Sharif Digital Repository

Evidently, environment contamination by water insoluble chemicals present at the industrial wastes could bring about catastrophic consequences to the biosphere. Biological based cleaning technologies are commonly considered as a practical remedy to remove these contaminations. In fact, these techniques are founded on the ability of certain microorganisms to degrade the contaminants. It is crystal clear that the availability of contaminants to the microorganisms is an essential parameter determining the final efficiency of the biodegradation process. In practice, the limited solubility of the contaminants in the aqueous phase leads to mass transfer constraints which consequently, decrease the... 

Empirical results in this research show that oil abundance in an economy tends to increase income inequality. Three mechanisms: Trade, civil liberties and imperfections of financial markets can explain this empirical finding, with the first being an alternative explanation for the Dutch disease. Besides, due to the influence it could have on parents underestimating the future costs of their children and because of the rents it produces, Oil abundance could reduce the opportunity cost of having children which results in a higher fertility rate. Moreover, empirical results confirm the negative relation between inequality and growth through the fertility mechanism. Therefore apart from... 

Some firms grow very rapidly, the others much more slowly. In this research we compare the founding strategies of 32 Iranian software industry new ventures that have grown very rapidly with those with much less growth. This study aims to compare these two groups of firms, in order to provide insights into the attributes of rapid-growth software firms founding strategies. Founding strategies, in this research, refers both to the characteristics of the entrepreneurs who establish the firm, and to the decisions regarding initial markets and products. Results indicate that high-growth firms used to have more experienced entrepreneurs (managerial, industry specific, and work experience). In... 

In the present work, Barium Titanate nanoparticles were synthesized by a facile hydrothermal method at 180oC for 4 hours and their sintering behavior was studied. The characterization tests illustrated that the obtained powder was BaTiO3 single phase with excess Ti content from stoichiometric composition. The average particle size of about 50 nm and a narrow particle size distribution was noticed. SEM investigations showed that the samples sintered at temperatures less than 1250oC had plate-like grains. This behavior resulted from twin plates existed in the grains and facetted grain boundaries. At the temperatures more than 1250oC, the grains became polygonal due to the formation of trace... 

Metallurgical initial defects, stress concentration due to change in geometry and induced tensile residual stress during welding create an extraordinary high possibility of fatigue cracks nucleation and propagation in the weld toe region. Despite this, the ever increasing use of welding in offshore, aerospace and automotive industries, as the most applied mechanical joint, has occasioned a very extensive attempt to achieve an in-depth understanding of failure mechanisms and fatigue life improvement techniques of welded joints. Generally, these techniques could be classified into two broad categories. The first consists of methods that modify the geometry and the other is related to the... 

Most countries regard to parameters such as equipment, cost, facilities, manpower, geographical conditions and environmental regulations select one (or combination) of the methods of burning in incinerators and burial in the landfill for municipal solid waste management. Both methods have undesirable environmental effects and are dangerous. Composting is another proposed option for solid waste management that is more consistent with the environment. In this process, different bacterial species transfer organic materials under aerobic conditions to the products such as CO2, H2O, minerals and compost. One of the effective and economical method for solid waste management is vermicomposting... 

Findings of economics in last decade shows that social and economic institutions have direct influence on economic performance of a society. However, these institutions are determined by the state. In different regimes, the political power is in the hand of different social groups with different preferences and goals; as a result, different social and economic policies and institutions are take place in different political regimes. In this research, we study economic performance of a society under control of two different political regimes: in first, the majority rules the state and in second, there is a totalitarian regime in which; the political power is concentrated in hand of a group of... 

In last decades as the international volume of trade increased significantly, examination of the relationship between trade and economic growth is one of the interesting topics for economists and policymakers. Trade can affect performance of economics by many channels, such as trade specialization, human and physical capital accumulation, knowledge and technology transfer. In this regard the aim of this thesis is the examination of trade specialization in industries with high productivity (as one of the trade influences) effects on economic growth.In this research based on Hausmann et al. (2006), we use an economic model with two sectors: modern and traditional. This model gives a primary... 

Polycaprolactone (PCL) scaffolds and its composites containing bioactive glass particles (45S5) and TiO2 nanostructures with pre-defined and controlled external and internal architecture were prepared via an indirect three-dimensional (3D) printing process. The scaffolds had an interconnected structure with macro- (400-500 μm) and micro- (~25 μm) pores. Bioactivity, mechanical behavior and kinetics of tissue growth in 3D scaffolds were studied. The size effect of biogactive glass particles (6 μm, 250 nm, <100 nm) and morphology of titania nanostructures (spherical, tube, leaf-like, and flower-like particles) were elaborated. The biogactive glass particles with different sizes were prepared... 

