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Search Results: 1 - 10 of 189868 matches for " G. Chauvin "
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Comportamiento diastólico durante la fase de "hipercontracción" post- isquémica en el miocardio atontado de conejo
G. E. Gonzalez,F. Mangas,A. Depetris Chauvin,S. Monroy
Medicina (Buenos Aires) , 2003,
Abstract: El objetivo del estudio fue determinar si la fase de "hipercontracción" (HC) que ocurre al comienzo de la reperfusión (R) en el miocardio atontado, presenta alteraciones diastólicas, y si la R con bajo Ca2+ modifica las mismas. Corazones aislados e isovolúmicos de conejos fueron divididos en 2 grupos. El grupo 1 (G1, n=11) fue perfundido con Ringer ([Ca2+]=2mM) y sujeto a 15 min de isquemia y 30 de R. El grupo 2 (G2, n=10) se reperfundió 10 min con Ringer ([Ca2+]=1mM) que fue incrementado a 1.5 y 2 mM a los 30 min de R. Se evaluó: la contractilidad miocárdica (+dP/dtmáx), la rigidez diastólica (presión diastólica final (PDFVI)) y la relajación (t1/2 y cociente +P/-P). Al minuto de R la contractilidad se recuperó en G1 (76.88±5.37% vs valor preisquémico) y fue atenuada en G2 (48.22±3.40% vs. valor preisquémico; P<0.05 vs G1). La PDFVI en G1 se incrementó desde el inicio de la R, aunque se correlacionó negativamente con el grado de HC (r= - 0.7477; p=0.008), o sea a mayor HC menor PDFVI. La R con bajo Ca2+ atenuó el aumento de PDFVI (P<0.05 vs G1) al minuto y a los 30 min. La relajación se enlenteció en forma continua hasta los 2 min en ambos grupos, (G1 vs G2, NS). En conclusión: La fase de HC se acompa a de alteraciones diastólicas. El grado de HC está en relación inversa con la PDFVI. Durante la R la rigidez continuó aumentando, mientras que la relajación se normalizó. La perfusión con bajo Ca2+ atenuó la HC y mejoró las alteraciones diastólicas solamente en lo referente a la rigidez. The objective was to determine whether "hypercontraction" (HC) that occurs at the beginning of reperfusion (R) in stunned myocardium is accompanied by diastolic alterations and determine if the R with low Ca2+ Ringer's solution modifies these alterations. Isolated isovolumic rabbit hearts were divided into 2 groups. Group 1 (G1, n=11) was perfused with Ringer's solution ([Ca2+]=2mM) and subjected to 15min of global ischemia and 30min of R. Group 2 (G2, n=10) was R during the first 10 min with ([Ca2+ ]=1mM), which was increased to 1.5 mM and 2 mM in the perfusate at 30 min of R. The left ventricular +dP/dtmáx, left ventricular end diastolic pressure (LVEDP) (stiffness index), and relaxation rate (t1/2 and +P/-P ratio) were measured, from the beginning of R every 10sec for 2min, and then at 5 and 30min. At 60 sec of R the +dP/dtmáx in G1 was increased (76,88±5,37% vs preischemic value) and was attenuated in G2 (48,22±3,40%; P<0.05 vs G1). The LVEDP in G1 was increased early in the R, although it was negatively correlated with HC degree (r=-0.7477; p=0.008). This increase wa
Aspects chimiques du procédé DIMERSOL de dimérisation des oléfines The Dimersol Process for Dimerization of Olefins
Commereuc D.,Chauvin Y.,Leger G.,Gaillard J.
Oil & Gas Science and Technology , 2006, DOI: 10.2516/ogst:1982030
Abstract: Quelques aspects chimiques du procédé DIMERSOL, de dimérisation des oléfines sont passés en revue. Après une introduction rappelant les divers types de catalyse de la réaction de dimérisation, les points suivants sont discutés : mécanisme de la réaction par les complexes du nickel, nature du catalyseur au nickel, cinétique de la réaction, interprétation chimique de l'effet des impuretés. The chemical aspects of the DIMERSOL Process for the dimerization of olefins are reviewed. After an introduction dealing with the various types of catalysis in the dimerization reaction, the following points are discussed: the mechanism of dimerization by nickel complexes, the nature of the nickel catalysts, the kinetics of the reaction, and a chemical interpretation of the effect of contaminants.
Near-IR coronagraphic imaging of the companion to HR 7672
A. Boccaletti,G. Chauvin,A. -M. Lagrange,F. Marchis
Physics , 2003, DOI: 10.1051/0004-6361:20031216
Abstract: This article presents coronagraphic images of the low-mass companion to the star HR 7672 observed at the Palomar 200 inch telescope and first detected at Gemini and Keck in the K band by \citet{liu02}. We obtained additional photometry in $J$($1.2\mu m$), $H$($1.6\mu m$) and $K_s$ ($2.2\mu m$) bands to cover the full near-IR domain and hence to further constrain the nature of the companion. A mass estimate of 58-71$ \mathrm{M_J}$ is derived from evolutionary models of very low-mass objects.
