1,076 research outputs found
The Most Metal-Poor Stars. II. Chemical Abundances of 190 Metal-Poor Stars Including 10 New Stars With [Fe/H] < -3.5
We present a homogeneous chemical abundance analysis of 16 elements in 190
metal-poor Galactic halo stars (38 program and 152 literature objects). The
sample includes 171 stars with [Fe/H] < -2.5, of which 86 are extremely metal
poor, [Fe/H] < -3.0. Our program stars include ten new objects with [Fe/H] <
-3.5. We identify a sample of "normal" metal-poor stars and measure the trends
between [X/Fe] and [Fe/H], as well as the dispersion about the mean trend for
this sample. Using this mean trend, we identify objects that are chemically
peculiar relative to "normal" stars at the same metallicity. These chemically
unusual stars include CEMP-no objects, one star with high [Si/Fe], another with
high [Ba/Sr], and one with unusually low [X/Fe] for all elements heavier than
Na. The Sr and Ba abundances indicate that there may be two nucleosynthetic
processes at lowest metallicity that are distinct from the main r-process.
Finally, for many elements, we find a significant trend between [X/Fe] versus
Teff which likely reflects non-LTE and/or 3D effects. Such trends demonstrate
that care must be exercised when using abundance measurements in metal-poor
stars to constrain chemical evolution and/or nucleosynthesis predictions.Comment: Accepted for publication in Ap
Regulation of Fas-Mediated Apoptosis by N-ras in Melanoma
Oncogenic ras has been shown to downregulate Fas receptor expression and increase Fas ligand expression and thus contribute to resistance to Fas-mediated cell death in several cell types. The effects of ras on Fas-mediated apoptosis have not been studied in melanoma. We studied the effects of activated N-ras by measuring Fas, Fas ligand, and FLIP expression as well as susceptibility to Fas-ligand-induced cell death in transfectants of WM35, a radial growth phase human melanoma cell line. Based on quantitative polymerase chain reaction and fluorescence-activated cell sorter analysis, we found that the ras transfectants expressed less Fas mRNA and surface Fas receptor. Cr51 release cytotoxicity assays demonstrated less susceptibility to Fas-mediated apoptosis in ras transfectants, correlating with the Fas mRNA and protein expression results. Ras inhibition with the specific inhibitor FTI-277 showed that downregulation of Fas in the ras transfectants could be reversed. This correlates with cytotoxicity experiments showing that ras inhibition increases susceptibility to Fas-mediated apoptosis. The control transfectants expressed FLIP but ras did not affect FLIP expression. The control and ras transfectants did not express Fas ligand as demonstrated by reverse transcriptase polymerase chain reaction and fluorescence-activated cell sorter analysis. Cytotoxicity assays further confirmed that these melanoma ras transfectants do not express functional Fas ligand. These results suggest that ras contributes to tumor progression by decreasing susceptibility to Fas-mediated cell death at least in part through downregulation of Fas receptor at the transcriptional level
Double-Rashba materials for nanocrystals with bright ground-state excitons
While nanoscale semiconductor crystallites provide versatile fluorescent
materials for light-emitting devices, such nanocrystals suffer from the "dark
exciton"\unicode{x2014}an optically inactive electronic state into which the
nanocrystal relaxes before emitting. Recently, a theoretical mechanism was
discovered that can potentially defeat the dark exciton. The Rashba effect can
invert the order of the lowest-lying levels, creating a bright excitonic ground
state. To identify materials that exhibit this behavior, here we perform an
extensive high-throughput computational search of two large open-source
materials databases. Based on a detailed understanding of the Rashba mechanism,
we define proxy criteria and screen over 500,000 solids, generating 173
potential "bright-exciton" materials. We then refine this list with
higher-level first-principles calculations to obtain 28 candidates. To confirm
the potential of these compounds, we select five and develop detailed
effective-mass models to determine the nature of their lowest-energy excitonic
state. We find that four of the five solids (BiTeCl, BiTeI, GaTe, and
KIO) can yield bright ground-state excitons. Our approach thus reveals
promising materials for future experimental investigation of bright-exciton
nanocrystals.Comment: 19 pages, 4 figure
SN1997cy/GRB970514 - A New Piece in the GRB Puzzle?
