Showing papers by "Azarbaijan Shahid Madani University published in 2014"

Symmetric and Asymmetric Design and Implementation of New Cascaded Multilevel Inverter Topology

Abstract: Nowadays, use of multilevel inverters in high-power applications clearly can be seen. High quality and lower distortion of the output voltage and low blocking voltage of semiconductor switches are being presented as the major privileges of the multilevel inverter compared to the traditional voltage source inverter. In this paper, a new topology of multilevel inverter is proposed as fundamental block. The proposed topology is generalized using series connection of the fundamental blocks. The proposed multilevel inverter has been analyzed in both symmetric and asymmetric operation modes. A great perfection in voltage levels number with minimum switching devices has been obtained in both symmetric and asymmetric modes. Thereafter, a detailed study of losses and peak inverse voltage (PIV) of the proposed multilevel inverter is given. Also, in continuation, a comparison between the proposed topology and the traditional one and a recently developed topology is carried out. Finally, a computer simulation using MATLAB/Simulink is presented and a laboratory prototype implementation verifies the results.

New Schwarzschild-like solutions in f(T) gravity through Noether symmetries

Abstract: Spherically symmetric solutions for $f(T)$ gravity models are derived by the so-called Noether symmetry approach. First, we present a full set of Noether symmetries for some minisuperspace models. Then, we compute analytical solutions and find that spherically symmetric solutions in $f(T)$ gravity can be recast in terms of Schwarzschild-like solutions modified by a distortion function depending on a characteristic radius. The obtained solutions are more general than those obtained by the usual solution methods.

Developed cascaded multilevel inverter topology to minimise the number of circuit devices and voltage stresses of switches

Abstract: In this study, a novel structure for cascade multilevel inverter is presented. The proposed inverter can generate all possible DC voltage levels with the value of positive and negative. The proposed structure results in reduction of switches number, relevant gate driver circuits and also the installation area and inverter cost. The suggested inverter can be used as symmetric and asymmetric structures. Comparing the peak inverse voltage and losses of the proposed inverter with conventional multilevel inverters show the superiority of the proposed converter. The operation and good performance of the proposed multilevel inverter have been verified by the simulation results of a single-phase nine-level symmetric and 17-level asymmetric multilevel inverter and experimental results of a nine-level and 17-level inverters. Simulation and experimental results confirmed the validity and effectiveness performance of the proposed inverter.

Energy conditions in f(R,G)gravity

Abstract: Modified gravity is one of the most favorable candidates for explaining the current accelerating expansion of the Universe. In this regard, we study the viability of an alternative gravitational theory, namely $$f(R,G)$$ , by imposing energy conditions. We consider two forms of $$f(R,G)$$ , commonly discussed in the literature, which account for the stability of cosmological solutions. We construct the inequalities obtained by energy conditions and specifically apply the weak energy condition using the recent estimated values of the Hubble, deceleration, jerk and snap parameters to probe the viability of the above-mentioned forms of $$f(R, G)$$ .

Cascade-multi-cell multilevel converter with reduced number of switches

Abstract: Recently applications of multilevel converters have been pointed out because of some advantages include high-quality output waveform, reduced harmonic distortion and lower electromagnetic interference. However, some drawbacks such as increased number of components like switches and dc power supplies and complex pulse width modulation control method are associated with these converters. In this study, a new cascade multilevel converter is introduced named `cascade-multi-cell' converter. First, the basic constitutive of the proposed multilevel converter has been explained. Then, symmetric and asymmetric configurations are presented. The number of switches and gate driver circuits in the proposed structure are less than the conventional cascade converter. Therefore its output voltage levels will be increased. Also, the number of on-state switches is reduced in presented topology, and so the conductive losses will be reduced. The peak inverse voltage of the proposed converter is equal with the traditional cascade converter. Finally, simulation and experimental results are presented. The presented results show the validity and effectiveness of the proposed multilevel structure.

Reconfiguration of semi-cascaded multilevel inverter to improve systems performance parameters

Abstract: In this study, a new topology of semi-cascaded multilevel inverter is proposed which is a proper alternative to be used in medium voltage applications. This structure consists of series connected sub-multilevel inverters blocks. The proposed topology is based on the connections of several cell units in an appropriate scheme with the help of six power switches. Compared to the traditional cascaded multilevel inverter, in suggested topology the number of switches, inverter cost and installation area are reduced significantly. Also, in comparison with semi-cascaded multilevel inverter, the proposed inverter works with lower total peak inverse voltage. The proposed inverter is able to be used as an asymmetrical inverter. To verify the operation and good performance of the proposed inverter the simulation and experimental results are obtained.

