Laser-induced fluorescence of ionic states is used to measure local ion densities and velocities in argon plasmas.

A new emission band at about $h\nu =2\mathrm{}$ eV is observed in GaSb which is excited by a Ndyttrium aluminum garnet laser. From the dependence on the crystal orientation and integrated intensity and from the line shape and its dependence on doping, it is concluded that the emission band cannot be attributed to nonlinear mixing of the laser line with the $E_g$ luminescence, but is caused by electronic interband anti-Stokes Raman scattering.

Doppler-broadening measurements have been performed on electron-irradiated copper during isochronal annealing. These results together with measurements on quenched gold indicate clearly that vacancies become mobile and form clusters in stage-III annealing.

The quadrupole interaction of the 247-keV level of ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$ in a Be host is observed to differ by a factor of 3.4 depending on whether the sample is prepared by the implantation of the parent radioactivities ${}_{}{}^{111}{}_{}{}^{}\mathrm{Ag}$ or ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$. Ion-channeling measurements have shown this difference to arise from the preference of implanted Ag to reside in substitutional sites and In in the tetrahedral interstitial sites of the Be lattice.

The dc and microwave conductivities of the new organic charge-transfer salt hexamethylene-tetraselenafulvalinium tetracyanoquinodimethanide (HMTSF-TCNQ) remain metallic in magnitude to temperatures at least as low as 1.1 K. At low $T$ we observe a resistance minimum and thermoelectric anomaly consistent with the theoretical result that density fluctuations can enhance the resistivity of a one-dimensional metal as $T\to 0$. Implications for ${\left(\mathrm{SN}\right)}_x$ and tetrathiafulvalene tetracyanoquinodimethane (TTF-TCNQ) are discussed.

We study the effect of short-range correlations using the renormalized harmonic approximation with Horner's modification of the pair-correlation function to allow for hardcore effects. Using a nearest-neighbor force model, based on Kr, the theory accounts quantitatively for Monte Carlo computer experiments at high temperatures.

Undulation spectra are observed in the luminescence of GaP: N codoped with an acceptor. New experimental data prove that the luminescence is a series of zero-phonon lines of excitons bound to N-acceptor pairs. The undulatory behavior originates from the averaged number of equivalent sites for different N-to-acceptor shells. Calculations show that this number has an approximately periodic fluctuation with the maxima separated by about 9 shells.

Experimental and theoretical evidence is reported of hybridization effects leading to strong nonparabolicity in the $E-K$ dispersion curves of the Ge anisotropy-split excitons. The measured density of states indicates substantial deviation from ideal-gas behavior even at a few kelvins. A splitting of 1.01 ± 0.03 meV is measured.

The critical dynamics of a model isotropic antiferromagnet is studied in $4-\epsilon$ dimensions above and at $T_{\mathrm{N}}$. The renormalization-group, characteristic-frequency exponent, and shape function are determined to order $\epsilon$. In particular we find fluctuation-induced peaks in the shape function at and above the Néel temperature. We find results in agreement with dynamical scaling.

The magnetic anisotropy energy makes spin fluctuations extremely anisotropic near the Curie and Néel temperatures. Because of this anisotropy of the fluctuations and the symmetry of the shear-wave phonon-spin interaction, only shear waves with both propagation and polarization vectors in the easy directions of magnetization have critical attenuation at the phase transition temperatures and other shear waves do not have it. Experimental results on the heavy rare-earth metals are in agreement with these theoretical predictions.

We compute the binding energy of the ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ and ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ $\mathrm{NN}$ states (known to be bound by 2.22 and - 0.07 MeV) using a covariant, singular-core, three-body model of the $\mathrm{NN}\pi$ system with ${{\mathcal{r}}_c}^{\mathrm{NN}}=0.7\mathrm{}$ fm, ${}_{}{}^3{}_{}{}^{}f_{\infty }^{}{}_{}{}^{}=1.8\mathrm{}$, and ${}_{}{}^1{}_{}{}^{}f_{\infty }^{}{}_{}{}^{}=0.3\mathrm{}$ as observed at high energy. For the $\pi N$ $P_{11}$ input we use ${{\mathcal{r}}_c}^{\pi N}=0.18\mathrm{}$ fm fitted (or $\frac{\hslash }{\mathrm{Mc}}=0.22\mathrm{}$ fm postulated) and find 3.26 (2.59) for ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ and 1.41 (0.73) for ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$.

