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Experimental Studies and Finite Element Analysis of Polymer Nanocomposites Reinforced with Graphene Sheets under Impact Loading

, M.Sc. Thesis Sharif University of Technology Zarei Darani , Sajad (Author) ; Naghdabadi, Reza (Supervisor) ; Sohrabpour, Saeed (Supervisor)

Abstract

In the experimental approach, graphene and Graphene Oxide (GO) were synthesized through a chemical method. In order to study the quality of GO, characterization tests were performed. Then, reinforced polymer with GO and graphene was made. Moreover, tension, compression and Split- Hopkinson pressure bar tests were performed on standard samples of reinforced polymer nanocomposite. The experimental data show that nanoparticles have a destructive effect in very low and high percentages for extension test as well as in high percentages for compression test. On the other hand, graphene is more effective than GO on improving material properties. Furthermore, comparison of compression results in...

Comparison of the Maximum Likelihood Ratio Detectors with the Hough Detectors in RADAR Detection Applications

, M.Sc. Thesis Sharif University of Technology Sharify Darani, Soroush (Author) ; Nayebi, Mohammd Mahdi (Supervisor)

Abstract

In this work, Hough detector has been compared with optimum detectors. We consider 2-D range-time data space, which is constructed by storing the radar returns from different range cells during several successive scans. In this space, target trajectory can be modeled as a straight line for short time intervals, and can be extracted by applying Hough transform transcendentally. In this work, a new detection method based on the likelihood ratio in the data space with Gaussian noise is introduced. ALR and GLR processors have been designed. Then formulas for probability of detection and false alarm rate is calculated, and verified via simulations. A new criterion for estimation quality is...

What drives mergers and acquisitions waves in developing countries? Evidences from Iranian banking industry

, Article Iranian Economic Review ; Volume 19, Issue 2 , 2015 , Pages 123-137 ; 10266542 (ISSN) Zarei, M ; Alambeigi, A ; Karimi, P ; Zarei, B ; Sharif University of Technology

2015

Abstract

Many Middle-East countries, like Iran, have dynamic banking industries and have observed merger and acquisitions (M&A) waves. M&A waves are usually defined in the developed world context and some of their main drivers were identified as: market timing, environment's shocks, merger manias, government regulation and regulatory, and technological changes. It has been discussed that merger waves and their reasons are among the ten most important unsolved mysteries in the field of finance (Brealey and Myers, 1991, p. 923), and as a result of this, it was not possible to completely clarify the reasons behind emerging M&A waves, especially in developing countries; for this reason in these...

The effects of mergers and acquisitions (M&As) on bank performance and entrepreneurial orientation (EO)

, Article Iranian Entrepreneurship: Deciphering the Entrepreneurial Ecosystem in Iran and in the Iranian Diaspora ; 2017 , Pages 361-375 ; 9783319506395 (ISBN); 9783319506388 (ISBN) Zarei, M ; Alambeigi, A ; Zarei, B ; Karimi, P ; Sharif University of Technology

Springer International Publishing 2017

Abstract

This chapter aims at pointing out that how mergers and acquisitions (M&As) as popular strategies which they are based on external growth approach have affected the performance of banks and entrepreneurial orientation (EO) in the context of Iranian financial sector. In this regard, it has been tried to investigate in what way EO moderates the relationships between the performance of banks in one hand, and M&As on the other hand. For this goal, 114 participants including the top and middle managers of the Iranian banks were chosen to be closely considered. The research is an applied research and a cross-correlation methodology has been used to spotlight on the probable relationships between EO...

A more accurate prediction of liquid evaporation flux

, Article Iranian Journal of Chemistry and Chemical Engineering ; Volume 23, Issue 2 , 2004 , Pages 45-53 ; 10219986 (ISSN) Khosravi Darani, K ; Sabzyan, H ; Zeini Isfahani, A ; Parsafar, G ; Sharif University of Technology

Iranian Journal of Chemistry and Chemical Engineering 2004

Abstract

In this work, a more accurate prediction of liquid evaporation flux has been achieved. The statistical rate theory approach, which is recently introduced by Ward and Fang and exact estimation of vapor pressure in the layer adjacent to the liquid-vapor interface have been used for prediction of this flux. Firstly, the existence of an equilibrium layer adjacent to the liquid-vapor interface is considered and the vapor pressure in this layer and its thickness calculated. Subsequently, by using the Fick's second law, an appropriate vapor pressure expression for the pressure of equilibrium layer is derived and by this expression and the statistical rate theory approach, evaporation flux is...

Adversarial Attack to Deep Learning Networks via Imperceptible Sparse Perturbation

, M.Sc. Thesis Sharif University of Technology Heshmati, Alireza (Author) ; Ghaemmaghami, Shahrokh (Supervisor) ; Marvasti, Farokh (Supervisor) ; Amini, Sajad (Co-Supervisor)

Abstract

Nowadays, methods based on deep learning networks are the most effective artificial in telligence methods. Although they have achieved success in various fields (such as machine vision and object recognition), practical and experimental cases show the fragility of deep learning networks against perturbations and unwanted changes of the input pattern. All these perturbations must be in a way that the main class of the perturbed input pattern can be rec ognized by human, but the network makes a mistake in recognizing its correct class. This thesis seeks a more accurate evaluation by designing adversarial attacks such that the main class of the adversarial pattern is detectable by human...

