Dynamical Hierarchies

<Guest Editor's Introduction&gt

Reversal of the lift force on an oblate bubble in a weakly viscous linear shear flow

We compute the flow about an oblate spheroidal bubble of prescribed shape set fixed in a viscous linear shear flow in the range of moderate to high Reynolds numbers. In contrast to predictions based on inviscid theory, the numerical results reveal that for weak enough shear rates, the lift force and torque change sign in an intermediate range of Reynolds numbers when the bubble oblateness exceeds a critical value that depends on the relative shear rate. This effect is found to be due to the vorticity generated at the bubble surface which, combined with the velocity gradient associated with the upstream shear, results in a system of two counter-rotating streamwise vortices whose sign is opposite to that induced by the classical inviscid tilting of the upstream vorticity around the bubble. We show that this lift reversal mechanism is closely related to the wake instability mechanism experienced by a spheroidal bubble rising in a stagnant liquid

Do Public Subsidies Have an Impact on New Firm Survival? An Empirical Study with French Data

firm survival, matched database, propensity score matching

Géométrie et gestion par l’élève de son espace de travail

Cet article traite d'une recherche collaborative réalisée avec une école-recherche associée au CIRADE et pratiquant une pédagogie du projet. Cette recherche avait pour objectifs de développer des outils d'exploration et de communication afin que l'élève puisse composer avec son environnement de travail, intégrer la gestion de l'espace dans ses apprentissages, évaluer ses besoins spatiaux. Les observations des chercheurs permettent d'analyser le développement des opérations intellectuelles et des compétences géométriques d'élèves de 5 à 12 ans en situation de concevoir et de gérer leur propre espace de travail.This article reports on a collaboration research project developed with a CIRADE-associated school involved in project teaching. The objectives of this research included the development of tools for exploring and comunicating to help the student deal with his work environment, the management of space in his learning, and the evaluation of his spatial needs. The authors' observations provided data to analyse the development of cognitive operations and of geometric abilities for students aged 5 to 12 who are in the process of conceptualizing and managing their work space.Este articulo présenta una investigacion realizada con la colaboracion de una escuela asociada al CIRADE donde se practica una pedagogia de proyectos. La investigacion tiene por objetivos desarrollar herramientas de exploraciôn y comunicaciôn con la finalidad de que los alumnos puedan crear dentro de su ambiente de trabajo, integrar esta administracion del espacio a sus aprendizajes y evaluar sus necesidades espaciales. Las observaciones de los investigadores permitieron analizar el desarrollo de las operaciones intelectuales y las competencias geométricas de alumnos de 5 a 12 anos en situaciones de concepcion y gestion de su propio espacio de trabajo.Dieser Artikel handelt von einem Forschungsprojekt, das in Zusam- menarbeit mit einer Grundschule unternommen wurde, die mit dem CIRADE in Verbindung steht und in der eine projektausgerichtete Pàdagogik betrieben wird. Mit dieser Forschung wurde versucht, Experimentier- und Kommunikationsmittel zu entwickeln, um dem Schiller zu helfen, sich in seiner Arbeitsumgebung zurechtzufmden, dièse Raumgestaltung in den Lernprozef? zu integrieren und seine ràumlichen Bedûrfnisse abzuschâtzen. Die angestellten Beobachtungen fiihren zur Analyse der Entwicklung der intellektuellen Verfahren und der geometrischen Kompetenz von funf-bis zwôlfjâhrigen Schulern, denen erlaubt wurde, ihren eigenen Arbeitsraum zu gestalten und zu verwalten

Chronic intestinal pseudo-obstruction in a Bernese Mountain Dog

Chronic Intestinal Pseudo-Obstruction (CIPO) is a rare syndrome characterized by chronic intestinal dilation and dysmotility in the absence of mechanical obstruction. A definite diagnosis of CIPO can only be made after histological examination of intestinal tissues. The present case describes a CIPO in a 2.5-year-old Bernese Mountain dog with a history of recurrent gastro-intestinal complaints suggestive for pseudo-obstruction. Histological lesions of small intestinal samples consisted of severe loss of smooth muscle cells of the tunica muscularis and diffuse infiltration of mononuclear cells. In addition, a hypertrophy of the lamina muscularis mucosa of the small intestinal tract was present. On the basis of these findings and the results of immunohistochemistry, a myopathic form of CIPO was diagnosed

Uniform Random Sampling of Traces in Very Large Models

This paper presents some first results on how to perform uniform random walks (where every trace has the same probability to occur) in very large models. The models considered here are described in a succinct way as a set of communicating reactive modules. The method relies upon techniques for counting and drawing uniformly at random words in regular languages. Each module is considered as an automaton defining such a language. It is shown how it is possible to combine local uniform drawings of traces, and to obtain some global uniform random sampling, without construction of the global model

In and out of Madagascar : dispersal to peripheral islands, insular speciation and diversification of Indian Ocean daisy trees (Psiadia, Asteraceae)

This study was supported by the European Union’s HOTSPOTS Training Network (MEST-2005-020561)Madagascar is surrounded by archipelagos varying widely in origin, age and structure. Although small and geologically young, these archipelagos have accumulated disproportionate numbers of unique lineages in comparison to Madagascar, highlighting the role of waif-dispersal and rapid in situ diversification processes in generating endemic biodiversity. We reconstruct the evolutionary and biogeographical history of the genus Psiadia (Asteraceae), a plant genus with near equal numbers of species in Madagascar and surrounding islands. Analyzing patterns and processes of diversification, we explain species accumulation on peripheral islands and aim to offer new insights on the origin and potential causes for diversification in the Madagascar and Indian Ocean Islands biodiversity hotspot. Our results provide support for an African origin of the group, with strong support for non-monophyly. Colonization of the Mascarenes took place by two evolutionary distinct lineages from Madagascar, via two independent dispersal events, each unique for their spatial and temporal properties. Significant shifts in diversification rate followed regional expansion, resulting in co-occurring and phenotypically convergent species on high-elevation volcanic slopes. Like other endemic island lineages, Psiadia have been highly successful in dispersing to and radiating on isolated oceanic islands, typified by high habitat diversity and dynamic ecosystems fuelled by continued geological activity. Results stress the important biogeographical role for Rodrigues in serving as an outlying stepping stone from which regional colonization took place. We discuss how isolated volcanic islands contribute to regional diversity by generating substantial numbers of endemic species on short temporal scales. Factors pertaining to the mode and tempo of archipelago formation and its geographical isolation strongly govern evolutionary pathways available for species diversification, and the potential for successful diversification of dispersed lineages, therefore, appears highly dependent on the timing of arrival, as habitat and resource properties change dramatically over the course of oceanic island evolution.Publisher PDFPeer reviewe