Tehran, Iran
Tehran, Iran

The University of Tehran , also known as Tehran University and UT, is Iran's oldest modern university. Based on its historical, socio-cultural and political pedigree, as well as its research and teaching profile, UT has been nicknamed "The mother university of Iran" . It is almost always ranked as the best university in Iran in national and international rankings. It is also the premier knowledge producing institute among all OIC countries. The university offers 111 bachelor degree programs, 177 masters' degree programs, and 156 Ph.D. programs. Many of the departments were absorbed into the University of Tehran from the Dar al-Funun established in 1851 and the Tehran School of Political science established in 1899.The University of Tehran is known as the symbol of higher education in Iran. The main campus of the University is located in the central part of the city. However, other campuses are spread across the city as well as in the suburbs such as the Baghe Negarestan Campus at the central eastern part of the city, the Northern Amirabad Campuses at the central western part of the city and the Abureyhan Campus in the suburb of the capital. The main gate of the University with its specific design and modern architecture is the logo of the University and in a more general sense, a logo of education in Iran. The University is one of the city’s attractions, hosting many international and cultural events attracting academia, foreign tourists as well as local residents. The major festive of Friday Prayers of the capital is held at the University’s main campus every Friday.Admission to the university's renowned undergraduate and graduate programs is very competitive and is limited to the top one percent of students who pass the national entrance examination administered yearly by the Ministry of Science, Research and Technology. Tehran University consistently makes the number one choice of qualifying applicants among all other universities of Iran. Wikipedia.

Time filter

Source Type

Shokri A.,University of Tehran | Bozorg Haddad O.,University of Tehran | Marino M.A.,University of California at Davis
Water Resources Management | Year: 2014

Damage caused by entered pollution in reservoirs can affect a water resource system in two ways: (1) Damages that are caused due to consumption of polluted water and (2) damages that are caused due to insufficient water allocation. Those damages conflict with each other. Thus, the crisis should be managed in a way that the least damage occurs in the water resource system. This paper investigates crisis management due to the sudden entrance of a 30 m3 methyl tert-butyl ether (MTBE) load to the Karaj dam in Iran, which supplies municipal water to the cities of Tehran and Karaj. To simulate MTBE advection, dispersion, and vaporization, the latter process is added to the CE-QUAL-W2 model. After that, the multi-objective NSGAII-ALANN algorithm, which is a combination of the NSGAII optimization method along with a multi layer perceptron (MLP), which is one of the most widely used artificial neural network (ANN) structures, is employed to extract the best set of decisions in which the two aforementioned damages are minimized. By assigning a specific importance to each objective function, after extracting the optimal solutions, it is possible to choose one of the solutions with the least damage. Four scenarios of entering pollution to the Karaj reservoir the first day of each season are considered, resulting in a Pareto set of operation policies for each scenario. Results of the proposed methodology indicate that if the pollution enters the reservoir in summer, by using one of the optimal policies extracted from the Pareto set of the 2nd Scenario, by a 36 % reduction in meeting the demand, allocated pollution decreases to about 60 %. In other seasons, there is a significant decrease in allocated pollution with a smaller reduction in the met demand. © 2014 Springer Science+Business Media Dordrecht.

Fallah-Mehdipour E.,University of Tehran | Bozorg Haddad O.,University of Tehran | Marino M.A.,University of California at Davis
Water Resources Management | Year: 2012

Reservoir operation policy depends on specific values of deterministic variables and predictable actions as well as stochastic variables, in which small differences affect water release and reservoir operation efficiency. Operational rule curves of reservoir are policies which relate water release to the deterministic and stochastic variables such as storage volume and inflow. To operate a reservoir system in real time, a prediction model may be coupled with rule curves to estimate inflow as a stochastic variable. Inappropriate selection of this prediction model increases calculations and impacts the reservoir operation efficiency. Thus, extraction of an operational policy simultaneously with inflow prediction helps the operator to make an appropriate decision to calculate how much water to release from the reservoir without employing a prediction model. This paper addresses the use of genetic programming (GP) to develop a reservoir operation policy simultaneously with inflow prediction. To determine a water release policy, two operational rule curves are considered in each period by using (1) inflow and storage volume at the beginning of each period and (2) inflow of the 1 st, 2 nd, 12 th previous periods and storage volume at the beginning of each period. The obtained objective functions of those rules have only 4.86 and 0.44 % difference in the training and testing data sets. These results indicate that the proposed rule based on deterministic variables is effective in determining optimal rule curves simultaneously with inflow prediction for reservoirs. © 2012 Springer Science+Business Media B.V.

Hamedi J.,University of Tehran | Mohammadipanah F.,University of Tehran | Ventosa A.,University of Seville
Extremophiles | Year: 2013

More than 70 species of halotolerant and halophilic actinomycetes belonging to at least 24 genera have been validly described. Halophilic actinomycetes are a less explored source of actinomycetes for discovery of novel bioactive secondary metabolites. Degradation of aliphatic and aromatic organic compounds, detoxification of pollutants, production of new enzymes and other metabolites such as antibiotics, compatible solutes and polymers are other potential industrial applications of halophilic and halotolerant actinomycetes. Especially new bioactive secondary metabolites that are derived from only a small fraction of the investigated halophilic actinomycetes, mainly from marine habitats, have revealed the huge capacity of this physiological group in production of new bioactive chemical entities. Combined high metabolic capacities of actinomycetes and unique features related to extremophilic nature of the halophilic actinomycetes have conferred on them an influential role for future biotechnological applications. © 2012 Springer Japan.

GharibNezhad E.,University of Tehran | Shayesteh A.,University of Tehran | Bernath P.F.,Old Dominion University
Monthly Notices of the Royal Astronomical Society | Year: 2013

Einstein A coefficients have been calculated for rovibronic lines of the A2π →X2σ+ and B'2σ+ →X2σ+ transitions of 24MgH. Using the experimentally determined analytic potential energy curve for the X 2σ+state, and the Rydberg-Klein-Rees potentials for the A2π and B'2σ+states, combined with the most recent ab initio transition dipole moments, rovibronic transition moments were computed. The rovibronic transition frequencies were obtained accurately by subtracting the published term values of the X 2σ+, A2π and B'2σ+ states. Using the rovibronic transition dipole moments, transition frequencies and the Hönl-London factors, the Einstein A coefficients were calculated individually for ~30 000 rovibronic lines of the A2π→X2σ+ and B'2σ+ →X2σ+ transitions of 24MgH. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Zeinoddini M.,University of Tehran | Parke G.A.R.,University of Surrey
International Journal of Damage Mechanics | Year: 2011

This article reports some interesting observations on the response of laterally impacted steel tubes, which in some respects have been considered to undergo an elastic shakedown. In an experimental study on the behavior of axially compressed tubes under lateral impacts, it has been noticed that after full development of plastic deformations in the impacted bodies, the structural system ceases to exhibit additional plastic responses. The impacted tubes then exhibit an elastic behavior. It has also been observed that the amplitude of the elastic excitations in the specimens becomes more restricted as the load configuration moves close to a dynamic failure state. With load conditions quite close to the dynamic failure limit, almost no elastic excitation has been perceived from the impacted specimens. Additional numerical and analytical investigations have been carried out on impacted tubes, frames, and nonlinear single-degree of freedom systems and similar results have been obtained. Despite the noncyclic nature of the external loads in these impact cases, a phenomenon similar to elastic shakedown has been observed. © The Author(s), 2011.

Ahmadi M.,University of Tehran | Bozorg Haddad O.,University of Tehran | Marino M.A.,University of California at Davis
Water Resources Management | Year: 2014

To extract optimal reservoir operation policies, it is important to consider different objectives simultaneously. In this study, by applying a meta-heuristic, multi-objective optimization approach, real-time optimal operation rules of Karoon4 dam are extracted as two-objectives by considering performance criteria of the reservoir as objective functions. The rules are extracted by relating water release to storage volume and inflow with simple linear equations for two states of real-time operation, which are called dependent on forecast state and independent of forecast state. In the dependent on forecast state, inflow volume is considered during the current period and in the independent of forecast state, inflow volume is considered during the period before the operation. In fact, by associating water release in each period to inflow during a past period, inflow forecasting is employed. Multi-objective optimization results of conflicting objectives of reliability and vulnerability in hydropower generation of Karoon4 are exhibited as a Pareto curve by employing the non-dominated sorting genetic algorithm II (NSGA-II). Each point on the Pareto curve represents an optimal operation policy. Actually, based on the priority and desired criterion of the reservoir operator, for the value of any criterion, the optimal value of another criterion and its optimal operation policy can be extracted by using a Pareto curve. Maximum reliabilities of Pareto curves in first and second states of real-time operation are 60.83 and 60.00 %, respectively, with corresponding minimum vulnerabilities of 8.52 and 9.08 %. Although the dependence of reservoir release in each period to inflow during the previous period (i.e., independent of forecast state) improves the values of objective functions compared with the dependent on forecast state, the difference is insignificant. Since the independent of forecast state of real-time operation does not depend on inflow forecasting, the small difference is negligible and so this state seems more efficient. Also, a comparison of results of long-term operation with real-time operation shows that bcomputed real-time operation rules are flexible and accurate. © 2013 Springer Science+Business Media Dordrecht.

Fallah-Mehdipour E.,University of Tehran | Bozorg Haddad O.,University of Tehran | Marino M.A.,University of California at Davis
Journal of Irrigation and Drainage Engineering | Year: 2013

Multicropping is the practice of growing two or more crops in the same space during a single growing season. Planning rules are mathematical equations that use previous experiences of a water resource system to balance the system's water supply and demand, and calculate multicrop areas in various periods. In this paper, linear and nonlinear planning rules are developed for optimal multicrop irrigation areas associated with reservoir operation policies in a reservoir-irrigation system. Reservoir operations are related to water allocations to each irrigated area by considering inflow and storage volume of the reservoir as the water supply in a monthly operation period. Evolutionary algorithms (EAs) can determine optimal multicropping patterns planning rules by considering various mathematical patterns. In this paper, three EAs, namely, (1) genetic algorithm (GA), (2) particle swarm optimization (PSO), and (3) shuffled frog leaping algorithm (SFLA) are employed and compared to maximize the total net benefit of the water resource system by supplying irrigation water for a proposed multicropping pattern over the planning horizon. Results show that the SFLA achieves the best solution, with the maximum value of the objective function in both linear and nonlinear planning rules compared to the GA and PSO. Moreover, the best yield of nonlinear rules is 45.52% better (higher) than that obtained by linear rules. © 2013 American Society of Civil Engineers.

Fallah-Mehdipour E.,University of Tehran | Bozorg Haddad O.,University of Tehran | Marino M.A.,University of California at Davis
Journal of Hydroinformatics | Year: 2013

The reservoir operational decision rule is an equation that can balance reservoir system parameters in each period by considering previous experiences of the system. That equation includes variables such as inflow, volume storage and released water from the reservoir that are commonly related to each other by some constant coefficients in predefined linear and nonlinear patterns. Although optimization tools have been extensively applied to develop an optimal operational decision rule, only optimal constant coefficients have been derived and the operational patterns are assumed to be fixed in that operational rule curve. Genetic programming (GP) is an evolutionary algorithm (EA), based on genetic algorithm (GA), which is capable of calculating an operational rule curve by considering optimal operational undefined patterns. In this paper, GP is used to extract optimal operational decision rules in two case studies by meeting downstream water demands and hydropower energy generation. The extracted rules are compared with common linear and nonlinear decision rules, LDR and NLDR, determined by a software package for interactive general optimization (LINGO) and GA. The GP rule improves the objective functions in the training and testing data sets by 2.48 and 8.53%, respectively, compared to the best rule by LINGO and GA in supplying downstream demand. Similarly, the hydropower energy generation improves by 48.03 and 44.21% in the training and testing data sets, respectively. Results show that the obtained objective function value is enhanced significantly for both the training and testing data using GP. They also indicate that the proposed rule, based on GP, is effective in determining optimal rule curves for reservoirs. © IWA Publishing 2013.

Keihan A.H.,Baqiyatallah Medical Sciences University | Keihan A.H.,University of Tehran | Sajjadi S.,Islamic Azad University at Roudehen
Electrochimica Acta | Year: 2013

This paper reports the greatly improved electrochemical properties of Prussian blue/carbon nanotubes (PB/CNTs) modified glassy carbon electrode via a room temperature ionic liquid (RTIL) treatment. Firstly, the GC electrodes were modified with nanocomposites of RTIL/CNTs. Then, the PB nanoparticles were electrodeposited onto the modified electrode surface. Compared with the PB/CNTs/GC, the PB/RTIL/CNTs/GC electrodes showed higher PB surface concentration value of 2.42 × 10-9 mol cm-2, indicating that PB deposition efficiency was improved by 1.8 fold. The apparent diffusion coefficient for K+ displayed value of 5.77 × 10 -11 cm2 s-1, which was one order of magnitude higher than that in the absence of RTIL. PB/RTIL/CNTs/GC modified electrodes showed higher electron transfer rate of 2.44 s-1 (2.35 times as much as that of PB/CNTs/GC electrodes). RTIL modified electrodes also displayed high sensitivity toward H2O2 reduction (185.90 μA mM -1 cm-2) with low detection limit of 0.49 μM. The RTIL modified electrodes stored dry at room temperature preserved almost 100% of their initial currents over a period of 1 month, a useful property for commercial applications. © 2013 Elsevier Ltd.

Govindan K.,University of Southern Denmark | Jafarian A.,University of Tehran | Khodaverdi R.,University of Tehran | Devika K.,University of Aalborg
International Journal of Production Economics | Year: 2014

Increasing environmental, legislative, and social concerns are forcing companies to take a fresh view of the impact of supply chain operations on environment and society when designing a sustainable supply chain. A challenging task in today's food industry is distributing high quality perishable foods throughout the food supply chain. This paper proposes a multi-objective optimization model by integrating sustainability in decision-making, on distribution in a perishable food supply chain network (SCN). It introduces a two-echelon location-routing problem with time-windows (2E-LRPTW) for sustainable SCN design and optimizing economical and environmental objectives in a perishable food SCN. The goal of 2E-LRPTW is to determine the number and location facilities and to optimize the amount of products delivered to lower stages and routes at each level. It also aims to reduce costs caused by carbon footprint and greenhouse gas emissions throughout the network. The proposed method includes a novel multi-objective hybrid approach called MHPV, a hybrid of two known multi-objective algorithms: namely, multi-objective particle swarm optimization (MOPSO) and adapted multi-objective variable neighborhood search (AMOVNS). MHPV features two strategies for leader selection procedures (LSP), (i.e. Grids) and crowding distance is compared to common genetic algorithms based on metaheuristics (i.e. MOGA, NRGA and NSGA-II). Results indicate that the hybrid approach achieves better solutions compared to others, and that crowding distance method for LSP outperforms the former Grids method. © 2013 Elsevier B.V.

Nasiri-Gheidari Z.,University of Tehran | Tootoonchian F.,Iran University of Science and Technology
Energy Conversion and Management | Year: 2010

In this paper a novel optimization algorithm based on imperialist competitive algorithm (ICA) is used for the design of a low speed single sided linear induction motor (LIM). This type of motors is used increasingly in industrial process specially in transportation systems. In these applications having high efficiency with high power factor is very important. So in this paper the objective function of design is presented considering both efficiency and power factor. Finally the results of ICA are compared with the ones of genetic algorithm and conventional design. Comparison shows the success of ICA for design of LIMs. © 2010 Elsevier Ltd.

Bakhtiarizadeh M.R.,University of Tehran | Moradi-Shahrbabak M.,University of Tehran | Ebrahimie E.,University of Adelaide
Gene | Year: 2013

The objective of this study was to gain insight into the underlying mechanisms of fat deposition. Two sheep breeds with large fat-tail (Lori-Bakhtiari) and with thin-tail (Zel) were used as models. To determine important and key candidate lipid metabolism related genes, comparative genomic approaches were employed. Gene expression profiles of adipose tissues were analyzed in human, pig, and cattle by express sequence tag (EST) analysis. EST analysis determined 65, 102 and 125 transcripts in human, pig and cattle respectively with at least 10 fold over-expression in the adipose tissue. Based on our comparative functional genomic analysis, seven genes were more abundant and common in investigated mammalian adipose tissues promising a conserved novel gene network in mammalian lipid metabolism. The candidate genes including fatty acid binding protein 4 (FABP4), fatty acid synthase (FASN), Stearoyl-CoA desaturase (SCD) and Lipoprotein lipase (LPL) were selected for further gene expression investigation within two sheep breeds. The real time PCR results showed that among the genes tested, FABP4 was expressed at higher levels than the others. The expression of FABP4 was significantly higher in the fat-tail of Lori-Bakhtiari than in the fat-tail and visceral adipose tissues of Zel (P < 0.05). The findings suggest that the FABP4 gene expression in the fat-tail is an important index of fat deposition. © 2013 Elsevier B.V.

Aslan N.,Cumhuriyet University | Shahrivar A.A.,Shahid Bahonar University of Kerman | Abdollahi H.,University of Tehran
Separation and Purification Technology | Year: 2012

This paper presents a novel effective method for the optimization of some operating parameters of a laboratory scale thickener on the dewatering performance with multiple performance characteristics based on the grey relational analysis (GRA). Lab-scale thickener operation parameters including feed flowrate, solid percent, flocculant dosage and feedwell height were optimized based on multiple performance characteristics. Sixteen experiments were conducted using GRA to optimize the parameters for lab-scale thickener parameters to generate two quality characteristics (the underflow solid percent and bed height of thickener). Analysis of the grey relational grade indicates that parameter significance and the optimal parameter combination for the lab-scale thickener are identified. The analytical results from two confirmation experiments using the optimal process parameters confirm that the above performance characteristics in dewatering of tailing can be improved effectively through this approach. © 2012 Elsevier B.V. All rights reserved.

Amin S.H.,University of Windsor | Razmi J.,University of Tehran | Zhang G.,University of Windsor
Expert Systems with Applications | Year: 2011

Supplier selection is a multi criteria decision-making problem that comprises tangible and intangible factors. The majority of previous supplier selection techniques do not consider strategic perspective. Besides, uncertainty is one of the most important obstacles in supplier selection. In this paper, quantified SWOT is applied in the context of supplier selection for the first time. SWOT (Strengths, Weaknesses, Opportunities and Threats) is one of the most well-known techniques for conducting a strategic study. In addition, the fuzzy logic and triangular fuzzy numbers are integrated with SWOT analysis - as a novel innovation - to deal with vagueness of human thought. SWOT analysis can consider both qualitative and quantitative criteria. The managers can understand the position of suppliers in a competitive environment with a glance at SWOT matrix. Moreover, a fuzzy linear programming model is proposed to determine how much should be purchased from each supplier. It is supposed that the demand is a fuzzy number. Besides, the capacity of warehouse is considered as a constraint. A case study is utilized concurrently to show the efficiency of the proposed model. © 2010 Elsevier Ltd. All rights reserved.

Zangeneh A.,Islamic Azad University at Damavand | Rahimi-Kian A.,University of Tehran
Energy | Year: 2011

To determine the optimal size, location and also the proper technology of distributed generation (DG) units in distribution systems, a static fuzzy multiobjective model is proposed in this paper. The proposed model can concurrently optimize a number of conflicting and competing objective functions including economic, technical and environmental attributes. The economic function is the profit of a distribution company (DisCo) from selling the DG output power to its customers. The contribution of this model is the consideration of some DG marginal revenues in the economic function. Inclusion of marginal revenues would not only reduce the investment risks of DG technologies, but also would enable the optimal penetration of DG units. The proposed DG planning framework considers various DG technologies such as photovoltaic (PV), wind turbine (WT), fuel cell (FC), micro-turbine (MT), gas turbine (GT) and diesel engine (DE). The system uncertainties (including those for the energy demand, energy price and DG technologies operating and investment costs) are modeled using fuzzy numbers. The numerical case studies have been carried out using the IEEE 37-node distribution test system to demonstrate the performance of the proposed DG planning model. © 2011.

Shokri A.,University of Tehran | Bozorg Haddad O.,University of Tehran | Marino M.A.,University of California at Davis
Water Resources Management | Year: 2013

Optimization algorithms are important tools for the solution of combinatorial management problems. Nowadays, many of those problems are addressed by using evolutionary algorithms (EAs) that move toward a near-optimal solution by repetitive simulations. Sometimes, such extensive simulations are not possible or are costly and time-consuming. Thus, in this study a method based on artificial neural networks (ANN) is proposed to reduce the number of simulations required in EAs. Specifically, an ANN simulator is used to reduce the number of simulations by the main simulator. The ANN is trained and updated only for required areas in the decision space. Performance of the proposed method is examined by integrating it with the non-dominated sorting genetic algorithm (NSGAII) in multi-objective problems. In terms of density and optimality of the Pareto front, the hybrid NSGAII-ANN is able to extract the Pareto front with much less simulation time compared to the sole use of the NSGAII algorithm. The proposed NSGAII-ANN methodology was examined using three standard test problems (FON, KUR, and ZDT1) and one real-world problem. The latter addresses the operation of a reservoir with two objectives (meeting demand and flood control). Thus, based on this study, use of the NSGAII-ANN integrative algorithm in problems with time-consuming simulators reduces the required time for optimization up to 50 times. Results of the real-world problem, despite lower computational-time requirements, show a performance similar to that achieved in the aforementioned test problems. © 2013 Springer Science+Business Media Dordrecht.

Zavvari M.,Islamic Azad University at Urmia | Ahmadi V.,University of Tehran
IEEE Electron Device Letters | Year: 2013

A single-photon detector based on an avalanche quantum dot IR photodetector is presented and designed for self-quenching and self-recovering operation at IR wavelength. The device consists of dot layers and resonant tunneling barriers in the absorption region. An additional layer, called the transient carrier buffer, is added to trap the backward holes. For an avalanche process, the accumulation of backward-traveling-avalanche-generated holes leads to a reduction in the electric field of the multiplication region and avalanche gain, and consequently, the detector is quenched. The detector is self-recovered by thermionic emission and tunneling currents. We study the self-quenching and self-recovery performance of the device. A detection efficiency of around 8% is obtained. © 1980-2012 IEEE.

A magnetic ion-imprinted polymer (Fe3O4@TiO2@SiO2-IIP) functionalized with -NH groups for the selective determination of Co(II) ions from environmental and biological samples is presented. This sorbent was synthesized by surface imprinting technique combined with sol-gel process using 3-(2-aminoethylamino) propyltrimethoxysilane (AAPTS) as a functional ligand, tetraethyl orthosilicate as across-linking agent, and Co(II) ion as the template. The prepared magnetic ion-imprinted polymer was characterized by infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), dynamic light scattering (DLS), and X-ray diffraction (XRD). Fe3O4@TiO2@SiO2-IIP showed higher capacity and selectivity than that of Fe3O4@TiO2@SiO2-NIP. The important parameters influencing the recovery such as pH, the volume and eluent concentration, contact time, and the amount of sorbent on extraction percentage of Fe3O4@TiO2@SiO2-IIP were studied and optimized. The linear range (LR), relative standard deviation(RSD) and limit of detection (LOD=3 Sb/m) for flame atomic absorption spectrometric determination of Co(II) ion, after its selective extraction by the prepared IIP polymer, were evaluated as 1-130 μg L-1, 1.22% and 0.15 μg L-1, respectively. The maximum capacity of Fe3O4@TiO2@SiO2-IIP and Fe3O4@TiO2@SiO2-NIP is 35.21 mg g-1and 10.34 mg g-1, respectively. The separation factor of Fe3O4@TiO2@SiO2-IIP for Co(II)/Pb(II), Co(II)/Ni(II), and Co(II)/Cd(II) are 41.17, 79.74, and 56.48, respectively. In addition, the spent magnetic ion-imprinted polymer can be refreshed by simply washing with an aqueous HNO3 solution, and there is no significant decrease in adsorption capacity after a test of upto seven cycles, demonstrating that the Fe3O4@ TiO2@SiO2-IIP is stable and reusable. © 2015 Published by Elsevier B.V.

Mohammadi S.,Amirkabir University of Technology | Mirsalim M.,Amirkabir University of Technology | Mirsalim M.,St. Mary's University | Vaez-Zadeh S.,University of Tehran
IEEE Transactions on Energy Conversion | Year: 2014

Analytical models play an important role in the design of electromagnetic devices by providing computationally efficient solutions. In this paper, by combining magnetic equivalent circuit approaches and Faraday's and Ampere's laws, a model for radial-flux eddy-current couplers is developed, which can easily handle complex geometries as well as account for iron saturation, all material properties, and three-dimensional (3-D) parameters. The characteristics and the design considerations of a surface-mounted permanent-magnet structure are presented. Also, a procedure aimed at an optimal design of the yoke thicknesses is utilized. Moreover, 2-D and 3-D finite-element methods are employed in the analyses and evaluation of the model. Finally, sensitivity analysis is performed to explore the impacts of the machine parameters on the device performance. © 2013 IEEE.

Ghorashi S.S.,University of Tehran | Valizadeh N.,Shahid Bahonar University of Kerman | Mohammadi S.,University of Tehran
International Journal for Numerical Methods in Engineering | Year: 2012

A novel approach based on a combination of isogeometric analysis (IGA) and extended FEM is presented for fracture analysis of structures. The extended isogeometric analysis is capable of an efficient analysis of general crack problems using nonuniform rational B-splines as basis functions for both the solution field approximation and the geometric description, and it can reproduce crack tip singular fields and discontinuity across a crack. IGA has attracted a lot of interest for solving different types of engineering problems and is now further extended for the analysis of crack stability and propagation in two-dimensional isotropic media. Concepts of the extended FEM are used in IGA to avoid the necessity of remeshing in crack propagation problems and to increase the solution accuracy around the crack tip. Crack discontinuity is represented by the Heaviside function and isotropic analytical displacement fields near a crack tip are reproduced by means of the crack tip enrichment functions. Also, the Lagrange multiplier method is used to impose essential boundary conditions. Moreover, the subtriangles technique is utilized for improving the accuracy of integration by the Gauss quadrature rule. Several two-dimensional static and quasi-static crack propagation problems are solved to demonstrate the efficiency of the proposed method and the results of mixed-mode stress intensity factors are compared with analytical and extended FEM results. © 2011 John Wiley & Sons, Ltd.

Soltanpour S.,Zanjan University of Medical Sciences | Jouyban A.,Tabriz University of Medical Sciences | Jouyban A.,University of Tehran
Journal of Molecular Liquids | Year: 2013

The solubility of lamotrigine in binary and ternary mixtures of N-methyl pyrrolidone and water with polyethylene glycols 200, 400, and 600 at 25 C is determined and mathematically represented using two cosolvency models, i.e. the log-linear model of Yalkowsky (method I), the Jouyban-Acree model (method II), and a combined version of the Jouyban-Acree model with Hansen partial solubility parameters (method III). The density of the solute free solvent mixtures is measured and employed to train the Jouyban-Acree model and subsequently the density of the saturated solutions is predicted. For methods I and II, the overall mean relative deviations (OMRDs) for fitting the solubility data of lamotrigine in binary mixtures are 39.1% and 5.1%, respectively. Further, the OMRDs for fitting the solubilities in ternary solvent mixtures for lamotrigine are 42.9% and 22.1% for methods I and II, respectively. In method III, the OMRD value for fitting all 122 data points by means of the combined version of the Jouyban-Acree model with Hansen solubility parameters is 12.7%. The trained version of the Jouyban-Acree model was produced by using the density of the solute free solutions, and the prediction of OMRD for the density of saturated solutions is 1.6%. © 2012 Elsevier B.V.

Moradi A.S.,University of Tehran | Hatzfeld D.,Joseph Fourier University | Tatar M.,International Institute of Earthquake Engineering and Seismology
Tectonophysics | Year: 2011

We present the results of a microearthquake study conducted in 2004 with 31 portable stations around the city of Tabriz, which is crossed by an active fault and has experienced several destructive earthquakes in the recent history. From April 24 until July 24, we recorded 80 earthquakes by more than 4 stations. We complement these data with earthquakes recorded by the 8 permanent seismological stations of the Tabriz network operated by Institute of Geophysics of the University of Tehran from August 1995 until March 2008. Among a total of 6377 events, only 394 earthquakes were recorded by more than 5 stations and located with statistical uncertainties (ERZ and ERH) less than 5. km and a Gap less than 270°. Most of these earthquakes are located along the Tabriz fault, at a depth ranging from the surface to 20. km, comparable to other studies conducted in Central Alborz. We computed 22 focal mechanisms most of which show right-lateral strike-slip motion along east-southeast planes, consistent with the geologic evidence for Quaternary slip. We do not see any peculiar pattern near the Tabriz pull-apart basin, or at both ends of the North Tabriz fault, where it terminates in EW trending reverse faults. This suggests that the fault is simpler (more mature) at depth than at the surface. © 2011 Elsevier B.V.

Rouhi M.,University of Tehran | Sohrabvandi S.,Shahid Beheshti University of Medical Sciences | Mortazavian A.M.,Shahid Beheshti University of Medical Sciences
Critical Reviews in Food Science and Nutrition | Year: 2013

Probiotics are from functional foods that bring health benefits for humans. Nowadays, a major development in functional foods is related to food containing probiotic cultures, mainly lactic acid bacteria or bifidobacteria. Probiotics must be alive and ingested in sufficient amounts to exert the positive effects on the health and the well-being of the host. Therefore, viability of probiotic products (the minimum viable probiotic cells in each gram or milliliter of product till the time of consumption) is their most important characteristic. However, these organisms often show poor viability in fermented products due to their detrimental conditions. Today, the variety of fermented meat products available around the world is nearly equal to that of cheese. With meat products, raw fermented sausages could constitute an appropriate vehicle for such microorganisms into the human gastrointestinal tract. In present article, the viability of probiotic microorganisms in fermented sausage, the main factors affect their viability, and the sensorial characteristics of final product are discussed. © 2013 Copyright Taylor and Francis Group, LLC.

Valipour M.,University of Tehran | Shekarchi M.,University of Tehran | Ghods P.,Carleton University
Cement and Concrete Composites | Year: 2014

The evaluation of the corrosion process for estimating the service life of concrete structure is of great importance to civil engineers. In this paper, the effects of different exposure conditions (i.e., tidal and splash zones) on macrocell and microcell corrosion of rebar in concrete were examined on concrete specimens with different w/c ratios in the Persian Gulf region. Experimental techniques such as macrocell corrosion rate measurement, Galvanostatic pulse, electrical resistivity, half-cell potential measurement, and numerical techniques were used to determine the corrosion rate and time-to-corrosion- initiation of rebar. Results showed that corrosion rates in the splash zone were higher than the ones in the tidal zone. This indicates that the propagation of corrosion in the splash zone is faster than the one in the tidal zone. There was also a strong correlation between the experimental results and those obtained from a numerical model in both tidal and splash zones. © 2013 Elsevier Ltd. All rights reserved.

Taleizadeh A.A.,University of Tehran | Pentico D.W.,Duquesne University
International Journal of Production Economics | Year: 2014

The classic Economic Order Quantity model assumes that the unit purchasing cost is not based on the order quantity. In practice, a supplier may offer purchasers an all-units discount. We develop a model and solution procedure for the EOQ with all-unit discounts and partial backordering at a constant rate. We show, and illustrate with a numerical example, how that model can be used to find the solution for the EOQ with discount and full backordering. A multi-factor experiment is used to gain insights into the improvement in performance of the proposed procedure relative to using the basic EOQ or the EOQ with full backordering and to identify the model parameters that have the greatest impact on the model's performance. © 2014 Elsevier B.V. All rights reserved.

Ali Goudarzi M.,International Institute of Earthquake Engineering and Seismology | Reza Sabbagh-Yazdi S.,University of Tehran
Soil Dynamics and Earthquake Engineering | Year: 2012

Nonlinear behavior of liquid sloshing inside a partially filled rectangular tank is investigated. The nonlinearity in the numerical modeling of the liquid sloshing originates from the nonlinear terms of the governing equations of the fluid flow and the liquid free surface motion as a not known boundary condition. The numerical simulations are performed for both linear and nonlinear conditions. The computed results using linear conditions are compared with readily available exact solution. In order to verify the results of the nonlinear numerical solution, a series of the shaking table tests on rectangular tank were conducted. Having verified linear and nonlinear numerical models, they are used for computation of near wall sloshing height at a series of real scale tanks (with various dimensions) under the both harmonic and earthquake base excitation. Finally, the nonlinear effects on liquid sloshing modeling are discussed and the practical limitations of the linear solution in evaluating the response of seismically excited liquids are also addressed. © 2012 Elsevier Ltd.

News Article | December 20, 2016
Site: www.prweb.com

SAE International announces that Katherine Avery, Research Scientist with Ford Motor Company’s Research and Innovation Center; and Mohammad J. Mahtabi, a third-year PhD student majoring in Mechanical Engineering at Mississippi State University, have been honored with the Henry O. Fuchs Student Award. Established in 1991, this award recognizes a graduate or recently graduated student (i.e. post doctorate or new professor) that is working in the field of fatigue research and applications. The purpose of this award is to promote the education of engineering students in the area of fatigue technology. This award honors the memory of Professor Henry O. Fuchs. Professor Fuchs participated in the SAE Fatigue Design & Evaluation Committee's research projects, was a member of the faculty who founded the SAE Fatigue Concepts in Design short course, published extensively in SAE and elsewhere in the technical community, and actively participated in the Surface Enhancement Division of the Committee which is responsible for many standards relating to surface treatments of metals for withstanding fatigue damage. As a graduate student, Avery was a visiting scholar at Ford, and had internships at Oak Ridge National Laboratory and Tenneco, Inc. She also served as a teaching assistant at the University of Michigan in 2011, and a guest lecturer at Kettering University in 2013. Avery has authored or co-authored several papers on durability and high temperature fatigue of metals through SAE International and ASME. Together with her research collaborators, Avery was a recipient of the 2012 SAE Arch T. Colwell Merit Award. At the University of Michigan, she and her faculty adviser, Dr. Jwo Pan, were honored with the 2015 Robert M. Caddell Award for Research for their joint contributions in the areas of materials and manufacturing. For her active role in student leadership, Avery was presented with the Distinguished Leadership Award and the MLK Spirit Award from the Deans of U of M’s College of Engineering in 2014. Avery serves on the Michigan Engineering Alumni Board and is a member of SAE International, ASME and SWE. She holds a bachelor’s degree in Mechanical Engineering from Kettering University, and a master’s degree and PhD in Mechanical Engineering from the University of Michigan. Mahtabi holds a bachelor’s degree from the University of Tehran and a master’s degree from Iran University of Science and Technology; he ranked as an honor student at both institutions. He is a third-year PhD student, majoring in Mechanical Engineering at Mississippi State University and is conducting his research at MSU’s Center for Advanced Vehicular Systems (CAVS) under supervision of Dr. Shamsaei. Mahtabi’s dissertation is on different aspects of fatigue behavior of NiTi, an equiatomic alloy of nickel and titanium. This material is categorized as a shape memory alloy (SMA), while also exhibiting superelastic behavior. NiTi has become a preferred choice for many applications in the automotive, aerospace and biomedical industries. In automotive industry, the material has been used in engine control systems, transmission control, and has the potential to be utilized in structural components, bumpers and crash structures. He is using several experimental, analytical, and computational techniques to model the fatigue behavior of SMAs and explain the relationship between various aspects of the material, such as microstructural features, phase transformation, and loading, including mean strain/stress and variable amplitude effects, on the fatigue resistance. His research involves many complex (and coupled) physical phenomena with the need to understand and model: cyclic deformation, phase transformation, superelasticity, and damage accumulation. Based on his dissertation research on experimental and computational fatigue and fracture analysis, he has published several journal articles, one book chapter, and presented in multiple conferences. SAE International is a global association committed to being the ultimate knowledge source for the engineering profession. By uniting more than 127,000 engineers and technical experts, we drive knowledge and expertise across a broad spectrum of industries. We act on two priorities: encouraging a lifetime of learning for mobility engineering professionals and setting the standards for industry engineering. We strive for a better world through the work of our philanthropic SAE Foundation, including programs like A World in Motion® and the Collegiate Design Series™.

News Article | April 26, 2016
Site: www.scientificamerican.com

Many of Iran’s once flourishing wetlands have dried dramatically in recent years. Lake Urmia in particular, the sixth largest salt lake in the world and a UNESCO Biosphere Reserve, is dangerously receding and threatens to vanish entirelly. Spanning an area larger than the Dead Sea and the Great Salt Lake combined, the dwindling lake lies tucked in the Zagros Mountain range in northwest Iran near the Turkish border. Hossein Akhani, a biologist at the University of Tehran, argues that Iran’s high water consumption and energy and agriculture demands put pressure on the lake. Disturbing photographs of the lake today compared to two decades ago show that now the southern half completely evaporates in summer. Plants, migrating birds like flamingos and pelicans, a unique species of brine shrimp, and other wildlife have begun to disappear. Akhani, a longtime advocate on conservation issues, argues that people should take emergency actions to stop the lake from contracting further. Only then, he says, can Iran try to bring water back—from dams, river flow, and treated wastewater—to replenish, revive and restore the lake to its natural state. He believes efforts to save it will be more fruitful as the international community lifts sanctions, following successful negotiations involving Iran’s nuclear program last year. As restrictions ease, Akhani says, there should be more opportunities to collaborate among scientists, conservationists, and international organizations. Akhani traveled to Washington, D.C. in February for his first meeting of the American Association for the Advancement of Science. In a symposium titled “Iran: Science Cooperation in a Post-Sanctions Era,” he spoke in  English—his second language—about Lake Urmia’s plight. Afterward, he met with me to answer questions, often pausing to translate a word properly or to convert from the Iranian calendar. How did you become involved in environmental and ecological research? In 1987 I was employed as a part-time researcher in Iran’s Natural History Museum. I performed studies of national parks and protected areas. Then I continued my research in saline habitats like Urmia Lake, and [I studied] biodiversity in protected areas including Gulestan National Park in eastern Iran, one of the richest natural parks in the Middle East. What was Lake Urmia like in the 1990s? It was a large lake and people often swam there. Many people believed that swimming in the salty lake was healthy for their skin. There were a lot of hotels and tourist centers, but now unfortunately most of them are out of business. Based on your research, what are the main reasons why the lake is receding? The main reason is the extensive water use in the basin, which happened after 54 dams were constructed in the area. There are only eight permanent rivers, so there is no chance for running water to flow into the lake. There are also a lot of wells, which pump water from underground aquifers. These two pressures prevent water from accumulating in the basin. When did you realize that the lake was shrinking and that this was a serious problem? In 2001, when I visited the northeastern part of the lake to collect plants, I saw that the lake is receding and there were many areas where the salt was exposed to earth. It was completely different from what I saw in 1987. Were plants and wildlife struggling to adapt? Over thousands of years, salts accumulated in the lake’s basin. When the lake shrinks, the area exposed to air is extremely salty. There is no chance for plants to grow there. After the lake became desiccated, we lost many vegetation types. Plants just dried up or were in bad condition. The salinity tolerance of brine shrimp is 160 grams of salt per liter, but now the salinity of the lake is almost 450 grams per liter, so they cannot survive these conditions. In the surrounding wetlands and estuaries, the salinity is lower, so we can still find them there. When the shrimp are gone and flamingoes come and find the remaining water extremely salty, then it’s dangerous for them. We’ve lost many migratory birds coming to the area. If nothing were done, what would happen to the lake? If land use and water consumption remained as it is now, then the lake would disappear pretty soon. There’s no doubt about that—unless there is an unexpected rainfall, but we cannot rely on that. We believe that the only way to help the lake survive is to take emergency actions to stop further reductions, and then try to restore it in a reasonable time and reduce water consumption in a well-managed plan. What do you think are the main courses of action Iran should take? Agriculture in the area is currently unsustainable. You could provide technologies and improved irrigation systems that require less water. Agricultural products that use lots of water, such as sugar beets and apples, should be reduced. Previously, the area was famous for its wine gardens and wine production, which needs one-fifth the water of apple production. We need to support the farmers to change the crops they are cultivating and the government needs to compensate them during this transition. Many dams transfer water to urban areas where the population has grown tremendously in recent decades. With the restoration projects running now, the construction of new dams is prohibited, fortunately. It should be our goal to remove many dams. It sounds similar to Mono Lake. Los Angeles was taking a lot of water from the lake and it was shrinking and its habitat was suffering. Mono Lake is a good example of a correct decision to restore a lake. Thanks to the activities of Friends of Mono Lake Reserve—about 16,000 people who were involved took judicial actions and got water rights back to the lake— it was a great success. We should learn from Mono Lake history. Owens Lake [in eastern California] is completely dry, and they are spending $1.2 billion dollars to prevent dust emission in the area. This lake is only 5% the size of Urmia Lake. If we were to use the same measures, it would take hundreds of billions of dollars. It is less costly and more practical to save the habitat. In your presentation, you mentioned the government’s current restoration plan. Are people working on it now? Yeah! The Urmia Lake Restoration Committee set up expert committees who made an action plan in 2014, which was approved. In the Iranian calendar for 2015 until 21st of March in 2016, 660 million dollars was invested in 88 projects in the area. For example, they gave 200 million cubic meters of dam water to the lake and connected two rivers so the water flows more easily. They are constructing a canal to bring water from a river near the Turkish border to the lake. They also started subsidizing agricultural sectors to reduce their water use. How will the lifting of the sanctions aid these efforts to restore the lake? When the sanctions are lifted, there will be more opportunities for cooperation between Iranian and international scientists. Then we can learn more from [similar water problems] in the States. The new era will also help restoration programs. Environmental conditions in Iran became worse after the revolution, because of sanctions and the eight-year war in Iran and Iraq. I’m sure that if relations between Iran and the world improve, then there will be chances for foreign investment in the country, implementing new jobs for people, and supporting industries that reduce pressure on the environment. Environmental problems are world problems, and the world should work together to solve them. But sanctions make them worse, when you can’t import necessary technologies, talent or manpower. Are people in other countries trying to help in some way? In recent years, the case of Urmia became more publicized in international media and generated interest among scientists and international organizations. For example, Japan invested $1 million in the area to improve agricultural management. Several international meetings took place in Iran, and even scientists from the United States came. The Iranian government is very open and welcomes any kind of contribution. Instead of criticizing Iran, the world should do something! It’s the duty of developed countries that have more scientific facilities and funding to help. What are your thoughts about how things will change after the sanctions are lifted, especially for Iranian scientists and science in Iran? Iran’s education and universities expanded in the last 20 years. There are more than four million students in Iranian universities and the number of scientific publications in Iran has increased. But during the sanctions, we couldn’t get equipment and didn’t have opportunities to participate in international conferences, and exchanging students became difficult. Lifting sanctions will be beneficial for Iranian universities and universities in developed countries. We have seen thousands of Iranian scholars [working] in the United States and Europe. Iran is a huge country and provides a unique platform for top researchers, especially in fields of photosynthesis, plants, adaptation to harsh environments, and other environmental and biodiversity issues. When the economic situation and the stability in the area improves, our educated students should have opportunities to stay, too. Are there other things that you’ve been thinking about lately or that you look forward to after the sanctions? Our big concern now is that [U.S.] Republican presidential candidates say that if they’re elected, they will cancel these agreements. This would disturb an achievement that cost decades of negotiations. We should not destroy what has been planted—such a very expensive cultivation. I hope we’ll always think that relations and cooperation are the best solution for solving problems. How long do we have to have conflicts? We are big nations! Not all Iranians love America—but they have a lot of enthusiasm for development, a better life, and to be in contact with the world. We have to try to respect each other in spite of our differences.

