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bahramian--ahmad-reza
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Fabrication and Characterization of Porous Carbon-Graphene Composite as an Absorbent for Industrial Pollutants
, Ph.D. Dissertation Sharif University of Technology ; Madaah Hosseini, Hamid Reza (Supervisor) ; Pourjavadi, Ali (Supervisor) ; Bahramian, Ahmad Reza (Co-Supervisor)
Abstract
The amount of fresh water suitable for various uses is decreasing day by day. This may be due to evaporation or contamination of water or such. Heavy metal cations, dyes, oils and solvents are the most important substances that contaminate water. There are various ways to remove these contaminants, one of which is the absorption of these substances by suitable absorbents. Carbon compounds have attracted much attention among all the absorbents used so far. The aim of this study is to produce carbon aerogels from an economic and modify its structure and properties by adding graphene nanosheets. In this study, Novalak-graphene oxide (GO) gel was fabricated using solvent-saturated vapor...
A novel low-complexity dynamic frequency selection algorithm for cognitive radios
, Article 4th IEEE International Symposium on Wireless Communication Systems 2007, ISWCS'07, Trondheim, 16 October 2007 through 19 October 2007 ; 2007 , Pages 558-562 ; 1424409799 (ISBN); 9781424409792 (ISBN) ; Khalaj, B. H ; Sharif University of Technology
2007
Abstract
In this paper, a non-cooperative distributed frequency selection algorithm is proposed for cognitive radio networks in which in addition to interference minimization, the minimization of implementation complexity and probability of interruption of secondary users are also addressed. The convergence and interference reduction property of the algorithm is also demonstrated using game theoretic concepts. In order to evaluate the performance of the algorithm, the associated optimization problem is formulated into a variant of graph colouring problem, and a centralized algorithm is also proposed as an approximation of the optimal solution. Finally, simulation results demonstrate that the proposed...
Joint dynamic frequency selection and power control for cognitive radio networks
, Article 2008 International Conference on Telecommunications, ICT, St. Petersburg, 16 June 2008 through 19 June 2008 ; 2008 ; 9781424420360 (ISBN) ; Khalaj, B. H ; Sharif University of Technology
2008
Abstract
In this paper, joint dynamic frequency selection and transmit power control problem with the goal of power minimization for a target SINR is investigated for cognitive radio networks. The optimization problem is formulated and three algorithms are proposed: A centralized algorithm based on graph coloring, and two distributed algorithms based on game theory; one for coordinated and the other for non-coordinated scenarios. Performance of the proposed algorithms in terms of power minimization and convergence speed is evaluated through simulations. Comparing the performance with the optimum solution, all three algorithms show near-optimum power minimization performance for the simulated...
Hydrodynamic characteristics of gas-solid tapered fluidized beds: Experimental studies and empirical models
, Article Powder Technology ; Volume 283 , October , 2015 , Pages 355-367 ; 00325910 (ISSN) ; Farhadi, F ; Bahramian, A ; Sharif University of Technology
Elsevier
2015
Abstract
Understanding the hydrodynamic behavior of tapered fluidized beds is essential for accurate design and better operation in these fluid-solid contactors. Minimum fluidization velocity, minimum velocity of full fluidization, maximum pressure drop and bed expansion ratio are more important hydrodynamic characteristics in tapered fluidized beds. In this study, based on experimental data, dimensional analysis has been used to develop dimensionless correlations for predicting hydrodynamic characteristics of Geldart B particles in tapered fluidized bed. The effects of bed geometry, static bed height, particle density, size, and sphericity and also interparticle forces on hydrodynamic behavior of...
Analysis and Improvement of QoS in Optical CDMA Networks Using Cross Layer Design Concepts
, M.Sc. Thesis Sharif University of Technology ; Pakravan, Mohammad Reza (Supervisor)
Abstract
According to the rapid growing in communication devices, users need higher rates for their usages. Fiber optics is one the major choices to support such rates. One of the simplest and cheapest networks is Local Area Network (LAN) as a Passive Optical Network (PON). In these networks, some computers are locally connected to a passive optical device and communicate through it. Multiple access to a shared channel is an important task in such a network. In this thesis, Code Division Multiple Access (CDMA) is used and a new algorithm for Multiple Access Control Sublayer (MAC) based on scheduling will be developed to improve Quality of Service (QoS) and stabilize the network.
