Sharif Digital Repository

In this thesis, we propose a QoS-aware routing algorithm for multimedia streaming that uses cross-layer information (application layer and physical layer) in Wireless Multimedia Sensor Networks (WMSN). Our goal is to use cross-layer information to route video packets efficiently and deliver a higher quality video in streaming applications. Our QoS-Aware Multi-Path Selection (QAMPS) method is based on multi-path multi-priority selection algorithm that uses Two-Phase geographic Greedy Forwarding (TPGF) as a routing algorithm. The proposed method guarantees QoS by splitting video streams into I-frames, P-frames and B-frames in the application layer and passes them to the network layer for... 

There are different approaches in modifications of General Relativity as the theory of gravity. The modified theories of gravity are important cases in this context, which mostly start by modifying the Einstein-Hilbert action, while keeping the general covariance. Within the modified theories of gravity, we consider two cases. The first is the f(R) theories of gravity, and the second is curvature squared theories of gravity with an action like S = ∫d4x pg( 116GR + (R)2 + R2 +(R)2). Curvature squared theories of gravity have interesting feautures, most important of which is renormalizability, in contrast with General Relativity. But this advantage, as noted by K.S. Stelle in 1977 comes at... 

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... 

Multiverse scenario has been recently addressed by physicists and they have found it useful in many areas of physics. In this dissertation, I have treated some issues about multiverse such as the kinds of multiverses, the arguments for or against multiverse, areas in which multiverse is introduced, etc. This dissertation has six chapters and an appendix. In the chapter one, some classifications of multiverse is introduced, and also some definitions of the concept of a world is presented. Then, my classification and definition of a multiverse and a world is introduced. In the chapter two, the concept of possible worlds in philosophy and its relationship with multiverse hypothesis is examined.... 

Hartry Field argues that meaning-besed approaches to explaining the apriority of certain propositions fail to succeed in their endeavour. He suggests that adoting what one cals a non-factualist view of justification itself removes the mystery of the apriority of such propositions, and sketches what such a view of justification involves. A priori justification is often thought mysterious or out of keeping with a naturalistic view of the world; strong forms of priori justification that involve empirical indefeasibility are often thought especially mysterious. While this is no doubt correct for excessive claims of a priority – for instance, claims to prori acces to features of the physical... 

In every theory with local symmetries, observales are mainly the gauge invariant quantities and fields are defined up to a local transformation.By choosing boundary conditions on field configurations and on the generating functions of gauge transformations, we can associate conserved charges to a particular subset of the generating functions. Thus field combinations which are related by these particular gauge transformations are physically distinct. These set of conserved charges usually form infinite-dimensional algebras such as Virasoro or BMS algebra. In addition, sets of all combinations of the associated fields form a phase space with a symplectic structure induced form the action of... 

In this survey we explore the black hole information problem, one of the most challenging issues in theoretical physics over the past few decades. According to the theory of general relativity, black holes can form through gravitational collapse of matter. At semiclassical level, however, black holes emit thermal Hawking-radiation and eventually completely evaporate. After evaporation the radiation state cannot retain all the information about the initial matter that underwent gravitational collapse, contradicting the principles of quantum mechanics. Various approaches have been proposed to address this issue. One such approach is the black hole complementarity principle, introduced by... 

The cosmic inflation paradigmwas first introduced as a possible solution to the standardBig Bang cosmology problems. [1]. The inflationary models not only provide a solutionfor so the called flatness and horizon problems, but also they predict perturbations asprimordial seeds of large scale structures of Universe. Inflationary models can connecthigh-energy physics to the experiments. There is a mutual relation between inflationand high energy physics. It is necessary to find a fundamental description of inflationarymechanism and on the other hand the observational predictions of inflationary modelscan put bound on free parameters of associated fundamental theories. Thanks to vastdata...