Direct Verification of the Kinetic Description of Wave Turbulence for Finite-Size Systems Dominated by Interactions among Groups of Six Waves.

The present work considers systems whose dynamics are governed by the nonlinear interactions among groups of 6 nonlinear waves, such as those described by the unforced quintic nonlinear Schrödinger equation. Specific parameter regimes in which ensemble-averaged dynamics of such systems with finite size are accurately described by a wave kinetic equation, as used in wave turbulence theory, are theoretically predicted. In addition, the underlying reasons that the wave kinetic equation may be a poor predictor of wave dynamics outside these regimes are also discussed. These theoretical predictions are directly verified by comparing ensemble averages of solutions to the dynamical equation with corresponding solutions of the wave kinetic equation.

Longitudinal and Transverse Instability of Ion Acoustic Waves.

Ion acoustic waves are found to be susceptible to at least two distinct decay processes. Which process dominates depends on the parameters. In the cases examined, the decay channel where daughter modes propagate parallel to the mother mode is found to dominate at larger amplitudes, while the decay channel where the daughter modes propagate at angles to the mother mode dominates at smaller amplitudes. Both decay processes may occur simultaneously and with onset thresholds below those suggested by fluid theory, resulting in the eventual multidimensional collapse of the mother mode to a turbulent state.

Kinetic simulations of the self-focusing and dissipation of finite-width electron plasma waves.

Two-dimensional simulations, both Vlasov and particle-in-cell, are presented that show the evolution of the field and electron distribution of finite-width, nonlinear electron plasma waves. The intrinsically intertwined effects of self-focusing and dissipation of field energy caused by electron trapping are studied in simulated systems that are hundreds of wavelengths long in the transverse direction but only one wavelength long and periodic in the propagation direction. From various initial wave states, both the width at focus Δm relative to the initial width Δ0 and the maximum field amplitude at focus are shown to be a function of the growth rate of the transverse modulational instability γTPMI divided by the loss rate of field energy νE to electrons escaping the trapping region. With dissipation included, an amplitude threshold for self-focusing γTPMI/νE∼1 is found that supports the analysis of Rose [Phys. Plasmas 12, 012318 (2005)].

Effective dispersion in the focusing nonlinear Schrödinger equation.

For waves described by the focusing nonlinear Schrödinger equation (FNLS), we present an effective dispersion relation (EDR) that arises dynamically from the interplay between the linear dispersion and the nonlinearity. The form of this EDR is parabolic for a robust family of "generic" FNLS waves and equals the linear dispersion relation less twice the total wave action of the wave in question multiplied by the square of the nonlinearity parameter. We derive an approximate form of this EDR explicitly in the limit of small nonlinearity and confirm it using the wave-number-frequency spectral (WFS) analysis, a Fourier-transform based method used for determining dispersion relations of observed waves. We also show that it extends to the FNLS the universal EDR formula for the defocusing Majda-McLaughlin-Tabak (MMT) model of weak turbulence. In addition, unexpectedly, even for some spatially periodic versions of multisolitonlike waves, the EDR is still a downward shifted linear-dispersion parabola, but the shift does not have a clear relation to the total wave action. Using WFS analysis and heuristic derivations, we present examples of parabolic and nonparabolic EDRs for FNLS waves and also waves for which no EDR exists.

Collisional damping rates for electron plasma waves reassessed.

Collisional damping of electron plasma waves, the primary damping for high phase velocity waves, is proportional to the electron-ion collision rate, ν_{ei,th}. Here, it is shown that the damping rate normalized to ν_{ei,th} depends on the charge state, Z, on the magnitude of ν_{ei,th} and the wave number k in contrast with the commonly used damping rate in plasma wave research. Only for weak collision rates in low-Z plasmas for which the electron self-collision rate is comparable to the electron-ion collision rate is the damping rate given by the commonly accepted value. The result presented here corrects the result presented in textbooks at least as early as 1973. The complete linear theory requires the inclusion of both electron-ion pitch-angle and electron-electron scattering, which itself contains contributions to both pitch-angle scattering and thermalization.

Attitudes of medical school faculty toward gifts from the pharmaceutical industry.

The American Medical Association (AMA) has recently published guidelines for the receipt of gifts from industry representatives. To examine faculty members' attitudes toward that AMA policy as it pertains to gifts from the pharmaceutical industry, the authors surveyed the faculty of the University of Kentucky College of Medicine in 1991. Of 462 faculty members, 248 (54%) completed the questionnaires. The faculty generally agreed with the AMA guidelines. A majority of the faculty believed that personal relationships had the potential to influence prescribing patterns but that gifts, in general, did not greatly influence prescribing behaviors. Compared with the 169 M.D. faculty, the 69 Ph.D. faculty significantly favored more restrictive policies (p less than .001). The authors discuss both the ethical considerations and the utility of guidelines for physician-industry interactions.

Mother-child development elective: a formal educational maternity leave.

Policies for maternity and parenting leave in physician training programs are often lacking or inadequate. A structured elective in mother-child development has been developed by the University of Kentucky Department of Family Practice Residency Program in an attempt to provide a practical alternative for the resident-in-training who is a new parent. The course provides for the integration of personal and professional activities into an educationally beneficial experience. The new course meets the requirements of both the American Board of Family Practice and the Residency Review Committee. The first participants in the elective course have been extremely positive about its merit.