Small-scale instabilities of an island wake flow in a rotating shallow-water layer

International audienceUnlike the standard two-dimensional Kármán street, the oceanic vortex streets which may occur behind isolated islands are affected by the earth's rotation and the vertical stratification of the thermocline. These effects induce a selective destabilisation of anticyclonic vorticity regions. Several experimental studies were devoted to the inertial instability, which induces transient and three-dimensional perturbations in a rotating fluid layer. However, these previous experiments correspond to a large or finite vertical h to horizontal L aspect ratio (α=h/L) while in an oceanic context this ratio is much smaller than unity (αsimilar, equals0.01). This vertical confinement induces a cutoff vertical scale for unstable perturbations. But, since dissipation preferentially damps smaller scales, the shallow-water aspect ratio α may become so small that no growth will occur. We present here the first experimental investigation of three-dimensional destabilizations of an island wake flow in a shallow-water configuration. These laboratory experiments where performed on the LEGI Coriolis Platform, with small aspect ratio (α=0.1) and large Reynolds numbers (Re=5000–35,000). We have shown that unstable three-dimensional perturbations occur when the island Rossby number View the MathML source is large enough (Ro>0.8) while the Reynolds number seems to control the duration of this transient instability. Qualitative dye visualisation reveals various types of passive tracer dispersion in the wake. Moreover, according to PIV measurements we have shown that, unlike experiments having large or finite aspect ratio (α≥1), the small-scale perturbations do not significantly reduce the local vorticity inside the unstable anticyclone. Hence, the shallow-water configuration (αmuch less-than1) seems to reduce the intensity and the impact of three-dimensional instabilities in the vortex street. Finally, for high Froude numbers, when the flow becomes supercritical and owing to the generation of large amplitude waves in the wake, the vortex street intensity is strongly reduced

Lion Feuchtwanger : le philologue et les cochons

In seinen Erzählungen und Romanen des Exils greift Lion Feuchtwanger den Nazismus mit rationalen Argumenten an und zieht die Anhänger der NS-Ideologie mit den Mitteln der Satire ins Lächerliche. Dennoch sind seine Werke auch dadurch gekennzeichnet, dass sie die spezifischen von der Philologie gegen diese unerhörte Barbarei eingesetzten Waffen zunehmend in Frage stellen. Der Nazismus zeichnet sich bekanntlich dadurch aus, dass er dem Irrationalen und dem Mythos einen großen Platz einräumt. Der Romancier schreckt nicht davor zurück, die Schwächen der Nazigegner ans Licht zu bringen, welche oft unfähig sind, sich dem neuen Zusammenhang anzupassen. Die Infragestellung der Philologie gegenüber dem Mythologischen und dem Irrationalen erreicht einen Höhepunkt mit dem Roman Die Brüder Lautensack (1943) und der Erzählung Odysseus und die Schweine (1947). In den beiden Erzähltexten werden die Mechanismen des poetischen schöpferischen Prozesses und der literarischen Überlieferung ironisch reflektiert.Dans ses récits et romans de l’exil, Lion Feuchtwanger dénonce le nazisme avec des arguments rationnels et ridiculise, par la satire, les partisans de l’idéologie nazie. Cependant, ses œuvres se distinguent aussi par la remise en question grandissante de la valeur intrinsèque des armes de la philologie contre cette barbarie inédite, laquelle repose en partie sur la place qu’elle accorde à l’irrationnel et au mythe. Le romancier n’hésite pas à mettre en lumière les limites des positions tenues par les personnages de résistants, souvent incapables de s’adapter à la nouvelle donne. Ce processus de remise en cause des moyens d’action philologiques face à l’utilisation de l’irrationnel et du mythologique atteint un degré nouveau avec le roman Die Brüder Lautensack (1943) et surtout la nouvelle Odysseus und die Schweine (1947). Dans ces deux œuvres, on assiste à une réflexion sur les mécanismes de création et de transmission du poétique et du mythologique ainsi qu’à une ironisation des moyens d’action littéraires.In his stories and novels of exile, Lion Feuchtwanger denounces Nazism with rational arguments and ridicules, by satire, the partisans of the Nazi ideology. However, his works are also distinguished by the growing questioning of the intrinsic value of the weapons of philology against this unprecedented barbarism, which gives a significant place to irrationality and myth. The novelist does not hesitate to highlight the limits of the positions held by the characters of resistants, often unable to adapt. This process of questioning the philological means of action against the use of the irrational and the mythological reaches a new level with the novel Die Brüder Lautensack (1943) and especially the short story Odysseus und die Schweine (1947). The two narratives ironically reflect the mechanisms of creation and transmission of poetics and mythology

