281 research outputs found
Increased fibrosis in a mouse model of anti-laminin 332 mucous membrane pemphigoid remains unaltered by inhibition of aldehyde dehydrogenase
Mucous membrane pemphigoid (MMP) is an autoimmune blistering disease characterized by autoantibodies against the basal membrane zone of skin and surface-close epithelia and predominant mucosal lesions. The oral cavity and conjunctivae are most frequently affected, albeit clinical manifestations can also occur on the skin. MMP-associated lesions outside the oral cavity typically lead to scarring. Mechanisms underlying scarring are largely unknown in MMP and effective treatment options are limited. Herein, we assessed the collagen architecture in tissue samples of an antibody-transfer mouse model of anti-laminin-332 MMP. In MMP mice, increased collagen fibril density was observed in skin and conjunctival lesions compared to mice injected with normal rabbit IgG. The extracellular matrix of MMP skin samples also showed altered post-translational collagen cross-linking with increased levels of both lysine- and hydroxylysine-derived collagen crosslinks supporting the fibrotic phenotype in experimental MMP compared to control animals. In addition, we evaluated a potential anti-fibrotic therapy in experimental anti-laminin-332 MMP using disulfiram, an inhibitor of the aldehyde dehydrogenase (ALDH), which has been implicated in immune-mediated mucosal scarring. In addition, disulfiram also acts as a copper chelator that was shown to block lysyl oxidase activity, an enzyme involved in formation of collagen crosslinks. Topical use of disulfiram (300 ÎĽM in 2 [w/v] methocel) did not improve ocular lesions in experimental MMP over the 12-day treatment period in disulfiram-treated mice compared to vehicle-treated mice (n=8/group). Furthermore, C57BL6/J mice (n=8/group) were treated prophylactically with 200 mg/kg p.o. disulfiram or the solvent once daily over a period of 12 days. Systemic treatment did not show any reduction in the severity of oral and ocular lesions in MMP mice, albeit some improvement in skin lesions was observed in disulfiram- vs. vehicle-treated mice (p=0.052). No reduction in fibrosis was seen, as assessed by immunohistochemistry. Whilst blocking of ALDH failed to significantly ameliorate disease activity, our data provide new insight into fibrotic processes highlighting changes in the collagenous matrix and cross-linking patterns in IgG-mediated MMP
Stellar Iron Abundances: non-LTE Effects
We report new statistical equilibrium calculations for Fe I and Fe II in the
atmosphere of Late-Type stars. We used atomic models for Fe I and Fe II having
respectively 256 and 190 levels, as well as 2117 and 3443 radiative
transitions. Photoionization cross-sections are from the Iron Project. These
atomic models were used to investigate non-LTE effects in iron abundances of
Late-Type stars with different atmospheric parameters.
We found that most Fe I lines in metal-poor stars are formed in conditions
far from LTE. We derived metallicity corrections of about 0.3 dex with respect
to LTE values, for the case of stars with [Fe/H] ~ -3.0. Fe II is found not to
be affected by significant non-LTE effects. The main non-LTE effect invoked in
the case of Fe I is overionization by ultraviolet radiation, thus classical
ionization equilibrium is far to be satisfied. An important consequence is that
surface gravities derived by LTE analysis are in error and should be corrected
before final abundances corrections.
This apparently solves the observed discrepancy between spectroscopic surface
gravities derived by LTE analyses and those derived from Hipparcos parallaxes.
