Sharif Digital Repository

In this paper, a new simple and complete technique of modeling and analysis of a matrix converter is presented based on the singular value decomposition (SVD) of modulation matrix. The proposed modeling method yields a new limitation between the matrix converter gain and its input power factor, which is more relaxed as compared to the limits reported so far in the literature. The SVD of the modulation matrix leads to a unified modulation technique which achieves the full capability of a matrix converter. It is shown that this approach is general and all other modulation methods established for a matrix converter are specific cases of this technique. The proposed modulation method can be used... 

In this paper, the reactive power control of a variable-speed permanent-magnet synchronous wind generator with a matrix converter at the grid side is improved. A generalized modulation technique based on singular value decomposition of the modulation matrix is used to model different modulation techniques and investigate their corresponding input reactive power capability. Based on this modulation technique, a new control method is proposed for the matrix converter which uses active and reactive parts of the generator current to increase the control capability of the grid-side reactive current compared to conventional modulation methods. A new control structure is also proposed which can... 

A matrix converter is a voltage/current source AC/AC frequency converter. In grid-connected operation of a variable-speed permanent magnet synchronous wind power generator, the matrix converter is normally controlled as a voltage source converter. In this control method, the generator-side voltage is synthesized from the grid-side voltage source. However, in the stand-alone mode of operation, the grid-side stiff voltage source is not available, and the input filter of the matrix converter is unstable. In this article, a new control method is presented that controls a permanent magnet synchronous wind generator in a stand-alone mode with a matrix converter as a current source converter. The... 

The catalytic activity of a mixture of ZnCl2: AlCl3 supported on silica gel was evaluated for the alkylation of phenols with benzyl alcohol, tret-butyl alcohol and styrene under microwave irradiation and solvent-free conditions. The catalyst preparation method, its characterization and reusability, were reported. The effect of the phenol to benzyl alcohol ratio and the time of reaction on the phenol conversion and distribution of products was investigated. A conversion percentage up to 97% was achieved when hydroquinone was used. A selective ortho- directed alkylation for phenol, α-naphthol and β-naphthol was observed. © Sharif University of Technology, December 2009  

An efficient and one-pot synthesis of thiopyrano[2,3-b]indole derivatives via Hetero Diels-Alder reaction of α,β-Unsaturated thio-oxindoles with electron poor acetylenes and Cyclic Dienophiles is described. In the proposed method the reaction is performed under neutral and one-pot reaction conditions, and also the substances can be mixed without any activation or modification and without using any catalysts  

This paper describes a new compensating system for the flicker and harmonics generated by a highly-varying load, e.g. a welding machine, connected between two phases of a three-phase system. The proposed system is an active filter with two-phase structure employed in a three-phase system. The system also employs simple and effective control strategies for dc-bus regulation and current control. The proposed system is a package with less switches compared to the conventional three-phase systems. It results in no increase in switch ratings, thus giving a more economic compensator. © 2006 IEEE  

The title compound, C32H26N2S2, is a new spiro thio-oxindole derivative which was synthesized with the aim that it might be effective in treating a number of diseases. In spite of the existence of the Csp 3 atom, the thio-oxindole group is almost planar. There are a number of intra-molecular C - H⋯S hydrogen bonds. © International Union of Crystallography 2007  

In this paper an analytical approach is proposed to formulate the proper set of phase currents reference to ride the permanent magnet synchronous generator (PMSG)-based wind turbine (WT) through faults properly, regardless of fault type. Hence, the WT is forced to inject required reactive current by grid codes together with active power injection, to help support grid frequency during faults and reduce the energy storage system (ESS) power rating. Moreover, it prevents pulsating active power injection to the grid. During grid faults, the DC-link voltage is controlled by the ESS instead of the grid-side converter (GSC) and the GSC controller applies calculated reference currents. The ESS... 

A novel fault ride-through strategy for wind turbines, based on permanent magnet synchronous generator, has been proposed. The proposed strategy analytically formulates the reference current signals, disregarding grid fault type and utilizes the whole system capacity to inject the reactive current required by grid codes and deliver maximum possible active power to support grid frequency and avoid generation loss. All this has been reached by taking the grid-side converter’s phase current limit into account. The strategy is compatible with different countries’ grid codes and prevents pulsating active power injection, in an unbalanced grid condition. Model predictive current controller is... 

Herein we report a new organocatalyst for the asymmetric Michael addition of nitroalkanes to α,β-unsaturated aldehydes. This catalyst incorporates a basic imidazole group in addition to the secondary amine responsible for activation of the α,β-unsaturated carbonyl compounds via iminium ion formation. The new organocatalyst is capable of catalyzing the enantioselective carbon-carbon bond formation with a high degree of enantiocontrol providing products in enantiomeric excesses of up to 92% and yields of up to to 91 %. These results constitute the best results so far reported for organocatalyzed Michael additions of nitroalkanes to α,β-unsaturated aldehydes, and provide proof of principle that... 

