4,868 research outputs found
Signatures of radial migration in barred galaxies: Azimuthal variations in the metallicity distribution of old stars
By means of N-body simulations, we show that radial migration in galaxy
disks, induced by bar and spiral arms, leads to significant azimuthal
variations in the metallicity distribution of old stars at a given distance
from the galaxy center. Metals do not show an axisymmetric distribution during
phases of strong migration. Azimuthal variations are visible during the whole
phase of strong bar phase, and tend to disappear as the effect of radial
migration diminishes, together with a reduction in the bar strength. These
results suggest that the presence of inhomogeneities in the metallicity
distribution of old stars in a galaxy disk can be a probe of ongoing strong
migration. Such signatures may be detected in the Milky Way by Gaia (and
complementary spectroscopic data), as well as in external galaxies, by IFU
surveys like CALIFA and ATLAS3D. Mixing - defined as the tendency toward a
homogeneous, azimuthally symmetric, stellar distribution in the disk - and
migration turns out to be two distinct processes, the effects of mixing
starting to be visible when strong migration is over.Comment: 8 pages, 10 figures, accepted for publication on Astronomy and
Astrophysic
Population of human ventricular cell models calibrated with in vivo measurements unravels ionic mechanisms of cardiac alternans
Cardiac alternansis an important risk factor in cardiac physiology, and is related to the initiation of many pathophysiological conditions. However, the mechanisms underlying the generation of alternans remain unclear. In this study, we used a population of computational human ventricle models based onthe O’Hara model [1] to explore the effect of 11 key factors experimentally reported to be related to alternans. In vivo experimental datasets coming from patients undergoing cardiac surgery were used in the calibration of our in silico population of models. The calibrated models in the population were divided into two groups (Normal and Alternans) depending on alternans occurrence. Our results showed that there were significant differences in the following 5 ionic currents between the two groups: fast sodium current, sodium calcium exchanger current, sodium potassium pump current, sarcoplasmic reticulum (SR) calcium release flux and SR calcium reuptake flux. Further analysis indicated that fast sodium current and SR calcium uptake were the two most significant currents that contributed to voltage and calcium alternans generation, respectively
Bars & boxy/peanut bulges in thin & thick discs: I. Morphology and line-of-sight velocities of a fiducial model
We explore trends in the morphology and line-of-sight (los) velocity of
stellar populations in the inner regions of disc galaxies, using N-body
simulations with both a thin (kinematically cold) and a thick (kinematically
hot) disc which form a bar and boxy/peanut (b/p) bulge. The bar in the thin
disc component is 50\% stronger than the thick disc bar and is more
elongated, with an axis ratio almost half that of the thick disc bar. The thin
disc b/p bulge has a pronounced X-shape, while the thick disc b/p is weaker
with a rather boxy shape. This leads to the signature of the b/p bulge in the
thick disc to be weaker and further away from the plane than in the thin disc.
