15,705 research outputs found
Approximate high energy alpha-particle nucleus collision model
Alpha particle-nucleus collision model for nucleon energy and angular distribution prediction and residual nuclei cross section
A preliminary report on the contact-independent antagonism of Pseudogymnoascus destructans by Rhodococcus rhodochrous strain DAP96253.
BackgroundThe recently-identified causative agent of White-Nose Syndrome (WNS), Pseudogymnoascus destructans, has been responsible for the mortality of an estimated 5.5 million North American bats since its emergence in 2006. A primary focus of the National Response Plan, established by multiple state, federal and tribal agencies in 2011, was the identification of biological control options for WNS. In an effort to identify potential biological control options for WNS, multiply induced cells of Rhodococcus rhodochrous strain DAP96253 was screened for anti-P. destructans activity.ResultsConidia and mycelial plugs of P. destructans were exposed to induced R. rhodochrous in a closed air-space at 15°C, 7°C and 4°C and were evaluated for contact-independent inhibition of conidia germination and mycelial extension with positive results. Additionally, in situ application methods for induced R. rhodochrous, such as fixed-cell catalyst and fermentation cell-paste in non-growth conditions, were screened with positive results. R. rhodochrous was assayed for ex vivo activity via exposure to bat tissue explants inoculated with P. destructans conidia. Induced R. rhodochrous completely inhibited growth from conidia at 15°C and had a strong fungistatic effect at 4°C. Induced R. rhodochrous inhibited P. destructans growth from conidia when cultured in a shared air-space with bat tissue explants inoculated with P. destructans conidia.ConclusionThe identification of inducible biological agents with contact-independent anti- P. destructans activity is a major milestone in the development of viable biological control options for in situ application and provides the first example of contact-independent antagonism of this devastating wildlife pathogen
An Extensive Collection of Stellar Wind X-ray Source Region Emission Line Parameters,Temperatures, Velocities, and Their Radial Distributions as Obtained from Chandra Observations of 17 OB Stars
Chandra high energy resolution observations have now been obtained from
numerous non-peculiar O and early B stars. The observed X-ray emission line
properties differ from pre-launch predictions, and the interpretations are
still problematic. We present a straightforward analysis of a broad collection
of OB stellar line profile data to search for morphological trends. X-ray line
emission parameters and the spatial distributions of derived quantities are
examined with respect to luminosity class. The X-ray source locations and their
corresponding temperatures are extracted by using the He-like f/i line ratios
and the H-like to He-like line ratios respectively. Our luminosity class study
reveals line widths increasing with luminosity. Although the majority of the OB
emission lines are found to be symmetric, with little central line
displacement, there is evidence for small, but finite, blue-ward line-shifts
that also increase with luminosity. The spatial X-ray temperature distributions
indicate that the highest temperatures occur near the star and steadily
decrease outward. This trend is most pronounced in the OB supergiants. For the
lower density wind stars, both high and low X-ray source temperatures exist
near the star. However, we find no evidence of any high temperature X-ray
emission in the outer wind regions for any OB star. Since the temperature
distributions are counter to basic shock model predictions, we call this the
"near-star high-ion problem" for OB stars. By invoking the traditional OB
stellar mass loss rates, we find a good correlation between the fir-inferred
radii and their associated X-ray continuum optical depth unity radii. We
conclude by presenting some possible explanations to the X-ray source problems
that have been revealed by this study.Comment: Published in 2007, ApJ, 668, 456. An Erratum scheduled for
publication in 2008, ApJ, 680, is included as an Appendix. The Erratum
corrects some tabulated data in 5 tables and 2 figure
The Environments around Long-Duration Gamma-Ray Burst Progenitors
Gamma-ray burst (GRB) afterglow observations have allowed us to significantly
constrain the engines producing these energetic explosions. Te redshift and
position information provided by these afterglows have already allowed us to
limit the progenitors of GRBs to only a few models. The afterglows may also
provide another observation that can place further constraints on the GRB
progenitor: measurements telling us about the environments surrounding GRBs.
Current analyses of GRB afterglows suggest that roughly half of long-duration
gamma-ray bursts occur in surroundings with density profiles that are uniform.
We study the constraints placed by this observation on both the classic
``collapsar'' massive star progenitor and its relative, the ``helium-merger''
progenitor. We study several aspects of wind mass-loss and find that our
modifications to the standard Wolf-Rayet mass-loss paradigm are not sufficient
to produce constant density profiles. Although this does not rule out the
standard ``collapsar'' progenitor, it does suggest a deficiency with this
model. We then focus on the He-merger models and find that such progenitors can
fit this particular constraint well. We show how detailed observations can not
only determine the correct progenitor for GRBs, but also allow us to study
binary evolution physics.Comment: 44 pages including 11 figure
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