Sharif Digital Repository

First and second law analyses of the pulse tube refrigerator cycle are performed in the present thesis. In this respect, mass, momentum and energy balance equations are employed to derive the system of governing equations. Three models have been resulted depending on the employed theoretical model to analyze the pulse tube and thermal regenerator sections. In the first model, the tube section governing equations have been descritised and finite volume technique has been employed to solve the equations. In the regenerator a linear trend was assumed for the pressure and temperature to complete the solution procedure. To improve the regenerator model, harmonic approximation technique has been... 

Nowadays, video search and retrieval is interesting for computer users and it has chief usages for multimedia systems. Video generation rate has increased and Internet as a communication framework is case of its transferring on the world. Because of these, importance of video files is more than past. Searching for finding content will be faster if video files would have indexed with a comprehensive system. The biggest step in this way is power of index generation that would be same or similar to human mind, for improvement of the clustering’s result or classification’s result. For generating suitable indexes, it is necessary to extracting effective features from videos and synthesizing these... 

Resource sharing is the most important feature of a Grid. Resource discovery enables users to find the most suitable resources to run Grid jobs on. Resource discovery systems are often centralized or hierarchical. These structures are usually prone to a single point of failure, and unbalanced distribution of processing and storage load, making them inefficient as the Grid grows. These challenges have led researchers to adapt distributed approaches, such as Peer-to-Peer file sharing solutions. The important differences between Grid resource discovery and P2P file discovery (e.g. different resource attributes, queries, change patterns etc.) make it difficult to port the existing solutions to... 

In this era, competition in economic fields is undeniable. According to huge amount of foreign trades between countries, economic prosperity of each country causes persuasion of foreign investors to come into that country for investment. Stock Exchanges is one sign of economic prosperity in each country, So prediction of the stock exchanges situation is very important. It is noteworthy that according to the importance of prediction in partial level, the necessity of predicting companies stock price is realized. According to the complicated term in this field, linear methods do not have appropriate efficiency for predicting, so nonlinear methods and especially Artificial Neural Networks are... 

Periodic orbits are one of the basic objects of interest in Dynamical systems. And methods for detecting, counting and determining the periods of periodic orbits are of great interest. In spite of this interest, periodic orbits remain difficult to detect. The most celebrated existence result is the Poincare-Bendixson theorem. Unfortunately, this theorem is false in general for higher dimensional systems. The success of fixed point theory inspired the hope that similar topological techniques could be of use in proving the existence of periodic orbits. In this Thesis we have analyzed some topological and geometrical theories which could be of use in proving the existence of periodic orbits.... 

The detuning of the structures equipped with Tuned Mass Dampers (TMDs) caused by their nonlinear behavior under strong ground motions is a real concern in their practical application. This thesis presents a feasibility study on the effectiveness of TMDs in reducing the seismic response and the resulting structural damage of reinforced concrete structures under intense ground motion. A number of 2-D concrete moment resisting frames with different numbers of stories are considered. TMDs are used as a mean to protect these structural models against ground excitation. The mass of TMDs are varied from 1% to 5% of the first effective modal mass of the structural models. IDARC 2-D program is used... 

Cost Estimation plays an essential and role in UAV (Unmanned Aerial Vehicles) Projects. By increasing the complexity of new unmanned systems, the importance of this task augments. Additionally, up to now, a comprehensive approach has not been adopted internationally. But in parallel a number of international companies and organizations has developed specific methods by themselves; confined to their corporate.
This project pursues developing a complexity-based model for cost estimation of unmanned aerial vehicles, especially Jet UAVs. However, it’s anticipated that this model may be utilized for all kind of systems, but it seems that jet UAVs use it with a better and more reliable... 

In the present study, effects of Post Aeration stage on moving bed biofilm reactor (MBBR) sludge and effluent quality was investigated by simulated wastewater. Reactors Volume were 3.2 and 5.9 Liter and their filling-fraction were 53% and 29%, respectively. All tests were done at 2.5 and 4.6 volume fraction, in which organic loading rates (OLR) were 2, 4, 6 g/L.d and Hydraulic retention times (HRT) were 3 and 6 hours. Increasing in HRT results in bioreactor efficiency improvement, the most efficiency values were found 81% and 84% for MBBR and MBBR-PA respectively at HRT of 6 hours and 53% filling-fraction. The greatest effect of post aeration on organic removal rate was obtained at HRT of 3... 

The phenomena of formation and detachment of droplets are of fundamental importance in studying two-phase flows, such as spraying processes, ink jet printing, emulosin, etc. Droplets are formed under the effects of surface tension forces. After formation, forces like gravity detach the droplet from the rest of the fluid. Recent advancements in computational fluid dynamics and computers have made it feasible to have advancement in simulation of complex flows, including two-phase phenomenon. On the other hand, the lattice Boltzmann method (LBM) has been developed into an alternative and promising numerical scheme for simulating multi-component fluid flows.
In this project, formation and... 

