their combination (e.g., vorticity) where they can be extracted from the reference fine grid. Once a background grid is generated, advancing-front triangulation (AFT) and then Delaunay tessellation are invoked to form the final (coarse) gridblocks. The algorithm produces grids varying smoothly from high- to low-density gridpoints, thus minimizing use of grid-smoothing and -optimization techniques. This algorithm is quite flexible, allowing choice of the gridding indicator, hence providing the possibility of comparing the grids generated with different indicators and selecting the best. In this paper, the capabilities of approach in generation of unstructured coarse grids from fine geological models are illustrated using 2D highly heterogeneous test cases. Flexibility of algorithm to gridding indicator is demonstrated using vorticity, permeability variation, and velocity. Quality of the coarse grids is evaluated by comparing their two-phase-flow simulation results to those of fine grid and uniform coarse grid. Results demonstrate the robustness and attractiveness of the approach, as well as relative quality/performance of grids generated by using different indicators. Copyright © 2010 Society of Petroleum Engineers. Source

Ghobadi A.F.,University of Akron | Taghikhani V.,Sharif University of Technology | Elliott J.R.,University of Akron
Journal of Physical Chemistry B | Year: 2011

The solubility of sulfur dioxide (SO2) and carbon dioxide (CO2) at P = 1 bar in a series of imidazolium-based room-temperature ionic liquids (RTILs) is calculated by Monte Carlo simulation in NPT ensemble using the OPLS-UA force field and Widom particle insertion method. The studied ILs were 1-butyl-3-methylimidazolium ([bmim]+) tetrafluoroborate ([BF4]-), [bmim]+ hexafluorophosphate ([PF 6]-), [bmim]+ bromide ([Br]-), [bmim]+ nitrate ([NO3]-), [bmim]+ bis-(trifluoromethyl) sulfonylimide ([Tf2N]-), and 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]). To validate the simulations, the liquid density of studied ILs and the solubility of CO2 in [bmim][PF6] was compared with corresponding experimental and theoretical studies reported in the literature, and a good agreement was obtained. The results of SO2 solubility demonstrate that the SO2 gas has the highest solubility in [bmim][NO3] and [bmim][Br] ILs and the lowest solubility in [bmim][PF6]. To describe the solubility order of polar gases such as SO2 and nonpolar gases like CO2, we have simulated the SO2/IL and CO 2/IL mixtures which made possible to investigate the interaction of solute molecules with anions and cations in the liquid phase. We introduced the ratio of solute - IL interaction over cation - anion interaction energy density as an index for solubility of gases in ILs. The results show that the proposed index can describe the solubility order of SO2 as well as CO 2 and it might be used as an alternative to standard methods of infinite dilution Henry's constant calculations when the solubility order is desired. © 2011 American Chemical Society. Source

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. Source

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

Although diffusive electrical connections in neuronal networks are instantaneous, excitatory/inhibitory couplings via chemical synapses encompass a transmission time-delay. In this paper neural networks with instantaneous electrical couplings and time-delayed excitatory/inhibitory chemical connections are considered and scaling of the spike phase synchronization with the unified time-delay in the network is investigated. The findings revealed that in both excitatory and inhibitory chemical connections, the phase synchronization could be enhanced by introducing time-delay. The role of the variability of the neuronal external current in the phase synchronization is also investigated. As individual neuron models, Hindmarsh-Rose model is adopted and the network structure of the electrical and chemical connections is considered to be Watts-Strogatz and directed random networks, respectively. © 2011 Elsevier B.V. Source

Rezaeezadeh A.,Sharif University of Technology
American Journal of Physics | Year: 2010

This paper introduces an experiment involving two identical small dipole magnets. One is hidden with arbitrary orientation in a black box. The second is suspended on a string above the box. By studying the horizontal and vertical oscillations of the suspended magnet, it is possible to determine the magnetic moment and the orientation of the hidden magnet, and the horizontal component of the Earth's magnetic field. © 2010 American Association of Physics Teachers. Source

Mohammadi A.,Sharif University of Technology
Journal of Non-Newtonian Fluid Mechanics | Year: 2016

Characterization of droplet-hydrogel interfaces is of crucial importance to engineer droplet-hydrogel composites for a variety of applications. In order to develop electrokinetic diagnostic tools for probing droplet-hydrogel interfaces, the displacement of a charged droplet embedded in a polyelectrolyte hydrogel exposed to an oscillating electric field is determined theoretically. The polyelectrolyte hydrogel is modeled as an incompressible, charged, porous, and elastic solid saturated with a salted Newtonian fluid. The droplet is considered an incompressible Newtonian fluid with no charges within the droplet. The droplet-hydrogel interface is modeled as a surface with the thickness of zero and the electrostatic potential ζ. The polymer is allowed to slide past the surface of the droplet, with the extent of the sliding quantified with the kinetic friction law, for which the tangential stress of the polymer is proportional to the relative velocity of the polymer and the droplet fluid. The standard regular perturbation method is used to obtain a leading-order solution in ζ-potential for the droplet harmonic displacement, neglecting inertial and temporal ion-concentration effects. It is found that the electrical response is modulated significantly by the polymer boundary condition at the droplet surface. At frequencies higher than a transitional frequency, the impact of the polymer boundary condition vanishes, and the response asymptotes to that with stick boundary condition for the polymer at the droplet surface. In addition, the oscillatory susceptibility of the droplet, defined as the ratio of the droplet displacement to the strength of an applied oscillatory non-electrical force, is determined theoretically; this theoretical study helps to evaluate the validity of the linear response theory used in interpretation of microrheological experiments done with droplets. It is observed that at frequencies less than the transitional frequency, the oscillatory susceptibility would indicate only slip boundary condition for the polymer at the inclusion surface unless the inclusion viscosity is infinity. © 2016 Elsevier B.V. Source

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¥ Source

Asoudeh M.,University of Tehran | Karimipour V.,Sharif University of Technology
Quantum Information Processing | Year: 2014

We show that networks of spin-1 particles connected in a special geometry and subject to Affleck-Kennedy-Lieb-Tasaki (AKLT) interaction are capable of perfectly transferring states of particles (qubits and qutrits) if we also allow a global control of the network in predetermined time intervals. The geometry can be one, two, and three dimensional. The strengths of the couplings have the same modulus, and only their signs differ on various bonds. Any particle which is routed in the network acquires relative phase shifts which can be corrected after it is extracted from the network. An advantage of this protocol is that one can route more than one particle through the network simultaneously. We show that a uniform magnetic fields do not deteriorate the fidelity and only change the relative phases in a controllable way. © 2013 Springer Science+Business Media New York. Source

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. Source

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. Source

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. Source

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. Source

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. Source

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. Source

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. Source

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. Source

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. Source

Asghari M.,Sharif University of Technology
International Journal of Solids and Structures | Year: 2010

In this paper, some basis-free expressions for the material time derivative of Lagrangian stress tensors are presented which are generally valid in all cases of coalescent principal stretches. The material is assumed to be elastic and isotropic. © 2009 Elsevier Ltd. All rights reserved. Source

Kiani K.,Sharif University of Technology
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2010

Single-walled carbon nanotubes (SWCNTs) can be promising delivery nanodevices for a diverse range of applications, however, little is known about their dynamical interactions with moving nanoscale particles. In this paper, dynamic response of a SWCNT subjected to a moving nanoparticle is examined in the framework of the nonlocal continuum theory of Eringen. The inertial effects of the moving nanoparticle and the existing friction between the nanoparticle surface and the inner surface of the SWCNT are incorporated in the formulation of the problem. The equivalent continuum structure associated with the SWCNT is considered and modeled using nonlocal Rayleigh beam theory under simply supported boundary conditions. The governing equations are then established both in the strong and weak forms. The set of linear equations are solved in the time domain using generalized Newmark-β method. The effects of mass weight of the moving nanoparticle, its velocity, and small scale effect parameter on the dynamic amplitude factors of longitudinal and transverse displacements as well as those of axial force and bending moment are studied in some detail. Additionally, the possibility of moving nanoparticle separation from the inner surface of the SWCNT is investigated. The role of influential parameters on the possibility of this phenomenon is also addressed and discussed. © 2010 Elsevier B.V. Source

