Sharif Digital Repository

Liquid crystals are the type of the matter which show different levels of symmetry and structural properties in between those of a crystalline solid and an isotropic liquid. They can form various phases such as uni- or bi-axial nematics that because of their applications in display technology, have been widely investigated. In this thesis, uniaxial and biaxial ellipsoid liquid crystals have been simulated by using molecular dynamics simulations using LAMMPS simulation software. By control of the density of the system in NVT ensemble, the phase transitions of the systems were investigated. In all the simulations, the mesogens interact with RE-squared coarse grained force field. By calculating... 

Nowadays, due to gearbox drawbacks, the direct-drive wind turbines have received much more attention. Permanent magnet synchronous machines are commonly used for this purpose. The flux reversal machine with a magnetic gearbox and high power density could be an appropriate alternative. Due to placement of permanent magnets on the stator, the machine has a simple and robust structure and provides more reliability. There is limited study on optimization of the flux reversal machine and the existing papers are not complete and many parameters like PM dimension, working temperature, and winding reactance are not considered in the optimization process.Considering the flux reversal machine... 

Micropollutants are a wide group of organic compounds that are detected in most compartments of the environment. Their environmental concentration is usually in the range of few ng/l to mg/l, but they remain biologically active even at such low concentrations; may be accumulated through the food chain, and pose a serious threat to the environment, fauna, and human health. Among micropollutants, pharmaceutical active compounds (PhACs) are of special concern. It is accepted that the main sources of PhACs in the environment are effluents from wastewater treatment plants (WWTPs), where conventional activated sludge processes are not able to degrade most of them. To address these concerns, the... 

Levofloxacin has been widely used in recent years as an antibiotic in the treatment of various bacterial infections. This drug compound is known as a newly emerging contaminant. In this study, the degradation of this pollutant has been investigated using advanced oxidation processes, biological process, and a combination of advanced oxidation-biological processes. In order to evaluate the degradation of levofloxacin with advanced oxidation processes, an electrochemical process was used. Advanced oxidation processes were carried out to optimize initial concentration parameters of the contaminant (5-15 milligrams per liter), electrolyte concentration (2.5-10 grams per liter), and current... 

Statistics show that plastic production in the world is increasing, with 335 million tonnes in 2016 reaching 367 million tonnes in 2020. Since the presence of plastics in the dimensions of micro and nano, especially in aquatic environments can have adverse effects on human health and other living organisms, it has raised major environmental concerns. Therefore, it is necessary to think of measures to remove them and develop efficient methods for eliminating and decomposing microplastics. Recently, the advanced oxidation processes have attracted much attention because of the ability to eliminate recalcitrant compounds. In this study, electrochemical techniques and Fenton-based techniques for... 

Cardio Vascular Diseases (CVD) is currently the most important cause of mortality in the world. Coronary artery disease (CAD-with 3 major epicardial vessels) is one of the significant CVD. Coronary angiography remains the gold standard for identifying the presence and absence of stenosis due to CAD. It is performed by inserting a catheter into the coronary artery, directly injecting radiopaque contrast material there and recording radiographic images in different view of arteries. Images of this invasive way show severity and area of stenosis.
A sign of CAD is endothelial dysfunction (inner artery layer) in peripheral arteries like the brachial artery. Due to a significant correlation... 

One of the major environmental problems in recent years is the presence of micropollutants that cause many problems for the environment and living organisms. Diclofenac is one of the micropollutants and endocrine disruptors. Conventional treatment methods do not have the ability to effectively remove pharmaceutical pollutants and micro-pollutants, and finding a suitable approach to remove these pollutants is of great importance. In recent years, biological methods such as the use of enzymes and molds have received attention, but due to the relative removal of pollutants, these methods have been combined with membrane technology to improve the level of pollutant removal and increase the... 