A table of non-LTE [Fe/H] and log g values for a sample of metal-poor late-type
stars is given.Comment: 22 pages, 9 figures, 1 table, ApJ style, accepte
The solar photospheric abundance of carbon.Analysis of atomic carbon lines with the CO5BOLD solar model
The use of hydrodynamical simulations, the selection of atomic data, and the
computation of deviations from local thermodynamical equilibrium for the
analysis of the solar spectra have implied a downward revision of the solar
metallicity. We are in the process of using the latest simulations computed
with the CO5BOLD code to reassess the solar chemical composition. We determine
the solar photospheric carbon abundance by using a radiation-hydrodynamical
CO5BOLD model, and compute the departures from local thermodynamical
equilibrium by using the Kiel code. We measure equivalent widths of atomic CI
lines on high resolution, high signal-to-noise ratio solar atlases. Deviations
from local thermodynamic equilibrium are computed in 1D with the Kiel code. Our
recommended value for the solar carbon abundance, relies on 98 independent
measurements of observed lines and is A(C)=8.50+-0.06, the quoted error is the
sum of statistical and systematic error. Combined with our recent results for
the solar oxygen and nitrogen abundances this implies a solar metallicity of
Z=0.0154 and Z/X=0.0211. Our analysis implies a solar carbon abundance which is
about 0.1 dex higher than what was found in previous analysis based on
different 3D hydrodynamical computations. The difference is partly driven by
our equivalent width measurements (we measure, on average, larger equivalent
widths with respect to the other work based on a 3D model), in part it is
likely due to the different properties of the hydrodynamical simulations and
the spectrum synthesis code. The solar metallicity we obtain from the CO5BOLD
analyses is in slightly better agreement with the constraints of
helioseismology than the previous 3D abundance results. (Abridged)Comment: Astronomy and Astrophysics, accepte
Formation of Zr I and II lines under non-LTE conditions of stellar atmospheres
The non-local thermodynaic equilibrium (non-LTE) line formation for the two
ions of zirconium is considered through a range of spectral types when the Zr
abundance varies from the solar value down to [Zr/H] = -3. The model atom was
built using 148 energy levels of Zr I, 772 levels of Zr II, and the ground
state of Zr III. It was shown that the main non-LTE mechnism for the minority
species Zr I is ultraviolet overionization. Non-LTE leads to systematically
depleted total absorption in the Zr I lines and positive abundance corrections,
reaching to 0.33 dex for the solar metallicity models. The excited levels of Zr
II are overpopulated relative to their thermodynamic equilibrium populations in
the line formation layers due to radiative pumping from the low-excitation
levels. As a result, the line source function exceeds the Planck function
leading to weakening the Zr II lines and positive non-LTE abundance
corrections. Such corrections grow towards lower metallicity and lower surface
gravity and reach to 0.34 dex for Teff = 5500 K, log g = 2.0, [M/H] = -2. As a
test and first application of the Zr I-Zr II model atom, Zr abundance was
determined for the Sun on the basis of 1D LTE model atmosphere. Lines of Zr I
and Zr II give consistent within the error bars non-LTE abundances, while the
difference in LTE abundances amounts to 0.28 dex. The solar abundance of
zirconium obtained with the MAFAGS solar model atmosphere is log eps(Zr) =
2.63+-0.07.Comment: published in Astron. Letters, 36, 664 (2010); Erratum was submitte
Non-LTE line formation for heavy elements in four very metal-poor stars
Stellar parameters and abundances of Na, Mg, Al, K, Ca, Sr, Ba, and Eu are
determined for four very metal-poor stars (-2.66 < [Fe/H] < -2.15) based on
non-LTE line formation and analysis of high-resolution (R ~60000 and 90000)
high signal-to-noise (S/N > 200) observed spectra. A model atom for H I is
presented. An effective temperature was obtained from the Balmer Halpha and
Hbeta line wing fits, the surface gravity from the Hipparcos parallax if
available and the non-LTE ionization balance between Ca I and Ca II. Based on
the hyperfine structure affecting the Ba II resonance line, the fractional
abundance of the odd isotopes of Ba was derived for HD 84937 and HD 122563 from
a requirement that Ba abundances from the resonance line and subordinate lines
of Ba II must be equal. For each star, non-LTE leads to a consistency of Teff
from two Balmer lines and to a higher temperature compared to the LTE case, by
up to 60 K. Non-LTE effects are important in spectroscopic determination of
surface gravity from Ca I/Ca II. For each star with a known trigonometric
gravity, non-LTE abundances from the lines of two ionization stages agree
within the error bars, while a difference in the LTE abundances consists of
0.23 dex to 0.40 dex for different stars. Departures from LTE are found to be
significant for the investigated atoms, and they strongly depend on stellar
parameters. For HD 84937, the Eu/Ba ratio is consistent with the relative solar
system r-process abundances, and the fraction of the odd isotopes of Ba, f_odd,
equals 0.43+-0.14. The latter can serve as a constraint on r-process models.
