420 research outputs found
Physical Properties and Baryonic Content of Low-Redshift Intergalactic Ly-alpha and O VI Absorption Systems: The PG1116+215 Sight Line
We present HST and FUSE observations of the intergalactic absorption toward
PG1116+215 in the 900-3000 A spectral region. We detect 25 Ly-alpha absorbers
at rest-frame equivalent widths W_r > 30 mA, yielding (dN/dz)_Ly-alpha =
154+/-18 over an unblocked redshift path of 0.162. Two additional weak Ly-alpha
absorbers with W_r ~ 15-20 mA are also present. Eight of the Ly-alpha absorbers
have large line widths (b > 40 km/sec). The detection of narrow OVI in the
broad Ly-alpha absorber at z=0.06244 supports the idea that the Ly-alpha
profile is thermally broadened in gas with T > 10^5 K. We find dN/dz ~ 50 for
broad Ly-alpha absorbers with W_r > 30 mA and b > 40 km/sec. If the broad
Ly-alpha lines are dominated by thermal broadening in hot gas, the amount of
baryonic material in these absorbers is enormous, perhaps as much as half the
baryonic mass in the low-redshift universe. We detect OVI absorption in several
of the Ly-alpha clouds along the sight line. Two detections at z=0.13847 and
z=0.16548 are confirmed by the presence of other ions at these redshifts, while
the detections at z=0.04125, 0.05895, 0.05928, and 0.06244 are based upon the
Ly-alpha and OVI detections alone. The information available for 13
low-redshift OVI absorbers with W_r > 50 mA along 5 sight lines yields
(dN/dz)_OVI ~ 14 and Omega_b(OVI) > 0.0027/h_75, assuming a metallicity of 0.1
solar and an OVI ionization fraction < 0.2. The properties and prevalence of
low-redshift OVI absorbers suggest that they too may be a substantial baryon
repository, perhaps containing as much mass as stars and gas inside galaxies.
The redshifts of the OVI absorbers are highly correlated with the redshifts of
galaxies along the sight line, though few of the absorbers lie closer than
600/h_75 kpc to any single galaxy. [abbreviated]Comment: 99 pages, 30 figures, aastex format, ApJS in pres
Phosphocholine-Modified Lipooligosaccharides of Haemophilus influenzae Inhibit ATP-Induced IL-1beta Release by Pulmonary Epithelial Cells
Phosphocholine-modified bacterial cell wall components are virulence factors enabling immune evasion and permanent colonization of the mammalian host, by mechanisms that are poorly understood. Recently, we demonstrated that free phosphocholine (PC) and PC-modified lipooligosaccharides (PC-LOS) from Haemophilus influenzae, an opportunistic pathogen of the upper and lower airways, function as unconventional nicotinic agonists and efficiently inhibit the ATP-induced release of monocytic IL-1beta. We hypothesize that H. influenzae PC-LOS exert similar effects on pulmonary epithelial cells and on the complex lung tissue. The human lung carcinoma-derived epithelial cell lines A549 and Calu-3 were primed with lipopolysaccharide from Escherichia coli followed by stimulation with ATP in the presence or absence of PC or PC-LOS or LOS devoid of PC. The involvement of nicotinic acetylcholine receptors was tested using specific antagonists. We demonstrate that PC and PC-LOS efficiently inhibit ATP-mediated IL-1beta release by A549 and Calu-3 cells via nicotinic acetylcholine receptors containing subunits alpha7, alpha9, and/or alpha10. Primed precision-cut lung slices behaved similarly. We conclude that H. influenzae hijacked an endogenous anti-inflammatory cholinergic control mechanism of the lung to evade innate immune responses of the host. These findings may pave the way towards a host-centered antibiotic treatment of chronic airway infections with H. influenzae
FUSE and STIS Observations of the Warm-Hot Intergalactic Medium towards PG1259+593
We use FUSE and STIS spectra to study intergalactic absorption towards the
quasar PG1259+593 (z=0.478). We identify 135 intergalactic absorption lines
with equivalent widths >10mA, tracing 78 absorption components in 72 Ly
alpha/beta absorption-line systems. We concentrate on the distribution and
physical properties of the WHIM as sampled by OVI and intrinsically broad Ly
alpha lines. The number of intervening OVI absorbers for equivalent widths W>24
mA is 3-6 over an unobscured redshift path of dz=0.368. This implies a number
