Sharif Digital Repository

The cosmic ray astronomy was born in 1937 when Victor Hess flied with his balloon to the height of 17,500 feet. He found that the cosmic rays come from out of atmosphere. There are three fundamental questions from that time. The goal of all cosmic ray's experimental activities and related theories is finding out the answer of these questions. The first question is about the energy and composition spectrum of cosmic rays. The second one is finding the sources which can product the very high energy particles such as the protons with the energy of 1021eV found in some observatory such as AGASA and Haverah Park. The last question is the process of diffusion of cosmic rays in the galaxy. One of... 

Metallic multilayer composites provide remarkable mechanical, electrical and magnetic properties. These kinds of composites are recently processed by severe plastic deformation methods. Accumulative roll bonding (ARB) is one of the SPD processes in which accumulation of strain by repeating cycles, leads to the ultra fine grains structures. The goal of this research is manufacturing of Al/AZ31 composite and investigating the relation between the rolling process parameters and the mechanical and physical properties of the final sheet. The initial composite was carried out by cladding of 1mm thick AZ31 sheet in between two commercially pure aluminum sheets with the same thickness (57%... 

Commercially pure titanium (CP-Ti) is an important groups of titanium family and because of high strength, low density, high corrosion resistance and biocompatibility, this group of titanium is a suitable choice for application at chemical, petrochemical and medicine industry. Nowadays surgeons have a tendency toward use of CP-Ti instead of Ti-6Al-4V alloy. Moreover, because of body anatomy limitation, use of thick sheets result in high volume and damage soft tissue. Therefore, for sheet thickness reduction, study of the effects of metallurgical and geometrical parameter on fracture behavior of thin sheets is important. In this study, the fracture behavior of CP-Ti thin sheets investigated.... 

Metallic multilayer composites provide remarkable mechanical, electrical and magnetic properties. These kinds of composites have been recently processed by severe plastic deformation (SPD) methods. Accumulative roll bonding (ARB) is one of the SPD processes in which accumulation of strain by repeating cycles, leads to the ultra fine grained materials. The goal of this research is manufacturing of Al/Ni composite sheets by ARB process considering the effects of thickness and number of initial sheets on their mechanical properties and microstructures. The initial composites were produced by commercially pure Al and Ni as the matrix and the reinforcement, respectively. Thickness of the Al... 

The DNA Molecule carries genetic information in almost all living organisms. The information coded on DNA is an instruction which organizes and conducts all living activities of the living organism. The role of DNA in biological processes is so fundamental that life, as we know, is not possible without DNA. Therefore, studying the biological properties of DNA is crucial for understanding the nature of life. In biological conditions, DNA molecule can be found in highly packed configurations. Since the DNA is a rather stiff molecule, the formation of these configurations cost a considerable amount of energy. The elasticity of DNA plays an important role here. The important question is: how... 

Cosmic Inflation, invented by Alan Guth in 1980’s, solves the shortcomings of the Standard Cosmology such as the flatness, the horizon and the monopoles problems and provides the seeds of large scale structure formation. The quantum fluctuations which are produced during inflationary epoch are redshifted and transferred from Microscopic scales to Macroscopic universe. We can observe this macroscopic fluctuations both on the CMB surface and on large scale structures. Data from WMAP and Planck missions(CMB space Telescopes) suitably confirms the general predictions of single field inflationary scenarios but still people search for finding primordial gravitational waves from the B-Mode signal... 

Asphalt concrete is a heterogeneous and multi-phase material that consists of aggregates, asphalt binder, and pores. These components create a complex microstructure. There is no consensus on how to quantify the microstructure and the required parameters from two-dimensional images. The load transfer can be managed by aggregate-aggregate or aggregate-mastic interactions that depend on the gradation, aggregate internal structure, and asphalt binder viscoelastic properties. The most important internal structure indices affecting the behavior of HMA are aggregate orientation, contact orientation, contact length, and number of contact points. In this research, the influence of aggregate... 

In this project we focused on Simulation of two-phase (gas-oil) flow in 2D anisotropic porous medium on unstructured grids by finite volume method.Since the permeability assumes to be full tensor, common discretization methods for pressure and flux equations couldn’t satisfy continuity conditions then a new method of discretization named continuous flux approximation introduced.In this new method, cell center pressure calculated by directly applying flux continuity conditions to control volume boundaries. In this project a ninepoint scheme is used, it means that for making the flux continuity conditions over each control volume in two dimensions all neighboring cells are involved.The reason... 

Rapid variation in permeability with strong anisotropy are common features in subsurface reservoirs. When formulating a finite-volume pressure equation scheme, continuous normal flux and pressure are key physical constraints that must be imposed at control-volume interfaces, across which strong discontinuities in permeability can occur.
The derivation of algebraic flux continuity conditions for full-tensor discretization operators has lead to families of efficient locally conservative flux-continuous control-volume distributed (CVD) finite- volume schemes for determining the discrete pressure and elocity fields in subsurface reservoirs [5, 9, 11, 13].
When applying these... 