Regarding the kinematics, we find that the los velocity of thick disc stars in
the outer parts of the b/p bulge can be \emph{larger} than that of thin disc
stars, by up to 40\% and 20\% for side-on and Milky Way-like orientations of
the bar respectively. This is due to the different orbits followed by thin and
thick disc stars in the bar-b/p region, which are affected by the fact that: i)
thin disc stars are trapped more efficiently in the bar - b/p instability and
thus lose more angular momentum than their thick disc counterparts and ii)
thick disc stars have large radial excursions and therefore stars from large
radii with high angular momenta can be found in the bar region. We also find
that the difference between the los velocities of the thin and thick disc in
the b/p bulge () correlates with the initial difference between
the radial velocity dispersions of the two discs () . We
therefore conclude that stars in the bar - b/p bulge will have considerably
different morphologies and kinematics depending on the kinematic properties of
the disc population they originate from.Comment: Accepted for publication in A&A. 15 pages (2 page appendix). 16
figure
A latest Cretaceous to earliest Paleogene dinoflagellate cyst zonation of Antarctica, and implications for phytoprovincialism in the high southern latitudes
The thickest uppermost Cretaceous to lowermost Paleogene (Maastrichtian to Danian) sedimentary succession in the world is exposed on southern Seymour Island (65° South) in the James Ross Basin, Antarctic Peninsula. This fossiliferous shallow marine sequence, which spans the Cretaceous–Paleogene boundary, has allowed a high-resolution analysis of well-preserved marine palynomorphs. Previous correlation of Cretaceous–Paleogene marine palynomorph assemblages in the south polar region relied on dinoflagellate cyst biozonations from New Zealand and southern Australia. The age model of the southern Seymour Island succession is refined and placed within the stratigraphical context of the mid to high southern palaeolatitudes. Quantitative palynological analysis of a new 1102 m continuous stratigraphical section comprising the uppermost Snow Hill Island Formation and the López de Bertodano Formation (Marambio Group) across southern Seymour Island was undertaken. We propose the first formal late Maastrichtian to early Danian dinoflagellate cyst zonation scheme for the Antarctic based on this exceptional succession. Two new late Maastrichtian zones, including three subzones, and one new early Danian zone are defined. The oldest beds correlate well with the late Maastrichtian of New Zealand. In a wider context, a new South Polar Province based on Maastrichtian to Danian dinoflagellate cysts is proposed, which excludes most southern South American marine palynofloras. This interpretation is supported by models of ocean currents around Antarctica and implies an unrestricted oceanic connection across Antarctica between southern South America and the Tasman Sea
On the kinematic detection of accreted streams in the Gaia era: a cautionary tale
The CDM cosmological scenario predicts that our Galaxy should
contain hundreds of stellar streams at the solar vicinity, fossil relics of the
merging history of the Milky Way and more generally of the hierarchical growth
of galaxies. Because of the mixing time scales in the inner Galaxy, it has been
claimed that these streams should be difficult to detect in configuration space
but can still be identifiable in kinematic-related spaces like the
energy/angular momenta spaces, E-Lz and Lperp-Lz, or spaces of orbital/velocity
parameters. By means of high-resolution, dissipationless N-body simulations,
containing between 25 and 35 particles, we model the
accretion of a series of up to four 1:10 mass ratio satellites then up to eight
1:100 satellites and we search systematically for the signature of these
accretions in these spaces. In all spaces considered (1) each satellite gives
origin to several independent overdensities; (2) overdensities of multiple
satellites overlap; (3) satellites of different masses can produce similar
substructures; (4) the overlap between the in-situ and the accreted population
is considerable everywhere; (5) in-situ stars also form substructures in
response to the satellite(s) accretion. These points are valid even if the
search is restricted to kinematically-selected halo stars only. As we are now
entering the 'Gaia era', our results warn that an extreme caution must be
employed before interpreting overdensities in any of those spaces as evidence
of relics of accreted satellites. Reconstructing the accretion history of our
Galaxy will require a substantial amount of accurate spectroscopic data, that,
complemented by the kinematic information, will possibly allow us to
(chemically) identify accreted streams and measure their orbital properties.
(abridged)Comment: Accepted on A&A. A high-resolution version of the paper is available
at http://aramis.obspm.fr/~paola/ELZ/Elz.pd
Radial Mixing due to Spiral-Bar Resonance Overlap: Implications to the Milky Way
We have recently identified a previously unknown radial migration mechanism
resulting from the overlap of spiral and bar resonances in galactic discs
(Minchev & Famaey 2010, Minchev et al. 2010). This new mechanism is much more
efficient than mixing by transient spirals and its presence is unavoidable in
all barred galaxies, such as our own Milky Way. The consequences of this are a
strong flattening in the metallicity gradient in the disc, an extended disc
profile, and the formation of a thick disc component, all taking place in only
a couple of Gyr. This timescale is drastically shorter than previously expected
and thus can put strong constraints on the longevity, strength and pattern
speeds of the Galactic bar and Spiral Structure.Comment: 4 pages, 2 figures, presented at ELSA 2010: Gaia, at the frontiers of
astrometry, 7-11 June 2010, S\`evres, Paris; To published in EAS Series;
Proceedings editors: C. Turon, F. Arenou & F. Meynadie
We have so much in common: Does shared variance between emotion-related constructs account for relationships with self-injury?
