6,260 results on '"Chabrier, A."'
Search Results
52. Enhanced Encodings for White-Box Designs
- Author
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Battistello, Alberto, Castelnovi, Laurent, Chabrier, Thomas, Goos, Gerhard, Founding Editor, Hartmanis, Juris, Founding Editor, Bertino, Elisa, Editorial Board Member, Gao, Wen, Editorial Board Member, Steffen, Bernhard, Editorial Board Member, Woeginger, Gerhard, Editorial Board Member, Yung, Moti, Editorial Board Member, Grosso, Vincent, editor, and Pöppelmann, Thomas, editor
- Published
- 2022
- Full Text
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53. Histoire constitutionnelle et politique de la Ve République
- Author
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Loïc Chabrier, Yann Saccucci and Loïc Chabrier, Yann Saccucci
- Published
- 2023
54. A Consistent Explanation for the Unusual Initial Mass Function and Star Formation Rate in the Central Molecular Zone (CMZ)
- Author
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Gilles Chabrier and Pierre Dumond
- Subjects
Milky Way Galaxy ,Astrophysics ,QB460-466 - Abstract
We examine various physical processes that may explain the shallow high-mass slope of the initial mass function (IMF), as well as the low star formation rate (SFR) in star-forming molecular clouds (MCs) in the Central Molecular Zone (CMZ). We show that the strong tidal field and shear experienced by the CMZ have opposite effects on the collapse of density fluctuations and cannot explain these properties. Similarly, we show that the intense magnetic field in the CMZ provides a negligible pressure support and, for the high densities at play, should not modify the probability density function of the turbulent gas flow, thus affecting negligibly the IMF. However, we show that, in contrast to the MCs in the Galactic disk, the ones in the CMZ experience only one single episode of turbulence cascade. Indeed, their rather short lifetime, due to their high mean densities, is similar to one typical turbulence crossing time. Consequently, according to the Hennebelle–Chabrier theory of star formation, within this “single turbulence cascade episode,” the cloud experiences one single field of turbulence-induced density fluctuations, leading eventually to gravitationally unstable cores. As shown in Hennebelle & Chabrier (2013), this yields a shallower IMF than usual and leads to the correct observed slope for the CMZ star-forming clouds. Similarly, this single large-scale turbulence event within the cloud lifetime yields a 5–6 times lower SFR than under usual conditions, in agreement with the observed values. Therefore, we suggest that this “single turbulence cascade” scenario can explain both the shallow IMF and low SFR of clouds in the CMZ.
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- 2024
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55. Ab initio based equation of state of dense water for planetary and exoplanetary modeling
- Author
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Mazevet, S., Licari, A., Chabrier, G., and Potekhin, A. Y.
- Subjects
Astrophysics - Earth and Planetary Astrophysics - Abstract
As a first step toward a multi-phase equation of state for dense water, we develop a temperature-dependent equation of state for dense water covering the liquid and plasma regimes and extending to the super-ionic and gas regimes. This equation of state covers the complete range of conditions encountered in planetary modeling. We use first principles quantum molecular dynamics simulations and its Thomas-Fermi extension to reach the highest pressures encountered in giant planets several times the size of Jupiter. Using these results, as well as the data available at lower pressures, we obtain a parametrization of the Helmholtz free energy adjusted over this extended temperature and pressure domain. The parametrization ignores the entropy and density jumps at phase boundaries but we show that it is sufficiently accurate to model interior properties of most planets and exoplanets. We produce an equation of state given in analytical form that is readily usable in planetary modeling codes and dynamical simulations (a fortran implementation can be found at http://www.ioffe.ru/astro/H2O/). The EOS produced is valid for the entire density range relevant to planetary modeling, for densities where quantum effects for the ions can be neglected, and for temperatures below 50,000K. We use this equation of state to calculate the mass-radius relationship of exoplanets up to 5,000M_Earth, explore temperature effects in ocean and wet Earth-like planets, and quantify the influence of the water EOS for the core on the gravitational moments of Jupiter., Comment: 13 pages, 18 figures. In v.2, Eq.(13) and the value of S_0 are corrected
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- 2018
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56. A closer look at the transition between fully convective and partly radiative low mass stars
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Baraffe, Isabelle and Chabrier, Gilles
- Subjects
Astrophysics - Solar and Stellar Astrophysics - Abstract
Recently, Jao et al. (2018) discovered a gap in the mid-M dwarfs main sequence revealed by the analysis of Gaia data Release 2. They suggested the feature is linked to the onset of full convection in M dwarfs. Following the announcement of this discovery, MacDonald & Gizis (2018) proposed an explanation based on standard stellar evolution models. In this paper we re-examine the explanation suggested by MacDonald & Gizis (2018). We confirm that nuclear burning and mixing process of $^3$He provide the best explanation for the observed feature. We also find that a change in the energy transport from convection to radiation does not induce structural changes that could be visible. Regarding the very details of the process, however, we disagree with MacDonald & Gizis (2018) and propose a different explanation., Comment: 5 pages, 6 figures, accepted for publication in Astronomy & Astrophysics
- Published
- 2018
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57. Impact of the Hall effect in star formation and the issue of angular momentum conservation
- Author
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Marchand, Pierre, Commerçon, Benoît, and Chabrier, Gilles
- Subjects
Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Astrophysics of Galaxies - Abstract
We present an implementation of the Hall term in the non-ideal magnetohydrodynamics equations into the adaptive-mesh-refinement code RAMSES to study its impact on star formation. Recent works show that the Hall effect heavily influences the regulation of the angular momentum in collapsing dense cores, strengthening or weakening the magnetic braking. Our method consists of a modification of the two-dimensional constrained transport scheme. Our scheme shows convergence of second-order in space and the frequency of the propagation of whistler waves is accurate. We confirm previous results, namely that during the collapse, the Hall effect generates a rotation of the fluid with a direction in the mid-plane that depends on the sign of the Hall resistivity, while counter-rotating envelopes develop on each side of the mid-plane. However, we find that the predictability of our numerical results is severely limited. The angular momentum is not conserved in any of our dense core-collapse simulations with the Hall effect: a large amount of angular momentum is generated within the first Larson core, a few hundred years after its formation, without compensation by the surrounding gas. This issue is not mentioned in previous studies and may be correlated to the formation of the accretion shock on the Larson core. We expect that this numerical effect could be a serious issue in star formation simulations., Comment: 17 pages, 21 figures. Accepted for publication in Astronomy & Astrophysics
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- 2018
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58. Protostellar birth with ambipolar and ohmic diffusion
- Author
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Vaytet, Neil, Commerçon, Benoît, Masson, Jacques, González, Matthias, and Chabrier, Gilles
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Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Astrophysics of Galaxies - Abstract
The transport of angular momentum is capital during the formation of low-mass stars; too little removal and rotation ensures stellar densities are never reached, too much and the absence of rotation means no protoplanetary disks can form. Magnetic diffusion is seen as a pathway to resolving this long-standing problem. We investigate the impact of including resistive MHD in simulations of the gravitational collapse of a 1 solar mass gas sphere, from molecular cloud densities to the formation of the protostellar seed; the second Larson core. We used the AMR code RAMSES to perform two 3D simulations of collapsing magnetised gas spheres, including self-gravity, radiative transfer, and a non-ideal gas equation of state to describe H2 dissociation which leads to the second collapse. The first run was carried out under the ideal MHD approximation, while ambipolar and ohmic diffusion was incorporated in the second calculation. In the ideal MHD simulation, the magnetic field dominates the energy budget everywhere inside and around the first core, fueling interchange instabilities and driving a low-velocity outflow. High magnetic braking removes essentially all angular momentum from the second core. On the other hand, ambipolar and ohmic diffusion create a barrier which prevents amplification of the magnetic field beyond 0.1 G in the first Larson core which is now fully thermally supported. A significant amount of rotation is preserved and a small Keplerian-like disk forms around the second core. When studying the radiative efficiency of the first and second core accretion shocks, we found that it can vary by several orders of magnitude over the 3D surface of the cores. Magnetic diffusion is a pre-requisite to star-formation; it enables the formation of protoplanetary disks in which planets will eventually form, and also plays a determinant role in the formation of the protostar itself., Comment: 18 pages, 11 figures, accepted for publication in Astronomy & Astrophysics
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- 2018
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59. Experimental investigations of a vibro-impact absorber attached to a continuous structure
- Author
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Chabrier, R., Chevallier, G., Foltête, E., and Sadoulet-Reboul, E.
