Kinetic properties of particle-in-cell simulations compromised by Monte Carlo collisions

he particle-in-cell method with Monte Carlo collisions is frequently used when a detailed kinetic simulation of a weakly collisional plasma is required. In such cases, one usually desires, inter alia, an accurate calculation of the particle distribution functions in velocity space. However, velocity space diffusion affects most, perhaps all, kinetic simulations to some degree, leading to numerical thermalization (i.e., relaxation of the velocity distribution toward a Maxwellian), and consequently distortion of the true velocity distribution functions, among other undesirable effects. The rate of such thermalization can be considered a figure of merit for kinetic simulations. This article shows that, contrary to previous assumption, the addition of Monte Carlo collisions to a one-dimensional particle-in-cell simulation seriously degrades certain properties of the simulation. In particular, the thermalization time can be reduced by as much as three orders of magnitude. This effect makes obtaining strictly converged simulation results difficult in many cases of practical interest

Researching Archival Histories of Radio

Introduction to the special issue on Historical Traces of European Radio Archives

X-band microwave generation caused by plasma-sheath instability

It is well known that oscillations at the electron plasma frequency may appear due to instability of the plasma sheath near a positively biased electrode immersed in plasma. This instability is caused by transit-time effects when electrons, collected by this electrode, pass through the sheath. Such oscillations appear as low-power short spikes due to additional ionization of a neutral gas in the electrode vicinity. Herein we present first results obtained when the additional ionization was eliminated. We succeeded to prolong the oscillations during the whole time a positive bias was applied to the electrode. These oscillations could be obtained at much higher frequency than previously reported (tens of GHz compared to few hundreds of MHz) and power of tens of mW. These results in combination with presented theoretical estimations may be useful, e.g., for plasma diagnostics.Comment: 12 pages, 7 figure

Kinetic-Ion Simulations Addressing Whether Ion Trapping Inflates Stimulated Brillouin Backscattering Reflectivities

An investigation of the possible inflation of stimulated Brillouin backscattering (SBS) due to ion kinetic effects is presented using electromagnetic particle simulations and integrations of three-wave coupled-mode equations with linear and nonlinear models of the nonlinear ion physics. Electrostatic simulations of linear ion Landau damping in an ion acoustic wave, nonlinear reduction of damping due to ion trapping, and nonlinear frequency shifts due to ion trapping establish a baseline for modeling the electromagnetic SBS simulations. Systematic scans of the laser intensity have been undertaken with both one-dimensional particle simulations and coupled-mode-equations integrations, and two values of the electron-to-ion temperature ratio (to vary the linear ion Landau damping) are considered. Three of the four intensity scans have evidence of SBS inflation as determined by observing more reflectivity in the particle simulations than in the corresponding three-wave mode-coupling integrations with a linear ion-wave model, and the particle simulations show evidence of ion trapping.Comment: 56 pages, 20 figure

Student Trauma in the Classroom

Trauma-related disruptive student behavior has risen sharply. With the increase in the number of students experiencing traumatic events, and the number of U.S. veterans entering college, disruptive behavior may worsen. The purpose of the present study was to explore faculty experiences with student traumatic behavior, as well as their training to deal with such behavior

A generalized nonlinear Schr\"odinger equation as model for turbulence, collapse, and inverse cascade

A two-dimensional generalized cubic nonlinear Schr\"odinger equation with complex coefficients for the group dispersion and nonlinear terms is used to investigate the evolution of a finite-amplitude localized initial perturbation. It is found that modulation of the latter can lead to side-band formation, wave condensation, collapse, turbulence, and inverse cascade, although not all together nor in that order.Comment: 12 pages, 5 figure

Gender Differences in CAM Usage in Undergraduates

The National Institutes of Health (NIH) recently opened a center for the study of the use of complementary and alternative medicine (CAM). While the NlH has conducted a few random sampling studies, none have examined the knowledge and use of CAM among undergraduates and whether these differ by gender. 111 college students were asked about the usage of a variety of CAM techniques, as well as about beliefs and opinions about CAM techniques. Several gender differences emerged. Implications for college wellness centers will be discussed

Feminist avenues for listening in: amplifying silenced histories of media and communication

This paper proposes a feminist critique of the media and communication field by offering a different soundtrack to guide future historical research. By shifting the focus from well-known protagonists, and acknowledging process and community rather than individuals, we aim to amplify ‘hidden’ domains of gendered labour and layers of media technologies and services. We propose the ‘listening in’ model as a different way to engage with histories of media and communication, providing four pathways for how the histories of film, radio and internet in particular have been theorised and researched. These pathways focus on multiplicities of expertise, layers of infrastructure, users, and the media canon. For the first pathway, we show how media production has always been a collective work of multiple expertise. The second pathway breaks with the distinction between media and communication and emphasises reciprocal processes of media production. For the third, we demonstrate how media theory and research have tended to assume specific ideal bodies while ignoring others. For the final pathway, we propose a rethinking of how media histories and theories are narrated via the usual protagonists and call for a new canon to achieve a richer and more nuanced understanding within the field