Sharif Digital Repository

Superconducting SQUID sensors are one of the most sensitive magnetic sensors that have been ever produced. Due to their high sensitivity, these sensors have many applications in different fields. Magnetic Imaging and far away targets detections are of these applications. In this project, a magnetic imaging system based on Superconducting SQUID sensors have been designed and implemented. In SQUID applications one of the most important problems is the cancelation of the unwanted fields including background low frequency and high frequency fields. In residential and urban areas the interference of Electricity network is considered as one of the major noise sources. While the high frequency... 

Prediction and calculation of shielding tensors of H, C, F and P nuclei of different molecules has been the subject of much research, because these nuclei have the greatest importance in NMR experiments. The optimum wave functions and calculation method were obtained using empirical models and factorial design. Based on preliminary experiences, the following four factors at two levels were selected: electron correlation, triple-ξ valence shell, diffuse function and polarization function. The wave functions for calculating gas phase 1H and 13C chemical shifts of various types of alcohols, amines and simple hydrocarbons were optimized using empirical model. The B3LYP/6-311+G wave function is... 

Superconducting Quantum Interference Devices (SQUIDs) are one of the most sensitive magnetic flux detectors. According to their high sensitivity, these sensors have many applications such as magnetic imaging, magnetocardiography and magnetoencephalography. In this project we have designed and implemented a fluxgate based active shield that would be used in magnetocardiography. One of the main concerns in RF-SQUID applications is suppression of the low and high frequency noises. These noise sources includes earth magnetic force, humming noise and RF noise caused by cell phones. These sources could unlock RF-SQUID sensors and hence needs to be shielded. Low frequency noise suppression could be... 

The continuous rise in electricity demand and the ever growing power generation in different power networks over the world have caused the short circuit level in the power systems to exceed the operational rating of the installed power devices (including cables, circuit breakers and buses). Replacing these devices with new higher rating devices is an expensive solution. From this point of view, utilizing fault current limiters is an economical solution. Superconducting fault current limiters form an efficient category of current limiters. This type is expected to be studied and used widely in future due to their advantages. In this thesis, the first chapter reviews the superconductivity... 

It is very important to determine why there is still external corrosion on pipelines even though NACE RP0169 criteria are satisfied. The cathodic shielding problem is the most relevant finding to this kind of situation. In this research, the shielding behavior of three types of coatings (FBE, 3LPE and Polyurethane) used in Iranian gas industries are evaluated under laboratory condition by four major procedures. It has been found out that the FBE coating has no shielding effect and instead 3LPE coating has a shielding effect by not allowing electrical conductivity through the coating. Finally, the Polyurethane coating presented a mid-behavior effect but almost near to non-shielding behavior.... 

In a nuclear reaction, particles such as gamma, neutron, alpha beta, etc. May be emitted. Environment and humans could be damaged severely if these radiations are not properly shielded. One of the main goals of this project is manufacture proper shields for neutron and gamma attenuation and absorption in mixed fields, benefiting the particular properties of composites. In preliminary stage of this project, with comprehensive studies, primary materials were selected. These materials are Tungsten, Polyethylene and Lithium Fluoride selected as Gamma absorber, thermalizer and thermalized neutron absorber respectively. In the next step, weight fractions of each material and thicknesses of... 

Due to the increasing need of use of drugs and insufficient efficiency of conventional methods, drug delivery systems has gathered a lot of interests. There are different systems existing for controlled drug delivery, among which is implementation of hydrogel microparticles (microgels) as carriers with high potential. The most important factor in these systems is size distribution of drug-carrying microgels and a narrow size distribution leads to a controlled and suitable release. Due to unique characteristics of microfluidic systems, significant focus has been placed on them nowadays for production of microgels with suitable morphology and narrow size distribution. Therefore, in this study... 

Flux-cored arc welding has become prevalent in the recent decades worldwide. One of the variants of this welding method is self-shielded welding which requires no external shielding, neither with mineral flux nor with shielding gases. In this study, the variation of microstructure and mechanical properties of flux-cored self-shielded welds was investigated and optimization of this properties was also carried out. For this purpose, a basic combination of powders was chosen from the literature to fabricate the flux-cored wire. These powders contain fluorine, calcium carbonate, aluminum, magnesium and iron. Then, same amount of alloying elements such as molybdenum and nickel was added to this... 

In this study, epoxy resin has been modified by nano-clay additives using direct mixing method and epoxy-clay nanocomposites were designed and produced with optimized percentage of clay content. By adding the powder of born carbide and lead oxide in nanocomposites new compounds are obtained. The results are used for protection against neutron and gamma rays, respectively. After preparation of epoxy-clay-born carbide and epoxy- clay-lead oxide nanocomposite the effects of irradiation and carbon fiber on mechanical and thermal properties of nanocomposites were examined. The Nanocomposites were exposed to Electron Beam Irradiation (EBI) in 100 and 500 kGy doses to investigate the effect of... 

Characterization of local magnetic activity of the heart muscles is named magnetocardiography (MCG), which measures magnetic field generated by electrical activity around heart. RF SQUID sensors are appropriate choice for measuring magnetic activity of the heart muscles. Because squid detects weak signals as low as fTesla, while heart magnetic field is near 50 pt which is one millionth of earth magnetic field and thousands of time weaker than the environment noise. One of the problems of mcg system is its urgency to shielding of unwanted magnetic field. In this project design of holders and resonators for well coupled input coil with RF SQUID is improved. As a result, at the first stage... 