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- 2022
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60. Magnetic neutron star cooling and microphysics
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Potekhin, A. Y. and Chabrier, G.
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Astrophysics - High Energy Astrophysical Phenomena ,Astrophysics - Solar and Stellar Astrophysics - Abstract
We study the relative importance of several recent updates of microphysics input to the neutron star cooling theory and the effects brought about by superstrong magnetic fields of magnetars, including the effects of the Landau quantization in their crusts. We use a finite-difference code for simulation of neutron-star thermal evolution on timescales from hours to megayears with an updated microphysics input. The consideration of short timescales ($\lesssim1$ yr) is made possible by a treatment of the heat-blanketing envelope without the quasistationary approximation inherent to its treatment in traditional neutron-star cooling codes. For the strongly magnetized neutron stars, we take into account the effects of Landau quantization on thermodynamic functions and thermal conductivities. We simulate cooling of ordinary neutron stars and magnetars with non-accreted and accreted crusts and compare the results with observations. Suppression of radiative and conductive opacities in strongly quantizing magnetic fields and formation of a condensed radiating surface substantially enhance the photon luminosity at early ages, making the life of magnetars brighter but shorter. These effects together with the effect of strong proton superfluidity, which slows down the cooling of kiloyear-aged neutron stars, can explain thermal luminosities of about a half of magnetars without invoking heating mechanisms. Observed thermal luminosities of other magnetars are still higher than theoretical predictions, which implies heating, but the effects of quantizing magnetic fields and baryon superfluidity help to reduce the discrepancy., Comment: 18 pages, 14 figures. In v3, a typo in a graphics code has been fixed, which caused a vertical shift by 0.3 of cooling curves in the figures (except the inset in Fig.2). In v2 and v4, typos were fixed in the bibliography list and in Eqs.(1)-(3)
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- 2017
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61. Focal Cerebral Arteriopathy of Childhood
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Fullerton, Heather J, Stence, Nicholas, Hills, Nancy K, Jiang, Bin, Amlie-Lefond, Catherine, Bernard, Timothy J, Friedman, Neil R, Ichord, Rebecca, Mackay, Mark T, Rafay, Mubeen F, Chabrier, Stéphane, Steinlin, Maja, Elkind, Mitchell SV, deVeber, Gabrielle A, and Wintermark, Max
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Allied Health and Rehabilitation Science ,Biomedical and Clinical Sciences ,Health Sciences ,Pediatric ,Brain Disorders ,Stroke ,Neurosciences ,Adolescent ,Anterior Cerebral Artery ,Brain Infarction ,Carotid Artery ,Internal ,Carotid Stenosis ,Cerebral Angiography ,Cerebral Arterial Diseases ,Child ,Child ,Preschool ,Computed Tomography Angiography ,Disease Progression ,Female ,Humans ,Infant ,Magnetic Resonance Angiography ,Male ,Middle Cerebral Artery ,Posterior Cerebral Artery ,Severity of Illness Index ,brain ischemia ,cerebrovascular disorders ,child ,follow-up studies ,humans ,VIPS Investigators ,Cardiorespiratory Medicine and Haematology ,Clinical Sciences ,Neurology & Neurosurgery ,Clinical sciences ,Allied health and rehabilitation science - Abstract
Background and Purpose- Focal cerebral arteriopathy (FCA)-a common cause of arterial ischemic stroke in previously healthy children-often progresses over days to weeks, increasing the risk of recurrent stroke. We developed a novel severity scoring system designed to quantify FCA progression and correlate with clinical outcomes. Methods- The VIPS study (Vascular Effects of Infection in Pediatric Stroke) prospectively enrolled 355 children with arterial ischemic stroke (2010-2014), including 41 with centrally confirmed FCA. Two neuroradiologists independently reviewed FCA cerebrovascular imaging, assigning a graded severity score of zero (no involvement) to 4 (occlusion) to individual arterial segments. The FCA severity score (FCASS) was the unweighted sum. In an iterative process, we modeled scores derived from different combinations of arterial segments to identify the model that optimized correlation with clinical outcome, simplicity, and reliability. Results- The optimal FCASS summed scores from 5 arterial segments: supraclinoid internal carotid artery, A1, A2, M1, and M2. The median (interquartile range) baseline FCASS was 4 (2-6). Of 33 children with follow-up imaging, the maximum FCASS (at any time point) was 7 (5-9). Twenty-four (73%) had FCA progression on follow-up with their maximum FCASS at a median of 8 (5-35.5) days poststroke; their median FCASS increase was 4 (2.5-6). FCASS did not correlate with recurrent arterial ischemic stroke. Maximum (but not baseline) FCASS correlated with 1-year pediatric stroke outcome measures ( P=0.037). Conclusions- Our novel scoring system for FCA severity correlates with neurological outcomes in the VIPS cohort and provides a tool for FCA treatment trials under development.
