Materials Literature
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In this paper we report the results of an extensive investigation of the La${}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{O}}_{3}$ system. Substitution of Mn by Co dilutes the double-exchange (DE) mechanism and changes the long range ferromagnetic order of ${\mathrm{La}}_{0.7}{\m…
In spite of the enormous amount of theoretical and experimental work on conducting polymers, the actual mechanism involved in the transition to a metallic regime is still an open and polemical question. Recently, Galv\~ao et al. have proposed, based on the study of long, disordered, one-dimensional chains, that disord…
For the last two decades, mixtures of D- and L-lactides, the DD and LL cyclic dimers of lactic acid enantiomers, were polymerized under various conditions of temperature, time, and initiators. Consequences of the dimeric structure of lactide molecules on the distribution of chiral units and on the properties of result…
We investigate the physics of the core reconstruction and associated structural excitations (reconstruction defects and kinks) of dislocations in silicon, using a linear-scaling density-matrix technique. The two predominant dislocations (the 90-degree and 30-degree partials) are examined, focusing for the 90-degree ca…
We have carried out first-principles total-energy calculations of (001) surfaces of the tetragonal and cubic phases of BaTiO${}_{3}$. Both BaO-terminated (type I) and TiO${}_{2}$-terminated (type II) surfaces are considered, and the atomic configurations have been fully relaxed. We found no deep-gap surface states for…
The paper reports a possible application of AgInSe_2 for opto-electronic switching. Material has been studied over a wide range of frequencies (5Hz to 1MHz), through measurements of conductance and capacitance, at different temperatures and illumination levels. The results indicate that there is an increase in capacit…
Compressed disks made from graphite and, its mechanical but not electrical isomorph, boron nitride as well as graphite-boron nitride powders, undergoing compression, are nearly ideal continuum percolation systems, as the ratio of their conductivities is nearly ${10}^{\ensuremath{-}18}$ and the scatter of the experimen…
Nanocrystalline TiC/amorphous carbon (a-C) composite films were synthesized at near room temperature with a hybrid process combining laser ablation of graphite and magnetron sputtering of titanium. Film microstructure was investigated by x-ray photoelectron spectroscopy, x-ray diffraction analyses, and transmission el…
Experimental Ti $K$-edge x-ray-absorption near-edge structure (XANES) spectra for a variety of Ti(IV)-bearing crystalline oxide model compounds are compared with those calculated using the ab initio multiple-scattering code FEFF7. A scattering-theoretic interpretation of various features in the experimental spectra, i…
The analytical formula, derived by Iglesias-Groth et al for the interaction energy between shells of spherical carbon onions using the surface continuum approximation, is shown to be in very good agreement with the numerical values obtained by Lu and Yang from the discrete summation over the van der Waals Lennard-Jone…
We have expressed the catalytic domain of Chinese hamster HMG-CoA reductase, and 13 point mutations involving the region around the single phosphorylation site for AMP-activated protein kinase. After phosphorylation, these were used to test the specificity of isoforms of protein phosphatase-2A [bovine PP2A(C) (catalyt…
Energy distributions of fast secondary electrons ejected from Cu and Si bombarded by positrons of energies in the range 50 to 2000 eV, incident at glancing angles $(\ensuremath{\le}5\ifmmode^\circ\else\textdegree\fi{})$ and at $35\ifmmode^\circ\else\textdegree\fi{}$, have been fit to the form ${\mathrm{AE}}^{\ensurema…
Two aerogel systems containing a ferroelectric liquid crystal (FLC) with smectic phases over a wider temperature range are investigated using dielectric spectroscopy. The second order transition from Sm-A to $\mathrm{Sm}\ensuremath{-}{C}^{*}$ is considerably broadened and the collective modes are detected for the FLC…
Visible/near-IR-range radiation hardening of a pair of low-OH/low-Cl silica-core optical fibers has been accomplished by γ-ray preirradiation at 27 C to a dose of 13 MGy(Si) at a dose rate of 1 Gy(Si)/s in the dark. Reirradiation under identical conditions three months later demonstrated a 25-fold decrease in the init…
We report our study of the effect of crystallinity on the magnetoresistance in epitaxial and polycrystalline La2/3Ba1/3MnO3 and La2/3Ca1/3MnO3 thin films. Magnetoresistance in epitaxial films exhibits field dependence and temperature dependence similar to bulk single crystals and sintered bulk ceramics. The polycrysta…
The presence of complex charge ordering (CO) phenomena in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{FeO}}_{3}$ $(0\ensuremath{\le}x\ensuremath{\le}0.7)$ has been revealed by transmission electron microscopy at low temperatures. In ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{FeO}}_{3}$ $(x\phantom{…
The high-pressure phases of FeO and MnO were studied by the first principles calculations. The present theoretical study predicts that the high-pressure phase of MnO is a metallic normal B8 structure (nB8), while that of FeO should take the inverse B8 structure (iB8). The novel feature of the unique high-pressure phas…
We discuss a method for determining the optimally-localized set of generalized Wannier functions associated with a set of Bloch bands in a crystalline solid. By ``generalized Wannier functions'' we mean a set of localized orthonormal orbitals spanning the same space as the specified set of Bloch bands. Although we min…
We suggest that the commonly accepted core structure of the 90\ifmmode^\circ\else\textdegree\fi{} partial dislocation in Si may not be correct, and propose instead a period-doubled structure. We present local-density approximation, tight-binding, and classical Keating-model calculations, all of which indicate that the…
The response of disordered P(d-S-b-MMA) diblock copolymers to variable strength surface fields has been studied by neutron reflectivity. Surface interactions were controlled by end grafting P(S-r-MMA) random copolymers with various styrene contents onto Si substrates. The degree interfacial segregation of the block co…