3 – Microstructural evolution

Abstract: Friction stir welding/processing (FSW/FSP) of metals and their alloys has been investigated widely in recent years. The microstructure of alloys affects the mechanical and physical properties of processed materials and joints, therefore studying microstructure evolution during FSW/FSP of alloys is necessary. Recent investigations show that dynamic restoration phenomenon can occur due to the coexistance of strain and heat, during FSW. Also, some investigators believe that static restoration phenomena can occur. The type of restoration phenomena depend on material properties and procedure, whose management can control the microstructure of joints or processed metals, and hence their mechanical properties. In this chapter, the microstructural concepts including different microstructural zones, types of microstructural studies and different restoration phenomena are described. Then, microstructural evolution during FSW/FSP of different metals and alloys is discussed. Moreover, some illustrative examples are added to the end of each section.

A novel nonenzymatic hydrogen peroxide sensor based on the synthesized mesoporous carbon and silver nanoparticles nanohybrid

Abstract: Here, we report the synthesis and characterization of a novel nanohybrid composed of mesoporous carbon and silver nanoparticles (MC/AgNPs) to use in amperometric sensing of hydrogen peroxide (H2O2). In this process, the MC was synthesized by using the mesoporous silica as a template and glucose as a carbon source. The AgNPs were produced by in situ chemical reduction of silver nitrate through glucose as a reducing and stabilizing agent in the presence of MC to give the desired MC/AgNPs nanohybrid. It was investigated by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and electrochemical measurements. The obtained nanohybrid was used to modify a glassy carbon electrode and to fabricate an amperometric sensor for H2O2 determination at a working potential of −200 mV vs. silver/silver chloride electrode in aqueous 0.1 M phosphate buffer solution (pH 7.0). The resulted sensor can detect H2O2 in the concentration range of 0.1–41 μM with a detection of limit 50 nM at a signal-to-noise ratio of 3.

A facile and efficient preparation of anatase titania nanoparticles in micelle nanoreactors: morphology, structure, and their high photocatalytic activity under UV light illumination

Abstract: In the present study, synthesis of titania (titanium dioxide, TiO2) nanoparticles, which show light absorption characteristics in the ultraviolet region, was successfully achieved in the CTAB micelle nanoreactors at room temperature. The shape (or surface morphology), size, elemental composition, crystal structure, and optical properties of these particles were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and ultraviolet-visible absorption (UV-Vis) spectroscopy. Besides, our proposed method allowed for the successful preparation of highly crystalline and well-dispersed anatase titania nanoparticles with a phase-pure. Evaluation of titania nanoparticles' photocatalytic activity was performed through degrading the methylene blue (MB) dye under ultraviolet light irradiation. Compared to the commercial P25 TiO2 powder, this result is indicative of a high photocatalytic MB dye degradation activity. Also, the effect of the amount of TiO2 nanoparticles in the MB dye degradation has been investigated in detail. Finally, the stability of photocatalytic activity of those nanoparticles has been evaluated.

Preparation and characterization of Fe3O4/graphene quantum dots nanocomposite as an efficient adsorbent in magnetic solid phase extraction: application to determination of bisphenol A in water samples

Abstract: This study describes the preparation, characterization and application of Fe3O4/graphene quantum dots (Fe3O4/GQDs) magnetic nanocomposite as a novel adsorbent for magnetic solid phase extraction (MSPE). The Fe3O4/GQDs was synthesized by a simple hydrothermal method and the resultant nanocomposite was characterized by X-ray powder diffraction, field emission scanning electron microscopy and Fourier transform infrared spectroscopy. The prepared nanocomposite was used for the preconcentration and determination of bisphenol A (BPA) in drinking water samples using high performance liquid chromatography with ultraviolet detection (HPLC-UV). Under optimal extraction and analytical conditions, the developed method demonstrated a wide dynamic linear range (0.1–300 ng mL−1), good linearity (R2 = 0.9958), low detection limit (12.3 pg mL−1) and a high enrichment factor (360). The developed MSPE-HPLC-UV method was successfully applied for the determination of leaked BPA from plastic bottles into drinking water samples after exposing it to sunlight. Satisfactory recoveries showed that the matrices under consideration do not significantly affect the extraction process. The adsorption efficiencies of Fe3O4/GQDs, Fe3O4/graphene and unmodified magnetic Fe3O4 nanoparticles were comparatively studied for the preconcentration and determination of BPA by HPLC-UV. Based on experimental results, Fe3O4/GQDs exhibit improved adsorption behaviour because of the unique surface properties of GQDs.

Successive-station monthly streamflow prediction using neuro-wavelet technique

Abstract: This study investigates the effect of discrete wavelet transform data pre-processing method on neural network-based successive-station monthly streamflow prediction models. For this aim, using data from two successive gauging stations on Coruh River, Turkey, we initially developed eight different single-step-ahead neural monthly streamflow prediction models. Typical three-layer feed-forward (FFNN) topology, trained with Levenberg-Marquardt (LM) algorithm, has been employed to develop the best structure of each model. Then, the input time series of each model were decomposed into subseries at different resolution modes using Daubechies (db4) wavelet function. At the next step, eight hybrid neuro-wavelet (NW) models were generated using the subseries of each model. Ultimately, root mean square error and Nash-Sutcliffe efficiency measures have been used to compare the performance of both FFNN and NW models. The results indicated that the successive-station prediction strategy using a pair of upstream-downstream records tends to decrease the lagged prediction effect of single-station runoff-runoff models. Higher performances of NW models compared to those of FFNN in all combinations demonstrated that the db4 wavelet transform function is a powerful tool to capture the non-stationary feature of the successive-station streamflow process. The comparative performance analysis among different combinations showed that the highest improvement for FFNN occurs when simultaneous lag-time is considered for both stations.

