It is shown that a singularity appears in the velocity-correlation function of a classical fluid in equilibrium at time equal to zero when a smooth interparticle potential tends to the hard-sphere potential.

Parametric excitation of the magnetostatic mode by finite-amplitude drift waves is considered. Both decay and modulational instabilities are analyzed. Expressions for the growth rates are obtained analytically. Application of our results to electron cross-field diffusion in tokamak devices is also discussed.

This paper presents an investigation of the nonlinear interaction of a Gaussian electromagnetic (EM) beam with an electrostatic ion-cyclotron wave in a collisionless hot magnetoplasma. The EM beam is assumed to be propagating perpendicular to the static magnetic field in the ordinary mode. On account of the Gaussian intensity distribution of the EM beam in a plane, transverse to the direction of propagation, a dc component of the ponderomotive force becomes finite and leads to the modification of the background electron and/or ion density. This leads to the coupling of the electrostatic ion-cyclotron wave with the pump EM beam. This coupling is so important that it may lead to the focusing of the electrostatic ion-cyclotron wave and under certain conditions may lead to Brillouin scattering of the EM beam.

A model for systems interacting via soft inverse-power potentials enables one to express the bridge function at the origin, $B\left(O\right)\mathrm{}$, directly in terms of the equation of state, and to find its physical meaning. The Lindemann, Ross, and van der Waals empirical melting criteria are unified by the empirical finding that $B\left(O\right)\mathrm{}$, calculated along the freezing line, is nearly independent of the pair potential and is nearly the same in two and three dimensions.

We have determined the mean charge $\overline{q}$ for projectiles $5\le Z_1\le 25$ exiting thin Al foils at a velocity $v=v_0$. The results are compared with previous data for the same projectiles exiting thin C foils. In the region $Z_i\sim 15$, the differences $\overline{q}\left(\mathrm{C}\right)-\overline{q}\left(\mathrm{A}l\right)$ are observed to be as large as solid-gas differences.

The long-wavelength diffusion involved in spinodal decomposition in the critical region depends upon transport of the concentration fluctuations by the hydrodynamic shear modes. As spinodal decomposition advances the concentration fluctuations become peaked at some wave number $k_0$. We demonstrate here that the Onsager coefficient for such a fluid is also strongly wave-number dependent and develops a logarithmic singularity at $k_0$. This will tend to enhance and speed up the spinodal decomposition and will significantly affect the comparison of theory with experiment.

Measurements of longitudinal ultrasonic absorption in a concentrated aqueous solution of the bile salt sodium deoxycholate at different temperatures enable a better characterization of the exhibited viscoelasticity. An analysis of the data in the viscoelastic region shows that the dynamic shear viscosity follows a temperature and concentration superposition principle and that the volume viscosity is small. Such conclusions support a previously suggested possibility of polymerization of the small "primary" micelles observed at low concentration.

A time-related study of relativistic-electron-beam (REB) interactions with thin targets, 5-μm gold, and 75 and 6-μm Mylar, was carried out from experimental data on anode and cathode voltage and transmitted current. REB absorption by a thin target is reflected by a variable drop in transmitted current. The use of a code to simulate the slowing of electrons in the material serves to show that for the nearest possible voltage and current input parameters, no significant difference is observed between REB—5-μm-gold-target and REB — 75-μm-Mylar-target interaction. However, a current transmission defect was observed with the thinner Mylar films.

The virial theorem for bound, virtual, and resonance states is derived, based on the virial theorem for scattering states proved by Demkov. The association of the complex virial theorem with Demkov's virial theorem is discussed.

Recently, Dash and Patnaik proposed some analytic functions as solutions for the diatomic Toda lattice. It is shown that these functions are not solutions for the classical equations of motion of the diatomic Toda lattice. The exact solutions for small wave numbers are given.

A numerical study is made of the decay of statistical dependence in chaotic orbits of the iterated mappings of Chirikov and of Rannou. The decay appears to be exponential; the decay exponent is proportional to, but smaller than, the Liapunov exponent.