- Published
- 2018
62. Exploring the impact of prior spontaneous miscarriage on stress among pregnant women during the first trimester: an observational study
- Author
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Coralie Barbe, Justine Ouy, Marie Boiteux-Chabrier, Leïla Bouazzi, Bach-Nga Pham, Sandra Carrau-Truillet, and Aline Hurtaud
- Subjects
pregnancy trimester, first ,stress ,spontaneous miscarriage ,delivery of health care ,cross-sectional studies ,Medicine (General) ,R5-920 - Abstract
Background: Spontaneous miscarriage (SM) is the most common complication of pregnancy. Its psychological repercussions are widely documented but few studies have investigated its effect on women’s experience of a subsequent pregnancy. Aim: To evaluate the impact of prior SM on the level of stress experienced by pregnant women during the first trimester of pregnancy. Design and setting: Cross-sectional, observational study, which was conducted between June and October 2021 in France. Method: A self-report questionnaire was distributed to women in the first trimester of pregnancy. Stress was assessed using the Antenatal Perceived Stress Inventory to yield an overall score and a score for three dimensions ('medical and obstetric risks or fetal health'; 'psychosocial changes during pregnancy'; and the ‘prospect of childbirth'). Women with a history of prior SM and those without were compared. Results: In total, 93 women were included; 63 without and 30 with a history of prior SM. Prior SM was not associated with the overall score. The score for the dimension 'medical and obstetric risks or fetal health' was significantly higher in women with prior SM (3.00±0.86 versus 2.34±0.80; β = 0.61 [95% confidence interval {CI} = 0.25 to 0.96]; P = 0.001). Prior SM was significantly associated with the items 'the baby’s health' (P = 0.048) and 'the echography' (P = 0.002). Conclusion: This study shows a significant impact of prior SM on the level of stress of pregnant women during the first trimester, particularly relating to the medical and obstetric risks or fetal health, underlining the need for appropriate psychological support to be provided to women who experience SM.
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- 2023
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63. A library of ATMO forward model transmission spectra for hot Jupiter exoplanets
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Goyal, Jayesh M., Mayne, Nathan, Sing, David K., Drummond, Benjamin, Tremblin, Pascal, Amundsen, David S., Evans, Thomas, Carter, Aarynn L., Spake, Jessica, Baraffe, Isabelle, Nikolov, Nikolay, Manners, James, Chabrier, Gilles, and Hebrard, Eric
- Subjects
Astrophysics - Earth and Planetary Astrophysics - Abstract
We present a grid of forward model transmission spectra, adopting an isothermal temperature-pressure profile, alongside corresponding equilibrium chemical abundances for 117 observationally significant hot exoplanets (Equilibrium Temperatures of 547-2710 K). This model grid has been developed using a 1D radiative-convective-chemical equilibrium model termed ATMO, with up-to-date high temperature opacities. We present an interpretation of observations of ten exoplanets, including best fit parameters and $\chi^{2}$ maps. In agreement with previous works, we find a continuum from clear to hazy/cloudy atmospheres for this sample of hot Jupiters. The data for all the 10 planets are consistent with sub-solar to solar C/O ratio, 0.005 to 10 times solar metallicity and water rather than a methane dominated infrared spectra. We then explore the range of simulated atmospheric spectra for different exoplanets, based on characteristics such as temperature, metallicity, C/O-ratio, haziness and cloudiness. We find a transition value for the metallicity between 10 and 50 times solar, which leads to substantial changes in the transmission spectra. We also find a transition value of C/O ratio, from water to carbon species dominated infrared spectra, as found by previous works, revealing a temperature dependence of this transition point ranging from $\sim$0.56 to $\sim$1-1.3 for equilibrium temperatures from $\sim$900 to $\sim$2600 K. We highlight the potential of the spectral features of HCN and C$_2$H$_2$ to constrain the metallicities and C/O ratios of planets, using JWST observations. Finally, our entire grid ($\sim$460,000 simulations) is publicly available and can be used directly with the JWST simulator PandExo for planning observations., Comment: No changes in replacement, main paper now made visible on arXiv as earlier the published Erratum associated with the paper was instead visible. 34 pages, 28 figures. Accepted for Publication in MNRAS. Full grid of model transmission spectra and chemical abundances are available here, https://drive.google.com/drive/folders/1tvlgSWyEAA0cX_yxnA5URD4Zo3Zj4GcH
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- 2017
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64. A complete study of the precision of the concentric MacLaurin spheroid method to calculate Jupiter's gravitational moments
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Debras, Florian and Chabrier, Gilles
- Subjects
Astrophysics - Earth and Planetary Astrophysics - Abstract
A few years ago, Hubbard (2012, 2013) presented an elegant, non-perturbative method, called concentric MacLaurin spheroid (CMS), to calculate with very high accuracy the gravitational moments of a rotating fluid body following a barotropic pressure-density relationship. Having such an accurate method is of great importance for taking full advantage of the Juno mission, and its extremely precise determination of Jupiter gravitational moments, to better constrain the internal structure of the planet. Recently, several authors have applied this method to the Juno mission with 512 spheroids linearly spaced in altitude. We demonstrate in this paper that such calculations lead to errors larger than Juno's error bars, invalidating the aforederived Jupiter models at the level required by Juno's precision. We show that, in order to fulfill Juno's observational constraints, at least 1500 spheroids must be used with a cubic, square or exponential repartition, the most reliable solutions. When using a realistic equation of state instead of a polytrope, we highlight the necessity to properly describe the outermost layers to derive an accurate boundary condition, excluding in particular a zero pressure outer condition. Providing all these constraints are fulfilled, the CMS method can indeed be used to derive Jupiter models within Juno's present observational constraints. However, we show that the treatment of the outermost layers leads to irreducible errors in the calculation of the gravitational moments and thus on the inferred physical quantities for the planet. We have quantified these errors and evaluated the maximum precision that can be reached with the CMS method in the present and future exploitation of Juno's data., Comment: 21 pages, 11 figures
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- 2017
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65. Cloudless atmospheres for young low-gravity substellar objects
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Tremblin, P., Chabrier, G., Baraffe, I., Liu, Michael. C., Magnier, E. A., Lagage, P. -O., de Oliveira, C. Alves, Burgasser, A. J., Amundsen, D. S., and Drummond, B.
- Subjects
Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Earth and Planetary Astrophysics - Abstract
Atmospheric modeling of low-gravity (VL-G) young brown dwarfs remains a challenge. The presence of very thick clouds has been suggested because of their extremely red near-infrared (NIR) spectra, but no cloud models provide a good fit to the data with a radius compatible with evolutionary models for these objects. We show that cloudless atmospheres assuming a temperature gradient reduction caused by fingering convection provides a very good model to match the observed VL-G NIR spectra. The sequence of extremely red colors in the NIR for atmospheres with effective temperature from ~2000 K down to ~1200 K is very well reproduced with predicted radii typical of young low-gravity objects. Future observations with NIRSPEC and MIRI on the James Webb Space Telescope (JWST) will provide more constrains in the mid-infrared, helping to confirm/refute whether or not the NIR reddening is caused by fingering convection. We suggest that the presence/absence of clouds will be directly determined by the silicate absorption features that can be observed with MIRI. JWST will therefore be able to better characterize the atmosphere of these hot young brown dwarfs and their low-gravity exoplanet analogues., Comment: Accepted in ApJ
- Published
- 2017
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66. Analytical core mass function (CMF) from filaments: Under which circumstances can filament fragmentation reproduce the CMF?
