Sharif Digital Repository

In this thesis, we analyze and compare switching and CPSP cryptography systems. CPSP is a dynamic system which can act as synchronized or self-synchronized stream cipher under specific conditions. To do the comparison, first we have a brief review of cryptography fundamentals like stream cipher systems, synchronized stream ciphers, and self-synchronized ones. Then, we consider chaos systems in general form and then we present their role in cryptography systems, and in continue by introducing switching cryptography systems and also CPSP cryptography systems, and analyzing their relation with self-synchronized stream ciphers, we do our statistical tests on them  

The application of biocatalysts in organic reactions refers to the use of enzymes, purified or crude, to increase the reaction rate. The usage of biocatalysts in organic reactions have many advantages, including biocompatibility, ease of separation, high yield, reusability without losing activity, high selectivity, and the use of water as the solvent. Furthermore, the carbon–carbon bond formation is one of the most important reactions in the synthesis of organic compounds, drugs, and biomolecules. Using enzymes in organic reactions can provide insightful information about the enzymes catalytic activities and paves the way for systematic investigation of their mechanisms. The enzymes... 

In recent years, the emergence of semi-supervised learning methods has broadened the scope of machine learning, especially for pattern classification. Besides obviating the need for experts to label the data, efficient use of unlabeled data causes a significant improvement in supervised learning methods in many applications. With the advent of statistical learning theory in the late 80's, and the emergence of the concept of regularization, kernel learning has always been in deep concentration. In recent years, semi-supervised kernel learning, which is a combination of the two above-mentioned viewpoints, has been considered greatly.
Large number of dimensions of the input data along with... 

Portfolio generating functions are positive twice continuously differentiable functions of the common or ranked market weights. The return on such portfolios related to the market with a stochastic differential equation that has two components: the logarithmic change in the value of the generating function, and a drift process that is of bounded variation. The goal of this study is to generalized portfolio generating functions theorem for ’ functions, in order to cover some important functions in economic such as Gini coefficients  

With intensified concerns of rising fuel vehicles that reduce fossil fuel globally and also prescript strict rules by standard institutes, vehicle manufacturers try to find a way for reducing the fuel of their products. One these methods use a continuously variable transmission (CVT) instead of manual and automatic gearboxes. Various CVT’s have been proposed in recent year.
One of the proposed systems is traction infinitely variable transmission (TIVT) that is type of traction drive continuously variable transmission and has been presented in 2007. Research on this system showed that average efficiency is about 96% that is high efficiency. Completed research in 2011 showed that despite... 

The investigations on hydrophobic surfaces have attracted lots of intrests in science and technology. Silica sols have been used extensively in the area of producing hydrophobic coatings. On the other hand, carbon-based materials have attracted of a great deal of scientific interest in recent years. The purpose of this research is synthesis and investigation on the properties of Silica- Graphene Oxide nanocomposite coating.Graphene Oxide synthesized by using Hummer’s method. Silica nanoparticles were prepared using sol-gel process and tetraethylorthosilicate (TEOS) as precursor. The surface hydroxyl groups of silica nanoparticles are replaced with Methyl groups by treatment with... 

Hyderogels are hydrophilic polymers with three dimensional network structure, due to their high water absoption, their application to life and industry is increasing from day to day, such as tissue engineering, actuators and sensors, drug delivery and therapeutic treatment. In this project, it has been attempted to produce polyacrylamide/alginate double network hydrogels with the use of graphene oxide nanosheets to indicate that it is possible to combine toughness and self-healing in a hydrogel with the opposite nature of each other. To evaluate mechanical properties, uniaxial tensile test and loading-unloading test were used. The results indicate that increase the weight ratio of acrylamide... 

In recent decades, many building projects have been implemented in the form of partnership agreements between the land owners and the private contractors, investing in the buildings’ construction. The growing trend of implementing such projects is due to the increased price of land and the constructors’ inability to separately buy a piece of land and implement their individual building projects. On the other hand, many owners cannot afford the construction cost of building projects. At present, this form of building partnership agreement arranged and concluded between the landowner and the contractor is not normally signed through balanced and thoroughly thought contract documents. This... 

