Sharif Digital Repository

Optical coherence tomography is a rapidly evolving imaging technique that enables non-invasive cross-sectional imaging of high-sensitivity semi-transparent samples (poor scattering). The biggest limitation of optical coherence tomography is the low penetration depth (about a few millimeters) in tissue. OCT is based on low-coherence interferometry. In this study, we investigate Michelson and Mach-Zehnder interferometers in OCT set-up and explain the advantages of using Mach-Zehnder interferometers in OCT systems. Furthermore, in this thesis, we have shown that by using Mie scattering, we can have forward scattering, hence the penetration increases. We have suggested this method as a solution... 

During the past few years, hexavalent chromium (Cr(VI)) is of environmental concern due to its high toxicity and mobility. Therefore, removing it from industrial wastewater is of chief significance. In this research, efficient photocatalyst materials (xµLTiO2NPs@ZIF-8) for the reduction of Cr(VI) from water resources were firstly synthesized. This composite was prepared by an in situ method with zeolitic imidazolate framework-8 as the matrix. TiO2 and ZIF-8 were selected for their excellent stability in aqueous media, high photoactivity, non-toxicity, and high surface area. The structure of the as-synthesized materials was characterized by X-ray powder diffraction (XRD), scanning electron... 

Fabrication of porous hybrid coatings, specially in combination with carbon compounds, can improve the electrochemical behavior of the coating. In this study, graphene oxide (GO) was first synthesized by tour method. After examining different methods to create a porous coating, the electrochemical coating method for simultaneous deposition of GO and nickel on the copper substrate was selected. CTAB was used to form nanometer porosity in the coating structure. In order to investigate the effect of GO on the properties of the deposited coating, two porous coatings of nickel (Ni) and nickel reduced-graphene oxide (Ni-rGO) were investigated by different analyzes. These analyzes include FESEM... 

Polylactic acid (PLA) is considered as a great option to be employed as 3D porous scaffold in tissue engineering applications owing to its excellent biocompatibility and processability. However, relatively weak mechanical properties, low degradation rate and inappropriate biodegradability limit its extensive usage. In order to overcome the mentioned challenges, micrometric magnesium (Mg) particles were incorporated into the PLA matrix by the fused deposition modeling (FDM) technique. The effects of various Mg contents (i.e., 2, 4, 6, 8 and 10 wt%) on the mechanical, thermal, structural, wettability, rheological, biodegradability characteristics and cellular behavior of the 3D porous PLA-Mg... 

Neural networks play an important role in industry nowadays. Matrix-vector multiplication (MVM) as one of the major building blocks of neural networks is conventionally implemented by electronic integrated circuits. In recent years, researchers have shown interest in implementing matrix-vector multiplication with a photonic approach to reduce the loss and increase the speed. By simultaneously using different degrees of freedom of light, such as amplitude, phase, wavelength, and angular momentum, it is possible to reduce the volume of electronic processors, increase computational accuracy, and higher processing capacity. In this research, matrix-vector multiplication is implemented by using... 

It is well known that Cu/Al2O3 nanocomposites have high potential for use in structural, electrical applications which enhanced mechanical characteristics are required. In the present work, in order to improve the in-situ oxidation kinetic of solute element, chromium was used instead of aluminum. At the initial stage, elemental Cu and Cr powders were mechanically alloyed for 60h under argon atmosphere. It was followed by mechanically milling of Cu-Cr pre-alloyed and Cu2O powders. The nanocomposite specimens, containing different amounts of Cr2O3, depending on the Cr content in the range of 1-3 wt. %, were produced by in-situ oxidation of Cu-Cr pre-alloyed powders. To prevent oxidation of... 

Basically, it is required that the materials used as electrical contacts should have good thermal and electrical conductivity and certain strength. The copper base composites with fine TiO2 particles as reinforcement have almost identical electrical and thermal conductivity with copper; in addition, they have the advantage over pure copper in high strength owing to the dispersion of the fine TiO2 particles, which improve copper matrix strength through impeding dislocation movement. In this present work, at the initial stage, Cu and Ti powders were mechanically alloyed for 60h under Argon atmosphere, and then added Cu2O powders as oxidant. The specimens, containing different amounts of TiO2,... 

In this research a copper- Tungsten carbided nanocomposite coating prepared by electrodeposition from a sulfate bath in order to increase the hardness and erosion resistance of cooper without loosing cooper's specific physical properties as like as electrical and thermal conductivity. Various parameters were evaluated for finding significant factors in electrodeposition of Cu-Co/WC composite. Current density and concentration of WC and SDS were selected as affective factors. The morphology and structure were characterized by XRD and SEM. The mechanical properties of the coatings, such as hardness, wear resistance and surface roughness were studied with Vickers hardness indentation; pin on... 

