Two-photon spectroscopy has been performed in a fast, accelerated atomic beam, with a resolution limited only by the natural linewidth of the upper excited level. The main feature of the experiment is the "creation" of a completely harmonic three-level atom, by using the relativistic transformation between the laboratory and atom rest frame. Thus resonant two-photon absorption, with a strength comparable to electricdipole transitions, takes place. The systematic effects of importance in spectroscopy are investigated.

Turbulence describable by the Korteweg-de Vries equation with a frictional dissipation is shown to self-organize to a soliton.

A two-dimensional particle simulation of the resistive filamentation instability on a charge- and current-neutralized beam is performed. The model equations employed depend essentially on only one dimensionless parameter, making feasible a numerical survey of the parametric dependence of the nonlinear behavior of the instability. The simulation results are analyzed with reference to the focusing requirements of heavy-ion beams acting as drivers for pellet fusion.

Detailed studies of the thermal conductance of a Mylar strip on which an adsorbed film of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ resides have been made at several temperatures as a function of the thickness of the helium film. The conductance in the vicinity of the superflow onset transition is observed to rise in a manner consistent with the predictions of Ambegaokar et al.

The thermal conductance of a ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ film has been studied in conjunction with torsional oscillator measurements of the superfluid response. A dramatic rise in the thermal conductance is observed just above the Kosterlitz-Thouless transition temperature determined by the torsional oscillator. In agreement with the theoretical predictions of Ambegaokar et al., the thermal conductance is found to diverge as the exponential of ${(T-T_c)}^{-\frac{1}{2}}$ for $T\to {T_c}^{+}$.

The crystal field experienced by the Pr ions in praseodymium metal produces singlet ionic ground states. The conduction electrons provide an indirect exchange coupling between the Pr ions which is not strong enough to produce long-range order but which does give rise to magnetic excitons. It is shown that these excitons contribute to the effective mass of the conduction electrons, an effect which is large and magnetic-field dependent.

Evidence for the Kosterlitz-Thouless vortex unbinding transition is reported in triangular planar arrays of proximity-coupled Pb-Sn junctions. The temperature dependence of the resistive transition and the nonlinear features of the current-voltage characteristics are consistent with recent theories of topological ordering in two-dimensional superconductors.

The localization length for disordered systems is calculated with a new recursive method. The scaling behavior of the conductance is determined. The assumptions about the $\beta$ function made in recent analytical work are confirmed. Only localized states are found for two dimensions. In three dimensions there is an Anderson transition at a critical disorder of $W_c=16\mathrm{}\pm 0.5$ with critical exponents for the conductivity and the localization length of $s=\nu =1.2\mathrm{}\pm 0.3$, respectively.

The frequency ($f$) and temperature ($T$) dependent conductivity ($\sigma$) is reported for cis-${\left(\mathrm{CH}\right)}_x$, trans-${\left(\mathrm{CH}\right)}_x$, and ammonia-compensated ${\left(\mathrm{CH}\right)}_x$. A strongly $T$-dependent dc $\sigma$ together with a weakly $T$-dependent ac $\sigma$ were observed for predominantly cis-${\left(\mathrm{CH}\right)}_x$ and for N${\mathrm{H}}_3$-compensated samples, similar to $\sigma \mathrm{}(f,t)\mathrm{}$ of many semiconductors. The trans-${\left(\mathrm{CH}\right)}_x$ has a larger "weakly" $T$-dependent dc $\sigma$ and anomalous strongly $T$-dependent ac $\sigma$. The latter results are in good agreement with Kivelson's theory of charge transport via intersoliton electron hopping.

The magnetic impurity contribution to the specific heat of metals is calculated as a function of temperature. The calculation, based on the solution of a recently proposed spinless model for the Kondo problem, shows the specific heat as a universal function of the temperature scaled by the Kondo temperature. The universal function is well described by the analytically solvable resonant-level model over the entire temperature range.