Ghader S.,University of Tehran | Nordstrom J.,Linköping University
Dynamics of Atmospheres and Oceans | Year: 2014

We derive a general form of well-posed open boundary conditions for the two-dimensional shallow water equations by using the energy method. Both the number and the type of boundary conditions are presented for subcritical and supercritical flows on a general domain. The boundary conditions are also discussed for a rectangular domain. We compare the results with a number of often used open boundary conditions and show that they are a subset of the derived general form. © 2014 Elsevier B.V.

Kianersi D.,Islamic Azad University at Tehran | Mostafaei A.,Islamic Azad University at Tehran | Amadeh A.A.,University of Tehran
Materials and Design | Year: 2014

In this paper, we aim to optimize welding parameters namely welding current and time in resistance spot welding (RSW) of the austenitic stainless steel sheets grade AISI 316L. Afterward, effect of optimum welding parameters on the resistance spot welding properties and microstructure of AISI 316L austenitic stainless steel sheets has been investigated. Effect of welding current at constant welding time was considered on the weld properties such as weld nugget size, tensile-shear load bearing capacity of welded materials, failure modes, failure energy, ductility, and microstructure of weld nuggets as well. Phase transformations that took place during weld thermal cycle were analyzed in more details including metallographic studies of welding of the austenitic stainless steels. Metallographic images, mechanical properties, electron microscopy photographs and micro-hardness measurements showed that the region between interfacial to pullout mode transition and expulsion limit is defined as the optimum welding condition. Backscattered electron scanning microscopic images (BE-SEM) showed various types of delta ferrite in weld nuggets. Three delta ferrite morphologies consist of skeletal, acicular and lathy delta ferrite morphologies formed in resistance spot welded regions as a result of non-equilibrium phases which can be attributed to the fast cooling rate in RSW process and consequently, prediction and explanation of the obtained morphologies based on Schaeffler, WRC-1992 and Pseudo-binary phase diagrams would be a difficult task. © 2014 Elsevier Ltd.

Shirzad T.,Islamic Azad University at Tehran | Shomali Z.H.,University of Tehran | Shomali Z.H.,Uppsala University
Geophysical Journal International | Year: 2013

In this study, we present an application of the ambient noise tomography (ANT) to study the near-surface geological structures of the metropolitan Tehran/Iran region. Short-period fundamental mode Rayleigh wave Green's functions were estimated using cross-correlations of the vertical component of the ambient noise from 2009 October to 2011 May using a variety of seismic sensors, for example, accelerometers and seismometers, deployed in the Tehran area. Standard common lowfrequency processing procedures were applied to the cross-correlations, and shorter time-windows comprising 10-min segments were used in the processing step to enhance the time resolution of the signal in the frequency range of interest (1-10 s). Stacking was also conducted using the rms of the estimated empirical Green's functions. Our results demonstrate that ambient seismic noise tomography is a viable technique at periods of 1-10 s in length, even when different sensor types are present. Analysis of the empirical Green's functions indicates that the dominant sources of ambient seismic noise originated from the same origin, and no significant seasonal or spatial variations in the ambient noise sources were observed. Multiple-filter analysis was used to extract the group velocities from the estimated empirical Green's functions,whichwere then inverted to image the spatially varying dispersion at periods of lengths between 1 and 7 s using tomographic inversion of the traveltimes estimated for each frequency. The resulting group velocity maps show high correlations with known geological and tectonic features of the study region. In general, most of the Tehran basin, with certain exceptions, could be clearly resolved with low group velocities, whereas the mountain ranges were found to be correlated with high group velocities. In the Tehran basin, for 2 and 3 s periods, the low-velocity zone deepens towards the south-southwest, which reflects thicker sediments in the southern part of the basin than in the north. This feature has also been observed in other geological studies. The Vs models also show that bedrock depth varies between 400 and 1400m from north to south within the Tehran basin. At longer periods main faults are associated with abrupt transitions between regions of high- to low-velocity anomalies. In general, our results indicate that ANT can be a flexible and effective approach for studying near-surface heterogeneity using short-period surface wave data. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Binazadeh T.,Shiraz University of Technology | Yazdanpanah M.J.,University of Tehran
ISA Transactions | Year: 2012

In this paper, the problem of robust partial stabilization is considered and two approaches for partial stabilization of uncertain nonlinear systems are presented. In these approaches, the nonlinear dynamical system is divided into two subsystems, which are called the first and the second subsystems. This division is done based on the required stability properties of the system's states. The reduced input vector (the vector that includes components of the input vector appearing in the first subsystem) is designed to asymptotically stabilize the first subsystem. In the first approach, a new partial stabilization technique, based on the first order sliding mode control idea is proposed. In the proposed method, hereafter called the partial sliding mode, a sliding surface is designed such that restricting the motion on this surface guarantees the stability of only the first part of the system's state. In the second approach, a Lyapunov-based controller is proposed for partial stabilization and then an additional feedback control is designed so that the overall feedback law guarantees a robust manner in the presence of uncertainties. © 2011 ISA. Published by Elsevier Ltd. All rights reserved.

Parvizi A.,Islamic Azad University at Tehran | Abrinia K.,University of Tehran
International Journal of Mechanical Sciences | Year: 2014

In this paper, an upper bound solution is used to determine the ring rolling power and force. An admissible velocity field and strain rates are derived from the parametric definition of streamlines in the deforming zone. Minimizing the upper bound power with respect to neutral point position, the neutral point situation and the rolling force are determined. The present method is validated using experimental results extracted from ring rolling mill. Moreover, using ABAQUS/Explicit software, the ring rolling process was simulated in every respect. Comparison of the present upper bound results with those from experimental study, finite element simulation and our previous slab analysis, have proved the accuracy of the present analysis. As compared with the FEM simulation, this method is very much quicker and less expensive and could be used as an engineering tool in the ring rolling industrial applications. © 2013 Elsevier Ltd.

Taleizadeh A.A.,University of Tehran | Noori-Daryan M.,Islamic Azad University at Tehran | Cardenas-Barron L.E.,Monterrey Institute of Technology
International Journal of Production Economics | Year: 2015

This paper develops a Vendor Managed Inventory (VMI) model for a two-level supply chain comprised of one vendor and several non-competing retailers in which both the raw material and the finished product have different deterioration rates. It is assumed that the market demand for the finished product is deterministic and price sensitive. The proposed inventory model optimizes the retail price, the replenishment frequency of raw material, the replenishment cycle of the product, and the production rate jointly with main objective of maximizing the total profit of the entire chain. In the development of the inventory model the Stackelberg approach is considered between the chain partners where the vendor is leader and the retailers are the followers. Moreover, the concavity of the profit functions is proven and based on this a solution algorithm is developed to find the optimal solutions. At the end, a numerical example is provided to illustrate the use of the production-inventory model and perform a sensitivity analysis. Finally, some conclusions and future research directions are proposed. © 2014 Elsevier B.V. All rights reserved.

Mohammadkazemi F.,University of Tehran | Azin M.,Iranian Research Organization for Science and Technology | Ashori A.,Iranian Research Organization for Science and Technology
Carbohydrate Polymers | Year: 2015

In this work, the effects of carbon sources and culture media on the production and structural properties of bacterial cellulose (BC) have been studied. BC nanofibers were synthesized using Gluconacetobacter xylinus strain PTCC 1734. Media used were Hestrin-Schramm (H), Yamanaka (Y), and Zhou (Z). Five different carbon sources, namely date syrup, glucose, mannitol, sucrose, and food-grade sucrose were used in these media. All the produced BC pellicles were characterized in terms of dry weight production, biomass yield, thermal stability, crystallinity and morphology by thermogravimetric analysis (TGA), x-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). The obtained results showed that mannitol lead to the highest yield, followed by sucrose. The highest production efficiency of mannitol might be due to the nitrogen source, which plays an important role. The maximum improvement on the thermal stability of the composites was achieved when mannitol was used in H medium. In addition, the crystallinity was higher in BC formed in H medium compared to other media. FE-SEM micrographs illustrated that the BC pellicles, synthesized in the culture media H and Z, were stable, unlike those in medium Y that were unstable. The micrographs of BC produced in media containing mannitol and sucrose provided evidence of the strong interfacial adhesion between the BC fibers without noticeable aggregates. © 2014 Elsevier Ltd. All rights reserved.

Yazdani-Chamzini A.,Islamic Azad University at Tehran | Yakhchali S.H.,University of Tehran
Tunnelling and Underground Space Technology | Year: 2012

The problem of Tunnel Boring Machine (TBM) selection has a significant impact on the speed and cost of excavating sector; so that it is a strategic issue. On the other hand, selecting the optimum TBM among a pool of alternatives is a multicriteria decision making (MCDM) problem. In this paper, an evaluation model based on the fuzzy analytic hierarchy process (AHP) and another fuzzy MCDM technique, namely fuzzy technique for order performance by similarity to ideal solution (TOPSIS) is developed to help the tunneling designers in the process of the TBM selection under fuzzy environment where the vagueness and uncertainty are taken into account with linguistic variables parameterized by triangular fuzzy numbers. The fuzzy AHP is applied to form the structure of the TBM selection problem and to determine weights of the evaluation criteria, and fuzzy TOPSIS method is utilized to acquire final ranking. A real world case study is illustrated in order to demonstrate the potential of the proposed model for the TBM selection issue. It demonstrates the effectiveness and capability of the proposed model. © 2012 Elsevier Ltd.

Nayeripour M.,Shiraz University of Technology | Hoseintabar M.,University of Tehran
Renewable and Sustainable Energy Reviews | Year: 2013

In this paper, a new control strategy for rapid changing of output power level of solid oxide fuel cell (SOFC) power plant is proposed based on the adaptive control strategy. In the proposed control strategy, the utilization factor (UF) of solid oxide fuel cell stack is kept constant in steady state by feeding hydrogen to the stack at its rate value. In transient state, the utilization factor of the stack changes in its allowable range by controlling the current drawn and power condition unit. This coordination returns the utilization factor of fuel cell (FC) system to its optimal value. The proposed control strategy will be very useful to protect SOFC stack from internal damage during large disturbances. In order to investigate the proposed control strategy and verify dynamic modeling, the MATLAB/SIMULIK software is used. The results show the capability of the proposed control strategy under rapid changes in load demand. © 2013 Elsevier Ltd.

Pahlevani A.H.,Iranian Research Institute of Plant Protection | Akhani H.,University of Tehran
Botanical Journal of the Linnean Society | Year: 2011

Euphorbia (Euphorbiaceae) is one of the largest and most diversified cosmopolitan genera of flowering plants. South-west Asia is a major centre of diversity and contains c. 65 annual species, 35 of which occur in Iran. In this article, the seed morphology of all Iranian annual species was studied, including E.aulacosperma and E.rhabdothosperma, both new records for Iran. Quantitative and qualitative macro- and micromorphological features of seeds and caruncles were investigated using stereomicroscopy and scanning electron microscopy. Caruncle characters (shape, size, colour) and seed characters (shape, size, colour, ornamentation) are often constant and useful in identification and classification. An identification key and scanning electron micrographs are provided for all known Iranian taxa. © 2011 The Linnean Society of London.

Nikoo M.R.,University of Tehran | Kerachian R.,University of Tehran | Karimi A.,Islamic Azad University at Tehran
Water Resources Management | Year: 2012

In this paper, a new methodology is proposed for simultaneous allocation of water and waste load in river basins. A nonlinear interval number optimization model is used to incorporate the uncertainties of model inputs and parameters. In this methodology, the bounds of the uncertain inputs are only required, not necessarily knowing their probability density or fuzzy membership functions. In the proposed model, the existing uncertainties in water demands and monthly available water are considered in the optimization model. Also the economic and environmental impacts of water allocation to the agricultural water users are taken into account. To have an equitable water and waste load allocation, benefits are reallocated to water users using some solution concepts of the cooperative game theory. Results of applying the methodology to the Dez river system in south-western part of Iran show its effectiveness and applicability for water and waste load allocation in an uncertain environment. © 2012 Springer Science+Business Media B.V.

Eskandari M.,Islamic Azad University at Tehran | Homaee M.,Tarbiat Modares University | Mahmodi S.,University of Tehran
Waste Management | Year: 2012

Landfill site selection is a complicated multi criteria land use planning that should convince all related stakeholders with different insights. This paper addresses an integrating approach for landfill siting based on conflicting opinions among environmental, economical and socio-cultural expertise. In order to gain optimized siting decision, the issue was investigated in different viewpoints. At first step based on opinion sampling and questionnaire results of 35 experts familiar with local situations, the national environmental legislations and international practices, 13 constraints and 15 factors were built in hierarchical structure. Factors divided into three environmental, economical and socio-cultural groups. In the next step, the GIS-database was developed based on the designated criteria. In the third stage, the criteria standardization and criteria weighting were accomplished. The relative importance weights of criteria and subcriteria were estimated, respectively, using analytical hierarchy process and rank ordering methods based on different experts opinions. Thereafter, by using simple additive weighting method, the suitability maps for landfill siting in Marvdasht, Iran, was evaluated in environmental, economical and socio-cultural visions. The importance of each group of criteria in its own vision was assigned to be higher than two other groups. In the fourth stage, the final suitability map was obtained after crossing three resulted maps in different visions and reported in five suitability classes for landfill construction. This map indicated that almost 1224. ha of the study area can be considered as best suitable class for landfill siting considering all visions. In the last stage, a comprehensive field visit was performed to verify the selected site obtained from the proposed model. This field inspection has confirmed the proposed integrating approach for the landfill siting. © 2012 Elsevier Ltd.

Ahadi A.,Islamic Azad University at Tehran | Riahi M.A.,University of Tehran
Geophysics | Year: 2013

The aim of designing deconvolution operators is to extract the reflectivity series from seismic sections. Due to the noise, source signature inconsistency, reflection/transmission, anelastic attenuation, and multiples, the amplitude of a propagating seismic wave varies as a function of time. Because of these factors the frequency spectra of seismic signals narrow with time. Recognition of reflectors using upgoing waves is one of the notable properties of vertical seismic profiling (VSP) data. Designing a deconvolution operator for VSP data based on downgoing waves is considered to be one of the most ideal deconvolution methods intended to produce high-resolution images in routine processing of zero-offset VSP data. For such an analysis, the Gabor deconvolution operator has been designed using the downgoing wavefield and then was applied to the upgoing wavefield, and hyperbolic smoothing was used to estimate the wavelet. The final result of applying the deconvolution operator is a VSP section with superior resolution. To compare this method with customary methods of deconvolution, the Wiener deconvolution was applied to the synthetic and real data, and the results were compared with those of the Gabor deconvolution. © 2013 Society of Exploration Geophysicists.

Keramati A.,University of Tehran | Salehi M.,Lulea University of Technology
Applied Soft Computing Journal | Year: 2013

This study investigates relative importance of website success factors in selecting the most preferred website. To identify relative importance of website success factors and to rank alternative websites with respect to success factors, Updated Delone and McLean Information System Success Model is extended through applying an analytic network process (ANP) approach. A field study with 383 academic internet users was performed. Relative importance of each website success factor with respect to their influence on using the e-recruitment website, and user satisfaction are identified. Furthermore relative significance of using the e-recruitment website and user satisfaction in achieving positive benefits are discovered. This study also found the relative preference of each website with respect to different success variable. Results indicate that ANP is an effective tool to provide an accurate solution for interdependencies that are able to affect the decision to be made for network like models. The findings of this study provide decision makers of e-commerce companies with useful insights to compare the preference of their website with others with respect to different success variables. Moreover, relative significance of different success variables in websites can be compared. © 2012 Elsevier B.V.

Pishgar-Komleh S.H.,University of Tehran | Ghahderijani M.,Islamic Azad University at Tehran | Sefeedpari P.,University of Tehran
Journal of Cleaner Production | Year: 2012

The aim of this research was to examine the energy consumption and CO 2 emission of potato production in three different farm size sin Esfahan province of Iran. For this purpose, data were collected from 300 farmers by a face to face questionnaire. The results revealed total energy consumption and GHG emission of 47 GJ ha -1 and 992.88 kg CO 2eq ha -1, respectively. The most significant energy consumer was chemical fertilizers (49%), especially nitrogen (40%) and followed by seed with share of 24%. The energy use efficiency, specific energy and energy productivity were determined to be 1.71, 2.12 MJ kg -1 and 0.47 kg MJ -1. The different cultivated area levels analysis revealed that, large farms used the least amount of energy input significantly. It was found that the contribution of indirect energy was higher than that of direct energy and also the proportion of non-renewable energy was more than renewable resources. The results of econometric model estimation revealed that the impact of seed, water for irrigation, diesel fuel and chemical fertilizer energy inputs were significantly positive on potato yield. The sensitivity analysis illustrated that the marginal physical productivity (MPP) value of chemical fertilizer, diesel fuel and seed energy were -1.78 and -1.63 and 1.54, respectively. © 2012 Elsevier Ltd. All rights reserved.

Kasaeian A.,University of Tehran | Ghalamchi M.,University of Tehran | Ghalamchi M.,Islamic Azad University at Tehran
Energy Conversion and Management | Year: 2014

An analytical and numerical study for geometrical optimizing of a solar chimney prototype at University of Tehran was performed. A fundamental mathematical model that describes the flow was presented, and the performance evaluation of solar chimney was simulated with operational and geometric configurations. The numerical predictions were validated through comparison with the experimental data of the solar chimney pilot which was constructed in height of 2 m and collector radius of 3 m. The results show that, the collector inlet of 6 cm, the chimney height of 3 m, and the chimney diameter of 10 cm were the best alternatives for the constructed solar chimney pilot. It is found that the velocity magnitude can be raised to 4-25% in different cases; also the analysis indicated that the height and diameter of the chimney are the most important physical variables for solar chimney design. © 2014 Elsevier Ltd. All rights reserved.

Abdollahzadeh H.,Islamic Azad University at Tehran | Jazaeri M.,Semnan University | Tavighi A.,University of Tehran
International Journal of Electrical Power and Energy Systems | Year: 2014

The on-line estimation of symmetrical components from network voltages and currents is widely used in the field of power quality monitoring and improvement of relevant disturbances, especially by CUstom Power Systems (CUPS). This paper proposes a new fast-converged estimation approach, which directly extracts amplitudes and phase angles of symmetrical components of desired frequencies from harmonic-distorted network voltages. The adequate convergence time and accuracy of this approach make it applicable in Dynamic Voltage Restorer (DVR) as an application in which the quickness of response is of the most important requirements. According to this objective, sensitivity analyses are prepared to assess the impacts of sag depth variations, phase angle jumps and frequency variations on the performance of the proposed algorithm. Further, in these analyses complete comparisons are made between the proposed approach and well-known algorithms such as KF, ADALINE and FFT using MATLAB/SIMULINK. The application of the proposed estimation approach in the DVR is realized by introducing a new control scheme. The proposed control scheme provides the compensation of different voltage sags through both pre-sag and in-phase strategies. Finally, simulation results, carried out in PSCAD/EMTDC environment, confirm the effectiveness of the suggested control scheme. © 2013 Elsevier Ltd. All rights reserved.

This paper is motivated by the lack of studies in the technical literature concerning to the three-dimensional vibration analysis of bi-directional FG rectangular plates resting on two-parameter elastic foundations. The formulations are based on the three-dimensional elasticity theory. The proposed rectangular plates have two opposite edges simply supported, while all possible combinations of free, simply supported and clamped boundary conditions are applied to the other two edges. This paper presents a novel 2-D six-parameter power-law distribution for ceramic volume fraction of 2-D FGM that gives designers a powerful tool for flexible designing of structures under multi-functional requirements. Various material profiles along the thickness and in the in-plane directions are illustrated using the 2-D power-law distribution. The effective material properties at a point are determined in terms of the local volume fractions and the material properties by the Mori-Tanaka scheme. The 2-D differential quadrature method as an efficient and accurate numerical tool is used to discretize the governing equations and to implement the boundary conditions. The convergence of the method is demonstrated and to validate the results, comparisons are made between the present results and results reported by well-known references for special cases treated before, have confirmed accuracy and efficiency of the present approach. Some new results for natural frequencies of the plates are prepared, which include the effects of elastic coefficients of foundation, boundary conditions, material and geometrical parameters. The interesting results indicate that a graded ceramic volume fraction in two directions has a higher capability to reduce the natural frequency than conventional 1-D FGM. © 2013 Springer Science+Business Media Dordrecht.

Hoseinifar S.H.,Gorgan University of Agricultural Sciences and Natural Resources | Soleimani N.,University of Tehran | Ringo E.,e Arctic University of Norway
British Journal of Nutrition | Year: 2014

The present study was conducted to investigate the effects of dietary fructo-oligosaccharide (FOS) (0, 1, 2 and 3 %) supplementation on the growth performance, haemato-immunological parameters, cultivable autochthonous (non-adherent) intestinal microbiota and stress resistance of common carp (Cyprinus carpio) fry (3.23 (sem 0.14) g). These parameters were measured after feeding the carp fry with the experimental diets for 7 weeks. Dietary FOS supplementation had no significant effects on the growth performance and food intake of carp fry compared with the control treatment. It also had no significant effects on the following haematological parameters: erythrocyte count; leucocyte counts (WBC); haematocrit; Hb; mean corpuscular volume; mean corpuscular Hb content; mean corpuscular Hb concentration. However, WBC and respiratory burst activity were significantly affected by dietary FOS supplementation. Evaluation of the cultivable autochthonous intestinal microbiota revealed a significant increase in the levels of total viable heterotrophic aerobic bacteria and lactic acid bacteria in fish fed diets supplemented with 2 and 3 % FOS. Furthermore, dietary FOS supplementation significantly increased the survival rate and stress resistance of carp fry compared with the control treatment. These results encourage conducting further research on the administration of FOS and other prebiotics in carp fry studies. © The Authors 2014.

Golshani L.,Islamic Azad University at Tehran | Pasha E.,University of Tehran
Information Sciences | Year: 2010

In this paper, we introduce the definition of the conditional Rényi entropy for continuous random variables and show that the so-called chain rule holds. Then, we use this rule to obtain another relation for getting the rate of Rényi entropy. Using this relation and properties of the Rényi entropy we obtain the Rényi entropy rate for stationary Gaussian processes. Finally, we show that the bound for the Rényi entropy rate is simply the Shannon entropy rate and that the Rényi entropy rate reduces to the Shannon entropy rate as α → 1. © 2009.

Savaloni H.,University of Tehran | Babaei R.,Islamic Azad University at Tehran
Applied Surface Science | Year: 2013

Silver chiral nano-flower sculptured thin films with 3-, 4- and 5-fold symmetry were produced on copper substrates using oblique angle deposition method in conjunction with rotation of sample holder with different speeds at different sectors of each revolution corresponding to symmetry order of the acquired nano-flower. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) were employed to obtain morphologies and nano-structure of the films. Raman spectroscopy was performed on all samples that were subject to impregnation by 4,4′-bipyridine (C10H 8N2) solution. A high degree of enhancement of the main bands at 1610, 1297, and 1009 cm-1 that can be assigned to the CC stretching mode, aromatic ring stretching ring and in-plane ring mode of 4,4′-bipyridine, is achieved. ©2013 Elsevier B.V. All rights reserved.

Khalili M.,Islamic Azad University at Tehran | Tavakkoli-Moghaddam R.,University of Tehran
Journal of Manufacturing Systems | Year: 2012

This paper deals with a bi-objective flowshop scheduling problem minimizing the makespan and total weighted tardiness, in which all jobs may not be processed by all machines. Furthermore, we consider transportation times between machines. Obtaining an optimal solution for this type of complex, large-sized problem in reasonable computational time by using traditional approaches and optimization tools is extremely difficult. This paper presents a new multi-objective electromagnetism algorithm (MOEM). The motivation behind this algorithm has risen from the attraction-repulsion mechanism of electromagnetic theories. Along with MOEA, we apply simulated annealing to solve the given problem. A set of experimental instances are carried out to evaluate the algorithm by advanced multi-objective performance measures. The related results show that a variant of our proposed MOEM provides sound performance comparing with other algorithms. © 2011 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.

Yaghoobi H.,Islamic Azad University at Tehran | Yaghoobi P.,University of Tehran
Meccanica | Year: 2013

This paper presents an analytical investigation on the buckling analysis of symmetric sandwich plates with functionally graded material (FGM) face sheets resting on an elastic foundation based on the first-order shear deformation plate theory (FSDT) and subjected to mechanical, thermal and thermo-mechanical loads. The material properties of FGM face sheets are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. An analytical approach is used to reduce the governing equations of stability and then solved using an analytical solution which is named as power series Frobenius method for symmetric sandwich plates with six different boundary conditions. A detailed numerical study is carried out to examine the influence of the plate aspect ratio, side-to-thickness ratio, loading type, sandwich plate type, volume fraction index, elastic foundation coefficients and boundary conditions on the buckling response of FGM sandwich plates. This has not been done before and serves to fill the gap of knowledge in this area. © 2013 Springer Science+Business Media Dordrecht.

Ojaroudi N.,University of Tehran | Amiri S.,Iranian Research Organization for Science and Technology | Geran F.,University of Tehran
Applied Computational Electromagnetics Society Journal | Year: 2013

In this paper, a kind of reconfigurable monopole antenna with multi-resonance and switchable band-notched function is designed and manufactured whose frequency characteristics can be reconfigured electronically to have a singleband notch function in order to block interfering signals from 5.15 GHz -5.35 GHz HiperLAN, 5 GHz -6 GHz WLAN or 7.25 GHz -7.75 GHz for downlink of X-band satellite communication systems. The proposed antenna consists of a square radiating patch, feed-line, and a ground plane with a Fork-shaped conductor-backed plane. By adding an inverted T-shaped and a pair of Lshaped parasitic structures in the ground plane, additional resonances are excited and hence much wider impedance bandwidth can be produced, especially at the higher band, which provides a wide usable fractional bandwidth of more than 135% (3.05 GHz-16.51 GHz). In order to generate reconfigurable band-stop performance, we use a pair of PIN diodes within the antenna configuration. By changing the ON/OFF conditions of the PIN diodes, the antenna can be used to generate a single notch band to isolate and block any interference in the UWB frequency range. The proposed antenna has a small dimension of 12 × 18 × 1.6 mm3. © 2013 ACES.

Abdolmohammadi S.,Islamic Azad University at Tehran | Afsharpour M.,University of Tehran
Chinese Chemical Letters | Year: 2012

An efficient synthesis of hexahydropyrido[2,3-d]pyrimidinetrione derivatives is achieved via tandem Knoevenagel-Michael addition of aromatic aldehydes, methylcyanoacetate and 4(6)-aminouracil in solvent-free conditions in the presence of 10 mol% of ZrO 2 nanoparticles (ZrO 2 NPs) as a heterogenous catalyst. The procedure is formed in high yields, short reaction time and an environmentally friendly specificity. © 2012 Shahrzad Abdolmohammadi.

Amid A.,Islamic Azad University at Tehran | Moalagh M.,Shahid Beheshti University | Zare Ravasan A.,University of Tehran
Information Systems | Year: 2012

Implementation of Enterprise Resource Planning systems (ERPs) is a complex and costly process, which usually results in serious failures. The majority of previous studies and research projects have been conducted in identifying ERP Critical Success Factors (CSFs) rather than Critical Failure Factors (CFFs). On the other hand, most studies have been devoted to developed countries, while in developing countries, many companies have moved towards using such systems. The majority of IT/IS management standards and guidelines have been developed by technologically-leading countries. But developing countries, which mostly confront with especial challenges, have a different condition from the implicit assumptions of leading countries. Iran is one of these countries that many of its ERP implementation projects led to failure. There is no comprehensive study that identifies ERP CFFs in Iranian industries. The main purpose of this study is to identify such factors and classify them to help other industries, consultants and implementers to prevent failures in the implementation of ERP projects. So, at first, with the semi structured interviews and literature reviews, 47 failure factors were identified. After that a questionnaire developed and sent to ERP project team members in Iranian industries that failed in their ERP projects. Robust Exploratory Factor Analysis (EFA) has been used for data analysis, which finally classified critical failure factors in seven groups named as vendor and consultant, human resources, managerial, project management, processes, organizational and technical. The results of this study have provided a very useful reference for scholars and managers to identify the relevant issues of ERP projects failure in developing countries. © 2011 Elsevier Ltd. All rights reserved.

Pirayesh H.,University of Tehran | Khanjanzadeh H.,Gorgan University of Agricultural Sciences and Natural Resources | Salari A.,Gorgan University of Agricultural Sciences and Natural Resources
Composites Part B: Engineering | Year: 2013

In this study, the suitability of walnut/almond shells as renewable underutilized agricultural wastes for wood based panel manufacturing was investigated. Particleboards containing different walnut/almond shells particle ratios (0%, 10%, 20%, 30% and 100%) were made using urea-formaldehyde (UF) resin. Some mechanical (modulus of elasticity, modulus of rupture and internal bond strength), physical (thickness swelling and water absorption) properties and formaldehyde emission of the particleboards were evaluated. The addition of walnut/almond particle significantly improved water resistance of the panels and greatly reduced their formaldehyde emissions. However, flexural properties and internal bond strength decreased with increasing walnut/almond shells content in the panels. The walnut/almond shells can be considered as an alternative raw material or filler in the manufacture of wood based particleboards used in indoor environment due to lower thickness swelling, water absorption and formaldehyde emission. Besides, using these underutilized materials in forest industry could decrease the pressure on forest resources and some job opportunities can be created. © 2012 Elsevier Ltd. All rights reserved.

Ahmadi M.H.,Islamic Azad University at Tehran | Ahmadi M.A.,Petroleum University of Technology of Iran | Mehrpooya M.,University of Tehran | Sameti M.,University of Tehran
Energy Conversion and Management | Year: 2015

Throughout present research, optimization investigations of an irreversible absorption heat pump system on the basis of a new thermo-ecological criterion. The objective functions which considered are the specific heating load, coefficient of performance (COP) and the ecological coefficient of performance (ECOP). Three objective functions of the ECOP, COP and the specific heating load are optimized simultaneously using the multi-objective optimization algorithm NSGAII. COP and ECOP are maximized and specific heating load is minimized in order to get the best performance. Decision making is done by means of three methods of LINAMP and TOPSIS and FUZZY. Finally, sensitivity analysis and error analysis was performed for the system. © 2014 Elsevier Ltd. All rights reserved.

Yazdani M.R.,Islamic Azad University at Tehran | Farzanehfard H.,Isfahan University of Technology | Faiz J.,University of Tehran
IEEE Transactions on Power Electronics | Year: 2011

Switching power supplies are sources of noise for sensitive circuits. Converters should comply with electromagnetic compatibility (EMC) rules so that the electromagnetic interference (EMI) caused by switching cannot interfere with the normal operation of adjacent circuits and also the converter itself. The produced interference can be in the form of conduction or radiation. In this paper, some techniques are used in switching converters to suppress EMI with emphasis on the conduction form. EMI analysis and evaluation of a conventional flyback converter and a proposed zero-current transition (ZCT) flyback converter is achieved by simulation and experimental results. In addition to evaluating some EMI suppression techniques, the main objective of this paper is to improve EMI in the topology design stage. The operating modes of the improved ZCT flyback are discussed. In addition to the efficiency improvement, the amount of EMI reduction of this ZCT flyback and the effectiveness of some EMI reduction techniques are shown by practical implementation. © 2011 IEEE.

Faraji G.,University of Tehran | Mashhadi M.M.,University of Tehran | Kim H.S.,Pohang University of Science and Technology
Materials Letters | Year: 2011

A severe plastic deformation (SPD) technique based on tubular channel angular pressing (TCAP) is proposed suitable for deforming cylindrical tubes to extremely large strains without changing their dimensions. The tube constrained by inner and outer dies is pressed by a hollow cylindrical punch into a tubular angular channel with three shear zones. This technique was applied to a commercial AZ91 magnesium alloy and a significant grain refinement was achieved even after single cycle TCAP. Microhardness of the tube increased to 78 Hv from an initial value of 51 Hv. This new SPD process is promising for future industrial applications. © 2011 Elsevier B.V. All Rights Reserved.

News Article | December 14, 2016
Site: www.sciencemag.org

During the 1920s and 1930s, Viennese physician and adventurer Alfons Gabriel fell under the spell of Iran's Lut Desert. Gabriel had crisscrossed arid parts of the Middle East, Pakistan, and Afghanistan by camel, observing and mapping areas into which few dared venture—lands with names such as Dasht-i-Naumid (the Desert without Hope) and Dasht-i-Margo (the Desert of Death). But a "confused mass of impassable tangled dunes" stymied his efforts to probe the interior of the Lut Desert, a tract of sand and fantastical rock formations in southeastern Iran that was said to be the hottest place on Earth. In March 1937, Gabriel finally conquered the central Lut—and barely made it out alive. He described his experiences a year later in a spellbinding talk to the Royal Geographical Society in London. Late one afternoon, Gabriel recounted, "the landscape darkened under red clouds … and a noise like the roaring of the sea began." The dust storm raged into the night. "For several anxious hours we lay, motionless and helpless, outstretched on the ground." Later, the voyagers were disoriented by mirages that were most vivid when the air was coolest, just before sunrise. Near the end of the 3-week journey, even their parched camels had had enough: "Their legs trembled; they panted, knelt down, and sometimes crept along on their knees." The allure of the Lut persists. Last month, a convoy of five SUVs carried 10 researchers and their guides, along with cameras, instruments, and hundreds of liters of water and fuel, into the heart of the desert. These modern explorers from Iran, the United States, and Europe were drawn not so much by the exotic landscape as by the puzzle of its unusual ecosystem. Many researchers had assumed that the Lut Desert is too hostile to sustain life, says Hossein Akhani, a plant biologist at the University of Tehran. The interior of the desert, an area nearly as big as West Virginia, is mostly devoid of plant life. But adventurers and the occasional scientist who traveled into the Lut had spotted diverse animal life, including insects, reptiles, and desert foxes. How that food web holds together without plants has been a mystery. A morbid, and possibly unique, phenomenon may be the answer. Dead birds are a frequent sighting in the desert. A few years ago, scientists in Iran began wondering whether migratory birds stray into the Lut and, overcome by the intense heat, fall from the sky like manna, forming the base of a food web. The expedition, organized by Akhani and Bahman Izadi, head of an environmental nonprofit in Shiraz, Iran, and a Lut explorer, set out to test the idea. Colleagues warned that in the fall, right after the heat of summer, the team might not find enough living things to tell. Creatures that burrowed or migrated to escape the heat would not have had time to venture back into the desert. Instead, the team confirmed the existence of a vibrant ecosystem and saw compelling signs that migratory birds do help nourish it. They also found that the bone-dry landscape conceals what they are calling a "hidden sea": a surprisingly shallow layer of salty groundwater that may also help sustain life. The Lut Desert also offers a less uplifting lesson—at least for people living on the knife edge of sustainability in arid regions. Climate change models predict that as temperatures rise, tracts of the Middle East that are naturally uninhabitable—not survivable without air conditioning—will expand. Those areas may come to resemble the transition zone between settlements on the Lut's edges and its supremely hostile core. After Gabriel's pioneering venture, the scientific literature on the Lut Desert remained sparse. One point was settled, though: Gabriel had noted that a contemporary, the German geographer Gustav Stratil-Sauer, "was of the opinion that the hottest region of the earth was not, as hitherto supposed, to be found in Sind, or Abyssinia, or in the Death Valley of California, but in the southern Lut." In 2005, an infrared radiometer on NASA's Aqua satellite measured a ground temperature of 70.7°C (159.3°F) at one spot in the Lut—the hottest satellite reading of ground temperature ever. And in April 2014, Morteza Djamali, a paleoecologist at the Mediterranean Institute of Marine and Terrestrial Biodiversity and Ecology in Marseilles, France, and his colleagues ventured into the central Lut to install a temperature logger at the same spot. In an experience worthy of Alfred Hitchcock, a swarm of locusts descended, picking nearby bird carcasses clean, cannibalizing each other, and biting the researchers. "I can imagine that a lonely traveler could be killed by these small creatures" in a few days, Djamali says. The hardship paid off, Djamali says. In July, the thermometer, planted 30 centimeters above the surface in the shade of a wooden cylinder, registered 61°C—some 5°C higher than the official shade record set in Death Valley in 1913. Bands of heat-absorbing black sand, primarily magnetite, together with topography that limits air movement help explain the blazing temperatures, Djamali says. That same year Akhani paid his first visit to the Lut, a quick scouting trip. A specialist in salt-loving plants, which grow in salty seeps in a few spots in the desert, he also had noticed the birds' carcasses and wondered what role they might play in the ecosystem. Cobbling together backing from the Iranian National Science Foundation, the Saeedi Institute for Advanced Studies at Kashan University in Iran, and other sources, he assembled a team of specialists from Iran and abroad that will spend the next 5 years prizing scientific secrets from the desert. The team set off last month on its maiden expedition, departing from Shahdad, an oasis on the Lut's western edge, and heading due north before arcing south in a path that bisected the desert. In some areas, yardangs, wind-sculpted rock formations several meters tall, sprouted from the desert like mushrooms. Heftier formations called kaluts reminded Akhani of "the ruins of an old city." Relics of what Djamali calls a "complex geoclimatic history," some are made of sandstone, whereas others were eroded from the beds of saline and playa lakes that dotted the landscape some 10 million years ago. The topography, whimsical or majestic, is a major reason the United Nations Educational, Scientific and Cultural Organization inscribed the Lut Desert on its World Heritage List last July. (Iran hopes it will beckon intrepid ecotourists.) Along their 700-kilometer journey, the researchers sampled soil and biota at 37 sites before emerging from the desert east of Bam, a city that suffered catastrophic damage from a 2003 earthquake. One day, the team struck out on foot into a canyon called Zabone Mar, which means "snake's tongue." By satellite, the canyon, about 15 meters wide with walls reaching 30 meters high, looks like a bifurcated tongue. "I noticed a weird noise," recalls expedition member Amir AghaKouchak, a hydrologist at the University of California (UC), Irvine. A continuous, soft crackling emanated from the walls. He speculates that the sound was the rock expanding as temperatures soared from nightly lows near 0°C up to fall daily maximums of about 40°C. "I just stopped and listened to this beautiful music." Or perhaps it was a siren call: The canyon is a death trap. Within its walls, the researchers found the remains of dozens of migratory birds. The birds may have sought shelter in the canyon's shade, but without water they would have quickly perished, AghaKouchak says. Mahmoud Ghasempouri, an ornithologist at Tarbiat Modares University in Tehran, collected carcasses of several migratory species. Why the birds make a fatal detour into the desert is a puzzle, he says. Even outside the canyon dead migratory birds were plentiful, and they often bore signs of having been scavenged by foxes. "I think that's their main food source," AghaKouchak says. Insects, too, are critical to the Lut's food web. Many nibble on plants on the desert's periphery and are in turn eaten by spiders, reptiles, and foxes in the Lut's interior, supplementing the nutrients in the ill-fated birds, says expedition member Hossein Rajaei, curator of Lepidoptera—moths and butterflies—at the Stuttgart State Museum of Natural History in Germany. Yet some live in the heart of the desert. When Rajaei set up light traps at night, he was surprised to count large numbers of moth species. "What do they do there? What do they eat there?" he asks. How the fly larvae he found in a pool of hypersaline water survive is another enigma, he says. And so is the question of how the Lut's denizens stay hydrated. The answer may lie just below the surface. Before the expedition began, AghaKouchak had scrutinized satellite sensor data from the Lut. To his surprise, microwaves emanating from the ground suggested that in some parts of the oven-hot desert, the soil is moist. Perplexed, AghaKouchak consulted a colleague, who proposed that the Lut's soil is so dry that microwaves were radiating from deeper layers of soil or even rocks, falsely indicating shallow moisture. Last month, in the heart of the desert, the team's convoy entered "a flat landscape, as far as you can see," the hydrologist says. A short distance onto the plain, one of the trucks broke through several centimeters of hard, crusty soil and sank, up to its axles—in mud. After another SUV pulled out the stricken vehicle, "you could actually see water" where the tires had been. "It was hard to believe," AghaKouchak says, "but the area is really, really wet." He thinks the moisture comes from distant mountains that ring the table-flat playa. Occasional rainfalls in the spring and early fall drain into the flat basin, he says. According to the team's guides, other areas of the Lut have similar features. Back at UC Irvine, AghaKouchak will attempt to correlate the local knowledge with satellite moisture data to map the extent of the hidden sea. No one lives in the heart of the Lut, and after a 6-year-long drought in Iran, settlements on the desert's fringes are in retreat. That may foreshadow the fate of other parts of the Middle East as global warming pushes summer temperatures still higher, says Elfatih Eltahir, an environmental engineer at the Massachusetts Institute of Technology in Cambridge. Last year, in Nature Climate Change, Eltahir and a colleague defined a naturally uninhabitable climate as one in which the heat index—temperature adjusted for humidity—exceeds 35°C for more than six straight hours. "What we are talking about are really extreme conditions," Eltahir says. "If a human being is exposed to that, very likely that person would die." In summer, areas of the Persian Gulf already exceed that threshold and would be unbearable without air-conditioning. Barring "significant mitigation," the uninhabitable areas near the Persian Gulf are likely to expand, including arid but still habitable regions of Iran. "Lut would be a good lab to study what an extreme environment would look like," AghaKouchak says. To probe such questions more deeply, Akhani's team plans to return in the spring. Among other things, they will bring more sophisticated instruments for measuring soil moisture and set up camera traps to study the ecology of the desert fox and other creatures in more detail. They also hope to decipher at a molecular level how the life forms adapt to broiling heat, Akhani says. In 2018, they may even attempt a summer expedition. "If we go then, we probably need to bring a physician," says AghaKouchak, who hastens to add, "I can't wait to go back."

