14N nuclear quadrupole resonance in nicotinic acid derivatives

Nitrogen-14 nuclear quadrupole resonance (NQR) spectra of nicotinic acid derivatives, known as antitumor agents, are reported and analyzed in the framework of the Townes and Dailey theory. A strong correlation exists between the charge difference σ_NC ? π at the pyridinic nitrogen and the inhibition of acetylcholinesterase by nicotinic acid derivatives, in which the inhibition potency (pI₅₀) increases as the charge difference σ_NC ? π increases. There are significant differences between ¹⁴N NQR spectra for the pyridinic nitrogen sites of nicotinic acid and nicotinamide; these can be explained in terms of the differences in hydrogen bond lengths.     

Raman probe studies of Nd: YAlG laser generated non-equilibrium excitations in GaAs

A survey is presented of the non-equilibrium excitations in GaAs that can be probed by Raman scattering. Intense Q-switched Nd:YAlG laser pulses are used both for generating the non-equilibrium excitations at low temperature, and for in-situ Raman scattering probe measurements. Particular emphasis is placed on the search for non-equilibrium, zone-edge slow TA phonons. We discovered that the difference frequency combination spectrum involving slow TA phonons is surprisingly coincident with the acceptor excitation line spectrum for the Zn impurity. The discrimination between the non-equilibrium phonon population and a non-equilibrium hole population on minority acceptors in n-GaAs is discussed.     

On the thermal conductivity of diamond under changes to its isotopic character

We show that the 50% increase of the room-temperature thermal conductivity of single-crystal diamond [1] upon increasing its isotopic purity is unlikely to be due to a decrease in phonon-isotope scattering alone. In addition, removal of the¹³C isotope can sharpen the phonon dispersion in a heretofore unappreciated way and thereby decrease the phonon-phonon Umklapp scattering enough to cause the observed results. In addition, the order-of-magnitude increase [1] in the UV damage threshold in the isotopically purer diamond is probably caused by similar effects. In fact, all physical processes wherein phonon wave-vector or energy thresholds are important should be affected by this mechanism.     

14N nuclear quadrupole resonance in N-acetyl amino acids

¹⁴N Nuclear quadrupole resonance (NQR) spectra of several N-acetyl amino acids and related compounds are reported and analyzed within the framework of the Townes and Dailey theory. The inductive effect of the chloroacetyl group on the nitrogen is discussed. A positive correlation between the π-σ_NC electron density at the nitrogen and the Taft inductive parameter σ* is observed, suggesting that the nitrogen π-charge density in the N-acetyl amino acids does not vary appreciably. NQR data for hippuric acid are compared to the ¹⁴N quadrupole parameters extracted from ENDOR data reported for X-irradiated hippuric acid.     

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)