Sharif Digital Repository

Wireless Sensor Networks have become widespread because of their flexibility, applicability and ability to precept data with high accuracy. However, the most limiting factor in their usage is the amount of available energy in nodes since energy depletion in a node means that it is dead, therefore many efforts have been done for optimum energy management in Wireless Sensor Networks. In many cases, the key solution to prolong the network lifetime is load balancing. In this way, all the nodes will die (approximately) together and the lifetime of network will be maximized. Load balancing can be implemented in all layers from physical layer to application. It should be noted that it is not always... 

In some cases, Mehrotra’s predictor–corrector algorithm might make very small steps in order to keep the iterate in a certain neighborhood of the central path, and thus implying the inefficiency of the algorithm. In this study, a different approach for controlling the iterates on the algorithm is investigated, which was recently introduced by Salahi and Terlaky. The approach is based on postponing the choice of the barrier parameter. To do so, a step size is fixed in the corrector step and then by solving a one dimensional optimization problem, the barrier parameter is computed. Finally, using the computed barrier parameter, the next step is taken. It has already been proved that the new... 

Automatic recognition of input characters and distinguishing image similarities have been of high interest specially as computer systems have become widely popular in industries and businesses. In this thesis, we present a method based on the Frechet distance for automatic character and image recognition. Frechet distance is a measure of similarity between polygon curves. The presented approach in this thesis is based on the work of Maheshvari,et.al.We first provide a literature review on the existing techniques, emphasizing the superior performance of rule-based algorithms, and introducing the different types of Frechet distances based on the characteristics of the input geometry. Then, we... 

Nowadays, solving large-scale unconstrained optimization problems has wide applications in data science and machine learning. Therefore, the development and analysis of efficient algorithms for solving unconstrained optimization problems is of great interest. Line search and trust region are two general frameworks for guaranteeing the convergence of algorithms for solving unconstrained optimization problems. Conjugate gradient (CG) methods and the conjugate residual (CR) balance by Hestenes and Stiefel, have been presented for solving linear systems with symmetric and positive definite coefficient matrices. The basic feature of CR, that is, residual minimization, is important and can be used... 

We describe two modified secant equations proposed by Yuan, Li and Fukushima. First, we study the approach proposed by Andrei. Then, we explain two hybrid conjugate gradient methods for unconstrained optimization problems. The methods are hybridizations of Hestenes-Stiefel and Dai-Yuan conjugate gradient methods. It is shown that one of the algorithms is globally convergent for uniformly convex functions and the other is globally convergent for general functions. Two approaches for computing the initial value of the steplength proposed by Babaie, Fatemi, and Mahdavi-Amiri and Andrei are used for accelerating the performance of the line search. We implement the algorithms and compare the... 

In order to achieve a compromised solution for a multi-objective problem, we make use of the Tchebycheff norm to minimize the distance from the current estimate of the objectives from the ideal point. Solutions obtained from the Tchebycheff approach are weakly efficient for multi-objective problems. For a better solution, the augmented weighted Tchebycheff norm has been proposed. Here, we use the satisficing tradeoff algorithm to solve the augmented weighted Tchebycheff problems. Since the supplier selection problem is usually a multi objective problem, we use the augmented weighted Tchebycheff method for obtaining its solutions. Numerical results are presented illustrating the performance... 

Despite the advantages of shrinking transistors’ dimensions, e.g. decrease in power consumption and fabrication cost and increase in their switching speed, it has an adverse impact on some characteristics of nano-scale (less than 130nm) transistors that can reduce the system lifetime. Bias Temperature Instability (BTI) and Hot Carrier Injection (HCI) are amongst the most important adverse effects of transistor shrinkage. These two effects, are known as transistor aging, decrease the switching speed of the transistors by increasing the threshold voltage and decreasing the charge carriers’ mobility in the channel of transistors. Temperature, operating voltage, and the size of transistors have... 

Power system restoration is the procedure of restoring generators, transmission lines and loads in a minimum time without damaging power system elements. There are different strategies to restore a power system after a blackout. The one that we will introduce here is the build-upward or parallel restoration strategy. In this method power system will be divided into some independent islands firstly and then the restoration process will begin in each island separately and at the same time. The islands then will be connected together to have a complete restored network. The significant advantage of this strategy is minimizing duration of restoration. On the other hand, the use of Wide Area... 

In recent years, stochastic-flow networks (SFNs) have been extensively applied to many problems such as distribution, power transmission, and telecommunication. In quality management and decision making, an important task is to design some performance indices in order to measure the performance of an SFN. The system reliability and unreliability are such two common performance indices.Hitherto, several research works have been conducted for evaluating these two performance indices.One approach for evaluating the reliability of SFNs is determining all the upper or lower boundary points (respectively, UBPs or LBPs).Here, we study four problems to determine: (1) all the UBPs in a two-terminal...