Interpretations of the "$\lambda$-point paradox" are narrowed significantly by recent experimental findings. Penney's proposal that the paradox originates in effects of room-temperature radiation falling on the disk is disproved. Further, by rotating the disk through the helium rather than rotating the liquid past the disk, the paradox is found to be dependent only on relative rotation. This invariance to absolute rotation of helium evidently eliminates any role of the rotational properties per se of the liquid.

The polarization of the free-free bremsstrahlung emitted radially for an anisotropic hot-electron plasma in a magnetic mirror has been measured by means of Compton scattering. The degree of polarization was found to be exceptionally sensitive to changes in system parameters. A quantum-mechanical nonrelativistic theory has been found to agree well with the experimental results.

In contrast to the acoustic mismatch theory of Bekarevich and Khalatnikov, it is suggested that the origin of the ultralow-temperature Kapitza resistance of a nonmagnetic liquid-${\mathrm{He}}^3$-solid interface is the inelastic scattering of single-quasiparticle excitations from the surface atoms of the solid boundary.

Infrared-reflectivity measurements on InSb surfaces having inscribed line gratings yield the first complete dispersion relation for surface plasmons.

We have carried out uv photoemission measurements on hexagonal ZnO cleaved in vacuum. The results of this study have placed the $\mathrm{Zn} 3d$ core level at 7.5 ± 0.2 eV below the valence-band maximum, some 3 eV lower than predicted by Rössler's Green's-function (Korringa-Kohn-Rostoker) band calculation. This assignment is in excellent agreement with recent x-ray photoemission measurements and is shown to be consistent with the low value of the effective number of free electrons calculated from the reflectivity.

While the ordinary electrostatic drift mode is stabilized by either high-$\beta$ effects or an admixture of cold plasma, a compressional drift mode is shown to be destabilized under these same circumstances. The condition of the instability is approximately given by $\frac{n_h}{n_c}<\frac{\beta \kappa _0^{}{}_{}{}^2\rho _i^{}{}_{}{}^2}{2}$, where $n_h$ and $n_c$ are the number densities of the hot and cold components, respectively; ${\kappa }_0$ is a measure of the density, temperature, or magnetic field gradients; and ${\rho }_i$ is the ion Larmor radius.

The contribution of magnetic surface states to the radio-frequency impedance of metals is considered in the low and high magnetic field limits. A peak in $\frac{\mathrm{dX}}{\mathrm{dH}}$ is predicted to occur at a field for which the length of a bounce along the skipping trajectory of the first quantum state is comparable to the mean free path. The model is compared with experiments on Cu.

Second-harmonic generation has been studied in InSb. The fundamental source was a ${\mathrm{CO}}_2$ laser, and the second-harmonic photon energies were near the band edge. The non-linear susceptibility $d_{14}$ is the largest known and shows significant frequency dependence. In a 2.6% range of photon energies, $\left|d_{14}\right|$ changes by 31% while the linear susceptibility at the second harmonic, ${\chi }^{\mathrm{lin}}\left(2\mathrm{}\omega \right)$, changes by only 2.8%. In addition $d_{14}=\left|d_{14}\right|e^{i\varphi }$ is complex with $\varphi \cong -50\mathrm{}°$.

A Monte Carlo method is used to calculate the shape of the transient photocurrent under flash excitation. It is shown that some of the anomalous features of the experimental data can be explained by including surface as well as bulk trapping in the model. In particular, this simple picture predicts the observed long tail of the pulse as well as the apparent field dependence of the mobility.

We report measurements of direct photon-echo intensity versus Cr concentration which indicate the presence of sizable radiation-damping effects in dark ruby. The departure from $n^2$ dependence for concentrations above 0.03% Cr demonstrates that modifications of self-induced transparency analyses are necessary in dense resonant media.

A calculation of the total-energy distribution of field-emitted electrons in the presence of chemisorbed atoms shows that $\frac{\left[j\right(\omega )-j_0(\omega \left)\right]}{j_0\left(\omega \right)}=\mathrm{Im}{G}_{\mathrm{aa}}\left(\omega \right)\exp \left[{\left(\frac{-2m\omega }{{\hslash }^2}\right)}^{\frac{1}{2}}{x}_a\right]$, where $j\left(\omega \right)$ and $j_0\left(\omega \right)$ are the current densities in energy in the presence and absence of absorbate, respectively; $\omega$ is measured from the vacuum level; $x_a$ is the surface-absorbate distance; and ${\pi }^{-1\mathrm{}}\mathrm{Im}{G}_{\mathrm{aa}}$ is the local density of states at the absorbate. This result is general and independent of the explicit form of $G_{\mathrm{aa}}$.

