On the Feasibility of Detecting Spacecraft Charging and Arcing by Remote Sensing

t is a sad fact that more than 50 years after the dawn of the space age, most spacecraft still do not have sensors onboard capable of detecting whether they are at potentials likely to put them at risk of severe charging and the concomitant arcing, or indeed, even capable of detecting when or if they undergo arcing. As a result, anomaly resolution has often been hit or miss, and false diagnoses are probably common. Until spacecraft are routinely launched with charging and arcing monitors, the best that can be achieved is detection through remote sensing, from the ground or by satellites. In this paper we examine a few remote sensing techniques that could be applied for detecting spacecraft charging and/or arcing.The first technique considered depends on the fact that when bombarded by high energy electrons, many types of dielectrics emit a glow that could be observed remotely, and would change with the degree of spacecraft charging. Only kilovolt electron strikes are effective at producing the glow. Thus, under geomagnetically calm conditions, if the glow were detected, high energy electron fluxes capable of spacecraft surface charging to kilovolt levels would be indicated. If the space plasma were disturbed, and the spacecraft were thus being charged negatively by a multitude of multi-kilovolt electrons, the ongoing charging would be seen as an enhanced surface glow. Although easily seen in the laboratory, this glow is likely to be too weak to be detected in space except for a satellite in eclipse. However, GEO satellites charge more in eclipse anyway. We will estimate whether the glow can be detected from both Earth and space. The second technique depends on the fact that when electrons above about 20 keV strike a surface, x-rays are produced (through bremsstrahlung). If immersed in a very high-temperature plasma (like that of the famous Galaxy 15 event or the ATS-6 record charging event) a spacecraft may thus be seen by the x-rays that are produced. It is generally conceded that in eclipse a spacecraft will charge negatively (in volts) up to the electron temperature of the surrounding plasma (in eV). Again, detection in eclipse is probably necessary, since solar x-rays reflected by spacecraft surfaces might make daytime detection impossible. This method would likely only indicate when the most severe charging conditions were ongoing, and would of necessity require detection by an orbiting satellite. Finally, when spacecraft arc, the arcs produce electromagnetic radiation. On PASP Plus and other scientific satellites, radio waves produced by arcs were used to determine the arc location, for instance. Arcs in laboratory conditions have been detected solely by radio emission, and oftentimes the visible light emitted is used to determine arc location and timing. While the radio noise produced is severe enough close by to produce radio interference in sensitive spacecraft electronics, it is likely to drop off rapidly, and most probably could only be detected by satellites orbiting nearby. However, the light produced may be substantial, and might be detected by a suitably filtered telescope even on Earth. Also, shortly after an arc, solar array surfaces glow for two reasons – firstly, while the arc is progressing, the coverglass surface is positively charged, and glows from electron excitation at its surface. If the arc does not completely discharge the surface, the glow may continue until ambient electrons collected completely neutralize it. Secondly, some of the cells in the array circuit are back-biased by the arc, and act as light emitting diodes. Both of these missions are broadband and may last for hundreds of microseconds. Possibilities for arc detection from Earth-bound optical and radio telescopes will be discussed

The impact of the demographic transition on dengue in Thailand: Insights from a statistical analysis and mathematical modeling

