Homogeneous electrocatalytic oxidation of captopril by iodide and its application to pharmaceutical analysis

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.     

Stereoselective (exo-specific) synthesis, dynamic 1H NMR and quantum chemical conformational and configurational analysis of norbornene-aziridine-E-imidoyl system

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.     

Numerical solution of singular IVPs of Lane–Emden type using a modified Legendre-spectral method

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.     

Electromagnetically induced polarization conversion

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.     

A numerical approach for analyzing quantum dot infrared photodetectors' parameters

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.     

Sonocatalyzed facile and mild one pot synthesis of gem-dichloroaziridine derivatives under alkaline conditions

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.     

A novel multicarrier CDMA transmission scheme for cognitive radios with sidelobe suppression

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.     

Comments on “Delayed-state-feedback exponential stabilization for uncertain Markovian jump systems with mode-dependent time-varying state delays”

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.     

Calculating the Anisotropic Permeability of Porous Media Using the Lattice Boltzmann Method and X-ray Computed Tomography

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.     

Analysis of exergy and parametric study of a v-corrugated solar air heater

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.