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hemmat-yar--afshin
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Optimal Method in Cognitive Radio Networks Routing
, M.Sc. Thesis Sharif University of Technology ; Hemmat Yar, Afshin (Supervisor)
Abstract
Cognitive radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. CR networks, however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse quality-of-service (QoS) requirements. Specifically, in cognitive radio ad hoc networks (CRAHNs), the distributed multi-hop architecture, the dynamic network topology, and the time and location varying spectrum availability are some of the key distinguishing factors. In this literature, we propose a new routing algorithm that tries to...
Evaluation of Granularity of Reconfigurable Architectures for Wireless Communication Applications
, M.Sc. Thesis Sharif University of Technology ; Hemmat yar, Afshin (Supervisor)
Abstract
Wireless communication applications need high computing power, flexibility and scalability. Although ASICs have the ability of high computing power but they are not flexible to changing or completing of communication protocols. On the other hand, general purpose microprocessors or DSPs are flexible, but do not provide sufficient computing power. Thus devices with reconfigurable architecture have been proposed as a compromise between ASICs and microperocessors. One of the main features of reconfigurable devices is the granularity. The granularity of a reconfigurable devices shows the amount of computing power incorporate in a processing element. In this thesis we have evaluated different...
Distributed Publisher-Subscriber Pattern for Content-Based Routing in Software Defined Networks
, M.Sc. Thesis Sharif University of Technology ; Hemmat Yar, Ali Mohammad Afshin (Supervisor)
Abstract
Content-based routing, as provided by publisher/subscriber systems,has evolved as a key paradigm for interactions between loosely coupled application components (content publishers and subscribers). Content-based routing aims to increase the efficiency of forwarding by utilizing the diversity of information exchanged between application components. Using content-based forwarding rules (also called content filters) installed on content-based routers (also termed brokers), bandwidth-efficiency is increased by only forwarding content to the subset of subscribers who are actually interested in the published content. Many middle-ware implementations for content-based publish/subscribe have been...
Modeling and Simulation of a High Power Photoconductive Semiconductor Switch (PCSS)
, M.Sc. Thesis Sharif University of Technology ; Faez, Rahim (Supervisor)
Abstract
There are a wide variety of light-triggered switches. Photoconductive semiconductor switches (PCSSs) have been investigated intensively for many applications owing to their unique advantages over other switches. The advantages of PCSSs make them a perfect choice for many important applications where high switching accuracy and high-power capability are required. Photoconductive switches are fabricated from a variety of semiconductors, including silicon carbide (SiC), gallium arsenide (GaAs) and gallium nitride (GaN). In Photoconductive semiconductor switches (PCSSs) the switching mechanism is initiated by optical illumination and laser source controls the flow of current. In the off or...
Simulation and investigation of a back-triggered 6H-SiC high power photoconductive switch
, Article 6th Annual International Power Electronics, Drive Systems, and Technologies Conference, PEDSTC 2015, 3 February 2015 through 4 February 2015 ; February , 2015 , Pages 253-256 ; 9781479976539 (ISBN) ; Faez, R ; Amiri, S ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2015
Abstract
This paper has investigated the performance of a linear, 6H-SiC high power photoconductive semiconductor switch. A three-dimensional device modeling with SILVACO ATLAS tools was used to model the optically initiated 6H-SiC switch. The 6H-SiC PCSS device is designed in a rear-illuminated, radial switch structure. The material properties of vanadium compensated 6H-SiC PSCC have been analyzed for breakdown, photocurrent profile such as rise and fall time in terms of their applications as a photoconductive switch at high bias conditions. This structure and also new type of illumination extends the blocking voltage by reducing the peak electric field near electrodes. In this presentation the...