Hosseinaei O.,University of Tennessee at Knoxville | Wang S.,University of Tennessee at Knoxville | Enayati A.A.,University of Tehran | Rials T.G.,University of Tennessee at Knoxville
Composites Part A: Applied Science and Manufacturing | Year: 2012

Hygroscopicity, low durability, and low thermal resistance are disadvantages of lignocellulosic materials that also plague wood-plastic composites (WPCs). Hemicellulose is the most hydrophilic wood polymer and is currently considered as a sugar source for the bioethanol industry. The objective of this research is to extract hemicellulose from woody materials and enhance the properties of WPC by diminishing the hydrophilic character of wood. Hemicellulose of Southern Yellow Pine was extracted by hot-water at three different temperatures: 140, 155, and 170 °C. Wood flour was compounded with polypropylene in an extruder, both with and without a coupling agent. Injection molding was used to make tensile test samples. The thermal stability of wood flour was found to have increased after extraction. Extraction of hemicellulose improved the tensile strength and water resistance of composites, which may indicate a decrease in the hygroscopicity of wood flour, better compatibility, and interfacial bonding of the filler and matrix. © 2012 Elsevier Ltd. All rights reserved.

Ejtemaei M.,Amirkabir University of Technology | Gharabaghi M.,University of Tehran | Irannajad M.,Amirkabir University of Technology
Advances in Colloid and Interface Science | Year: 2014

In recent years, extraction of zinc from low-grade mining tailings of oxidized zinc has been a matter of discussion. This is a material which can be processed by flotation and acid-leaching methods. Owing to the similarities in the physicochemical and surface chemistry of the constituent minerals, separation of zinc oxide minerals from their gangues by flotation is an extremely complex process. It appears that selective leaching is a promising method for the beneficiation of this type of ore. However, with the high consumption of leaching acid, the treatment of low-grade oxidized zinc ores by hydrometallurgical methods is expensive and complex. Hence, it is best to pre-concentrate low-grade oxidized zinc by flotation and then to employ hydrometallurgical methods. This paper presents a critical review on the zinc oxide mineral flotation technique. In this paper, the various flotation methods of zinc oxide minerals which have been proposed in the literature have been detailed with the aim of identifying the important factors involved in the flotation process. The various aspects of recovery of zinc from these minerals are also dealt with here. The literature indicates that the collector type, sulfidizing agent, pH regulator, depressants and dispersants types, temperature, solid pulp concentration, and desliming are important parameters in the process. The range and optimum values of these parameters, as also the adsorption mechanism, together with the resultant flotation of the zinc oxide minerals reported in the literature are summarized and highlighted in the paper. This review presents a comprehensive scientific guide to the effectiveness of flotation strategy. © 2013 Elsevier B.V.

Hosseinabadi Farahani M.,University of Tehran | Hosseini L.,Amirkabir University of Technology
International Journal of Advanced Manufacturing Technology | Year: 2013

This paper considers the single machine scheduling problem with a new version of time-dependent processing times. The processing time of a job is defined as a piecewise linear function of its start time. It is preferred that the processing of each job be started at a specific time which means that processing the job before or after that time implies additional effort to accomplish the job. The job-processing time is a nonmonotonic function of its start time. The increasing rate of processing times is job independent and the objective is to minimize the cycle time. We show that the optimal schedule is V shaped and propose an optimal polynomial time algorithm for the problem. © 2012 Springer-Verlag London Limited.

Hamta N.,Amirkabir University of Technology | Fatemi Ghomi S.M.T.,Amirkabir University of Technology | Jolai F.,University of Tehran | Akbarpour Shirazi M.,Amirkabir University of Technology
International Journal of Production Economics | Year: 2013

This paper addresses multi-objective (MO) optimization of a single-model assembly line balancing problem (ALBP) where the operation times of tasks are unknown variables and the only known information is the lower and upper bounds for operation time of each task. Three objectives are simultaneously considered as follows: (1) minimizing the cycle time, (2) minimizing the total equipment cost, and (3) minimizing the smoothness index. In order to reflect the real industrial settings adequately, it is assumed that the task time is dependent on worker(s) (or machine(s)) learning for the same or similar activity and sequence-dependent setup time exists between tasks. Finding an optimal solution for this complicated problem especially for large-sized problems in reasonable computational time is cumbersome. Therefore, we propose a new solution method based on the combination of particle swarm optimization (PSO) algorithm with variable neighborhood search (VNS) to solve the problem. The performance of the proposed hybrid algorithm is examined over several test problems in terms of solution quality and running time. Comparison with an existing multi-objective evolutionary computation method in the literature shows the superior efficiency of our proposed PSO/VNS algorithm. © 2012 Elsevier B.V. All rights reserved.

Bahrami M.,Amirkabir University of Technology | Dehghani K.,Amirkabir University of Technology | Besharati Givi M.K.,University of Tehran
Materials and Design | Year: 2014

The main object of the present study is to investigate the effect of nano-sized SiC particle on the mechanical properties of the friction stir welding (FSW) joints. Prior to FSW, nano-sized SiC particles were incorporated into the joint line. A combination of three rotational speeds and three traveling speeds were applied. Microstructural evaluation using optical microscopy (OM) and scanning electron microscopy (SEM) revealed a banded structure consisting of particle-rich and particle-free regions in stir zone (SZ). The joints fabricated with rotational speed of 1250. rpm and traveling speeds of 40 and 50. mm/min, exhibited the highest mechanical properties. Owing to the presence of SiC nano-particles, at 1250. rpm and 40. mm/min, ultimate tensile strength (UTS) and percentage of elongation were improved by 31% and 76.1%, respectively. Significant increase in UTS and percentage of elongation were attributed to the pinning effect and increased nucleation sites associated with SiC nano-particles. Moreover, reinforcement particles resulted in breaking of primary grains. On the other hand, at 1250. rpm and 40. mm/min, SiC-included specimen showed superior ductility to SiC-free specimen. The fracture morphologies were in good agreement with corresponding ductility results. © 2013 Elsevier Ltd.

Nasiri A.,University of Tehran | Shariaty-Niasar M.,University of Tehran | Rashidi A.M.,Research Institute of Petroleum Industry RIPI | Khodafarin R.,Research Institute of Petroleum Industry RIPI
International Journal of Heat and Mass Transfer | Year: 2012

Thermal conductivity and stability of carbon nanotube (CNT) structures in water-based nanofluid, as well as their dependence to temperature and time variation are of a great concern. In order to investigate such dependence, five different structures, namely SWNT (single wall CNT), DWNT (double wall CNT), FWNT (few wall CNT) and two different multiwalls were applied in this study. The experiments reveal that the maximum UV-VIS absorbance of the solution corresponds to the dispersion of SWNT in the base fluid. The results from zeta size distribution and thermal conductivity demonstrate that as the number of nanotube wall increase, both stability and thermal conductivity decrease. © 2011 Elsevier Ltd. All rights reserved.

Bahrami M.,Amirkabir University of Technology | Besharati Givi M.K.,University of Tehran | Dehghani K.,Amirkabir University of Technology | Parvin N.,Amirkabir University of Technology
Materials and Design | Year: 2014

The main purpose of this research is to investigate the influence of pin geometry on the macrostructure, microstructure and mechanical properties of the friction stir welds, reinforced with SiC nano-particles. Toward this end, friction stir welding (FSW) conducted using five geometrically different pin tools. Other welding parameters were remained unchanged. Microstructural evaluation using optical microscopy (OM) and scanning electron microscopy (SEM) revealed a banded structure consisting of particle-rich and particle-free regions in stir zone (SZ). The most uniform particle distribution was found in the case of using threaded tapered pin tool. On the other hand, it was discovered that the reinforcements had severely accumulated in the SZ of specimen friction stir welded (FSWed) with four-flute cylindrical pin tool. Moreover, threaded tapered and four-flute cylindrical specimens showed the highest and the lowest microhardness, respectively. In spite of four-flute cylindrical specimen, other specimens failed in base metal during tensile testing. Besides, the highest ultimate tensile strength (UTS) was recorded for the specimen FSWed with triangular pin tool. Fracture surface of tensile specimens were also studied employing SEM technique. © 2013 Elsevier Ltd.

Momeni A.,Amirkabir University of Technology | Abbasi S.M.,University of Tehran
Materials and Design | Year: 2010

Hot deformation behavior of the alloy Ti-6Al-4V was investigated via conducting hot compression tests at temperatures of 800-1150°C and at strain rates, ranging from 0.001s-1 to 1s-1, at an interval of an order of magnitude. The apparent differences of flow stress curves obtained in dual phase α+β and single phase β regions were analyzed in term of different dependence of flow stress to temperature and strain rate and different microstructural evolutions. The values of strain rate sensitivity and apparent activation energy were obtained respectively as 0.20 and 530kJ/mol for two phase microstructure. However, for single phase β microstructure they were approximated as 0.19 and 376kJ/mol, respectively. It was found that in two phase region the values of strains corresponding to peak point, εp, and the highest rate of flow softening, ε*, are almost independent to Zenner-Hollomon parameter. In single phase region, εp and ε* exhibited a direct relationship to Z parameter and the corresponding empirical equations were proposed. © 2010 Elsevier Ltd.

Jamil M.,National University of Sciences and Technology | Mahomed F.M.,University of Witwatersrand | Momeni D.,University of Tehran
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

In this Letter by utilizing the Noether symmetry approach in cosmology, we attempt to find the tachyon potential via the application of this kind of symmetry to a flat Friedmann-Robertson-Walker (FRW) metric. We reduce the system of equations to simpler ones and obtain the general class of the tachyon's potential function and f(R) functions. We have found that the Noether symmetric model results in a power law f(R) and an inverse fourth power potential for the tachyonic field. Further we investigate numerically the cosmological evolution of our model and show explicitly the behavior of the equation of state crossing the cosmological constant boundary. © 2011 Elsevier B.V.

Chehrazi E.,Amirkabir University of Technology | Taheri Qazvini N.,University of Tehran
Iranian Polymer Journal (English Edition) | Year: 2013

The influence of nanoconfinement on segmental relaxation behavior of poly(methyl methacrylate) and poly(styrene-ran-acrylonitrile) miscible blend and its nanocomposites with spherical and layered nanoparticles have been investigated. Dynamic mechanical analysis was employed to examine the effect of geometry of nanoparticles on the temperature dependence and relaxation function breadth of segmental dynamics (α-relaxation) in the glass transition region. The maxima of the loss modulus curves were used to fit to the Vogel-Fulcher-Tamman equation to describe the temperature dependence of the characteristic relaxation times. Furthermore, the T g-normalized semi-logarithmic Arrhenius plots (fragility plots) were exploited to indicate the changes in cooperative segmental motions across the glass transition. The master curves for relaxation modulus were also constructed for each sample as a function of time using the time-temperature superposition principle. The investigated nanocomposites showed a narrower segmental dispersion in the glass transition region compared to the neat systems. The relaxation modulus master curves were fitted by the Kohlrausch-Williams-Watts (KWW) function. It was observed that the distribution parameter of segmental relaxation time increased with addition of nanoparticles which was correlated with a decrease in fragility index. In addition, the increase of the KWW distribution parameter (β KWW) for spherical silica nanocomposites was less than that for nanocomposites prepared with layered silicates (organoclay). © 2013 Iran Polymer and Petrochemical Institute.

Firouzi M.,University of Tehran | Gharehpetian G.B.,Amirkabir University of Technology
IEEE Transactions on Energy Conversion | Year: 2013

The interaction between wind turbines and grid results in increasing short-circuit level and fault ride-through (FRT) capability problem during fault condition. In this paper, the bridge-type fault current limiter (FCL) with discharging resistor is used for solving these problems. For this FCL, a control scheme is proposed, which uses the dc reactor current as control variable, to adjust the terminal voltage of induction generator (IG) without measuring any parameters of system. In this paper, the wind energy conversion system (WECS) is a fixed-speed system equipped with a squirrel-cage IG. The drivetrain is represented by a two-mass model. The analytical and simulation studies of the bridge-type FCL and proposed control scheme for limiting the fault current and improving FRT capability are presented and compared with the impact of the application of the series dynamic braking resistor (SDBR). © 1986-2012 IEEE.

Salamat-Talab M.,Iran University of Science and Technology | Nateghi A.,University of Tehran | Torabi J.,Amirkabir University of Technology
International Journal of Mechanical Sciences | Year: 2012

In this paper, Modified couple stress theory is developed for third-order shear deformation functionally graded (FG) micro beam. Classical Continuum theories are not able to capture size effects while higher order continuum theories consider material length scale parameters to improve the results in micro scales by interpreting size dependencies. By applying Hamilton's principle, governing equations, boundary and initial conditions are derived for a FG micro beam. It is assumed that properties of the FG micro beam follow a power law form through thickness. In addition, Poisson's ratio is assumed constant in the current model. Bending and free vibration of the simply supported FG micro beam is analyzed to illustrate size effects. It is observed that if the thickness of the beam is in the order of the material length scale parameter, size effects are more considerable. It is shown that size dependencies of FG micro beams are quite different from isotropic homogeneous beams as they have maximum and minimum size effects for certain values of power index of material distribution and Poisson's ratio. Moreover, it is shown that the results obtained by the present model deviates significantly from those in which Poissons effect is neglected. Also, the effect of Poisson's ratio on the deflection and natural frequency based on modified couple stress theory is proven to be different from Classical one. The numerical results for simply supported thin beams show that the first natural frequency estimated by the current model is higher than the classical one. In addition, it is observed that size effect is more significant for higher vibration modes. © 2012 Elsevier Ltd. All rights reserved.

Ghodousian A.,University of Tehran | Khorram E.,Amirkabir University of Technology
Fuzzy Sets and Systems | Year: 2012

In this paper, optimization of a linear objective function with fuzzy relational inequality constraints is investigated whereby an arbitrary function is considered as fuzzy composition. The feasible solution set is determined and compared with some common results in the literature. A necessary and sufficient condition and three other necessary conditions are presented to conceptualize the feasibility of the problem. It is shown that in general a lower bound is always attainable for the optimal objective value. Moreover, we prove that the optimal solution of the problem is obtained if the problem is defined by a non-decreasing or non-increasing function. An algorithm is presented to summarize the process and an example is described to illustrate the algorithm. © 2012 Elsevier B.V.

Abdollahi M.,Wayne State University | Arvan M.,University of Tehran | Razmi J.,University of Tehran
Expert Systems with Applications | Year: 2015

Supply chain environment is more dynamic and unpredictable than the past; therefore, it needs to be highly flexible in order to reconfigure in response to changes in their environment on the spur of the moment. This study presents a framework for supplier selection based on product-related and organization-related characteristics of the suppliers to be more competitive in the market and flexible to overcome probable changes in demands, supplies etc. Product-related and organization-related characteristics are those which are named in this study as lean and agile criteria respectively. Comprehensively digging up the literature, we extract the best criteria representing both leanness and agility of an organization. The aim of this paper is to select an appropriate supplier portfolio based on two afore-mentioned concepts. Supplier selection problem is solved using a combination of multi-criteria decision making (MCDM) methods. Due to the interaction between the criteria, analytical network process (ANP) is applied for determining the weight of each criterion for each alternative (supplier), and then data envelopment analysis (DEA) is used to rank them. The reason that DEA is used in this study is that when the number of suppliers increases, ANP approach tends to work inefficiently. Moreover, for determining the accurate interdependencies between the proposed criteria, fuzzy decision making trial and evaluation laboratory (DEMATEL) is applied. The framework is applied on a real case to demonstrate its applicability and feasibility. © 2014 Elsevier Ltd. All rights reserved.

Mahpeykar S.M.,Amirkabir University of Technology | Koohsorkhi J.,University of Tehran | Ghafoori-Fard H.,Amirkabir University of Technology
Nanotechnology | Year: 2012

Long vertically aligned ZnO nanowire arrays were synthesized using an ultra-fast microwave-assisted hydrothermal process. Using this method, we were able to grow ZnO nanowire arrays at an average growth rate as high as 200nmmin 1 for maximum microwave power level. This method does not suffer from the growth stoppage problem at long growth times that, according to our investigations, a normal microwave-assisted hydrothermal method suffers from. Longitudinal growth of the nanowire arrays was investigated as a function of microwave power level and growth time using cross-sectional FESEM images of the grown arrays. Effect of seed layer on the alignment of nanowires was also studied. X-ray diffraction analysis confirmed c-axis orientation and single-phase wurtzite structure of the nanowires. JV curves of the fabricated ZnO nanowire-based mercurochrome-sensitized solar cells indicated that the short-circuit current density is increased with increasing the length of the nanowire array. According to the UVvis spectra of the dyes detached from the cells, these increments were mainly attributed to the enlarged internal surface area and therefore dye loading enhancement in the lengthened nanowire arrays. © 2012 IOP Publishing Ltd.

Naderi R.,University of Tehran | Mahdavian M.,Sahand University of Technology | Darvish A.,Amirkabir University of Technology
Progress in Organic Coatings | Year: 2013

Protective performance of the epoxy primer containing strontium aluminum polyphosphate (SAPP) as a zinc-free phosphate-based anticorrosion pigment is aimed to assess in this work through taking advantage of electrochemical impedance spectroscopy (EIS) and electrochemical noise method (ENM). The absence of zinc offers an excellent environmentally friendly profile to the class of inhibiting compound. In the pigment extracts, the electrochemical techniques revealed superiority of SAPP compared to the conventional zinc phosphate (ZP). The behavior was connected to precipitation of a protective layer on the surface exposed to SAPP. In comparison with ZP, the most effective SAPP content in the protective primer was then determined using EIS. © 2012 Elsevier B.V.

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.

Sanayei A.,Wayne State University | Farid Mousavi S.,University of Tehran | Yazdankhah A.,Islamic Azad University at Bonab
Expert Systems with Applications | Year: 2010

During recent years, how to determine suitable suppliers in the supply chain has become a key strategic consideration. However, the nature of supplier selection is a complex multi-criteria problem including both quantitative and qualitative factors which may be in conflict and may also be uncertain. The VIKOR method was developed to solve multiple criteria decision making (MCDM) problems with conflicting and non-commensurable (different units) criteria, assuming that compromising is acceptable for conflict resolution, the decision maker wants a solution that is the closest to the ideal, and the alternatives are evaluated according to all established criteria. In this paper, linguistic values are used to assess the ratings and weights for these factors. These linguistic ratings can be expressed in trapezoidal or triangular fuzzy numbers. Then, a hierarchy MCDM model based on fuzzy sets theory and VIKOR method is proposed to deal with the supplier selection problems in the supply chain system. A numerical example is proposed to illustrate an application of the proposed model. © 2009.

Gharagheizi F.,University of Tehran | Sattari M.,Research Institute of Petroleum Industry RIPI
Industrial and Engineering Chemistry Research | Year: 2010

A quantitative structure property relationship study was performed to develop a model for the prediction of triple-point temperature of pure components. For developing this model, 638 pure components were used, and, for whichever, 1664 molecular descriptors were determined. As a standard tool for subset variable selection, genetic algorithm-based multivariate linear regression (GA-MLR) technique was used. The obtained model is a seven parameters multilinear equation that has a squared correlation coefficient of 0.9410 (R2 = 0.9410). © 2010 American Chemical Society.

Hosseinifard B.,Amirkabir University of Technology | Moradi M.H.,Amirkabir University of Technology | Rostami R.,University of Tehran
Computer Methods and Programs in Biomedicine | Year: 2013

Diagnosing depression in the early curable stages is very important and may even save the life of a patient. In this paper, we study nonlinear analysis of EEG signal for discriminating depression patients and normal controls. Forty-five unmedicated depressed patients and 45 normal subjects were participated in this study. Power of four EEG bands and four nonlinear features including detrended fluctuation analysis (DFA), higuchi fractal, correlation dimension and lyapunov exponent were extracted from EEG signal. For discriminating the two groups, k-nearest neighbor, linear discriminant analysis and logistic regression as the classifiers are then used. Highest classification accuracy of 83.3% is obtained by correlation dimension and LR classifier among other nonlinear features. For further improvement, all nonlinear features are combined and applied to classifiers. A classification accuracy of 90% is achieved by all nonlinear features and LR classifier. In all experiments, genetic algorithm is employed to select the most important features. The proposed technique is compared and contrasted with the other reported methods and it is demonstrated that by combining nonlinear features, the performance is enhanced. This study shows that nonlinear analysis of EEG can be a useful method for discriminating depressed patients and normal subjects. It is suggested that this analysis may be a complementary tool to help psychiatrists for diagnosing depressed patients. © 2012 Elsevier Ireland Ltd.

Naderi R.,University of Tehran | Attar M.M.,Amirkabir University of Technology
Progress in Organic Coatings | Year: 2014

In the field of protective coatings, zinc-free pigments are proposed as promising anticorrosion compounds due to their excellent environmentally- friendly profile. In this paper, cathodic disbonding performance of a solvent-borne epoxy primer incorporating strontium aluminum polyphosphate (SAPP) as a zinc-free phosphate-based anticorrosion pigment was investigated. Regardless of the applied potential, the presence of SAPP in the coating formulation caused slower growth of the delamination area in comparison to ZP. According to the data obtained from EIS and SEM/EDX, this behavior was attributed to locally controlled pH and the precipitated film restricting active zones available for electrochemical reactions. © 2014 Elsevier B.V.

Foumani M.,University of Tehran | Jenab K.,Society of Reliability Engineering
International Journal of Production Research | Year: 2012

In this paper, reentrant robotic cells composed of a robot with swap ability for a single part type is studied. In this regard, we restrict our attention to the two-machine reentrant cell scheduling problem. In the cell, a part visits the machines at least once. To minimise the cycle time, the sequence of robot moves must be optimised. Based on our previous study on the optimality of robotic cells, we restrict our investigation to only one-unit cycles. Therefore, all one-unit cycles are generated and their cycle time formulae are developed. Initially, we determine both essential and sufficient conditions for different cycles to be optimal and present the regions of optimality when each part reenters the first machine two times. We determine optimality conditions for different cycles when each part reenters both machines two times. Finally, sensitivity analysis is performed for both cases and the influence of the parameter values in the regions of optimality for each cycle is shown. © 2012 Copyright Taylor and Francis Group, LLC.

Vahidi B.,University of Tehran | Fatouraee N.,Amirkabir University of Technology
Journal of Biomechanics | Year: 2012

Arterial embolism is responsible for the death of lots of people who suffers from heart diseases. The major risk of embolism in upper limbs is that the ruptured particles are brought into the brain, thus stimulating neurological symptoms or causing the stroke. We presented a computational model using fluid-structure interactions (FSI) to investigate the physical motion of a blood clot inside the human common carotid artery. We simulated transportation of a buoyant embolus in an unsteady flow within a finite length tube having stenosis. Effects of stenosis severity and embolus size on arterial hemodynamics were investigated. To fulfill realistic nonlinear property of a blood clot, a rubber/foam model was used. The arbitrary Lagrangian-Eulerian formulation (ALE) and adaptive mesh method were used inside fluid domain to capture the large structural interfacial movements. The problem was solved by simultaneous solution of the fluid and the structure equations. Stress distribution and deformation of the clot were analyzed and hence, the regions of the embolus prone to lysis were localized. The maximum magnitude of arterial wall shear stress during embolism occurred at a short distance proximal to the throat of the stenosis. Through embolism, arterial maximum wall shear stress is more sensitive to stenosis severity than the embolus size whereas role of embolus size is more significant than the effect of stenosis severity on spatial and temporal gradients of wall shear stress downstream of the stenosis and on probability of clot lysis due to clot stresses while passing through the stenosis. © 2012 Elsevier Ltd.

Akbari T.,University of Tehran | Rahimikian A.,University of Tehran | Kazemi A.,Iran University of Science and Technology
Energy Conversion and Management | Year: 2011

This paper presents a multi-stage stochastic model for short-term transmission expansion planning considering the available transfer capability (ATC). The ATC can have a huge impact on the power market outcomes and the power system reliability. The transmission expansion planning (TEP) studies deal with many uncertainties, such as system load uncertainties that are considered in this paper. The Monte Carlo simulation method has been applied for generating different scenarios. A scenario reduction technique is used for reducing the number of scenarios. The objective is to minimize the sum of investment costs (IC) and the expected operation costs (OC). The solution technique is based on the benders decomposition algorithm. The N-1 contingency analysis is also done for the TEP problem. The proposed model is applied to the IEEE 24 bus reliability test system and the results are efficient and promising. © 2011 Elsevier Ltd. All rights reserved.

Hendi S.H.,Yasouj University | Momeni D.,University of Tehran
European Physical Journal C | Year: 2011

In this paper, we consider F(R) = R + f (R) theory instead of Einstein gravity with conformal anomaly and look for its analytical solutions. Depending on the free parameters, one may obtain both uncharged and charged solutions for some classes of F(R) models. Calculation of Kretschmann scalar shows that there is a singularity located at r = 0. The geometry of uncharged (charged) solution corresponds to the Schwarzschild (Reissner–Nordström) singularity. Further, we discuss the viability of our models in detail. We show that these models can be stable, depending on their parameters and in different epochs of the universe. © Springer-Verlag/Società Italiana di Fisica 2011

Kaveh A.,Iran University of Science and Technology | Motie Share M.A.,University of Tehran | Moslehi M.,University of Tehran
Acta Mechanica | Year: 2013

An improved version of the charged system search (CSS) algorithm is introduced which is called magnetic charged system search (MCSS). In the new algorithm, magnetic forces are considered in addition to electrical forces, using the Biot-Savart law. Each charged particle (CP), as a search agent, exerts magnetic forces on other CPs based on the variation of its objective function value during its last movement and its distance between other CPs. This additional force provides useful information for the optimization process and enhances the performance of the CSS algorithm. The efficiency of the MCSS is examined by application of this algorithm to well-known mathematical benchmarks and three well-studied engineering design problems. The results are compared to those of the CSS, and the improvements are highlighted. © 2012 Springer-Verlag Wien.

Torabi A.R.,University of Tehran | Ayatollahi M.R.,Iran University of Science and Technology
European Journal of Mechanics, A/Solids | Year: 2014

The aim of this research was to present a brittle fracture model for predicting the compressive failure load of engineering components weakened by V-notches with end holes (VO-notches). For this purpose, two well-known brittle fracture models in tension, namely the point stress (PS) and the mean stress (MS) were applied to the compressive stress field around the VO-notches and for each model a closed-form expression was obtained for the compressive mode I notch fracture toughness. In order to evaluate the validity of PS and MS criteria, the theoretical values of compressive notch fracture toughness were compared with the experimental results reported recently in literature dealing with fracture in fine-grained isostatic graphite plates containing V-notches with end holes subjected to pure compression. The results showed that while the MS model with a total discrepancy of 5% was an appropriate failure criterion, the PS model with about 86% accuracy could not predict the experimental results satisfactorily.©2013 Elsevier Masson SAS. All rights reserved.

Bandari S.,University of Tehran | Herzog J.,University of Duisburg - Essen
European Journal of Combinatorics | Year: 2013

In this paper we consider monomial localizations of monomial ideals and conjecture that a monomial ideal is polymatroidal if and only if all its monomial localizations have a linear resolution. The conjecture is proved for squarefree monomial ideals where it is equivalent to a well-known characterization of matroids. We prove our conjecture in many other special cases. We also introduce the concept of componentwise polymatroidal ideals and extend several of the results known for polymatroidal ideals to this new class of ideals. © 2012 Elsevier Ltd.

Maleki A.,Iran University of Science and Technology | Rezayan A.H.,University of Tehran
Tetrahedron Letters | Year: 2014

A one-pot, three-component reaction for the synthesis of pyrido[2′,1′:2,3]imidazo[4,5-c]isoquinolines starting from 2-aminopyridines, phthalaldehyde, and trimethylsilyl cyanide in good to high yields is described. © 2014 Elsevier Ltd. All rights reserved.

Tolaminejad B.,Iran University of Science and Technology | Dehghani K.,University of Tehran
Materials and Design | Year: 2012

In the present research, equal channel angular extrusion (ECAE) of commercial purity aluminum (1070) was conducted using route BC. For ECAE processing a proper die set was designed and constructed. Electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) analyses were used to evaluate the microstructure and texture of the extruded materials. The results reveal two distinct processing regimes: from 1 to 4 passes the microstructure evolves from elongated subgrains to a rather equiaxed array of ultrafine grains and from 4 to 8 passes there is no strict change in the average grain size. The boundary misorientation angle and the fraction of high-angle boundaries increase rapidly up to 4 passes and at a slower rate from 4 to 8 passes. Also, the variation of hardness and yield stress with number of extrusion was documented up to 8 passes. The present results showed that first ECAE pass has resulted in enhancement of mechanical properties more than four times over the annealed condition. Further ECAE processing has resulted in slight improvement. Based on two strengthening mechanisms, variations of the strength as a function of the pass numbers were related to the calculated dislocation densities and the average boundary spacing. © 2011 Elsevier Ltd.

Nejad M.Z.,Yasouj University | Rastgoo A.,University of Tehran | Hadi A.,University of Tehran
International Journal of Engineering Science | Year: 2014

Presented in this paper is an exact closed-form analytical solution for elasto-plastic deformations and stresses in a rotating disk made of functionally graded materials (FGMs) in which the elasto-perfectly-plastic material model is employed. As for the yield criterion, the well-known Tresca's model is used. The material properties are assumed to vary according to the power law whereas the Poisson's ratio is kept constant. For various values of inhomogeneity constant, the so-obtained solution is then used to study the distribution of limit angular speed, displacement and stresses versus the radial direction. Moreover, the effect of increasing the angular speed on the propagation of the plastic zone is investigated. This analysis reveals that the plasticity can occur in different regions of the disk. To the best of authors' knowledge, so far all previous exact solutions for the elasto-plastic analysis of FGM disks address the case of constant material density. The novelty of this work is to present an exact solution by taking into account the variation of density. The results show that the variation of density has a significant influence on the distribution of deformations and stresses. Furthermore, the effect of changing Poisson's ratio on the value of the critical material parameter is demonstrated. © 2014 Elsevier Ltd. All rights reserved.

Mahmoudabadi A.,University of Tehran | Seyedhosseini S.M.,Iran University of Science and Technology
IATSS Research | Year: 2014

The present paper proposes an iterative procedure based on chaos theory on dynamic risk definition to determine the best route for transporting hazardous materials (Hazmat). In the case of possible natural disasters, the safety of roads may be seriously affected. So the main objective of this paper is to simultaneously improve the travel time and risk to satisfy the local and national authorities in the transportation network. Based on the proposed procedure, four important risk components including accident information, population, environment, and infrastructure aspects have been presented under linguistic variables. Furthermore, the extent analysis method was utilized to convert them to crisp values. To apply the proposed procedure, a road network that consists of fifty nine nodes and eighty two-way edges with a pre-specified affected area has been considered. The results indicate that applying the dynamic risk is more appropriate than having a constant risk. The application of the proposed model indicates that, while chaotic variables depend on the initial conditions, the most frequent path will remain independent. The points that would help authorities to come to the better decision when they are dealing with Hazmat transportation route selection. © 2013 International Association of Traffic and Safety Sciences.

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.

Mousavian Z.,University of Tehran | Diaz J.,Autonomous University of the State of Morelos | Masoudi-Nejad A.,University of Tehran
Seminars in Cell and Developmental Biology | Year: 2016

By the development of information theory in 1948 by Claude Shannon to address the problems in the field of data storage and data communication over (noisy) communication channel, it has been successfully applied in many other research areas such as bioinformatics and systems biology. In this manuscript, we attempt to review some of the existing literatures in systems biology, which are using the information theory measures in their calculations. As we have reviewed most of the existing information-theoretic methods in gene regulatory and metabolic networks in the first part of the review, so in the second part of our study, the application of information theory in other types of biological networks including protein-protein interaction and signaling networks will be surveyed. © 2015 Elsevier Ltd.

Karimi A.,Iran University of Science and Technology | Navidbakhsh M.,Iran University of Science and Technology | Yousefi H.,University of Tehran
International Journal of Materials Research | Year: 2014

Polyvinyl alcohol (PVA) is a suitable material for biomedical and pharmaceutical applications. This paper presents a scientific study on the stiffness, strength, and energy absorption characteristics of a fabricated PVA sponge under different strain rates with a view to using it as an alternative biodegradable and biocompatible material. A range of tensile tests, such as stress failure and cyclic, on PVA sponge have been carried out. The stress-strain curves in all strain rates (1, 20, 100 mm min-1) indicated a near constant plateau stress over a long strain range, which is ideal for energy absorption applications. It was found that the PVA sponge biomaterial exhibited remarkable stiffness, strength, and energy absorption capacities that are comparable to those of some biomaterials with the same density range. PVA sponge can also bear suitable stress both at low and high strain rates which enables it to be implemented in most tissue engineering scaffolds. © Carl Hanser Verlag GmbH & Co. KG.

Shokrieh M.M.,Iran University of Science and Technology | Saeedi A.,Iran University of Science and Technology | Chitsazzadeh M.,University of Tehran
Materials and Design | Year: 2014

In this research, the influence of adding multi-walled carbon nanotubes at various contents on the mechanical properties of chopped strand mat/polyester composites was investigated. Initially, the effect of the sonication time on the dispersion of carbon nanotube at the highest weight ratio (0.5. wt.%) was inspected. To achieve this goal, a new technique based on scanning electron microscopy, which utilizes the burn-off test, was introduced to visualize the dispersion state of carbon nanotubes. Subsequently, the effect of addition of multi-walled carbon nanotube on the tensile and flexural properties of the fiber reinforced composites was studied. The results of mechanical tests showed that adding only 0.05. wt.% carbon nanotube enhanced the flexural strength of the hybrid composite by 45% while the tensile strength was not changed significantly. Improvements in the tensile and flexural moduli were also observed. Moreover, theoretical relations between the tensile, flexural and compressive moduli based on the classical beam theory were employed to determine the effect of carbon nanotube on the compressive modulus of composites. The theoretical result showed 31% enhancement in the compressive modulus. © 2013 Elsevier Ltd.

Kaveh A.,Iran University of Science and Technology | Rahami H.,University of Tehran
International Journal for Numerical Methods in Engineering | Year: 2010

In this paper, an efficient method is developed for the analysis of regular structures. A structure is called regular if its model can be formed by a graph product. Here, instead of direct solution of the equations corresponding to a regular structure or finding the inverse of the stiffness matrix directly, modal analysis is used, and eigenvectors are employed for calculating the displacements and then internal forces of the structures. For this purpose, first an efficient method is developed for calculating the eigenvectors of the product graphs, and then a method is presented for using these eigenvectors for evaluating the displacements of a structure. © 2010 John Wiley & Sons, Ltd.

Fallahi A.,Iran Power Generation, Transmission and Distribution Management Co. | Ebrahimi R.,Iran University of Science and Technology | Ghaderi S.F.,University of Tehran
Energy | Year: 2011

This paper provides an empirical analysis of the determinants of energy efficiency in 32 power electric generation management companies over the period 2005-2009. The study uses non-parametric Data Envelopment Analysis (DEA) to estimate the relative technical efficiency and productivity change of these companies. In order to verify the stability of our DEA model and the importance of each input variable, a stability test is also conducted. The results of the study indicate that average technical efficiency of companies decreased during the study period. Nearly half of the companies (14) are below this average level of 88.7% for five years. Moreover, it is shown that the low increase of productivity changes is more related to low efficiency rather than technology changes. © 2011 Elsevier Ltd.

Shojaei I.,University of Tehran | Kaveh A.,Iran University of Science and Technology | Rahami H.,University of Tehran
Computers and Structures | Year: 2013

In this paper an efficient method is presented for the analysis of those structures which can be converted to regular forms. The stiffness matrix for such regular structures can easily be inverted using their eigenvalues and eigenvectors. Many non-regular structures can be converted to regular forms. Here the presented method solves not only all the regular forms but also non-regular forms convertible to regular ones. The efficiency of the method is more significant when it is used in reanalyzing and rehabilitating structures where the stiffness matrix should be inverted in each step. © 2013 Elsevier Ltd. All rights reserved.

Kousha K.,University of Tehran | Thelwall M.,University of Wolverhampton | Rezaie S.,Shahid Beheshti University
Journal of Informetrics | Year: 2010

Previous research has shown that citation data from different types of Web sources can potentially be used for research evaluation. Here we introduce a new combined Integrated Online Impact (IOI) indicator. For a case study, we selected research articles published in the Journal of the American Society for Information Science & Technology (JASIST) and Scientometrics in 2003. We compared the citation counts from Web of Science (WoS) and Scopus with five online sources of citation data including Google Scholar, Google Books, Google Blogs, PowerPoint presentations and course reading lists. The mean and median IOI was nearly twice as high as both WoS and Scopus, confirming that online citations are sufficiently numerous to be useful for the impact assessment of research. We also found significant correlations between conventional and online impact indicators, confirming that both assess something similar in scholarly communication. Further analysis showed that the overall percentage for unique Google Scholar citations outside the WoS were 73% and 60% for the articles published in JASIST and Scientometrics, respectively. An important conclusion is that in subject areas where wider types of intellectual impact indicators outside the WoS and Scopus databases are needed for research evaluation, IOI can be used to help monitor research performance. © 2009 Elsevier Ltd.

