Sharif Digital Repository

In this project a knee prostheses wear testing simulator based on a parallel mechanism for applying forces and torques, is designed. First according to ISO 14243 standard required degrees of freedom and design constraints are determined and also regarding simulator requirements some considerations in design are outlined. Considering all of these parameters, literature has been searched for proper parallel mechanism and because no suitable parallel mechanism, which is a 3 DoF 2T1R paralle mechanism with rotational degree about z axis, has been found; several new designs of proper mechanism have been presented. Scoring different mechanisms according to outcomed parameters from standard and... 

As you know in lean supply chains, it is tried to: reduce the wastes of resources and achieve more production with lower consumption of resources. This system is very well suited for many supply chains in which the final determinant factors are price and quality. In contrast, recently, the concept of agile supply chain has been introduced, insisting on flexibility and high service level. Opposite to lean supply chain, agile supply chain needs safety stock to be able to respond to market’s changes.
Regarding the dissimilarities of these models –including the disagreement in the allocation of safety stock to nodes– In this thesis, in addition to studying and comparing these two approaches,... 

Recently, there has been much interest in sparse channel estimation, i.e. recovering a channel which has much less non zero tabs than its length. These channels have been observed in underwater and broadband wireless channels. In the last few years methods available to estimate these channels have used sparse structure information to improve the estimates. However, these methods are vulnerable to noise and interference. In other words, these methods do not use channel posterior information obtained from the received signal and this is detrimental to the estimator performance. In order to solve these problems in this thesis, motivated by CoSAMP algorithm which is a sparse signal processing... 

The standard ΛCDM model is built upon the cosmological principle, which states that the universe is homogeneous and isotropic on large scales (greater than 100 Mpc). A crucial test of this principle involves analyzing the Cosmic Microwave Background (CMB) radiation, which exhibits a dipole anisotropy on the order of ΔT/T∼10^−3. This dipole is commonly interpreted as owing to our motion with respect to the CMB rest frame. A model-independent approach to validate this kinematic hypothesis is to determine the dipole moment in the angular distribution of large-scale structures. According to the cosmological principle, the rest frame of the large-scale structure distribution should align with the... 

The combination of Compton imaging and positron emission tomography, also known as Compton-PET, has gained attention due to its improved spatial resolution and imaging sensitivity compared to PET imaging alone. Compton-PET simulated system consists of two concentric detector rings. The inner ring with a smaller diameter is called the Compton scattering detector, the scatterer, and the outer ring, which has the dual applications of Compton scattering detection and PET detector, is called the absorber. Improving the images is possible by increasing resolution, contrast, and reducing noise, and the quality of nuclear medicine images also depends on these three characteristics. Considering the... 

We study the expected value of stopping times in stochastic processes. Since there is no rigorous solution for computing stopping times in many processes, our approach is based on estimation using well-known methods in the Reinforcement Learning literature. The primary method in this research is the temporal difference algorithm. With some modifications, we can study the role of some state features in determining the stopping time. Moreover, without a complicated mathematical analysis, we can find functions closely enough to the goal function.Furthermore, we compare our proposed algorithm to the well-known regression methods and show our algorithm's advantages and disadvantages. The primary... 

The primary purpose of acidizing operations in the oil and gas industry is to enhance hydrocarbon production. Acidizing has been a common and conventional method for years, especially when production engineers face issues like declining reservoir pressure leading to reduced production rates. Initially, the treatment solution is referred to as matrix acidizing. In acidizing operations, different additives are combined with the acid to control its behavior in the reservoir. These additives may include iron control agents, corrosion inhibitors, friction reducers, and more. Incompatibility among these additives, the acid, and reservoir fluids can lead to severe damage to the reservoir.... 

The goal of this research is the simulation of the annular combustion chamber of the turbine engine utilized by liquid fuel. The achievement to this goal will lead to create numerical tools for parametric study, analysis and combustion chamber designing.For this reason simple geometry has been considered. This simplicity of geometry causes to facilitate in parametric study and decrease in saving time for modeling and meshing. This combustion chamber is a simplified model of engine CF6. In recent study, the k – ε realizable model has been used for turbulence modeling. For non-adiabatic condition, chemical reaction is dissolved by utilizing probability density function along with laminar... 

During the last few years, the study of urban environment structures is considered as a research field of interest in remote sensing. In satellite observations of the earth's surface, continuous imaging in terms of time and space has caused the remote sensing technique to be proposed as a useful and efficient tool for the analysis of urban areas. Obtaining quantitative spatial information from the urban environment in fields such as determining the height of buildings plays an essential role in urban planning, monitoring damage to buildings, establishing communication bases and digital cities. During the last two decades, the use of Tomosar approach in order to reconstruct the structures of... 

In this work, the dynamic competition between firms providing internet services is studied. The framework is Markov equilibrium whereby structural parameters are obtained using two-step estimations, allowing for analyzing the situation in case of subsidies for service upgrade. The results show that such subsidy has little effect on the number of firms while increasing the number of fast firms  

Estimating the price elasticity of gas demand involves complexities depending on the gas market structure and pricing mechanisms in different countries. Distinguishing between supply and demand shocks and block pricing are among the main challenges that can cause endogeneity in elasticity estimates. Iran's domestic gas network, one of the largest and most extensive household gas markets, is divided into five climatic zones based on weather conditions. The pricing steps for these five climates during the five cold months are such that a customer in a warmer climate pays higher prices. Conversely, the pricing steps for the seven warm months are the same for all climates. This policy creates a...