72 research outputs found
Fiber tracking in q-ball fields using regularized particle trajectories
No full textMost of the approaches dedicated to fiber tracking from diffusion-weighted MR data rely on a tensor model. However, the tensor model can only resolve a single fiber orientation within each imaging voxel. New emerging approaches have been proposed to obtain a better representation of the diffusion process occurring in fiber crossing. In this paper, we adapt a tracking algorithm to the q-ball representation, which results from a spherical Radon transform of high angular resolution data. This algorithm is based on a Monte-Carlo strategy, using regularized particle trajectories to sample the white matter geometry. The method is validated using a phantom of bundle crossing made up of haemodialysis fibers. The method is also applied to the detection of the auditory tract in three human subjects
Joined segmentation of cortical surface and brain volume in MRI using a homotopic deformable cellular model
No full text
Bilan de l'évolution des sols sous culture intensive dans une station expérimentale en milieu tropical humide
No full textA Grimari (RCA ), station agricole située sous un climat tropical humide (Soudano guinéen) et cultivée depuis 45 ans, on a comparé les caractéristiques pédologiques d'un certain nombre de profils cultivés avec des profils voisins restés en végétation naturelle. On constate une baisse très sensible (30%) de la macroporosité et une diminution de la stabilité structurale. La matière organique a évolué en quantité et en composition. Il y a diminution des composés les plus polymérisés au profit des composés à petite molécule. Le calcium et le magnésium échangeables qui, précisèment, sont surtout liés aux acides humiques gris et à l'humine suivent la même évolution (perte de 40%). Le pH a également baissé de 0,7 unité. Cependant, d'après les documents disponibles, cette évolution a dû se dérouler principalement au cours des premières années; elle se poursuit actuellement au ralenti. La fertilité du sol reste moyenne et ses variations semblent plutot liées aux facteurs physiques eux-mêmes en grande partie dépendant de la qualité de l'humus. (RESUME D'AUTEUR
Bilan de l'évolution des sols sous culture intensive dans une station expérimentale en milieu tropical humide
No full textA Grimari (RCA ), station agricole située sous un climat tropical humide (Soudano guinéen) et cultivée depuis 45 ans, on a comparé les caractéristiques pédologiques d'un certain nombre de profils cultivés avec des profils voisins restés en végétation naturelle. On constate une baisse très sensible (30%) de la macroporosité et une diminution de la stabilité structurale. La matière organique a évolué en quantité et en composition. Il y a diminution des composés les plus polymérisés au profit des composés à petite molécule. Le calcium et le magnésium échangeables qui, précisèment, sont surtout liés aux acides humiques gris et à l'humine suivent la même évolution (perte de 40%). Le pH a également baissé de 0,7 unité. Cependant, d'après les documents disponibles, cette évolution a dû se dérouler principalement au cours des premières années; elle se poursuit actuellement au ralenti. La fertilité du sol reste moyenne et ses variations semblent plutot liées aux facteurs physiques eux-mêmes en grande partie dépendant de la qualité de l'humus. (RESUME D'AUTEUR
TOI 762 A b and TIC 46432937 b: Two Giant Planets Transiting M-dwarf Stars
No full textHartman, Joel D. et al.--Full list of authors: Hartman, Joel D.; Bayliss, Daniel; Brahm, Rafael; Bryant, Edward M.; Jordán, Andrés; Bakos, Gáspár Á.; Hobson, Melissa J.; Sedaghati, Elyar; Bonfils, Xavier; Cointepas, Marion; Almenara, Jose Manuel; Barkaoui, Khalid; Timmermans, Mathilde; Dransfield, George; Ducrot, Elsa; Zúñiga-Fernández, Sebastián; Hooton, Matthew J.; Pedersen, Peter Pihlmann; Pozuelos, Francisco J.; Triaud, Amaury H. M. J.; Gillon, Michaël; Jehin, Emmanuel; Waalkes, William C.; Berta-Thompson, Zachory K.; Howell, Steve B.; Furlan, Elise; Ricker, George R.; Vanderspek, Roland; Seager, Sara; Winn, Joshua N.; Jenkins, Jon M.; Rapetti, David; Collins, Karen A.; Charbonneau, David; Burke, Christopher J.; Rodriguez, David R.We present the discovery of TOI 762 A b and TIC 46432937 b, two giant planets transiting M-dwarf stars. Transits of both systems were first detected from observations by the NASA TESS mission, and the transiting objects are confirmed as planets through high-precision radial velocity observations carried out with Very Large Telescope/ESPRESSO. TOI 762 A b is a warm sub-Saturn with a mass of 0.251 ± 0.042 MJ, a radius of 0.744 ± 0.017 RJ, and an orbital period of 3.4717 days. It transits a mid-M-dwarf star with a mass of 0.442 ± 0.025 M☉ and a radius of 0.4250 ± 0.0091 R☉. The star TOI 762 A has a resolved binary star companion, TOI 762 B, that is separated from TOI 762 A by 3farcs2 (∼319 au) and has an estimated mass of 0.227 ± 0.010 M☉. The planet TIC 46432937 b is a warm super-Jupiter with a mass of 3.20 ± 0.11 MJ and radius of 1.188 ± 0.030 RJ. The planet's orbital period is P = 1.4404 