Materials Literature
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The electrical conductivity for a system of electrons described by the single-band Hubbard Hamiltonian is studied. An expression for the electrical conductivity that is applicable in the narrow-band regime, i.e., the bandwidth $\ensuremath{\Delta}$, much smaller than intra-atomic Coulomb repulsion $I$ is derived. It i…
We have calculated the temperature coefficient of the long-wavelength refractive index of several group-IV and III-V semiconductors, using the Penn model for the electronic contribution to the dielectric constant. The isotropic band gap of this model is identified with the band gap at the $X$ point of the Brillouin zo…
Optical absorption and fluorescence spectra of Ho3+ in LaF3 have been obtained between 2500 and 21 000 Å. From an analysis of the data, it was possible to assign 2J + 1 Stark components to the observed states below 26 000 cm−1. A least-squares fit of 22 assigned J levels, with the inclusion of configuration interactio…
Macroscopic thermal dilatation coefficients as well as those of the lattice have been precisely measured along principal crystallographic directions of magnesium single crystals in the temperature range between room temperature and 650\ifmmode^\circ\else\textdegree\fi{}C. The vacancy concentration was thus obtained as…
The crystallographic structure of hexagonal NiS has been determined at temperatures above and below the metal-semiconducting transition. The powder x-ray diffraction peak intensities were used to determine the atom positions in both phases. The symmetry of the unit cell is found to change from $\frac{P{6}_{3}}{mmc({D}…
The wave-number- and frequency-dependent dielectric function of a semiconductor is derived and calculated in terms of a model consisting of an electron gas with an energy gap. From it are deduced, as a function of the gap width, ($i$) the screening of a point defect, ($\mathrm{ii}$) the annihilation rate of positrons,…
A simple theoretical model for metal-insulator transitions is presented. It is based on the existence of both localized (ionic) and band (Bloch) states. It differs from other theories in that it assumes the one-electron states to be essentially unchanged by the transition. The electron-hole interaction is responsible…
The electrical and optical properties of materials which are characterized by narrow bands in the vicinity of the Fermi energy are discussed. For such materials, electronic correlations and the electron-phonon coupling must be considered explicitly. Correlations in $f$ bands and in extremely narrow $d$ bands can be ha…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMandelic acid racemase from Pseudomonas putida. Evidence favoring a carbanion intermediate in the mechanism of actionGeorge L. Kenyon and George D. HegemanCite this: Biochemistry 1970, 9, 21, 4036–4043Publication Date (Print):October 13, 1970Publication History Published onl…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCharacterization of the product formed by renaturation of α1-CB2, a small peptide from collagenKarl A. Piez and Merry R. ShermanCite this: Biochemistry 1970, 9, 21, 4129–4133Publication Date (Print):October 13, 1970Publication History Published online1 May 2002Published inis…
Abstract Carbon fibres of Young modulus 410 GN m-2 (60 x 106 lbf in-2) consist of graphite crystallites (La about 9 nm) with their basal planes having a preferred orientation of within 10° to the fibre axis. They are made by the pyrolysis of polyacrylonitrile textile fibres. Inter-molecular reactions occur between th…
Abstract Fully alined long chain polymers would have a Young modulus in the alinement direction similar to that of steel. Practically available polymeric materials have moduli less than one-tenth, and usually less than one-fiftieth of this, even with a high degree of molecular alinement. The paradox is of course resol…
The temperature dependence of birefringence in the liquid crystal methoxybenzylidene-$n$-butylaniline has been obtained by measuring the birefringence of a thin sample placed between crossed polarizers. Measurements of transmitted laser light yield minima and maxima which can be related to the difference in refractive…
The growth of single crystal oxides for optical and magnetic purposes is commonly carried out using platinum containers. Modifications to container design have been important factors in improving growth conditions. A new composite three-layer crucible has been fabricated in platinum and iridium for growing crystals of…
Singularities of the spin structure in helimagnets are studied on the basis of the description of disclinations already made for cholesteric mesophases. The main differences arise from the possibility of two chiralities in helimagnets (i.e. two directions of rotation about the helical axis) and from the strong couplin…
Indices of refraction of monoclinic Pb2MoO5 crystal have been measured in the visible region at room temperature. The values obtained at 589.3 mμ are nX=2.1833±0.0005, nY=2.1967±0.0005, nZ=2.3188±0.0006, and (+)2V=38.2±1.4°. Dispersion characteristics of the refractive indices are well explained by the two-oscillator…
The methods of analysing thermally activated dislocation glide using applied stress τ as an independent variable, (τ, T) analysis, or the effective local stress τ∗ as the variable, (τ∗, T) analysis, are compared. Each scheme is self-consistent and the two are mutually compatible. The (τ, T) analysis refers to a real t…
Abstract The effects of single and multiple washing and of resoiling‐rewashing of cotton and synthetic fabrics have been studied in Tergotometer tests at various levels of temperature, detergent concentration and water hardness. The soiling mixture consisted of a seven component sebum tagged with tritium and carbon‐14…
Electron microscopy evidence is given for a grain boundary dislocation (GBD) acting as a Frank-Read source of a lattice dislocation (LD) in pure α-iron near room temperature. Thermal stresses generated by the electron beam are responsible for the last stage of operation of the source which was activated before observa…
Residual thermal stresses are present in cross-plied graphite-epoxy composites due to the anisotropic thermal and mechanical properties of the individual layers. Experimental measurements and analytical calculations of the thermal stress induced in two different cross-plied composites during fabrication are presented…