Sharif Digital Repository

In this thesis we study the strongly correlated electron systems and investigate the interply between electron-electron and electron-phonon interactions using a non-perturbative method, known as Dy- namical Mean Field Theory (DMFT). This method is capable of going beyond standard perturbation techniques. DMFT is by construction a local theory which neglects spatial correlations. In a first step, we approach the problem of interplay between these two interactions in the normal state of cuprate materials using the Holstein-Hubbard model. We then introduce orbital degrees of freedom, and study the polaron crossover and the pairing transition for a two-orbital model with Jahn-Teller coupling to a... 

In this project, we have studied the geometric and electronic structures of CdS nano-particles. The bulk CdS is known to be a semiconductor with the experimental energy gap of 2.42eV which is more than twice the theoretical resuls based on LDA or GGA energy functionals used in the density functional theory. However the calculations based on Kohn-Sham formalism used in DFT (KS-DFT) predicts the geometric structure of bulk semiconductors fairly well. Therefore, we have employed the KS-DFT formalism for our CdS nano-particles and have used the Gaussian as well as SIESTA computer codes to predict the geometric structures of these nano-semiconductor-particles. For calculating their electronic... 

It has been five years since the new education system was started, according to which fundamental changes have been applied to school text books. The mentioned changes in the text books are based on “the fundamental transformation document” and “Iran’s national educational curriculum”. In “Iran’s national educational curriculum”, eleven fields concerning pedagogy and learning are explicitly mentioned; one of these eleven fields is “training and learning work and technology”. One of the merits which has been stressed in this field, is “technological thinking”. Nowadays, methods of extending and reinforcing the technological thinking have come to be the subject of investigations in many... 

Diverse methods of producing semi-solid metal have been the subject of extensive study for the past 40 years. Among all these methods, electromagnetic stirring (EMS) and gas induced semi solid (GISS) have been used on a commercial scale. Considering the fact that in previous studies the intensity of electromagnetic field in the central part of the stirring chamber was negligible, a hollow cylinder with an almost pure iron core was utilized in the central part of the chamber in order to intensify the electromagnetic field in the center and to introduce gas bubbles into the melt. Aluminum A356 alloy was stirred by a three phase electromagnetic stirrer and introduction of gas bubbles under... 

The process of energy transfer in quantum systems is an interesting phenomenon due to the emergence of quantum effects . This phenomena can be studied in one of two possible spaces : real space and energy space of the system . In addition , to evaluate how this process is successful , one can define an efficiency as the population of a target state . Finding the approaches to increase this quantity takes into account one of the main objectives of the current researches . On the other hand , isolating the quantum systems from the surrounding environment (bath) in practice is impossible and then interaction between them is inevitable . In this research , we provide a comprehensive... 

In this project we tried to examine the effective variables on rent to price ratio and how the variations in R/P influence households’ decisions. Using rent to price ratio, the efficiency of Housing market has been inspected. However, the results for Tehran are in contrast to efficiency assumptions. Moreover, having access to unique database which remarkably increase the accuracy of our estimation, the relation between rent risks and House price has been examined. The results show that rent fluctuations has positive impact on house price. Rent to Price ratio has different applications and we tried to determine the variables that can explain this ratio. Literature review demonstrate that... 

This thesis deals with a theoretical and experimental investigation of different approaches for reduction of electronic recombination in the semiconductor/Dye interface of dye sensitized solar cells (DSSC) including dye coverage, core-shell structures and energy level distributions. Interface of ZnO/TiO2 in the core-shell structure have been studied by density functional theory and the energy level distribution of surface atoms, recombination and Fermi level changes, open circuit voltage and surface dipole distributions have been discussed.
The presence of TiO2 shell increases the ZnO surface dipole moment, and shifts the ZnO conduction and valence bands to higher energies. Also, it... 

Train scheduling is one of the most complicated stages of railway planning. In this stage, the arrival and departure times of trains at stations are determined. In this thesis, we studied train scheduling on a two-way and single track railway in order to minimize the total travel times of trains subject to a set of operational constraints and prayer time related constraints that determines the optimal station for prayer. In this project, we tried to simulate the real constraints exist in IRAN railway network and the objective function considers customer’s and railway management’s satisfaction, simultaneously. First, a mathematical programming is proposed for this problem. After demonstrating... 

