The Effectiveness of a Simple Helmholtz coil-like Magnetic Shield at Reducing X-ray-like Background in Space-based X-ray Detectors

Both active and passive magnetic shielding have been used extensively during past and current X-ray astronomy missions to shield detectors from soft protons and electrons entering through telescope optics. However, simulations performed throughout the past decade have discovered that a significant proportion of X-ray-like background originates from secondary electrons produced in spacecraft shielding surrounding X-ray detectors, which hit detectors isotropically from all directions. Here, the results from Geant4 simulations of a simple Helmholtz coil-like magnetic field surrounding a detector are presented, and it is found that a Helmholtz coil-like magnetic field is extremely effective at preventing secondary electrons from reaching the detector. This magnetic shielding method could remove almost all background associated with both backscattering electrons and fully absorbed soft electrons, which together are expected to account for approximately two thirds of the expected off-axis background in silicon-based X-ray detectors of several hundred microns in thickness. The magnetic field structure necessary for doing this could easily be produced using a set of solenoids or neodymium magnets providing that power requirements can be sufficiently optimised or neodymium fluorescence lines can be sufficiently attenuated, respectively.Comment: 20 pages, 6 figure

Optimal Electrodynamic Tether Phasing Maneuvers

We study the minimum-time orbit phasing maneuver problem for a constant-current electrodynamic tether (EDT). The EDT is assumed to be a point mass and the electromagnetic forces acting on the tether are always perpendicular to the local magnetic field. After deriving and non-dimensionalizing the equations of motion, the only input parameters become current and the phase angle. Solution examples, including initial Lagrange costates, time of flight, thrust plots, and thrust angle profiles, are given for a wide range of current magnitudes and phase angles. The two-dimensional cases presented use a non-tilted magnetic dipole model, and the solutions are compared to existing literature. We are able to compare similar trajectories for a constant thrust phasing maneuver and we find that the time of flight is longer for the constant thrust case with similar initial thrust values and phase angles. Full three-dimensional solutions, which use a titled magnetic dipole model, are also analyzed for orbits with small inclinations

The percutaneous absorption of soman in a damaged skin porcine model and the evaluation of WoundStat™ as a topical decontaminant

PURPOSE: The aim of this study was to evaluate a candidate haemostat (WoundStat™), down-selected from previous in vitro studies, for efficacy as a potential skin decontaminant against the chemical warfare agent pinacoyl methylfluorophosphonate (Soman, GD) using an in vivo pig model. MATERIALS AND METHODS: An area of approximately 3 cm2 was dermatomed from the dorsal ear skin to a nominal depth of 100 µm. A discrete droplet of 14C-GD (300 µg kg-1) was applied directly onto the surface of the damaged skin at the centre of the dosing site. Animals assigned to the treatment group were given a 2 g application of WoundStat™ 30 s after GD challenge. The decontamination efficacy of WoundStat™ against GD was measured by the direct quantification of the distribution of 14C-GD, as well as routine determination of whole blood cholinesterase and physiological measurements. RESULTS: WoundStat™ sequestered approximately 70% of the applied 14C-GD. Internal radiolabel recovery from treated animals was approximately 1% of the initially applied dose. Whole blood cholinesterase levels decreased to less than 10% of the original value by 15 min post WoundStat™ treatment and gradually decreased until the onset of apnoea or until euthanasia. All treated animals showed signs of GD intoxication that could be grouped into early (mastication, fasciculations and tremor), intermediate (miosis, salivation and nasal secretions) and late onset (lacrimation, body spasm and apnoea) effects. Two of the six WoundStat™ treated animals survived the study duration. CONCLUSIONS: The current study has shown that the use of WoundStat™ as a decontaminant on damaged pig ear skin was unable to fully protect against GD toxicity. Importantly, the findings indicate that the use of WoundStat™ in GD contaminated wounds would not exacerbate GD toxicity. These data suggest that absorbent haemostatic products may offer some limited functionality as wound decontaminants.Peer reviewedFinal Accepted Versio