The simplest definition of Total Factor Productivity is the rate of converting inputs to outputs. In other words, with fixed inputs and a raise in the Total Factor Productivity, more output can be achieved. In this study, we review the existing methods for calculating this variable and its determining factors. On the basis of Diewert’s criteria, Fisher index is known to be the most appropriate indicator to calculate production, price and productivity indices. Fisher index is obtained by dividing the index of output to input in which in addition to values of output and input, price data are also used. Between prices and values used in this calculation only price series for wages are not... 

The purpose of this thesis is to find upper bounds for the eigenvalues of natural operators acting on functions on a compact Riemannian man-ifold (M, g) such as the Laplace–Beltrami operator and Laplace-type operators. In the case of the Laplace–Beltrami operator, two aspects are investigated:
The first aspect is to study relationships between the intrinsic geometry and eigenvalues of the Laplace–Beltrami operator. In this regard, we obtain upper bounds depending only on the dimension and a conformal invariant called min-conformal volume. Asymptotically, these bounds are consistent with the Weyl law. They improve previous results by Korevaar and Yang and Yau. The proof relies on the... 

The aim of this thesis is to examine different perspectives on stochastic integrals of fractional Brownian motion. We examine two main perspectives. In the first perspective, we present Mallivan idea in general and in the second idea Riemannian calculus perspective in briefly.In first, we explain basic idea in Mallivan calculus for example Hida spaces, operator δ and we try as ordinary Brownian motion, in this work follow the same trend. The next step, as conventional stochastic integrals Martingle Dob inequality, we introduce torques to find an upper bound for this integral.In Mallivan perspective, we are looking for a formula to maintain Ito formula in a certain space.In the following... 

In recent years, the national health systems have supported the idea of home-based rehabilitation, since receiving cares at hospital environments is too expensive both in money and time. This method reduces the patients’ commuting to the clinics. Moreover, it enables them to practice the prescribed movements at any time.Most of the existing systems compute the patient’s motion performance in a zero-one manner which does not distinguish any small progress in his condition. Thus, a non-task based method which can assess precisely the patient’s level is yet missing. This project aims to develop a set of motion performance indices which can judge the upper limb motions in a home-based... 

Studying the major effects of facility layout on competitive abilities has been a field of interest for researchers. Selection of production layout is amongst the most important decisions because it has a major role on the efficiency of a company like the ability of quick respond to customers’ diverse needs.
In this study we intend to obtain a ranking of production layouts considering agility in production which leads to responding quickly to the diversity of demand. Considering the nature of a decision making problem, we use PSI method. This is a multi attribute decision making method in which there is no need for considering the relative importance between the attributes. The main... 

Various application of polyethylene material in different industries caused to modern techniques for controlling and measuring specifications of micro-particle suspension. Many industries try to increase stability of suspensions in front of their phase separation.
Because of the consequences of suspension homogeneity, at first, we measured this property. Then, the stability was tested by three different methods. In the first method, the transmitted laser light was measured to assay the suspensions stability. In the second, number of sediments of particles was counted. Sedimentation velocity of particles was measured directly by using a horizontal microscope as the third method. The... 

Concentration brings a twofold result to the market. From one side, it reduces the competition and then the number of varieties in the market, which discourages consumption; from another side, however, it reduces the price of goods due to increasing returns to scale and so encourages consumption. This controversial role of concentration raises the question that which degree of concentration might be, say, optimum for the market. Based on the Krugman approach, this study makes a relation between the number of firms, export volume, marginal and average fixed cost of production. We show that when number of firms reduces in the market, export volume could increase because of a reduction in... 

This study aimed at using industrial organization approach for banks and the use of models of determining the market structure and the level of competition in Iran’s banking industry. Models of market structure determination are divided into two categories: structural models that are the same as calculation of concentration indices using market share and non-structural models that are the same as revenue-cost nature of economic enterprises. Structural models have been established based on two theories of structure-conduct-performance (SCP) and efficient structure (ES). The difference between these two perspectives depends on the good or bad nature of concentration in banking services market.... 

Railway managers have strong economic incentive to minimize the cost of track maintenance in order to conserve safety standards and provide adequate service levels for train operators. The main object of this study is to provide a method for railway repairing and maintaining management and improve previous researchs.
In this study, a cumulative damage model based upon a nonhomogeneous Markov process is developed to model track deterioration. The maintenance of deteriorating facilities can be a great challenge because the process of deteriorating has random features for some facilities.
The genetic algorithm is used to find the optimal repair for each possible track state in the... 

Integrated SOFC plants, because of the high efficiency and optimum energy consumption, are important processes that have many applications. According to the importance of these plants, their optimum operability and favorable operations are also very important. One of the ways to optimize the process performance is the suitable selection of the control structures. The objective of this project is to analyze the operability or inherent controllability of integrated SOFC plants in the absence of any controller. In this work, the controllability of the process have been investigated with using the output controllability index and the other indexes such as relative gain array, singular value and...