395 research outputs found
Epidemiological survey for bivalve molluscs diseases in France
No full textRE: 4 ref.; SC: 0I; ZA; VE; CASource type: Electronic(1) http://upei-resolver.asin-risa.ca?sid=SP:CABI&id=pmid:&id=&issn=0754-2186&isbn=&volume=&issue=%2031%2f32&spage=14&pages=14&date=1997&title=Epidemiologie%20et%20Sante%20Animale&atitle=Epidemiological%20survey%20for%20bivalve%20molluscs%20diseases%20in%20France.&aulast=Thebault&pid=%3Cauthor%3EThebault%2c%20A%3bBerthe%2c%20F%3bRenault%2c%20T%3C%2Fauthor%3E%3CAN%3E19982203423%3C%2FAN%3E%3CDT%3EJournal%20article%3C%2FDT%3
REFLECTIONS ON A PROBLEM OF THEBAULT,V.
No full textThis paper is concerned with an elementary problem of V. Thebault which has remained unsolved until recently. We offer a natural solution of the problem and relate it to the classical notable configurations of the triangle
Gira efectuada en el Noroeste Argentino - Diablillos, Inca Viejo, Sierra de Calalaste, Pirquitas
No full textFil: Thebault, J. Y. Ministerio de Industria y Minería. Servicio Nacional Geológico Minero; Argentina.Fil: Pasquín, L. C. Banco Nacional de Desarrollo (BANADE). Poder Ejecutivo Nacional; Argentina.Fil: Guillou, Jorge A. Plan NOA-1; Argentina.El presente informes cuenta con un plano sobre la "Geología y alteración. Área de Reserva Nº 1 - Diablillos".Informe traducido del francés por L. P. Moens.Los mapas y planos escaneados del informe se encuentran disponibles en soporte papel en la delegación SEGEMAR Tucumán, en caso de requerir la consulta, por favor escribir al correo [email protected]
Plant diversity enhances the reliability of belowground processes
No full textTheory predicts that the probability that an ecosystem will provide a consistent level of functioning over a given unit of time, i.e. the reliability of ecosystem processes, should increase with species richness. There is growing evidence that plant diversity increases the temporal stability of productivity, but only a few studies have investigated its impact on the reliability of ecosystem processes, and information on whether this propagates to the belowground system is virtually lacking. Using a microcosm experiment with plant communities varying in species and functional group diversity and two decomposer groups (earthworms and Collembola) we investigated the effects of plant diversity on the reliability of the belowground system and vice versa, the effect of decomposers on the reliability of plant productivity. Generally, plant diversity increased the reliability of above- and belowground processes by significantly increasing the reliability of eight out of eleven measured ecosystem parameters (six out of nine belowground responses). Plant functional group diversity had a stronger stabilising effect than species richness on above- and belowground processes including plant shoot and total biomass, microbial basal respiration and Collembola densities. By contrast, in the presence of both decomposer groups the reliability of decomposer populations was reduced. The results indicate that plant diversity effects propagate into the belowground system and increase the reliability of belowground processes via more consistent plant derived belowground inputs. (C) 2010 Elsevier Ltd. All rights reserved.German Science Foundation [FOR 456
Whole clam culture as a quantitative diagnostic procedure of Perkinsus atlanticus (Apicomplexa, Perkinsea) in clams Ruditapes decussatus
No full textThe protozoan parasite Perkinsus atlanticus (Azevedo, 1989) causes severe losses among cultured clams, Ruditapes decussatus. This parasite is routinely diagnosed by means of histology or incubation of gills in fluid thioglycollate medium. However, in order to develop models of experimental reproduction of the disease, a procedure for infection intensity evaluation was required. Thus, a diagnostic method has been developed, based on the culture of all clam tissues in fluid thioglycollate medium, followed by sodium hydroxide lysis, and iodine staining of the parasites on cellulose filters. This method was compared with histology. Results suggest that histology is not sensitive enough to detect low levels of infection. The whole-clam culture technique allows detection of low levels or early infection of clams by P. atlanticus. Moreover, this method provides a quantification of infection intensity as number of parasites per gramme wet weight tissue.TR: CS9912312Source type: Electronic(1
Time Remains
No full textHow should one understand the implications of general covariance for the role of time in classical theories of gravity? On one popular view, the essential lesson is that change is relational in a strong sense, such that all it is for a physical degree of freedom to change is for it to vary with regard to a second physical degree of freedom. At a quantum level, this view of change as relative variation leads to a fundamentally timeless formalism for quantum gravity, with the universe eternally frozen in an energy eigenstate. Here we will start from at different interpretation of the classical theory, and, in doing so, show how one may avoid this acute ‘problem of time’ in quantum gravity. Under our view, duration is still regarded as relative, but temporal succession is taken to be absolute. This approach to the classical theory of gravity forms the basis for an alternative relational quantization methodology, such that it is possible to conceive of a genuinely dynamical theory of quantum gravity within which time, in a substantive sense, remains.
