125 research outputs found
Chandra and FUSE spectroscopy of the hot bare stellar core H1504+65
H1504+65 is an extremely hot hydrogen-deficient white dwarf with an effective
temperature close to 200,000 K. We present new FUV and soft X-ray spectra
obtained with FUSE and Chandra, which confirm that H1504+65 has an atmosphere
primarily composed of carbon and oxygen. The Chandra LETG spectrum (60-160
Angstroem) shows a wealth of photospheric absorption lines from highly ionized
oxygen, neon, and - for the first time identified in this star - magnesium and
suggests relatively high Ne and Mg abundances. This corroborates an earlier
suggestion that H1504+65 represents a naked C/O stellar core or even the C/O
envelope of an O-Ne-Mg white dwarf.Comment: 15 pages, 10 figures, accepted for publication in A&
High-resolution ultraviolet spectroscopy of PG1159-035 with HST and FUSE
PG1159-035 is the prototype of the PG1159 spectral class which consists of
extremely hot hydrogen-deficient (pre-) white dwarfs. It is also the prototype
of the GW Vir variables, which are non-radial g-mode pulsators. The study of
PG1159 stars reveals insight into stellar evolution and nucleosynthesis during
AGB and post-AGB phases. We perform a quantitative spectral analysis of
PG1159-035 focusing on the abundance determination of trace elements. We have
taken high-resolution ultraviolet spectra of PG1159-035 with the Hubble Space
Telescope and the Far Ultraviolet Spectroscopic Explorer. They are analysed
with non-LTE line blanketed model atmospheres. We confirm the high effective
temperature with high precision (Teff=140,000+/-5000 K) and the surface gravity
of logg=7. For the first time we assess the abundances of silicon, phosphorus,
sulfur, and iron. Silicon is about solar. For phosphorus we find an upper limit
of solar abundance. A surprisingly strong depletion of sulfur (2% solar) is
discovered. Iron is not detected, suggesting an upper limit of 30% solar. This
coincides with the Fe deficiency found in other PG1159 stars. We redetermine
the nitrogen abundance and find it to be lower by one dex compared to previous
analyses. The sulfur depletion is in contradiction with current models of AGB
star intershell nucleosynthesis. The iron deficiency confirms similar results
for other PG1159 stars and is explained by the conversion of iron into heavier
elements by n-capture in the s-processing environment of the precursor AGB
star. However, the extent of the iron depletion is stronger than predicted by
evolutionary models. The relatively low nitrogen abundance compared to other
pulsating PG1159 stars weakens the role of nitrogen as a distinctive feature of
pulsators and non-pulsators in the GW Vir instability strip.Comment: A&A accepted, 13 pages, 10 figure
Iron abundance in hot hydrogen-deficient central stars and white dwarfs from FUSE, HST, and IUE spectroscopy
We present a first systematic investigation of the iron abundance in very hot
(Teff>50,000K) hydrogen-deficient post-AGB stars. Our sample comprises 16
PG1159 stars and four DO white dwarfs. We use recent FUSE observations as well
as HST and IUE archival data to perform spectral analyses with line blanketed
NLTE model atmospheres. Iron is not detected in any PG1159 star. In most cases
this is compatible with a solar iron abundance due to limited quality of HST
and IUE data, although the tendency to an iron underabundance may be
recognized. However, the absence of iron lines in excellent FUSE spectra
suggests an underabundance by at least 1 dex in two objects (K1-16 NGC 7094). A
similar result has been reported recently in the [WC]-PG1159 transition object
Abell 78 (Werner et al. 2002). We discuss dust fractionation and s-process
neutron-captures as possible origins. We also announce the first identification
of sulfur in PG1159 stars.Comment: Accepted for publication in A&A, 10 pages, 9 figure
Vasopressors and Inotropes in the Treatment of Human Septic Shock: Effect on Innate Immunity?
Catecholamines have been suggested to modulate innate immune responses in experimental settings. The significance hereof in the treatment of human septic shock is unknown. We therefore sought if and how vasopressor/inotropic doses relate to pro-inflammatory mediators during treatment of septic shock. We prospectively studied 20 consecutive septic shock patients. For 3 days after admission, hemodynamic variables, lactate and plasma levels of interleukins (IL)-6 and 8, tumor necrosis factor (TNF)-α, and elastase-α1-antitrypsin were measured six hourly. Doses of vasoactive drugs were recorded. Of the 20 patients, nine died in the intensive care unit. Dobutamine doses were positively associated and related to TNF-α plasma levels, independently of disease severity, hemodynamics, and outcome, in multivariable models. Dopamine doses were positively associated with IL-6, and norepinephrine was inversely associated with IL-8 and TNF-α levels. Our observations suggest that catecholamines used in the treatment of human septic shock differ in their potential modulation of the innate immune response to sepsis in vivo. Dobutamine treatment may contribute to circulating TNF-α and dopamine to IL-6, independently of activated neutrophils. Conversely, norepinephrine may lack pro-inflammatory actions
Self-assembled hydrogel fibers for sensing the multi-compartment intracellular milieu
Targeted delivery of drugs and sensors into cells is an attractive technology with both medical and scientific applications. Existing delivery vehicles are generally limited by the complexity of their design, dependence on active transport, and inability to function within cellular compartments. Here, we developed self-assembled nanofibrous hydrogel fibers using a biologically inert, low-molecular-weight amphiphile. Self-assembled nanofibrous hydrogels offer unique physical/mechanical properties and can easily be loaded with a diverse range of payloads. Unlike commercially available E. coli membrane particles covalently bound to the pH reporting dye pHrodo, pHrodo encapsulated in self-assembled hydrogel-fibers internalizes into macrophages at both physiologic (37°C) and sub-physiologic (4°C) temperatures through an energy-independent, passive process. Unlike dye alone or pHrodo complexed to E. coli, pHrodo-SAFs report pH in both the cytoplasm and phagosomes, as well the nucleus. This new class of materials should be useful for next-generation sensing of the intracellular milieu
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PEG−peptide conjugates
The remarkable diversity of the self-assembly behavior
of PEG−peptides is reviewed, including self-assemblies formed by PEG−peptides with β-sheet and α-helical (coiled-coil) peptide sequences. The modes of self-assembly in solution and in the solid state are discussed. Additionally, applications in bionanotechnology and synthetic materials science are summarized
A fluorogenic cyclic peptide for imaging and quantification of drug-induced apoptosis
Programmed cell death or apoptosis is a central biological process that is dysregulated in many diseases, including inflammatory conditions and cancer. The detection and quantification of apoptotic cells in vivo is hampered by the need for fixatives or washing steps for non-fluorogenic reagents, and by the low levels of free calcium in diseased tissues that restrict the use of annexins. In this manuscript, we report the rational design of a highly stable fluorogenic peptide (termed Apo-15) that selectively stains apoptotic cells in vitro and in vivo in a calcium-independent manner and under wash-free conditions. Furthermore, using a combination of chemical and biophysical methods, we identify phosphatidylserine as a molecular target of Apo-15. We demonstrate that Apo-15 can be used for the quantification and imaging of drug-induced apoptosis in preclinical mouse models, thus creating opportunities for assessing the in vivo efficacy of anti-inflammatory and anti-cancer therapeutics
Application of high-resolution mass spectrometry to determination of baclofen in a case of fatal intoxication
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