Background: An increase in the average age of dengue hemorrhagic fever (DHF) cases has been reported in Thailand. The cause of this increase is not known. Possible explanations include a reduction in transmission due to declining mosquito populations, declining contact between human and mosquito, and changes in reporting. We propose that a demographic shift toward lower birth and death rates has reduced dengue transmission and lengthened the interval between large epidemics. Methods and Findings: Using data from each of the 72 provinces of Thailand, we looked for associations between force of infection (a measure of hazard, defined as the rate per capita at which susceptible individuals become infected) and demographic and climactic variables. We estimated the force of infection from the age distribution of cases from 1985 to 2005. We find that the force of infection has declined by 2% each year since a peak in the late 1970s and early 1980s. Contrary to recent findings suggesting that the incidence of DHF has increased in Thailand, we find a small but statistically significant decline in DHF incidence since 1985 in a majority of provinces. The strongest predictor of the change in force of infection and the mean force of infection is the median age of the population. Using mathematical simulations of dengue transmission we show that a reduced birth rate and a shift in the population's age structure can explain the shift in the age distribution of cases, reduction of the force of infection, and increase in the periodicity of multiannual oscillations of DHF incidence in the absence of other changes. Conclusions: Lower birth and death rates decrease the flow of susceptible individuals into the population and increase the longevity of immune individuals. The increase in the proportion of the population that is immune increases the likelihood that an infectious mosquito will feed on an immune individual, reducing the force of infection. Though the force of infection has decreased by half, we find that the critical vaccination fraction has not changed significantly, declining from an average of 85% to 80%. Clinical guidelines should consider the impact of continued increases in the age of dengue cases in Thailand. Countries in the region lagging behind Thailand in the demographic transition may experience the same increase as their population ages. The impact of demographic changes on the force of infection has been hypothesized for other diseases, but, to our knowledge, this is the first observation of this phenomenon

Stellar Nucleosynthesis in the Hyades Open Cluster

We report a comprehensive light element (Li, C, N, O, Na, Mg, and Al) abundance analysis of three solar-type main sequence (MS) dwarfs and three red giant branch (RGB) clump stars in the Hyades open cluster using high-resolution and high signal-to-noise spectroscopy. For each group (MS or RGB), the CNO abundances are found to be in excellent star-to-star agreement. Our results confirm that the giants have undergone the first dredge-up and that material processed by the CN cycle has been mixed to the surface layers. The observed abundances are compared to predictions of a standard stellar model based on the Clemson-American University of Beirut (CAUB) stellar evolution code. The model reproduces the observed evolution of the N and O abundances, as well as the previously derived 12C/13C ratio, but it fails to predict by a factor of 1.5 the observed level of 12C depletion. Li abundances are derived to determine if non-canonical extra mixing has occurred in the Hyades giants. The Li abundance of the giant gamma Tau is in good accord with the predicted level of surface Li dilution, but a ~0.35 dex spread in the giant Li abundances is found and cannot be explained by the stellar model. Possible sources of the spread are discussed; however, it is apparent that the differential mechanism responsible for the Li dispersion must be unrelated to the uniformly low 12C abundances of the giants. Na, Mg, and Al abundances are derived as an additional test of our stellar model. All three elements are found to be overabundant by 0.2-0.5 dex in the giants relative to the dwarfs. Such large enhancements of these elements are not predicted by the stellar model, and non-LTE effects significantly larger (and, in some cases, of opposite sign) than those implied by extant literature calculations are the most likely cause.Comment: 40 pages, 6 figures, 6 tables; accepted by Ap

Evaluation of the diagnostic accuracy of prototype rapid tests for human African trypanosomiasis

Peer reviewedPublisher PD

Spectroscopic Confirmation of Faint Lyman Break Galaxies at Redshifts Four and Five in the Hubble Ultra Deep Field

We present the faintest spectroscopically confirmed sample of redshift four and five Lyman break galaxies to date. The sample is based on slitless grism spectra of the Hubble Ultra Deep Field region from the GRAPES (Grism ACS Program for Extragalactic Science) and PEARS (Probing Evolution and Reionization Spectroscopically) projects, using the G800L grism on the HST Advanced Camera for Surveys. We report here confirmations of 39 galaxies, pre-selected as candidate Lyman break galaxies using photometric selection criteria. We compare a "traditional" V-dropout selection to a more liberal one (with V-i > 0.9), and find that the traditional criteria are about 64% complete and 81% reliable. We also study the Lyman alpha emission properties of our sample. We find that Lyman alpha emission is detected in about 1/4 of the sample, and that our broad-band color selected sample includes 55% of previously published line-selected Lyman alpha sources. Finally, we examine our stacked 2D spectra. We demonstrate that strong, spatially extended (arcsecond scale) Lyman alpha emission is not a generic property of these Lyman break galaxies, but that a modest extension of the Lyman alpha photosphere (compared to the starlight) may be present in those galaxies with prominent Lyman alpha emission.Comment: Submitted to The Astrophysical Journal. Reduced spectra from both GRAPES and PEARS are available from STScI, at http://www.stsci.edu/science/grapes/ and at http://archive.stsci.edu/prepds/pears

