Sharif Digital Repository

The heavy ion collision experiments are in progress in order to investigate how the Universe has evolved after the Big Bang. The recent observations show that a nearly perfect fluid is produced after heavy ion collisions. An appropriate incorporation of the relativistic hydrodynamics and the field theory would help us to describe the dynamics of QCD (Quantum Chromodynamics) matter under extreme conditions, and to survey the expected phase transitions. The majority of efforts to investigate the characteristics of the QCD plasma are devoted to an ideal, non-dissipative one. To get the results which are highly in accordance with the experiment, it is necessary to bring also in mind the role of... 

Kinetic terms of effective action including derivative of classical field become significant, when we have a dynamical field.These terms have been calculated as a function of the fermionic propagator in NJL model, which is an effective model of QCD. In this thesis, after briefly reviewing
the effect of constant background magnetic field on the propagator considered by Ritus method, we explicitly determine the kinetic terms in terms of Ritus eigenfunctions. Finally, we numerically calculate these terms at finite temperature and chemical potential according to the imaginary time method  

One of the long-lived problems in the theory of quantum chromo dynamics is the violation of parity (P) and charge-parity (CP) symmetries in strong interactions. The existence of gluon configurations sourcing from topology leads to degeneracy in the vacuum structure of the theory. This phenomenon is realized by the addition of an extra term proportional to the parameter to QCD Lagrangian. Experimental estimates of neutron electric dipole, predicts a very small value for this parameter. There is no verified justification for this discrepancy. Recently at the relativistic heavy ion collider laboratory (RHIC) some experimental evidence has been found which indicates local CP violation in... 

Relativistic hydrodynamics and kinetic theory are often used to analyze the experimental data from heavy ion collisions. One of the most important observations is the anisotropy in the number density of the detected particles after the collision in the longitudinal and perpendicular directions with respect to the reaction plane. On the other hand, very strong magnetic fields are created during the early stages of non-central heavy ion collisions. The presence of constant background magnetic fields, aligned in the perpendicular direction to the reaction plane, can be one of reasons for the aforementioned anisotropy in the number density of detected particles. In this thesis, we study the... 

In heavy ion collisions, extremely large electromagnetic fields are produced by fast-moving charged nucleons. They are sufficiently large to affect the low energy QCD processes and thus produce observable effects, whose occurrence is, however, directly related to the lifetime of these fields. In the present dissertation, the evolution of electromagnetic fields is studied in a plasma of quarks and gluons, by analytically solving the equations of relativistic magnetohydrodynamics (RMHD). The onideal Bjorken RMHD is solved by introducing the method of nonconserved charges. Assuming an electromagnetic force-free condition, the electric and magnetic fields are found to be either parallel or... 

In particle physics, spontaneous chiral symmetry breaking generates new phases of quark matter, and leads to significant changes od quark masses. The Nambu-Jona–Lasinio (NJL) model is a useful fermionic model which describes the spontaneous chiral symmetry breaking through the creation of a condensate. This model can be for instance used to determine various phases of Quantum Chromodynamics (QCD) in finite electromagnetic fields. This work consists of several parts. First, we describe the spontaneous chiral symmetry breaking in detail. Second, we extract the NJL model from the Lagrangian density of QCD. Third, we derive a covariant form of the partition function of a fermionic system.... 

Relativistic collisions of heavy ions lead to the formation of a new phase of matter called Quark-Gluon Plasma (QGP). In addition, strong magnetic fields generates in these collisions that its direction is perpendicular to the collision axis. This strong magnetic field affects the dynamics of particles in the QGP, and causes the appearance of the Landau levels in the particle’s energy spectrum. In this master thesis, we investigate the impact of the magnetic field on dilepton production and synchrotron radiation. We calculate the scattering probability of quark and anti-quark annihilation and dilepton creation by taking all Landau Levels into account. Then, by assuming that the magnetic... 

With intensified concerns of rising fuel vehicles that reduce fossil fuel globally and also prescript strict rules by standard institutes, vehicle manufacturers try to find a way for reducing the fuel of their products. One these methods use a continuously variable transmission (CVT) instead of manual and automatic gearboxes. Various CVT’s have been proposed in recent year.
One of the proposed systems is traction infinitely variable transmission (TIVT) that is type of traction drive continuously variable transmission and has been presented in 2007. Research on this system showed that average efficiency is about 96% that is high efficiency. Completed research in 2011 showed that despite... 

The investigations on hydrophobic surfaces have attracted lots of intrests in science and technology. Silica sols have been used extensively in the area of producing hydrophobic coatings. On the other hand, carbon-based materials have attracted of a great deal of scientific interest in recent years. The purpose of this research is synthesis and investigation on the properties of Silica- Graphene Oxide nanocomposite coating.Graphene Oxide synthesized by using Hummer’s method. Silica nanoparticles were prepared using sol-gel process and tetraethylorthosilicate (TEOS) as precursor. The surface hydroxyl groups of silica nanoparticles are replaced with Methyl groups by treatment with... 