The present ph.D. thesis consists of three sections including the static calculation, neutron noise calculation and neutron noise source unfolding in VVER-1000 reactor core. The multi-group, two dimensional neutron diffusion equations and corresponding adjoint equations are solved in the static calculation. The spatial discretization of equations is based on Galerkin Finite Element Method (GFEM) using unstructured triangle elements generated by Gambit software. The static calculation is performed for both linear and quadratic approximations of shape function; baesd on which results are compared. Using power iteration method for the static calculation, the neutron and adjoint fluxes with the... 

Process of casting with evaporative patterns and unbonded sand is a new method that due to different economic, environmental and technological benefits is considered to large and small industrial parts manufacturing in recent years. Different parameters are effective on the surface and metallurgical quality in this process, such as foam density, sand type and size, level and mode of vibration, sand compaction, coating and pouring time and temperature. If coating permeability that is function of type, thickness and concentration of coating is chosen improper, pyrolysis vapor of foam don’t exit completely and in this condition carbon of vapor deposit on the metal surface and produces defect... 

Nurse scheduling problem has received a great amount of attention during recent years. In this problem number of needed nurses from different skill levels is given for each Location-shift during planning horizon, and the goal is to allocate each nurse to shifts, such that the demand of each location-shift is satisfied. Many researches have been done with the aim of minimizing the number of needed nurses to satisfy the demand of locationshifts or maximizing nurses preferences to work in desired shifts. In this research an integer programming model is proposed to minimize the number of needed nurses and maximize nurses preferences simultaneously. The proposed mathematical model is appropriate... 

In this research the risk of oil price for Iran and Opec basket is studied. Several methods in order to estimate Value at Risk (VaR) such as Standard Historical Simulation, Historical Simulation with Autoregressive Forecast, Historical Simulation with moving average forecast, and ARMA are examined. The experiment is performed based on daily oil prices, from January 2005 to December 2009. The data is divided into two smaller time periods. The first, from 2005 to 2008, was used to estimate the model coefficients. The second part of data, i.e., the data gathered in 2009, was used for forecasting purposes. The result of experiment show that Historical Simulation with Autoregressive Forecasts... 

Wireless mesh networks (WMN) appeared as popular communication networks supporting high speed and high throughput applications. They consist of mesh routers and mesh clients and they have unique characteristics like self organizing and self configuring of the mesh nodes that bring a great deal of efficiency, reliability and robustness to networks and decreases networks maintenance cost notably. Also WMNs provide an integration of different types of wireless networks by exploiting the gateway involvement. One of the important group communication technologies that offers high level of bandwidth conservation and efficiency is multicasting. It also decreases the cost of communication compared to... 

In this thesis, two-level optimal control of uncertain and non-uncertain large-scale systems is presented. In the proposed two-level approach, using a decomposition/coordination framework, the large-scale system is first decomposed into several interactive subsystems, at the first-level, where a smaller optimization problem is solved at each subsystem. At the second-level, a substitution type prediction method, as a coordination strategy, is used to predict the interaction between subsystems. The coordinator mainly evaluates the next update for the coordination parameters and continues to exchange information with the first-level, so that the overall optimum solution is obtained. It is shown... 

Regard to high temperature and using dry fuel in engines with CNG (Compressed Natural Gas), wear problems and instability of valve seat insert (VSI) in these types of engines have been increased. Today some of high alloy steel (consist of Cr,Ni,Co,W,Mo, . . .), Ni-base alloy or Co-base alloy are used in manufacturing VSI. It's clear these materials have high price. In powder metallurgy methods high percentage alloy is used for manufacturing VSI. These are the reasons why casting method for VSI manufacturing has been pleasant to be used.
In this project the cast iron has been used for CNG engine VSI, by adding some elements like Mo,V,W, and Nb. The graphite has been used as solid... 

The analysis of gamma-ray spectra of low resolution detectors is difficult and sometimes impossible, as a result of photo peak’s overlapping. The usual methods of radiation spectra analysis based on fitting of peaks to mathematical curves or detecting of peaks with numerical calculation, are valid for high resolution detectors. However these methods are less successful for lower resolution detectors such as the common scintillators. The wide peaks in the spectrum maybe overlap and make it difficult to analysis. To solve this problem, we test here a method, based on the use of the artificial neural network. At first spectra of elements are converted to the patterns which are suitable for the...