„Mein lieber Antipode…“ Heinrich Manns Briefe an Ludwig Ewers (1889‑1894)

Heinrich Manns Briefe an den Jugendfreund Ludwig Ewers (1889-1894) dokumentieren am besten und quasi als einzige Quelle die allererste Schaffensperiode des Schriftstellers. In diesen manchmal sehr langen Briefen inszeniert sich der angehende Novellist und Romancier als Dilettant und bespricht die eigenen literarischen Versuche sowie diejenigen des Briefpartners. Seine Kritik an den Fehlern des Freundes ist für ihn auch der Anlass zu ästhetischen Überlegungen. Trotz der späteren Entwicklungen des Autors, der diese Anfänge verleugnet hat, werden doch einige Aspekte seiner Erzählkunst bereits deutlich.Les lettres que le jeune Heinrich Mann (1871-1950) a écrit son ami Ludwig Ewers entre 1889-1894 sont le témoin privilégié et quasi unique de la toute première période créatrice de l’auteur. Dans ces lettres, qui sont parfois très longues, le futur nouvelliste et romancier se met en scène comme dilettante et commente ses premiers essais dans le domaine littéraire ainsi que ceux de son correspondant. La critique qu’il fait des insuffisances de son ami est aussi pour lui l’occasion d’exposer ses réflexions esthétiques. Malgré toutes les évolutions ultérieures de l’auteur, qui a renié les œuvres de cette première période, certains aspects de sa conception de l’art narratif sont déjà présents ici. En particulier, sa conception du « réalisme » permet, au-delà des contradictions d’un tout jeune homme et de certains points discutables, de jeter un regard intéressant dans son atelier d’écrivain.The letters of young Heinrich Mann (1871-1950) to the friend Ludwig Ewers between 1889-1894 uniquely witness the very first creative period of this author. In these letters, which are sometimes quite long, the future novelist and novellas-author Heinrich Mann shows himself as a dilettante and comments his firs literary experiences and those of is correspondent. He critics the friend’s inadequacies and it is for him the occasion to expose his own esthetical reflexions. Despite of the later evolutions of the author, who went back on this period, many aspects of his narrative conception are already present here. In particular, his own idea of “realism” allows to look at his laboratory, even though some points are problematic

Dynamiques et stabilités de tourbillons océaniques en intéraction avec la côte et la topographie

