Sharif Digital Repository

Trying both to understand the brain and to emulate some of its strengths has been one of the greatest human desires since ancient times. One of these amazing abilities is recognizing via vision. As a result, image recognition has been turned into one of the most attractive areas of research in Computer Vision field since recently. The challenging problem begins to rise where occlusion, scale, rotation and various light conditions contribute and manipulate the paradigm of image recognition. Although recognitions with these challenging problems are some of the capabilities that the brain has, but these are not all. One of the remarkable abilities of the brain is to recognize concepts through... 

Nowadays, the use of distributed generation (DG) units and microgrid systems is mainly limited to their operation in the grid-connected mode. In the grid-connected mode, a microgrid including its loads and DG units is connected to the main grid at the point of common coupling (PCC). In this case, the main grid provides fixed voltage and frequency for the microgird and each DG unit regulates its power components based on the conventional dqcurrent control strategy. Autonomous (islanded) operation of a microgrid, however, is not as straightforward as its operation in the grid-connected mode, i.e., control and power management of an islanded microgrid is very difficult due to the stochastic... 

Nowadays, power electronics converters with pulse width modulation (PWM) are widely used in different power circuits. Operation of semi-conductive switches during on and off conditions causes switching dissipation and consequently decreases the efficiency of the PWMs. Recently, by increasing the required power for power electronics applications, quasi-resonant converters attract attentions. Quasi-resonant converters, by adding resonant circuits to the PWM converters causes the soft switching operation (switching with zero current or voltage) and decreases the energy loss. In conventional control methods of these converters, the nonlinear average circuit model is linearized around the... 

Nowadays, the use of distributed generation (DG) units and microgrid systems is mainly limited to their operation in the grid-connected mode. In the grid-connected mode, a microgrid including its loads and DG units is connected to the main grid at the point of common coupling (PCC). In this case, the main grid provides fixed voltage and frequency for the microgird and each DG unit regulates its power components based on the conventional dq-current control strategy. Autonomous (islanded) operation of a microgrid, however, is not as straightforward as its operation in the grid-connected mode, i.e., control and power management of an islanded microgrid is very difficult due to the stochastic... 

Because of widespread use of optical communication systems, analysis of optical wavepacket behavior during propagation in optical devices is of great importance. On the other hand, constant demand for improving the quality of data transmission and increasing data processing speed raises the necessity of studying novel electromagnetic structures for the purpose of designing new optical devices. Therefore, Photonic Crystal (PC) based structures, for their unique optical properties, have been subject of vast investigation in last two decades. Control of optical wavepacket behavior in photonic crystal based structures is considered in the present dissertation. Depending on the structure under... 

converters in electric vehicles, it is necessary to reduce their dimensions and increase their efficiency. It is expected that in the near future wide band gap semiconductors will be used to achieve these goals. On the other hand, usage of planar transformers is necessary to achieve slim and compact converter designs in electric vehicles. Clearly, planar transformers offer a significant advantage in replacing bulky wired transformers in high frequency LLC resonant converters with WBG transistors. planar transformers also have several other advantages, including low flux leakage, modular structure, and low thermal resistance.However, in planar transformers, due to the proximity and large area... 

In today’s microwave communication, oscillators play a very important role as signal sources, so, the design of an oscillator with suitable parameters can affect the final performance of a communication system. Among different parameters, phase noise is of utmost importance since this parameter can lead to interference in multi-frequency channel systems and thus its estimation and measurement is vital. In an oscillator, in addition to measurement, the most important problem is to reduce phase noise. In fact, for improving the performance of a transmitter-receiver ( e.g. receiver sensitivity ), one of the solutions is using a local oscillator with low phase noise. Our purpose in this project... 

Magnetic resonance imaging (MRI) is a highly efficient method that can provide acceptable contrast between soft tissues. But the big disadvantage of this method is that its acquisition is slow. To find the reason of being time-consuming should the procedure be surveyed. In the magnetic resonance imaging, location information obtained using phase and frequency encoding gradients. So the output is matrix of image data in the frequency domain, which is called k space. For the formation of the k space phase, need to apply gradients several times and this is the main reason of dullness of the system. Therefore, in this project using software methods try to reduce the scan time as possible. Among... 

Phase noise is one factor determining the quality of radar and telecommunication systems. Oscillators play an important role in system phase noise, as a signal generator for information modulation. Due to the greater impact of flicker noise at near carrier frequency than other types of phase noise sources, its reduction will greatly impact the phase noise of the telecommunication system. In this research, the simulation of phase noise and flicker noise of an oscillator with various types of bias circuit methods, such as bias with two independent sources, self-bias, improved self-bias, active bias, and low-frequency feedback, has been done. Then, a microwave dielectric resonator oscillator... 

Using Variational Method, two important hydrodynamic phenomena, “internal gravity waves” and “gravity currents”, are modelled theoretically in this research. Variational method as a robust technique for modelling complicated problems related to fluid mechanics gives us the ability of finding closed-form formula for predicting the behavior of the flow in an ideal fluid system. In the first part of this research, focusing on the nonlinear resonant interaction between surface and internal waves, we model the evolution of interfacial waves on the interface of a two-layer fluid system. This phenomenon play an important role in the mixture of the fluid and cascade of energy in the environment.... 

