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Aminzadeh H.,Islamic Azad University at Shahrood
International Journal of Circuit Theory and Applications | Year: 2011

In analog signal-processing applications, settling performance of the employed operational amplifiers (opamps) is usually of great matter. Under low-voltage environment of modern technologies where only a few transistors are allowed to be stacked, three-stage amplifiers are gaining more interest. Unfortunately, design and optimization of three-stage opamps based on settling time still suffer from lack of a comprehensive analysis of the settling behavior and closed-form relations between settling time/error and other parameters. In this paper, a thorough analysis of the settling response of three-stage nested-Miller-compensated opamps, including linear and non-linear sections, is presented. This analysis leads to a design methodology which determines the circuit requirements for desired settling time/error. Based on settling time, it allows optimizations in power consumption and area. Copyright © 2010 John Wiley & Sons, Ltd.

Mohammadhosseini M.,Islamic Azad University at Shahrood
Journal of Essential Oil-Bearing Plants | Year: 2015

Volatile constituents from minimal amounts of flowers, leaves and stems of Salvia mirzayanii were obtained using a manual headspace solid phase microextraction (HS-SPME) device equipped with four types of commercially available fibers, namely polydimethylsiloxane (PDMS), polydimethylsiloxane-carboxene (PDMS-CAR), polydimethylsiloxane-divinylbenzene (PDMS-DVB) and divinylbenzene-carboxene-polydimethyl siloxane (DVB-CAR-PDMS). After selection of the best-performing fiber (PDMS-CAR) and optimization of the corresponding variables, the fiber was conditioned by placing it for 25 min in the headspace of a vial containing the powdered plant organs, immediately after which it was inserted onto injection port of the GC-MS. Chromatographic analyses were performed using DB-5 and fused silica HP-5MS capillary columns with temperature programming. This study also revealed that the most abundant compounds in both in flower and leaf volatile fractions were monoterpene hydrocarbons, whereas that of stem contained mostly oxygenated monoterpenes. © 2015, Har Krishan Bhalla & Sons.

Hierarchical zeolite consists of both microporous and unordered mesoporous structures. A composite of Polypyrrole/thiol-functionalized Beta/MCM-41 (PPy/SH-Beta/MCM-41) was prepared, characterized by FE-SEM, FT-IR, XRD, TGA and BET analysis and applied in the investigation of its adsorption characteristics for the removal of Hg2+ ions from aqueous solutions. Thiol-functionalized Beta/MCM-41 (SH-Beta/MCM-41) was prepared by 3-mercaptopropyltrimethoxysilane (MPTMS) in the presence of aerosil-200 as a silica source by two-step hydrothermal crystallization procedure. Batch mode experiments were conducted and three kinetic models were used to describe the adsorption process. The experimental data fitted very well with the Pseudo-second-order kinetic model. The calculated thermodynamic parameters (ΔH, ΔS and ΔG) revealed that the adsorption of Hg 2+ onto PPy/SH-Beta/MCM-41 is an endothermic and spontaneous process. It was found that temperature has a positive effect on the removal efficiency and that PPy/SH-Beta/MCM-41 is potentially able to remove Hg2+ ions from aqueous solutions at even high concentrations (400 mg L-1). The recovery of Hg2+ from the PPy/SH-Beta/MCM-41 adsorbent was found to be more than 90% using 0.5 M H2SO4, and the ability of the absorbent to be reused for removal of Hg2+ was investigated. © 2013 Elsevier B.V.

Ammonia adsorption on the external surface of C30B 15N15 heterofullerene was studied using density functional calculations. Three models of the ammonia-attached C30B 15N15 together with the perfect model were optimized at the B3LYP/6-31G level. The optimization process reveals that dramatic influences occurred for the geometrical structure of C30B15N 15 after ammonia adsorption; the B atom relaxes outwardly and consequently the heterofullerene distorts from the spherical form in the adsorption sites. The chemical shielding (CS) tensors and nuclear quadrupole coupling constants of B and N nuclei were calculated at the B3LYP/6-311G (*) (*) level. Our calculations reveal that the B atom is chemically bonded to NH3 molecule. The B atom in the NH3-attached form has the largest chemical shielding isotropic (CSI) value among the other boron nuclei. The CQ parameters of B nuclei at the interaction sites are significantly decreased after ammonia adsorption. © 2011 Elsevier B.V. All rights reserved.

Domingo L.R.,University of Valencia | Emamian S.R.,Islamic Azad University at Shahrood
Tetrahedron | Year: 2014

Analysis of 12 three-atom-components (TACs) participating in [3+2] cycloaddition (32CA) reactions towards ethylene and acetylene allows establishing good correlations between the pseudodiradical character, the hardness η, and the nucleophilicity N index of the TAC with the feasibility of these non-polar reaction. These results allow the introduction of the pr index, which comprises the two aforementioned DFT reactivity indices. The increase of the pr index for an allylic-type TAC goes accompanied by a linear decrease of the activation enthalpy of the reaction. The present study makes it possible to establish a useful classification of 32CA reactions into zw-type reactions involving TACs with a high zwitterionic character, and pr-type reactions involving TACs with a high pseudodiradical character. © 2014 Elsevier Ltd. All rights reserved.