Due to special physical and mechanical properties of intermetallic compounds,somehow in between of the metallic and ceramic extremes, their applications are increased in different industries. Among these materials, titanium aluminides due to their low density, high specific strength and excellent corrosion and oxidation resistance has got more attention. Because of similar high temperature properties and lower density, these compounds are suitable alternatives for nickel base superalloys. Accumulative Roll Bonding (ARB) of pure metallic sheets and the following heat treatment in production of intermetallic compounds can be considered as a manufacturing process. The goal of this study is... 

In this paper, the elastic response of a surface-stiffened transversely isotropic half-space subjected to a surface normal load is addressed. The half-space is reinforced by a Kirchhoff thin plate bonded to its surface. Two different boundary conditions are considered across the plate-half-space interface: (i) the classic approach in which the plate in-plane deformation is neglected by writing the interfacial boundary conditions across the plate mid-plane, and (ii) the refined approach that considers the in-plane deformation of plate due to bending by writing the boundary conditions across the bottom face of plate. By virtue of appropriate displacement potentials, the complete set of elastic... 

Most of petroleum reservoirs of Iran are fractured reservoirs which has different properties, geometrical structure and drive mechanism in comparison with conventional reservoirs. The major difference is the existence of interaction between fractures and matrix respectively with a high and very low permeable (or imperable) medi. One simulation method for these fractures is discrete fracture network (DFN) modeling which is used in this study to investigate dynamic properties of these fractures. In this study, matrix is assumed as an impermeable media then dynamic properties like effective permeability of fracture network for different realization reservoirs are calculated and and evaluated by... 

This study aims to provide a multiscale model of traumatic brain injury including the three levels of macro, meso, and microscale information. In order to do this, a macroscale voxel-baed model of human head was constructed. The model was designed and generated to include mesoscale tissue information as well as a voxel-based approach to include voxel-based microscale data and to be coupled in a multiscale framework. Next, three different microscale models were constructed. The variations of fractional anisotropy within one standard deviation in the regions (including 60% to 70% of voxels) can change the stiffness of the tissue by up to the considerable amount of 40%. The microscale models... 

Polymeric film for packaging applications are commonly made from a variety of polyethylenes using a blown film process. Nowadays high density polyethylene with bimodal molecular weight distributions are used to improve the performance and the final properties. In the present study samples with different bimodal molecular weight distribution in a similar film preparation are developed. The EX5 sample from the Jam Petrochemical showed microstructure with heavily oriented stack of lamellae in the machine direction. In contrast, the 7000F sample from the Mehr Petrochemical presented a microstructure with a lower degree of lamellae, containing lamella twist and more link between the crystalline... 

One of the common methods of removing blood clots is angioplasty with stents. Due to the fact that the mechanical properties of the stent are directly related to the microtube it is made of. Therefore, investigating the mechanical properties of microtubes is very important. One of the ways used to evaluate the plasticity of microtubes; Drawing a graph is the limit of shaping. The purpose of this research is to extract the forming limit diagram of magnesium microtube by simulating the hydroforming process in Abaqus software. First, in order to confirm the modeling, the hydroforming process for aluminum has been simulated and compared with the existing experimental results. The comparison... 

Nowadays dielectric substrates are widely used in Microwave Integrated Circuits. These substrates are made layer by layer in order to have favorable mechanical and thermal properties. The materials of the layers are usually different from each other and often each layer is a combination of different materials. This difference in material type and manufacturing method causes the substrate to have a different permitivity coefficient in two major directions, namely parallel and perpendicular direction. In fact, the electric field observes a different permitivity coefficient in each direction. This causes a problem in circuits that have both perpendicular and parallel electric field... 

Obtaining the mechanical properties of body tissues in a non-destructive manner is clinically important and has wide applications in the diagnosis and prevention of diseases. one of non-destructive methods is elastography, which requires proper modeling of the tissue and then analysis of the wave propagation in it and obtaining the propagation relations and the dispersion curves. Study of the literature revealed that many simplifications have been used in most modelings of arteries and so far the anisotropy of the artery and its layers with the effects of surrounding tissues and blood have not been studied Therefore, the aim of this study is to model the artery as a two-layer orthotropic... 

The standard ΛCDM model is built upon the cosmological principle, which states that the universe is homogeneous and isotropic on large scales (greater than 100 Mpc). A crucial test of this principle involves analyzing the Cosmic Microwave Background (CMB) radiation, which exhibits a dipole anisotropy on the order of ΔT/T∼10^−3. This dipole is commonly interpreted as owing to our motion with respect to the CMB rest frame. A model-independent approach to validate this kinematic hypothesis is to determine the dipole moment in the angular distribution of large-scale structures. According to the cosmological principle, the rest frame of the large-scale structure distribution should align with the...