Materials Literature
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A new procedure for simultaneous refinement of structural and microstructural disorder parameters for polycrystalline materials is proposed. It is based on the Rietveld method combined with Fourier analysis for broadened peaks. Crystallite size and shape and r.m.s. microstrain are regarded as fitting parameters, repla…
Percolation and Bruggeman's effective media theories, as they apply to the electrical conductivity of composites, are reviewed, and a general effective media (GEM) equation, which combines most aspects of both percolation and effective media theories, is introduced. It is then shown that the GEM equation quantitativel…
The structure of photochromic systems based on different classes of spiropyrans, which are promising materials for the optical recording of information and control of luminous fluxes is examined. The structural factors which affect the photochemical activity of spiropyrans and the stability of the coloured forms deriv…
Abstract Measured thermal transport data are interpreted using data obtained by careful microstructural characterization concerning the porosity distribution and graphite grain sizes. The separate thermal conductivity components for one-dimensional composites are deduced using a simple series addition to determine גf1…
We have determined the effects of imposing dichotomous noise on the magnetic Fr\'eedericksz transition in the nematic liquid crystal MBBA. Various states of the nematic orientation occur, depending on the magnitude of the dc field and the amplitude and correlation time of the noise component. The resultant phase diagr…
For pt.III see Phys. Chem. Minerals, vol.16, p.365 (1988). The time evolution of Al-Si ordering and ferroelastic distortion in isothermally annealed Mg cordierite (Mg 2 Al 4 Si 5 O 18 ) is studied using Raman spectroscopy. The transition from the initial hexagonal to the modulated structure is found to be discontinuou…
Abstract The organic matrix of the radula teeth of the chiton Acanthopleura hirtosa has been examined by a variety of techniques to identify and partially characterize the major structural component and to elucidate the complex architectural arrangement of matrix fibres. The teeth are initially composed solely of orga…
We have measured Raman spectra of a diamond film prepared on the (111) surface of cubic boron nitride(c-BN) by the dc plasma chemical vapor deposition method. The polarization property of the Raman line of diamond agrees well with that of LO phonon for the (111) surface of c-BN. The agreement between the polarization…
Tetragonal crystals of hen egg white lysozyme undergo a reversible transformation, accompanied by loss of water, when the relative humidity of the environment is reduced to about 90%. The structure of the low humidity form has been analyzed, using x-ray data collected at 88% relative humidity, in order to explore the…
The electrical transport properties of zinc oxide varistors are correlated with the chemistry of their grain boundaries. An adsorbed layer of bismuth, about 5 Å thick, is necessary to create potential barriers at the grain boundaries. The height of these potential barriers depends sensitively on the excess amount of o…
Via ellipsometry, the time-dependent profiles of liquid droplets spreading completely on plane solid substrates are measured in the range 0--200 \AA{}. Two different surfaces are used, a ``high-energy'' surface (wettable by water) and a ``low-energy'' surface (Langmuir-Blodgett layer of a double-bond-terminated fatty…
A series of interstitial ternary nitrides R 2 Fe 17 N y with 2.3<y<2.9 has been prepared for R=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y. The nitrides have structures related to those of Th 2 Zn 17 or Th 2 Ni 17 , but the unit cell volumes are 6-7% greater, and the magnetic ordering temperatures some 400 K high…
The study of magnetic phase transitions in insulating molecular solids provides new insights into mechanisms of magnetic coupling in the solid state and into critical phenomena associated with these transitions. Only a few such materials are known to display cooperative magnetic properties. The use of high-spin molecu…
The enzymatic degradation of cellulose is an important process, both ecologically and commercially. The three-dimensional structure of a cellulase, the enzymatic core of CBHII from the fungus Trichoderma reesei reveals an alpha-beta protein with a fold similar to but different from the widely occurring barrel topology…
Photoluminescence, thermoluminescence and temperature dependent EPR measurements on Zn 4 B 6 O 13 are reported and discussed. The photoluminescence properties show that the intrinsic violet emission of this compound may originate from a strongly localised self-trapped exciton state. Four types of UV-induced paramagnet…
We study the effects of hydrodynamic interactions on the diffusion of hard spheres in concentrated suspensions. Using a multiple-light-scattering technique that measures the early-time behavior, we find ${\mathit{D}}_{\mathrm{eff}}$/${\mathit{D}}_{0}$=1-(1.86\ifmmode\pm\else\textpm\fi{}0.07)\ensuremath{\varphi}, where…
Current interest in all-optical waveguide devices has created a need for suitable nonlinear materials and fabrication techniques. To meet this need, we have made optical waveguides using ion exchange in two glasses, which were designed both to have large optical nonlinearities and to be compatible with the ion-exchang…
Dans le cadre d'etude des sediments de l'habitat des bivalves dulcaquicoles, une technique d'echantillonnage des eaux interstitielles, primitivement decrite pour les lits rocheux d'eaux courantes par Husmann, a ete modifiee pour une utilisation a long terme dans les sables et graviers d'eaux courantes ou stagnantes.La…
Abstract The hydrothermal treatment of an (NH4)2O/MoO3 mixture at 200 °C (teflon autoclave) yields (NH 4 ) 2 Mo 2 O 7 , (NH 4 ) 8 Mo 10 O 34 and the title compound (NH 4 ) 2 Mo 4 O 13 (I).
The structure of yeast triosephosphate isomerase (TIM) has been solved at 3.0-A resolution and refined at 1.9-A resolution to an R factor of 21.0%. The final model consists of all non-hydrogen atoms in the polypeptide chain and 119 water molecules, a number of which are found in the interior of the protein. The struct…