This paper accompanies a more technical paper , with which it may be read in parallel
La qualité rédactionnelle des premiers écrits philosophiques
No full textInternational audienceContexte général : Les DVP (Lipman, Daniel, Lévine, Tozzi) sont proposées comme modalités officielles (I.O., 2015) de mise en réflexion des élèves (Rispail, et Coll., 2007, Auriac & Colletta, 2015). Le suivi longitudinal d’élèves évalue la qualité rédactionnelle (Slusarczyk, 2011, suivi CE2-4ème). La classe de 4ème collège marque positivement une autogestion de l’écrit mais négativement une rupture enseignant-enseigné (Slusarczyk, 2016). Expérimentation Des élèves, philosophant depuis la 6ème (Slusarczyk, et coll., 2015), ont manifesté leur souhait d’écrire et poursuive les DVP. 4 classes expérimentales versus témoins (même secteur géographique) d’élèves de 4ème (2016) rédigeront des textes (de type philosophique) qui constituent les données. Les enseignants ont été formés avec une méthode complémentaire : carto-Philo (Thebault, 2015). Sont pré-expérimentées les consignes d’écriture dans 5 collèges de secteurs variés, pour obtenir une consigne productive (thème, structure, déclencheur, cible) auprès d’élèves lambda (5ème et 4ème). Données & Résultats : Un corpus de 400 textes (pré-expérimentation 5ème /4ème) rédigés en juin 2016 vérifiera l’impact de deux thèmes (T1 : rêve, T2 : homme-animal), de cinq déclencheurs croisant différemment a) Reproduction œuvre d’art, b) Dialogue philosophique, c). Mots clefs. Le corpus de 400 textes (septembre 2016) vérifiera les compétences d’écriture philosophique (deux années d’expériences philo) des philosophant versus non philosophant. Un troisième corpus de 400 textes (octobre) explorera les débuts de transformation d’écriture des philosophant versus non philosophant. Les résultats portent pour la pré-expérimentation sur : longueur des textes, nombre et qualités des idées, nombre et qualité des exemples, niveau de connexion des idées/concepts, écart aux textes d’expert (rédigés par des philosophes). L’expérimentation (vagues des textes septembre et octobre) vérifiera en plus le degré de qualité des textes produits (cf. Slusarczyk, 2010) : cohérence, densité, clarté du texte et qualité du vocabulaire, degré de philosophicité, nombre d’idées consensuelles, divergentes, créatives
Experimental transmission of Marteilia refringens with special consideration of its life cycle
No full textThe life history of Marteilia refringens was investigated. The infectivity of purified early and late stages of M. refringens to oysters (Ostrea edulis) was tested in the laboratory using different routes of inoculation. Naturally infected oysters were monitored in experimental tanks to study infection progression through serial samples. Horizontal transmission was tested by cohabitation with carrier oysters in experimental tanks. The role of the environment in the transmission of M. refringens was studied in the field. The experiments provided no evidence to support direct horizontal transmission of M. refringens, but suggested that intermediate or alternative hosts, or free-living stages, are essential in the life cycle of the parasite..RE: 46 ref.; SC: ZA; VE; CA; PA; 0YSource type: Electronic(1) http://upei-resolver.asin-risa.ca?sid=SP:CABI&id=pmid:&id=&issn=0177-5103&isbn=&volume=34&issue=2&spage=135&pages=135-144&date=1998&title=Diseases%20of%20Aquatic%20Organisms&atitle=Experimental%20transmission%20of%20Marteilia%20refringens%20with%20special%20consideration%20of%20its%20life%20cycle.&aulast=Berthe&pid=%3Cauthor%3EBerthe%2c%20F%20C%20J%3bPernas%2c%20M%3bZerabib%2c%20M%3bHaffner%2c%20P%3bThebault%2c%20A%3bFigueras%2c%20A%20J%3C%2Fauthor%3E%3CAN%3E19990802291%3C%2FAN%3E%3CDT%3EJournal%20article%3C%2FDT%3
Modelle rotationssymmetrischer, kollisionsdominierter Trümmerscheiben
No full textDie vorliegende Arbeit behandelt Modelle der Größenverteilung und der räumlichen Verteilung des Materials in sogenannten zirkumstellaren Trümmerscheiben mit Rotationssymmetrie. Diese Scheiben, die als Überbleibsel der Planetenenstehung betrachtet werden, umkreisen Hauptreihensterne und bestehen aus Objekten von submikrometergroßem Staub bis möglicherweise hin zu Planetesimalen von einigen hundert Kilometern Durchmesser. Kollisionen und das Herauswerfen sehr kleinen Staubes durch den stellaren Strahlungsdruck führen bei ansonsten ungestörten Scheiben zu einem stetigen Ausdünnen. Als Werkzeug zur Modellierung wurde dabei einerseits eine numerische Implementierung der kinetischen, statistischen Theorie verwendet. Andererseits wurden analytische Näherungen zur Verifizierung und Interpretation der erhaltenen Ergebnisse entwickelt. Am Beispiel der Trümmerscheibe um Wega wurden erwartete typische Wellen in der Staubgrößenverteilung bestätigt sowie die Produktions- und verlustrate ungebundener Kleinstmeteoroiden bestimmt. Dabei wurde festgestellt, dass die andernorts empirisch ermittelte große Menge dieses vom Strahlungsdruck dezimierten kleinsten Staubes im Widerspruch steht zu den hier erhaltenen numerischen Ergebnissen