density of OVI systems, dN/dz, of ~8-16 along this sight line. This range is
consistent with estimates from other sight lines, supporting the idea that
intervening intergalactic OVI absorbers contain an substantial fraction of the
baryonic mass in the low-redshift Universe. We identify a number of broad Ly
alpha absorbers with large Doppler parameters (b~40-200 km/s) and low column
densities (N(HI)<10^14 cm^-2). For pure thermal broadening, these widths
correspond to temperatures of ~1x10^5 to 3x10^6 K. While these broad absorbers
could be caused by blends of multiple, unresolved lines, continuum undulations,
or by kinematic flows and Hubble broadening, we consider the possibility that
some of these features are single-component, thermally broadened Ly alpha
lines. These systems could represent WHIM absorbers that are too weak, too
metal-poor, and/or too hot to be detected in OVI. If so, their widths and their
frequency in the PG1259+593 spectrum imply that these absorbers trace an even
larger fraction of the baryons in the low-redshift Universe than the OVI
absorbing systems (abridged version).Comment: 71 pages, 25 figures; accepted for publication in ApJ
Detection of Dust in High-Velocity Cloud Complex C -- Enriched Gas Accreting onto the Milky Way
We present the detection of dust depletion in Complex C, a massive,
infalling, low-metallicity high-velocity cloud in the northern Galactic
hemisphere that traces the ongoing accretion of gas onto the Milky Way. We
analyze a very high signal-to-noise HST/COS spectrum of AGN Mrk 817 formed by
coadding 165 individual exposures taken under the AGN STORM 2 program, allowing
us to determine dust-depletion patterns in Complex C at unprecedented
precision. By fitting Voigt components to the O I, S II, N I, Si II, Fe II, and
Al II absorption and applying ionization corrections from customized Cloudy
photoionization models, we find sub-solar elemental abundance ratios of
[Fe/S]=-0.42+/-0.08, [Si/S]=-0.29+/-0.05, and [Al/S]=-0.53+/-0.08. These ratios
indicate the depletion of Fe, Si, and Al into dust grains, since S is mostly
undepleted. The detection of dust provides an important constraint on the
origin of Complex C, as dust grains indicate the gas has been processed through
galaxies, rather than being purely extragalactic. We also derive a low
metallicity of Complex C of [S/H]=-0.51+/-0.16 (31% solar), confirming earlier
results from this sightline. We discuss origin models that could explain the
presence of dust in Complex C, including Galactic fountain models, tidal
stripping from the Magellanic Clouds or other satellite galaxies, and
precipitation of coronal gas onto dust-bearing ``seed" clouds.Comment: 8 pages, 3 figures, accepted for publication in ApJ Letters. This
version has been updated with proof correction
Designing Cathodes and Cathode Active Materials for SolidâState Batteries
Solid-state batteries (SSBs) currently attract great attention as a potentially safe electrochemical high-energy storage concept. However, several issues still prevent SSBs from outperforming today\u27s lithium-ion batteries based on liquid electrolytes. One major challenge is related to the design of cathode active materials (CAMs) that are compatible with the superionic solid electrolytes (SEs) of interest. This perspective, gives a brief overview of the required properties and possible challenges for inorganic CAMs employed in SSBs, and describes state-of-the art solutions. In particular, the issue of tailoring CAMs is structured into challenges arising on the cathode-, particle-, and interface-level, related to microstructural, (chemo-)mechanical, and (electro-)chemical interplay of CAMs with SEs, and finally guidelines for future CAM development for SSBs are proposed
A FUSE Survey of Molecular Hydrogen in Intermediate-Velocity Clouds in the Milky Way Halo
Far Ultraviolet Spectroscopic Explorer (FUSE) data is used to investigate the
molecular hydrogen (H_2) content of intermediate-velocity clouds (IVCs) in the
lower halo of the Milky Way. We analyze interstellar absorption towards 56
(mostly extragalactic) background sources to study H_2 absorption in the Lyman-
and Werner bands in 61 IVC components at H I column densities >10^19 cm^-2. For
data with good S/N (~9 per resolution element and higher), H_2 in IVC gas is
