Electron interactions and the electrical resistivity of alkali metals at low temperatures

The contribution of the electron-electron umklapp scattering processes to the electrical resistivity of sodium, potassium, rubidium and cesium at low temperatures has been evaluated using a simplified spherical Fermi-surface model with an isotropic transition probability. Our values of the electrical resistivity so obtained compare fairly well with the recent experimental values for sodium, potassium and rubidium. Our theoretical results have also been compared with the other available data in the literature due to Lawrence and Wilkins and MacDonald and Geldart.     

Dynamic stiffness matrix of a general cable element

Summary A computational scheme for determining the dynamic stiffness coefficients of a linear, inclined, translating and viscously/hysteretically damped cable element is outlined. Also taken into account is the coupling between inplane transverse and longitudinal forms of cable vibration. The scheme is based on conversion of the governing set of quasistatic boundary value problems into a larger equivalent set of initial value problems, which are subsequently numerically integrated in a spatial domain using marching algorithms. Numerical results which bring out the nature of the dynamic stiffness coefficients are presented. A specific example of random vibration analysis of a long span cable subjected to earthquake support motions modeled as vector gaussian random processes is also discussed. The approach presented is versatile and capable of handling many complicating effects in cable dynamics in a unified manner.The work reported in this paper has been carried out as a part of a research project on dynamics of extensible cables funded by the Department of Science and Technology, Government of India. The financial support received is gratefully acknowledged.     

Ultrasonic attenuation in potassium at low temperatures

The contribution of the electron-electron interactions to the ultrasonic attenuation in potassium at low temperatures has been evaluated using a simplified spherical Fermi-surface model with an isotropic umklapp transition probability. Our results show that the e-e scattering processes contribute very little to the ultrasonic attenuation in K at low temperatures as compared to the electron-photon interactions.     

A systematic scheme of qualitative analysis for anions. III

The completeness of precipitation of anions and basic radicals by the two group reagents, zinc acetate and cadmium nitrate, has been investigated. It has been shown that the two reagents precipitate many of the anions quantitatively and can thus be used for their gravimetric estimation.     

Reactions involving selenium metal as an electrophile. The enolate - selenolate transformation

When enolate ions are allowed to react with selenium metal, followed by methyl iodide, the corresponding α-methylselenenyl derivatives are produced in high yield.     

Topotaxy in the oxidation of valentinite,Sb2O3, to cervantite,Sb2O4

The oxidation of orthorhombic Sb₂O₃, valentinite, to orthorhombic Sb₂O₄, cervantite, has been shown by single crystal x-ray diffraction techniques to be a topotactic reaction. The orientation relationships between the two lattices have been determined by making use of a hybrid crystal. It has been found that the individual axes in the two oxides are parallel. The two crystal structures have been compared in the appropriate orientation and their close similarity has been established. The shifts of the individual atoms in valentinite during the process of oxidation have been calculated to be not more than 0·6 Å. It has been established that the reduction of cervantite to valentinite also takes place topotactically.     

Fluoride ion detection by 8-hydroxyquinoline-Zr(IV)-EDTA complex

A simple fluorescent detection based on the ligand exchange mechanism is proposed for the fluoride ion in aqueous media. This procedure is based on the exchange of 8-hydroxyquinoline (oxine) coordinated to Zr(IV) by fluoride ion without interference from other common anions. The ternary complex of oxine with [Zr(H(2)O)(2)EDTA].2H(2)O formed by replacing two water molecules in aqueous solution provides a sensitive signalling system for fluoride ion in the concentration range from 6 x 10(-7)M to 8 x 10(-4)M. The green fluorescence (lambda(max)=532 nm) exhibited by the complex upon excitation at 247 nm decreases in intensity with fluoride addition with a detection limit of 12 ppb. The complexation reaction between oxine and Zr(IV)-EDTA and the ligand exchange reaction with fluoride ion has been investigated by UV-vis and fluorescence spectroscopies combined with the PM3 semi-empirical quantum chemical calculations. Job's method of continuous variation and the molar ratio method ascertain a 1:1 stoichiometry composition of the chelate in aqueous media.     

Effect of temperature on the fluorescence emission of 2H-chromen-2-one derivative in non-polar and polar solvents

The effect of temperature (293-333 K) on the fluorescence emission of 4-(5-methyl-3-phenyl-benzofuran-2-yl)-6-chloro-2H-chromen-2-one (MPBClC) is recorded in non-polar (1,4-dioxane, and toluene), and polar (butanol and DMSO) solvents. It is found that there is no shift in the position of fluorescence maxima, but the intensity decreases with increase in temperature, which depends on the polarity of the solvent. A mechanism of fluorescence quenching with rise in temperature is discussed in terms of the relative location of lowest ¹(ππ^?) and ³(nπ^?) states, and the energy difference between them. The change in temperature brings about a change in the probabilities of radiative and non-radiative transition. The radiationless deactivation of excited-state in the absence of quencher is temperature-dependent and its thermal activation energy has been determined.     

Dielectric, thermal and optical study of an unusually shaped liquid crystal

Dielectric measurements have been carried out for the determination of real and imaginary parts of the permittivity of a newly synthesized, unusually shaped liquid crystal. The sample has been investigated in the frequency range from 100 Hz to 10 MHz within a temperature range 80-130 °C. The dielectric measurements in the smectic A phase indicate a Cole-Cole type of dispersion, and the activation energy was found to be 5.5 meV by using the Arrhenius plot of relaxation time. In addition to this, thermal and optical transmittance studies have also been conducted in the above mentioned temperature range, and the temperature dependence of these parameters has been discussed in detail. The phase transition temperature obtained from a differential scanning calorimetry (DSC) study matches within 2 °C that was obtained from an optical transmittance study. The dielectric and optical behavior of the unusually shaped liquid crystal has been explained on the basis of a proposed theoretical model in which a sample possesses two different conformers having induced polarizations in opposite directions.