Zahedi E.,Islamic Azad University at Shahrood
Superlattices and Microstructures | Year: 2015

The electronic, optical, and photocatalytic properties of ribbon-like Bi2S3 have been investigated at different external applied pressures 0-9.18 GPa using the density functional theory (DFT) method within the generalized gradient approximation. The electronic structures and optical properties indicate that ribbon-like Bi2S3 is p-type semiconductor with indirect band gap. The photocatalytic activity of ribbon-like Bi2S3 decreases with increasing in the hydrostatic pressure. Based on band structure and density of states (DOS) calculations the conduction and valence bands of ribbon-like Bi2S3 are mostly derived from Bi 6p and S 3p states. The charge density distribution indicates that the nature of Bi-S bonds is covalent. The calculated optical properties indicate that ribbon-like Bi2S3 is ultra violet light response photocatalyst. Calculated position of valence band and conduction band potentials indicate that ribbon-like Bi2S3 has strong oxidation ability for water splitting into O2, but for water splitting into H2 and subsequently increasing of photocatalytic activity co-catalyst should be added. © 2015 Elsevier Ltd. All rights reserved.

Farzaneh-Gord M.,Shahrood University of Technology | Deymi-Dashtebayaz M.,Islamic Azad University at Shahrood
Energy | Year: 2011

Turbine air inlet cooling is one of many available commercial methods to improve the efficiency of an existing gas turbine. The method has various configurations which could be utilized for almost all installed gas turbines. This paper presents a comparison between two commons and one novel inlet air cooling method using turbo-expanders to improve performance of a gas turbine located at the Khangiran refinery in Iran. These methods have been applied to one of the refinery gas turbines located at the Khangiran refinery in Iran. Two common air cooling methods use evaporative media or a mechanical chiller. The idea behind the novel method is to utilize the potential cooling and power capacity of the refinery natural gas pressure drop station by replacing throttling valves with a turbo-expander. The study is part of a comprehensive program with the goal of enhancing gas turbine performance at the Khangiran gas refinery. Based on the results, it is found that using turbo-expanders is the most economically feasible option and so is recommended to be utilized for improving gas turbine performance at the Khangiran refinery. © 2010 Elsevier Ltd.

Khoshvaght-Aliabadi M.,Islamic Azad University at Shahrood
Energy Conversion and Management | Year: 2014

Heat transfer and flow characteristics of the sinusoidal-corrugated channel with Al2O3-water nanofluid are analyzed by a 2-D numerical simulation. A parametric study method is used to analyze the performance of sinusoidal-corrugated channel in practical applications like plate-fin compact heat exchangers. The effects of channel height, channel length, wave length, wave amplitude, and phase shift at different Reynolds numbers (6000-22,000) and nanoparticle volume fractions (0-4%) are evaluated. Nusselt number and Darcy friction factor are considered as performance parameters. It is found that the channel height and wave amplitude have the highest influences on Nusselt number and friction factor values, respectively. Also, the results show that the nanofluid flow inside the sinusoidal-corrugated channels offers higher values of Nusselt number compared to the base fluid, while the friction factor of both the nanofluid and the base fluid gets almost the same values. Finally, correlations are proposed to predict Nusselt number and friction factor of the water and Al2O3-water nanofluid flows in the sinusoidal-corrugated channels. © 2014 Elsevier Ltd. All rights reserved.

Javadian H.,Islamic Azad University at Shahrood
Journal of Industrial and Engineering Chemistry | Year: 2014

The aim of this research is to investigate sorption characteristics of polyaniline/polypyrrole copolymer nanofibers (PANI/PPy copolymer nanofibers) for the removal of Co(II) ions from aqueous solution. The adsorbent is characterized using FE-SEM, TEM, FTIR, TGA, DSC and BET surface area. The sorption of Co(II) ions by batch method is applied and the optimum conditions are investigated. In optimum condition, removal efficiency was 99.68% for 100mgL-1 Co(II) solution. It is found that temperature has a positive effect on the removal efficiency. It can be concluded that PANI/PPy copolymer nanofibers are potentially able to removal of Co(II) ions from aqueous solutions. © 2014 The Korean Society of Industrial and Engineering Chemistry.

Zahedi E.,Islamic Azad University at Shahrood
Comptes Rendus Chimie | Year: 2013

Adsorption of nitrogen dioxide on the exterior surface of C 30B15N15 through B atom of adsorbent is studied using the DFT-B3LYP/6-31G* level. Independent to the orientation, the NO2 molecule presents strong chemisorption with large charge transfer from C30B15N15 to adsorbed gas. NBO (natural electron configuration of adsorbing B atom), AIM analysis and spin density distributions indicate that the chemisorption of NO2 on the C 30B15N15 in all studied complexes are covalent in nature. © 2012 Académie des sciences.

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