Sharif Digital Repository

This paper describes a novel Direct Torque Control (DTC) method for adjustable speed Doubly-Fed Induction Machine (DFIM) drives which is supplied by a two-level Space Vector Modulation (SVM) voltage source inverter (DTC-SVM) in the rotor circuit. The inverter reference voltage vector is obtained by using input-output feedback linearization control and a DFIM model in the stator a-b axes reference frame with stator currents and rotor fluxes as state variables. Moreover, to make this nonlinear controller stable and robust to most varying electrical parameter uncertainties, a two layer recurrent Artificial Neural Network (ANN) is used to estimate a certain function which shows the machine... 

This paper is an extension of an earlier work on electron correlations in semiconducting GaAs-based quasi-one-dimensional quantum wires. The extension was twofold. First, we developed the Singwi, Tosi, Land, and Sölander (STLS) scheme for multisubband structures. Secondly, we developed the multisubband ladder approximation diagrammatic technique. By using the results obtained for the spin symmetric and spin antisymmetric interpolarization and intrapolarization potentials, we calculate the corresponding electron-electron effective potentials. Our results for a two-subband model show that these effective potentials have an attractive part implying the occurrence of s-wave and p-wave pairings,... 

Zeolite-based photocatalysts were prepared by the sol-gel and deposition methods. The photocatalysts were characterised by X-ray diffraction, nitrogen adsorption-desorption isotherms, FTIR spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectrometry. The activity of the prepared photocatalysts was evaluated by the UV-induced degradation of acid blue 92, a textile dye in common use. The effect of various parameters, such as catalyst concentration, initial dye concentration, thiosulphate concentration and pH, on the rate and efficiency of the photocatalytic degradation of acid blue 92 was investigated. The results showed that each parameter influenced the degradation... 

This article presents results of an investigation on age-hardening behavior of superalloy AEREX 350. Microhardness testing was employed to evaluate the age-hardening response of the alloy while optical, scanning, and transmission electron microscopy techniques were used to characterize the major phases formed during the aging process. No significant hardening was found in solution-treated samples aged at temperatures up to about 680 °C. Aging at 700 °C up to 950 °C, however, caused a characteristic hardening response. This hardening was concurrent with the formation of γ', an ordered phase with L12 structure, as fine precipitate distributed throughout the fcc matrix. In the temperature range... 

In this paper, results of an investigation on the strain hardening responses of superalloy MP35N with two average grain sizes of 38 and 1 μm, during room temperature tensile testing are reported. The microstructural evolution of the deformed samples was studied using optical and transmission electron microscopy (TEM) techniques. The strain hardening behavior of the 38 μm material was rather similar to that previously reported for low stacking fault energy (SFE) fee alloys. The plastic behavior of the fine grain material, however, was unexpected. In the strain range of 0.1-0.4, the work hardening rate of the fine grain size sample was evidently lower than that of the large grain size... 

This study demonstrates a new kind of photocatalytic system via utilization of the superior specific properties inherent in Pickering emulsion. We designed the new photocatalytic system using a novel p–n heterojunction Ag3PO4/BiPO4 (AB) as a photocatalytic active component, multiwalled carbon nanotubes (MWCNTs) and graphene (GR) as a hydrophobic conducting nanostructure to form the stabilized Pickering emulsion. The photocatalytic activity of the as-prepared stabilized Pickering emulsion-based system (Pe-bp system) was studied by monitoring the change in Acid Blue 92 dye (AB92) concentration under both visible and UV light irradiation. The results revealed that the Pe-bp system exhibits a... 

ZnO and Mordenite zeolite (MOR) nanoparticles were prepared by precipitation process using ultrasonic irradiation and hydrothermal method, respectively. Supported ZnO catalysts were prepared and the effect of different supports on the photocatalytic activity of ZnO nanoparticles was investigated. All prepared samples were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform-Infra Red Spectroscopy (FTIR), UV–vis spectroscopy (UV–vis) and BET surface area technique. The photocatalytic activity of the synthesized catalysts was elucidated using the photo-oxidation of Acid Blue 92 (AB92) as a hazardous pollutant under UV light. The effect of different... 

