Sharif Digital Repository

The main question of this thesis is if and to what extent does the Social Security retirement benefits cause early retirement. This is important because the more individuals are willing to retire earlier, the larger are the Social Security liabilities to pay the retirement benefts, and also it means that more people are leaving the labor force, hence a lower labor force participation. The research was conducted on a sample of men extracted from the Social Security Or-ganization data sets, employing Option Value and Peak Value models to estiamte a binary choice model. The results indicate that Social Security (in the form of retirement benefits) have a significant effect on retirement ... 

Pricing plays an important and essential role in the profit and income of companies. The importance of pricing is not only related to its role in the company's profitability, but it also changes the customer's understanding and loyalty towards the company and can create the company's reputation or destroy it. Determining the right price will increase product sales and increase customer loyalty and create a competitive advantage for the company. One of the most important and influential variables in product pricing is the amount of demand. The main challenge of companies for product pricing is the uncertainty in their demand. In order to deal with this problem, data-driven pricing is used.... 

One of the major challenges in Additive Manufacturing is the creation of residual stresses due to the high temperature gradient in the solidification zone. This will cause problems such as cracks in the structure, metallurgical defects as well as deformation and dimensional accuracy reduction in the finished product. The purpose of this study is to perform mathematical modeling and computer simulation of the selective laser melting process (SLM) to predict these stresses as well as identify the effective parameters on this phenomenon. The conditions were adjusted in this model with the actual coefficients of the device. Additionally, the powder used in this project is Ti6Al4V material. By... 

Lead-containing solder alloys in particular Sn-37Pb is the most common alloy used in electronics industry, this alloy has the good mechanical properties and excellent wetting properties and low prices. Recently, increasing environmental and health concerns over the toxicity of lead combined with strict legislation to ban the use of lead-based solders have provided an inevitable driving force for the development of lead-free solder alloys. A group of these lead-free solders are nanocomposite solders that because of having the reinforcement nano particles exhibit lots of unique properties, such as good mechanical and thermal properties. The aim of this research produce a new tin base... 

More than 70 weight percentage of using parts in diverse industries (such as military, civil, automobile productions and etc.) are produceed by the casting processes. For each one of the casting procceses, mold cavity is requisite for arrived molten metal in the mold cavity to get eventuated as a solidified part. Based on mold ilk, if the mold is permanent, the cast part must be capable to be remoeved from the the mold inside. For the non-permanent mold (asssuming multi-piece and non-monolithic), if the model requires to be removed from the mold inside after molding and before casting, only model (no cast part) has to be moldable (why for removing the solidified cast part from the... 

Physical and mechanical properties of cast alloys is partly a function of the morphology and volume fraction of phases from freezing. The microstructure of the eutectic solidification is function of physical properties (especially mobility and surface tension) and the volume fraction of phases involved in the evolution. The prediction of solidification microstructures will be very helpful for improving the mechanical properties of casting alloys and designing of new families of alloys. The theoretical study of the formation of eutectic microstructures is very difficult and almost impossible in general cases and empirical studies are expensive. The purpose of this study is to predict the... 

In this thesis, by deliberately embedding “emplacements” in the system to locally break the inversion and the time reversal symmetries, the manifold of all possible microstructures is navigated in pursuit of the one that can give rise to maximal magnetoelectric effect mediated by elastic energy of piezoelectric-piezomagnetic phases via their interface --- needless to mention the low intensity of such an effect in single-phase multiferroics. The configuration with the maximal coupling is sought within the context of phase-field modeling. In order to numerically track the conserved dissipative dynamics of the interface (namely, the Cahn-Hilliard equation) --- that is nonlocal by the nature of... 

During the past decades, structural parameters are used as a tool for studying the formation and evolution of galaxies. Sersic parameter is one of these parameterswhich also known as shape parameter. Sometimes, measuring such parameters depend on the observed wavelength. So far, this dependence has been rarely attended. In this thesis we are trying to know how and why these parameters depend on the wavelength  

Functional design of coating system for the primary mirror of the Iranian National Observatory (INO) is done. This telescope has a 3.4 m primary mirror in diameter, made of Zerodur from Schott. Although similar coating systems are in use since years ago, this is the first attempt to design a system for such a large surface case in Iran. Systematic approach led us first to clarify and identifying the design requirements. Lower limit of 80% for reflectance on all wavelength range from 325-1000 nm, thickness of 100 nm with un-uniformity of 5 nm, adhesion enough to pass the selotape test and surface roughness of less than 8 nm. Study of the available methods for coating and selection of the best... 

