Emission and absorption coefficients of bremsstrahlung by high-temperature partially degenerate electrons are calculated for high-density plasmas where Coulomb coupling between ions is not weak. It is shown that the ion correlation substantially reduces these coefficients. The scaling property of the correlation effect with respect to the ionic charge number is analyzed.

Kα x-ray spectra of heliumlike titanium, Ti xxi, from Tokamak Fusion Test Reactor (TFTR) plasmas have been observed with a high-resolution crystal spectrometer and have been used as a diagnostic of central plasma parameters. The data allow detailed comparison with recent theoretical predictions for the Ti xxi heliumlike lines and the associated satellite spectrum in the wavelength range from 2.6000 to 2.6400 Å. Improved values for the excitation rate coefficients of the Ti xxi resonance line, the intercombination lines, and the forbidden line, and new theoretical results on the wavelengths and transition probabilities for berylliumlike satellites due to transitions of the type 1$s^2$2lnl’-1s2p2l’’nl’’’ with n=2–4 have been calculated.

These data complement the theory given in an earlier paper [F. Bely-Dubau et al., Phys. Rev. A 26, 3459 (1982)]. The experimental data are in excellent agreement with the theoretical predictions for the entire satellite spectrum. For plasmas with electron temperatures, $T_e$, in the range from 1.2 to 1.8 keV, there is also good general agreement between theory and experiment for the heliumlike lines of Ti xxi. The observed intensity ratios of the intercombination and forbidden lines to the resonance line are, however, larger than the predicted values by as much as an order of magnitude for electron temperatures $T_e$<1.2 keV. The enhancement of these lines is correlated with the abundance of lithiumlike titanium.

The experimental data indicate that still other atomic processes, in addition to those considered by the theory, are important for the excitation of these lines. The experimental results are documented to stimulate further analysis. The observed wavelengths agree to within an uncertainty of 0.5 mÅ with predictions from calculations which include relativistic and radiative corrections up to the third order in α. The central ion temperature and the central toroidal rotation velocity of TFTR plasmas with ohmic and neutral beam heating were obtained from Doppler measurements of the Ti xxi resonance line.

Wavelength shifts of the apparent resonance line profile due to unresolved dielectronic satellites, which can be important corrections to Doppler-shift measurements of plasma rotation velocities, have been determined as a function of the ion and electron temperatures and the fitting limits. Results on the electron temperature and the relative charge-state density of lithiumlike and heliumlike titanium were derived from the satellite spectrum and have been interpreted with plasma modeling. These results are of interest for the determination of the ionization equilibrium and the impurity transport.

A new method of deriving expressions for any thermodynamic-state function as an average of the appropriate microscopic dynamical functions over the microcanonical distribution is presented. The results are valid for any system of classical particles interacting through a potential depending only on their relative positions and have a primary application to calculating thermodynamic quantities in molecular-dynamics computer-simulation studies. A Laplace-transform method is used to express any combination of energy and volume (or strain) derivatives of the microcanonical phase volume as averages of specific dynamical functions and their fluctuations. A unique result is the occurrence of the average reciprocal kinetic energy in these equations. These derivatives are then related to thermodynamic-state functions using the Legendre relations and the basic definition connecting the entropy to the phase-space volume. In particular, the complete microcanonical expressions for the adiabatic elastic constants are derived for the first time. The equations derived by this method are consistent with results from the literature pertaining to the classical microcanonical ensemble. The equivalence is obtained in the limit that the number of particles in the system approaches infinity, but the results diverge for systems with few particles. Numerical results from molecular-dynamics simulations of a simple model system are used to substantiate these points.

The nonlinear Navier-Stokes-Langevin equations are used to describe fluctuations in a compressible fluid with uniform shear flow. The hydrodynamic modes for small deviations from the macroscopic nonequilibrium state are calculated, including linear mode coupling of the fluctuating variables with the macroscopic velocity field. The associated correlation functions are determined with the full nonlinear dependence on shear rate required for long times and/or large shear rate. The stationary and joint probability densities are also constructed from the associated Fokker-Planck equation. As an application of these results, the lowest-order mode-coupling contributions to the renormalized shear viscosity are evaluated.

