Sharif Digital Repository

In the past, opinion polls have generally been conducted using statistical techniques and the comments of those samples, which, in addition to its various challenges, require much power and cost per poll. Today, due to the high penetration rate of social networks in society, a very large fraction of people discuss such issues in terms of their opinions and preferences in these networks, and hence, these networks can be a valuable source of information to get the opinions of people in a short time, and by lower cost.The purpose of this thesis is to enhancing the results of the surveys which have already performed using various methods of text processing in social networks by using the graph... 

In recent decades the Due to development of coating techniques and the diversity of high organic matter, Discussion of organic coating materials being raised. Moreover, because of many applications of organic thin film in electronic and optical systems for example OTFTs and OLEDs Organic thin film growth topic is very interesting for scientists. Among these, some scientists study the theory and another bunch of scientists pay to practical aspects of this topic. In this thesis I pay to the theoretical level of Organic thin film growth and I simulate the system includes a collection of molecules, Went on to study some statistical properties of the system will be discussed and the dynamic... 

According to the rapid growing in communication devices, users need higher rates for their usages. Fiber optics is one the major choices to support such rates. One of the simplest and cheapest networks is Local Area Network (LAN) as a Passive Optical Network (PON). In these networks, some computers are locally connected to a passive optical device and communicate through it. Multiple access to a shared channel is an important task in such a network. In this thesis, Code Division Multiple Access (CDMA) is used and a new algorithm for Multiple Access Control Sublayer (MAC) based on scheduling will be developed to improve Quality of Service (QoS) and stabilize the network.
In the scheduling... 

The integration of pricing and production planning decisions has attracted many researchers and industry professionals, as these decisions directly affect the highest and lowest levels of a company. In this thesis, an integrated production-price problem for two complementary products is studied. Regarding the negative correlation of the two products, different sales strategies, including unbundling, pure bundling and mixed bundling, are used and three distinct models are proposed for each one. In the models, real and important assumptions such as production capacity limitation, shared resources, and the cost of preparation are considered. The goal of solving these models is to determine the... 

Three-dimensional biological scaffolds, as an emerging strategy in bone tissue engineering, enable the treatment of bone injuries without the need for grafting and implantation. The selection of suitable materials and fabrication methods for producing bone scaffolds is one of the key challenges in bone tissue engineering. This research focuses on the production of poly-lactic acid-bioactive glass S58 composite scaffolds using 3D printing. A solvent-based method was employed to produce poly-lactic acid composites containing bioactive glass particles (0.5, 1, and 1.5 weight percent). The composites were printed after the extrusion process and filament production for evaluating microstructural,... 

In the present work, at first Al-20 wt% Ti nanocomposite was fabricated via mechanical alloying in high energy vibratiory mill for 1-4 hours. Particles morphology, crystallite size changes and phases transformation were investigated during mechanical alloying. Next, the powders which mechanically alloyed for 2 and 4 hours was compressed by hot extrusion at 500 ℃. The extruded specimens were investigated by different tests such as density, hardness, tensile and differential scanning calorimetry (DSC). Microscopic analysis and phases transformation were also investigated by optical microscopy (OM), field emission electron microscope (FESEM) and X-ray diffraction. Then, the samples were heat... 

Over the past several years, TiO2 has become a focus of considerable researches as it possesses unique optical, catalytic and electrical properties in different applications such as sensors, water purification and dye-sensitized solar cells (DSSC). The goal of this research was synthesis of 1-Dimentional TiO2 nanostructure with suitable properties for DSSC applications. Two different TiO2 powders including micron-size anatase and mesoporous powders (produced from reaction of TiC and HNO3) along with KOH or NaOH were employed in hydrothermal process. The process was performed in two different containers including autoclave and balloon-shaped flask. The products were characterized by X-Ray... 

Improvement of semiconductors photocatalytic activity by different means has always been one of the challenges for researchers. Semiconductors doping for band-gap engineering and changing morphology to increase specific surface area and photocatalytic reaction sites are amongst these efforts. In this research simultaneous effect of these two parameters for three morphologies containing nanoparticle, nanowire and micro dandelion, simultaneously doped with carbon and nitrogen has been investigated. Final purpose of this thesis is to decrease the band-gap energy close to soft UV photon energies to make surface photodynamic therapy possible. Nanoparticle morphology with size distribution between... 

low-molecular-weigth aminothiols such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) play a critical role in many biochemical pathways . Their level in biological fluids such as human plasma and urine are important for clinical diagnostics of a variety of diseases.
We report herein the development of a highly sensitive colorimetric method for detection of cysteine and glutathione using the citrate capped gold nanoparticles (Au-NPs). This thiol containing molecules exhibit intriguing reactivities with Au nanoparticles. The reactivity involves the displacement of the citrate shell by the thiolate shell which is followed by intermolecular electrostatic interactions or... 