Rahvar S.,Sharif University of Technology
Monthly Notices of the Royal Astronomical Society | Year: 2016

Gravitational microlensing has been used as a powerful tool for astrophysical studies and exoplanet detections. In the gravitational microlensing, we have two images with negative and positive parities. The negative-parity image is a fainter image and is produced at a closer angular separation with respect to the lens star. In the case of a red-giant lens star and large impact parameter of lensing, this image can be eclipsed by the lens star. The result would be dimming the flux receiving from the combination of the source and the lens stars and the light curve resembles to an eclipsing binary system. In this work, we introduce this phenomenon and propose an observational procedure for detecting this eclipse. The follow-up microlensing telescopes with lucky imaging camera or space-based telescopes can produce high-resolution images from the events with reddish sources and confirm the possibility of blending due to the lens star. After conforming a red-giant lens star and source star, we can use the advance photometric methods and detect the relative flux change during the eclipse in the order of 10-4-10-3. Observation of the eclipse provides the angular size of source star in the unit of Einstein angle and combination of this observation with the parallax observation enable us to calculate the mass of lens star. Finally, we analysed seven microlensing event and show the feasibility of observation of this effect in future observations. © 2016 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Mahdi Barakchian S.,Sharif University of Technology
Journal of Forecasting | Year: 2012

Do long-run equilibrium relations suggested by economic theory help to improve the forecasting performance of a cointegrated vector error correction model (VECM)? In this paper we try to answer this question in the context of a two-country model developed for the Canadian and US economies. We compare the forecasting performance of the exactly identified cointegrated VECMs to the performance of the over-identified VECMs with the long-run theory restrictions imposed. We allow for model uncertainty and conduct this comparison for every possible combination of the cointegration ranks of the Canadian and US models. We show that the over-identified structural cointegrated models generally outperform the exactly identified models in forecasting Canadian macroeconomic variables. We also show that the pooled forecasts generated from the over-identified models beat most of the individual exactly identified and over-identified models as well as the VARs in levels and in differences. Copyright © 2011 John Wiley & Sons, Ltd. Source

Mirmohammadi H.S.,Isfahan University of Technology | Eshghi K.,Sharif University of Technology
Computers and Operations Research | Year: 2012

We propose an efficient optimal algorithm for determining the lot sizes for purchase component in Material Requirement Planning (MRP) environments with deterministic time-phased demand and zero lead time. In this model, backlog is not permitted, the unit purchasing price is based on the all-units discount system with single price break point and resale of the excess units is acceptable at the ordering time. The problem is divided into the sub-plans with specific properties by the dynamic programming (DP) method already presented. By modifying the main structure of the DP method, we present a branch-and-bound algorithm to obtain the optimal ordering policy for each sub-plans. Furthermore, we prove some useful fathoming rules to make the branch-and-bound algorithm very efficient. It has also been shown that the worst-case time complexity function of the presented algorithm is O(N4) where N is the number of periods in the planning horizon. Finally, we show the efficiency of the presented algorithm and its fathoming rules by solving some test problems which are randomly generated in various environments. © 2011 Elsevier Ltd. All rights reserved. Source

Khorasani S.,Sharif University of Technology
Solid-State Electronics | Year: 2016

We present an explicit solution of carrier and field distributions in abrupt PN junctions under equilibrium. An accurate logarithmic numerical method is implemented and results are compared to the analytical solutions. Analysis of results shows reasonable agreement with numerical solution as well as the depletion layer approximation. We discuss extensions to the asymmetric junctions. Approximate relations for differential capacitance C-V and current-voltage I-V characteristics are also found under non-zero external bias. © 2016 Elsevier Ltd. All rights reserved. Source

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. Source

Ahmadizadeh M.,Sharif University of Technology
Computers and Structures | Year: 2013

An effective iterative method is proposed for three-dimensional large-displacement analysis of structures consisting of slack cables as the primary load-bearing system. This approach takes advantage of substructuring technique that is specially tailored to address the analysis and form-finding problem of slack cables subjected to arbitrary loads, and to reduce the overall analysis costs. At the overall structural level, a robust procedure is employed for detecting the instabilities and limiting the corresponding incremental displacements. The effectiveness of the proposed method for the analysis of highly unstable or variable-form structures is demonstrated by a number of analysis examples of slack cable systems. © 2013 Elsevier Ltd. All rights reserved. Source

Hoseini P.,Urmia University | Shayesteh M.G.,Urmia University | Shayesteh M.G.,Sharif University of Technology
Digital Signal Processing: A Review Journal | Year: 2013

In this paper, we propose a hybrid algorithm including Genetic Algorithm (GA), Ant Colony Optimisation (ACO), and Simulated Annealing (SA) metaheuristics for increasing the contrast of images. In this way, contrast enhancement is obtained by global transformation of the input intensities. Ant colony optimisation is used to generate the transfer functions which map the input intensities to the output intensities. Simulated annealing as a local search method is utilised to modify the transfer functions generated by ant colony optimisation. And genetic algorithm has the responsibility of evolutionary process of antsE characteristics. The employed fitness function operates automatically and tends to provide a balance between contrast and naturalness of images. The results indicate that the new method achieves images with higher contrast than the previously presented methods from the subjective and objective viewpoints. Further, the proposed algorithm preserves the natural look of input images. © 2012 Elsevier Inc. Source

Suresh K.,University of Wisconsin - Madison | Takalloozadeh M.,Sharif University of Technology
Structural and Multidisciplinary Optimization | Year: 2013

The objective of this paper is to introduce and demonstrate an algorithm for stress-constrained topology optimization. The algorithm relies on tracking a level-set defined via the topological derivative. The primary advantages of the proposed method are: (1) the stresses are well-defined at all points within the evolving topology, (2) the finite-element stiffness matrices are well-conditioned, making the analysis robust and efficient, (3) the level-set is tracked through a simple iterative process, and (4) the stress constraint is precisely satisfied at termination. The proposed algorithm is illustrated through numerical experiments in 2D and 3D. © 2013 Springer-Verlag Berlin Heidelberg. Source

Darbandi M.,Sharif University of Technology | Roohi E.,Ferdowsi University of Mashhad
International Journal for Numerical Methods in Fluids | Year: 2013

We extend a hybrid DSMC/Navier-Stokes (NS) approach to unify the DSMC and the NS simulators in one framework capable of solving the mixed non-equilibrium and near-equilibrium flow regions efficiently. Furthermore, we use a one-way state-based coupling (Dirichlet-Dirichlet boundary-condition coupling) to transfer the required information from the continuum region to the rarefied one. The current hybrid DSMC-NS frame is applied to the hypersonic flows over nanoflat plate and microcylinder cases. The achieved solutions are compared with the pure DSMC and NS solutions. The results show that the current hybrid approach predicts the surface heat transfer rate and shear stress magnitudes very accurately. Some important conclusions can be drawn from this study. For example, although the shock wave region would be a non-equilibrium region, it is not necessary to use a pure DSMC simulator to solve it entirely. This is important when the researchers wish to predict the surface properties such as velocity slip, temperature jump, wall heat flux rate, and friction drag magnitudes accurately. Our investigation showed that our hybrid solution time would be at least 40% (for the flat plate) and 35% (for the cylinder) of the time that must be spent by a pure DSMC solver to attain the same accuracy. © 2013 John Wiley & Sons, Ltd. Source

Abdzadeh-Ziabari H.,Urmia University | Shayesteh M.G.,Sharif University of Technology
IEEE Transactions on Vehicular Technology | Year: 2013

This paper addresses the problem of frame detection in orthogonal frequency-division multiplexing (OFDM) systems. Using fourth-order statistics, a novel approach is presented for detection of a preamble composed of two identical parts in the time domain. First, it is demonstrated that sufficient statistics for detection of a periodic preamble do not exist, and conventional methods are not optimal. Next, looking at the detection of a preamble from the viewpoints of hypothesis testing and classification, a new method is presented based on the idea that fourth-order statistics can increase class separability (between-class distance) and consequently improve detection performance. It is proven that the proposed method has a considerably lower probability of false alarm. Along with the missed-detection performance comparisons, it will be presented that the new scheme offers a superior detection performance and makes threshold selection significantly easier. © 1967-2012 IEEE. Source

