A circumbinary disc model for the variability of the eclipsing binary CoRoT 223992193

We calculate the flux received from a binary system obscured by a circumbinary disc. The disc is modelled using two dimensional hydrodynamical simulations, and the vertical structure is derived by assuming it is isothermal. The gravitational torque from the binary creates a cavity in the disc's inner parts. If the line of sight along which the system is observed has a high inclination $I$, it intersects the disc and some absorption is produced. As the system is not axisymmetric, the resulting light curve displays variability. We calculate the absorption and produce light curves for different values of the dust disc aspect ratio $H/r$ and mass of dust in the cavity $M_{\rm dust}$. This model is applied to the high inclination ($I=85^{\circ}$) eclipsing binary CoRoT 223992193, which shows 5-10% residual photometric variability after the eclipses and a spot model are subtracted. We find that such variations for $I \sim 85^{\circ}$ can be obtained for $H/r=10^{-3}$ and $M_{\rm dust} \ge 10^{-12}$ M$_{\odot}$. For higher $H/r$, $M_{\rm dust}$ would have to be close to this lower value and $I$ somewhat less than $85^{\circ}$. Our results show that such variability in a system where the stars are at least 90% visible at all phases can be obtained only if absorption is produced by dust located inside the cavity. If absorption is dominated by the parts of the disc located close to or beyond the edge of the cavity, the stars are significantly obscured.Comment: 17 pages, 6 figures, accepted for publication in MNRA

La question de la réduction d’incertitude chez F. Knight

Cet article porte sur la réduction d’incertitude chez F. Knight, question centrale chez cet auteur et que nous analysons ici en détail. L’implication la plus intéressante, du point de vue de la théorie de la firme, est la proposition selon laquelle l’organisation est réductrice d’incertitude.This paper is about reducing uncertainty in F. Knight's work where the proposal according to which organization is an uncertainty reducer seems to be central

Breast-feeding in Geneva: Prevalence, duration and determinants

Summary: A telephone survey was carried out with the objective of measuring the prevalence, duration and determinants of breast-feeding in the canton of Geneva, between August and December 1993. The participants were 278 out of 320 families with a telephone number in Geneva, from a random sample of families in which a child had been born in Geneva in the preceding 15 months. Prevalence of breast-feeding at 1 day of life was 93.3%, at 3 months 62.5%, at 4 months 51.1%, at 6 months 28.1%; median duration was 4.2 months. For complete (exclusive or predominant) breast-feeding, results were: 1 day 87.3%, 3 months 37.5%, 4 months 19.4%, 6 months 3.8%; median duration 2.4 months. Initial prevalence of breast-feeding was significantly higher in girls (97.2%) than in boys (89.4%, p<0.01). Duration of breast-feeding was shorter in children of women who smoked (p<0.001). Relative risks for no breast-feeding at 4 months were 1.53 (95% confidence limits 1.20-1.96) for less than 15 cigarettes per day during pregnancy, and 3.65 (2.19-6.09) for 15 cigarettes or more. Duration of breast-feeding was shorter if the mother worked as an employee. Prevalence and duration were higher if the mother was originally from Africa, Asia, Middle-East or Latin American countries. Although the initial prevalence of breast-feeding was relatively high, only half of children were breast-fed at 4 months. Promotive efforts are needed to increase the duration of breast-feeding, in particular by legislation on maternal protection. Further studies are required to clarify gender differences in breast-feedin

La question de la réduction d’incertitude chez F. Knight

This paper is about reducing uncertainty in F. Knight's work where the proposal according to which organization is an uncertainty reducer seems to be central. Cet article porte sur la réduction d’incertitude chez F. Knight, question centrale chez cet auteur et que nous analysons ici en détail. L’implication la plus intéressante, du point de vue de la théorie de la firme, est la proposition selon laquelle l’organisation est réductrice d’incertitude.

High-pressure annealing of a prestructured nanocrystalline precursor to obtain tetragonal and orthorhombic polymorphs of Hf3N4

Transition metal nitrides containing metal ions in high oxidation states are a significant goal for the discovery of new families of semiconducting materials. Most metal nitride compounds prepared at high temperature and high pressure from the elements have metallic bonding. However amorphous or nanocrystalline compounds can be prepared via metal-organic chemistry routes giving rise to precursors with a high nitrogen:metal ratio. Using X-ray diffraction in parallel with high pressure laser heating in the diamond anvil cell this work highlights the possibility of retaining the composition and structure of a metastable nanocrystalline precursor under high pressure-temperature conditions. Specifically, a nanocrystalline Hf3N4 with a tetragonal defect-fluorite structure can be crystallized under high-P,T conditions. Increasing the pressure and temperature of crystallization leads to the formation of a fully recoverable orthorhombic (defect cottunite-structured) polymorph. This approach identifies a novel class of pathways to the synthesis of new crystalline nitrogen-rich transition metal nitrides

Spin alignment of stars in old open clusters

Stellar clusters form by gravitational collapse of turbulent molecular clouds, with up to several thousand stars per cluster. They are thought to be the birthplace of most stars and therefore play an important role in our understanding of star formation, a fundamental problem in astrophysics. The initial conditions of the molecular cloud establish its dynamical history until the stellar cluster is born. However, the evolution of the cloud's angular momentum during cluster formation is not well understood. Current observations have suggested that turbulence scrambles the angular momentum of the cluster-forming cloud, preventing spin alignment amongst stars within a cluster. Here we use asteroseismology to measure the inclination angles of spin axes in 48 stars from the two old open clusters NGC~6791 and NGC~6819. The stars within each cluster show strong alignment. Three-dimensional hydrodynamical simulations of proto-cluster formation show that at least 50 % of the initial proto-cluster kinetic energy has to be rotational in order to obtain strong stellar-spin alignment within a cluster. Our result indicates that the global angular momentum of the cluster-forming clouds was efficiently transferred to each star and that its imprint has survived after several gigayears since the clusters formed.Comment: 14 pages, 3 figures, 1 table. Published in Nature Astronom

