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tayebi--ahmad
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Differential Item Functioning (DIF)in Terms of Gender in a High Stakes Test
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad (Supervisor)
Abstract
Validation is an important enterprise especially when the test to be validated is a high-stakes one the results of which bring about life-changing implications for the candidates (Roever, 2001). Messick’s (1988) notion of construct irrelevant factors is pertinent in test validation. Demographic variables like gender, field of study and age can affect test results and interpretations. A fair test needs to be neutral when it comes to construct irrelevant factors such as gender. Differential Item Functioning is a way of making sure that the test does not favor one group of test takers over the others. The current study investigated differential item functioning (DIF) in terms of gender in the...
Developing Inventory Control Policies with No Ordering Costs in Two-Echelon Supply Chains
, Ph.D. Dissertation Sharif University of Technology ; Haji, Rasoul (Supervisor)
Abstract
This dissertation attempts to develop four inventory control models for two-echelon supply chains. For the all models, the retailers face Poisson demand and lost sales during a stockout. There is also a time-dependent holding cost and a cost per unit of lost sales. However, there is no (or negligible) cost associated with placing an order.
For the first model, we consider a two-echelon inventory system with one central warehouse and a number of retailers. The central warehouse applies (R, Q) policy and retailers apply base stock policy. In this model, we approximate the arrival process of the central warehouse and obtain the total cost of the system, as well as the optimal solution....
For the first model, we consider a two-echelon inventory system with one central warehouse and a number of retailers. The central warehouse applies (R, Q) policy and retailers apply base stock policy. In this model, we approximate the arrival process of the central warehouse and obtain the total cost of the system, as well as the optimal solution....
Proposing a Two-Stage Stochastic Model and a Heuristic Solution Method for a Green Supply Chain Location-Routing Problem with Stochastic Demand Considering Time Windows
, M.Sc. Thesis Sharif University of Technology ; Rafiee, Majid (Supervisor)
Abstract
Location-routing problems are a class of well-known supply chain problems. the purpose of these problems are to locate depots, assign customers to the located depots, and to determine the routes in a way to minimize the costs of the supply chain.In the past two decades, with a rise in environmental problems including air pollution, green location-routing problems have been introduced and studied, problems in which environmental aspects such as air pollution have been considered.In this study, first, we model a two-stage stochastic green location routing problem; this problem includes a certain number of cities that each represent a customer. the locations of the cities are known and each...
Joint order (1, T) policy for a two-echelon, single-item, multi-retailer inventory system with Poisson demand
, Article Computers and Industrial Engineering ; Volume 119 , 2018 , Pages 353-359 ; 03608352 (ISSN) ; Haji, R ; Ghalebsaz Jeddi, B ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
This study considers a two-echelon inventory system with one central warehouse and a number of non-identical retailers with Poisson demands, constant lead times, and lost sales for a single item. The warehouse works as a cross-docking terminal with no inventory and coordinates shipments to retailers. We apply the Joint order (1, T) policy in such an inventory system. In the standard (1, T) policy, the warehouse sends one unit of the item to each retailer in a fixed cycle time, which is calculated by considering each retailer separately. In the joint order (1, T) policy, the warehouse decides to replenish one unit of the item for each retailer in a cycle time which is adjusted to be an...
The effect of additives on the properties of HAp-Al2O3nano-composite powders
, Article Journal of Ceramic Processing Research ; Volume 17, Issue 10 , 2016 , Pages 1033-1041 ; 12299162 (ISSN) ; Mirjalili, F ; Samadi, H ; Nemati, A ; Sharif University of Technology
Hanyang University
2016
Abstract
Hydroxyapatite is the most important bio ceramic, due to its structure and chemical composition which is similar to bone. Since feeble fracture toughness, brittleness and low tensile strength have restricted their use, for overcoming this problem, they were often used as a secondary component. HAp-Al2O3 nano-composite powder combined the benefits of biocompatibility of HAp and high strength of Al2O3. When HAp-Al2O3 nano-composite powders were sintered at a higher temperature than 1100- 1200°C, HAp was decomposed and converted to the second phase of TCP, due to the formation of calcium aluminate increasing decomposition speed of HAp to TCP at higher degree than 1100-1200°C temperatures;...