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. Source

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. Source

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. Source

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. Source

Fathi Rasekh M.,Sharif University of Technology
Structural Chemistry | Year: 2012

The geometries of the complexes of Be 2+, Mg 2+, and Ca 2+ metal cations with borazine ring were studied. The complexes were optimized at the B3LYP level and the 6-311++G(d,p) basis set. Then, the interaction energies corrected by basis set super position error were calculated in the same level. The results show that interaction energy is strongly dependent on the charge-to-size ratio of the cation. Therefore, Be 2+ cation has the most interaction energy value with respect to Mg 2+ and Ca 2+ metal cations. Natural bond orbital analysis was performed to calculate the charge transfer and natural population analysis of the complexes. Quantum theory of atoms in molecules was also applied to analyze the properties of the bond critical points (CPs) (electron densities and their Laplacians) involved in the coordination between borazine ring and the metal cations. There are also some important correlations between the interaction energies, the electron densities (ρ(r)), and the Laplacian of the densities (∇ 2ρ(r)) in (3, +3) CPs with the equilibrium distance from cation to the geometric center of the ring (R e). Finally, nucleus-independent chemical shift method is also used for calculation of aromaticity values of borazine ring and its complexes. © 2012 Springer Science+Business Media, LLC. Source

Nasiri-Gheidari Z.,Sharif University of Technology | Lesani H.,University of Tehran
IEEE Transactions on Energy Conversion | Year: 2013

-In this paper, a new optimized structure for two-speed, capacitor-run, single-phase axial flux induction motor (AFIM) for direct-drive operation is presented. Although, there are many advantages for direct-drive systems, their axial forces between the stator and rotor increases with reduction in air-gap length and is of serious concern. An increase in the air-gap length will result in the deterioration of performance characteristics of the motor. In this paper, a new construction technique is proposed to fabricate an AFIM with adjustable air-gap length. After presenting a comprehensive design algorithm, all geometrical dimensions and electrical equivalent circuit parameters are analytically calculated. Then, a multiobjective and multivariable optimization for a high efficiency and power factor with minimum usage of core materials is carried out. Optimization process is verified using three-dimensional, time-stepping finite-element analyses, and finally, the prototype of the optimal motor is fabricated and tested. Good agreements between analytic, finite element, and experimental results show the success of the proposed design. © 1986-2012 IEEE. Source

Jalili M.,Sharif University of Technology
IEEE Transactions on Neural Networks and Learning Systems | Year: 2013

In this paper, we review the literature on enhancing synchronizability of diffusively coupled dynamical networks with identical nodes. The last decade has witnessed intensive investigations on the collective behavior over complex networks and synchronization of dynamical systems is the most common form of collective behavior. For many applications, it is desired that the synchronizability - the ability of networks in synchronizing activity of their individual dynamical units - is enhanced. There are a number of methods for improving the synchronization properties of dynamical networks through structural perturbation. In this paper, we survey such methods including adding/removing nodes and/or edges, rewiring the links, and graph weighting. These methods often try to enhance the synchronizability through minimizing the eigenratio of the Laplacian matrix of the connection graph - a synchronizability measure based on the master-stability-function formalism. We also assess the performance of the methods by numerical simulations on a number of real-world networks as well as those generated through models such as preferential attachment, Watts-Strogatz, and Erds-Rényi. © 2012 IEEE. Source

Abdi M.,Sharif University of Technology | Abdi M.,University of Camerino | Pirandola S.,University of York | Tombesi P.,University of Camerino | Vitali D.,University of Camerino
Physical Review Letters | Year: 2012

We propose a protocol for entanglement swapping which involves tripartite systems. The generation of remote entanglement induced by the Bell measurement can be easily certified by additional local measurements. We illustrate the protocol in the case of continuous variable systems where the certification is effective for an appropriate class of three-mode Gaussian states. We then apply the protocol to optomechanical systems, showing how mechanical entanglement between two remote micromechanical resonators can be generated and certified via local optical measurements. © 2012 American Physical Society. Source

Shoaei E.,Sharif University of Technology
Solar Energy Materials and Solar Cells | Year: 2016

The potential for using Thermophotovoltaic (TPV) generators as an alternative for recovering energy losses in steel production industry is assessed. A mathematical model for the assessment of the performance of TPV application in the iron and steel industry has been developed. In order to support the mathematical model, a sample TPV apparatus in laboratory scale based on an IR emitter has been designed and assembled. The key modeling parameters of TPV generator include: the open circuit voltage, the short circuit current density and fill factor of the TPV cell. These parameters have been considered in the model as functions of several variables such as: the emitter (hot steel slab) temperature, the cell temperature, the distance between the cells and emitter, the spectral response and the cell energy gap. The External Quantum Efficiency (EQE) as an important indicator of the cell's spectral response is included in the model. Moreover, the variation of the emitter temperature has been considered. Several tests have been carried out for different values of the cell-emitter gap. It has been found that when the GaSb cells are used for energy recovery, a minimum temperature of 873 °C is required. The upper limit of the emitter temperature is usually determined in steel production process associated with hot rolling process which has a temperature around 1250 °C. Finally, the total efficiency of the system was obtained to 4.12%, when GaSb cell with temperature of 27 °C and slab emitters with temperature of 1257 °C are used. The results of the simulation of the model in a casting process at the Mobarakeh Steel Complex have shown a potential of energy recovery of 26.987 MJ per year. © 2016 Elsevier B.V. All rights reserved. Source

Ebrahimi M.,Sharif University of Technology
Journal of Magnetism and Magnetic Materials | Year: 2016

In self-controlling hyperthermia therapy, once the desired temperature is reached, the heat generation ceases and overheating is prevented. In order to design a system that generates sufficient heat without thermal ablation of surrounding healthy tissue, a good understanding of temperature distribution and its change with time is imperative. This study is conducted to extend our understanding about the heat generation and transfer, temperature distribution and temperature rise pattern in the tumor and surrounding tissue during self-controlling magnetic hyperthermia. A model consisting of two concentric spheres that represents the tumor and its surrounding tissue is considered and temperature change pattern and temperature distribution in tumor and surrounding tissue are studied. After describing the model and its governing equations and constants precisely, a typical numerical solution of the model is presented. Then it is showed that how different parameters like Curie temperature of nanoparticles, magnetic field amplitude and nanoparticles concentration can affect the temperature change pattern during self-controlling magnetic hyperthermia. The model system herein discussed can be useful to gain insight on the self-controlling magnetic hyperthermia while applied to cancer treatment in real scenario and can be useful for treatment strategy determination. © 2016 Elsevier B.V. All rights reserved. Source

Barzanjeh S.,University of Camerino | Abdi M.,University of Camerino | Abdi M.,Sharif University of Technology | Milburn G.J.,University of Queensland | And 2 more authors.
Physical Review Letters | Year: 2012

We describe a reversible quantum interface between an optical and a microwave field using a hybrid device based on their common interaction with a micromechanical resonator in a superconducting circuit. We show that, by employing state-of-the-art optoelectromechanical devices, one can realize an effective source of (bright) two-mode squeezing with an optical idler (signal) and a microwave signal, which can be used for high-fidelity transfer of quantum states between optical and microwave fields by means of continuous variable teleportation. © 2012 American Physical Society. Source

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. Source

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. Source

Tavazoei M.S.,Sharif University of Technology
IEEE Transactions on Circuits and Systems I: Regular Papers | Year: 2015

In this note, it is shown that some of the results reported in the above titled paper on the behavior analysis of a fractional order system are not consistent with reality. To support this claim, theoretical justifications and numerical results are presented. Also, it is analytically explained that why such inconsistencies have been occurred in the aforementioned paper. © 2004-2012 IEEE. Source

