Sharif Digital Repository

In this thesis, first, random lasing in a three dimensional disordered medium has been simulated using FDTD method and some properties of random lasers which were observed by others in the previous experiments have theoretically been shown. Our simulation results show that when the density of particles increases to an upper limit, the intensity of lasing modes is enhanced. Also, the effects of pumping rate and particle size on the number of lasing modes and their intensity are studied. Lasing threshold of laser modes in different disordered systems is calculated and it is shown that by an appropriate selection of the central frequency of gain line-shape, the output power intensity of random... 

The focus of this thesis is the computation of the discrepancy for any given distribution of points on S2. The problem of the distribution of points on the sphere has a long history and Thomson’s Problem, inspired by early atomic theory dating back to 1904, was a landmark. While Thomson’s Problem is based on the Coulomb potential, the discrepancy measures the deviation of the number of points in a set from the expected one. The Polar Coordinates method was introduced in the context of Thomson’s problem. In this thesis the order of the growth of the discrepancy for this method is investigated and a modification of it is shown to lead to the best known results. In addition a new algorithm is... 

Many of natural porous media, especially oil reservoirs, have strong heterogeneities that span a wide range of scales. These heterogeneities are manifested in the form of strong variations in the permeability field. These variations can be of several orders of magnitude within a small distance. Therefore, the flow in porous media is a multiscale Phenomenon. Due to prohibitive size of input data, numerical simulation of such problems needs extremely large computer memory and computational time, which can be impractical in some cases. In recent years, multiscale methods as a powerful tool have been employed to tackle this problem. In present study, a family of non-iterative Multiscale Finite... 

In this study, using the correspondence principle and Laplace transform, the results obtained in the elastic medium for the Eshelby inclusion problem are expanded into the linear viscoelastic medium. The simplicity and breadth of application of the correspondence principle is so great that it enables one to obtain closed-form solutions in Laplace domain for problems that have closed form solutions in elastic media. However, in complex problems, the long formulas lead the user to apply numerical methods to perform inverse Laplace transform. First, by taking advantage of Green’s function the strain and stress fields are obtained in Laplace domain for the points lying inside and outside of an... 

In recent years, GPUs have become a popular choice for high-performance general-purpose systems. However, since general-purpose applications do not always utilize processing and memory resources efficiently, energy consumption in these systems has not been managed effectively. As the variety of resources within GPUs continues to increase, the problem of low utilization has become more critical. Past solutions have focused on integrating resources and using multi-tasking, but these methods have limitations in terms of performance and security. Therefore, this research proposes new methods for improving the resource utilization and energy efficiency of GPUs. This dissertation first examines...