Sharif Digital Repository

Magnesium is one of most important elements in bio hedroxyapatite. Magnesium effects on all stages of bone growth metabolism. Also increases bone’s osteoblastic and osteoclastic activities. That’s why incorporation of Mg ions into hudroxyapatite structure has become one of interesting fields for bone implants production. In addition Mg can improve sintering and mechanical properties of HAp. Thet’s why in this investigation the effect of incorporated Mg into HAp structure has been studied. Three kinds of powders have been prepared to perform this study. Pure HAp nano powder produced via sol-gel method, Mg contain HAp nano powder produced via sol-gel method and a mixture of nano HAp and nano... 

The purpose of this study was aimed to evaluate the effect of Alumina on the sintering, phase development, mechanical properties and biocompatibility of fluoridated hyroxyapatite sintered via conventional furnace and microwave assisted oven. Green compacts having 30wt% Alumina nanoparticles were sintered without pressure at various temperatures (1000-1400°C) for one hour in conventional furnace. Phase composition, thermal behavior and morphological analyses were performed using X-ray diffraction (XRD), simultaneous thermogravimetry and differential thermal analysis (STA), and Scanning Electron Microscopy (SEM), respectively. With the increase in temperature and the Alumina content, severe... 

Regarding the ever-increasing usage of text generation and analysis in Natural Language Processing field, Language Modeling and Masked Language Modeling have been recently one of the most frequent tasks. Besides, many pretrained models such as BERT have been proposed due to the lack of rich datasets and computational resources among researchers. These models can be finetuned on other datasets in downstream tasks. Although these Transformer-based deep neural networks have performed perfectly in many problems, they still have some shortcomings in a few tasks.Furthermore, structured data like graphs have been recently used extensively in Natural Language Processing and researchers have taken... 

HCCI engines have lower NOX and PM emissions and higher thermal efficiency compared to spark ignition engines. But these engines have some deficiencies which up to now have prevented their widespread employment. These engines have not been very successful at high loads and speeds and in these conditions normally produce high pollution and noise. In order to solve this problem the present research proposes to equip the HCCI engines with fuel injection system so that at low loads and speeds operate at HCCI engine mode and at loads and speeds higher than pre-set limits, use the fuel injection system in order to operate at a combined HCCI and compression ignition engine mode and provide a... 

Many studies on hybrid vehicles have been done in the past few years. The Full hybrid vehicles need a large number of batteries creating up to 300V to meet the required voltage of electric motor. The size and weight of the batteries cause some problems. This research investigates the mild hybrid vehicle. This vehicle includes a small electric motor and a high power internal combustion engine. In most cases the car’s driving force is created by internal combustion part. A small electric motor, which can operate as engine starter, generator and traction motor, is located between the engine and automatically shifted multi-gear transmission (gearbox). The clutch is used to disconnect the gearbox... 

Some researches have been carried out in the last 20 years in order to increase the present IC engines thermal efficiency and their optimum performance. (HCCI) engine is viewed as a combination of spark-ignition (SI) and compression-ignition (CI) engines. This is because HCCI engines use premixed fuel/air mixture like SI engines and have auto ignition combustion after the mixture is compressed like CI engines. Control of combustion and ignition timing are the main challenges of these engines. Ignition delay, compression ratio, fuel air equivalence ratio and intake temperature and pressure are considered to be the most effective parameters on HCCI combustion.HCCI engines have great potentials... 

The idea of improving performance of internal combustion engines has always been important for researchers and manufacturers. In recent decades, due to limited resources of fossil fuels and introduction of vehicle emission regulations, researchers have undertaken more efforts to achieve goals such as increased horsepower, reduced fuel consumption and pollutant emissions reductions. Homogeneous charge compression ignition engine is a modern and efficient design that has attracted attention of many researchers. In[[ these engines, homogenous mixture of fuel and air enters into the combustion chamber and with a mechanism of self ignition, produces more power and has less fuel consumption... 

The partially stratified charge (PSC) approach involves micro-direct-injection of pure fuel or a fuel air mixture, to create a rich zone in the region around the spark plug. A theoretical model is presented in this research to predict ignition delay and combustion process in partially stratified charge engine. It considers flame progress through rich and lean regions. Step by step calculations will be carried out in both regions. The process continues to the point where all the fuel is burned. At each step for one degree rotation of the crank shaft, there is a change in cylinder volume and mole fraction burned due to burning of a fraction of the mixture. Considering heat transfer from the... 

The electric field induced response of a charged droplet in an uncharged gel is calculated theoretically. For modeling, the gel is considered as a soft porous solid that is saturated with a Newtonian electrolyte and modeled as a continuum that contains 3 phases: a porous, soft and compressible solid, an incompressible Newtonian fluid and the ions inside fluid. Droplet is modeled as a charged incompressible Newtonian fluid immiscible with the gel. The droplet-gel interface is considered as a surface with electrostatic potential ζ . After obtaining governing equations, they solved by using perturbation methodology and linear superposition. Boundary conditions, especially at the droplet-gel... 

Nanoparticles can be applied as chemical agent in enhnaced oil recovery like surfactants and polymers. One of nanoparticles usefull capabilities is modification of their surface. This research investigates this capabilty of nanoparticles in enhanced oil recovery. Surface modification of nanoparticles with both agents can bring new abilities to these materials. Here surface of silica nanoparticles is modified by hydrophilic agent comprising PEG groups, hydrophobic agent comprising propyl group and both agents. FT-IR tests showed that grafting of modifiyng agents on surface of nanoparticles is well done. To investigate effect of nanoparticles surface modification on nanoparticles capability in... 