- Author
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Lee, Yueh-Ning, Hennebelle, Patrick, and Chabrier, Gilles
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Astrophysics - Astrophysics of Galaxies - Abstract
Observations suggest that star formation in filamentary molecular clouds occurs in a two-step process, with the formation of filaments preceding that of prestellar cores and stars. Here, we apply the gravo-turbulent fragmentation theory of Hennebelle & Chabrier 08, 09, 13 to a filamentary environment, taking into account magnetic support. We discuss the induced geometrical effect on the cores, with a transition from 3D geometry at small scales to 1D at large ones. The model predicts the fragmentation behavior of a filament for a given mass per unit length (MpL) and level of magnetization. This CMF for individual filaments is then convolved with the distribution of filaments to obtain the final system CMF. The model yields two major results: (i) the filamentary geometry naturally induces a hierarchical fragmentation process, first into groups of cores, separated by a length equal to a few filament Jeans lengths, i.e. a few times the filament width. These groups then fragment into individual cores. (ii) Non-magnetized filaments with high MpL are found to fragment excessively, at odd with observations. This is resolved by taking into account the magnetic field treated simply as additional pressure support). The present theory suggests two complementary modes of star formation: while small (spherical or filamentary) structures will collapse directly into prestellar cores, according to the standard Hennebelle-Chabrier theory, the large (filamentary) ones, the dominant population according to observations, will follow the afore-described two-step process.
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- 2017
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67. Advection of potential temperature in the atmosphere of irradiated exoplanets: a robust mechanism to explain radius inflation
- Author
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Tremblin, P., Chabrier, G., Mayne, N. J., Amundsen, D. S., Baraffe, I., Debras, F., Drummond, B., Manners, J., and Fromang, S.
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Astrophysics - Earth and Planetary Astrophysics - Abstract
The anomalously large radii of strongly irradiated exoplanets have remained a major puzzle in astronomy. Based on a 2D steady state atmospheric circulation model, the validity of which is assessed by comparison to 3D calculations, we reveal a new mechanism, namely the advection of the potential temperature due to mass and longitudinal momentum conservation, a process occuring in the Earth's atmosphere or oceans. At depth, the vanishing heating flux forces the atmospheric structure to converge to a hotter adiabat than the one obtained with 1D calculations, implying a larger radius for the planet. Not only do the calculations reproduce the observed radius of HD209458b, but also the observed correlation between radius inflation and irradiation for transiting planets. Vertical advection of potential temperature induced by non uniform atmospheric heating thus provides a robust mechanism explaining the inflated radii of irradiated hot Jupiters., Comment: accepted in ApJ
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- 2017
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68. Enhanced Encodings for White-Box Designs.
- Author
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Alberto Battistello, Laurent Castelnovi, and Thomas Chabrier
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- 2021
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69. A High-Order Infective Countermeasure Framework.
- Author
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Guillaume Barbu, Luk Bettale, Laurent Castelnovi, Thomas Chabrier, Nicolas Debande, Christophe Giraud 0001, and Nathan Reboud
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- 2021
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70. Generalizing Statistical Ineffective Fault Attacks in the Spirit of Side-Channel Attacks.
- Author
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Guillaume Barbu, Laurent Castelnovi, and Thomas Chabrier
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- 2021
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71. Generalizing Statistical Ineffective Fault Attacks in the Spirit of Side-Channel Attacks
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Barbu, Guillaume, Castelnovi, Laurent, Chabrier, Thomas, Goos, Gerhard, Founding Editor, Hartmanis, Juris, Founding Editor, Bertino, Elisa, Editorial Board Member, Gao, Wen, Editorial Board Member, Steffen, Bernhard, Editorial Board Member, Woeginger, Gerhard, Editorial Board Member, Yung, Moti, Editorial Board Member, Bhasin, Shivam, editor, and De Santis, Fabrizio, editor
- Published
- 2021
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72. From Sketches to Morphing: New Geometric Views on the Epistemological Role of Drawing
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Chabrier, Renaud, Sarti, Alessandro, Series Editor, Flash, Tamar, editor, and Berthoz, Alain, editor
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- 2021
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73. Implementation of Motor Function Measure score percentile curves - Predicting motor function loss in Duchenne muscular dystrophy
- Author
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Fontaine-Carbonnel, Stéphanie, De Montferrand, Camille, Ragot-Mandry, Sylvie, Chabrier, Stéphane, Mehouas, Manuella Fournier, Rauscent, Hélène, Cances, Claude, Rivier, François, Urtizberea, Jon Andoni, Peudenier, Sylviane, Brochard, Sylvain, Lagrue, Emmanuelle, Hafner, Patricia, Schmidt, Simone, Schädelin, Sabine, Rippert, Pascal, Hamroun, Dalil, Fabien, Solenn, Henzi, Bettina, Putananickal, Niveditha, Rubino-Nacht, Daniela, Vuillerot, Carole, and Fischer, Dirk
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- 2022
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74. Probing the Milky Way Stellar and Brown Dwarf Initial Mass Function with Modern Microlensing Observations
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Gilles Chabrier and Romain Lenoble
- Subjects
Stellar mass functions ,Initial mass function ,Astrophysics ,QB460-466 - Abstract
We use recent microlensing observations toward the central bulge of the Galaxy to probe the overall stellar plus brown dwarf initial mass function (IMF) in these regions well within the brown dwarf domain. We find that the IMF is consistent with the same Chabrier IMF characteristic of the Galactic disk. In contrast, other IMFs suggested in the literature overpredict the number of short-time events, and thus of very low mass stars and brown dwarfs, compared with observations. This again supports the suggestion that brown dwarfs and stars predominantly form via the same mechanism. We show that claims for different IMFs in the stellar and substellar domains arise from an incorrect parameterization of the IMF. Furthermore, we show that the IMF in the central regions of the bulge seems to be bottom-heavy, as illustrated by the large number of short-time events compared with the other regions. This recalls our previous analysis of the IMF in massive early-type galaxies and suggests the same kind of two-phase formation scenario, with the central bulge initially formed under more violent, burst-like conditions than the rest of the Galaxy.
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- 2023
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75. A Consistent Explanation for the Unusual Initial Mass Function and Star Formation Rate in the Central Molecular Zone (CMZ)
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Chabrier, Gilles, primary and Dumond, Pierre, additional
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- 2024
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76. Disease aetiology and progression shape the inter-patient multi-omics profile of clear cell renal carcinoma
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McKay, James, primary, Penha, Ricardo, additional, Sexton-Oates, Alexandra, additional, Senkin, Sergey, additional, Park, Hanla, additional, Atkins, Joshua, additional, Holcatova, Ivana, additional, Hornakova, Anna, additional, Savic, Slavisa, additional, Ognjanovic, Simona, additional, Swiatkowska, Beata, additional, Lissowska, Jolanta, additional, Zaridze, David, additional, Mukeria, Anush, additional, Janout, Vladimir, additional, Chabrier, Amelie, additional, Cahais, Vincent, additional, Cuenin, Cyrille, additional, Scelo, Ghislaine, additional, Foll, Matthieu, additional, Herceg, Zdenko, additional, Brennan, Paul, additional, Smith-Byrne, Karl, additional, and Alcala, Nicolas, additional
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- 2024
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77. Design and Preliminary Evaluation of a Dextrous Encounter Type Force Feedback Interface.
