Sum and difference frequency generation in acoustoelectric domains in GaAs

Very distinct sum and difference frequency generation has been observed by Brillouin scattering in acoustoelectric domains in GaAs. Comparison of the two processes show that sum frequency generation is the much stronger process in the earliest stages of flux growth.     

Kinetics and rate constants for the reaction of tri-n-butylgermanium hydride with methyl iodide and carbon tetrachloride. The combination of methyl and trichloromethyl radicals in solution.

The kinetics of the photoinitiated reductions of methyl iodide and carbon tetrachloride by tri-n-butylgermanium hydride in cyclohexane at 25°C have been studied and absolute rate constants have been measured. Rate constants for the combination of CH₃? and CCl₃? radicals are equal within experimental error and are also equal to the values found for the self-reactions of most non-polymeric radicals in low viscosity solvents, i.e. ～1–3 × 10⁹ M^?1 sec^?1. Rate constants for hydrogen atom abstraction by CH₃? and CCl₃? radicals are both ～1?2 × 10⁵ M^?1 sec^?1. Tri-n-butyltin hydride is about 10–20 times as good a hydrogen donor to alkyl radicals as is tri-n-butylgermanium hydride. The strength of the germanium–hydrogen bond, D(n-Bu₃Ge–H) is estimated to be approximately 84 kcal/mole.     

Screening theory of the specific heat transition in dirty bulk superconductors in a magnetic field

The specific heat of a dirty bulk superconductor in a magnetic field has been calculated using a screening treatment of the order parameter fluctuations. The results agree qualitatively with the measurements of Barnes and Hake. The transition width scales as $\text{H}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$.     

Critical correlation function to order ϵ3

The zero-field, two-point correlation function of an n-vector system in d = 4 ? ?dimensions is calculated to order ?³ for T ? T_c, using a dispersion theory approach to the scaling function g(g²ξ²)     

14N nuclear quadrupole resonance in several liquid crystals in their solid state

Nitrogen-14 nuclear quadrupole resonance (NQR) spectra in several liquid crystals in their solid state have been detected at 77 K, using a pulsed spectrometer. The quadrupole coupling constants (e²qQ) and asymmetry parameters (η) for the nitrogens have been calculated.     

Statistical mechanics of zero-dimensional ginzburglandau fields: Accuracy of the screening approximation

The screening approximation of Ferrell and Scalapino (n ^/s-1 expansion) is tested in the exactly soluble zero-dimensional case. The expansion is carried to fifth order inn ^?1, where, forn = 2, it appears to start diverging. Forn=1 divergence sets in at the second-order term. The“self-consistent” screening approximation of Bray and Rickayzen converges more rapidly but is more difficult to apply in higher dimensionalities. The usefulness of the zero-dimensional case for checking the enumeration of the Feynman graphs which appear in third and higher order is emphasized.     

A determination of the distributions of quadrupole coupling constants in borate glasses using B10 NMR

A method is presented for extracting the distribution of quadrupolar coupling constants (Q_cc) for 3-coordinated boron atoms in glasses containing B₂O₃. Results are presented for vitreous B₂O₃ and seven sodium borate glasses. There is essentially no change in the average coupling constant and the distribution of coupling constants, over the composition region from 0–35 mol.% Na₂O. It is noted that a distribution in asymmetry parameter (η) can also be obtained and that it should be possible to relate the distributions in Q_cc and η to distributions in bond angles and bond lengths in the glasses.     

Collision-narrowing of Raman spectrum for spin-density fluctuations of electrons in n-GaAs

The inelastic light-scattering spectrum for single-particle excitations in n-GaAs has been found to be considerably $\text{narrower}$ than the Gaussian form usually predicted for a Maxwell-Boltzmann energy distribution. In this paper, we compare the contribution to the narrowing for two factors: collisions and the momentum-dependence of resonant enhancement terms. The analysis is restricted to the spin-density fluctuation mechanism, which has been found to be best suited for probing the electron distribution.