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. Source

Jalali M.A.,Sharif University of Technology
Astrophysical Journal | Year: 2013

We use the Fokker-Planck equation and model the dispersive dynamics of solid particles in annular protoplanetary disks whose gas component is more massive than the particle phase. We model particle-gas interactions as hard sphere collisions, determine the functional form of diffusion coefficients, and show the existence of two global unstable modes in the particle phase. These modes have spiral patterns with the azimuthal wavenumber m = 1 and rotate slowly. We show that in ring-shaped disks, the phase-space density of solid particles increases linearly in time toward an accumulation point near the location of pressure maximum, while instabilities grow exponentially. Therefore, planetesimals and planetary cores can be efficiently produced near the peaks of unstable density waves. In this mechanism, particles migrating toward the accumulation point will not participate in the formation of planets, and should eventually form a debris ring like the main asteroid belt or classical Kuiper Belt objects. We present the implications of global instabilities to the formation of ice giants and terrestrial planets in the solar system. © 2013. The American Astronomical Society. All rights reserved.. Source

Kargarian M.,University of Texas at Austin | Langari A.,Sharif University of Technology | Langari A.,Max Planck Institute For Physik Komplexer Systeme | Fiete G.A.,University of Texas at Austin
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

The expected phenomenology of noninteracting topological band insulators (TBIs) is now largely theoretically understood. However, the fate of TBIs in the presence of interactions remains an active area of research with novel, interaction-driven topological states possible, as well as new exotic magnetic states. In this work we study the magnetic phases of an exchange Hamiltonian arising in the strong interaction limit of a Hubbard model on the honeycomb lattice whose noninteracting limit is a two-dimensional TBI recently proposed for the layered heavy transition metal oxide compound (Li,Na) 2IrO 3. By a combination of analytical methods and exact diagonalization studies on finite-size clusters, we map out the magnetic phase diagram of the model. We find that strong spin-orbit coupling can lead to a phase transition from an antiferromagnetic Neél state to a spiral or stripy ordered state. We also discuss the conditions under which a quantum spin liquid may appear in our model, and we compare our results with the different but related Kitaev-Heisenberg-J 2-J 3 model which has recently been studied in a similar context. © 2012 American Physical Society. Source

Golnabi H.,Sharif University of Technology
Optics and Lasers in Engineering | Year: 2012

Design and operation of three different optical designs based on the light intensity modulation for investigation of the humidity effects on the air index of refraction are described. The measurement variable is the transmitted power, which depends on the refractive index of the medium in the path of a fiber-to-fiber optical design. Three different probes (probe #1, #2, and #3) are tested in which probe #1 and probe #2 can also check the presence of water or any other transparent liquid in the gap between the two axial fibers. Performances of the new systems are tested as a refractive index monitoring mean and experimental results are given. The variations of the modulated powers as functions of the air humidity change in the light path are determined for the reported optical designs. For probe #1 for a power variation of 255-315 nW, the relative humidity changes from 32% to 41%. For probe #2 for 5 mm gap distance, for a power change of 2470-2754 nW, the relative humidity changes from 54.95% to 90.39%. For probe #3 for the 10 mm fiber gap, a power change 929.5-972.9 nW is noted for the relative humidity change of 33.0-76.75%. Power variations as a function of the axial fiber gap distances are also given and the optimum condition for the highest sensitivity is obtained. Probe #3 shows a higher sensitivity compared to probe #1 and it is superior to probe #2 because it operates in a fog-free condition. Finally, the calibration curve for each probe is given that can be used for the operation of the probe as a humidity sensor. © 2012 Elsevier Ltd. Source

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. Source

Ebrahimi R.,Islamic Azad University at Tehran | Ehsan M.,Sharif University of Technology | Nouri H.,University of the West of England
International Journal of Electrical Power and Energy Systems | Year: 2013

This paper proposes a new algorithm to determine the best connection of multiple distributed generations (DGs) on distribution networks according to type of customers. The considered DG technology is combined heat and power (CHP) in various sizes which can be extended to other technologies. Different types of demand, such as industrial, residential and commercial are defined by the load model that is voltage dependent and the load patterns from real life hourly demand data. This method which is based on multi-year multi-period power flow is useful for Distribution Network Operators (DNOs) when they are faced with voltage dependent load models in their networks. However it can be used in constant load models with multi-period or single demand. The proposed optimization is from the DNO's perspective and aims to maximize their present value of profit against the supplying costs of the network. It is shown that by definition of an appreciated economic based objective function, the customer type can significantly affect the optimal DG options in distribution network planning. Finally, this method is tested using the 69-bus radial system. Furthermore, a comparative study for different customer demand types is shown for various cases and results are discussed in this paper. © 2012 Elsevier Ltd. All rights reserved. Source

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. Source

Rajabi M.,Alzahra University | Dariani R.S.,Alzahra University | Iraji Zad A.,Sharif University of Technology
Sensors and Actuators, A: Physical | Year: 2012

Here, the UV photodetection of ZnO rods grown on porous silicon substrates are reported. Laterally interconnected ZnO rods have been synthesized by chemical vapor transport and condensation method on porous silicon substrates. As characterized by current-voltage measurements the I-V characteristics have linear behavior, indicating space charge effect. The device exhibits photocurrent response of 0.027 A/W for 325 nm UV light under -5 V bias. The rise and decay time constants under these conditions are 19 and 62 s, respectively. © 2012 Elsevier B.V. All rights reserved. Source

Shojaie E.,Kerman Graduate University of Technology | Mirzaei A.,Kerman Graduate University of Technology | Bahrampour A.,Sharif University of Technology
Optics Letters | Year: 2014

The present study demonstrates numerically a novel approach to perform a controllable single-mode random laser, using stimulated Raman gain. Due to the narrow linewidth of the Raman line shape, only one of the modes of the passive random system can lase. The robust control on the emission spectrum was achieved through the selection of any desired quasi-modes, by adjusting the pump wavelength in order to place the center of Raman line shape on desired quasi-modes. This approach was proved using a developed nonlinear transfer matrix method for a 1D Raman random system. The proposed method includes the Raman gain saturation and the frequency-dependent index of refraction. © 2014 Optical Society of America. Source

Saidi M.H.,Sharif University of Technology
Journal of Heat Transfer | Year: 2012

The present study considers both the hydrodynamic and thermal characteristics of combined electroosmotic and pressure driven flow in a microannulus. Analytical solutions are presented using the Debye-Hückel linearization along with the uniform Joule heating and negligible viscous dissipation assumptions, whereas exact results are achieved numerically. Here, the range of validity for the Debye-Hückel linearization is found to be about two times of that for a parallel plate microchannel. Accordingly, this linearization may successfully be used to evaluate the potential and velocity distributions up to the zeta potentials of 100 mV, provided that the dimensionless Debye-Hückel parameter is above 10; nevertheless, the calculated wall shear stresses may be significantly different from the exact ones, even for lower zeta potentials. The viscous heating effects are found to be limited to low values of the dimensionless Debye-Hückel parameter. These effects are pronounced in the presence of a favorable pressure gradient, whereas the opposite is true for an opposed pressure gradient. Furthermore, the influence of increasing the annular geometry parameter, that is the inner to outer radii ratio, generally is to decrease both the inner and outer Nusselt numbers. It is also revealed that the pressure effects vanish at higher values of this parameter. © 2012 American Society of Mechanical Engineers. Source

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. Source

A new method for the evaluation of separation quality in hyphenated chromatographic measurements based on the information-theoretic concept of mutual information (MI) is developed. The MI values for the purest spectra selected using the simple-to-use interactive self-modeling mixture analysis (SIMPLISMA) and orthogonal projection approach (OPA) methods are calculated according to the differential information entropy (Shannon entropy). To calculate the MI values for more than two variables, the Kozachenko-Leonenko (KL) estimation of the Shannon entropy is used. The MI values of the purest spectra can reliably reflect the degree of peak overlap in the chromatographic direction. Herein, the developed method is employed on different simulated and real GC-MS and HPLC-DAD datasets (i.e., chromatographic segments and chromatographic fingerprints) to evaluate the potential of this new method. Inspection of the results showed that minimization of MI values is a good criterion for comprehensive evaluation of separation quality in hyphenated chromatographic measurements and to reach to the best chromatographic separation. Additionally, the performance of this method is compared with the previously developed overlap index (OVI) criterion and classical univariate criteria, such as ΣRs and ΠRs, which showed an improvement in all cases. As demonstrated by simulated and real chromatographic data, the MI index gives not only a comprehensive criterion for evaluation of separation quality, but also provides reliable information for the purity assessment of compounds of interest. Furthermore, the MI index can be used as a reliable criterion for multivariate optimization of hyphenated chromatographic measurements. © the Partner Organisations 2014. Source

