By using stepwise excitation in an atomic beam, we have excited slow-moving atoms to pure high-lying quantum states at densities low enough to avoid loss by collision. The atoms were detected with high efficiency by Stark ionization. Results are presented of a study of the threshold field for ionization for $s$ states of sodium with principal quantum number $n$ from 26 to 37.

We elucidate the kinetic process of plasma heating by the resonant excitation of the shear Alfvén wave. The heating occurs as a result of the damping of the modified (by the finite ion Larmor radius and electron inertia) Alfvén wave which is excited by mode conversion at the resonant layer. The heating rates of ions and of electrons are comparable in the collisional regime; otherwise electrons are predominantly heated.

We propose an approximate but simple and general procedure for treating resonance broadening in weak-turbulence interactions. The resonance-broadening corrections to the wave-particle, wave-wave, nonlinear-Landau-damping, and four-wave weak-turbulence equations are computed as examples. The procedure may be used to predict at the outset whether resonance broadening occurs in a specific higher-order process.

We report calculations which suggest that there is a physically important four-atom exchange process in bcc ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and thus an important four-spin term in the exchange Hamiltonian. A simple, mean-field analysis of this Hamiltonian appears to account for a number of the perplexing properties of bcc ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. An understanding of other properties may require treatment of the exact four-spin term. It is our hope to stimulate such effort by this Letter.

A nearly-free-electron model for explaining the relative stability of some metallic alloys against crystallization is proposed. Arguments are presented which show that in an alloy the maximum stability corresponds to the composition for which the Fermi level lies at a minimum of the density of states. In this case any small enough perturbation around this configuration will increase the total electron energy. This approach predicts the correct composition range of metal glasses.

The magnon dispersion curve of Gd metal has been determined from first principles by use of augmented-plane-wave energy bands and wave functions. The exchange matrix elements $I(\overrightarrow{\mathrm{k}}, {\overrightarrow{\mathrm{k}}}^{\prime })$ between the $4f$ electrons and the conduction electrons from the first six energy bands were calculated under the assumption of an unscreened Coulomb interaction. The results are in good overall agreement with experiment provided the $I(\overrightarrow{\mathrm{k}}, {\overrightarrow{\mathrm{k}}}^{\prime })$ are diminished by a constant scale factor of about 2 which may be caused by screening.

We have determined the extent of residual inhomogeneous broadening in the "sharp" mixed-crystal spectrum of the large organic molecule pentacene; and we report a technique for the direct fluorescence measurement of excited-vibrational-state bandwidths. We have found the lifetime of the 267-${\mathrm{cm}}^{-1\mathrm{}}$ vibronic band in pentacene to be greater than 0.2 nsec.

High-angular-resolution (∼8×${10}^{-6\mathrm{}}$ rad), high-energy (75 keV), electron scattering from graphite thin films demonstrates energy losses due to the excitation of optical surface guided modes. Measurements of the dispersion offer considerable support for the anisotropic dielectric constant proposed by Tosatti and Bassani.

High-angular-resolution (∼8×${10}^{-6\mathrm{}}$ rad), high-energy (75 keV), electron scattering from graphite thin films demonstrates energy losses due to the excitation of optical surface guided modes. Measurements of the dispersion offer considerable support for the anisotropic dielectric constant proposed by Tosatti and Bassani.

Strongly anisotropic magnets at low temperatures with many (quenched) nonmagnetic impurities are shown to deviate from usual dynamical scaling assumptions near the critical concentration; instead of the time, the logarithm of the time is the basic variable. Analysis of previous Monte Carlo data confirms the static droplet picture used here, which fulfills for the first time the homogeneity, analyticity, and symmetry requirements of static scaling.

The magnetic orientation of native and synthetic nucleic acids has been observed for the first time by measuring the Cotton-Mouton effect in magnetic fields $B$ up to 14 T. Our data give evidence that a partial alignment of the nucleic acids takes place in the plane perpendicular to $B$ and that the diamagnetically anisotropic bases are responsible for this orientation. The method reported here represents a new way to determine the persistence length of flexible polymers.