days, and it undergoes grazing transits of its early M-dwarf host star, which has a mass of 0.563 ± 0.029 M☉ and a radius of 0.5299 ± 0.0091 R☉. TIC 46432937 b is one of the highest-mass planets found to date transiting an M-dwarf star. TIC 46432937 b is also a promising target for atmospheric observations, having the highest transmission spectroscopy metric or emission spectroscopy metric value of any known warm super-Jupiter (mass greater than 3.0 MJ, equilibrium temperature below 1000 K). © 2024. The Author(s). Published by the American Astronomical Society.We thank the anonymous referee for their careful reading this paper, and helpful comments that have improved the quality of the work. J.H. and G.B. acknowledge funding from NASA grant No. 80NSSC22K0315. A.J. and R.B. acknowledge support from ANID—Millennium Science Initiative—ICN12_009. R.B. acknowledges support from FONDECYT Project 11200751. A.J. acknowledges support from FONDECYT project 1210718. We acknowledge funding from the European Research Council under the ERC Grant Agreement No. 337591-ExTrA. This research has made use of the Exoplanet Follow-up Observation Program (ExoFOP; DOI:10.26134/ExoFOP5) website, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. This paper made use of data collected by the TESS mission and which are publicly available from the Mikulski Archive for Space Telescopes (MAST) operated by the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by NASA's Science Mission Directorate. The specific observations from MAST analyzed in this paper can be accessed from DOI:10.17909/e3cp-9907. We acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. The contributions at the Mullard Space Science Laboratory by EMB have been supported by STFC through the consolidated grant ST/W001136/1. The postdoctoral fellowship of K.B. is funded by F.R.S.-FNRS grant T.0109.20 and by the Francqui Foundation. This publication benefits from the support of the French Community of Belgium in the context of the FRIA Doctoral Grant awarded to M.T. M.G. is F.R.S.-FNRS Research Director and E.J. is F.R.S.-FNRS Senior Research Associate. F.J.P. acknowledges financial support from the grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033 and through projects PID2019-109522GB-C52 and PID2022-137241NB-C43. Based on data collected by the SPECULOOS-South Observatory at the ESO Paranal Observatory in Chile. The ULiege's contribution to SPECULOOS has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013; grant Agreement No. 336480/SPECULOOS), from the Balzan Prize and Francqui Foundations, from the Belgian Scientific Research Foundation (F.R.S.-FNRS; grant No. T.0109.20), from the University of Liege, and from the ARC grant for Concerted Research Actions financed by the Wallonia-Brussels Federation. This work is supported by a grant from the Simons Foundation (PI: Queloz; grant No. 327127). Based on data collected by the TRAPPIST-South telescope at the ESO La Silla Observatory. TRAPPIST is funded by the Belgian Fund for Scientific Research (Fond National de la Recherche Scientifique, FNRS) under the grant No. PDR T.0120.21, with the participation of the Swiss National Science Fundation (SNF). D.R. was supported by NASA under award number NNA16BD14C for NASA Academic Mission Services.With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001131-S).Peer reviewe
Bihan. Assessment of the early organization and maturation of infants’ cerebral white matter fiber bundles: a feasibility study using quantitative diffusion tensor imaging and tractography
No full textThe human infant is particularly immature at birth and brain maturation, with the myelination of white matter fibers, is protracted until adulthood. Diffusion tensor imaging offers the possibility to describe non invasively the fascicles spatial organization at an early stage and to follow the cerebral maturation with quantitative parameters that might be correlated with behavioral development. Here, we assessed the feasibility to study the organization and maturation of major white matter bundles in eighteen 1-to 4-monthold healthy infants, using a specific acquisition protocol customized to the immature brain (with 15 orientations of the diffusion gradients and a 700 s mm À2 b factor). We were able to track most of the main fascicles described at later ages despite the low anisotropy of the infant white matter, using the FACT algorithm. This mapping allows us to propose a new method of quantification based on reconstructed tracts, split between specific regions, which should be more sensitive to specific changes in a bundle than the conventional approach, based on regionsof-interest. We observed variations in fractional anisotropy and mean diffusivity over the considered developmental period in most bundles (corpus callosum, cerebellar peduncles, cortico-spinal tract, spinothalamic tract, capsules, radiations, longitudinal and uncinate fascicles, cingulum). The results are in good agreement with the known stages of white matter maturation and myelination, and the proposed approach might provide important insights on brain development.
- …
