Sharif Digital Repository

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... 

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... 

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  

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... 

Nowadays binary sensors such as infrared sensors are vastly employed in industrial, commercial and general applications due to their simplicity and low price. Beam sensors are common type of these sensors which can detect objects when they cross its beam. Sequence of sensors which are crossed in a time order is called sensor word. Consider an object, produced sensor word shows the order which it has crossed the beams. If we have more than one object then sensor word is combination of all sensor words produced by all object. We need to separate each sensor word. In this research, sensor word is developed to Fixed-Charge Minimum Cost Maximum Flow Network type.In this case, the consequent... 

In present thesis, the effect of cosmological constant, Λ, in bending of light by spherical symmetric mass has been studied. At first we obtain the Schwarzschild-de Sitter solution as spherical symmetric solution of General relativity field equations with cosmological constant, without we suppose the solution is static. Then we obtain gravitational lens equation by considering the space geometry and we benefited from several approach to specify the contribution of cosmological constant to the deflection angle. Furthermore we put new upper bounds on the value of the lambda independently of cosmological constraints. Finally for study the contribution of lambda in gravitational lensing... 

Gravitational lensing affects not only the position and number of images of cosmic objects but also their shapes. In the so-called weak gravitational lensing effects related to shape of the cosmic objects are studied. These require high quality images and wide field of view. Because of technology development and production of multi-chip CCD cameras in recent decades, we are witnessing an increase in the number of projects using weak lensing techniques. Taking instrumental errors into account, the first step in weak lensing studies should be the proper data reduction to produce final images in which instrumental errors are removed and have sufficient precision to be processed. In This thesis... 

In recent years, the use of embedded processors has grown increasingly in wide range of computer systems; so that most of manufactured CPUs are used in emebedded systems many of which are safty-critical systems such as medical devices, aircraft flight control, space systems, nuclear systems, etc. The incidence of failure in these systems can cause irreversible damages on human life, financial or environmental matters. Silicon process technology trends, such as reducing the threshold voltage, increasing the frequency and decreasing the size of transistors, not only caused increase in single-bit fault rate but also caused occurance of multi-bit faults. Due to importance ofcorrect operation of... 

We have tried this for the first time to reperesent a comprehensive description of the evolution of a perfect fluid in inhomogeneous relativistic models.We solve Einstein equations using numerical methods.In this procedure we can evaluate the effect of pressure in perfect fluid evolution.Also we look at the behavior of the various horizons, and in the end we will present a cosmological model to a black hole  

In this research, steady state and transient performance of a single spool axial turbojet engine (without afterburner) is studied. Performance maps of main components such as; compressor, combustor and turbine are extracted from a similarity (geometry independent) approach.Then using nested loops method, steady state model of the turbojet engine is developed and using shaft dynamics and volume packing equations, transient model of the turbojet engine is analyzed. Steady state and transient simulations results of an engine are validated by experimental data and then effect of changes on input parameters such as; polar moment of inertia, Mach number, fuel heating value, pressure and... 

Over the past two decades, several studies have been investigated on synthesis and properties of semi-conductor quantum dots because of their applications in sensors, LEDs, detectors, solar cells, etc. One of challenging issues in synthesizing these nano-particles is their size distribution. In this study, Cadmium Selenide was synthesized by the method of colloidal synthesis. X-ray diffraction showed that the crystalline nano-particles have wurtzite structure. For obtaining a uniform size distribution, effect of various parameters such as molar ratio of components and reaction temperature on the growth kinetics of these particles, were studied. Results showed that molar ratio of Selenium to... 

Studing the Scattering Amplitudes has a crucial importance in Quantum Field Theory; and nowadays; there have been many progress in computing these observables: Scattering amplitudes respect the symmetries of a theory: However; it is possible for them to have more symmetries than ones can be seen from the lagrangian of the theory: On the other hand; Feynman diagrams which manifest the locality and unitarity of the theory are not applicable in these kind of theories; since for computing the easiest scattering amplitudes thousends of these diagrams must be computed: In this work; we are going to see using BCFW recursion relation and onshell diagrams how it is easy to compute the scattering... 

In the most cosmological models which already have putted forth, metric has a spherical symmetry; however, according to the galaxy’s shape is not a real approximation. In order to build a more acqurate model, by applying a particular conformal transformation on the static vacuum solution, we introduce a new metric which is axially symmetric and also it approaches to FLRW metric at space infinity. The cosmological model according to this metric has especial features;The solution we have found represent a spacetime which is axially symmetric although it leads to a spherically symmetric Einstein tensor. Therefore, we have found a solution of Einstein equations representing a spherically...