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ebrahimi-brojeni--javad
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Approximation Algorithms for the Matroid-Constraint Maximum Subdeterminant
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi Brojeni, Javad (Supervisor)
Abstract
let Mn n be a positive semmi definite matrix and M:= (U; B) be a matroid. Consider the problem of finding S 2 B such that det(MS;S) is maximized, in witch MS; S is the submatrix of M, restricted to rows and columns of S. This problem has a variety of applications including page ranking algorithms. The problem above is an NP-hard problem in the general case. However, there are several approximating and estimating algorithms for some special cases, which are interesting. Also, exactly solving the problem is NP-hard, even for some special matroids. As an example, one can consider the uniform matroids. Khachiyan introduced a greedy algorithm with dd approximation factor. Afterward, Di summa et...
Determining Factors of Foreign Direct Investment Using Gravity Model
, M.Sc. Thesis Sharif University of Technology ; Abedini, Javad (Supervisor)
Abstract
Foreign direct investment (FDI) has considerably increased in recent years and achieved two percent of the world GDP in 2009. The positive impact of FDI on many national economic variables such as export and employment has been a great motivation for countries to seek it. In spite of many promoting factors in Iran, the Iranian FDI inflow still remains small. Using a huge panel dataset including 2604 real observations, this study aims to recognize and evaluate the impact of main factors influencing FDI inwards across the world. Based on a theoretical approach, we develop an empirical gravity model which includes not only the traditional mass variables but also some specific factors to FDI...
Is There any Price Bubble in the Iranian Housing Market: a Structural Analysis Across Iranian Provinces Over 1375-1389
, M.Sc. Thesis Sharif University of Technology ; Abedini, Javad (Supervisor)
Abstract
During the two last decades, Iranians have faced with a wide and substantial increase in housing prices, especially in great metropolitans such as Tehran, Mashhad, Isfahan and Shiraz. This easily could be refered to a hyperinflation which significantly impeded the access of low and medium income families to housing. This study uses a structure model to recognize the responsible factors of such a rise in housing prices and to show whether there is any price bubble in market. The model consists of both supply and demand side determinants to explain the price changes across Iranian provinces over 1375-1390, in a panel data context. In particular, we use a longer and larger database which also...
Descriptive Complexity for Counting Problems
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi Boroojeni, Javad (Supervisor)
Abstract
Descriptive complexity refers to the difficulty of expressing a problem in a formal language, allowing for a complete and precise description of the problem, including output specifications for function problems. Despite the success of the descriptive approach in computational complexity, this approach has been predominantly used for decision problems. In contrast to decision problems, a counting problem can be considered as a function with the range of natural numbers. This thesis focuses on the examination of counting problems from a descriptive perspective, exploring the connection between their descriptive and computational versions. Toward this goal, weighted logic is utilized to...
Vertex domination of generalized Petersen graphs
, Article Discrete Mathematics ; Volume 309, Issue 13 , 2009 , Pages 4355-4361 ; 0012365X (ISSN) ; Jahanbakht, N ; Mahmoodian, E ; Sharif University of Technology
2009
Abstract
In a graph G a vertex v dominates all its neighbors and itself. A set D of vertices of G is (vertex) dominating set if each vertex of G is dominated by at least one vertex in D. The (vertex) domination number of G, denoted by γ (G), is the cardinality of a minimum dominating set of G. A set D of vertices in G is efficient dominating set if every vertex of G is dominated by exactly one vertex of D. For natural numbers n and k, where n > 2 k, a generalized Petersen graphP (n, k) is obtained by letting its vertex set be {u1, u2, ..., un} ∪ {v1, v2, ..., vn} and its edge set be the union of {ui ui + 1, ui vi, vi vi + l} over 1 ≤ i ≤ n, where subscripts are reduced modulo n. We prove a necessary...
Theory of Log-concave and Completely Log-concave Polynomials
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi Broujeni, Javad (Supervisor)
Abstract
One powerful methods to study combinatorial structures is to use polynomials. From 2006 onwards, by introducing and examining the properties of a class of polynomials called stable polynomials, deep connections were made between combinatorial structures and polynomials, and this led to special applications in solving problems such as van der Waerden conjecture conjecture and the proof of existence of Ramanojan graphs. In 2018, classes of polynomials called log-concave polynomials and completely log-concave polynomials were introduced, which led to the solution of an old conjecture, called Mason conjecture, in the field of matroid theory. The main purpose of this dissertation is to study the...
Algebraic and Combinatorial Bounds for the Hat Guessing Number of Graphs
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi Boroojeni, Javad (Supervisor)
Abstract
A number of players are positioned on the vertices of a finite graph, and each is wearing a hat whose color has been randomly and equally likely selected from a finite set of colors. Player A sees Player B if and only if there is a directed edge from the vertex corresponding to A to the vertex corresponding to B. The players must agree on a specific strategy before the game begins and carry it out. Once the game begins, no communication is allowed between the players, and each player must simultaneously guess the color of their own hat. The team wins if at least one guess is correct. For a given directed graph, we define the 'guessing number' of the graph as the maximum number of colors for...