Developing BIM Vision and BIM Strategic Plan for Municipalities
, M.Sc. Thesis Sharif University of Technology ; Alvanchi, Amin (Supervisor)
Abstract
The municipality is an administrative, public and non-state institution that falls into the city district of the most countries’ administrative divisions. This institution has relatively autonomy and independent power. Municipalities are trying to apply the best approaches (Such as Building Information Modeling (BIM) as a procedure contributing the project management) to save time and money, as well as to satisfy the citizens in the implementation of civil projects. This study examines and evaluates the readiness of municipalities to modify the construction projects based on BIM. In addition, a pattern for identifying BIM applications, evaluating the organization readiness and the needs of...
Futuristic Greedy Algorithm on some NP-complete Problems
, Ph.D. Dissertation Sharif University of Technology ; Izadi, Mohammad (Supervisor)
Abstract
Many problems in the field of 0-1 integer programming are NP-Complete. Execution time for exact solving these problems is very high due to many constraints and decision variables. Hence, scientists use Fast algorithms, for example, the Greedy algorithms, in the approximated solution of these problems.A classic greedy approach may not search the whole solution space for better choices. However, other methods with a greedy approach, such as meta heuristic and hyper heuristic, in addition to local search, consider the more search space. These methods search randomly, so it does not provide a good guarantee for finding the proper solutions. Finding suitable solutions in this category of...
Nanofluid flooding in a randomized heterogeneous porous media and investigating the effect of capillary pressure and diffusion on oil recovery factor
, Article Journal of Molecular Liquids ; Volume 320 , December , 2020 ; Esfandeh, S ; Hosseinizadeh, E ; Sharif University of Technology
Elsevier B.V
2020
Abstract
In the initial recovery stage, only 5 to 15% of hydrocarbons can be extracted from oil reservoirs, so it is necessary to supply energy from an external reservoir or to use advanced solutions to increase oil recovery. By using secondary recovery method and flooding, greater amount of oil can be extracted. In this study, a new procedure of flooding using nanofluid was simulated. The nanofluid and source rock were modeled as a single phase and heterogeneous porous media, respectively. The geometry was considered as a two-dimensional rectangular area. Two phase Darcy equations and mass transfer equations were utilized to simulate this process. Moreover, the effects of different volume fractions...
Investigation on nanofluid flooding effect on enhancement oil recovery process in a random pore distribution incomplete cone
, Article International Communications in Heat and Mass Transfer ; Volume 117 , October , 2020 ; Hosseinizadeh, E ; Mosaferi, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
By reducing the exploration of new oil reservoirs, enhanced oil recovery from previous oil reservoirs is a solution to supply energy demand. In order to develop the production, various technologies and methods have been proposed such as steaming, direct heating, flooding by nano-fluid, chemical injection, polymer injection and etc. In the present study, nanofluid flooding has been attempted on a rock reservoir with incomplete cone geometry and its performance has been evaluated on oil recovery. The porous media is considered heterogeneous in simulation in accordance with oil reservoirs. The heterogeneous geometry considered in this study is incomplete cone that is heterogeneous in a random...
Flooding numerical simulation of heterogeneous oil reservoir using different nanoscale colloidal solutions
, Article Journal of Molecular Liquids ; Volume 302 , 15 March , 2020 ; Hosseinizadeh, E ; Esfandeh, S ; Sharif University of Technology
Elsevier B.V
2020
Abstract
In this study, flooding of oil reservoir by implementing Nanoscale colloidal solutions as a working fluid is simulated. All oil reservoirs are heterogeneous porous media; therefore, in this investigation for more accurate prediction of the problem, the porous media is considered heterogeneous. The governing equations of this problem are solved by finite element method (FEM). Moreover two-phase equations of Darcy and mass transfer equations are used. In this paper, the effect of temperature and volume fractions of nanoparticles on the rate of oil recovery is investigated. The SiO2, Al2O3, and CuO nanoparticles are used in the enhanced oil recovery (EOR) process. Also, in order to solve the...
