Nondispersive hopping transport has been observed in disordered poly($N$-vinylcarbazole) (PVK) but not in the related polymer 3 Br-PVK. The results demonstrate that a hopping-time distribution $\psi \mathrm{}\left(t\right)\mathrm{}\sim t^{-(1+\alpha )}$ can account for the transit-time dispersion in a limited temperature range but that more complicated $\psi \mathrm{}\left(t\right)\text{'}\mathrm{s}$ are necessary to model the results in a broader temperature range. The subtle relation between sample morphology and transient dispersion is demonstrated.

The enhancement factor $\kappa$ in the electric dipole sum rule for $A=3\mathrm{}$ nuclei is calculated using the bound-state wave function obtained from a solution of the Faddeev equations with the Reid soft-core two-nucleon potential. We find $\kappa =0.8\mathrm{}$ for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{H}$. The $S-D$ interference terms are found to be very important. Our result is consistent with experimental data for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$.

A general technique for the spectroscopic study of excited molecular vibrational states is reported. The technique, which involves molecular vibrational energy transfer, is applied to the study of $\nu =1\mathrm{}\to 2$ vibration-rotational transitions of ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$O for which no suitable technique is available for exciting it to the $\nu =1\mathrm{}$ state. The technique also yields direct measurements of the vibrational-energy-transfer rates.

The transition probability per unit time for nonresonant two-photon absorption from the $1s$ to the $2s$ state of atomic hydrogen is obtained analytically using both the electric-dipole interaction $-e\overrightarrow{\mathrm{E}}·\overrightarrow{\mathrm{r}}$ and the Coulomb-gauge interaction $-\left(\frac{e}{m}\right)\overrightarrow{\mathrm{A}}·\overrightarrow{\mathrm{p}}$. The two rates are different, except in the case of resonance. In situations like this, gauge invariance can be used to show that results calculated from the $-e\overrightarrow{\mathrm{E}}·\overrightarrow{\mathrm{r}}$ interaction are always correct.

We show that information about quasimolecular electronic binding energies in transient atomic systems of $Z=Z_1+Z_2$ up to 184 can be obtained from three sources: (1) the impact-parameter dependence of the ionization probability; (2) the ionization probability in head-on collisions as a function of total nuclear charge $Z$; (3) the delta-electron spectrum in coincidence with $K$-vacancy formation in asymmetric collisions. Experiments are proposed and discussed.

This paper reports on the analysis of a spatially extended collection of two-level systems inside a cavity filled with electromagnetic radiation. A new feature of the analysis is the consideration of different strengths of coupling between different atoms and the field (due to the variation of the field intensity inside the cavity). The results are qualitatively different from those obtained under the assumption of equal coupling for all atoms.

Evidence is presented which suggests that a class of modified Bessel-function distributions may have special significance in describing the statistics of radiation scattered by media characterized by a wide range of length scales. It is shown that these distributions may be obtained mathematically by applying a limit procedure to the random-walk problem with a variable number of steps. The choice of distribution for the step-number fluctuations is briefly discussed.

A small-diameter, low-energy, test electron beam is injected along ${\overrightarrow{\mathrm{B}}}_0$ into a collisionless plasma in which current-driven ion sound turbulence can be generated. The scattering of the test particles across ${\overrightarrow{\mathrm{B}}}_0$ due to fluctuating fields ${\overrightarrow{\mathrm{E}}}_w\perp {\overrightarrow{\mathrm{B}}}_0$ gives a direct measure for the turbulent spatial diffusion coefficient $D_{e\perp }$. Investigation of the velocity-space diffusion shows strong pitch-angle scattering effects. No significant anomalous resistivity is observed.

The parametric decay of a finite-extent cold-electron plasma wave (slow wave) was studied experimentally. Using a frequency of ${\omega }_0\gtrsim 10{\omega }_{\mathrm{pi}}$, it was found that the decay waves propagated along the pump wave rather than in the ${\overrightarrow{\mathrm{E}}}_0\times \overrightarrow{\mathrm{B}}$ direction. This is in agreement with the recent theoretical predictions of finite-length stabilization.

Experiments on ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$ show that the orientation of the orbital field $\hat{l}$ depends on the sign of the applied magnetic field, as if there were a ferromagnetic magnetization along $\hat{l}$ estimated by $\left|\right(10\mathrm{} \mathrm{mG}\left)\right(1-\frac{T}{T_c}\left){\chi }_N\right|$, in agreement with a recent prediction by Leggett.