Nonlinear Filters Applied to Tightly Coupled Integration of INS/GPS/PL for Precise Navigation in Automatic Landing of UAVs

, M.Sc. Thesis Sharif University of Technology Heidari Darani, Mohammad Mehdi (Author) ; Nobahari, Hadi (Supervisor) ; Ghanbarpour Asl, Habib (Supervisor)

Abstract

One of the most dangerous phases of the flight is landing. Newly automatic landing is noticed. The vital element in an automatic landing system is navigation system. In this document, a PL/INS/DGPS auto landing system is introduced.In a PL based navigation system, accuracy is highly under the influence of relative geometry between PLs position and flight path. Therefore, it is necessary to locate PLs on the best position. An optimization is used to find PLs best configuration that increases the navigation performance. Tightly coupling of INS and GPS/PL is preferred, because some problems lead to GPS satellite signal unavailability

Efficient Visibility Computation and Simplification in Different Environments

, Ph.D. Dissertation Sharif University of Technology Zarei, Alireza (Author) ; Ghodsi, Mohammad (Supervisor)

Abstract

In this thesis, we considered several types of the visibility problem. These problems include computing the visibility polygon of a point observer inside a polygonal domain, maintaining visibility polygon of a moving point observer, visibility coherence in space, maintaining visibility polygon of a moving segment observer and visibility dependent simplification. Furthermore, we considered these problems in both offline and streaming settings. These problems arise in different practical areas, such as computer graphics, machine vision, robotics, motion planning, geographic information systems (GIS) and computational geometry. We obtained effective theoretical results as well as superior...

Investigating Geometric Proximity Problems on Moving Points

, M.Sc. Thesis Sharif University of Technology Rahmati, Zahed (Author) ; Zarei, Alireza (Supervisor)

Abstract

An interesting theoretical and practical set of problems in computer science is concerned with the study of spatial relations among objects in a geometric space. Examples of such problems for a set of points P are finding the closest pair of the points P, partitioning space into regions such that all points of a region have minimum distance to the same point in P, and computing the Euclidean minimum spanning tree on P. Moreover, we need mechanisms to efficiently update these properties when the points P are allowed to move or may be inserted or deleted. This is to avoid re-computation of these properties from scratch. Here, we consider the Euclidean minimum spanning tree (EMST) of a set of...

Planar Visibility Counting

, M.Sc. Thesis Sharif University of Technology Alipour, Sharareh (Author) ; Zarei, Alireza (Supervisor)

Abstract

Planar visibility computing is defined as determining the region of the plane that is visible from a specific observer. This concept has many applications in computer graphics, robotic and computer games. In this thesis we consider two visibility problems: the visibility testing problem which checks the inter-visibility of two objects and the visibility counting problem which counts the number of visible objects from an observer. For these problems we propose new algorithms which have some improvements compare to the previous ones

Investigating Path Simplification Problems

, M.Sc. Thesis Sharif University of Technology Emadi, Ghobad (Author) ; Zarei, Alireza (Supervisor)

Abstract

A basic technique in data reduction is to approximate a collection of data by another collection of smaller size. Then, the resulted data are easier to be processed or maintained. An example of such large scale data is the ordered sequence of n points describing a path or a region boundary. We are given a sequence of points p , p , ..., p , and we consider the 1 2 n problem of approximating these points by a path with k < n line segments which error of this path is not greater than special value. Various criterions are defined to compute the path simplification error.This problem can be used in GIS, Image Processing and Computer Graphics problems. In this thesis, we consider special case...

Introducing a suitable Controller for Rowing Activity in Patients with Spinal CordInjuries using FES

, M.Sc. Thesis Sharif University of Technology Zarei, Mohammad (Author) ; Jahed, Mehran (Supervisor)

Abstract

Disconnections in neural paths from the central nervous system to the muscles or vice versa cause different neuropathies, thus paralysis in different limbs may occur. As a result of the lack of muscular activity and the decrease in blood perfusion in paralyzed limbs, problems like osteoporosis, increase in the risk of breaking, decline in muscle size, cardiovascular diseases, renal dysfunction, bedsores, etc may happen. In order to induce movement in paralyzed limbs, thus preventingmentioned problems, rowing exercise through Functional Electrical Stimulation (FES) may be utilized. In FES, electrical Stimulation using current stimulating pulses is applied to contracting and relaxing muscles,...

Computational Geometry Problems in Black Box Model

, M.Sc. Thesis Sharif University of Technology Tehranchi, Farnaz (Author) ; Zarei, Alireza (Supervisor)

Abstract

Moving data is becoming more and more important in different areas such as air traffic control, mobile communications, geographical information systems, GPS and other advanced technologies. In most cases, the path trajectory of such moving data is not known in advance. Moreover, they can change the direction and their speed of motion. Recently, a moving model, called black box model, has been proposed for such environments. In this model, there is a sequence of time stamps in which the position of each object is reported and the maximum displacement of each object in a time step is bounded by a known constant, dmax. In this thesis, we use this model to solve some computational...