We study the Abelian Sandpile Model and its relation with surface growth. ese two models are related through their field theories and equations of motion. It has been shown that the different features of different sandpile models can be expressed in terms of the noise term in the surface growth equation. A mapping between the simplest sandpile model, the BTW model, and a surface growth has already been introduced. is surface growth has not been studied in details so far. In this thesis we study different features of this surface growth corresponding to the BTW model, continuous sandpile model and also massive abelian sandpile model. We also consider different boundary conditions  

One of the most important issues in welding is residual stresses. It is desirable to produce less residual stresses when possible and to reduce them which remain in the structure. At the present, various methods have been developed to reduce the residual stresses. The most important methods are heat treatment, shot peening, and grinding. The main problem in using these methods is cost, and for large structures these methods are often impractical. In recent decades, a technique called vibratory stress relief has been developed. It is used for large structures without limitation of size and weight; besides, the cost of this process is much less in comparison with other conventional methods... 

In this project, bioleaching has been investigated as a solution for detoxification and metal recovery of spent hydrocracking catalysts of Tehran petroleum refinery which is listed as a hazardous waste. In this project four stages has been accomplished as follows: 1- Adaptation of Penicillium simplicissimum and Aspergillus niger with different heavy metals present in a spent hydrocracking catalyst, individually and with mixture of metals as well as adaptation by spent catalyst which the cumulative action of multi-metals enhanced the toxic effect; 2- The one-step, two-step, and spent medium bioleaching of the spent catalyst by the adapted fungi in batch cultures were investigated and... 

In this thesis, following a short introduction to investment problem, this problem is investigated with both probabilistic and universal approach. Using the concept of the set of reference algorithms, we present a mathematical definition for universality. We then give examples of universal algorithms for investment and prove their universality. These algorithms are:
Universal Portfolios without Side Information, Universal Portfolios with Side Information, Universal Portfolios with Semi-Constant Rebalanced Portfolio, Universal Portfolios with Switching.
We then present a new algorithm called “Universal Portfolio with Multiple Side Information Sources”. This algorithm is applied in... 

Edwards-Wilkinson’s equation can be achieved from a Hamiltonian. When we have the Hamiltonian for the system, there are common approaches that makes it out of critical. In other words,the ”mass” should be added to the system. In this study we have tried to simulate and solve analytically these models that are involved mass term. We try to onstruct these mass terms in a way that have a minimum impact on the system and we study the quantities that characterize the out of critical behaviors  

The number of GPS satellites, which are spent their life and work, have been increasingly on the rise. Hence with knowledge of debris numbers, we can get an estimate of collisions risk probability and functional interference of active satellites in the future time. In this study, by using three methods, least-squares, RBF and ANFIS and statistical data the growth pattern of retired satellite numbers has been expected in the future. Numbers estimated by curve fitting methods in 2014 have been compared to the number of satellites disabled and growth estimation error has been analyzed by two models. Solar activity, the sun's radiation incidence angle on the satellite solar panel and the Earth's... 

In this study, Tehran Stock Exchange market has been studied over a period of five years, and not only return of Simple Momentum Strategy but also returns of several Enhanced Momentum Strategies are calculated and compared with each other. The results obtained in this study are so different from the results obtained previously. For instance, unlike results of the previous researches, Simple Momentum Strategy had no significant return while the Contrarian Strategy yielded considerable return. Some elements in the Enhanced Momentum Strategies improved its performance while some others have worsened it. For example, low book to market value weakened the return of Momentum Strategy and... 

In this Thesis, the behaviour of stell brace was studied in finite element models. In this section, a comparison between the results of these models and the results of experimental models which were done in past years, was carried out. It shows that these result is in good agreement with each other, Moreover it has been found that the primary cause of failure in the sample is local bucking and then change in the geometry of sample which will be followed by strain jumping in next cycles which shows the importance of local buckling due to the proximity of this event to strain jumps and can be accepted as braces limit state design.Finally, we try to predict the time of failure of samples with... 

A significant part of the power system energy losses occurs in the distribution transformers. The high loss share of these transformers in yearly electric energy losses of the country’s power network contributes to about 8% of the 20% total national electric energy losses. On the other hand due to the high rate of yearly increase in electric energy usage in the country, optimal distribution transformer planning and sizing pays an important role in reduction of these losses in the coming years. To address these concerns, the distribution companies should optimize the utilization of electric energy sources which results in an increase in their profits. This thesis introduces a new detailed... 

Steel Concentrically Braced Frames are common lateral load resisting frames. Poor design of this system can lead it to premature failure of braces. This failure may be due to non-elastic buckling of brace members or their connections. Design Codes divide Concentrically Braced frames into two groups: Ordinary Concentrically Braced Frames and Special Concentrically Braced Frames and for each, specific limitations have been determined for width to thickness ration and slenderness. Many of these limitation have been obtained on the basis of experimental tests. In this thesis steel braces behavior under cyclic loading is studied. For parametric investigation, Finite Element Method is used. Abaqus...