Excitation functions of the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^{12}{}_{}{}^{}\mathrm{C}, p){}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ reveal a distinct set of resonances in the ${\frac{11}{2}}^{+}$, ${\frac{13}{2}}^{+}$, (${\frac{15}{2}}^{+}$), and (${\frac{17}{2}}^{+}$) members of the ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ $K^{\pi }={\frac{3}{2}}^{+}$ ground-state band near $E_x\left({}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}\right)=25.2, 28.2, \mathrm{and} 33.3$ MeV. These plus earlier data suggest the possible existence of an excited collective band in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ with very high deformation and large ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ width.

The ($d$, ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$) $\alpha$-transfer reaction on several even-$A$ and odd-$A$ tin isotopes has been investigated at $E_d=35\mathrm{}$ MeV. A significant reduction (∼ factor 2) in transition strength is observed for the odd-$A$ target nuclei. This reduction is attributed to the "blocking" effect of unpaired nucleons and is comparable to that observed in ($p, t$) reactions.

Chlorine ions at 70 and 140 MeV energy impinge upon ∼1-μg/${\mathrm{cm}}^2$ Cu targets, in one case after emerging from a carbon prefoil and in the second striking Cu on the back side of a carbon foil. The latter approach leads to an appreciable increase in the Cu $K$ x-ray yield, an effect which is explained in terms of residual Cl $K$-shell excitation and which is in accord with a simple model of competing rearrangement processes.

Quantum beats have been observed in both linear- and circular-polarized light using a beam-tilted-foil geometry for the $3s{}_{}{}^3{}_{}{}^{}S-3p{}_{}{}^3{}_{}{}^{}P$ transition of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ iv. Beats between the $F=0\mathrm{}$ and $F=1\mathrm{}$ hyperfine levels—forbidden in the case of excitation by untilted foils—were observed. A value of $A=695\mathrm{}\pm 15$ MHz was obtained for the hyperfine coupling constant of the upper term.

The half-width of the leakage aperture of plasma through a low-$\beta$ line cusp is found to be twice the hybrid gyroradius ${\left(r_e{r}_i\right)}^{\frac{1}{2}}$ with $r_e$ and $r_i$ as the electron and ion gyroradii. This steady-state width is shown to develop in a time less than the ion gyroperiod.

Velocity distributions of the electrons have been measured by a Thomson-scattering method with an eight-channel polychoromator in the initial stage of a linear turbulent-heating experiment. Flat-top distributions were observed associated with high-frequency fluctuations ($\omega \lesssim {\omega }_{\mathrm{pi}}$) just before the onset of fast heating of the electrons. Those results were compared with computer simulations and theoretical analysis based on quasilinear process.

Experimental and theoretical studies of the nonresonant lower-hybrid beam-plasma instability have been carried out. The instability has a maximum growth rate when the phase velocity of the wave along the magnetic field lines is comparable to the electron thermal velocity. Electron heating associated with this instability has also been observed.

The isomorphic phase transition in the system ${\mathrm{Ce}}_{1-x}{\mathrm{Th}}_x$, which is characterized by a delocalization of the $4f$ electron and a concomitant volume change, has been studied through measurements of the density and resitivity. For samples near the critical composition ($x\simeq 0.264$) derivatives of these quantities diverge with mean-field exponents. Such mean-field behavior implies a long-force range, and suggests that electroelastic coupling dominates the critical behavior.

Tracer diffusion data in the literature for HTO and DTO in both liquid ${\mathrm{H}}_2$O and ${\mathrm{D}}_2$O are interpreted in terms of a general equation usually employed to explain the isotope effect in solids. The results appear to be consistent with the stereo pictures of the time-dependent structure of liquid water which emerge from the molecular-dynamics study of Rahman and Stillinger.