Sharif Digital Repository

Causality and locality are two of the fundamental problems in physics and physicists have different interpretations of them. In new physics theories like Quantum mechanics and Quantum field theory, the main point of discussion is that whether these two theories are local and causal or not? In first chapter, we introduce the principle of causality. The second and third chapters cover causality in Quantum mechanics and Quantum field theory.The last chapter is about locality  

Nowadays, pile usage in construction of deep foundations has increased significantly, instead of shallow foundation in areas that shallow foundations doesn’t provide enough bearing capacity and measuring the velocity and acceleration due to pile driving is very important. Because, all responses of building and individuals located near the pile driving site influenced by these three parameters: pile vertical displacement, peak particle acceleration (PPA) and peak particle velocity (PPV). One can estimates these important parameters by numerical analysis of pile driving process in different distances and depths to determining the effect of pile driving. Compared values obtained from numerical... 

The continuous rise in electricity demand and the ever growing power generation in different power networks over the world have caused the short circuit level in the power systems to exceed the operational rating of the installed power devices (including cables, circuit breakers and buses). Replacing these devices with new higher rating devices is an expensive solution. From this point of view, utilizing fault current limiters is an economical solution. Superconducting fault current limiters form an efficient category of current limiters. This type is expected to be studied and used widely in future due to their advantages. In this thesis, the first chapter reviews the superconductivity... 

Terahertz waves which includes frequencies between 100 GHz to 10 THz of electromagnetic spectrum have found many applications in science, medical treatments and industry. One of the recent methods to produce these waves is using nonlinear properties of superconductors based on Josephson junctions which inherently appear in some superconductors called BSCCO. Stack of intrinsic junctions of these superconducting materials can radiate terahertz waves by only applying a DC voltage across them. This Thesis investigates some of these structures based on Josephson junctions to produce coherent radiation of terahertz waves. For the optimization of the radiation power, this study also investigates... 

Expert finding in bibliographic networks has received increasing attention in recent years. This task concerns with finding relevant researchers for a given topic. In this thesis, we propose a model to determine authority of authors who have participated in the Communities. This model has a little improvement over community based baseline model. However, due to the low performance of community based models, the proposed authority based model cannot improve the document based baseline models either. Therefore, we try to improve document based models, instead of community based models and have proposed two other models which are based on authors’ topic dominance for expert finding. Document... 

Nowadays, too much attention has been paid to Solid Oxide Fuel Cells (SOFC). One of the key components in SOFC is interconnect which plays an important role in SOFC performance. Interconnect can be either a metallic or ceramic layer that sits between each individual cell. The reduction in operating temperature of SOFC resulted in interests in using metallic interconnectors. However, the oxidation of these metallic materials is big challenge. Chromium (Cr), Nickel (Ni) and Iron (Fe) alloys have been employed to overcome this deficiency. However, these alloys bring another difficulty which is the presence of active elements such as Cr which reduces the performance of interconnects by forming... 

Fullerenes are molecular solid materials which are composed of 3D closed shell carbon-only structure. As soon as mass production of fullerenes was performed, the synthesis and characterization of endohedral fullerenes having at least one non-carbon element in the hollow fullerene cage, was started (in which about 30 atoms inserted in it so far). Furthermore, because of low efficiency and purity of these nano-particles, nowadays characterization of fullerenes is one of the most important research fields. In this project, we firstly optimized the fullerene production parameters in an arc discharge reactor to reach convenient efficiency. Then, the synthesis of endohedral fullerene by vaporizing... 

In the present research, model-based reasoning is introduced and explained based on Giere’s explanation of model. In other word, this research could be regarded as a reconstruction of model in Giere’s books and papers due to prpose a clear explanation of model-based reasoning. In the second chapter, after the introduction, the concept of model in Giere’s distinguished book, “Explainnig Science: A Cognitive Approach” (1988) is introduced and analyzed. In the second chapter, however, the concept of model in Giere’s recent works is traced. “An agent-based account of model” and “focusing on functionality rather than ontology” could be explained as the two important differences between his... 

Micro-rotating machinery with compact energy sources and high power density has been developed in the recent decade to run portable electronic devices. To achieve efficiency targets, these miniaturized turbo-machinery must spin at elevated rotational speeds which sometimes can reach up to one million revolutions per minute. At this relatively high spinning rate, the rotordynamic behavior of these systems plays an important role in the stage of design. On the other hand, the classical continuum theory has been proven not to be able to appropriately predict the mechanical behavior of the small-scale structures. To overcome overall mentioned weakness, in this thesis the rotor of micro-engines...