Nanofluid flooding for enhanced oil recovery in a heterogeneous two-dimensional anticline geometry
, Article International Communications in Heat and Mass Transfer ; Volume 118 , November , 2020 ; Esfandeh, S ; Hosseinizadeh, E ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
In the present study, we try to numerically simulate the nanofluid flooding method, which is one of the newest methods in this field. For this purpose, the nanofluid is considered as a single phase fluid that enters the porous petroleum reservoir containing oil. Since all porous petroleum reservoirs are heterogeneous, the porous grid is also considered heterogeneous and is solved using the finite element numerical method. The geometry considered in this study is a two-dimensional anticline medium that is heterogeneous. In this study, the effect of using different volume fractions of nanoparticles in nanofluid is studied. Capillary pressure or diffusion are considered in simulation and their...
Effect of radial structure on the performance of lateral high-power GaAs photoconductive switch
, Article IEEE International Conference on Electro Information Technology, 21 May 2015 through 23 May 2015 ; Volume 2015-June , 2015 , Pages 436-439 ; 21540357 (ISSN) ; 9781479988020 (ISBN) ; Moreno, E ; Rasouli, F ; Alizad, S. H ; Sharif University of Technology
IEEE Computer Society
2015
Abstract
In this paper, the effect of radial structure on the performance of a linear-lateral GaAs high power photoconductive semiconductor switch (PCSS) is investigated. For this purpose a three-dimensional device modeling is used to model the optically initiated GaAs switch. In this simulation a p-type device with carbon as shallow acceptor is compensated by deep donor EL2 level as a trap level. The PCSS device is designed in a back-triggered, radially symmetric switch structure which extends the blocking voltage by reducing the peak electric field near the electrodes. Device modeling was performed and the effect of different trap concentrations on dark I-V characteristics has been investigated. In...
Study of Melting and Rapid Solidification of TiAl alloy and Formation of its Diffusion Bonded Structure using Molecular Dynamics Simulation
, M.Sc. Thesis Sharif University of Technology ; Aashuri, Hossin (Supervisor) ; Simchi, Abdolreza (Co-Advisor)
Abstract
The rapid pace of development of nanoscience and nanotechnology and their applications in various fields have made the study of materials in smaller scales more important than any time ever. Having an insight of materials’ microstructure and the mechanism of different phenomena in the atomic scale will be very beneficent in designing new and advanced materials or modifying the current manufacturing processes. Since molecular dynamics (MD) method has been well known as a mean of studying materials in atomic scale, it has been used in this study to investigate two different phenomena. The selection of the appropriate interatomic potential is of great importance in MD; Embedded Atom Method...
The Dynamic Interfacial Phenomena Investigations on Mobile Fluid Surfaces: Experimental Studies and CFD Simulations
, Ph.D. Dissertation Sharif University of Technology ; Bastani, Dariush (Supervisor) ; Miller, Reinhard (Co-Advisor) ; Yar Javadi, Ali (Co-Advisor)
Abstract
Understanding the hydrodynamic and physical chemistry basis of surface phenomena is very important for many branches of basic science like Chemical Engineering, Mechanics, Space Engineering, and Material Engineering in the level of fundamental studies and applications. In addition to the common technologies, the role of surface phenomena in novel technologies is also very essential. For example, nanotechnology, chemical or physical sensors, or micro electrical systems in which surface phenomena is playing a main role. Therefore, understanding the basis of surface science is very important for any development in many industrial and fundamental studies. The main topic of this thesis which is a...
Seawater Purification System by Solar Energy
, M.Sc. Thesis Sharif University of Technology ; Abbaspour Tehrani Fard, Majid (Supervisor)
Abstract
World population is increasing with a rapid paste while the availability of freshwater is becoming more scared. There is a severe lack of fresh water in the world today. Desalination of seawater is one of the significant options in hand to solve this problem. In this research a hybrid solar collector- high efficiency water purification system is introduced which can help to solve this problem with an interesting economic outlook. Renewable energies and desalination plants are two different technologies, which can be combined in various ways. The interface between the renewable energy system and the desalination system is met at the place/subsystem where the energy generated by the renewable...
