Sharif Digital Repository

Efficient processor allocation and job scheduling algorithms are critical if the full computational power of large-scale multicomputers is to be harnessed effectively. Processor allocation is responsible for selecting the set of processors on which parallel jobs are executed, whereas job scheduling is responsible for determining the order in which the jobs are executed. Many processor allocation strategies have been devised for mesh-connected multicomputers and these can be divided into two main categories: contiguous and non-contiguous. In contiguous allocation, jobs are allocated distinct contiguous processor submeshes for the duration of their execution. Such a strategy could lead to high... 

Electromagnetic wave scattering from rough surfaces has been the subject of intensive investigations over the past several decades for its applications in important remote sensing problems. The problem of scattering from random rough surfaces hasn't full analytical closed form solution. In millimeter-wave band some surfaces like asphalt, concrete, which has roughness in millimeter range, must be considered as rough surfaces. A major part of the literatures are specified to numerical and statistical approach. In this thesis the electromagnetic waves scattering from rough surfaces in millimeter-wave band is studied. The main goal of this thesis is to find the available ways for applying the... 

In this thesis the scattering analysis of periodic rough surfaces is studied using the Spectral Finite Difference Time Domain (SFDTD) method. This method takes advantages of both wideband frequency response and stability criterion for all incident angles compared to other methods in solving the periodic problems. In the SFDTD method a wave with Constant Transverse Wavenumber (CTW) is used as the incident wave. As a result, the problem of time delay in periodic boundary is solved and Periodic Boundary Condition (PBC) can be implemented in time domain directly. Periodic rough surfaces are important part of electromagnetic propagation surfaces. Therefore analysis of scattering from these... 

Analysis of periodic structures is an important topic in the electromagnetic wave theory. Also, scattering from rough surfaces is of importance due to its theoretical and practical aspects. Integral equation approaches in combination with the Method of Moments (MoM) are among the most frequently used techniques for solving scattering problems related to rough surfaces due to their flexibility in modeling different geometries. Here, the electromagnetic wave scattering from periodic rough surfaces is carried out using MoM and a closed form Green’s function that accelerates the computation. Different methods, previously proposed to accelerate the convergence of periodic Green’s function are... 

Temperature reduction from room temperature to liquid nitrogen temperature has a significant effect in improvement of semiconductor devices operation such as field effect transistors. Nowadays cryoelectronics as a considerable branch of electronics is concerned by several groups. In order to optimize the procedure of low temperature IC design and fabrication we investigated the temperature effects on different parameters of MOSFET in this thesis. Several transistors in a variety of channel lengths were fabricated in different technology files. Wide measurement experiments were done on these transistors in order to find their drain current vs. drain to source voltage characteristics. From... 

Measuring the human brachial arterial diameter has significant applications in medical research. This is conventionally carried out using ultrasonography which is costly and operator-skill dependent. The objective of this project is to come up with substitute solutions based on optical measurement. Reflectance photoplethysmography (PPG) over the radial artery has been considered to this end. Monte Carlo method has been employed to simulate light propagation in the wrist area, along with a model comprising tissue, artery and bone, made of simple solid geometries. Functions of optical parameters such as refractive index, absorption coefficient, scattering coefficient and anisotropy factor have... 

Non-destructive testing method is for detect specimen flaws such as (crack, porosity, impure, welding defects, corrosion etc.) without destruction the specimen under inspection. Particular characteristic of radiography is an image product from specimen inside under testing where help to identity and better comprehend at flaw nature. Photon scattering is one of important factor to reduce image quality and signal to noise ratio. Scattered photons can due toexistent ingredient in the radiography environment and curvature of material transmission pipe where cause the disorder creation in the radiography images. In this research, pipe radiography simulated using the TIC and TIR radiography... 

The release of toxic materials causes tragic accidents every year. There are various techniques in order to mitigate the release effect of these materials such as Application of air jets, steam curtains and water curtains. In this study first, previous works are reviewed in order to select the best technique for the mitigation of heavy toxic gas release. Then CFD modeling is used to simulate this technique.
A field situation in which chlorine gas was released upwind of water spray was simulated using the open-source software FDS (Fire Dynamic Simulator), a CFD model. Only mechanical effects of water sprays are considered; hence the effect of absorbtion is neglected. Finally tha... 

