Numerical methods are used to investigate absorption of either intense or weak electromagnetic waves obliquely incident on a nonuniform plasma with and without the presence of a dc magnetic field. The numerical formulation includes the full set of Maxwell's equations and three moments of the Boltzmann equation with a ponderomotive-force description. The investigation includes a study of the reflection and absorption of the incident wave as a function of angle of incidence as well as the complex electric and magnetic fields, electron-flow, dc magnetic field generation, and kinetic energy gained by resonant electrons within the plasma. Selected field snapshots are directly compared to particle-simulation predictions where a thousandfold reduction in computation time allows a detailed investigation of the wave-plasma interaction for laser wavelengths.

The stability of stationary envelope waves (one- and two-dimensional cases) has been analyzed based on a perturbation method similar to that of Schmidt. The cylindrically symmetric envelope wave is found to be stable to an $s$-state perturbation with a negative dispersion in a cubically nonlinear medium. However, the envelope wave is unstable to a $p$-state perturbation under the same conditions.

The profiles of the Balmer lines emitted in a laser-produced plasma by the ions ${\mathrm{B}}^{4+}$ to ${\mathrm{F}}^{8+}$ have been observed. For the Balmer-$\alpha$ line the fine-structure components are broadened and partially merged by the Stark effect, the thermal Doppler broadening, and the motional Doppler shift. To these lines a simplified model for an expanding plasma, used previously for the analysis of the Lyman lines of the same ions, has been applied. The results are in very good agreement with the observations, showing the overall validity of the interpretation. The various broadening mechanisms have been unfolded and in particular for the range of electron densities considered here a transition between the weak- and strong-field approximations for the Sark broadening is evident.

Critical phenomena in a fluid mixture near the consolute point have been investigated with the use of an ultracentrifuge. This method provides an opportunity to determine both dynamical and static properties of the system. The sedimentation and diffusion coefficients have been measured and a huge sedimentation effect has been observed with the coefficient $s$ diverging as ${(T-T_c)}^{-1\mathrm{}\pm 0.1}$ while approaching the critical point. The susceptibility $\frac{\partial c}{\partial \mu }$ has been measured in a wide range of concentration variations. The results confirm scaling theory. Some nonlinear effects, including an instability of the mixture close to $T_c$, have been observed.

Molecular-dynamics calculations are reported for binary mixtures of ions of like charge in a uniform neutralizing background. For a system simulating the mixture ${\mathrm{H}}^{+}$-${\mathrm{He}}^{2+}$ the calculations show that the spectrum of charge fluctuations is dominated by a propagating plasmon mode with a lifetime which is finite even in the long-wavelength limit. At high charge densities there is an additional low-frequency contribution to the spectrum; this is shown to arise from a coupling between charge fluctuations and fluctuations in mass density. The results are in satisfactory agreement with a simple hydrodynamic calculation, though it appears that in practice the hydrodynamic limit is never fully attained; it is also found that a memory-function approach incorporating the coupling of mass and charge gives a good description of the collective dynamical modes at high charge densities.

The authors examine the accuracy of the WKB approximation used in previous work to compute soliton free energies at low temperatures; this examination is crucial in establishing the validity of a simple physical phenomenology as an alternative to the transfer-operator method of calculation. For the ${\phi }^4$ and double sine-Gordon potentials a method developed by Goldstein (1929) is adapted which is known to give correct results in the sine-Gordon case. For all three potentials, the WKB approximation is in error by the factor ${\left(\frac{e}{\pi }\right)}^{\frac{1}{2}}$.

Photon echoes generated from visible transitions in the noble gases helium, neon, and argon are observed and the collisional relaxation rates are measured. The photon echoes are excited on transitions initiating from metastable states which are populated by electron impact in an rf discharge. The photon-echo intensity is measured as a function of time after the discharge is turned off and as a function of gas pressure. The reduction of the echo intensity in these two experiments is attributed to relaxation of the metastable population in the afterglow and dephasing collisions, respectively. The dependence of the photon-echo damping time on transition wavelength and perturber gas is interpreted by means of a simple van der Waals model for the excited-atom and perturber-gas interaction.

