International Journal of Modern Physics B

We have examined the superposition approximation introduced by J. G. Kirkwood. One discusses the origin of mistakes when using this approximation for calculating structural and thermodynamic properties of systems.

Atomic environment of xFe₂O₃·(80-x)Bi₂O₃·20Ga₂O₃ heavy glasses (0≤x≤20 mol%) was investigated with respect to electronic structure of the samples. Data obtained from Bi 4f, Ga 2p, Fe 2p, and O 1s core-level photoelectron spectra indicate changes in the local order on the account of partial substitution of bismuth by iron. The bismuth cations behave essentially as network formers while the iron and gallium ones acts as network modifiers. The number of nonbridging oxygens depends on Fe₂O₃ content.

The influence of electron–phonon interaction on third-harmonic generation in cylindrical quantum wires are investigated. The third-harmonic generation coefficient is obtained using compact-density-matrix approach and iterative method, and the numerical results are presented for GaAs cylindrical quantum wires. The results show that the third-harmonic generation coefficient is greatly enhanced after taking into consideration the influence of electron–phonon interaction. It is about thirty times larger than that obtained by just considering electron states when electron–phonon resonance is met.

Pyrazinamide (PZA) is among the first-line drugs for the treatment of tuberculosis, which seems to reappear as a frequent disease. In this study we investigate the structural changes induced in these samples as evidenced by thermal behaviour and electron spin resonance of new transition metal complexes of PZA. We is search for a correlation between structure and thermal transformations described as multi-step processes consisting in crystalline phase transition, decomposition, melting and thermo-oxidation.

A discussion is made on the appearance of strong effective magnetic field with a new quantum state induced by the zero-point plasma oscillation in semi-localized half-filling electron system in the 2D network of circular molecular orbits. With the help of numerical calculation we study the appearance of superconductivity in the Cu and Ru oxide superconductor employing the field-induced quantum state and a gauge-field pairing model, and succeed in giving a unified explanation to the two apparently different types of oxide superconductivity. It is found that in the Cu oxide superconductor singlet pairing of d_x²-y² symmetry occurs in each CuO₂ layer at the decoupling of the zero-spin-sum singlet FQHE state by small carrier doping, while in the Ru oxide superconductor triplet electron pairing is caused by two neighboring RuO₂ layers at the decoupling of the spin-polarized FQHE Ψ_1,1,1 state where the pairs have d_3z²-r² symmetry with horizontal node on the Fermi surface. Numerical calculation gives critical temperature consistent with experimental observation.

Crystals of MnSi_1.73 were prepared by Spark Plasma Sintering (SPS) technique, analyzed by X-ray diffraction (XRD), and invested by metalogragh and scanning electron microscopy (SEM). The growth processes of the samples were studied. It was found that the Mn–Si powders partly formed MnSi_1.73 crystals at 912–937 K under the mechanical pressure of 20 MPa in low vacuum (about 5.0 Pa), and fully formed MnSi_1.73 crystals after sintered at 1173 K for 15 minutes under 40 MPa.

Glasses of the xCr₂O₃·(100-x)[70TeO₂·25B₂O₃·5PbO] system, with 0≤x≤20 mol%, were prepared and investigated by infrared and Raman spectroscopies in attempt to determine the local structure of glasses. The results shown that BO₃ and BO₄ are the main structural units of the glass system and the chromium ions are located in the network. It is evidenced the presence of TeO₃ and TeO₄ units as possible structural units in our glasses.

By studying the critical properties of a 2D Bose–Einstein condensation (BEC) in traps, we obtain the accurate analytic expressions of transition temperature, condensed fraction, and specific heat. The analytic results fit in fairly well with numerical results. We find that an isotropical potential favors most for condensation to occur. With the aid of Bloch summation, we study the distributions of coordinates and momenta of the system. Some clear physical pictures are presented.

Phyllotaxis of plant organs, bacterial ordering and animal coat patterns are analyzed for homogeneity and density. The patterns are approximated by 15 tiles and characterized by the self-coordination numbers T₁, T₂, T₃ of the nearest, next-nearest and third neighbors of the vertices of the tiles. Homogeneous structures with integer T_i values and maximum densities are obtained for distichous, whorled or spiral growth of leaves. Similar T₁ values, such as T₁=5 and 6 of sunflower seeds or bacteriae, give rise to maximum density. Inhomogeneous structures like the striped patterns of zebras with T₁=1, 2 and 3 connections have a higher density than homogeneous stripes with T₁=2. Maximum density is also obtained in icosahedral viruses.

Influences of perturbative disorders to the photonic properties of one-dimensional periodic dielectric/metal superlattices have been numerically studied. In the calculations, two different disorders were considered, i.e. the disorder in position and in thickness of the metallic layers. Significant modifications induced by the disorders have been found in the photonic band structures. The modifications vary according to the type as well as the degree of the disorders. Both enhanced and attenuated transmissions have been observed in the photonic band gap. Detailed discussions on the calculated photonic band structures would provide useful information on how to obtain desired photonic band structures by introducing certain disorders.

Based on a pseudopotential scheme, the composition dependence of energy band-gaps of zinc-blende Mg_xZn_1-xSe ternary alloys in the composition range of 0≤x≤1 are determined. The effect of deviation of lattice constants of the alloys of interest from Vegard's law on the optical bowing parameter and system transition between the direct and indirect structures is discussed.