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 ... 

With regard to recent progress in decreasing of operating temperature of Solid Oxide Fuel Cell (SOFC), metallic interconnect use widely than ceramic interconnect. Metallic interconnect have interested due to their low cost, easy fabrication and high electronic and thermal conductivity.oxidation resistance of metals is big challenge, because of low conductivity of formed oxide layers that led to increasing of electrical conductivity. Ferritic stainless steel is among the most thriving candidate alloy because of BCC structure that its coefficient of temperature expansion is close to that of other SOFC. Nonetheless, the increase of electrical resistance over the time and the evaporation of... 

Dynamic response of structures, against ground motion, is one of the most important issues in earthquake engineering. A variety of approaches and apparatus have been developed for this purpose. One of these equipments is metallic dampers. Such apparatuses provide damping, accompanied with reasonably strong lateral stiffness; hence, they are named as “Added Damping And Stiffness” (ADAS). The present study aims to evaluate the performance of a common metal damper consisted of triangular metal plates known as “Triangular Added Damping And Stiffness” (TADAS). In this investigation, the performance of TADAS, in an eight story irregular in plan steel structure, is extensively considered. A 3-D... 

The amount of water entering the dam is one of the types of information that has a direct impact on how to plan the discharge and storage of the dam's water supply. Given the precise input streamflow predictions of the next few days, the corresponding authorities can better manage the amount of water that should remain in the storage in the days to come. In this regard, it is no longer necessary to release huge amounts of stored water due to the lack of information on the volume of water entering. Consequently, the volume of water stored in the reservoir, increases. Also, the probability of occurrence of potential hazards such as dam overflow is prevented.Over the last few years, due to the... 

In the present study, the concentration of lithium in Iranian brines was investigated and studied using the electrodialysis method. First, the desired electrodialysis cell and unit were designed and fabricated. Then, by performing electrodialysis tests on three different samples of artificial brines with varying ion concentrations, the best and most suitable concentration for use in the process was determined. Then, in the two sections of experimental and designed experiments using Minitab software and the full factorial method, the concentration and separation of lithium ions from monovalent and divalent cations present in brines were examined. The results indicate that at medium voltages... 

With the increase in the number of regulatory agencies and the proliferation of the idea of regulatory state since the second half of the 20th century, regulators have become one of the important pillars of governance systems. In Iran, the communication market can be considered one of the leading markets in having a modern regulatory body. This thesis deals with the evaluation and analysis of the situation of Iran's communications regulator. In the descriptive layer, relying on regulatory governance literature, we examine Iran's communications regulator from the perspective of institutional indicators of independence, accountability, and tools. We argue that the characteristics of regulators... 

Art is one of the most dynamic and turbulent areas of human life; Where the artist sees his work as creation and every moment puts a new curtain in front of man. But these artistic creations do not all meet the same fate. Some make noise; But they pass very soon and do not leave a trace of themselves in anyone's mind and heart. Some others capture many lives and remain in the historical memory of people. What is the secret of this difference? To answer this question, the current research focuses on the field of music. We want to answer the question of how some innovations in the field of music fit in the mind of the audience and some of them disappear in a short period of time and are... 

Conformal Field Theory provides an efficient method for studying physical problems in critical point. Correlation length becomes converge in this point. It can also be clarified that some curves are observed in geometrical phase transition which are conformal invariant and they can be studied using SLE(k). The first mathematical generalization of SLE(k) while keeping the self-similarity property, leads to SLE(k,p). Conformal field theory and SLE are interrelated and their parameters are interpretable for each other. One usually studies the problem in the upper-half plane. Here we consider the problem using a map like (w=L/π Ln z) between the upper-half plane and a special region (e.g. a... 

Achieving low group velocity of light can result progress in many fields. In this project by using complex time domain frequency, achieving method to zero group velocity is proposed. The proposed structures in this thesis consist of two lossless and lossy structures which by considering the modes with complex time frequency are excitable. Using leaky modes to analyze these structures, made them suitable as they can be excited from free space. Using slow light can lead to optimized devices because of the more interaction of light and matter which besides smaller devices too. Additionally slow light is being considered in designing optical memories, quantum computers, optical processors and... 

Saline and fresh water lakes comprise a high proportion of the surface water resources and take effects from climate, hydrological, geomorphological changes and human activities in their basins. Variation in area of lakes causes changes in weather and local climate of their basins. Due to high environmental value of lakes and their particular effects on the ecosystem of the region, they have been always center of attention. Lake Urmia as the greatest lake in IRAN and the second largest saline lake in the world always has been considered by many researchers. In recent years Lake Urmia has had many changes such as decrease in area and level. Various factors such as climate change, periodic... 

The problem of inferring a graph from a set of graph signals over it plays a crucial role in the field of Graph Signal Processing (GSP). When provided with a graph that best models the structure of data, the GSP algorithms can offer high data processing capability. However, a meaningful graph of data is not always available, hence in some applications, the graph needs to be learned from the data itself. When the data is corrupted and missing, this task becomes even more challenging. In this paper, we present a graph learning algorithm that is capable of learning the underlying structure of data from an incomplete and noisy dataset of graph signals. We propose an algorithm that jointly... 