It is shown that any time-dependent description of quantum systems derived from the variational principle is equivalent to Hamilton's description of a classical system. This is done by establishing the fact that the Euler's equations from the variation of the wave function in any parametrization can be transformed to a system of Hamilton's equations. The problem of obtaining collective dynamical variables in quantum many-body systems is discussed in the light of this equivalence.

Wall stabilization of the free boundary $n=1\mathrm{}$ magnetohydrodynamic modes of the spheromak has been studied numerically. Line tying of the open field lines has been found to improve stability dramatically. The dependence of stability on separatrix shape and current profile has also been determined.

The effects of boundaries are studied in a new calculation of three-dimensional magnetohydrodynamic turbulence in a reversed-field pinch configuration. Our model, which assumes a Gibbs distribution of the turbulent fields, predicts magnetohydrodynamic fluctuations about a Bessel-function-model mean magnetic field. The effects of these fluctuations can be seen in a calculable field autocorrelation tensor.

The birefringence in mixtures of 4-cyano-4′-octyloxybiphenyl (80CB) and 4-cyano-4′-hexyloxybiphenyl (60CB) has been studied near the nematic—to—smectic-$A$ ($\mathrm{NA}$) and smectic-$A$—to—reentrant-nematic ($A{N}^{\prime }$) transitions. There is an overall increase in the birefringence at the $\mathrm{NA}$ transition and an overall decrease at the $A{N}^{\prime }$ transition. The birefringence change at the transitions decreases with increasing concentration $x$ of 60CB and vanishes at $x=0.28\mathrm{}$. The birefringence and the transition enthalpy behave similarly.

The first direct radiative lifetime measurements in W I are described. Radiative lifetimes of 15 levels from the $5d^{4}6s\left(a{}_{}{}^6{}_{}{}^{}D\right)6p\left(z{}_{}{}^7{}_{}{}^{}D_{}^0{}_{}{}^{}\right)$, $5d^{4}6s\left(a{}_{}{}^6{}_{}{}^{}D\right)6p\left(z{}_{}{}^5{}_{}{}^{}F_{}^0{}_{}{}^{}\right)$, $5d^5\left(a{}_{}{}^6{}_{}{}^{}S\right)6p\left(z{}_{}{}^7{}_{}{}^{}P_{}^0{}_{}{}^{}\right)$,, and $5d^{4}6s\left(a{}_{}{}^6{}_{}{}^{}D\right)6p\left(z{}_{}{}^5{}_{}{}^{}P_{}^0{}_{}{}^{}\right)$ terms are reported with an accuracy of ±5%. The lifetimes are measured using time-resolved laser-induced fluorescence and a novel atomic-beam source. This novel hollow cathode effusive beam source produces an intense beam of ground-state W atoms and metastable W atoms.

Jancovici's recent exact analysis of the two-dimensional one-component plasma is extended to include a constant surface charge density on the system. The density profile away from the boundary is evaluated exactly in the thermodynamic limit as a function of bulk particle and surface charge densities at the temperature $T=\frac{q^2}{2k_B}$, where $q$ is the particle charge.

Cross sections are calculated for the process $\mathrm{K}\left(4^{2}P\right)+\mathrm{Mu}\to \mathrm{K}\left(4^{2}S\right)+\mathrm{Mu}$ at impact energies from 4 meV to 0.5 eV. The deexcitation probability in a Mu collision is greater than that in an H collision at the same relative translational energy and impact parameter by over four orders of magnitude.

Measurements are reported of the quantum fluctuations in superfluorescence delay times. The fluctuations depend strongly on the Fresnel number $F$ of the sample. For $F\approx 1$ fair agreement with recent theories is obtained, while for larger $F$ the fluctuations are smaller. A qualitative explanation for this $F$ dependence is proposed. No correlation has been found between the delay times of pulses emitted from opposite ends of the same sample.

Measurements of electron cyclotron radiation near the fundamental frequency on the high-and low-magnetic-field side of the TFR tokamak are reported. In the presence of a superthermal electron component the measured intensities are asymmetric. A theoretical explanation based on the combined effects of the electron relativistic mass variation and the $\frac{1}{R}$ variation of the tokamak magnetic field is discussed.