Monte Carlo data and duality arguments, applied to a lattice model, are presented which indicate that a three-dimensional type-II superconductor should have a transition asymptotically equivalent to that of a superfluid with reversed temperature axis, and not a first-order transition. Results may apply to the nematic—smectic-$A$ transition.

It is shown that shocks preferentially accelerate partially ionized heavy elements over protons. Within the framework of a previously published model of injection, the spectra of different ion species are calculated from thermal to ultrarelativistic energies. For typical astrophysical parameters, the predicted enhancement is in qualitative agreement with observations for a ${10}^6$-K preshock plasma; ions with $Z>\mathrm{}10\mathrm{}$ are enhanced by about an order of magnitude or so. The continuing increase with energy of the heavy-element abundances into the air-shower regime is discussed.

A two-parameter real-space renormalization-group approach to the site-percolation problem in a square lattice is proposed. The two parameters are the concentration $p$ of active first-neighbor bonds, and the concentration $q$ of occupied sites. From these two parameters one can calculate two independent critical exponents, and the others can be obtained through scaling relations, with no need of external applied fields.

The Burgers equation is linearized on the Schwartz space $S$. It follows that the Burgers equation can be defined by a Hamiltonian formalism and that it has an infinity of time-independent constants of motion in involution.

Grand unified gauge theories that contain fractionally charged color-singlet fermions are considered. The minimal theory of this type is an SU(7) model which requires a rich structure of new physics in the energy region 100-1000 GeV.

The systematics of the onset of deformation in the $N=88-90\mathrm{}$ region is reexamined in light of the recently discovered shell closure at $Z=64\mathrm{}$. It is shown that the microscopic explanation of the origin of deformation already proposed for the $A\sim 100$ region is equally applicable here and leads to a new interpretation of the $A\sim 150$ region.

New 500-MeV $p_{\mathrm{pol}}$+${}_{}{}^{40,48}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ elastic $\frac{d\sigma }{d\Omega }$ and $A_y\left(\theta \right)$ data are presented. The small-momentum-transfer data are not reproduced by the second-order Kerman-McManus-Thaler optical potential which uses free nucleon-nucleon amplitudes. The systematics of these results, taken together with previous 800-MeV results, suggest that medium modifications to the $\mathrm{NN}t$ matrix are required to obtain an accurate description of the 500-800-MeV proton-nucleus elastic data in general.

The first observation of muonium (${\mu }^{+}{e}^{-}$) in vacuum, produced when a low-energy positive muon beam impinges on a thin foil target, is reported. It is found that ${\mu }^{+}{e}^{-}$ emerges from the foil surface predominantly with energies of less than 20 keV. The results show that the Clinton P. Anderson Meson Physics Facility stopped-muon channel operating at $E=4.0\mathrm{}$ MeV with an average flux of 3×${10}^6$${\mathrm{\mu }}^{+}$/s can produce roughly ${10}^3$${\mathrm{\mu }}^{+}$${\mathrm{e}}^{-}$/s in vacuum from thin targets of Be, C, Al, Cu, Ag, and Au.

A subharmonic route to chaos including period-doubling bifurcations up to $\frac{f}{8}$ has been observed in experiments on acoustical turbulence (acoustic cavitation noise). The system also shows signs of reverse bifurcation with increasing control parameter (acoustic driving pressure amplitude). In view of the large variety of phenomena observed and yet to be expected the system investigated may well serve as a further experimental paradigm of nonlinear dynamical systems besides Rayleigh-Bénard and circular couette flow.

The transition from laminar to Taylor vortex flow in a couette apparatus with fixed ends has been studied. The reversibility of the transition has been examined with use of a reflectance technique with Kalliroscope tracer with a variety of geometries and fluids. Very little hysteresis is found, providing the speed is ramped with a dimensionless acceleration less than a certain value. Contrary to earlier expectations, it is not possible to neglect the effect of the ends of the apparatus simply by making the apparatus longer.