It is shown that for systems developing stationary periodic patterns there exists at most one stable wavelength state if a supercritical region is connected to a subcritical one by the imposition of a slow spatial variation of the external parameters. In nonpotential systems the selected wavelength depends on the particular combination of parameters that vary but not on the (slow) rate of spatial variation. Suitable parameter variations force the system into a dynamic state.

Molecular-dynamics calculations for interacting waterlike particles are used to estimate values of percolation exponents. Results are consistent with accepted values for ordinary random-bond percolation for a three-dimensional lattice. Study of a correlated-site percolation problem, defined by the connectivity of those water molecules that are four-coordinated, shows no evidence for different exponents. Thus there is no obvious basis for the frequent criticisms against the application of lattice percolation models to describe continuum correlated systems such as polymer gels.

It is shown that inclusion of the $D$ state of the alpha particle in the distorted-wave amplitude for ($\alpha , d$) reactions causes a strong $J$ dependence. The $S-D$—state interference is destructive for transitions with natural-parity $J$ transfers and constructive for unnatural-parity $J$ values, thus causing, for example, an odd-even staggering in the variation with $J$ of the cross sections for exciting the states of a given multiplet. This provides a possible explanation for recent observations on the reaction ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}(\alpha , d){}_{}{}^{210}{}_{}{}^{}\mathrm{Bi}$. A similar $J$ dependence is predicted for (${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, $\alpha$) reactions.

A calculation of the $\rho$-meson self-energy in nuclear matter with use of realistic interactions is presented. No collective effects as predicted by Toki and Comfort are observed. This discrepancy is traced back to their use of a strong $\rho$ exchange. An analysis of realistic interactions (Reid, Bonn, Paris) shows that $\mathrm{NN}$ phase shifts uniquely specify a weak effective $\rho$ exchange for momentum transfers up to 3 ${\mathrm{fm}}^{-1\mathrm{}}$.

The first results of direct measurements of heavy-ion reaction cross sections, ${\sigma }_R$, with use of the beam attenuation method are reported. For the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ system ${\sigma }_R$ was measured at three incident energies, 112, 360, and 996 MeV. The data show deviations from the geometrical reaction cross section and agree with recent theoretical predictions based on Glauber theory.

Angular distribution of alpha particles with respect to the spin direction of residual nuclei from fusion of 176-MeV ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ with ${}_{}{}^{150}{}_{}{}^{}\mathrm{Nd}$ has been measured with the spin spectrometer. Below the Coulomb barrier, the ratio of the 90° to 0° yields with respect to spin direction increases with decreasing $E_{\alpha }$. This effect is not shown by a statistical-model calculation using penetrabilities for spherical potentials, which suggests that the $\alpha$-mitting nuclei are deformed with their longest axis perpendicular to the spin direction. If so, the deformation increases as the spin rises from ∼ 34 to $64\hslash$.

Laboratory experiments on collision-induced emission are reported. The light source is hydrogen-argon mixtures, shock heated to temperatures up to 2850 K and densities up to 49 amagats in a shock tube. For the fundamental vibration-rotation band of ${\mathrm{H}}_2$, absolute intensity, band strength and shape, and the dependence on temperature and density have been determined.

A theory of stimulated emission of bremsstrahlung by an electron experiencing a sequence of collisions is presented. It is shown that amplification of the electromagnetic wave is greatly enhanced by an accumulative effect developed in that sequence. Calculations for the values of the amplification are in good agreement with measurements made for electromagnetic millimeter-wave radiation.

An exact analytic solution of the scalar wave equation in a rotationally symmetric focused-Gaussian-amplifying medium is constructed from coupled Gaussian-Laguerre solutions of the free-space wave equation. The solution allows for the analytic construction of the characteristic eigenmodes of the system and has direct application to Raman, dye, and free-electron lasers.

An experimental study of the fluctuations of a millimeter-wave transient Rydberg-atom maser is presented. The photon-number probability distribution is shown to evolve in time from a Bose-Einstein to a bell-shaped distribution. The experiment is a quantitative check of single-mode superradiance theory.

Optical tristability via optical pumping has been observed in the transmission of a Fabry-Perot interferometer containing Na vapor irradiated by light from a cw dye laser on the high-frequency wing of the $D_1$ line. For linearly polarized incident light, three stable states appear in the polarization of the transmitted light: ${\sigma }_{+}$ dominant, ${\sigma }_{-}$ dominant, and linear polarization.