A robust voice activity detection based on wavelet transform
, Article 2nd International Conference on Electrical Engineering, ICEE, Lahore, 25 March 2008 through 26 March 2008 ; 2008 ; 9781424422937 (ISBN) ; Manzuri, M. T ; Karami, M ; Tayebi, H ; Sharif University of Technology
2008
Abstract
Voice activity detection is an important step in some speech processing systems, such as speech recognition, speech enhancement, noise estimation, speech compression ... etc. In this paper a new voice activity detection algorithm based on wavelet transform is proposed. In this algorithm we use the energy in each sub band, and by two methods we extract feature vector from these values. Experimental results demonstrate advantage over different VAD methods. ©2008 IEEE
Manufacture of Smart Drug Delivery System with UCST Polymers
, M.Sc. Thesis Sharif University of Technology ; Ramazani, Ahmad (Supervisor)
Abstract
Smart heat-sensitive polymers play a unique role in drug delivery systems due to reversible behavior in response to environmental changes, especially temperature changes. Among the heat-sensitive polymers, UCST polymers due to their specific behavior and very little-known polymers with this feature are the subject of many new researches. In the present study, New designed temperature-sensitive polymers with UCST capability based on acrylamide and vinyl acetate were synthesized. These copolymers were synthesized in different percentages of acrylamide by free radical polymerization in solution conditions. All polymers compounds were characterized by H-NMR, FT-IR, DSC and GPC measurements. The...
Comments on the " A comparative study of chelating and cationic ion exchange resins for the removal of palladium (II) complexes from acidic chloride media"
, Article Journal of Hazardous Materials ; Volume 229-230 , 2012 , Pages 461-462 ; 03043894 (ISSN) ; Khanchi, A. R ; Outokesh, M ; Tayebi, A ; Sharif University of Technology
2012
Evaluation of whisker alignment and anisotropic mechanical properties of ZK60 alloy reinforced with SiCw during KOBO extrusion method
, Article Journal of Manufacturing Processes ; Volume 84 , 2022 , Pages 344-356 ; 15266125 (ISSN) ; Wang, Y ; Yarigarravesh, M ; Tayyebi, M ; Tayebi, M ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
In current study, microstructure and high-temperature mechanical properties of ZK60 magnesium alloy reinforced by SiC whiskers were investigated after casting, the KOBO extrusion and aging processes. For this purpose, ZK60/SiCw composite specimens were prepared by stir casting technique. In order to achieve a laminar structure and improve the strength, the samples were subjected to KOBO extrusion technique and precipitation hardening, resulting in improved strength and increased ductility. The former is due to grain refining and formation of precipitates in the microstructure, while the latter is attributed to grain refining and formation of laminar structure. To evaluate the strength of the...
Numerical study of lorentz force interaction with micro structure in channel flow
, Article Energies ; Volume 14, Issue 14 , 2021 ; 19961073 (ISSN) ; Ali, K ; Ahmad, S ; Cai, J ; Sharif University of Technology
MDPI AG
2021
Abstract
The heat transfer Magnetohydrodynamics flows have been potentially used to enhance the thermal characteristics of several systems such as heat exchangers, electromagnetic casting, adjusting blood flow, X-rays, magnetic drug treatment, cooling of nuclear reactors, and magnetic devices for cell separation. Our concern in this article is to numerically investigate the flow of an incompressible Magnetohydrodynamics micropolar fluid with heat transportation through a channel having porous walls. By employing the suitable dimensionless coordinates, the flow model equations are converted into a nonlinear system of dimensionless ordinary differential equations, which are then numerically treated for...
LDPE/EVA/graphene nanocomposites with enhanced mechanical and gas permeability properties
, Article Polymers for Advanced Technologies ; Volume 26, Issue 9 , 2015 , Pages 1083-1090 ; 10427147 (ISSN) ; Ramazani S. A ; Hamed Mosavian, M. T ; Tayyebi, A ; Sharif University of Technology
John Wiley and Sons Ltd
2015
Abstract
In the present work, graphene oxide (GO) and reduced graphene oxide (RGO) were incorporated at low-density polyethylene (LDPE)/ethylene vinyl acetate (EVA) copolymer blend using solution casting method. Monolayer GO with 1-nm thickness and good transparency was synthesized using the well-known Hummers's method. Fourier transform infrared and X-ray photoelectron spectroscopy data exhibited efficient reduction of GO with almost high C/O ratio of RGO. Scanning electron microscopy showed the well distribution of GO and RGO within LDPE/EVA polymer matrix. The integrating effects of GO and RGO on mechanical and gas permeability of prepared films were examined. Young's modulus of nanocomposites are...
