Sodium atoms are excited to either the $3{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ or $3{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ state using a linearly polarized dye-laser beam and are subsequently ionized using a linearly polarized nitrogen-laser beam. Angular distributions of the ejected electron have been both measured and calculated for several relative orientations of the photon polarization vectors. The difference between the $s$- and $d$-continuum partial-wave phase shifts ${\delta }_s-{\delta }_d$ and the ratio of the radial dipole matrix elements ($\frac{d_s}{d_d}$) are obtained.

We have observed spontaneous Raman processes in a sodium atomic beam. When one sodium $3p{}_{}{}^2{}_{}{}^{}P$ fine-structure level is strongly excited by a dye laser, the other level, is weakly populated by spontaneous Raman emission and the absorption of another laser photon. This effect is detected by further stepwise excitation plus photoionization. The observed magnitude agrees well with theory. This technique is much more sensitive than methods involving direct observation of the Raman emission.

We have carried out theoretical and experimental studies of the excitation of surface electromagnetic waves by volume electromagnetic radiation of finite beam width. The excited leaky surface electromagnetic waves are found to build up along the excitation region and to propagate as free damped waves beyond. Correspondingly, the spatial dependence of the reflected intensity is found to exhibit a two-peak interference structure at the leading edge of the excitation region followed by an exponential decay beyond.

Presented numerically is an apparently paradoxical nonlinear process that a two-stream instability is stabilized by inhomogenizing or "grooving" an initially homogeneous plasma, not by limiting the stream which is the direct cause of the instability. For a relatively wide and slow electron stream, the instability is shut off by reducing the speed to the threshold value (ion sound speed), as is naturally expected. For a narrow and fast stream, however, the instability is shown to be stabilized by the grooving effect.

It is shown that a region containing closed timelike lines cannot evolve from regular initial data in a singularity-free asymptotically flat space-time. Furthermore, the causality assumption made in the black-hole uniqueness proofs is justified: It is demonstrated that no physically realistic nonsingular black hole can have a causality-violating exterior.

We report evidence, from a study of multihadron final states produced in the wide-band photon beam at Fermilab, for the production of a new antibaryon state which decays into $\overline{\Lambda }{\pi }^{-}{\pi }^{-}{\pi }^{+}$. The mass of this state is 2.26 ± 0.01 ${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c}}^2$ and its decay width is less than 75 ${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{c}}^2$. We also report evidence of a state of higher mass (∼2.5 ${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c}}^2$) which decays into the state at 2.26 ${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c}}^2$.

We report a correlation between the kinetic energy loss and nucleon diffusion for Kr- and Xe-induced reactions on heavy targets. Although this correlation suggests that these two phenomena occur on the same general time scale, the rate of kinetic energy loss decreases with interaction time. Evidence is presented to show that the initial energy dissipation rate is consistent with a frictional force which is proportional to the relative velocity.

Measurements of the fusion cross sections for ${}_{}{}^{10,11}{}_{}{}^{}\mathrm{B}$+${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$+${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$+${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ at sub-Coulomb-barrier energies, together with earlier results for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, show that the average energy dependence of the fusion cross section can change dramatically with only small variations in the mass and charge of the interacting nuclei.

A new technique of laser photofragment spectroscopy is introduced and applied to a study of transitions from the $v=4\mathrm{}$ level of the $a^4{\Pi }_{\mathrm{u}}$ state of ${\mathrm{O}}_2^{+}$ to predissociating levels of the $f^4{\Pi }_g$ state near the dissociation limit. A resolution of 0.5 MeV is obtained, and specific $\Omega ,J$ levels of the $a$ state are identified. Much higher resolution is possible.

The analytic continuation of homogeneous, isotropic turbulence in nonintegral dimensions $d$ is not realizable for $d<\mathrm{}2\mathrm{}$ because the energy spectrum generally becomes negative. Recent arguments, in favor of an $\frac{8}{3}$ crossover dimension below which the Kolmogorov 1941 theory is exact, are found questionable. The existence of a crossover dimension $d_c (\approx 2.03)$ at which the direction of the energy cascade reverses is supported by a second-order closure calculation.

Auxiliary heating of a linear $\theta$-pinch plasma column by an externally driven radial magnetoacoustic oscillation has been experimentally investigated. The axial field of the $\theta$ pinch was modulated in time at the frequency of the plasma's fundamental radial magnetoacoustic oscillation. The dissipation in the plasma column was sufficient to transfer into the plasma at least 9% of the energy stored in the auxiliary capacitor bank used to drive the oscillation.

We have measured the strong x-ray emission of compressed neon gas fill in glass microballoons, irradiated by a four-beam laser system. X-ray pinhold imaging and spatially resolved x-ray spectroscopy lead to estimates of the compressed-gas temperature and the compression of the glass shell. We find that the product of glass shell thickness and density at maximum compression is less than 2.5×${10}^{-3\mathrm{}}$ g/${\mathrm{cm}}^2$. This is consistent with a degraded compression of the so-called "explosive-pusher mode."

