Sharif Digital Repository

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... 

In this thesis first we will review gravitational lensing and microlensing, then we will introduce all direct and indirect methods for detecting exo-planets. gravitational microlensing is one of these methods in detecting exo-planets. In the second part first we will explain a powerful numerical method for calculating magnification, position and the shape of images by combining of tree code and inverse rays hooting algorithm. Then we simulated the caustic crossing of Hot Jupiters using that algorithm. Finally with performing Monte-Carlo simulation we will obtain the detection efficiency for detecting this class of exo-planets during caustic crossing and we will estimate the number of these... 

In this work we investigate the propagattion of light in inhomogenous cosmic spacetime within general relativity framework. We use Lemaitr-Tolaman-Bondi metric for modeling inhomogenous spacetime. For investigation of gravitational lensing we need to solve geodesic equaions in this model. Beacuse of nonlinearity and complexity of these equations we should apply numerical methods. At first we used Runge-Kutta method with adaptive step size, but beacuse of stiffness of these equaions, the results of this method did not match to approximation methods for low deflection angles. So we try semi-implicit Rosenbrock method. Then for inspection of thin lens approximation for the first time; we... 

Near Horizon Extremal Geometries (NHEG), are geometries which may appear in the near horizon region of the extremal black holes. These geometries have SL(2;R)U(1)n isometry, and constitute a family of solutions to the theory under consideration. In the first part of this report,their thermodynamic properties are reviewed, and their three universal laws are derived. In addition, at the end of the first part, the role of these laws in black hole thermodynamics is presented. In the second part of this thesis, we review building their classical phase space in the Einstein-Hilbert theory. The elements in the NHEG phase space manifold are built by appropriately chosen coordinate transformations of... 

In my Thesis we are going to explain Large Scale Weak Lensing observations by weak field approximation of non-local modified gravity. We try to explain the weak lensing of galaxy clusters after collision without any need to dark matter, which could be an important test of the modified gravity model.One of the important questions of modern cosmology is the nature of dark matter,the concept which was created to explain what ordinary baryonic matter can’t explain.However, one alternative way is to modify Einstein’s General Relativity. One of the main pillars of General Relativity is the locality assumption. Non-local gravity puts aside this assumption. The Newtonian limit of this theory is... 

In this thesis we first discuss the final fate of a spherical symmetric distribution of matter which has undergone a gravitational collapse, by reviewing some classical collapse models. Our emphasis will be on the visibility of singularity after it forms. Then we will mention some general aspects of quantum field theories in curved space-time and after that we investigate the quantum background effects on the evolution of a spherical symmetric and homogeneous distribution of dust. In fact by calculating the quantum corrections—due to massless scalar fields which are arbitrarily coupled to the background geometry— on the geometry of collapsing sphere, one can obtain the quantum corrected... 

When in a binary system one of the stars passes behind another star eclipsing binary will occur and light’s intensity will decrease. Now with assumption that one of its component be Black Hole When another star passes behind of it the star’s light is amplified by Microlensing.With detection of this amplification we can find black hole’s mass. Of course in this phenomenon the degeneracy will be broken completely and we can obtain all of the quantity. From another specification of this event we can call the shortness and repetitive of Einestein’time .The Einestein’s time is approximately a few hours and depending on system’s period this event will be repeated in specific time.Finally Black... 

In this study numerical methods are used for modeling flow and simulation of aerosol transport and deposition in alveolar zone of human lung. The flow modeling is done by FLUENT code, using its moving boundaries feature. For particle tracking we developed a code that uses results of velocity field obtained by FLUENT code. Two-dimensional the axisymmetric model was investigated in this study, and was exhibited that rhythmically expanding walls in alveolar duct model has significant influence on flow patterns and particles transport mechanism. In this study we also developed a three-dimensional model of a single alveolated duct with moving boundaries allowing for the cyclic expansion and... 

One of the biggest challenges facing cosmologists is finding the nature of dark matter. The cosmological observations, like the Rotation Curve, Gravitational Weak Lensing and Cosmic Microwave Background radiation indicate that baryonic matter alone cannot explain the density of matter in the universe. In the context of standard cosmological models, it means that the universe is made of an unknown component(Dark Matter), which aprroximately has 27% of total energy-momentum of the universe. The Modify Gravity and General Relativity are alternative theories that introduced to describe this observation. In This thesis, we introduce the issue of the measurements of accelerated observers in... 

In this thesis by studying the extreme physical conditions near black hole horizons and singularity, we attack intriguing problems in the exciting era of quantum black holes and gravitational wave astronomy. We considered the backreaction of the energy due to quantum fluctuations of the background fields for a Schwarzschild black hole, in semi-classical gravity. We have shown that it results in modification of the horizon and also formation of an inner horizon. The process of the collapse of a thin shell stops before formation of the singularity. After the collapse stops the reverse process takes place. We also demonstrate the existence of a cold remnant for the black hole. We generalized... 