The extensive use of nonlinear loads such as motor drives and new generation of home appliances has caused a deterioration of power quality in power systems. The use of active power filters due to the fast variation of the loads has been recommended by power engineering. In this method, the harmonic profiles are controlled by applying active filters in a distribution feeder. Optimal placement of active filters in a distribution system due to the increase of harmonic generation loads has attracted researchers. However placement of each filter is the major concern that researchers face. In this paper, a new objective function is introduced to determine the optimal number and location of active... 

Industrial wastewater treatment has always been one of the significant human being problems for the years. In particular, sewage containing heavy metals that, if discharged into nature, would have irreversible effects on the ecosystem and human health. Due to their toxic nature, heavy metals will reduce the efficiency of wastewater treatment systems if they are not efficiently treated. Also, the removal of Nitrate from the wastewater, which is one of the most stable nitrogen oxides, has always been a serious human problem in the treatment of effluents due to their high solubility in water. The simultaneous presence of nitrate and heavy metals in the effluent will cause many problems in the... 

Many future space missions, will require a high level of autonomy to service, repair, refuel, reconfigure satellites. As we know there is no project that has demonstrated an actual online pathpelanning for a terminal rendezvous phase in docking maneuver, for an uncooperative tumbling target. Particularly when the target is in a noncircular orbit. Such missions require a 6DOF precise position and attitude tracking maneuver that safely can avoid collision to the target and are capable of flying around. This thesis introduce a new guidance method for vectorial approach to the target in terminal rendezvous phase and applies a Sliding Mode method for attitude tracking control with respect to... 

Today, the need for high-speed machine tools, in areas such as defense, medical and electronic for producing parts with millimeter dimensions, and with features smaller than the millimeter, increased. To meet this need, the machine tool can be used with smaller dimensions and with high speed. These machines are able to produce these parts with high production rates.The project aims to improve technical design and construction of a micro spindle to achieve sustained speed about one hundred thousand RPM. In this project, the first step in understanding the fundamentals of the theory and the system components, and the whole operation was performed. The design is based on studies carried out in... 

In this thesis, a cellular model of electroporation process and its detection by ultrasound signals is proposed. Electroporation is permeabilization of the cell membrane, caused by an external electric field. The resulted pores open cell’s membrane to large or hydrophilic molecules. The process of Electroporation has been used in Gene therapy and treatment of solid tumors. In this project, first we made a phantom of electroporated tissue and a phantom of normal tissue and then we simulated their responses to a linear array ultrasound transducer. By comparision of received signals from phantoms the probable effect of electroporation on ultrasound RF signals revealed. Results show up to 5 %... 

Nowadays, all of the devices that measure blood pressure commercially at home are using wrist or arm cuffs preventing the systolic or diastolic blood pressure from being measured continuously. Various parameters such as blood flow with some degree of correlation with blood pressure that can be measured noninvasively have been suggested. However, these parameters do not produce accurate estimates for blood pressure. Pulse Transit Time (PTT) which is defined as the interval between the R peak of ECG signal and the next PPG signal valley has shown to have over 90% correlation with systolic blood pressure in past studies. In this thesis, the relationship between the value of the systolic blood... 

Routine ultrasound calibration methods have some restrictions such as: low bandwidth, low frequency resolution, limited spatial resolution, the high cost of test and risk of damage to the transducer when exposed to high powers. In this thesis, a new technique based on microbubble resonance is proposed. Non-linear resonating microbubbles produce harmonics;the first harmonic may be masked by reflection from larger microbubbles as well as unwanted reflections which cause ambiguity in the determination of the amplitude of the excited pressure. Therefore, the second harmonic is used, with a single characteristic peak. In order to model the physical phenomenon, the second harmonic generated in the... 

Measuring the human brachial arterial diameter has significant applications in medical research. This is conventionally carried out using ultrasonography which is costly and operator-skill dependent. The objective of this project is to come up with substitute solutions based on optical measurement. Reflectance photoplethysmography (PPG) over the radial artery has been considered to this end. Monte Carlo method has been employed to simulate light propagation in the wrist area, along with a model comprising tissue, artery and bone, made of simple solid geometries. Functions of optical parameters such as refractive index, absorption coefficient, scattering coefficient and anisotropy factor have...