8,429 research outputs found
Environmental protection requirements for scout/shuttle auxiliary stages
The requirements for enabling the Scout upper stages to endure the expected temperature, mechanical shock, acoustical and mechanical vibration environments during a specified shuttle mission were determined. The study consisted of: determining a shuttle mission trajectory for a 545 kilogram (1200 pound) Scout payload; compilation of shuttle environmental conditions; determining of Scout upper stages environments in shuttle missions; compilation of Scout upper stages environmental qualification criteria and comparison to shuttle mission expected environments; and recommendations for enabling Scout upper stages to endure the exptected shuttle mission environments
DNA and pacific commensal models : applications, construction, limitations, and future prospects
Components of the Pacific transported landscape have been used as proxies to trace the prehistoric movement of humans across the Pacific for almost two decades. Analyses of archaeological remains and DNA sequences of plants, animals, and microorganisms moved by or with humans have contributed to understanding prehistoric migration, trade, exchange, and sometimes revealed the geographic origins of particular plants and animals. This paper presents the basic elements of a DNA-based commensal model and discusses the phylogenetic and population genetic approaches these models employ. A clear delineation of the underlying assumptions of these models and the background information required to construct them have yet to appear in the literature. This not only provides a framework with which to construct a commensal model but also highlights gaps in current knowledge. The ways in which commensal models have enriched archaeological reconstructions will be highlighted, as will their current limitations. With these limitations in mind, options will be outlined for augmenting commensal models through the application of established techniques and new technologies in order to provide the best tools for reconstructing ancient human mobility and behavior in the Pacific and beyond
Atomic data for the astrophysics : Fe XII soft X-ray lines.
We present new large-scale R-matrix (up to n = 4) and distorted-wave (DW, up to n = 6) scattering calculations for electron collisional excitation of Fe xii. The first aim is to provide accurate atomic data for the soft X-rays, where strong decays from the n = 4 levels are present. As found in previous work on Fe x, resonances attached to n = 4 levels increase the cross-sections for excitations from the ground state to some n = 4 levels, when compared to DW calculations. Cascading from higher levels is also important. We provide a number of models and line intensities, and list a number of strong unidentified lines. The second aim is to assess the effects of the large R-matrix calculation on the n = 3 transitions. Compared to our previous (n = 3) R-matrix calculation, we find overall excellent agreement to within a few percent, however a few key density diagnostic EUV intensities differ by about 60% at coronal densities. The new atomic data result in lower electron densities, resolving previous discrepancies with solar observations
Collision strengths for nebular [O III] optical and infrared lines
We present electron collision strengths and their thermally averaged values for the nebular forbidden lines of the astronomically abundant doubly ionized oxygen ion, O2+, in an intermediate coupling scheme using the Breit–Pauli relativistic terms as implemented in an R-matrix atomic scattering code. We use several atomic targets for the R-matrix scattering calculations including one with 72 atomic terms. We also compare with new results obtained using the intermediate coupling frame transformation method. We find spectroscopically significant differences against a recent Breit–Pauli calculation for the excitation of the [O iii] λ4363 transition but confirm the results of earlier calculations
Atomic data for the x-ray lines of Fe viii and Fe ix
The distorted wave extension of the autostructure code has been used to calculate energy levels, radiative transition probabilities and collisional excitation rates of Fe viii and Fe ix up to n = 6 for Fe ix and n = 7 for Fe viii. We have compared some of the data with previous calculations, finding overall agreement for radiative transition rates, but interesting differences for some collisional data. We have merged our data for the higher energy levels with published R-matrix collisional excitation rates for the lower ones to calculate spectral line intensities and compare them with observations. In particular, we have focused on the transitions from high energy levels of Fe viii & Fe ix which are present in the 93–95 Å region. A few new identifications are tentatively provided. We find that Fe ix 5f–3d and Fe viii 7f–3d transitions only comprise a small fraction of the observed lines in the 93–95 Å region for quiet Sun conditions, and thus their contribution to the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) 94 Å band is expected to be small
ORFEUS II and IUE Spectroscopy of EX Hydrae
Using ORFEUS-SPAS II FUV spectra, IUE UV spectra, and archival EUVE deep
survey photometry, we present a detailed picture of the behavior of the
magnetic cataclysmic variable EX Hydrae. Like HUT spectra of this source, the
FUV and UV spectra reveal broad emission lines of He II, C II-IV, N III and V,
O VI, Si III-IV, and Al III superposed on a continuum which is blue in the UV
and nearly flat in the FUV. Like ORFEUS spectra of AM Her, the O VI doublet is
resolved into broad and narrow emission components. Consistent with its
behavior in the optical, the FUV and UV continuum flux densities, the FUV and
UV broad emission line fluxes, and the radial velocity of the O VI broad
emission component all vary on the spin phase of the white dwarf, with the
maximum of the FUV and UV continuum and broad emission line flux light curves
coincident with maximum blueshift of the broad O VI emission component. On the
binary phase, the broad dip in the EUV light curve is accompanied by strong
eclipses of the UV emission lines and by variations in both the flux and radial
velocity of the O VI narrow emission component. The available data are
consistent with the accretion funnel being the source of the FUV and UV
