Experiments are proposed which address the question of the existence of the "invisible" axion for the whole allowed range of the axion decay constant. These experiments exploit the coupling of the axion to the electromagnetic field, axion emission by the sum, and/or the cosmological abundance and presumed clustering of axions in the halo of our galaxy.

In the scattering of a fermion and a gauge-theory monopole, "charge-mixing" boundary conditions on fermion fields play an important role. The apparent paradox of charge non-conservation suggested by these boundary conditions is shown to be spurious by a careful discussion of gauge invariance, charge, and the monopole state.

An effective fermion interaction of maximum particle rank four, comprised of operators which form the integrity basis of an SU(3)→R(3) algebra, has been found sufficient to reproduce almost exactly, within a single leading irreducible representation of pseudo SU(3), the ground- and gamma-band rotational structure as well as the concomitant interband and intraband $B\left(E2\mathrm{}\right)\mathrm{}$ strengths of states in the strongly deformed nuclei. Results are given for ${}_{}{}^{164}{}_{}{}^{}\mathrm{Er}$.

Large cross sections for neutron-pickup reactions have been observed for ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$, ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ti}$, and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ at incident energies of 250, 300, and 375 MeV, respectively. These reactions, which occur with energy losses of only ∼5 MeV, contribute about 25% to the total reaction cross section.

The population of a beam of lithium atoms has been transferred from a low angular momentum Rydberg state to a state with $\mathrm{}\left|m\right|=n-1\mathrm{}$, with nearly 100% efficiency. Selective field ionization is employed to detect the high $\mathrm{}\left|m\right|\mathrm{}$ state. Transfer occurs by a series of adiabatic rapid passages; it can also occur by a single multiphoton process.

An approximate description of Rayleigh-Taylor bubble motion is given in terms of a Fourier series expansion of the velocity potential. Consistent predictions for the steady-state velocity, the bubble curvature, and the first three Fourier coefficients are obtained. A simple model of nonsteady bubble motion is developed. It is found that an exponential amplitude dependence is responsible for a rapid transition to the steady-state regime when the amplitude becomes larger than $\sim \frac{\lambda }{6\pi }$.

The transition to geostrophic turbulence in a rotating annulus experiment has characteristics which differ from the scenarios for the transition to turbulence which have been previously described. Estimates of dimension from the experimental data suggest a mechanism in which a discrete symmetry of the preturbulent state plays an important role. The techniques used for the dimension estimates are new and substantially more efficient than those used previously.

Evidence is presented for low-dimensional strange attractors in Couette-Taylor flow data. Computations of the largest Lyapunov exponent and metric entropy show that the system displays sensitive dependence on initial conditions. Although the phase space is very high dimensional, analysis of experimental data shows that motion is restricted to an attractor of dimension 5 for Reynolds numbers up to 30% above the onset of chaos. The Lyapunov exponent, entropy, and dimension all generally increase with Reynolds number.

The first experimental observation is reported of type-III Pomeau-Manneville intermittencies in a hydrodynamical system: the Rayleigh-Bénard instability studied in confined geometry. From optical measurements, return maps have been constructed and distribution of the laminar period lengths has been measured. These results are in complete agreement with the theoretical model.

The dynamical properties of the hydrodynamic discontinuity associated with a slow-burning premixed gaseous flame front are studied with use of laser diagnostics. The fluctuating motion of the front around its equilibrium position and its effects on the flow are studied in the case of an intrinsically stable front propagating downwards in a weekly turbulent flow. A strong negative feedback on the exciting turbulence is observed in the spectrum of the upstream flow close to the front. A theoretical analysis is also provided.

Neutron-scattering techniques have been used to determine the momentum distribution $n\left(\overrightarrow{\mathrm{p}}\right)$ for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ for different temperatures and densities. $n\left(\overrightarrow{\mathrm{p}}\right)$ is found to be a strong function of density and thus brings into question any direct relationship between the condensate fraction and the pair distribution function $g(r,T)\mathrm{}$.

The spectral dimension $d_s=\frac{2d_f}{d_w}$ is calcualted for the diffusion-limited aggregation model of colloids and dendritic growth; here $d_f$ is the fractal dimension of the aggregate, and $d_w$ the fractal dimension of a random walk on the cluster substrate. $d_s=1.2-1.4\mathrm{}$ is found for $d=2\mathrm{} \mathrm{and} 3$, to within the accuracy of the present Monte Carlo calculations. Thus Witten-Sander aggregates may possess the same remarkable "superuniversality" discovered for percolation clusters and argued to possibly hold for all homogeneous fractals.

A sharp peak occurs in the temperature-dependent power absorbed by a two-dimensional sheet of electrons for temperatures near the melting transition when the electrons are driven parallel to the underlying helium surface with an ac voltage. The temperature at the absorption maximum is measured as a function of driving frequency, and the results are interpreted as the power absorbed by dislocations which move in response to the externally imposed stress.

The commensurate solid and fluid coexistence region of monolayer ${\mathrm{N}}_2$ on graphite was mapped out in an exhaustive vapor-pressure-isotherm study. The tricritical exponent ${\beta }_t$ that describes the shape of the coexistence boundary was found to be equal to 0.55 ± 0.02, in very good agreement with recent theoretical predictions. The tricritical temperature, the end point of coexistence, was found to be 85.37±0.06 K.

The authors propose to probe the effects of a surface on critical behavior by x-ray and neutron scattering under conditions of total reflection. It is shown that the temperature and angular dependence of the scattered intensity at grazing angles allows one to determine the three critical surface exponents ${\beta }_1$, ${\gamma }_{11}$, and ${\eta }_{\parallel }$.

Strong evidence for the formation of a bound magnetic polaron in $n$-${\mathrm{Cd}}_{0.90}$${\mathrm{Mn}}_{0.10}$Se has been obtained from time-resolved experiments by picosecond laser spectroscopy. In particular, time-varying Stokes shifts associated with a neutral donor bound exciton have been measured to follow the evolution of the polaron at $T=2\mathrm{}$ K. From analysis of data a formation time of approximately 400 psec is inferred for the conditions of the experiment.

The conductivity fluctuations giving $\frac{1}{f}$ noise in bismuth were found to be extremely nonscalar, with local instantaneous anisotropy in between that of dyads and of traceless tensors. This result requires a symmetry-breaking noise-generating mechanism. Temperature dependence and detailed spectral data show that the $\frac{1}{f}$ kinetics are thermally activated and that the net noise magnitude in thick films is a decreasing function of temperature. A crude model accounting for these results is presented.

The quasiparticle transport current induced in a superconducting aluminum film by a temperature gradient has been detected by measurements of the spatially decaying charge imbalance generated near the end of the sample where the current is divergent. The results are in good agreement with theory when the nonuniformity of the temperature gradient is taken into account. In particular, the inferred value of the thermopower agrees well with the value obtained when the aluminum is in the normal state.

From an analysis of magnetohydrodynamic turbulent processes, the authors conclude that the frequent observation of outward-propagating Alfvénic fluctuations in the solar wind can arise from early states of in situ turbulent evolution, and need not reflect coronal processes as has hitherto been assumed.

The author analyzes the spectrum, amplitude, and evolution of a tangled primeval magnetic field generated by macroscopic dynamo activity arising during a first-order phase transition in the early universe. The effects of the field on the matter distribution at late times could be much larger than that of the adiabatic or isothermal density fluctuations generated by the transition. With optimistic assumptions, magnetic fields generated during a transition at $T\sim 0.2$ GeV could lead to the collapse of gas clouds of $\simeq {10}^{1-5}{M}_{\odot }$ after recombination, and to the formation of pregalactic stars or quasars.