A wave propagating obliquely with respect to a magnetic field has many resonances, located at $v_{\parallel }=\frac{(\omega -n\Omega )}{k_{\parallel }}$. When they overlap, there is a transition between regular and stochastic particle motion, leading to a strong decrease in the final wave amplitude. Simulations confirm this result. In the regime where particle motion is regular, the usual trapping oscillations disappear as the angle of propagation increases, because of phase mixing of the bounce frequencies in different resonances.

A novel geometry in which it is possible to do x-ray diffraction from a horizontal surface of fluids is applied to liquid crystals. A large-diameter drop of octyloxycyanobiphenyl (8OCB) on a glass plate treated for homeotropic alignment yields perfect alignment of the smectic-$A$ layers at the top surface over an area of several square millimeters. The surface in the bulk nematic as well as in the isotropic phase was found to consist of smectic-$A$ layers with a penetration depth equal to the longitudinal smectic-$A$ correlation length ${\xi }_{\parallel }\sim {(T-T_{\mathrm{NA}})}^{-{\nu }_{\parallel }}$ determined previously.

A predicted general property of liquid mixtures, the transition from complete to partial wetting at a temperature away from the critical consolute point, is verified experimentally. The system 2,6-lutidine + water undergoes such a transition at $T-T_c\simeq 15$ K, as indicated by the difference in capillary parameters measured by the capillary rise and meniscus curvature in thin Pyrex tubes above this temperature. The experiment provides an estimate of the differential binding energy between the two species of fluid molecules and the wall.

A Monte Carlo study of a system of interacting dislocation vectors reveals the possibility of two types of phase transitions. For a system with a large dislocation core energy, unbinding of dislocation pairs causes a continuous phase transition. With a small core energy a first-order transition is produced by formation of grain boundaries. This possibly resolves the discrepancy between the Kosterlitz-Thouless theory and previous computer experiments of atomistic systems.

Transverse cw NMR has been performed on superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$ at 2.72 bars in a cylindrical bulk geometry (radius = 1 mm). The map of the temperature-dependent $n$ texture in the cylinder, $\hat{n}(\overrightarrow{\mathrm{r}}, T)$, is obtained by deconvolution of the NMR spectra. The textural free energy is obtained from $\hat{n}(\overrightarrow{\mathrm{r}}, T)$ and used to derive the magnetic bending coefficient $R_C{H}_B=(37.4\mathrm{}\pm 5){\epsilon }^{\frac{1}{2}}$ cm G, where $\epsilon =1-\frac{T}{T_c}$, revealing for the first time the Landau-Ginzburg character.

A specific-heat study of a tetrahedrally bonded amorphous semiconductor at very low temperatures (0.08-2.5 K) is reported. Through an investigation of as-evaporated and annealed amorphous Ge films it can be shown that the contribution by low-energy excitations considered akin to the amorphous state is at least six times smaller than in vitreous silica. The specific heat observed below 1 K is mainly attributed to localized unpaired electronic states ("dangling bonds") situated in clusters.

Microscopic calculations are presented of the surface and interface structure of the binary electron-hole liquid in $〈111〉$ -stressed Ge at $T=0\mathrm{}$. The separation of the electron-hole droplet into two coexisting phases is found to have a surface precursor. The phase separation is predicted to occur without any nucleation process or hysteresis effects even though the phase transition is first order. Perfect wetting between the two liquid phases is predicted. Experimental implications are discussed.

Rigorous, self-consistent, all-electron, full-potential linearized augmented plane wave studies reveal that the lowering of the W(001) work function upon cesiation arises from a complex multiple dipole formation mechanism: Essentially, Cs forms a metallic overlayer with its valence electrons strongly polarized and its $5p$ semicore shell polarized oppositely.

Photoinduced transmission was observed in the picosecond time domain in phosphorus-doped $a$-Si: H and connected with deep hole traps produced by doping. The hole transport was found to be dispersive starting before 5 ps and temperature dependent. This shows that the energy distribution of shallow traps is exponential beginning below ${10}^{-2\mathrm{}}$ eV from the valence-band top. The deep traps are negatively charged defects, the trapped holes are removed from the recombination process, and their distribution peaks at 0.45 eV above the valence-band top.

Variational solutions of the pairing-plus-quadrupole Hamiltonian are obtained for a system of protons and neutrons moving in a set of degenerate single-particle orbitals. The role played by pairs of particles coupled to angular momentum $\lambda$ different from 0 and 2 has been studied. It is found that pairs of particles coupled to angular momentum $\lambda =4\mathrm{}$ are essential to obtain the properties of the ground state of deformed nuclei. Even pairs of particles coupled to angular momentum $\lambda =6\mathrm{}$ can play an important role in many cases.