Perihaematomal oedema evolution over two weeks after spontaneous intracerebral haemorrhage and association with outcome:prospective cohort study

Introduction We know little about the evolution of perihaematomal oedema (PHO) &amp;gt;24 hours after ICH onset. We aimed to determine the trajectory of PHO after ICH onset and its association with outcome. Methods We did a prospective cohort study using a pre-specified scanning protocol in adults with first-ever spontaneous ICH and measured absolute PHO volumes on CT head scans at ICH diagnosis and 3±2, 7±2 and 14±2 days after ICH onset. We used the largest ICH if ICHs were multiple. The primary outcomes were (a) the trajectory of PHO after ICH onset and (b) the association between PHO (absolute volume at the time when most repeat CT head scans were obtained, and change in PHO volume at this time compared with the first CT head scan) and poor functional outcome (modified Rankin scale 3-6 at 90 days). We pre-specified multivariable logistic regression models of this association adjusting analyses for potential confounders: age, GCS, infratentorial ICH location and intraventricular extension. Results In 106 participants of whom forty nine (46%) were female, with a median ICH volume 7ml (interquartile range [IQR] 2-22ml), the trajectory of median PHO volume was an increase from 14ml (IQR 7-26ml) at diagnosis to 18ml (IQR 8-40ml) at 3±2 days (n=87), 20ml (IQR 8-48ml) at 7±2 days (n=93) and 21ml (IQR 10-54ml) at 14±2 days (n=78) (p=&amp;lt;0.001). PHO volume at each time point was collinear with ICH volume at diagnosis (│r│&amp;gt;0.7) but the change in PHO volume between diagnosis and each time point was not. Given collinearity, we used total lesion (i.e. ICH+PHO) volume instead of PHO volume in a logistic regression model of its association at each time point with outcome. Increasing total lesion (ICH+PHO) volume at day 7±2 was associated with poor functional outcome (adjusted OR per ml 1.02, 95% CI 1.00-1.03; p=0.036) but the increase in PHO volume between diagnosis and day 7±2 was not associated with poor functional outcome (adjusted OR per ml 1.03, 95% CI 0.99-1.07; p=0.132). Conclusion PHO volume increases throughout the first two weeks after onset of mild to moderate ICH. Total lesion (ICH+PHO) volume at day 7±2 was associated with poor functional outcome but the change in PHO volume between diagnosis and day 7±2 was not. Prospective cohort studies with larger sample sizes are needed to investigate these associations and their modifiers.</p

Integrative GWAS and co-localisation analysis suggests novel genes associated with age-related multimorbidity

Abstract Advancing age is the greatest risk factor for developing multiple age-related diseases. Therapeutic approaches targeting the underlying pathways of ageing, rather than individual diseases, may be an effective way to treat and prevent age-related morbidity while reducing the burden of polypharmacy. We harness the Open Targets Genetics Portal to perform a systematic analysis of nearly 1,400 genome-wide association studies (GWAS) mapped to 34 age-related diseases and traits, identifying genetic signals that are shared between two or more of these traits. Using locus-to-gene (L2G) mapping, we identify 995 targets with shared genetic links to age-related diseases and traits, which are enriched in mechanisms of ageing and include known ageing and longevity-related genes. Of these 995 genes, 128 are the target of an approved or investigational drug, 526 have experimental evidence of binding pockets or are predicted to be tractable, and 341 have no existing tractability evidence, representing underexplored genes which may reveal novel biological insights and therapeutic opportunities. We present these candidate targets for exploration and prioritisation in a web application