Releasing All-Pairs Shortest Distances of Public Graphs with Differential Privacy
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi Boroojeni, Javad (Supervisor)
Abstract
In the context of differential privacy, a data holder has confidential information about users. The goal is to provide a randomized algorithm that takes this information as input and outputs an aggregation of the input. The algorithm must have the property that for any neighboring input pairs, the output distribution of the algorithm is close. One problem in differential privacy research is the release of shortest distances in a weighted graph. This model, first studied by Adam Sealfon, involves an edge-weighted graph G=(V, E) with weights w : E → R, where the topology of the graph is public and the private information is the weight of the edges. The aim is to provide an (ϵ, δ)-DP algorithm...
Multivariate Mutual Information via Secret-key Agreement
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi, Javad (Supervisor)
Abstract
Shannon (1948) for the first time defined the "mutual information'' parameter for two random variables, but still there is no common definition for multivariate mutual information has been agreed upon, despite the multitude of research on the subject and various proposed definitions. In 2015, a study suggested that the maximum rate of secret-key, in the secret-key agreement problem, is a suitable candidate for defining multivariate mutual information. Csiszár and Narayan's research on the secret-key agreement problem provides an accessible bound for the maximum rate of secret-key rate, which in the bivariate case is the shannon's mutual information. The proposed definition has all expected...
The Problom of Forcing Number of Perfect Matching
, M.Sc. Thesis Sharif University of Technology ; Mahmoodian, Ebadollah (Supervisor) ; Ebrahimi Borogerdi, Javad (Supervisor)
Abstract
The notions of forcing edge and the forcing number of a perfect matching first appeared in 1991 by Harary, Klein and Živković. The root of these concepts can be traced to the works by Randić and Klein in 1985-1987, where the forcing number was introduced under the name of “innate degree of freedom” of a Kekulé structure, which plays an important role in the resonance theory in chemistry. Over the past three decades, more research has been done on the forcing set of perfect matchings. Here, we introduce bounds on the forcing number of perfect matching of some graphs that have already been known. Then, we extend the concept of forcing to fractional perfect matching and we introduce fractional...
How to Explicitly Solve a Thue-Mahler Equation
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi Borojeni, Javad (Supervisor) ; Ghadermarzi, Amir (Supervisor)
Abstract
David Hilbert posed a list of mathematical problems in 1900. Hilbert's tenth problem was "Is there an algorithm to determine whether a given Diophantine equation, has a solution with all unknowns taking integer values." Although Matiyasevich Showed that the answer to this problem is negative in the general case; the answer of this problem for a specific diophantine equation $f(x,y) $ that has rational coefficients, is unknown. Thue-Mahler equation is a diophantine equation of the form: $$F(x,y)=c\cdot p_1^{z_1}\cdots p_v^{z_v}$$ where $F$ is homogeneous with integer coefficients, degree $n\geq3$ and $p_1,\ldots p_v$ are distinct rational primes ($v\geq1$). All the unknowns are...
BQP and the Polynomial Hierarchy
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi Broojeni, Javad (Supervisor) ; Abolfath Beigi, Salman (Co-Supervisor)
Abstract
The relation between BQP and PH has been one of the most fundamental open questions since the beginning of the field of quantum computational complexity. Despite the common belief that BQP contains problems outside the polynomial hierarchy, no real progress had been made in solving the problem even in relativized world. In 2009, Aaronson took the first serious step by proposing an oracle problem to separate the relation version of these two complexity classes. Finally, based on Aaronson’s works, in 2018 Raz and Tal separated BQP and PH relative to an oracle in a breakthrough work. This thesis studies the tools and techniques used to solve this challenging problem
A fuzzy random minimum cost network flow programming problem [electronic resource]
, Article Journal of Industrial and Systems Engineering (JISE)-Iranian Institute of Industrial Engineering ; Article 3, Volume 6, Issue 1, Spring 2012, Page 34-47 ; Eshghi, Kourosh ; Sharif University of Technology
Abstract
In this paper, a fuzzy random minimum cost flow problem is presented. In this problem, cost parameters and decision variables are fuzzy random variables and fuzzy numbers respectively. The object of the problem is to find optimal flows of a capacitated network. Then, two algorithms are developed to solve the problem based on Er-expected value of fuzzy random variables and chance-constrained programming. Furthermore, the results of two algorithms will be compared. An illustrative example is also provided to clarify the concept
Special classes of mathematical programming models with fuzzy random variables [electronic resource]
, Article Journal of Intelligent and Fuzzy Systems, Published In: IOS Press ; Volume 19, Number 2, 2008 ; Nematian, Javad ; Sharif University of Technology
Abstract
In this paper, we will discuss two special classes of mathematical programming models with fuzzy random variables. In the first model, a linear programming problem with fuzzy decision variables and fuzzy random coefficients is introduced. Then an algorithm is developed to solve the model based on fuzzy optimization method and fuzzy ranking method. In the second model, a fuzzy random quadratic spanning tree problem is presented. Then the proposed problem is formulated and solved by using the scalar expected value of fuzzy random variables. Furthermore, illustrative numerical examples are also given to clarify the methods discussed in this paper
A special class of fuzzy integer programming model with all different constraints [electronic resource]
, Article Scientia Iranica ; Vol. 16, No. 1, pp. 1-10, 2009 ; Nematian, Javad ; Sharif University Of Technology
Abstract
In this paper, a fuzzy approach is applied to special classes of integer programming problems with all diierent constraints. In the rst model, a fuzzy integer programming model is developed to represent the all-diierent constraints in mathematical programming. In order to solve the proposed model, a new branching scheme for the Branch and Bound algorithm is also presented. In the second model, a special class of large-scale multi-objective fuzzy integer programming problems with all-diierent constraints is introduced. A solution method for the proposed model is also developed by using the decomposition technique, weighting method and Branch and Bound algorithm. An illustrative numerical...
