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861.
Potassium iodide was used as a homogeneous electrocatalyst for the oxidation of captopril. Cyclic voltammetry and chronoamperometry were used in kinetic studies. The diffusion coefficient and catalytic rate constant were calculated to be 4.94?×?10?5?cm2?s?1 and 1.87?×?103?M?1?s?1, respectively. Linear sweep voltammetry was applied to quantitative determination of captopril; a linear calibration curve was obtained in the range of 4.0?C500???M of captopril with a limit of detection of 0.84???M and a sensitivity of 0.035 A?M?1. The method was applied to the determination of the drug in its tablets and validation methods showed that the results were quite satisfactory. 相似文献
862.
Hossein A. Dabbagh Alireza Najafi Chermahini 《Journal of the Iranian Chemical Society》2012,9(3):339-348
Stereoselective (exo-specific) synthesis, dynamic 1H NMR and computational analysis of exo-N??-{3-azatricyclo[3.2.1.0.2,4]oct-3-yl)mesithyloxy)methylene}-1-benzensulfunamide (3) were investigated. Aziridine nitrogen inversion gives rise to two sets of configurations where the N-substituent is Syn (S) or Anti (A) to C7 of the norbornyl ring. At lower temperature, the proton signals of aziridine exo-E-3 decoalesces to show two syn conformers and one anti conformer (exo-E-3 1 S ? $ \leftrightharpoons $ ?exo-E-3 2 S ? $ \leftrightharpoons $ ?exo-E-3 3 A ) with ratio of 60:20:20, respectively. Experimentally, the Gibbs free energy of activations [??G ? (kcal/mol) ?±?0.08] were calculated 11.96, 12.45 for 3 isomerizations. The standard Gibbs free energy (??G o kcal/mol) 0.174, 0, 0.174, and 0.298 at 213?K and energy minimum 6.64, 4.77 and 1.78 were calculated for 3 1S? $ \leftrightharpoons $ ?3 2S, 3 2S? $ \leftrightharpoons $ ?3 3 A , 3 1 S? $ \leftrightharpoons $ ?3 3 A isomerizations, respectively. The enthalpy (??H ?, kcal/mol) and entropy (??S ?, cal?mol?1?K?1) of activation for the nitrogen inversion of aziridine of 3 were calculated 11.2 and ?0.80, respectively. 相似文献
863.
In this paper, a numerical method for singular initial value problems of the Lane–Emden type in the second-order ordinary differential equations is proposed. The method changes solving the equation to solving a Volterra integral equation. We have applied the improved Legendre-spectral method to solve Lane–Emden type equations. The Legendre Gauss points are used as collocation nodes and Lagrange interpolation is employed in Volterra term. The results reveal that the method is effective, simple and accurate. 相似文献
864.
Alexander B. Khanikaev S. Hossein Mousavi Chihhui Wu Nima Dabidian Kamil B. Alici Gennady Shvets 《Optics Communications》2012,285(16):3423-3427
Electromagnetically induced transparency and polarization conversion due to interference between two polarization-selective plasmonic resonances coexisting in the same planar metamaterial are studied. The metasurface represents a periodic array of two topologically distinct metamolecules combined on the same substrate: i) monopole antennas connected to wires and supporting a high-Q resonance radiatively coupled to x-polarization, and ii) dipolar antennas supporting a low-Q resonance coupled to y-polarization. We demonstrate that due to the interaction between these modes through a capacitive coupling between the metamolecules, one can observe a circularly-polarized Electromagnetically Induced Transparency (EIT) and thereby achieve an efficient ultra-thin quarter-wave plate. 相似文献
865.
Hamed Dehdashti Jahromi Mohammad Hossein Sheikhi Mohammad Hasan Yousefi 《Optics & Laser Technology》2012,44(3):572-577
Quantum dot infrared photodetectors (QDIPs) have many advantages over other types of semiconductor-based photodetectors. However some of its characteristics have been investigated theoretically, there are many unstudied points. In this paper a new approach is presented to evaluate quantum dot infrared photodetectors dark current and photocurrent. In this study, it is assumed that both thermionic emission and field-assisted tunneling mechanisms determine the dark current of quantum dot detectors. Based on these assumptions, new formula for average number of electron in a quantum dot for both, dark and illumination condition is calculated, which is more accurate than the previous reported formulas; because in deriving previous reported formulas, it was assumed only thermionic emission determines dark current but field-assisted tunneling mechanisms has not been considered. Then numerical method is used to calculate the average number of electron in a quantum dot and to determine dark current and photocurrent. The theoretical results are compared with experimental data. They have good agreement with available experimental data. 相似文献
866.
