A quantum theory is presented to explain the anomalously high ionization rates observed from some point defects in semiconductors in regions of large electric field. This spectacular enhancement is shown to originate from phonon-assisted tunnel ionization. Comparison with experiment is made in the case of four defects in GaAs and GaP and results in values of the Franck-Condon shift and effective phonon frequency that are in very good agreement with values deduced from other experiments.

A high-resolution scan of the metal-insulator transition in Si: P at millikelvin temperatures has been obtained by applying uniaxial stress. A sharp, but continuous, metal-insulator transition is resolved, with conductivities below Mott's "minimum" value ${\sigma }_{\mathrm{M}}$. These measurements join smoothly with previous low-resolution experiments, ruling out any discontinuity at ${\sigma }_{\mathrm{M}}$. The reproducible critical behavior disagrees with predictions of existing scaling theories of localization.

A model is presented for the temperature dependence of adsorbate photoemission line widths. By approximating the initial and final states as displaced harmonic oscillators, an analytic form for the observed line width is obtained. Comparison with angle-resolved photoemission spectra of xenon on Cu(110) yields excellent agreement.

The magnetic hyperfine field at ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ in uncharacterized ${\mathrm{Fe}}_2$${\mathrm{O}}_3$ films has been measured as a function of depth by a new technique combining high-energy-resolution conversion-electron spectroscopy with Mössbauer resonance absorption. The hyperfine field $H\left(t\right)\mathrm{}$ was mapped as a function of depth $t$ into the sample. It reaches the bulk value 51.761 ± 0.008 T at a depth of $t_0<~18\pm 3$ Å below the surface of the film and drops to $H_s<~50.6\pm 0.2$ T at the surface.

Two new lattice models, which do not appear to be related to gauge models, are proposed. The unique feature of these models is that they describe stable baglike structures. These models may be relevant to many fields of physics; in particular, some of the basic features of high-energy physics are obtained in these models.

Computer simulations indicate that the range of the force responsible for chiral symmetry breaking in quantum chromodynamics is relatively short, independent of confinement, and depends strongly on the color representation of the quarks. Chiral-symmetry restoration temperatures are obtained for quarks in either the fundamental or the adjoint representations of color SU(2). Results on higher representations support the symmetry-breaking pattern ("tumbling") suggested by Raby, Dimopoulos, and Susskind.

It is demonstrated that the orbital angular momentum $l_z$ of a particle of charge $q$ orbiting around a tube with magnetic flux $\Phi$ is quantized in units $l_z=\mathrm{integer}-\frac{q\Phi }{2\pi }$. A very simple physical argument for this is presented, and applied to understand the Dirac quantization condition and the charge-spin relation for particles bound to magnetic monopoles. The unusual statistics of flux-tube-charged-particle composites is discussed.

Some issues in dyon theory are discussed: retention of the charge $\frac{e\theta }{2\pi }$ in the chiral limit, the spin-statistics connection, and the indefiniteness of anomalous charges.

The spin-spin correlation parameter $C_{\mathrm{LL}}=(L, L; 0, 0)$ has been measured for $p-p$ elastic scattering around ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=90\mathrm{}°$ up to $p_{\mathrm{lab}}=5\mathrm{}$ GeV/c. An interesting energy dependence is observed in $C_{\mathrm{LL}}$ and the results are interpreted by comparison with other available data.

Evidence for the rare decay ${\pi }^0\to e^{+}{e}^{-}$ has been obtained in an experiment which measured the invariant mass spectrum of $e^{+}{e}^{-}$ pairs produced by 300-MeV/c ${\pi }^{-}$ mesons interacting in a liquid-hydrogen target. The branching ratio is (1.8±0.6)×${10}^{-7\mathrm{}}$, about four times larger than the unitarity lower limit.

Axion models have a spontaneously broken $Z\left(N\right)\mathrm{}$ symmetry. The resulting discretely degenerate vacua and domain-wall solitons are incompatible with the standard cosmology. It is possible, however, to introduce a small $Z\left(N\right)\mathrm{}$ breaking interaction into axion models without upsetting the Peccei-Quinn mechanism. In that case the domain walls disappear a certain time after their formation in the early universe. Their presence for a limited time period might lead to galaxy formation.

