582 research outputs found
Differential graded contact geometry and Jacobi structures
We study contact structures on nonnegatively-graded manifolds equipped with
homological contact vector fields. In the degree 1 case, we show that there is
a one-to-one correspondence between such structures (with fixed contact form)
and Jacobi manifolds. This correspondence allows us to reinterpret the
Poissonization procedure, taking Jacobi manifolds to Poisson manifolds, as a
supergeometric version of symplectization.Comment: 9 pages. v2: Added references, improved proof of Proposition 3.3. v3:
Expanded introduction, clarifying remarks, some changes of sign conventions.
Main results are unchanged. v4: Final version, implementing changes suggested
by referee
An improved model for the accurate calculation of parallel heat fluxes at the JET bulk tungsten outer divertor
Parallel heat flux calculations at the JET divertor have been based on the assumption that
all incoming heat is due to the projection of the heat flux parallel to the magnetic line, q ,
plus a constant background. This simplification led to inconsistencies during the analysis of
a series of dedicated tungsten melting experiments performed in 2013, for which infrared
(IR) thermography surface measurements could not be recreated through simulations unless
the parallel heat flux was reduced by 80% for L-mode and 60% for H-mode. We give an
explanation for these differences using a new IR inverse analysis code, a set of geometrical
corrections, and most importantly an additional term for the divertor heat flux accounting for
non-parallel effects such as cross-field transport, recycled neutrals or charge exchange. This
component has been evaluated comparing four different geometries with impinging angles
varying from 2 to 90°. Its magnitude corresponds to 1.2%–1.9% of q , but because it is not
affected by the magnetic projection, it accounts for up to 20%–30% of the tile surface heat
flux. The geometrical corrections imply a further reduction of 24% of the measured heat
flux. In addition, the application of the new inverse code increases the accuracy of the tile
heat flux calculation, eliminating any previous discrepancy. The parallel heat flux computed
with this new model is actually much lower than previously deduced by inverse analysis of IR temperatures—40% for L-mode and 50% for H-mode—while being independent of
the geometry on which it is measured. This main result confirms the validity of the optical
projection as long as a non-constant and non-parallel component is considered. For a given
total heating power, the model predicts over 10% reduction of the maximum tile surface
heat flux compared to strict optical modelling, as well as a 30% reduced sensitivity to
manufacturing and assembling tolerances. These conclusions, along with the improvement in
the predictability of the divertor thermal behaviour, are critical for JET future DT operations,
and are also directly applicable to the design of the ITER divertor monoblocks.EURATOM 63305
Evaluation of the bovine ATP-binding cassette subfamily A member 13 (ABCA13) as a potential biomarker for sensitive detection of animals with focal pathological forms of subclinical paratuberculosis
Trabajo presentado al: ICP 15th International Association for Paratuberculous, Dublín, 12-16 Junio. 2022.Peer reviewe
The dependence of oxygen and nitrogen abundances on stellar mass from the CALIFA survey
Context. The study of the integrated properties of star-forming galaxies is central to understand their formation and evolution. Some of these properties are extensive and therefore their analysis require totally covering and spatially resolved observations. Among these properties, metallicity can be defined in spiral discs by means of integral field spectroscopy (IFS) of individual H ii regions. The simultaneous analysis of the abundances of primary elements, as oxygen, and secondary, as nitrogen, also provides clues about the star formation history and the processes that shape the build-up of spiral discs. Aims. Our main aim is to analyse simultaneously O/H and N/O abundance ratios in H ii regions in different radial positions of the discs in a large sample of spiral galaxies to obtain the slopes and the characteristic abundance ratios that can be related to their integrated properties. Methods. We analysed the optical spectra of individual selected H ii regions extracted from a sample of 350 spiral galaxies of the CALIFA survey. We calculated total O/H abundances and, for the first time, N/O ratios using the semi-empirical routine Hii-Chi-mistry, which, according to Pérez-Montero (2014, MNRAS, 441, 2663), is consistent with the direct method and reduces the uncertainty in the O/H derivation using [N ii] lines owing to the dispersion in the O/H-N/O relation. Then we performed linear fittings to the abundances as a function of the de-projected galactocentric