3,346 research outputs found
A Quarter Century, Not a Raised Voice
This dedication was in recognition of Wilbert D. Hamâs retirement from the University of Kentucky College of Law faculty. Wilber D. Ham served on the faculty from 1949 until 1986
Properties of Hot Stars in the Wolf-Rayet galaxy NGC5253 from ISO Spectroscopy
ISO-SWS spectroscopy of the WR galaxy NGC5253 is presented, and analysed to
provide estimates of its hot young star population. Our approach differs from
previous investigations in that we are able to distinguish between the regions
in which different infrared fine-structure lines form, using complementary
ground-based observations. The high excitation nebular [SIV] emission is formed
in a very compact region, which we attribute to the central super-star-nucleus,
and lower excitation [NeII] nebular emission originates in the galactic core.
We use photo-ionization modelling coupled with the latest theoretical O-star
flux distributions to derive effective stellar temperatures and ionization
parameters of Teff>38kK, logQ=8.25 for the compact nucleus, with Teff=35kK,
logQ<8 for the larger core. Results are supported by more sophisticated
calculations using evolutionary synthesis models. We assess the contribution
that Wolf-Rayet stars may make to highly ionized nebular lines (e.g. [OIV]).
From our Br(alpha) flux, the 2" nucleus contains the equivalent of
approximately 1000 O7V star equivalents and the starburst there is 2-3Myr old;
the 20" core contains about 2500 O7V star equivalents, with a representative
age of 5Myr. The Lyman ionizing flux of the nucleus is equivalent to the 30
Doradus region. These quantities are in good agreement with the observed mid-IR
dust luminosity of 7.8x10^8 L(sun) Since this structure of hot clusters
embedded in cooler emission may be common in dwarf starbursts, observing a
galaxy solely with a large aperture may result in confusion. Neglecting the
spatial distribution of nebular emission in NGC5253, implies `global' stellar
temperatures (or ages) of 36kK (4.8Myr) and 39kK (2.9 or 4.4Myr) from the
observed [NeIII/II] and [SIV/III] line ratios, assuming logQ=8.Comment: 16 pages, 7 figures, uses mn.sty, to appear in MNRA
Would Reducing Tenure Probabilities Increase Faculty Salaries?
The simplest competitive labor market model asserts that if tenure is a desirable job characteristic for professors, they should be willing to pay for it by accepting lower salaries. Conversely, if an institution unilaterally reduces the probability that its assistant professors receive tenure, it will have to pay higher salaries to attract new faculty. Our paper tests this theory using data on salary offers accepted by new assistant professors at economics departments in the United States during the 1974-75 to 1980-81 period, along with data on the proportion of new Ph.Ds hired by each department between 1970 and 1980 that ultimately received tenure in the department or at a comparable or higher quality department. We find evidence that a tradeoff did exist. Equally important, departments that offer low tenure probabilities to assistant professors also paid higher salaries to their tenured faculty. We attribute this to their need to pay higher salaries to attract tenured faculty from the external market.
