Sharif Digital Repository

By increasing the use of Internet and sharing information in this platform, servers are equipped with more robust hardware and a wider bandwidth network. But the growth of data and services is such that a server, no matter how powerful, does not have the ability to respond all users! Several servers are used to solve this problem. Data centers, content delivery networks, and so on are emerged depending on types of service. One of the important issues in these systems is how to distribute loads between servers in a proportional manner. In this thesis, we first examine the relationship between cost and response time on user requests. Cost can be considered as a communication cost or financial... 

Although in the network information theory most of results are based on applying random codes, one of the important challenges is to design linear structured codes that achieves the performance close to the performance of random codes. Recently, it is shown that lattice codes can be designed as good codes for quantization and also capacity-achieving in additive white Gaussian noise (AWGN) channel. Due to such a good performance, lattice codes can be designed properly and applied in various problems in network information theory.In this work, we study the performance of lattice codes for the following problems:1. Gaussian multiple access channel (MAC) with state: A joint source channel coding... 

At the molecular level, proteins control almost all the biochemical reactions in the cells. In order for proteins to function, they must be able to fold into their unique 3D structure. Deformation of protein structure due to some environmental phenomena such as pH, high temperature, and stress may cause unfolding of proteins and finally result in formation of protein fibrils called "amyloid". Amyloid has been found in a number of human diseases such as Alzheimer, type II diabetes, and Parkinson. Recently pyridazine has been under spotlight due to its unique chemical properties such as high dipole moment and higher solubility in biological solvents. In this study, we aim at using a... 

Considering atmospheric wave propagation as a complex phenomenon, it can be represented as a function of variety of parameters such as: properties of atmosphere, boundary conditions, surface characteristics, source related parameters and etc. the aim of this work is to study the propagation of sound mechanisms in troposphere layer and numerical simulation of sound field in order to investigate the wind effect and turbulence in wave propagation. In this manner, the Green’s function parabolic equation (GFPE) is hired to solve the governing equation for sound propagation in a moving inhomogeneous atmosphere. To achieve this, a code is generated using MATLAB software to predict the long range... 

With advances in technology, production and propagation of sound waves in the air has become very important. One of the main goals of study of these waves is controlling them. The environment plays the most important role in sound propagation. Therefore, the properties of the environment and their effects should be studied. One such concern studied widespread previously, is porosity and porous media effects on the properties of a fluid flow and sound waves through it. An important application of this study is sound proofing systems. In this project two-dimensional numerical simulation of aeroacoustic waves passing through a porous media is carried out, using Lattice Boltzmann Method. The aim... 

Bubble cluster has attracted the interests of many researches since the early twentieth century. Despite its easy generation and numerous occurrences, its study is extremely complex. Describing the dynamical behavior of bubble clusters is possible when quite a few simplifying assumptions are utilized. In other words, one can observe that with current approaches, the relevant theoretical researches are not very valuable. In this research, however, lattice Boltzmann method, a rather recent mesoscopic approach, was used to study the behavior of bubbles in a bubble cluster. Of course, this is only the beginning and there is a long way before getting close to experimental results. However, there... 

Shock wave–bubble interaction is not yet fully understood, while has many important applications. Such physics for example appears in sonoluminescense phenomenon, wherein a sinusoidal pressure field causes a gas bubble to first become large and then small enough to collapse. In this complex physics, spherical shock wave also appears right before, during, and right after the bubble bursting. On the other hand, modeling the interface between the liquid and gas in such problems, in which the gas becomes compressible is challenging. In this regard, Ghost-Fluid/Front Tracking method has shown to be very practical. In this work, the Euler equations have been computationally solved to simulate the... 

The Phenomena of generation and propagation of pressure waves (e.g. sounds) are of fundamental importance in studying fluid dynamics. Conventional computational fluid dynamics (CFD) simulations has always been part of the investigation. On the other hand, the lattice Boltzmann method (LBM) has been developed into an alternative and promising numerical method for simulating sound propagation in heterogeneous media with complex geometries. In this project, propagation of sound waves in a liquid was simulated, using lattice Boltzmann method (LBM) and particularly phononic model. To survey effect of different viscosities on this phenomenon, the kinematic viscosity of the medium was varied and... 

Troposphere layer includes complex flows which their effects in acoustic sensors are indicated as acoustic wave noise.It is essential to analyze these complex flows to recognize how to reduce the noise. In this thesis we have perused and modeled the sound wave propagation in troposphere layer.Given data are some thermal and velocity profiles of atmospheric flowsthe assumptions are: 1- gravity waves are negligible, 2- air density depends only on altitude, 3- sound waves parabolic equation assumptions are applied. Our goal Is to find the sound pressure level originated from a sound source in troposphere layer.This thesis emphasizes on analysis, recognition and modeling of the problem. Main... 

In the present project, a stringed cavity, specifically the body of the Persian Setar, was studied using computational simulation. This study was carried out via acoustic approaches, based on structural and sound wave interactions. At first, the effects of different structural components were considered, separately. Based on vibrational modal analysis, dynamic characteristics of the elastic structure was investigated in terms of calculated vibrational normal modes. Then, the details of the whole structure was analyzed and the effects of these details on the quality of the produced sounds were investigated by applying some specific changes. The eigenmodes of Setar’s sound board and body, and... 

During various stages of processing uranium in Uranium conversion facility (UCF) in Isfahan, significant amounts of liquid waste is produced which leads to evaporation ponds. Since the concentration of uranium in evaporation ponds is relatively high, it seems to addition to environmental issues with recycled uranium from existing pools is also economically. Various physical and chemical methods for removal of uranium waste is used such as solvent extraction, ion exchange, chemical precipitation, membrane processes, etc. Each method has advantages and disadvantages. The ion exchange method, The due to lower cost, less acid pollution with organic copmpounds, convenience and high selectivity...