A new algorithm for fault location on transmission lines by optimal PMU placement
, Article International Transactions on Electrical Energy Systems ; Volume 25, Issue 10 , 2015 , Pages 2071-2086 ; 20507038 (ISSN) ; Salehi Dobakhshari, A ; Ranjbar, A. M ; Tayebi, A ; Sharif University of Technology
John Wiley and Sons Ltd
2015
Abstract
In this paper, the problem of placing a minimum number of phasor measurement units (PMUs) in a transmission system is considered so that faults on all lines of the network can be diagnosed and located irrespective of their locations. For this purpose, a PMU placement algorithm is applied to calculate the required data for impedance-based fault location of any fault line in the network, achieving the full potential of the circuit laws throughout the system. Another algorithm is then proposed to compute the voltage and current values of the fault line for fault-location purposes. Moreover, as many networks are already equipped with PMUs, the proposed algorithm makes it possible to locate...
ZnO quantum dots-graphene composites: Formation mechanism and enhanced photocatalytic activity for degradation of methyl orange dye
, Article Journal of Alloys and Compounds ; Volume 663 , 2016 , Pages 738-749 ; 09258388 (ISSN) ; Outokesh, M ; Tayebi, M ; Shafikhani, A ; Şengör, S. S ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
The current study demonstrates homogenous decorating of zinc oxide quantum dots (QDs) onto graphene oxide (GO) surface via simple chemical method. The AFM image exhibited that the prepared graphene was 0.8 nm thick and hence practically monolayer. Average size of the ZnO QDs was estimated by transmission electron microscopy around 3 nm. Instrumental and chemical analyses demonstrated formation of a strong bond between ZnO QDs and GO, through C-O-Zn and C-Zn bridges. The UV-visible spectra displayed that the introduction of graphene sheets to ZnO QDs resulted in higher absorption intensity of UV as well as widening of adsorption window toward visible light for ZnO-Graphene due to chemical...
Novel visible light photocatalytic and photoelectrochemical (PEC) activity of carbon-doped zinc oxide/reduced graphene oxide: supercritical methanol synthesis with enhanced photocorrosion suppression
, Article Journal of Alloys and Compounds ; Volume 723 , 2017 , Pages 1001-1010 ; 09258388 (ISSN) ; Soltani, T ; Lee, B. K ; Outokesh, M ; Tayebi, M ; Sharif University of Technology
2017
Abstract
Carbon-doped zinc oxide/reduced graphene oxide (C-ZnO/rGO) was prepared by a facile one-pot supercritical methanol method. The synthesized C-ZnO/rGO nanocomposite with flower-like ZnO micro-rods (MRs) synergistically inherited all the advantages of carbon doping and rGO heterojunction and exhibited high photocatalytic activity for the photodegradation of methyl orange (MO) under visible light. The x-ray diffraction (XRD) results indicated that in presence of GO, a new carbon-doped phase was formed at the high temperature and pressure of supercritical methanol. The x-ray photoelectron spectroscopy (XPS) at low binding energies demonstrated that the valence band of C-ZnO-rGO is up-shifted by...
Newly designed ternary hematite-based heterojunction for PEC water splitting
, Article Applied Surface Science ; Volume 550 , 2021 ; 01694332 (ISSN) ; Eftekharinia, B ; Tayebi, M ; Lee, B. K ; Naseri, N ; Sharif University of Technology
Elsevier B.V
2021
Abstract
Hematite is recognized as a promising photoanode for photoelectrochemical water oxidation to produce solar hydrogen due to its favorable properties. However, the high charge carrier recombination rate due to low electrical conductivity and sluggish oxygen reduction kinetics of pure hematite hinder its photocatalytic activity. This work proposed a new hematite-based heterostructure of Ti-Fe2O3/Fe2TiO5/FeOOH, synthesized through a hydrothermal method. The photoanode morphology was branched nanorods that expanded their surface area and improved charge transfer at the photoanode/electrolyte interface. In a novel and complement modification approach, a thin pseudobrookite interlayer was applied...
