Sharif Digital Repository

In this paper, a new zero-voltage-switching high power-factor (PF) rectifier with Line-Modulated Fixed-Off-Time current control is introduced, that off time is a function of the instantaneous line voltage. The auxiliary circuit provides soft switching for all semiconductor devices, without any extra current and voltage stress on the main switches. The proposed converter is bridgeless, and all semiconductor devices are soft switched. In addition, there is no extra stress on the switches. Thus, the conduction and switching losses are reduced and maximum efficiency is achieved. A 250W, with an input ac voltage of 90265 Vrms and an output voltage 400 Vdc, 100 kHz is designed and simulated to... 

In this paper, a new zero-voltage-switching, high power-factor, bridgeless rectifier is introduced. In this topology, an auxiliary circuit provides soft switching for all of the power semiconductor devices. Thus the switching losses are reduced and the highest efficiency can be achieved. The proposed converter has been analyzed and a design procedure has been introduced. The control circuit for the converter has also been developed. Based on the given approach, a 250 W, 400 Vdc prototype converters has been designed at 100 kHz for universal input voltage (90-264 Vrms) applications. A maximum efficiency of 94.6% and a power factor correction over 0.99 has been achieved. The simulation and... 

Despite the great potential of carbon nanotubes (CNTs) in various areas of biomedicine, concerns regarding their carcinogenicity, inefficient dispersion in aqueous solutions and biological activity in vivo still remain. One important and feasible route to overcome these barriers is modification of CNTs with polymers, which are widely studied and play a vital role in biological and biomedical fields, especially in drug delivery. This comprehensive review focuses on the achievements of our and other groups in currently used methods to functionalize the surface of CNTs with polymers to produce anticancer drug delivery systems. We have intensively studied covalent and noncovalent interactions... 

In this paper, the FHA and a simple TDA approaches have been used to derive the normalized maximum switching frequency of wide adjustable range LLC resonant converter for realizing the ZVS operation even under the worst-case conditions. By accounting the resonant current higher harmonics, more accurate expressions are derived. These analyses demonstrate that the normalized maximum switching frequency depends on the dead-time and the converter inductance ratio. It also depends on the ratio of the converter resonant capacitor and the effective capacitance appeared in parallel with the power MOSFETs drain-sources. The simulated and experimental results are in good agreement with the derived... 

LLC-LC resonant converter is a suitable circuit topology to design switched-mode power supplies for wide-output-voltage and wide-output-load applications. In this paper, a design procedure is introduced to optimize this converter. Unlike soft switching techniques for pulse width modulated converters, which usually apply an active auxiliary circuit to reduce switching losses and EMI, in the proposed converter, not only such circuits are not used, but also all of the parasitic elements are merged to the converters main components. Zero-voltage switching (ZVS) operation is realized for all power devices under all operating conditions. Thus, this converter is a suitable choice for... 

LLC resonant converter is one of the most suitable circuit topologies that have been introduced for designing constant output voltage switched-mode power supplies. In this paper, a design procedure is introduced for using this converter as a wide output range voltage source. Unlike constant output voltage applications which need small converter inductance ratio and narrow switching frequency variations, for wide output range applications, large values of these parameters are needed simultaneously and should be optimized. Instead of minimizing the components stresses, leading to a great value of the inductance ratio, proper choice of the converter parameters resulting in a smaller inductance... 

LLC resonant converter has been widely used in dcdc converters. In this paper, optimum dead-time and maximum switching frequency of a wide-adjustable-range LLC resonant converter are investigated for realizing the zero voltage switching (ZVS) operation even under the worst-case conditions. Analyses demonstrate that these parameters depend on the converter inductance ratio and ratio of the converter resonant capacitor and the effective capacitance appeared in parallel with the drainsources of the power MOSFETs. The necessary dead time for realizing the ZVS operation can be minimized by choosing the normalized maximum switching frequency, properly. Using the dead-time optimum value, soft... 

LLC resonant converter with significant resonant inductance is proposed for designing an adjustable wide-range regulated voltage source. Large resonant inductance increases output voltage adjustment range and conversion efficiency, particularly at light loads. Soft switching is achieved for all power devices under all operating conditions by choosing the dead time and maximum switching frequency properly and operating in the converter's inductive region. Using a power-factor-correction (PFC) converter reduces the resonant converter's output voltage dependence to the variations of the main ac input voltage. Thus, the compensation of the load variations and the wide-range adjustment of the... 

LLC resonant converter has been used widely as dc-dc converter for achieving constant dc voltage. In this paper, an LLC resonant converter, by adding an inductance to its conventional topology and considering the rectifying stage stray inductances, is proposed for an adjustable wide range regulated current source (20-200 A dc) for using as ion implanter's filament power supply. The additional inductor increases output current adjustment range and efficiency, especially at light loads. Transformer's leakage inductances and rectifying stage stray inductances have been considered. Because of these inductances, the rectifier stage always works in continuous conduction mode, and its conduction... 

Wound-Rotor (WR) resolvers are similar to two-phase synchronous generators. Their difference is related to the excitation signal. While DC voltage is used for exciting synchronous generator, high frequency AC voltage is employed for that of resolver. The common waveform for excitation signal of resolver is sinusoidal voltage. However, preparing the high frequency sinusoidal voltage in the resolver to digital converter (RDC) is always a challenge. Therefore, in this paper different high frequency AC waveforms are applied as the excitation signal of the resolver and the estimated position, resulted from RDC, is discussed. The aim of this work is to find an appropriate excitation waveform that... 