Taleizadeh A.A.,University of Tehran | Mohammadi B.,Iran University of Science and Technology | Cardenas-Barron L.E.,Monterrey Institute of Technology | Samimi H.,Iran University of Science and Technology
International Journal of Production Economics | Year: 2013

In this paper, for the first time, an inventory control model to determine the optimal order and shortage quantities of a perishable item when the supplier offers a special sale is developed. Four possible cases based on decision that the purchaser might make about the first replenishment policy (using regular economic order quantity model at reduced price or regular price), if he did not take the special order, and coincidence of special period length with positive or negative inventory level of the last regular period length during the special period, are investigated. Moreover several useful theorems are suggested through which one can find closed-form solution directly when there are integer operators involved in an objective function. At the end, in order to illustrate the proposed theorems and the solution method some numerical examples are solved and a sensitivity analysis is reported too. © 2013 Elsevier B.V.

Lesani M.,University of Tehran | Bahaari M.R.,University of Tehran | Shokrieh M.M.,Iran University of Science and Technology
Composite Structures | Year: 2013

This paper presents the failure pattern, ultimate static strength and detailed behavior of steel tubular T-joints strengthened by fiber reinforced polymer (FRP) obtained from numerical investigations under an axial brace compressive loading. The joints were analyzed in two cases in which FRP was included and excluded considering typical glass/epoxy composite. The results obtained from the numerical modeling revealed the influence of the FRP wrap in joint ultimate capacity enhancement. In addition, the state of stresses and deflections of the steel substrate were all improved as a result of FRP application which clearly showed an upgrade in overall joint behavior. The orientation and extent of FRP reinforcement has been proposed based on practical applications. The modes of failure observed throughout the numerical analysis were local bending of the chord member, punching shear due to ovalization and plastic failure of the chord. The FRP-Strengthened joint hindered the occurrence of these failure modes. The FRP plies were capable to withstand a minimum of 50% of the joint ultimate load with no sign of failure. The critical regions of the plies were around the saddle point and the adjacent ovalized area of the chord shell. © 2012 Elsevier Ltd.

Lesani M.,University of Tehran | Bahaari M.R.,University of Tehran | Shokrieh M.M.,Iran University of Science and Technology
Journal of Constructional Steel Research | Year: 2013

This paper presents the failure pattern, ultimate static strength and detailed behavior of un-stiffened T and Y tubular joints under axial brace compressive loading using finite element method performed by ABAQUS software package. Properties of the un-stiffened tubular joints were extracted from the available experimental-based tubular joint database. Utilizing the Modified Riks Method in numerical analyses led to an accurate simulation of joint behavior and also helped to investigate its correct failure pattern. The modes of failure observed throughout the numerical analysis were local bending of the chord member, ovalization and plastic failure of the chord. The results obtained from the numerical modeling revealed the critical areas on the joint surface with respect to ovalization, deflections and stresses. Also, the ultimate strength predicted by the numerical analysis was compared and validated with available experiment results. Despite the fact that much research has been conducted on tubular joints which have mostly focused on the estimation of ultimate strength or stress concentration factors rather than detail study of joint behavior, the present detail investigation has provided a thorough understanding of joint behavior under axial compressive loads. Such an in-depth and detail tubular joint investigation has been rarely reported in the open literature. © 2012 Elsevier Ltd. All rights reserved.

Nateghi A.,University of Tehran | Salamat-talab M.,Iran University of Science and Technology
Composite Structures | Year: 2013

Thermal effect on buckling and free vibration behavior of functionally graded (FG) microbeams based on modified couple stress theory is presented. Classical and first order shear deformation beam theories are adopted to count for the effect of shear deformations. Hamilton's principle is applied to give the governing equations, boundary and initial conditions of the FG microbeam. Using generalized differential quadrature (GDQ) method buckling load and natural frequency of FG microbeam with different boundary conditions are obtained. Some numerical results are presented to investigate effects of different parameters including temperature changes, material length scale parameter, beam thickness, Poisson's ratio and power index of material distribution on the FG microbeam behavior. Numerical results show that modified couple stress theory predicts higher values of buckling load and natural frequency for FG microbeams. In addition, it is observed that higher temperature changes signify size dependency of FG microbeam. It is shown that Poisson's effect on buckling load and natural frequency predicted by the current model differs significantly from classical one. Study of power index of material distribution proved that the behavior of FG microbeams differ considerably from homogeneous isotropic ones. © 2012 Elsevier Ltd.

Asgharifard Sharabiani P.,Iran University of Science and Technology | Haeri Yazdi M.R.,University of Tehran
Composites Part B: Engineering | Year: 2013

Nonlinear free vibration of functionally graded nanobeams is studied in this paper within the framework of Euler-Bernoulli beam model including the von Kármán geometric nonlinearity. It is assumed that material properties follow power law distributions through thickness direction. A second order nonlinear ordinary differential equation with quadratic and cubic nonlinear terms is obtained by using the free vibration modes of the corresponding linear problem. The direct numerical integration method is employed to find the natural frequencies of FG nanobeams with different boundary conditions. Numerical results demonstrate the normalized natural frequencies in different nanobeam dimensions, vibration amplitudes and volume fraction indices of FG material. Finally, the surface effects on the phase plane trajectory of fundamental mode time-dependent function have been shown. © 2012 Elsevier Ltd. All rights reserved.

Sedghi-Asl M.,Yasouj University | Rahimi H.,University of Tehran | Salehi R.,University of Tehran
Transport in Porous Media | Year: 2014

As the flow velocity and Reynolds number increase in rockfilled porous media, the flow deviates from Darcy conditions and enters into a new phase known as non-Darcy conditions. Due to a linear relationship between hydraulic gradient and the flow velocity in Darcy formula, the flow can be analyzed with no difficulty. However, as the velocity increases the Darcy law is violated, the flow becomes turbulent, making the analysis more challenging. In this paper a laboratory packed column was built to study high-velocity flow through granular materials and new experimental data have been obtained. The laboratory experiments include application of for six different sizes of rounded aggregates and using different hydraulic gradients to assess the flow behavior. Using new experimental data, the validity of four widely-used head-loss equations were evaluated. The results indicated that the Sidiropoulou et al. (Hydrol Process 21:534-554, 2007) and Ergun's head-loss equations yield satisfactory results comparing to other available relationships. © 2013 Springer Science+Business Media Dordrecht.

Ansari-Rad M.,University of Tehran | Anta J.A.,Pablo De Olavide University | Bisquert J.,Jaume I University
Journal of Physical Chemistry C | Year: 2013

The main electronic feature of many nanocrystalline semiconductors and organic materials is the presence of a distribution of localized states in the system with a broad energy dispersion. Carrier transport and recombination in these energetically disordered systems have raised increasing attention, in relation to applications in novel optoelectronic devices. We provide a general view of the physical interpretation of carrier transport coefficients (diffusion coefficient and mobility) and recombination lifetime in the presence of the localized states. We aim to carefully distinguish between the quantities that appear in the continuity equation for a small perturbation of the charge carriers (collective diffusion coefficient and lifetime) and those that are related to the behavior of the individual carriers (single-particle quantities). As an important example, charge-carrier transport and recombination in the case of multiple trapping model will be discussed in detail, for both exponential and Gaussian distributions. We address important aspects of the interpretation of lifetime and charge-transfer rates related to recombination in nanostructured organic and hybrid solar cells. Finally, to clarify different definitions for diffusion coefficient and lifetime, we use Monte Carlo simulation to calculate the diffusion coefficient, the mobility, and the lifetime (for both linear and nonlinear recombination) in the Gaussian DOS. We also justify the validity of the generalized Einstein relation in the case of a non-Boltzmann distribution of the carriers. Definitions and calculations provided in this paper have important consequences for both the interpretation of measurements and the calculation with advanced transport and recombination models. © 2013 American Chemical Society.

Kaveh A.,Iran University of Science and Technology | Rahami H.,University of Tehran
Acta Mechanica | Year: 2011

In this paper, block circulant matrices and their properties are investigated. Basic concepts and the necessary theorems are presented and then their applications are discussed. It is shown that a circulant matrix can be considered as the sum of Kronecker products in which the first components have the commutativity property with respect to multiplication. The important fact is that the method for block diagonalization of these matrices is much simpler than the previously developed methods, and one does not need to find an additional matrix for orthogonalization. As it will be shown not only the matrices corresponding to domes in the form of Cartesian product, strong Cartesian product and direct product are circulant, but for other structures such as diamatic domes, pyramid domes, flat double layer grids, and some family of transmission towers these matrices are also block circulant. © 2010 Springer-Verlag.

Samavati V.,University of Tehran | Adeli M.,Iran University of Science and Technology
Carbohydrate Polymers | Year: 2014

The present work is focused on the optimization of hydrophobic compounds extraction process from the carbohydrate matrix of Iranian Pistacia atlantica seed at laboratory level using ultrasonic-assisted extraction. Response surface methodology (RSM) was used to optimize oil seed extraction yield. Independent variables were extraction temperature (30, 45, 60, 75 and 90 C), extraction time (10, 15, 20, 25, 30 and 35 min) and power of ultrasonic (20, 40, 60, 80 and 100 W). A second order polynomial equation was used to express the oil extraction yield as a function of independent variables. The responses and variables were fitted well to each other by multiple regressions. The optimum extraction conditions were as follows: extraction temperature of 75 C, extraction time of 25 min, and power of ultrasonic of 80 W. A comparison between seed oil composition extracted by ultrasonic waves under the optimum operating conditions determined by RSM for oil yield and by organic solvent was reported. © 2013 Elsevier Ltd.

Kousha K.,University of Wolverhampton | Thelwall M.,University of Tehran | Rezaie S.,Shahid Beheshti University
Journal of the American Society for Information Science and Technology | Year: 2011

Citation indictors are increasingly used in some subject areas to support peer review in the evaluation of researchers and departments. Nevertheless, traditional journal-based citation indexes may be inadequate for the citation impact assessment of book-based disciplines. This article examines whether online citations from Google Books and Google Scholar can provide alternative sources of citation evidence. To investigate this, we compared the citation counts to 1,000 books submitted to the 2008 U.K. Research Assessment Exercise (RAE) from Google Books and Google Scholar with Scopus citations across seven book-based disciplines (archaeology; law; politics and international studies; philosophy; sociology; history; and communication, cultural, and media studies). Google Books and Google Scholar citations to books were 1.4 and 3.2 times more common than were Scopus citations, and their medians were more than twice and three times as high as were Scopus median citations, respectively. This large number of citations is evidence that in book-oriented disciplines in the social sciences, arts, and humanities, online book citations may be sufficiently numerous to support peer review for research evaluation, at least in the United Kingdom. © 2011 ASIS&T.

Emrouznejad A.,Aston University | Amin G.R.,University of Tehran
Information Sciences | Year: 2010

Determining the Ordered Weighted Averaging (OWA) operator weights is important in decision making applications. Several approaches have been proposed in the literature to obtain the associated weights. This paper provides an alternative disparity model to identify the OWA operator weights. The proposed mathematical model extends the existing disparity approaches by minimizing the sum of the deviation between two distinct OWA weights. The proposed disparity model can be used for a preference ranking aggregation. A numerical example in preference ranking and an application in search engines prove the usefulness of the generated OWA weights. © 2009 Elsevier Inc. All rights reserved.

Eshghi M.,University of Tehran | Hamzavi M.,Islamic Azad University at Shahrood
Communications in Theoretical Physics | Year: 2012

In this paper, we solve the Dirac equation under spin symmetry limit for attractive radial potential including a Coulomb-like tensor interaction. By using the parametric generalization of the Nikiforov-Uvarov method, the energy eigenvalues equation and the corresponding wave functions have been obtained in closed forms. Some numerical results are given too. © 2012 Chinese Physical Society and IOP Publishing Ltd.

Tamimi B.,University of Tehran | Canizares C.A.,University of Waterloo | Vaez-Zadeh S.,University of Tehran
IEEE Transactions on Power Systems | Year: 2010

This paper presents a comparative investigation of various representations of reactive power limits in maximum loadability and active and reactive power market studies. Previously proposed optimal power flow (OPF) models for these types of analyses are first reviewed and briefly discussed. Different models for representing reactive power limits in these optimization problems are then presented, concentrating in particular on the proper modeling of the generators' capability curves as terminal voltages change, which has been identified as a shortcoming of previous studies. Comparative numerical analyses of the effect of various reactive power limit models in maximum loading and active and reactive power dispatch and pricing levels are presented and discussed, to thus quantify the effect these various limit representations have on the corresponding results. Two test systems, namely, the CIGRE-32 benchmark system and a 1211-bus dispatch model of a European network, are used for numerical studies. The presented results show that in most OPF applications, the improvement on the reactive power limits representation lead to subtle differences at the cost of increased computational complexity, which in some cases may be difficult to justify in practice. © 2010 IEEE.

Nikbakht G.,University of Tehran | Esmailnejad A.,Shiraz University
Immunogenetics | Year: 2015

Major histocompatibility complex (MHC) is the best characterized genetic region controlling disease resistance and immune responses in chicken. MHC genes are also involved in various non-immune functions such as productive traits and reproductive success. The genetic diversity of MHC in an Iranian indigenous chicken (Khorasan) was studied, and association of the MHC alleles with production traits was determined. The MHC polymorphism was ascertained by genotyping the LEI0258 microsatellite locus by PCR-based fragment analysis. LEI0258 microsatellite marker is a genetic indicator for MHC, which is located on microchromosome 16 and strongly associated with serologically defined MHC haplotypes. A total of 25 different LEI0258 alleles (185–493 bp) and 76 genotypes were identified in 313 chickens. An allele of 361 bp had the highest frequency (26.44 %), and alleles of 207 and 262 bp had the lowest (0.16 %). High level of heterozygosity (87 %) and good genotype frequency fit to the Hardy–Weinberg equilibrium was observed in this population (P = 0.238). The association study also revealed a significant influence of MHC alleles on body weight, egg weight, egg laying intensity, and weight of sexual maturity in Khorasan population (P < 0.05). The information obtained from this study indicates a high MHC genetic diversity and the association of MHC alleles with important production traits in Khorasan chicken. These data would be applicable in designing breeding and genetic resource conservation for indigenous chicken populations. © 2015, Springer-Verlag Berlin Heidelberg.

Ghods A.H.,University of Waterloo | Fu L.,University of Waterloo | Rahimi-Kian A.,University of Tehran
IEEE Transactions on Intelligent Transportation Systems | Year: 2010

This paper tackles the problem of real-time optimal control of traffic flow in a freeway network deployed with coordinated and integrated traffic controllers. One promising approach to this problem is casting the underlying dynamic control problem in a model predictive framework. The challenge is that the resulting optimization problem is computationally intractable for online applications in a network with a large number of controllers. In this paper, a game-theoretic approach with distributed controllers is proposed to address the foregoing issue. The efficiency of the proposed method is tested for a coordinated ramp metering and variable-speed limit control applied to a stretch of freeway network. The parallel nature of the optimization algorithm makes it suitable for solving large-scale problems with high accuracy. The speed and accuracy of the proposed solution approach are examined and compared with that of the conventional optimization method in a case study to demonstrate its superior performance. © 2006 IEEE.

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.

Jafarlou S.,University of Waterloo | Neshat M.,University of Tehran | Safavi-Naeini S.,University of Waterloo
Optics Express | Year: 2013

A hybrid analysis of a continuous-wave terahertz photomixer source structure with plasmonic nano-grating electrodes is presented. Using the hybrid analysis, the enhancement of the optical power absorption due to the presence of the one-dimensional metallic nano-grating is investigated by defining an absorption enhancement factor. We show that the proposed absorption enhancement factor can be used as a design tool, whose maximization provides the optimum geometrical parameters of the nano-grating. Based on drift-diffusion model, the photocurrent enhancement due to the nano-grating electrodes is studied under three different bias configurations. Moreover, the dependence of the photocurrent on the physical parameters of the photomixer is analyzed. © 2013 Optical Society of America.

Dowlati M.,University of Valencia | de la Guardia M.,University of Valencia | Dowlati M.,University of Tehran | Mohtasebi S.S.,University of Tehran
TrAC - Trends in Analytical Chemistry | Year: 2012

Machine vision is a non-destructive, rapid, economic, consistent and objective inspection tool and is also an evaluation technique based on image analysis and processing with a variety of applications.We review the use of machine vision and imaging technologies for fish-quality assessment.This review updates and condenses a representative selection of recent research and industrial solutions proposed in order to evaluate the general trends of machine vision and image processing in the visible range applied for inspection of fish and fish products. In order to determine freshness and composition, it is necessary to measure and to evaluate size and volume, to estimate weight, to measure shape parameters, to analyze skin and fillet in different color shades, to recognize fish species and sex, and to detect defects.Considering the overall trends, we propose some future directions for research. © 2012 Elsevier Ltd.

Jeddi K.,University of Waterloo | Sarikhani K.,University of Waterloo | Qazvini N.T.,University of Tehran | Chen P.,University of Waterloo
Journal of Power Sources | Year: 2014

Development of lithium/sulfur (Li/S) batteries is limited by their low Coulombic efficiency and low cycle life, which are mainly due to active mass loss and polysulfide dissolution into the electrolyte solution. Here we report a new approach to overcome these drawbacks by employing a novel composite polymer electrolyte that not only facilitates rapid transport of lithium ions for electrochemical reactions with sulfur, resulting in improved capacity of the battery, but also prevents the generated polysulfides from shuttling between the electrodes during cycling of the battery. Improved performance of the battery was achieved: An initial discharge capacity of 1648mAhgsulfur-1 and reversible capacity of 1143mAhgsulfur-1 were obtained after 100 cycles at 0.2 C (1 C = 1672 mA h g-1), which could be among the highest reversible capacities reported for Li/S batteries so far. © 2013 Elsevier B.V. All rights reserved.

Sabokbar N.,Shiraz University | Khodaiyan F.,University of Tehran
Journal of Food Science and Technology | Year: 2015

Mixture of pomegranate juice and whey was evaluated as a potential substrate for production of a novel probiotic beverage by kefir grains. Different fermentation conditions were used as viz: two fermentation temperature (19 ºC and 25 ºC) and two levels of kefir grains inoculum (5 % and 8%w/v). pH, acidity, lactose consumption as well as organic acids formation were determined during 32 hours of fermentation. Results showed that kefir grains were able to utilize lactose and decrease pH, increase acidity, produce lactic acid and acetic acid, while the level of citric acid decreased. It was observed these change depended on temperature and level of kefir grains with the highest changes at the temperature of 25 ºC and kefir grains inoculum of 8%w/v. Pomegranate juice and whey mixture therefore may serve as a suitable substrate for the production of novel probiotic dairy-fruit juice beverage by kefir grains and the sensory characteristics of this beverage were shown desirable results. © 2014, Association of Food Scientists & Technologists (India).

Bahmani M.,Islamic Azad University at Dehloran | Eftekhari Z.,University of Tehran
Comparative Clinical Pathology | Year: 2013

This paper describes a selection of the ethnoveterinary medicines used for herd dogs in the southern regions of Ilam province, Iran. Traditional botanical medicine is the primary mode of healthcare for most of the rural population in Ilam province. In this study, a questionnaire was distributed among 45 residential areas in 22 rural zones of the southern areas of Ilam province. The objective of this study was the recognition of natural medicinal methods using medicinal plants, and the classification of ethnoveterinary applications and collection of domestic science. Twenty-two medicinal plants from 16 families were identified. The main application of these plants was for the detection and treatment of digestive disorders using Citrullus colocynthis, Aristolochia clematis, Scrophularia deserti, Quercus brantii, Ceracus microcarpa, Echium strigosa, Pistacia atlantica, and Pistacia khinjuk which have been applied using Euphurbia graminifolius, Peganum harmala, Salsola rigida, Artemisia herba-alba, Amygdalus arabica, jolbak of salt water, Peganum harmala L., and Nicotina tabacum for external and internal parasite disorders. S. deserti for ophthalmic disorders, and P. atlantica, P. khinjuk, and Q. brantii for respiratory disorders were applied. The present study confirmed the traditional medical effects of some plants and revealed the unique medical effects of other plants, which if recognized could be useful in the creation of new ideas and increasing knowledge for the modern pharmaceutical industry. Since very few clinical trials have been conducted on plants native to Ilam province, it is necessary that more research be conducted to ensure that labeled and standardized products are introduced for human consumption. © 2012 The Author(s).

Taherdangkoo M.,Shiraz University | Hossein Shirzadi M.,University of Tehran | Yazdi M.,Shiraz University | Hadi Bagheri M.,Brigham and Women's Hospital
Swarm and Evolutionary Computation | Year: 2013

One of most popular data clustering algorithms is K-means algorithm that uses the distance criterion for measuring the correlation among data. To do that, we should know in advance the number of classes (K) and choose K data point as an initial set to run the algorithm. However, the choice of initial points is a main problem in this algorithm, which may cause that the algorithm converges to local optima. So, some other clustering algorithms have been proposed to overcome this problem such as the methods based on K-means (SBKM), Genetic Algorithm (GAPS and VGAPS), Particle Swarm Optimization (PSO), Ant Colony Optimization (Dynamic ants), Simulated Annealing (SA) and Artificial Bee Colony (ABC) algorithm. In this paper, we employ a new meta-heuristic algorithm. We called it blind, naked mole-rats (BNMR) algorithm, for data clustering. The algorithm was inspired by social behavior of the blind, naked mole-rats colony in searching the food and protecting the colony against invasions. We developed a new data clustering based on this algorithm, which has the advantages such as high speed of convergence. The experimental results obtained by using the new algorithm on different well-known datasets compared with those obtained using other mentioned methods showed the better accuracy and high speed of the new algorithm. © 2013 Elsevier B.V.

News Article | November 20, 2015
Site: www.techtimes.com

Iran has been working on robots for years, but its latest marvel might be the best yet. This little guy is called the Surena III, and it is a humanoid robot capable of climbing stairs among other neat things. The robot, developed by researchers of the Center for Advanced Systems and Technologies at the University of Tehran, has the height of around 6 feet and weight of 216 pounds. That's basically the height and weight of a normal human being right there, folks. We also understand that the robot uses established functionalities based on the open-source software called Robot Operating System. Interestingly enough, Surena III comes with the ability to interact with its surroundings. It uses facial recognition sensors to tell what is what before physically interacting with objects, humans or even other humanoids, something the previous version could not do. Apart from climbing the stairs, Surena III can maneuver terrains, though we are not certain how difficult the terrain must be to navigate without the robot falling over. When it comes down to the speed, the Iranian-made humanoid can walk at 0.4 miles per hour. Not the most impressive, but that is faster when compared to the old model, so it can be considered as a decent enough improvement. The overall technology is impressive, the sensors that make it possible for the Surena III to recognize faces and objects, comes from the Microsoft Kinect sensor. As we all should already know, apart from tracking and recognizing faces and objects, Kinect allows users to issue voice commands. So, it makes sense that the humanoid robot understands around 200 Persian words. Pretty impressive, right? We agree. The Surena III is remarkable, especially if you put into account that not too many countries in the world have managed to create a robot this sophisticated.

Bahram M.,University of Tartu | Polme S.,University of Tartu | Koljalg U.,University of Tartu | Zarre S.,University of Tehran | Tedersoo L.,University of Tartu
New Phytologist | Year: 2012

• Altitudinal gradients strongly affect the diversity of plants and animals, yet little is known about the altitudinal effects on the distribution of microorganisms, including ectomycorrhizal fungi. • By combining morphological and molecular identification methods, we addressed the relative effects of altitude, temperature, precipitation, host community and soil nutrient concentrations on species richness and community composition of ectomycorrhizal fungi in one of the last remaining temperate old-growth forests in Eurasia. • Molecular analyses revealed 367 species of ectomycorrhizal fungi along three altitudinal transects. Species richness declined monotonically with increasing altitude. Host species and altitude were the main drivers of the ectomycorrhizal fungal community composition at both the local and regional scales. The mean annual temperature and precipitation were strongly correlated with altitude and accounted for the observed patterns of richness and community. • The decline of ectomycorrhizal fungal richness with increasing altitude is consistent with the general altitudinal richness patterns of macroorganisms. Low environmental energy reduces the competitive ability of rare species and thus has a negative effect on the richness of ectomycorrhizal fungi. Because of multicollinearity with altitude, the direct effects of climatic variables and their seasonality warrant further investigation at the regional and continental scales. © 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.

Harsini J.S.,Guilan University | Lahouti F.,University of Tehran | Levorato M.,Stanford University | Zorzi M.,University of Padua
IEEE Transactions on Wireless Communications | Year: 2011

This paper presents performance analysis and cross-layer design approaches for hybrid ARQ (HARQ) protocols in wireless networks, which employ adaptive modulation and coding (AMC) in conjunction with adaptive cooperative diversity and are subject to time-correlated fading channels. We first consider a point-to-point scenario, i.e., non-cooperative HARQ with AMC. Utilizing a Markov channel model which accounts for the temporal correlation in the successive transmission of incremental redundancy by the HARQ protocol, we derive the system throughput and the packet loss probability based on a rate compatible punctured convolutional code family. Next, we consider a cooperative HARQ (CHARQ) scheme in which a relay node, also equipped with AMC, retransmits redundancy packets when it is able to decode the source information packet correctly. For this scenario, we also derive the throughput and packet loss performance. Finally, we present a cross-layer AMC design approach which takes into account the hybrid ARQ protocol at the link layer. The results illustrate that including AMC in the HARQ protocols leads to a substantial throughput gain. While the performance of the AMC with HARQ protocol is strongly affected by the channel correlation, the CHARQ protocol provides noticeable performance gains over correlated fading channels as well. © 2006 IEEE.

Jaberian H.,University of Tehran | Piri K.,Bu - Ali Sina University | Nazari J.,Islamic Azad University at Mahābād
Food Chemistry | Year: 2013

Different parts of three plants (Primula auriculata, Fumaria vaillantii and Falcaria vulgaris) were extracted with three different solvents to yield 72 crude extracts. The phytochemical analysis (chemical screening, GC-MS) of three plants was investigated for their antioxidant and antibacterial activity using nine Gram-positive and Gram-negative bacteria. The principal antioxidant and antimicrobial components were determined using HPLC with UV detection. All extracts possessed antibacterial activity especially methanolic extracts from flowers of P. auriculata. The DPPH-radical scavenging assay exhibited high antioxidant activities in three plants (more than 80% at 50 μg). The F. vulgaris showed high content of carvacrol (29.8%) as main component. The contents of carvacrol and fumaric acid in the methanolic-water extracts were 1119 and 1966 mg/l respectively. Our results indicate that these plants would be able to promise sources of natural products with potential antibacterial and antioxidant activity. © 2012 Elsevier Ltd. All rights reserved.

Berto F.,University of Padua | Barati E.,University of Tehran
Materials and Design | Year: 2011

The main purpose of the paper is twofold. First, to provide a new set of experimental results on fracture of U-notched samples, made of two different materials; second, to apply a fracture criterion based on the strain energy density (SED) averaged over a control volume to assess the fracture load of blunt-notched components under three point bending. Two different materials are considered in the tests: a composite material (Al-15%SiC) tested at room temperature and a steel with a ferritic-pearlitic structure tested at -40°C. All samples are weakened by U-notches characterized by different values of notch root radius and notch depth. The theoretical loads to failure as determined according to the SED criterion are compared with the experimental data from more than 40 static tests and with a SED-based scatter band recently reported in the literature for a number of materials exhibiting a brittle behaviour under static loads. © 2010 Elsevier Ltd.

Hashemizadeh S.,University of Tehran | Sardari M.,University of Tehran | Rezayof A.,University of Tehran | Rezayof A.,Institute for Research in Fundamental Sciences
Progress in Neuro-Psychopharmacology and Biological Psychiatry | Year: 2014

In the present study, the effects of bilateral microinjections of cannabinoid CB1 receptor agonist and antagonist into the basolateral amygdala (intra-BLA) on nicotine-induced place preference were examined in rats. A conditioned place preference (CPP) apparatus was used for the assessment of rewarding effects of the drugs in adult male Wistar rats. Subcutaneous (s.c.) administration of nicotine (0.2. mg/kg) induced a significant CPP, without any effect on the locomotor activity during the testing phase. Intra-BLA microinjection of a non-selective cannabinoid CB1/CB2 receptor agonist, WIN 55,212-2 (0.1-0.5. μg/rat) with an ineffective dose of nicotine (0.1. mg/kg, s.c.) induced a significant place preference. On the other hand, intra-BLA administration of AM251 (20-60. ng/rat), a selective cannabinoid CB1 receptor antagonist inhibited the acquisition of nicotine-induced place preference. It should be considered that the microinjection of the same doses of WIN 55,212-2 or AM251 into the BLA, by itself had no effect on the CPP score. The administration of a higher dose of AM251 (60. ng/rat) during the acquisition decreased the locomotor activity of animals on the testing phase. Interestingly, the microinjection of AM251 (20 and 40. ng/rat), but not WIN55,212-2 (0.1-0.5. μg/rat), into the BLA inhibited the expression of nicotine-induced place preference without any effect on the locomotor activity. Taken together, these findings support the possible role of endogenous cannabinoid system of the BLA in the acquisition and the expression of nicotine-induced place preference. Furthermore, it seems that there is a functional interaction between the BLA cannabinoid receptors and nicotine in producing the rewarding effects. © 2014 Elsevier Inc.

Shojaee E.,University of Tehran | Mohammadizadeh M.R.,University of Tehran | Mohammadizadeh M.R.,Institute for Research in Fundamental Sciences
Journal of Physics Condensed Matter | Year: 2010

Elastic and thermal properties of the TiO2 lattice in anatase and rutile phases were studied in the framework of density functional perturbation theory within the local density approximation (LDA) and generalized-gradient approximation (GGA). The full elastic constant tensors of the polymorphs were calculated by linear fits to the acoustic branches of the phonon band structure near the center of the first Brillouin zone in symmetry directions of the crystals. It was observed that the elastic constants within the GGA are in better agreement with experiment. In addition, the Born effective charges, dielectric tensor, heat capacity, mean sound velocity and Debye temperature were calculated. The heat capacity at room temperature and the Debye temperature within the LDA are in better agreement with the experimental results. Therefore, using the phonon band structure and the density of states, one can obtain the important mechanical and thermal properties of materials. © 2009 IOP Publishing Ltd.

Alijanpour S.,University of Tehran | Rezayof A.,University of Tehran | Zarrindast M.-R.,Tehran University of Medical Sciences | Zarrindast M.-R.,Institute for Research in Fundamental Sciences
Addiction Biology | Year: 2013

The present study evaluated the involvement of the dorsal hippocampal cannabinoid CB1 receptors in the combined effect of ethanol and nicotine on passive avoidance learning in adult male mice. The results indicated that pre-training administration of ethanol (1 g/kg, i.p.) impaired memory retrieval. Pre-test administration of ethanol (0.5 and 1 g/kg, i.p.) or nicotine (0.5 and 0.7 mg/kg, s.c.) significantly reversed ethanol-induced amnesia, suggesting a functional interaction between ethanol and nicotine. Pre-test microinjection of a selective CB1 receptor agonist, ACPA (3 and 5 ng/mouse), plus an ineffective dose of ethanol (0.25 g/kg) or nicotine (0.3 mg/kg) improved memory retrieval, while ACPA by itself could not reverse ethanol-induced amnesia. Pre-test intra-CA1 microinjection of a selective CB1 receptor antagonist, AM251 (0.5-2 ng/mouse), did not lead to a significant change in ethanol-induced amnesia. However, pre-test intra-CA1 microinjection of AM251 prevented the ethanol (1 g/kg) or nicotine (0.7 mg/kg) response on ethanol-induced amnesia. In order to support the involvement of the dorsal hippocampal CB1 receptors in nicotine response, the scheduled mixed treatments of AM251 (0.1-1 ng/mouse), ACPA (5 ng/mouse) and nicotine (0.3 mg/kg) were used. The results indicated that AM251 reversed the response of ACPA to the interactive effects of nicotine and ethanol in passive avoidance learning. Furthermore, pre-test intra-CA1 microinjection of the same doses of ACPA or AM251 had no effect on memory retrieval. These findings show that the cannabinoid CB1 receptors of dorsal hippocampus are important in the combined effect of ethanol and nicotine on passive avoidance learning. © 2011 Society for the Study of Addiction.

Abbasalizadeh S.,Royan Institute for Stem Cell Biology and Technology | Baharvand H.,Royan Institute for Stem Cell Biology and Technology | Baharvand H.,University of Tehran
Biotechnology Advances | Year: 2013

Recent technological advances in the generation, characterization, and bioprocessing of human pluripotent stem cells (hPSCs) have created new hope for their use as a source for production of cell-based therapeutic products. To date, a few clinical trials that have used therapeutic cells derived from hESCs have been approved by the Food and Drug Administration (FDA), but numerous new hPSC-based cell therapy products are under various stages of development in cell therapy-specialized companies and their future market is estimated to be very promising. However, the multitude of critical challenges regarding different aspects of hPSC-based therapeutic product manufacturing and their therapies have made progress for the introduction of new products and clinical applications very slow. These challenges include scientific, technological, clinical, policy, and financial aspects. The technological aspects of manufacturing hPSC-based therapeutic products for allogeneic and autologous cell therapies according to good manufacturing practice (cGMP) quality requirements is one of the most important challenging and emerging topics in the development of new hPSCs for clinical use. In this review, we describe main critical challenges and highlight a series of technological advances in all aspects of hPSC-based therapeutic product manufacturing including clinical grade cell line development, large-scale banking, upstream processing, downstream processing, and quality assessment of final cell therapeutic products that have brought hPSCs closer to clinical application and commercial cGMP manufacturing. © 2013 Elsevier Inc.

Neshat M.,University of Tehran | Armitage N.P.,Johns Hopkins University
Journal of Infrared, Millimeter, and Terahertz Waves | Year: 2013

Ellipsometry is a technique whereby the measurement of the two orthogonal polarization components of light reflected at glancing incidence allows a characterization of the optical properties of a material at a particular frequency. Importantly, it obviates the need for measurement against a standard reference sample, so can provide reliable spectroscopic information even when surface morphology is unknown, of marginal quality and/or a reference is unavailable. Although a standard technique in the visible range, it has not been widely applied in the Terahertz (THz) spectral range despite its potential utility. This is largely because of the technical difficulties that these frequencies present. This review details recent progress in the implementation of THz range ellipsometry. We discuss a variety of configurations including various kinds of laboratory and facility based sources using both continuous wave and pulsed spectroscopic methods. We discuss the general problems encountered when trying to import the methodologies of visible range ellipsometry to the THz range and give examples of where the technique has been successful thus far. © 2013 Springer Science+Business Media New York.

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

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

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

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

Tahamtan S.,University of Tehran | Halvaee A.,University of Tehran | Emamy M.,University of Tehran | Zabihi M.S.,Iranian National Center for Laser Science and Technology
Materials and Design | Year: 2013

Al206/5vol.%Al2O3p cast composites were fabricated by the injection of reinforcing particles into molten Al alloy in two different forms, i.e. as Al2O3 particles and milled particulates of alumina with Al and Mg powders. The resultant milled powders (Master Metal Matrix Composite (MMMC)) were then added into the molten Al alloy both in semi-solid state and above liquidus temperature. Effects of powder addition technique, reinforcement particle size and casting temperature on distribution and incorporation of reinforcing particles into molten Al alloy were investigated. Morphology evolution of powders during milling, microscopic examinations of composite and matrix alloy were studied by scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis was also used to determine the possible interaction between powders after ball milling process. Results showed that injection of powders in the form of MMMC leads to considerable improvement in incorporation and distribution of Al2O3p in the Al206 matrix alloy leading to the improvement in tensile properties. Improvement in tensile properties is attributed to the better wetting of Al2O3p by melt as well as removing microchannels and roughness on alumina particles as a consequence of ball milling process. © 2013 Elsevier Ltd.

Torabi A.R.,University of Tehran | Campagnolo A.,University of Padua | Berto F.,University of Padua
Materials and Design | Year: 2015

The present paper reports some experimental, theoretical and numerical results on brittle fracture of notched components made of Polymethylmethacrylate (PMMA). First, fracture experiments were carried out at room temperature on V-notches with end holes (VO-notches) under mode II loading by means of a recently proposed disk-type specimen, called the Brazilian disk containing central VO-notches (VO-BD specimen) made of PMMA for different notch angles and various notch radii.Then, the well-established averaged strain energy density (SED) criterion over the specified control volume which embraces the notch border was formulated and employed to predict theoretically the experimental fracture loads. The center of the control volume is located on the notch edge, where the principal stress reaches its maximum value. The correct orientation is obtained by a rigid rotation of the crescent-shaped volume while the size depends on the fracture toughness and the ultimate strength of the material. This methodology has been already used in the literature to analyze U- and V-shaped notches subject to different loading modes with very good results and advantages with respect to classic approaches.In this contribution it was demonstrated that SED works well also on VO-notches under pure mode II loading. © 2014 Elsevier Ltd.

Torabi A.R.,University of Tehran | Berto F.,University of Padua
International Journal of Damage Mechanics | Year: 2014

The brittle fracture criterion, namely the strain energy density (SED) over a control volume, which embraces the notch edge, is utilized in the present research to assess the experimentally obtained fracture loads of several U-notched Brazilian disk (UNBD) specimens made of a type of commercial graphite under pure mode II loading. The results show that the SED criterion could successfully predict the fracture loads of graphite specimens for different notch tip radii with an average discrepancy of about ±10%. It is proved in this investigation that not only the SED criterion works well on brittle fracture of notched graphite components under pure mode I, mixed mode I/II and pure mode III loading conditions, but also under pure mode II loading. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions. nav.

Saberi A.A.,University of Tehran | Saberi A.A.,Institute for Research in Fundamental Sciences
Physics Reports | Year: 2015

Percolation is the simplest fundamental model in statistical mechanics that exhibits phase transitions signaled by the emergence of a giant connected component. Despite its very simple rules, percolation theory has successfully been applied to describe a large variety of natural, technological and social systems. Percolation models serve as important universality classes in critical phenomena characterized by a set of critical exponents which correspond to a rich fractal and scaling structure of their geometric features. We will first outline the basic features of the ordinary model. Over the years a variety of percolation models has been introduced some of which with completely different scaling and universal properties from the original model with either continuous or discontinuous transitions depending on the control parameter, dimensionality and the type of the underlying rules and networks. We will try to take a glimpse at a number of selective variations including Achlioptas process, half-restricted process and spanning cluster-avoiding process as examples of the so-called explosive percolation. We will also introduce non-self-averaging percolation and discuss correlated percolation and bootstrap percolation with special emphasis on their recent progress. Directed percolation process will be also discussed as a prototype of systems displaying a nonequilibrium phase transition into an absorbing state. In the past decade, after the invention of stochastic Löwner evolution (SLE) by Oded Schramm, two-dimensional (2D) percolation has become a central problem in probability theory leading to the two recent Fields medals. After a short review on SLE, we will provide an overview on existence of the scaling limit and conformal invariance of the critical percolation. We will also establish a connection with the magnetic models based on the percolation properties of the Fortuin-Kasteleyn and geometric spin clusters. As an application we will discuss how percolation theory leads to the reduction of the 3D criticality in a 3D Ising model to a 2D critical behavior. Another recent application is to apply percolation theory to study the properties of natural and artificial landscapes. We will review the statistical properties of the coastlines and watersheds and their relations with percolation. Their fractal structure and compatibility with the theory of SLE will also be discussed. The present mean sea level on Earth will be shown to coincide with the critical threshold in a percolation description of the global topography. © 2015 Elsevier B.V.

Ghasemi-Varnamkhasti M.,University of Tehran | Mohtasebi S.S.,University of Tehran | Siadat M.,Supelec
Journal of Food Engineering | Year: 2010

The appreciation of food is based on the perception of many senses; in fact for a total estimation the human senses are involved. Biomimetics as the 'abstraction of good design from nature' is to analyze and tap nature's huge reservoir of potential innovative solutions. These biological solutions are cost-efficient, multi-functional and environmentally friendly. Human sense inspired sensor technologies such as multi arrays of sensors are of interest to food industry for food control and sensory evaluation. These systems mimic the human sense to provide a decision on final food quality and safety. Nanotechnology techniques and biosensors are the recent advances in these systems. Odor and taste sensors are interestingly under consideration to food engineers and scientist for application in food processing tasks such as drying, packaging, sorting and so on. Soft computing together with computer development is the promising outlook to enhance the performance of these sensing systems to food quality and safety characterization. This paper deals with some aspects of such systems (odor sensor and taste sensor) and some of more recent applications and advances for food control in food research and technology are discussed as well. © 2010 Elsevier Ltd. All rights reserved.

