Infrared spectra of the superionic conductors Na,K, Rb,Ag and Ti β-aluminates

A detailed analysis of the infrared reflectivity spectra of the superionic conductors X β-aluminates (X = Na, K, Ag, Rb and Tl) is presented. A Kramers-Kronig analysis and the oscillator fits to the data have yielded the frequencies of the transverse optic and associated longitudinal optic modes. A model which ignores the coupling between the spinel blocks accounts for the number of observed infrared modes as well as the Raman modes. It is shown that even for the modes characteristic of the motions of the disordered X-ions, the wave vector selection rule is still valid. The results are discussed with the available theoretical calculations.     

Phonons in titanium doped vitreous silica

In this paper we report the infrared and Raman studies of titanium doped silicate glasses for a number of Ti concentrations. New modes associated with the titanium groups are identified. The observed shifts and broadenings in the spectra of vitreous silica are discussed in the context of random network models. The “anomalous” decrease in density with the addition of titanium is attributed to an increase in the average intertetrahedral angle of the SiO₄ network.     

The influence of disturbed conditions and increased solar activity on geomagnetic distortion of the equatorial ionospheric F2 region

The principal diurnal anomalies in the maximum electron density of ionospheric F2 layer over Kodaikanal are discussed. From an analysis of data obtained over half a solar cycle, it has been found that the phenomena of rapid increase in the electron densities following sunrise, the diurnal asymmetry and the maintenance of abnormally high ionic densities after sunset undergo systematic changes during stormy conditions. In order to examine whether these changes are accounted for by additional movements during disturbed conditions, magnitudes of movement terms of the continuity equation at three heights, for the quiet as well as the disturbed days, have been computed and discussed. The changes in the pattern of diurnal variation of N _m F2 with solar activity and the mechanism responsible for these changes are also discussed. From an analysis of published F2 layer data obtained at a number of stations with magnetic dip between ± 40°, it has been shown that the ratio of morning to afternoon peak densities yields a fair measure of equatorial F2 layer distortion anomaly. From solar cycle variation in diurnal asymmetry, an attempt has been made to estimate the extent by which the anomalous belt widens during sunspot maximum.     

Discotic liquid crystals. A brief review

Progress in the field of discotic liquid crystals is summarized, with emphasis on experimental results rather than theoretical developments. Examples are given of discotic mesogens (including metallo-mesogens) and discotic polymers, and the structures of the mesophases identified to date are described.     

Synthesis,properties, and molecular structure of bis(thiobenzoato-S)tellurium(II), C14H10O2S2Te(II)

The synthesis, properties, and structural characterization of the title compound, C₁₄H₁₀O₂S₂Te, are reported. The crystals are monoclinic, space groupC2/c (No. 15) witha=24.369(6),b=4.333(2),c=14.569(3) Å, and=109.56(2)°,V=1449.57 ų,M=402, andD _x =1.843 g cm^–3 forZ=4. The structure was solved by the heavy-atom method and refined by full-matrix least squares toR=0.029 andR _w =0.027 for 772 diffractometer data. Crystal structure analysis and IR spectroscopic study indicate that the tellurium is covalently bonded to sulfur. There are weak secondary interactions between tellurium and oxygen which complete an S₂O₂ coordination around tellurium.     

The optical rotatory dispersion of quartz

Many formulæ have been proposed to express numerically the rapid increase of the rotatory power of quartz with decrease of wavelength. An examination of these formulæ shows that they are wholly inappropriate for the case of quartz. It has been shown that the entire range of data from the visible to the extreme ultraviolet is accurately represented by a new type of formula involving only two constants,viz.,

$$\rho = \frac{{k\lambda ^2 }}{{(\lambda ^2 - \lambda _0 ^2 )^2 }},$$     

Thermal conductance of Andreev interferometers

We calculate the thermal conductance G(T) of diffusive Andreev interferometers, which are hybrid loops with one superconducting arm and one normal-metal arm. The presence of the superconductor suppresses G(T); however, unlike a conventional superconductor, G(T)/G(T)(N) does not vanish as the temperature T-->0, but saturates at a finite value that depends on the resistance of the normal-superconducting interfaces, and their distance from the path of the temperature gradient. The reduction of G(T) is determined primarily by the suppression of the density of states in the proximity-coupled normal metal along the path of the temperature gradient. G(T) is also a strongly nonlinear function of the thermal current, as found in recent experiments.