Hyderogels are hydrophilic polymers with three dimensional network structure, due to their high water absoption, their application to life and industry is increasing from day to day, such as tissue engineering, actuators and sensors, drug delivery and therapeutic treatment. In this project, it has been attempted to produce polyacrylamide/alginate double network hydrogels with the use of graphene oxide nanosheets to indicate that it is possible to combine toughness and self-healing in a hydrogel with the opposite nature of each other. To evaluate mechanical properties, uniaxial tensile test and loading-unloading test were used. The results indicate that increase the weight ratio of acrylamide... 

In recent decades, many building projects have been implemented in the form of partnership agreements between the land owners and the private contractors, investing in the buildings’ construction. The growing trend of implementing such projects is due to the increased price of land and the constructors’ inability to separately buy a piece of land and implement their individual building projects. On the other hand, many owners cannot afford the construction cost of building projects. At present, this form of building partnership agreement arranged and concluded between the landowner and the contractor is not normally signed through balanced and thoroughly thought contract documents. This... 

After the review of formation of Landau levels (LL) in non-relativistic quantum mechanics, we have obtained LL in a certain gauge A_μ=(0,-B_0/2 y,B_0/2 x) at 2+1 &3+1 dimension. then give a summary of Quantum Field Theory at non-zero temperature . obtaining LL and two-point Green function in non-uniform magnetic field which determined with A_μ=(0,0,√qB ξe^(-(t+x) ),0).Next we calculate magnetic susceptibility of in such a field with finite chemical potential and temperature. Finally we compare the obtained results with uniform magnetic field one  

In the present thesis, the effect of external magnetic fields on two-flavor Color Superconductive (2SC) phase, as one of the phases in the QCD phase diagram, is studied. To do this, an effective two-flavor Nambu-Jona Lasinio Lagrangian is used, which consists of two mass gaps, s = ?¯qq and ? = ? . The nonzero values of chiral and color mass these gaps induce spontaneous chiral and color symmetry breaking, and consequently two different phases. There is also a third phase, the normal phase, where s = ? = 0. We calculate the transition curves and the critical points in terms of three intensive quantities, the temperature, the chemical potential and the external magnetic field. We study, in... 

The main focus of this dissertation is to investigate the effects of the created background magnetic field on some of the observables that are relevant in heavy ions experiments. Based on the phase diagram of Quantum Chromodynamics, it is expected that in extreme conditions such as high temperature or in dense medium, a new phase of matter arises, which is known as Quark-Gluon Plasma (QGP). Due to the vital role of collective behaviors, this phase behaves similar to a perfect fluid rather than a gas. In addition, the colliding nucleons have potential of creating very strong magnetic fields because of their electric charges and relativistic speeds. Therefore the investigation of the effects... 

In accomplishment of knowledge management in real world, organization can be in different processes of awareness about importance of knowledge management and its achievements. Recognition of strength and weakness points of organization helps to logical planning and success in performance of knowledge management. For avoiding from failing in knowledge management projects, it is necessary that before stating for project performance, evaluate development level of organization from viewpoint of knowledge management, and determine some approaches for control of general problems of knowledge management, like abundance of information, work complexities, knowledge Storage.
In literature of... 

In modern society, engineers, technical managers are responsible for planning, design, construction, exploitation of simplest to most complex systems. Crashes cause disruption of systems at different levels and can be considered as a serious threat to society and the environment, thus consumers and people expect reliable products and systems. There are different methods for increasing the reliability of systems, one of them is related to their quality and another way is related to use of standby systems. Also maintenance and repairing have major role for keeping up reliability or availability of systems. In the first part of project, optimization the reliability of system by standby... 

Aluminum alloys have many applications in various industries such as automotive and aerospace due to their high strength to weight ratio. Today, much research is being done on the strength of metals and alloys after severe plastic deformation. Among these studies, limited work has been done on the hot deformation behavior of alloys that have undergone a severe plastic deformation process. In this research, aluminum alloy 2024-O is subjected to various passes under a type of severe plastic deformation process called multi-directional forging. Samples were divided into zero passes (annealed), one pass, three passes and five passes. After preparing pressure samples from them, hot pressure with... 

Using the general structure of the vacuum polarization tensor П_μν (k_0→0,k) in the infrared (IR) limit, k_0→0 , the ring contribution to the QED effective potential at finite temperature and the nonzero magnetic field is determined beyond the static limit, (k_0→0,k→0). The resulting ring potential is then studied in weak and strong magnetic field limits. In the weak magnetic field limit and at high temperature the improved ring potential consists of a term proportional to T^4 α^(5/2), in addition to the expected term T^4 α^(3/2) arising from the static limit. In the limit of the strong magnetic field, where QED dynamics is dominated by the lowest Landau level, the ring potential includes a... 

In this thesis NJL and quark-meson models, as effective models for quantum chro-modynamics in low energies, are studied mainly. After reviewing models and phe-nomena related to the strong interaction in zero and non-zero temperature, firstly the critical coupling of NJL model for non-zero temperature and chemical potential is calculated. Then, the contribution of ring diagrams in the effective potential of quark-meson model is presented. Finaly, the effect of ring diagrams of quark-meson model on chiral phase transition is investigated. For NJL model, it is shown that the chemical potential lowers the critical coupling for chiral phase transition. Also for quark-meson model, it is shown that...