Materials Literature
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We report time-resolved measurements of photoluminescence in bulk a-${\mathrm{SiO}}_{2}$ using 7.9- and 6.4-eV excitation. Time-resolved spectra have been obtained at room temperature and 25 K, and the intensity and decay rates of various luminescence bands have been measured as a function of temperature. Bands at 1.9…
The electronic structure of amorphous carbon and hydrogenated amorphous carbon (a-C:H) has been investigated through calculations on a number of model structures containing different configurations of ${\mathrm{sp}}^{2}$ and ${\mathrm{sp}}^{3}$ sites. We find that the most stable arrangement of ${\mathrm{sp}}^{2}$ sit…
Two important factors that determine the mechanism and temperature of the alpha - beta phase transition in solid oxygen are analysed: the magneto-elastic coupling which increases the temperature of the transition, and the antiferromagnetic order in the beta -phase which stabilises this phase at low temperatures, thus…
Order parameters, as measured from N.M.R. experiments, are reported for a series of small rigid molecules dissolved in the liquid crystals N-(p-ethoxybenzylidene)-p′-n-butylaniline, Merck ZLI 1132, and a 55 wt per cent 1132 mixture of the two. Previous studies have shown that in this mixture the external electric fiel…
Neutron spin-echo measurements have been performed on the ionic system ${\mathrm{Ca}}_{0.4}$${\mathrm{K}}_{0.6}$(${\mathrm{NO}}_{3}$${)}_{1.4}$ around the glass transition temperature ${\mathrm{T}}_{0}$, in order to determine the time dependence of the density correlation function ${\mathrm{\ensuremath{\varphi}}}_{\ma…
Polypentafluorostyrene (PPFS), polymethylacrylate (PMA), and poly(pentafluorostyrene-co-methylacrylate), poly(PFS-co-MA) were prepared and the wetting characteristics of polymer blends of PPFS and PMA were compared with that of poly(PFS-co-MA) via contact angle measurements. The critical surface tension of polypentafl…
The kinetics of tetrabutyl titanate catalyzed transesterification of dimethyl terephthalate with poly(tetramethylene ether) glycol of various molecular weight has been studied in the presence and absence of 1,4-butanediol. Detailed analysis of experimental data with a proposed kinetic model indicates that the equal re…
Tensile properties of polyethertherketone (PEEK) have been studied at 125, 25, and −100°C for thin films prepared with different thermal histories. Initial morphology was controlled by rate of cooling from the melt. Amorphous films resulted from quenching the melt, while semicrystalline films were obtained by cooling…
Hydrolysis of polyester fabrics with sodium hydroxide has been studied with a view to imparting hydrophilicity and other comfort-related properties to polyester textiles. Effect of reaction parameters such as treatment time concentration of alkali, and temperature on the extent of hydrolysis is examined and the modifi…
Abstract The 2,7‐diazapyrenium group (DAP 2+ ) combines the features of pyrene, of methylviologen, and of nucleicacid intercalators and may thus present a variety of interesting properties. The cations 1 and 2 and the bis‐diazapyrenium species 3 have been synthesized and shown to bind molecular anions like aromatic po…
A new, low bias tilt field-effect liquid crystal display (LCD) is presented with better image quality than supertwist or superbirefringence LCD’s at the same high level of multiplexing. In its positive contrast mode, the display image is black on white with virtually no inherent coloration and with a comparably large…
We have used surface extended x-ray absorption fine structure (SEXAFS) to study the local geometry around barium atoms on thermionic cathodes. On the surfaces of tungsten and tungsten-osmium alloy dispenser cathodes Ba is bonded to oxygen with a well-defined short-range order. The Ba-O distance is similar (2.62\ifmmod…
We determined the crossover frequency ${\mathrm{\ensuremath{\omega}}}_{\mathrm{co}}$ between phonon and fracton regimes from the study of the low-frequency inelastic light scattering in superionic borate glasses of the type (AgI${)}_{\mathit{x}}$(${\mathrm{Ag}}_{2}$O\ensuremath{\cdot}${\mathrm{B}}_{2}$${\mathrm{O}}_{3…
Abstract In our recent overview of liquid crystalline polyesters of trans ‐4,4′‐stilbenedicarboxylic acid (SDA) and aliphatic glycols, 1 we reported that “… the 1,3‐propanediol polyester did not exhibit thermotropic liquid crystallinity (no stir opalescence or DSC endotherm above T m ), perhaps because of the relative…
In previous work, the authors have shown that electrical aging of polyethylene under ac voltage was due to the build-up of a space charge which was accompanied by light emission. Study of the electroluminescence allowed us to estimate the quantity of charges trapped in the material when ac voltage was applied to the p…
Semielliptical surface flaws of different sizes were introduced into Al 2 O 3 by Knoop microhardness indentation. The specimens were fractured by four‐point bending and the profiles of the indentation flaws were determined by observing the fracture surfaces with a scanning electron microscope. The relation between the…
Analytical studies of the collapse of (1) hemispherical, point initiated, (2) hemispherical, surface initiated and (3) conical, point initiated warheads, using the HELP and EPIC hydrocodes predicted tubular or layered jets. Each shaped charge geometry studied revealed a different flow pattern during the jet formation…
Abstract Multilayer composite films consisting of polyolefins, either polypropylene, linear low density or medium density polyethylene, a thin adhesive layer, and a polyamide in various ratios were prepared using two basically different processes. The first, a conventional blown film process in which the extrudate is…
Abstract The adsorption and reaction of thiophene and methylthiophenes in the interlayer of Cu 2+ - and Fe 3+ -montmorillonites were investigated by resonance Raman spectroscopy. Thiophene and 3-methylthiophene polymerized to form cations of polythiophene and polymethylthiophene respectively, which were characterized…
The cation and anion exchange capacities (CEC and AEC) as functions of pH were measured for 12 soil samples from various parts of Quebec. In addition to the index cation Ca, Al was measured in the replacing solutions in order to evaluate the contribution of Al to pH-dependent CEC at low pH. Although all of the soils p…