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Modeling and Simulating of Water Distribution in Different Layers of Direct Methanol Fuel Cell
, M.Sc. Thesis Sharif University of Technology ; Baghalha, Morteza (Supervisor)
Abstract
A two-dimensional, two-phase, nonisothermal model was developed in this work to investigate the water transport characteristic and water distribution in a direct methanol fuel cell (DMFC). Emphasis is placed on exploring the water distribution in different layers of DMF. The water and methanol crossover through the membrane were considered with the effect of diffusion, electro-osmotic drag, and convection. Governing equations including the prton and electron transport, continuity, momentum, species transport for methanol, water, and gases species, and the auxiliary equations are coupled to determine the output parameters. These parameters are the concentration distribution of the species,...
Ni-doped TiO2 Photoanode Electrodes for Dye-sensitized Solar Cells Applications
, M.Sc. Thesis Sharif University of Technology ; Mohammadi, Mohammad Reza (Supervisor)
Abstract
A new strategy for enhancing the efficiency of TiO2 dye sensitized solar cells (DSSCs) doped with Ni ions with different molar percentages (i.e., 0, 0.5, 1, 5 and 10 mol%) was reported. The samples were prepared by sol-gel route and characterized by means of XRD, DRS, UV-visible, FESEM and photovoltaic measurment techniques. It was found that Ni-doped TiO2 nanoparticles had a mixture of anatase, rutile and brookite crystal structures. Moreover, the band gap energy was decreased with increasing Ni molar ratio, The highest cell efficiency of 5.4% was achieved for 1mol% Ni-doped TiO2, being 42% greater than that of pure TiO2 nanoparticles
Determination of the Plastic Zone at the Tip of a Crack in Pressure-Sensitive Materials Using RKPM
, M.Sc. Thesis Sharif University of Technology ; Mohammadi Shoja, Hossein (Supervisor) ; Jahanshahi, Mohsen (Supervisor)
Abstract
This project presents an outline of the crack tip stress fields in the presence of a plastic enclave around a growing fatigue crack using RKPM and Drucker-Prager criterion for pressure sensitive materials such as concrete and rock. Two distinguished features of RKPM are the arbitrarily high order smoothness and the interpolation property of the shape function which has kronecker delta property at the associated nodes. This method has proved to handle extreme material deformation and moving discontinuities. For the frictional materials such as rock in geotechnical engineering, a non-associated or associated Drucker- Prager plasticity model is appropriate for modeling its constitutive...
Reliability of Components Operating under Creep- Fatigue Conditions
, Ph.D. Dissertation Sharif University of Technology ; Farrahi, Gholamhossein (Supervisor) ; Wang, Bin (Co-Supervisor) ; Mehmanparast, Ali (Co-Supervisor)
Abstract
The probabilistic behavior and the reliability of high-temperature defective components under creep-fatigue conditions have been assessed, considering different sources of uncertainty in “material behavior”, “geometric parameters” and “operation conditions”. For this purpose, deterministic calculations of creep-fatigue crack growth have been derived based on the R5 procedure, and then these relationships have been used at the heart of the probabilistic assessments. One of the aims of this dissertation was to present a procedure for assessing the reliability of defective components operating under creep-fatigue conditions. This procedure has been implemented on a benchmark problem, i.e....