Two recently studied experimental systems are shown to constitute realizations of two-dimensional anisotropic $N$-vector models. Along with a renormalization-group treatment of a general Hamiltonian encompassing these models, we discuss new kinds of multicritical points, nonuniversal critical behavior, and experiments for further study of these systems.

The normal-fluid viscosity of liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$ has been determined in the neighborhood of the superfluid transition using the torsional-oscillator technique of Andronikashvili. In the pressure range from 11.90 to 19.64 bars and for reduced temperatures $t\equiv \frac{T}{T_c}>0.98\mathrm{}$, the $B$-phase viscosity may be described by $\frac{\eta }{{\eta }_c}=1-[A{\mathrm{}(1-t)\mathrm{}}^{\frac{1}{2}}-B(1-t\left)\right]$, where ${\eta }_c$ is the value of the viscosity at the transition temperature. $A$ and $B$ have the values 6.3±0.2 and 20.0±1.0, respectively.

I show that intrinsic plasmons are created in x-ray photoemission experiments on the conduction bands of simple metals. Unlike the core case, the plasmons are produced by many-body effects and are a direct consequence of electron correlation. A theory of the intrinsic plasmon production is given and a calculation of the electron energy-loss spectra in conduction-band x-ray photoemission from Mg and Na is presented. The calculation takes into account both intrinsic and extrinsic plasmon production and the agreement with experiment is good.

The third law of thermodynamics is used to show that the primary pyroelectric coefficient as $T\to 0$ K cannot have a linear temperature dependence when the coefficient is negative and when the specific heat is proportional to $T^3$. The argument is consistent with previous microscopic theories that predict a cubic temperature dependence for the pyroelectric coefficient but not with those that predict a linear temperature dependence. Electrocaloric cooling effects in lithium sulfate monohydrate below 1 K must then be smaller than predicted earlier.

A systematic study was made of negative-ion formation by sputtering from a Mo(100) surface with and without adsorbate layers. Correlation with the work-function change when the surface electronic state was modified by a Cs overlayer reveals a possible tunneling mechanism. Tunnel barrier widths and heights were estimated for ${\mathrm{Mo}}^{-}$, ${\mathrm{O}}^{-}$, ${\mathrm{H}}^{-}$, and ${\mathrm{D}}^{-}$ from the experimental data.

The nuclear spin-lattice relaxation rates of ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{D}$ in stoichiometric PdH and PdD indicate a significant increase in the spin density at the deuteron site over that at the proton site. The results are analyzed theoretically in two distinctly different models involving the zero-point vibrations of the hydrogen. The implication of these results for the understanding of the reverse isotope effect on $T_c$ is discussed.

The spectrum of light Brillouin scattered from thermally excited surface ripples on an elastically isotropic solid is calculated. The theory shows good agreement with recently measured Brillouin spectra of polycrystalline aluminum and nickel.

Large isotope shifts in the ground state of an acceptor $A_2$ ($E_{\mathrm{val}}+11.31\mathrm{}$ meV) and a donor $D$ ($E_{\mathrm{cond}}-12.34\mathrm{}$ meV) have been observed for the first time with photoelectric spectroscopy in pure germanium. The shifts ($\Delta E^{A_2}=+21\mathrm{}\pm 3$ μeV; $\Delta E^D=-51\mathrm{}\pm 3$ μeV) occur in germanium crystals grown in deuterium instead of hydrogen. $A_2$ and $D$ are observed at concentrations < 4×${10}^{11}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The isotope shift is a direct proof that the centers $A_2$ and $D$ contain hydrogen.

Measurements of the low-field ac susceptibility on ternary alloys of Pd + 0.35 at.% Fe and a Mn concentration of 0 to 8 at.% reveal, for three distinct regimes of Mn concentration, (a) a giant-moment ferromagnetism, (b) a high-temperature ferromagnetic phase followed by a lower-temperature spin-glass transition, and (c) a spin-glass phase. Our results for the susceptibility and the $T-c$ phase diagram are satisfactorily explained by the spin-glass theory of Sherrington and Kirkpatrick.

The Edwards- Anderson spin-glass phase is studied via time-dependent Ginzburg- Landau models with quenched impurities. A perturbation expansion is used to study the dynamics and statics without the use of the replica method. It is shown that the spin correlation function has a $t^{-\frac{1}{2}}$ long-time tail in the spin-glass phase.