In the scheduling...
In the scheduling...
Scattering Theory on Locally symmetric Spaces
, M.Sc. Thesis Sharif University of Technology ; Razvan, Mohammad Reza (Supervisor)
Abstract
Scattering theory on locally symmetric space first was studied by Peter Lax and Ralph Phillips. They studied the and develop scattering theory on it. Without the Fourier analysis tools this theory was completed with a lot of computations. In this thesis first we try to construct Fourier analysis by definition Fourier transform then by means of new tools we prove very short version of scattering theory on locally symmetric space . In general case for studying scattering theory we need firs spectral decomposition of Hilbert space of square integrable functions locally symmetric spaces of rational rank one is achieved by quotient of symmetric space where G is Lie group and K is maximal...
Comparing the Performance of Centrifuge, Membrane Filter and Filter Press for Clarification of Lipase Enzyme
, M.Sc. Thesis Sharif University of Technology ; Rousta Azad, Reza (Supervisor)
Abstract
Lipases (Triacyl Glycerol Acyl Hydrolase, EC.3.1.1.3) are multidimensional biocatalysts which have many applications in food industrials, dairy, fats and oils processing, detergents, synthesis of pure chemical and pharmaceutical materials, paper industrial and cosmetics. Generally, industrial enzymes are produced extracellularly, so their separation from a low-cost complex medium (usually used for production) is one of the cost stages in their production process. Filtration is the most economical method of separation in the production of enzymes, but due to the small size of colloidal particles and cell masses present in the fermentation environment, its use is subject to limitations. In...
Developing an Applied Model for Energy Management in Dairy Production Industry
, M.Sc. Thesis Sharif University of Technology ; Mokhtar, Ali Reza (Supervisor) ; Miremadi, Ali Reza (Supervisor)
Abstract
Reviewing trends of energy consumption in the world reveals that sooner or later energy resources will be depleted. This concerning rate of consumption has brought about more greenhouse gases (GHG) emission influencing deleteriously on environment and climate. Human has continued energy consumption to maintain and improve the quality of his life through industrial production. Industry as a significant energy user owns considerable contribution to this consumption. Several attempts have been carried out to develop energy management systems in order to improve the energy efficiency of industrial sectors. Whilst they are comprehensive and could be applied to any sector, there is lack of...
Formability analysis of Tailor Welded Blank Pridaction with Friction Stret Weld
, M.Sc. Thesis Sharif University of Technology ; Asempour, Ahmad (Supervisor) ; Naghdabadi, Reza (Supervisor)
Abstract
The Tilor welded blank (TWB) two or more sheets with different thickness or strength which are welded together. The automobile designer are searching for new methods to reduce the cars’ weight and producing cost in order to diminish fuel consumption so they can survive in the competitive market. One way to achieve to this seemingly Contradictory demands, is using TWB in cars’ body. One of the most applicable methods to investigate the formability of metals sheets, is Forming Limit Diagrams (FLD). Three ways to determine the FLD are: Analytical Method, Experimental Methods, and Numerical Method. The experimental method to determine FLD, require metal sheets to undergo in different strain...
Effect of obesity on spinal loads during load-reaching activities: A subject- and kinematics-specific musculoskeletal modeling approach
, Article Journal of Biomechanics ; Volume 161 , 2023 ; 00219290 (ISSN) ; Arjmand, N ; El-Rich, M ; Parnianpour, M ; Sharif University of Technology
Elsevier Ltd
2023
Abstract
Obesity has been associated to increase the risk of low back disorders. Previous musculoskeletal models simulating the effect of body weight on intervertebral joint loads have assumed identical body postures for obese and normal-weight individuals during a given physical activity. Our recent kinematic-measurement studies, however, indicate that obese individuals adapt different body postures (segmental orientations) than normal-weight ones when performing load-reaching activities. The present study, therefore, used a subject- and kinematics-specific musculoskeletal modeling approach to compare spinal loads of nine normal-weight and nine obese individuals each performing twelve static...