We present observations of SN1997cy, a supernova discovered as part of the
Mount Stromlo Abell Cluster SN Search, which does not easily fit into the
traditional classification scheme for supernovae. This object's extraordinary
optical properties and coincidence with GRB970514, a short duration gamma ray
burst, suggest a second case, after SN1998bw/GRB980425, for a SN-GRB
association. SN1997cy is among the most luminous SNe yet discovered and has a
peculiar spectrum. We present evidence that SN1997cy ejected approximately 2
solar masses of 56Ni, supported by its late-time light curve, and FeII/[FeIII]
lines in its spectrum, although it is possible that both these observations can
be explained via circumstellar interaction. While SN1998bw and SN1997cy appear
to be very different objects with respect to both their gamma ray and optical
properties, SN1997cy and the optical transient associated with GRB970508 have
roughly similar late-time optical behavior. This similarity may indicate that
the late-time optical output of these two intrinsically bright transient events
have a common physical process. Although the connection between GRB970514 and
SN1997cy is suggestive, it is not conclusive. However, if this association is
real, followup of short duration GRBs detected with BATSE or HETE2 should
reveal objects similar to SN1997cy.Comment: 26 pages including 6 postscript figures and 3 tables. Submitted to
ApJ. Re-calibrated photometry - objects are about 0.3mags brighter than in
original versio
THE ROLE OF EHEALTH IN DISASTERS: A STRATEGY FOR EDUCATION, TRAINING AND INTEGRATION IN DISASTER MEDICINE
This paper describes the origins and progress of an international project to advance disaster eHealth (DEH) â the application of eHealth technologies to enhance the delivery of healthcare in disasters. The study to date has focused on two major themes; the role of DEH in facilitating inter-agency communication in disaster situations, and the fundamental need to promote awareness of DEH in the education of disaster managers and health professionals. The paper deals mainly with on-going research on the second of these themes, surveying the current provision of disaster medicine education, the design considerations for a DEH programme for health professionals, the key curriculum topics, and the optimal delivery mode
Estimating Seroprevalence of SARS-CoV-2 in Ohio: A Bayesian Multilevel Poststratification Approach with Multiple Diagnostic Tests
Globally the SARS-CoV-2 coronavirus has infected more than 59 million people
and killed more than 1.39 million. Designing and monitoring interventions to
slow and stop the spread of the virus require knowledge of how many people have
been and are currently infected, where they live, and how they interact. The
first step is an accurate assessment of the population prevalence of past
infections. There are very few population-representative prevalence studies of
the SARS-CoV-2 coronavirus, and only two American states -- Indiana and
Connecticut -- have reported probability-based sample surveys that characterize
state-wide prevalence of the SARS-CoV-2 coronavirus. One of the difficulties is
the fact that the tests to detect and characterize SARS-CoV-2 coronavirus
antibodies are new, not well characterized, and generally function poorly.
During July, 2020, a survey representing all adults in the State of Ohio in the
United States collected biomarkers and information on protective behavior
related to the SARS-CoV-2 coronavirus. Several features of the survey make it
difficult to estimate past prevalence: 1) a low response rate, 2) very low
number of positive cases, and 3) the fact that multiple, poor quality
serological tests were used to detect SARS-CoV-2 antibodies. We describe a new
Bayesian approach for analyzing the biomarker data that simultaneously
addresses these challenges and characterizes the potential effect of selective
response. The model does not require survey sample weights, accounts for
multiple, imperfect antibody test results, and characterizes uncertainty
related to the sample survey and the multiple, imperfect, potentially
correlated tests
Heteroresistance to the model antimicrobial peptide polymyxin B in the emerging Neisseria meningitidis lineage 11.2 urethritis clade: mutations in the pilMNOPQ operon
Clusters of Neisseria meningitidis (Nm) urethritis among primarily heterosexual males in multiple US cities have been attributed to a unique nonâencapsulated meningococcal clade (the US Nm urethritis clade, US_NmUC) within the hypervirulent clonal complex 11. Resistance to antimicrobial peptides (AMPs) is a key feature of urogenital pathogenesis of the closely related species, Neisseria gonorrhoeae. The US_NmUC isolates were found to be highly resistant to the model AMP, polymyxin B (PmB, MICs 64â256 ”g mlâ1). The isolates also demonstrated stable subpopulations of heteroresistant colonies that showed near total resistant to PmB (MICs 384â1024 ”g mlâ1) and colistin (MIC 256 ”g mlâ1) as well as enhanced LLâ37 resistance. This is the first observation of heteroresistance in N. meningitidis. Consistent with previous findings, overall PmB resistance in US_NmUC isolates was due to active Mtr efflux and LptAâmediated lipid A modification. However, whole genome sequencing, variant analyses and directed mutagenesis revealed that the heteroresistance phenotypes and very highâlevel AMP resistance were the result of point mutations and IS1655 element movement in the pilMNOPQ operon, encoding the type IV pilin biogenesis apparatus. Crossâresistance to other classes of antibiotics was also observed in the heteroresistant colonies. Highâlevel resistance to AMPs may contribute to the pathogenesis of US_NmUC
- âŠ