Sharif Digital Repository

This thesis has been done with the goal of comprehensive neutronic calculation of a small size High Temperature Gas Cooled Reactor and HTTR was selected as a reference reactor for simulations. Calculations are divided into four parts of zero and full power stochastic calculations, deterministic calculations and noise analysis. In zero power calculations, an algorithm is proposed for modeling random arrangement of TRISO particles in the fuel compacts of HTTR. The effect of this arrangement on criticality calculations, i.e. effective multiplication factor and critical position of control rods, is then compared with regular arrangement. In the second part, full power calculations with the use... 

Magnesium and its alloys have gained much attention in medical applications, especially bio-degradable stents. However, they have not been used extensively due to their natural limitations, such as weak mechanical properties. WE43 magnesium alloy has gained attention as a bio-alloy due to its high temperature and good corrosion resistance. The present study aims to use a combination of ECAP and direct tube extrusion to fabricate thin wall tubes with good mechanical properties using WE43 magnesium alloy. In the first phase, the ECAP process at 370°C were conducted up to 4 passes on the homogenized samples to reach ultrafine grain structure. Subsequent to ECAP, direct tube extrusion at 230 °C,... 

Batteries have always been used as one of the most important sources of electricity storage and supply. Among different types of batteries, lithium-ion batteries are widely used in various fields and engineering applications due to their high-density energy/power, high discharge/charge rate, and long life. The most common of these applications are using these batteries in all-electric and hybrid vehicles, which reduce environmental problems. Due to the high cost of these types of batteries and the environmental issues of battery decomposition, researchers are seeking to discover long-lasting batteries that lithium titanate oxide batteries have the most extended lifespan among lithium-ion... 

Due to the expansion of web applications, they have been gradually enhanced as to their usage of information and services. As a result, web users are faced with growing complexity, which has raised concerns not only on the quality and validity of information, but also on how the information is presented. This has resulted in the advent of a new branch of web systems called adaptive web systems, which focus on the adaptation of content, presentation and navigation based on the properties of the runtime environment and the preferences of the users. Generally, the concept of adaptivity can be appeared in the fields of non-functional services and requirements. Although this research is only... 

Pile foundations suffered severe damages during the past earthquakes in all around the world. These damages were more severe in laterally spreading grounds and they mostly have been observed in gently sloping grounds and coastal areas. In these cases, Pile foundations not only are subjected to structures inertial loads and kinematic loads of liquefied soil but also lateral spreading intensifies damages. Thus, in the recent decade, several researches have been conducted to investigate the behavior of pile foundations in liquefiable and laterally spreading grounds, however, some uncertainties still remain in modeling of soil-pile interaction. In this study, the effects of liquefaction- induced... 

In this thesis we investigating two models of cancer invasion .First, a general mathematical model of cancer invasion is presented. In this model there are three factors: tumor cell, extracellular matrix and enzyme. The model consists of a parabolic partial differential equation (PDE) describing the evolution of tumor cell density , an ordinary differential equation modeling of extracellular matrix and a parabolic PDE governing the evolution of the matrix degrading enzyme concentration. This model is investigated in two special versions for existence and uniqueness of global solutions. In the first model we neglect the remodeling term, this model is named the chemotaxis-haptotaxis model.... 

EOQ and EPQ models have been among the most important and commonly used techniques for about 100 and 60 years respectively .But, they are involved in some assumptions that sometimes prevent them from being implemented in real situation of industry and production. One of these unrealistic assumptions is that all of items received or produced are of perfect quality. In order to overcome this constraint and make the mentioned models closer to the real environmentsome researches have been done. To this end,following the previous attemptsin this project we assumed to have destructive inspections and existence of imperfect and rejected items after rework. In our models, considering 3 circumstances... 

Mars rover Curiosity is a mobile scientific laboratory which it’s mission is to assess the biological potential of the landing site and characterize the geology of the landing region. This rover communicate to a Mars orbiter named MRO satellite in the UHF band which relies the signals to the Earth stations. Also this rover communicate to the Earth stations directly in the X band. In this thesis, we determine the technical characteristics of stations and simulate Earth-Mars radio links. So we calculate :
1. determine the technical characteristics of Earth stations
2. determine the technical characteristics of satellite and Curiosity
3. Earth-Mars orbital position in the... 

The present study deals with designing controller for Therapeutic Exercise Robots which belongs to larger group namely Rehabilitation robots. Therapeutic exercise robots are often realized in shape of exoskeleton robots. The main line of present research is involved with, designing controller for lower limb therapeutic exercise robots and offering and implementing technical rehabilitation ideas. Firstly, in order to have a reliable position-control, considering practical limitations (e.g. system uncertainties), a robust adaptive control has been designed. Adaptive control can deals with parameters uncertainties and covering unstructured uncertainties (e.g. disturbance and noise) can be... 

Before a construction project gets under way an attempt is made to examine different ways and scenarios for its implementation. Through such a process the more appropriate scenarios should be selected based on several criteria that are not necessarily at the same level in terms of importance. The purpose of this study is to examine different scenarios for implementing operations in the pre-construction phase of a project, based on several competing criteria with different importance levels in order to achieve a more efficient execution plan. This paper presents a new framework that integrates discrete event simulation (DES) and data envelopment analysis (DEA) to rank different scenarios for... 

The need for further improving the operation of the electronic and optoelectronic devices to raise the speed of the circuits, and to decrease their power dissipation, has led many researchers to investigate the structure of 2D material, such as graphene, transition metal dichalcogenides (TMDs) as MoS2, and other 2D compounds such as BN, due to their prominent electronic properties. TMDs have the highest significant potential for the next generation transistors due to their salient semiconductor characteristics such as electron mobility, band gap, and conductivity. For instance, Graphene is a favorable candidate for analog devices due to zero bandgap. Regarding the importance of bandgap in... 

In the last decades, Reaction Time research has been extended to cognitive science and more specifically human information-processing research and has gained momentum (Shim, 1996). The present study examined the reaction time in processing marked and unmarked structures with regard to the four types of conditionals (considered as unmarked, less marked, marked and strongly markedness, respectively) and prepositions (preposition pied piping that is considered as unmarked and preposition stranding as marked). To this end, two softwares were developed for which the items relating to conditionals were chosen from the Bernet’s test (1985) and the ones pertinent to prepositions were taken from...