distances. Results. The analysis of the radial distribution both for O/H and N/O in the non-interacting galaxies reveals that both average slopes are negative, but a non-negligible fraction of objects have a flat or even a positive gradient (at least 10% for O/H and 4% for N/O). The slopes normalised to the effective radius appear to have a slight dependence on the total stellar mass and the morphological type, as late low-mass objects tend to have flatter slopes. No clear relation is found, however, to explain the presence of inverted gradients in this sample, and there is no dependence between the average slopes and the presence of a bar. The relation between the resulting O/H and N/O linear fittings at the effective radius is much tighter (correlation coefficient ρ = 0.80) than between O/H and N/O slopes (ρ = 0.39) or for O/H and N/O in the individual H ii regions (ρ = 0.37). These O/H and N/O values at the effective radius also correlate very tightly (less than 0.03 dex of dispersion) with total luminosity and stellar mass. The relation with other integrated properties, such as star formation rate, colour, or morphology, can be understood only in light of the found relation with mass.E.P.M., J.M.V., C.K., S.P., and J.I.P. acknowledge support from the Spanish MICINN through grants AYA2010-21887-C04-01 and AYA2013-47742-C4-1-P and the Junta de Andalucia for grant EXC/2011 FQM-7058. R.G.B., R.G.D., and E.P. acknowledge support from grants AYA2014-57490-P and JA-FQM-2828. Support for L.G. is provided by the Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS. L.G. acknowledges support by CONICYT through FONDECYT grant 3140566Peer Reviewe
CoRoT/ESTA-TASK 1 and TASK 3 comparison of the internal structure and seismic properties of representative stellar models: Comparisons between the ASTEC, CESAM, CLES, GARSTEC and STAROX codes
We compare stellar models produced by different stellar evolution codes for
the CoRoT/ESTA project, comparing their global quantities, their physical
structure, and their oscillation properties. We discuss the differences between
models and identify the underlying reasons for these differences. The stellar
models are representative of potential CoRoT targets. Overall we find very good
agreement between the five different codes, but with some significant
deviations. We find noticeable discrepancies (though still at the per cent
level) that result from the handling of the equation of state, of the opacities
and of the convective boundaries. The results of our work will be helpful in
interpreting future asteroseismology results from CoRoT.Comment: 26 pages, 21 figures, accepted for publication in Astrophysics and
Space Science, CoRoT/ESTA Volum
Low-mass pre--main-sequence stars in the Magellanic Clouds
[Abridged] The stellar Initial Mass Function (IMF) suggests that sub-solar
stars form in very large numbers. Most attractive places for catching low-mass
star formation in the act are young stellar clusters and associations, still
(half-)embedded in star-forming regions. The low-mass stars in such regions are
still in their pre--main-sequence (PMS) evolutionary phase. The peculiar nature
of these objects and the contamination of their samples by the evolved
populations of the Galactic disk impose demanding observational techniques for
the detection of complete numbers of PMS stars in the Milky Way. The Magellanic
Clouds, the companion galaxies to our own, demonstrate an exceptional star
formation activity. The low extinction and stellar field contamination in
star-forming regions of these galaxies imply a more efficient detection of
low-mass PMS stars than in the Milky Way, but their distance from us make the
application of special detection techniques unfeasible. Nonetheless, imaging
with the Hubble Space Telescope yield the discovery of solar and sub-solar PMS
stars in the Magellanic Clouds from photometry alone. Unprecedented numbers of
such objects are identified as the low-mass stellar content of their
star-forming regions, changing completely our picture of young stellar systems
outside the Milky Way, and extending the extragalactic stellar IMF below the
persisting threshold of a few solar masses. This review presents the recent
developments in the investigation of PMS stars in the Magellanic Clouds, with
special focus on the limitations by single-epoch photometry that can only be
circumvented by the detailed study of the observable behavior of these stars in
the color-magnitude diagram. The achieved characterization of the low-mass PMS
stars in the Magellanic Clouds allowed thus a more comprehensive understanding
of the star formation process in our neighboring galaxies.Comment: Review paper, 26 pages (in LaTeX style for Springer journals), 4
figures. Accepted for publication in Space Science Review
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
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