The application of acoustic waves as a diagnostic tool in medicine is highly regarded. Because of the mechanical and Noninvasive nature of this waves when penetrate in the body will not have any adverse effects on the body. Thus development and operation of these waves is growing every day. If abnormal changes in soft tissues (such as tumors inside the body) is created, by the reflected sound waves easily recognizable although it is experimental, and a little scientific studies have been conducted on the contrast of soft tissue and acoustic waves. Soft tissues of the human body Because of the asymmetric structure has a non-uniform physical and mechanical properties in different directions,... 

Miscible displacement in fluid flowing through a porous medium plays an important role in many environmental and industrial applications; for instance, miscible displacements in enhanced oil recovery processes and pollutant spreading in groundwater. A large number of numerical approaches have been developed to solve the advection-dispersion equation that describes the behavior of miscible displacement in porous media. Most of these numerical models suffer from numerical dispersion. Random walk seems to be an effective method to overcome this problem especially in heterogeneous media. Here, a random walk model was developed and used for simulating miscible displacement in heterogeneous porous... 

By using Mie theory and experimental data for complex refractive index of Au and Ag nanoparticles, the scattering and absorption efficiency of these nanoparticles in silicon medium (crystalline, Polycrystalline and amorphous silicon) was investigated. It was shown that Ag and Au nanoparticles can be used for confine the light, in desired wavelength band, inside the solar cell.The optimum nanoparticle size for using in this kind of solar cells was about 70-80 nm. In amorphous silicon confined photons cannot participate in electron-hole generation so the application of these metal nanoparticles in this kind of solar cells cannot be useful. Also the complex refractive index for equivalent... 

An important and interesting aspect of graphene plasmons (GPs) is their tunability via gating or chemical doping. This property can be used for controlling the propagation of GPs by using spatially non-uniform conductivity profiles in a single flake of graphene. Conductivity patterns are made by locally adjusting the chemical potential of graphene. The chemical potential in turn can be locally tuned by means of chemical doping or gate voltage. Therefore, it is important to know how GPs propagate on a graphene layer with patterned conductivity. In this thesis we will investigate this problem. First, we consider the scattering problem of GPs normally incident on an arbitrary conductivity... 

In the framework of surface elasticity theory, the scattering of in-plane elastic waves by a multicoated nanofiber embedded in an elastic matrix is studied. Atoms near an interface experience a local environment different from it within the bulk. Going from macro to nano dimensions, surface to volume ratio increases significantly. Thus, on this scale it is important to consider the surface/interface properties as well as the bulk properties. In this dissertation, the surface/interface is modeled by a very thin layer in which the traction and displacement are discontinuous. Effects of surface/interface parameters on the dynamic stress concentration factor (DSCF) and scattering cross section... 

Optical coherence tomography is a rapidly evolving imaging technique that enables non-invasive cross-sectional imaging of high-sensitivity semi-transparent samples (poor scattering). The biggest limitation of optical coherence tomography is the low penetration depth (about a few millimeters) in tissue. OCT is based on low-coherence interferometry. In this study, we investigate Michelson and Mach-Zehnder interferometers in OCT set-up and explain the advantages of using Mach-Zehnder interferometers in OCT systems. Furthermore, in this thesis, we have shown that by using Mie scattering, we can have forward scattering, hence the penetration increases. We have suggested this method as a solution... 

In quantum mechanics different states of a system can only be found after a measurement is performed and before the measurement the system may not be in any particular state unless it was prepared in a certain manner. Even so there is no telling the state of system. This behavior raised questions such as: why results of a measurements happen to be in certain states and not in others? And also why an apparatus picks one result over the others? The Decoherence and Transition from quantum to classical behavior may hold the answer to this questions. An example of such transition, one can name the wave-particle duality in double slit experiment. Another example is the formation of straight tracks... 

This thesis analyzes the scattering of a propagating electron from a single bound electron .The study demonstrates how the scattering of the propagating electron from the bound electron causes entanglement between two electrons. The study then considers the impact of spin-dependent scattering in the presence of Hartree and exchange potentials. In the first step, only an exchange potential is studied. Transmission coefficients are calculated for spin-flip and non-spin-flip states by solving the Hamiltonian equation in different regions, applying the continuity boundary conditions for the wave function and its derivative in each region, and using the transfer matrix method. Transmission... 

One of the common methods for cancer treatment is radiotherapy, which is used in combination with other treatment methods, such as surgery and chemotherapy, as one of the fundamental strategies in treating many cancer patients. This approach not only helps achieve more effective results in cancer treatment, but also enables patients to experience fewer side effects compared to other treatment methods and improves their quality of life. Optimization in radiotherapy is the primary step in the process of determining the optimal radiation doses for each patient. This process involves adjusting the intensity and direction of the beams in such a way that provides significant therapeutic benefits...