Sharif Digital Repository

Transferred Electron Device is a semiconductor device being capable of generating oscillation in microwave frequencies. Applying a bias voltage to the device and putting it in a resonant circuit, a periodic waveform in the output current is observed. The cause of the generation of oscillation in the device is related to the characteristics of velocity-field in the device. In some part of the characteristics, it is observed that increasing the field inside the device causes the velocity of electrons to be reduced. This causes the generation of the negative conductance and the oscillation of the output current under some conditions. The purpose of this thesis is to represent an equivalent... 

This study develops a new framework for the assessment of land subsidence occurrence rate. The proposed framework considers the combined effects of saturated and unsaturated soil behavior. Accordingly, the biot consolidation theory was used for investigating subsidence in the saturated zone while the soil shrinkage curve, i.e., the void ratio-suction curve, was used in the determination of unsaturated zone subsidence. Specifically, groundwater decline and land climate change were used as the main contributing factor in investigating the land subsidence in the saturated and unsaturated zone, respectively. The approach presented in this study is based on using numerical modeling in PLAXIS 2D... 

In the present study, Friction Stir Process (FSP) was used to refine the microstructure of pure commercial copper in order to improve the mechanical properties. Since FSP can be considered as a hot deformation process, theoretical Models were utilized to simulate both thermal history and strain rate distribution. Zener-Hollomon parameter (Z) was then utilized to predict the microstructure of Stir Zone (SZ) which undergoes the Dynamic Recrystallization (DRX). Temperature distribution was formulated and solved by a commercial software COMSOL Multiphysics. Strain rate was analyzed using theoretical models and the codes were written by MATLAB. The predicted grain size was not in a good agreement... 

In this thesis, the problem of locating a source based on the time difference of arrival (TDOA) has been studied and three different methods have been presented to improve the precision of the positioning. The first method is a solution to the least square error (LSE) by utilizing a convex problem. Generally, the mentioned problem is a non-convex problem; however, it is possible to convert it to a convex one by some relaxation in the constraints. By some justifiable and insightful relaxation, not only we obtain a convex problem, but also the exact solution of the main problem is derived. The second method is using high perturbed TDOA measurements which severely affected the localization.... 

Results showed that 9 factors of “Brand Equity”, “Product Quality”, “Service Quality”, “Service Recovery”, “Perceived Value”, “Relationship”, “Employee Satisfaction”, “Physical Environment” and “Distribution Channel” are most effective factors by researchers that have effect on customer satisfaction. Thus, the Macromodel of this research was designed based on these factors. Due to limitations and context of the research, “Service Quality”, “Service Recovery” and “Relationship” were chosen in the final model. Results of questionnaire showed that the 5 parameters of “Service Recovery Speed”, “Reliability”, “Responsiveness”, “Empathy” and “Seller-focused antecedents” was the most important... 

In this project, Dissimilar Friction Stir Welding (FSW) between aluminum alloys (1100-H12 and 5083-O) and Magnesium alloy (AZ31B-O) with 3mm thickness were butt joined. Fusion welding of aluminum/magnesium alloys has failed because of forming much more intermetallic compounds. By using friction stir welded samples, effect of welding parameters such as tool travel speed, tool rotation rate, tool position respect to weld centerline, and sheet position respect to tool direction on mechanical (tensile strength, yield strength and elongation) and microstructural properties of the welds were investigated. After several tests, range of optimum parameters were obtained. In both 1100 and 5083 alloys,... 

Since traffic lights are the only mechanized system at street level, their operation mode affects traffic congestion. Since traffic lights organize vehicles at crossways, the target of traffic light smartification is to reduce waiting time based on the density of traffic flows. There are many topics that work in this field to recognize traffic before making any decision based on traffic. Hence, if it is possible to introduce an algorithm for change static timing and predetermined timing of the traffic lights, it can affect the density of traffic at the large scale. This dissertation introduces an algorithm to reduce traffic congestion using traffic lights and correct timing. In this case,... 

In this thesis, combustion of liquid fuel spray under the condition of hot and diluted oxidizer, has been investigated. To this end, a novel type laboratory-scale test rig was designed to study the physics governing the MILD-Spray combustion conditions with an applied approach. The underlined test rig eliminates the operational problems of its predecessor test stands and is used for a heavier fuel with much more complex chemical composition (kerosene). The test section is axially symmetrical, in which the fuel is injected by a pressure-swirl atomizer in the direction of hot and diluted co-flowing air. With the use of the aforesaid test rig, the effect of variables such as oxygen...