The in-plane ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}(d, d_1\gamma )$ angular correlation has been measured at an incident energy of 10 MeV. Analyses of the experimental data with distorted-wave and coupled-channel Born-approximation calculations show that multistep processes are important to describe this reaction although the distorted-wave Born approximation reproduces quite well the differential cross section.

The longitudinal polarization of the new Yale University-Stanford Linear Accelerator Center polarized-electron beam has been determined at laboratory energies between 6.47 and 19.40 GeV. Spin-dependent elastic electron-electron scattering (Møller scattering) has been found to be a practical technique for polarization measurements at high energies. The results are consistent with the energy and angular dependence predicted by quantum electrodynamics and with an energy-independent beam polarization of 0.76±0.03.

It is suggested that bound states can emerge in field theory as alternate solutions to the Bethe-Salpeter equation, not corresponding to the Neumann-series (perturbation-theory) solution. These new solutions are asymptotically similar to elementary-particle solutions and imply nonperturbative anomalous dimensions in the Wilson operator-product expansion. For Goldstone bosons in standard quark models as well as for certain solvable ladder models, these are the only bound-state solutions.

The interaction of a two-level atom with an external electromagnetic field is examined in the framework of quantum electrodynamics, without any assumption about Markoffian behavior or stationarity. It is found that spontaneous emission in the vacuum and the rate of fluorescence in an external field do not depend on quantum properties of the electromagnetic field, whereas the correlation functions do.

Longitudinal ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ nuclear relaxation times at low temperature have been measured by an optical-pumping technique, using solid ${\mathrm{H}}_2$ coatings on the cell walls. Relaxation times longer than 2 days at 4.2 K were obtained with a 3-cm-diam cell. Preliminary results with other coatings (solid ${\mathrm{D}}_2$, Ne, etc.) are reported.

The current carried by a beam of electrons which have been scattered from an arbitrary potential is shown to exhibit fluctuations with a $\frac{1}{f}$ spectrum up to $f=0\mathrm{}$. The exponent of $f$ is smaller than unity by an amount determined by infrared radiative corrections. This amount is essentially the fine-structure constant $\alpha$ and practically coincides with the $\frac{1}{f}$ noise coefficient for one carrier. Similar noise is expected from current carriers in any medium.

The quantum theory of $\frac{1}{f}$ noise developed in the preceding Letter is extended by showing that because of interaction with the electromagnetic field, an alternating current carried by a beam of electrons emerging from some scattering process will present phase fluctuations with a $\frac{1}{f}$ spectrum. These fluctuations are expected in any ac current. They have similar power spectra, also determined by infrared radiative corrections, to dc $\frac{1}{f}$ noise.

Electron-plasma waves driven unstable by an electron beam are observed to be backscattered by stationary density perturbations to form standing waves. Above a certain threshold these standing waves develop into sharply localized ($\sim 10{\lambda }_{\mathrm{D}}$) intense fields, $\frac{{E_{max}}^2}{4\pi n_0\kappa T_e}\approx 1$. Significant fractions of beam electrons are scattered in velocity space by these stationary spikes of high-frequency field.

Single crystals of iron-doped Ta${\mathrm{S}}_2$ grown from sintered powders of composition ${\mathrm{Fe}}_{0.05}$-Ta${\mathrm{S}}_2$ show a rise in critical temperature to above 3 K and an enhanced anisotropy of $H_{c2\mathrm{}}$ which is comparable to that observed in $2H$-Ta${\mathrm{S}}_2$${\mathrm{}\left(\mathrm{pyridine}\right)\mathrm{}}_{\mathrm{½}}$. Single crystals grown from ${\mathrm{Fe}}_{0.05}$${\mathrm{T}}_{0.95}$${\mathrm{S}}_2$ powders are stabilized in the $1T$ phase and are semiconducting at all temperatures below room temperature with no resistive anomaly at 200 K.