Important features of the nanoparticles properties are their high superficial area and being able to reform their surface. In this study, the repairable property used to reform surface of silica nanoparticles (Those are used more frequently than other nanoparticles). Repairing of surface are doing to use nanoparticles as a surface-active material in enhanced oil recovery. Silane compounds with different chain length are used to create hydrophobic nanoparticles and PEG compounds are used to create hydrophilic nanoparticles. Also amphiphilic nanoparticles are created with a combination of both hydrophilic and hydrophobic compounds. To investigate the usefulness of nanofluids are made up of the... 

The main purposes of this project are simulation, design, and fabrication of a microfluidic system based on dielectrophoresis (DEP) exploiting AC voltages for separation of microparticles. Generally, this project can be divided into two parts. First, the engineering section including design and fabrication of microchip, and second biological samples preparation for investigating the system performance. The main advantages of proposed system are eliminating joule heating, a significant problem in insulating based dielectrophoresis systems, overcoming problems related to metal contamination in biological samples, the main problem of conventional dielectrophoresis platforms, and removing... 

The main goals of this research are design, simulation, and fabrication of a microfluidic system working based on dielectrophoresis. This research divided into two different parts, the first of which is the simulation of a microfluidic system, and second of which is an attempt for fabrication of microfluidic system. For the fabrication of the microfluidic system, different methods were used. In the simulation part, the enrichment of different particles was investigated, and the effects of different parameters on the enrichment were assessed. It was observed that as flow rate increases, the enrichment amount diminishes. Furthermore, as the microfluidic depth decreases, the enrichment amount... 

Surface modification is an important property of nano particles. In this project surface of silica nano particles modified with hydrophobic and hydrophilic groups to imrprove surface activity of nano particles. Purpose of this project is to study surface activity of surface modified silica nano particles in different temperatures from 20 to 70 degree centigrade. Also effect of salt and time on the surface activity is studied. At first nano particles modified just with haydrophobic groups and then just with hydrophilic groups (hydrophobic and hydrophilic nano particles) and after that, the surface modification done with both hyadrophilic and hydrophobic groups (amphiphilic nanoparticles).... 

In recent years, desulfurization has received much attention due to its devastating environmental effects. The existence of sulfur compounds has effects such as corrosion, poisoning of catalysts, reduction of heat of combustion and reduction of price. Sulfur compounds in hydrocarbon fuels also produce sulfur oxides caused by combustion then they enter the atmosphere, and cause acid rain. Acid rain dissolves building materials, poisons lakes, and destroys forests. Therefore, removing sulfur or converting it to less harmful substances is one of the most important processes in refineries. The method studied in this research is the use of adsorption desulfurization method by microchannel which... 

The present paper is an attempt to critically measure interfacial tension with microchannels and achieve the quantity of adsorption in the liquid – liquid interfaces and comparing the adsorption of surfactants and nanoparticles surface modificated as well. At this point we need to make emulsion and it is necessary for droplets to be monodispersed due to analyze these droplets in this paper. According to this condition for our droplets microsystems are the best options. As we know surfactants were already known as a stabilizing emulsion agent and in this paper nanoparticles are suggested as suitable alternatives for surfactants which can be absorbed as if they are in the water / oil... 

Emulsions are the intermittent dispersion of liquid droplets that have many applications such as polymerization, dyeing, cosmetics, food industry, etc. Droplets can be created in a variety of ways, but the most important point in emulsification and the greatest efficiency of its applications is when the formed droplets are uniform. In the emulsification process, there is a key parameter called interfacial tension, which affects the behavior of the formed droplets, such as their stability and morphology, and its precise measurement is very effective in the quality control of the mentioned applications. Be. In this research, droplet formation in microfluidic systems due to uniform droplet... 

Conical nanochannels have desirable electrokinetic properties due to asymmetry,including ionic current rectification and ion selectivity. The present study numerically addressed the effect of slip length on the ionic current rectification and ion selectivity in conical-shaped electrolyte-loaded nanochannels with and without a coated polyelectrolyte layer. The electrolyte was considered a salted incompressible Newtonian fluid. The polyelectrolyte layer was also modeled as a rigid and charged porous solid saturated with a salted Newtonian fluid. The electrolyte-polyelectrolyte layer interface was modeled as a surface, considering ion partitioning with distinct physical properties across the... 

In this study, the performance of electrocoalescence in a microfluidic device was investigated through numerical simulations. The microfluidic device consisted of two immiscible fluids, a continuous phase, and a dispersed phase, which were modeled as incompressible Newtonian fluids. The interface between the two phases was tracked using a phase-field model. A flow-focusing geometry was employed to crate water droplets in oil. The dispersed droplets were then pass over a set of electrodes. The merging of two adjacent droplets in the microfluidic device was observed by applying a constant electric field. The voltage of 60 V is the lowest voltage at which the regular merging of pairs of drops... 

This thesis analyzes the scattering of a propagating electron from a single bound electron .The study demonstrates how the scattering of the propagating electron from the bound electron causes entanglement between two electrons. The study then considers the impact of spin-dependent scattering in the presence of Hartree and exchange potentials. In the first step, only an exchange potential is studied. Transmission coefficients are calculated for spin-flip and non-spin-flip states by solving the Hamiltonian equation in different regions, applying the continuity boundary conditions for the wave function and its derivative in each region, and using the transfer matrix method. Transmission...