590 research outputs found
Thermal tolerance, climatic variability and latitude
The greater latitudinal extents of occurrence of species towards higher latitudes has been attributed to the broadening of physiological tolerances with latitude as a result of increases in climatic variation. While there is some support for such patterns in climate, the physiological tolerances of species across large latitudinal gradients have seldom been assessed. Here we report findings for insects based on published upper and lower lethal temperature data. The upper thermal limits show little geographical variation. In contrast, the lower bounds of supercooling points and lower lethal temperatures do indeed decline with latitude. However, this is not the case for the upper bounds, leading to an increase in the variation in lower lethal limits with latitude. These results provide some support for the physiological tolerance assumption associated with Rapoport's rule, but highlight the need for coupled data on species tolerances and range size
A method for detection of structure
Context. In order to understand the evolution of molecular clouds it is
important to identify the departures from self-similarity associated with the
scales of self-gravity and the driving of turbulence.
Aims. A method is described based on structure functions for determining
whether a region of gas, such as a molecular cloud, is fractal or contains
structure with characteristic scale sizes.
Methods. Using artificial data containing structure it is shown that
derivatives of higher order structure functions provide a powerful way to
detect the presence of characteristic scales should any be present and to
estimate the size of such structures. The method is applied to observations of
hot H2 in the Kleinman-Low nebula, north of the Trapezium stars in the Orion
Molecular Cloud, including both brightness and velocity data. The method is
compared with other techniques such as Fourier transform and histogram
techniques.
Results. It is found that the density structure, represented by H2 emission
brightness in the K-band (2-2.5micron), exhibits mean characteristic sizes of
110, 550, 1700 and 2700AU. The velocity data show the presence of structure at
140, 1500 and 3500AU. Compared with other techniques such as Fourier transform
or histogram, the method appears both more sensitive to characteristic scales
and easier to interpret.Comment: Astronomy and Astrophysics, in pres
Revealing the inner circumstellar disk of the T Tauri star S Coronae Australis N using the VLTI
Copyright © ESO, 2012Aims. We investigate the structure of the circumstellar disk of the T Tauri star S CrA N and test whether the observations agree with the standard picture proposed for Herbig Ae stars.
Methods. Our observations were carried out with the VLTI/AMBER instrument in the H and K bands with the low spectral resolution mode. For the interpretation of our near-infrared AMBER and archival mid-infrared MIDI visibilities, we employed both geometric and temperature-gradient models.
Results. To characterize the disk size, we first fitted geometric models consisting of a stellar point source, a ring-shaped disk, and a halo structure to the visibilities. In the H and K bands, we measured ring-fit radii of 0.73 ± 0.03 mas (corresponding to 0.095 ± 0.018 AU for a distance of 130 pc) and 0.85 ± 0.07 mas (0.111 ± 0.026 AU), respectively. This K-band radius is approximately two times larger than the dust sublimation radius of ≈0.05 AU expected for a dust sublimation temperature of 1500 K and gray dust opacities, but approximately agrees with the prediction of models including backwarming (namely a radius of ≈0.12 AU). The derived temperature-gradient models suggest that the disk is approximately face-on consisting of two disk components with a gap between star and disk. The inner disk component has a temperature close to the dust sublimation temperature and a quite narrow intensity distribution with a radial extension from 0.11 AU to 0.14 AU.