The optimum wave functions and calculation method were obtained using a 24 factorial design. Based on preliminary experiences, the following four factors at two level was selected: electron correlation, triple-ξ valence shell, diffuse function and polarization function.
The wave functions for calculating gas phase 1H chemical shifts of primary and secondary alcohols were optimized using factorial design as multivariate technique. Gas-phase experimental 1H chemical shifts of 18 alcohols were used to establish the best levels of theory for obtaining 1H chemical shift, among them the new experimental values of 1H chemical shifts of 10 alcohols were obtained in our laboratory. HF/6-31G(d,p)... 

Artificial neural networks are systems based on the brain’s functionality which in many cases are able to process highly complex computational tasks like speech recognition, image recognition ,and time series prediction. Due to the complexity of training algorithms in recurrent neural networks, reservoir computers have significant importance in machine learning.Due to low power consumption and crosstalk, high bandwidth and high-speed computing in optics, reservoir computing has proceeded to optical implementations. A reservoir computer consists of three layers: the input layer, reservoir, and output layer. A recurrent neural network is usually used as the reservoir in reservoir computers.... 

Quantum Information Processing (QIP) is one of the active areas of research in both theoretical and experimental physics. Any experimental technique that is used for a scalable implementation of QIP must satisfy DiVincenzo’s criteria [17]. Nuclear Magnetic Resonance (NMR) satisfies many of these conditions, but it is not scalable and cannot initialize the qubits to pure state [28]. NMR can be a great platform for studying the fundamentals of QIP. In this project, for a two­qubit system, we prepare pseudo pure states from the initial mixed states by using unitary operations and implement CNOT gates. According to the results of our experiments, we can apply all the gates with high fidelity.... 

A typical problem in applied mathematics and science is to estimate the future state of a dynamical system given its current state. One approach aimed at understanding one or more aspects determining the behavior of the system is mathematical modeling. This method frequently entails formulation of a set of equations, usually a system of partial or ordinary differential equations. Model parameters are then measured from experimental data or estimated from computer simulation or other methods. Solutions to the model are then studied through mathematical analysis and numerical simulation usually for qualitative fit to the dynamical system of interest and any relative time-series data that is... 

In this thesis we investigate the use of periodic array of metallic structures which mimics the propagation of the surface plasmon-polaritons waves. The TEM modes supported by these structured surfaces are referred to as the spoof surface plasmon-polaritons. They have many properties in common with the electron plasma and can be described by a plasma-like effective permittivity, when the structure is on a scale much smaller than the wavelength. In this thesis we extend this concept to include different kinds of structured surfaces like cut through metallic slits array and square array of rectangular metallic pillars which support TEM modes. We show that although these structured surfaces... 

Methamphetamine (meth) abuse and addiction (MA), with its serious medical, psychiatric and social complications, is a growing national disaster in Iran. Response control deficit during exposure to drug related cues is one of the main neurocognitive cores in MA and results in continued drug use and treatment failure. There have been many studies focused on cue exposure, but most of their paradigms required subjects to passively view the cues; this aspect of these paradigms cause a wide gap between reality and experimental studies. Developing a functional and structural neuroimaging protocol to map realistic brain circuits that are involved in craving among meth users is of importance.... 

Structures with time-varying electromagnetic properties can potentially yield non-reciprocity, amplification, harmonic generation, and other interesting wave propagation phenomena. To date, some studies have dealt with time-varying media and circuits, including time-varying optical ring resonators having degenerate travelling wave resonances. In time-varying ring resonators, the clockwise and counter clockwise resonances lose their degeneracy, and non-reciprocity is observed. One of the main challenges of such research is the need to induce time-variations in the entirety of the resonator or structure, which makes their implementation very limited or impossible in practice. The purpose of... 

Hydrodynamics of flow is affected by physical and biological interactions between flow and aquatic vegetation. This study represents the role of array distribution on lateral dispersion in emergent aquatic vegetation using two flexible and semi-rigid models. Experiments were carried out with three different arrangements, including random, staggered, and in-line. The Reynolds numbers at the stem scale ranged from 120 to 690, and the stem densities were 1% and 1.44%. Furthermore, the effects of stem flexibility and, specifically, stem resonance on lateral dispersion were examined. An image processing technique was used to measure plume width and calculate lateral dispersion. It was found that... 

One of the most important issues in medical image processing is the registration of images with various imaging modalities, because in this case, one can take advantage of these imaging modalities and sometimes fuse and use the useful information of each one in the form of a single image.As it was said, MRI and ultrasound images each have their own disadvantages and advantages, and by considering these two modalities, they have tried to integrate the good features of these two. As we know, one of the destructive cases in the MRI image is the inhomogeneity of the image, a inhomogeneity due to the fact that the main magnetic field is not constant and makes the parts of the image brighter or... 

Shear modulus and damping ratio are the most important parameters for evaluating and designing the performance of geotechnical systems under dynamic loads. According to the definition, the secant shear modulus is the slope of the hysteresis shear stress-shear strain loop. Also, the damping ratio indicates the dissipation of wave energy during propagation in the soil. This research presents an experimental laboratory study on the effect of non-plastic fines content and hydraulic hysteresis on the Gmax of unsaturated sand-silt mixtures. A significant part of the previous research has been done to determine Shear modulus and damping ratio parameters. It has been done in completely saturated or...