By combination of 1-ethyl-3-methyl immidazolium ethyl sulfate as a typical room temperature ionic liquid (IL) and graphene oxide (GO) nanosheets, a nanocomposite was introduced for improving the direct electrochemistry and electrocatalytic activity of glucose oxidase (GOx). The enzyme on the IL–GO-modified glassy carbon electrode exhibited a quasireversible cyclic voltammogram corresponding to the flavine adenine dinucleotide/FADH2 redox prosthetic group of GOx. At the scan rate of 100 mV s−1, the enzyme showed a peak-to-peak potential separation of 82 mV and the formal potential of −463 mV (vs Ag/AgCl in 0.1 M phosphate buffer solution, pH 7.0). The kinetic parameters of the charge transfer... 

Long-time interaction of dewetting nanodroplets is investigated using a long-wave approximation method. Although three-dimensional (3D) droplets evolution dynamics exhibits qualitative behavior analogous to two-dimensional (2D) dynamics, there is an extensive quantitative difference between them. 3D dynamics is substantially faster than 2D dynamics. This can be related to the larger curvature and, as a consequence, the larger Laplace pressure difference between the droplets in 3D systems. The influence of various chemical heterogeneities on the behavior of droplets has also been studied. In the case of gradient surfaces, it is shown how the gradient direction could change the dynamics. For a... 

Mesoscopic hydrodynamic equations are solved to investigate late-stage evolution of thin liquid films over step topographies. Different geometrical parameters including step height and initial position and configuration of resultant masses of dewetting (droplets) are probed to find their effects on the mass evolution of the system. Our results indicate that increasing the step height and locating the droplets close to the step enhance the dynamics and accelerate smaller droplet collapse  

In this paper, the reduced master equation which is a fast simulation method of spin dependent transport in ferromagnetic single electron transistors is presented, for first time. This simulation method follows steady state master equation in which all charge states of the system are considered, whereas charge states are decreased in reduced master equation. This method is based on two degrees of electron freedom which are charge and spin. This is applied in the condition that orthodox tunneling theory is applicable to calculate the tunneling rate of electrons through barriers. The comparison between the I-V characteristics of a ferromagnetic single-electron transistor by following the... 

Employing a biharmonic boundary integral method with linear elements, coarsening dynamics of nanodroplets on topographical step heterogeneity is investigated. It is shown that the step height and droplet configuration have an influential effect on the dynamics. Increasing the step height slows down the process while locating the droplets close to the step boosts the coarsening rate. Considering a slip boundary condition enhances the dynamics and reveals a transition in the droplet migration direction. Our results reveal that increasing the surface wettability weakens the dynamics. Various types of the disjoining pressure over the step are also considered and their effects on the coarsening... 

LiCoO2 nanopowders, one of the most important cathode materials for lithium-ion batteries, were synthesized via a modified sol-gel process assisted with triethanolamine (TEA) as a complexing agent. The influence of three different chelating agents including acrylic acid, citric acid, and oxalic acid on the size and morphology of particles was investigated. Structure and morphology of the synthesized powders were characterized by thermogravimetric/ differential thermal analyses (TG/DTA), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Results indicate that the powder processed with TEA and calcinated at 800 °C had an excellent hexagonal ordering of α-NaFeO2 -type (space... 

Microchannels are at the forefront of today's cooling technologies. They are widely being considered for cooling of electronic devices and in micro heat exchanger systems due to their ease of manufacture. One issue which arises in the use of microchannels is related to the small length scale of the channel or channel cross-section. In this work, the maximum heat transfer and the optimum geometry for a given pressure loss have been calculated for forced convective heat transfer in microchannels of various cross-section having finite volume for laminar flow conditions. Solutions are presented for 10 different channel cross sections: parallel plate channel, circular duct, rectangular channel,...