convincingly detected in 14 cases at column densities varying between ~10^14
and ~10^17 cm^-2. We find an additional 17 possible H_2 detections in IVCs in
FUSE spectra with lower S/N. The molecular hydrogen fractions, f, vary between
10^-6 and 10^-3, implying a dense, mostly neutral gas phase that is probably
related to the Cold Neutral Medium (CNM) in these clouds. If the H_2 stays in
formation-dissociation equlibrium, the CNM in these clouds can be characterized
by compact (D~0.1 pc) filaments with volume densities on the order of n_H~30
cm^-3. The relatively high detection rate of H_2 in IVC gas implies that the
CNM in these clouds is ubiquitous. More dense regions with much higher
molecular fractions may exist, but it would be difficult to detect them in
absorption because of their small size.Comment: 36 pages, 11 figures; accepted for publication in Ap
The FUSE Spectrum of PG0804+761: A Study of Atomic and MolecularGas in the Lower Galactic Halo and Beyond
We present an analysis of interstellar and intergalactic absorption lines in
the FUSE spectrum of the low-redshift quasar PG0804+761 (z=0.100) at
intermediate resolution (FWHM=25 km/s) in the direction l=138.3, b=31.0. With a
good signal-to-noise ratio and the presence of several interesting Galactic and
extragalactic absorption components along the sight line, this spectrum
provides a good opportunity to demonstrate the ability of FUSE to do both
interstellar and extragalactic science. Although the spectrum of PG0804+761 is
dominated by strong absorption from local Galactic gas, we concentrate our
study on absorption by molecular hydrogen and neutral neutral and ionized
metals related to an intermediate-velocity cloud in the lower Galactic halo at
-55 km/s, and on absorption from OVI extended to negative velocities. In the
IVC, weak molecular hydrogen absorption is found in 5 lines for rotational
levels 0 and 1, leading to a total H_2 column density of log N = 14.71(+-0.30).
We derive an OI gas-phase abundance for the IVC of 1.03(+0.71-0.42) solar.
Absorption by OVI is found at velocities as negative as -110 km/s, but no
absorption from any species is found at velocities of -180 km/ where absorption
from the nearby high-velocity Complex A would be expected. We suggest that the
extended OVI absorption traces hot gas above the Perseus spiral arm. Finally,
we find intergalactic absorption by an intervening HI Ly betax absorber at
z=0.019 and absorption by HI, CIII and OVI in an associated system at z=0.102.
No intervening OVI absorbers are seen in the spectrum of PG0804+761.Comment: 27 pages, 6 figures; accepted for publication in Ap
Science-rich Sites for In Situ Resource Utilization Characterization and End-to-end Demonstration Missions
Within the European Space Agencyâs âCommercial In Situ Resource Utilization (ISRU) Demonstration Mission Preparation Phase,â we examined two types of lunar sites in preparation for an ISRU demonstration mission. First, we considered poorly characterized potential resource sites. For these so-called characterization sites, precursor missions would investigate the material properties and address strategic knowledge gaps for their use as ISRU feedstock. Regions of interest for characterization missions include the Aristarchus plateau, Montes Harbinger/Rimae Prinz, Sulpicius Gallus, and Rima Bode. Regional pyroclastic deposits at the Aristarchus plateau and adjacent Montes Harbinger/Rimae Prinz exhibit remotely sensed low-Ti, high-Fe2+ compositions. They differ from the high-Ti pyroclastics at Rima Bode and Sulpicius Gallus, which are similar to the pyroclastics northwest of the Taurus Littrow valley (Apollo 17 site). Thus, exploration of the Aristarchus plateau would allow investigation of previously uncharacterized materials, whereas Rima Bode or Sulpicius Gallus would allow comparison to Apollo 17 pyroclastics. Any of these sites would enable evaluation of reported H2O/OH in these deposits. Second, we examined a possible site for a direct ISRU demonstrator mission. For a stand-alone end-to-end (E2E) ISRU demonstrator, a fuller understanding of the physical and compositional characteristics of potential feedstock is required for mission risk reduction. In this case, locations near preexisting sites would allow