Materials Literature
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Abstract A reproducible method for obtaining water‐soluble chitin and a relationship between solubility and degree of deacetylation of chitin were studied. It was found that the regenerated chitin isolated at low temperature from an alkali chitin solution left at 25°C for 48 to 77h showed very good solubility in water…
Field emission cathodes fabricated using thin-film techniques and electron beam microlithography are described, together with effects obtained by varying the fabrication parameters. The emission originates from the tip of molybdenum cones that are about 1.5 μm tall with a tip radius around 500 Å. Such cathodes have be…
We show that longitudinal optical (LO) vibrational modes account for several previously unexplained peaks in the Raman spectra of vitreous Ge${\mathrm{O}}_{2}$ and Si${\mathrm{O}}_{2}$. Identification of LO modes in these and other glasses reduces the complexity of the spectra that must be explained by simple structur…
A model is presented for the structure and properties of active centers in lone-pair semiconductors, based on the possibility of unique bonding configurations which can arise from the presence of nonbonding orbitals. It is shown that the lowest-energy neutral center is unstable towards the creation of different positi…
The Raman spectra of the layer-structure compounds $2H\ensuremath{-}\mathrm{Nb}{\mathrm{Se}}_{2}$ and $2H\ensuremath{-}\mathrm{Ta}{\mathrm{Se}}_{2}$ have been measured between 2 and 300 K. A low-energy peak in the Raman spectrum is found to soften at the charge-density-wave phase transition. This peak is attributed to…
Abstract The process of vulcanization, which links the polymer molecules into a three dimensional network, enables reversible thermodynamic measurements to be made on elastomeric materials from which the entropy and energy contributions to the free energy of deformation can be determined. The molecular processes respo…
Deep centres of the ZnS: Cl single crystals are investigated by the method of impurity electroabsorption (IEA) and photoconductivity (PhC). In accordance with estimations fulfilled a number of the levels obtained are ascribed to V″Zn; (VZnClS)′ and V′Zn and also to (VZnGaZn)′, whose energy levels are obtained in a pre…
The electrical, thermoelectric, magnetic, and crystallographic properties of Ga-doped VO2 single crystals V1−xGaxO2 (0 ≦ x ≦ 0.013) are investigated. By Ga-doping the transition temperature of the semiconductor-metal transition of VO2 is elevated and the resistivity discontinuity is little increased. The T–x-phase dia…
A method of calculating the anisotropy of Poisson's ratio is applied to trigonal and tetragonal crystals in the literature. The method of calculation is extended to hexagonal crystals. The results are illustrated by reference to Tl and Cd.
YOHCO3, or thorhombic, P212~2~; a = 4.809 (1), b=6 .957 (l), c=8 .466 (1) A; Z = 4 , de= 3.89 g c m -a. The final R for 737 reflections was 0.0518. The carbonate-group distances and angles are C-O(1) 1.288 (9), C-O(2) 1.279 (9), C-O(3) 1-287 (8) A, O(1)-C-O(2) 122.8 (7), O(1)-C-O(3) 118-7 (6), and O(2)-C-O(3) 1183 (7)…
Magnetic susceptibility and nuclear magnetic resonance of Cu and Cl nuclei have been studied in monocrystals of [C6H5(CH2)nNH3]2CuCl4 with n=1,2,3 below 4.2 K. These compounds are two-dimensional ferromagnets with a dominant XY-type anisotropy. For the compound with n=1, the Ising anisotropy is extremely small. The NM…
Results of the standard dynamical theory of x-ray diffraction by Bragg planes parallel to a crystal surface are reproduced using Abel\'es's 2 \ifmmode\times\else\texttimes\fi{} 2 matrix method for finding reflection and transmission by layered isotropic structures. In addition to giving a somewhat different insight in…
Important structural features of the two low-temperature phases of ${\mathrm{RbAg}}_{4}$${\mathrm{I}}_{5}$, designated $\ensuremath{\beta}$,$\ensuremath{\gamma}$ in order of decreasing temperature, have been determined, even though the precise structure of the $\ensuremath{\gamma}$ phase is unattainable because of the…
We have extended previous measurements of electrical resistivity and Hall coefficient of single crystals of cubic ${\mathrm{Na}}_{x}\mathrm{W}{\mathrm{O}}_{3}$ to a wider range of values of $x$ and of sample temperature. These new data cover a temperature range from 4.2 to 300 K, and a range of $x$ values from $x=0.22…
Energy-loss experiments with 50-keV electrons on thin polycrystalline films of Al and In yielded data for the surface plasmon dispersion up to ${k}_{\ensuremath{\parallel}}=0.47 \mathrm{and} 0.42$ ${\mathrm{\AA{}}}^{\ensuremath{-}1}$, respectively. The wave-vector dependence of the surface plasmon frequency of Al show…
By ’’photodoping’’ with silver, chalcogenide glasses become almost insoluble in alkaline solutions. This letter examines the applicability of this effect to silicon microfabrication technology. Suitable processing techniques and exposure characteristics are investigated. It is shown that the (Ag) -Se-Ge glass system c…
An interaction between chiral molecules is derived in terms of the orientations of their long molecular principal axes. In analogy with Maier–Saupe and Goossens the derivation is based on the electric multipole expansion. The molecules are assumed to behave as if they were cylindrically symmetric, i.e., the system is…
The Prigogine–Defay ratio, Π≡ΔCp Δκ/TV (Δα)2, has been derived for systems whose states need to be specified in terms of a number of order parameters z by considering the conditions of tangency of the equilibrium free energy surface and the free energy surface for constant values of the order parameters. It is shown t…
We describe in detail a new method for solving the coupled linear differential equations which appear in the theoretical statement of many types of scattering phenomena. Combining the speed advantage of propagation methods with the inherent stability of R-matrix methods, this method is fast and is unaffected by expone…
Some aspects of phase transition behavior have been studied for a classical system of particles which interact in pairs via repelling Gaussian potentials. In a specific low-temperature, low-density limit, this model acts as though it were composed of rigid spheres. Study of lattice sums suggests that at T=0, a fcc cry…