The $n=2\mathrm{}$ rotational instability is the most dangerous gross instability in a field-reversed theta pinch. It is demonstrated for the first time that the instability is completely suppressed by superposing a quadrupole field which is much smaller than the axial confinement field at the separatrix. The experimental threshold intensity of the field for stabilization is about 2.5 times less than that predicted by theoretical stability analysis.

It is argued that surface undulations observed after self-sustained rapid crystallization of amorphous films result from a thermal instability that induces a periodically varying crystallization rate. Its physical origin is discussed for a simple nonlinear heat-conduction model which yields good agreement with experimental observations. A numerical analysis of the nonlinear oscillations shows that these may, in turn, bifurcate via a series of period-doubling bifurcations.

The thermal conductivity of single-crystal ${\left(\mathrm{KBr}\right)}_{1-x} {\left(\mathrm{KCN}\right)}_x$, $0.05<~x<~0.5$, in the temperature range 0.08-100 K shows behavior characteristic of amorphous solids. The low-temperature specific heats ($T<\mathrm{}2.5\mathrm{}$ K), measured on long (∼ 50 s) and on short (< 0.2 ms) time scales, also are identical to those found in amorphous solids. It is proposed that the KBr-KCN system provides a connecting link between the low-energy excitations in amorphous solids and in spin-glasses.

The coupled rotational-translational excitations in ${\mathrm{}\left(\mathrm{KBr}\right)\mathrm{}}_{0.992}$${\mathrm{}\left(\mathrm{KCN}\right)\mathrm{}}_{0.008}$ were studied by inelastic neutron scattering. For the first time the $A_{1g}-T_{2g}$ tunneling transition and the $A_{1g}-E_g$ librational excitation were followed at the transition from the paraelastic to the structural glass state. The drastic reduction of the $T_{2g}$ rotation-translation coupling suggests that the number of free-ion tunneling states is reduced in favor of cluster reorientation modes which are effectively decoupled from the lattice.

Ferdinand and Fisher have discovered some unusual lattice-shape effects on the finite-size-induced specific-heat peak shift in the two-dimensional Ising-model critical region. It is shown that they are well approximated by keeping only the two largest eigenvalues of the transfer matrix, and may be expressed entirely in terms of a one-dimensional Ising array of domain walls. Approximate expressions for the effective coupling and number of spins are given. It is also pointed out that in general domain walls should be thermodynamically important for such finite-size effects.

The first measurements are presented of the phase diagram of a noise-induced phase transition for a model, nonlinear system with multiplicative noise proposed by Horsthemke and Lefever. Measurements of two of the critical exponents are also presented. The present results are in good agreement with theoretical predictions based on the Stratonovic treatment of the stochastic evolution equation.

A Landau expansion including sixth- and eighth-degree terms is studied for the cubic $\mathrm{XY}$ model. A new ordered phase with "generic symmetry" is found. The angle of rotation $\theta$ of the associated order parameter depends continuously on temperature. The transition from the disordered phase into this new phase must always be first order, irrespective of both the sign of the quartic term and the inclusion of higher-degree terms in the expansion. This prediction can be verified experimentally by studying the temperature dependence of $\theta$. ${\mathrm{Tb}}_2$${\left(\mathrm{M}\mathrm{o}{\mathrm{O}}_4\right)}_3$ should be a good candidate.

A phenomenological model of the solid-phase epitaxial growth process is proposed to account for the influence of substrate orientation and doping on growth kinetics. The model combines structural features of the amorphous-crystalline interface with electronic processes related to changes in the Fermi level. The basic premise is that the concentration of kinklike growth sites at the interface, and hence the growth velocity, can be influenced by doping in a manner analogous to the enhancement of dislocation velocities by doping.

${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectra at 4.2 K of Au-Fe alloys with Fe concentration between 10.5 and 33 at.% are well described by two superposed six-line spectra. Presumably, these derive from two different chemical environments which are identified with the $〈420〉$-platelet and solid-solution phases.

The infrared absorption spectrum of solid ${\mathrm{D}}_2$ at 4.2 K has been studied with the sample irradiated by a 15-MeV proton beam. Three beam-induced spectral features have been observed. Comparison of these features with those previously seen in a sample doped with tritium conclusively establishes the presence and indicates the nature of a radiation-induced absorption process. After turning off the proton beam, these features persist for times of the order of hours; they can be quenched by heating the sample to ∼ 11 K.