Conclusions. Both our geometric and temperature-gradient models suggest that the T Tauri star S CrA N is surrounded by a circumstellar disk that is truncated at an inner radius of ≈ 0.11 AU. The narrow extension of the inner temperature-gradient disk component implies that there is a hot inner rim.International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the Universities of Bonn and Cologn
Table ronde sur la place de la chirurgie dans les douleurs chroniques du membre supérieur
RésuméLa douleur chronique est d’origine plurifactorielle, elle réalise une véritable maladie à la fois neuromusculaire et psychosociale. Elle met en jeu l’individu dans sa globalité. Il ne faut pas limiter la consultation à une approche uniquement physique et ne pas s’abriter derrière des examens complémentaires inutiles. Il faut savoir écouter le patient, rechercher des éléments de catastrophisme, une hypervigilance, une stratégie d’évitement et évaluer le contexte socioprofessionnel. Le rôle des facteurs psychosociaux est déterminant dans le processus de chronicisation de la douleur et quant aux possibilités de réinsertion professionnelle. La place de la chirurgie peut se résumer au traitement d’une épine irritative (facteur déclenchant) sous réserve qu’elle soit toujours active et que sa suppression permette la régression de l’ensemble du tableau. Mais, le plus souvent, les signes sont mal limités avec une hypersensibilisation plus ou moins diffuse et un dysfonctionnement secondaire de l’ensemble du membre supérieur, une exclusion fonctionnelle et des éléments de déconditionnement sont présents et le contexte psychosocial est défavorable. La prise en charge ne peut alors être que pluridisciplinaire et réalisée au mieux en centre de réadaptation
Oxygen as a Driver of Early Arthropod Micro-Benthos Evolution
BACKGROUND: We examine the physiological and lifestyle adaptations which facilitated the emergence of ostracods as the numerically dominant Phanerozoic bivalve arthropod micro-benthos. METHODOLOGY/PRINCIPAL FINDINGS: The PO(2) of modern normoxic seawater is 21 kPa (air-equilibrated water), a level that would cause cellular damage if found in the tissues of ostracods and much other marine fauna. The PO(2) of most aquatic breathers at the cellular level is much lower, between 1 and 3 kPa. Ostracods avoid oxygen toxicity by migrating to waters which are hypoxic, or by developing metabolisms which generate high consumption of O(2). Interrogation of the Cambrian record of bivalve arthropod micro-benthos suggests a strong control on ecosystem evolution exerted by changing seawater O(2) levels. The PO(2) of air-equilibrated Cambrian-seawater is predicted to have varied between 10 and 30 kPa. Three groups of marine shelf-dwelling bivalve arthropods adopted different responses to Cambrian seawater O(2). Bradoriida evolved cardiovascular systems that favoured colonization of oxygenated marine waters. Their biodiversity declined during intervals associated with black shale deposition and marine shelf anoxia and their diversity may also have been curtailed by elevated late Cambrian (Furongian) oxygen-levels that increased the PO(2) gradient between seawater and bradoriid tissues. Phosphatocopida responded to Cambrian anoxia differently, reaching their peak during widespread seabed dysoxia of the SPICE event. They lacked a cardiovascular system and appear to have been adapted to seawater hypoxia. As latest Cambrian marine shelf waters became well oxygenated, phosphatocopids went extinct. Changing seawater oxygen-levels and the demise of much of the seabed bradoriid micro-benthos favoured a third group of arthropod micro-benthos, the ostracods. These animals adopted lifestyles that made them tolerant of changes in seawater O(2). Ostracods became the numerically dominant arthropod micro-benthos of the Phanerozoic. CONCLUSIONS/SIGNIFICANCE: Our work has implications from an evolutionary context for understanding how oxygen-level in marine ecosystems drives behaviour
Strong near-infrared emission in the sub-AU disk of the Herbig Ae star HD 163296: evidence of refractory dust?
This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.We present new long-baseline spectro-interferometric observations of the Herbig Ae star HD 163296 (MWC 275) obtained in the
H and K bands with the AMBER instrument at the VLTI. The observations cover a range of spatial resolutions between ∼3 and
∼12 milliarcseconds, with a spectral resolution of ∼30. With a total of 1481 visibilities and 432 closure phases, they represent the
most comprehensive (u, v) coverage achieved so far for a young star. The circumstellar material is resolved at the sub-AU spatial scale
and closure phase measurements indicate a small but significant deviation from point-symmetry. We discuss the results assuming that
the near-infrared excess in HD 163296 is dominated by the emission of a circumstellar disk. A successful fit to the spectral energy
distribution, near-infrared visibilities and closure phases is found with a model in which a dominant contribution to the H and K band
emission originates in an optically thin, smooth and point-symmetric region extending from about 0.1 to 0.45 AU. At a distance of
0.45 AU from the star, silicates condense, the disk becomes optically thick and develops a puffed-up rim, whose skewed emission can
account for the non-zero closure phases. We discuss the source of the inner disk emission and tentatively exclude dense molecular gas
as well as optically thin atomic or ionized gas as its possible origin. We propose instead that the smooth inner emission is produced by
very refractory grains in a partially cleared region, extending to at least ∼0.5 AU. If so, we may be observing the disk of HD 163296
just before it reaches the transition disk phase. However, we note that the nature of the refractory grains or, in fact, even the possibility
of any grain surviving at the very high temperatures we require (∼2100−2300 K at 0.1 AU from the star) is unclear and should be
investigated further.We acknowledge fundings from CNRS and INAF (grant
ASI-INAF I/016/07/0). This work was in part performed under contract with
the Jet Propulsion Laboratory (JPL) funded by NASA through the Michelson
Fellowship Progra
Strong near-infrared emission in the sub-AU disk of the Herbig Ae star HD163296: evidence for refractory dust?
