A detailed account is given of the x-ray spectroscopic diagnosis of plasmas formed by exploding pusher microballoons. The measurements of the electron temperature from the shell and from the core is described. A method for self-consistently fitting all the observed lines of one state of ionization is shown, giving a diagnosis for the electron density and the opacity. Further, it is shown that the self-consistency is only achieved when full line-broadening calculations, taking into account the shifts and asymmetries dependent on the charge of the emitter, are used for the optically thin profiles. It is also shown that non-local-thermodynamic-equilibrium effects are important in the description of the radiation transfer.

Approximate analytic solutions are given for several equations obtained from a similarity analysis of the nonlinear diffusion equation ${\rho }_t-\overrightarrow{\nabla }·\left(D\overrightarrow{\nabla }\rho \right)=0\mathrm{}$, where the diffusion coefficient $D$ is of the form $D\sim {\rho }^n$. The solution technique is also demonstrated for a case where $D$ is inhomogeneous as well as nonlinear ($D\sim r^{\gamma }{\rho }^n$, where $r$ is the radial coordinate). The approach is general, algebraically simple, and flexible enough to allow applications to many related problems. The analytic predictions are compared to previous numerical results for some cases and shown to yield good agreement.

In this paper we report on the observation of characteristic "steps" in the continuum spectrum of high-temperature tokamak plasmas associated with recombination radiation from impurity ions. During special argon-seeded discharges on the Princeton Large Torus tokamak the x-ray spectrum exhibited large enhancements over the bremsstrahlung continuum beginning with energies of 4.1 keV. This corresponds to the radiative capture of free electrons by hydrogenlike argon into the ground state of heliumlike argon. The size of these edges increased to unexpectedly large values with minor radius (decreasing electron temperature), consistent with a departure of the hydrogenlike species from the predictions of corona equilibrium. Hence, the coronal equilibrium equations must be modified to account for the radial transport of argon. A simple particle diffusion model is proposed, with the Ar XVIII radial profiles evaluated from the size of the recombination edges. For the case of moderate density ($〈n_e〉\sim 3\times {10}^{13}$ ${\mathrm{cm}}^{-3\mathrm{}}$) and temperature ($T_e\mathrm{}\left(0\right)\mathrm{}\sim 1.5$ keV) discharges the outward radial transport velocity is found to be approximately 10 m/sec.

Adsorption of a dense film on a weakly attractive substrate is studied using a lattice-gas model in the mean-field approximation. The model and method of solution are much the same as those employed by de Oliveira and Griffiths. In the present theory, the particles of the gas interact via either a Lennard-Jones (6-12) potential or a nearest-neighbor potential, and a gas particle interacts with the substrate through a (9-3) potential. For sufficiently weak substrate potentials no film is found. For sufficiently strong ones a film forms and grows with increasing vapor pressure or chemical potential either continuously or in one-atomic-layer steps as found by de Oliveira and Griffiths. For potentials of intermediate strength, there is a discontinuity in the film thickness from a partial layer to an arbitrarily large number of layers, depending on the temperature, as the vapor pressure is increased. The phase diagram in these cases is strikingly similar to that found by Ebner and Saam from a density-functional theory of nonuniform fluids; there is, however, a sizable difference in the substrate potential strengths at which the large discontinuity in film thickness appears.

We propose a general framework for the study of the first-order transition in monolayers of amphiphilic molecules. We introduce the variation of internal molecular parameters versus density and temperature. We obtain an asymmetry of the coexistence curve with a ($T_c-T$) power law. With a simple model we find results in good qualitative agreement with the experimental results of Won Kim and Cannell. In conclusion, we examine also the coexistence curves of monolayer with two polar-head molecules.

Generalized oscillator strengths (GOS) for inner-shell bound-bound transitions in an ion are evaluated using an analytic perturbation theory for screened Coulomb potentials. Simple analytical expressions are obtained for the momentum-transfer dependence of the GOS for an ion of nuclear charge $Z$. These formulas may be useful in characterizing transitions in highly ionized medium-$Z$ and high-$Z$ atoms in hot dense plasmas. As an illustration of the method, results are presented for $K-L$ transitions in an Fe impurity atom in a hydrogen plasma. Good agreement is found with numerical calculations for the same transitions.

The basis for a density-functional theory of inhomogeneous electron systems at finite temperatures is a suitable exchange-correlation potential. A local potential is presented here for a wide range of densities and temperatures based on the first-order exchange and sum of ring diagrams for the interacting homogeneous electron gas. The validity of this scheme in the different temperature-density regions is discussed. It is found that the correlations dominate over the first-order exchange contributions over a wide range of temperatures for a given density.

A strong steady dense-fluid shock wave is simulated with 4800-atom nonequilibrium molecular dynamics. The resulting density, stress, energy, and temperature profiles are compared with corresponding macroscopic profiles we derive from Navier-Stokes continuum mechanics. The differences found are relatively small.

Long-wavelength thermal fluctuations in a fluid with a linear shear are investigated. Certain equal-time correlations are found to have a long-range part. The dynamic structure factor is modified in such a way that the Landau-Plazcek ratio no longer holds. A light-scattering experiment is proposed to test some of these results.

