We have measured the charge and magnetic form factors of tritium for values of the momentum transfer up to 31.3 ${\mathrm{fm}}^{-2\mathrm{}}$. The data are compared with calculations for the three-body system including meson-exchange-current contributions.

Villars's equations, first derived from the adiabatic limit of time-dependent Hartree-Fock theory, are presented here as a set of exact conditions for the decoupling (in the adiabatic limit) of a sub-system from a classical Hamiltonian system. It is emphasized that these conditions do not incorporate all the required decoupling conditions. By combining the additional requirements with Villars's equations, we obtain a mathematically complete system, which will yield exact solutions where such exist, but which can also be applied to cases of approximate decoupling.

The hyperfine structure and isotope shifts of ${}_{}{}^{189,191,193}{}_{}{}^{}\mathrm{Tl}_{}^m{}_{}{}^{}$ and ${}_{}{}^{193}{}_{}{}^{}\mathrm{Tl}$ have been observed by means of collinear atom beam laser spectroscopy. Deduced deformations for the ${\frac{9}{2}}^{-}$ isomers are larger than for the ${\frac{1}{2}}^{+}$ ground states and increase with decreasing neutron number. This explains a strong neutron-number dependence of the odd-proton energy levels in these nuclei near the $Z=82\mathrm{}$ shell closure. Despite different deformations, rotational properties are nearly identical in ${}_{}{}^{185-199}{}_{}{}^{}\mathrm{Tl}$. Microscopic theory ascribes this to a systematic balance between changing deformation and neutron pairing.

The quantum Langevin equation is used to calculate an exact expression for the free energy of a quantum oscillator interacting, via dipole coupling, with a blackbody radiation field. In particular, we obtain a temperature-dependent shift in the free energy. This result may then be used to obtain corresponding results for the energy, the partition function, and other thermodynamic quantities.

Generalized oscillator strengths are calculated from four-state close-coupling-approximation differential cross sections for the $4s{}_{}{}^2{}_{}{}^{}S\to 4p{}_{}{}^2{}_{}{}^{}P$ transition in Cu by electron impact at 10, 20, and 60 eV. They neither converge to a universal curve at small momentum transfer squared, $K^2$, nor extrapolate readily and unambiguously to the optical $f$ value at $K^2=0\mathrm{}$. Favorable agreement is obtained with those deduced from the measurements by Trajmar et al. at 20 and 60 eV after an energy-independent normalization factor of 0.36 has been applied to the data.

First results of a powerful, quick, and efficient technique for measuring the multipole content of the angular distributions characterizing electron loss in ion-atom collisions are compared to theory. Contrasting dipole properties of continuum-capture distributions are discussed. Two examples of future experimental opportunities are provided.

Using a method for nonlinear laser spectroscopy which eliminates the effects of laser jitter in nearly degenerate four-wave mixing, we present the first direct measurement of the ground-state relaxation rate of optically excited ${\mathrm{Cr}}^{3+}$ ions in Cr: YAl${\mathrm{O}}_3$. The Lorentzian linewidth of the emission resonance is 9.8 Hz (FWHM). The mechanism of ground-state relaxation is established to be fluorescent decay of the ${}_{}{}^2{}_{}{}^{}E$ metastable level.

It is demonstrated numerically that a tokamak plasma can be evolved continuously from a near-circular cross-section shape to a $\frac{4}{1}$ vertically elongated racetrack. All intermediate stages and the final state are stable to axisymmetric MHD modes. The stabilization is provided by the vacuum vessel walls on the ideal time scale and by an orthogonal active feedback system on the resistive time scale.

A relativistic electron-beam-driven virtual-cathode device has produced 500±130 MW at 17 GHz and 100±30 MW in the band from 30 to 40 GHz on a single typical machine firing. Computer calculations demonstrate that the source of the 17-GHz component is the reflexing of coherent electron bunches between the real and virtual cathodes. Oscillations in the virtual cathode and harmonic generation associated with reflexing electron bunches cause the higher-frequency components.

Low-frequency electrostatic fluctuations are investigated experimentally in an unmagnetized plasma. The turbulence is generated by ion-ion-beam instabilities. Real-time signals are recorded and investigated statistically on a conditional basis. The formation and propagation of structures with a relatively long lifetime in terms of the average bounce period is observed. Particles bouncing in the potential well associated with these "eddies" will necessarily remain correlated for times determined by the eddy lifetime. The results thus provide evidence for clump formation in plasmas.

The existence of large-sized satellite faces on crystals of the mineral calaverite (${\mathrm{Au}}_{1-x}{\mathrm{Ag}}_x{\mathrm{Te}}_2$) is reported. These anomalous high-index faces can be related directly to the wave vector q of the displacive incommensurate modulation recently found in the crystal structure. If we extend the classical morphological law of rational indices to include q as a fourth basic vector, the high-index faces can be described by four low integers ($\mathrm{hklm}$).