Division-Free Binary-to-Decimal Conversion

International audienceThis article presents algorithms that convert multiple precision integer or floating-point numbers from radix $2$ to radix $10$ (or to any radix $b > 2$). Those algorithms, based on the ''scaled remainder tree'' technique, use multiplications instead of divisions in their critical part. Both quadratic and subquadratic algorithms are detailed, with proofs of correctness. Experimental results show that our implementation of those algorithms outperforms the GMP library by up to 50\%

Services à la personne : renforcer l’encadrement intermédiaire pour accroítre l’efficacité et l’attractivité des métiers

L'étude éclaire le partage de l'encadrement de l'aide à domicile, entre les responsables de secteur d’une part et les assistants techniques d’autre part. La question de la lisibilité des compétences des uns et des autres est au cœur de cet article. La création d’une certification professionnelle ciblée contribuerait à objectiver et à valoriser les fonctions des encadrants pour résoudre les questions de professionnalisation et d'attractivité de ce secteur professionnel.The study examines the management of home care work, between sector managers on the one hand and technical assistants on the other. Clear understanding of the skill sets of either group is central to the article. The creation of a targeted vocational qualification scheme would help develop professional pathways for managers in order to resolve the issues of professionalisation within this sector.In der Untersuchung wird das Management von Haushaltshilfen beleuchtet, das von den Branchenverantwortlichen und technischen Assistenten gemeinsam getragen wird. Kern des Artikels ist die Transparenz der Kompetenzen der verschiedenen Beteiligten. Die Schaffung einer gezielten beruflichen Zertifizierung könnte dazu beitragen, die Professionalisierungslaufbahnen der Führungskräfte auszubauen, um Probleme der Professionalisierung und Attraktivität dieser Berufsbranche zu lösen.   El estudio ilustra el reparto del encuadre de la ayuda a domicilio entre los responsables de sector, por una parte, y los asistentes técnicos por otra. La cuestión de la legibilidad de las competencias de unos y otros está en el corazón de este artículo. La creación de una certificación profesional precisa contribuiría a construir los itinerarios de profesionalización de los encuadrantes para resolver las cuestiones de profesionalización y de atractivo de este sector profesional

Crossing the Brown Dwarf Desert Using Adaptive Optics: A Very Close L-Dwarf Companion to the Nearby Solar Analog HR 7672

We have found a very faint companion to the active solar analog HR 7672 (HD 190406; GJ 779; 15 Sge). Three epochs of high resolution imaging using adaptive optics (AO) at the Gemini-North and Keck II Telescopes demonstrate that HR 7672B is a common proper motion companion, with a separation of 0.79" (14 AU) and a 2.16 um flux ratio of 8.6 mags. Using follow-up K-band spectroscopy from Keck AO+NIRSPEC, we measure a spectral type of L4.5+/-1.5. This is the closest ultracool companion around a main sequence star found to date by direct imaging. We estimate the primary has an age of 1-3 Gyr. Assuming coevality, the companion is most likely substellar, with a mass of 55-78 Mjup based on theoretical models. The primary star shows a long-term radial velocity trend, and we combine the radial velocity data and AO imaging to set a firm (model-independent) lower limit of 48 Mjup. In contrast to the paucity of brown dwarf companions at <~4 AU around FGK dwarfs, HR 7672B implies that brown dwarf companions do exist at separations comparable to those of the giant planets in our own solar system. Its presence is at variance with scenarios where brown dwarfs form as ejected stellar embryos. Moreover, since HR 7672B is likely too massive to have formed in a circumstellar disk as planets are believed to, its discovery suggests that a diversity of physical processes act to populate the outer regions of exoplanetary systems.Comment: Astrophysical Journal, in pres

Synthesis of Tetragonal and Orthorhombic Polymorphs of Hf3N4 by High-Pressure Annealing of a Prestructured Nanocrystalline Precursor

Hf3N4 in nanocrystalline form is produced by solution phase reaction of Hf(NEtMe)4 with ammonia followed by low-temperature pyrolysis in ammonia. Understanding of phase behavior in these systems is important because early transition-metal nitrides with the metal in maximum oxidation state are potential visible light photocatalysts. A combination of synchrotron powder X-ray diffraction and pair distribution function studies has been used to show this phase to have a tetragonally distorted fluorite structure with 1/3 vacancies on the anion sites. Laser heating nanocrystalline Hf3N4 at 12 GPa and 1500 K in a diamond anvil cell results in its crystallization with the same structure type, an interesting example of prestructuring of the phase during preparation of the precursor compound. This metastable pathway could provide a route to other new polymorphs of metal nitrides and to nitrogen-rich phases where they do not currently exist. Importantly it leads to bulk formation of the material rather than surface conversion as often occurs in elemental combination reactions at high pressure. Laser heating at 2000 K at a higher pressure of 19 GPa results in a further new polymorph of Hf3N4 that adopts an anion deficient cottunite-type (orthorhombic) structure. The orthorhombic Hf3N4 phase is recoverable to ambient pressure and the tetragonal phase is at least partially recoverable