In this thesis we study one of the applications of algebraic topology to computer science and define some tools to analyze concurrent programs. For this purpose a geometric space is corresponded to every concurrent program and a partial order is considered on this space, so every path on it corresponds to an execution of the program. Some of these paths which are dihomotop (homotop in partial ordered spaces) with each other induce the same execution of the program. By defining “Fundamental Category” in which objects are points of the space and morphisms are dihomotopy classes, the space that should be analyzed shrinks to a smaller one. By defining component category in the next step, without... 

In accomplishment of knowledge management in real world, organization can be in different processes of awareness about importance of knowledge management and its achievements. Recognition of strength and weakness points of organization helps to logical planning and success in performance of knowledge management. For avoiding from failing in knowledge management projects, it is necessary that before stating for project performance, evaluate development level of organization from viewpoint of knowledge management, and determine some approaches for control of general problems of knowledge management, like abundance of information, work complexities, knowledge Storage.
In literature of... 

In modern society, engineers, technical managers are responsible for planning, design, construction, exploitation of simplest to most complex systems. Crashes cause disruption of systems at different levels and can be considered as a serious threat to society and the environment, thus consumers and people expect reliable products and systems. There are different methods for increasing the reliability of systems, one of them is related to their quality and another way is related to use of standby systems. Also maintenance and repairing have major role for keeping up reliability or availability of systems. In the first part of project, optimization the reliability of system by standby... 

Aluminum alloys have many applications in various industries such as automotive and aerospace due to their high strength to weight ratio. Today, much research is being done on the strength of metals and alloys after severe plastic deformation. Among these studies, limited work has been done on the hot deformation behavior of alloys that have undergone a severe plastic deformation process. In this research, aluminum alloy 2024-O is subjected to various passes under a type of severe plastic deformation process called multi-directional forging. Samples were divided into zero passes (annealed), one pass, three passes and five passes. After preparing pressure samples from them, hot pressure with... 

In this thesis we study three versions of K−theory. The most well-known vesrsion is topological K−theory, a generalization of Grothendieck works on algebraic varieties to the topological setting by Atyiah and Hirzebruch. Since its birth it has been an indespensible tool in topology,differential geometry and index theory. In the early 1970s C∗−algebraic version of K−theory introduced through associating two abelian groups,K0(A)and K1(A)to a C∗−algebra like A. These functors proved to be a powerful machine, making it possible to calculate the K−theory of a great many C∗−algebras. At last,algebraic K−theory is dealig with linear algebra over a ring R by associating it, a sequence of abelian... 

In this essay, by putting in the framework of linear-quadratic optimal control (LQ),we study and solve the mean-variance portfolio selection problem. Two models will be studied in our work; in one we assume that the price process satisfies a diffusion stochastic differential equation, while in the second model, we assume it to satisfy a jump-diffusion stochastic differential equation. In both models, a formula for the efficient frontier is obtained. This essay is mainly obtained from the works of the following articles and books:
1)X.Y. Zhou and D. Li, Continuous-Time Mean-Variance Portfolio Selection:A Stochastic LQ Framework. Applied Mathematics and Optimization. 42(2000),... 

Using customer relationship management systems has led to the formation of databases containing businesses customer information. Increased competition in the markets, limited resources and high costs of attracting new customers compared to retaining existing customers have made customer retention an inevitable subject for business owners. Meanwhile, insurance companies, which due to their long history have suitable databases of product information and their customers, have resorted to using their databases to manage the relationship with their customers. In this research, while predicting customers churn in health insurance, as one of the most widely used products of domestic insurance... 

This research considers the permutation flowshop scheduling problem with sequence‐dependent set‐up times .In this model, every job has a distinct due date and a tardy penalty rate. A mathematical model is developed for the proposed problem. As it has been proved to be strongly NP‐hard, only small‐size problems can be solved with the mathematical approaches. Thus, a meta heuristic algorithm based on the Particles Swarm Optimization (PSO) algorithm is developed to solve the real size problems. Particle swarm optimization (PSO) has been developing rapidly and has been applied, as it is easily understood and realized. Since the PSO algorithm has been introduced for the continuous solution space,...