Non-linear Plasma Wake Growth of Electron Holes

An object's wake in a plasma with small Debye length that drifts \emph{across} the magnetic field is subject to electrostatic electron instabilities. Such situations include, for example, the moon in the solar wind wake and probes in magnetized laboratory plasmas. The instability drive mechanism can equivalently be considered drift down the potential-energy gradient or drift up the density-gradient. The gradients arise because the plasma wake has a region of depressed density and electrostatic potential into which ions are attracted along the field. The non-linear consequences of the instability are analysed in this paper. At physical ratios of electron to ion mass, neither linear nor quasilinear treatment can explain the observation of large-amplitude perturbations that disrupt the ion streams well before they become ion-ion unstable. We show here, however, that electron holes, once formed, continue to grow, driven by the drift mechanism, and if they remain in the wake may reach a maximum non-linearly stable size, beyond which their uncontrolled growth disrupts the ions. The hole growth calculations provide a quantitative prediction of hole profile and size evolution. Hole growth appears to explain the observations of recent particle-in-cell simulations

Collisional Effects on Nonlinear Ion Drag Force for Small Grains

The ion drag force arising from plasma flow past an embedded spherical grain is calculated self-consistently and non-linearly using particle in cell codes, accounting for ion-neutral collisions. Using ion velocity distribution appropriate for ion drift driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if non-linear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided.Comment: Fig 1. corrected in this versio

Sub-arcsecond radio and optical observations of the likely counterpart to the gamma-ray source 2FGL J2056.7+4939

We have searched and reviewed all multi- wavelength data available for the region towards the gamma-ray source 2FGL J2056.7+4939 in order to con- strain its possible counterpart at lower energies. As a result, only a point-like optical/infrared source with flat-spectrum radio emission is found to be consistent with all X-ray and gamma-ray error circles. Its struc- ture is marginally resolved at radio wavelengths at the sub-arcsecond level. An extragalactic scenario appears to be the most likely interpretation for this object.Comment: 5 pages, 3 figures, 1 tabl

Simulations of the ILC Electron Gun and ElectronBunching System

The International Linear Collider (ILC) is a proposed electron-positron collider, expected to provide insight into important questions in particle physics. A part of the global R&D effort for the ILC is the design of its electron gun and electron bunching system. The present design of the bunching system has two sub-harmonic bunchers, one operating at 108 MHz and one at 433MHz, and two 5-cell 1.3 GHz (L-band) bunchers. This bunching system has previously been simulated using the Phase and Radial Motion in Electron Linear Accelerators (PARMELA) software, and those simulations indicated that the design provides sufficient bunching and acceleration. Due to the complicated dynamics governing the electrons in the bunching system we decided to verify and expand the PARMELA results using the more recent and independent simulation software General Particle Tracer (GPT). GPT tracks the motion and interactions of a set of macro particles, each of which represent a number of electrons, and provides a variety of analysis capabilities. To provide initial conditions for the macro particles, a method was developed for deriving the initial conditions from detailed simulations of particle trajectories in the electron gun. These simulations were performed using the Egun software. For realistic simulation of the L-band bunching cavities, their electric and magnetic fields were calculated using the Superfish software and imported into GPT. The GPT simulations arrived at similar results to the PARMELA simulations for sub-harmonic bunching. However, using GPT it was impossible to achieve an efficient bunching performance of the first L-band bunching cavity. To correct this, the first L-band buncher cell was decoupled from the remaining 4 cells and driven as an independent cavity. Using this modification we attained results similar to the PARMELA simulations. Although the modified bunching system design performed as required, the modifications are technically challenging to implement. Further work is needed to optimize the L-Band buncher design

Combined endovascular and surgical treatment in vertebral arteriovenous fistula

A 7-year-old girl with a right-sided congenital arteriovenous fistula in the neck was admitted with signs of cardial incompensation. Her fistula was fed from the right vertebral artery in antegrade as well as retrograde directions. A steal from the intracranial arteries was established. In addition, smaller feeding arteries from the neck were found. She was operated on with ligation of the right vertebral artery proximal to the fistula but the attempted ligation of the artery cranially to the fistula was unsuccessful. She was therefore embolized by the formation of a plug of platinum fiber coils in the upper right vertebral artery. Catheterization was performed from the left vertebral artery via the basilar artery. Persisting minor feeders to the fistula from cervical arteries were embolized in a second session. Finally, surgical extirpation of the fistula was performed together with the operative ligation of a crossover feeding artery from the left vertebral artery. Her heart size, heart rate and blood pressure were successively normalized. </jats:p

Feasibility of Coping Effectiveness Training for Caregivers of Children with Autism Spectrum Disorder: a Genetic Counseling Intervention

© 2017, National Society of Genetic Counselors, Inc. Caregivers of children with autism spectrum disorder (ASD) may find it difficult to feel a sense of control and to cope with the overall physical and emotional demands of caring for their child. While caregivers are able to successfully cope with a high level of stress, there are limits to their resources and abilities to cope over time. Genetic counselors working with affected families may be able to help parents more effectively manage stress related to the disorder. Few short-term interventions have been reported in genetic counseling yet implementation of evidence-based examples may be achievable. This study aimed to assess the feasibility of a coping effectiveness training (CET) intervention designed to enhance coping self-efficacy (CSE) among caregivers of children with ASD, with the eventual goal of translating this intervention into genetic counseling practice. A randomized treatment-control design was used to investigate the feasibility of an intervention using CET among caregivers of children with ASD. The primary outcome was the feasibility of the intervention; the secondary outcome was improvements in CSE in the intervention group as compared to the control group. Caregivers were recruited and randomized into the treatment (n=15) or control (n=13) groups. Of these, 22 completed the study (retention: 78.6%). The intervention was highly feasible; most caregivers found the CET helpful, practical, useful, and relatively easy to attend. The treatment group demonstrated significantly increased CSE from pre-intervention to post-intervention (p=0.02). Between group differences were not significant when comparing the pre-post changes. We provide preliminary evidence that CET may be beneficial to caregivers of children with ASD. The results of this feasibility study support development of a phase II study of this intervention in a larger cohort, aimed to be implemented into a genetic counseling setting