The resonance cones existing below the ion cyclotron frequency, ${\omega }_{\mathrm{ci}}$, are shown, theoretically and experimentally, to be the asymptotes of hyperbolic constant-phase surfaces of low-frequency ion acoustic waves. Above ${\omega }_{\mathrm{ci}}$ the surfaces transform into ellipses that are related to the electrostatic ion cyclotron waves and ion acoustic waves.

A collisional instability driven by electron temperature gradients is described which appears to explain the major characteristics of the precursors of the internal disruptions. The threshold is reached when a certain parameter $\left|\mu \right|>\mathrm{}\sqrt{3}$. For the ST and TFR tokamaks, we estimate $1\lesssim \left|\mu \right|\lesssim 5$ at the radius where $q=1\mathrm{}$. For $\left|\mu \right|=3\mathrm{}$, the theoretical growth rate ${\gamma }_{\mathrm{th}}\sim \mathrm{}(2-3)\mathrm{}\times {10}^3$ ${\sec }^{-1\mathrm{}}$ compares well with the experimental value ${\gamma }_{\exp }\sim 3\times {10}^3$ ${\sec }^{-1\mathrm{}}$. The predicted shape of the wave profile is also in qualitative agreement with experiment.

By heat pulse experiments it is demonstrated that selectively narrow-band laser-excited perylene, matrix-isolated in Langmuir films provides a memory for detecting high-frequency acoustical phonons. This phonon memory, the phonon-modulated fluorescence spectrum, and Debye-Waller factor variations can be explained by the electron-phonon interaction, statistically distributed dye sites, and a model in which dye-site changes in noncrystalline matrices, containing two-level configurations, are induced by phonons and photons.

This Letter describes a theoretical treatment of the excellent experimental results of Boato, Cantini, and Mattera for the He-LiF(001) system, in terms of a hard corrugated model for the surface. From the agreement achieved between theory and experiments, I conclude that one can represent the corrugated surface by $z_1\mathrm{}(x,y)=\frac{1}{2}{\zeta }_1\left[cos\right(\frac{2\pi x}{a})+cos(\frac{2\pi y}{a}\left)\right]+\frac{1}{2}{\zeta }_2\left\{cos\right[\frac{2\pi \mathrm{}(x+y)\mathrm{}}{a}]+cos[\frac{2\pi \mathrm{}(x-y)\mathrm{}}{a}\left]\right\}$, with ${\zeta }_1=0.307\mathrm{}\pm 0.003$ Å and ${\zeta }_2=0.017\mathrm{}\pm 0.003$ Å. This implies that the ${\mathrm{Li}}^{+}$ appear to be displaced upwards from the crystal surface by 0.036±0.006 Å.

The electronic wave function of ${\mathrm{Cr}}^{5+}$ ($3d^1$) in K${\mathrm{H}}_2$As${\mathrm{O}}_4$ and K${\mathrm{H}}_2$P${\mathrm{O}}_4$ is identified as $d_{x^2-y^2}$. Its symmetry property in the hydrogen-bonded tetrahedron allows a rotational motion of $d_{x^2-y^2}\perp c$ which breaks the symmetry in the Halperin-Varma sense. We show that its local coupled relaxation time is one order of magnitude longer than the slow ferroelectric cluster dynamics which can be identified with the same center independently and that the motion perpendicular to the $c$ axis must be the cause.

X-ray photoelectron spectra of rare-earth borides exhibit systematic variations of the $4f$ lifetime width with the rare-earth number across the series, with the $4f$ binding energy, and with the number of boron neighbors. Valence band spectra and theoretical band structures make it possible to understand these observations in terms of an interatomic Auger process, here a $5d\to 4f$ recombination, with simultaneous excitation of an electron-hole pair from boron $2sp$ states.

We report the discovery of a new method for the generation of light. This technique yields a broad-band light source with a high frequency linear cutoff which is dependent only upon the applied voltage through the quantum relation $h{\nu }_{\mathrm{co}}=\left|\mathrm{eV}\right|\mathrm{}$. The light source consists of a metal-insulator-metal tunneling junction. The effect can be interpreted in terms of inelastic tunneling excitation of optically coupled surface plasmon modes.

The present experimental determination of the pressure dependence of $T_N$ establishes that in Cr-alloys richer than about 1.35 at.% Si, the transition is to a commensurate phase. This can be rationalized only if Si acts as an electron donor to the Cr $d$ band and if it goes interstitially into the Cr lattice. The magnetic phase diagram ($P-T_N$) for Cr-Si alloys has been determined.