Materials Literature
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The internal friction (Q−1) in KH2PO4, RbH2PO4, and RbH2AsO4 crystals is investigated using the torsion pendulum technique at frequencies of some Hz in the temperature range from −240°C to the crystal decomposition temperature. The low frequency mechanism of the Q−1 in the vicinity of the Curie point for the crystals…
Abstract This paper discusses the transition in a nematic liquid crystal from a strongly distorted orientation of the anisotropic axis to uniform alignment in a situation of some practical interest. If a nematic with positive dielectric or diamagnetic anisotropy is initially at rest between parallel plates with the an…
A structural model on tellurite glasses, based on neutron diffraction data, is proposed. The coordination scheme of Te is determined and the binding system of the basic coordination polyhedra is establihsed. The role of the modifier (Fe2O3) in the glasses is discussed. The atomic density radial distribution function o…
The thermally stimulated and tunneling luminescence spectra of X-irradiated KCl and KBr, as well as thermal bleaching and thermally stimulated current of X-irradiated KBr are studied at 4.2 to 77 K. The activation energies of I- and H-centre thermal diffusion are determined. The possibilities of radiative tunneling ch…
A new theoretical approach to studying surface vibrations in amorphous solids is applied to silicon dioxide. The method entails modeling the surface as a Bethe lattice with a dangling bond, and treating the two-dimensional nature of the surface and the surface topography as small perturbations. The theory successfully…
A method has been suggested to evaluate the phonon magnification for any general direction inside a cubic crystal. The method consists in establishing the functional relationship between the polar variables (${\ensuremath{\theta}}_{s},{\ensuremath{\varphi}}_{s}$) of the group-velocity vector $\stackrel{\ensuremath{\ri…
The harmonic-generation technique was used to measure the third-order elastic constants ${C}_{111}$ of four types of fused silica. The samples differed in amount of OH content and directional homogeneity. The results indicate that a relatively large OH content in fused silica may give rise to a relatively greater valu…
Dimeric porphyrins covalently linked directly at their periphery (β,β′-biporphyrins) or via a hydrocarbon chain (CH 2 ) n , where n = 1–8, have been synthesized from the corresponding β,β′-linked bispyrroles.
Neutron irradiation of vitreous silica produces changes of the same relative magnitude in the low-temperature excess specific heat ${C}_{\mathrm{ex}}$, the anomalous thermal conductivity $\ensuremath{\kappa}$, and the anomalous temperature dependence of ultrasonic velocity, $\frac{\ensuremath{\Delta}v}{v}$. It is ther…
Low-energy-electron diffraction, Auger-electron spectroscopy, electron-energy-loss, and ultraviolet-photoelectron spectroscopies were used to study the structure, composition, and electron energy distribution of a clean single-crystal (111) face of strontium titanate (perovskite). The dependence of the surface chemica…
The algal flora of a small tundra pond near Tuktoyaktuk, N.W.T., was examined during the ice-free period in 1974. A total of 166 species were identified from three communities, the euplankton, the tychoplankton, and the periphyton. The taxa containing the highest proportion of species were the Chlorophyceae, Cyanophyc…
The electrical transport properties of BaTi${\mathrm{O}}_{3}$ are discussed against the background of recent defect-chemistry investigations and in the light of the small-polaron nature of the charge carriers. Seebeck-effect measurements and chemical investigations on highly doped BaTi${\mathrm{O}}_{3}$:La ceramics ar…
The electronic properties of various types of SrTi${\mathrm{O}}_{3}$ surfaces have been studied by using ultraviolet-photoemission and electron-energy-loss spectroscopy, low-energy electron diffraction and Auger spectroscopy. Vacuum-fractured surfaces exhibit weak photoemission in the region of the bulk band gap, whic…
Abstract In grundsätzlichen Überlegungen weist der Verfasser nach, daß die nachgerade als Dogma allgemein akzeptierte Auffassung einer definierten Molekülstruktur der Materie in bestimmten Bereichen zweifelhaft ist (zum Beispiel verdünnte Gase, Molekularstrahlen), da die definierte Molekülstruktur keine zwingend notwe…
A new method is described for studying, reproducibly, the kinetics of crystallization of minerals under conditions of constant solution composition even at very low supersaturations. For calcium phosphates the method provides direct evidence for octacalcium phosphate as the precursor to hydroxyapatite precipitation at…
An analysis of the static polarizabilities of alkali halides has been presented on the basis of two potential forms for the short range repulsive interactions. The first form is that due to Born and Mayer in which the repulsive energy is considered to depend on interionic separation. The second form is that recently p…
A new species of Uronema isolated from New Jersey soils is described. The apical cell of the unbranched filament of U. trentonense is consistently pointed and a holdfast is invariably formed at the basal cell. The apical cell shows varying degrees of acumination and the holdfast exhibits several morphological forms.
It is shown that thermoelectric voltage measurements in the mixed-conduction region can be used to determine accurately the extrinsic hole concentration p 77K in Pb 0.8 Sn 0.2 Te. For the p 77K range, 10 16 -10 18 cm -3 , this can be achieved by a thermoelectric voltage measurement over the temperature range 295-395K.…
Single crystals of anthracene were grown from the melt following extensive purification efforts including liquid chromatography, sublimation and multiple zone refining in specially designed crystal growing tubes. Platelets cleaved from these crystals were tested for purity and perfection by measuring carrier yields us…
NazSzO3.5HzO, monoclinic, P2~/c, Z = 4. Cell parameters at 25 + 2°C, a = 5.9522 (9), b = 21.618 (6), c = 7.543 (3) A, fl = 103.804 (24) °, were determined by least-squares refinement from the first moments of 40 neutron diffraction Bragg reflections; 2 = 1.0155 /k based on NaC1 a 0 = 5.64037 /k. The structure was refi…