Dielectric relaxation in cyano complexes of the K4Me11(CN)6·3 H2O type. I. Ferroelectric behaviour

Several K₄Me¹¹ (CN)₆·3 H₂O type cyano complexes belonging to the C_2h crystal class were studied to examine their ferroelectricity and the dielectric-relaxation process. Isomorphous substances obtained through replacing the Fe^2? ion by Ru²⁺, Os²⁺ and Mn²⁺ ions show ferroelectric behaviour and dielectric relaxation, in both the ferro- and para-electric phases. It was found, through a careful analysis of the shape of the dielectric-absorption band, that a polydispersive nature appears in the whole temperature range explored and becomes very pronounced in the immediate vicinity of the transition temperature. The distribution of the relaxation times has been described by means of the Williams-Watts decay function.     

Theoretical studies on the conformation of saccharides

The stereochemistry of d-glucopyranose has been studied theoretically in 11 solvents. The stability of the individual conformers in solution has been compared using a method in which the total energy is divided into the energy of an isolated molecule and the solvation energy. The structure and the energy of the isolated molecule have been estimated by geometry optimization using the PCILO quantum chemical method. The solvation energy consists of electrostatic, dispersion, and cavity terms which have been determined from calculated properties of the solute and physiochemical properties of the solvents. The influence of the solvent on rotation of the individual pendant groups and the stability of anomers have been investigated. The calculated composition of the anomeric mixture of d-glucopyranose in various solvents at 25°C (e.g., in pyridine 49% is -anomer, in dimethyl sulfoxide 46%, and in water 32%) is in good agreement with the available experimental data and clearly demonstrates that the solvation properties of - and -d-glucopyranose differ. Based on the calculated abundances of anomers the magnitude of the anomeric effect has been estimated and compared with the results of corresponding calculations on other compounds.     

Photoluminescence of glassy and single-crystalline GeSe2 measured at 77K

Photoluminescence (PL) and excitation (E) spectra of glassy and crystalline GeSe₂ at 77 K have a broad-band peaked at energy $\text{E}{}_{\mathrm{R}}\text{<}\text{1}\text{2}\text{E}{}_{\mathrm{g}}$. PL spectra have a Gaussian form: the Stokes shift (W_S=?ω?E_R) for crystalline GeSe₂ is greater than that for the glass. The absorption coefficient α at the maxima of E spectra is ～ 10²cm^-1 for the glassy form, and ～ 10⁴cm^-1 for the crystalline form. The results are interpreted in terms of the Mott-Davis-Street model supposing a strong electron-phonon coupling in these types of amorphous semiconductors which explains the large Stokes shift and the broad emission band.     

Elasto-plastic response of a multi-layered spherical vessel to internal blast loading

Dynamic response of a multi-layered spherical vessel subjected to intermittent internal blast loading is analysed. The vessel is composed of N concentric unsupported spherical shells of identical material and of the same thickness, separated by evacuated gaps of equal thickness. The wall material is assumed to be elasto-plastic obeying the bilinear stress-strain law. Taking into account of the wave interactions induced by inter-laminar impacts, response of the vessel system was calculated up to five cycles of vibration and the results are presented for several gap sizes.     

Sound attenuation in acoustically lined curved ducts in the absence of fluid flow

A study has been made of the sound attenuation in a lined curved duct with rectangular cross-section. In this study, the derivation of the eigenvalue equation was based on the continuity of the normal component of the particle displacement and the matching of the acoustic pressure on the acoustic lining surface. The sound attenuation was calculated by using the acoustic energy expression for the waves propagating in a curved duct. For a given duct geometry and known acoustic lining impedances, a computer program was developed to solve for the eigenvalues and to obtain the sound attenuation of the propagating waves in the lined curved duct. It was found that in the case studied here the fundamental mode was least attenuated. The total sound attenuation was calculated on the assumption that the amplitudes for all propagating waves were equal at a given frequency. Effects of aspect ratio, bend angle and the acoustic impedance on the sound attenuation were investigated in the present work.     

Diffusion coefficients of metals in inert gases: Comparison of calculations with experimental data

In the present work some simple methods of calculation of the diffusion coefficient by using the model and experimental interaction potentials are discussed. An applicability of such calculations for diffusion of metals in inert gases is analyzed.