sowie zu grundlegenden Argumenten. Desweiteren konnte allgemeingültig die radiale Abhängigkeit der Dichte der von einem Planetesimalgürtel erzeugten Staubverteilung numerisch bestimmt werden. Diese wird von lose gebundenen Staubteilchen auf hochexzentrischen Bahnen dominiert. Bezüglich der Langzeitentwicklung einer Trümmerscheibe konnte festgestellt werden, dass diese maßgeblich bestimmt wird vom Übergang der Population der großen und größten Planetesimale von der in der Wachstumsphase entstandenen Größenverteilung hin zum Gleichgewicht zerstörerischer Kollisionen. Relevant ist dies sowohl unmittelbar für den zeitlichen Verlauf der Masse und der Leuchtkraft des beobachtbaren Staubes als auch indirekt für die daraus gefolgerte Gesamtmasse einer Scheibe. Es konnte gezeigt werden das die gemachten Vorhersagen mit Beobachtungsstatistiken vereinbar sind. Mittels Numerik und Analytik wurden Skalierungsregeln ermittelt. Diese Regeln beschreiben die Abhängigkeit der Kollisionszeitskalen von Scheibenmasse, Scheibenradius und mittlerer Bahnexzentrizität der Planetesimale.The subject of the work presented here has been models of the size distribution and the spatial distribution of the material in rotationally symmetric so-called debris disc around main-sequence stars. These discs, which are considered remnants of the formation of planetary systems, are an ensemble of objects from sub-micron-sized dust to planetesimals with diameters up to hundreds of kilometres. Mutual collisions and the ejection of very small dust by the stellar radiation pressure lead to a steady decay of otherwise unperturbed debris discs. The models used are a numerical implementation of the kinetic theory of statistical physics as well as analytic approximations intended for verification and interpretation. Exemplified by the debris disc found around Vega, the expected wavy size distribution in the dust regime is confirmed, and the production and loss rate is determined for the unbound micro-meteoroids that are ejected from the system due the stellar radiation pressure. It is concluded that the elsewhere proposed high abundance of those unbound grains is incompatible with the numerical results presented here and with more fundamental considerations. A general conclusion is drawn concerning the radial distribution of dust produced by a planetesimal belt: it is dominated by barely bound grains on highly eccentric orbits. The long-term evolution of a debris disc is shown to be dominated by the slow transition of the population of planetesimals from the size distribution set in the planet formation and growth phase to the steady-state size distribution defined by disruptive collisions. This transition is directly relevant to the temporal evolution of the observable dust masses and luminosities and indirectly to the deduced total disc masses. The developed models are compatible with observational statistics. From numerics and analytics, scaling laws are derived for the dependence of the collisional timescales on the disc mass, the radial distance to the star, and the planetesimals' orbital eccentricities
Debris discs in binaries: a numerical study
No full textInternational audienceContext. Debris disc analysis and modelling provide crucial information about the structure and the processes at play in extrasolar planetary systems. In binary systems, this issue is more complex because the disc should also respond to the companion star's perturbations.Aims. We explore the dynamical evolution of a collisionally active debris disc for different initial parent body populations, diverse binary configurations, and optical depths. We focus on the radial extent and size distribution of the disc in a stationary state.Methods. We numerically followed the evolution of 10(5) massless small grains, initially produced from a circumprimary disc of parent bodies following a size distribution in dN proportional to s(-3.5)ds. Grains were submitted to both stars' gravity and radiation pressure. In addition, particles were assigned an empirically derived collisional lifetime.Results. For all the binary configurations, the disc extends far beyond the critical semi-major axis a(crit) for orbital stability. This is due to the steady production of small grains, placed by radiation pressure on eccentric orbits reaching beyond acrit. The amount of matter beyond acrit depends on the balance between collisional production and dynamical removal rates: it increases for more massive discs, as well as for eccentric binaries. Another important effect is that, in the dynamically stable region, the disc is depleted from its smallest grains. Both results could lead to observable signatures.Conclusions. We have shown that a companion star can never fully truncate a collisionally active disc. For eccentric companions, grains in the unstable regions can contribute significantly to the thermal emission in the mid-IR. Discs with sharp outer edges, especially bright ones such as HR4796A, are probably shaped by other mechanisms
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