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On the complexity of isoperimetric problems on trees [electronic resource]
, Article Discrete Applied Mathematics ; Volume 160 Issue 1-2, January, 2012 Pages 116-131 ; Javadi, Ramin ; Sharif Univercity of Technology
Abstract
This paper is aimed at investigating some computational aspects of different isoperimetric problems on weighted trees. In this regard, we consider different connectivity parameters called minimum normalized cuts/isoperimetric numbers defined through taking the minimum of the maximum or the mean of the normalized outgoing flows from a set of subdomains of vertices, where these subdomains constitute a partition/subpartition. We show that the decision problem for the case of taking k-partitions and the maximum (called the max normalized cut problem NCP^M), and the other two decision problems for the mean version (referred to as IPP^m and NCP^m) are NP-complete problems for weighted trees. On...
On nodal domains and higher-order Cheeger inequalities of finite reversible Markov processes [electronic resource]
, Article Stochastic Processes and their Applications ; Volume 122, Issue 4, April 2012, Pages 1748–1776 ; Javadi, Ramin ; Miclo, Laurent ; Sharif Univercity of Technology
Abstract
Let LL be a reversible Markovian generator on a finite set View the MathML sourceV. Relations between the spectral decomposition of LL and subpartitions of the state space View the MathML sourceV into a given number of components which are optimal with respect to min–max or max–min Dirichlet connectivity criteria are investigated. Links are made with higher-order Cheeger inequalities and with a generic characterization of subpartitions given by the nodal domains of an eigenfunction. These considerations are applied to generators whose positive rates are supported by the edges of a discrete cycle ZNZN, to obtain a full description of their spectra and of the shapes of their eigenfunctions, as...
On the isoperimetric spectrum of graphs and its approximations [electronic resource]
, Article Journal of Combinatorial Theory, Series B ; Volume 100, Issue 4, July 2010, Pages 390–412 ; Hajiabolhassan, Hossein ; Javadi, Ramin ; Sharif University of Technology
Abstract
In this paper1 we consider higher isoperimetric numbers of a (finite directed) graph. In this regard we focus on the nth mean isoperimetric constant of a directed graph as the minimum of the mean outgoing normalized flows from a given set of n disjoint subsets of the vertex set of the graph. We show that the second mean isoperimetric constant in this general setting, coincides with (the mean version of) the classical Cheeger constant of the graph, while for the rest of the spectrum we show that there is a fundamental difference between the nth isoperimetric constant and the number obtained by taking the minimum over all n-partitions. In this direction, we show that our definition is the...
Isoperimetric Problems on Graphs
, Ph.D. Dissertation Sharif University of Technology ; Daneshgar, Amir (Supervisor)
Abstract
This thesis is concerned with studying several aspects of the generalized isoperimetric problems on weighted graphs. In this regard, as a generalization of well-known Cheeger constant, we define k-th isoperimetric constant as the minimum of normalized outgoing flow over all k-subpartitions (disjoint subsets) of the vertex set. Also, we investigate basic properties of these parameters and particularly we prove a Federer-Fleming-type theorem. We then introduce a generalized Cheeger conjecture which is a generalization of celebrated Cheeger inequality and relates defined isoperimetric constants to higher eigenvalues of Laplace operator. In order to find a partial proof for this conjecture, we...
Wide-band Direction Finding Based on Time Modulated Array
, M.Sc. Thesis Sharif University of Technology ; Behnia, Fereidoon (Supervisor)
Abstract
This thesis studies the problem of finding direction of arrival reecieved signals. One of the methods of direction finding is Time Modulated Array (TMA). Recently, a lot of research has been carried on using TMA for direction finding. Indeed, ease of implementation and resistance to noise has made this method interesting for researchers. The major drawback of these methods is that the baseline of array antenna needs not to be bigger than half of the wavelength of the maximum frequency and if this criterion is not met, the results will be multiple ambiguous solutions. However, sometimes, it is needed to have a bigger baseline (for instance, the case in which diameter of the antennas is bigger...
Wide-band Direction Finding Based on Time Modulated Array
, M.Sc. Thesis Sharif University of Technology ; Behnia, Fereidoon (Supervisor)
Abstract
This thesis studies the problem of finding direction of arrival reecieved signals. One of the methods of direction finding is Time Modulated Array (TMA). Recently, a lot of research has been carried on using TMA for direction finding. Indeed, ease of implementation and resistance to noise has made this method interesting for researchers. The major drawback of these methods is that the baseline of array antenna needs not to be bigger than half of the wavelength of the maximum frequency and if this criterion is not met, the results will be multiple ambiguous solutions. However, sometimes, it is needed to have a bigger baseline (for instance, the case in which diameter of the antennas is bigger...