We present new long-baseline spectro-interferometric observations of the
HerbigAe star HD163296 obtained in the H and K bands with the AMBER instrument
at VLTI. The observations cover a range of spatial resolutions between 3 and 12
milli-arcseconds, with a spectral resolution of ~30. With a total of 1481
visibilities and 432 closure phases, they result in the best (u,v) coverage
achieved on a young star so far. The circumstellar material is resolved at the
sub-AU spatial scale and closure phase measurements indicate a small but
significant deviation from point-symmetry. We discuss the results assuming that
the near-infrared excess in HD163296 is dominated by the emission of a
circumstellar disk. A successful fit to the spectral energy distribution,
near-infrared visibilities and closure phases is found with a model where a
dominant contribution to the H and K band emissions arises from an optically
thin, smooth and point-symmetric region extending from about 0.1 to 0.45 AU. At
the latter distance from the star, silicates condense, the disk becomes
optically thick and develops a puffed-up rim, whose skewed emission can account
for the non-zero closure phases. We discuss the nature of the inner disk
emission and tentatively rule out dense molecular gas as well as optically thin
atomic or ionized gas as its possible origin. We propose instead that the inner
emission traces the presence of very refractory grains in a partially cleared
region, extending at least to 0.5 AU. If so, we may be observing the disk of
HD163296 just before it reaches the transition disk phase. However, we note
that the nature of the refractory grains or even the possibility for any grain
to survive at the very high temperatures we require (~2100-2300 K at 0.1 AU
from the star) is unclear and should be investigated further.Comment: 14 pages; 12 figures; accepted by A&
A low optical depth region in the inner disk of the HerbigAe star HR5999
Circumstellar disks surrounding young stars are known to be the birthplaces
of planets, and the innermost astronomical unit is of particular interest. We
present new long-baseline spectro-interferometric observations of the HerbigAe
star, HR5999, obtained in the H and K bands with the AMBER instrument at the
VLTI, and aim to produce near-infrared images at the sub-AU spatial scale. We
spatially resolve the circumstellar material and reconstruct images using the
MiRA algorithm. In addition, we interpret the interferometric observations
using models that assume that the near-infrared excess is dominated by the
emission of a circumstellar disk. We compare the images reconstructed from the
VLTI measurements to images obtained using simulated model data. The K-band
image reveals three main elements: a ring-like feature located at ~0.65 AU, a
low surface brightness region inside, and a central spot. At the maximum
angular resolution of our observations (1.3 mas), the ring is resolved while
the central spot is only marginally resolved, preventing us from revealing the
exact morphology of the circumstellar environment. We suggest that the ring
traces silicate condensation, i.e., an opacity change, in a circumstellar disk
around HR 5999. We build a model that includes a ring at the silicate
sublimation radius and an inner disk of low surface brightness responsible for
a large amount of the near-infrared continuum emission. The model successfully
fits the SED, visibilities, and closure phases, and provides evidence of a low
surface brightness region inside the silicate sublimation radius. This study
provides additional evidence that in HerbigAe stars, there is material in a low
surface brightness region, probably a low optical depth region, located inside
the silicate sublimation radius and of unknown nature.Comment: 11 pages, 10 figure
First AMBER/VLTI observations of hot massive stars
AMBER is the first near infrared focal instrument of the VLTI. It combines
three telescopes and produces spectrally resolved interferometric measures.
This paper discusses some preliminary results of the first scientific
observations of AMBER with three Unit Telescopes at medium (1500) and high
(12000) spectral resolution. We derive a first set of constraints on the
structure of the circumstellar material around the Wolf Rayet Gamma2 Velorum
and the LBV Eta Carinae
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