Separating Colored Points

, M.Sc. Thesis Sharif University of Technology Assadian, Navid (Author) ; Zarei, Alireza (Supervisor)

Abstract

Separating colored points is one of the important problems in computational geometry. In separating colored points problems a set of colored points in Euclidean space are given that each color designates a set of certain data.Different problems can be defined in the colored points subject. Among them,separating colored points is studied in this thesis. It is supposed that two sets of blue and red points are given. It is desired to find the minimum number of rectangles that separate the blue points from the red points. It is demonstrated hat if P ̸= NP then there is no polynomial time algorithm for solving this problem. Then, a constant factor approximation algorithm is introduced and applied...

3D-Reconstruction Using Static and Mobile Stereo-Camera for 3D-Reconstruction

, M.Sc. Thesis Sharif University of Technology Boomari, Hossein (Author) ; Zarei, Alireza (Supervisor)

Abstract

3D-object modeling and its representation in computers are one of the interested fields in computer science and engineering and problems like object and environment modeling, representation, storage and physical interactions are some of the important problems in this field. Increasing the applications of the technologies like localization, machine vision and virtual reality made the 3D-object modeling and its related problems, like 3D-model extraction and reconstruction, a nowadays interested challenges and a variety of solutions such as time of flight sensors,
structured light, sonar sensors and multi-camera reconstruction are presented for it. Multi-camera solutions, just like the...

Parameterized Approximation Algorithms for Bounded Diameter Minimum Steiner Tree Problem

, M.Sc. Thesis Sharif University of Technology Mashreghi, Ali (Author) ; Zarei, Alireza (Supervisor)

Abstract

Given a graph G with a set of terminals, two weight functions c and d defined on the edge set of G, and a bound D, a popular NP-hard problem in designing networks is to find the minimum cost Steiner tree (under function c) in G, to connect all terminals in such a way that its diameter (under function d) is bounded by D. Marathe et al. [1] proposed an (O(log2n);O(log2n)) approximation algorithm for this bicriteria problem, where n is the number of terminals. The first factor reflects the approximation ratio on the diameter bound D, and the second factor indicates the cost-approximation ratio. Later, Kapoor and Sarwat [2] introduced a parameterized approximation algorithm with performance...

Micro-Grid Protection in Presence of Inverter Based Distributed Generation

, M.Sc. Thesis Sharif University of Technology Zarei, Fariborz (Author) ; Parniani, Mostafa (Supervisor)

Abstract

In this study, control and protection of low voltage microgrids have been analyzed. Studied microgrid takes the advantages of inverter based distributed generation. One of the most important issues in inverter based microgrids is the control of its distributed generation. Since, the low voltage networks have single phase loads and many imbalances, these imbalances can affect the control of IBDGs (inverter based distributed generations). This issue in the islanded mode of operation is the most important, because in this mode of operation, IBDGs control the network voltage and frequency.
In this thesis, the different control strategies of IBDGs are reviewed, and then modified to address...

Cryptographic Hash Functions from Expander Graphs

, M.Sc. Thesis Sharif University of Technology Zarei, Afshin (Author) ; khazaei, Shahram (Supervisor)

Abstract

A hash function maps efficiently every finite length string to a fixed one. The output represents the entire content of the input, similar to digital fingerprint of input text. In order to be able to use a hash function in cryptography, it should be hard to find two distinct inputs with the same output (collision), because finding a collision in hash functions leads to malicious attacks on many security systems.We say a hash function is provably collision resistant, if finding a collision can be reduced to the known hard problems. Family of MD hash functions are one of the most famous applied hash functions which are considerably used in industrial applications. However, they are not...

Unsupervised Pattern Recognition in DATA Strams

, M.Sc. Thesis Sharif University of Technology Khavarian, Mehrdad (Author) ; Zarei, Alireza (Supervisor)

Abstract

Pattern recognition in data streams using bounded memory and bounded time is a difficult task. There are many techniques for recognizing patterns but when we talk about data streams these algorithms became useless since there are no enough memory to store all data. In data stream model the entire data is not available at any time and we don’t have enough time processing each data.
In this thesis we consider current methods for recognizing patterns from a data streams. The goal pattern in this study was the minimum total area of k convex polygons encloses all data

Reconstructing an Environment from Visibility Information

, M.Sc. Thesis Sharif University of Technology Mehrpour, Sahar (Author) ; Zarei, Alireza (Supervisor)

Abstract

One of the methods to detect an unknown environment, is using the visual information about the environment. In this problem, we have an unknown two-dimensional environment consists of a set of edges and vertices that the geometric positions of vertices is not speciﬁed and only the combinatorial structure of the environment is available. In addition, certain information such as visibility of two vertices in the environment is known. The goal is to recognize the geometric shape of the environment with this information.This problem has many applications in Robotics particularly in dynamic envi- ronment where objects are moving.
In this thesis, we examine this problem in diﬀerent conditions...