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nassimi--ali-mohammad
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Predicting Upper and Lower Limits of Flammability
, M.Sc. Thesis Sharif University of Technology ; Nassimi, Ali Mohammad (Supervisor)
Abstract
A mixture of a fuel and an oxidant can give rise to a self-propagating flame if the oxidant/fuel ratio is within a specific range. The boundaries of this range are called explosive limits. Lower explosive limit (LEL)—defined as the least fuel concentration capable of self-propagating a flame—and upper explosive limit (UEL)—defined as the greatest fuel concentration capable of self-propagating a flame—are properties of a fuel-oxidizer mixture. These limits are important aspects of burning. It is not possible for flame to propagate out of these ranges. The values of these limits are necessary to prevent accidental explosions during chemical processes. In this work, a direct use of group...
A Study of the Exact Solution for the Quantum-classical Liouville Equation in the Mapping Basis
, M.Sc. Thesis Sharif University of Technology ; Nassimi, Ali Mohammad (Supervisor)
Abstract
Full quantum description of dynamics for complex quantum systems, such as many chemical systems, is not feasible. Thus, via quantum-classical methods, one may divide the system into a quantum subsystem and a classical bath. Quantum degrees of freedom are settled in the discrete Hilbert space; however, the bath's degrees of freedom reside in the continuous phase space. The mapping approach to quantum-classical dynamics maps each quantum state onto a fictitious harmonic oscillator. After mapping, the Wigner transform is applied to these oscillators. Thus quantum degrees of freedom are placed in phase space on the same footing as the classical degrees of freedom. In this formalism, dynamics...
Comparing Predictions of Thermal Theory of Flame Propagation and Density Theory of Flame Propagation
,
M.Sc. Thesis
Sharif University of Technology
;
Nassimi, Ali Mohammad
(Supervisor)
Abstract
A significant portion of the substances used in the chemical industry are toxic and hazardous, posing major safety hazards. In this regard, studies on the flammability limits of flammable materials are important and necessary. Flammability limits are the range of fuel-oxidant mixtures that can lead to flame propagation. This project examines the flammability limits of different fuels. In this study, a set of fuels have been selected as the fuel world, and to select these compounds, their molecular structure as well as thermodynamic properties such as standard enthalpy of formation and standard enthalpy of combustion have been considered. It has been shown that by redefining the fuel world,...
Predicting Explosive Limits of Flammable Compounds via Phenomenological Relations
, M.Sc. Thesis Sharif University of Technology ; Nassimi, Ali mohammad (Supervisor) ; Tafazzoli, Mohsen (Supervisor)
Abstract
In this work, we establish the constancy of expansion ratio (density factor) and adiabatic flame temperature for predicting lower explosive limits and further establish the constancy of expansion ratio for measuring upper explosion limits. Flammability limits are important characteristics of combustion processes. The flame can only propagate in a specific range of ratios of concentration of fuel to oxidant. The maximum of this concentration ratio that make possible propagation of flame in a mixture, is called upper flammability limit. The minimum of this ratio that make flame propagation possible is called lower flammability limit. Limits of flammability change with initial conditions such...
Predicting flammability limits through thermal theory and density theory of flame propagation
, Article Fire and Materials ; 2021 ; 03080501 (ISSN) ; Sharif University of Technology
John Wiley and Sons Ltd
2021
Abstract
Flammability limits are important safety parameters of each flammable material. Thermal theory of flame propagation suggests existence of a threshold temperature above which a flame propagates. Density theory of flame propagation suggests existence of a threshold density factor above which a flame propagates; density factor is defined as the ratio of before ignition to after ignition density. Based on a general version of thermal theory of flame propagation, constancy of values of adiabatic flame temperature at each flammability limit can be used to predict flammability limits. Similarly, based on a general version of the density theory of flame propagation, constancy of values of density...
Sensitivity of the population of states to the value of q and legitimate range of q in tsallis statistics
, Article Journal of the Iranian Chemical Society ; Volume 6, Issue 2 , 2009 , Pages 341-344 ; 1735207X (ISSN) ; Parsafar, G ; Sharif University of Technology
2009
Abstract
In the framework of the Tsallis statistical mechanics, we study the change of the population of states when the parameter q is varied, for some model systems; the results show that the difference between predictions of the Boltzmann-Gibbs and Tsallis statistics can be much smaller than the precision of any existing experiment. Also, the relation between privilege of rare and frequent events and the value of q is restudied. It is shown that positive q privilege frequent and negative q privilege rare events. Finally, the convergence criteria of the partition function of some simple model systems, in the framework of Tsallis statistical mechanics, is studied. Based on this study, we conjecture...
