Sharif Digital Repository

In the era of precision cosmology it is desirable to know if the collapse of an overdensity region within a FRW cosmological model leads to a black hole similar to that of Schwarzschild. Even the simple question of an event horizon within a dynamical universe is not a trivial one. This subject of studying collapsing over-densities within an expanding universe is called ”cosmological black holes”. Our aim is to construct such a black hole in the simplest possible scenario and study its similarities and differences to the familiar Schwarzschild one in vacuum. Therefore questions of rotating or charged black holes are not dealt with in our work. We insist, however, that the solution is dynamic... 

One of the main subjects that has been vastly studied recently, is the final fate of Black holes with Hawking radiation. Radiation of a black hole changes the black hole, thus horizons of the black hole will also have dynamics. For a radiating black hole the inward flux of matter and the flux of radiation are two important factors for determining black hole energymomentum tensor that determine dynamics of different kinds of horizons. Quantum flux calculation needs choosing a proper quantum state as vacuum for calculating the expectation value of energy-momentum tensor. In this thesis we have attempted to write a useful reference and we hope it could help the reader to prepare for studying... 

Compact Objects involve White Dwarfs,Neutron Stars and Black Holes which are formed from the gravitational collapse of main sequence stars after their nuclear fuel is finished.The special characteristic of all Compact Objects is that they are high density which requires a vast knowledge of nuclear physics with strong and weak interactions ,electromagnetic and numerical methods.we need general relativistic simulation of stars because the theories are simple and some are not in agreement with observations. studying of astro physical constraints on equation of state ,stability and cooling of Neutron Stars and pulsation of gravitational waves is needed nowadays. in first part of this thesis,we... 

Isolated black holes in equilibrium are intrinsically simple objects: They are much simpler than ordinary matter around us because they can be described by only a few parameters such as their mass, angular momentum, and charge. This simplicity, however, is apparent only because one never has an isolated black hole. Black holes in centers of galaxies or intermediate-mass black holes always have complex distributions of matter around them, such as galactic nuclei, accretion disks, strong magnetic fields, other stars, planets, etc., and are therefore actively interacting with their surroundings. However, even having been removed from all macroscopic objects and fields in space, a black hole... 

There has been a growing interest in studying asymptotically AdS space times given the AdS/CFT conjecture. Among different models finding the one which decribes broader phenomena is important.The importance of a dynamical metric stems from the fact that one can see thermalization in its dual description. We introduce a dynamical metric and study apparent horizon formation and energy evolution as well. We plot its appparent horizion curve and show that it aproaches the static limit within our numerical accuracy. We then review quasi-normal modes of this space time  

Multi-Scale finite volume (MSFV) method have been developed and applied for multiphase flow in porous media. The most important advantage of MSFV method is its computational efficiency. In this thesis we apply and implement this method to porous media simulation. Then, computational parameters such as coarsening ratio, effect of threshold on adaptive computation and different boundary conditions for computing basis functions are investigated. The two difficulties of sMSFV method are problems with high permeability contrast and problems with high course grid aspect ratio which are considered. In standard MSFV (sMSFV) method reduced boundary condition is used to determine the basis and... 

Although general relativity is the underlying assumption in modern cosmology, there are still many simplifying assumptions neglecting higher order general relativistic effects. Given the precision cosmology and future surveys and the amount of data on large scales, higher order relativistic effects are to be taken into account. We will consider two categories of relativistic effects on large scale structures. First, the inhomogeneities between the source and the observer may lead to observable effects neglected so far. As future surveys will probe the universe on large scales, these effects have been the focus of recent studies. The observables being defined first, are cosmic rulers and... 

The Atomic Energy Organization of Iran (AEOI) has launched a program of low level waste management. This program also includes waste produced at Uranium Conversion Facility (UCF) of Esfahan. The liquid waste, which was generated during the operation of plant and concentrated in lagoon, was characterized for the development of the treatment process. The aim of this study was to recovery of uranium content of liquid waste in the lagoon. The recovery of uranium has the advantage of saving this valuable metal and the avoidance of unacceptable discarding solution to the environment. Uranium may be recovered from an aqueous solution by precipitation, solvent extraction and ion exchange.... 

With occurring severe earthquakes, damages of columns in RC buildings can lead to overall failure and collapse. So retrofitting of such columns that do not comply with the design requirements is necessary to prevent such phenomena. A variety of methods has been introduced so far for retrofitting. The key factors in determining the retrofitting methods are being economic and easily implemented in the design. Confining concrete columns with pre-stressed steel strips is a new technique that is simple and economic. Previous experimental experiments have shown that this method can enhance ductility and overall seismic behavior of such columns.
In the present study three and six story frames... 

Digital image analysis of histological datasets is a currently expanding field of research. Histological images are inherently complex in nature and contain a wide variety of visual information. Graph-based methods have recently gained immense popularity, as these methods can effectively describe tissue architecture and provide adequate numeric information for subsequent computer-based analysis. Graphs have the ability to represent spatial arrangements and neighborhood relationships of different tissue components, which are essential characteristics observed visually by pathologists during the investigation of specimens. In this thesis, we proposed an automatic approach for classification... 

Engineering of properties was previously not possible. With the advent of additive manufacturing, it became possible to produce structures with architected microstructures, known as lattice structures. The popularity of these structures, due to their lightweight and tunable properties, has increased the importance of their optimal mechanical analysis. Since direct analysis of these structures is computationally prohibitive due to their high level of detail, homogenization methods have been proposed as an alternative. Since these methods couldn't capture size effects, higher-order homogenization methods were introduced. However, despite their good accuracy, these methods are still rarely used... 

Reinforcement Learning (RL) is a branch of machine learning that tries to improve agent’s behaviour through interaction with environment and receiving reinforcement signal. As the size of environment increases, decision-making would be more difficult and learning time will increase. On of the main approaches for decreasing learning complexity is to define skills. Skill is a behavioural unit consists of primitive actions. Humans learn and use a lot of skills in their life. Walking, eating, passing the door to reach kitchen and going to airport for travelling are examples of such skills that humans utilize them for daily activities. Agent can learn skills once and then uses them in other...