Possible signatures of two-nucleon pion production processes in reactions $A(p_{\mathrm{pol}}, {\pi }^{-})A+1\mathrm{}$ near threshold are identified: a dependence of the analyzing power on the total angular momentum, and a simple scaling of the cross section with subshell occupancy for the struck target neutron. Measurements for ${}_{}{}^{12,13,14}{}_{}{}^{}\mathrm{C}(p_{\mathrm{pol}}, {\pi }^{-})$ exhibit these expected features, supporting the view that the fundamental $\mathrm{NN}\to \mathrm{NN}\pi$ processes dominate in nuclear pion production.

A precision measurement with the SIN bent-crystal spectrometer of the wavelength of the $2p_{\frac{3}{2}}-1\mathrm{}{s}_{\frac{1}{2}}$ transition in muonic ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ yields $\lambda =16.473\mathrm{}766\left(89\right)\mathrm{}$ pm, the accuracy being an order of magnitude higher than that of earlier investigations. The rms charge radius of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ is deduced as ${〈{\mathcal{r}}^2〉}^{\frac{1}{2}}=2.4832\mathrm{}\left(18\right)\mathrm{}$ fm, differing by 2.4 standard deviations from the most accurate electron-scattering results. Consequences of attributing this discrepancy to a $\mu -N$ interaction beyond QED are discussed.

Calculations of the photoabsorption spectra for Ba, ${\mathrm{Ba}}^{+}$, and ${\mathrm{Ba}}^{++}$ near the $4d$ ionization threshold have been performed with the time-dependent local density approximation. The results are in quantitative agreement with recent experimental data and indicate that the sharp resonant structure below threshold is due to transitions to hybridized $f$ states which are strongly modified by electron-electron interactions.

With use of a full three-turning-point WKB analysis, a simple formula is obtained for the ionization rate of hydrogenic atoms. Contrary to current belief, WKB ionization rates are found to be excellent approximations to exact numerical calculations. In addition, the symmetries of the WKB solution are explored and it is shown that the resonance parameters can all be written as simple functions of three objects, ${I_{\xi }}^{\mathrm{}\left(j\right)\mathrm{}}$, ${I_{\eta }}^{\mathrm{}\left(j\right)\mathrm{}}$, and ${\theta }^{\mathrm{}\left(j\right)\mathrm{}}$, which can easily be calculated on programmable pocket calculators.

Optical pumping by a single-frequency cw ring dye laser of thick sodium vapor targets ($\mathrm{NL}>\mathrm{}{10}^{13}$ atoms/${\mathrm{cm}}^2$) without buffer gas has been investigated for application in a polarized ion source. The atomic polarization of the sodium was determined from the optical rotation of a second dye laser tuned midway between the $D$ lines. Rate-equation calculations reproduce the experimental data and predict very high polarizations ($P>~0.8$) with the use of one or more single-frequency dye lasers in thick alkali-metal vapor targets.

Tunneling of right-hand-polarized electromagnetic waves through the evanescent resonance/cutoff layer which exists for propagation parallel to a magnetic field has been measured for the first time. The results are compared with the cold-plasma model of Budden and a hot-plasma model, both of which are in reasonable agreement with the experiment.

The first measurements of the growth and saturation of ion acoustic waves generated by optical mixing are presented. At lower power levels, the parameter dependence of the ion waves is shown to agree in detail with the predictions of optical mixing theory. However, at higher power levels a nonlinear saturation is observed and identified as increased Landau damping due to ion heating.

Anomalous microwave absorption has been observed in the organic superconductor ${\mathrm{TMTSF}}_2$${\mathrm{AsF}}_6$ (TMTSF: tetramethyltetraselenafulvalene) below its metal-nonmetal transition near 12 K. This absorption is unambiguously identified as antiferromagnetic resonance by the excellent agreement between a spin-wave calculation and the pronounced dependence on temperature and magnetic field orientation. This result dramatically confirms earlier indications of magnetic ordering or spin-density waves and, furthermore, indicates that the spin-density-wave amplitude is considerably larger than previous estimates of < 1%.

Below 5.5 K minimally strained crystals of ${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$${\mathrm{ClO}}_4$ (TMTSF: tetramethyltetraselenafulvalene) exhibit vanishing spin-resonance intensity and reduced conductivity at low microwave power. More intense microwave electric fields along the needle axis nonlinearly restore both the resonance signal and the conductivity, indicating the presence of charged spin-density waves. Very anisotropic antiferromagnetic resonances are observed at 1.6 K, confirming that an itinerant spin-density-wave state precedes the onset of superconductivity at 1.3 K.