Implications of ocean acidification for marine microorganisms from the free-living to the host-associated
Anthropogenic CO2 emissions are causing oceans to become more acidic, with consequences for all marine life including microorganisms. Studies reveal that from the microbes that occupy the open ocean to those intimately associated with their invertebrate hosts changing ocean chemistry will alter the critical functions of these important organisms. Our current understanding indicates that bacterial communities associated with their host will shift as pH drops by another 0.2â0.4 units over the next 100 years. It is unclear what impacts this will have for host health, however, increased vulnerability to disease seems likely for those associated with reef corals. Natural CO2 seeps have provided a unique setting for the study of microbial communities under OA in situ, where shifts in the bacterial communities associated with corals at the seep are correlated with a decline in abundance of the associated coral species. Changes to global biogeochemical cycles also appear likely as photosynthesis and nitrogen fixation by pelagic microbes becomes enhanced under low pH conditions. However, recent long-term studies have shown that pelagic microbes are also capable of evolutionary adaptation, with some physiological responses to a decline in pH restored after hundreds of generations at high pCO2 levels. The impacts of ocean acidification (OA) also will not work in isolation, thus synergistic interactions with other potential stressors, such as rising seawater temperatures, will likely exacerbate the microbial response to OA. This review discusses our existing understanding of the impacts of OA on both pelagic and host-associated marine microbial communities, whilst highlighting the importance of controlled laboratory studies and in situ experiments, to fill the current gaps in our knowledge
Far-UV FUSE spectroscopy of the OVI resonance doublet in Sand2 (WO)
We present Far-Ultraviolet Spectroscopic Explorer (FUSE) spectroscopy of Sand
2, a LMC WO-type Wolf-Rayet star, revealing the OVI resonance P Cygni doublet
at 1032-38A. These data are combined with HST/FOS ultraviolet and Mt Stromlo
2.3m optical spectroscopy, and analysed using a spherical, non-LTE,
line-blanketed code. Our study reveals exceptional stellar parameters:
T*=150,000K, v_inf=4100 km/s, log (L/Lo)=5.3, and Mdot=10^-5 Mo/yr if we adopt
a volume filling factor of 10%. Elemental abundances of C/He=0.7+-0.2 and
O/He=0.15(-0.05+0.10) by number qualitatively support previous recombination
line studies. We confirm that Sand 2 is more chemically enriched in carbon than
LMC WC stars, and is expected to undergo a supernova explosion within the next
50,000 yr.Comment: 17 pages, 4 figures, AASTeX preprint format. This paper will appear
in a special issue of ApJ Letters devoted to the first scientific results
from the FUSE missio
Global patterns in the divergence between phylogenetic diversity and species richness in terrestrial birds
2,3,8-trisubstituted quinolines with antimalarial activity
FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICO - CNPQCombination therapy drugs are considered a fundamental way to control malaria as it mimimizes the risk of emergence of resistance to the individual partner drugs. Consequently, this type of therapy constitutes a driving force for the discovery of new drug901212151231FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICO - CNPQFUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICO - CNPQSEM INFORMAĂĂOSEM INFORMAĂĂOWe especially thank Prof. Marcos Eberlin (Thomsom Laboratory) for HRMS analyses. We are grateful to Sergio Wittlin, Sibylle Sax and the Swiss Tropical and Public Health Institute (Basel, Switzerland) for conducting the resistance assays. We thank Mark We
A Survey of Local Group Galaxies Currently Forming Stars: III. A Search for Luminous Blue Variables and Other H-alpha Emission-Lined Stars
We describe a search for H-alpha emission-lined stars in M31, M33, and seven
dwarfs in or near the Local Group (IC 10, NGC 6822, WLM, Sextans B, Sextans A,
Pegasus and the Phoenix dwarf) using interference filter imaging with the KPNO
and CTIO 4-m telescope and Mosaic cameras. The survey is aimed primarily at
identifying new Luminous Blue Variables (LBVs) from their spectroscopic
similarity to known LBVs, avoiding the bias towards photometric variability,
which may require centuries to manifest itself if LBVs go through long
quiescent periods. Followup spectroscopy with WIYN confirms that our survey
detected a wealth of stars whose spectra are similar to the known LBVs. We
"classify" the spectra of known LBVs, and compare these to the spectra of the
new LBV candidates. We demonstrate spectacular spectral variability for several
of the new LBV candidates, such as AM2, previously classified as a Wolf-Rayet
star, which now shows FeI, FeII and Balmer emission lines but neither the NIII
4634,42 nor HeII 4686 emission that it did in 1982. Profound spectral changes
are also noted for other suspected and known LBVs. Several of the LBV
candidates also show >0.5 mag changes in V over the past 10-20 years. The
number of known or suspected LBVs is now 24 in M31, 37 in M33, 1 in NGC 6822,
and 3 in IC 10. We estimate that the total number of LBVs in M31 and M33 may be
several hundred, in contrast to the 8 known historically through large-scale
photometric variability. This has significant implications for the time scale
of the LBV phase. We also identify a few new WRs and peculiar emission-lined
objects.Comment: Accepted by the Astronomical Journal. Version with higher quality
figures may be downloaded from http://www.lowell.edu/users/massey/has.pdf.g
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