In this research, rapid and efficient preparation of 2,2-dichloro-1,3-diarylaziridines through the reaction of Schiff base compounds with dichlorocarbene yielded in situ from chloroform and sodium hydroxide without any phase transfer catalyst under ultrasonic irradiation is described. The advantages of this reaction are very short reaction times, excellent product yields, simplicity of the method and high purity of products. 相似文献
867.
Morteza Rajabzadeh Hossein Khoshbin 《International Journal of Communication Systems》2013,26(11):1485-1499
Noncontiguous multicarrier code division multiple access (MC‐CDMA) is an effective multiple access method for cognitive radio systems that can deploy the noncontiguous vacant parts of a certain spectrum shared with the users of a primary system. However, the large spectral sidelobes of the Fourier transform based implementation of the MC‐CDMA interfere with the adjacent primary transmission. In this paper, a novel complex signature sequence set is proposed for synchronous downlink MC‐CDMA based cognitive radio networks to suppress the sidelobes. To do so, the minimization of the sidelobes power is developed as an eigen‐optimization problem that is optimally solved by using the eigenvalue decomposition method. The optimal complex signature sequences are chosen as the eigenvectors attained by the eigenvalue decomposition of a symmetric matrix that is dependent of the spectral characteristics of the primary users. Simulation results show that by a slight decrease in the maximum number of active users compared with full load, the sidelobes can be considerably suppressed. The effect of cyclic prefix length, the bandwidth of the primary system and the number of active users on the sidelobe suppression performance is analyzed through numerical simulations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
868.
In this note some points for paper [Huabin Chen, Chuanxi Zhu, Peng Hu, Yong Zhang, Delayed-state-feedback exponential stabilization for uncertain Markovian jump systems with mode-dependent time-varying state delays, Nonlinear Dyn. (2012), doi:10.1007/s11071-012-0324-3] are presented. 相似文献
869.
Calculating the Anisotropic Permeability of Porous Media Using the Lattice Boltzmann Method and X-ray Computed Tomography 总被引:1,自引:0,他引:1
Yuan Gao Xiaoxian Zhang Pratap Rama Ying Liu Rui Chen Hossein Ostadi Kyle Jiang 《Transport in Porous Media》2012,92(2):457-472
A lattice Boltzmann (LB) method is developed in this article in a combination with X-ray computed tomography to simulate fluid
flow at pore scale in order to calculate the anisotropic permeability of porous media. The binary 3D structures of porous
materials were acquired by X-ray computed tomography at a resolution of a few microns, and the reconstructed 3D porous structures
were then combined with the LB model to calculate their permeability tensor based on the simulated velocity field at pore
scale. The flow is driven by pressure gradients imposed in different directions. Two porous media, one gas diffusion porous
layer used in fuel cells industry and glass beads, were simulated. For both media, we investigated the relationship between
their anisotropic permeability and porosity. The results indicate that the LB model is efficient to simulate pore-scale flow
in porous media, and capable of giving a good estimate of the anisotropic permeability for both media. The calculated permeability
is in good agreement with the measured date; the relationship between the permeability and porosity for the two media is well
described by the Kozeny–Carman equation. For the gas diffusion layer, the simulated results showed that its permeability in
one direction could be one order of magnitude higher than those in other two directions. The simulation was based on the single-relaxation
time LB model, and we showed that by properly choosing the relaxation time, it could give similar results to those obtained
using the multiple-relaxation time (MRT) LB method, but with only one third of the computational costs of MRTLB model. 相似文献
870.
Mahdi Hedayatizadeh Yahya Ajabshirchi Faramarz Sarhaddi Said Farahat Ali Safavinejad Hossein Chaji 《Heat and Mass Transfer》2012,48(7):1089-1101
Solar air heater requires investigation for enhancement of solar energy conversion into heat. Different configurations with various artificial roughness geometries are proposed to date. In present study attention is paid on ways leading to more delivery of exergy by a v-corrugated solar air heater through parametric study. Effects of aspect ratio of the collector, inlet air temperature, mass flow rate per collector area etc. are studied. 相似文献