Due to the importance of using pure proteins in the industry and basic research in order to study them in the structural contexts and interactions of proteins in recent years, purification methods have been extensively developed. The purification steps usually depend on the size of the protein, its physical and chemical properties, the binding affinity and the biological activity of the protein in question, In the purification process, the protein portion is separated from the non-protein portion. The biggest challenge is when we want to separate different proteins. Different chromatographic methods are used, depending on the properties of the impure proteins. One of these chromatographic... 

bulk metallic glass Unlike metal materials that have a crystalline structure, amorphous glass is an amorphous material with an irregular atomic structure that simultaneously has the same physical properties as metals. Due to the absence of crystal defects such as dislocation and grain boundaries, these materials show unique mechanical properties such as high strength and elastic strain, abrasion resistance and proper corrosion. However, their plastic deformation is heterogeneous, concentrated, and accompanied by sudden failure. Unlike metals, these materials do not have a long-range crystalline order, and their atomic structure includes short-range and mid-range order. The short-range order... 

The luminosity gap between the two brightest galaxies of the galaxy groups and clusters is a statistics criteria for studying the time of the formation of these gravitational systems. So far, the luminosity gap of galaxy systems is studied in local universe (z~0). This parameter is a good criteria to understand the structure formation models. In this project we investigate the evolution of luminosity gap statistic in high redshift universe (z~0.4). The evolution of luminosity with redshift is a proper tool for investigating the evolution of galaxies in different environments during the time  

We study the fundamental and the photometric plane of a sample of 50 dwarf galaxies within the core of Coma cluster observed with DEIMOS on Keck II down to R-band luminosity of -15 Magnitudes. The Calcium triplet lines in the wavelength range between 7500 to 10,000 ˚A, allow us to obtain the velocity dispersion for the sample galaxies with high precision. We also performed a comprehensive error analysis to better estimate the uncertainties of this key observable. We also carried out a galaxy structure modeling using the ACS I-band images for a larger sample. We found larger velocity dispersions for fainter dwarfs than what expected from mass-luminosity trends of brighter Coma galaxies. In... 

Continuous casting is one of the ingot production methods in which the product has uniform chemical structure, low defects and high production rates. These days, carbon steel and nonferrous alloys are mainly produced by this special method. The design of continuous casting process includes a lot of difficulties due to its technological complexity. One of the most important aspects of this process is the heat transfer during solidification. In the present study, a new mathematical model and its corresponding numerical solution method have been introduced to establish the condition of directional solidification along the major ingot’s axis. The controlling parameters used in the model are... 

The current study is dedicated to free vibration and buckling analysis of thick FGM conical shells conveying hot flows with the consideration of initial geometric imperfections. To this end, the higher order governing equations of motion and the corresponding boundary conditions are derived using Hamiltonian formulations. Due to the solution procedure of Frobenius series expansion, the differential form of equations is obtained by applying by part integration to the integral form of equations of motion. Radial and longitudinal temperature distributions are considered while pressure distribution and geometric imperfection variations are found to be in longitudinal direction, only. The final... 

The present study aims at investigating the stability of flexible spinning cylinders conveying flow in an external fluid Medium. Using the linearized Navier-Stokes equations for the flow, a two-dimensional model is developed governing the fluid motion. The resultant force exerted on the flexible cylinder wall due to the fluid interactions is calculated as a function of the lateral acceleration. Applying the Hamilton principle, the governing equations of flexural vibration of the rotary flexible cylinder mounted on simply supported axles are derived. Having the forces due to the conveying fluid calculated and substituting into the governing equations, a coupled field governing equations of... 

The purpose of this study is to develop the reduced order nonlinear modeling of single cell closed section thin walled composite beams. In this way, global behavior of one dimensional beam under axial load, bending and torsional moment is produced. This model is based on the classical lamination theory, and the nonlinear model is developedby usingthe von-karman strains. In this process the effects of material anisotropy and axial warping are considered. Numerical results are obtained for thin-walledcomposites box beams, addressing the effects of fiber angle and laminate stacking sequence. The nonlinear model is compared with theoretical results of homogeneous beams and the natural... 

This study aims at investigating the vibration analysis and stability of Graphene Nano-Ribbon (GNR) under a magnetic field using continuum mechanics approach and an efficient hybrid modal-molecular dynamics method. The force distribution on the GNR due to the magnetic field is determined by Maxwell's equations, Biot-savart law, magnetic dipoles and Lorentz force law.
Using the continuum mechanics model, the vibration of the GNR in a magnetic field is investigated by some problems and the resonance frequencies, stability boundaries and critical load are studied.
Furthermore, in this present study, an efficient hybrid modal-molecular dynamics method is developed for the vibration...