Sharif Digital Repository

Pulse tube refrigerator due to the relatively high efficiency, high reliability of linear compressor and the absence of moving parts in the cold area is known as one of the best options to generate up to one kW of cooling power at temperatures from 4 to 123 K. More recently, the use of the device at a temperature of about 150 K, makes use of it even outside of cryogenic temperature. The most important part of the device is regenerator, so understanding the nature of the flow and interaction of gas and solid network in the retrievers is necessary. In this study, Inertance pulse tube refrigerator (IPTR) is simulated using Ansys Fluent in two different conditions. In the first condition the... 

Optical telecommunication has received much attention due to its high capacity in the fast transmission of information over long distances. Each optical communication system includes a light source as a transmitter, an optical detector as a receiver, and an optical waveguide as a transmission and connection medium. Optical waveguides are used in a wide group of optical devices such as couplers, modulators, sensors, lasers and optical amplifiers. For this reason, optical waveguides are one of the main components of optical circuits used to form and connect devices within communication systems. Among the waveguides, subwavelength grating waveguide as a periodic structure is of central... 

In this PhD thesis, we propose a structure capable of performing two dimensional isotropic differentiation, gradient and divergence computation. This differentiator works based on exciting surface plasmon polaritons at an air-silver interface. In order to excite surface plasmon polaritons, Kretschmann configuration is exploited. For the purpose of implementing the mentioned operator, our proposed two dimentional differentiator is, in fact, a combination of two Kretschmann configurations that are introduced into thetrahedral structure that two of its sides are silver-coated. At the next step, our proposed structure is compared with other differentiators in the literature and it is shown that... 

Atom transfer radical polymerization (ATRP) is a convenient approach to synthesis of polymer with narrow molecular weight distribution. ATRP of acrylamide (AAm) is taken into consideration because of the intrinsic properties of acrylamide such as water solubility and biocompatibility. As reported in many recent works, polymerization of acrylamide by this method didn’t provide monomodal molecular weight distributions. In best condition with strong ligands such as Me4Cyclam, polymerization was carried out in a short time with high yield but polymerization was not highly controlled. It was shown that polymerization of acrylamide under typical ATRP condition displayed a much lower ATRP... 

One of the major problems in cancer treatment is the side effects of the drugs. Nowadays, scientists are developing smart nanocarriers which used for diagnosis and delivering drugs in order to circulate through blood vessels, pass the immune system, attach to cancer cells and kill them without any side effects. In the first research of this thesis, magnetic nanoparticles were coated by modified alginate and used as smart nanocarriers. Magnetic nanocarrier were sysnthesized based on hydrophobic coating of oleic acid and hydrazine oleate-modified alginate shell. The resulting carrier is pH-sensitive and the alginate shell removes in the low pH medium. DOX was placed between hydrophobic chains.... 

The purpose of the study was four-fold: first to investigate the predictive adequacy of the Task-Induced Involvement Load Hypothesis which contends that higher-load inducing tasks yield better retention rates in incidental learning situations, second, to examine whether type of dictionary search could affect vocabulary retention, third, to investigate the effect of translation direction on retention rate, and finally to determine the most effective tasks. To meet these ends, six groups of EFL learners - all male, aging 19-25, majoring in various fields of engineering sciences were assigned to the study. Each one of the groups performed distinct tasks which were as follow: reading... 

In recent years, quantum sensing based on spin defects in solid-state materials, particularly nitrogen vacancy defects in diamond, has been a significant research topic in the field of quantum technologies. Its applications have been demonstrated in various areas such as biology, microelectronics chips, and condensed matter physics. The aim of this research is to construct a magnetic imaging microscope based on an ensemble of diamond crystals using the continuous wave optically detected magnetic resonance method (CW-ODMR). By constructing an epifluorescence microscope and simultaneously exciting the diamond sample with green light and microwave radiation, it is possible to obtain information... 

In this study, the micro and nano particles of substituted strontium hexaferrites with nominal composition of SrFe12-xTix/2Znx/2O19 (x=0, 0.5, 1, 1.5, 2 and 2.5) were prepared by a co-precipitaion method. Ferrite-PVA composites (70:30) with thickness of 1.8mm were prepared at 220°C and 50Mpa. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), energy dispersive spectrometer (EDS), vibrating sample magnetometer (VSM) and vector network analyzer (VNA) were employed for characterization of synthesized powders and composites. XRD and FTIR results showed that single phase hexaferrite were obtained for almost all of the... 

