A general theory, based on central limit theorems and unitary-group decompositions of the microscopic $H$, is given for the nuclear level density. The density appears in terms of convolutions of noninteracting-particle densities with easily calculable interaction functions given explicitly in terms of the Hamiltonian matrix elements.

The production of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, Li, ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$, B, C, N, O, and F has been studied in the reaction 90-MeV ${}_{}{}^3{}_{}{}^{}\mathrm{He}$+${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Ag}$. Although the yields of the heavier elements are orders of magnitude less than for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, the energy spectra, charge, and angular distributions indicate that an equilibrium statistical process is responsible for the production of these heavy nuclei in the backward hemisphere.

The spin dependence of the electron-impact ionization of Na has been measured up to 2 eV above threshold with high precision to search for the existence of characteristic oscillations which would support the Coulomb-dipole theory of threshold ionization. The authors have been unable to observe any statistically significant oscillations. The present results are fully consistent with the Wannier theory.

A measurement is reported of the velocity dependence of the total cross section for Yb optical radiator-Xe perturber collisions in which the active atom is in a superposition of dissimilar ($S$ and $P$) states. The total cross section is found to vary with relative velocity in a simple manner, consistent with van der Waals scattering as the dominant interaction for this nonclassical system.

An analogy is drawn between continuum elastic theories of the blue phase of cholesteric liquid crystals and recent theories of frustration in configurational glasses. Both involve the introduction of a lattice of disclination lines to relieve frustration; the frustration is due to an intrinsic curvature in the natural form of parallel transport. A continuum theory of configurational glasses is proposed.

A Boltzmann-equation analysis of low-temperature ($T<\mathrm{}100\mathrm{}$ K) electron drift mobilities in naphthalene reveals that acoustic-phonon scattering of electrons in extended energyband states provides a quantitative interpretation of the temperature dependence of these mobilities.

Experiments performed in the linear chain compound Nb${\mathrm{Se}}_3$ demonstrate that the oscillations associated with the current-carrying charge-density-wave condensate decrease with increasing volume of the specimens. The observed dependence of the oscillating current density $\Delta j_1$ on volume $\Omega$, $\Delta j_1\propto {\Omega }^{-\frac{1}{2}}$, is attributed to interference between independent charge-density-wave domains which oscillate at the same frequency but randomly in phase.

Diffractive and rotationally mediated selective adsorption scattering resonances are reported for $n$-${\mathrm{H}}_2$ $p$-${\mathrm{H}}_2$ $n$-${\mathrm{D}}_2$ and $o$-${\mathrm{D}}_2$ on Ag(111). Small resonance shifts and line-width differences are observed between $n$-${\mathrm{H}}_2$ and $p$-${\mathrm{H}}_2$ indicating a weak orientation dependence of the laterally averaged ${\mathrm{H}}_2$/Ag(111) potential. The $p$-${\mathrm{H}}_2$ and $o$-${\mathrm{D}}_2$ levels were used to determine the isotropic component of this potential, yielding a well depth of ∼ 32 meV.

uv photoemission and electron-energy-loss measurements of Si(111)-7 × 7 between $T=15\mathrm{} \mathrm{and} 300$ K reveal significant temperature-dependent changes in the occupied surface states and their transitions which can be associated with electron-phonon coupling at the surface. Several new surface states and transitions are determined at low temperatures, including a highly localized (∼2-meV-wide), half-occupied state that resides within a 100-meV-wide surface-state band gap and determines the Fermi-level position.

The relationship $m$ vs $H$ for the alloys ${\mathrm{Ni}}_{79}$${\mathrm{Mn}}_{21}$ and ${\mathrm{Au}}_{81}$${\mathrm{Fe}}_{19}$ has been investigated at 1.5 and 4.2 K. Below a certain field $H_a$, it is linear, reversible, and governed by anisotropy fields even in the zero-field-cooled state. These fields are correlated with the spatial distribution of the spontaneous magnetization during cooling. A procedure allowing their suppression is presented. It leads to a radical change of the hysteresis loops without affecting significantly the degree of irreversibility.

Both sum- and difference-frequency generation in organic materials are demonstrated and explored under conditions where all three waves (${\omega }_1$ and ${\omega }_2$ ingoing and ${\omega }_1\pm {\omega }_2$ outgoing) are resonant with molecular transitions. The experiments are carried out in centrosymmetric media in which a small electric field is used to distinguish the polar sublattices. Unique electric field dependences of the parametric signals were discovered. The spectroscopic line narrowing and dephasing-induced coherent-emission resonances of these ${\chi }^{\mathrm{}\left(2\right)\mathrm{}}$ processes make them useful new spectroscopic methods.