extrapolation of ground truth to nearby deposits. Because a Ti-rich pyroclastic deposit appears advantageous from beneficiation and compositional perspectives, we examine an example E2E demo site northwest of the Taurus Littrow valley. Hydrogen and methane reduction, as well as the FrayâFarthingâChen Cambridge process, could be tested there.BMWi, 50OW1504, MissionsunterstĂŒtzende Arbeiten und geologische Untersuchungen der lunaren OberflĂ€che mit Daten der Lunar Reconnaissance Orbiter Camera (LROC)BMWi, 50OW2001, MissionsunterstĂŒtzende und wissenschaftliche Arbeiten mit Daten der Lunar Reconnaissance Orbiter Camera (LROC) und Vorbereitung zukĂŒnftiger Mondmissione
Origins of the Highly Ionized Gas along the Line of Sight towards HD 116852
We present Hubble Space Telescope Imaging Spectrograph (HST/STIS) and Far
Ultraviolet Spectroscopic Explorer (FUSE) observations of high ion interstellar
absorption along the sight line to HD 116852. At a distance of 4.8 kpc, HD
116852 is an O9 III star lying in the low Galactic halo, -1.3 kpc from the
plane of the Galaxy in the direction l = 304.9, b = -16.1. The STIS E140H
grating observations provide high-resolution (FWHM = 2.7 km/s) spectra of the
resonance doublets of Si IV, C IV, and N V. These data are complemented by
medium-resolution (FWHM = 20 km/s) FUSE spectra of O VI. We find evidence for
three distinct types of highly ionized gas present in the data. First, two
narrow absorption components are resolved in the Si IV and C IV profiles, at
approximate LSR velocities of -36 and -10 km/s. These narrow components appear
to be produced in gas associated with the Norma and Sagittarius spiral arms, at
approximate z-distances of -1.0 and -0.5 kpc, respectively. Second, we detect
an intermediate-width component in C IV and Si IV, at 17 km/s, which we propose
could arise at the conductive interface at the boundary between a low column
density neutral or weakly ionized cloud and the surrounding hot medium.
Finally, a broad collisionally ionized component of gas responsible for
producing the smooth N V and O VI profiles is observed; such absorption is also
present to a lesser degree in the profiles of Si IV and C IV. The broad O VI
absorption is observed at a velocity displaced from the broad C IV component by
almost 20 km/s, an amount large enough to suggest that the two ions may not
co-exist in the same physical location.Comment: 39 pages, 6 figures; accepted for publication in January 10, 2003
edition of The Astrophysical Journa
FAS-dependent cell death in α-synuclein transgenic oligodendrocyte models of multiple system atrophy
Multiple system atrophy is a parkinsonian neurodegenerative disorder. It is cytopathologically characterized by accumulation of the protein p25α in cell bodies of oligodendrocytes followed by accumulation of aggregated α-synuclein in so-called glial cytoplasmic inclusions. p25α is a stimulator of α-synuclein aggregation, and coexpression of α-synuclein and p25α in the oligodendroglial OLN-t40-AS cell line causes α-synuclein aggregate-dependent toxicity. In this study, we investigated whether the FAS system is involved in α-synuclein aggregate dependent degeneration in oligodendrocytes and may play a role in multiple system atrophy. Using rat oligodendroglial OLN-t40-AS cells we demonstrate that the cytotoxicity caused by coexpressing α-synuclein and p25α relies on stimulation of the death domain receptor FAS and caspase-8 activation. Using primary oligodendrocytes derived from PLP-α-synuclein transgenic mice we demonstrate that they exist in a sensitized state expressing pro-apoptotic FAS receptor, which makes them sensitive to FAS ligand-mediated apoptosis. Immunoblot analysis shows an increase in FAS in brain extracts from multiple system atrophy cases. Immunohistochemical analysis demonstrated enhanced FAS expression in multiple system atrophy brains notably in oligodendrocytes harboring the earliest stages of glial cytoplasmic inclusion formation. Oligodendroglial FAS expression is an early hallmark of oligodendroglial pathology in multiple system atrophy that mechanistically may be coupled to α-synuclein dependent degeneration and thus represent a potential target for protective intervention
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