A model for the dynamics of cold dense fluids proposed by Zwanzig is exploited to evaluate the self-diffusion coefficient, the shear viscosity, and the thermal conductivity directly from the Green-Kubo time correlation formulas. The Stokes-Einstein relation is found to be extremely sensitive to the precise form of the waiting-time distribution for cell jumps. The lifetime for a cell jump is estimated via a sum rule. Properties of the thermal conductivity are discussed.

A model for solitonlike excitation in DNA is presented and assessed in the context of previous models of collective excitations in other biological systems. A qualitative analysis describes the mechanisms of some DNA function, in particular opening of DNA base pairs to initiate protein synthesis. A formalism is presented which analyzes quantitatively the above-mentioned model, predicts the threshold for B-DNA→A-DNA transition, and specifies the parameters of particular electromagnetic stimulations that can produce or initiate a variety of DNA responses and effects. The example of insulin production is discussed in detail and theoretical predictions are given for the parameters of an electromagnetic signal reproducing the stimulation to a cell which would lead to insulin production as a response.

As pointed out by Miracky, Devoret, and Clarke [Phys. Rev. A 31, 2509 (1985)] a Josephson junction biased by a dc current can display switching noise. A detailed understanding of this phenomenon requires a careful analysis of the structure of invariant manifolds of the corresponding dissipative dynamical system. We show that the observed noise results from a complicated bifurcation between chaotic attractors in terms of crises.

A generic situation for the bifurcation of stationary states is considered. The separation of the relaxation time scales is such that the adiabatic-elimination method is incompatible with the linearization of the reduced equation of motion around the unstable steady state. Thus, the system is assumed to have departed considerably from the critical point. The functional dependence of the fast-relaxing degree of freedom on the order parameter is obtained by finding the nonadiabatic center-manifold equation. 2 This equation is an extension of the adiabatic-elimination procedure since it holds even in the case of a small separation of time scales. The results are applied to a system studied extensively where the reduced equation of motion admits a bistable viscous potential. The macroscopic equations of motion are compatible with the obtained stochastic description.

The issue of diffusion on fractals is addressed with stress on the question of how to generalize the diffusion equation for Euclidean lattices to the case of fractal lattices. Such an equation is proposed on the basis of scaling arguments. The solutions of this equation are interpreted as analytic envelopes of the exact probability distribution P(r,t) which is far from smooth. In fact it is shown that P(r,t) has discontinuities which appear self-similarly on all length scales. The exactly soluble examples of Sierpiński gaskets embedded in general dimension d are analyzed. The predstudied by assuming that the sticking probability of the particles depends on the local orientation of the interface. Directional solidification is simulated by the deposition of particles undergoing biased random walks. Linearly stable patterns are generated if the basic features of the directional solidification experiments are taken into account. The resulting patterns are very similar to those observed experimentally.

Generalizations of the diffusion-limited aggregation model are considered in order to simulate pattern formation during solidification. The two-dimensional clusters grown on a seed particle are initially circular but at later stages the process crosses over into dendritic growth. The effects of an anisotropic surface tension are studied by assuming that the sticking probability of the particles depends on the local orientation of the interface. Directional solidification is simulated by the deposition of particles undergoing biased random walks. Linearly stable patterns are generated if the basic features of the directional solidification experiments are taken into account. The resulting patterns are very similar to those observed experimentally.

The Glauber approximation is used to calculate doubly differential cross sections (DDCS) for electron-impact ionization of helium in the incident energy range 224.58–2824.58 eV. The present calculation is done for the symmetric geometry, i.e., the two outgoing electrons have equal energies, and for a scattering angle of 45°. A comparison is made of the present DDCS with the results of absolute measurements.

