Range and spectral density of very slow negative muons have been measured with novel techniques. The intensity around and below 1 keV agrees with semiclassical calculations but contradicts some quantum-mechanical theories of the Coulomb capture.

A simple nonlinear, one-dimensional spherical Brillouin-backscatter model adapted from kinetic simulations and Kruer's theory to a fluid code (LASNEX) is described. Laser absorption and Brillouin reflection are plotted for $0.265 \mu \mathrm{m}<{\lambda }_0<10.6\mathrm{} \mu \mathrm{m}$ and 3×${10}^{13}$ W/${\mathrm{cm}}^2$${10}^{16}$ W/${\mathrm{cm}}^2$ on gold disks (pulse length=1 nsec) and the calculated absorption is compared with experiments. Kinetic simulations suggest methods of reducing the Brillouin backscatter, such as use of a wide bandwidth and multiline laser.

The Green's-function Monte Carlo method, which yields an exact ground-state solution to the Schrödinger equation for Bose systems, is applied to liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, a fermion system. With the use of a technique that projects out states of selected symmetry, strict upper bounds to the ground-state energy of many-fermion systems have been constructed. An upper bound has been found for liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ of - 2.20±0.05°K at the experimental equilibrium density. This energy is more than 1°K below Jastrow variational results and much nearer the experimental value of - 2.47±0.01°K.

Reconstruction of the Fe(110) surface by a quarter monolayer of S is shown by lowenergy electron-diffraction intensity analysis to correspond to a model in which hardsphere atoms displace to a unique jamming point. After reconstruction the S atoms sit in fourfold hollows of touching Fe atoms with S-Fe bond lengths of 2.17 and 2.36 Å. A general construction for 2×2 reconstructions with rectangular symmetry is given and applied to this case and to Ni(001)(2×2)-C.

A magnetic-field—and temperature—dependent line is observed in the Raman spectra of a $n$-type semimagnetic semiconductor: ${\mathrm{Cd}}_{0.95}$${\mathrm{Mn}}_{0.05}$Se. It is attributed to spin-flip Raman scattering, with "giant" Stokes shift: 75 ${\mathrm{cm}}^{-1\mathrm{}}$ in 1 T at 1.6 K. A small zero-field Stokes shift is observed, which is attributed to an exchange-induced magnetic molecule under the electronic orbit of neutral donors.

A theoretical study of topological excitations (kinks) in a one-dimensional one-third-filled Peierls system is presented. The charges associated with the kinks are found to be fractional $Q=\pm \frac{1}{3}e,\pm \frac{2}{3}e$. Calculations of the spatial widths and electronic structure of different types of kinks are carried out numerically. Possible applications to tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) are mentioned.

An exact solution for the soliton lattice in the half-filled-band Peierls condensate is found. In the limit of weak coupling (infinite momentum cutoff $\Lambda$) the soliton-soliton interaction decays as a repulsive exponential while for finite $\Lambda$ it decays as ${\mathrm{}\left(\mathrm{distance}\right)\mathrm{}}^{-1\mathrm{}}$ and is attractive! This yields phase separation in doped polyacetylene or a first-order lock-in transition of a spin-Peierls system. A mapping into the low-temperature two-dimensional sine-Gordon system is shown, where a lock-in transition has exponent $\beta =1\mathrm{}$ for finite $\Lambda$.

It is observed that a reversible step period rearrangement on clean nickel single-crystal surfaces occurs in the immediate vicinity of the Curie temperature. Reversible carbon segregation is observed on the same crystal surfaces below the Curie point. The segregated carbon is carbidic, not graphitic, and indicates a change in the nickel surface electronic structure occurring at the ferromagnetic transition. Measured carbon coverages indicate a change greater than 0.2 eV per carbon atom in the heat of segregation at the Curie point.

From thermodynamic and causality considerations a general upper bound on the rate at which information can be transferred in terms of the message energy is inferred. This bound is consistent with Shannon's bounds for a band-limited channel. It prescribes the minimum energy cost for information transferred over a given time interval. As an application, a fundamental upper bound of ${10}^{15}$ operations/sec on the speed of an ideal digital computer is established.

It is shown that, for systems which enter chaos through period doubling bifurcations, the integrated noise power spectrum in the chaotic regime behaves as $N\left(\mathcal{r}\right)=N_0{(\mathcal{r}-{\mathcal{r}}_c)}^{\sigma }$, with $\sigma =1.5247\mathrm{}\dots$. Furthermore, the existence of a new universal constant which describes the scaling behavior of the average bandwidth in the strange attractor is reported. These results are directly applicable to experiments probing the onset of turbulence in physical systems.