In this research we focus on study and fabrication of ZnO composite nanofibers by electrospinning method for photocatalytic application. The most important challenges in the field of photocatalyst are photocatalytic activity under the visible light and efficiency enhancement. ZnO is a wide band gap semiconductor and it is not active under the visible light. In Iran, we have more than 300 sunny days in a year. Therefore fabrication and application of photocatalytic material with activity under the sun light that contained 40% of visible light is so vital in our country. In the first part of this project, ZnO-CNT nanofibers were fabricated and carbon doped in the crystal lattice of the ZnO.... 

This project aims at forgery detection in digital videos. Most of existing methods are based on similar methods for image forgery detection. Therefore, they do not have sufficient accuracy in case of video forgery detection. In this project, we focus on local copy/move attacks in digital videos and propose 3 solutions for 3 problems in this field: 1) detection of copy/move along time axis (temporal copy/move), 2) detection of copy/move along x and y axes (spatial copy/move) and 3) detection of original and fake part in case of finding a duplication. For each of these 3 problems a feature extraction algorithm and a forgery detection algorithm are proposed. Feature extraction algorithms are... 

Machine learning, artificial intelligence and cognitive science have been very popular in recent years. In the meantime, thanks to the significant increase in computing power of computers and easy access to large amounts of data, deep neural networks have been favored by researchers in recent years. With the help of these networks, high accuracy methods have been proposed in solving image processing, speech processing, time series processing, etc. Deep neural networks consist of multiple layers of neurons that perform layer-by-layer processing. In recent years, ideas have been proposed to use specific structures in neural systems and add external elements such as memory to these systems.... 

In this thesis, we introduce limited-sharing multi-party computation; in which there is a network of workers (processors) and a set of sources, each having access to a massive matrix as a private input. These sources aim to offload the task of computing a polynomial function of the matrices to the workers, while preserving the privacy of data. We also assume that the load of the link between each source and each worker is upper bounded by a fraction of each input. The objective is to minimize the number of workers needed to perform the computation, such that even if an arbitrary subset of t 1 workers, for some t 2 N, collude, they cannot gain any information about the input matrices. This... 

Liquid storage tanks are important components of lifeline and industrial facilities. Since,many tanks have borne serious damages during past earthquakes, Forcasting seismic behavior of tanks have attracted for numerous researchers who investigated seismic behavior of liquid storage tanks. This Thesis investigates the effects of slab foundation flexibility on seismic behavior of anchored and unanchored aboveground cylindrical steel storage tanks. In this study, finite elements method by ABAQUS software is used for three tanks with height to diameter ratios (H/D) of 0.343 , 0.85, and 1.53. These tanks are excited by seven one-way and three two-way earthquake records which were scaled to Iran... 

In this project the effect of rolling temperature on mechanical properties and microstructure evolution of a low carbon steel was studied. The steel was rolled up to a nominal strain of 67% at three different temperatures consisted of room, blue brittleness, and subzero temperature. Micreohardnessand tensile tests were used to characterize the recrystallization kinetics. Optical and scanning electron microscopic examinations were carried out to evaluate the mechanical, grain size, and the kinetics of static recrystallization by the Avrami equation. The results indicated that the volume fraction of static recrystallization increases with the increase in annealing period. The Avrami exponent... 

In this dissertation we aim to survey the concepts and results concerning Total Domination Set. Consider graph G = (V;E). Let S be a subset of V . S is Total Domination Set in G if every vertex in V is adjacent to at least one vertex in S.Furthermore, we call S a k-Total Domination Set if every vertex in V is adjacent to at least k vertices in S. The size of the smallest Total Domination and k-Total Domination Set in a graph G is respectively called the Total Domination and k-Total Domination Number of G.Now, if there is a sequence of subsets of V like S = V0; V1; V2; : : : ; Vl = V so that for each i, every vertex in Vi is connected to at least k vertices in Vi1, S is a Dynamical k-Total...