Theoretical and Experimental Investigation of Particle Size Distribution in a Tapered Fluidized Bed for TiO2
, Ph.D. Dissertation Sharif University of Technology ; Farhadi, Fathollah (Supervisor) ; Bahramian, Alireza (Co-Advisor)
Abstract
This dissertation discusses the development of dimensionless correlations for predicting hydrodynamic parameters and CFD simulation of gas-solid two phase flow in conical fluidized beds. This research mainly focuses on the impact of particle size distribution on hydrodynamic parameters. The first section describes the experiments that were carried out with a number of gas–solid systems in a conical column to study certain important characteristics of the fluidized bed. Generalized empirical correlations, based on dimensionless analysis, have been developed in order to predict minimum fluidization velocity, minimum velocity of full fluidization, maximum pressure drop and bed expansion ratios....
Fluid Suspended Films in Present of Electric Field and Voltage
, Ph.D. Dissertation Sharif University of Technology ; Amjadi, Ahmad (Supervisor) ; Ejtehadi, Mohammad Reza ($item.subfieldsMap.e)
Abstract
Scientists want to know how they can control fluids motion. They use electric fields for controlling the fluids in different dimensions. In small size, application of electric fields is very important because of biological applications. We use electric current and field for rotating freely suspended films. Here, we study soap, polar and non-polar liquids, MBBA liquid crystal and ferrofluids films. We show that the surface charge plays the crucial role in rotating the films.We study the correlation between rotation of a film and different physical quantities.Our experiments confirm that dipole moments of fluid molecules do not show a clear effect on the rotation. Increasing the dipole moment...
Development of a computational fluid dynamics compositional wellbore simulator for modeling of asphaltene deposition
, Article ACS Omega ; Volume 6, Issue 37 , 2021 , Pages 24196-24208 ; 24701343 (ISSN) ; Rasaei, M. R ; Bahramian, A ; Ghazanfari, M. H ; Sharif University of Technology
American Chemical Society
2021
Abstract
The asphaltene problem is a two-step process: (1) asphaltene precipitation, as predicted by the thermodynamic model, and (2) asphaltene deposition, the amount of which is estimated by the kinetic model. Asphaltene precipitation is a prerequisite but not a sufficient condition for deposition. Deposition is dependent on other factors such as surface properties, phase behavior, rheology, and flow patterns. As a result, in addition to understanding thermodynamic and kinetic models, it is critical to also understand flow models. In fact, multiphase flow modeling is at the core of simulation, and it must be coupled with thermodynamic and kinetic models. Numerous studies on modeling asphaltene...
Stabilization of the Finite element Analysis of the Fluid-Structure Interaction in Micro Systems in Small Time Steps
, Ph.D. Dissertation Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Assempour, Ahmad (Supervisor)
Abstract
Fluid-structure interaction plays an important role in the performance of various Microsystems. In many micro-devices such as micropumps, microvalves and micromixers, the fluid flow is driven by a vibrating solid membrane. Since the fluid also plays a role in resistance to the solid vibration and deformation, the solid vibration and the fluid flow are always coupled and a full fluid-structure interaction (FSI) analysis is required in order to investigate the performance characteristics of these devices. Since the frequency of the solid vibration is normally high in micro-devices, the time step size required for the finite element analysis of the fluid-structure interaction in these devices...
A Fuzzy Multi-Criteria Approach to Sustainable Development Case Study of Hendurabi Island in Iran
,
Ph.D. Dissertation
Sharif University of Technology
;
Abrishamchi, Ahmad
(Supervisor)
;
Maknoon, Reza
(Co-Supervisor)
Abstract
The main objective of this research is to provide a framework by which decision-makers can evaluate and compare alternatives for sustainable development planning under uncertain dynamic future considering the risk and uncertainty associated with human judgment as well as the uncertain future. This approach combines the Delphi method, fuzzy set theory, and a discrete multi-criteria method based on prospect theory (TODIM). TODIM (an acronym in Portuguese for iterative MCDM) method is a particular multi-criteria approach based on the prospect theory. A qualitative Delphi technique is used to identify a set of qualitative sustainability criteria and to rate the alternatives accordingly. The...
