Sharif Digital Repository

Polyethylene (PE) is used as an insulation material for wires and cables because of its excellent electrical properties. For such application, it can be exposed to the high energy irradiation such as gamma ray and electron beam (EB), making possible crosslinking of the PE. Most of the properties of PE are improved greatly after irradiation, but it was harden and split easily. Due to the flexibility of EVA, depending on the vinyl acetate content, it can improve the toughness of the LDPE significantly upon addition to this polymer. As a result, radiation induced LDPE/EVA blend has been a good candidate for the wire and cable insulation. Also, upon addition of a few amount of OC, different... 

Coding information data is one of the ways to prevent noise effect on the information bits, during passing communication channels. Coding data gives the possibility to detect and correct the data in the receiver. The LDPC codes which were first introduced by Gallager in the 1962 are forward error correction codes and can approach the Shannon’s capacity to within hundredths of a decibel.
In this project a modified algorithm for decoding these group of codes is introduced, which can achieve acceptable bit error rate, while it can have better throughput than the same implementations. This algorithm is implemented partial-parallel for IEEE802.11n standard in ASIC. It is shown that, it has... 

Melt blending of polymers is a rather cheap and easy approach for obtaining new set of properties compared to synthesizing new polymeric materials. For the same reason, binary and ternary polyethylene blends are made to provide added value for different applications. Polyethylene blends are commonly composed of high density polyethylene (HDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDPE). Although the Mechanical and physical properties of polyethylene binary blends have been studied extensively, microstructure and mechanical properties of polyethylene ternary blends have been the subject of very few studies. In this work, samples with 40-60 Wt. % HDPE and... 

Code-based cryptosystems could be a suitable alternative to the cryptosystems based on number theory. It is shown that cryptosystems based on descrete logarithm and factoring is vulnerable to the Shor’s algorithm running on quantum computers, while code-based cryptosystemsare thought to be secure against this cryptanalysis. Despite its security, large key size and low transmission rate keep thesecryptosystems impractical. Reliability is one of our inevitable desires in communication systems along with security.In order to fulfill these desires, joint encryption-encoding schemes has been released.Using LDPC codes in joint encryption-encoding schemes, as an alternative to classical linear... 

Atherosclerosis is one of the most important and common causes of death in the world. Atherosclerosis typically affects medium and large arteries in the body and it leads to plaque formation in arterial wall. The first stage of plaque formation has been related to accumulation of low density lipoproteins in arterial wall.
The purpose of this research is presenting a four-layer model to describe the LDL transport in the arterial wall. The endothelium, intima, internal elastic lamina (IEL) and media are all treated as macroscopically homogeneous porous media and the volume-averaged porous media equations are employed to model various layers. The physiological parameters within the various... 

In this thesis, hemodynamic parameters of flow and deposition of low density lipoproteins (LDL) on wall of coronary arteries with taking into account their curvature on the heart are studied. At first, numerical solution of the blood flow by assumption of blood as incompressible and Newtonian fluid for steady and pulsatile inlet is done. Then by assuming LDL particles as dilute solute in the blood, LDL transport from artery lumen into arterial wall is studied. LDL accumulation and penetration into the vessel wall cause thickening of the walls and eventually eclipse it and its known as the first stage of atherosclerosis disease. The results show that low shear region occurs on inner wall... 

Heart attack is considered as one of the most common reasons of morality all over the world. Coronary Atherosclerosis is known as the major causes of heart attack. The commence and proceed of this disease is related to cross of Low Density Lipoprotein. In this project, based on numerical simulation using ANSYS Fluent, hemodynamic variables and the rate of LDL particles penetration to porous wall of coronary artery is investgated. The geometry is the first bifurcation of Left Anterior Descending and is located on the supposed sphere that represents heart configuration. Sinsuidal variations of shere radii, simulates pulsating movement of heart. Heart diameter is supposed to remain constant... 

Due to increased atherosclerosis-caused mortality, identification of its genesis and development is of great importance. Although, key factors of the origin of the disease is still unknown, it is widely believed that cholesterol particle penetration and accumulation in arterial wall is mainly responsible for further wall thickening and decreased rate of blood flow during a gradual progression. To date, various effective components are recognized whose simultaneous consideration would lead to a more accurate approximation of Low Density Lipoprotein (LDL) distribution within the wall. In this research, a multilayer Fluid-Structure Interaction (FSI) model is studied to simulate the penetration... 

