248 research outputs found
Microcirculation vs. Mitochondria-What to Target?
Circulatory shock is associated with marked disturbances of the macro- and microcirculation and flow heterogeneities. Furthermore, a lack of tissue adenosine trisphosphate (ATP) and mitochondrial dysfunction are directly associated with organ failure and poor patient outcome. While it remains unclear if microcirculation-targeted resuscitation strategies can even abolish shock-induced flow heterogeneity, mitochondrial dysfunction and subsequently diminished ATP production could still lead to organ dysfunction and failure even if microcirculatory function is restored or maintained. Preserved mitochondrial function is clearly associated with better patient outcome. This review elucidates the role of the microcirculation and mitochondria during circulatory shock and patient management and will give a viewpoint on the advantages and disadvantages of tailoring resuscitation to microvascular or mitochondrial targets
The galactic population of white dwarfs
Original paper can be found at: http://www.iop.org/EJ/conf DOI: 10.1088/1742-6596/172/1/012004 [16th European White Dwarfs Workshop]The contribution of white dwarfs of the different Galactic populations to the stellar content of our Galaxy is only poorly known. Some authors claim a vast population of halo white dwarfs, which would be in accordance with some investigations of the early phases of Galaxy formation claiming a top-heavy initial– mass– function. Here, I present a model of the population of white dwarfs in the Milky Way based on observations of the local white dwarf sample and a standard model of Galactic structure. This model will be used to estimate the space densities of thin disc, thick disc and halo white dwarfs and their contribution to the baryonic mass budget of the Milky Way. One result of this investigation is that white dwarfs of the halo population contribute a large fraction of the Galactic white dwarf number count, but they are not responsible for the lion's share of stellar mass in the Milky Way. Another important result is the substantial contribution of the – often neglected – population of thick disc white dwarfs. Misclassification of thick disc white dwarfs is responsible for overestimates of the halo population in previous investigations.Peer reviewe
Faint NUV/FUV Standards from Swift/UVOT, GALEX and SDSS Photometry
At present, the precision of deep ultraviolet photometry is somewhat limited
by the dearth of faint ultraviolet standard stars. In an effort to improve this
situation, we present a uniform catalog of eleven new faint (u sim17)
ultraviolet standard stars. High-precision photometry of these stars has been
taken from the Sloan Digital Sky Survey and Galaxy Evolution Explorer and
combined with new data from the Swift Ultraviolet Optical Telescope to provide
precise photometric measures extending from the Near Infrared to the Far
Ultraviolet. These stars were chosen because they are known to be hot (20,000 <
T_eff < 50,000 K) DA white dwarfs with published Sloan spectra that should be
photometrically stable. This careful selection allows us to compare the
combined photometry and Sloan spectroscopy to models of pure hydrogen
atmospheres to both constrain the underlying properties of the white dwarfs and
test the ability of white dwarf models to predict the photometric measures. We
find that the photometry provides good constraint on white dwarf temperatures,
which demonstrates the ability of Swift/UVOT to investigate the properties of
hot luminous stars. We further find that the models reproduce the photometric
measures in all eleven passbands to within their systematic uncertainties.
Within the limits of our photometry, we find the standard stars to be
photometrically stable. This success indicates that the models can be used to
calibrate additional filters to our standard system, permitting easier
comparison of photometry from heterogeneous sources. The largest source of
uncertainty in the model fitting is the uncertainty in the foreground reddening
curve, a problem that is especially acute in the UV.Comment: Accepted for publication in Astrophysical Journal. 31 pages, 13
figures, electronic tables available from ApJ or on reques
Hot subdwarfs from the ESO Supernova Ia Progenitor Survey: II. Atmospheric parameters of subdwarf O stars
We address the origin and evolutionary status of hot subdwarf stars by
studying the optical spectral properties of 58 subdwarf O (sdO) stars.
