Materials Literature
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The results of studies on the structure and nature of the electronic states of spiropyrans (SP) and the products of their photochromic reactions as well as the mechanism of the dissociation of the Cspiro–O bond and the formation of a coloured form of the SP are surveyed and analysed. Also analysed are the mechanisms o…
Model calculations were performed to test the possibility of solving crystal structures of proteins by Patterson search techniques with three-dimensional structures obtained from nuclear magnetic resonance (NMR) interproton distance restraints. Structures for crambin obtained from simulated NMR data were used as the t…
A brief historical perspective and a review of the current research on amorphous or glassy materials are presented. Glass formation by natural processes and by laboratory synthesis techniques is described. Recent efforts to characterize and model the atomic scale structure of amorphous phases are surveyed. The relatio…
A novel foam structure is presented, which exhibits a negative Poisson's ratio. Such a material expands laterally when stretched, in contrast to ordinary materials.
The differential resistance of ${\mathrm{NbSe}}_{3}$ measured in the presence of combined ac and dc electric fields exhibits interference features. Our experimental results for the dependence of these features on ac amplitude and frequency are in complete and dramatic disagreement with predictions of the classical mod…
Mercury photosensitized decomposition of SiH4 is used to study surface reactions of SiH3 on hydrogenated amorphous silicon (a-Si:H). The method involves modeling of gas phase production, reaction and diffusion to the walls of reactive species, in a parallel plate reactor, combined with measurements of surface reflecti…
From a simple master-equation description of viscous liquids it is shown that there exist two different kinds of glass transitions. Slow glass transitions lead to a Gaussian, while fast glass transitions lead to an exponential distribution of frozen-in energies in the glass. It is argued that amorphous semiconductors…
A newly developed integrated SQUID magnetic spectrometer yields direct high-resolution measurements of the optically induced magnetization in a 10 \ensuremath{\mu}m-diam sample of ${\mathrm{Cd}}_{0.8}$${\mathrm{Mn}}_{0.2}$Te. Both the magnitude and the picosecond dynamics of the magnetic response have been studied and…
Viscosity data for supercooled liquids are reexamined in terms of the random-potential model with use of the concept developed for treatment of electronic transport in random media with energetic disorder. \ensuremath{\eta}(T) is found to obey the predicted exp[(${\mathrm{T}}_{0}$/T${)}^{2}$] law covering 10 decades i…
The authors describe a method to estimate the critical supersaturation sigma c above which a growing crystal face becomes kinetically rough. They discuss the relation of sigma c with the step free energy kT gamma . The method is tested with computer simulations of the growth of the (001) face of a simple cubic crystal…
Comb polymers with semi-flexible main chains and rod-like nematogenic side chains form interesting nematic phases, largely as a consequence of competition between polymer entropy and rod order. The authors model this competition taking main chains of various stiffness and side groups of various length. Depending on vo…
Usual Penrose tilings are defined by a set of five phases gamma j which add up to an integer. The authors study the general case where the phases add up to any number and show that these generalised tilings can be obtained with four tiles (two thick rhombi and two thin rhombi) with different colourings of the edges. T…
Thermoreflectance spectra of Pb1-xGexTe (x=0, 0.02, 0.03, 0.07 and 0.1) have been investigated in the energy range 1.2 to 4.4 eV at temperatures above and below the phase transition temperature. The change of the interband transitions on the Ge content x in the cubic phase (300 K) have been obtained. Thermoreflectance…
A lattice dynamics model for ionic crystals with complex anions is developed and applied to experimental phonon dispersion curves for orthorhombic CaSO 4 . The model treats the sulphate as a rigid unit and includes long-range Coulomb interactions. Fifteen force constants and three atomic charges are fitted to the expe…
Wheat straw-g-polyacrylonitrile (PAN), containing 40% PAN, was saponified with sodium hydroxide and isolated under three sets of saponification and work-up conditions. Each reaction mixture was separated into a water-soluble and a water-insoluble fraction, which were individually analyzed for percentages (by weight) o…
Using the Guinier plot, the 200 reflection profile of ramie cellulose I was resolved into two components. One component represented a crystallite size of ∼ 20 Å, and the other component represented a crystallite size of ∼ 61 Å. These components were followed during the conversion of cellulose I to Na–cellulose I, in o…
When cellulose is mercerized slowly, the initial conversion is from the cellulose I crystal structure to that of Na–cellulose I. The conversion is a crystal-to-crystal phase transformation, without passage through an amorphous state. The analysis of crystallite sizes of cellulose I and Na-cellulose I during this trans…
Molecular-dynamics calculations are used to characterize the structure and dynamics of the two solid bilayer phases of the n-alkane tricosane (${\mathrm{C}}_{23}$${\mathrm{H}}_{48}$). In the crystalline orthorhombic phase at 38\ifmmode^\circ\else\textdegree\fi{}C, chains undergo translational, rotational, and torsiona…
We obtain quasicrystalline structures in Monte Carlo simulations of a simple two-component Lennard-Jones system in two dimensions. The quasicrystal, which shows tenfold symmetry, appears to be an equilibrium state of the system. Although the structure corresponds to tiling of the plane with rhombuses, it is not a Penr…
Using electroreflectance spectroscopy, we have observed new optical transitions near 0.76, 1.25, and 2.31 eV in an ordered strained-layer Ge-Si superlattice. The possible origins of these transitions are discussed in terms of modification of the electronic band structure by the sample structure.