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. Source

Movaghar A.,Sharif University of Technology
Queueing Systems | Year: 2011

Consider a number of parallel queues, each with an arbitrary capacity and multiple identical exponential servers. The service discipline in each queue is first-come-first-served (FCFS). Customers arrive according to a state-dependent Poisson process. Upon arrival, a customer joins a queue according to a state-dependent policy or leaves the system immediately if it is full. No jockeying among queues is allowed. An incoming customer to a parallel queue has a general patience time dependent on that queue after which he/she must depart from the system immediately. Parallel queues are of two types: type 1, wherein the impatience mechanism acts on the waiting time; or type 2, a single server queue wherein the impatience acts on the sojourn time. We prove a key result, namely, that the state process of the system in the long run converges in distribution to a well-defined Markov process. Closed-form solutions for the probability density function of the virtual waiting time of a queue of type 1 or the offered sojourn time of a queue of type 2 in a given state are derived which are, interestingly, found to depend only on the local state of the queue. The efficacy of the approach is illustrated by some numerical examples. © 2011 Springer Science+Business Media, LLC. Source

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. Source

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. Source

Hajian-Hoseinabadi H.,Sharif University of Technology
IEEE Transactions on Power Delivery | Year: 2013

This study aims at quantitatively assessing the availability indices of various substation automation systems. In order to illustrate the proposed technique, first, nine types of substation automation architectures are reviewed. The reliability block diagrams of various substation automation architectures are then developed. Subsequently, comparative studies are performed to demonstrate the most reliable architectures in comparison with the others. The results obtained by the proposed approach show the impact of repair on availability indices of the automation system. Finally, different sensitivity analyses are conducted for all architectures, where the impact of varying availability of all components on reliability indices of the automation system is illustrated. © 1986-2012 IEEE. Source

Akhavan O.,Sharif University of Technology
Carbon | Year: 2010

Graphene thin films with very low concentration of oxygen-containing functional groups were produced by reduction of graphene oxide nanosheets (prepared by using a chemical exfoliation) in a reducing environment and using two different heat treatment procedures (called one and two-step heat treatment procedures). The effects of heat treatment procedure and temperature on thickness variation of graphene platelets and also on reduction of the oxygen-containing functional groups of the graphene oxide nanosheets were studied by atomic force microscopy and X-ray photoelectron spectroscopy. While formation of the thin films composed of single-layer graphene nanosheets with minimum thickness of 0.37 nm and nearly without any functional group bonds was observed at the high temperature of 1000 °C in the one-step reducing procedure, similar high quality graphene thin films were obtained at the lower temperature of 500 °C in our two-step reducing temperature. The results also indicated possibility of efficient reduction of the graphene oxide thin films at even lower heat treatment temperatures (≤500 °C). © 2009 Elsevier Ltd. All rights reserved. Source

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. Source

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. Source

Shavandi H.,Sharif University of Technology | Bozorgi B.,University of Tabriz
International Journal of Advanced Manufacturing Technology | Year: 2012

Nowadays, location of distribution centers integrated with inventory or transportation decision play an important role in optimizing supply chain management. Location-inventory models analyze the location and inventory policies in distribution network, simultaneously. Developing location-inventory models under fuzzy environment can enrich the model, and this is our approach in this article. We consider the demand as a fuzzy variable and formulate the problem using credibility theory in order to locate distribution centers (DCs) as well as determining inventory levels in DCs. The derived model belongs to nonlinear mixed integer programming problems, and we presented a genetic algorithm to solve it. Numerical results show that the performance of the proposed algorithm is reasonable. © 2012 Springer-Verlag London Limited. Source

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. Source

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. Source

Tavazoei M.S.,Sharif University of Technology
IEEE Transactions on Fuzzy Systems | Year: 2012

In this letter, it is shown that some of the equalities that were used in the proof of the main theorem of the paper given by Lin and Lee are not consistent with fractional calculus principles. Simple counterexamples are provided to confirm this point. Moreover, correct versions of equations that were derived in the mentioned theorem are presented. Based on these corrections, the synchronization scheme proposed in the mentioned paper is investigated. © 2012 IEEE. Source

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. Source

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. Source

Mohammadi M.R.,Sharif University of Technology | Fray D.J.,University of Cambridge
Particuology | Year: 2011

Perovskite-type barium strontium titanate (BST) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol-gel route at room temperature. The prepared sol had a narrow particle size distribution of about 20 nm. X-ray diffraction (XRD) revealed that phase composition and preferable orientation growth of BST depended upon the annealing temperature. Transmission electron microscope (TEM) images showed that the crystallite size of the powders decreased with increasing annealing temperature from 8 nm at 25 °C down to 5 nm at 800 °C. Field emission scanning electron microscope (FE-SEM) analysis and atomic force microscope (AFM) images revealed that BST thin films had mesoporous and nanocrystalline structure with average grain size of 30 nm at 600 °C. Based on Brunauer-Emmett-Teller (BET) analysis, the synthesized BST showed mesoporous structure containing pores with needle and plate shapes and BET surface area in the range of 49-32 m2/g at 500-800 °C. © 2011 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved. Source

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. Source

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. Source

Ramezani S.,Kharazmi University | Ghobadi M.,Ilam University | Bideh B.N.,Sharif University of Technology
Sensors and Actuators, B: Chemical | Year: 2014

The objective of the work ahead is presentation of a new carbon paste electrode (CPE) modified by TiO2 nanoparticles (TiO2NPs) and 1,2-bis-[o-aminophenyl thio] ethane (APTE) ligand as a selective cation receptor for determination of the Cd (II) ions using differential pulse anodic stripping voltammetry (DPASV). The electrode shows an excellent tendency to Cd (II) ions in presence of some interfering species. Under the optimum conditions, a linear calibration curve was obtained in the concentration range of 2.9 nM to 4.6 μM with a correlation coefficient of 0.9969 in the anodic potential of 0.54 (V vs. Ag/AgCl). The metal detection limit was 2.0 nM after 10 min preconcentration (S/N = 3). The sensor shows high applicability in solutions with the optimal pH of 9.0 adjusted by 0.1 M phosphate buffer as supporting electrolyte and open circuit accumulation optimum time of 10 min. The stability of the modified electrode was studied in the period of 2 months week by week. The results showed that for a series of several determinations of Cd (II) at 25 μM relative standard deviations (RSDs) are below 3.4% for modified CPEs. Eventually, the electrode was successfully used for determination of Cd (II) in tap water, Livergol herbal medicine and garden soil aqueous samples. © 2013 Elsevier B.V. Source

Tavakoli R.,Sharif University of Technology
International Journal of Advanced Manufacturing Technology | Year: 2014

The goal of the present study is to predict the formation of solidification induced defects in castings by thermal criteria functions. In a criterion function method, the heat transfer equation is firstly solved, and then the susceptibility of defect formation at every point in the casting is predicted by computing a local function, criterion function, using results of the thermal analysis. In the first part of the paper, some famous criteria functions, in particular, the Pellini and Niyama criteria, are analyzed and their shortcomings are discussed in details. Then, a new criterion function is suggested to decrease the shape-dependency issue of the former criteria. The feasibility of the new method is studied by comparing numerical results against some archived experimental data. © 2014 Springer-Verlag London. Source

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. Source

Ebrahimi H.P.,University of Wisconsin - Madison | Tafazzoli M.,Sharif University of Technology
Concepts in Magnetic Resonance Part A: Bridging Education and Research | Year: 2012