Combining them with the results of our previously studied subdwarf B (sdB)
stars, we aim at investigating possible evolutionary links. We analyze
high-resolution ESO VLT UVES spectra from the ESO Supernova Ia Progenitor
Survey (SPY). Effective temperatures, gravities, and helium abundances are
determined simultaneously by fitting the profiles of H and He lines using
dedicated synthetic spectra in NLTE. Evidence for cool companions to 8 sdOs as
well as a binary consisting of two sdO stars is found. A correlation between He
abundances and the presence of carbon and/or nitrogen lines emerges: below
solar He abundance, no sdO shows C or N lines. In contrast, C and/or N lines
are present in ALL sdOs with super- solar He abundance. We thus use the solar
He abundance to divide our sample into He-deficient and He-enriched sdOs. While
He-deficient sdOs are scattered in a wide range of the Teff-log(g)-diagram,
most of the He-enriched sdOs cluster in a narrow region at Teff = 40,000 ...
50,000K and log(g)=5.5 ... 6.0. An evolu- tionary link between sdBs and sdOs
appears plausible only for the He-deficient sdOs indicating that they are the
likely successors to sdBs. The properties of He-enriched sdOs cannot be
explained with canonical single star evolutionary models. Alternative scenarios
(late hot flasher) as well as for binary evolution (white dwarf merger;
post-RGB evolution) are tested. While we regard the post-RGB scenario as
inappropriate, the white dwarf merger and the late hot flasher scenarios remain
viable to explain the origin of He-enriched sdOs.Comment: 14 pages, 10 figures, Astronomy & Astrophysics accepte
Know Your Neighborhood: A Detailed Model Atmosphere Analysis of Nearby White Dwarfs
We present improved atmospheric parameters of nearby white dwarfs lying
within 20 pc of the Sun. The aim of the current study is to obtain the best
statistical model of the least-biased sample of the white dwarf population. A
homogeneous analysis of the local population is performed combining detailed
spectroscopic and photometric analyses based on improved model atmosphere
calculations for various spectral types including DA, DB, DC, DQ, and DZ stars.
The spectroscopic technique is applied to all stars in our sample for which
optical spectra are available. Photometric energy distributions, when
available, are also combined to trigonometric parallax measurements to derive
effective temperatures, stellar radii, as well as atmospheric compositions. A
revised catalog of white dwarfs in the solar neighborhood is presented. We
provide, for the first time, a comprehensive analysis of the mass distribution
and the chemical distribution of white dwarf stars in a volume-limited sample.Comment: 104 pages, 22 figures, 2 tables, accepted for publication in the
Astrophysical Journal Supplemen
The stellar content of the Hamburg/ESO survey. I. Automated selection of DA white dwarfs
We describe automatic procedures for the selection of DA white dwarfs in the
Hamburg/ESO objective-prism survey (HES). For this purpose, and the selection
of other stellar objects (e.g., metal-poor stars and carbon stars), a flexible,
robust algorithm for detection of stellar absorption and emission lines in the
digital spectra of the HES was developed. Broad band (U-B, B-V) and narrow band
(Str\"omgren c_1) colours can be derived directly from HES spectra, with
precisions of sigma(U-B)=0.092mag; sigma(B-V)=0.095mag; sigma(c_1)=0.15mag.
We describe simulation techniques that allow to convert model or slit spectra
to HES spectra. These simulated objective-prism spectra are used to determine
quantitative selection criteria, and for the study of selection functions. We
present an atlas of simulated HES spectra of DA and DB white dwarfs.
Our current selection algorithm is tuned to yield maximum efficiency of the
candidate sample (minimum contamination with non-DAs). DA candidates are
selected in the B-V versus U-B and c_1 versus W_\lambda(Hbeta+Hgamma+Hdelta)
parameter spaces. The contamination of the resulting sample with hot subdwarfs
is expected to be as low as ~8%, while there is essentially no contamination
with main sequence or horizontal branch stars. We estimate that with the
present set of criteria, ~80% of DAs present in the HES database are recovered.
