Materials Literature
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Saffman-Taylor experiments are conducted in a circular axisymmetric Hele-Shaw cell. We show that when a small pre-existent isolated bubble comes into contact with the tip of a finger, this finger starts growing faster, its radius of curvature at the extremity is reduced, and it takes a parabolic shape. When its veloci…
Realistic ab initio total-energy calculations are performed to investigate the electronic and geometric structure of crystalline ${\mathrm{As}}_{2}$${\mathrm{Se}}_{3}$. Results include the following: total energies for various distortions, the equilibrium geometric structure, intralayer and interlayer cohesive energie…
I define a hopping Hamiltonian for independent electrons on a two-dimensional, infinite, quasiperiodic Penrose lattice with a particular on-site potential, depending upon a parameter r. I then find the exact ground-state wave function for this Hamiltonian. The wave function is shown numerically to have a power-law dec…
We define a one-parameter family of hopping Hamiltonians with an on-site potential, for independent electrons on a two-dimensional quasiperiodic Penrose lattice. The resulting models include the vibrational modes of the lattice. This problem is then investigated numerically---exploiting the symmetries of the model inc…
The method of molecular-dynamics simulation for an assembly of 6480 soft spheres is used to investigate the layerwise structure of a {111} solid-liquid interface for an fcc crystal. A heterogeneous two-phase structure in each layer is suggested by a 2D Voronoi polygonal analysis but this is not supported by various or…
The structural environment of Bi incorporated in Ge chalcogenide glasses has been found from extended x-ray absorption fine-structure data to consist of threefold coordination. An increase by a factor of 2 in the Debye-Waller factor occurs as the carrier type changes from $p$ to $n$. A mechanism involving the suppress…
A new method for calculating the effect of stacking faults on x-ray and neutron-diffraction patterns is developed. Using a computer-generated, statistically faulted crystal model, we show that it is possible to examine the effect of various types of faults in different lattice types from a simple and unified point of…
A new electro-optical material based on nematic liquid crystal dispersed in a polymer matrix has recently been introduced by Fergason. This technology (termed NCAP, for nematic curvilinear aligned phase) is suitable for making very large area (thousands of square centimeter) light valves and displays. The device consi…
The thermoluminescence (TL) of LiF (TLD-100) has been studied over the temperature range 90 to 300K. A total of nine glow peaks are observed in this temperature interval. The most intense peak is the one at 137K. Besides this, three other peaks at 149, 254 and 275K are well resolved and their growth with exposure coul…
The authors establish rigorously the relationship between the growth constant of uniform trees with two branch points and that of self-avoiding walks. For combs, they estimate the corresponding exponent and study the mean-square lengths of the internal and external branches.
The mean square displacement (MSDS) of the ions in the perovskite KZnF 3 have been derived from neutron scattering measurements between 4 and 1073K. The results are compared with the values calculated in the quasi-harmonic approximation. In the high-temperature regime, only a slight increase of F - -ion anharmonicity…
Abstract With the aim to investigate the influence of structural isomerism on the mesomorphic thermal stability in main chain thermotropic polycondensates, a series of poly(azomethines) and low molecular weight models have been prepared. The model compounds exhibit smectic and/or nematic mesophases whose stabilites ar…
The authors have attempted to provide a relatively brief outline of the current situation regarding the formation and properties of charge density wave states in low-dimensional transition metal compounds. They have chosen to illustrate the types of problem involved by specifically focusing on 1T- and 2H-TaS 2 and TaS…
Abstract The B' localized mode, infrared absorption peak (which is due to {100} platelets) and its relations with other features in the infrared absorption spectrum of type la diamonds have been investigated. It is recognized that it is possible, on the basis of their one-phonon infrared absorption spectra, to separat…
We discuss the electromagnetic scattering of a plane wave by an axionic domain wall, under an arbitrary incident angle. We estimate the reflection coefficient which depends on the plane wave frequency and angle and take always a very small value. The two independent circular polarizations propagate with different velo…
The competition between the charge-density-wave and singlet-superconducting phases is investigated for a strong-coupling quasi-one-dimensional system. For a half-filled band each phase appears separately, while for a quarter-filled band a coexistence region is found.
Triphenylstibinedibromide and its derivatives with tribromo-, and pentachlorophenols have been used as flame-retardant additives for polypropylene. Maximum limiting oxygen index of 31.5 against 18.2 for unfilled polypropylene was obtained in a sample containing 10 phr of triphenylstibinedibromide. However, V-0 rating…
Crystals of CaF2 containing different concentrations of Ce3+ and Mn2+ ions were investigated by means of optical absorption and photoluminescence. The results suggest the preferential pairing of the Mn2+ ions with Ce3+ ions in tetragonal sites (i.e. sites in which the Ce3+ ion is locally compensated by an F-interstiti…
Abstract A semiempirical method is proposed, by which the role of kinetical constraints to the growth in closed tube chemical vapour transport can be evidenced. The method is based on the evaluation of the ratio (Φ) between the quantity D which is related to the semiempirically‐determined average diffusivity of the ga…
Abstract The Poole‐Frenkel effect is often observed in the field‐dependent properties of amorphous materials. Experimentally, it is frequently found that the slopes of log σ versus E 1/2 plots differ from that predicted by the Poole‐Frenkel equation and several theorems have been postulated to explain this discrepancy…