Sharif Digital Repository

Uranium is the most important element in the nuclear fuel cycle. Recovery of uranium from waste produced at every stage of the fuel cycle is not only economically important, but also environmentally important. In the production phase of uranium hexafluoride, certain amount of solid waste is produced in the bottom of the fluorination reactor. In order to extract the uranium from this waste, we have to eliminate the fluorine contained in the waste. This is because the fluorine forms strong complex with uranyl ions during the extraction process, and prevents from efficient extraction of uranium. In the current thesis؛ first, we examined the characteristics of the waste ... 

Liquefaction of gases is one of the applications of cryogenic science. Among the gases, Helium has the lowest boiling point, which at a pressure of 1atm is approximately 4.2K. Liquid helium can be used to cool superconductors in transportation equipment, military radars, and medical imaging equipment. For helium liquefaction, various cycles are used; these cycles have different parameters in their structure such as of input mass fraction to expanders, heat exchanger effectiveness, expander arrangement and ... which their analysis for improving the performance of the cycle is important. In this research, the aim is to study 2, 3 and 4 expander cycle with various parameters and structure. For... 

Estimation of demand, for example, for transportation is an important issue for the planning and programming of various systems. Thus, enhancing the predictability power of such models is of high value. Demand stems from choices of individuals, and choice is subject to uncertainty and fuzziness. Uncertainty comes from many factors including incomplete information of decision-maker, and fuzziness comes from many other factors including personal perception regarding the value of the variables affecting choice. This study tries to introduce a new approach in building choice models, in which variables are transformed into another variable by the help of a global wisdom. This wisdom shows the... 

As the crowded cities require public transportation and because of lack of space on the ground, Subway and boring underground tunnels encountered. In this thesis the interaction of boring the line 7 of Tehran metro with the existing station of line 1 of Tehran metro (Molavi station) is studied. By changing the soil specification, The surface settlement is significant so the soil specification is one of the important parameters of the interaction. For comparinf the effect of these parameters, the soil settlement and bending moments is investigated in different parts of station while the lower tunnel is passing beneath it. The 3D Abaqus software is used for modeling this interaction. In... 

In Persian language, there are some special uncertainties and complexities regarding the extraction of phonemes due to its flexible structure. In this work, we try to solve two problems caused by this issue, homographs disambiguation and Ezafe recognition in Persian text to speech systems.
In this work, two methods are presented for solving the two problems. The first one is a pattern recognition method based on Aho-Corasick algorithm that has the best performance according to the execution time. The second method is a hidden Markov model tagger based on Viterbi algorithm that uses bigram and trigram statistics. These methods are run on 10 million word corpus and the results are compared... 

Airplanes usually experience minor position change and height loss during cruise flight, but under normal circumstances the aircraft total energy is adequately acceptable to maintain the trajectory and the desired performance without severe oscillations. On the other hand, if the airplane encounters a wind-shear or microburst during take-off or landing phases, it would be a dangerous situation, as the aircraft kinetic and potential energy levels are not as high.
In this research, a model predictive controller is designed and investigated to allow a transport category aircraft to either escape or penetrate the microburst. In this regard, initially a DMC controller is designed for 6-DoF... 

Recently, Needs for construction of rock structures and underground ones such as tunnels, dam foundations, power plants and caverns built to keep oil, gas and nuclear waste has increased dramatically. In order to design, construct and excavate these underground structures safely and economically, full understanding of rock mass properties, suitable tools and practical techniques of drilling are necessary. Because of existing this discontinuities, including joints and layered rock masses and their effects on mechanical behavior of rock mass, it is necessary for the geomechanical profile, shear strength and failure mechanism of rock mass to be accurately indentified. Shear strength criterions... 

Nanopositioning is the technology to control position of the objects with precision of the scale of nanometers. Nowdays, This technology emerged as one of the components of research and production in the micro and nanometer dimensions, helping researches and producers to carry out many state of the art projects. A nanopositioning device, consists of a support to path guidance, an actuator to apply force and motion, a driving circuit for communication with the actuator, a sensor for measuring displacement, a circuit for reading sensor’s data, a controlling algorithm to reach the desired precision, a controlling hardware to enforce controlling logic, a power supply and a graphical user... 