The petroleum industry suffers from reservoir souring phenomena, which has negative impacts on production facilities, health, and environment. Injection of incompatible water into the reservoir (waterflooding), which is considered as an enhanced oil recovery (EOR) method, is one of the most common causes of reservoir souring. In general, injected brine, especially seawater, contains high amounts of sulfate ion (SO42−). A high concentration of sulfate in the presence of sulfate-reducing bacteria (SRB) leads to the microbial reservoir souring. During this phenomenon, sulfide, specifically hydrogen sulfide gas (H2S) appears in the producing fluid of the reservoir. In this paper, a coupled... 

The liver plays a complex role in metabolism and detoxification, and better tools are needed to understand its function and to develop liver-targeted therapies. In this study, we establish a mechanobiological model of liver transport and hepatocyte biology to elucidate the metabolism of urea and albumin, the production/detoxification of ammonia, and consumption of oxygen and nutrients. Since hepatocellular shear stress (SS) can influence the enzymatic activities of liver, the effect of SS on the urea and albumin synthesis are empirically modeled through the mechanotransduction mechanisms. The results demonstrate that the rheology and dynamics of the sinusoid flow can significantly affect... 

A new efficient catalytic system was investigated for the epoxidation of various olefins by cis-dioxo-bis[2-(2′-hydroxyphenyl)-oxazolinato]molybdenum(VI), cis-[MoO2(phox)2], and TBHP as oxidizing agent. Using this system as catalyst for the oxidation of aliphatic substrates at 80 °C gives the epoxide as the sole product with yields up to 100% and turnover frequency up to 5000 h-1. The efficiency of the catalyst is strongly influenced by the nature of solvent, reaction time and temperature, and a significant increase in the epoxide yields is observed in higher temperatures and longer reaction times. © 2009 Elsevier B.V  

Implementation of effective cancer treatment strategies requires consideration of how the spatiotemporal heterogeneities within the tumor microenvironment (TME) influence tumor progression and treatment response. Here, we developed a multi-scale three-dimensional mathematical model of the TME to simulate tumor growth and angiogenesis and then employed the model to evaluate an array of single and combination therapy approaches. Treatments included maximum tolerated dose or metronomic (i.e., frequent low doses) scheduling of anti-cancer drugs combined with anti-angiogenic therapy. The results show that metronomic therapy normalizes the tumor vasculature to improve drug delivery, modulates... 

Ostracism has been recognized as conceptually and empirically distinct from harassment. Drawing from theory and research that suggests that employees have a strong need to belong in their organizations, we examine the comparative frequency and impact of ostracism and harassment in organizations across three field studies. Study 1 finds that a wide range of employees perceive ostracism, compared with harassment, to be more socially acceptable, less psychologically harmful, and less likely to be prohibited in their organization. Study 2 surveyed employees from a variety of organizations to test our theory that ostracism is actually a more harmful workplace experience than harassment.... 

This work presents an innovative design for a flow-through dielectrophoretic cell sorting based on silicon bulk microelectrodes featuring sidewall undercuts. The microelectrodes are configured into an interdigitated array with digits extending across the flow chamber at an oblique angle against the flow stream. Target cells under dielectrophoretic forces and hydrodynamic drag can slide along the digits to a dedicated outlet. The design has been showcased for continuous-flow sorting of viable and non-viable mammalian cells, achieving a throughput of 16,600 cells/min, an order of magnitude higher than those reported for existing continuous-flow cell sorting designs using thin-film or... 

The search for efficient chemotherapy drugs and other anti-cancer treatments would benefit from a deeper understanding of the tumor microenvironment (TME) and its role in tumor progression. Because in vivo experimental methods are unable to isolate or control individual factors of the TME and in vitro models often do not include all the contributing factors, some questions are best addressed with systems biology mathematical models. In this work, we present a new fully-coupled, agent-based, multi-scale mathematical model of tumor growth, angiogenesis and metabolism that includes important aspects of the TME spanning subcellular-, cellular- and tissue-level scales. The mathematical model is... 

Sets of rosettes of stress probes have been performed on Hostun sand in a flexible boundary true triaxial apparatus. These have shown the effect of stress history on the local distortional stiffness of the sand. Histories have included isotropic compression, and deviatoric paths with increasingly complex shapes. These tests were performed and interpreted against a background of kinematic hardening and bounding surface plasticity, using stress response envelopes to reveal evolving distortional stiffness. Use of response envelopes to study volumetric stiffness appears to be less helpful but the phase transformation surfaces that can be extracted seem somewhat independent of recent stress... 

Atomic emission detection (AED) is a sensitive as well as a selective detection technique for gas chromatography (GC) and provides element-specific information. A rapidly increasing number of applications in many different areas illustrates the versatility and analytical power of the technique - especially when complex samples have to be analysed. The complementary use of GC-AED and GC with mass-spectrometric detection often yields the most rewarding results. © 2002 Published by Elsevier Science B.V. All rights reserved