Adsorption Of Uranium from Phosphoric acid and Waste Water with Microcapsules Contains Selective Extractants
, M.Sc. Thesis Sharif University of Technology ; Ghofrani, Mohammad Bagher (Supervisor) ; Khanchi, Alireza (Supervisor) ; Outokesh, Mohammad (Co-Advisor)
Abstract
Uptake characteristics of alginate microcapsules containing D2EHPA/TOPO for adsorption of uranium from industrial effluent were examined using batch, stirred and column method .stable alginate microcapsules in dried form was developed by immobilizing of D2EHPA/TOPO in porous matrix of calcium alginate. Characteristics of microcapsules were carrying out by destructive chemical analysis, BET, SEM and TG .the synthesized microcapsules showed a good column properties and high selectivity and reusability. In addition, isotherm adsorption of calcium alginate and microcapsules were fitted with frendlich's equation .the microcapsules also demonstrated that, the uptake percentage was constantly high...
Microstructure, fractography, and mechanical properties of hardox 500 steel tig-welded joints by using different filler weld wires
, Article Materials ; Volume 15, Issue 22 , 2022 ; 19961944 (ISSN) ; Haowei, M ; Yarigarravesh, M ; Assari, A. H ; Tayyebi, M ; Tayebi, M ; Hamawandi, B ; Sharif University of Technology
MDPI
2022
Abstract
This paper deals with the effects of three low-carbon steel filler metals consisting of ferritic and austenitic phases on the weld joints of the tungsten inert gas (TIG) welding of Hardox 500 steel. The correlation between the microstructure and mechanical properties of the weld joints was investigated. For this purpose, macro and microstructure were examined, and then microhardness, tensile, impact, and fracture toughness tests were carried out to analyze the mechanical properties of joints. The results of optical microscopy (OM) images showed that the weld zones (WZ) of all three welds were composed of different ferritic morphologies, including allotriomorphic ferrite, Widmanstätten...
A self-similar approach to study nanofluid flow driven by a stretching curved sheet
, Article Symmetry ; Volume 14, Issue 10 , 2022 ; 20738994 (ISSN) ; Jamshed, W ; Ahmad, S ; Bashir, H ; Ahmad, S ; Tag El Din, E.S.M ; Sharif University of Technology
MDPI
2022
Abstract
Nano-fluids have considerable importance in the field of thermal development that relates to several industrial systems. There are some key applications in recent construction systems flow, as well as microscale cooling gadgets and microstructure electric gadgets for thermal migration. The current investigation concludes the study of electrically conducting nano-fluid flow and heat transfer analysis in two-dimensional boundary layer flow over a curved extending surface in the coexisting of magnetic field, heat generation and thermal radiation. The small sized particles of copper (Cu) are taken as nanoparticles and water is assumed to be the base fluid. We used quasi-linearization and central...
Thin Film Thickness Measurement Using Colors of Interference Fringes
, M.Sc. Thesis Sharif University of Technology ; Amjadi, Ahmad (Supervisor)
Abstract
There are several methods for measuring thin film thickness, however, for the analysis of liquid film motors [1] we need a method which is capable of measuring the thickness using a single image of the film. In this work, we use the colors that appear on thin films, such as soup bubbles, which is a result of light interference to calculate the thickness of the layer
Effect of Amplitude of Electric Field on the Rotation of Liquid Film
, M.Sc. Thesis Sharif University of Technology ; Amjadi, Ahmad (Supervisor)
Abstract
By direct and alternating electric field applied to thin film of liquid suspended in the air we can spin out and control it. Rotation pattern depends on the geometry of the electrodes and the applied magnetic field. This is called a rotating liquid film (Liquid Film Motor). To determine the cause of rotation, different models have been proposed. In this project we have tried to check the accuracy of any of the models. Using particle velocimetry using the photo, we calculate the velocity pattern. Then, using the Navier-Stokes equation calculate the acceleration and viscosity from the velocity. Then, for a special arrangement using a finite diffrent method, electric potential and the electric...