Sharif Digital Repository

In the special theory of relativity, it is not necessary to propose that there is no privileged frame of reference but because this formalism is of the epistemological level, we can not deduce this ontological conclusion. On the other hand, there are different physical motivations for a privileged frame of reference and also there is an alternative physical model for special relativity called inertial transformations which is similar to the special theory of relativity at the observational level, but there is a privileged frame of reference in that theory. In this paper, I have tried to collect motivations for a privileged frame of reference in physics, in order to prepare a source for those... 

Mutually coupled oscillator arrays have been considered. Detuning of free running frequencies of perimeter elements has been used in these arrays in order to steer the beam without phase shifters. Characteristic equations of transient and steady-state conditions of amplitude and phase of the elements of coupled oscillator arrays has been derived. Literature review is done in coupled oscillator arrays. Sensitivity analysis of beam pointing angle due to free running frequencies of elements in coupled oscillator arrays has been done and the various planar arrays has been compared. Sensitivity analysis of beam pointing angle due to phase error of elements in conventional phased array antennas... 

In this study, numerical modeling of the micromechanical behavior of gravel aggregates applicable for base and sub-base of roads and railways under triaxial compression tests is conducted. The material is a type of well-graded gravelly soil with a maximum particle size of 20 mm, whose application is recommended by the UK Highways Agency. The prominent role of this material in the performance and endurance of the roads shows the importance of studying its behavior to acquire a better understanding of its mechanical properties. A number of triaxial tests using monotonic and cyclic loadings have been performed in the laboratory to investigate the behavior of this type of material. In the... 

Today, in our beloved country of Iran and other parts of the world, reinforced concrete structures are used in large industrial projects, in some cases we see their very early failure even before the time of operation. This issue in the southern coasts of the country due to special weather conditions (humidity and high temperature) and the existence of the offensive ions such as chlorine and sulfate in seawater are more important and we always face with severe corrosion of reinforcement and reduced service life of concrete structures in these areas. Despite this, little research has been done on the reliability of concrete facilities in the vicinity of the Caspian Sea in the north of the... 

The purpose of this work is to introduce an inverse finite element tool for prediction of the blank geometry and forming severity in stamping of 3D sheet metal parts. To achieve this goal total deformation theory of plasticity has been employed. In this method the final 3D part is unfolded on the flat surface and therefore the problem is reduced to two dimensional computations. Some tooling effects including blank holder force, bending and unbending and effect of draw bead are also considered. To investigate the capability of this work, predictions of the blank shape and strain distribution and forming severity have been performed on two circular and square parts. The results have been... 

In the classical theories of plasticity, plastic deformation of material is modeled with a macro- scopic viewpoint and without considering the existing physical mechanisms at the crystal scale. However, plastic deformation stems from slip phenomena and evolution of crystalline structure. Furthermore the effects of initial texture of material on its mechanical properties, like formability, and also texture evolution of material can only be calculated by considering these physical mecha- nisms.The main purpose of this thesis is to predict forming limit diagrams of sheet metals based on crystal plasticity approach by considering the effect of initial material texture and presentation of... 

Hydrocracking is a hydrogen addition process that permits refineries to convert heavier, less expensive crudes, into highly-valued transportation fuels such as gasoline, kerosene and diesel. Development of an accurate kinetic model for hydrocracking reactions is crucial to correctly predict the detailed product distribution under different operating conditions for a range of feedstocks as well as for reactor design, process optimization and catalyst selection. In this thesis a mechanistic kinetic model was developed for thermal hydrocracking of a paraffinic feedstock. This model was based on a molecular approach that was able to capture the fundamental chemistry of hydrocracking process. To... 

The cornea is a transparent, avascular, multilayer, connective tissue. When the erosion process of these cells occur, where natural and quick restoration is expected, corneal disorders begin. Regeneration of corneal tissue, using a biocompatible method is a great point of interest. Nowadays, scaffold based on amniotic membrane is used as a basement membrane in the regeneration of corneal tissue. Lots of researches focused on using auto graft scaffold to decrease the inflammation and infection of an allografts and synthetic scaffolds, while overcoming amniotic membrane’s weak mechanical properties. The aim of this survey is to construct an appropriate scaffold from patient’s own blood to...