Most of the shallow acceptor levels due to boron in single-crystal silicon can be neutralized by atomic hydrogen at temperatures between 65 and 300°C. This treatment can result in a sixfold increase in resistivity.

A negative magnetoresistance proportional to $B^2$ is found in the two-dimensional electron gas of GaAs-${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ heterostructures. It is explained by the conductivity correction due to the electron interaction effect in disordered two-dimensional systems. The high-field electron lifetime, estimated both from the interaction effect and from the Shubnikov-de Haas oscillations, is much shorter than the zero-field lifetime, demonstrating the predominance of long-range potential fluctuations in high-mobility GaAs-${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ samples.

An exact solution of the Schrödinger equation for a charge $e$ in the potential of a flux tube along the $z$ axis and a Dirac magnetic monopole of strength $g$ at the origin is obtained. Single-valued solutions exist even with $2eg\ne \mathrm{integer}$. When $2eg=\mathrm{integer}$ and single-valuedness holds, solutions with $\left|J_z\mathrm{}\right|<\mathrm{}\left|eg\right|$ have a centrifugal barrier (and hence behavior at the origin) independent of flux, but solutions with $\left|J_z\mathrm{}\right|>\mathrm{}\left|eg\right|$ have a flux-dependent centrifugal barrier.

A phenomenological Landau model which describes a simple continuous transition from a high-symmetry phase to a phase associated with a nonmaximal isotropy subgroup—hitherto conjectured impossible—is constructed. A novel feature of the model is that a single order parameter describes successive simple continuous phase transitions between three or more phases of different symmetries. Effects of fluctuations are considered within a renormalization-group approach.

A new quantum field-theoretical technique is developed and used to explore the relationship between even-space-time-dimensional axial anomalies and background-field-induced fermion numbers and Euler-Heisenberg effective actions in odd-dimensional space-times.

It is suggested that the inequality $m_B>\frac{3}{2}{m}_M$ is a rigorous result in quantum chromodynamics. The analog for a ($q_1\dots q_N$) baryon in $\mathrm{SU}\mathrm{}\left(N\right)\mathrm{}$ is $m_B>\left(\frac{1}{2}N\right)m_M$. The inequality is proved for weak coupling and a version of the strong-coupling expansion where a separation $H_{q_1{q}_2{q}_3}=H_{12}+H_{23}+H_{31}$ of the problem can be achieved. Implications for quantum chromodynamics and composite models are briefly discussed.

$\gamma$-ray transitions of energy 2.034 ± 0.023 MeV in the hypernucleus ${}_{\Lambda }{}^7{}_{}{}^{}\mathrm{Li}$ and 3.079 ± 0.040 MeV in the hypernucleus ${}_{\Lambda }{}^9{}_{}{}^{}\mathrm{Be}$ are observed. In both cases, the energy of the $\gamma$ ray in the hypernucleus ${}_{\Lambda }{}^A{}_{}{}^{}Z$ is very close to the energy of the first excited state of the nuclear core. The $\gamma$ rays are interpreted as arising from core transitions in the presence of the $\Lambda$ particle. The size of the shift places limits on the strength of the $\Lambda N$ spin-dependent interaction.

The search for parity nonconservation in heavy elements has been extended to the 1.28-μm ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}\to {}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ magnetic dipole transition in atomic lead. The experimental result, $R=\mathrm{Im}\left(\frac{E1\mathrm{}}{M1\mathrm{}}\right)=(-9.9\mathrm{}\pm 2.5)\times {10}^{-8\mathrm{}}$, agrees, within the present uncertainties in experiment and atomic theory, with the prediction, $R=-13\mathrm{}\times {10}^{-8\mathrm{}}$, derived from the Weinberg-Salam-Glashow theory of weak neutral-current interactions.

The analysis of the electrons emitted in the decay of the $6s^{2}6p^2+h\nu \to 6s6p^2\left({}_{}{}^4{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\right)n{p}_{\frac{3}{2}}$ resonance series of Pb shows that negative contributions occur in the $6p^{-1\mathrm{}}{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ channel and positive contributions in the $6p^{-1\mathrm{}}{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ channel due to interference with the direct photoionization process. These contributions effectively cancel. Hence the series is difficult to observe in absorption, but can easily be delineated in emission.