Modification of carbohydrate polymers via grafting in air. 1. Ceric-Induced synthesis of starch-g-polyacrylonitrile in presence and absence of oxygen [electronic resource]
, Article Starch - Starke ; Volume 54, Issue 3-4, pages 140–147, April 2002 ; Zohurian Mehr, Mohammad J
Abstract
Monomer grafting, a unique technique for polysaccharide modification, is always performed under inert (e.g., N2) atmosphere. This work is the first report related to evaluating the possibility and efficiency of the grafting of acrylonitrile (AN) onto starch in presence of oxygen. Thus, corn starch (in both granular and gelatinized states) as well as soluble starch were grafted by AN using a ceric-carbohydrate redox initiating system. Graft copolymerizations were performed under nitrogen, air, and oxygen atmospheres at similar conditions. Grafting occurrence was verified using chemical and spectral proofs. The polymerization mechanism and kinetics were investigated by recording the...
Modification of carbohydrate polymers via grafting in Air. 2. Ceric-Initiated graft copolymerization of acrylonitrile onto natural and modified polysaccharides [electronic resource]
, Article Starch - Stärke ; Volume 54, Issue 10, pages 482–488, October 2002 ; Zohuriaan-Mehr, Mohammad J
Abstract
Acrylonitrile (AN) was grafted onto various natural and modified polysaccharides (i.e., gum arabic, gum tragacanth, xanthan gum, sodium alginate, chitosan, sodium carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose) by using ceric-carbohydrate redox initiating system. After overcoming practical problems, mainly from the high viscosity of the aqueous solutions of the different substrates, the graft copolymerization reactions were run either in air or in N2 atmosphere under similar conditions. Grafting was confirmed using chemical and spectral (FTIR) proofs. The reactions were kinetically investigated using semi-empirical expressions and time-temperature profiles. An anomalous...
Modeling of in Plane Behavior of Retrofitted Adobe Walls with Finite Element Method under Cyclic Loading
, M.Sc. Thesis Sharif University of Technology ; Bakhshi, Ali (Supervisor) ; Ghannad, Mohammad Ali (Co-Advisor)
Abstract
Statistical studies indicate the fact that in Iran, like many other developing countries, a significant percentage of buildings are made of traditional materials and most of them are adobe buildings especially in rural areas. Furthermore, geological data indicates that Iran is located in alps-Himalayas seismic zone and exposed by destructive earthquakes and adobe buildings suffer the most damages comparing with other type of the structures. According to these explanations, this research deals with adobe buildings behavior and provides solutions for reinforcing them and improving the seismic response of these buildings. These studies include numerical modeling with finite elements methods by...
Silica chloride/wet SiO2 as a novel heterogeneous system for the deprotection of acetals under mild conditions [electronic resource]
, Article Phosphorus, Sulfur, and Silicon and the Related Elements ; Volume 178:2667-2670, Issue 12, 2003 ; Pourjavadi, Ali ; Zolfigol, Mohammad Ali ; Bamoniri, Abdolhamid
Abstract
A combination of silica chloride and wet SiO2 was used as an effective deacetalizating agent for the conversion of acetals to their corresponding carbonyl derivatives under mild and heterogeneous condition
Distributed Fault-tolerant Computation for Massive Data
, M.Sc. Thesis Sharif University of Technology ; Maddah-Ali, Mohammad Ali (Supervisor)
Abstract
In this thesis we consider the problem of distributed computation by many processors.We mainly concentrate on matrix multiplication problem in this thesis because of its importance. A distributed system consists of N worker processors and one master processor. The master processor should distribute the computation between workers and after computation in each of them, collect the results. In this thesis, we are going to mitigate the effect of straggler processors by using coding methods. Straggler processors can cause delays in the computation time.In this thesis, we firstly introduce a method to multiply any number of matrices in each other. The proposed method occurred in one shot without...
Incomplete Reduction of Iron Ore in a Fluidized Bed Reactor
, M.Sc. Thesis Sharif University of Technology ; Halali, Mohammad (Supervisor)
Abstract
The main goal of current investigation was partial reduction of Fe2O3 available in Hematite-rich ore to Magnetite by Fludization Bed method. The reductive gas, CO, was produced by incomplete combustion of Acetylene and Airmixed in inappropriate ratio. X-Ray Diffraction and X-Ray Florescence analyses were implemented in order to conducting qualitative analysis of present phases before and after reduction of the ore. Quantitative analysis of the same phases was also conducted by Titration. The latter analysis revealed the precise magnitude of available iron in each of the oxide containing phases. The chemical composition of the reactor gas was also determined before and after reduction...
Sequential Competitive Facility Location In Continuous Geometric Space
, M.Sc. Thesis Sharif University of Technology ; Abam, Mohammad Ali (Supervisor)
Abstract
Abstract The problem of competetive facility location can be defined as follows: There are a number of customers in the form of points in space, and two players arrange a number of facilities in the form of points in space, given some limitations, respectively. Each customer’s connection to each facility has a cost for the customer and an advantage for the facility, and each customer wants to be connected to at most one of the facilities which has the lowest cost for him. The goal is to find the strategy of placing the facilities and determining the cost which the facility receives from the customer, in such a way that the player’s profit is maximised.In this thesis, we first sought to...
