Materials Literature
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Abstract Studies of the thermal and photodegradation of two commercial polymers, stabilized and unstabilized low‐density polyethylene, show the effects of weathering on differential scanning calorimetry (DSC) curves. The shape and the size of the melting peak vary significantly in thermal aging and in accelerated phot…
The luminescence of cerium-doped barium fluoride crystals has been investigated as a function of wavelength and time. For excitation UV light, X-rays and gamma rays were used. The well known cross luminescence (CL) near 200 nm and self-trapped exciton luminescence (STE) near 300 nm, which are due to excitations of the…
Abstract The thermal conductivities of unidirectional gel‐spun polyethylene fiber‐reinforced composites have been measured parallel (K∥︁) and perpendicular (K⊥) to the fiber axis from 15 to 300K. The axial thermal conductivity K∥︁ varies linearly with volume fraction v f of fiber, while the transverse thermal conducti…
A general formula for the optical-luminescence yield spectra arising from the core excitation is derived, making use of a simple phenomenological model. In this model, it is assumed that various excitations from core electron levels give rise to an identical luminescence in the individual yields. A smaller yield of th…
Photoablation of polymers by pulsed excimer laser radiation is commonly believed to be a controlled layer-by-layer removal process. A mass spectrometer was used to monitor neutral species ejected from polyimide samples in vacuum by 248 nm laser radiation. For fluences close to threshold, the ablation rate starts to dr…
The total energy of ZnS as a function of unit-cell volume has been calculated for the zinc-blende and rocksalt structures by the first-principles Hartree-Fock linear-combination-of-atomic-orbitals method. The calculated structural properties of both phases and the transition pressure between them agree very well with…
We consider the weakly first-order phase transition between the isotropic and ordered phases of nematics in terms of the behavior of topological line defects. Specifically, we present analytical and Monte Carlo results for a new coarse-grained theory of nematics which incorporates the inversion symmetry of nematics as…
We present a theoretical approach to study the conformational and thermodynamical properties of grafted polymer layers. The theory is based on the generalization of a mean-field approach previously used to treat chain packing in amphiphilic aggregates. The theory can be used for any chain model, for any mixture of gra…
We present dynamic light scattering data which show that aqueous gelatin gels display a power-law relaxation to a nonergodic background. In the pregel sol this power law is termined by a stretched exponential which restores ergodicity and which has a q dependent characteristic time proportional to the viscosity. The p…
Abstract The solubility of carbon dioxide, methane, and propane in poly(dimethyl silmethylene) [(CH 3 ) 2 SiCH 2 ] x and poly(tetramethyl silhexylene siloxane) [(CH 3 ) 2 Si (CH 2 ) 6 Si (CH 3 ) 2 O] x was measured in the temperature range from 10.0 to 55.0°C and at elevated pressures. The present results are compared…
Abstract The glass transition ( T g ) of thin polystyrene films (ca. 3000 A˚) cast on silicon wafers was determined by a new technique. An ellipsometer was used to determine the refractive index and thickness of the polystyrene films. T g was determined by measuring the temperature dependence of the refractive index.…
High quality, low resistivity (2.6×10−4 Ω cm), 0.32-μm-thick amorphous and polycrystalline, pure and Sn-doped, In2O3 films prepared by high density plasma-assisted electron beam evaporation were used to investigate the effect of Sn doping on the electronic transport properties of this material. Amorphous films with hi…
We report ab initio calculations of the lattice constants and the electronic band structure of the hexagonal wurtzite-structure semiconductors ZnO and ZnS. We employ the local-density approximation and solve the Kohn-Sham equations for nonlocal, separable, and norm-conserving pseudopotentials self-consistently. We use…
Highly supersaturated nanocrystalline FexCu100−x alloys (10≤x≤95) have been prepared by mechanical alloying of elemental crystalline powders. The development of the microstructure is investigated by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The results are compared wit…
The preparation of CeO 2 thin films on sapphire by DC reactive magnetron sputtering of metallic Ce target in an argon-oxygen mixed gas is reported. The resputtering of the film deposited facing the target track was observed. The films deposited far from the sputtering system axis exhibited well-oriented crystalline st…
The effect of sulphur addition on some structural properties of a-Se was studied for compositions up to about 30 at.% S. The sulphur in the binary amorphous semiconductor system Se-S was found to affect the density (d), microhardness (VH), dielectric constant ( in ) and tendency to crystallization (T c -T g ), as well…
Data are reported on the luminescence spectra generated by X-ray and electron irradiation of optical fibres, fibre preforms and silica. The impurities and imperfections in the fibre core have a higher luminescence efficiency than those in the substrate material. The core luminescence provides a major fraction of the t…
The electronic and geometrical structures of exchange-coupled open-shell systems such as bis(methylene) methane and the chromium–methylene cation were investigated by the molecular orbital and its extended methods: RHF, UHF, UNO-CAS, RMP, UMP, PUMP, APUMP, UCCSD(T), UNO-CI and QCISD(T). The fully optimized geometries…
Sputtering of highly oriented pyrolytic graphite (HOPG) by 248-nanometer laser radiation was studied. Neutral carbon atoms and small clusters were ejected with significantly higher translational energies than were expected from a simple model of thermal vaporization in the absence of a potential barrier. The HOPG also…
As diamond-producing catalysts, 12 transition metals such as iron, cobalt, and nickel were first reported by General Electric researchers more than 30 years ago. Since then, no additional elemental catalyst has been reported. An investigation of the catalytic action of group V elements is of great interest from the vi…