Quantum mechanical energy levels and wave functions have been calculated for the motion of chemisorbed hydrogen atoms on Ni surfaces. The results show considerable quantum effects for the adatom in both the ground and the excited states. The description of the adparticles as being delocalized along the surface offers a novel interpretation of several phenomena, in particular the vibrational excitations.

The velocity of positronium (Ps) formed when 1-2-keV positrons are implanted into an Al(111) target and diffuse to the clean surface has been measured. The time-of-flight distribution exhibits a sharp step at a Ps energy 2.62(4) eV in excellent agreement with the expected Ps work function ${\varphi }_{\mathrm{Ps}}=-2.60\mathrm{}\left(3\right)\mathrm{}$ eV obtained from the known electron and positron work functions of Al(111). The presence of less than a monolayer of oxygen reduces the step amplitude by a factor of 2. It is shown that this spectrum is a measure of the surface density of states.

A double acceptor binding three holes has been observed for the first time with photoconductive far-infrared spectroscopy in beryllium-doped germanium single crystals. This new center, ${\mathrm{Be}}^{+}$, has a hole binding energy of ∼5 meV and is only present when free holes are generated by ionization of either neutral shallow acceptors or neutral Be double acceptors. The ${\mathrm{Be}}^{+}$ center thermally ionizes above 4 K. It disappears at a uniaxial stress ≳${10}^9$ dyn ${\mathrm{cm}}^{-2\mathrm{}}$ parallel to [111] as a result of the lifting of the valence-band degeneracy.

A disordered ferromagnet is studied with use of the Hubbard model. A systematic method of finding the spin transverse susceptibility for any random configuration is developed. The computer results for a one-dimensional case reveal gapless magnetic excitations centered around a wave vector corresponding to the first maximum of the structure factor in qualitative accordance with recent experimental data.

Surface plasmon losses excited on spherical, He-filled cavities in Al are studied with use of transmission electron energy-loss spectroscopy. It is found that the excitation energy of the $l=1\mathrm{}$ (dipole) surface plasmon mode decreases with increasing He concentration, in line with predictions of an effective-medium theory taking into account the dipole-dipole interactions between bubbles in dense populations, the density dependence of the He dielectric constant, and a density-dependent atomic polarizability of the He in the bubbles.

Measurements have been made of the cosmic-background-radiation spectrum at five wavelengths (0.33, 0.9, 3, 6.3, and 12 cm) with use of radiometers with wavelength-scaled corrugated-horn antennas having very low sidelobes. A single large-mouth (0.7-m-diam) liquid-helium-cooled absolute reference load was used for all five radiometers. The results of the observations are consistent with previous measurements and represent a significant improvement in accuracy at low frequencies.

Results are presented on the atomic structure of gold (110) surfaces obtained by high-resolution electron microscopy. When covered by carbon, the 1×1 surface without surface relaxations is stable. Without carbon, a rough 2×1 reconstruction occurs with the missing-row structure, a 20%±5% outer-atom expansion and a 10% occupancy of atoms displaced outwards by 40%±20% down the channels. Local regions of 1×1 surface also exhibit a 10%±5% expansion of the outermost atoms.

A theory of Josephson-type phenomena is presented, in which the two macroscopic quantum states are the two components of an incommensurate charge-density wave with opposite wave vectors. The Fermi levels of these two states are split for a moving charge-density wave and impurity scattering induces quantum oscillations. Such oscillations may be responsible for the observed narrow-band noise in materials such as Nb${\mathrm{Se}}_3$ and Ta${\mathrm{S}}_3$.

It is demonstrated that in the new-inflationary-universe scenario based on a Coleman-Weinberg-type potential all the bubbles evolve through the SU(4) ⊗ U(1) local minimum. The transition from this local minimum to the SU(3) ⊗ SU(2) ⊗ U(1) global minimum is first order, and so the scenario does not solve all of the cosmological problems.

Energy spectra of protons and helium nuclei in the primary cosmic rays were measured above 1 TeV in a series of balloon flights of emulsion chambers. Differential spectra may be represented by power laws of indices -2.81±0.13 and -2.83±0.20 for protons and He, respectively. No index change was observed for either species over the energy ranges 5-500 TeV for protons and 2-50 TeV/nucleon for He. Intensities were consistent with extrapolations of previously published data below 1 TeV/nucleon.