One of the methods that is used nowadays in enhanced oil recovery is surfactant flooding. The main mechanisms of surfactant flooding in reservoir consist of reduction of interfacial tension between water and oil and modification of rock wettability. In this study, the authors simulate the surfactant injection process in Darcy scale and in one-dimensional, multicomponent, multiphase state, and effects of physical phenomena such as adsorption, dispersion, convection, and exchange between fluids and solids are considered. Wettability alteration of reservoir rock due to presence of surfactant in injected fluid is detected in relative permeability and capillary pressure curves. First, the authors... 

This research investigates the effect of process parameters on the geometry and properties of In625 parts, manufactured by the direct laser metal deposition (DLMD) process. For this purpose, eight parts, consisting of 5 layers on top of each other, were manufactured, and the effect of laser power, laser focal plane position, and scanning speed on the height, width, and surface smoothness of each of them was investigated using design of experiment (DOE). The experimental results showed that the height of the parts manufactured by 800 W/mm and 200 W/mm of energy density is 3.69 mm and 6.12 mm, respectively. The thickness of the parts manufactured by 80 W/mm and 200 W/mm of energy density is... 

One of the most important production issues in oil fields is high water production which may lead to wells killing and reduction in an economical production period. With the increment of water production or decrease of reservoir pressure, reservoir drawdown pressure reduces which causes reduction in oil production rate. To preserve the reservoir production, we should apply one of the proposed methods; namely, increasing the reservoir pressure, preventing water source invasion or using artificial lift technique. To compensate this reduction, continuous gas injection into the wells can be used. The injected gas combines with fluid in tubing and the density of the fluid decreases, thereby... 

The role of emulsions as a prevalent phenomenon is broadly investigated in the petroleum industry since forming the emulsion has many severe harmful implications. Heavy components of crude oil such as wax and asphaltene make the water-in-oil (w/o) emulsion more stable, while the role of these components on the emulsion viscosity has not been fully understood. In this regard, to find a proper demulsifier to break these emulsions, it is necessary to know the mechanisms of emulsion formation by heavy oil components. In this study, the effects of waxy-oil and asphaltenic-oil on w/o emulsion were investigated by measuring volume and viscosity of the formed emulsion after an elapsed time, followed... 

Tabriz city in NW Iran is a seismic-prone province with recurring devastating earthquakes that have resulted in heavy casualties and damages. This research developed a new computational framework to investigate four main dimensions of vulnerability (environmental, social, economic and physical). An Artificial Neural Network (ANN) Model and a SWOT-Quantitative Strategic Planning Matrix (QSPM) were applied. Firstly, a literature review was performed to explore indicators with significant impact on aforementioned dimensions of vulnerability to earthquakes. Next, the twenty identified indicators were analyzed in ArcGIS, a geographic information system (GIS) software, to map earthquake... 

Tabriz city in NW Iran is a seismic-prone province with recurring devastating earthquakes that have resulted in heavy casualties and damages. This research developed a new computational framework to investigate four main dimensions of vulnerability (environmental, social, economic and physical). An Artificial Neural Network (ANN) Model and a SWOT-Quantitative Strategic Planning Matrix (QSPM) were applied. Firstly, a literature review was performed to explore indicators with significant impact on aforementioned dimensions of vulnerability to earthquakes. Next, the twenty identified indicators were analyzed in ArcGIS, a geographic information system (GIS) software, to map earthquake... 

Modeling and analysis of information system vulnerabilities helps us to predict possible attacks to networks using the network configuration and vulnerabilities information. As a fact, exploiting most of vulnerabilities result in access rights alteration. In this paper, we propose a new vulnerability analysis method based on the Take-Grant protection model. We extend the initial Take-Grant model to address the notion of vulnerabilities and introduce the vulnerabilities rewriting rules to specify how the protection state of the system can be changed by exploiting vulnerabilities. Our analysis is based on a bounded polynomial algorithm, which generates the closure of the Take-Grant graph... 

Combining the advection-diffusion equation approach with Monte Carlo simulations we study chaperone driven polymer translocation of a stiff polymer through a nanopore. We demonstrate that the probability density function of first passage times across the pore depends solely on the Péclet number, a dimensionless parameter comparing drift strength and diffusivity. Moreover it is shown that the characteristic exponent in the power-law dependence of the translocation time on the chain length, a function of the chaperone-polymer binding energy, the chaperone concentration, and the chain length, is also effectively determined by the Péclet number. We investigate the effect of the chaperone size on... 

We study the translocation of stiff polymers through a nanopore, driven by the chemical-potential gradient exerted by binding proteins (chaperones) on the trans side of the pore. Bound chaperones prevent backsliding through the pore and, therefore, partially rectify the polymer passage. We show that the sequence of chain monomers with different binding affinity for the chaperones significantly affects the translocation dynamics. In particular, we investigate the effect of the nearest-neighbor adjacency probability of the two monomer types. Depending on the magnitude of the involved binding energies, the translocation speed may either increase or decrease with the adjacency probability. We...