Sharif Digital Repository

The purpose of this Thesis is designing and constructing of high voltage power supply with very low ripple. Proposed method of this thesis is formed of two sections. In this proposed structure, in first section, structure is on basis of diodes rectifier that has been used for producing main portion of output load energy. Second section uses with aim of regulating of first stage voltage. In attention to existence of noises and available offsets in different sections of proposed circuits, model is basis of two stages structure. Sampling of output voltage by using of resistance divider for main loop of circuit has been done. So noises and offsets available in circuit act as prevented factor... 

Power Inverter or DC to AC voltage converter is one of the most important and widely discussed topics in the world of power electronics and systems such as DC/DC converters. Increasing the switching frequency of the inverter, in addition to its many advantages, also creates challenges that will be addressed in this dissertation. To build a high frequency yet reliable inverter, you need accurate and comprehensive information about the inverter circuitry, parasitic elements, switches and their behavior against fault conditions such as short circuit, protection requirements and etc.In this dissertation, several MOSFET transistors is shorted under various test conditions while parameters... 

The ultra-narrow pulse generator have being used for direct production of pulsed power. One of these structures is being used to make a bipolar pulse and its main feature is the utilization of the real transmission lines (not PFN) with an intricate structure that caused volume to be compressed. It is desired to reach an appropriate design by analyzing the output waveform and its relation to the transmission line parameters. A little piece of work has been done in the past but there were some differences from our anticipations in the waveforms, like pre-pulse, long rise and fall times and overshoot that caused by some non-idealities in the structure. What we have done in this project is to... 

The TWT is highly sensitive to the ripple amplitude of its power supply output voltage. If the amplitude of the output voltage's ripple exceeds a certain limit, the amplitude of the undesired harmonics in the power spectrum of the TWT is greatly increased. Increasing the amplitude of undesired harmonics in the TWT output power spectrum reduces the accuracy and performance of the TWT. Therefore, for optimum TWT performance, a low-ripple power supply is essential. Typically, a low-frequency rectifier or high-frequency switching structure is used to build a high-voltage DC power supply. In this thesis, the different structures of high voltage DC power supplies are studied. Next, by focusing on... 

Mostly, the high voltage DC power supplies have output voltage ripple. In such an applications like power supply of microwave lamps in radar systems, low output voltage ripple is an important point of operational characteristics. On the other hand, measuring the low voltage ripple will be a challenge that can lead to recognize of its reasons and reduce its amplitude. In this thesis, different ways of ripple measurement constraints is described, then a method based on high pass filters for output voltage ripple measurement is implemented. The impact of components tolerance and their parasitic components like shunt parasitic resistance of a capacitor in filter operational characteristics is... 

In this dissertation, initial conditions that cause chaotic movement in the relativistic restricted three body problem was obtained by the fast Lyapunov indicator and the time-frequency analysis. With general relativistic model, we can proceed with more accuracy in the design of stable orbit and this chaotic amplification effect could be used as a novel test of general relativity  

Conveying a successful message within a language profoundly stems from not only a linguistically appropriate utterance, but also a pragmatically appropriate discourse too. Broadly considering various facets of pragmatics, pragmatic assessment has not been potentially brought into perspective, and, as a result, the literature deserves more comprehensive attention. This study, guided by the principles of mixed methods design, pursued three purposes: to inspect the matches and mismatches, to explore rating variations, and to assess the rater consistency between the holistic and analytic rating methods of agreement and disagreement speech acts in L2 by non-native English teachers. To address... 

Today, catalysts have shown the growing applications in chemical industries especially for drug synthesis. Using immobilized heterogeneous catalysts is a sensible way to benefit from advantages of both heterogeneous and homogeneous catalysts. In this regards, homogeneous catalysts are immobilized on to a solid support through various methods. However, low loading amount of homogenous part and subsequently insufficient catalytic activity are main limitations of immobilized heterogeneous catalysts. For this reason, polymeric supports have been introduced to immobilize metal ions or nanoparticles. These polymeric supports not only possess advantages such as anti-corrosive properties, simple... 

Outsourcing is currently a challenging issue in the auto industry. On one hand, outsourcing has be-come a competitive imperative for automakers due to its significant benefits. On the other hand, it involves many aspects of risks that could potentially hurt core competencies of a firm. As such, in the auto industry, it is highly critical to make optimal outsourcing decisions for which an integrated framework offering a holistic view seems quite necessary. In this thesis, based on four fundamental research questions of “Who?”, “What?”, “Whom?” and “How?”, an integrated framework for outsourcing in the auto industry is developed in order to identify effective outsourcing factors and associated... 

The accessibility of broadband Internet to home users has pushed video broadcasting applications up, in the list of most favorite applications in todays Internet. Such applications involve delivering the data which generated in a single sender to a set of users which are scattered around the world. While it was formerly believed that the IP-Multicasting is the mean to provide this kind of services, the trend has altered to the use of Application Layer Multicasting techniques due to their deployment simplicty. Since their advent, Peer to Peer applications has mitigated many problems previously unsolved in the field of communication. File sharing, distributed file systems, distributed data... 

Sustainable management of water resources is an important issue today, because it can play a role in achieving environmental protection and economic prosperity. Lake Urmia is a remarkable ecological system, because it includes a unique habitat with native and migratory species, maintains the temperature balance of the region, prevents the formation of dust in the region and is one of the largest Tourism and recreational destinations and a source of income for many people in the Area. However, over the past two decades, the intensification of agricultural activities, the indiscriminate use of water, and climate fluctuations have put significant pressure on it and have led to a gradual... 

Diffractive optical elements with binary surface profile are of great importance in integrated optical applications. Being easy to fabricate and having high degree of freedom in design, such devices play an outstanding role in optical applications. Specifically, binary (multilevel) lenses are investigated in this dissertation. These lenses are fabricated through conventional IC fabrication methods (lithography, etching, …) and have an acceptable performance and small aberration with proper design. Different scalar and vectorial methods for the analysis of finite aperture diffractive optical elements have been investigated and advantages and disadvantages of each one have been discussed....