What is commonly called the Gutzwiller wave function $\psi$, an approximate ground state of the single-band Hubbard Hamiltonian, is considered here for $N$-site $N$-electron rings, when the number $D$ of doubly occupied sites is small ($N=6, 10, 14, 18$). For $D\to 0$ spin correlations in $\psi$ surprisingly close to the exact values at zero bandwidth are found (i.e., those of the antiferromagnetic Heisenberg-model ground state). But the energy is grossly in error. A simple modification of $\psi$ reproduces the exact energy with remarkable accuracy.

Tunnel junctions of the type Al-$I-M$ ($M\equiv \mathrm{A}\mathrm{u},\mathrm{C}\mathrm{u},\mathrm{A}\mathrm{g}$) prepared on ${\mathrm{CaF}}_2$-roughened substrates emit broadband visible light. It is found that the light intensity variation with wave-length in the range 350 to 700 nm images the electron energy-loss function, $\mathrm{Im}(-\frac{1}{\epsilon })$, of each metal $M$ as calculated from its optical constants. It is concluded that surface plasmons are damped above the interband transition in Au at 2.5 V and in Cu at 2.25 V. The findings are in harmony with data from surface-enhanced Raman spectroscopy.

Synchrotron-radiation experiments were performed at ultralow (<0.1 monolayer) coverages to test the weakly-interacting-cluster model for Al adsorption on GaAs(110). The evolution of the Al $2p$ peak revealed two different submonolayer adsorption states, one below and one above 0.1 monolayer coverage, as predicted by the model. These results demonstrate that experiments at ultralow coverages are crucial to the understanding of the Schottky barrier formation.

Percolation theory is extended to the case of circuit elements with nonlinear $I-V$ characteristics, particularly the special cases $V=I^{\alpha }\mathcal{r}$, which form the universality classes. Near the percolation threshold the "conductance" $\frac{I}{V^{\frac{1}{\alpha }}}$ vanishes like ${(p-p_c)}^t$, where $t$ depends on $\alpha$ and dimensionality. The Skal-Shklovskii-De Gennes model gives $t\left(\alpha \right)=(d-1\mathrm{})\mathrm{}\nu +\frac{(\varphi -\nu )}{\alpha }$, where $\varphi$ is only weakly dependent on $\alpha$ and $d$, and approaches unity at $d=6\mathrm{}$. Renormalization methods are used to study the $\alpha$ dependence of $t$ in two dimensions.

A model of the two-nucleon interaction derived from the potential model of the quark structure of baryons is proposed. This model leads to a nonlocal Schrödinger equation for the deuteron which has been solved numerically. The model parameters are consistent with those fitted to baryon spectroscopy and the predicted deuteron properties are in even better agreement with experiment than the authors had dared hope.

It has been shown by other workers that some of the fragments of relativistic heavy-ion collisions have an anomalously short interaction length but may revert to normal nuclei within ∼${10}^{-11\mathrm{}}$ sec. Lead-glass detectors were used to search for delayed high-energy $\gamma$ rays emitted from projectile fragments of 940-MeV/u ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ interactions with a steel target. The present negative result casts doubt on some recent models in which anomalous states decay electromagnetically to normal nuclei.

Simulation of the magnetohydrodynamic Kelvin-Helmholtz instability in a compressible plasma shows that a super-Alfvénic shear flow parallel to the magnetic field develops into small eddies, which strongly compress, twist, and hence amplify the magnetic field, and that a sub-fast (magnetosonic) shear flow transverse to the magnetic field evolves into a fast shock. The anomalous viscosity due to the instability is important in understanding a viscous drag at the solar-wind-magnetosphere interface.

Strong Langmuir turbulence has recently been described by a statistical treatment of collapsing cavities. This work is extended and corrected by derivation of a transfer rate valid for both the inertial and dissipative ranges, and the power-law distribution of fast electrons is obtained. Self-consistent modifications of similarity laws are calculated in the dissipative range, which change dramatically the conventional features of collapse. Limitations to collapse are also discussed.

A Hamiltonian formalism is developed for the drift-orbit trajectories of particles in toroidal systems in the presence of stochastic fields. The equations of motion are integrated numerically to investigate the modification of neoclassical diffusion in a tokamak due to the onset of stochasticity. A significant increase in the diffusion coefficient is observed below the stochastic threshold for electrons, whereas ions are typically not affected until the magnetic field has become quite stochastic.

A study of a laser-annealing system using a new molecular dynamics method modified to faithfully simulate typical experimental conditions is presented. Following melting, the recrystallization interface is layer structured in the melt. Rapid recrystallization, impurity segregation and constitutional undercooling, and the dynamics of the processes are demonstrated.

Commensurate adsorbed surface phases, particularly $p\times 1$ rectangular and $\sqrt{3}\times \sqrt{3}$ hexagonal phases, exhibit two (or more) classes of domain wall, reflecting a lower than ideal symmetry; these compete statistically and undergo wetting transitions. Scaling arguments and model calculations indicate that new types of continuous melting transitions, possibly already seen in Kr on graphite, can thereby arise.