The present work has proposed an integrated methodology for combined gas & electricity distribution network expansion planning, which considers network expansion constraints (substation installation, feeder/pipeline installation, etc), load growth, and conversion technologies. The planning aims to determine the optimal reinforcement of existing energy network to meet the load growth in the planning horizon. To take the advantages of new technologies, CHP, fuel cell, & microturbine have been included in the problem.This paper employs gravitational search algorithm (GSA) to solve multi-objective problem, including minimization of cost, voltage drop, & pressure drop. GSA that introduced in... 

Intensity or phase Modulation of a wavefront is possible by means of optical devices. Placing a grating or lens on the way of a wavefront, will alter the phase or intensity of it and this will make a diffraction pattern. Spatial Light Modulator (SLM) is an optical device which is the most important part of a video projector. One can apply grating, lens and other phases on the wavefront using this device.In this project we used SLM to modify phase of laser beam and then we made many focal points such that they could displace independently. The result of this project can be used in designing and creating a holographic optical tweezers.Moreover, A. Einstein proved that the light could be... 

With the first detection of Gravitational Waves (GWs) in 2015 by the Laser Interferometer Gravitational-Wave Observatory (LIGO), there opened a new window to perceive the universe.Gravitational Waves Astronomy is a new area in cosmology, which its aim is to study the sources of Gravitational Waves, their distribution in the universe and its connection to formation and evolution of structures. In this thesis, we investigate the statistics of background radiation of GWs as a phenomenon in the context of stochastic processes, which radiated form indistinct sources. For this purpose, we will first evaluate the angular distribution function of background radiation of GWs and their relation to the... 

In this thesis, we investigate two subjects in gravitational microlensing. In first part we study wave optics effect in light curve of a binary system. Gravitational lensing occurs when light deflects in a gravitational field. This deflection produces multi-images from real one. In microlensing regime, images can not be detected separately and gravitational lensing appears as magnifying source’s flux . Microlensing has been studied mostly in geometric optics regime. At larger wavelengths, mostly at radio wavelengths, we expect to see the effects of wave optics in microlensing. Stars at radio wave are faint and to detect them we need a powerful radio telescope. In the near future, SKA (Square... 

The standard model of Cosmology known as CDM is established as a cornerstone of modern cosmology. The Cosmic Microwave Background radiation (CMB) and Large Scale Structure (LSS) Observations indicate that almost all observations can be described by a 6-parameter standard model with an initial condition of almost Gaussian, isotropic, scale invariant and adiabatic which can be sourced by inflationary models. Recent observations of Planck collaboration shows almost no deviation from standard picture of single field slow roll inflation. Despite the success of the standard model, the physics of early universe, the nature of dark matter and dark energy is still unknown. The large scale structure... 

The standard model of Cosmology (SM), based on Einstein’s theory of general relativity (GR), is the best model in describing the cosmic-scale observations. In galactic scales, however, galactic dynamics show a discrepancy between the observed luminous mass and the predicted value from the theory. Two approaches are suggested to eliminate this inconsistency: assuming the existence of dark matter within the context of GR, or modifying the theory of gravity in galactic scales, like MOND or MOG. In this thesis, we study the spherical collapse and the formation of shell galaxies in MOG, in comparison with SM. We introduce the action and the field equations of MOG and the equation of motion of a... 

the gravitational wave (GW) which is a prediction of General Relativity has entered a new era after being detected by Ligo observatory in 2015. new discoveries are still being made. the discovery of GW is a new opportunity for studying gravity, astrophysical sources of GWs like binary black-holes or binry neutron stars as well as testing cosmology models.on the other hand, it should be mentioned that the astronomy of gravitational waves is in its dawn stage. in future having numerous precise detectors and by accumulation of data, speaking about exact phenomena and statistical analysis will become meaningful. as in the case of cosmic microwave background physics, in which researchers started... 

A new heuristic controller, called nonlinear model predictive control based on gravitational search algorithm, is proposed for nonlinear systems. Nonlinear model predictive control involves the solution at each sampling instant of a finite horizon optimal control problem subject to nonlinear system dynamics and constraints. The new controller formulates nonlinear model predictive control problem as a single stochastic dynamic optimization problem and uses a system of virtual masses to find the best control signal at each sampling instant. For this purpose, a cost function is defined to evaluate each point of the search space. This function minimizes simultaneously the tracking error, control... 

In this manuscript we used the method of coset construction to describe theories of spontaneous symmetry breaking. The mathematical details are included in chapter 2. The utility of the method is that without any knowledge of the UV part of a theory we can construct IR part by just knowing the symmetry breaking pattern. We used the method for some symmetry breaking patterns to construct general relativity, massive gravity and also some symmetry breaking patterns corresponding to conformal gravity  

In this thesis, inspired by foundational discussions about the concepts of energy and entropy in the gravitational theory, we study the definitions of these concepts and the roles they play in that theory. The definitions considered in this thesis are derived from canonical formalism. To this end, first of all, the variational principle and the canonical structure in the gravitational theory, especially in situations where the spacetime is bounded, is carefully studied and the boundary and corner actions as well as the canonical structure on the boundaries in three cases of non-null, null and general boundaries are derived. Based on this study, two canonical approaches, namely the...