Efficient and reliable ray tracing, some challenges and proposed solutions. ا
, Article 8th European Conference on Antennas and Propagation, EuCAP 2014 ; April , 2014 , PP. 1589-1592 ; ISBN: 978-8890701849 ; Shishegar, A. A ; Sharif University of Technology
Abstract
Ray tracing has been widely accepted as a versatile and reliable method for indoor propagation modeling. Several published articles have addressed the computational efficiency and reliability as the most challenging problems of ray tracing and have presented various solutions. Such challenges are discussed in this paper and some possible solutions are presented
k-anonymity-based horizontal fragmentation to preserve privacy in data outsourcing
, Article Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 11 July 2012 through 13 July 2012, Paris ; Volume 7371 LNCS , 2012 , Pages 263-273 ; 03029743 (ISSN) ; 9783642315398 (ISBN) ; Hadavi, M. A ; Jalili, R ; Sharif University of Technology
Springer
2012
Abstract
This paper proposes a horizontal fragmentation method to preserve privacy in data outsourcing. The basic idea is to identify sensitive tuples, anonymize them based on a privacy model and store them at the external server. The remaining non-sensitive tuples are also stored at the server side. While our method departs from using encryption, it outsources all the data to the server; the two important goals that existing methods are unable to achieve simultaneously. The main application of the method is for scenarios where encrypting or not outsourcing sensitive data may not guarantee the privacy
Calibration of forming limit diagrams using a modified Marciniak-Kuczynski model and an empirical law
, Article Materials and Design ; Volume 34 , Feb , 2012 , Pages 185-191 ; 02641275 (ISSN) ; Assempour, A ; Sharif University of Technology
2012
Abstract
The major problem in determining the forming limit diagram (FLD) with the Marciniak-Kuczynski (M-K) model is the necessity of an experimental point in order to find the initial inhomogeneity coefficient and calibrate the diagram. The purpose of the present work is to eliminate this requirement. To do this, the usual assumption of geometrical inhomogeneity has been replaced with material inhomogeneity and it has been shown that the sensitivity of the diagram to variations of the inhomogeneity factor is reduced greatly with the new assumption. Using this advantage and collecting enough experimental data for different materials, an empirical law in terms of sheet thickness has been proposed...
Multiproduct EPQ model with single machine, backordering and immediate rework process
, Article European Journal of Industrial Engineering ; Volume 5, Issue 4 , 2011 , Pages 388-411 ; 17515254 (ISSN) ; Sadjadi, S. J ; Niaki, S. T. A ; Sharif University of Technology
Abstract
Production systems with scrapped and rework items have recently become an interesting subject of research. While most attempts have been focused on finding the optimal production quantity in a simple production system, little work appears on a joint production environment. In this research, two joint production systems in a form of multiproduct single machine with and without rework are studied where shortage is allowed and backordered. For each system, the optimal cycle length, the backordered and production quantities of each product are determined such that the cost function is minimised. Proof of the convexity of the involved objective functions of each model is provided and numerical...
Novel organic dyes with anchoring group of barbituric/thiobarbituric acid and their application in dye-sensitized solar cells
, Article Synthetic Metals ; Volume 209 , November , 2015 , Pages 1-10 ; 03796779 (ISSN) ; Salimi Beni, A ; Najafi Chermahini, A ; Ghahary, R ; Teimouri, A ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
Abstract New bi-anchoring donor-π-acceptor metal-free organic dyes based on diphenylamine as donor, and barbituric acid and thiobarbituric acid as the acceptor/anchor were synthesized, characterized and used in dye-sensitized solar cells applications. Among the fabricated dye sensitized solar cells, device based on the diphenylamine as donor, and barbituric acid as the acceptor exhibits a high power conversion efficiency of 1.53% with a short circuit current density of 3.71 mA cm-2, an open-circuit photo voltage of 0.55 V and a fill factor of 0.75% under AM 1.5 illumination (85 mW cm-2) compared to the other fabricated devices. The structure of synthesized dyes was optimized and their...
Determination of minimum miscibility pressure in N2–crude oil system: A robust compositional model
, Article Fuel ; Volume 182 , 2016 , Pages 402-410 ; 00162361 (ISSN) ; Mohagheghian, E ; Fathinasab, M ; Mohammadi, A. H ; Sharif University of Technology
Elsevier Ltd
Abstract
Nitrogen has been valued as an economical alternative injection gas for gas-based enhanced oil recovery (EOR) processes. Minimum miscibility pressure (MMP) is the most important parameter to successfully design N2 flooding. In this communication, a data bank covering wide ranges of thermodynamic and compositional conditions was gathered from open literature. Afterward, a rigorous approach, namely least square support vector machine (LSSVM) optimized with coupled simulated annealing (CSA) was proposed to develop a reliable and robust model for the prediction of MMP of pure/impure N2–crude oil. The results of this study showed that the proposed model is more reliable and accurate than the...