Siavoshi F.,University of Tehran | Saniee P.,University of Tehran
World Journal of Gastroenterology | Year: 2014

Helicobacter pylori (H. pylori) are resistant to hostile gastric environments and antibiotic therapy, reflecting the possibility that they are protected by an ecological niche, such as inside the vacuoles of human epithelial and immune cells. Candida yeast may also provide such an alternative niche, as fluorescently labeled H. pylori were observed as fast-moving and viable bacterium-like bodies inside the vacuoles of gastric, oral, vaginal and foodborne Candida yeasts. In addition, H. pylori -specific genes and proteins were detected in samples extracted from these yeasts. The H. pylori present within these yeasts produce peroxiredoxin and thiol peroxidase, providing the ability to detoxify oxygen metabolites formed in immune cells. Furthermore, these bacteria produce urease and VacA, two virulence determinants of H. pylori that influence phago-lysosome fusion and bacterial survival in macrophages. Microscopic observations of H. pylori cells in new generations of yeasts along with amplification of H. pylori -specific genes from consecutive generations indicate that new yeasts can inherit the intracellular H. pylori as part of their vacuolar content. Accordingly, it is proposed that yeast vacuoles serve as a sophisticated niche that protects H. pylori against the environmental stresses and provides essential nutrients, including ergosterol, for its growth and multiplication. This intracellular establishment inside the yeast vacuole likely occurred long ago, leading to the adaptation of H. pylori to persist in phagocytic cells. The presence of these bacteria within yeasts, including foodborne yeasts, along with the vertical transmission of yeasts from mother to neonate, provide explanations for the persistence and propagation of H. pylori in the human population. This Topic Highlight reviews and discusses recent evidence regarding the evolutionary adaptation of H. pylori to thrive in host cell vacuoles. © 2014 Baishideng Publishing Group Co., Limited. All rights reserved.

Ghandi M.,University of Tehran | Zarezadeh N.,University of Tehran
Tetrahedron | Year: 2013

We have developed a facile and efficient method for the synthesis of functionalized novel furylquinolines. A variety of quinoline-furan conjugates were obtained via the condensation of 2-chloroquinoline-3-carbaldehyde with acetylenecarboxylates and isocyanides in good to excellent yields. © 2013 Elsevier Ltd. All rights reserved.

Masteri-Farahani M.,University of Tehran | Tayyebi N.,University of Tehran
Journal of Molecular Catalysis A: Chemical | Year: 2011

In this work, a new magnetically recoverable nanocatalyst was developed by covalent binding of a Schiff base ligand, N,N′-bis(3- salicylidenaminopropyl)amine (salpr), on the surface of silica coated magnetite nanoparticles (SCMNPs) and followed complexation with MoO 2(acac) 2. Characterization of the prepared nanocatalyst was performed with different physicochemical methods such as FT-IR and atomic absorption spectroscopies, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). Finally, catalytic activity of the prepared MoO 2salpr/SCMNPs was examined in the epoxidation of olefins with tert-butyl hydroperoxide (TBHP) and cumene hydroperoxide (CHP). © 2011 Elsevier B.V.

Momeni D.,University of Tehran
International Journal of Theoretical Physics | Year: 2011

Hořava proposed a non-relativistic renormalizable theory of gravitation, which is reduced to general relativity (GR) in large distances (infra-red regime (IR)). It is believed that this theory is an ultra-violet (UV) completion for the classical theory of gravitation. In this paper, after a brief review of some fundamental features of this theory, we investigate it for a static cylindrical symmetric solution which describes Cosmic string as a special case. We have also investigated some possible solutions, and have seen that how the classical GR field equations are modified for generic potential V(g). In one case there is an algebraic constraint on the values of three coupling constants. Finally as a pioneering work we deduce the most general cosmic string in this theory. We explicitly show that how the coupling constants distort the mass parameter of cosmic string. We deduce an explicit function for mass per unit length of the space-time as a function of the coupling constants. We compare this function with another which Aryal et al. (Phys. Rev. D 34:2263, 1986) have found in GR. Also we calculate the self-force on a massive particle near Hořava-Lifshitz straight string and we give a typical order for the coupling constantg9. This order of magnitude proposes a cosmological test for validity of this theory. © 2011 Springer Science+Business Media, LLC.

Khoshnevisan B.,University of Tehran | Rafiee S.,University of Tehran | Omid M.,University of Tehran | Yousefi M.,University of Tehran | Movahedi M.,University of Tehran
Energy | Year: 2013

This study was carried out in Esfahan province of Iran. Data were collected from 260 farms in Fereydonshahr city with face to face questionnaire method. The objective of this study was to predict wheat production yield and (greenhouse gas) GHG emissions on the basis of energy inputs. Accordingly, several (artificial neural network) ANN models were developed and the prediction accuracy of them was evaluated using the quality parameters. The results illustrated that average total input and output energy of wheat production were 80.1 and 38 GJ ha-1, respectively. Electricity, chemical fertilizers and water for irrigation were the most influential factors in energy consumption with amount of 39.5, 23.3 and 6.17 GJ ha-1, respectively. Energy use efficiency and energy productivity were 0.032 GJ kg-1 and 34.1 kg GJ-1, respectively. The ANN model with 11-3-2 structure was the best one for predicting the wheat yield and GHG emissions. The coefficients of determination (R2) of the best topology were 0.99 and 0.998 for wheat yield and GHG emissions, respectively. © 2013 Elsevier Ltd.

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

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

Shafiei S.E.,Shahrood University of Technology | Soltanpour M.R.,University of Tehran
International Journal of Innovative Computing, Information and Control | Year: 2011

This paper addresses a neural-network-based chattering free sliding mode control (SMC) for robot manipulators including structured and unstructured uncertainties in both manipulator and actuator dynamics by incorporating a PID outer loop. The main idea is that the robustness property of SMC and good response characteristics of PID are combined to achieve more acceptable performance. Uncertainties in the robot dynamics and actuator models are compensated by a two-layer neural network. External disturbance and approximation error are counteracted by robust signal with adaptive gain. The stability of closed-loop system is guaranteed by developed control scheme. Finally, the proposed methodology is applied to a two-link elbow robot as a case of study. The simulation results show the effectiveness of the method and its robustness to uncertainties and disturbances. ICIC International © 2011.

Grinding is a precision machining process which is widely used in the manufacture of components requiring fine tolerances and smooth finishes. Grinding is recognized as one of the most environmentally unfriendly manufacturing processes. The use of Minimum Quantity Lubrication (MQL) is of great significance in conjunction between large cutting fluids application and dry machining. It can reduce the amount of frictional heat generation and provide some cooling in the tool-workpiece interface and hence keep the workpiece temperatures lower than those in a completely dry machining. The ability to predict surface roughness and grinding force is important to many aspects of grinding process optimization, monitoring, and control. This paper presents the predictive modeling of surface roughness and grinding force based on a new semi-analytical model, and design and analyses of experiment, as a function of the grinding parameters, wheel types and coolant-lubricant properties. In addition, MQL oil flow rate, air pressure and nozzle distance to the grinding zone are adopted for evaluation by full factorial design of experiments. In this case, a 22×41 mixed full factorial design has been selected considering the number of factors used in the present study. The main effects of factors and interactions were considered in this paper, and regression equations were derived using response surface methodology (RSM). © 2015 Elsevier Ltd.

Poursafa P.,University of Tehran | Kelishadi R.,Isfahan University of Medical Sciences
Inflammation and Allergy - Drug Targets | Year: 2010

Atherosclerosis begins in early life. The role of platelets is well-documented from its early stages. A wealth of evidence associates atherosclerotic cardiovascular disease with inflammatory diseases. The role of environmental factors, including air pollution, remains overlooked. Some studies have documented the effect of air pollution on inflammatory and pro-thrombotic factors implicated in the progression of cardiovascular diseases. In particular, the increase of platelet count and platelet hyper-reactivity towards agonists are emerging as markers of hematologic and hemostatic changes in response to the exposure to air pollutants. The systemic pro-inflammatory and pro-thrombotic response to the inhalation of fine and ultrafine particulate matters is seemingly associated with platelet activation. This association may have a clinical significance, particularly in the presence of cardiometabolic risk factors, and may indicate the need for antiplatelet treatment. It is of particular relevance to further study the significance of platelet activation and anti-platelet therapies in primordial/primary preventive measures in children and adolescents at risk of accelerated atherosclerosis. © 2010 Bentham Science Publishers Ltd.

Ghorbanian V.,McGill University | Faiz J.,University of Tehran
Mechanical Systems and Signal Processing | Year: 2015

This paper deals with the comprehensive detailed concepts of the rotor broken bars fault in industrial induction motors. It reviews the most important and applicable techniques for fault detection, and addresses fault diagnosing procedures at different supply modes including line-start and inverter-fed modes. Moreover, new analytical and experimental aspects of fault are proposed using the time and frequency domain variations of the motor variables such as current, voltage, electromagnetic torque and speed. Since the faulty motor behavior cannot be correctly identified without considering the motor operating condition, and the capability of the previous fault indicators are studied deeply in order to investigate their applicability at different conditions. These conditions include various faults, load and reference speed levels and also fault location. All in all, a precise condition assessment of the rotor broken bar induction motors, suitable for industrial purposes, is presented considering motor supply and conditions changes. © 2014 Elsevier Ltd.

Soleimani-Damaneh M.,University of Tehran
International Journal of Computer Mathematics | Year: 2011

In this paper, we discuss modelling and solving some multiobjective optimization problems arising in biology. A class of comparison problems for string selection in molecular biology and a relocation problem in conservation biology are modelled as multiobjective optimization programmes. Some discussions about applications, solvability and different variants of the obtained models are given, as well. A crucial part of the study is based upon the Pareto optimization which refers to the Pareto solutions of multiobjective optimization problems. For such solution, improvement of some objective function can only be obtained at the expense of the deterioration of at least one other objective function. © 2011 Taylor & Francis.

In this paper for the first time ensemble methods including Decision Tree, Bagging and Random Forest have been proposed in the field of earthquake precursors to detect GPS-TEC (Total Electron Content) seismo-ionospheric anomalies around the time and location of Chile earthquake of 27 February 2010. All of the implemented ensemble methods detected a striking anomaly in time series of TEC data, 1. day after the earthquake at 14:00. UTC. The results indicate that the proposed methods due to their performance, speed and simplicity are quite promising and deserve serious attention as a new predictor tools for seismo-ionospheric anomalies detection. © 2016 COSPAR.

Karami M.,University of Tehran | Mahmudi R.,University of Tehran
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2013

The microstructural and textural evolution of the Mg-6Li-1Zn (LZ61), Mg-8Li-1Zn (LZ81), and Mg-12Li-1Zn (LZ121) alloys were investigated in the as-extruded condition and after being equal channel angularly pressed (ECAPed) for one, two, and four passes. The shear punch testing technique was employed to evaluate the room-temperature mechanical properties of the extruded and ECAPed materials. Microstructural analysis revealed that the grain refinement in both LZ61 and LZ121 alloys could be achieved after multipass ECAP through the continuous dynamic recovery and recrystallization process. For the LZ81 alloy, however, the occurrence of Li loss in the four passes of ECAP condition partly offsets the grain refining effect of the ECAP process by increasing grain size and volume fraction of the α phase. Textural studies in both LZ61 and LZ81 alloys indicated that the developed fiber texture after extrusion could be replaced by a typical ECAP texture, where the basal planes are mainly inclined about 45 deg to the extrusion axis. The increased volume fraction of the β phase in LZ81 significantly affected the α-phase texture by decreasing the intensity of the maximum orientations of the basal and prismatic planes in all deformation conditions, compared with the LZ61 alloy. It was also observed that the abnormal grain growth might be promoted by the strong texture developed in the extruded LZ121 alloy. This texture became more randomized when the number of ECAP passes increased. The SPT results showed that the shear yield stress, ultimate shear strength and normalized displacement in all studied alloys were improved through the grain refinement strengthening caused by ECAP. It was also established that increasing Li content decreased the shear strength and enhanced the shear elongation in all deformation conditions. © 2013 The Minerals, Metals & Materials Society and ASM International.

Omranpour H.,University of Tehran | Motahari S.,University of Tehran
Journal of Non-Crystalline Solids | Year: 2013

Effective parameters that enhanced mechanical properties of silica aerogel during aging were investigated. Silica aerogel was made by tetraethyl orthosilicate (TEOS), water, methanol and ammonium fluoride (NH4F) as catalyst using a one-step method. Aging on the samples were performed under three different solvents including n-hexane, methanol and water for different time periods and also different temperatures. Subsequently, solvent exchange with n-hexane, modification under trimethyl chlorosilane (TMCS) solution and the ambient pressure drying (APD) were applied on all samples. The Fourier transform infrared spectroscopy (FTIR), Brunauer, Emmett and Teller (BET) method and compression tests were carried out on the produced samples. Both the compression strength and compression modulus of the gel increased with increasing of the time and temperature of aging. Those samples aged under water showed higher mechanical properties. On the contrary, the specific compression strength and modulus of samples aged in water were declined drastically. © 2013 Elsevier B.V. All rights reserved.

Heydarzadeh Sohi M.,University of Tehran | Ghadami F.,University of Tehran
Tribology International | Year: 2010

In this work, the properties of air plasma sprayed WC-12%Co coating before and after heat treatment were compared with the properties of the hard chromium electrodeposit. WC-12%Co coatings were heat treated at 650, 900 and 1150 °C for 1 h in an argon atmosphere. XRD patterns confirmed the formation of an amorphous phase in the as-sprayed coating. This amorphous phase gradually transformed to η-carbides in the course of heat treatment of the coating. This transformation was confirmed by the XRD analysis of the coatings heat treated above 900 °C. Pin-on-disc wear test results showed that WC-12%Co coatings had a significantly better tribological performance as compared with that of the hard chromium electrodeposits. The results also indicated that heat treatment of the WC-12%Co coatings at 900 °C gave the highest wear resistance among the coatings, which was due to the formation of hard η-carbides at this temperature. © 2009 Elsevier Ltd. All rights reserved.

Valipour M.,University of Tehran | Montazar A.A.,University of Tehran
Advances in Environmental Biology | Year: 2012

In SWDC model after determining equations related to the irrigation efficiency, by using hierarchical analysis, the necessary coefficients for goal function containing all irrigation efficiencies were calculated. All the equations obtained for the irrigation efficiencies are a function of input discharge. Therefore, by using genetic algorithm, the amount of optimal input discharge was calculated to achieve goal function (maximum total efficiency). Finally, the results were compared with WinSRFR model. Providing some graphs in WinSRFR model, the optimum combinations of length and width of the system or discharge and cutoff time could be selected in order to achieve full irrigation. While performing sensitivity analysis (based on under the control parameters in irrigation surface and efficiency coefficients) was effective in achieving better scenarios.

Dastbaz A.,University of Tehran | Keshtkar A.R.,Nuclear Science and Technology Research Institute, Iran
Applied Surface Science | Year: 2014

In this study, SiO2 nanoparticles were modified by 3-aminopropyltriethoxysilane (APTES) and then applied to prepare a novel polyacrylonitrile (PAN) composite nanofiber adsorbent by the electrospinning method. In addition, the adsorbent was characterized by SEM, BET, and FTIR analyses. Then the effects of pH, SiO2 and APTES content, adsorbent dosage, contact time and temperature were investigated. Moreover, adsorption experiments were carried out with initial concentrations in the range of 30-500 mg L-1 and the adsorbent affinity for metal ions was in order of Th4+ > U6+ > Cd2+ > Ni2+. Furthermore, it was observed that the optimum pH for adsorption was different for each metal. Some isotherm and kinetic models were applied to analyze the experimental data, among which the Langmuir and pseudo-second order models were better than the others. The regeneration study showed that the adsorbent could be used for industrial processes repeatedly without any significant reduction in its adsorption capacity. Based on the Langmuir model, the maximum adsorption capacity of Th4+, U6+, Cd2+, and Ni 2+ at 45 C was 249.4, 193.1, 69.5 and 138.7 mg g-1, respectively. Besides, the calculated thermodynamic parameters showed an endothermic as well as chemical nature through the adsorption process. © 2014 Elsevier B.V.

Vatankhah A.R.,University of Tehran
Journal of Irrigation and Drainage Engineering | Year: 2012

This research presents a new weir section with n-segment linear sides and a horizontal bottom. For large n, the section sides of the weir become smooth curves. However, piecewise-linear sides provide a weir shape simple enough for ease of construction. General headdischarge equations are analytically derived for the flow discharge. The proposed weir with n-segment linear sides can be applied in an optimization procedure to produce a wide range of head-discharge behaviors. An elegant optimization model that implements the general equations is presented and applied in the design of linear and quadratic weirs. This simple model is solved using the Solver toolbox of Microsoft Excel. The versatility of the proposed weir is demonstrated by optimizing the weir parameters to obtain the maximum ranges of measurement under linear and quadratic characteristics. These weirs have least relative errors because of their linear and quadratic headdischarge relationships and are very useful as a flow recorder in irrigation canals. Optimum design parameters for these weirs are presented in a simple dimensionless form suitable for water structure designers to adjust the weir dimensions to suit field conditions. Application of the proposed weir section is not limited to these two weirs; it can also be used to design other specific weirs. © 2012 American Society of Civil Engineers.

Geranmayeh A.R.,University of Tehran | Mahmudi R.,University of Tehran
Materials Chemistry and Physics | Year: 2013

Creep behavior of an Mg-6Al-1Zn-0.7Si cast alloy was investigated by compression and impression creep test methods in order to evaluate the correspondence of impression creep results and creep mechanisms with conventional compression test. All creep tests were carried out in the temperature range 423-523 K and under normal stresses in the range 50-300 MPa for the compression creep and 150-650 MPa for impression creep tests. The microstructure of the AZ61-0.7Si alloy consists of β-Mg17Al 12 and Mg2Si intermetallic phases in the α-Mg matrix. The softening of the former at high temperatures is compensated by the strengthening effect of the latter, which acts as a barrier opposing recovery processes. The impression results were in good agreement with those of the conventional compressive creep tests. The creep behavior can be divided into two stress regimes, with a change from the low-stress regime to the high-stress regime occurring, depending on the test temperature, around 0.009 < (σ/G) < 0.015 and 0.021 < (σimp/G) < 0.033 for the compressive and impression creep tests, respectively. Based on the steady-state power-law creep relationship, the stress exponents of about 4-5 and 10-12 were obtained at low and high stresses, respectively. The low-stress regime activation energies of about 90 kJ mol-1, which are close to that for dislocation pipe diffusion in the Mg, and stress exponents in the range of 4-5 suggest that the operative creep mechanism is pipe-diffusion-controlled dislocation viscous glide. This behavior is in contrast to the high-stress regime, in which the stress exponents of 10-12 and activation energies of about 141 kJ mol-1 are indicative of a dislocation climb mechanism similar to those noted in dispersion strengthening mechanisms. © 2013 Elsevier B.V. All rights reserved.

Gholizadeh M.,University of Tehran | Salmasi F.R.,University of Tehran
IEEE Transactions on Industrial Electronics | Year: 2014

This paper considers the estimation of the state of charge and state of health for lithium-ion batteries, while an inclusive model is taken into account. The model includes two RC subnetworks, which represent the fast and slow transient responses of the terminal voltage. Nevertheless, the linear part of the model is unobservable. On the other hand, the nonlinear behavior of the open-circuit voltage versus state of charge is also included in the model. The proposed observer tackles the aforementioned problems to attain a reliable estimation of the state of charge. Moreover, as opposed to the methods in which the nonlinearities or uncertainties in the model are disregarded or those terms are discarded using a conventional sliding-mode observer, an analytical method is considered to estimate the additive nonlinear or uncertainty term in the model. This approach leads to a very accurate model of the battery to be used in a battery management system. Moreover, an online parameter estimation method is proposed to estimate the battery's state of health. The proposed scheme benefits from an adaptive rule for the online estimation of the series resistance in the lithium-ion battery based on the accurately identified model. Experimental tests certify the performance and feasibility of the proposed schemes. © 1982-2012 IEEE.

Kalantar-Hormozi A.,University of Tehran
Archives of Iranian Medicine | Year: 2013

Although the exact time of performing plastic surgery is not addressed in the medical and historical literature, it can be supposed that these surgical procedures have a long and fascinating history. Recent excavations provided many documents regarding the application of medical instruments, surgical and even reconstructive procedures during the pre-historic and ancient periods. Actually, there is no historical definite time-zone separating general and cosmetic operations in the pre-modern time; however, historically there have been many surgeons who tried to perform reconstructive procedures during their usual medical practice. This article presents a brief look at the history of plastic surgery form the ancient to the contemporary era, with a special focus on Iran.

Shafiei-Zarghani A.,University of Tehran | Kashani-Bozorg S.F.,University of Tehran | Hanzaki A.Z.,University of Tehran
Wear | Year: 2011

An innovative technique, friction stir processing (FSP) was employed for the fabrication of Al/Al2O3 nano-composite surface layer on an Al alloy substrate. Aluminum work pieces with pre-placed nano-sized Al2O3 powder which was filled in a shallow groove were subjected to various numbers of passes from one to four. Scanning electron microscopy studies showed that increase in the number of FSP passes causes a more uniform dispersion of alumina particles and thus, decreases particles clustering. In addition, an increasing in the number of FSP passes was found to decrease the matrix grain size of the surface nano-composite layers. The mean micro hardness value of the surface nano-composite layer was found to be improved by almost three times as compared to that of the as-received Al alloy substrate. A significant improvement in wear resistance was exhibited by surface nano-composite layer in comparison to the as-received substrate. The surface nano-composite layer produced by four FSP passes showed superior wear resistance; this is attributed to its greater micro hardness value (due to presence of finer matrix grains and uniform dispersion nano-sized Al2O3 particles). © 2010 Elsevier B.V.

Shafiei M.,University of Tehran | Ziaee A.-A.,University of Tehran | Amoozegar M.A.,Extremophiles Laboratory
Process Biochemistry | Year: 2010

An extracellular halophilic α-amylase from Nesterenkonia sp. strain F was purified to homogeneity by 80% ethanol precipitation, Q-Sepharose anion exchange and Sephacryl S-200 gel filtration chromatography, with a 10.8-fold increase in specific activity. The molecular mass of the amylase was estimated to be 100 kDa and 106 kDa by SDS-PAGE and gel filtration chromatography, respectively. The enzyme showed maximal activity at pH 7.5 and 45 °C. The amylase was active in a wide range of salt concentrations (0-4 M) with its maximum activity at 0.5 M NaCl or 1 M KCl and was stable at the salts concentrations between 1 M and 4 M. Fe3+, Cu2+, Zn2+ and Al3+ strongly inhibited the enzyme, whereas Ca2+ stimulated the amylase activity. The α-amylase was inhibited by EDTA, but was not inhibited by PMSF and β-mercaptoethanol. The enzyme showed remarkable stability towards 0.5% SDS and sarcosyl, and 2% each of Triton X-100, Tween 80 and Tween 20. Km value of the amylase for soluble starch was 4.5 mg/ml. The amylase hydrolyzed 38% of raw wheat starch and 20% of corn starch in a period of 48 h. The major products of soluble starch hydrolysis were maltose, maltotriose and maltotetraose, indicating an α-amylase activity. © 2010 Elsevier Ltd. All rights reserved.

Hoseinifar S.H.,Young researchers club | Mirvaghefi A.,University of Tehran | Merrifield D.L.,University of Plymouth
Aquaculture | Year: 2011

A study was conducted to assess the effects of dietary commercial inactive brewer's yeast Saccharomyces cerevisiae var. ellipsoideus on the growth performance, survival rate, haematology, serum biochemical parameters and the intestinal microbiota of juvenile beluga sturgeon (Huso huso). Beluga juveniles (11.44 ± 0.56. g) were randomly allocated into 9 oval tanks (350. L) at a density of 35 fish per tank and triplicate groups were fed either a basal control diet (0% yeast) or the basal diet supplemented with yeast (at 1 or 2%). After 6. weeks of feeding on the experimental diets, growth factors (final weight, specific growth rate (SGR) and feed conversion ratio (FCR)), survival rate, haematological parameters and serum metabolic products (cholesterol, glucose and total protein) were measured. Additionally, autochthonous culturable haeterotrophic bacteria and lactic acid bacteria (LAB) levels were determined by culture based methods. The results indicate that dietary supplementation of 2% S. cerevisiae var. ellipsoideus significantly improved final weight, weight gain, SGR and FCR compared to the control treatment (P< 0.05). However survival rate, haematological parameters and serum biochemical parameters were not significantly affected by dietary yeast (P> 0.05). Although the total autochthonous intestinal heterotrophic bacterial counts were not affected by dietary treatment (P> 0.05), autochthonous LAB levels were significantly elevated in fish fed 2% dietary yeast (P< 0.05). These results indicate that inactive S. cerevisiae var. ellipsoideus improves growth performance and modulates intestinal microbiota of beluga sturgeon without detrimentally impacting the basic haematological parameters assessed. Thus, we suggest that low level brewer's yeast may be used as a growth promoter for juvenile beluga sturgeon. © 2011 Elsevier B.V.

Sheikhalishahi M.,University of Tehran
International Journal of Computer Integrated Manufacturing | Year: 2014

Advanced nations have almost finished public infrastructure and rushed into a maintenance period. From now on, the importance of maintenance will increase more and more. In this paper, maintenance activity planning problem is considered. First, maintenance activities are simulated by means of VisualSlam. Production and maintenance functions are estimated using historical data. Then simulation is carried out for different scenarios which are combinations of periodic maintenance and number of maintenance crew, and outputs are computed. Several outputs including machines and operators availability, reliability, efficiency and queue length are computed. Since the problem is multi-criteria, data envelopment analysis (DEA) method is used to select the preferred policy. To show the applicability and superiority of the proposed algorithm, the data for a series production line is used and different scenarios are investigated. The proposed approach of this study would help managers to identify the preferred strategy considering and investigating various parameters and scenarios.© 2013 Taylor & Francis.

Heydari J.,University of Tehran
Computers and Industrial Engineering | Year: 2014

In this paper, the issue of supply chain coordination (SCC) in a buyer-seller supply chain (SC) with an order size constraint is investigated. The buyer keeps safety stock to cope with lead time demand uncertainties from customers' side. Unsatisfied demand will be lost. Therefore the whole SC sales volume depends on the service level provided by the buyer. By proposing a time-based temporary price discount in each replenishment cycle, the seller intends to convince the buyer to optimize its safety stock globally. Maximum and minimum discounts, which are acceptable for both parties, are determined and an appropriate discount schedule is derived. A set of numerical experiments are conducted to show performance of the proposed model. The results show that the safety stock coordination is profitable; the proposed model is capable of coordinating supply chain. In addition, the model can share extra benefits between SC members fairly. © 2014 Elsevier Ltd. All rights reserved.

Vatankhah A.R.,University of Tehran
Flow Measurement and Instrumentation | Year: 2014

The best hydraulic section is usually used as a guide or starting point in open channel design. The semi-circle and semi-regular polygons such as semi-square, semi-hexagon and semi-octagon have the minimum wetted perimeter for a given area, and consequently are the best hydraulic sections from the hydraulic point of view.This study introduces two types (Type I and Type II) of semi-regular polygons as the best hydraulic sections. Both of the sections have the same wetted perimeter and area and thus are equally efficient. However, Type I semi-regular polygon with flat bottom is suitable when excavation depths are shallow, and Type II semi-regular polygon with angled bottom is used when deeper cuts are needed. In this research, general solutions of the normal depth are also presented for Type I and Type II semi-regular polygon sections. © 2014 Elsevier Ltd.

Motamedi D.,University of Tehran | Mohammadi S.,University of Tehran
Engineering Fracture Mechanics | Year: 2010

This paper is dedicated to simulation of dynamic analysis of fixed cracks in orthotropic media using an extended finite element method. This work is in fact an extension to dynamic problems of the recently developed orthotropic extended finite element method for fracture analysis of composites. In this method, the Heaviside and near-tip enrichment functions are used in the framework of the partition of unity for modeling crack discontinuity and crack-tip singularities within the classical finite element method. In this procedure, elements that include a crack are not required to conform to crack edges. Therefore, mesh generation can be performed without any need to comply to crack edges and the method is capable of modeling the crack propagation without any remeshing. To determine the fracture properties, mixed-mode dynamic stress intensity factors (DSIFs) are evaluated by means of domain separation integral (J'-integral) method. Results of the proposed method are compared with other available analytical and computational results. © 2010 Elsevier Ltd.

Meshkini A.,University of Tehran | Yazdanparast R.,University of Tehran
International Journal of Biochemistry and Cell Biology | Year: 2012

Evidence is emerging that Foxo family proteins serve as biochemical signal integrators in complex signaling networks mediating and modulating diverse cellular functions. Herein, we report that besides the well-established function of Foxo3a as a transcriptional regulator of multiple target genes in nucleus, a substantial fraction of Foxo3a translocates to mitochondria leading to disruption of mitochondrial membrane potential, release of cytochrome c and caspase activation during erythroid differentiation mediated by guanosine 5′-triphosphate (GTP). In fact, non transcriptional role of Foxo3a in mitochondria was achieved through the protein-protein interaction with pro-apoptotic protein Bax and its translocation to mitochondrial membrane. Furthermore, our results revealed that mitochondrial localization of Foxo3a was modulated by intracellular GTP content which is sensed by PKC signaling element. Collectively, our findings provided insight into a novel Foxo3a mechanism in leukemia cells which led to engagement of cells in the maturation pathway. © 2012 Elsevier Ltd.

Mahdavi H.,University of Tehran | Nook M.E.,University of Tehran
Polymer International | Year: 2010

A commercial high-impact polypropylene (hiPP) was fractionated by temperature-gradient elution fractionation into nine fractions. All fractions were studied using Fourier transform infrared spectroscopy and differential scanning calorimetry. The amount of ethylene in the fractions was also determined. The results demonstrate that the ethylene-propylene statistical copolymer (or ethylene-propylene rubber, EPR) content in this hiPP is rather low and the amounts of ethylene-propylene segmented copolymer and ethylene-propylene block copolymer (that act as adhesive and compatibilizer between elastomeric phase and matrix, respectively) are negligible. Furthermore, the morphology of the resin was studied using scanning electron microscopy observations of microtome-cut original and etched samples, which reveals that EPR particles are too large and their distribution inside the matrix is not uniform. Copyright © 2010 Society of Chemical Industry.

Hashemi L.,University of Tehran | Morsali A.,University of Tehran
Journal of Inorganic and Organometallic Polymers and Materials | Year: 2010

A new nano-sized lead(II) coordination polymer, {[Pb 2(μ-3-bpdh)(μ-NO 3) 3(NO 3)] n (1); (3-bpdh = 2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene)}, was synthesized by a sonochemical method. The structure of 1, which may be considered coordination polymer of lead(II), consists of metallocyclic chains formed by bridging NO 3 - and 3-bpdh ligands, thereby making a 2D array of Pb(NO 3) 2 and 3-bpdh. The thermal stability of compound was studied by thermogravimetric and differential thermal analyses. The new nano-structure coordination polymer was characterized by powder X-ray diffraction, elemental analysis and IR spectroscopy. The scanning electron microscopy shows the particle size of the 1 prepared by the sonochemical method is about 95 nm. The PbO nanoparticles were obtained by thermolysis of 1 at 180 °C with oleic acid as a surfactant. The scanning electron microscopy shows that the size of the PbO particles are ~60 nm. © 2010 Springer Science+Business Media, LLC.

Seyed Ebrahimi S.H.,University of Tehran | Emamy M.,University of Tehran
Materials and Design | Year: 2010

This study was undertaken to investigate the influence of Al-5Ti-1B and Al-5Zr master alloys on the structural characteristics and tensile properties of Al-12Zn-3 Mg-2.5Cu aluminum alloy. The optimum amount for Ti and Zr containing master alloys was selected as 1 wt.% and 6 wt.%, respectively. The results also showed that Ti containing master alloy is more effective in reducing average grain size of the alloy. T6 heat treatment was applied for all specimens before tensile testing. In heat treated condition, the average tensile strength of 505 MPa was found to be increased to 621 MPa for sample refined with 1 wt.% Al-5Ti-1B (0.05 wt.% Ti). SEM fractography of the fractured faces of several castings showed an overall macroscopically brittle appearance at low magnifications. At higher magnifications, unrefined specimens showed cracking along the grains, whereas Ti-refined specimens showed cracks in individual intermetallic compounds. © 2009 Elsevier Ltd. All rights reserved.

Masoudpanah S.M.,University of Tehran | Mahmudi R.,University of Tehran
Materials and Design | Year: 2010

The shear punch testing (SPT) technique and the uniaxial tension tests were employed to evaluate the mechanical properties of the equal channel angularly pressed (ECAPed) AZ31 magnesium alloy. After extruding, the material was ECAPed for 1, 2, and 4 passes using route BC. The grain structure of the material was refined from 20.2 to 1.6μm after 4 passes of ECAP at 200°C. The 4 pass ECAPed alloy showed lower yield stress and higher ductility as compared to the as-extruded condition, indicating that texture softening has overcome the strengthening effects of grain refinement. The same trends in strength and ductility were also observed in shear punch testing. Similar shear strength and ductility values of the samples taken perpendicular to the extrusion direction (ED) and normal direction (ND) after 4 passes of ECAP indicated that {0002} basal planes were inclined (∼45°) to the extrusion axis. The shear punch testing technique was found to be a useful method for verifying directional mechanical properties of the miniature samples of the ECAPed magnesium alloys. © 2010 Elsevier Ltd.

Attarnejad R.,University of Tehran | Shahba A.,University of Tehran
Meccanica | Year: 2011

This paper deals with enhancing the existing Finite Element formulations through employing basic principles of structural mechanics accompanied with mathematical techniques. Introducing the concept of Basic Displacement Functions (BDFs), the free vibration analysis of rotating tapered beams is studied from a mechanical point of view. It is shown that exact shape functions could be derived in terms of BDFs. The new shape functions turn out to be dependent on the rotational speed, circular frequency, the position of element along the beam and variation of cross-sectional dimensions along the element. Dynamic BDFs are obtained by applying Adomian Modified Decomposition Method (AMDM) to the governing differential equation of motion. Carrying out numerical examples, the competency of the method is verified. © 2010 Springer Science+Business Media B.V.

Vatankhah A.R.,University of Tehran
Ain Shams Engineering Journal | Year: 2013

Normal and critical depths are important parameters in the design of open channels and analysis of gradually varied flow. In trapezoidal and parabolic channels, the governing equations are highly nonlinear in the normal and critical flow depths and thus solution of the implicit equations involves numerical methods (except for critical depth in parabolic channels). In current research explicit solutions have been obtained using the non-dimensional forms of the governing equations. For the trapezoidal cross section, the maximum error of critical flow depth is less than 6 × 10-6% (near exact solution) and the maximum error of normal depth is less than 0.25% (very accurate solution). The maximum error of normal flow depth for parabolic cross section is also less than 8 × 10-3% (near exact solution). Proposed explicit equations have definite physical concept, high accuracy, easy calculation, and wide application range compared with the existing direct equations. © 2012 Ain Shams University. Production and hosting by Elsevier B.V. All rights reserved.

Rabbani M.,University of Tehran
International Journal of Industrial Engineering Computations | Year: 2013

Location Allocation is one of the most important decision making problems, which attracted many operational researchers during recent decades and many solution procedures are developed so far to cope with this problem. This paper proposes a new graph theory based method to cope with small size capacitated location allocation problems. Additionally, a genetic algorithm is utilized to solve medium and large scale problems. Finally, through some computational experiments, the quality and capability of these algorithms are shown. © 2013 Growing Science Ltd. All rights reserved.

Massumi A.,University of Tehran | Moshtagh E.,University of Tehran
Structural Design of Tall and Special Buildings | Year: 2013

Many vital reinforced concrete (RC) buildings experience moderate or severe earthquakes in their lifetime because they are located in hazardous areas. However, their importance cause to be evaluated by different types of damage functions. In these procedures, structures are usually modelled. These models neither correctly display the effects of the cracks that emerge and plastic hinges nor precisely consider the effects of asymmetric configuration and infill panels. Furthermore, the actual nonlinear dynamic behaviour of existing buildings could be evaluated by assessing nonlinear dynamic characteristics such as the fundamental period. These dynamic characteristics, which are obtained by some field tests such as forced and/or ambient vibration methods, comprise the aforementioned effects. This paper offers a damage index (pattern) for seismic damage assessment of RC buildings based on the variation of the nonlinear fundamental period, which is obtained by field tests. Finally, the seismic situation of existing RC buildings that have experienced an earthquake is precisely and expeditiously assessed by this new damage index. © 2010 John Wiley & Sons, Ltd.

Torabi A.R.,University of Tehran
International Journal of Fracture | Year: 2013

The load-bearing capacity of several U-notched specimens, reported in literature, made of very ductile steel and loaded under symmetric three-point bending were theoretically estimated by using the Equivalent Material Concept (EMC), proposed originally by the author, combined with two well-known brittle fracture models namely the mean stress (MS) and the point stress (PS) criteria. The results revealed that the MS-EMC model with an accuracy of more than 90% was more efficient than the PS-EMC model with about 72% accuracy. By using the MS-EMC model, one can predict well the onset of mode I cracking in U-notched ductile components under large-scale yielding conditions without requiring conducting elastic-plastic analyzes or using ductile fracture criteria. © 2013 Springer Science+Business Media Dordrecht.

Ghasemi M.,University of Tehran | Raza M.,Baqiyatallah Medical Sciences University | Dehpour A.R.,University of Tehran
Journal of Psychopharmacology | Year: 2010

Although there is evidence of the involvement of N-methyl-D-aspartate receptors (NMDAR) in the action of lithium, its role in the antidepressant effects of lithium in a behavioural model remains unclear. In this study, we evaluated the effects of NMDAR antagonists on the antidepressant-like effects of lithium in the mouse forced swimming test. Lithium (30 and 100 mg/kg, i.p.) significantly (P < 0.01) reduced the immobility times of mice, whereas at lower doses (5 and 10 mg/kg) had no effect. NMDA antagonists ketamine (2 and 5 mg/kg, i.p.), MK-801 (0.1 and 0.25 mg/kg, i.p.) and ifenprodil (1 and 3 mg/kg, i.p.) significantly (P < 0.05) decreased the immobility time. Lower doses of ketamine (0.5 and 1 mg/kg), MK-801 (0.01 and 0.05 mg/kg) and ifenprodil (0.1 and 0.5 mg/kg) had no effect. Combined treatment of subeffective doses of lithium (10 mg/kg) and ketamine (1 mg/kg), MK-801 (0.05 mg/kg) or ifenprodil (0.5 mg/kg) robustly (P < 0.001) exerted an antidepressant-like effect. The noneffective dose of a NMDA agonist (NMDA, 75 mg/kg, i.p.) prevented the antidepressant-like effect of lithium (30 mg/kg). None of the drugs at subactive doses or in combination with lithium had significant effect on the locomotor activity in the open field test. We for the first time suggested a role for NMDAR signalling in the antidepressant-like effects of lithium, providing a new approach for treatment of depression. © 2010 British Association for Psychopharmacology.

Zangeneh S.,University of Tehran | Farhangi H.,University of Tehran
Materials and Design | Year: 2010

The present work was carried out to investigate the influence of serviced-induced microstructural changes on the failure of cobalt-base superalloy X-45 using in a first stage gas turbine nozzle. The obtained results show that the continuous film of carbides in the grain boundaries and the formation of needle like phases in the interior of grains are due to transformation of primary carbides M6C type to secondary carbides M23C6 type as a result of high-temperature operations. This dense and continuous net of the carbides reduces ductility and toughness of the alloy in comparison with the initial values. Therefore, failure was facilitated by cyclic stresses during start-up/shutdown of gas turbine. © 2010 Elsevier Ltd.

Sheibani S.,University of Tehran | Heshmati-Manesh S.,University of Tehran | Ataie A.,University of Tehran
Acta Materialia | Year: 2010

In this study, the effect of the presence of Al2O3 nanoparticles during mechanical alloying on the extension of Cr solid solubility in Cu was investigated. The lattice parameter, dislocation density and crystallite size were evaluated by the X-ray diffraction technique. Also, the microstructure was characterized by scanning electron microscopy and transmission electron microscopy. The final product was a nanocrystalline and supersaturated Cu-Cr solid solution with a mean crystallite size ranging from 8 to 19 nm depending on the composition. The Gibbs free energy changes in these systems due to the dislocation density and crystallite size variations during milling were calculated. It was found that the presence of Al2O 3 nanoparticles was beneficial to the process, and this was particularly related to its significant contribution to the increase of strain part of Gibbs free energy changes. © 2010 AWE and Crown Copyright. Published by Elsevier Ltd. All rights reserved.

The Dirac equation have been solved for the q-deformed hyperbolic Scarf potential coupled to a Coulomb-like tensor potential under the spin symmetry. The parametric generalization of the Nikiforov-Uvarov method is used to obtain the energy eigenvalues equation and the normalized wave functions.