Distributed Verifiable Computing: Algorithms and Analysis
, M.Sc. Thesis Sharif University of Technology ; Maddah Ali, Mohammad Ali (Supervisor)
Abstract
Zero knowledge proofs allow a person (prover) to convince another person (verifier) that he has performed a specific computation on a secret data correctly, and has obtained a true answer, without having to disclose the secret data. QAP (Quadratic Arithmetic Program) based zkSNARKs (zero knowledge Succinct Non-interactive Argument of Knowledge) are a type of zero knowledge proof. They have several properties that make them attractive in practice, e.g. verifier's work is very easy. So they are used in many areas such as Blockchain and cloud computing. But yet prover's work in QAP based zkSNARKs is heavy, therefore, it may not be possible for a prover with limited processing resource to run...
Privacy Preserving Communication Schemes for Light Clients in Blockchain Networks: Algorithms and Analysis
, M.Sc. Thesis Sharif University of Technology ; Pakravan, Mohammad Reza (Supervisor) ; Maddah Ali, Mohammad Ali (Co-Supervisor)
Abstract
Lightweight clients are a type of blockchain users who do not store all the blocks in the blockchain due to limited resources. These users store only a small part of each block and when needed, request transactions from full nodes that store the entire blockchain. These users have no role in block validation and only want to receive transactions related to their addresses with proof of the inclusion in the block from full nodes.Since light clients rely on full nodes for receiving transactions, their privacy against full nodes is important. The current implementation of Bitcoin uses Bloom filters for privacy, but this offers very little privacy to the users.In this thesis, we study the...
Constants of explosive limits
, Article Chemical Engineering Science ; Volume 173 , 2017 , Pages 384-389 ; 00092509 (ISSN) ; Jafari, M ; Farrokhpour, H ; Keshavarz, M. H ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
This work defines density factor as the ratio of before ignition density to after ignition density of the ignition mixture. This work provides an estimation method for explosive limits of various fuels under room temperature and pressure by showing that for a large universe of fuels, constant adiabatic flame temperature and density factor are appropriate approximations at the lower explosive limit while only a constant density factor might be an appropriate approximation at the upper explosive limit. Thus the assumption of a constant adiabatic flame temperature can be used in calculating lower explosive limit while the assumption of a constant density factor can be used in approximating...
Power System Load Frequency Control Considering Renewable Energy Sources
, M.Sc. Thesis Sharif University of Technology ; Ranjbar, Ali Mohammad (Supervisor)
Abstract
Power system frequency regulation entitled load frequency control (LFC) has been one of the important control problems in electric power system design and operation. Off-normal frequency can directly impact on power system operation and system reliability. A large frequency deviation can damage equipment, degrade load performance, cause the transmission lines to be overloaded and can interfere with system protection schemes, ultimately leading to an unstable condition for the power system . On the other hand, the increasing need for electrical energy in the 21st century, as well as limited fossil fuel reserves and the increasing concerns with environmental issues for the reduction of carbon...
Perusing Metal Perusing Metal Insulator Transistors with in the Dynamical Field Approximation at Finite Temperature
, Ph.D. Dissertation Sharif University of Technology ; Vesaghi, Mohammad ALi (Supervisor)
Abstract
The aim of this work is to investigate some theoretical models developed in recent years for describing electronic correlation and apply them to some special problems and metallicity and insulating behavior of one type of paramagnetic systems. One of the vast‐applied and effective routines for investigating the strongly correlated electron systems is Dynamical Mean Field Theory (DMFT). In the first part, the equations of DMFT are solved on nearly real frequency axis with a effective and more reliable solver a little parameter γ above the real axis. This approach appears fine structures that can’t be captured with the ...
On a Bounded Budget Network Creation Game
, M.Sc. Thesis Sharif University of Technology ; Safari, Mohammad Ali (Supervisor)
Abstract
In this thesis, we consider a network creation game in which, each player (vertex) has a limited budget to establish links to other players. In our model, each link has a unit cost and each agent tries to minimize its cost which is its local diameter or its total distance to other players in the (undirected) underlying graph of the created network. Two variants of the game are studied: in the MAX version, the cost incurred to a vertex is the maximum distance between that vertex and other vertices, and in the SUM version, the cost incurred to a vertex is the sum of distances between that vertex and other vertices. We prove that in both versions pure Nash equilibria exist, but the problem of...
Pushover Analysis for Soil-Structure Systems
, M.Sc. Thesis Sharif University of Technology ; Ghannad, Mohammad Ali (Supervisor)
Abstract
Controlling damage level of structures for an earthquake with certain intensity is the main purpose in seismic performance based design. This is done by estimating and confining the structure displacements and related global and local response parameters. Even though nonlinear time history analysis method is the most exact method for predicting seismic behavior of structures, but its application is limited because of being complex. Nonlinear static analysis procedure (Pushover analysis) which is based on analyzing the structure subjected to the incremental lateral load is an alternative method that has been recommended by recent structural codes. In order to consider the soil-structure...