Background: Emotion regulation, distress tolerance, experiential avoidance, and both positive and negative affect have all been linked to NSSI. These constructs are proposed to be distinct; however, they share conceptual similarities. For example, some people may regulate emotions by avoiding stressful situations, conflating emotion regulation and avoidance. We tested if constructs linked with NSSI (when studied in isolation), remain significant correlates of NSSI when considered alongside related constructs (with which they may share variance). Method: University students (n = 487, M = 21.36, SD = 2.48, 74% female, 40% with lived experience of self-injury) completed well-validated self-report measures of NSSI, difficulties with emotion regulation, distress tolerance, experiential avoidance, emotional reactivity, positive and negative affect, and alexithymia. Results: As predicted, emotion-related constructs were generally highly correlated. Additionally, with the exception of lack of emotional awareness, all constructs were significantly associated with NSSI in bivariate analyses. In multivariate analyses, associations were substantially attenuated. Positive affect, distress tolerance, and experiential avoidance were negatively associated with NSSI, and limited emotion regulation strategies was positively associated with NSSI. No other constructs were uniquely associated with NSSI and exploratory factor analyses indicated that all constructs loaded onto a single factor Limitations: Cross-sectional design rules out temporal sequencing. Conclusion: Findings raise the possibility that associations between some emotion-related constructs (e.g., alexithymia) and NSSI may reflect variance shared with other emotion-related constructs. If true, this will have important theoretical, clinical, and measurement implications for NSSI research
Associations between non-suicidal self-injury and experiential avoidance: A systematic review and Robust Bayesian Meta-analysis
Objectives: Non-suicidal self-injury (NSSI) is the intentional and deliberate damage to an individual's own body tissue without the intent to suicide. Individuals who have higher self-reported levels of experiential avoidance are more likely to report a history of NSSI. The current study systematically reviewed the literature and meta-analysed studies assessing associations between experiential avoidance and self-injury. Method: An extensive review was conducted of several databases (including ProQuest, Joanna Briggs, Web of Science, PsychArticles, PubMed, Scopus, and Ovid). Nineteen articles (two dissertations) met the inclusion criteria for the systematic review and 14 were analysed in a Robust Bayesian Meta-analysis. This review was registered through PROSPERO (CRD42020198041). Results: There was a small to medium, pooled effect size (d = 0.48, 95 % Credibility Interval 0.00–0.85). There was strong evidence for this effect size (Bayes Factor = 12.16), although there was considerable heterogeneity between studies (τ =0.68, 95 % CI [0.44, 0.1.05]). The analysis testing whether these findings may be due to publication bias was inconclusive (Bayes Factor = 2.45). Limitations: The majority of studies included were cross-sectional, in English, and most studies were of university students. While some studies reported on recency/frequency of NSSI there was not enough data to conduct meta-analysis. Conclusion: These results suggest there is a robust association between history of NSSI and experiential avoidance. However, as most studies operationalise avoidance as a unidimensional construct, it is not clear which aspects of avoidance differentiate individuals with and without a history of NSSI
Geoengineering by stratospheric SO<sub>2</sub> injection: results from the Met Office HadGEM2 climate model and comparison with the Goddard Institute for Space Studies ModelE
We examine the response of the Met Office Hadley Centre's HadGEM2-AO climate model to simulated geoengineering by continuous injection of SO<sub>2</sub> into the lower stratosphere, and compare the results with those from the Goddard Institute for Space Studies ModelE. Despite the differences between the models, we find a broadly similar geographic distribution of the response to geoengineering in both models in terms of near-surface air temperature and mean June–August precipitation. The simulations also suggest that significant changes in regional climate would be experienced even if geoengineering was successful in maintaining global-mean temperature near current values, and both models indicate rapid warming if geoengineering is not sustained
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