2,719 research outputs found
HR4049: signature of nova nucleosynthesis ?
The post-Asymptotic Giant Branch (AGB) star HR4049 is in an eccentric binary
system with a relatively short period probably surrounded by a dusty
circumbinary disk. Extremely anomalous oxygen isotopic ratios, O16/O17 ~
O16/O18 ~ 7, have been measured from CO_2 molecules likely residing in the
disk. Such a composition cannot be explained in the framework of AGB and
post-AGB evolution while it can be qualitatively associated with the
nucleosynthesis occurring during nova outbursts. We discuss nova models, the
presence of a white dwarf companion to HR4049 and possible scenarios for the
dynamical evolution of this binary system. Circumbinary disks in which mixing
occurs between red-giant and nova material may also be invoked as the site of
formation of some rare types of meteoritic presolar grains.Comment: 4 pages, 2 figures, submitted for the proceedings of the 8th Nuclei
in the Cosmos symposium (Vancouver, Canada, 19-23 July 2004
Minor and Trace Element and Re-Os Chemistry of the Upper Devonian Woodford Shale, Permian Basin, West Texas: Insights into Metal Abundance and Basin Processes
The trace and minor element and Re–Os geochemistry of the Upper Devonian Woodford Shale are analyzed in order to characterize elemental abundances, to identify associations among trace elements and to constrain paleoceanographic conditions and depositional processes. This organic-carbon-rich mudstone in the Permian Basin, west Texas, is a major source of hydrocarbons in the basin and is coeval with many other Upper Devonian shales in North America. The Woodford lacks enrichment in many trace metals. Only Mo, U, S and Se are significantly enriched. Other redox sensitive elements are depleted or similar to average shale composition, including Pb, Bi, Cr, Ti, Cu, Zn, Co, and V. Elements associated with granitic sources such as rare earths, Th, Ce, and TiO2 are also depleted relative to average shale; this appears to be related to be a source control. A strong basin reservoir effect is noted among several redox sensitive elements, including Mo, Cu and Ni, which largely accounts for the depletion. Dilution by biogenic silica had an additional effect on metal concentrations. Multivariate factors analysis identified associations between elements, including groupings of: rare earth elements; elements enriched in granitic crust; silica, varying antithetically with elements in carbonate minerals; organic carbon, Mo and U; V; phosphate; Fe and S. Noteworthy among the results are the different behavior of redox-sensitive elements, suggesting different precipitation mechanisms or varying dependence on reservoir effects. A strong redox effect is noted in the TOC/Ptot ratio at approximately the Frasnian–Famennian boundary, indicating an abrupt transition to an anoxic column boundary that coincides with a short-term significant fall in sea level. This suggests that anoxia was induced by isolation of the basin from the global ocean. However with the exception of the uppermost Famennian, initial 187Os/188Os values determined from Re–Os geochronology for the Permian Basin are similar to correlative sections of the Appalachian and Peace River Basins of North American and the Rhenohercynian basin of Europe. This indicates that although the Permian Basin became restricted during the upper Devonian and early Mississippian, ocean connectivity remained between regional and global basins
Thermodynamics as an alternative foundation for zero-temperature density functional theory and spin density functional theory
Thermodynamics provides a transparent definition of the free energy of
density functional theory (DFT), and of its derivatives - the potentials, at
finite temperatures T. By taking the T to 0 limit, it is shown here that both
DFT and spin-dependent DFT (for ground states) suffer from precisely the same
benign ambiguities: (a) charge and spin quantization lead to "up to a constant"
indeterminacies in the potential and the magnetic field respectively, and (b)
the potential in empty subspaces is undetermined but irrelevant. Surprisingly,
these simple facts were inaccessible within the standard formulation, leading
to recent discussions of apparent difficulties within spin-DFT.Comment: RevTeX, to appear in Phys. Rev.