In this study insitu Al-Al3Ti-Al2O3 nanocomposite has been fabricated based on thermal decomposition of tialite (Al2TiO5) precursor in aluminium matrix through powder metallurgy method. Also the effect of high energy mechanical milling and hot extrusion on this procedure has been investigated. In the first step nano-structured tialite were synthesized through citrate sol gel methods. Then, different volume fraction of tialte was mixed with aluminium by high energy vibratory milling. The results of X-ray differaction analysis, scanning electron microscopy and differential thermal analysis showed that mechanical milling can degrade stability of tialite and cause strain-induced decomposition,... 

Soft magnetic materials are widely used in industries such as automotive, electrical, electronics, and telecommunications. These materials are essential for electromotors, inductors, transformers, and generators. The introduction of FineMet soft magnetic alloy has been a significant development in the design and production of nanocrystalline soft magnetic materials, leading to extensive research on these types of alloys. This particular study investigates the impact of applying an external magnetic field on the magnetic properties of Fe82.9Si4.2B12.3C0.6 amorphous alloy. The study begins by examining the kinetics of α-Fe phase crystallization using DSC. The results indicate that the... 

In the present study, the performance of the Capacitive Deionization (CDI) method for water purification was investigated using a prototype CDI system developed with flexible activated carbon fabric. A significant portion of water contaminants are ionic in nature. These contaminants encompass a wide range of substances, from harmless to highly hazardous, including alkali and alkaline earth metals, heavy metals, halogens, nitrates, sulfates, phosphates, and more. In the CDI method, the specific design of the electrodes and the purification cell allows for the application of an electric potential difference between a pair of electrodes as the ion-laden water flows through them. This causes... 

Iron oxide nanoparticles were synthesized using microemulsion technique as MRI contrast agents. Utilization of nanoparticles for biological applications and in this case as MRI contrast agents needs particles to be of small size and also narrow size distribution. For this aim, the effect of several parameters on size and size distribution has been studied. These parameters include water/surfactant ratio, precursor’s concentration and amount of polymer employed to improve nanoparticles colloidal stability. XRD, FE-SEM and TEM results reveal that the synthesized nanoparticles had small size (about 10 nm iron oxide core and 20 nm overall diameter) and possessed narrow size distribution (15-21... 

Photodynamic therapy that has developed over last century, now has become more widely used medical tool for the treatment of various diseases such as cancer. This technique involves delivery of photosensitizing drugs, irradiation of light and motivation of drugs. The limitation of light penetration in body tissue, may resolve by application of upconversion nanoparticles. Upconverting nanoparticles could help treatment of cancer tumors in deep or critical points of body by converting high penetrating Near-Infrared emissions to higher energy visible emissions.In this research Er3+-Yb3+ Co-doped titanium dioxide upconversion nanoparticles prepared by Sol-gel method. The phase structure and... 

Due to high strength, hardness and high resistance to abrasion, ceramics are difficult for machining. Also as the conductivity coefficient of these materials is low, major amount of produced heat during machining process will be absorbed in the cutting tool which causes intensive wear in cutting tool edge. As a result employing traditional machining for these materials because of low machining speed, tool wear, high roughness and large cutting force, has little efficiency in practice. Therefore non-traditional machining method may improve efficacy. In this thesis effect of utilizing ultrasonic vibration in machining process of fused cast silica ceramic has been studied. Aim of this study at... 

In the present investigation, the mechanical alloying (MA) technique was employed to produce nanocrystalline Al-Ti alloys. Elemental Al and Ti powders were mixed with different compositions (0, 5, 10, and 20 wt.% Ti) and then, milled in a planetary ball-mill up to 40 h. The variations of powder morphology and particle size, apparent and tap densities, microstructure, grain size, lattice strain, and microhardness were studied with increasing the milling time. While dissolution of Ti in the Al matrix resulted to the formation of supersaturated Al-Ti solid solution in the samples containing 5 and 10 wt.% Ti, the specimen with 20 wt.% Ti, eventually, led to nanocomposite powder with different... 

Sparse-view computed tomography (CT) is recently proposed as a promising method to speed up data acquisition and alleviate the issue of CT high-dose delivery to patients. However, traditional reconstruction algorithms are time-consuming and suffer from image degradation when faced with sparse-view data. To address this problem, we propose two new frameworks based on deep learning (DL) that can quickly produce high-quality CT images from sparsely sampled projections and is able for clinical use. Our first DL-based proposed model is based on the convolution, and residual neural networks in a parallel manner, named the parallel residual neural network (PARS-Net). Besides, our proposed PARS-Net... 

A great deal of information are continuously generated by users in different contexts such as social networks and online service providers in terms of temporal marked events. These events indicate that what happened to who by when and where.Modeling such events and predicting future ones has interesting applications in different domains such as item recommendation in online service providers and trending topic prediction in online social networks. However, complex longitudinal dependencies among such events makes the prediction task challenging. Moreover, nonstationarity of generative model of events and large size of events, makes the modeling and learning the models challenging.In this...