The textures of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$ in the presence of superflow in zero magnetic field are investigated numerically. A dynamic texture of domains is found at high flow rates. Within a domain the texture is essentially aligned parallel or antiparallel to the flow. Dissipative precessional motion occurs within localized domain walls. This texture may help to explain recent experimental results which are apparently in conflict with previous theory.

Surface-phonon dispersion curves have been measured by He-atom inelastic scattering for Pt(111) along the $〈1\overline{1}0〉$ and $〈11\overline{2}〉$ azimuths with greatly reduced scatter compared with earlier work. Along the $〈1\overline{1}0〉$ direction the results reveal a number of anomalous kinks in the Rayleighmode dispersion curve. Comparison with the corresponding anomaly in the bulk suggests that the effect is due to a two-dimensional surface Kohn anomaly.

Diffuse low-energy-electron diffraction measurements at 46 eV for a disordered O/W(100) surface at 120 K have been interpreted by theory to give the local geometry of the oxygen atoms. This first application of the technique shows that phonon scattering does not prevent interpretation of data, and demonstrates sensitivity to surface geometry comparable with that in conventional LEED experiments on ordered surfaces. $R$ factors for the optimum geometry are very low, indicating a highly reliable determination. The prospects for the use of this technique in a whole range of situations previously inaccessible to LEED are thereby opened.

Fundamental problems associated with universality in phase transitions on hierarchical lattices are examined. It is shown that the critical properties actually depend on more details of the lattice than are usually acknowledged. The claim that the fractal dimension and the connectivity serve as criteria for universality is called into question. There is a lack of conclusive evidence, theoretical or experimental, to establish the validity of universality on hierarchical lattices. It therefore seems that universality is but an extrapolated hypothesis that can hope to hold only in a very restricted or approximate sense. It is more likely that the principle of universality is violated.

Interfacial tensions $\sigma$ in the tricritical region of mixtures of ethane with higher alkanes were measured by surface light scattering. At each of the two critical end points $\sigma$ for the noncritical interface shows the predicted behavior: $\sigma$ and $\frac{d\sigma }{\mathrm{dT}}$ appear continuous while $\frac{d^2\sigma }{d{T}^2}$ changes sign. Results for the $\alpha \gamma$ interface suggest high adsorption. The tricritical exponent for $\sigma$ varies across the three-phase region and appropriate ratios of $\sigma$ do not approach unity, in disagreement with a van der Waals-type theory of interfaces.

We observe for the first time the transformation of glassy alloys (${\mathrm{Pd}}_{100-x-y}{\mathrm{U}}_x{\mathrm{Si}}_y$, $x\simeq y\simeq 20$ at.%) into a metastable icosahedral phase with quasicrystalline order upon annealing. The icosahedral symmetry of the latter phase is confirmed by x-ray and electron diffraction. This phase can be formed only within a very narrow compositional range (< 2 at.%) of U and Si, suggestive of a strong chemical ordering in it. The icosahedral and glassy phases have similar electrical transport properties. However, magnetic-susceptibility results indicate that the electronic structure of the icosahedral phase is very different from its glassy and crystalline (U${\mathrm{Pd}}_3$) counterparts.

We attempt to resolve the angular momentum paradox in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$ by connecting it to the phenomenon of charge fractionalization and by writing the current as a weighted Fermi-surface sum of fractional charges. We also give a novel interpretation of the twist term in terms of topology on the Fermi surface.

The high-temperature decomposition of thin (∼100Å) Si${\mathrm{O}}_2$ layers on Si(001) under ultrahighvacuum annealing conditions has been studied by means of ion scattering and microscopy techniques. Si${\mathrm{O}}_2$ is removed from the Si surface by the formation and lateral growth of holes in the oxide, exposing regions of atomically clean Si, while the surrounding oxide retains its initial thickness. Surface diffusion of Si inside the holes supplies Si for reaction with Si${\mathrm{O}}_2$ at the periphery, so that a volatile product (presumably SiO) can be formed.

The effect of high magnetic fields on the electronic structure of very anisotropic systems with charge- or spin-density waves is examined. In materials where there is lack of perfect nesting at the Fermi surface the density wave produces small electron and hole pockets. Calculations show that the presence of a high magnetic field in certain directions destroys these pockets, opens a gap in the electronic spectrum at the Fermi level, and leads to a metal-insulator transition. This effect has been recently observed in the low-temperature charge-density-wave phase of Nb${\mathrm{Se}}_3$.