Mohtat A.,University of Tehran | Dehghan-Niri E.,University of Tehran
Journal of Sound and Vibration | Year: 2011

The primary purpose of this contribution is to develop a novel framework for generalized robust design of tuned mass damper (TMD) systems as passive vibration controllers for uncertain structures. This versatile strategy is intended to be free of any restriction on the structureTMD system configuration, the performance criterion, and the number of uncertain parameters. The main idea pursued is to adopt methods and concepts from the robust control literature, including: (1) the linear fractional transformation (LFT) formulation pertaining to the structured singular value (μ) framework; (2) the concept of weighted multi-input multi-output (MIMO) norms for characterizing performance; and (3) a worst-case performance assessment method to avoid the unacceptable computation burden involved with exhaustive search or Monte Carlo methods in the presence of multiple uncertainties. Based on these, the robust design framework is organized into four steps: (1) modeling and casting the overall dynamics into the proposed LFT framework that isolates the TMD system as the controller, and the uncertainties as a structured perturbation to the nominal dynamics; (2) setting up the optimization problem based on generalized indices of nominal performance, robustness, and worst-case performance; (3) implementing a genetic algorithm (GA) for solution of the optimization problem; and (4) post-processing the results for systematic visualization, validation, and selection of preferred designs. This strategy has been implemented on several illustrative design examples involving a seismically excited multi-story building with different combinations of assumptions on the uncertainty, TMD configuration, excitation scenarios, and performance criteria. The resulting solution sets have been studied through various post-processing methods, including visualization of Pareto fronts, uncertain frequency response plots, time-domain simulations, and random vibration analysis. © 2010 Elsevier Ltd.

Nikkhoo A.,University of Tehran
Mechanical Systems and Signal Processing | Year: 2014

In this paper, the constitutive equation of motion for an Euler-Bernoulli beam in which a number of piezoelectric patches are bonded to the bottom and top surfaces of it, and arbitrary boundary conditions, is derived by employing Hamilton's principle. Assuming a number of linear springs with high stiffness as intermediate supports, the motion equation of a multi-span smart beam could be found. Classical linear optimal control algorithm with displacement-velocity and velocity-acceleration feedbacks is used. Utilizing eigenfunction expansion method, the equation of motion is decoupled into a number of ordinary differential equations. All the numerical examples are presented for the simple boundary conditions. The applied dynamic excitations are a rectangular impulse, moving load and the moving mass. Parametric studies on the capability of the control system in vibration suppression of the beams under these dynamic loads are achieved. The obtained results reveal the efficiency of the proposed control system in reducing the response of the beam structures to the required levels. Copyright © 2013 Published by Elsevier Ltd. All rights reserved.

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

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

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.

Amoabediny G.,University of Tehran
Biotechnology and applied biochemistry | Year: 2010

In the present study, a new online monitoring method for the determination of the CO sensitivity of micro-organisms, based on the values of the respiration factors [OTR (oxygen transfer rate) and CTR (carbon dioxide transfer rate)], obtained by using the RAMOS (respiratory activity monitoring system) device considering a variety of aeration rates in the measuring flask, is investigated. Based on the data of the OTR, obtained by RAMOS under a variety of specific aeration rates, the proposed new method was developed as an online monitoring method for CO sensitivity of micro-organisms in shaken bioreactors. A maximum accumulated CO concentration of 12% was derived in applied methods, provided that the cultivation system is carried out under optimal conditions. Additionally, to predict these conditions, an unsteady-state gas transfer model in shaken bioreactors would be very advantageous. The data of OTR obtained using the RAMOS device were analysed and recalculated by a programme considering the calibration factor (Cf). The major advantage of the new method is the possibility to determine the metabolic activity, regardless of manual sampling.

Valipour M.,University of Tehran
Journal of Agricultural Science | Year: 2012

Accurate computing of amount of pressure loss is very important in sprinkle and trickle irrigation system design. Not correctly adjusted of pressure loss are causes lack of appropriate performance or failure of sprinkle and trickle irrigation system. By tapered pipes, pressure loss adjusted using increasing or decreasing of pressure head. In this study using HydroCalc software, ability of single and tapered pipes in pressure loss adjusting has been compared. Single and tapered laterals were able to adjusting of pressure loss but single manifolds were not able to achieving to the desired pressure head. In single lateral-tapered manifold system due to the lower pressure loss in laterals, can be use from several types of pipe diameters for manifolds but in tapered lateral-tapered manifold system due to the more pressure loss in laterals, the choice is limited. The best diameters for tapered manifolds with single lateral were 69.2-36.8 mm, 69.2-58.2-36.8 mm, and 58.2-46.0-36.8 mm whereas the best diameters for tapered manifold with tapered lateral were 69.2-46.0-36.8 mm.

Foroutan-Nejad C.,University of Tehran
Physical Chemistry Chemical Physics | Year: 2012

The influence of presence of counter ions and π-complexation with benzene on the bonding and magnetic properties of Al 4 2-, the most studied all-metal cluster, is studied here. It is shown that complexation by either counter ions or benzene decreases the delocalization index between Al atoms and the magnitude of bond magnetizability, that is a Quantum Theory of Atoms in Molecules, QTAIM, -based magnetic index of aromaticity. Benzene forms two types of π-complexes with the Al 4 framework; CH-π (T-shaped) complexes and parallel π-π stacking (PPS) complexes. It is shown that variation in the π-charge of the Al 4 framework affects the relative stability of the T-shaped/PPS complexes. Free Al 4 2- forms a stable T-shaped anion-π complex with benzene but in the presence of cations, formation of PPS complexes is more favourable, energetically. It is suggested that this property could be used for designing molecular switches and tuneable anion sensors. This journal is © the Owner Societies.

Alihoseinzadeh A.,University of Tehran | Khodadadi A.A.,University of Tehran | Mortazavi Y.,University of Tehran
International Journal of Hydrogen Energy | Year: 2014

In this study, effects of Au and CuO loadings in Au/CuO-ZnO nanocatalysts for preferential oxidation of carbon monoxide in H2-rich streams (PROX) are investigated. CuO-ZnO supports were synthesized by a co-precipitation method. Au was also incorporated into the catalysts by a deposition- precipitation procedure. The catalysts were characterized by XRD, BET surface area, FESEM, HRTEM, H2-TPR, FTIR, and CO-TPD. 2-10 nm Au nanoparticles are dispersed on CuO-ZnO support and significantly enhance the reducibility of CuO. The Au/CuO-ZnO catalysts containing low amount of CuO were found to be more active for PROX compared to the Au/ZnO catalyst. Moreover, as more CuO is added to Au/ZnO, the CO2 selectivity increases in the whole PROX temperature range. The catalyst containing 2 wt% Au and 1 wt% CuO on ZnO exhibited the highest activity and selectivity in the operating temperature range of PEM fuel cells. The activity of this catalyst also remained almost intact during 900 min of PROX time on stream at 80 C. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights.

Peyghambarzadeh S.M.,University of Tehran | Vatani A.,University of Tehran | Jamialahmadi M.,Petroleum University of Technology of Iran
Applied Thermal Engineering | Year: 2013

In this paper, a systematic comparison is performed to investigate fouling of suspended particles under forced convective and subcooled flow boiling heat transfer. For this purpose, two different types of fouling are separately considered: crystallization fouling of dissolved CaSO4 particles in water and particulate fouling of suspended Al2O3 particles in n-heptane. The effect of hydraulic parameters such as fluid velocity and also bubble generation under subcooled flow boiling are studied. Results of the experiments demonstrate that creation of boiling condition in the heat exchanger has opposite influence in these two types of fouling. It means that bubble generation on the heat transfer surface promotes scale formation under crystallization fouling. This is due to the fact that increased bubble generation creates higher supersaturation beneath the vapor bubble, therefore, increasing the crystal concentration in the boundary layer. On the other hand, boiling condition inhibits the scale formation under particulate fouling because the suspended particles are repelled from the boundary layer by the strong turbulences created by the swarm of bubbles. © 2012 Elsevier Ltd. All rights reserved.

Gholami A.,University of Tehran | Hosseini S.M.,Tarbiat Modares University
IEEE Transactions on Signal Processing | Year: 2011

Estimating a reliable and stable solution to many problems in signal processing and imaging is based on sparse regularizations, where the true solution is known to have a sparse representation in a given basis. Using different approaches, a large variety of regularization terms have been proposed in literature. While it seems that all of them have so much in common, a general potential function which fits most of them is still missing. In this paper, in order to propose an efficient reconstruction method based on a variational approach and involving a general regularization term (including most of the known potential functions, convex and nonconvex), we deal with i) the definition of such a general potential function, ii) the properties of the associated "proximity operator" (such as the existence of a discontinuity), and iii) the design of an approximate solution of the general "proximity operator" in a simple closed form. We also demonstrate that a special case of the resulting "proximity operator" is a set of shrinkage functions which continuously interpolate between the soft-thresholding and hard-thresholding. Computational experiments show that the proposed general regularization term performs better than ℓp -penalties for sparse approximation problems. Some numerical experiments are included to illustrate the effectiveness of the presented new potential function. © 2011 IEEE.

Toloo M.,Islamic Azad University at Central Tehran | Nalchigar S.,University of Tehran
Expert Systems with Applications | Year: 2011

The success of a supply chain is highly dependent on selection of best suppliers. These decisions are an important component of production and logistics management for many firms. Little attention is given in the literature to the simultaneous consideration of cardinal and ordinal data in supplier selection process. This paper proposes a new integrated data envelopment analysis (DEA) model which is able to identify most efficient supplier in presence of both cardinal and ordinal data. Then, utilizing this model, an innovative method for prioritizing suppliers by considering multiple criteria is proposed. As an advantage, our method identifies best supplier by solving only one mixed integer linear programming (MILP). Applicability of proposed method is indicated by using data set includes specifications of 18 suppliers. © 2011 Elsevier Ltd. All rights reserved.

Rajabpour A.,University of Tehran | Vaez Allaei S.M.,University of Tehran | Kowsary F.,University of Tehran
Applied Physics Letters | Year: 2011

The thermal conductivity of hybrid graphene-graphane nanoribbons (GGNRs) have been investigated using nonequilibrium molecular dynamics simulations. The interface between graphene and graphane leads to a Kapitza resistance with strongly dependence on the imposed heat flux direction. We introduce GGNRs as promising thermal rectifiers at room temperature. By calculating phonon spectra, underlying mechanisms were investigated. © 2011 American Institute of Physics.

Attarnejad R.,University of Tehran | Shahba A.,University of Tehran
International Journal for Numerical Methods in Biomedical Engineering | Year: 2011

Introducing the concept of basic displacement functions (BDFs), free vibration analysis of rotating tapered beams is studied from a mechanical point of view. Holding pure structural/mechanical interpretations, BDFs are obtained by solving the governing static differential equation of flapwise motion of rotating Euler-Bernoulli beams and imposing appropriate boundary conditions. Following the principles of structural mechanics, it is shown that exact shape functions and consequently structural matrices could be derived in terms of BDFs. The new shape functions capture the effects of variation of both cross-sectional area and moment of inertia along the element and the stiffening effect of centrifugal force. The method is employed to determine the natural frequencies of tapered rotating beams with different variations of cross-sectional dimensions and the results are in good agreement with those in the literature. Finally, the effects of rotational speed and taper ratio on the natural frequencies are investigated. © 2009 John Wiley & Sons, Ltd.

Hadavandi E.,Sharif University of Technology | Shavandi H.,Sharif University of Technology | Ghanbari A.,University of Tehran
Expert Systems with Applications | Year: 2011

Success in forecasting and analyzing sales for given goods or services can mean the difference between profit and loss for an accounting period and, ultimately, the success or failure of the business itself. Therefore, reliable prediction of sales becomes a very important task. This article presents a novel sales forecasting approach by the integration of genetic fuzzy systems (GFS) and data clustering to construct a sales forecasting expert system. At first, all records of data are categorized into k clusters by using the K-means model. Then, all clusters will be fed into independent GFS models with the ability of rule base extraction and data base tuning. In order to evaluate our K-means genetic fuzzy system (KGFS) we apply it on a printed circuit board (PCB) sales forecasting problem which has been used as the case in different studies. We compare the performance of an extracted expert system with previous sales forecasting methods using mean absolute percentage error (MAPE) and root mean square error (RMSE). Experimental results show that the proposed approach outperforms the other previous approaches. © 2011 Published by Elsevier Ltd.

Rafiei H.,University of Tehran | Rabbani M.,University of Tehran
Computers and Industrial Engineering | Year: 2011

Hybrid Make-To-Stock (MTS)/Make-To-Order (MTO) is one of the product delivery strategies which have recently attracted practitioners' and academicians' interest to meet requirements of today competitive environment. Two important decisions involved in hybrid MTS/MTO context are order partitioning and determining Order Penetration Point (OPP) location. In this paper, a model is developed to first decide on which product is manufactured upon MTS, which one upon MTO and which one upon hybrid strategy. Then, a fuzzy analytic network process (ANP) is utilized to locate the OPP for the products which are decided to be manufactured upon hybrid strategy. Finally, a real industrial case study is reported to show applicability of the proposed model. © 2011 Elsevier Ltd. All rights reserved.

Abbaspour R.A.,University of Tehran | Samadzadegan F.,University of Tehran
Expert Systems with Applications | Year: 2011

This paper addresses the problem of time-dependent tour planning in complex and large urban areas that may be of importance for different groups of people. The problem is determination of chronological sequences of attractive points during a specific period via several modes of transportation system. The proposed approach adopted a nested architecture in which tour planning routine calls multimodal shortest path subroutine to generate an itinerary based on user preferences and restrictions of interesting points. Two adapted genetic algorithms were employed in the engine of both blocks. In these algorithms, chromosomes with variable lengths and particularly defined evolutionary stages are used. The proposed process has been tested over the dataset of city of Tehran. The evaluation consists of preparation of 400 tours with different initial points, start time, and tour durations. It was assumed that just three modes of walking, bus, and subway are used to travel between points of interest. Moreover, some tests are applied to dataset to illustrate the adaptability and time-dependency nature of method. The experimental results and related indices such as optimality ratios show that the proposed algorithm can find optimum tour according to introduced constraints. © 2010 Elsevier Ltd. All rights reserved.

Tavakkoli-Moghaddam R.,University of Tehran | Azarkish M.,University of Tehran | Sadeghnejad-Barkousaraie A.,University of Tehran
Expert Systems with Applications | Year: 2011

This paper presents a new mathematical model for a bi-objective job shop scheduling problem with sequence-dependent setup times and ready times that minimizes the weighted mean flow time (Fw) and total penalties of tardiness and earliness (E/T). Obtaining an optimal solution for this complex problem especially in large-sized problem instances within reasonable computational time is cumbersome. Thus, we propose a new multi-objective Pareto archive particle swarm optimization (PSO) algorithm combined with genetic operators as variable neighborhood search (VNS). Furthermore, we use a character of scatter search (SS) to select new swarm in each iteration in order to find Pareto optimal solutions for the given problem. Some test problems are examined to validate the performance of the proposed Pareto archive PSO in terms of the solution quality and diversity level. In addition, the efficiency of the proposed Pareto archive PSO, based on various metrics, is compared with two prominent multi-objective evolutionary algorithms, namely NSGA-II and SPEA-II. Our computational results show the superiority of our proposed algorithm to the foregoing algorithms, especially for the large-sized problems. © 2011 Elsevier Ltd. All rights reserved.

Ali Saberi A.,University of Tehran | Ali Saberi A.,University of Cologne
Physical Review Letters | Year: 2013

Remarkable global correlations exist between geometrical features of terrestrial surfaces on Earth, current mean sea level, and its geological internal processes whose origins have remained an essential goal in the earth sciences. Theoretical modeling of the ubiquitous self-similar fractal patterns observed on Earth and their underlying rules is indeed of great importance. Here I present a percolation description of the global topography of Earth in which the present mean sea level is automatically singled out as a critical level in the model. This finding elucidates the origins of the appearance of scale invariant patterns on Earth. The criticality is shown to be accompanied by a continental aggregation, unraveling an important correlation between the water and long-range topographic evolutions. To have a comparison point in hand, I apply such an analysis to the lunar topography which reveals various characteristic features of the Moon. © 2013 American Physical Society.

Panahi H.,University of Tehran | Tavakkoli-Moghaddam R.,University of Tehran
Expert Systems with Applications | Year: 2011

This paper considers an open shop scheduling problem that minimizes bi-objectives, namely makespan and total tardiness. This problem, due to its complexity, is ranked in the class of NP-hard problems. In this case, traditional approaches cannot reach to an optimal solution in a reasonable time. Thus, we propose an efficient method based on multi-objective simulated annealing and ant colony optimization, in order to solve the given problem. Furthermore a decoding operator is applied in order to improve the quality of generated schedules. Finally, we compare our computational results with a well-known multi-objective genetic algorithm, namely NSGA II. In addition, comparisons are made in single objective case. The outputs show encouraging results in the form of the solution quality. © 2010 Elsevier Ltd. All rights reserved.

Pishvaee M.S.,University of Tehran | Rabbani M.,University of Tehran
Advances in Engineering Software | Year: 2011

The configuration of the supply chain network has a strong influence on the overall performance of the supply chain. A well designed supply chain network provides a proper platform for efficient and effective supply chain management. The supply chain network should be designed in the way that could meet the customer needs with an efficient cost. This paper studies the responsive, multi-stage supply chain network design (SCND) problem under two conditions: (1) when direct shipment is allowed and (2) when direct shipment is prohibited. First, two mixed integer programming models are proposed for multi-stage, responsive SCND problem under two abovementioned conditions. Then, to escape from the complexity of mixed integer mathematical programming models, graph theoretic approach is used to study the structure of the SCND problems and it is proven that both of SCND problems considered in this paper could be modeled by a bipartite graph. Finally, since such network design problems belong to the class of NP-hard problems, a novel heuristic solution method is developed based on a new solution representation method derived from graph theoretic view to the structure of the studied problem. To assess the performance of the proposed heuristic solution method, the associated results are compared to the exact solutions obtained by a commercial. © 2010 Elsevier Ltd. All rights reserved.

Modarres M.,University of Tehran | Tafrihi A.,University of Tehran
Nuclear Physics A | Year: 2015

The nucleonic matter operator-dependent two-body correlation and distribution functions, for different two-body potentials, e.g. the Av18 and the Av8' interactions, are calculated, using the lowest order constrained variational (LOCV) approach. It is shown that the LOCV results are reasonably consistent with the corresponding predictions of the more sophisticated methods, i.e. the Fermi hypernetted chain approach in the single-operator approximation (FHNC/SOC) and the Monte Carlo (MC) technique. The main reason for this consistence is the LOCV normalization constraint of the two-body radial distribution function, which is optimally satisfied at the two-body cluster approximation. In this way, the many-body effects, which are considered in the FHNC/SOC and the MC calculations, become negligible. Furthermore, in the LOCV formalism, the spin-orbit correlation function is employed, instead of the tensor correlation function, in the P23-F23 channel. It is demonstrated that using the Av18 interaction, the nuclear (neutron) matter equation of state, for the former case, fairly differs from that of the latter case, especially at high densities. However, applying the Reid potential, the former and the latter equations of state lie close together. Finally, it should be mentioned that the spin-orbit dependent distribution functions, which have not been reported by the FHNC/SOC method, can be evaluated in the LOCV framework, for the Av18 and the Av8' potentials. © 2015 Elsevier B.V.

Ahmadi M.H.,University of Tehran | Ahmadi M.-A.,Petroleum University of Technology of Iran | Pourfayaz F.,University of Tehran
European Physical Journal Plus | Year: 2015

Developing new technologies like nano-technology improves the performance of the energy industries. Consequently, emerging new groups of thermal cycles in nano-scale can revolutionize the energy systems’ future. This paper presents a thermo-dynamical study of a nano-scale irreversible Stirling engine cycle with the aim of optimizing the performance of the Stirling engine cycle. In the Stirling engine cycle the working fluid is an Ideal Maxwell-Boltzmann gas. Moreover, two different strategies are proposed for a multi-objective optimization issue, and the outcomes of each strategy are evaluated separately. The first strategy is proposed to maximize the ecological coefficient of performance (ECOP), the dimensionless ecological function (ecf) and the dimensionless thermo-economic objective function (F. Furthermore, the second strategy is suggested to maximize the thermal efficiency (η), the dimensionless ecological function (ecf) and the dimensionless thermo-economic objective function (F). All the strategies in the present work are executed via a multi-objective evolutionary algorithms based on NSGA∥ method. Finally, to achieve the final answer in each strategy, three well-known decision makers are executed. Lastly, deviations of the outcomes gained in each strategy and each decision maker are evaluated separately. © 2015, Società Italiana di Fisica and Springer-Verlag Berlin Heidelberg.

Sabetghadam S.,University of Tehran | Ahmadi-Givi F.,University of Tehran
Environmental Science and Pollution Research | Year: 2014

Light extinction, which is the extent of attenuation of light signal for every distance traveled by light in the absence of special weather conditions (e.g., fog and rain), can be expressed as the sum of scattering and absorption effects of aerosols. In this paper, diurnal and seasonal variations of the extinction coefficient are investigated for the urban areas of Tehran from 2007 to 2009. Cases of visibility impairment that were concurrent with reports of fog, mist, precipitation, or relative humidity above 90 % are filtered. The mean value and standard deviation of daily extinction are 0.49 and 0.39 km-1, respectively. The average is much higher than that in many other large cities in the world, indicating the rather poor air quality over Tehran. The extinction coefficient shows obvious diurnal variations in each season, with a peak in the morning that is more pronounced in the wintertime. Also, there is a very slight increasing trend in the annual variations of atmospheric extinction coefficient, which suggests that air quality has regressed since 2007. The horizontal extinction coefficient decreased from January to July in each year and then increased between July and December, with the maximum value in the winter. Diurnal variation of extinction is often associated with small values for low relative humidity (RH), but increases significantly at higher RH. Annual correlation analysis shows that there is a positive correlation between the extinction coefficient and RH, CO, PM10, SO2, and NO2 concentration, while negative correlation exists between the extinction and T, WS, and O3, implying their unfavorable impact on extinction variation. The extinction budget was derived from multiple regression equations using the regression coefficients. On average, 44 % of the extinction is from suspended particles, 3 % is from air molecules, about 5 % is from NO2 absorption, 0.35 % is from RH, and approximately 48 % is unaccounted for, which may represent errors in the data as well as contribution of other atmospheric constituents omitted from the analysis. Stronger regression equation is achieved in the summer, meaning that the extinction is more predictable in this season using pollutant concentrations. © 2013 Springer-Verlag Berlin Heidelberg.

Najafabadi T.A.,University of Tehran | Salmasi F.R.,University of Tehran | Jabehdar-Maralani P.,University of Tehran
IEEE Transactions on Industrial Electronics | Year: 2011

A sensor fault detection and isolation unit is considered for induction-motor drives based on an adaptive observer with rotor-resistance estimation. Generally, closed-loop induction-motor drives with voltage-source inverters use a speed or position, a dc-link voltage, and two or three phase-current sensors. In the proposed fault-detection and isolation unit, the estimated phase currents and rotor resistance are sent to a decision-making unit, which identifies the faulty sensor type based on a deterministic rule base. In the case of a current-sensor failure, it also detects the phase with erroneous sensor output. It is shown that, unlike the other proposed model-based fault-tolerant systems, using a bank of observers is not necessary, and only one current observer with rotor-resistance estimation is sufficient for isolation of all sensors' faults. The accuracy of the proposed approach is analytically proved. Furthermore, extensive simulation and experimental tests verify the effectiveness of the proposed method at different operating conditions. © 2010 IEEE.

Fakhari A.,University of Tehran | Rahimian M.H.,University of Tehran
Computers and Fluids | Year: 2011

In this paper, a multi-relaxation-time lattice Boltzmann method for multiphase flows is employed to simulate different modes of deformation and fragmentation of an axisymmetric falling droplet under buoyancy force. To show the accuracy of the model, the Laplace law for stationary drops is conducted first. Then, drop deformation and breakup in a free fall is studied in an axially symmetric pipe. Surface tension effects as well as impacts of gas and drop viscosities are investigated for a wide range of Eötvös, Morton, and Archimedes numbers. The drag coefficient of the drop, as it falls, is measured and compared to the empirical correlations, and reasonable agreement is shown. The findings are further verified by comparing a typical bag breakup mechanism with experimental observations. It is seen that at low Eötvös numbers the drop deforms slightly and reaches a steady state. Increase of Eötvös number enhances the rate of deformation, and at a high enough Eötvös value breakup of the drop happens. While the gas viscosity is shown to have a trivial effect on the breakup of the droplet, drop viscosity is the overriding factor in the mechanism of disintegration. Consequently, various breakup modes of the falling droplet are observed just by varying the drop-based Archimedes number. By capturing different breakup mechanisms of a falling droplet such as bag breakup, shear breakup, and, particularly, multimode breakup, the present lattice Boltzmann method exhibits an excellent superiority over the sharp interface tracking schemes that fail to capture dissociation of the interface. © 2010 Elsevier Ltd.

Keramati A.,University of Tehran | Ardabili S.M.S.,University of Tehran
Telecommunications Policy | Year: 2011

To survive in the challenging environment of a global market, organizations must recognize and analyze customer attitudes. To be competitive, organizations must recognize and forecast customer preferences and behaviors to maximize customer retention before their rivals do so. This research identifies factors that affect customer churn, the single most valuable of an organizations assets. One years data from call log files relating to 3150 customers were selected randomly from an Iranian mobile operator call-center database. Binomial Logistic Regression was the method of analysis used in this research. The results of this research indicate that a customers dissatisfaction, their amount of service usage and certain demographic characteristics have the most influence on their decision to remain or churn. The results also imply that customer status (active or inactive status) mediates the relationship between churn and the cause of churn. The Iranian governments current plan to privatize the telecommunications industry without deregulation leads to a non-square competition environment. Deregulation in favor of delegating more authorities of customer care is necessary in order to develop a square private competition environment in the Iranian mobile telecommunications industry. © 2011 Elsevier Ltd. All rights reserved.

Amiri M.,Allame Tabatabaee University | Golozari F.,University of Tehran
International Journal of Advanced Manufacturing Technology | Year: 2011

In this paper, we attempt to introduce an algorithm which considers not only time factor but also cost, risk, and quality criteria to determine the critical path under fuzzy environment. In this algorithm first, decision makers allocate time, cost, risk, and quality to each activity. We are lacking in data and information, so in the proposed algorithm, the ratings of each activity and the weight of each criterion are described by fuzzy numbers and linguistic variables, which can be expressed in triangular fuzzy number. Linguistic variables are applied to represent the intensity of preferences of one criterion over another. Then, we add up triangular fuzzy numbers to determine the final evaluation value of each criterion for paths. Next, we use fuzzy TOPSIS, a technique for order preferences by similarity to an ideal solution, a method proposed by the authors in another paper, to choose the best alternative. Finally, numerical example is solved to illustrate the procedure of proposed method at the end of this paper. © Springer-Verlag London Limited 2010.

Bastami A.H.,University of Tehran | Olfat A.,University of Tehran
IEEE Transactions on Vehicular Technology | Year: 2011

Due to the half-duplex transmission nature of cooperative protocols, almost all cooperative diversity systems suffer from low spectral efficiency. In general, adaptive modulation can offer a good tradeoff between spectral efficiency and bit-error-probability (BEP) performance of wireless communication systems. In this paper, we propose two adaptive modulation schemes for the cooperative system with detect-and-forward relaying that simultaneously exploit the cooperative diversity gain and improve the spectral efficiency of the system. In the first scheme, which is similar to conventional selection relaying, the relay decides independently whether to forward the source messages to the destination or not by comparing the instantaneous received signal-to-noise ratio (SNR) with a predetermined fixed threshold, which is independent of the instantaneous modulation scheme. In contrast, in the second scheme, the relay and the destination jointly decide whether the relay will participate in the second phase of the protocol or remain silent. This second scheme can be viewed as a combination of selection and incremental relaying and achieves higher spectral efficiency in comparison with its nonincremental counterparts. We evaluate the performance of the protocols in terms of the end-to-end BEP, the average spectral efficiency, and the outage probability for both identically and nonidentically distributed Rayleigh fading environments. In our analysis, we consider M-ary phase-shift keying (M-PSK) modulation, M-ary pulse-amplitude modulation (M-PAM), and M-ary quadrature-amplitude modulation (M-QAM) schemes and examine the impact of error propagation from the relay to the destination on the end-to-end performance of the system in detail. Moreover, we derive a closed-form expression for the optimal relaying threshold that effectively mitigates error propagation and minimizes the end-to-end BEP of the system. The high-SNR analysis demonstrates that both proposed schemes provide full diversity. © 2011 IEEE.

Omid M.,University of Tehran
Expert Systems with Applications | Year: 2011

This paper presents an expert system for sorting open and closed shell pistachio nuts. A prototype was set up to detect closed shell pistachio nuts by dropping them onto a steel plate and recording the acoustic signals that was generated when a kernel hit the plate. To determine the important characteristics and to unravel the significance of these signals, further analysis or processing was required. J48 decision tree (DT) is used for both feature selection and classification. Initially, the J48 DT was used for selecting the best statistical features that will discriminate among two classes from impact acoustic signals. The output of J48 DT algorithm was then converted into crisp IF-THEN rules and membership function sets of the fuzzy classifier. Four IF-THEN rules, generated from the extracted features of J48 DT, were required by the fuzzy classifier. To evaluate the performance of the expert system, data on 300 nuts of open and closed shells were used. The data were initially divided into two parts: 210 instances (70%) for training and the remaining 90 instances (30%) for testing the classifier. The correct classification rate and RMSE for the training set were 99.52% and 0.07, and for the test set were 95.56% and 0.21, respectively. These encouraging results as well as the robustness of the FIS based expert system makes the approach ideal for automated inspection systems. © 2010 Elsevier Ltd. All rights reserved.

Gordiz K.,University of Tehran | Vaez Allaei S.M.,University of Tehran | Kowsary F.,University of Tehran
Applied Physics Letters | Year: 2011

Using nonequilibrium molecular dynamics simulations, we show if a multi-walled carbon nanotube (MWNT) is heated asymmetrically, an evident thermal rectification can be detected. We attribute the observed rectification to the asymmetric radial thermal transport between constructing layers in MWNT. The underlying physics is explained by calculating temperature distribution of MWNT layers and phonon power spectrum. Thermal rectification in this carbon nanotube based thermal rectifier does not diminish by increasing the system size, and exists in a wide range of temperatures. These results open a door in the applicability of MWNTs in nanoscale engineering of thermal transport devices. © 2011 American Institute of Physics.

Parabronema skrjabini is a spirurid nematode of the family Habronematidae that lives in the abomasum of ruminants such as sheep and goats. The purpose of this study was to investigate the molecular aspects of Parabronema skrjabini in sheep. The worms were collected from sheep in Sanandaj (west of Iran). The first internal transcribed spacer (ITS) of ribosomal DNA (rDNA) nucleotide fragments of Parabronema skrjabini were amplified by polymerase chain reaction (PCR) using two pairs of specific primers (Para-Ir-R and Para-Ir-F). ITS1 homology in the sequence of this study was 69% compared with the sequence data in GenBank. To our knowledge, this is the first study in the world exploring the genetic diversity of P. skrjabini in sheep based on ITS1.

Aleenejad M.,University of Tehran | Iman-Eini H.,University of Tehran | Farhangi S.,University of Tehran
IET Power Electronics | Year: 2013

In this study, fault-tolerant operation of multilevel cascaded H-bridge (CHB) inverters is presented and a novel switching strategy based on space vector modulation is proposed. A faulty power switch in high power converters can lead to expensive downtime, loss of productivity and increased costs. Various power switch faults and their influence on space vector diagram of CHB inverters are investigated. In the event of a fault, the output voltage of inverter is reduced and redundant switching states are used to generate balanced line-to-line voltages. By adding some devices to the basic structure, CHB inverter will operate with maximum achievable output voltage. Simulation and experimental results are shown for a five-level CHB inverter to validate the proposed modulation technique. © The Institution of Engineering and Technology 2013.

Mohammad-Abadi M.,University of Tehran | Daneshmehr A.R.,University of Tehran
International Journal of Engineering Science | Year: 2015

In this study, by using the modified couple stress theory, the vibration analysis of composite laminated beams in order of micron is developed. It should be mentioned that this theory is capable to capture the size effect by considering the material length scale parameters unlike the classical continuum theories. The Hamilton's principle is applied to obtain the governing equations and boundary conditions of micro composite laminated beams. By considering three beam models, i.e. Euler-Bernoulli, Timoshenko and Reddy beam models, the differences between them and the effect of shear deformation are studied. This is the first study that introduces the couple stress-curvature relation for Reddy beam model properly. Furthermore, three boundary conditions, i.e. hinged-hinged, clamped-hinged and clamped-clamped and four types of lamination, i.e. [0, 0, 0], [0, 90, 0], [90, 0, 90] and [90, 90, 90] are investigated. Using generalized differential quadrature (GDQ) method, the governing equations are numerically solved and natural frequencies are obtained. Also, the governing equations are analytically solved for hinged-hinged boundary condition by employing the Fourier series expansions. Comparison between results obtained by GDQ method and analytical solution for hinged-hinged boundary condition reveals the GDQ method as an accurate and powerful method to solve the governing equations. © 2014 Elsevier Ltd. All rights reserved.

Torabi A.R.,University of Tehran
International Journal of Fracture | Year: 2013

The experimentally obtained tensile load-bearing capacity of fifteen U-notched polycrystalline graphite plates reported in literature was theoretically estimated by means of two well-known brittle fracture models, namely the mean stress (MS) and the point stress (PS) criteria. The results showed that while the mean discrepancies between the experimental and the theoretical results for both the models are very good and approximately equal, the discrepancies are significantly different for various notch tip radii. Meanwhile, the results of MS and PS criteria were compared with the results of the strain energy density (SED) criterion reported in literature. Relatively similar value of mean discrepancy was also obtained for the SED model. It was demonstrated in this research that for small values of the notch tip radius, the MS model is the most appropriate failure criterion while the PS and SED criteria are much better models for medium radii. Moreover, for large notch tip radii, the MS and PS criteria are better choices for tensile fracture assessment of U-notched graphite plates than the SED criterion. © 2013 Springer Science+Business Media Dordrecht.

Torabi A.R.,University of Tehran
International Journal of Fracture | Year: 2013

The U-notched maximum tangential stress (UMTS) criterion, proposed originally and utilized previously by the author and his co-researcher for predicting mixed mode I/II fracture in plexi-glass (PMMA) and also pure mode II fracture in PMMA and soda-lime glass, was employed to estimate the experimental results reported in literature dealing with brittle fracture of many U-notched fine-grained isostatic graphite plates under combined tensile/shear loading conditions. By using the fracture curves of the UMTS criterion, which can predict the onset of brittle fracture in terms of the notch stress intensity factors (NSIFs) in the entire domain from pure mode I to pure mode II, the mixed mode fracture toughness (i.e. the load-bearing capacity) of U-notched graphite plates was successfully estimated. © 2013 Springer Science+Business Media Dordrecht.

Nasseri M.,University of Tehran | Moeini A.,University of Tehran | Tabesh M.,University of Tehran
Expert Systems with Applications | Year: 2011

In this paper, a hybrid model which combines Extended Kalman Filter (EKF) and Genetic Programming (GP) for forecasting of water demand in Tehran is developed. The initial goal of the current work is forecasting monthly water demand using GP for achieving an explicit optimum formula. In the proposed model, the EKF is applied to infer latent variables in order to make a forecasting based on GP results of water demand. The available dataset includes monthly water consumption of Tehran, the capital of Iran, from 1992 to 2002. Five best formulas based on GP results on this dataset are presented. In these models, the first five to three lags of observed water demand are used as probable and independent inputs. For each model, sensitivity of the results for each input is measured mathematically. A model with the most compatibility of the computed versus the observed water demand is used for filtering based on EKF method. Results of GP and hybrid models of EKFGP demonstrate the visible effect of observation precision on water demand prediction. These results can help decision makers of water resources to reduce their risks of online water demand forecasting and optimal operation of urban water systems. © 2010 Elsevier Ltd. All rights reserved.

Kianmehr E.,University of Tehran | Baghersad M.H.,University of Tehran
Advanced Synthesis and Catalysis | Year: 2011

The copper-catalyzed coupling of aromatic boronic acids with potassium cyanate in the presence of an alcohol has been employed for the synthesis of arylcarbamates. This simple and highly efficient approach can be carried out in air at room temperature and, importantly, no base, ligand, or additive is required. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Torabi A.R.,University of Tehran | Amininejad S.H.,University of Tehran
International Journal of Damage Mechanics | Year: 2014

In the present research, two brittle fracture criteria were developed in terms of the notch stress intensity factors to predict mode I fracture in engineering components weakened by V-notches with end holes (VO-notches). The criteria were based on the point stress and the mean stress failure concepts. To evaluate the validity of the criteria, first, 36 new fracture tests were conducted on a new notched specimen, namely the Brazilian disk containing central V-notch with end hole (VO-BD specimen) made of polymethyl-metacrylate. Three notch angles and four notch radii were considered in the experiments. Then, the experimentally obtained fracture loads were converted to the corresponding mode I notch fracture toughness values by mean of the finite element method in order to compare the test results with the theories. It was found that very good agreement exists generally between the experimental and theoretical results. Also, found in this research was that by increasing the VO-notch angle, the accuracy of the mean stress criterion decreases, particularly for larger notch radii. Although the accuracy of the criteria depends significantly on the notch geometry, except for the angle 90°, the average discrepancies of the mean stress criterion were less than 8.5% as well as those of the point stress criterion for the entire angles showing acceptable accuracy of the predictions. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Mollasalehi H.,University of Tehran | Yazdanparast R.,University of Tehran
Analytical Biochemistry | Year: 2012

Lack of an appropriate detection method for isothermal RNA amplification technique, known as nucleic acid sequence-based amplification (NASBA), is considered as a major defect for its vast applications. In that regard, novel detection methods as fast, specific, and sensitive as the gold nanoprobe detection technique are highly demanded and non-crosslinking gold nanoprobes are regarded as the ideal choice. In this study, we attempted to integrate these two techniques (RNA amplification and nanoprobe detection) into a single detection-associated amplification method. In that line, essential adjustments such as amplicon dilution, disturbing reagent extraction, ion adjustment, and modification of the hybridization protocol were needed due to the ribonucleic acid nature of NASBA products and the presence of some interfering reagents in the amplification reaction environment. The adjustments successfully resulted in the gold nanoparticle-based detection of NASBA products with naked eyes in a whole operational time of less than 3.5 h (including nucleic acid extraction, amplification, and detection). Furthermore, the developed assay was successfully applied to detect dnaK messenger RNA of Salmonella typhimurium. The developed colorimetric method facilitated the detection step of NASBA leading to an ideal methodology for rapid assays and serves as an ideal alternative to the highly expensive reverse transcription polymerase chain reaction (RT-PCR) approach. © 2012 Elsevier Inc. All rights reserved.

Kebriaei H.,University of Tehran | Araabi B.N.,University of Tehran | Rahimi-Kian A.,University of Tehran
IEEE Transactions on Power Systems | Year: 2011

In this paper, the problem of short-term load forecasting is redefined and solved with a new metric, which is the extension of the conventional sum of squared error (SSE) metric. The proposed metric is a nonsymmetric penalty function with different penalties for over-forecasting and under-forecasting. Therefore, a large family of approaches that utilize gradient-based methods such as artificial neural networks with back propagation learning and regressions method with least squares estimate are not useful in this case. To solve this problem, a modified radial basis function (RBF) network, which uses the genetic algorithm to estimate the weights of the network is presented. This network has the ability to handle the new penalty function. In addition, a fuzzy inference system is combined with the modified RBF network to incorporate the impact of temperature on load. As a real case study, we tried to forecast the electric power load of Mazandaran area in Iran. The comparison between the proposed method and the well-known RBF network demonstrates the efficiency of the proposed method with the new forecasting metric. © 2006 IEEE.

Sanaye-Pasand M.,University of Tehran | Jafarian P.,University of Tehran
IEEE Transactions on Power Delivery | Year: 2011

This paper introduces adaptive decision-making logic to improve the performance of distance protection of transmission lines. The proposed approach incorporates the trajectory of the measured impedance into the relay final decision-making logic through a weighting procedure. Two criteria are used to weigh the impedance plane appropriately, where higher weights are assigned to the faults occurring at the interior areas of the relay protective zone and low resistance faults. The weights assigned to impedance samples are added together considering the amount of smoothness of the measured impedance trajectory. An adaptive neurofuzzy inference system (ANFIS) is used to implement the proposed decision logic. Meanwhile, the fault current amplitude is considered as the other input of the ANFIS network to accelerate the relay operation for close-in faults and to incorporate an index for the source-to-line impedance ratio into the final decision-making logic. Extensive simulation studies using PSCAD/EMTDC software indicate that the proposed approach provides a very reliable technique to make the distance protective scheme faster and smarter. It helps to achieve the optimal compromise between the protective relay operation time and security. © 2011 IEEE.