Transient and steady state study of a rear-illuminated 6H-SiC photoconductive semiconductor switch
, Article Optik ; Volume 127, Issue 11 , 2016 , Pages 4615-4620 ; 00304026 (ISSN) ; Faez, R ; Moreno, E ; Rasouli, F ; Radfar, F ; Zaimbashi, M ; Sharif University of Technology
Elsevier GmbH
2016
Abstract
In this paper characteristics of a linear, 6H-SiC photoconductive semiconductor switch are presented. The vanadium-doped semi-insulated 6H-SiC PCSS device is designed in a back-triggered, radial switch structure. For this purpose, three-dimensional (3D) device modeling tool was used to model and test the optically initiated 6H-SiC switch. Dark I-V characteristic results show that newly proposed rear-illuminated radial switch structure extends the blocking voltage by reducing the peak electric fields near electrodes. Also this radial structure has higher dark resistance as compared to the previous 6H-SiC PCSS experimental results. The ON-state characteristics of vanadium compensated 6H-SiC...
Linear analysis of the stability of particle-laden stratified shear layers
, Article Canadian Journal of Physics ; Vol. 92, issue. 2 , 2014 , pp. 103-115 ; ISSN: 00084204 ; Firoozabadi, B ; Afshin, H
2014
Abstract
Hydrodynamic instabilities at the interface of stratified shear layers could occur in various modes and have an important role in the mixing process. In this work, the linear stability analysis in the temporal framework is used to study the stability characteristics of a particle-laden stratified two-layer flow for two different background density profiles: smooth (hyperbolic tangent) and piecewise linear. The effect of parameters, such as bed slope, viscosity, and particle size, on the stability is also considered. The pseudospectral collocation method employing Chebyshev polynomials is used to solve two coupled eigenvalue equations. Based on the results, there are some differences in the...
A Survey on the Concept of Quantum Theory: Measurement Problem and A Critical Approach to Decoherence Interpretation
, M.Sc. Thesis Sharif University of Technology ; Shafiee, Afshin (Supervisor)
Abstract
Studying the puzzling aspects of quantum phenomenon is quite important subject from different points of view. It must be specially regarded through some major aspects such as: wave-particle dualty, Bell’s theorem no-go theorems, complementarity, entanglement and measurement problem. In this project, we survey subsequently the above topics with a careful attention regarding the measurement problem. One of the most relevant ways claiming to solve measurement problem is the decoherence theory. Scrutinizing the details of formalism and description basis of decoherence, we critically explain and asses the different aspects of this theory
A Survey on Some Modern Approaches to Quantum Thermodynamics
,
M.Sc. Thesis
Sharif University of Technology
;
Shafiee, Afshin
(Supervisor)
Abstract
The relationship between quantum theory and thermodynamics has gained so much attention in recent years. Thermodynamics is indeed a phenomenological science and its theoretical foundations are not clear as well. In the nineteenth century, Boltzmann tried to establish a connection between concepts of thermodynamics and classical mechanics (as a consistent theoretical domain). With development of quantum mechanics in twentieth century, the possibility of analyzing and formulating of the multi-particle systems based on quantum formalism increased. Quantum approach to thermodynamic phenomena has been studied in various ways. Here basic questions are, e.g. how to define Thermodynamic entities...
An Investigation of Leggett’s Inequality
, M.Sc. Thesis Sharif University of Technology ; Shafiee, Afshin (Supervisor)
Abstract
Quantum correlations are among most intriguing problems in physics. Bell’s inequality which was proved in 1964 provides with us the possibility of comparing the predictions of quantum theory with what an underlying local realistic theory may reproduce for some given observables in correlated states. The violation of Bell’s inequality in practice prohibits the existance of such underlying theories. Yet, it is not clear which of the assumption, i.e., locality or reality is responsible for explaining the experimentally verified violations. In 2003, a Nobel prizewinner A. J. Leggett proved a new inequality in which the locality assumption was not crucial. Here, we explore different aspects of...