A novel nonlinear transport equation for the time-dependent single-particle occupation numbers in an equilibrating fermion system is derived. In the case of constant transport coefficients its analytical solution together with an expression for the equilibration time is obtained. Applications in mean-field theories extended to include particle collisions for the description of low-energy heavy-ion reactions are envisaged.

In ${\mathrm{Na}}^{+}$-${\mathrm{Na}}^{*}$ scattering in the energy range $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=25-50\mathrm{}$ eV the molecular states $\sigma$, ${\pi }^{+}$, and ${\pi }^{-}$ of the resulting ionic quasimolecule ${\mathrm{Na}}_2^{+}$ are prepared by laser-optical pumping of the sodium atom to the $3{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$, $F=3\mathrm{}$ state. Selection is made with linearly or circularly polarized light. With this novel approach, one can discuss the transition from the space-fixed to the body-fixed reference frame in detail. There is clear evidence for conservation of reflection symmetry with respect to the scattering plane and the implications are considered.

An interference term has been observed in an induced transition between damped substates of $2S_{\frac{1}{2}}$ atomic hydrogen which is formally odd under time reversal. The magnetic-field dependence of this term through the $2S_{\frac{1}{2}}-2\mathrm{}{P}_{\frac{1}{2}}$ level crossing provides a distinct characterization of the interaction of the atom and the radiation field. The results are central to the design and interpretation of the hydrogen parity experiment.

Ion-cyclotron fluctuations in the tandem mirror experiment have wave characteristics consistent with the Alfvén ion-cyclotron instability. The oscillations are coherent, have small azimuthal mode numbers, and have frequencies as low as 12% below the diamagnetically depressed, minimum ion-cyclotron frequency in the end cell. Polarization is in the direction of ion gyration, and azimuthal propagation is in either the electron or the ion diamagnetic direction, with the former prevailing.

Absorption efficiency has been measured in laser-irradiated plane-target experiments with various laser wavelengths (1.06, 0.53, and 0.26 μm), pulse durations (100 ps, 2 ns), and intensities (${10}^{10}$-2×${10}^{15}$ W/cm). Results show a strong increase of absorption for long pulses, low intensities, and short wavelengths which favor inverse bremsstrahlung absorption. A one-dimensional Lagrangian hydrocode (film) is used to interpret these results.

It is shown that, in dense plasmas, dielectronic capture into doubly excited ionic states followed by the ladderlike excitation-ionization chain becomes important in the excitation-ionization process of ions. For the example of a hydrogenlike ion, its contribution to the excitation $1s\to 2s$, $2p$ and also to the ionization has been evaluated by the method of the quasi steady-state solution to the rate equations. The increase is found to be substantial, i.e., by more than a factor of 2 for both the excitation and ionization rate coefficients.

Measurements are reported of the pressure dependence of the real part of the dielectric constant of subcritical and supercritical Hg vapor. Abrupt upward deviations from normal Clausius-Mosotti behavior, which are exhibited in an extremely narrow pressure range in the subcritical vapor phase, indicate that the vapor-liquid phase transition near the critical region is preceded by a heretofore undetected "plasma transition." It is concluded that the dielectric anomaly is caused by the formation of dense, charged thermodynamically stable droplets.

Field-emission energy distributions are presented for $n$-type Si (0.001 Ω cm), with both field-desorbed and flash-recrystallized surfaces, indicating that emission occurs primarily from surface states ∼0.4 eV below the Fermi level, $E_{\mathrm{F}}$, and lower. At reduced temperature and high field, emission begins to appear at higher energy up to $E_{\mathrm{F}}$. Further, for smooth, recrystallized surfaces, multiple peaks are observed in the energy distributions, of 0.1- to 0.2-eV separation.

Angle-resolved photoemission data along the $\overline{\Gamma }-\overline{J}$ symmetry line in the surface Brillouin zone of the Si(111) 2 × 1 surface show that there exists only one dangling-bond band. This fact removes the experimental basis for the introduction of electron correlation effects for the Si(111) 2 × 1 surface. The dangling-bond band shows a large positive energy dispersion, which favors the recently suggested $\pi$-bonded chain model instead of the widely considered buckling model.

The electron paramagnetic transition of a magnetic ion in light scattering is reported. Intense Raman lines are observed corresponding to the $\Delta m_S=\pm 1$ transitions within the Zeeman multiplet of ${\mathrm{Mn}}^{++}$, as well as their combinations with the zone-center longitudinal-optical phonons which interact with band electrons and, in turn, through exchange interaction, with ${\mathrm{Mn}}^{++}$. The phase transition to the magnetically ordered low-temperature phase is manifested in the evolution of the paramagnetic transition into a magnon line.