The lower Eu/Ba ratio and f_odd = 0.22+-0.15 found for HD 122563 suggest that
the s-process or the unknown process has contributed significantly to the Ba
abundance in this star.Comment: accepted for publication in A&A, November 16, 200
A primordial star in the heart of the Lion
Context: The discovery and chemical analysis of extremely metal-poor stars
permit a better understanding of the star formation of the first generation of
stars and of the Universe emerging from the Big Bang. aims: We report the study
of a primordial star situated in the centre of the constellation Leo (SDSS
J102915+172027). method: The star, selected from the low resolution-spectrum of
the Sloan Digital Sky Survey, was observed at intermediate (with X-Shooter at
VLT) and at high spectral resolution (with UVES at VLT). The stellar parameters
were derived from the photometry. The standard spectroscopic analysis based on
1D ATLAS models was completed by applying 3D and non-LTE corrections. results:
An iron abundance of [Fe/H]=--4.89 makes SDSS J102915+172927 one of the lowest
[Fe/H] stars known. However, the absence of measurable C and N enhancements
indicates that it has the lowest metallicity, Z<= 7.40x10^{-7} (metal-mass
fraction), ever detected. No oxygen measurement was possible. conclusions: The
discovery of SDSS J102915+172927 highlights that low-mass star formation
occurred at metallicities lower than previously assumed. Even lower metallicity
stars may yet be discovered, with a chemical composition closer to the
composition of the primordial gas and of the first supernovae.Comment: To be published in A&
Consistent responses of soil microbial communities to elevated nutrient inputs in grasslands across the globe
Soil microorganisms are critical to ecosystem functioning and the maintenance of soil fertility. However, despite global increases in the inputs of nitrogen (N) and phosphorus (P) to ecosystems due to human activities, we lack a predictive understanding of how microbial communities respond to elevated nutrient inputs across environmental gradients. Here we used high-throughput sequencing of marker genes to elucidate the responses of soil fungal, archaeal, and bacterial communities using an N and P addition experiment replicated at 25 globally distributed grassland sites. We also sequenced metagenomes from a subset of the sites to determine how the functional attributes of bacterial communities change in response to elevated nutrients. Despite strong compositional differences across sites, microbial communities shifted in a consistent manner with N or P additions, and the magnitude of these shifts was related to the magnitude of plant community responses to nutrient inputs. Mycorrhizal fungi and methanogenic archaea decreased in relative abundance with nutrient additions, as did the relative abundances of oligotrophic bacterial taxa. The metagenomic data provided additional evidence for this shift in bacterial life history strategies because nutrient additions decreased the average genome sizes of the bacterial community members and elicited changes in the relative abundances of representative functional genes. Our results suggest that elevated N and P inputs lead to predictable shifts in the taxonomic and functional traits of soil microbial communities, including increases in the relative abundances of faster-growing, copiotrophic bacterial taxa, with these shifts likely to impact belowground ecosystems worldwide
The solar photospheric nitrogen abundance. Analysis of atomic transitions with 3D and 1D model atmospheres
CONTEXT: In recent years, the solar chemical abundances have been studied in
considerable detail because of discrepant values of solar metallicity inferred
from different indicators, i.e., on the one hand, the "sub-solar" photospheric
abundances resulting from spectroscopic chemical composition analyses with the
aid of 3D hydrodynamical models of the solar atmosphere, and, on the other
hand, the high metallicity inferred by helioseismology. AIMS: After
investigating the solar oxygen abundance using a CO5BOLD 3D hydrodynamical
solar model in previous work, we undertake a similar approach studying the
solar abundance of nitrogen, since this element accounts for a significant
fraction of the overall solar metallicity, Z. METHOD: We used a selection of
atomic spectral lines to determine the solar nitrogen abundance, relying mainly
on equivalent width measurements in the literature. We investigate the
influence on the abundance analysis, of both deviations from local
thermodynamic equilibrium ("NLTE effects") and photospheric inhomogeneities
("granulation effects"). RESULTS: We recommend use of a solar nitrogen
abundance of A(N)=7.86+-0.12 whose error bar reflects the line-to-line scatter.
CONCLUSION: The solar metallicity implied by the CO5BOLD-based nitrogen and
oxygen abundances is in the range 0.0145<= Z <= 0.0167. This result is a step
towards reconciling photospheric abundances with helioseismic constraints on Z.
Our most suitable estimates are Z=0.0156 and Z/X=0.0213.Comment: To be published on A&
Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA
An investigation of the hadronic final state in diffractive and
non--diffractive deep--inelastic electron--proton scattering at HERA is
presented, where diffractive data are selected experimentally by demanding a
large gap in pseudo --rapidity around the proton remnant direction. The
transverse energy flow in the hadronic final state is evaluated using a set of
estimators which quantify topological properties. Using available Monte Carlo
QCD calculations, it is demonstrated that the final state in diffractive DIS
exhibits the features expected if the interaction is interpreted as the
scattering of an electron off a current quark with associated effects of
perturbative QCD. A model in which deep--inelastic diffraction is taken to be
the exchange of a pomeron with partonic structure is found to reproduce the
measurements well. Models for deep--inelastic scattering, in which a
sizeable diffractive contribution is present because of non--perturbative
effects in the production of the hadronic final state, reproduce the general
tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil
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