Constraints on Phases of Supersymmetric Flavour Conserving Couplings
In the unconstrained MSSM, we reanalyze the constraints on the phases of
supersymmetric flavour conserving couplings that follow from the electron and
neutron electric dipole moments (EDM). We find that the constraints become weak
if at least one exchanged superpartner mass is >O(1 TeV) or if we accept large
cancellations among different contributions. However, such cancellations have
no evident underlying symmetry principle. For light superpartners, models with
small phases look like the easiest solution to the experimental EDM
constraints. This conclusion becomes stronger the larger is the value of
. We discuss also the dependence of , and
decay on those phases.Comment: 38 pages, 22 figures, uses epsfig.sty, axodraw.sty (not included);
error in sign of gluino contribution to EDM of u and d quarks and few figures
corrected, important conclusions unchange
Simvastatin Prevents and Reverses Depigmentation in a Mouse Model of Vitiligo
Vitiligo is a common autoimmune disease of the skin that results in disfiguring white spots. There are no Food and Drug Administration (FDA)-approved treatments, and current treatments are time-consuming, expensive, and of low efficacy. We sought to identify new treatments for vitiligo, and first considered repurposed medications because of the availability of safety data and expedited regulatory approval. We previously reported that the IFN-γ-induced chemokine CXCL10 is expressed in lesional skin from vitiligo patients, and that it is critical for the progression and maintenance of depigmentation in our mouse model of vitiligo. We hypothesized that targeting IFN-γ signaling might be an effective new treatment strategy. Activation of signal transducer and activator of transcription 1 (STAT1) is required for IFN-γ signaling and recent studies revealed that simvastatin, an FDA-approved cholesterol-lowering medication, inhibited STAT1 activation in vitro. Therefore, we hypothesized that simvastatin may be an effective treatment for vitiligo. We found that simvastatin both prevented and reversed depigmentation in our mouse model of vitiligo, and reduced the number of infiltrating autoreactive CD8+ T cells in the skin. Treatment of melanocyte-specific, CD8+ T cells in vitro decreased proliferation and IFN-γ production, suggesting additional effects of simvastatin directly on T cells. Based on these data, simvastatin may be a safe, targeted treatment option for patients with vitiligo. © 2015 The Society for Investigative Dermatology
On the role of exploitation and exploration strategies in the maintenance of cognitive biases: Beyond the pursuit of instrumental rewards
Why can initial biases persist in repeated choice tasks? Previous research has shown that frequent rewards can lure the decision maker into premature exploitation of a supposedly best option, which can result in the persistence of initial biases. Here, we demonstrate that even in the absence of rewards, initial biases can be perpetuated through a positive testing strategy. After eliciting a biased preference for one of two equally rewarding options, participants (N = 203) could sample freely from both options without the lure of any financial rewards. When participants were told to rule out alternatives in this phase, they explored the supposedly worse option and thereby managed to overcome their initial bias. When told to optimize their strategy, however, they exhibited a positive testing strategy resulting in the continued exploitation of the supposedly better option, a bias they maintained in an incentivized choice phase and later judgments. Across all participants, individual tendencies to exploit one option in earlier phases predicted biased behavior in subsequent phases. The findings highlight that not only the pursuit of instrumental rewards can lead to exploitation and the maintenance of initial biases. We discuss potential consequences for interventions
Missing out by pursuing rewarding outcomes: Why initial biases can lead to persistent suboptimal choices.
While there are abundant reasons that might lead us to form wrong first impressions, further interaction (sampling) opportunities should allow us to attenuate such initial biases. Sometimes, however, theses biases persist despite repeated sampling opportunities, such as in superstitions or stereotypes. In two studies (Ns = 100), we investigate this phenomenon.We demonstrate that in a task in which participants could repeatedly choose between two options to gain rewards, erroneous initial impressions about yielded outcomes can lead to persisting biases toward a clearly inferior option. We argue that a premature focus on reward pursuit (exploitation) rather than exploration is the cause of these biases, which persist despite plenty of opportunities and a presumed motivation to overcome them. By focusing on a supposedly best option, participants never give themselves the chance to sufficiently try out alternatives and thereby overcome their initial biases. We conclude that going for the money is not always the best strategy
Discrimination, labour markets and the Labour Market Prospects of Older Workers: What Can a Legal Case Teach us?
As governments become increasingly concerned about the fiscal implications of the ageing population, labour market policies have sought to encourage mature workers to remain in the labour force. The ‘human capital’ discourses motivating these policies rest on the assumption that older workers armed with motivation and vocational skills will be able to return to fulfilling work. This paper uses the post-redundancy recruitment experiences of former Ansett Airlines
flight attendants to develop a critique of these expectations. It suggests that policies to increase
older workers’ labour market participation will not succeed while persistent socially constructed age- and gender- typing shape labour demand. The conclusion argues for policies sensitive to the institutional structures that shape employer preferences, the competitive rationality of
discriminatory practices, and the irresolvable tension between workers’ human rights and employers’ property rights
A population-based, cross-sectional study of the prevalence and correlates of sedentary behaviour of adults with intellectual disabilities
Background:
High levels of sedentary behaviour have a negative impact on health and well-being. There is limited evidence on the prevalence and correlates of sedentary behaviour of adults with intellectual disabilities (ID).
Methods:
A population-based sample of adults with ID were invited to take part in a comprehensive health check programme. Demographic and health data were collected during a structured interview and physical examination. Screen time was used as a proxy measure of sedentary behaviour. Bivariate and multivariate statistical modelling examined correlates of screen time.
Results:
Fifty per cent of the 725 participants reported four or more hours of screen time per day. Male gender, higher levels of intellectual ability, mobility problems, obesity, not having hearing impairment and not having epilepsy were all significantly associated with higher screen time in the final multivariate model (R2 = 0.16; Hosmer–Lemeshow goodness of fit statistic P = 0.36).
Conclusions:
This is the first study to publish population-based data on the prevalence and correlates of sedentary behaviour in adults with ID. Compared with adults who do not have ID, adults with ID have higher levels, and different correlates, of sedentary behaviour. A better understanding of the social context of sedentary behaviour will inform the design of effective behaviour change programmes for adults with ID
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Ohmic Contacts to n-type GaSb and n-type GaInAsSb
An investigation with the objective of improving n-type ohmic contacts to GaSb-based devices is described. This study involves a series of n-GaInAsSb and n-GaSb samples with varying doping, grown on both n-GaSb and semi-insulating GaAs substrates. These samples were fabricated into mesa-etched TLM structures, and the specific contact resistivity and sheet resistance of these layers as a function of majority electron concentration were measured. Extremely low specific contact resistivities of about 2 x 10{sup -6} {Omega}-cm{sup 2} and sheet resistances of about 4 {Omega}/{open_square} are found for n-type GaInAsSb doped at about 3 x 10{sup 18} cm{sup -3}
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