Characterization of the Mercury pulsed power x-ray source spectrum using multichannel density aerogel Cherenkov detectors.

The Aerogel Cherenkov Detector for Cygnus (ACD/C) is a time-dependent, x-ray spectral detector that uses SiO2 aerogels spanning an index of refraction (n = 1.02-1.07) corresponding to a 1.1-2.3 MeV x-ray energy threshold. The ACD/C was developed for pulsed power x-ray sources like Cygnus located at the Nevada National Site and Mercury located at the Naval Research Laboratory (NRL). Aerogels sit between the measurement capabilities of gas (>2 MeV) and solids such as fused silica (>0.3 MeV). The detector uses an aluminum converter to Compton scatter incoming x-rays and create relativistic electrons, which produce Cherenkov light in an aerogel or a fused silica medium. The ACD/C was fielded at the NRL when Mercury was tuned to produce up to 4.8 MeV endpoint bremsstrahlung. Despite a high radiation and electromagnetic interference background, the ACD/C was able to achieve high signal over noise across five aerogel densities and fused silica, including a signal to noise for a 1.1 MeV aerogel threshold. Previous experiments at Cygnus observed a signal that was comparable to the noise (1×) at the same threshold. The ACD/C observed time-resolved rise and fall times for different energy thresholds of the photon spectrum. Monte Carlo simulations of the ACD/C's aerogel response curves were folded with a simulation of Mercury's photon energy spectrum and agree within the error to the observed result.

Improved Time to Notification of Impending Brain Death and Increased Organ Donation Using an Electronic Clinical Decision Support System.

Early referral of patients to an organ procurement organization (OPO) may positively affect donation outcomes. We implemented an electronic clinic decision support (CDS) system to automatically notify our OPO of children meeting clinical triggers indicating impending brain death. Medical records of all patients who died in a pediatric critical care unit or were referred for imminent death for 3 years prior to installation of the initial CDS (pre-CDS) and for 1 year after implementation of the final CDS (post-CDS) were reviewed. Mean time to OPO notification decreased from 30.2 h pre-CDS to 1.7 h post-CDS (p = 0.015). Notification within 1 h of meeting criteria increased from 36% pre-CDS to 70% post-CDS (p = 0.003). Although an increase in donor conversion from 50% pre-CDS to 90% post-CDS did not reach statistical significance (p = 0.0743), there were more organ donors post-CDS (11 of 24 deaths) than pre-CDS (seven of 57 deaths; p = 0.002). Positive outcomes were achieved with the use of a fully automated CDS system while simultaneously realizing few false-positive notifications, low costs, and minimal workflow interruption. Use of an electronic CDS system in a pediatric hospital setting improved timely OPO notification and was associated with increased organ donation.

Anisotropy and feedthrough in magneto-Rayleigh-Taylor instability.

The magneto-Rayleigh-Taylor instability (MRT) of a finite slab is studied analytically using the ideal MHD model. The slab may be accelerated by an arbitrary combination of magnetic pressure and fluid pressure, thus allowing an arbitrary degree of anisotropy intrinsic to the acceleration mechanism. The effect of feedthrough in the finite slab is also analyzed. The classical feedthrough solution obtained by Taylor in the limit of zero magnetic field, the single interface MRT solution of Chandrasekhar in the limit of infinite slab thickness, and Harris' stability condition on purely magnetic driven MRT, are all readily recovered in the analytic theory as limiting cases. In general, we find that MRT retains robust growth if it exists. However, feedthrough may be substantially reduced if there are magnetic fields on both sides of the slab, and if the MRT mode invokes bending of the magnetic field lines.

Effect of soft metal gasket contacts on contact resistance, energy deposition, and plasma expansion profile in a wire array Z pinch.

Soft metal gaskets (indium and silver) were used to reduce contact resistance between the wire and the electrode in an aluminum wire Z pinch by more than an order of magnitude over the best weighted contact case. Clamping a gasket over a Z-pinch wire compresses the wire to the electrode with a greater normal force than possible with wire weights. Average contact resistance was reduced from the range of 100-3000 Omega (depending on wire weight mass) to 1-10 Omega with soft metal gaskets. Single wire experiments (13 microm Al 5056) on a 16 kA, 100 kV Marx bank showed an increase in light emission (97%) and emission volume (100%) of the plasma for the reduced contact resistance cases. The measured increases in plasma volume and light emission indicate greater energy deposition in the ablated wire. Additionally, dual-wire experiments showed plasma edge effects were significantly decreased in the soft metal gasket contact case. The average height of the edge effects was reduced by 51% and the width of the edge effects was increased by 40%, thus the gasket contact case provided greater axial uniformity in the plasma expansion profile of an individual wire.