Sharif Digital Repository

In recent years peer-to-peer video streaming systems have become the major alternative for traditional client-server models, and several P2P streaming applications have attracted a large number of users on the Internet. In a mesh based P2P streaming architecture a video stream is portioned into video blocks and each peer pulls these video blocks from its neighbors. Since the uplink bandwidth of each peer is its main constraint in transmission video blocks, efficient block scheduling can play an important role in improving the perceived video quality by peers. Moreover, the granularity of video blocks can have a significant impact on the performance of the system. In this thesis, we propose... 

Decreasing travel time is one of the main goals of passengers in urban areas for which transportation operators use various policies. Among these policies, expanding public transportation facilities is one of the urban planner major purposes. Considering the fact that making these facilities needs great investment, optimize use of the current facilities is valuable. Waiting time in transit station has influence on increasing passengers’ travel time and inconsistency, so coordination between different transit lines is necessary. In this thesis, creating coordination among different transit lines in a transit network by the use of integer programming is studied in the form of two models. In... 

In this thesis, we investigate the problem of OFDM channel estimation exploiting channel sparsity. Due to the sparse nature of the scattering objects, most of wireless multipath channel have a sparse impulse response. Therefore it is possible to use the methods in the field of sparse signal processing for the purpose of estimating such channels for better accuracy, and efficient spectrum usage.
First of all the problem of OFDM channel estimation using scattered pilots is stated. Then the so-called IMAT methods together with the other sparse signal processing methods are used for the purpose of estimating channel nonzero taps. Furthermore, since efficient use of spectrum in... 

The Vehicle Routing Problem with Simultaneous Pick-up and Delivery (VRPSPD) and maximum time for traversing of each tour is a variant of the classical vehicle routing problem (VRP) where clients require simultaneous delivery and pick-up. Deliveries are supplied from a single depot at the beginning of the vehicle’s service, while pick-up loads are taken to the same depot at the conclusion of the service. Also the required time for traversing each route should not encroach the specified limit.
In this research, the aforesaid problem was introduced and a mixed integer programming model developed for it. Because of being NP-Hard and impossibility of solving it in the large instances, two... 

There are many applications for micro aerial vehicles (MAV) and in nature they are flying as birds and insects. It can be said that a MAV that can mimic flying capabilities of birds and insects can be used as a solution for flying in low Reynolds number regimes. It seems that Flapping Wing MAVs have better performance than fixed and rotary wings MAV in low Reynolds number regimes. So far there haven’t been many theories and methods introduced for controlling flapping wing MAVs and many researches failed to provide a convenient way for designing an effective controller. On the other hand, models presented in literature for aerodynamics, dynamics and kinematics of flapping wing are not... 

A statistically-based method has been developed for automated identification of steady state. The method is computationally inexpensive when compared to conventional techniques. The R-statistic is dimensionless and independent of the measurement level. Because it is a ratio of estimated variances, it is also independent of the process variance. Simulations show that for recommended critical values are also effectively independent of the magnitude and distribution of the noise.
A fuzzy-logic-based methodology for on-line steady state and transient state identification is introduced. Although steady state identification is complicated by the presence of noise, fuzzy logic can help capture... 

In this work steady state and dynamic performances of quaternary distillation column sequences designed based on steady state and dynamic cost functions have been investigated. To quantify the dynamic performance, product loss due to disturbances has been considered in the objective function. In addition, variations of operating costs such as utilities have been considered in the objective function. To separate a quaternary mixture into four products, twenty two configurations have been used. It has been observed that the feed composition, disturbance frequency and magnitude affect the dynamic behavior strongly. To decrease the optimization computational load, a scheme that provides a... 

Design, analysis and practical implementation of the filter trust-region algorithms are investigated. First, we introduce two filter trust-region algorithms for solving the unconstrained optimization problem. These algorithms belong to two different class of optimization algorithms: (1) The monotone class, and (2) The non-monotone class. We prove the global convergence of the sequence of the iterates generated by the new algorithms to the first and second order critical points. Then, we propose a filter trust-region algorithm for solving bound constrained optimization problems and show that the algorithm converges to a first order critical point. Moreover, we address some well known... 

In this dissertation, we design channel access strategies for opportunistic spectrum access in cognitive radio networks. It is assumed that the secondary transmitter and receiver hop across spectrum opportunities synchronously. This synchronization between the transmitter and the receiver can be separated in two phases: In the first phase, two Secondary Users (SUs) meet each other for the first time in a spectrum opportunity and exchange control messages. In the second phase, two SUs hop across available channels to transfer data. Rendezvous algorithm can facilitate the first meeting of two SUs. For the first phase, we propose a blind rendezvous algorithm and study its features. We show that... 