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Anthony Chabrier, Florian Gosselin, and Wael Bachta
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- 2020
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78. Rock, Paper, Scissors.
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Juliette Chabrier
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- 2023
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79. Shadow.
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Juliette Chabrier
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- 2023
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80. Self-consistent evolution of accreting low-mass stars and brown dwarfs
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Baraffe, I., Elbakyan, V. G., Vorobyov, E. I., and Chabrier, G.
- Subjects
Astrophysics - Solar and Stellar Astrophysics - Abstract
We present self-consistent calculations coupling numerical hydrodynamics simulations of collapsing pre-stellar cores and stellar evolution models of accreting objects. We analyse the main impact of consistent accretion history on the evolution and lithium depletion of young low-mass stars and brown dwarfs. These consistent models confirm the generation of a luminosity spread in Herzsprung-Russell diagrams at ages $\sim$ 1-10 Myr. They also confirm that early accretion can produce objects with abnormal Li depletion, as found in a previous study that was based on arbitrary accretion rates. The results strengthen that objects with anomalously high level of Li depletion in young clusters should be extremely rare. We also find that early phases of burst accretion can produce coeval models of similar mass with a range of different Li surface abundances, and in particular with Li-excess compared to the predictions of non-accreting counterparts. This result is due to a subtle competition between the effect of burst accretion and its impact on the central stellar temperature, the growth of the stellar radiative core and the accretion of fresh Li from the accretion disk. Only consistent models could reveal such a subtle combination of effects. This new result could explain the recent, puzzling observations of Li-excess of fast rotators in the young cluster NGC 2264. Present self-consistent accreting models are available in electronic form., Comment: 14 pages, 8 figures, accepted for publication in Astronomy and Astrophysics
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- 2016
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81. Magnetically self-regulated formation of early protoplanetary discs
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Hennebelle, Patrick, Commercon, Benoit, Chabrier, Gilles, and Marchand, Pierre
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Astrophysics - Astrophysics of Galaxies - Abstract
The formation of protoplanetary discs during the collapse of molecular dense cores is significantly influenced by angular momentum transport, notably by the magnetic torque. In turn, the evolution of the magnetic field is determined by dynamical processes and non-ideal MHD effects such as ambipolar diffusion. Considering simple relations between various timescales characteristic of the magnetized collapse, we derive an expression for the early disc radius, $ r \simeq 18 \, {\rm AU} \, \left({\eta_{\rm AD} / 0.1 \, {\rm s}} \right)^{2/9} \left({B_z / 0.1\, {\rm G}} \right) ^{-4/9} \left({M / 0.1 \msol} \right) ^{1/3},$ where $M$ is the total disc plus protostar mass, $\eta_\mathrm{AD}$ is the ambipolar diffusion coefficient and $B_z$ is the magnetic field in the inner part of the core. This is about significantly smaller than the discs that would form if angular momentum was conserved. The analytical predictions are confronted against a large sample of 3D, non-ideal MHD collapse calculations covering variations of a factor 100 in core mass, a factor 10 in the level of turbulence, a factor 5 in rotation, and magnetic mass-to-flux over critical mass-to-flux ratios 2 and 5. The disc radius estimates are found to agree with the numerical simulations within less than a factor 2. A striking prediction of our analysis is the weak dependence of circumstellar disc radii upon the various relevant quantities, suggesting weak variations among class-0 disc sizes. In some cases, we note the onset of large spiral arms beyond this radius., Comment: accepted for publication in ApJ Letters
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- 2016
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82. Atmospheres and radiating surfaces of neutron stars with strong magnetic fields
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Potekhin, A. Y., Ho, W. C. G., and Chabrier, G.
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Astrophysics - High Energy Astrophysical Phenomena ,Astrophysics - Solar and Stellar Astrophysics - Abstract
We review the current status of the theory of thermal emission from the surface layers of neutron stars with strong magnetic fields $B\sim 10^{10}-10^{15}$ G, including formation of the spectrum in a partially ionized atmosphere and at a condensed surface. In particular, we describe recent progress in modeling partially ionized atmospheres of central compact objects in supernova remnants, which may have moderately strong fields $B\sim 10^{10}-10^{11}$ G. Special attention is given to polarization of thermal radiation emitted by a neutron star surface. Finally, we briefly describe applications of the theory to observations of thermally emitting isolated neutron stars., Comment: 27 pages, 5 figures, invited review at the conference "The Modern Physics of Compact Stars 2015" (Yerevan, Armenia, Sept. 30 - Oct. 3, 2015), edited by R. Avagyan, A. Saharian, and A. Sedrakian. In v.2, a citation (Ref.114) is corrected
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- 2016
83. A chemical solver to compute molecule and grain abundances and non-ideal MHD resistivities in prestellar core collapse calculations
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Marchand, Pierre, Masson, Jacques, Chabrier, Gilles, Hennebelle, Patrick, Commerçon, Benoit, and Vaytet, Neil
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Astrophysics - Astrophysics of Galaxies ,Astrophysics - Solar and Stellar Astrophysics - Abstract
We develop a detailed chemical network relevant to the conditions characteristic of prestellar core collapse. We solve the system of time-dependent differential equations to calculate the equilibrium abundances of molecules and dust grains, with a size distribution given by size-bins for these latter. These abundances are used to compute the different non-ideal magneto-hydrodynamics resistivities (ambipolar, Ohmic and Hall), needed to carry out simulations of protostellar collapse. For the first time in this context, we take into account the evaporation of the grains, the thermal ionisation of Potassium, Sodium and Hydrogen at high temperature, and the thermionic emission of grains in the chemical network, and we explore the impact of various cosmic ray ionisation rates. All these processes significantly affect the non-ideal magneto-hydrodynamics resistivities, which will modify the dynamics of the collapse. Ambipolar diffusion and Hall effect dominate at low densities, up to n_H = 10^12 cm^-3, after which Ohmic diffusion takes over. We find that the time-scale needed to reach chemical equilibrium is always shorter than the typical dynamical (free fall) one. This allows us to build a large, multi-dimensional multi-species equilibrium abundance table over a large temperature, density and ionisation rate ranges. This table, which we make accessible to the community, is used during first and second prestellar core collapse calculations to compute the non-ideal magneto-hydrodynamics resistivities, yielding a consistent dynamical-chemical description of this process., Comment: Accepted for publication in A&A, 14 pages, 26 figures
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- 2016
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84. Near-Infrared Spectroscopy of the Y0 WISEP J173835.52+273258.9 and the Y1 WISE J035000.32-565830.2: the Importance of Non-Equilibrium Chemistry
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Leggett, S. K., Tremblin, P., Saumon, D., Marley, M. S., Morley, Caroline V., Amundsen, D. S., Baraffe, I., and Chabrier, G.
