Materials Literature
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Unidirectional charge flow was observed in potassium tantalum niobate, ${\mathrm{KTa}}_{0.6}$${\mathrm{Nb}}_{0.4}$${\mathrm{O}}_{3}$, films. These films of relaxor-type diffuse phase transition material were formed by metalorganic deposition and had a polarization gradient normal to the surface of the films. Novel cha…
We have measured the temperature dependence of the photoluminescence of porous silicon and have found that it disagrees with the expected behavior of crystalline or amorphous silicon. We also found that soaking the samples in oxygen and simultaneously illuminating them with light results in the quenching of the photol…
Abstract Some resins have been synthesized by reacting quinacetophenone with substituted benzoic acids and furfuraldehyde in the presence of basic catalysts. The resins have been characterized by IR spectra of the characteristic groups. The number average molecular weights of the resins have been evaluated by the cond…
Abstract Polyethylene was reacted with maleic anhydride and N ‐phenylmaleimide in solution. The effect of modification on its physico–chemical properties, such as mechanical, oxygen gas transmission, water vapor transmission, and grease resistance properties, was studied.
Abstract New model compounds for poly[ N,N′ ‐bis(phenoxyphenyl)pyromellitimide] have been synthesized in order to investigate the formation of imine bonds which are proposed to form during the curing process and lead to crosslinking in the bulk polymer. Raman studies show that terminal amines can react with imide carb…
Abstract The amount and structure of the crystals formed by the solvent‐induced crystallization (SIC) following a sorption‐desorption cycle of five fluids (benzene, toluene, chloroform, methylene chloride, and carbon disulfide) in amorphous PEEK was determined by wideangle x‐ray scattering (WAXS). The SIC crystal stru…
The quality of hot-filament chemical-vapor-deposited diamond films has been quantitatively assessed by 1H and 13C nuclear-magnetic-resonance (NMR) spectroscopy. As the carbon mole fraction increases from 0.053 to 0.074 in the gas phase, film quality in terms of sp2 carbon content, bonding disorder, and spin-lattice re…
The spin dependence of low-energy electron absorption and reflection from ferromagnetic Fe(110) is investigated using the normalized difference between the absorption (or reflection) of electrons polarized parallel and antiparallel to sample magnetization. The resulting absorption and reflection spin asymmetries are f…
The temperature-dependent optical spectra of the major insulating forms of polyaniline—the fully reduced leucoemeraldine base, half-oxidized emeraldine base (EB), and fully oxidized pernigraniline base (PNB)—and of two oligomeric model compounds for polyaniline are reported. All three forms of the polymer possess a ∼3…
Depolarized Rayleigh spectra of ortho-terphenyl (OTP) were measured in the temperature range from Tg to Tg+190 K. Two samples prepared with and without ‘‘clusters’’ were used for the measurement. Four different Fabry–Perot interferometers covering the time range from about 0.5 ps to 100 ns were employed. Two relaxatio…
Studies have been conducted to further characterize overoxidized polypyrrole films grown on carbon electrodes. Differences in apparent diffusion coefficients for various probes are interpreted via a model based on both hydrophobic and electrostatic interactions between the probe and polymer film. These electrode coati…
The crystal structure of the histidine-containing phosphocarrier protein (HPr) of the phosphoenolpyruvate:sugar phosphotransferase system (PTS) from Bacillus subtilis has been determined at 2.0-A resolution and refined to a crystallographic residual error R-factor of 0.150. The secondary-structure folding topology of…
I describe a systematic study of the effects of vapor-transport growth conditions on the properties of ${\mathrm{NbSe}}_{3}$. Pinning of charge-density waves (CDW's) in ${\mathrm{NbSe}}_{3}$ that is not intentionally doped is primarily by impurities rather than by intrinsic defects. A substantial fraction of these imp…
Abstract Segmented polyurethane elastomers based on a mixture of castor oil and poly(propylene glycol), 4,4'‐diphenylmethane diisocyanate, and 1,4‐butanediol were prepared. The ultimate, thermal, dynamic mechanical behavior and morphology were studied. The use of castor oil shifts the main transition region of the sof…
Abstract Hydrogenated nitrile rubber was prepared by using palladium acetate as the homogeneous catalyst system. The effect of different reaction parameters on the level of hydrogenation was studied. The extent of hydrogenation increased with increase in reaction time, temperature, pressure, and catalyst concentration…
The band structures of \ensuremath{\alpha}-rhombohedral ${\mathrm{B}}_{12}$ (\ensuremath{\alpha}-r-${\mathrm{B}}_{12}$) and \ensuremath{\alpha}-tetragonal ${\mathrm{B}}_{50}$ (\ensuremath{\alpha}-t-${\mathrm{B}}_{50}$) crystals have been calculated by means of the first-principles orthogonalized linear combination of…
An accurate first-passage simulation technique formulated by the authors [J. Appl. Phys. 68, 3892 (1990)] is employed to compute the effective conductivity σe of distributions of penetrable (or overlapping) spheres of conductivity σ2 in a matrix of conductivity σ1. Clustering of particles in this model results in a ge…
An attempt has been made to clarify the anisotropy in the optical absorption and nanostructure of thin films prepared by oblique codeposition of Ag and SiO2. At a low concentration of Ag, the columnar structure grows toward the incident direction of vapor flux of SiO2, and Ag is dispersed in that structure as small me…
Abstract The effect of heating on four chemically synthesized polyanilines, three of which were doped by HCI, H 2 SO 4 , HCIO 4 , and one sample which was dedoped, was investigated. The structural variations during thermal decomposition were studied by real‐time synchrotron radiation diffractometry and correlated with…
We report the results of a seiies of ab initio calculations on the structure and on the vibrational spectra of pyrrole and pyrrole oligomers performed with double zeta quality basis set.