Polarization-sensitive optical coherence tomography is a non-invasive imaging technique that is capable of producing two-dimensional or three-dimensional images using the additional properties of light, as well as qualitative examination of the sample. This system, like optical coherence tomography, is mainly used in ophthalmology as a powerful tool for the early detection of eye diseases. PS-OCT can obtain high-resolution cross-sectional images of ocular fibrous structures, such as the retina or anterior segment, which show birefringence when injured. The main purpose of this dissertation is to develop an analytical model of system layout to study important parameters such as birefringence.... 

Zinc oxide is a wide band gap semiconductor material with wide applications as conductive oxides used in electro-optical devices. Thin films of doped zinc oxide (e.g. Al:ZnO, B:ZnO) are already used in thin-film solar cell technologies as electrodes. Chemical bath deposition (CBD) is a promising method for fabricating transparent and conductive ZnO layers at low temperatures (<100 °C) on nonconductive and temperature-sensitive substrates. Having a natural crystal habit, ZnO readily grows rod-like arrays when grown in an aqueous solution by CBD, posing challenges when attempting to deposit dense and conductive layers. The purpose of this study was to deposit dense and conductive zinc oxide... 

In this experiment, first the Fe and Al powders with atomic ratio of 25 and 75 were mixed by mechanical alloying process. After obtaining the optimum conditions of milling, nano structural Fe3Al powder was synthesized by 40 hours alloying with a Ball to Powder Ratio (BPR) of 20:1. The synthesized powder was then milled with different weight ratios of titanium and Cr for 30 hours. Morphological changes, size of powder particles, lattice strain, grain size and phase transitions were studied for different powders in different time spans during milling process by means of scanning electron microscopy, X-ray diffraction and grain size analyzer. The smallest grain size gained for milled powder... 

For application such as electrical contacts and spot welding electrodes, both high electrical conductivity and wear resistance are required. Additionally, such parts should have structural stability at evaluated temperature. Copper based composites containing carbides or oxides reinforcement can be the good choice for production of such parts. In present work, in-situ Cu/NbC composite via mechanical alloying with homogenous distribution of nano reinforcement particle has been produced. For this purpose, in first stage, copper powder was milled with 5, 8, 10 and 12 wt. % of niobium powder in two types of mills, i. e. vibratory dicky mill and planetary ball mill for 5 and 32 h respectively. At... 

In applications requiring high density and good mechanical properties, tungsten heavy alloys are of interest [1]. Due to lack of intermetallic phase in microstructure of 90W-7Ni-3Fe alloy, it is more attractive to use. At present work, the powder metallurgically produced specimens were cold swaged. At this work, during the production and swaging, some parameters were changed. Powders of tungsten, nickel and iron were milled for an hour with the speed of 50 rpm in Retsch Planetry/PM 400 MA ball mill. At the first route, elemental powders mixture after 1 minute were reached to 30MPa, after that were heated at rate of 50°C/min to 1500°C in vacuum (hot press or HP). At the second route, powders... 

With high power conversion efficiency, comparable to silicon solar cells, the conventional perovskite solar cells (PSCs) are leading the photovoltaic research scene. However, they have poor stability in operation due to instability of organic-inorganic hybrid PSCs. Several methods have been proposed to improve their stability including Substitution of the organic component by an inorganic one For example, inorganic perovskite compound such as 〖 CsPbI〗_3 with bandgap about 1.7 eV is a good candidate. However, it requires high synthesis temperature (about 300 ℃), and the resulting cell has a lower efficiency than the organic one. Introduction of Cs, as an inorganic element, into organic... 

One of the most important applications of aluminum alloys is the automobile's piston, which is affected by wear and tension. Nowadays, the addition of abrasion-resistant particles to molten metal and the production of composite pieces has been considered industrially. In this research, composites of A356/SiC (3, 8 and 12 %wt.) were producted by electromagnetic stir casting. In this study, after optimizing the stir casting conditions for the production of samples, the influence of electromagnetic stirrer on the microstructure and distribution of particles in the melt was studied. Moreover effect of adding SiC particles on abrasion behavior of A356 alloy was checked. Electromagnetic stirring... 

The aim of this research is to study the effect of surfactant type and the concentration reactants on the size, shape and magnetic properties of iron-gold core-shell magnetic nanoparticles (NPs) useable for biomedical application. The reverse micelle procedure was employed to synthesize iron NPs using two surfactants of CTAB and SDS. A gold shell with a thickness in the range of 10 to 40 nm was induced by reverse micelle method in order to prevent oxidation of the iron core. The size and morphology of NPs were studied by transition electron microscopy (TEM). It was found that the size of NPs increases by the increasing the reactants concentration while the morphology of the NPs was not... 

In this investigation, effect of processing parameters on the soft magnetic properties of nanocrystalline Fe85Si10Ni5 (at. %)-phenolic resin composites were studied. The nanostructured powders were obtained by mechanical milling in a high-energy vibratory disc mill. Annealing was performed to decrease internal strains and density of dislocations. The microstructure, morphology and DC magnetic properties of the milled powders were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and a vibrating sample magnetometer (VSM). Bulk samples were obtained by compaction in different pressures and temperatures. The effects of different compaction treatments and annealing...