Higgs-Mediated tau -> 3 mu in the Supersymmetric Seesaw Model

Recent observations of neutrino oscillations imply non-zero neutrino masses and flavor violation in the lepton sector, most economically explained by the seesaw mechanism. Within the context of supersymmetry, lepton flavor violation (LFV) among the neutrinos can be communicated by renormalization group flow to the sleptons and from there to the charged leptons. We show that LFV can appear in the couplings of the neutral Higgs bosons, an effect that is strongly enhanced at large tan(beta). In particular, we calculate the branching fraction for tau -> 3 mu and mu -> 3 e mediated by Higgs and find that they can be as large as 10^{-7} and 5x10^{-14} respectively. These modes, along with B^0 -> mu mu, can provide important evidence for supersymmetry before direct discovery of supersymmetric partners occurs. Along with tau -> mu gamma and mu -> e gamma, they can also provide key insights into the form of the neutrino Yukawa mass matrix.Comment: 9 pages LaTeX, 2 figures. Added a discussion of mu -> 3e and its ramifications for probing neutrino mass matrix. Also added references, fixed typos, and made one notational chang

p39R861-4, a type 2 A/C2 plasmid carrying a segment from the A/C1 RA1

The largest plasmid in the strain 39R861, which is used as a plasmid size standard, was recovered by conjugation and sequenced to determine its exact size. Plasmid p39R861-4 transferred at high frequency. Though reported to be the A/C1 plasmid RA1, p39R861-4 is a 155794 bp Type 2 A/C2 plasmid in which a 39 kb segment derived from RA1 that includes a relative of the RA1 resistance island replaces 26.5 kb of the Type 2 backbone. p39R861-4 includes a single copy of IS10 and two resistance islands with a CR2-sul2 region in each of them. The 84 kb of backbone between the resistance islands is inverted relative to other known A/C plasmids and this inversion has arisen via recombination between the CR2-sul2 regions that are inversely oriented. The resistance islands prior to inversion were one related to but longer than that found in RA1, and a form of the ARI-B island identical to one found in the A/C2 plasmid R55. They contain genes conferring resistance to tetracycline (tetA(D)), sulphonamides (sul2) and florfenicol and chloramphenicol (floR). The tet(D) determinant is flanked by two IS26 in a transposon-like structure named Tntet(D). Both resistance islands contain remnants of the two ends of the integrative element GIsul2, consistent with the sul2 gene being mobilized by GIsul2 rather than by CR2

A New Perspective on Cosmic Coincidence Problems

Cosmological data suggest that we live in an interesting period in the history of the universe when \rho_\Lambda \sim \rho_M \sim \rho_R. The occurence of any epoch with such a "triple coincidence" is puzzling, while the question of why we happen to live during this special epoch is the "Why now?" problem. We introduce a framework which makes the triple coincidence inevitable; furthermore, the ``Why now?'' problem is transformed and greatly ameliorated. The framework assumes that the only relevant mass scales are the electroweak scale, M_{EW}, and the Planck scale, M_{Pl}, and requires \rho_\Lambda^{1/4} \sim M_{EW}^2/M_{Pl} parametrically. Assuming that the true vacuum energy vanishes, we present a simple model where a false vacuum energy yields a cosmological constant of this form.Comment: 5 pages, 1 figure, uses psfig. Refs added, slightly enhance

Ultrafast Structure and Dynamics in the Thermally Activated Delayed Fluorescence of a Carbene-Metal-Amide

Thermally activated delayed fluorescence has enormous potential for the development of efficient light emitting diodes. A recently discovered class of molecules (the carbene – metal – amides, CMAs) are exceptionally promising as they combine the small singlet - triplet energy gap required for thermal activation with a large transition moment for emission. Calculations suggest that excited state structural dynamics modulate the critical coupling between singlet and triplet states, but do not agree on the nature of those dynamics. Here we report ultrafast time resolved transient absorption and Raman studies of CMA photodynamics. The measurements reveal complex structural evolution following intersystem crossing on the tens to hundreds of picoseconds timescale, and a change in the low frequency vibrational spectrum between singlet and triplet states. The latter is assigned to a change in frequency or amplitude associated with a Raman active mode localized on the metal centre

Application performance of elements in a floating–gate FPAA

Field–programmable analog arrays (FPAAs) provide a method for rapidly prototyping analog systems. Currently available commercial and academic FPAAs are typically based on operational amplifiers (or other similar analog primitives) with only a few computational elements per chip. While their specific architectures vary, their small sizes and often restrictive interconnect designs leave current FPAAs limited in functionality, flexibility, and usefulness. In this paper, we explore the use of floating–gate devices as the core programmable element in a signal processing FPAA. A generic FPAA architecture is presented that offers increased functionality and flexibility in realizing analog systems. In addition, the computational analog elements are shown to be widely and accurately programmable while remaining small in area. 1. LOW–POWER SIGNAL PROCESSING The future of FPAAs lie in their ability to speed the implementatio