Planetary systems in close binary stars: the case of HD196885
G. Chauvin,H. Beust,A. -M. Lagrange,A. Eggenberger
Physics , 2010,
Abstract: Planets can form and survive in close binaries, although dynamical interactions with the secondary component can actually significantly impact the giant planet formation and evolution. Rare close binaries hosting giant planets offer therefore an ideal laboratory to explore the properties and the stability of such extreme planetary systems. In the course of our CFHT and VLT coronographic imaging survey dedicated to the search for faint companions of exoplanet host stars, a close (about 20 AU) secondary stellar companion to the exoplanet host HD196885 A was discovered. For more than 4 years, we have used the NaCo near-infrared adaptive optics instrument to monitor the astrometric position of HD196885 B relative to A. The system was observed at five different epochs from August 2005 to August 2009 and accurate relative positions were determined. Our observations fully reject the stationary background hypothesis for HD196885 B. The two components are found to be comoving. The orbital motion of HD196885 B is well resolved and the orbital curvature is even detected. From our imaging data combined with published radial velocity measurements, we refine the complete orbital parameters of the stellar component. We derive for the first time its orbital inclination and its accurate mass. We find also solutions for the inner giant planet HD196885 Ab compatible with previous independent radial velocity studies. Finally, we investigate the stability of the inner giant planet HD196885 Ab due to the binary companion proximity. Our dynamical simulations show that the system is currently and surprisingly more stable in a high mutual inclination configuration that falls in the Kozai resonance regime. If confirmed, this system would constitute one of the most compact non-coplanar systems known so far. It would raise several questions about its formation and stability
The evolution of the use of lithic supports in the Late Glacial sequence of the El Rasca o cave (Mirones-Cantabria)
Chauvin, Adriana
Trabajos de Prehistoria , 2007,
Abstract: The aim of this paper is to evaluate the nature of lithic production and the selection of lithic supports for retouching during the Late Glacial sequence of El Rasca o Cave. Some metric and technological attributes were selected in order to evaluate the prehistoric production aims and the technological changes which probably took place during the sequence La finalidad del presente trabajo es evaluar la producción y selección para el retoque de los soportes líticos a lo largo de la secuencia Tardiglaciar de la cueva de El Rasca o. Para el análisis, se seleccionó una muestra a la que se aplicó una serie de criterios tipométricos y de análisis tecnológico. Con estos elementos se evaluó cuál era el objetivo de la producción en cada nivel y cuál fue su variación en el tiempo.
Space-Charge Effect
N. Chauvin
Physics , 2014, DOI: 10.5170/CERN-2013-007.63
Abstract: First, this chapter introduces the expressions for the electric and magnetic space-charge internal fields and forces induced by high-intensity beams. Then, the root-mean-square equation with space charge is derived and discussed. In the third section, the one-dimensional Child-Langmuir law, which gives the maximum current density that can be extracted from an ion source, is exposed. Space-charge compensation can occur in the low-energy beam transport lines (located after the ion source). This phenomenon, which counteracts the spacecharge defocusing effect, is explained and its main parameters are presented. The fifth section presents an overview of the principal methods to perform beam dynamics numerical simulations. An example of a particles-in-cells code, SolMaxP, which takes into account space-charge compensation, is given. Finally, beam dynamics simulation results obtained with this code in the case of the IFMIF injector are presented.
Probing the Impact of Stellar Duplicity on Planet Occurrence
A. Eggenberger,S. Udry,G. Chauvin,J. -L. Beuzit,A. -M. Lagrange,M. Mayor
Physics , 2009,
Abstract: The presence of a stellar companion closer than ~100 AU is likely to affect planet formation and evolution. Yet, the precise effects and their actual impact on planet occurrence are still debated. To bring observational constraints, we have conducted with VLT/NACO a systematic adaptive optics survey for close stellar companions to 130 solar-type stars with and without planets. In this paper we present observational and preliminary statistical results from this survey. Observational results reveal about 20 true companions, of which 4 are new companions to planet-host stars. As to preliminary statistical results, they suggest that circumstellar giant planets are less frequent in binaries closer than ~100 AU than around single stars, in possible agreement with the theoretical studies that predict a negative impact of stellar duplicity on giant planet formation in binaries closer than ~100 AU. These statistical results will need confirmation, however, as they are severely limited by small sample sizes.