Application of the Coset Construction Method in Theories of Spontaneous Symmetry Breaking: Gravitation as an Example
, M.Sc. Thesis Sharif University of Technology ; Torabian, Mahdi (Supervisor)
Abstract
In this manuscript we used the method of coset construction to describe theories of spontaneous symmetry breaking. The mathematical details are included in chapter 2. The utility of the method is that without any knowledge of the UV part of a theory we can construct IR part by just knowing the symmetry breaking pattern. We used the method for some symmetry breaking patterns to construct general relativity, massive gravity and also some symmetry breaking patterns corresponding to conformal gravity
The Assessment of Irregular Mid-Rise Steel Structures with Outriggers
, M.Sc. Thesis Sharif University of Technology ; Mofid, Masood (Supervisor)
Abstract
The system considered on this structure is for the design on mid-high Buildings from 15 and 20 floors above the base level and n floors below the base level and the limitation of the number of floors is due to the computer facility and restrictions. There is going to be an irregularity in some chosen floor at lower-floor, mid-floor, or upper-floor which is assuming one floor from the structure to have a different height with respect to the others. The height of the considered floor is going to increase up to 25% with respect to the other floors and the design of outriggers with these three assumptions is going to be assessed separately. In this system, a central core of steel is constructed...
Design and Efficient Implementation of Equalizer and Synchronizer Block in Recent Telecommunication Links Standards
, M.Sc. Thesis Sharif University of Technology ; Shabany, Mahdi (Supervisor)
Abstract
Today, telecommunication links transmit information wirelessly at high rates; The transmission channel is not ideal and the transmitted signal undergoes changes in the channel and then reaches the receiver; Also, the processing blocks in the transmitter and receiver are not completely similar and ideal; These two factors make it difficult for the receiver to recover the transmitted information and actually receives a signal that bears little resemblance to the transmitted signal. The most important effect that the channel has on the transmitted signal is due to the multi-path of the channel between the transmitter and the receiver, which causes a signal to reach the receiver through the...
Design and Baseband Hardware Implementation of LiFi WLAN Multi-User Modem
,
M.Sc. Thesis
Sharif University of Technology
;
Shabany, Mahdi
(Supervisor)
Abstract
In recent years, after the emergence of the benefits of optical wire communication, which successfully replaced electromagnetic technologies in some applications. Attention to wireless optical communication technologies has also increased. These technologies will also find their place in telecommunication systems after maturing according to the specific characteristics of light in the coming years. This thesis is a report on the implementation of a LiFi system, which aims to create a wireless local area network based on optical communication. Previously, reports have been written about the implementation of this system, but in this thesis, for the first time, the implementation of hardware...
Combinatorial Curvature of Graphs
, M.Sc. Thesis Sharif University of Technology ; Daneshgar, Amir (Supervisor) ; Javadi Jourtani, Ramin (Supervisor)
Abstract
There are a variety of notions of curvature that one could define on graphs. In this thesis, we introduce one of them which is called the ”Combinatorial Curvature”. This curvature is defined on graphs embedded on a surface, however as the name suggests,the combinatorial curvature of a vertex depends only on the combinatorial properties of the graph, and not on the geometric properties of the surface on which the graph is embedded. More precisely, the combinatorial curvature of a vertex is a function of the degree of the vertex and the faces which are incident to that vertex.In the main part of this thesis, we have tried to collect the most important results about the combinatorial curvature....
PPW Inequality on Graphs
, M.Sc. Thesis Sharif University of Technology ; Daneshgar, Amir (Supervisor) ; Javadi Joratani, Ramin (Co-Supervisor)
Abstract
The ratio of the two first non-trivial Dirichlet eigenvalues is the subject of the Payne-Polya-Weinburger Conjecture and Inequality. The PPW Conjecture was proven by M. Ashbaugh and R. Benguria. Ashbaugh and Benguria later proved a similar result for domains on the n-sphere. On the other hand, discrete counterparts of universal inequalities from (continuous) have been studied in the graph theory setting. This thesis surveys results related to the PPW inequality on graphs
Experimental Investigation of Enhanced Imbibition of Low Salinity/Smart Water in Fractured Porous Media: Effect of Fluid/Fluid and Rock/Fluid Interactions
, M.Sc. Thesis Sharif University of Technology ; Fatemi, Mobeen (Supervisor) ; Masihi, Mohsen (Supervisor)
Abstract
Many of oil reservoirs in Iran that are fractured, do not have high Recovery Factor (RF), therefor Enhanced Oil Recovery (EOR) methods are exerted in them. In fractured reservoirs, due to high capillary pressure in matrix and low amount of it in fracture, the wetting phase tends to imbibe to the matrix from the fracture. Altering the wettability of reservoir rock from Oil-Wet (OW) to Water-Wet (WW) enables the injected water to imbibe to matrix and sweep its oil. Also reducing oil/water IFT turns oil to small droplets, helps them to pass narrow pores and be produced. In one of the new EOR methods called chemical EOR, chemical additives are injected to the reservoirs along with water to...