One of the results of recent interesting calculations on electron states in the rare-gas fluids has been reinterpreted and verified by experiment. The extent of electron quasilocalization in dense argon gas near the critical region is less than that in xenon at the same relative density $\frac{n}{n_c}$ and temperature $\frac{T}{T_c}$.

The oscillator strengths for the $4s^2{}_{}{}^1{}_{}{}^{}S-4s4p{}_{}{}^1{}_{}{}^{}P$ resonance line in the ZnI isoelectronic sequence have been obtained for GaII, GeIII, and AsIV by means of lifetime measurements utilizing beam-foil spectroscopy at low initial ion energies. The energy dependence of the emission cross sections for the resonance transition and for the main cascades populating the resonance state in GaII exhibit significantly different energy dependence, which allows an elimination or strong reduction in the influence of the cascades by performing the lifetime measurements at low initial ion energies, for GaII at 100-150 keV. The experimental oscillator strengths are in good agreement with recent calculations by Froese-Fischer and Hansen.

Acoustic wave generation is induced in the afterglow of a weakly ionized helium plasma by the presence of a uniform axial magnetic field. Acoustic wave oscillations are generated at a gas pressure as low as 0.04 Torr by the application of an axial magnetic field of strength equal to 75 G.

In the interference region of two electron waves the current density oscillates in time, but no photons are emitted. Therefore these "beats" cannot be used to operate a free-electron laser, contrary to a recent claim.

An ac current originating from the "beating" of two beams of electrons originating from the same source will radiate at the same frequency as any other ac current would radiate.

A recent proposal by H. Schwarz is analyzed. General principles of quantum mechanics are used to limit the possibilities for radiation from beats in an electron beam.

The internal and free energies of a two-dimensional one-component plasma model, in the high-temperature Debye approximation, are reinvestigated, and a domain of validity for this model is discussed.

The results of a molecular-dynamics calculation of the two-body correlation function relevant to depolarized light scattering within the dipole-induced-dipole (DID) model are presented for argon at a density (62 amagat) which is a true low-density limit. The comparison with the memory-function approach and the analysis of the ${sech}^2\mathrm{}\left(x\right)\mathrm{}$ termination is discussed. The theoretical analysis is also applied to recent experiments.

The authors question the suggestion that plasmon dispersion increases for small values of the coupling over its random-phase-approximation value, and conclude that, contrary to what has been stated in the literature, it does not: high-frequency-moment sum-rule and Kramers-Kronig arguments, when properly treated, do not entail such a consequence.

In this paper a theorem is proved which shows that a physical system with an inner-shell vacancy corresponds to the saddle-point energy solution in the Rayleigh-Ritz variation method if the vacancy is built explicitly into the wave function. This enables us to calculate the inner-shell-vacancy states of a many-body system from first principles. This method is very easy to use and should be applicable to many areas of physics.

The probability $P_{\mathrm{KK}}$ of double-$K$-shell-vacancy creation per $K$-electron-capture decay of ${}_{}{}^{103}{}_{}{}^{}\mathrm{Pd}$ has been determined by means of a $K\alpha$-x-ray—$K$-x-ray coincidence experiment: $P_{\mathrm{KK}} =(3.13\mathrm{}\pm 0.31)\times {10}^{-5\mathrm{}}$. The energy shift of the hypersatellite Rh $K{\alpha }_1^H$-x-ray line was found to be 512±10 eV.

The authors have made extensive new measurements in Rydberg ($n=6-11\mathrm{}$) $D$, $F$, and $G$ states of helium. The new data represent over 1100 individual resonance scans, totalling some 2200 h of data-collection time. In order to perform such a large number of runs, data logging has been automated by interfacing a microcomputer to an apparatus previously used to make fine-structure measurements in one- and two-electron atoms. An exhaustive analysis of possible systematic line-center shifts, including black-body radiation effects, was carried out. The root-mean-square one-standard-deviation experimental uncertainty is 294 kHz for our 67 measurements. The large quantity of new measurements has allowed us to perform a global least-squares fit to all existing state-resolved data in $D$, $F$, and $G$ states. The complete structure of the $D$, $F$, and $G$ manifolds is now known for $n\ge 6$ to a precision of a few megahertz or better. Current theoretical calculations for a typical (30-GHz) interval differ from the measurements by 6×${10}^{-8\mathrm{}}$ a.u., or over 1000 experimental standard deviations.