Kinematic analysis and membership status of TWA22ABR
R. Teixeira,C. Ducourant,G. Chauvin,A. Krone-Martins,M. Bonnefoy,I. Song
Physics , 2009, DOI: 10.1051/0004-6361/200912173
Abstract: TWA22 was initially regarded as a member of the TW Hydrae association (TWA). In addition to being one of the youngest (~8Myr) and nearest (~20pc) stars to Earth, TWA22 has proven to be very interesting after being resolved as a tight, very low-mass binary. This binary can serve as a very useful dynamical calibrator for pre-main sequence evolutionary models. However, its membership in the TWA has been recently questioned despite due to the lack of accurate kinematic measurements. Based on proper motion, radial velocity, and trigonometric parallax measurements, we aim here to re-analyze the membership of TWA22 to young, nearby associations. Using the ESO NTT/SUSI2 telescope, we observed TWA22AB during 5 different observing runs over 1.2 years to measure its trigonometric parallax and proper motion. This is a part of a larger project measuring trigonometric parallaxes and proper motions of most known TWA members at a sub-milliarcsec level. HARPS at the ESO 3.6m telescope was also used to measure the system's radial velocity over 2 years. We report an absolute trigonometric parallax of TWA22AB, 57.0mas, corresponding to a distance 17.5pc from Earth. Measured proper motions of TWA22AB are -175.8mas/yr in right ascension and -21.3mas/yr in declination. Finally, from HARPS measurements, we obtain a radial velocity 14.8km/s.
OTS44: Disk and accretion at the planetary border
V. Joergens,M. Bonnefoy,Y. Liu,A. Bayo,S. Wolf,G. Chauvin,P. Rojo
Physics , 2013, DOI: 10.1051/0004-6361/201322432
Abstract: We discover that the very low-mass brown dwarf OTS44 (M9.5, ~12 M_Jup) has significant accretion and a substantial disk, which demonstrates that the processes that accompany canonical star formation occur down to a central mass of a few Jupiter masses. We discover in VLT/SINFONI spectra that OTS44 has strong, broad, and variable Paschen beta emission that is evidence for active accretion at the planetary border. We also detect strong Halpha emission of OTS44 in a literature spectrum and determine an Halpha EW (-141 A) that is indicative of active accretion. Both the Pa beta and Halpha emission lines have broad profiles with wings extending to velocities of about +/-200 km/s. We determine the mass accretion rate of OTS44 based on Halpha to 7.6x10^{-12} Msun/yr, which shows that OTS44 has a relatively high mass-accretion rate considering its small central mass. This mass rate is nevertheless consistent with the general decreasing trend found for stars of several solar masses down to brown dwarfs. Furthermore, we determine the properties of the disk surrounding OTS44 through radiative transfer modeling of flux measurement from the optical to the far-IR (Herschel) by applying a Bayesian analysis. We find that OTS44 has a highly flared disk (beta >1.2) with a mass of 9.1x10^{-5} M_Sun, i.e. about 0.1 M_Jup or 30 M_Earth. We show that the ratio of disk-to-central-mass of about 10^{-2} found for objects between 0.03 Msun and 14 Msun is also valid for OTS44 at a mass of ~0.01 M_Sun. Our observations are in line with an isolated star-like mode of the formation of brown dwarfs down to 0.01 M_Sun.
A companion candidate in the gap of the T Cha transitional disk
N. Huelamo,S. Lacour,P. Tuthill,M. Ireland,A. Kraus,G. Chauvin
Physics , 2011, DOI: 10.1051/0004-6361/201016395
Abstract: T Cha is a young star surrounded by a cold disk. The presence of a gap within its disk, inferred from fitting to the spectral energy distribution, has suggested on-going planetary formation. We observed T Cha in L' and K_s with NAOS-CONICA, the adaptive optics system at the VLT, using sparse aperture masking. We detected a source in the L' data at a separation of 62+-7 mas, position angle of 78+-1 degrees, and a contrast of delta L' = 5.1+-0.2 mag. The object is not detected in the Ks band data, which show a 3-sigma contrast limit of 5.2 mag at the position of the detected L' source. For a distance of 108 pc, the detected companion candidate is located at 6.7 AU from the primary, well within the disk gap. If T Cha and the companion candidate are bound, the comparison of the L' and Ks photometry with evolutionary tracks shows that the photometry is inconsistent with any unextincted photosphere at the age and distance of T Cha. The detected object shows a very red Ks-L' color for which a possible explanation would be a significant amount of dust around it. This would imply that the companion candidate is young, which would strengthen the case for a physical companion, and moreover that the object would be in the substellar regime, according to the Ks upper limit. Another exciting possibility would be that this companion is a recently formed planet within the disk. Additional observations are mandatory to confirm that the object is bound and to properly characterize it.
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