A power plant cooling tower is like a tower, which needs to be studied very carefully from the aerodynamics point of view. Both the aerodynamics forces on the plume and intake stram are affected by the local winds and the performance of cooling tower decreases. There is a symmetric turbulent flow through the cooling tower if there is no. Wind blowing creates different vorticies, which appear in the lower section of the tower. Their periodic and wuick movments causes deficiency in towers performance and efficiency. Additionally there is wind effect on the plane of cooling tower and this causes a chocked plume which is named Wind Cover. The objective of this study is to decrease the adverse... 

In this research, we studied the effect of compatibilizer and short glass fiber on microstructure and mechanical properties of PBT/PC blends. Fisrt, Antioxidants and sodium pyrophosphate dibasic were used to suppress transesterification in PBT/PC Blend. The results showed that best composition occur when both of them are used. In the next step, we used 3%wt MBS (methyl methacrylate-butadiene-styrene) and saw that this weight percent of this compatibilizer doesn’t useful. Moreover addition of short glass fiber to PBT/PC was examined and the results showed that mechanical properties of composite are extensively increased. Also in this step, we proved this idea that we can replace some of PBT... 

Seismic resistant structural systems or lateral load-bearing systems must enjoy adequate resistance and hardness against lateral forces and displacements in addition to resisting large deformations to absorb and dissipate energy. Since Iran is located in a seismic area and almost all metropolises of Iran are located in the vicinity of faults, it is critically important to pay close attention to development and application of efficient seismic systems in the constructional system of Iran. The HKB (Hat Knee Bracing) system is a lateral load-bearing system, the construction of which is inspired from divergent bracing systems. In other words, as in... 

In this research, coating with polymer solution was considered for improve the surface adhesion of natural jute fibers with polymer matrix. This coating was performed by two polymers, polyurethane and polystyrene, in order to create compatibility between natural fibers and unsaturated polyester resin. Impregnation and coating of fibers were done by dissolving these polymers in a suitable solvent and creating a thin coating on the fibers. 2%, 5% and 10% solutions of each polymer were prepared for impregnating fibers and the pultrusion process of the resulting fibers was performed using unsaturated polyester resin. The polyurethane were not compatible with jute fibers and caused a loss of... 

The poor economic performance of natural resource abundant countries has been studied for a long time and in order to alleviate this problem some different solutions are suggested by economists. One stream among these solutions are those focusing on the distribution mechanism of natural resource revenues and the ownership of these resources. In this study, it is intended to address the effect of change in the ownership of natural resources on politicians’ behavior and people welfare by using political economy approach. Also the optimal share of people from natural resources as a function of political and economic institutions is discussed. In this study, it is shown theoretically that under... 

Articular cartilage is devoid of blood vessels, lymphatics, and nerves which gives it a very limited intrinsic healing and repair capabilities. Being under constant harsh biomechanical environment, makes maintaining the health of articular cartilage a vital principle in having healthy joints. Tissue engineering as a method for regeneration of damaged tissue have attracted a lot of attention. Articular cartilage engineered scaffolds act as a macro scale drug delivery system which in addition to having a good mechanical properties similar to that of cartilage tissue, have to provide a highly porous environment for cell migration and proliferation. The aim of this study is to fabricate a drug... 

As a connective tissue devoid of blood vessels, lymphatics, and nerves, articular cartilage has limited self-repair capabilities. This is because essential nutrients and signals necessary for cell proliferation are restricted. Despite advances in therapeutic approaches, complete repair of damaged cartilage remains a major challenge in medicine. Tissue engineering has attracted considerable attention as a novel approach for the repair of damaged tissues, including cartilage. In this study, a temperature-sensitive and injectable hydrogel based on chitosan-bacterial nanocellulose and silk fibroin was designed and optimized for controlled release of quercetin. After selecting a constant ratio of... 

The importance of housing, as one of the most important consumable and investable household goods, is not hidden from anyone. The cost of housing (which can include the cost of renting a property, the cost of repaying a purchase loan, or the opportunity cost of its purchase capital) is a large part of the consumption basket expenses of households. Housing is considered the biggest asset of many Iranian households. As a result, access to an accurate prediction with the least error becomes doubly important for Iranian families. In addition to households, knowing the factors affecting the equilibrium price and estimation of housing valuation for governments (a useful tool for fair taxation) and... 

Self-Assembly (SA) plays a critical role in the formation of different phenomena in nature. This phenomenon can be defined as an arrangement of meaningful patterns with the aggregate behavior of simpler structures. One of the examples of Self-Assembly can be considered of the formation of ice crystals from ice molecules. Previous works mainly focus on graph grammar and self-assembly in fully observable environments. These algorithms mainly consist of two main stages: first, constructing simpler structures and then joining these simpler structures to form a complex structure. The challenges of the previous work can be considered as the necessity of a central controller in the formation of...