Materials Literature
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A microscopic theory of the flow alignment in nematic liquid crystals is presented. The calculation is based on a thermodynamic sum rule derived earlier. The temperature dependence of the flow-alignment angle is obtained in terms of the nematic order parameter $S(T)$. The theory favors stable flow alignment, but the o…
Experimental evidence for a transition from localized to extended states in a two-dimensional band tail is obtained by measuring the conductivity in $n$- and $p$-type inversion layers in Si as a function of electron density and temperature (4.2 to 0.4\ifmmode^\circ\else\textdegree\fi{}K). A transition from metallic to…
Scanning electron microscope techniques show that Eocene opaline claystones (fuller's earth and buhrstone) of the Atlantic and Gulf Coastal Plain, deposits long considered volcanic in origin, are actually highly altered diatomites formed as transgressive facies in normal marine continental shelf environmnents. These f…
In iron-doped rutile (TiO 2 ) charge compensation is necessary since most of the iron substitutes as Fe 3+ for Ti 4+ . The well known EPR spectrum of iron-doped rutile is due to Fe 3+ substitutional ions in a perfect lattice. However, EPR measurements at 9.2 GHz revealed several additional EPR spectra which are explai…
The excited states of 24 Mg with excitation energies less than 14.0 MeV were studied by inelastic electron scattering in the momentum transfer range 0.4 to 1.14 fm -1 . Ground state transition probabilities and transition radii were deduced for 9 known levels with excitation less than 11 MeV and evidence was obtained…
The decay time of the cathodoluminescence emission from the H3 centre has been measured for diamonds containing nitrogen concentrations up to 0.15 atomic per cent, the nitrogen being predominantly in the A form. In five diamonds with low nitrogen concentrations, <or approximately=0.01 atomic per cent, the mean decay t…
Neutron diffraction experiments have been made to reveal the nature of the interstitial order-disorder transformation in the ZrO system using single crystals. The disordering transition of the alloy with O/Zr ⪅ 0.3 occurs below 450 °C, while in the composition O/Zr = 0.3 to 0.4 the disordering undergoes stepwise in s…
Using Poisson's method the demagnetization energy of magnetic dipole distributions is formulated and the equations are solved for the special case of doubly periodic distributions in infinite plates having arbitrary components of magnetization. As an example the energy of a simple bubble lattice with charged domain wa…
The recombination of oxygen in large excess of argon has been studied between 300 and 10 000 °K by trajectory calculations. Reasonable agreement between the computed results and the experimental rate data was obtained by assuming that the interaction between oxygen and argon atoms was 0.3 kcal/mol. The present calcula…
The dynamical critical phenomena associated with the structural phase transition of N${\mathrm{D}}_{4}$ Br (${T}_{c}=215$ \ifmmode^\circ\else\textdegree\fi{}K) have been studied by neutron-scattering techniques. The measurements of the low-energy part of neutron spectra of N${\mathrm{D}}_{4}$Br single crystals have be…
The steady-state photoresponse of the layer-structure crystal ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ is reported as a function of wavelength, light intensity, and electric field strength, using aqueous salt solutions as transparent electrodes. The photocurrent spectrum follows the edge-absorption spectrum for photon en…
The photochemical isomerization of azobenzene in solution can be sensitized by dyes which have low-lying triplet states (rose Bengal, eosin Y, fluorescein, methylene blue) but cannot be inhibited by such compounds. The two triplet levels, T β c and T α c of the cis form are indistinguishable experimentally. On the oth…
The photochemical isomerization of azobenzene can be sensitized by aromatic compounds (chrysene, phenanthrene, naphthalene) or by carbonyls (benzil, biacetyl). Comparison of the photostationary states and the initial quantum yields of isomerization leads to the deduction of a mechanism for this sensitization. The trip…
An expression is obtained for the relaxation time for scattering of phonons by platelets of precipitated impurities of atomic masses and volume different from the host. For large-diameter platelets a closed expression was used in a model describing plateletlike nitrogen precipitates in type-$\mathrm{I}a$ diamonds. A f…
The variation in the ferroelectric transition temperature with deuteration is described by a linear function only if the deuteration level in the crystal is considered. A least-squares fit of these data resulted in the relation Tc=121.7K + 1.07m, with m in mole% D. The effective distribution coefficient (keff) of deut…
The pure ${\mathrm{As}}^{75}$ nuclear quadrupole resonances (NQR) of crystalline and amorphous ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ have been investigated and compared. The temperature dependence of the resonance frequencies, the asymmetry parameters $\ensuremath{\eta}$, and the orientation of the principal axes of t…
The role of many-body effects in the radiationless decay of an excited atom in the vicinity of a metallic surface is studied. In particular we calculate the decay rate for deexcitation by surface-plasmon emission and find it to be a rather likely process. The rate depends on the surface-plasmon dispersion relation and…
Polarity-dependent memory switching has been observed in devices of crystalline SnSe and SnSe2 with aluminum contacts. Two types of low-level switching (1 V/1 mA) with reversed polarity dependence can be obtained in suitably formed devices of either material. In addition, a high-level (100 V/10 mA) polarized memory sw…
It is well established that exposure of KCl:AgCl (or KCl:TlCl) crystals at 77 K to ionizing radiation results in the trapping of holes as $\mathrm{Cl}_{2}^{}{}_{}{}^{\ensuremath{-}}$, ${V}_{K}$ centers, and electrons as ${\mathrm{Ag}}^{0}$ (${\mathrm{Tl}}^{0}$). These crystals emit luminescence at 77 K which persists…
The influence of pressure on lattice vibrations in two molecular crystals, the ring-molecule elemental crystal orthorhombic sulfur and the layer-structure chalcogenide crystal ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$, has been measured by observations of their first-order Raman-scattering spectra at pressures to 10 kbar.…