The commutation of transfer matrices of $q$-state lattice models is studied and solutions which generalize both the $q=2\mathrm{}$ ferroelectric models and the special $q=3\mathrm{}$ models of Stroganov are found. For cases which are continuously connected to a shift operator, associated commuting Hamiltonians are given and free energies calculated.

The ${}_{}{}^{231}{}_{}{}^{}\mathrm{Pa}$ neutron-induced fission cross section from 140 to 400 keV was resolved into finer structures. For some of the fractionated vibrational resonances in this energy region, the assignment of spectroscopic parameters may support evidence for an asymmetrically deformed third minimum in the ${}_{}{}^{232}{}_{}{}^{}\mathrm{Pa}$ fission barrier. Also, for the first time, narrow fission resonances are observed above 1.3 eV exhibiting an average fission width ${〈{\Gamma }_f〉}_{\mathrm{ob}\mathrm{}\mathrm{s}}=8\mathrm{}$ μeV.

The first experimental evidence of transfer from alignment to orientation of laserexcited atoms due to anisotropic collisions is reported. The experiment has been made with respect to neon atoms in the $2p_4$ state, excited by a single-mode laser, which collide with the ground-state neon atoms, and good agreement between experiment and theory is found.

Refined observations of parity nonconservation in the $6{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}-7\mathrm{}{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ transition in ${}_{81}{}^{203,205}{}_{}{}^{}\mathrm{Tl}$ are reported. Absorption of circularly polarized 293-nm photons by $6{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ atoms in an $E$ field results in polarization of the $7{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ state, through interference of the Stark $E1\mathrm{}$ amplitude with $M1\mathrm{}$ and parity-nonconserving $E1\mathrm{}$ amplitudes. Detection of this polarization yields the circular dichroism $\delta =+(2.8\mathrm{}\pm \left\{1.0\right\}\left\{0.9\right\})\times {10}^{-3\mathrm{}}$, which agrees with theoretical estimates based on the Weinberg-Salam model, for ${{sin}^2\theta }_W=0.23\mathrm{}$.

Parity-nonconserving optical rotation has been observed and measured on the 8757-ÅA magnetic-dipole absorption line in atomic bismuth vapor. The result, $R\equiv \mathrm{Im}\left(\frac{E_1}{M_1}\right)=(-10.4\mathrm{}\pm 1.7)\times {10}^{-8\mathrm{}}$, is of the approximate size calculated with use of the Weinberg-Salam theory of the weak neutral-current interaction with ${{sin}^2\theta }_{\mathrm{W}}=0.23\mathrm{}$.

The total and delayed $K$-Auger-electron emission of Ne, ${\mathrm{N}}_2$, and S${\mathrm{F}}_6$ targets was investigated after 1.4-MeV/u ${\mathrm{Kr}}^{18+}$ and ${\mathrm{Ar}}^{12+}$ impact. The lines of promptly decaying $1s2ln{l}^{\prime } (n>~3)$ states observed nanoseconds after projectile impact demonstrate that selective electron capture from neutral target atoms into outer-shell orbitals of slow recoils is an important production mechanism for certain states in highly stripped target atoms. Contributions of prompt and delayed excited states are observed as well as specific cascades to inner-shell states.

Frequency conversion by parametric processes in stimulated Raman scattering is analyzed in the limit where the Raman shift is much smaller than the laser frequency. An exact solution is obtained which shows that the conversion efficiency to the higher orders may be large. The conditions for obtaining high efficiency are discussed.

There exists a regime in parameter space where a small high-field Ohmically heated tokamak may be capable of reaching thermonuclear ignition. Results of numerical simulations of the minimum ignition conditions are presented, including empirical, sawtooth, and magnetic-field ripple diffusion and the effects of impurities. An ignition condition is derived and compared with the results of the numerical simulations.

A series of experiments is described which provides an unambiguous description of the steady-state properties of turbulence in pure superfluid flow. The turbulence is qualitatively different from that observed in counterflow but comparable to the homogeneous turbulence described by theory.

Strong thermal-relaxation effects have been observed in vitreous silica at low temperatures on a time scale of order ${10}^3$ s, which are attributed to slowly relaxing low-energy excitations intrinsic to the amorphous state. With the use of a simplified version of the tunneling model, a density of states is derived for these excitations, which is comparable in magnitude to the density of the fast-relaxing excitations derived from phonon-scattering experiments.