Fuzzy random minimum cost network problem [electronic resource]
, Article Journal of Industrial and Systems Engineering ; Vol. 6, No. 1, pp 34-47, 2012 ; Eshghi, Kourosh ; Sharif University of Technology
Abstract
In this paper, a fuzzy random minimum cost flow problem is presented. In this problem, cost parameters and decision variables are fuzzy random variables and fuzzy numbers respectively. The object of the problem is to find optimal flows of a capacitated network. Then, two algorithms are developed to solve the problem based on Er-expected value of fuzzy random variables and chance-constrained programming. Furthermore, the results of two algorithms will be compared. An illustrative example is also provided to clarify the concept
A ZVS-resonant bifilar drive circuit for SRM with a reduction in stress voltage of switches
, Article International Aegean Conference on Electrical Machines and Power Electronics, ACEMP 2011 and Electromotion 2011 Joint Conference, Istanbul ; 2013 , Pages 125-128 ; 9781467350037 (ISBN) ; Najmi, V ; Ebrahimi, S ; Oraee, H ; Sharif University of Technology
2013
Abstract
Switched Reluctance Motors (SRMs) are widely used in high-speed and low voltage applications because of their attractive features such as robustness and simplicity. No winding on the rotor of this type of motors allows reaching high speed which is desired for many applications. Drive circuits of SRMs also play an important role in their performance and operation. In this paper, a new bifilar drive circuit for this type of motors has been proposed. This novel configuration has been tested and investigated by PSIM software. Results show that the new bifilar drive circuit highly reduces the voltage stresses on semiconductor switches, and also considerably reduces the switching losses which are...
Production of Uranium Dioxide Nano Powder With Hydrothermal Method in Supercritical Water Reactor
, M.Sc. Thesis Sharif University of Technology ; Outokesh, Mohammad (Supervisor) ; Ahmadi, Javad (Supervisor) ; Karimi Sabet, Javad (Co-Advisor)
Abstract
Hydrothermal supercritical method is one of the most suitable methods for metal oxide nano powder, ceramics and mineral catalyst synthesis. Metal oxides nanopowder in its pure or mixed form has wide potential application as chemical industrial catalyst, hot Superconductors, magnetic material, gas sensors and car catalyst convertors. One of the most important metal oxides aspects of application is uranium oxide as nuclear reactor fuel is used. In addition, UO2 is selective catalyst for converting methane to methanol process and Decomposition of organic Chlorine material. In Supercritical hydrothermal method done in high pressure reactor with critical to fluid, is new method for the...
Energy management of smart home considering residences' satisfaction and PHEV
, Article 2018 International Conference on Smart Energy Systems and Technologies, SEST 2018, 10 September 2018 through 12 September 2018 ; 2018 ; 9781538653265 (ISBN) ; Shokri Gazafroudi, A ; Corchado, J. M ; Ebrahimi, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
Regarding the increasing number of electrical devices in the smart homes that leads to increase in total electricity consumption and cost, it is essential to use energy management methods to reduce the electricity cost. However, this can cause resident's dissatisfaction. Hence, it is important to define a method in which cost and dissatisfaction be optimized simultaneously. Among different services, an electric vehicle is the one that can be used as an energy storage system, so it can reduce the daily cost despite of increasing the total energy consumption. In this paper, we study the effect of the EV on the cost and dissatisfaction in our proposed method. © 2018 IEEE
Measured impact of different back-off points and cooling methods on pulse-to-pulse stability and sidelobe level of a high-power solid-state amplifier
, Article IET Radar, Sonar and Navigation ; Volume 14, Issue 2 , 2020 , Pages 335-340 ; Khodarahmi, E ; Ebrahimi, E ; Ahmadi, B ; Jalali, M ; Sharif University of Technology
Institution of Engineering and Technology
2020
Abstract
Using solid-state power amplifiers for next generation of weather radars becomes feasible by pulse compression techniques. In this study a 1.5 kW solid-state power amplifier (transmitter) for C-band weather radars is designed and fabricated by GaN high electron mobility transistor (HEMT) technology. An experimental setup based on heterodyne receiver with 16-bit digitiser is developed to investigate the behavior of the power amplifier under different cooling methods and back-off points. Several measurements with shaped LFM pulse show an approximately identical pulse to pulse (P2P) stability for 3 dB compression, P1dB and 2 dB back-off points while the best sidelobe level (SLL) is achieved for...