Conversion electrons from electromagnetic transitions preceding the fission decay of the shape isomers ${}_{}{}^{236,238}{}_{}{}^{}\mathrm{U}$ have been measured. For both isomers highly converted transitions are observed which are tentatively interpreted as the decay of the lowest $\beta$-vibrational band, via $E0\mathrm{}$ transitions, at excitation energies of 686.0±0.7 and 647.8±0.9 keV, respectively.

A master equation that describes the effect of spontaneous emission on laser-induced autoionization is formulated and its solution is obtained for arbitrary laser strengths. The radiative decay is shown to affect drastically the nature of spectra near confluence. Analytic expressions for widths and positions are given to demonstrate the new features of spectra.

Measurements of the hyperfine Zeeman transitions ($\Delta M_{\mu }=\pm 1$, $\Delta M_J=0\mathrm{}$) in the ground state of the muonic helium atom (${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{++}{}_{}{}^{}{\mu }^{-}{e}^{-}$) at magnetic fields of 11.5 and 13.6 kG have yielded values for the hfs interval, $\Delta \nu =4465.004\mathrm{}\left(29\right)\mathrm{}$ MHz (6.5 ppm), and for the negative-muon magnetic moment, $\frac{{\mu }_{{\mu }^{-}}}{{\mu }_p}=3.183\mathrm{}28\left(15\right)\mathrm{}$ (47 ppm). The theoretical value for $\Delta \nu$, including relativistic, radiative, and recoil contributions, agrees with our measured value but is much less precise because of inadequate knowledge of the Schrödinger wave function.

Experiments have been performed on the circular Couette system that reveal the existence of two simultaneous traveling azimuthal waves in a highly nonlinear fluid flow. These waves can have the same or different wave numbers, but they are nearly dispersionless. Flow visualization, scattering intensity, and Doppler velocimetry techniques were used, and intensity measurements were made in both laboratory and rotating reference frames.

Small-amplitude double layers and solitary waves containing magnetic-field-aligned electric field components have been observed for the first time in the auroral plasma between altitudes of 6000 and 8000 km in association with electron and ion velocity distributions that indicate the presence of electric fields parallel to the magnetic field. The double layers may account for a large portion of the parallel potential drop that accelerates auroral particles.

Time-integrated, spectrally resolved measurements between 400 and 750 nm have been made of light backscattered from plasmas produced by 450-psec pulses from a 351-nm laser at ${10}^{13}$ to ${10}^{15}$ W/${\mathrm{cm}}^2$. Threshold and saturation behavior for the two-plasmon decay and the absolute and convective Raman instabilities have been observed. The scattered light spectra suggest the presence of a steepened density profile at the quarter critical density.

Axisymmetric compressional Alfvén (fast) waves, which propagate into a region of increasing magnetic field in a cylindrical plasma, are observed to be converted into ioncyclotron (slow) waves via ion-cyclotron resonances.

It is shown that vortex-line-density fluctuations in counterflowing He II can be greatly enhanced by modulating the heater with a noise generator. This technique is used to test Vinen's equation for vortex-line turbulence. Vinen's equation, linearized to describe fluctuations, appears to be correct except near the lambda transition.

The rate $\nu$ at which negative ions nucleate charged vortex rings in isotopically pure superfluid helium-4 has been measured for electric fields of up to 2.5×${10}^6$ V ${\mathrm{m}}^{-1\mathrm{}}$ with pressures and temperatures within $17<P<\mathrm{}25\mathrm{}$ bars, $0.3<T<\mathrm{}0.9\mathrm{}$ K. It is found that the nucleation process is completely quenched ($\nu =0\mathrm{}$) for $E>\mathrm{}2\mathrm{}\times {10}^6$ V ${\mathrm{m}}^{-1\mathrm{}}$. The implications of this result for theories of the nucleation mechanism are discussed.