A macroscopic traffic flow model that includes driver sensitivity to the number of free spaces ahead
, Article Transportmetrica B ; 2017 , Pages 1-17 ; 21680566 (ISSN) ; Nassiri, H ; Sharif University of Technology
Abstract
This paper addresses the first-order extension of the Lighthill–Whitham– Richards (LWR) macroscopic traffic flow model. Although previous studies have focused on the fluid aspect of traffic flow, none have addressed the sensitivity of drivers to the number of free spaces within a certain distance ahead of the subject driver. To incorporate driver behavior, we used the number of free spaces ahead of subject drivers and their sensitivity to the number of free spaces within a certain distance ahead. The resulting model is a convection-diffusion model. By computing Einstein's diffusion equation and comparing it with the diffusion coefficient in the extended model, a theoretical relation for the...
Optimizing shipment, ordering and pricing policies in a two-stage supply chain with price-sensitive demand
, Article Transportation Research Part E: Logistics and Transportation Review ; Volume 45, Issue 4 , 2009 , Pages 564-571 ; 13665545 (ISSN) ; Akbari Jokar, M. R ; Sharif University of Technology
Elsevier Ltd
2009
Abstract
In this paper we focus on a two-stage supply chain consisting of one vendor and one buyer. We develop an integrated production-inventory-marketing model to determine the relevant profit-maximizing decision variable values. The model proposed is based on the joint total profit of both the vendor and the buyer, and it finds out the optimal ordering, shipment and pricing policies. We are able to ascertain the optimal decision variable values employing an analytical solution procedure. The numerical evidence suggests that it is more beneficial for the buyer and the vendor to cooperate with each other when the demand is more price sensitive. © 2008 Elsevier Ltd. All rights reserved
A thorough analysis of potential geothermal project locations in Afghanistan
, Article Sustainability (Switzerland) ; Volume 12, Issue 20 , 12 October , 2020 , Pages 1-17 ; Hosseini Dehshiri, S. J ; Hosseini Dehshiri, S. S ; Jahangiri, M ; Techato, K ; Sharif University of Technology
MDPI AG
2020
Abstract
In recent decades, many countries have shown a growing interest in the use of renewable energies for power generation. Geothermal energy is a clean and environmentally friendly source of renewable energy that can be used to produce electricity and heat for industrial and domestic applications. While Afghanistan has undeniably good geothermal potential that can be utilised to alleviate the country’s current energy limitations, so far this potential has remained completely untapped. In this study, the suitability of 21 provinces for geothermal project implementation in Afghanistan was evaluated using multiple multi-criteria decision-making (MCDM) methods. The stepwise weight assessment ratio...
A macroscopic traffic flow model that includes driver sensitivity to the number of free spaces ahead
, Article Transportmetrica B ; Volume 8, Issue 1 , 2020 , Pages 290-306 ; Nassiri, H ; Sharif University of Technology
Taylor and Francis Ltd
2020
Abstract
This paper addresses the first-order extension of the Lighthill–Whitham– Richards (LWR) macroscopic traffic flow model. Although previous studies have focused on the fluid aspect of traffic flow, none have addressed the sensitivity of drivers to the number of free spaces within a certain distance ahead of the subject driver. To incorporate driver behavior, we used the number of free spaces ahead of subject drivers and their sensitivity to the number of free spaces within a certain distance ahead. The resulting model is a convection-diffusion model. By computing Einstein's diffusion equation and comparing it with the diffusion coefficient in the extended model, a theoretical relation for the...
Design and operation of a double-fiber displacement sensor
, Article Optics Communications ; Volume 281, Issue 4 , 2008 , Pages 614-620 ; 00304018 (ISSN) ; Azimi, P ; Sharif University of Technology
2008
Abstract
Design and operation of a double-fiber sensor for displacement measurements are reported in this study. In this arrangement, one fiber transmits the laser light to the target and the second one receives the light reflected off the target and transmits to a photodetector. Utilizing inexpensive plastic optical fibers offers advantages such as higher reflexability and more robustness at a reasonable cost, which are required for some applications. The novelties of the reported design are compactness of the fiber probe, flexibility, long dynamic range (22 mm), and it is possible to use the source and the detector at the same side. The displacement of the target causes the intensity modulation and...
Application and performance comparison of high-resolution central schemes for the black oil model
, Article International Journal of Numerical Methods for Heat and Fluid Flow ; Volume 17, Issue 7 , 2007 , Pages 736-753 ; 09615539 (ISSN) ; Taghizadeh Manzari, M ; Kazemzadeh Hannani, S ; Sharif University of Technology
2007
Abstract
Purpose - The purpose of this paper is to investigate the performance of a specific class of high-resolution central schemes in conjunction with the black oil models for hydrocarbon reservoir simulation. Design/methodology/approach - A generalized black oil model is adopted, in which the solubility of gas in both oil and water and evaporation of oil are considered, leading to a system of equations prone to degeneracy. A computer code is generated and three test cases are solved to evaluate the performance of various schemes in terms of accuracy and discontinuity handling. Findings - It is shown that, although some of the central schemes are highly sensitive to the choice of...
