Sharif Digital Repository

Let M be a closed manifold, oriented manifold of dimension -d. Let be the space of smooth loops in M. Chas and Sullivan defined a product on the homology H⋆(LM) of degree -d. They then investigated other structure that this product induces including a Batalin-Vilkovisky structure, and a lie algebra structure, and a lie algebra structure on the S1 equivariant homology HS1 ⋆ (LM). This algebraic structure as well as the others came under the general heading of the string topology of M  

In this research, a new step-by-step and comprehensive method for the design of back-to-back converters in the presence of nonlinear and constant power loads is proposed. Common methods for the design and control of back-to-back converters consider the design procedure independent of the linearity and dynamic of the load, also, the control system design and performance of the load-side and grid-side inverters of back-to-back converters are assumed to be independent of each other which is shown in this thesis that this assumption is not valid in the presence of nonlinear loads. These methods result in challenges and problems regarding stability and power quality indices of back-to-back... 

Currently, precision positioning plays a pivotal role in technology. The need for accurate positioning in applications such as robotics, optoelectronics and micro and nano technology increases day by day. To begin with, we wanted to make a miniature prototype of a micro actuator but in this regard, we are faced with several problems. Some major problems were the high cost of this prototype plus the fact that we did not have the necessary equipment with acceptable resolution for making such a system, so we decided to decrease the scale and build it in micro scale which is accessible for us. The main idea and design of this micro actuator is by Mrs. Akbari. During this project, the researcher... 

A structural system will normally fail as a result of a chain of failures of different components. In this thesis, fatigue reliability of fixed offshore platforms is investigated through analyzing different failure scenarios. In order to evaluate the occurrence probability of a special scenario, each failure scenario is divided into a finite number of sub-scenarios. To do this, all combinations of time sequences are generated for a given sequence of failures, using a specially developed program.
In order to calculate the occurrence probability of each scenario, a massive reliability analysis should be done for each of corresponding sub-scenarios. Knowing that there are a large number of... 

In today’s world, large internet companies carry a lot of data. The tests with low triggering rate are designed for causal inference. By regarding the economic scale of Internet companies and high decision -making speeds, it is essential to use variance reduction methods to estimate the causal effect of treatment with sufficient precision. To this goal, the trigger- dilute analysis method is designed and used. When it comes to partial triggering, the stimulation analysis method loses its efficiency, so a new replacement method is designed in which an unbiased estimation along with the reduction of variance is presented to estimate ITT within one-way experiments. This method is based on the... 

In the process of extraction and refining of crude oil, a considerable amount of waste water are produced and if they are not removed, they would become one of the most hazardous environmental factors. Furthermore, purification and separation of such wastewaters are extremely costly, which with an increase in separation efficiency can lead to a decrease in valuable product loss. On the other hand, in the extraction process from oil reservoirs, because of porous and permeable nature of them, solid particles may be added to the extracted crude oil, which can result in an obstruction in pipelines and transport equipment.The most conventional method for separating a mixture of water, oil, and... 

Osteoarthritis is one of the most common cartilage-destroying diseases that causes pain and inflammation in joints such as the knee. Intra-articular sustained-release drug delivery systems are effective strategies to prevent the side effects of systemic drug use on other organs, control the rate of drug release at the injection site, and reduce the number of injections during treatment. In this study, polycaprolactone microparticles containing triamcinolone acetonide drug (TA-loaded PCL MPs) by single emulsion solvent evaporation method. In order to investigate the effect of two variables of polymer molecular mass and also the ratio of drug to polymer on particle size and drug encapsulation... 

Membrane bioreactors (MBRs) which are commonly understood as the combination of membrane filtration and biological treatment using activated sludge have several advantages, but membrane fouling reduces the membrane efficiency, permeability and lifetime. An alternative is replacing a moving bed biofilm reactor (MBBR) with the activated sludge system which may reduce the effect of membrane fouling. The sludge produced in MBBRs has poor settling characteristics, therefore, their efficiency is limited by the sedimentation tank performance and they require a larger settling surface. The combination of moving bed biofilm reactors and membrane bioreactors can compensate for the drawbacks of both of... 

Fully developed fluid flow and heat transfer is numerically investigated in micro-channels. There are many techniques to intensify heat transfer for internal flows, such as: increasing Reynolds number, extending surface area of channel wall and also disrupting the boundary layer thickness on the wall. Among these, extension wall surface area is a common technique. There are several ways to extend surface area including finned, slotted, chemically etched, grooved as well as porous media adhered wall surface. One other method that we work on it is modifying wall cross-section and usage of uniform suction porous media. The governing equations include the momentum equation of the core region... 

Value at risk of an asset, is the asset’s expected maximum loss for a certain period of time and at a specified confidence level. Value-at-Risk can be calculated in the bank with its inter-nal method or standardized method. when a method have more violation number then bank need to keep more daily capital requirements. under the Basel 2 agreement if the violation of method more than 10 times in year, the Bank uses the standardized method.
There are trade off Between daily capital charge and violations. Therefore, existing methods for calculating the value at risk, usually lead to much daily capital charge or many violations. Studies show with combination of different methods to calculate... 

Journals and conferences in computer science are the major venue for publishing new achievement in the field. It is an expert opinion that a number of top conferences in computer science are even more important than journals. In this work we aim at studying this in terms of citation analysis. To this end, we took 100 top journals and 63 top conferences and extracted their citation graph through Scopus dataset. We then constructed the citation graph in which the nodes were the journals and conferences and the links corresponded to the citations of the papers. We used various measures to rank the nodes in the graph. The ranking methods included Prestige, PageRank, Eigenfactor, HITS and SALSA.... 

The long term evolution (LTE) standard is introduced and developed by the 3rd generation partnership project (3GPP) based on orthogonal frequency division multiplexing (OFDM). OFDM systems, in spite of having many advantages such high performance in bandwidth usage, are very sensitive to inter carrier interference (ICI) as a drawback. In order to prevent ICI, the frequency offset, mainly caused by the miss-match between oscillators' frequency and also between the sampling frequency of the transmitter and the receiver, should be estimated and compensated. Frequency synchronization is a part of the tasks of a synchronizer. In this thesis, main tasks of a synchronizer are illustrated and... 

Value-at-Risk (VaR) is the most commontool for risk management. This tool is used to measure market risk and also used as a basis in determining financial standards for international financial institutions. VaR is the maximum loss of the asset portfolio at the specified confidence level and certain time horizon. Many parametric, nonparametric and semi parametric methods have been invented for VaR estimation. Each one of these methods has its advantages and disadvantages and different methods may perform better in differnet situations.When estimating VaR, we can choose one of these methods or we can combine the VaRs estimated by different methods. There are few researches conducted on VaR...