A Parallel Algorithm for Data Clustering
, M.Sc. Thesis Sharif University of Technology ; Daneshgar, Amir (Supervisor) ; Javadi Jurtani, Ramin (Supervisor)
Abstract
Data clustering, is one of the most important problems in computer science. It has countless applica-tions in many different topics like machine learning, image processing, computer vision and bioinfor-matics. However, current algorithms for this problem do not have high accuracy and speed. In this thesis, we have proposed a parallel algorithm for data clustering based on the solution of Isoperimetric problem on trees. In addition, we have implemented the algorithm on GPU as a powerful, cheap and mostly available hardware. Finally, by doing different practical experiments, we have shown that the algorithm has more than 20x speed-up over the sequential algorithm without changing in the...
Non-invasive and Continuous Blood Pressure Measurement Using Pulse Transit Time without Cuff Requirement
, M.Sc. Thesis Sharif University of Technology ; Shabany, Mahdi (Supervisor)
Abstract
This thesis addresses cuff-less blood pressure (BP) estimation, for systolic blood pressure (SBP) and diastolic blood pressure (DBP) estimation with the aid of the processing of vital signals. Both with and without calibration per person approaches for BP estimation are considered. A data acquisition hardware is designed for high-resolution sampling of phonocardiogram (PCG), Photoplethysmogram (PPG) and electrocardiogram (ECG). Using these signals, pulse transit time (PTT) and pulse arrival time (PAT) indexes, which would be used for BP estimation with calibration, are extracted. For the BP estimator model using the calibration, A nonlinear model based on PTT or PAT, via modeling the vessels...
Turbulence Equation-of-State Interaction Modeling in Large Eddy Simulation
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor)
Abstract
In most real combustion systems, flow is turbulent (e.g., diesel engines). Therefore, a reliable turbulence modeling approach is necessary to design and analyze a system with turbulent flow. Direct numerical simulation (DNS), Large eddy simulation (LES), and Reynolds-averaged Navier-Stokes (RANS) are the three most mature Computational fluid dynamics (CFD) methods for turbulent flow simulations. Because of LES’s good accuracy and acceptable computational cost. In this project, LES is chosen to simulate the turbulent flow field.Modeled turbulence subgrid scales' interaction with nonlinear flow parameters, needs modeling. In supercritical and transcritical conditions, Equation-of-state is a...
Simulation of Turbulent Premixed Flame using Laminar Flamelet Decomposition Method
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor)
Abstract
The purpose of this study is to simulate a turbulent premixed flame with the help of the Laminar Flamelet Decomposition method. Numerical simulation is considered the main approach for studying this flame. A Bunsen-type premixed burner, which has a novel approach to making different levels of turbulence, has been used for modeling the premixed flame. To reduce the cost of numerical calculations, the Reynolds-averaged Navier-Stokes approach has been chosen for the CFD simulation. In this study, the Laminar Flamelet Decomposition model is the main combustion model for analyzing the turbulent premixed flame and with this method, the rate of reactions for all the reaction species will be...
Mobility Aware Intelligent Reflecting Surfaces Assisted Communications : A Deep Reinforcement Learning Approach
, M.Sc. Thesis Sharif University of Technology ; Jafari Siavoshani, Mahdi (Supervisor)
Abstract
The stacked intelligent metasurface has been introduced as an innovative technology in signal processing, enabling the rapid and instantaneous control of electromagnetic waves at the speed of light. In this research, the performance of a wireless system is investigated, where a tunable reconfigurable intelligent surface facilitates communication between a base station equipped with a stacked intelligent metasurface and downstream users, in scenarios where the line-of-sight link is unavailable. One of the main motivations for using stacked intelligent metasurfaces is the reduction in energy consumption, as their presence eliminates the need for radio frequency chains. Unlike traditional...
A Priori Investigation of Laminar Flamelet Decomposition and Conditional Source-term Estimation Methods in Turbulent Premixed Flames
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor)
Abstract
An a priori analysis is performed to assess the performances of Laminar Flamelet Decomposition (LFD) and Conditional Source-term Estimation (CSE) methods in predicting conditional and unconditional filtered production rates and mass fractions for turbulent premixed flames over a wide range of Karlovitz numbers, which is an indicator for the level of turbulence-chemistry interaction in premixed combustion.In LFD, it is assumed that a turbulent flame is composed of strained laminar flamelets. By presuming the functional form of the probability density function (PDF) of the progress variable and inverting the integral equation for the unconditional filtered mass fractions of one of the species,...
Improving the Measurement of the Chemiluminescence of Methylidyne (CH*)Species with the Help of Thermometry by Soot Pyrometry Method
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor) ; Mardani, Amir (Supervisor)
Abstract
This research introduces temperature measurement by a non-intrusive pyrometric method of the ratio of two colors of soot. For pyrometry, the spectral sensitivity of the Nikon D7100 camera was obtained by developing a neural network based on the results of photographing colored papers and their spectrum, and this camera was used for temperature measurement. Based on the dependence of soot radiation on temperature and the spectral sensitivity of the camera, a calibration chart has been extracted on the ratio of the green channel to the red channel of the camera with the soot temperature, which is used to produce the temperature contour using the flame image. The temperature contour of...