We use two methods to obtain contributions through order ${\gamma }^3$ ($\gamma$ being the plasma parameter) to the pair correlation, three-particle correlation, and four-particle correlation functions of a one-component classical plasma. The first approach is through the conventional perturbation expansion of the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy, the second, which is new, relies upon a chain of generalized nonlinear fluctuation-dissipation theorems in terms of response functions of increasing nonlinearity. Our results to order ${\gamma }^1$, ${\gamma }^2$, and ${\gamma }^3$ for the three-particle correlation function reproduce earlier findings obtained by other methods; the order ${\gamma }^3$ contributions to the three-particle and four-particle correlation functions are new results.

In this communication the authors have investigated the generation of lower hybrid electrostatic wave at the difference frequency of two microwaves (having either uniform or Gaussian intensity distribution). A two-fluid model of the plasma along with Maxwell's equations has been used to obtain expressions for the intensity and power of the excited lower hybrid wave at the difference frequency. It is shown that when the pump waves are Gaussian in nature, the excited lower hybrid wave is focused together with the two pump waves. The simultaneous focusing of the three waves substantially enhances the transfer of power to the excited lower hybrid wave.

The local density of a nonuniform fluid is calculated from the first equation of the Born-Green-Yvon hierarchy by modeling the pair correlation function. For that purpose, the mean force term is divided into two parts, corresponding to the mutual repulsion of the fluid atoms and the their mutual attraction, respectively. In the repulsive force term the interaction is approximated by a hard-sphere interaction and the pair correlation function is taken locally as that of a homogeneous hard-sphere fluid at some average density determined by spatial coarse graining. In the attractive force term the particles are taken to be uncorrelated. The formalism is applied to (a) the free-liquid surface, (b) gas adsorption on a wall at low temperatures, and (c) a liquid in contact with a wall. In all cases good agreement with existing computer simulations is obtained. An interesting feature arises for the free-liquid surface, where the equation turns out to be an eigenvalue equation for the coexisting liquid density. For this case the surface tension is also calculated.

Starting from the appropriate Smoluchowski equation, the pair-correlation function and the associated static structure factor are calculated for a colloidal suspension which undergoes a shear flow. Terms nonlinear in the shear rate are taken into account. The results obtained are in qualitative agreement with the elliptically distorted Debye-Scherrer rings which have recently been observed by Clark and Ackerson.

By investigating analytically and numerically the transitions of elliptic fixed points into hyperbolic ones we arrive at a description of the spreading of regions of stochasticity. Two types of fixed points are studied: those that exist for arbitrarily small perturbations, and those that are emitted from the former by increased perturbation strengths. Good agreement is found with computer studies of the standard mapping. An example of a related mapping is also presented where nearly all fixed points are parabolic, and it is shown that connected stochasticity exists for arbitrarily small perturbation parameters.

Molecular-dynamics calculations on krypton gas at 297 K have been performed taking into account three-body interactions. The purpose of this paper is to show (i) that the experimental structure data can be well described if we use the Axilrod-Teller form for the three-body potential and (ii) that the three-body potential contribution to dynamic correlations is about one order of magnitude larger than to static correlations. The experimental determination of the dynamic correlation functions can be done with sufficient accuracy by neutron scattering experiments and we expect that the ratio of error to effect for these functions is distinctly smaller than in the case of the structure data.

The electrodynamic properties of a classical one-component two-dimensional plasma are studied on the basis of a self-consistent-field approximation including the short-range correlations between particles. The static screening, the plasma dispersion relation for arbitrary wave number, and the dynamic structure factor are determined in a self-consistent scheme. The results are compared with the earlier calculations based on the random-phase approximation. Sizable differences are found revealing accurately the effects associated with correlations between particles. Our results mark a definite improvement over those calculations.

A theory for the memory function of the phase-space correlation function is presented, based on a general kinetic approach. The memory function is separated into an essentially binary-collision part and a more collective tail represented by a mode-mode coupling term, which includes recollisions to all orders. From the resulting expression for the memory function we obtain calculable expressions for the longitudinal and transverse current correlation functions.

Numerical results for the dynamic structure factor $S\left(\mathrm{qw}\right)\mathrm{}$ in liquid rubidium are presented based on a kinetic theory presented in an earlier paper. The results are in quantitative agreement with those obtained from molecular dynamics calculations and experiments. In the theory, different dynamical processes such as single binary collisions and nonlinear couplings to density and current fluctuations, are separated, and we investigate their relative contributions to the relevant memory function, as well as their effect on the shape of $S\left(\mathrm{qw}\right)\mathrm{}$.

It is shown that Mandel's argument that the electric dipole interaction in quantum electrodynamics is inconsistent with Maxwell's equations relies on the use of the wrong canonical momenta in the multipolar form of the Hamiltonian; the field conjugate to the vector potential in the Coulomb gauge is proportional to the transverse displacement vector and not, as in the minimal-coupling form of the Hamiltonian, to the transverse electric field, and similarly the canonical momenta of the charged particles differ in the two cases. Some consequences of this for time-dependent perturbation theory are discussed.

It is shown that both Hamiltonians, one with $-\overrightarrow{\mu }·\overrightarrow{\mathrm{E}}$ and the other with $-\overrightarrow{\mu }·\overrightarrow{\mathrm{A}}$ as interaction energy between an atom and the electromagnetic field, lead to Maxwell's equations. In contrast to the viewpoint in Mandel's paper, $\overrightarrow{\mathrm{E}}$ is considered to be proportional to the canonically conjugate field of the vector potential.