In this study, polyethylene films made of LDPE / LLPE / reinforced with mechanical barrier of clay and reactant of iron nanoparticles were made in their optimal combination and necessary improvements were made on them. Investigations show that, independent of volume fraction, the addition of spherical nanoparticles does not have much effect on reducing the polymer matrix’s permeability. In nanocomposites containing cylindrical particles, for considerable reduction of the permeability, over 20 volume percent of nanoparticles it is required, while in platelet nanoparticles, less than 10% vol is sufficient. In clays with modifier concentration above the cation exchange capacity, there is less... 

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... 

Atherosclerosis, due to the penetration of low-density lipoprotein particles (LDL) into the arterial wall, is one of the most common and death-leading diseases in today's world. Due to its importance, extensive research has been conducted on the factors that affect this disease. In this thesis, a numerical study of the effects of Wall Shear Stress (WSS), non-Newtonian behavior of blood, different hematocrit values, and blood pressure on LDL permeation through the artery wall layers are investigated in a 4-layer wall model of a coronary bifurcation. To obtain the velocity and concentration fields in the domain, momentum, Brinkman, and mass transport equations are solved in the lumen and wall... 

One of the most important goals we pursue in telecommunications science is to send and receive information from telecommunication channels. By designing a powerful telecommunication system consisting of a transmitter and a receiver, we achieve this goal. Speed of data transmission, accuracy of received information and speed of data extraction are some of the criteria by which the performance of a telecommunication system can be evaluated. No telecommunication channel is free of noise. For this reason, additional information is added to the original information in the transmitter, which can still be extracted if the original information is noisy. This process is called coding. Following... 

In this thesis, the effect of heart dynamic motion and pulsatile inflow on blood hemodynamics and LDL permeation into the arterial wall in a 3-D coronary artery bifurcation was investigated. To determine the effect of each factor alone and simultaneous effect of both factors i.e. heart dynamic motion and pulsatile inflow, flow simulations were performed in four cases i.e. steady-static, steady-dynamic, pulsatile-static, and pulsatile-dynamic. The results of flow simulations showed that dynamic geometry and pulsatile inflow have considerable impact on temporal variations of wall shear stress (WSS), even though the effect of pulsatile inflow on WSS variation dominates over the effect of... 

Nowadays, cardiovascular diseases are among the most prevalent cause of death worldwide. Besides, atherosclerosis is a cardiovascular disease happening with the continuous narrowing of vessels, especially medium and large-sized arteries. Moreover, the human aorta is vulnerable to this phenomenon. Atherosclerosis happens when the excess LDL in the blood flow penetrates the arterial wall. Then, the LDL is oxidized, thereby recruiting monocytes as the response against oxidized LDL. After monocytes enter the arterial wall, they differentiate and become macrophages. Macrophages then transform into foam cells by ingesting the oxidized LDL. The fatty foam cells are eventually responsible for the... 

Atherosclerosis is a vascular disorder caused by inflammation of the arterial wall. This inflammation leads to the accumulations of low-density lipoprotein (LDL) cholesterol, monocytes, macrophages and fat-laden foam cells at the site of inflammation, often referred to as plaque formation. This work uses a mathematical model for simulating the deposition of atheroma plaque in coronary arteries. In this study, the effect of time average wall shear stress (TAWSS), oscillatory shear index (OSI), non-Newtonian characteristics of blood and variable hematocrit values on the occurrence of atherosclerosis in a three-dimensional coronary artery was numerically investigated. Simulations was conducted... 

Statistics show that plastic production in the world is increasing, with 335 million tonnes in 2016 reaching 367 million tonnes in 2020. Since the presence of plastics in the dimensions of micro and nano, especially in aquatic environments can have adverse effects on human health and other living organisms, it has raised major environmental concerns. Therefore, it is necessary to think of measures to remove them and develop efficient methods for eliminating and decomposing microplastics. Recently, the advanced oxidation processes have attracted much attention because of the ability to eliminate recalcitrant compounds. In this study, electrochemical techniques and Fenton-based techniques for...