Sharif Digital Repository

This study examines radar imaging as a pivotal subject in both military and civilian radar applications. The core challenge lies in overcoming the inherent limitations in enhancing radar image resolution, which primarily depends on fundamental parameters such as bandwidth and imaging angle. Due to practical constraints in optimizing these parameters, out-of-band data estimation has emerged as an effective solution. To address this, a parametric model for radar returns has been developed based on electromagnetic principles, formulated as a function of frequency and angle. For parameter extraction, Chapter 3 introduces a novel method to improve the classification accuracy of localized and... 

The Weil group WF is assigne to every local field F. Langlands Correspondence is a bijetion between semisimple two-dimensional Deligne representations of Weil Group WF and irreducible representations of GL2(F) which fixes assigned L-functions and local constants. In this thesis we have classified an important class of irreducible representations of GL(2) over local fields called Principal Series. We also tried to give a taste of Langlands Correspondence to the reader. First we explain preliminaries and introduce locally profinite groups and their smooth representations. Then we classify representations of GL2(F) when F is finite. Then we study GL2(F) when F is a local field. Finally we... 

The k-center problem—covering a set of points using k congruent balls with minimum radius—is a well-known clustering model in computer science with a wide range of applications. The k-center is a well known NP-Hard problem. In this thesis, we focus on the k-center problem with outliers in high dimensional data streams. Due to increase in data size, we focus on the data stream model of the problem. Moreover, in real-world applications, where input points are noisy, it is very important to consider outliers. In this thesis, we study 1-center and 2-center with outliers in high dimensional data streams in Euclidean space. We provide a 1:7-approximation streaming algorithm for 1-center with z... 

Szemeredi's theorem is one of the significant theorems in additive combinatorics which was started by Van Der Waerden's theorem in 1927. Erdos and Turan conjectured generalized versions of Van Der Waerden's theorem in several ways included Szemeredi's theorem. In 1975 Szemeredi proved the conjecture using complicated combinatorial methods. In 1977 H. Furstenberg proved Szemeredi's theorem via the Ergodic theory approach which led to prove polynomial Szemeredi's theorem and multi-dimensional Szemeredi's theorem. The Ergodic approach is the only known approach so far to these generalizations of this theorem which is named Ergodic Ramsey theory and led to some other problems in Ergodic theory... 

The value of data transmission has surprisingly increased in the past years. Years ago, transmission of a few by telegraph systems satisfied human needs. But the amount of data transmitted increases exponentially and that is where engineers face real challenges. In the first generation of mobile networks, the voice was transmitted using Analog technology but in the second generation it switched to digital systems. In third and fourth generation systems data rate and quality of service was increased. A big change from the third to fourth generation networks was being an all IP network, meaning everything including voice and data were transmitted in packet switched networks. This creates... 

Poorly damped Low Frequency electromechanical Oscillations (LFOs) confine the capability of power system transmission lines. This phenomenon, which is the result of dynamic interactions among generator groups, may make the system prone to small- signal instability in some cases. Due to the use of some system controllers such as AVRs, these oscillations are inevitable.
Hence, electromechanical modes detection and assessing stability margin are important requirement in power system planning and operation, and can provide significant help to power system operators by preventing stability problems.
From the distant past, in order to monitor small-signal stability, power system operators... 

Nowadays in Iran service providers, are using copper lines in access networks. They rent these lines from a governmental telecommunication company during a complicated and time consuming process. In this thesis, the most common access technologies have been analyzed in order to find an alternative solution for copper lines. Based on the studies in this thesis, it is clear that Wimax technology can be an appropriate solution comparing with Wi-Fi and 3G from the point of quality and speed. The UNIDO methodology has been used in this economical assessment (feasibility study). In this methodology, all the running and fixed costs and revenue as well, have been estimated. In the next step,... 

The present work investigates joining of two MoSi2 parts through Cusil/Zr/Cusil interlayer with Cusil being a commercial eutectic of Ag-Cu alloy. The joining operation was implemented in an inert gas tube furnace by brazing. The brazing temperature ranged at 800-930°C while the operation lasted for 1hr. Interfacial microstructure was studied by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD) techniques. Applying the temperature of 830°C was led to uniform dense joint consisting of various reaction phases with excellent bonding within interfaces. Diffusion of Si to the liquid phase will transform MoSi2 to Mo5Si3 which bears Ag to some... 

The aim of this study is to design a control system for an autonomous underwater vehicle and evaluate this system for different missions. Due to the non-linear behavior of the target robot, both linear and non-linear behavior of the system was studied. Model Predictive control method has been implemented since it can outline both linear and non-linear controllers. The first non-linear dynamics of this robot, maneuvering equipment, and external disturbances (waves and ocean current) were modeled. Then, to design the linear controller, the equations of motion have been linearized around the working point(cruise speed). In order to analyze both designed controllers, various duties have been... 

Considering the importance of maintaining palm trees, this research focuses on the design of a climbing robot utilizing wheels. The goals of this robot include easy installation on the tree, climbing despite variations in trunk diameter and surface irregularities, maintaining static balance to prevent falling in a stationary state, and enabling tree pruning. Additionally, descending from the tree is an essential capability of this robot. For climbing, a rotating wheel and four auxiliary wheels are employed. A motor with a gearbox drives the rotating wheel, while the auxiliary wheels, supported by spring-lock mechanisms, provide the necessary force to prevent slipping and ensure stable... 

Identifying driving behaviors and building an efficient and accurate driving behavior recognition model is of paramount importance for improving driving safety. Nowadays, with the ubiquity of smartphone sensors, many researchers are using smartphone sensory data to create models which forecast driving behaviors. This research introduces a logit model that predicts nine types of driving events using accelerometer and gyroscope sensors with an accuracy of 76 percent  

In majority of the (standalone or grid-connected) PV Systems, predefined rule-based algorithms are utilized in order to manage and control the flow of power. The function of these algorithms is to send the generated energy from solar panels either to load for consumption, or to battery for storage, or to the grid for sale. Their performance is based on predefined instructions and regardless of load change and consumption patterns. Therefore the total efficiency of these systems depend greately upon individual user’s load type and consumption pattern. In current research, an optimum and dynamic energy management algorithm is proposed using dynamic programming (DP) method, in order to increase...