An extensive GIAO (gauge-including atomic orbital) calculation has been made within Hartree-Fock (HF), density functional theory (DFT) and second-order Møller-Plesset perturbation theory (MP2), in conjunction with selected basis sets for the prediction of 19F chemical shift values of 26 different F nuclei in small fluorine-containing molecules. The effect of four factors, namely, electron correlation treatment, triple-ξ valence shell, diffuse function and polarization function were assessed using a systematic comparison of the results. Based on types of series, the optimized wave functions were proposed for different molecules. An additional comparison of the principal components of the shift tensor has been used as a supplementary study to confirm the validity of the results. For the series of molecules studied, the diffuse function is the most effective factor used in this applied model and the presence of polarization function is important to minimize the difference between theoretical and experimental values. By including the electron correlation treatment, DFT approach with large basis sets provides the most reliable results. In addition, two 2 4 factorial designs were considered to assess the reliability of applied scheme for selection the most efficient basis function and the results were discussed in this procedure. © 2012 Wiley Periodicals, Inc. Source

Fallah Nezhad M.S.,University of Yazd | Akhavan Niaki S.T.,Sharif University of Technology
Information Sciences | Year: 2010

In this research, an iterative approach is employed to analyze and classify the states of uni-variate quality control systems. To do this, a measure (called the belief that process is in-control) is first defined and then an equation is developed to update the belief recursively by taking new observations on the quality characteristic under consideration. Finally, the upper and the lower control limits on the belief are derived such that when the updated belief falls outside the control limits an out-of-control alarm is received. In order to understand the proposed methodology and to evaluate its performance, some numerical examples are provided by means of simulation. In these examples, the in and out-of-control average run lengths (ARL) of the proposed method are compared to the corresponding ARL's of the optimal EWMA, Shewhart EWMA, GEWMA, GLR, and CUSUM [11] methods within different scenarios of the process mean shifts. The simulation results show that the proposed methodology performs better than other charts for all of the examined shift scenarios. In addition, for an autocorrelated AR(1) process, the performance of the proposed control chart compared to the other existing residual-based control charts turns out to be promising. © 2009 Elsevier Inc. All rights reserved. Source

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. Source

Mohammadi A.,Sharif University of Technology
Transport in Porous Media | Year: 2014

Mixing in droplets is an essential task in a variety of microfluidic systems. Inspired by electrokinetic mixing, electric field-induced hydrodynamic flow inside a charged droplet embedded in an unbounded polyelectrolyte hydrogel is investigated theoretically. In this study, the polyelectrolyte hydrogel is modeled as a soft, and electrically charged porous solid saturated with a salted Newtonian fluid, and the droplet is considered an incompressible Newtonian fluid. The droplet-hydrogel interface is modeled as a surface, which is located at the plane of shear, with the electrostatic potential ζ. The fluid inside the droplet attains a finite velocity owing to hydrodynamic coupling with the electroosmotic flow arising from the droplet and polymer charge. The fluid velocity inside the droplet is linearly proportional to the electroosmotic flow velocity in the charged gel and the electroosmotic flow velocity beyond the electrical double layer of a charged interface. It is found that the polymer boundary condition at the droplet surface and the viscosities of the fluids inside and outside the droplet significantly modulate the interior fluid flow. The ionic strength and the permeability of the polymer network impact the flow differently depending on whether the flow arises from the droplet or polymer charge. Finally, the displacement of a charged droplet embedded in a gel under the influence of an external electric field is undertaken. This work is motivated by experimental attempts, which can register sub-nanometer-scale inclusion displacements in hydrogels, to advance electrical microrheology as a diagnostic tool for probing inclusion-hydrogel interfaces. In the absence of polymer charge, a close connection is found between the electrical response of a charged droplet when it is immobilized in an uncharged incompressible gel and when it is dispersed in a Newtonian electrolyte. © 2014 Springer Science+Business Media Dordrecht. Source

Rabbani A.,Petroleum University of Technology of Iran | Jamshidi S.,Sharif University of Technology
International Journal of Rock Mechanics and Mining Sciences | Year: 2014

Porosity and specific surface are two prominent factors in describing the hydraulic properties of porous media. Determination of these two important parameters leads to identify the capability of porous media to conduct the fluids. In the present study, a new relationship between porosity and specific surface of sandstones has been developed. Micro-CT data from 10 types of sandstones has been utilized in order to present a porosity-specific surface correlation. This correlation also contains the average grain radius of each rock obtained by image processing algorithms. Finally, the correlation is tested on the provided data to evaluate its precision. The simplicity and applicability of the presented relationship can be attended to modify the Carman-Kozeny equation for sandstones. © 2014 Elsevier Ltd. Source

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. Source

Ashiri R.,Islamic Azad University at Dezful | Nemati A.,Sharif University of Technology | Sasani Ghamsari M.,Solid State Group
Ceramics International | Year: 2014

In this report, crack-free nanostructured barium titanate thin films are prepared by a sol-gel processing method. Glacial acetic acid, barium acetate, titanium tetraisopropyl alkoxide, 2-propanol and deionized water are used as precursors for preparing stable precursor solution. Then very thin films (thickness=26 nm) are deposited on fused silica substrates. In order to prepare crack-free thin films of BaTiO3, much attention is given to solvent evaporation process and a controlled pre-drying process is developed. It is found that the control of the process, especially in the initial stage of drying process is crucial and important for preparation of the crack-free ultrathin nanostructured BaTiO3 films. In our proposed method, as-deposited thin films undergo a slow drying process in saturated vapor pressure of the precursor solution. The above process leads to the formation of crack-free nanostructured BaTiO3 thin films. Structure and morphology of the thin films are characterized by XRD, SEM and AFM characterization methods. Results indicate that the thin films are crack-free with a dense nanogranular structure. © 2014 Elsevier Ltd and Techna Group S.r.l. Source

Azadi M.,Sharif University of Technology | Azadi M.,Iran Khodro 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. Source

Beygi M.H.A.,Babol Noshirvani University of Technology | Kazemi M.T.,Sharif University of Technology | Nikbin I.M.,Babol Noshirvani University of Technology | Amiri J.V.,Babol Noshirvani University of Technology
Materials and Design | Year: 2013

The paper describes an experimental research on fracture characteristics of self-compacting concrete (SCC). Three point bending tests conducted on 154 notched beams with different water to cement (w/c) ratios. The specimens were made from mixes with various w/c ratios from 0.7 to 0.35. For all mixes, common fracture parameters were determined using two different methods, the work-of-fracture method (WFM) and the size effect method (SEM). Test results showed that with decrease of w/c ratio from 0.7 to 0.35 in SCC: (a) the fracture toughness increases linearly: (b) the brittleness number is approximately doubled: (c) the effective size of the process zone cf in SEM and the characteristic length (lch) in WFM decrease which may be explained by the change in structural porosity of the aggregate-paste transition zone; and (d) the fracture surface of concrete is roughly smoother, which can be attributed to the improved bond strength between the aggregates and the paste. Also, the results showed that there is a correlation between the fracture energy measured by WFM (GF) and the value measured through SEM (Gf) (GF≅2.92Gf). © 2013 Elsevier Ltd. Source

In this paper, we investigated phase synchronization in delayed dynamical networks. Non-identical spiking Hindmarsh-Rose neurons were considered as individual dynamical systems and coupled through a number of network structures such as scale-free, Erdos-Rényi, and modular. The individual neurons were coupled through excitatory chemical synapses with uniform or distributed time delays. The profile of spike phase synchrony was different when the delay was uniform across the edges as compared to the case when it was distributed, i.e., different delays for the edges. When an identical transmission delay was considered, a quasi-periodic pattern was observed in the spike phase synchrony. There were specific values of delay where the phase synchronization reached to its peaks. The behavior of the phase synchronization in the networks with non-uniform delays was different with the former case, where the phase synchrony decreased as distributed delays introduced to the networks. © 2013 American Institute of Physics. Source

Hassanzadeh F.,University of North Carolina at Greensboro | Collan M.,Lappeenranta University of Technology | Modarres M.,Sharif University of Technology
IEEE Transactions on Fuzzy Systems | Year: 2012