continuum and the O VI broad emission component, and the white dwarf being the
source of the O VI narrow emission component.Comment: 21 pages, 10 Postscript figures; LaTeX format, uses aaspp4.sty;
table2.tex included separately because it must be printed sideways - see
instructions in the file; accepted on 1999 Feb 20 for publication in The
Astrophysical Journa
A Bayesian method for evaluating and discovering disease loci associations
Background: A genome-wide association study (GWAS) typically involves examining representative SNPs in individuals from some population. A GWAS data set can concern a million SNPs and may soon concern billions. Researchers investigate the association of each SNP individually with a disease, and it is becoming increasingly commonplace to also analyze multi-SNP associations. Techniques for handling so many hypotheses include the Bonferroni correction and recently developed Bayesian methods. These methods can encounter problems. Most importantly, they are not applicable to a complex multi-locus hypothesis which has several competing hypotheses rather than only a null hypothesis. A method that computes the posterior probability of complex hypotheses is a pressing need. Methodology/Findings: We introduce the Bayesian network posterior probability (BNPP) method which addresses the difficulties. The method represents the relationship between a disease and SNPs using a directed acyclic graph (DAG) model, and computes the likelihood of such models using a Bayesian network scoring criterion. The posterior probability of a hypothesis is computed based on the likelihoods of all competing hypotheses. The BNPP can not only be used to evaluate a hypothesis that has previously been discovered or suspected, but also to discover new disease loci associations. The results of experiments using simulated and real data sets are presented. Our results concerning simulated data sets indicate that the BNPP exhibits both better evaluation and discovery performance than does a p-value based method. For the real data sets, previous findings in the literature are confirmed and additional findings are found. Conclusions/Significance: We conclude that the BNPP resolves a pressing problem by providing a way to compute the posterior probability of complex multi-locus hypotheses. A researcher can use the BNPP to determine the expected utility of investigating a hypothesis further. Furthermore, we conclude that the BNPP is a promising method for discovering disease loci associations. © 2011 Jiang et al
A simple and robust method for connecting small-molecule drugs using gene-expression signatures
Interaction of a drug or chemical with a biological system can result in a
gene-expression profile or signature characteristic of the event. Using a
suitably robust algorithm these signatures can potentially be used to connect
molecules with similar pharmacological or toxicological properties. The
Connectivity Map was a novel concept and innovative tool first introduced by
Lamb et al to connect small molecules, genes, and diseases using genomic
signatures [Lamb et al (2006), Science 313, 1929-1935]. However, the
Connectivity Map had some limitations, particularly there was no effective
safeguard against false connections if the observed connections were considered
on an individual-by-individual basis. Further when several connections to the
same small-molecule compound were viewed as a set, the implicit null hypothesis
tested was not the most relevant one for the discovery of real connections.
Here we propose a simple and robust method for constructing the reference
gene-expression profiles and a new connection scoring scheme, which importantly
allows the valuation of statistical significance of all the connections
observed. We tested the new method with the two example gene-signatures (HDAC
inhibitors and Estrogens) used by Lamb et al and also a new gene signature of
immunosuppressive drugs. Our testing with this new method shows that it
achieves a higher level of specificity and sensitivity than the original
method. For example, our method successfully identified raloxifene and
tamoxifen as having significant anti-estrogen effects, while Lamb et al's
Connectivity Map failed to identify these. With these properties our new method
has potential use in drug development for the recognition of pharmacological
and toxicological properties in new drug candidates.Comment: 8 pages, 2 figures, and 2 tables; supplementary data supplied as a
ZIP fil
Near-infrared Observations of Nova V574 Puppis (2004)
We present results obtained from extensive near-infrared spectroscopic and
photometric observations of nova V574 Pup during its 2004 outburst. The
observations were obtained over four months, starting from 2004 November 25
(four days after the nova outburst) to 2005 March 20. The near-IR JHK light
curve is presented - no evidence is seen from it for dust formation to have
occurred during our observations. In the early decline phase, the JHK spectra
of the nova are dominated by emission lines of hydrogen Brackett and Paschen
series, OI, CI and HeI. We also detect the fairly uncommon Fe II line at 1.6872
micron in the early part of our observations. The strengths of the HeI lines at
1.0830 micron and 2.0585 micron are found to become very strong towards the end
of the observations indicating a progression towards higher excitation
conditions in the nova ejecta. The width of the emission lines do not show any
significant change during the course of our observations. The slope of the
continuum spectrum was found to have a lambda^{-2.75} dependence in the early
stages which gradually becomes flatter with time and changes to a free-free
spectral dependence towards the later stages. Recombination analysis of the HI
lines shows deviations from Case B conditions during the initial stages.
However, towards the end of our observations, the line strengths are well
simulated with case B model values with electron density n_e = 10^{9-10}
cm^{-3} and a temperature equal to 10^4 K. Based on our distance estimate to
the nova of 5.5 kpc and the observed free-free continuum emission in the later
part of the observations, we estimate the ionized mass of the ejecta to be
between 10^{-5} and 10^{-6} solar-mass.Comment: 10 pages, 8 figures, Accepted for publication in MNRA
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