Jafarian P.,University of Tehran | Sanaye-Pasand M.,University of Tehran
IET Generation, Transmission and Distribution | Year: 2011

This study presents a sub-cycle power frequency-based fault direction discrimination and fault classification algorithm for the series-compensated transmission lines. Also, it provides an accurate estimation for the fault occurrence instant which is helpful in synchronised waveforms-based pilot protective schemes. The proposed algorithm is based on capturing the initial change in the voltage and current waveforms caused by occurrence of a fault. The high-frequency components of the fault signals are first filtered out, and then the signals are sampled at a relatively low sampling rate. Unlike the conventional relative-phase-angle-based directional relays, the proposed algorithm is not affected by the current and voltage inversion phenomena due to the presence of series capacitor in the fault loop. Extensive simulation studies are performed to evaluate the proposed algorithm performance. The obtained results show that the proposed algorithm provides a simple and a very fast and reliable protection technique for power transmission lines. This algorithm also covers non-compensated transmission lines and is able to well discriminate the fault direction even if the post-fault voltage amplitude becomes too small. It is also tested using some real data recorded from a high-voltage transmission system. © 2011 The Institution of Engineering and Technology.

Farivar G.,University of Tehran | Asaei B.,University of Tehran
IEEE Transactions on Energy Conversion | Year: 2011

In this paper, an effective new approach for estimating the operating temperature of a photovoltaic (PV) module by using the simple diode model is presented. The developed method is simple and does not need any additional hardware. The proposed approach uses an analytical formula to derive the temperature from the maximum power point voltage and current. Since the temperature estimation (TE) is based on the model of the PV module, at first the model is explained. In the model, effects of the temperature coefficients are considered. Moreover, a new approach to find all parameters of a PV module model is described. Unlike other methods, the parameters extraction method that is proposed here only needs manufacturer data from the datasheet and does not need any additional information. Effectiveness of the new TE procedure is investigated through some conducted simulations in MATLAB/Simulink environment and its validity is verified by experiment on a REC-AE220 solar module. © 2011 IEEE.

Varkani A.K.,University of Tehran | Daraeepour A.,Iran Grid Management Company IGMC | Monsef H.,University of Tehran
Applied Energy | Year: 2011

Competitive structure of power markets causes various challenges for wind resources to participate in these markets. Indeed, production uncertainty is the main cause of their low income. Thus, they are usually supported by system operators, which is in contrast with the competitive paradigm of power markets. In this paper, a new strategy for increasing the profits of wind resources is proposed. In the suggested strategy, a Generation Company (GenCo), who owns both wind and pumped-storage plants, self-schedules the integrated operation of them regarding the uncertainty of wind power generation. For presenting an integrated self-schedule and obtaining a real added value of the strategy, participation of the GenCo in energy and ancillary service markets is modeled. The self-scheduling strategy is based on stochastic programming techniques. Outputs of the problem include generation offers in day-ahead energy market and ancillary service markets, including spinning and regulation reserve markets. A Neural Network (NN) based technique is used for modeling the uncertainty of wind power production. The proposed strategy is tested on a real wind farm in mainland, Spain. Moreover, added value of the strategy is presented in different conditions of the market. © 2011 Elsevier Ltd.

Aflaki S.,University of Tehran | Hajikarimi P.,University of Tehran
Construction and Building Materials | Year: 2012

In this research, the effects of four modifiers including crumb rubber, gilsonite, styrene-butadiene-styrene (SBS) and polyphosphoric acid (PPA) on the mechanical and rheological properties of asphalt binder at low service temperature are investigated. The main objective of this paper is to rank modifiers due to their effect on low service performance characteristics of asphalt binder for all type and extent of observed modified asphalt binders. For this purpose, the bending beam rheometer (BBR) test is performed on different extent of modifiers at five temperatures: -6°C, -12°C, -18°C, -24°C and -30°C. Asphalt binder is categorized as a viscoelastic material. Among several linear viscoelastic models, the Burgers model is selected for describing the mechanical behavior of modified asphalt binders. Four Burgers parameters are calculated by means of the principle of multiple non-linear regression and then these parameters are used for comparing the performance of asphalt binders by these three approaches: SuperPAVE Performance Grading (PG) protocol, dissipated energy ratio and derivation of creep compliance. Utilizing these three approaches, modified asphalt binders are ranked based on higher quantity of low temperature, dissipated energy ratio and derivation of creep compliance for all type and extent of modifiers alongside. Results show that each approach produces a particular grading which is not same as another one. In spite of variation of rankings, among the all evaluated modified asphalt binders, crumb rubber modified asphalt binder totally shows superior performance on low service temperature in all three methods. © 2012 Elsevier Ltd. All rights reserved.

The objective of this study was to compare feed-forward artificial neural network (ANN) and M5 model tree for estimating reference evapotranspiration (ET0) only on the basis of the remote sensing based surface temperature (Ts) data. The input variables for these models were the daytime surface temperature at the cold pixel obtained from the AVHRR/NOAA sensor and extraterrestrial radiation (Ra). The study has been carried out in five irrigated units that cultivate sugar cane, which located in the Khuzestan plain in the southwest of Iran. A total of 663 images of NOAA–AVHRR level 1b during the period 1999–2009, covering the area of this study were collected from the Satellite Active Archive of NOAA. The FAO-56 Penman–Monteith model was used as a reference model for assessing the performance of the two above approaches. The study demonstrated that modelling of ET0 through the use of M5 model tree gave better estimates than the ANN technique. However, differences with the ANN model are small. Root mean square error and R2 for the comparison between reference and estimated ET0 for the tested data set using the proposed M5 model are 13.7 % and 0.96, respectively. For the ANN model these values are 14.3 % and 0.95, respectively. © 2016 Springer Science+Business Media Dordrecht

Changizian P.,University of Tehran | Zarei-Hanzaki A.,University of Tehran | Roostaei A.A.,University of Tehran
Materials and Design | Year: 2012

In the field of deformation process modeling, constitutive equations are invariably used as a calculation basis to estimate the materials flow responses. Accordingly, in the present study, a constitutive analysis has been conducted on the AZ81 magnesium alloy employing experimental stress-strain data obtained from isothermal hot compression tests. These tests had been done in the temperature range of 250-450°C under strain rates of 0.003, 0.03 and 0.3s-1. The effects of the temperature and strain rate on hot deformation behavior have been expressed in terms of an exponent-type Zener-Hollomon equation. Furthermore, the influence of strain has been included in the constitutive equation by considering its effect on different material constants. Consequently, a model to predict the high-temperature flow behavior of AZ81 magnesium alloy has been established. The true stress-true strain curves predicted by the extracted model are in good agreement with the experimental results, thereby confirming the validity of the developed constitutive relation. © 2012 Elsevier Ltd.

Mostofi A.,University of Tehran | Bargi K.,University of Tehran
Marine Structures | Year: 2012

In this paper, special behavior of floating piers in the berthing event is assessed, and a new approach is presented for the analysis of these kinds of piers for berthing impact. Accurate estimation of berthing force is an important matter for appropriate design of mooring piles in these piers. In the pier design references, the traditional approach used in the design of fixed piers is extended to floating piers, ignoring distinctive response of these piers to berthing impact. In this paper, the fact of mobility and flexibility of structural system of floating piers are taken into consideration, and it is proved that energy absorption mechanism in these piers is different from that of fixed piers. Thus a new analytical approach and corresponding closed form formulations are presented in this paper for evaluating impact energy and induced berthing forces in these piers. The validity of presented method is shown by numerical simulations. Comparison of results of analysis by new and traditional methods in two typical piers shows that the traditional method underestimates berthing force in floating piers. © 2011 Elsevier Ltd.

Hemayattalab R.,University of Tehran
Research in Developmental Disabilities | Year: 2010

The purpose of this study was to investigate the effects of physical training and calcium intake on bone mineral density (BMD) of students with mental retardation. Forty mentally retarded boys (age 7-10 years old) were randomly assigned to four groups (no differences in age, BMD, calcium intake and physical activity): training groups with or without calcium supplementation (Tr+Ca+ and Tr+Ca-) and nontraining groups with or without calcium supplementation (Tr-Ca+ and Tr-Ca-). The intervention involved 45. min of physical training performed 3 sessions a week and/or the addition of dietary calcium-rich food using enriched cow milk with vitamin D containing 230. mg calcium per serving, over 6 months. Paired-samples t-test and ANOVA analysis was used to determine the main and combined effects of training and calcium on BMD. All groups showed greater femoral neck BMD after 6 months. The increase in femoral neck BMD in the Tr+Ca+ group was 10% greater than increase in the Tr+Ca- group (not significant). Apparently, the effect of training was greater than calcium intake because the Tr+Ca- group achieved 4% greater BMD than Tr-Ca+ group (not significant). In this study, both training groups had greater BMD than the control group (Tr-Ca-) (P<0.05).In these participants with inadequate calcium intakes, additional exercise and calcium supplementation resulted in a 6-20% greater increase in BMD than controls at the loaded site (femoral neck). These results help to provide more evidence for public health organizations to deal with both exercise and nutrition issues in children for the achievement of peak BMD. © 2010 Elsevier Ltd.

Rafiee R.,University of Tehran | Heidarhaei M.,Islamic Azad University at Semnan
Composite Structures | Year: 2012

The main goal of this research is to predict Young's modulus of carbon nanotubes using a full non-linear finite element model. Spring elements are used to simulate molecular interactions in atomic structure of carbon nanotube. All interactions are simulated non-linearly. A parametric study is performed to investigate effects of chirality and diameter on the Young's modulus of single walled carbon nanotubes. Unlike the results of presented linear finite element models, the results of current model imply on independency of Young's modulus from chirality and diameter. Obtained results from this study are in a good agreement with experimental observations and published data. © 2012 Elsevier Ltd.

Dolatkhah A.,University of Tehran | Golbabaei P.,University of Tehran | Besharati Givi M.K.,University of Tehran | Molaiekiya F.,University of Tehran
Materials and Design | Year: 2012

Friction stir processing (FSP) is a novel process for refinement of microstructure, improvement of material's mechanical properties and production of surface layer composites. In this investigation via friction stir processing, metal matrix composite (MMC) was fabricated on surface of 5052 aluminum sheets by means of 5 μm and 50. nm SiC particles. Influence of tool rotational speed, traverse speed, number of FSP passes, shift of rotational direction between passes and particle size was studied on distribution of SiC particles in metal matrix, microstructure, microhardness and wear properties of specimens. Optimum of tool rotational and traverse speed for achieving desired powder dispersion in MMC was found. Results show that change of tool rotational direction between FSP passes, increase in number of passes and decrease of SiC particles size enhance hardness and wear properties. © 2011 Elsevier Ltd.

Faraji G.,University of Tehran | Jafarzadeh H.,University of Tehran
Materials and Manufacturing Processes | Year: 2012

A new plastic deformation technique based on accumulative torsion back (ATB) processing is proposed. The principle of ATB is that the material is subjected to the repetitive shear deformation by utilizing alternate twisting with a simple twist instrument. The process was investigated experimentally on commercially pure aluminium. Additionally, simulation of the process was also carried out, using the commercial finite element code ABAQUS/Explicit. Moreover, effects of process parameters such as twisting angle and number of passes on the results were studied. Results show that the ATB method is capable of imposing high strain values via strain accumulation by repeating the process, which is of great importance in producing ultrafine-grained or nanostructured materials. Elimination of the friction, low process loads, high productivity, and simple instrument are four important advantages of the ATB processing. © Taylor and Francis Group, LLC.

Nasiri N.,University of Tehran | Emamy M.,University of Tehran | Malekan A.,University of Tehran
Materials and Design | Year: 2012

In the present work, the effect of extra Si addition on the microstructure and tensile properties of Al-15%Mg2Si composite has been investigated. The Al-15%Mg2Si composite ingot was made by in situ process and different amounts of extra Si (0.5, 1, 1.5, 2, 5 and 7wt.% Si) were added to the remelted composite. Optical microscopy and scanning electron microscopy (SEM) indicated that the addition of extra Si up to 2wt.%, reduces the average Mg2Si particle size from 39μm to 26μm and increases the volume fraction of α-Al phase from 6% to 22%. Addition of extra Si content up to 7wt.% leads to the formation of primary Mg2Si particles with larger size (38μm). The results of tensile test revealed that the addition of extra Si improves ultimate tensile strength (UTS) and elongation values of the composite from 176MPa and 1.7% to 222MPa and 3.0% respectively. Fractographic analysis of specimens exposed a cellular nature for the fracture surface. On the cellular fracture surface, the features of both brittle and ductile fracture were present simultaneously. Raising the amount of extra Si up to 7% has increased the number and decreased the size of dimples. These microstructural findings led to a change in the mode of fracture from brittle to ductile and increased elongation values. © 2011 Elsevier Ltd.

Rezayat M.,Sharif University of Technology | Akbarzadeh A.,Sharif University of Technology | Owhadi A.,University of Tehran
Composites Part A: Applied Science and Manufacturing | Year: 2012

Recently accumulative roll bonding has been used as a novel method to produce particle reinforced metal matrix composites. In this study, aluminum matrix composite reinforced by submicron particulate alumina was successfully produced and the effects of number of ARB cycles and the amount of alumina content on the microstructure and mechanical properties of composites were investigated. According to the results of tensile tests, it is shown that the yield and tensile strengths of the composite are increased with the number of ARB cycles. Scanning electron microscopy (SEM) reveals that particles have a random and uniform distribution in the matrix by the ARB cycles and a strong mechanical bonding takes place at the interface of particle-matrix. It is also found that the tensile strength of the composite, as a function of alumina content, has a maximum value at 2 vol.%, which is 5.1 times higher than that of the annealed aluminum. © 2011 Elsevier Ltd. All rights reserved.

Torabian S.,University of Tehran | Mirghaderi S.R.,University of Tehran | Keshavarzi F.,University of Tehran
Journal of Constructional Steel Research | Year: 2012

Built-up box-columns are commonly used in rigid orthogonal moment resisting frames; however, the installation and welding of necessary horizontal continuity plates inside the columns are both labour-consuming and costly tasks. Accordingly, a new beam-to-box-column connection, called a diagonal through-plate connection, is presented in this paper to provide a new load path different from that of conventional connections and to facilitate the construction process of the connection. As the stiffness, strength and ductility of square box columns are almost similar around any axis, this connection is composed of vertical plates that pass through the diagonal axes of a square box-column and are welded to the box corners. In this paper, a detailed analysis and design procedure are presented for the proposed connection. In addition, the behaviour of the designed specimens was examined both experimentally and numerically. The cyclic response of the relatively identical test specimens showed that the connection withstands more than a 0.06-rad story drift with permissible strength degradation as well as that the connection can be qualified as a connection of special moment resisting frames within the limited sizes under investigation. Test observations and verified finite element results revealed that the column plates contribute effectively to the stiffness and strength of the connection panel zone; however, the panel zone remains relatively elastic throughout the test. A comprehensive parametric study was conducted using the finite element method to provide more detailed insight into the connection behaviour, including the load transferring mechanism and panel zone behaviour. © 2011 Elsevier Ltd. All rights reserved.

Ramezanalizadeh H.,University of Tehran | Heshmati-Manesh S.,University of Tehran
International Journal of Refractory Metals and Hard Materials | Year: 2012

In this study, MoSi 2-Al 2O 3 nano-composite powder was prepared by mechanical alloying. Mixture of MoO 3, Si and Al powders was exposed to high energy ball milling. Phase compositions and structural evolutions during milling were investigated by X-ray diffraction (XRD) analysis. The morphology of the milled powders was evaluated by scanning electron microscope (SEM). Within short milling times [15, 25 and 60 minutes in ball to powder weight ratios (BPR) of 35:1, 20:1 and 10:1, respectively], a combustion process occurred within the milling powder and the process mechanism was characterized to be mechanically activated self-propagating high-temperature synthesis (MASHS) type. From XRD results it was found that during the combustion process, MoO 3 was completely reduced with Al and the resulting Mo reacted with Si to produce molybdenum disilicide and eventually a MoSi 2-Al 2O 3 nano-composite powder formed within a short period of time. Further milling resulted in reduced mean crystallite sizes and increased lattice micro strain in the product phases. After 30 hours of milling in BPR of 35:1, the mean crystallite sizes were found to be 10, 9 and 11 nm for Al 2O 3, α-MoSi 2 and β-MoSi 2, respectively. Also, effect of stearic acid addition as a Process Control Agent (PCA) was studied and the results showed that its usage postpones the reaction initiation and reduces mean crystallite sizes. © 2011 Elsevier Ltd. All rights reserved.

Eskandari M.,University of Tehran | Zarei-Hanzaki A.,University of Tehran | Marandi A.,University of Tehran
Materials and Design | Year: 2012

In recent years, the transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) steels have been the focus of great attention thanks to their excellent tensile strength-ductility combination. Accordingly the mechanical behavior of an advanced microalloyed TRIP-TWIP steel, the compression tests were conducted from 25 to 1000 °C. This experimental steel shows a high compressive strength of 1280. MPa with the yield strength of 385. MPa as well as an outstanding strain hardening rate of about 14,000. MPa at the 25 °C. In addition the results indicate that the plastic deformation in the range of 25-150 °C is controlled by both the strain-induced martensite formation and mechanical twinning. However the mechanical twinning has been speculated as the only deformation mechanism in the temperature range of 150-1000 °C. This as well has led to an outstanding grain refinement via grain partitioning. The occurrence of mechanical twinning at such high temperatures is a novel observation in this grade of TRIP-TWIP high manganese steels. © 2012.

Zohoor M.,K. N. Toosi University of Technology | Besharati Givi M.K.,University of Tehran | Salami P.,K. N. Toosi University of Technology
Materials and Design | Year: 2012

Nowadays, fabrication of metal matrix composites (MMCs) with high mechanical properties and modified microstructures has attracted many attentions. One of the methods to produce MMCs is friction stir processing (FSP) which is a novel modifying technique. In this investigation, production of AA5083 aluminum alloy with reinforced layers using copper particles via FSP was discussed. Microstructural characterization was performed through optical microscopy (OM) and scanning electron microscopy (SEM). Effects of rotational speed, FSP pass numbers and Cu particles' size were investigated on microstructure, particles distribution pattern and microhardness. Results showed that the specimens with micro and nano-sized particles present fine grains and higher level of hardness. Tensile properties of specimens friction stir processed with and without Cu particles were also evaluated. According to the results, the composite with nano-sized particles exhibited enhanced tensile strength and ductility rather than AA5083 aluminum alloy. X-ray diffraction (XRD) studies were carried out on the specimens FSPed with Cu particles in order to identify the phases present in the stir zone (SZ) of the specimens. © 2012 Elsevier Ltd.

Kashefi N.,University of Tehran | Mahmudi R.,University of Tehran
Materials and Design | Year: 2012

The effects of 0.5, 1.0 and 2.0wt.% Y additions on the microstructure and creep behavior of the as-cast AZ80 alloy were investigated by impression tests. The tests were performed at temperatures in the range 423-523K, under punching stress in the range 150-650MPa. At low temperatures up to 473K, the AZ80+0.5Y alloy had the highest creep resistance among all materials tested, whereas with increasing temperature from 473K to 523K, the AZ80+1.0Y alloy had a better performance. This can be attributed to the fact that at low temperatures the presences of β-Mg17Al12 and Al2Y phases together with solid solution hardening effects of Al in the Mg matrix strengthen the AZ80+0.5Y alloy. At higher temperatures, AZ80+1.0Y with a higher volume fraction of the more thermally stable Al2Y and lower amounts of the less stable β-Mg17Al12 exhibits better creep behavior. The stress exponents and activation energies were almost the same for all alloy systems studied, 6.0-8.8 and 90-119kJ/mol, respectively. The observed decreasing trend of creep-activation energy with stress suggests that two parallel mechanisms of lattice and pipe-diffusion-controlled dislocation climb are competing. Climb of dislocations with an additional particle strengthening effect controlled by dislocation pipe diffusion is dominant at high stresses, whereas climb of dislocations is the controlling mechanism at low stresses. © 2012 Elsevier Ltd.

Mansoori B.,University of Tehran | Modirsanei M.,University of Tehran
Veterinary Parasitology | Year: 2012

An experiment was carried out to assess the influence of tannic acid (TA) on integrity of the intestine in broiler chicks vaccinated against coccidiosis and challenged with the disease. In a 2×2 factorial design, the trial had five groups of 10 chickens each, including positive (group 2) and negative (group 1) controls. The chickens were kept on wood shavings and fed a commercial maize and soybean-based starter-grower diet. From day 1, groups 3 and 5 received TA (10gkg -1) in their diet. On day 4, birds of groups 4 and 5 were vaccinated orally against coccidiosis with anti-coccidial vaccine, Livacox T™. Each dose of the vaccine contained 300-500 sporulated oocysts of each of Eimeria acervulina, Eimeria maxima and Eimeria tenella. On day 18, all experimental groups except for the negative (group 1) were challenged with 10-fold dose of Livacox T™ to produce a mild coccidiosis infection. Faecal samples of individual birds were collected on day 23, and the number of faecal oocysts was determined. d-Xylose absorption test was also carried out on all birds on day 23. Immediately after d-xylose absorption test, all birds were killed humanely and the intestinal tract was removed, weighed and examined for gross lesions. Results showed that negative (group 1) and positive controls (group 2) had the highest and lowest levels of plasma d-xylose post-ingestion of the substrate, respectively. Vaccination and/or feeding TA raised the level of plasma d-xylose in infected birds, although this was not significant for TA-fed birds. Vaccination reduced but TA increased the total number of oocysts per gram of faeces. Birds of groups 2-5 had distinct intestinal lesions when compared with group 1. However, vaccination prevented intestinal lesions. Relative weights of intestinal parts were the lowest in group 1 and the highest in group 2. Vaccination but not TA reduced the relative weights of intestinal parts in infected birds. It was concluded that dietary tannins may reduce the efficacy of anticoccidial vaccines and alter the proper development of immunity against the disease. © 2012 Elsevier B.V.

Motamedi M.,University of Tehran | Eskandari M.,University of Tehran | Yeganeh M.,University of Tehran
Materials and Design | Year: 2012

Elastomers, particularly rubbers, are viscoelastic polymers with low Young's modulus. In this research, carbon nanotubes were used in the rubber and a rubber-carbon nanotube composite was modeled by ABAQUS™ software. Due to hyperelastic behavior of the rubber, strain function energy was used for the modeling. A sample of rubber was tested and uniaxial, biaxial, as well as planar test data obtained in these tests were used to get an energy function. Polynomial and reduced polynomial form are two common methods to achieve strain energy function. In this paper, elasticity modulus and Poisson ratio were measured for a representative volume element (RVE) of composite. Rubber was also considered as an elastic material and its composite properties in this state compared by hyperelastic rubber matrix assumption. ABAQUS was used to create a three dimensional finite element model of a single long wavy nanotube with diameter of D which perfectly bonded to matrix material. Nanotube waviness was modeled by sinusoidal carbon nanotube shape. Results showed that mechanical properties of the rubber will extremely change by adding carbon nanotube. Furthermore, several volume fractions of carbon nanotube in rubber were modeled and it was shown that stiffness of nanocomposite increases by more volume fraction of carbon nanotubes. © 2011 Elsevier Ltd.

Mazahery A.,University of Tehran | Shabani M.O.,Iranian Materials and Energy Research Center
Journal of Materials Engineering and Performance | Year: 2012

In this study, different volume fractions of B 4C particles were incorporated into the aluminum alloy by a mechanical stirrer, and squeeze-cast A356 matrix composites reinforced with B 4C particles were fabricated. Microstructural characterization revealed that the B 4C particles were distributed among the dendrite branches, leaving the dendrite branches as particle-free regions in the material. It also showed that the grain size of aluminum composite is smaller than that of monolithic aluminum. X-ray diffraction studies also confirmed the existence of boron carbide and some other reaction products such as AlB 2 and Al 3BC in the composite samples. It was observed that the amount of porosity increases with increasing volume fraction of composites. The porosity level increased, since the contact surface area was increased. Tensile behavior and the hardness values of the unreinforced alloy and composites were evaluated. The strainhardening behavior and elongation to fracture of the composite materials appeared very different from those of the unreinforced Al alloy. It was noted that the elastic constant, strain-hardening and the ultimate tensile strength (UTS) of the MMCs are higher than those of the unreinforced Al alloy and increase with increasing B 4C content. The elongation to fracture of the composite materials was found very low, and no necking phenomenon was observed before fracture. The tensile fracture surface of the composite samples was indicative of particle cracking, interface debonding, and deformation constraint in the matrix and revealed the brittle mode of fracture. © ASM International.

Borjali S.,University of Tehran | Allahkaram S.R.,University of Tehran | Khosravi H.,University of Tehran
Materials and Design | Year: 2012

In the present study, high pressure heat-resistant cast stainless steels (HP steels) modified with niobium and titanium were investigated in as-cast conditions and after being used in pyrolysis furnaces. Life span of the studied specimens obtained from pyrolysis furnace was 5years. Microstructural changes were studied via scanning electron microscopy (SEM) equipped with energy dispersive spectrum (EDS), optical microscopy (OM), and X-ray diffraction (XRD). The effect of temperature and carbon diffusion on the microstructure, chromium-rich carbides, the NbC transformation to G-phase and other precipitates formed during service condition were discussed. The results showed that two major phases, namely chromium and niobium carbides, existed in the as-cast specimens. Temperature and carbon diffusion influenced the composition and volume fraction of secondary precipitates. Chromium and niobium carbides were transformed to M23C6 and G-phase respectively during service. Higher working temperatures do not always cause coarsening of precipitates. However, factors such as decarburization and carbon diffusion have important roles, too. © 2011 Elsevier Ltd.

Ebrahimzadeh H.,University of Tehran | Mousavi S.A.A.A.,University of Tehran
Materials and Design | Year: 2012

Laser welding is one of the most popular methods for joining hot crack sensitive alloys and thin materials because of its low heat input and high heat intensity. In this study, a Nd:YAG pulsed micro laser machine with maximum 6. J pulse energy was used for joining 49Ni-Fe soft magnetic alloy. Welding of samples was carried out autogenously by changing the pulse duration, focused beam diameter, voltage, frequency and welding speed. All samples were bead on plate welded. Scanning electron microscopy (SEM), optical microscopy and microhardness measurements were used for survey of results. Results show that weld bead size and grain size increase with voltage and heat input increase with pulse frequency. However, weld penetration depth and weld craters reduce with pulse frequency. The study shows that the average peak power density and pulse frequency are two important parameters that results in the formation of weld crater and porosity in the weld zone. Formation of hot cracks in the weld metal depends on the weld pool shape. Cylindrical weld pools are sensitive to hot cracks. Therefore, in order to reduce hot cracks in the weld bead, it is necessary to decrease voltage and increase pulse duration time, focused beam diameter and pulse frequency. © 2012 Elsevier Ltd.

Salmasi F.R.,University of Tehran | Najafabadi T.A.,University of Tehran
IEEE Transactions on Energy Conversion | Year: 2011

An adaptive observer with online estimation of rotor and stator resistances is considered for induction motors, while only one phase current is measured. Generally, an induction motor drive controller needs at least two phase-current sensors. Nevertheless, failure of one current sensor results in degradation of motor drive performance and reliability, and also state and parameter estimation errors. Furthermore, any controller or observer in induction motor drives should be robust to rotor and stator resistance variations. The proposed observer is capable of concurrent estimation of stator currents and rotor fluxes with online tuning of rotor and stator resistances, while rotor speed and only one phase current are available. Stability and convergence of the observer are analytically verified based on the partial stability theory. The observer equations and adaptation laws can be easily implemented, which makes it attractive for industrial development of fault tolerant drives. A complex programmable logic device is implemented for the experimental setup that controls an intelligent power module including insulated gate bipolar transistors. Extensive simulation and experimental tests verify the asymptotic convergence of the proposed observer. © 2011 IEEE.

Jafarian P.,University of Tehran | Sanaye-Pasand M.,University of Tehran
IET Generation, Transmission and Distribution | Year: 2011

This study presents an adaptive data window algorithm for fast and accurate signal phasor estimation. The proposed approach is based on weighted least error squares algorithm as well as variable data window estimation technique. An adaptive model is used for the input signal during the two stages. The first stage is considered to accelerate the relay first zone operation. This is done through applying a forgetting factor in the cost function computation, by which the effect of older samples on the estimation is reduced to decrease the initial inertia of the phasor estimator. The second stage starts one cycle after occurrence of the fault. This algorithm is used to improve the estimation accuracy and helps to obtain better estimation for the fault location. To verify the performance of the proposed algorithm, various simulation studies are carried out. The algorithm is also evaluated using some field data recorded from a high-voltage transmission system. The obtained results confirm accurate, fast and reliable response of the proposed algorithm. It not only accelerates the relay operation but also improves the digital filters' capability of reducing the estimation error because of power system frequency deviation, harmonics, inter-harmonics and decaying dc component. © 2011 The Institution of Engineering and Technology.

Sabokpa O.,University of Tehran | Zarei-Hanzaki A.,University of Tehran | Abedi H.R.,University of Tehran | Haghdadi N.,University of Tehran
Materials and Design | Year: 2012

In the present work, the capability of artificial neural network (ANN) has been evaluated to describe and to predict the high temperature flow behavior of a cast AZ81 magnesium alloy. Toward this end, a set of isothermal hot compression tests were carried out in temperature range of 250-400°C and strain rates of 0.0001, 0.001 and 0.01s-1 up to a true strain of 0.6. The flow stress was primarily predicted by the hyperbolic laws in an Arrhenius-type of constitutive equation considering the effects of strain, strain rate and temperature. Then, a feed-forward back propagation artificial neural network with single hidden layer was established to investigate the flow behavior of the material. The neural network has been trained with an in-house database obtained from hot compression tests. The performance of the proposed models has been evaluated using a wide variety of statistical indices. The comparative assessment of the results indicates that the trained ANN model is more efficient and accurate in predicting the hot compressive behavior of cast AZ81 magnesium alloy than the constitutive equations. © 2012 Elsevier Ltd.

Alibabaie S.,University of Tehran | Mahmudi R.,University of Tehran
Materials and Design | Year: 2012

This study investigates the microstructure and impression creep behavior of the ultra high-temperature Zn-3Cu-4Al (ZCA34), Zn-3Cu-5Al (ZCA35), and Zn-3Cu-6Al (ZCA36) solder alloys under constant punch stress in the range of 70-800MPa and at temperatures in the range of 345-495K. The results showed that for all loads and temperatures, increasing Al content of the alloys results in higher creep rates, and thus lower creep resistances. This is attributed to the partial spheroidisation of the lamellar eutectic structure, and the four phase transformation α+ε→T'+η. The former may ease grain boundary sliding at high temperatures and the latter results in a lesser amount of the more creep resistant ε-phase. The stress exponents of 5.0-7.9 and activation energy values of 52.5-100.3kJmol-1, are indicative of a dislocation climb controlled creep mechanism. The observed increasing trend of creep activation energy with temperature means that two parallel mechanisms of lattice-diffusion-controlled and pipe-diffusion-controlled dislocation climb are competing. Dislocation climb controlled by pipe diffusion is the rate controlling mechanism at low temperatures, whereas dislocation climb controlled by lattice diffusion is the dominant creep mechanism at high temperatures. © 2012 Elsevier Ltd.

Sanaye-Pasand M.,University of Tehran | Jafarian P.,University of Tehran
IEEE Transactions on Power Delivery | Year: 2011

This paper introduces a state-diagram-based protective algorithm for parallel circuit transmission lines using local information obtained at the relay bus. A new cross-differential technique is proposed which compares the currents in the corresponding phases of the parallel circuits in a 2-D space. A companion impedance-based algorithm is used to cover the evolving faults and some conditions in which the cross-differential technique is not able to discriminate the internal faults alone. The effect of the mutual coupling between parallel circuits on the measured impedances is adaptively compensated according to the status of the parallel circuit currents in the segmented 2-D space. The proposed state-diagram-based algorithm combines the outputs of the cross-differential and impedance-based techniques to provide a reliable response under all of the operating statuses of the parallel circuits. Extensive simulation studies using PSCAD/EMTDC software indicate that the proposed approach provides very reliable protection for the double-circuit transmission lines. It covers intercircuit and evolving faults, and is able to reliably select the faulted phases. © 2011 IEEE.

Saffarian A.,University of Tehran | Sanaye-Pasand M.,University of Tehran
IEEE Transactions on Power Systems | Year: 2011

In the modern power systems operating at lower stability margins, conventional non-adaptive schemes cannot offer adequate protection for securing the power system, especially against combinational events. For major disturbances, the active power deficit is usually accompanied by reactive power deficit and frequency stability and voltage stability of the system are jeopardized simultaneously. In this paper, three adaptive combinational load shedding methods are proposed to improve operation of the conventional underfrequency load shedding scheme in order to enhance power system stability following severe disturbances. The proposed methods use locally measured frequency and voltage signals to counteract such events. In the proposed algorithms, load shedding is started from the locations which have higher voltage decay for longer period of time. The speed, location, and amount of load shedding are changed adaptively depending on the disturbance location, voltage status of the system, and the rate of frequency decline. Operation of the conventional and the proposed load shedding methods have been simulated in an actual large network. Obtained simulation results confirm that the proposed methods provide considerable enhancement in the power system voltage stability margin, and by using the proposed algorithms, various power system blackouts could be prevented. © 2011 IEEE.

The equivalent material concept (EMC), proposed recently by the author for predicting the tensile load-bearing capacity of ductile metallic materials weakened by V-notches, was utilized together with the mean stress (MS) criterion to estimate the experimentally obtained maximum loads that several ductile steel bolts with V-shaped threads can sustain. It was found that the MS-EMC criterion could estimate the experimental results successfully. By usin of V-threaded ductile steel bolts without conducting tensile fracture g the MS-EMC model, one can obtain well the tensile load-bearing capacitytest. © 2012 Elsevier Ltd.

This paper describes a detailed evaluation of the performance and characteristic behaviour of feed-forward artificial neural network (ANN) and M5 model tree for estimating reference evapotranspiration (ET0) at four meteorological sites in an arid climate. The input variables for these models were the maximum and minimum air temperature, air humidity and extraterrestrial radiation. The FAO-56 Penman-Monteith model was used as a reference model for assessing the performance of the two approaches. The results of this study showed that the ANN estimated ET0 better than the M5 model tree but both models performed well for the study area and yielded results close to the FAO56-PM method. Root mean square error and R2 for the comparison between reference and estimated ET0 for the tested data using the proposed ANN model are 5.6 % and 0.98, respectively. For the M5 model tree method these values are 8.9 % and 0.98, respectively. The overall results are of significant practical use because the temperature and Humidity-based model can be used when radiation and wind speed data are not available. © 2014 Springer Science+Business Media Dordrecht.

Barmouz M.,University of Tehran | Givi M.K.B.,University of Tehran
Composites Part A: Applied Science and Manufacturing | Year: 2011

In this study, multi-pass friction stir processing (MFSP) is used for improvement of microstructural and mechanical properties of in situ Cu/SiC composites. Field emission scanning electron microscopy and optical microscopy images indicate that multi-pass FSP notably enhances the separation and dispersion of SiC particles and also reduces the grain size in the composite matrix, SiC particles size and porosity contents. According to the results, higher microhardness values and remarkably enhanced tensile properties were caused by higher number of FSP passes. It was also found that the average friction coefficients of composites fabricated by multi-pass FSP were noticeably reduced compared to the pure copper. Addition of SiC particles led to enhancement of electrical resistivity of pure copper. A negligible difference between the electrical resistivity of composites fabricated by 1, 4 and 8-pass FSP was also detected. © 2011 Elsevier Ltd. All rights reserved.

Sharifitabar M.,University of Sistan and Baluchestan | Nami H.,University of Tehran
Composites Part B: Engineering | Year: 2011

In this research, microstructures and hardness profiles across the interface of friction stir welded joints between monolithic 2024-T4 aluminum alloy (AA) and Al/Mg2Si metal matrix cast composite (MMC) and effects of one and two welding passes on these parameters were investigated. Results showed that there were complicated patterns of materials flow in the stir zone (SZ) especially in samples welded in two passes. This region was free of defects like voids and tunnel defects in samples welded in one pass. But some defects were formed in samples welded in two passes. Stirring caused fragmentation and rearrangement of Mg2Si large particles in the stir zone and thermo mechanically affected zone (TMAZ) of MMC, respectively. Eutectic phase has formed on the grain boundaries of 2024 AA in thermo mechanically affected zone due to high heat input to the joint area during welding. In samples welded in one pass, hardness increased from the base metal to the stir zone on the MMC side, reached a maximum in the middle of the joint interface and decreased at about 2 mm away from the joint interface center on 2024 AA side. But, hardness variation in the sample welded in two passes was complicated and there was alternating decrease and increase in hardness value at the joint interface. © 2011 Elsevier Ltd. All rights reserved.

Yousefi A.,University of Tehran | Rastgoo A.,University of Tehran
Composite Structures | Year: 2011

A formulation for the free vibration analysis of functionally graded (FG) spatial curved beams is presented by taking into account the effects of thickness-curvature. The governing equation is based on the firstorder shear deformation theory (FSDT) and Ritz method is employed to obtain the natural frequencies. The curved beams presented are in the form of the cylindrical helical spring. The material distribution is in the direction of the curvature of the curved beam. The results for isotropic planar curved beams are validated with the known data in the literature. The effects of helix pitch angle, number of turns and boundary conditions on frequency parameters of spatial curved beams are investigated. © 2011 Elsevier Ltd.

Shabani M.O.,Iranian Materials and Energy Research Center | Mazahery A.,University of Tehran
JOM | Year: 2011

In this paper, a relatively new approach is presented in order to predict the microstructure of A356 using finite element technique and artificial neural network. In the training and test modules of the neural network, different primary and secondary dendrite arm spacing obtained from finite element method were used as inputs and eutectic volume percentage, silicon volume percentage, silicon rod spacing, average length of silicon rods and silicon rod diameter were used as outputs. After the training set was prepared, the neural network was trained using different training algorithms, hidden layers and neurons number in hidden layers. The results of this research were also used to form analytical equations followed with solidification codes for SUT Cast software. © 2011 TMS.

Hasani G.H.,University of Tehran | Mahmudi R.,University of Tehran
Materials and Design | Year: 2011

Mechanical behavior of hot rolled Mg-3Sn-1Ca (TX31) magnesium alloy sheets were studied in the temperature range 25-350°C. The microstructure of the alloy consisted of the eutectic structure of α-Mg+Mg2Sn and a dispersion of needle-like CaMgSn. The highest room-temperature ductility of 18% was obtained by hot rolling of the cast slabs at 440°C, followed by annealing at 420°C. The high temperature tensile deformation of the material was characterized by a decrease in work hardening exponent (n) and an increase in strain rate sensitivity index (m). These variations resulted in respective drops of proof stress and tensile strength from 126.5MPa and 220MPa at room temperature to 23.5MPa and 29MPa at 350°C. This was in contrast to the ductility of the alloy which increased from 18% at room temperature to 56% at 350°C. The observed variations in strength and ductility were ascribed to the activity of non-basal slip systems and dynamic recovery at high temperatures. The TX31 alloy showed lower strength than AZ31 magnesium alloy at low temperatures, while it exhibited superior strength at temperatures higher than 200°C, mainly due to the presence of thermally stable CaMgSn particles. © 2011 Elsevier Ltd.

Mazahery A.,University of Tehran | Ostadshabani M.,Iranian Materials and Energy Research Center
Journal of Composite Materials | Year: 2011

In this study, 0.75, 1.5, 2.5, 3.5, and 5 vol.% of alumina nanoparticles were incorporated into the A356 aluminum alloy by a mechanical stirrer and then, cylindrical specimens were cast at 800°C and 900°C. A uniform distribution of reinforcement, grain refinement of aluminum matrix, and presence of the minimal porosity was observed by microstructural characterization of the composite samples. Characterization of mechanical properties revealed that the presence of nanoparticles significantly increased compressive and tensile flow stress at both casting temperatures. The highest compressive flow stress was obtained by 2.5 vol.% of Al 2O 3 nanoparticles. It is then observed that the flow stress decreases when Al 2O 3 concentration increased further to 5 vol.% irrespective of the amount of deformation and casting temperature. It was revealed that the presence of nano-Al 2O 3 reinforcement led to significant improvement in 0.2% yield strength and ultimate tensile stress while the ductility of the aluminum matrix is retained. Fractography examination showed relatively ductile fracture in tensile-fractured samples. © 2011 The Author(s).

