Materials Literature
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Neat polymerization of bisphenol-linked phthalonitrile monomers, which contain no active hydrogen atoms, is extremely difficult and requires several days of continuous heating at 260–290°C before a viscosity increase becomes evident. In the presence of a nucleophilic compound such as an organic amine, the cure time an…
We present revised absolute values of the elastic constants and order parameters of several cyanobiphenyls. The calculations make use of our earlier measurements of Freedericksz threshold fields and refractive indices, and corrected values of normalizing constants, particularly in respect of the anisotropy of magnetic…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffect of viscosity and temperature on torsional relaxation of molecular rotorsRafik O. Loutfy and Bradley A. ArnoldCite this: J. Phys. Chem. 1982, 86, 21, 4205–4211Publication Date (Print):October 1, 1982Publication History Published online1 May 2002Published inissue 1 Octo…
We analyze the structural relationship between microscopic and macroscopic tensors which characterize the linear- and nonlinear-optical properties of molecular crystals exhibiting a strong donor-acceptor intramolecular interaction, with particular reference to methyl-(2,4-dinitrophenyl)-aminopropanoate (MAP). The quas…
Linear elasticity theory is used to describe the stresses around indentations in hard, brittle materials. Unorthodox plasticity theory is introduced, and related to two simple elastic fields. These, combined in varying proportions, are shown to be consistent with many of the crack patterns observed in glasses and cera…
A simple indentation technique for measuring the hardness‐to‐modulus ratio of elastic/plastic materials was developed. The method, which is based on measurement of the elastic recovery of the in‐surface dimensions of a Knoop indentation, allows ready evaluation of the hardness‐to‐modulus ratio to an accuracy better th…
Efficiency of three-wave interactions in molecular crystals depends on the conjugation of the molecular unit, which in turn is a one- or two-dimensional property. This strong anisotropy reduces the number of non-negligible molecular lowest-order hyperpolarizability coefficients to four. The lowest-order macroscopic op…
Diffraction by a dielectric surface-relief grating is analyzed using rigorous coupled-wave theory. The analysis applies to arbitrary grating profiles, groove depths, angles of incidence, and wavelengths. Example results for a wide range of groove depths are presented for sinusoidal, square-wave, triangular, and sawtoo…
Recent developments in the theoretical analysis and experimental study of frequency-dependent loss by relaxation in amorphous semiconductors are reviewed. A unified theoretical treatment of the complex a.c. conductivity is given, within the pair approximation, for single electron tunnelling and hopping in both uncorre…
The linear chain model of Wieting is used here to predict the frequency of the E 1g Raman active mode in the layer compound 2H-niobium selenide. A careful Raman study near this predicted frequency has shown a weak band whose polarisation suggests that it is the E 1g mode.
The latest model proposed for the P2 centre shows that the paramagnetic electron is associated mainly with one carbon atom. The observation of the carbon-13 hyperfine interaction with this carbon is reported, and the appropriate hyperfine parameters for this interaction are given.
Time correlation formulae for the phenomenological coefficients for isothermal matter transport in solids have been derived earlier by application of the linear response method to a system whose kinetics is characterised by the jump probabilities for vacancy, interstitial or other defect mechanisms. These formulae are…
The literature data on polyelectrolyte complexes (PEC), mainly non-stoichiometric PEC (N-PEC), are analysed. Interpolyelectrolyte reactions, leading to the formation of N-PEC as well as the methods of synthesis of these macromolecular compounds are examined. The structure of water-soluble N-PEC, which constitute a new…
Picosecond self-diffraction is observed from transient orientational gratings produced in germanium by an anisotropic (in $k$ space) filling of the optically coupled states by direct absorption of the nearly monochromatic polarized exciting radiation, the first direct observation of anisotropic state filling in semico…
An inelastic scattering process is observed between 2.5 and 4.0 eV when clusters of 10- to 50-nm-diam aluminum spheres are excited by a 1-nm-diam probe of 100-keV electrons. This inelastic scattering is a maximum when the incident electron probe is positioned within 10 nm of the smaller of two touching spheres. The ob…
ABSTRACT The erosion and cleaning effects of jets are enhanced when the degree of cavitation occurring on or near the bottom of the hole is increased. A new, STRuctured Acoustically Tuned Oscillating Jet ("STRATOJET") system causes the formation of large discrete vortex rings that promote cavitation to depths several…
Four UHV spectroscopies used for the compositional and chemical analysis of surfaces are discussed. These are X-ray Photoemission, Auger Spectroscopy, Secondary Ion Mass Spectroscopy, and Ion Scattering (both low and high energy). Descriptions of the basic processes and information contents are given, followed by a co…
Gd 3+ in glasses exhibit sharp g approximately=6.0 features in the EPR spectra. It is demonstrated that these features can be adequately accounted for by using the 'rhombic' spin Hamiltonian H=g c beta H.S+D(S z 2 -(S/3)(S+1))+E(S x 2 -S y 2 ) in the strong crystal field case. Computer simulations of the experimental…
Magnetic susceptibility, Mossbauer spectroscopy and powder neutron diffraction experiments have shown that iron(III) phosphate, FePO 4 , undergoes a novel spin reorientation transition at 17K between two antiferromagnetic phases. The ordered magnetic moments lie in the basal plane of the trigonal unit cell between the…
Transverse magnetoresistance is measured at magnetic fields up to 6.5 T at temperatures of 77K and 4.2K for highly oriented graphites; four samples of kish graphite with different crystallinity. The effect of the structural perfection of graphite on the field dependence of the exponent n in he magnetoresistance Delta…