Effect of graphene oxide on morphological and structural properties of graphene reinforced novolac-derived carbon aerogels: A modified Quasi-Percolation Model
, Article Ceramics International ; Volume 46, Issue 8 , 2020 , Pages 11179-11188 ; Madaah Hosseini, H. M ; Pourjavadi, A ; Bahramian, A. R ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Graphene reinforced polymer derived carbon (carbon/graphene) aerogels were synthesized by carbonization of novolac/graphene oxide aerogels. Novolac/graphene oxide aerogels were synthesized using solvent-saturated-vapor-atmosphere technique. To this aim, 20 wt% solution of novolac resin with 0, 2, and 5 wt% graphene oxide in 2-propanol were made and were cured in an autoclave. Wet aerogels were dried in air and were carbonized at 800 °C in nitrogen atmosphere. Eliminating the time-consuming methods of drying like supercritical and freeze drying is one of the advantages of this method of synthesis of organic aerogles. Fourier transform infrared spectroscopy, field emission scanning electron...
Human Capital Development and Utilization Methodology in a Public Sector Organization: Dynamic Capability Approach
, M.Sc. Thesis Sharif University of Technology ; Kermanshah, Ali (Supervisor) ; Sanjari, Ahmad Reza (Supervisor)
Abstract
It is proposed, in this research, a methodology for a public sector organization to integrate policy making in human capital development and utilization area. In this case the researcher used system dynamics method for modeling and analyzing the situation, to describe the mechanisms that produce the difficulties in the organization. The researcher mentioned the differences between public sector and profit organization, in designing the main part of the model and also the use of dynamic capability approach in designing human capital development parts of it. The model built in this research, describe the events before and after the 1990s separately, according to the different policy making...
Optimal Asset Allocation with Hidden Markov Regime Switching
,
M.Sc. Thesis
Sharif University of Technology
;
Bahramgiri, Mohsen
(Supervisor)
;
Jalali Naeni, Ahmad Reza
(Supervisor)
Abstract
Asset allocation is one of the core economic functions of security markets. By purchasing and selling securities individuals are able to effectively time their stream of consumption and to allocate their temporarily unused wealth among competing investments. To time the stream of future consumption optimally, the question arises as to how wealth is allocated most effciently on security markets. The purpose of this thesis is to develop an optimal Asset Allocation with Hidden Markov Regime Switching means and volatilities. We use the historical weekly information of three Indices in Wallstreet stock exchange: Stock, bond and commodity. First we use these historical information from...
Improvement and Expansion of Characteristic Green’s Function-Complex Images Method for Extraction of Green’s Function of Finite Dielectric Structures
, Ph.D. Dissertation Sharif University of Technology ; Shishegar, Amir Ahmad (Supervisor) ; Faraji-Dana, Reza (Co-Advisor)
Abstract
Finite dielctric structures are commonly used in optical devices, Microwave Integrated Circuitc (MICs) and printed antennas. To analyze these structures, full-wave analysis methods cannot be employed easily. They need huge computer resources and are time-consuming especially for electrically large structures. On the other hand, asymptotic techniques may not be exact enough for these structures. In this thesis, MPIE technique is chosen as an accurate and efficient technique for analyzing these structres. To use this technique, the magnetic vector potential and electric scalar potential are required. Uniform and closed-form spatial Green's function for finite dielectric structures is...
Effect of tiO_2 Nanoparticles on Heat and Drag Properties of Dilute Polymer Solutions
, M.Sc. Thesis Sharif University of Technology ; Ramezani Saadat Abadi, Ahmad (Supervisor) ; Mohammadi, Mohammad Reza ($item.subfieldsMap.e)
Abstract
In the present work, the experiments were carried out for two types of PAM (3330 and 3630) with three distinct concentrations (25, 40 and 55 ppm) and TiO_2-water nanofluid for four concentrations (1.5, 2, 2.5 and 3 vol. %), and the Nusselt number and friction factor for each of them expressed separately. The Reynolds number was in the range from 11000 to 21000. The steady state turbulent convective heat transfer and friction factor of the combination of TiO_2-water nanofluid and polymer 3330 in the coiled tube were investigated. The effects of the Reynolds number for 2 vol. % nanoparticles which consists of 25 ppm PAM (3330) determined at the constant temperature of 24°C. It was observed...