The first consistent calculation of the plasmon linewidth and frequency shift due to the electron-ion density correlations is presented for dense plasmas, relevant to inertial-confinement fusion and astrophysics, in which electrons are strongly degenerate. It is found that the plasmons in the dense matter are strongly damped, so that a substantial absorption is expected near the plasmon line; the frequency shift, on the other hand, turns out to be relatively small.

Electron heat transport is studied by numerically solving the Fokker-Planck equation, with a spherical harmonic representation of the distribution function. The first two terms ($f_0, f_1$) suffice, even in steep temperature gradients. Deviations from the Spitzer-Härm law appear for $\frac{\lambda }{L_T}\left[\right(\mathrm{mean}\mathrm{free}\mathrm{path})/(\mathrm{temperature}\mathrm{gradient}\mathrm{length}\left)\right]\gtrsim 0.01$, as a result of non-Maxwellian $f_0$. For $\frac{\lambda }{L_T}\gtrsim 1$, the heat flux is $\frac{1}{3}$ of the free-streaming value. In intermediate cases, a harmonic law describes well the hottest part of the plasma.

An analytical method is developed for the investigation of the nonlinear state resulting from instability saturation by resonant mode coupling.

Raman scattering spectra obtained with 20-psec 1.064-μm laser pulses incident at 45° on nickel-foil targets show an intensity-dependent red shift relative to the subharmonic of the laser frequency. In conjunction with temperature data deduced from x-ray measurements, the results imply a change from the absolute to the convective instability with increasing intensity. The observation of Raman scattering is correlated with the appearance of a high-energy tail in the x-ray spectrum above 100 keV.

A system has been discovered in which the characteristic energies of a valence instability and a magnetic ordering instability can be brought into parity. This leads to a novel phase diagram where a line of second-order magnetic transitions terminates at a line of first-order valence transitions which, in turn, terminates at a critical point. Microscopic Mössbauer-effect measurements of the order parameters across both magnetic and valence instabilities, along with bulk magnetic susceptibility measurements, are presented.

This paper reports observation, in a mixture of potassium palmitate-$d_3$, potassium laurate, and water, of a lamellar phase above 41°C, a phase of elongated cylindrical aggregates below 36°C, and, in the intermediate temperature region, a phase in which the ${}_{}{}^2{}_{}{}^{}\mathrm{H}$-NMR spectral patterns can be calculated from a model of elongated ribbon-shaped aggregates. The size of the ribbons can be determined from the spectra and is found to vary with temperature. The results are consistent with ${}_{}{}^2{}_{}{}^{}\mathrm{H}$-NMR spectra of ${}_{}{}^2{}_{}{}^{}\mathrm{H}$${}_2{}^{}{}_{}{}^{}\mathrm{O}$ in the same and other ternary mixtures.

Laser-induced periodic structure on solid surfaces can be understood as a universal phenomenon which occurs for a broad range of wavelengths and different laser polarization states in both polariton-active and -inactive media. Circularly polarized light has been used, for the first time, to generate periodic structures; these show an interesting dependence on the sense of rotation.

The authors have studied whether numerically generated sequences from the logistic parabola $f_b\mathrm{}\left(x\right)=4\mathrm{bx}(1-x)\mathrm{}$ with $b$, $x\in \mathrm{}[0,1]\mathrm{}$, for values of $b$, above the Feigenbaum critical value $b_{\infty }$, are truly chaotic or whether they are periodic but with exceedingly large periods and very long transients. Using the logistic parabola the authors calculate via Monte Carlo simulation the average walk length for trapping on a one-dimensional lattice with a centrosymmetric trap. Comparison with exact results suggests that the only "truly chaotic" sequence is the one for which $b=1\mathrm{}$.

Correlations of linear polarizations of pairs of photons have been measured with time-varying analyzers. The analyzer in each leg of the apparatus is an acousto-optical switch followed by two linear polarizers. The switches operate at incommensurate frequencies near 50 MHz. Each analyzer amounts to a polarizer which jumps between two orientations in a time short compared with the photon transit time. The results are in good agreement with quantum mechanical predictions but violate Bell's inequalities by 5 standard deviations.