A yet higher degree of internal completeness could be reached at the expense of
higher contamination. However, the external completeness is limited by
additional losses caused by proper motion effects and the epoch differences
between direct and spectral plates used in the HES.Comment: A&A in press. 15 pages, 15 figures. Includes table with coordinates
and magnitudes for 46 spectroscopically confirmed DA white dwarfs and hot
subdwarf
Interactions between a Trawl Fishery and Spatial Closures for Biodiversity Conservation in the Great Barrier Reef World Heritage Area, Australia
Background\ud
The Queensland East Coast Otter Trawl Fishery (ECOTF) for penaeid shrimp fishes within Australia's Great Barrier Reef World Heritage Area (GBRWHA). The past decade has seen the implementation of conservation and fisheries management strategies to reduce the impact of the ECOTF on the seabed and improve biodiversity conservation. New information from electronic vessel location monitoring systems (VMS) provides an opportunity to review the interactions between the ECOTF and spatial closures for biodiversity conservation.\ud
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Methodology and Results\ud
We used fishing metrics and spatial information on the distribution of closures and modelled VMS data in a geographical information system (GIS) to assess change in effort of the trawl fishery from 2001–2009 and to quantify the exposure of 70 reef, non-reef and deep water bioregions to trawl fishing. The number of trawlers and the number of days fished almost halved between 2001 and 2009 and new spatial closures introduced in 2004 reduced the area zoned available for trawl fishing by 33%. However, we found that there was only a relatively minor change in the spatial footprint of the fishery as a result of new spatial closures. Non-reef bioregions benefited the most from new spatial closures followed by deep and reef bioregions.\ud
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Conclusions/Significance\ud
Although the catch of non target species remains an issue of concern for fisheries management, the small spatial footprint of the ECOTF relative to the size of the GBRWHA means that the impact on benthic habitats is likely to be negligible. The decline in effort as a result of fishing industry structural adjustment, increasing variable costs and business decisions of fishers is likely to continue a trend to fish only in the most productive areas. This will provide protection for most benthic habitats without any further legislative or management intervention
Rocky Planetesimals as the Origin of Metals in DZ Stars
{Abridged}. An analysis of the calcium and hydrogen abundances, Galactic
positions and kinematics of 146 DZ stars from the Sloan Digital Sky Survey
demonstrates that interaction with the interstellar medium cannot account for
their externally polluted atmospheres. The calcium-to-hydrogen ratios for the
37 DZA stars are dominated by super-solar values, as are the lower limits for
the remaining 109 DZ stars. All together their metal-contaminated convective
envelopes contain 10^{20+-2} g of calcium, commensurate with the masses of
calcium inferred for large asteroids. It is probable that these stars are
contaminated by circumstellar matter; the rocky remains of terrestrial
planetary systems. In this picture, two predictions emerge: 1) at least 3.5% of
all main sequence A- and F-type stars build terrestrial planets; and 2) the DZA
stars are externally polluted by both metals and hydrogen, and hence constrain
the frequency and mass of water-rich, extrasolar planetesimals.Comment: Accepted to MNRA
Doom and Boom on a Resilient Reef: Climate Change, Algal Overgrowth and Coral Recovery
Background: Coral reefs around the world are experiencing large-scale degradation, largely due to global climate change, overfishing, diseases and eutrophication. Climate change models suggest increasing frequency and severity of warming-induced coral bleaching events, with consequent increases in coral mortality and algal overgrowth. Critically, the recovery of damaged reefs will depend on the reversibility of seaweed blooms, generally considered to depend on grazing of the seaweed, and replenishment of corals by larvae that successfully recruit to damaged reefs. These processes usually take years to decades to bring a reef back to coral dominance
The stellar content of the Hamburg/ESO survey. II. A large, homogeneously-selected sample of high latitude carbon stars
We present a sample of 403 faint high latitude carbon (FHLC) stars selected
from the digitized objective prism plates of the Hamburg/ESO Survey (HES).
Because of the ~15 Angstroem spectral resolution and high signal-to-noise ratio
of the HES prism spectra, our automated procedure based on the detection of C_2
and CN molecular bands permits high-confidence identification of carbon stars
without the need for follow-up spectroscopy. From a set of 329 plates (87% of
the survey), covering 6400 square degrees to a magnitude limit of V~16.5, we
analyze the selection efficiency and effective surface area of the HES FHLC
survey to date. The surface density of FHLC stars that we detect (0.072 +/-
0.005 square degrees) is 2-4 times higher than that of previous objective prism
and CCD surveys at high galactic latitude, even though those surveys claimed a
limiting magnitude up to 1.5 magnitudes fainter. This attests to the highest
selection sensitivity yet achieved for these types of stars.Comment: 8 pages, 6 figures; A&A in pres
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