Sharif Digital Repository

The aim of this investigation is the experimental study of nozzle exhaust jet flow effects on aerodynamic behavior of an air vehicle at transonic speeds. For this sake, a secondary jet injection is used by the ejector into test model. The ejector total pressure for jet injection varies between 0 (jet off) to 4 bar for simulating nozzle exhaust jet flow and supplying intake’s required mass flow rate. All tests were conducted at QRC Trisonic wind tunnel and at Mach number of 0.5 to 0.85 and angles of -4 to 6 deg. The aerodynamic force and pressure results were recorded in order to analyze the exhaust jet flow. This study revealed that the aerial vehicle drag becomes bigger than its free flight... 

In this thesis the usage of probabilistic reasoning in collaborative filtering is investigated. The problem of predicting users' rating is formulated as a Bayesian decision problem and a generative probabilistic model is used in order to find the optimal decision. Two different probabilistic models are considered: user based model and rating based model. In user based model prediction of ratings is based on structural learning of Bayesian networks. In rating based model, we assume a predefined Bayesian network represents the joint distribution over model variables and rating prediction is carried out using McMc inference method. MovieLens dataset is chosen to evaluate and compare the results... 

In this thesis, heterogenous catalysts based on magnetic nanoparticles coated with organosilanes and poly(ionic liquids) were synthesized. These catalysts were synthesized by hydrolysis of tetraethyl organosilanes and other organosilicons such as 3-aminopropyl triethoxy silane and polymerization of some monomers in the presence of ionic cross-link agents. The synthesized matrixes were used to stabilize precious metals such as Pd and Au. The magnetic properties of the catalysts aid to easy separation from the reaction medium by an external magnetic field. High thermal stability low toxicity and high-level loading of metals are some beneficiaries of the magnetic catalysts. At the end,... 

Since the classical continuum theory fails to deal with the problems associated with defects, stress concentrators, and relevant deformation phenomena in solids, alternative approaches that can detect the atomistic nature of materials' fracture are required. The deficiency of the capture the size effect which yields delusively high values for some components of the stress field right on the edge of the stress concentrators, and its weakness in describing the complex interaction between small inhomogeneities, cracks and the like when they are only a few nanometers apart, are among some of the disadvantages of the classical approach. In recent years, however, atomistic methods are emerging to... 

Aluminum Bronzes have many applications in marine environments. These alloys suffer from both hot cracking and cold cracking. In order to overcome the hot cracking and cold cracking, Semisolid Stir Joining method and a proper thermal cycle was used respectively. Effects of temperature, stirring rate, and tool type were investigated in Semisolid Stir joining method. In this method, butt joint design was used in order to place specimens, and the specimens were heated up to specific temperatures (920, 925, 930°C). A stirrer (Cylindrical and Grooved tool) with three rotational speeds (800, 1200, 1600 RPM) was introduced into the stir weld seam. Welded specimens were cooled to the 900°C... 

The low female labor force participation rate in the Iranian labor market relative to the global average and even to countries that do not differ significantly from the socio-economic characteristics of our country is one of the important questions of the Iranian labor market. In this study, we seek to answer the question of whether the economic participation rate of married women will increase if the gender gaps in wages, job findings and job losses among women and men are eliminated in the Iranian labor market. To answer this question using household expenditure and income data and labor force data, we show that between the two categories of occupations, in terms of the share of women's... 

Shot peening is a cold-working process commonly used in industry to improve the fatigue performance, stress corrosion resistance and surface nano-crystallization of metallic parts. This process extends fatigue life via two mechanisms: Preventing the crack growth due to compressive residual stresses and, preventing the crack initiation because of increased material hardness. These mechanisms are the results of the bombardment of the component's surface with small spherical particles. In this research, an analytical model is developed for estimating the residual stress distribution induced by shot peening process. The modifications of the developed analytical model are related to...