Version publication recto-versoOceanic meso-scale vortices and flows contribute significantly to the transport of water and heat in ocean. To understand their dynamics and their interactions with topographical features, it is essential to characterize the salt exchange, the movement of biological species or pollutants. In particular, surface currents and eddies, located in the first hundred or two hundred metres, play a crucial role in exchange between the coastal zone and the open sea. This is a study of modelling two experimental idealized phenomena that could participate actively in the horizontal and vertical exchanges in the ocean surface layer. Unlike the standard bidimensional Kármán street, the oceanic vortex streets which may occur behind isolated islands are affected by the earth's rotation and the vertical stratification of the thermocline. These effects induce a selective destabilisation of anticyclonic vorticity regions. Several experimental studies were carried out on the LEGI Coriolis Platform, to characterize the dynamical processes of these instabilities. The LEGI rotating tank (13 m in diameter) allows us to reach a small aspect ratio, while using a shallow water configuration. Qualitative dye visualisations and PIV measurements allow us to identify different dynamic regimes, in a given range of Rossby and Reynolds numbers. We show that these instabilities occur at the anticyclonic boundary layer around the island. The other part of this work concerns the dynamic of a surface-intensified vortex interacting with the coast or the shelf. The first data sets of the EGYPT cruises in the eastern Mediterranean sea reveal a large meso-scale vortex travelling along the Libyo-Egyptian shelf. The observed westward drift speed is significantly faster than expected from the beta-effect only. Idealised experiments are carried out on the ENSTA turntable, to model a simple interaction of the coast or the shelf wih the dynamics of a surface anticyclone, in a two layer configuration. The drift speed of this surface vortex is double when it is initially at the base of the shelf, showing a feedback between the deep layer and the surface flow.Les tourbillons et les écoulements méso-échelles océaniques contribuent de façon importante au transport de masses d'eau et de chaleur dans l'océan. La compréhension de leurs dynamiques, et de leurs interactions avec la topographie, est primordiale, pour caractériser les échanges thermohalins, le déplacements d'espèces biologiques ou de polluants. En particulier, les courants et tourbillons de surface, situés dans les cent ou deux cents premiers mètres de profondeur, jouent un rôle capital dans les échanges entre la zone côtière et la zone hauturière. Cette thèse porte sur la modélisation expérimentale idéalisée de deux phénomènes pouvant participer activement aux échanges horizontaux et verticaux dans la couche supérieure océanique. Les sillages d'îles peuvent être le lieu d'instabilités fortes dans les zones anticycloniques de l'écoulement. Des expériences ont été réalisées sur la Plateforme Coriolis (LEGI) à Grenoble, pour identifier les régimes dynamiques de ces instabilités. Ce dispositif (13 mètres de diamètre) a permis d'atteindre de faibles rapports d'aspects géométriques, tout en travaillant avec un dispositif couche-mince. Des visualisations avec colorants et des mesures du champ de vitesse horizontal par intercorrélation de particules ont été réalisées, afin d'étudier la sensibilité des instabilités dans les anticyclones pour différentes gammes de nombres de Reynolds et de Rossby. Nous montrons que ces instabilités sont présentes dès la couche limite anticyclonique, autour de l'île. L'autre partie de ce travail concerne la dynamique d'un tourbillon de surface, en interaction avec la côte ou le talus océanique. Des mesures récentes (campagne EGYPT-1) nous ont permis de mesurer la dérive particulière d'un anticyclone de surface le long de la côte libyenne. Cette dérive vers l'est ne peut s'expliquer par la simple prise en compte de l'effet beta ou de l'effet miroir le long de la côte. Des expériences idéalisées sont menées sur la table tournante de l'ENSTA, afin de modéliser de façon simple l'interaction d'une côte ou d'un talus sur la dynamique d'un anticyclone, à la surface d'un dispositif bi-couche. La vitesse de ce tourbillon de surface voit notamment sa dérive doubler lorsqu'il se trouve initialement à la base de la pente, montrant ainsi l'existence d'une rétroaction possible de la couche du fond sur la dynamique de la couche de surface

Inertial instability of von Karman street in a rotating shallow-water layer

The rotation alters the stability of 2D anticyclonic flow with respect to 3D perturbations. Experiments have shown that such instability induces a transient destabilization of anticyclonic vortices in von Kármán street, when w/f 5 000). We have shown that unstable 3D-perturbations occur for large enough Rossby number (Ro > 0.8) while the Reynolds number seems to control the duration of this transient instability. According to PIV measurements we have shown that, unlike the deepwater configuration, the small-scale perturbations do not reduce the local vorticity inside the unstable antiyclone. Finally, for high Rossby numbers, when the flow becomes supercritical (Fd > 1), due to the generation of high amplitude wave wake the vortex street intensity is strongly reduced

Detection of Organics at Mars: How Wet Chemistry Onboard SAM Helps

For the first time in the history of space exploration, a mission of interest to astrobiology could be able to analyze refractory organic compounds in the soil of Mars. Wet chemistry experiment allow organic components to be altered in such a way that improves there detection either by releasing the compounds from sample matricies or by changing the chemical structure to be amenable to analytical conditions. The latter is particular important when polar compounds are present. Sample Analysis at Mars (SAM), on the Curiosity rover of the Mars Science Laboratory mission, has onboard two wet chemistry experiments: derivatization and thermochemolysis. Here we report on the nature of the MTBSTFA derivatization experiment on SAM, the detection of MTBSTFA in initial SAM results, and the implications of this detection

An eHealth Framework for Managing Pediatric Growth Disorders and Growth Hormone Therapy

