Materials Literature
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Summary 1. A review is given of the optical and architectural analogies between cholesteric liquid crystals and certain insect cuticles (Coleoptera: Scarabaeidae). Earlier observations on the optical properties (reflexion of circularly polarized light and high form optical rotation) are confirmed and extended. Both ch…
In 1903 F. Heusler reported that it was possible to make ferromagnetic alloys from non-ferromagnetic constituents copper-manganese bronze and group B elements such as aluminium and tin. Further investigations showed that the magnetic properties of these alloys are related to their chemical, L21, structure, and to the…
It is shown by way of model orientation patterns how conduction in nematic liquid crystals may cause a torque per unit volume that more than offsets the dielectric torque felt in the insulating state. This conduction-induced torque arises from an anisotropy of the conductivity or of the dielectric constant. It is part…
The dielectric constants, electrical conductivity, specific heat, and pyroelectric coefficients of ferro-electric Sr1−xBaxNb2O6 (SBN) are investigated as a function of temperature in the range 10°–500°K, and as a function of the Sr/Ba composition of the material. A simple technique for measuring absolute pyroelectric…
Recent attempts have been made to assess the relative merits of the free volume and entropy theories of viscous flow in glass-forming liquids by accurate measurement of viscosity over wide temperature ranges, and subsequent comparison with the equations derived from these theories. In the author's view, this effort is…
By using a thin NiO single-crystal sample, it has been possible to observe electroreflectance spectra between 3.0 and 5.0 eV. The results of this study and a recent photoconductivity investigation suggest that an energy-band description which includes the $3d$ electrons is necessary for a full description of NiO inter…
Results of electron-proton inelastic scattering at 6\ifmmode^\circ\else\textdegree\fi{} and 10\ifmmode^\circ\else\textdegree\fi{} are discussed, and values of the structure function ${W}_{2}$ are estimated. If the interaction is dominated by transverse virtual photons, $\ensuremath{\nu}{W}_{2}$ can be expressed as a f…
Abstract Polysulphone, prepared from 2.2‐bis(4‐hydroxyphenyl)propane and 4.4′‐dichlorodiphenyl sulphone, degrades when heated at 380°C i. vac. The mol. wt. increases with time of heating until after about 3 hrs gelation occurs. In addition to crosslinking scission processes have been shown to be important. Degradation…
Abstract The influence of different annealing treatments on the crystalline order of isotactic paracrystalline polypropylene is described. The result support an intramolecular transformation mechanism based on a rewinding of hellcal segments of different lengths having opposite senses of spiralization. Such a mechanis…
The rate of vaporization of graphite filaments has been measured from 2500 to 3400°K in vacuum and in He by pulse heating techniques. At 3400°K, the rate of vaporization was sufficiently high that a direct determination of the heat of vaporization could be obtained. The experimental results have been correlated with t…
Electrolysis measurements on crystals of ammonium dihydrogen phosphate (ADP) have confirmed the results of Murphy, showing that protons are mobile in the solid. The ac conductance of ADP crystals along the c axis over the temperature range 40–150°C has been shown to fit the expression σ = 1.26 × 102 × exp[− (11.08 ± 0…
G[ Fe (III)] is measured in pulse-irradiated O2-saturated solutions of 20 to 160 μMFe(II), at the pH's 0.46, 1.51, and 2.74 H2SO4 and HClO4 and with dose rates between 1 and 8 krad/1 μsec pulse. Based on homogeneous kinetics, the results are interpreted by a system of 18 reactions. The formation of the hydrogen sesqui…
A unified treatment is given of impurity-induced phonon scattering resonances in thermal conductivity. A mean scattering rate may be defined within the relaxation-time approximation which has a nearly common Lorentzian form for all resonances occurring at a given frequency, except that the width may vary. The peak mea…
Sputtered films of ferroelectric Bi4Ti3O12 have been prepared by using targets containing excess Bi to compensate for loss of Bi in the deposition process. Epitaxial growth has been achieved on MgO and epitaxial Pt substrates. Studies of dielectric properties suggest that the sputtered films are suitable for use in hi…
The phonon dispersion curves of Si are calculated from the dielectric screening theory using approximations based on Phillips's bond-charge model for covalent crystals. The off-diagonal ($K\ensuremath{\ne}{K}^{\ensuremath{'}}$) elements of the inverse dielectric function ${\ensuremath{\epsilon}}^{\ensuremath{-}1}(\mat…
The luminescence of Tb3+-activated CeF3, CePO4, CeBO3, and CeAlO3 has been investigated. Energy transfer from the Ce3+ host lattice to the Tb3+ ion occurs by Ce3+–Ce3+ and Ce3+–Tb3+ transfer. From a study of the Ce3+ luminescence in the analogous La compounds it can be concluded that the probability of the former tran…
An Auger electron spectrometer for studies of solid surfaces which is considerably more sensitive than currently used instruments has been developed. The greatly improved signal-to-noise ratio of the spectrometer made it possible to display the 0–1000 eV Auger spectrum on an oscilloscope at a scanning rate of 20 000 V…
A luminescence band with a half-width of about 0.6 eV at liquid-nitrogen temperature, which can be excited by uv light and x rays, has been observed in irradiated and additively colored MgO crystals at 3.13 eV. By combining ESR and optical studies, this emission band has been identified as due to ${F}^{+}$ centers (ox…
The fluorescence and absorption spectra of trivalent europium ions in glass were measured and compared with the spectra of single crystals of ${\mathrm{Gd}}_{2}$${\mathrm{O}}_{3}$: Eu. It was determined that there is a great similarity between the optical properties of the rare-earth glasses and rare-earth sesquioxide…
The absorption spectrum of cerium-doped Ca${\mathrm{F}}_{2}$ has been observed at several temperatures. When the cerium is reduced to the divalent state at room temperature, the absorption spectrum of ${\mathrm{Ce}}^{2+}$ is found to be unstable against thermal decay or bleaching by visible light; furthermore, this sp…