In this study, low carbon plain steels joined with TLP bonding method using Fe-44Ni-7B-4Mo interlayer, The bonding parameters (holding time, temperature) have been changed to find optimum conditions of TLP bonding. Microstructure and properties of joints have also been investigated. Dual phase processing of the used steel has been carried out during joints homogenization. Microstructural studies with scanning electron microscope and optical microscope showed that isothermal solidification completed at holding for 50 minutes at the bonding temperature of 1180℃. These parameters are taken as optimum conditions of TLP bonding. Microstructure of the isothermally solidified zone (joint region)... 

After World War II, steel bearings containing copper element have been developed by the Navy of the United States of America with the HSLA-100 brand. Since 1890 and in order to manufacture tanks and tools for the body of navy equipment, the steel HY 80 was used instead of HSLA-100. Because of the high carbon content, the welding properties of the HY 80 are low. Furthermore, increasing of hardness and decreasing of toughness in the heat-affected zone generated during the welding process lead to susceptibility of this alloy to hydrogen cracking and brittle fracture. Therefore, in order to minimize the cost of welding, low-alloy high strength steel (HSLA) is used which contain copper. Reducing... 

This study tries to introduce chemical coatings to reducing evaporation from Lake Urmia(LU). In LU, average annual evaporation is estimated at more than 1,000 mm, more than 80% of evaporation occurring in the warmer months of the year. Therefore, by reducing water evaporation, especially in the warmer months of the year, the most crucial factor in water outflow from LU can be reduced.At first, on the scale of class A evaporation pan in Tehran, three kinds of chemical coatings constituted stearic acid, jojoba oil, and fatty alcohols of style and stearyl to reduce evaporation from the LU is investigated. Then the best coating that includes combine of style and stearyl alcohols with stearic... 

In this work, we report on a developed single-channel high-Tc SQUID based MCG system for operation in unshielded environment. In brief, our system consists of a liquid Nitrogen Dewar and two high-Tc rf-SQUID capsuled in a holding probe,which is connected via coaxial cables to our multichannel rf-SQUID readout electronics.The rf-SQUIDs were patterned from about 200 nm△10 nm thick YBCO films sputtered on 1 mm thick LaAlO3 substrates. The holding probe integrates rf-SQUIDs, LC resonant circuits, and shielding coils. We have investigated the effects of the lumped element tank circuit resonator parameters on the rf-SQUID signal characteristics and based on the simulation and experimental... 

Microfluidic systems have the ability to produce microgels with uniform size distribution and spherical shape due to the laminar flow and better control of the flow rates. Spherical microgels with same size can be used as high-potential carriers for drug release. An important challenge in the production of these drug-carrying microgels is the simultaneous process of drug loading into microgels and their production. The overall goal of this project was to produce drug-carrying microgels with uniform size distribution that show controlled drug release. To achieve this goal, various factors such as the type of polymer, the type of drug, the volume ratio of the polymer and the drug and the... 

Occurrence of scouring around the seabed pipelines can lead to pipe failure and pose a serious threat to the marine environment, economic losses and waste of oil and gas. Therefore, to prevent the occurrence of scouring, by simulating this phenomenon and identifying the parameters affecting it, we can help to design a more efficient placement of pipes in the seabed. Various methods such as potential flow theory and turbulent single-phase and two-phase models have been proposed to simulate this phenomenon. The purpose of this article is to simulate and investigate the effective parameters of this phenomenon by combining computational fluid dynamics and separate elements. The innovation of... 

Loosening of uncemented tibial component is one the most common causes of total knee prosthesis failure which is a result of short-term factors such as instability and incomplete osseointegration as well as long-term factors such as peri-prosthetic stress shielding and bone atrophy. Porous cellular structures for tibial stem have been considered as a solution to this problem. This project is aimed to achieve an optimal gradient porous cellular design of tibial stem that in addition to sufficient mechanical strength, provides a perfect osseointegration and prevents bone resorption by incorporating appropriate porosity size, small micro-motion and favorable stress distribution on bone. A... 

In this study, using the MCNPX computer code based on the Monte Carlo method, the properties of protection against gamma-rays of the glass system with the combination of (55-x)Bi2O3-15Pb3O4-20Al2O3-10ZnO-xTiO2 with certain concentrations (x= 0, 5, 10, 15, 20, 25, 30 and 35 mol percent) and in nano and micro dimensions by calculating several parameters related to photon attenuation such as half value layer (HVL), Tenth value layer (TVL), mean free range (MFP), mass attenuation coefficient (m), linear attenuation coefficient (l), effective atomic number (Zeff) and buildup factor (BF) for We investigated different energy levels in the range of 1500-100 keV. To verify the simulation results,... 

If nuclear radiation is not weakened and absorbed, it can cause serious damage to human devices or the environment. Dual-purpose dry casks are one of the sources of nuclear radiation production as a place to keep the spent fuel assemblies. One of the ways to protect against them is to use shield. One of the most common of them is composite shield. The composite used in this study has a polymer matrix. The matrix of the used polymer is epoxy resin. In this study, two separate composites have been made to attenuate neutron and gamma radiation. In this thesis, first, by using the MCNPX code, the necessary simulations for the design and construction of composite shields have been carried out.... 

Flexible cones are one of the latest bone loss treatment methods in the ever-increasing revision total knee arthroplasty. This study is conducted to assess the biomechanical performance of the tibial flexible cellular cones in enhancing the initial stability of the implant system through the analysis of implant micromotion, as well as minimizing stress shielding through the analysis of strain distribution in the bone. The research evaluates the impact of various geometrical variables, including the thickness of the porous wall, the presence, type, width, number, and location of the inner solid wall notches on the spring stiffness and stress distribution of these cones. The research...