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Astrophysics - Solar and Stellar Astrophysics - Abstract
We present new near-infrared spectra, obtained at Gemini Observatory, for two Y dwarfs: WISE J035000.32-565830.2 (W0350) and WISEP J173835.52+273258.9 (W1738). A FLAMINGOS-2 R=540 spectrum was obtained for W0350, covering 1.0 < lambda um < 1.7, and a cross-dispersed GNIRS R=2800 spectrum was obtained for W1738, covering 0.993-1.087 um, 1.191-1.305 um, 1.589-1.631 um, and 1.985-2.175 um, in four orders. We also present revised YJH photometry for W1738, using new NIRI Y and J imaging, and a re-analysis of the previously published NIRI H band images. We compare these data, together with previously published data for late-T and Y dwarfs, to cloud-free models of solar metallicity, calculated both in chemical equilibrium and with disequilibrium driven by vertical transport. We find that for the Y dwarfs the non-equilibrium models reproduce the near-infrared data better than the equilibrium models. The remaining discrepancies suggest that fine-tuning the CH_4/CO and NH_3/N_2 balance is needed. Improved trigonometric parallaxes would improve the analysis. Despite the uncertainties and discrepancies, the models reproduce the observed near-infrared spectra well. We find that for the Y0, W1738, T_eff = 425 +/- 25 K and log g = 4.0 +/- 0.25, and for the Y1, W0350, T_eff = 350 +/- 25 K and log g = 4.0 +/- 0.25. W1738 may be metal-rich. Based on evolutionary models, these temperatures and gravities correspond to a mass range for both Y dwarfs of 3-9 Jupiter masses, with W0350 being a cooler, slightly older, version of W1738; the age of W0350 is 0.3-3 Gyr, and the age of W1738 is 0.15-1 Gyr., Comment: Accepted on March 30 2016 for publication in ApJ
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- 2016
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85. Cloudless atmospheres for L/T dwarfs and extra-solar giant planets
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Tremblin, P., Amundsen, D. S., Chabrier, G., Baraffe, I., Drummond, B., Hinkley, S., Mourier, P., and Venot, O.
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Astrophysics - Earth and Planetary Astrophysics ,Astrophysics - Solar and Stellar Astrophysics - Abstract
The admitted, conventional scenario to explain the complex spectral evolution of brown dwarfs (BD) since their first detections twenty years ago, has always been the key role played by micron-size condensates, called "dust" or "clouds", in their atmosphere. This scenario, however, faces major problems, in particular the J-band brightening and the resurgence of FeH absorption at the L to T transition, and a physical first-principle understanding of this transition is lacking. In this paper, we propose a new, completely different explanation for BD and extrasolar giant planet (EGP) spectral evolution, without the need to invoke clouds. We show that, due to the slowness of the CO/CH4 and N2/NH3 chemical reactions, brown dwarf (L and T, respectively) and EGP atmospheres are subject to a thermo-chemical instability similar in nature to the fingering or chemical convective instability present in Earth oceans and at the Earth core/mantle boundary. The induced small-scale turbulent energy transport reduces the temperature gradient in the atmosphere, explaining the observed increase in near infrared J-H and J-K colors of L dwarfs and hot EGPs, while a warming up of the deep atmosphere along the L to T transition, as the CO/CH4 instability vanishes, naturally solves the two aforementioned puzzles, and provides a physical explanation of the L to T transition. This new picture leads to a drastic revision of our understanding of BD and EGP atmospheres and their evolution., Comment: Accepted in ApJL, comments welcome
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- 2016
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86. Theoretical limits on magnetic field strengths in low-mass stars
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Browning, Matthew K., Weber, Maria A., Chabrier, Gilles, and Massey, Angela P.
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Astrophysics - Solar and Stellar Astrophysics - Abstract
Observations have suggested that some low-mass stars have larger radii than predicted by 1-D structure models. Some theoretical models have invoked very strong interior magnetic fields (of order 1 MG or more) as a possible cause of such large radii. Whether fields of that strength could in principle by generated by dynamo action in these objects is unclear, and we do not address the matter directly. Instead, we examine whether such fields could remain in the interior of a low mass object for a significant time, and whether they would have any other obvious signatures. First, we estimate timescales for the loss of strong fields by magnetic buoyancy instabilities. We consider a range of field strengths and simple morphologies, including both idealized flux tubes and smooth layers of field. We confirm some of our analytical estimates using thin flux tube magnetohydrodynamic (MHD) simulations of the rise of buoyant fields in a fully-convective M-dwarf. Separately, we consider the Ohmic dissipation of such fields. We find that dissipation provides a complementary constraint to buoyancy: while small-scale, fibril fields might be regenerated faster than they rise, the dissipative heating associated with such fields would in some cases greatly exceed the luminosity of the star. We show how these constraints combine to yield limits on the internal field strength and morphology in low-mass stars. In particular, we find that for stars of 0.3 solar masses, no fields in flux tubes stronger than about 800 kG are simultaneously consistent with both constraints., Comment: 19 pages, 10 figures, accepted to ApJ
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- 2015
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87. Recognition, identification, and diagnosis announcement of neonatal arterial ischemic stroke: A combined exploratory quantitative and qualitative study on parents’ lived experiences
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Leal Martins, Cindy, Chabrier, Stéphane, and Fluss, Joel
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- 2021
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88. Additional validation study and French cross-cultural adaptation of the Pediatric Stroke Outcome Measure–Summary of Impressions (PSOM-SOI)
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Morard, Marie-Doriane, Dinomais, Mickael, Bull, Kim, Rippert, Pascal, Chevignard, Mathilde, deVeber, Gabrielle, Chabrier, Stéphane, and Vuillerot, Carole
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- 2021
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89. Accident vasculaire cérébral périnatal : nosographie, présentation clinique, pathogénie, facteurs de risque et génétique
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Chabrier, S., Kossorotoff, M., Chevin, M., and Fluss, J.
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- 2021
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90. Chronique judiciaire : le public féminin en procès
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Chabrier, Amélie, primary
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- 2022
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91. Enhanced Encodings for White-Box Designs
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Battistello, Alberto, primary, Castelnovi, Laurent, additional, and Chabrier, Thomas, additional
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- 2022
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92. A connectome‐based approach to assess motor outcome after neonatal arterial ischemic stroke
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Mariam Al Harrach, Pablo Pretzel, Samuel Groeschel, François Rousseau, Thijs Dhollander, Lucie Hertz‐Pannier, Julien Lefevre, Stéphane Chabrier, Mickael Dinomais, and the AVCnn study group
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box and block test ,cerebral palsy ,connectome ,diffusion weighted imaging ,MRI ,Neonatal arterial ischemic stroke ,Neurosciences. Biological psychiatry. Neuropsychiatry ,RC321-571 ,Neurology. Diseases of the nervous system ,RC346-429 - Abstract
Abstract Objective Studies of motor outcome after Neonatal Arterial Ischemic Stroke (NAIS) often rely on lesion mapping using MRI. However, clinical measurements indicate that motor deficit can be different than what would solely be anticipated by the lesion extent and location. Because this may be explained by the cortical disconnections between motor areas due to necrosis following the stroke, the investigation of the motor network can help in the understanding of visual inspection and outcome discrepancy. In this study, we propose to examine the structural connectivity between motor areas in NAIS patients compared to healthy controls in order to define the cortical and subcortical connections that can reflect the motor outcome. Methods Thirty healthy controls and 32 NAIS patients with and without Cerebral Palsy (CP) underwent MRI acquisition and manual assessment. The connectome of all participants was obtained from T1‐weighted and diffusion‐weighted imaging. Results Significant disconnections in the lesioned and contra‐lesioned hemispheres of patients were found. Furthermore, significant correlations were detected between the structural connectivity metric of specific motor areas and manuality assessed by the Box and Block Test (BBT) scores in patients. Interpretation Using the connectivity measures of these links, the BBT score can be estimated using a multiple linear regression model. In addition, the presence or not of CP can also be predicted using the KNN classification algorithm. According to our results, the structural connectome can be an asset in the estimation of gross manual dexterity and can help uncover structural changes between brain regions related to NAIS.
