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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.

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.

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.

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