3,815 research outputs found
The Volatility Trend of Protosolar and Terrestrial Elemental Abundances
We present new estimates of protosolar elemental abundances based on an
improved combination of solar photospheric abundances and CI chondritic
abundances. These new estimates indicate CI chondrites and solar abundances are
consistent for 60 elements. We compare our new protosolar abundances with our
recent estimates of bulk Earth composition (normalized to aluminium), thereby
quantifying the devolatilization in going from the solar nebula to the
formation of the Earth. The quantification yields a linear trend , where is the Earth-to-Sun abundance ratio and
is the 50 condensation temperature of elements. The best fit
coefficients are: and . The
quantification of these parameters constrains models of devolatilization
processes. For example, the coefficients and determine a
critical devolatilization temperature for the Earth K. The terrestrial abundances of elements with are depleted compared with solar abundances,
whereas the terrestrial abundances of elements with are indistinguishable from solar abundances. The
terrestrial abundance of Hg ( = 252 K) appears anomalously high under the
assumption that solar and CI chondrite Hg abundances are identical. To resolve
this anomaly, we propose that CI chondrites have been depleted in Hg relative
to the Sun by a factor of . We use the best-fit volatility trend to
derive the fractional distribution of carbon and oxygen between volatile and
refractory components (, ). We find (, ) for carbon and (, ) for
oxygen.Comment: Accepted for publication in Icarus. 28 pages, 12 figures, 5 tables.
Compared to v1, the results and conclusion are the same, while discussion of
results and implications is expanded considerabl
Tissue Inhibitor of Metalloproteinase–3 (TIMP-3) induces FAS dependent apoptosis in human vascular smooth muscle cells
Over expression of Tissue Inhibitor of Metalloproteinases-3 (TIMP-3) in vascular smooth muscle cells (VSMCs) induces apoptosis and reduces neointima formation occurring after saphenous vein interposition grafting or coronary stenting. In studies to address the mechanism of TIMP-3-driven apoptosis in human VSMCs we find that TIMP-3 increased activation of caspase-8 and apoptosis was inhibited by expression of Cytokine response modifier A (CrmA) and dominant negative FAS-Associated protein with Death Domain (FADD). TIMP-3 induced apoptosis did not cause mitochondrial depolarisation, increase activation of caspase-9 and was not inhibited by over-expression of B-cell Lymphoma 2 (Bcl2), indicating a mitochondrial independent/type-I death receptor pathway. TIMP-3 increased levels of the First Apoptosis Signal receptor (FAS) and depletion of FAS with shRNA showed TIMP-3-induced apoptosis was FAS dependent. TIMP-3 induced formation of the Death-Inducing Signalling Complex (DISC), as detected by immunoprecipitation and by immunofluorescence. Cellular-FADD-like IL-1 converting enzyme-Like Inhibitory Protein (c-FLIP) localised with FAS at the cell periphery in the absence of TIMP-3 and this localisation was lost on TIMP-3 expression with c-FLIP adopting a perinuclear localisation. Although TIMP-3 inhibited FAS shedding, this did not increase total surface levels of FAS but instead increased FAS levels within localised regions at the cell surface. A Disintegrin And Metalloproteinase 17 (ADAM17) is inhibited by TIMP-3 and depletion of ADAM17 with shRNA significantly decreased FAS shedding. However ADAM17 depletion did not induce apoptosis or replicate the effects of TIMP-3 by increasing localised clustering of cell surface FAS. ADAM17-depleted cells could activate caspase-3 when expressing levels of TIMP-3 that were otherwise sub-apoptotic, suggesting a partial role for ADAM17 mediated ectodomain shedding in TIMP-3 mediated apoptosis. We conclude that TIMP-3 induced apoptosis in VSMCs is highly dependent on FAS and is associated with changes in FAS and c-FLIP localisation, but is not solely dependent on shedding of the FAS ectodomain
The Keck Aperture Masking Experiment: spectro-interferometry of 3 Mira Variables from 1.1 to 3.8 microns
We present results from a spectro-interferometric study of the Miras o Cet, R
Leo and W Hya obtained with the Keck Aperture Masking Experiment from 1998 Sep
to 2002 Jul. The spectrally dispersed visibility data permit fitting with
circularly symmetric brightness profiles such as a simple uniform disk. The
stellar angular diameter obtained over up to ~ 450 spectral channels spaning
the region 1.1-3.8 microns is presented. Use of a simple uniform disk
brightness model facilitates comparison between epochs and with existing data
and theoretical models. Strong size variations with wavelength were recorded
for all stars, probing zones of H2O, CO, OH, and dust formation. Comparison
with contemporaneous spectra extracted from our data show a strong
