Materials Literature
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Effects of grain size and grain growth in Nb‐doped BaTiO 3 on temperature and frequency dependencies of the dielectric constant were investigated. When 0.65 μm powder is sintered to an average grain size of 1 μm, two dielectric constant peaks indicate the presence of Nb‐free BaTiO 3 and of Nb‐containing material. Sing…
The extended Poole-Frenkel model presented here includes the variation of the barrier height with electric field in directions both opposite and forward to the electric force on an electron. The equation for the voltage-current characteristics based on this model gives not only the usual Poole-Frenkel equation at extr…
Electrical conduction is studied in polyethylene terephthalate and to a limited extent in polyethylene over a range of fields up to 1·2 × 10 6 V cm −1 . In common with previous investigations, it is found that the current decays with time according to an inverse power law, but this can be obviated by a conditioning pr…
Abstract The dynamic mechanical properties of polyester and polyether urethane block polymers have been investigated at four frequencies (3.5, 11, 35 and 110 Hz) in the temperature range of — 150 to 200°C. The existence of a two phase structure was demonstrated in these systems by the observation of two major transiti…
Electrostatic properties of the point-plane electrode configuration are reviewed in the hyperbolic approximation. Simple expressions for the field in the neighbourhood of the tip are derived under the assumption that space-charge distortion is absent. Current induced by a charge carrier moving along a field line is in…
This paper describes a procedure which optimizes the fitting of a `model' of a protein to an electron density map. The technique seeks to minimize ∫ (Qo−Qm)2dv where Qo is the observed electron density and Qm is a density associated with a model in terms of which the observed densities are interpreted. Qm consists of…
A review of molecular-beam epitaxy of GaAs and the observation of surface structures with high-energy electron diffraction in an ultrahigh-vacuum system is described. The utilization of these surface structures as growth conditions to produce n- and p-type layers when doped with Sn, Ge, and Mg, and the electrical and…
The physical properties of many of the rare-earth intermetallic compounds have been collected together. They are discussed in terms of the role that the magnetic exchange and crystal field interactions play in determining these properties. It is pointed out that in this vast number of materials there is an ideal chanc…
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A method for increasing the rate of convergence of general crystal lattice sums of the type \sum_{j \ne k} qjqkr−njk is described. The method is applicable for n > 3, or for n > 0 if \sum_{\rm cell} qj = 0. A numerical example is given for the London dispersion energy (n = 6) of the benzene crystal. The calculation ef…
A new technique is proposed for the mathematical process of reconstruction of a three-dimensional object from its transmission shadowgraphs; it uses convolutions with functions defined in the real space of the object, without using Fourier transforms. The object is rotated about an axis at right angles to the directio…
The Maier-Saupe model of the nematic phase with an orientational order parameter is extended to the smectic $A$ phase by introducing a new order parameter, the amplitude of a density wave in the direction of the nematic preferred axis. Self-consistent equations for the two order parameters are derived from an anisotro…