The electrocatalytic examination of cephalosporins at carbon paste electrode modified with CoSalophen
, Article Talanta ; Volume 71, Issue 4 , 2007 , Pages 1669-1674 ; 00399140 (ISSN) ; Rouhollahi, A ; Shahrokhian, S ; Haghgoo, S ; Aghajani, S ; Sharif University of Technology
Elsevier
2007
Abstract
The electrocatalytic oxidation of cephalexin and cefazolin has been studied at a carbon paste electrode modified with cobalt salophen (CoSal) by cyclic voltammetry. The selectivity of the carbon paste modified with CoSal in detecting cephalexin and cefazolin was examined. To suggest the electrocatalytic mechanism for electro-oxidation of cefazolin, the electrochemical behavior of ceftriaxone was investigated which has a thiol group out of the beta lactam ring. The electrocatalytic oxidation of these antibiotics is shown to be irreversible at the CoSal modified electrode. Scan rate dependence of cefazolin, which is a sulfur-containing compound, has been examined. The results indicated that...
Synthesis of an alginate-poly(sodium acrylate-co-acrylamide) superabsorbent hydrogel with low salt sensitivity and high pH sensitivity
, Article Journal of Applied Polymer Science ; Volume 101, Issue 5 , 2006 , Pages 2927-2937 ; 00218995 (ISSN) ; Sharifnia, N ; Hosseinzadeh, H ; Sharif University of Technology
2006
Abstract
This article describes the synthesis and swelling behavior of a superabsorbing hydrogel based on sodium alginate (NaAlg) and polyacrylonitrile (PAN). The physical mixture of NaAlg and PAN was hydrolyzed with a solution of NaOH to yield an alginate-poly(sodium acrylate-co-acrylamide) [Alg-poly(NaAA-co-AAm)] superabsorbent hydrogel. A proposed mechanism for hydrogel formation was suggested, and the structure of the product was established with Fourier transform infrared spectroscopy. The effects of reaction variables were systematically optimized to achieve a hydrogel with a swelling capacity as high as possible. Under the optimized conditions concluded, the maximum capacity of swelling in...
Scanning tunneling spectroscopy of porous silicon in presence of methanol
, Article Sensors and Actuators, B: Chemical ; Volume 120, Issue 1 , 2006 , Pages 172-176 ; 09254005 (ISSN) ; Iraji zad, A ; Vaseghinia, S ; Sharif University of Technology
2006
Abstract
In this research, we used the scanning tunneling spectroscopy (STS) technique to probe the local electrical properties of the surface of meso-porous silicon and its substrate, including local density of states (DOS) in air and in methanol environment to increase our knowledge of sensing phenomena. Meso-porous silicon was prepared on p+-type Si which has high sensitivity toward methanol. Observations revealed that while the surface electrical properties of p+-type Si have not sensible change toward methanol, average local density of state of the porous layer increases after the exposure to methanol especially in the E < EF region. Moreover, large number of surface states is produced in band...
Simulation and exergy-method analysis of an industrial refrigeration cycle used in NGL recovery units
, Article International Journal of Energy Research ; Volume 30, Issue 15 , 2006 , Pages 1336-1351 ; 0363907X (ISSN) ; Jarrahian, A ; Pishvaie, M. R ; Sharif University of Technology
2006
Abstract
The behaviour of an industrial refrigeration cycle with refrigerant propane has been investigated by the exergy method. An natural gas liquid recovery unit with its refrigeration cycle has been simulated to prepare the exergy analysis. Using a typical actual work input value; the exergetic efficiency of the refrigeration cycle is determined to be 26.51 % indicating a great potential for improvements. The obtained simulation results reveal that the exergetic efficiencies of the air cooler(s) and chilling sections get the lowest rank among the other compartments of refrigeration cycle. Refrigeration calculations have been carried out through the analysis of T-S and P-H diagrams where...