According to the impossible trinity, countries can only enjoy from two of the following choices simultaneously: fixed exchange rate, free capital flow and independent monetary policy. A part of the economics literature has tried to verify the theory empirically. Some of the researches like Klein and Shambugh(2015) has concluded that the trilemma is valid on the occasion of transferring the effect of base countries interest rate changes to other countries. On the other side, a few papers like Ray(2013) has shown that an independent monetary policy can just be obtained by a closed capital flow and a float exchange rate system can not necessarily give central banks the autonomy of monetary... 

In this research, it has been tried to answer jobless growth in Iran’s economy between 2005 to 2011. At first, the added value and employment of various major sectors will be investigated. It will be observed that two major sectors, agriculture and industry, have been experienced jobless growth. After having been investigated more, it will be shown that the major part loss of the job in the agriculture is relating to unwaged family workers. In the industry about all the loss of the job has been happened in the textile sub-sector. In these two sectors, the most of the separated people has been inactive. Getting inactive and not being allocated of the separated people have been led to... 

In this thesis, the collisions of two fluorine-C60 nanoparticles have been studied using molecular dynamics simulation. The main purpose of this thesis is to present a completely new method based on the definition of the vertical and tangential coefficient of restitution, although by using the combination of the simulation and theory results, we can obtain the approximate parameters of physical properties of nanoparticles, such as hardness coefficient, surface tension, friction coefficient, etc.At first, two fluorine C60 under different conditions, including collision velocity, collision angle, initial temperature, initial rotational angle of the molecule, and various potential applications... 

The Brushless Doubly Fed Machine (BDFM) has the potential to be employed either as a motor in drive application or as a generator in variable wind power applications. The Doubly Fed Induction Generator (DFIG) is, currently, the main generator used for wind power applications while it suffers from the existence of slip-ring and brushes. The BDFM can potentially achieve the characteristics such as those of the DFIG while it benefits from the brushless operation.
The dynamic behavior and transient states of BDFM must be analyze so that it can be a rival for DFIG in wind power application and improvement of their behavior under faults. Due to brushless configuration of BDFM, the losses are... 

Nowadays, indoor air quality (IAQ) is a major concern, particularly in cleanrooms where IAQ is controlled to ensure the extreme standards of cleanliness. For this reason, the particles rising from obstacles and distribution inside the indoor environments and cleanrooms are of great importance. In this study, effects of temperature field, releasing height of particles, and obstacle motion on particles rising from the obstacles inside the three-dimensional cleanroom were investigated by Lagrangian and dynamic mesh methods. The results indicated that, the greater the temperature difference between the top surface of the obstacle and airflow, the more the percentage of the particles risen from... 

The purpose of this research is to investigate the residual stresses generates during solidification of a casting part and the effect of casting geometry and thermal treatment conditions on these stresses. The pattern was designed with to arms to ensure tensile tension. CO2 process was used for modeling and due to the high hardness of the mold, it also acts as a constraint and exacerbates the tension. To measure tensions in parts, two methods consist of Hole Drilling, and an innovative method based on heat treatment and dimension change have been used. The results of the two methods show the same values of stress. The Hole Drilling method is a verified and high-precision method, which is... 

Friction stir welding (FSW) is considered a significant manufacturing process for joining of different metals and alloys and usage of this process has been developed in different industries. Accordingly, extensive works have been done on FSW of different engineering materials. However many ambiguous problems related to thermo-mechanical behavior of this process have not been solved yet. This research investigates FSW behavior of a hardenable aluminum alloy, AA2017. Firstly, thermo-mechanical response of the material has been predicted using a three-dimensional finite element analysis performed in ABAQUS software. Then, microstructural events such as grain size, distribution of second phase...