The objective of this research is to develop a practical research and development (R&D) portfolio selection model that addresses the effective R&D project valuation issue, while tackling R&D uncertainty in portfolio optimization. Fuzzy set theory is employed to capture and model the uncertain project information. To evade the well-known complexities of fuzzy real option valuation, the recently developed fuzzy pay-off method is used to more effectively valuate R&D projects. The resulting problem is formulated as a fuzzy zero-one integer programming model that handles uncertainty of input data in order to determine the optimal portfolio. Two satisfaction measures, which are based on possibility and necessity theory, are employed to solve the resulting fuzzy model. An example is presented to compare these measures, as well as to illustrate the simplicity and applicability of the proposed approach. © 1993-2012 IEEE. Source

Safaei A.S.,Tarbiat Modares University | Kazemzadeh R.B.,Tarbiat Modares University | Niaki S.T.A.,Sharif University of Technology
International Journal of Advanced Manufacturing Technology | Year: 2012

Shewhart charts are the most popular control charts that can be used to monitor variable quality characteristics in a production process. In this paper, a multi-objective model of the economic statistical design of the X-bar control chart is first proposed by incorporating the Taguchi loss function and the intangible external costs. The model minimizes the mean hourly loss cost while minimizing out-of-control average run length and maintaining reasonable in-control average run length. A multiobjective evolutionary algorithm, namely NSGA-II, is then developed and used to obtain the Pareto optimal solution of the model. Some sensitivity analyses are next performed to investigate the effect of parameter estimation on the chart performances. Finally, a comparison study with a traditional economic design model reveals that the proposed multiple objective design of the X-bar control chart offers a better approach and more practical outcomes for the practitioners. © Springer-Verlag London Limited 2011. Source

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. Source

Salehi S.,Petroleum University of Technology of Iran | Shahrokhi M.,Sharif University of Technology
International Journal of Systems Science | Year: 2012

In this article, design of an adaptive control scheme for a class of uncertain single-input single-output systems in strict feedback form via a backstepping technique has been proposed. It is assumed that system output and its derivatives are available. By virtue of the observability concept, it is shown that for this class of systems there exists a one-to-one map, which maps output and its derivatives to system states. By means of this mapping and using linearly parametrised approximators, such as fuzzy logic systems or neural networks, the uncertain nonlinear dynamics and unavailable states are estimated. The proposed adaptive controller guarantees that the closed-loop system is uniformly ultimately bounded and the influence of minimum approximation error on the L 2-norm of the output tracking error is attenuated arbitrarily. The effectiveness of the proposed scheme has been demonstrated through simulation results. © 2011 Copyright Taylor and Francis Group, LLC. Source

Amini A.,Sharif University of Technology | Unser M.,Ecole Polytechnique Federale de Lausanne
IEEE Transactions on Information Theory | Year: 2014

We adopt an innovation-driven framework and investigate the sparse/compressible distributions obtained by linearly measuring or expanding continuous-domain stochastic models. Starting from the first principles, we show that all such distributions are necessarily infinitely divisible. This property is satisfied by many distributions used in statistical learning, such as Gaussian, Laplace, and a wide range of fat-tailed distributions, such as student's-t and α-stable laws. However, it excludes some popular distributions used in compressed sensing, such as the Bernoulli-Gaussian distribution and distributions, that decay like exp (-O(|x|p)) for 1 < p < 2. We further explore the implications of infinite divisibility on distributions and conclude that tail decay and unimodality are preserved by all linear functionals of the same continuous-domain process. We explain how these results help in distinguishing suitable variational techniques for statistically solving inverse problems like denoising. © 2014 IEEE. Source

Hajirasouliha I.,University of Nottingham | Asadi P.,Sharif University of Technology | Pilakoutas K.,University of Sheffield
Earthquake Engineering and Structural Dynamics | Year: 2012

In this paper, a practical method is developed for performance-based design of RC structures subjected to seismic excitations. More efficient design is obtained by redistributing material from strong to weak parts of a structure until a state of uniform deformation or damage prevails. By applying the design algorithm on 5, 10 and 15-storey RC frames, the efficiency of the proposed method is initially demonstrated for specific synthetic and real seismic excitations. The results indicate that, for similar structural weight, designed structures experience up to 30% less global damage compared with code-based design frames. The method is then developed to consider multiple performance objectives and deal with seismic design of RC structures for a design spectrum. The results show that the proposed method is very efficient at controlling performance parameters and improving structural behaviour of RC frames. © 2011 John Wiley & Sons, Ltd. Source

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. Source

Tavakoli R.,Sharif University of Technology
Computer Methods in Applied Mechanics and Engineering | Year: 2014

A new computational algorithm is introduced in the present study to solve multimaterial topology optimization problems. It is based on the penalization of the objective functional by the multiphase volume constrained Ginzburg-Landau energy functional. The update procedure is based on the gradient flow of the objective functional by a fractional step projected steepest descent method. In the first step, the new design is found based on the projected steepest descent method to ensure the reduction in the objective functional, simultaneously satisfying the control constraints. In the second step, regularization step, an H1 regularity of the solution is ensured while keeping the feasibility of solution with respect to the set of control constraints. The presented algorithm could be accounted as a constrained H1 optimization algorithm, which, according to our knowledge, has not been reported to solve such kind of problems yet. The success and efficiency of the presented method are shown through several test problems. Numerical results show that the presented algorithm ends with a near 0-1 topology and its computational cost scales sub-linearly by the number of phases. For the sake of reader convenience and the ease of further extension, the MATLAB implementation of the presented algorithm is included in the appendix. © 2014 Elsevier B.V. Source

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. Source

Sepehri M.,Sharif University of Technology
Enterprise Information Systems | Year: 2012

A collaborative supply chain seeks to coordinate its members to produce and distribute products along the chain for minimum overall costs to satisfy customer demand. An integrated multi-period, multi-product and multi-stage supply chain model is developed. A collaborative supply chain grid (CSCG) system gathers necessary information on operations and resources from members of the supply chain. It then guides the members on ordering decisions for a minimum overall cost, while continuously re-directing them as new data becomes available. An actual CSCG system has been implemented in a collaborative auto industry with diverse and dynamic membership, yielding an approximately 26% reduction in total supply chain costs. © 2012 Taylor and Francis Group, LLC. Source

Maleki E.,Sharif University of Technology
Materials Today: Proceedings | Year: 2016

Severe plastic deformation methods such as severe shot peening are used in order to improve mechanical properties of the components by surface microstructure nanocrystallization. Severe shot peening is one of the popular mechanical surface treatments generally aimed at generating nanograined layer and compressive residual stress close to the surface. Moreover, artificial neural network has been used as an efficient approach to predict and optimize the engineering problems. In present study effects of conventional and severe shot peening on cast iron were modelled by means of artificial neural networks and they were compared. The obtained results indicate that severe shot peening has superior effects on improvement of materials mechanical and metallurgical properties than conventional shot peening. Back propagation error algorithm and data of experimental tests on nodular cast ironwith ferrite-pearlite matrix were employed to train networks. Neural network testing was carried out using different experimental data which they were not used during networks training. In present paper distance from the surface is regarded as an input parameter and microhardness, residual stress and full width at half maximum are gathered as output parameters. The predicted values for full width at half maximum, microhardness and residual stress have the least statistical errors, respectively. The results demonstrate that there is a reasonable and applicable agreement among the experimental and predicted values, illustrating that the developed neural network can be employed to model the conventional and severe shot peening processes. © 2016 Elsevier Ltd. Source

Tavakkoli M.M.,Sharif University of Technology | Abbasi S.M.,University of Tehran
Materials and Design | Year: 2013

