Materials Literature
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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.
This paper compares the biophysical and mechanistic properties of a typical type I dehydroquinase (DHQase), from the biosynthetic shikimate pathway of Escherichia coli, and a typical type II DHQase, from the quinate pathway of Aspergillus nidulans. C.d. shows that the two proteins have different secondary-structure co…
Abstract The dielectric relaxation behavior of poly(phenylene sulfide), PPS, has been investigated from room temperature to 180°C. This study was undertaken to examine the mobility of the amorphous phase through the glass transition region, to determine the contribution that rigid amorphous phase material makes to the…
We study the effects of electron-electron interactions in halogen-bridged mixed-valence transition-metal linear-chain complexes (MX chains) applying a simple 3/4-filled two-band discrete tight-binding (extended) Peierls-Hubbard model with both on-site and intersite electron-phonon couplings. We employ a variety of met…
We consider a 3/4-filled, two-band discrete tight-binding Peierls-Hubbard model for an isolated chain of a halogen-bridged, mixed-valence, transition-metal linear-chain complex (HMMC or MX chain). We have employed the adiabatic approximation in which the quantum fluctuations associated with phonons are implicitly trea…
Raman-scattering spectra of LO-phonon modes in CdSe microcrystals of various sizes in a germanate glass matrix are measured. The frequency of the peak shifts towards the lower-frequency side and the bandwidth broadens with decreasing microcrystal size. The size dependences of the peak shift and the broadening of the b…
Long-time self-diffusion coefficients in concentrated colloidal dispersions of silica spheres, with various interaction potentials, were measured with the fluorescence recovery after photobleaching technique. Charge stabilized spheres were measured in solutions of LiCl in dimethylformamide with varying ionic strength.…
The electronic structures of various Si clusters of different sizes (with hydrogenated surfaces) are evaluated using a nearest-neighbor empirical tight-binding Hamiltonian which describes well the band structure and fundamental band gap of crystalline silicon. The largest cluster contains 3109 Si atoms and 852 H atoms…
Abstract The development of a detailed model describing particle growth in olefin copolymerization systems is presented. The Multigrain Model considers in detail monomer sorption, mass transfer, and changing porosity within the growing particle, as well as heat and mass transfer across the external film of the particl…
The formation of hydrogen-bonded structure in the folding reaction of ubiquitin, a small cytoplasmic protein with an extended beta-sheet and an alpha-helix surrounding a pronounced hydrophobic core, has been investigated by hydrogen-deuterium exchange labeling in conjunction with rapid mixing methods and two-dimension…
Atomic mean-square displacements for frequencies above 10 11 Hz have been determined from neutron time-of-flight data in the glassy, liquid and crystalline phase of selenium. As in many other substances, the difference between the values in the disordered and the ordered phase shows a strong increase with increasing t…
We show how relatively standard Monte Carlo techniques can be used to probe the free-energy barrier that separates the crystalline phase from the supercooled liquid. As an illustration, we apply our approach to a system of soft, repulsive spheres [v(r)=ε(σ/r)12]. This system is known to have a stable face-centered-cub…
The effect of irradiation (UV-visible light) on a nematic liquid crystal doped with a photoactive azobenzene derivative was investigated. The selective irradiation results in either an E implies Z or Z implies E isomerization of the azobenzene unit. The effect of the isomerization is to cause a reversible depression o…
The interference modulated transmission spectra T( lambda ) at normal incidence for amorphous arsenic sulphide semiconducting films deposited by thermal evaporation were obtained in the spectral region from 300 nm up to 2000 nm. The straightforward analysis proposed by Swanepoel (1983), which is based on the use of th…