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- 2021
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93. Complete piano music
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Chabrier, Emmanuel, 1841-1894., Klien, Walter. Instrumentalist, Kyriakou, Rena, 1918-1994. Instrumentalist, Chabrier, Emmanuel, 1841-1894. Air de ballet., Chabrier, Emmanuel, 1841-1894. Bourrée fantasque., Chabrier, Emmanuel, 1841-1894. Capriccio, piano., Chabrier, Emmanuel, 1841-1894. Cortège burlesque., Chabrier, Emmanuel, 1841-1894. Habanera, piano,, Chabrier, Emmanuel, 1841-1894. Impromptu, piano,, Chabrier, Emmanuel, 1841-1894. Marche des Cipayes., Chabrier, Emmanuel, 1841-1894. Morceaux, piano., Chabrier, Emmanuel, 1841-1894. Pièces pittoresques., Chabrier, Emmanuel, 1841-1894. Souvenirs de Munich., Chabrier, Emmanuel, 1841-1894. Suite de valses., and Chabrier, Emmanuel, 1841-1894. Valses romantiques.
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- 1994
94. Genome-wide association analyses identify new susceptibility loci for oral cavity and pharyngeal cancer
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Lesseur, Corina, Diergaarde, Brenda, Olshan, Andrew F, Wünsch-Filho, Victor, Ness, Andrew R, Liu, Geoffrey, Lacko, Martin, Eluf-Neto, José, Franceschi, Silvia, Lagiou, Pagona, Macfarlane, Gary J, Richiardi, Lorenzo, Boccia, Stefania, Polesel, Jerry, Kjaerheim, Kristina, Zaridze, David, Johansson, Mattias, Menezes, Ana M, Curado, Maria Paula, Robinson, Max, Ahrens, Wolfgang, Canova, Cristina, Znaor, Ariana, Castellsagué, Xavier, Conway, David I, Holcátová, Ivana, Mates, Dana, Vilensky, Marta, Healy, Claire M, Szeszenia-Dąbrowska, Neonila, Fabiánová, Eleonóra, Lissowska, Jolanta, Grandis, Jennifer R, Weissler, Mark C, Tajara, Eloiza H, Nunes, Fabio D, de Carvalho, Marcos B, Thomas, Steve, Hung, Rayjean J, Peters, Wilbert HM, Herrero, Rolando, Cadoni, Gabriella, Bueno-de-Mesquita, H Bas, Steffen, Annika, Agudo, Antonio, Shangina, Oxana, Xiao, Xiangjun, Gaborieau, Valérie, Chabrier, Amélie, Anantharaman, Devasena, Boffetta, Paolo, Amos, Christopher I, McKay, James D, and Brennan, Paul
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Biological Sciences ,Genetics ,Cancer ,Clinical Research ,Dental/Oral and Craniofacial Disease ,Digestive Diseases ,Human Genome ,Aetiology ,2.1 Biological and endogenous factors ,Aged ,Case-Control Studies ,Female ,Genetic Markers ,Genetic Predisposition to Disease ,Genetic Variation ,Genome-Wide Association Study ,HLA Antigens ,Haplotypes ,Humans ,Male ,Middle Aged ,Mouth ,Mouth Neoplasms ,Papillomaviridae ,Papillomavirus Infections ,Pharyngeal Neoplasms ,Medical and Health Sciences ,Developmental Biology ,Agricultural biotechnology ,Bioinformatics and computational biology - Abstract
We conducted a genome-wide association study of oral cavity and pharyngeal cancer in 6,034 cases and 6,585 controls from Europe, North America and South America. We detected eight significantly associated loci (P < 5 × 10-8), seven of which are new for these cancer sites. Oral and pharyngeal cancers combined were associated with loci at 6p21.32 (rs3828805, HLA-DQB1), 10q26.13 (rs201982221, LHPP) and 11p15.4 (rs1453414, OR52N2-TRIM5). Oral cancer was associated with two new regions, 2p23.3 (rs6547741, GPN1) and 9q34.12 (rs928674, LAMC3), and with known cancer-related loci-9p21.3 (rs8181047, CDKN2B-AS1) and 5p15.33 (rs10462706, CLPTM1L). Oropharyngeal cancer associations were limited to the human leukocyte antigen (HLA) region, and classical HLA allele imputation showed a protective association with the class II haplotype HLA-DRB1*1301-HLA-DQA1*0103-HLA-DQB1*0603 (odds ratio (OR) = 0.59, P = 2.7 × 10-9). Stratified analyses on a subgroup of oropharyngeal cases with information available on human papillomavirus (HPV) status indicated that this association was considerably stronger in HPV-positive (OR = 0.23, P = 1.6 × 10-6) than in HPV-negative (OR = 0.75, P = 0.16) cancers.