Emamy M.,University of Tehran | Jafari Nodooshan H.R.,Islamic Azad University at South Tehran | Malekan A.,University of Tehran
Materials and Design | Year: 2011

Current study investigates the effect of different concentrations of yttrium (0.1-1.0wt.%) on the microstructure, hardness and tensile properties of Al-15%Mg2Si cast composite. The microstructural study of the composite revealed the presence of both primary and secondary Mg2Si phases in all specimens and also Y-containing intermetallics at higher concentrations of the respected element. It was also found that Y addition does not change the size and morphology of primary Mg2Si particles considerably, but the pseudo-eutectic Mg2Si was changed from a flake-like morphology to fine fibrous or rod-like. The results obtained from mechanical testing demonstrated that the addition of Y increases both hardness and ultimate tensile strength (UTS) values. Further investigations on tensile test revealed optimum Y level (0.5wt.%) for improving both UTS and elongation values. Fracture surfaces via scanning electron microscopy (SEM) revealed that all specimens with large facets of primary Mg2Si particles succumb to brittle fracture. The large and brittle Mg2Si phases may act as crack initiators, while fine rod-like morphology of eutectic Mg2Si in Al-Mg2Si-0.5Y can be a barrier to the propagation of cracks and thus enhance the elongation values. At higher Y contents, an intermetallic phase (Al2Y) introduced on eutectic cell boundaries, appears to be the favored path for crack propagation. © 2011 Elsevier Ltd.

Allahkaram S.R.,University of Tehran | Golroh S.,University of Tehran | Mohammadalipour M.,University of Tehran
Materials and Design | Year: 2011

Cu-Al2O3 nano-composite coatings have high potential for use in applications in which high mechanical properties together with high corrosion resistance are required. In the present study it is intended to produce copper nano-alumina composite coatings with various nano-alumina contents in order to investigate the effect of alumina reinforcement particles on corrosion resistance and mechanical properties such as hardness and wear resistance. The composite coatings were deposited using direct current (DC) and pulse current (PC) plating. The microstructures of the coatings produced from both methods were examined via scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The wear behaviors, micro hardness, coating thickness, corrosion rate and coating porosity were examined using appropriate methods. Compared to DC deposition, PC plating facilitated higher amounts of particle incorporation with more uniform distribution. The results indicated that the mechanical properties of the applied coatings with incorporated nano-alumina reinforcement were far more superior as compared to its own matrix as well as non-composite copper coatings. It was also found out that increasing the amount of nano-alumina content in the coating, led to enhanced general properties of the coatings. © 2011 Elsevier Ltd.

Alipour M.,University of Tehran | Emamy M.,University of Tehran
Materials and Design | Year: 2011

In this study the effect of Al-5Ti-1B grain refiner on the structural characteristics and hardness of Al-12Zn-3Mg-2.5Cu aluminum alloy has been investigated. The alloy was produced by modified strain-induced melt activation (SIMA) process. Reheating condition to obtain a fine globular microstructure was optimized. The specimens subjected to deformation ratio of 40% (at 300 °C) and various heat treatment times (5-40. min) and temperature (550-620 °C) regimes were characterized in this study. Microstructural study was carried out on the alloy by the use of optical and scanning electron microscopy (SEM) in both unrefined and Ti-refined conditions. The results showed that for the desired microstructures of the alloy during SIMA process, the optimum temperature and time are 575 °C and 20. min respectively. The hardness test results of the alloy also revealed that T6 heat treatment is more effective in hardness enhancement of all specimens in comparison with SIMA processing. © 2011 Elsevier Ltd.

Shabani M.O.,Iranian Materials and Energy Research Center | Mazahery A.,University of Tehran
Archives of Metallurgy and Materials | Year: 2011

In order to predict the mechanical properties of A356, a relatively new approach is presented in this paper using finite element technique which combines mechanical properties data in the form of experimental and simulated microstructures. In this work, the comparison of this model's predictions with the ones in the literature is presented. It is revealed that predictions of this study are consistent with the other works and experimental measurements for A356 alloy. The results of this research were also used in order to form an analytical equations followed with solidification codes for SUT (Sharif University Technology) software.

Mahdavi S.,University of Tehran | Akhlaghi F.,University of Tehran
Tribology Letters | Year: 2011

The influence of graphite content on the dry sliding wear characteristics of Al6061/Gr composites along with Al6061/30SiC/Gr hybrid composites has been assessed using a pin-on-disc wear test. The composites with different volume fraction of graphite particles up to 13% were processed by in situ powder metallurgy (IPM) technique. The porosity and hardness of the resultant composites were also examined. It was found that an increase in the graphite content reduced the porosity, hardness, and friction coefficient of both types of composites. The hybrid composites were more porous and exhibited higher hardness and lower coefficient of friction at identical graphite contents. The increased graphite content in the range of 0-13 vol.% resulted in increased wear rate of Al/Gr composites. The Al/30SiC composite exhibited a lower wear rate as compared with the base alloy and graphite addition up to 9 vol.% improved the wear resistance of these hybrid composites. However, more graphite particles addition resulted in increased wear rate. SEM micrographs revealed that the wear mechanism was changed from mostly adhesive in the base alloy sample (Al/0Gr) to the prominently abrasive and delamination wear for Al/Gr and Al/SiC/Gr/composites. © 2011 Springer Science+Business Media, LLC.

Barmouz M.,University of Tehran | Besharati Givi M.K.,University of Tehran | Seyfi J.,University of Tehran
Materials Characterization | Year: 2011

The main aim of this study is to produce copper reinforced metal matrix composite (MMC) layers using micron sized SiC particles via friction stir processing (FSP) in order to enhance surface mechanical properties. Microstructural evaluation using optical microscopy (OM) and scanning electron microscopy (SEM) indicated that an increase in traverse speed and a decrease in rotational speed cause a reduction in the grain size of stir zone (SZ) for the specimens friction stir processed (FSPed) without SiC particles. With the aim of determining the optimum processing parameters, the effect of traverse speed as the main processing variable on microstructure and microhardness of MMC layers was investigated. Higher traverse speeds resulted in poor dispersion of SiC particles and consequently reduced the microhardness values of MMC layers. It was found that upon addition of SiC particles, wear properties were improved. This behavior was further supported by SEM images of wear surfaces. Results demonstrated that the microcomposite produced by FSP exhibited enhanced wear resistance and higher average friction coefficient in comparison with pure copper. Tensile properties and fracture characteristics of the specimens FSPed with and without SiC particles and pure copper were also evaluated. According to the results, the MMC layer produced by FSP showed lower strength and elongation than pure copper while a remarkable elongation was observed for FSPed specimen without SiC particles. © 2010 Elsevier Inc. All rights reserved.

Dini M.,University of Tehran | Tabesh M.,University of Tehran
Water Resources Management | Year: 2014

Water distribution systems, where flow in some pipes is not measured or storage tanks are connected together, calculation of demand pattern coefficients of the network is difficult. Since, Hazen-Williams coefficients of the network are also unknown; the problem is becoming unintelligible further. The present study proposes a new method for simultaneous calibration of demand pattern and Hazen-Williams coefficients that uses the Ant Colony Optimization (ACO) algorithms coupled with the hydraulic simulator (EPANET2) in a MATLAB code. In this paper demand pattern and Hazen-Williams coefficients are the calibration parameters and measured data consist of nodal pressure heads and pipe flows. The defined objective function minimizes the difference between the measured and simulated values. The new proposed method was tested on a two-loop test example and a real water distribution network. The results show that the new calibration model is able to calibrate demand pattern and Hazen-Williams coefficients simultaneously with high precision and accuracy. © 2014 The Author(s).

Faraji G.,University of Tehran | Asadi P.,University of Tehran
Materials Science and Engineering A | Year: 2011

The microstructures, wear property and micro-hardness of AZ91 Mg alloy/alumina particle reinforced nano-composite produced by friction stir processing (FSP) were investigated. The initial microstructures of the AZ91 were composed of irregularly distributed β-phases (Al12Mg17), while the FSPed specimens were characterized by the homogeneous distribution of alumina particles, the recrystallized grain structure and the dissolution of β-phase. The results showed an improvement in the hardness, wear property of the FSPed zone as results of more grain refinement and pinning effect of nano-alumina particles as compared to those of the base metal. The hardness of the FSPed zone was a higher and more homogeneously distributed and the wear resistance as evaluated by Dry sliding wear tests, was superior, as compared with the base metal. © 2010 Elsevier B.V.

Mahmudi R.,University of Tehran | Alizadeh R.,University of Tehran | Geranmayeh A.R.,University of Tehran
Scripta Materialia | Year: 2011

The superplasticity of a fine-grained Sn-5 wt.% Sb alloy, processed by equal-channel angular pressing (ECAP), was investigated by impression testing in the temperature range of 298-370 K. The deformation response of the ECAPed material with a grain size of 2.5 μm conforms to regions I, II and III, typical of superplastic behavior. In region II, the strain rate sensitivity indices of 0.42-0.60 and activation energy of 42 kJ mol-1 are indicative of a superplastic deformation behavior dominated by grain boundary sliding. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Ramedani Z.,University of Tehran | Rafiee S.,University of Tehran | Heidari M.D.,University of Tehran
Energy | Year: 2011

The aims of this study were to determine the energy consumption and evaluation of inputs sensitivity for soybean production in Kordkuy county of Iran. The data used in this study were obtained from 32 farmers using a face-to-face questionnaire base of random sampling method. The sensitivity of energy inputs was estimated using the marginal physical productivity (MPP) method and partial regression coefficients on soybean yield. The results indicated that the total input and output energy use was to be 18,026.50 and 71,228.86 MJ ha-1 respectively. With 66.67%, the diesel fuel was the highest within the energy equivalents and followed by chemical fertilizers and water for irrigation with 14.32% and 6.18% respectively. The input-output ratio was found as 4.62 (used efficiency). The share of direct, indirect, renewable and non-renewable was 74%, 26%, 14% and 86% respectively. The econometric model estimation emphasized that the seed was significantly positive on yield. The sensitivity analysis indicated the MPP value of 2.42 for seed, indicates that with an additional use of 1 MJ of seed energy would lead to an increase in yield by 2.42. The impact of direct, indirect and non-renewable energies on yield was significant. © 2011.

In this paper, I investigate conceptual categories derived from developmental processing in a deep neural network. The similarity matrices of deep representation at each layer of neural network are computed and compared with their raw representation. While the clusters generated by raw representation stand at the basic level of abstraction, conceptual categories obtained from deep representation shows a bottom-up transition procedure. Results demonstrate a developmental course of learning from specific to general level of abstraction through learned layers of representations in a deep belief network. © 2016, © The Author(s) 2016.

Shabani M.O.,Iranian Materials and Energy Research Center | Mazahery A.,University of Tehran
Synthetic Metals | Year: 2011

In the present study, wear properties of A356 unreinforced alloy and composites with different vol.% of boron carbide particles were investigated. It is noted that composites exhibit better wear resistance compared to unreinforced alloy. According to the differences in wear rates of the composites, two separate wear rate were identified as low and high wear rate regimes. A combination of artificial neural network (ANN) and finite element technique (FEM) was implemented in order to predict the composites wear behavior. The FEM method is used for discretization and to calculate the transient temperature field of quenching. It is observed that predictions of ANN are consistent with experimental measurements for A356 composite and considerable savings in terms of cost and time could be obtained by using neural network model. © 2011 Elsevier B.V. All rights reserved.

Vatankhah A.R.,University of Tehran
Proceedings of the Institution of Civil Engineers: Water Management | Year: 2012

Side weirs or lateral weirs are widely used for water level control in water treatment plants and irrigation and drainage systems. The side weir is a fixed structure installed at one side of a channel to divert flow laterally. Computation of the water surface profile along the side weir is essential in determination of the discharge over the side weir. An analytical solution of the dynamic equation for spatially varied flow with decreasing discharge, in prismatic channels with a side weir, is available in the technical literature only for the special case of a rectangular channel based on the constant specific energy assumption. However, in irrigation networks, the most common irrigation channels are of trapezoidal cross-section. This paper presents an elegant analytical solution for establishing the water surface profile along a side weir in a trapezoidal channel. Since triangular and rectangular cross-sections are special cases of the trapezoidal cross-section, the proposed analytical solution is also applicable to these crosssections. The solution, which yields a direct computation of the flow profile in subcritical and supercritical flow regimes, should be a useful engineering tool for the evaluation and design of side weirs in open channels.

Hamedani S.R.,University of Tehran | Shabani Z.,University of Tehran | Rafiee S.,University of Tehran
Energy | Year: 2011

The aim of this study was to determine energy consumption and the relationship between energy input and yield for potato production in Kaboud Rahang region of Hamadan state. The data used in this study are collected by questionnaire. The results revealed that nitrogen fertilizer (39%), diesel (21%), seed (14.9%), water (7.5%) and manure (6.4%) consumed the bulk of energy. In the surveyed farms, average yield and energy consumption were calculated as around 28613.7 kg/ha, 92296.3 MJ/ha, respectively. The results also showed that energy ratio, specific energy and energy productivity were 1.1, 3.2 MJ/kg and 0.3 kg/MJ, respectively. An econometric model was developed to estimate the impact of energy inputs on yield by using parametric methods. For this purpose, potato yield, an endogenous variable was assumed to be a function of energy inputs: fertilizer manure, chemical, machinery, human, water for irrigation, diesel and seed. The empirical results indicated that variables: fertilizer, chemical, seed and human were found statistically significant and contributed to yield. Among statistically significant exogenous variables, seed, water for irrigation, chemical, human and fertilizer were ranked in terms of elasticities. © 2011 Elsevier Ltd.

Halimehjani A.Z.,University of Tehran | Marjani K.,University of Tehran | Ashouri A.,University of Tehran
Green Chemistry | Year: 2010

Highly efficient, one-pot and three component reactions of amines and carbon disulfide with alkyl vinyl ethers via Markovnikov addition reaction were carried out in water under a mild and green procedure with excellent yields and complete regiospecificity. © The Royal Society of Chemistry 2010.

Vatankhah A.R.,University of Tehran
Advances in Water Resources | Year: 2010

The specific energy and specific force equations have many applications in open-channel flow problems. At present, these equations have analytical solution only for rectangular channels. Trial and error procedure also graphical solutions are the existing methods of solving these equations. No analytical solutions are available in the technical literature for these equations in trapezoidal and triangular channels because it is presumed that these equations are quintic equations. The inversion of such equations consists of finding the roots of quintic equations. In the current study for a given channel geometry and discharge, the subcritical (supercritical) depth is analytically found in terms of the other supercritical (subcritical) depth. For this purpose, by considering physically meaningful domains, a quintic equation has been reduced to a quartic equation. In the next step, this quartic equation has been converted to a resolvent cubic equation and two quadratic equations. This research shows these steps clearly to reach an acceptable physical analytic solution for water depth in trapezoidal and triangular channels. © 2009 Elsevier Ltd. All rights reserved.

Rajabpour A.,University of Tehran | Vaez Allaei S.M.,University of Tehran
Applied Physics Letters | Year: 2012

Using nonequilibrium molecular dynamics simulations, the effect of inter-layer s p 3 bonding on the thermal conductivity of bilayer graphene were investigated. Up to 5 fractions of randomly distributed inter-layer s p 3 bonds, lead to considerable decreases in the thermal conductivity of bilayer graphene, up to 70. Phonon power spectrum calculations revealed the strong influence of s p 3 inter-layer bonds-compared to weak effect of inter-layer Lennard-Jones interactions-on the thermal transport of the system. These measurements propose the application of the inter-layer s p 3 bonding in designing nanoscale devices with tunable thermal conductivities. © 2012 American Institute of Physics.

Heidari M.D.,University of Tehran | Omid M.,University of Tehran
Energy | Year: 2011

This paper examines the energy use patterns and energy input-output analysis of major greenhouse vegetable productions in Iran. Data from 43 farmers were obtained using a face-to-face questionnaire method. The majority of farmers in the surveyed region were growing cucumber and tomato. Total input energy was found to be 141493.51 and 131634.19 MJ ha -1 for cucumber and tomato productions, respectively. Among input energy sources, diesel fuel and fertilizers contained highest energy with 54.17-49.02% and 21.64-24.01%, respectively. The energy ratio was found to be 0.69 and 1.48 for cucumber and tomato productions, respectively. Econometric model evaluation showed the impact of human labor for cucumber and chemicals for tomato was significant at 1% levels. Sensitivity analysis indicated that the MPP value of energy inputs were between -5.87 and 7.74. RTS (returns to scale) values for cucumber and tomato yields were found to be 1.29 and 0.76; thus, there prevailed an IRS of cucumber for estimated model. The net return was found positive, as 22651.13 and 78125.08 $ ha -1 for cucumber and tomato, respectively. The benefit-cost ratios from cucumber and tomato productions were calculated to be 1.68 and 3.28, respectively. Among the surveyed greenhouses, the result indicated tomato cultivation was more profitable. © 2010 Elsevier Ltd.

Babajani-Feremi A.,Ford Motor Company | Soltanian-Zadeh H.,Ford Motor Company | Soltanian-Zadeh H.,University of Tehran
NeuroImage | Year: 2010

We previously proposed an integrated electroencephalography (EEG), magnetoencephalography (MEG), and functional Magnetic Resonance Imaging (fMRI) model based on an extended neural mass model (ENMM) within a single cortical area. In the ENMM, a cortical area contains several minicolumns where strengths of their connections diminish exponentially with their distances. The ENMM was derived based on the physiological principles of the cortical minicolumns and their connections within a single cortical area to generate EEG, MEG, and fMRI signals. The purpose of this paper is to further extend the ENMM model from a single-area to a multi-area model to develop a neural mass model of the entire brain that generates EEG and MEG signals. For multi-area modeling, two connection types are considered: short-range connections (SRCs) and long-range connections (LRCs). The intra-area SRCs among the minicolumns within the areas were previously modeled in the ENMM. To define inter-area LRCs among the cortical areas, we consider that the cell populations of all minicolumns in the destination area are affected by the excitatory afferent of the pyramidal cells of all minicolumns in the source area. The state-space representation of the multi-area model is derived considering the intra-minicolumn, SRCs', and LRCs' parameters. Using simulations, we evaluate effects of parameters of the model on its dynamics and, based on stability analysis, find valid ranges for parameters of the model. In addition, we evaluate reducing redundancy of the model parameters using simulation results and conclude that the parameters of the model can be limited to the LRCs and SRCs while the intra-minicolumn parameters stay at their physiological mean values. The proposed multi-area integrated E/MEG model provides an efficient neuroimaging technique for effective connectivity analysis in healthy subjects as well as neurological and psychiatric patients. © 2010 Elsevier Inc.

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.

Nasrabadi T.,University of Tehran
International Journal of Environmental Research | Year: 2015

Twenty water samples from a river system in southern Caspian Sea basin were collected and analyzed for physicochemical parameters and metals (Cu, Zn, As, Cd, Pb, Ni and Mn). In order to evaluate the risk potential of metal pollution in river water, use of two indices namely heavy metal pollution index (HPI) and contamination index (Cd) accompanied by cluster analysis was taken in to consideration. Stations located within the upstream of the river (1 to 13) seemed to encounter low risk potentials while the downstream stations (14 to 20) approved to hold higher risks. The results also showed relatively meaningful correlation among different metals which may be attributed to their same entry source, mainly mining and quarrying activities in the central parts of the basin following by municipal and industrial wastewater discharge to the river in downstream. The convergence of both indices in this study was also of interest. Although the mean values of both indices were below the critical values, severe precautions must be taken into consideration especially in the stations holding high risk potentials. Extreme use of river water for drinking, agriculture and industrial purposes within the water basin, relatively biota-rich characteristic of the river and Caspian Sea as the final sink of the river are among the most significant reasons that make the river monitoring implementation inevitable. © 2015, University of Tehran. All rights reserved.

Majidi B.,University of Tehran | Shemirani F.,University of Tehran
Analytical Methods | Year: 2012

A new methodology ultrasound assisted cold-induced aggregation microextraction (USA-CIAME) was developed for the determination and extraction of ultra trace levels of Au 3+ from aqueous hydrochloric acid solutions by pure ionic liquid (IL), in the absence of chelating agents. The extraction behaviour of metal ions by [Hmim]PF 6 was particularly studied. Moreover, the stripping of metal ions from the IL phase was investigated. Au 3+ in IL phase can be quantitatively recovered by NaPF 6. Recycle testing indicated that IL loss can be avoided by the additon of [Hmim] + to the initial AuCl 4 - solutions before extraction and/or using PF 6 - solutions for stripping. The main factors affecting Au 3+ extraction, the amount of IL, the pH of the sample solutions, and the chloride ion concentration on extraction efficiencies were carefully studied. A linear calibration was obtained for 1.5 to 200 μg L -1 of Au 3+ and the limit of detection was 0.59 μg L -1. The validation of this method was done by recovery and determination of trace amount of gold in river, sea water and geological samples with satisfactory results. © 2012 The Royal Society of Chemistry.

Torabi A.R.,University of Tehran | Fakoor M.,University of Tehran | Pirhadi E.,University of Tehran
International Journal of Solids and Structures | Year: 2014

Fracture phenomenon was investigated both experimentally and theoretically for a type of coarse-grained polycrystalline graphite weakened by a U-shaped notch under mixed mode loading. First, 36 disc-type graphite specimens containing a central U-notch, so called in literature as the U-notched Brazilian disc (UNBD), were prepared for four different notch tip radii and the fracture tests were performed under mode I and mixed mode I/II loading conditions. Then, the experimentally obtained fracture loads and the fracture initiation angles were predicted by using the U-notched maximum tangential stress (UMTS) and the newly formulated U-notched mean stress (UMS) fracture criteria. Both the criteria were developed in the form of the fracture curves and the curves of fracture initiation angle, in terms of the notch stress intensity factors (NSIFs). The results showed that while the criteria could predict successfully the experimental notch fracture toughness values, the UMS criterion provides slightly better predictions than the UMTS criterion, particularly for shear-dominant deformations. Also, found in this research was that the curves of fracture initiation angle were almost identical for the two criteria which both could predict well the experimental results. © 2013 Elsevier Ltd. All rights reserved.

Momeni D.,University of Tehran
International Journal of Theoretical Physics | Year: 2011

The aim of this letter is to propose a new description to the time varying gravitational constant problem, which naturally implements the Dirac's large numbers hypothesis in a new proposed holographic scenario for the origin of gravity as an entropic force. We survey the effect of the Stochastic motion of the test particle in Verlinde's scenario for gravity (Verlinde in arXiv:1001.0785, 2010). Firstly we show that we must get the equipartition values for t→∞ which leads to the usual Newtonian gravitational constant. Secondly, the stochastic (Brownian) essence of the motion of the test particle, modifies the Newton's 2nd law. The direct result is that the Newtonian constant has been time dependence in resemblance as Setare and Momeni (arXiv:1004.0589, 2010). © 2011 Springer Science+Business Media, LLC.

Hassanpour Isfahani A.,University of Tehran | Vaez-Zadeh S.,University of Tehran
IEEE Transactions on Magnetics | Year: 2011

The capabilities of proper start-up and synchronization are important issues in the design of line-start permanent magnet synchronous motors. Failing in early start-up or in synchronization under certain conditions prevents the widespread use of these motors. In order to draw useful guidelines for the design of line-start permanent magnet synchronous motors, the contradictory effects of a large value of magnetizing inductance in improving early start-up and deteriorating synchronization of line-start permanent magnet synchronous motors are analyzed in this paper. The analysis is done through three different methods. First, the effect of magnetizing inductance on average and pulsating torques of the motors during asynchronous operation is investigated and the role of these torques in start-up and synchronization performances of the motors is discussed. A critical load is then determined in terms of motors parameters as a torque limit above which the motors cannot start. The effect of magnetizing inductance, magnet flux, and saliency on the critical load is also investigated. A dynamic d-q model of the motors is then implemented to support the discussions by analyzing two line start motors with different magnetizing inductances. Finite-element-based analyses are then carried out for both motors to consider motors parameters variation, skin effect, saturation, rotor asymmetry, and cross magnetization. A good agreement between the finite-element method and dynamic simulation results is evident. Finally, some design guidelines are proposed for the proper selection of the magnetizing inductance in motor designs for different applications. © 2006 IEEE.

Aflaki S.,University of Tehran | Memarzadeh M.,University of Tehran
Construction and Building Materials | Year: 2011

The effect of CRM aspects on rheological properties of asphalt binder such as improvement in the performance grade (PG) for low, intermediate, and high service temperatures are evaluated and the binder's dynamic viscosity changes were studied in this research. Enhancement also resulted in the binder's fatigue and rutting indices. At the same time, the effects of low/high shear blending conditions on the rheological properties were investigated. The effect of interactions between blending conditions and modifier content were studied by utilizing the analysis of variance (ANOVA) method and hypothesis tests. © 2010 Elsevier Ltd. All rights reserved.

Fazel-Najafabadi M.,University of Tehran | Kashani-Bozorg S.F.,University of Tehran | Zarei-Hanzaki A.,University of Tehran
Materials and Design | Year: 2011

A 304 stainless steel plate was lap joined to a CP-Ti one by friction stir welding technique. Stainless steel was selected as the top member. Sound dissimilar joints were achieved using an advancing speed of 50. mm/min and rotation speeds in the range of 700-1100. rpm. A region of vortices of bimetallic weld of 304 stainless steel and CP-Ti was formed in the lap joint fabricated using the highest applied tool rotation speed; this was associated with plasticizing of both members with the aid of a double-shoulder tool. In addition, due to complex material flow, mechanical interlock features were shaped that consists of extruded stainless steel into the plasticized titanium region. A maximum shear strength value of ∼119. MPa was achieved; this was found to be close to that of CP-Ti. The lap joint was strengthened by the formation of vortices of bimetallic weld of 304 stainless steel and CP-Ti and mechanical interlock features at joint interface due to complex materials flow. © 2010 Elsevier Ltd.

Gholizadeh S.,Urmia University | Pirmoz A.,University of Tehran | Attarnejad R.,University of Tehran
Journal of Constructional Steel Research | Year: 2011

In this paper, load carrying capacity of simply supported castellated steel beams, susceptible to web-post buckling, is studied. The accuracy of the nonlinear finite element (FE) method to evaluate the load carrying capacity and failure mode of the beams is discussed. In view of the high computational burden of the nonlinear finite element analysis, a parametric study is achieved based on FE and an empirical equation is proposed to estimate the web-posts' buckling critical load of the castellated steel beams. Also as other alternatives to achieve this task, the traditional back-propagation (BP) neural network and adaptive neuro-fuzzy inference system (ANFIS) are employed. In this case, the accuracy of the proposed empirical equation, BP network and ANFIS are examined by comparing their provided results with those of conventional FE analysis. The numerical results indicate that the best accuracy associates with the ANFIS and the neural network models provide better accuracy than the proposed equations. © 2011 Elsevier Ltd. All rights reserved.

Nayyeri G.,University of Tehran | Mahmudi R.,University of Tehran
Materials and Design | Year: 2011

Mg-Sn based alloys have great potential for high temperature applications because of the formation of the thermally stable Mg2Sn phase in the as-cast condition. In the present investigation, for further enhancement of the mechanical properties, 0.7, 1.4 and 2wt.% of Ca was added to the base Mg-5%Sn alloy. The dendritic structure of the base alloy was refined after the addition of Ca. It was found that the Mg-5%Sn-2%Ca alloy had the highest hardness, strength, and creep resistance among all tested materials. This is attributed to the higher volume fraction of CaMgSn second phase particles which act as the main strengthening agent in the investigated system. Results also showed that while long-term annealing treatment softened the base Mg-5Sn alloy, there was not much change in the hardness and strength of the Ca-containing materials, implying that CaMgSn intermetallic particles have successfully increased the microstructural stability of the materials. © 2010 Elsevier Ltd.

Rabizadeh T.,University of Tehran | Allahkaram S.R.,University of Tehran
Materials and Design | Year: 2011

Composite coatings were prepared using hypophosphite reduced electroless nickel bath containing 7g/L SiO2 nano-particles at pH 4.6±0.2 and temperature 90±2°C. Deposition rate for SiO2 nano-composite coatings was 10-12μm/h. The amount of SiO2 nano-particles co-deposited in the Ni-P matrix was around 2wt.%. The analyzes of coating compositions, carried out by Energy Dispersive Analysis of X-ray (EDAX), showed that plain Ni-P and Ni-P/nano-SiO2 deposits contained around 8wt.% phosphorus. The X-ray diffraction (XRD) pattern of Ni-P/nano-SiO2 coating was very similar to that of plain electroless Ni-P coating, whose structure was also amorphous. Scanning electron microscopy (SEM) morphology of the surface deposits revealed that some agglomeration occurred because of the absence of surfactant. Electrochemical impedance spectroscopy and polarization tests showed that addition of nano-SiO2 particles demonstrated significant improvement of corrosion resistance of Ni-P coatings in salty atmosphere. © 2010 Elsevier Ltd.

Adabi M.,University of Tehran | Amadeh A.,University of Tehran
International Journal of Refractory Metals and Hard Materials | Year: 2011

In this study, the effect of infiltration parameters on composition of W-ZrC composites produced by displacive compensation of porosity (DCP) method was investigated. For this purpose, a porous tungsten carbide preform was prepared by cold isostatic pressing (CIP) of tungsten carbide powder and polyvinyl alcohol (PVA). The porous preform was debinded for 4 h at 400 °C and sintered for 4 h at 1400 °C. The sintered preform was then infiltrated by molten Zr2Cu at 1300 °C and 1200 °C for 1, 3, 5 and 7 h. Scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDS) and X-ray diffraction (XRD) were used to study the cross section of infiltrated specimens. The results indicated that the amount of tungsten and zirconium carbide phases increased by increasing the infiltration temperature, whereas the effect of infiltration time on composition of W-ZrC composite was negligible. © 2010 Elsevier Ltd. All rights reserved.

Vafaeesefat A.,University of Tehran
Materials and Manufacturing Processes | Year: 2011

The aim of this article is to propose an algorithm to predict the initial blank shape from the desired part in the sheet metal forming process. The algorithm is based on iterative finite element (FE) sheet metal forming simulations. To find a new blank shape, the boundary of the part is projected on the deformed blank. The transformation of the projected boundary on the initial blank defines the new blank boundary. Since the proposed algorithm is based on three-dimensional projections, it is not restricted to the part shape and the initial guess of the blank shape. The proposed algorithm is applied to square cup and oil pan drawings to confirm its validity. The results show that the proposed method can reach the optimum blank shape within a few iterations. The outcomes are in good agreement with experimental data. © Taylor & Francis Group, LLC.

Akbari-Garakani M.,University of Tehran | Mehdizadeh M.,Niroo Research Institute
Materials and Design | Year: 2011

The present work was carried out to investigate the effect of long-term service exposure on microstructure and mechanical properties of a gas turbine hot gas path component, made of Alloy 617. The results showed significant service-induced microstructural changes, such as excessive grain boundary Cr-rich M23C6 carbides formation and some oxidation features in the exposed material in compare with the solution-annealed material. Also it was found that the yield strength and hardness of the alloy have increased while the ductility of the alloy has decreased. In the similar test conditions, the stress-rupture life of the exposed alloy decreased considerably compared to the solution-annealed sample, which could be attributed to the microstructural degradation, especially formation of continuous M23C6 carbides on grain boundaries. © 2011 Elsevier Ltd.

Akbarimousavi S.A.A.,University of Tehran | GohariKia M.,University of Tehran
Materials and Design | Year: 2011

Friction welding process is a solid state joining process that produces a weld under the compressive force contact of one rotating and one stationary work piece. In this study, the friction welding of dissimilar joints of AISI 316L stainless steel and cp-titanium is considered. The optical, scanning electron microscopy studies of the weld were carried out. Moreover, the X-ray diffraction analysis was performed. The integrity of welds was achieved by the micro hardness and tensile tests. The fracture surface was examined by the scanning electron microscopy. The study showed that the magnitude of tensile strength of the dissimilar welded specimen was below that of the titanium base material if preheating was not applied at the interface. The high weld tensile strength was achieved by preheating the 316L stainless steel material to 700°C, smoothing and cleaning of the contact surfaces. Results illustrated that in dissimilar joints, different phases and intermetallic compounds such as FeTi, Fe2Ti, Fe2Ti4O, Cr2Ti and sigma titanium phase were produced at the interface. The presence of brittle intermetallic compounds at the interface resulted in degradation of mechanical strength which in turn led to premature failure of joint interface in the service condition. Preheating caused to produce oxide layer at the interface which was harmful for bonding. The oxide layer could be eliminated by applying pressure and smoothing the surface. Results of hardness tests illustrated that the high hardness was occurred in the titanium side adjacent to the joint interface. Moreover, the optimum operational parameters were obtained in order to achieve the weld tensile strength greater than the weak titanium material. © 2011 Elsevier Ltd.

Mahmudi R.,University of Tehran | Kabirian F.,University of Tehran | Nematollahi Z.,University of Tehran
Materials and Design | Year: 2011

The effects of 2wt.% rare earth element addition on the microstructure evolution, thermal stability and shear strength of AZ91 alloy were investigated in the as-cast and annealed conditions. The as-cast structure of AZ91 consists of α-Mg matrix and the β-Mg17Al12 intermetallic phase. Due to the low thermal stability of this phase, the strength of AZ91 significantly decreased as the temperature increased. The addition of rare earth elements refined the microstructure and improved both thermal stability and high-temperature mechanical properties of AZ91. This was documented by the retention of the initial fine microstructure and ultimate shear strength (USS) of the rare earth elements-containing material after long-term annealing at 420°C. The improved stability and strength are attributed to the reduction in the volume fraction of β-Mg17Al12 and retention of the thermally stable Al11RE3 intermetallic particles which can hinder grain growth during the annealing process. This behavior is in contrast to that of the base material which developed a coarse grain structure with decreased strength caused by the dissolution of β-Mg17Al12 after exposure to high temperature. © 2011 Elsevier Ltd.

Ghorashi S.S.,University of Tehran | Mohammadi S.,University of Tehran | Sabbagh-Yazdi S.-R.,University of Tehran
Engineering Fracture Mechanics | Year: 2011

A new approach for modeling discrete cracks in two-dimensional orthotropic media by the element free Galerkin method is described. For increasing the solution accuracy, recently developed orthotropic enrichment functions used in the extended finite element method are adopted along with a sub-triangle technique for enhancing the Gauss quadrature accuracy near the crack. An appropriate scheme for selecting the support domains near a crack is employed to reduce the computational cost. In this study, mixed-mode stress intensity factors are obtained by means of the interaction integral to determine the fracture properties. Several problems are solved to illustrate the effectiveness of the proposed method and the results are compared with available results of other numerical or (semi-) analytical methods. © 2011 Elsevier Ltd.

Heidary D.S.B.,University of Tehran | Akhlaghi F.,University of Tehran
Acta Materialia | Year: 2011

In the present study settling of SiC particles in composite slurries of aluminum A356 alloy/SiC was investigated experimentally and the results were compared with theoretical predictions. The influence of size and volume fraction of SiC particles in different Al/SiC slurries together with thermal history during alloy solidification on the distribution of particles along the height of cylindrical composite samples was studied by image analysis of microstructures. In the theoretical part, the effect of particle shape, agglomeration of particles and hindered settling on the settling velocity of SiC particles was studied by using the Stokes equation with some relevant correction factors. It was found that by using the measured viscosity of slurries in the Stokes equation a good agreement between the experimental results and theoretical predictions could be obtained. A computer program was written using MATLAB software in which the Stokes equation was employed, and in addition to the above-mentioned correction factors, the collision and agglomeration of particles were also considered. This program was able to simulate reasonably accurately the settling of SiC particles in the solidifying alloy. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Faiz J.,University of Tehran | Ojaghi M.,University of Zanjan
IEEE Transactions on Magnetics | Year: 2011

A new index is introduced for eccentricity fault diagnosis in three-phase squirrel-cage induction motors. Basically, some physical quantities of the motors structure such as air gap length influence this index, while other operational factors including motor supply, control type, load level, and its fluctuation cannot affect the proposed index. The influence of various eccentricity faults upon this index is investigated and shows the segregation ability of different eccentricity types by the index. It is indicated that the change of load, speed, and saturation level can slightly change the index value. Experimental results confirm the simulation results. © 2011 IEEE.

Gharabaghi M.,University of Tehran | Aghazadeh S.,University of Tehran
Current Opinion in Colloid and Interface Science | Year: 2014

Wetting and spreading phenomena are the most important parameters for understanding of froth flotation practice. The wetting and spreading of fluids on the solid surface should be considered in the high efficiency flotation process. These phenomena involve surface tension forces, contact line dynamics, surface roughness and heterogeneity, contact angles, bubble-particle interactions and other factors. This review highlights the various concepts of contact angles and well-known equations in this respect and compares these equations. Based on this review, flotation selectivity and efficiency are highly dependent on solid-liquid contact angles and collision, collection, attachment, and stability efficiency could be predicted by wetting and spreading roles. In order to control flotation performance, efforts should be made to determine wetting characteristic of the flotation process. It is imperative that an improved understanding of wetting and spreading phenomena in the phase's interfaces will provide an improved and efficient flotation practice. It is proposed that future research should focus on the scientific and engineering aspect of wetting and spreading phenomena on flotation and on the development of a method to enhance flotation performance by controlling these phenomena. © 2014 Elsevier Ltd.

Golobostanfard M.R.,University of Tehran | Abdizadeh H.,University of Tehran
Microporous and Mesoporous Materials | Year: 2014

Titania/carbon nanotube (CNT) composite films containing hierarchical interconnected porous structure have the advantages of high surface area of mesoporous structure and micro-channels of titania as well as high conductivity and charge separation properties of CNTs. In this research, the composites were prepared with controlled phase separation of titania sol. The main parameters to control the phase separation and macroporous morphology of the films including water content, stabilizer content, polyethylene glycol content, sol concentration, and deposition speed were investigated. X-ray diffraction and Raman spectroscopy confirmed the presence of CNTs together with anatase titania phase. Transmission electron microscopy showed that a very thin layer of titania was formed on CNT surface which improved interface of TiO2/CNT. It was found that macropores grew either with increasing water or polyethylene glycol content. However, stabilizer content and deposition speed had an inverse effect on macropores formation. Furthermore, sol concentration caused binodal decomposition and hence widened the pore size distribution. Although CNTs were ineffective in macropores formation, they strongly affected the transparency and charge separation of the composite films. © 2013 Elsevier Inc. All rights reserved.

Samavati V.,University of Tehran | Yarmand M.S.,University of Tehran
Carbohydrate Polymers | Year: 2013

A central composite rotatable design (CCRD) was used to evaluate the effects of extraction time, extraction temperature, particle size of mulberry leaf, number of extraction and water to the mulberry leaf ratio on extraction yield of mulberry leaf crude polysaccharides (MLCP). The response surface methodology (RSM) showed that the significant quadratic regression equation with high R2 (=0.9782) was successfully fitted for extraction yield of MLCP as function of independent variables. The overall optimum region was found to be at the combined level of extraction time 5 h, extraction temperature 85 °C, particle size of mulberry leaf (mesh) 40, number of extraction 4 and water to mulberry leaf ratio 18. At this optimum point, extraction yield of MLCP was 12.0017 ± 0.42%. No significant (p > 0.05) difference was found between the actual and predicted (11.6286 ± 0.19) values. The results demonstrated that MLCP had strong scavenging activities on DPPH and hydroxyl radicals. Overall, MLCP may have potential applications in the medical and food industries. © 2013 Elsevier Ltd. All rights reserved.

Samavati V.,University of Tehran | Manoochehrizade A.,Islamic Azad University at Ahvāz
Carbohydrate Polymers | Year: 2013

Ultrasonic technology was applied for polysaccharide extraction from the leaves of Dodonaea viscosa and response surface methodology (RSM) was used to optimize the effects of processing parameters on polysaccharide extraction yield. Three independent variables were extraction time (X1), extraction temperature (X2) and ultrasonic power (X3), respectively. The statistical analysis indicated the independent variables (X1, X2, X3), the quadratic terms (X 11 and X33) and the interaction terms (X1X 2, X1X3, X2X3) had significant effects on the yield of polysaccharides (P < 0.05). The optimal extraction conditions of D. viscosa leaf were determined as follows: extraction time 50.54 min, extraction temperature 85 °C and ultrasonic power 400 W. Under these conditions, the experimental yield of polysaccharides was 9.455 ± 0.24%, which was agreed closely with the predicted value (9.398%). The evaluation of anti-oxidant activity suggested that the polysaccharide exhibited significant protection against DPPH and hydroxyl radicals and could be explored as a nutraceutical agent. Crown Copyright © 2013 Published by Elsevier Ltd. All rights reserved.