Synthesis, characterization and pH-controllable methotrexate release from biocompatible polymer/silica nanocomposite for anticancer drug delivery

Abstract: The objective of this study was to develop pH-responsive silica nanoparticles by imidazole-based ionic liquid for controlled release of methotrexate. In this article, we synthesized pH-responsive cationic silica nanoparticles by graft copolymerization of vinyl functionalized silica nanoparticles and methacrylic acid (MAA) monomer. Imidazole-based ionic liquid (Im-IL) was verified by (1)HNMR and Fourier-transform infrared (FTIR) spectroscopy. The synthesized functionalized silica particles were characterized and confirmed by various technologies including the scanning electron microscopy (SEM), the infrared spectroscopy (IR) and the thermogravimetric analysis (TGA). SEM results reveal the uniformity in size/shape of silica particles. This nanosystem is modified for targeted delivery of an anticancer agent methotrexate. The nanocomposite-MTX complex was formed at physiological pH (7.4) due to the electrostatic interactions between anionic carboxylic group of MTX molecules and cationic rings in carrier, while, the release of which can be achieved through the cleavage of the nanocomposite-MTX complex by protonation of carboxyl groups in the MTX segment that are sensitive to variations in external pH at weak acidic conditions. FT-IR spectroscopy showed the presence of light interactions between the silicate silanols and the drug. MCF7 cells were incubated with the MTX-free nanocomposite and MTX-loaded nanocomposite at various concentrations for 24, 48 and 72 h, and the data showed that the nanocomposites themselves did not affect the growth of MCF7 cells. Antitumor activity of the MTX-loaded nanocomposites against the cells was kept over the whole experiment process. The results showed that the MTX could be released from the fibers without losing cytotoxicity.

Parallel switch-based chopper circuit for DC capacitor voltage balancing in diode-clamped multilevel inverter

Abstract: In recent years, the multilevel inverters have become a practical solution for high-voltage application and power quality issues. In all multilevel topologies with several DC links, the voltage balancing of DC capacitors is known as a key problem. In this study, a novel topology of chopper circuit for DC capacitor voltage balancing in diode-clamped multilevel inverters (DCMLIs) is proposed. Presented topology has less number of switches with respect to other proposed topologies in literatures. Suggested topology is modular and has high reliability. Based on the presented control system for chopper switches, only one switch is turned on at each interval. Therefore the conduction and switching losses of the chopper circuit are reduced. Referring to the simulation results, fast dynamic response of suggested chopper and reduction in voltage stress on switches can be seen clearly. Computer-aided simulations are performed through MATLAB Simulink software. A prototype chopper circuit has been implemented and tested. The experimental results are also presented to verify the performance of the proposed chopper circuit and its control system for DC capacitors voltage balancing in DCMLIs.

Cofiniteness of Local Cohomology Modules

Abstract: Let M be a non-zero finitely generated module over a commutative Noetherian local ring (R, 𝔪). In this paper we consider when the local cohomology modules are finitely generated. It is shown that if t ≥ 0 is an integer and $\mathfrak{p}\in {\rm Supp\,} H^{t}_\mathfrak{p}(M)$, then $H^{t+\dim R/\mathfrak{p}}_\mathfrak{m}(M)$ is not 𝔭-cofinite. Then we obtain a partial answer to a question raised by Huneke. Namely, if R is a complete local ring, then $H^{n}_\mathfrak{m}(M)$ is finitely generated if and only if 0 ≤ n ∉ W, where $W=\{t+\dim R/\mathfrak{p}\,|\,\mathfrak{p}\in {\rm Supp\,} H^t_\mathfrak{p}(M)\backslash V(\mathfrak{m})\}$. Also, we show that if J ⊆ I are 1-dimensional ideals of R, then $H^t_I(M)$ is J-cominimax, and $H^t_I(M)$ is finitely generated (resp., minimax) if and only if $H^t_{IR_\mathfrak{p}} (M_\mathfrak{p})$ is finitely generated for all $\mathfrak{p}\in {\rm Spec\,}R$ (resp., $\mathfrak{p}\in {\rm Spec\,}R\backslash {\rm Max\,}R$). Moreover, the concept of the J-cofiniteness dimensi...

The existence of solutions for some fractional finite difference equations via sum boundary conditions

Abstract: In this manuscript we investigate the existence of the fractional finite difference equation (FFDE) via the boundary condition and the sum boundary condition for order , where , , and . Along the same lines, we discuss the existence of the solutions for the following FFDE: via the boundary conditions and and the sum boundary condition for order , where , , , and with . MSC:34A08.