In this paper, the effect of molybdenum on the grain boundary segregation of other elements was studied in Incoloy 901 superalloy. Initially, five alloys were prepared with different percentages of Mo by using a vacuum induction furnace. Then, these alloys were remelted by Electro-slag remelting (ESR) process and after homogenizing at 1160 °C for 2. h followed by air cooling, were rolled. The effect of Mo on segregation of elements was evaluated with Scanning Electron Microscopy, Linear Analysis, and the mechanical tests. The results showed that the grain boundary segregations of elements in Incoloy 901 superalloy were decreased by increasing of molybdenum content up to 6.7% and the mechanical properties (tensile and hardness properties) were improved. Also, the segregations of elements were increased by increasing the percentage of Mo from 6.7 to 7.5, and the mechanical properties were reduced. © 2012 Elsevier Ltd. Source

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. Source

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. Source

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. Source

Solhjoo S.,Sharif University of Technology
Computational Materials Science | Year: 2010

Friction plays an important role in metal forming operations. Therefore, many techniques are developed for evaluation of friction in large deformation processes. Among them the "Barrel Compression Test" (BCT) is a very simple method that quantitatively evaluates the constant friction factor, m, simply by compressing a cylindrical specimen. BCT was analyzed by Avitzur [B. Avitzur, Metal Forming Processes and Analysis, McGraw-Hill, 1968] using the upper bound theory. Ebrahimi et al. [R. Ebrahimi, A. Najafizadeh, J. Mater. Process. Technol. 152 (2004) 136-143] suggested a method in order to make Avitzur's mathematical results applicable. However, they made an assumption in their work which results in some miscalculations. In this note their mathematical analysis is corrected and also the method is modified. © 2010 Elsevier B.V. All rights reserved. Source

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. Source

Tavazoei M.S.,Sharif University of Technology
IEEE Transactions on Circuits and Systems II: Express Briefs | Year: 2011

This paper investigates the step responses of fractional order systems in the viewpoint of extrema existence in such responses. It is proven that a fractional order system with a commensurate order between zero and one has an extrema-free step response if its integer counterpart has such a step response. In addition, it is shown that the step response of a stable fractional order system with a commensurate order between one and two cannot be monotonic. Based on these achievements, some further results on the step response of different classes of fractional order systems are presented. © 2011 IEEE. Source

Azadi M.,Sharif University of Technology
Journal of Mechanical Science and Technology | Year: 2011

This paper presents a finite element method (FEM) free and forced lateral vibration analysis of beams made of functionally graded materials (FGMs). The temperature dependency of material properties along with damping had not previously been taken into account in vibration analysis. In the present study, the material properties were assumed to be temperature-dependent, and were graded in the thickness direction according to a simple power law distribution of the volume fractions of the constituents. The natural frequencies were obtained for functionally graded (FG) beams with various boundary conditions. First, an FG beam was assumed to be isotropic (metal rich) and the results were compared with the analytical solution and the results for ANSYS and NASTRAN software. Finally, dynamic responses were obtained for damped and un-damped systems. Numerical results were obtained to show the influences of the temperature dependency of the materials properties, the boundary conditions, the volume fraction distribution (the index of power law, N) and the geometrical parameters. © 2011 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg. Source

Jalilia M.,RMIT University | Jalilia M.,Sharif University of Technology
NeuroReport | Year: 2014

Electroencephalography (EEG)-based functional brain networks have been investigated frequently in health and disease. It has been shown that a number of graph theory metrics are disrupted in brain disorders. EEG-based brain networks are often studied in the whole-brain framework, where all the nodes are grouped into a single network. In this study, we studied the brain networks in two hemispheres and assessed whether there are any hemispheric-specific patterns in the properties of the networks. To this end, resting state closed-eyes EEGs from 44 healthy individuals were processed and the network structures were extracted separately for each hemisphere. We examined neurophysiologically meaningful graph theory metrics: global and local efficiency measures. The global efficiency did not show any hemispheric asymmetry, whereas the local connectivity showed rightward asymmetry for a range of intermediate density values for the constructed networks. Furthermore, the age of the participants showed significant direct correlations with the global efficiency of the left hemisphere, but only in the right hemisphere, with local connectivity. These results suggest that only local connectivity of EEG-based functional networks is associated with brain hemispheres. NeuroReport 25:1266-1271 © 2014 Wolters Kluwer Health - Lippincott Williams & Wilkins. Source

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. Source

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. Source

An unconditionally energy stable time stepping scheme is introduced to solve Cahn-Morral-like equations in the present study. It is constructed based on the combination of David Eyre's time stepping scheme and Schur complement approach. Although the presented method is general and independent of the choice of homogeneous free energy density function term, logarithmic and polynomial energy functions are specifically considered in this paper. The method is applied to study the spinodal decomposition in multi-component systems and optimal space tiling problems. A penalization strategy is developed, in the case of later problem, to avoid trivial solutions. Extensive numerical experiments demonstrate the success and performance of the presented method. According to the numerical results, the method is convergent and energy stable, independent of the choice of time stepsize. Its MATLAB implementation is included in the appendix for the numerical evaluation of algorithm and reproduction of the presented results. © 2015 Elsevier Inc. Source

Sepehri M.,Sharif University of Technology
Scientia Iranica | Year: 2011

Cooperation among supply chain members, both horizontally and vertically, has become the norm in practice. Unlike traditional supply chains with members competing to reduce their individual costs, the overall cost of the entire supply chain is minimized in a cooperative supply chain. The savings from cooperation may be shared among the members, while a lower average cost and a lower cost variation is materialized for individual members. The problem is formulated as an integrated flow network and expanded to multi-period and multi-product, with the possibility of holding inventories in a multi-stage, multi-member cooperative supply chain. Simulation results indicate an approximately 26% reduction in total costs of the supply chain, utilizing this formulation over competitive setups. In a multiperiod chain, members may hold an inventory or use an inventory policy. As the holding costs increase, the problem decomposes into a single period (just-in-time) again. The disturbing bullwhip effect disappears in cooperative supply chains. © 2011 Sharif University of Technology. Production and hosting by Elsevier B.V. All rights reserved. Source

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. Source

Tavazoei M.S.,Sharif University of Technology
Journal of Computational and Nonlinear Dynamics | Year: 2011

This paper deals with the problem of stabilizing the unstable fixed points of a class of fractional-order chaotic systems via using static output feedback. At first, a static output feedback controller designed to stabilize a fixed point of a fractional-order chaotic system is considered. Then, the maximal allowable perturbation bound around the nominal value of the output feedback gain of the designed controller, such that the stability of the intended fixed point in the closed-loop system is guaranteed, is analytically determined. Also, some numerical examples are presented to confirm the validity of the analytical results of the paper. © 2011 American Society of Mechanical Engineers. Source

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. Source

Moosavi A.,Sharif University of Technology
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

Mesoscopic hydrodynamic equations are solved to investigate coarsening dynamics of two interacting nanodroplets on chemically patterned substrates. The effects of different parameters such as the surface chemical pattern, the slip length, the profile of the disjoining pressure, the size of the droplets, and the contact angles on the coarsening are studied. Our results reveal that the presence of a chemical heterogeneity can enhance or weaken the coarsening dynamics depending on the pattern type and positions of the droplets on the substrate. Also increasing the contact angles to values larger than a critical value may qualitatively change the coarsening process, and the profile of the disjoining pressure and the slippage can appreciably modify the coarsening rate. © 2012 American Physical Society. Source

Tavazoei M.S.,Sharif University of Technology
Journal of Process Control | Year: 2010

Integral performance indices as quantitative measures of the performance of a system are commonly used to evaluate the performance of designed control systems. In this paper, it is pointed out that due to existence of non-exponential modes in the step response of a fractional-order control system having zero steady state error, integral performance indices of such a system may be infinite. According to this point, some simple conditions are derived to guarantee the finiteness of different integral performance indices in a class of fractional-order control systems. Finally, some numerical examples are presented to show the applicability of the analytical achievements of the paper. © 2009 Elsevier Ltd. All rights reserved. Source

Merrikh-Bayat F.,University of Zanjan | Karimi-Ghartemani M.,Sharif University of Technology
IET Control Theory and Applications | Year: 2010

This paper deals with the problem of designing the PI λDμ-type controllers for minimum-phase fractional systems of rational order. In such systems, the powers of the Laplace variable, s, are limited to rational numbers. Unlike many existing methods that use numerical optimisation algorithms, the proposed method is base