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- 2016
95. Ambipolar diffusion in low-mass star formation. I. General comparison with the ideal MHD case
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Masson, Jacques, Chabrier, Gilles, Hennebelle, Patrick, Vaytet, Neil, and Commerçon, Benoit
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Astrophysics - Solar and Stellar Astrophysics - Abstract
In this paper, we provide a more accurate description of the evolution of the magnetic flux redistribution during prestellar core collapse by including resistive terms in the magnetohydrodynamics (MHD) equations. We focus more particularly on the impact of ambipolar diffusion. We use the adaptive mesh refinement code RAMSES to carry out such calculations. The resistivities required to calculate the ambipolar diffusion terms were computed using a reduced chemical network of charged, neutral and grain species. The inclusion of ambipolar diffusion leads to the formation of a magnetic diffusion barrier in the vicinity of the core, preventing accumulation of magnetic flux in and around the core and amplification of the field above 0.1G. The mass and radius of the first Larson core remain similar between ideal and non-ideal MHD models. This diffusion plateau has crucial consequences on magnetic braking processes, allowing the formation of disk structures. Magnetically supported outflows launched in ideal MHD models are weakened when using non-ideal MHD. Contrary to ideal MHD misalignment between the initial rotation axis and the magnetic field direction does not significantly affect the results for a given mu, showing that the physical dissipation truly dominate over numerical diffusion. We demonstrate severe limits of the ideal MHD formalism, which yield unphysical behaviours in the long-term evolution of the system. This includes counter rotation inside the outflow, interchange instabilities, and flux redistribution triggered by numerical diffusion, none observed in non-ideal MHD. Disks with Keplerian velocity profiles form in all our non-ideal MHD simulations, with final mass and size which depend on the initial magnetisation. This ranges from a few 0.01 solar masses and 20-30 au for the most magnetised case (mu=2) to 0.2 solar masses and 40-80 au for a lower magnetisation (mu=5)., Comment: Accepted in A&A section 7 (on Wednesday, september the 16th, year 2015)
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- 2015
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96. Early Results from VLT-SPHERE: Long-Slit Spectroscopy of 2MASS 0122-2439B, a Young Companion Near the Deuterium Burning Limit
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Hinkley, Sasha, Bowler, Brendan P., Vigan, Arthur, Aller, Kimberly M., Liu, Michael C., Mawet, Dimitri, Matthews, Elisabeth, Wahhaj, Zahed, Kraus, Stefan, Baraffe, Isabelle, and Chabrier, Gilles
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Astrophysics - Earth and Planetary Astrophysics - Abstract
We present 0.95-1.80 $\mu$m spectroscopy of the $\sim$12-27 $M_{\rm Jup}$ companion orbiting the faint ($R$$\sim$13.6), young ($\sim$120 Myr) M-dwarf 2MASS J01225093--2439505 ("2M0122--2439 B") at 1.5 arcsecond separation (50 AU). Our coronagraphic long-slit spectroscopy was obtained with the new high contrast imaging platform VLT-SPHERE during Science Verification. The unique long-slit capability of SPHERE enables spectral resolution an order of magnitude higher than other extreme AO exoplanet imaging instruments. With a low mass, cool temperature, and very red colors, 2M0122-2439 B occupies a particularly important region of the substellar color-magnitude diagram by bridging the warm directly imaged hot planets with late-M/early-L spectral types (e.g. $\beta$ Pic b and ROXs 42Bb) and the cooler, dusty objects near the L/T transition (e.g. HR 8799bcde and 2MASS 1207b). We fit BT-Settl atmospheric models to our $R$$\approx$350 spectrum and find $T_{\rm eff}$=1600$\pm$100 K and $\log(g)$=4.5$\pm$0.5 dex. Visual analysis of our 2M0122-2439 B spectrum suggests a spectral type L3-L4, and we resolve shallow $J$-band alkali lines, confirming its low gravity and youth. Specifically, we use the Allers & Liu (2013) spectral indices to quantitatively measure the strength of the FeH, VO, KI, spectral features, as well as the overall $H$-band shape. Using these indices, along with the visual spectral type analysis, we classify 2M0122-2439 B as an intermediate gravity (INT-G) object with spectral type L3.7$\pm$1.0., Comment: Accepted to ApJ Letters, 8 pages, 4 figures, some minor typographical issues were fixed
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- 2015
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97. Fingering convection and cloudless models for cool brown dwarf atmospheres
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Tremblin, P., Amundsen, D. S., Mourier, P., Baraffe, I., Chabrier, G., Drummond, B., Homeier, D., and Venot, O.
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Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Earth and Planetary Astrophysics - Abstract
This work aims to improve the current understanding of the atmospheres of brown dwarfs, especially cold ones with spectral type T and Y, whose modeling is a current challenge. Silicate and iron clouds are believed to disappear at the photosphere at the L/T transition, but cloudless models fail to reproduce correctly the spectra of T dwarfs, advocating for the addition of more physics, e.g. other types of clouds or internal energy transport mechanisms. We use a one-dimensional (1D) radiative/convective equilibrium code ATMO to investigate this issue. This code includes both equilibrium and out-of-equilibrium chemistry and solves consistently the PT structure. Included opacity sources are H2-H2, H2-He, H2O, CO, CO2, CH4, NH3, K, Na, and TiO, VO if they are present in the atmosphere. We show that the spectra of Y dwarfs can be accurately reproduced with a cloudless model if vertical mixing and NH3 quenching are taken into account. T dwarf spectra still have some reddening in e.g. J - H compared to cloudless models. This reddening can be reproduced by slightly reducing the temperature gradient in the atmosphere. We propose that this reduction of the stabilizing temperature gradient in these layers, leading to cooler structures, is due to the onset of fingering convection, triggered by the destabilizing impact of condensation of very thin dust., Comment: Accepted in ApJL
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- 2015
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98. New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
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Baraffe, I., Homeier, D., Allard, F., and Chabrier, G.
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Astrophysics - Solar and Stellar Astrophysics - Abstract
We present new models for low-mass stars down to the hydrogen-burning limit that consistently couple atmosphere and interior structures, thereby superseding the widely used BCAH98 models. The new models include updated molecular linelists and solar abundances, as well as atmospheric convection parameters calibrated on 2D/3D radiative hydrodynamics simulations. Comparison of these models with observations in various colour-magnitude diagrams for various ages shows significant improvement over previous generations of models. The new models can solve flaws that are present in the previous ones, such as the prediction of optical colours that are too blue compared to M dwarf observations. They can also reproduce the four components of the young quadruple system LkCa 3 in a colour-magnitude diagram with one single isochrone, in contrast to any presently existing model. In this paper we also highlight the need for consistency when comparing models and observations, with the necessity of using evolutionary models and colours based on the same atmospheric structures., Comment: 7 pages, 8 figures, Astronomy & Astrophysics in press
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- 2015
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99. The Mass-Dependence of Angular Momentum Evolution in Sun-Like Stars
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Matt, Sean P., Brun, A. Sacha, Baraffe, Isabelle, Bouvier, Jérôme, and Chabrier, Gilles
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Astrophysics - Solar and Stellar Astrophysics - Abstract
To better understand the observed distributions of rotation rate and magnetic activity of sun-like and low-mass stars, we derive a physically motivated scaling for the dependence of the stellar-wind torque on Rossby number. The torque also contains an empirically-derived scaling with stellar mass (and radius), which provides new insight into the mass-dependence of stellar magnetic and wind properties. We demonstrate that this new formulation explains why the lowest mass stars are observed to maintain rapid rotation for much longer than solar-mass stars, and simultaneously, why older populations exhibit a sequence of slowly rotating stars, in which the low-mass stars rotate more slowly than solar-mass stars. The model also reproduces some previously unexplained features in the period-mass diagram for the Kepler field, notably: the particular shape of the "upper envelope" of the distribution, suggesting that ~95% of Kepler field stars with measured rotation periods are younger than ~4 Gyr; and the shape of the "lower envelope," corresponding to the location where stars transition between magnetically saturated and unsaturated regimes., Comment: Accepted for publication in Astrophysical Journal Letters; 6 pages, 3 figures
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- 2014
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100. Justice
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Chabrier, Amélie, primary
- Published
- 2021
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