Auger electrons resulting from across-the-gap recombination are believed to have been identified by their velocity distribution which does not depend on the energy of the exciting photons.

The power density of bremsstrahlung and the recombination rate are found for a fully ionized, nonrelativistic hydrogen plasma dominated by long-range collisions. The results show that the bremsstrahlung energy radiated per unit volume per second is greater than previously predicted.

A dynamical study of electron-exciton collision process in pure germanium is made by means of millimeter-wave cyclotron resonance combined with a photopulse technique. It is found that carrier recombination occurs primarily via exciton formation and subsequent annihilation process. The exciton lifetime is determined as a function of temperature.

Photoemission studies of the Pd/H system show a band of hydrogen-induced energy states centered at 1 eV below the bottom of Pd-derived d bands of width 4.4 eV. These results show that the widely accepted simple "proton model" of Pd/H is misleading. Our augmented-plane-wave calculations of PdH, ${\mathrm{Pd}}_4$${\mathrm{H}}_3$, and ${\mathrm{Pd}}_4$H exhibit these lowlying states and also explain why the added number of electrons (0.6) in $\beta$-phase PdH exceeds the number of $d$-band holes (0.36) in Pd.

The sign and magnitude of the nuclear quadrupole splitting in rhenium metal have been determined by heat-capacity measurements down to 19 mK. We find an average coupling constant $\frac{e^2\mathrm{qQ}}{h}=-246\mathrm{}\pm 2$ MHz for the two rhenium isotopes. This gives an electric field gradient at the nucleus of $q=-100\mathrm{}{q}_{\mathrm{lat}}$, where $q_{\mathrm{lat}}$ is the source gradient produced by the ${\mathrm{Re}}^{7+}$ ion cores in the hcp lattice.

We calculate the free energy of a linear binary metallic alloy using an exact transfer-matrix formalism. We obtain for the first time the electronic band structure when there is nonvanishing short-range order and calculate the temperature dependence of the short-range order parameter. Following Foo and Amar, we also introduce long-range order via two sublattices, but we find this necessarily raises the free energy. We conclude that the first-order phase transition of Foo and Amar is spurious, being an artifact of their assumption of long-range order and neglect of short-range order.

The observed mass distribution for thermal-neutron-induced fission of ${}_{}{}^{257}{}_{}{}^{}\mathrm{Fm}$ is strongly symmetric, whereas that for spontaneous fission of ${}_{}{}^{257}{}_{}{}^{}\mathrm{Fm}$ is found to be predominantly asymmetric with, however, some symmetric fission present. The mass distributions were derived from energy measurements on coincident fission fragments. The onset of symmetric fission at ${}_{}{}^{257}{}_{}{}^{}\mathrm{Fm}$ supports theories relating asymmetric fission to the second hump of the fission barrier.

A nuclear Thomas-Fermi model is used to determine the ground state of matter at subnuclear densities allowing for inhomogeneities on a nuclear scale ("clusters"). The "neutron drip" phase transition occurs at 3.7 × ${10}^{11}$ ${\mathrm{g}/\mathrm{c}\mathrm{m}}^3$. As a function of the average density the proton number $Z$ of the clusters first increases from $Z\simeq 29$ at 1.4 × ${10}^8$ ${\mathrm{g}/\mathrm{c}\mathrm{m}}^3$ to a maximum of $Z\simeq 35$ at ∼3.0 × ${10}^{12}$ ${\mathrm{g}/\mathrm{c}\mathrm{m}}^3$ and then decreases until the clusters gradually evanesce just above ${10}^{14}$ ${\mathrm{g}/\mathrm{c}\mathrm{m}}^3$; this transition is smooth.

More than 100 000 cosmic-ray tracks from extensive air showers were scanned in pictures of cloud chambers after the manner of McCusker. In addition, positive- and negative-ion columns were separated by an electric field, and individual droplets were counted; histograms of numbers of tracks versus droplet density are shown. Artificially produced low-droplet-count tracks have been used to measure the scanning efficiency for quarklike tracks. To date the upper limit for the $\frac{2}{3}e$ quark flux is 3 × ${10}^{-11\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ ${\mathrm{sr}}^{-1\mathrm{}}$, and the limit for $\frac{1}{3}e$ particles is 3 × ${10}^{-10\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ ${\mathrm{sr}}^{-1\mathrm{}}$.