Pseudopotential molecular-structure calculations have been performed on the NaH system to obtain the five lowest ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }$ and two lowest ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }$ molecular states. The resulting eigenfunctions and eigenvalues were used in a perturbed-stationary-state calculation where electron-translation factors have been incorporated to first order in the collision velocity. The ion-pair formation cross section for H+Na→${\mathrm{H}}^{\mathrm{-}}$+${\mathrm{Na}}^{+}$ is found to have a maximum value of 3.3×${10}^{\mathrm{-}16}$ cm at 1 keV/amu. The ion-ion mutual neutralization cross section for ${\mathrm{H}}^{\mathrm{-}}$+${\mathrm{Na}}^{+}$→H+Na rises monotomically with decreasing collision velocity and is ∼1×${10}^{\mathrm{-}14}$ ${\mathrm{cm}}^2$ at energies from 0.1 to 5.0 keV/amu.

The wave function for a system with an energy-independent nonlocal potential is determined from its phase shifts to a good approximation, using a fixed-energy inversion method.

The triple-differential cross sections for the ionization of atomic hydrogen by fast electrons are analyzed in the case of coplanar asymmetric geometry with use of the modified Glauber approximation. Our results show an improved agreement with the recent measurements taken at 250 eV incident electron energy, compared to the second-Born-approximation or the eikonal Born-series results.

Nuclei of ${}_{54}{}^{}{}_{}{}^{}\mathrm{Xe}$, ${}_{67}{}^{}{}_{}{}^{}\mathrm{Ho}$, ${}_{79}{}^{}{}_{}{}^{}\mathrm{Au}$, and ${}_{92}{}^{}{}_{}{}^{}\mathrm{U}$ accelerated at the Lawrence Berkeley Laboratory Bevalac to energies between 1200 and 900 MeV/n have been stopped in nuclear emulsions. The observed residual ranges have been compared with those calculated from various models of energy loss and shown to be most consistent with a calculation that includes those higher-order correction terms proposed previously to describe the energy loss of highly charged particles, for which the first Born approximation is not valid.

We derive the exact asymptotic behavior of the second Born approximation for electron capture. The transfer probability as a function of impact parameter and the cross section is shown to go like (lnE${)}^2$/E, where E is the collision energy. This result is the same as for the impulse approximation, and is independent of the initial- and final-state wave functions. In particular, it is also true for capture to the continuum.

Recent experiments on the Xe 5s β parameter in the vicinity of the Cooper minimum have shown a marked disagreement with truncated 13-channel relativistic random-phase approximation (RRPA) calculations. RRPA calculations including 26 channels have been performed. The results show that the truncation is not responsible for the disagreement, which must be due to non-RRPA correlations.

Relative transition probabilities for 74 electric dipole lines belonging to the 6p-nd (n=7,8,9) transition arrays of Xe i have been determined by means of emission-line-intensity measurements. For 72 of these transitions no other experimental values have been published to our knowledge. The radiative lifetime for the 7d${\mathrm{}(7/2)\mathrm{}}_4$, 7d${\mathrm{}(7/2)\mathrm{}}_3$, 7d${\mathrm{}(5/2)\mathrm{}}_3$, and 7d${\mathrm{}(5/2)\mathrm{}}_2$ levels was measured, obtaining the following results: 96±7, 117±9, 113±9, and 115±10 ns, respectively. By means of these lifetime values, twelve of the measured relative transition probabilities have been put on an absolute scale. Comparison is made with our calculations using jK coupling and Coulomb approxiamtion and with the existing experimental and theoretical results of other authors.

We argue that the formation of patterns in diffusion-limited aggregation on a linear substrate, as studied by Vicsek, is essentially just the short-time instabilities in the Saffman-Taylor problem of hydrodynamics. Predictions about the wavelength of the pattern are made and checked against the numerical data.

It has previously been reported by Easwar et al. that the two phases of a critical mixture take an unexpectedly long time to mutually dissolve if the system is raised above its critical temperature (T>$T_c$) and strongly stirred. Further experiments have identified a trivial explanation for this effect. The system cools on mixing, and this can temporarily drive it back into the two-phase region (T<$T_c$). The experimental technique used here can possibly be exploited to measure the surface energy temporarily stored in a turbulently stirred two-phase system.