anti-correlation between the observed angular diameter and flux. These
variations consolidate the notion of a complex stellar atmosphere consisting of
molecular shells with time-dependent densities and temperatures. Our findings
are compared with existing data and pulsation models. The models were found to
reproduce the functional form of the wavelength vs. angular diameter curve
well, although some departures are noted in the 2.8-3.5 micron range.Comment: 10 pages, 10 figures Accepted to Ap
A close halo of large transparent grains around extreme red giant stars
Intermediate-mass stars end their lives by ejecting the bulk of their
envelope via a slow dense wind back into the interstellar medium, to form the
next generation of stars and planets. Stellar pulsations are thought to elevate
gas to an altitude cool enough for the condensation of dust, which is then
accelerated by radiation pressure from starlight, entraining the gas and
driving the wind. However accounting for the mass loss has been a problem due
to the difficulty in observing tenuous gas and dust tens of milliarcseconds
from the star, and there is accordingly no consensus on the way sufficient
momentum is transferred from the starlight to the outflow. Here, we present
spatially-resolved, multi-wavelength observations of circumstellar dust shells
of three stars on the asymptotic giant branch of the HR diagram. When imaged in
scattered light, dust shells were found at remarkably small radii (<~ 2 stellar
radii) and with unexpectedly large grains (~300 nm radius). This proximity to
the photosphere argues for dust species that are transparent to starlight and
therefore resistant to sublimation by the intense radiation field. While
transparency usually implies insufficient radiative pressure to drive a wind,
the radiation field can accelerate these large grains via photon scattering
rather than absorption - a plausible mass-loss mechanism for lower-amplitude
pulsating stars.Comment: 13 pages, 1 table, 6 figure
Witten's Invariants of Rational Homology Spheres at Prime Values of and Trivial Connection Contribution
We establish a relation between the coefficients of asymptotic expansion of
trivial connection contribution to Witten's invariant of rational homology
spheres and the invariants that T.~Ohtsuki extracted from Witten's invariant at
prime values of . We also rederive the properties of prime invariants
discovered by H.~Murakami and T.~Ohtsuki. We do this by using the bounds on
Taylor series expansion of the Jones polynomial of algebraically split links,
studied in our previous paper. These bounds are enough to prove that Ohtsuki's
invariants are of finite type. The relation between Ohtsuki's invariants and
trivial connection contribution is verified explicitly for lens spaces and
Seifert manifolds.Comment: 32 pages, no figures, LaTe
Direct Detection of the Brown Dwarf GJ 802B with Adaptive Optics Masking Interferometry
We have used the Palomar 200" Adaptive Optics (AO) system to directly detect
the astrometric brown dwarf GJ 802B reported by Pravdo et al. 2005. This
observation is achieved with a novel combination of aperture masking
interferometry and AO. The dynamical masses are 0.1750.021 M and
0.0640.032 M for the primary and secondary respectively. The
inferred absolute H band magnitude of GJ 802B is M=12.8 resulting in a
model-dependent T of 1850 50K and mass range of
0.057--0.074 M.Comment: 4 Pages, 5 figures, emulateapj format, submitted to ApJ
Lung function in South African children with cystic fibrosis
Objective: To determine the pattern of lung function in stable cystic fibrosis (CF) patients and to investigate the relationship of abnormal lung function to demographic variables, CF genotype and pulmonary colonisation with Pseudomonas aeruginosa (PA)Design: A descriptive study done at the CF clinic at Red Cross War Memorial Children's Hospital in Cape Town.Methods: Data were recorded and pulmonary function testing (PFT) was performed in 42 CF patients.Results: 29 patients (69%) had mild disease,. while 11 (26%) and 2 (5%) had moderate and severe disease respectively. Twenty-four patients (57'%) demonstrated lower airway obstruction (LAO). Patients with moderate or severe disease were significantly older than those with mild disease (13.3 (3.7) years (mean (SD)) compared with 11.1 (3.0) years (t =2.1; P =OM)). PA colonisation status differed significantly with the pattern of lung function (X2 =6.6; P = 0.04) and severity of lung disease (X2=12.6; P =0.002.). Nine (35%) of the 26 patients tested before and after broncbodilator therapy showed a positive response.Conclusion: The majority of patients had mildly impaired or normal lung function, with LAO predominating. A minority of patients were bronchodilator-responsive. PA colonisation may be associated with the development of abnormal lung function and more severe pulmonary disease.
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