Background: The use of technology to support health and health care has grown rapidly in the last decade across all ages and medical specialties. Newly developed eHealth tools are being implemented in long-term management of growth failure in children, a low prevalence pediatric endocrine disorder. Objective: Our objective was to create a framework that can guide future implementation and research on the use of eHealth tools to support patients with growth disorders who require growth hormone therapy. Methods: A total of 12 pediatric endocrinologists with experience in eHealth, from a wide geographical distribution, participated in a series of online discussions. We summarized the discussions of 3 workshops, conducted during 2020, on the use of eHealth in the management of growth disorders, which were structured to provide insights on existing challenges, opportunities, and solutions for the implementation of eHealth tools across the patient journey, from referral to the end of pediatric therapy. Results: A total of 815 responses were collected from 2 questionnaire-based activities covering referral and diagnosis of growth disorders, and subsequent growth hormone therapy stages of the patient pathway, relating to physicians, nurses, and patients, parents, or caregivers. We mapped the feedback from those discussions into a framework that we developed as a guide to integration of eHealth tools across the patient journey. Responses focused on improved clinical management, such as growth monitoring and automation of referral for early detection of growth disorders, which could trigger rapid evaluation and diagnosis. Patient support included the use of eHealth for enhanced patient and caregiver communication, better access to educational opportunities, and enhanced medical and psychological support during growth hormone therapy management. Given the potential availability of patient data from connected devices, artificial intelligence can be used to predict adherence and personalize patient support. Providing evidence to demonstrate the value and utility of eHealth tools will ensure that these tools are widely accepted, trusted, and used in clinical practice, but implementation issues (eg, adaptation to specific clinical settings) must be addressed. Conclusions: The use of eHealth in growth hormone therapy has major potential to improve the management of growth disorders along the patient journey. Combining objective clinical information and patient adherence data is vital in supporting decision-making and the development of new eHealth tools. Involvement of clinicians and patients in the process of integrating such technologies into clinical practice is essential for implementation and developing evidence that eHealth tools can provide value across the patient pathway.Peer reviewe

Investigating the Origin of Chlorohydrocarbons Detected by the Sample Analysis at Mars (SAM) Instrument at Rocknest

The search for organic compounds on Mars, including molecules of either abiotic or biological origin is one of the key goals of the Mars Science Laboratory (MSL) mission. Previously the Viking and Phoenix Lander missions searched for organic compounds, but did not find any definitive evidence of martian organic material in the soils. The Viking pyrolysis gas chromatography mass spectrometry (GCMS) instruments did not detect any organic compounds of martian or exogenous origin above a level of a few parts-per-billion (ppb) in the near surface regolith at either landing site [1]. Viking did detect chloromethane and dichloromethane at pmol levels (up to 40 ppb) after heating the soil samples up to 500 C (Table 1), although it was originally argued that the chlorohydrocarbons were derived from cleaning solvents used on the instrument hardware, and not from the soil samples themselves [1]. More recently, it was suggested that the chlorohydrocarbons detected by Viking may have been formed by oxidation of indigenous organic matter during pyrolysis of the soil in the presence of perchlorates [2]. Although it is unknown if the Viking soils contained perchlorates, Phoenix did reveal relatively high concentrations (~0.6 wt%) of perchlorate salt in the icy regolith [3], therefore, it is possible that the chlorohydrocarbons detected by Viking were produced, at least partially, during the experiments [2,4]. The Sample Analysis at Mars (SAM) instrument suite on MSL analyzed the organic composition of the soil at Rocknest in Gale Crater using a combination of pyrolysis evolved gas analysis (EGA) and GCMS. One empty cup procedural blank followed by multiple EGA-GCMS analyses of the Rocknest soil were carried out. Here we will discuss the results from these SAM measurements at Rocknest and the steps taken to determine the source of the chlorohydrocarbons

Adrenocortical tumours in children and adolescents: The EXPeRT/PARTNER diagnostic and therapeutic recommendations

Adrenocortical tumours (ACTs) are rare during childhood. A complete surgical resection provides the best chance of cure, but the role and efficacy of the adjuvant therapy are still controversial. Various histologic criteria of malignancy for ACTs adopted in children do not facilitate comparative studies and are not completely shared. Therefore, a sharp demarcation between benign and malignant lesions has not been recognised, making it difficult to identify who potentially needs perioperative therapy. This manuscript presents the internationally harmonised recommendations for the diagnosis and treatment of ACTs in children and adolescents, established by the European Cooperative Study Group for Paediatric Rare Tumours (EXPeRT) group within the EU-funded project PARTNER (Paediatric Rare Tumours Network - European Registry)