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  

QSAR studies play an important role in drug design and lead optimization by developing a mathematical relationship between the chemical structures of compounds and their biological activities.By using such an approach one could predict the activities of newly designed compounds before a decision is made whether these compounds should be really synthesized or tested. The main aim of the present work was to develop a QSAR model for predicting the inhibitory activity of acetyl CoA carboxylase (ACC)derivatives as anti-diabetic inhibitors. Since variable selection is a critical step in every QSAR study, four different algorithms, based on Monte Carlo cross-validation techniques, were... 

An implementation of Digital Section of a DVB-T receiver has been introduced in this research. Nowadays, low-power and area-efficient designs have proven their importance in IC design aspect, so many low-power and area efficient approaches have been considered in this implementation. This design has been segregated into independent blocks, and each of them has been designed respect to the design goals. After that, all these blocks linked together and a whole system design implemented in gate level, then downloaded into a FPGA (Field programmable Gate Array) to test the timing and functionality of implemented blocks. In this thesis, some innovations have been introduced. A new algorithm for... 

There are a lot of Fractured reservoirs around the world that have large portion of oil production. These reservoirs have complex structure and fractures have important role in production but the remaining oil in matrix causes that the oil recovery decreases. One of the most important factors in these reservois are wettability. Because most of the fractured reservoirs are oil wet and water injection process in these reservoirs are not effective and chemical EOR methods such as surfactant flooding method is used. Surfactant improve oil recovery by two reasons: 1- reduction of interfacial tension between oil and water . 2-Wettability alteration of matrix. The porpose of this project is... 

The efficient scheduling of independent and sequential tasks on distributed and heterogeneous computing resources within grid computing environments is an NP-complete problem. Therefore, using heuristic approaches to solve the scheduling problem is a very common and also acceptable method in these environments. In this thesis, a new task scheduling algorithm based on bee colony optimization approach is proposed. The algorithm uses artificial bees to appropriately schedule the submitted tasks to the grid resources. Applying the proposed algorithm to the grid computing environments, the maximum delay and finish times of the tasks are reduced.Furthermore, the total makespan of the environment... 

Project scheduling is one of the branches in operations research and management sciences fields. Different goals have been considered in project scheduling, but financial goals are one of the most important criterions in this research area. The project with the conditions considered in this thesis is an NP-Hard problem and solving it in real size problems is only possible with heuristic or meta- heuristic methods. This research deals with the Project Procurement scheduling, considering warehouse space constraint. The purpose of this research is to minimize the total cost of this problem by determining the optimal activity start time and material ordering schedule subject to constraints. We... 

In this Thesis pricing has been used in Job-shop scheduling problem in detailed scheduling point of view. Also, in this study, due date is price-dependent variable in wich the manufacturer has the ability to choose one item from some pairs of prices and due dates for every jobs in order to maximize the total profit, i.e. revenue less scheduling cost. In this problem, total weighted tardiness has been choosen for scheduling cost. In this research, pairs of prices and due dates has been studied. According to the complexity of this problem, a Genetic algorithm has been proposed to solving the problem. As a managerial insight, it shown that joint optimization of pricing and scheduling decisions... 

In this research, we introduce a semi-supervised manifold regularization framework for hu- man pose estimation. Here we aim the three major challenges in discriminative human pose estimation. We utilize the unlabeled data to reduce the need to labeled data and compen- sate for the complexities in the input space. We model the underlying manifold by a nearest neighbor graph. Due to depth ambiguity which is the main challenge in this problem, the true underlying manifold of the data bends and gets too close to itself is some areas which results in poor graph construction. To solve this problem, we argue that the optimal graph is a subgraph of the k-nearest neighbor graph and employ an... 

Simulation optimization has been one of the most important topics in recent years. It is especially useful when the objective function cannot be computed directly or some of the parameters are stochastic. Buffer allocation problem is one of the important problems related to production lines. In this problem the objective is to determine the buffers between workstations so that the throughput is maximized. Non-linear and combinatorial nature of the problem, stochastic factors like machine breakdown or processing times and most importantly lack of a distinct relation for the objective function are the reasons of using simulation ... 

Resource sharing is one of the most interesting features of grid computing. These resources can include CPU, main memory, secondry memory, network bandwith, or data. How to allocate these resources to the tasks remains a complex problem in this domain. The concentration of this thesis is on workflow scheduling. In this case, the works are composed of several tasks, in the way that some tasks have control or data dependency with others. In other words, we have to schedule a DAG (Directed Acyclic Graph) representation of tasks on limited proceccing units. The principle of workflow scheduling optimization is to minimize the makespan, but in the economic scheduling, cost reduction beside... 

Nowadays, World is witnessing an epidemic increase in Robotic Concepts and its usage in diverse fields such as Explore and Rescue Missions, Conservation and Guarding of Environments and various Millenarian Applications. While, different Goals like increasing the precision and speed of missions performance, and decreasing the costs have been always the major priorities in design and building robots. One of the best methodologies to achieve aforementioned goals is to replace a highly capable robot with a group of simple and restricted robots. This suggestion is inspired by the nature and lots of its animals, like birds, fishes and insects. These creatures use socializing in order to forage and...