Simultaneous Spectrophotometric Determination of Sulfamethoxazole and Trimethoprim in Drugs.

Abstract

Two methods, namely first derivative and classical least squares methods are selected and applied for comparative purposes to analyze uv-spectra of the methanolic solutions of the cited components in synthetic binary mixtures and in a number of antibacterial pharmaceutical preparations, viz. three tablets and two syrups produced by Egyptian companies. The former technique is based on measuring the absorbances at zero-crossing wavelengths, 288 and 240 nm for the two drugs, respectively. Calibration curves are rectilinear in the range 4 –20 μg/ml of both components. The latter method is based on a pure standard full-spectra treatment ranged from 350 to 200 nm at 2 nm intervals to compute the concentration of unknowns. A statistical analysis of the results is reported.     

单壁碳纳米管储氢的第一原理分子动力学模拟

本文用第一性原理平面波赝势方法模拟研究了手性单壁碳纳米管与氢分子的相互作用,考察了碳纳米管直径对储氢性能的影响。对单壁碳纳米管储氢的模拟结果表明: (1)物理吸附时,H2可以吸附在空腔内,也可以吸附在管与管之间的空隙中,纳米管内部的氢吸附力均高于管外,而“完好无损”的H2分子不能够穿过管壁而进入管内。(2)化学吸附时,碳纳米管对氢的吸附首先出现在管的边缘附近,碳纳米管局部会发生形变,SWCNTs的张力会随C-H键的增加而增大,系统不稳定。（3）随着直径的增加,纳米管内、外的氢吸附力差异减小。     

The origin of ferromagnetism in Pd-doped CdS

The electronic structures and magnetic properties of Pd-doped CdS have been studied by a first principles study. We find that the material becomes 100% spin-polarized when Pd substitutes for Cd atom in a 3×3×2 CdS supercell, and forms a diluted magnetic semiconductor (DMS). A long-range ferromagnetic (FM) coupling is obtained between two Pd dopants. We concluded that the hybridized Pd(4d)–S(3p)–Cd(4d)–S(3p)–Pd(4d) chain through p–d coupling is responsible for the long-range FM coupling.     

Electronic,magnetic and elastic properties of ε-phases Fe3X(X=B,C, N) from density-functional theory calculations

First principles calculations have been performed for ε-phases Fe₃X(X=B/C/N) with hexagonal close-packed Fe sublattices. The calculated equilibrium structural parameters of ε-Fe₃C and ε-Fe₃N are in agreement with experimental results. The crystal structure of the ε-Fe₃B is predicted. In the view of the formation energy, the phase stabilities grow up from ε-Fe₃B, θ-Fe₃N, ε-Fe₃C, θ-Fe₃C, θ-Fe₃B to ε-Fe₃N. The bonding nature in ε-Fe₃X (X=B/C/N) is described as a complex mixture of covalent, ionic and metallic characters. The average magnetic moments (Ms) of the ε-Fe₃B, ε-Fe₃C and ε-Fe₃N are 1.53, 1.61 and 1.66 μ_B/atom, respectively. The Ms of Fe are 2.17, 2.23 and 2.25 μ_B in ε-Fe₃B, ε-Fe₃C and ε-Fe₃N, respectively. The Ms of B/C/N are −0.39/−0.26/−0.08 μ_B.The Debye temperatures of ε-Fe₃X (X=B/C/N) are predicted as 427, 565 and 555 K.     

Electronic and optical properties of pure and Mo doped anatase TiO2 using GGA and GGA+U calculations

Comparative GGA and GGA+U calculations for pure and Mo doped anatase TiO₂ are performed based on first principle theory, whose results show that GGA+U calculation provide more reliable results as compared to the experimental findings. The direct band gap nature of the anatase TiO₂ is confirmed, both by using GGA and GGA+U calculations. Mo doping in anatase TiO₂ narrows the band gap of TiO₂ by introducing Mo 4d states below the conduction band minimum. Significant reduction of the band gap of anatase TiO₂ is found with increasing Mo doping concentration due to the introduction of widely distributed Mo 4d states below the conduction band minimum. The increase in the width of the conduction band with increasing doping concentration shows enhancement in the conductivity which may be helpful in increasing electron–hole pairs separation and consequently decreases the carrier recombination. The Mo doped anatase TiO₂ exhibits the n-type characteristic due to the shifting of Fermi level from the top of the valence band to the bottom of the conduction band. Furthermore, a shift in the absorption edge towards visible light region is apparent from the absorption spectrum which will enhance its photocatalytic activity. All the doped models have depicted visible light absorption and the absorption peaks shift towards higher energies in the visible region with increasing doping concentration. Our results describe the way to tailor the band gap of anatase TiO₂ by changing Mo doping concentration. The Mo doped anatase TiO₂ will be a very useful photocatalyst with enhanced visible light photocatalytic activity.     

Travelling wave solutions of nonlinear partial equations by using the first integral method

In this paper, the first integral method is employed for constructing the new exact travelling wave solutions of nonlinear partial differential equations. The power of this manageable method is confirmed by applying it for two selected nonlinear partial equations. This approach can also be applied to other systems of nonlinear differential equations.     

Lévy processes on a first order model

The classical notion of Lévy process is generalized to one that takes as its values probabilities on a first or‐der model equipped with a commutative semigroup. This is achieved by applying a convolution product on definable probabilities and the infinite divisibility with respect to it (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the Wang–Uhlenbeck Problem in Discrete Velocity Space

The arguably simplest model for dynamics in phase space is the one where the velocity can jump between only two discrete values, ±v with rate constant k. For this model, which is the continuous-space version of a persistent random walk, analytic expressions are found for the first passage time distributions to the origin. Since the evolution equation of this model can be regarded as the two-state finite-difference approximation in velocity space of the Kramers–Klein equation, this work constitutes a solution of the simplest version of the Wang–Uhlenbeck problem. Formal solution (in Laplace space) of generalizations where the velocity can assume an arbitrary number of discrete states that mimic the Maxwell distribution is also provided.     

微通道板增益模型的首次碰撞问题

研究了入射电子首次碰撞微通道板(MCP)所产生的二次电子的初能量对基于“能量正比假设”的MCP增益模型的影响,给出的增益公式与实验结果在很大的电压范围内符合较好。     

Calculus of variations on time scales: weak local piecewise Crd solutions with variable endpoints

A nonlinear calculus of variations problem on time scales with variable endpoints is considered. The space of functions employed is that of piecewise rd-continuously Δ-differentiable functions (C¹_prd). For this problem, the Euler-Lagrange equation, the transversality condition, and the accessory problem are derived as necessary conditions for weak local optimality. Assuming the coercivity of the second variation, a corresponding second order sufficiency criterion is established.