ID-HALL, a new double stage Hall thruster design. I. Principle and hybrid model of ID-HALL

International audienceIn Hall thrusters, ions are extracted from a quasineutral plasma by the electric field induced by the local drop of electron conductivity associated with the presence of a magnetic barrier. Since the electric field is used both to extract and accelerate ions and to generate the plasma, thrust and specific impulse are not independent in a Hall thruster. There is a need for versatile thrusters that can be used for a variety of maneuvers, i.e., that can operate either at high thrust or at high specific impulse for a given power. The double stage Hall thruster (DSHT) design could allow a separate control of ionization and acceleration, and hence separate control of thrust and specific impulse. In the DSHT configuration, a supplementary plasma source (ionization stage), independent of the applied voltage, is added and placed upstream of the magnetic barrier (acceleration stage). The DSHT concept is also well adapted to the use of alternative propellants, lighter and with a less efficient ionization than xenon. Several designs of double stage Hall thrusters have been proposed in the past, but these attempts were not really successful. In this paper, we present a brief review of the main DSHT designs described in the literature, we discuss the relevance of the DSHT concept, and, on the basis of simple physics arguments and simulation results, we propose a new design, called ID-HALL (Inductive Double stage HALL thruster). In this design, the ionization stage is a magnetized inductively coupled RF plasma. The inductive coil is inside the central cylinder of the thruster and located nearby the acceleration stage. Preliminary modeling results of this DSHT are described. Published by AIP Publishing. https://doi

Transdisciplinary participatory-action-research from questions to actionable knowledge for sustainable viticulture development

Viticulture negatively impacts the environment, biodiversity, and human health; however, despite the widely acknowledged challenges that this intensive agricultural activity poses to sustainable development, measures to reduce its invasiveness are constantly being deferred or rebuffed. Constraints to change are linked to vine cultivation methods, the impacts of climate change on vine resilience and disease sensitivity, and socio-economic models, as well as growing criticisms from society. Research and training have thus far failed to provide solutions or mobilise stakeholders on a large scale. Such resistance to sustainable practices development calls into question the effectiveness of knowledge production systems and relations between scientists, winegrowers, and society: Have scientific disciplines overly isolated themselves from each other and from the wider society to the point of losing the capacity to incorporate alternative forms of knowledge and reasoning and achieve collaborative action? Herein, we describe our findings from a participatory action research project that began in Westhalten, France, in 2013 and ultimately spread to Switzerland and Germany over the next 6 years. We show that participatory action research can mobilise long-term collaborations between winegrowers, NGOs, advisers, elected officials, members of civil society, and researchers, despite differing visions of viticulture and the environment. The epistemological framework of this research promotes consensus-building by valuing complexity and dissensus in knowledge and reasoning such that all actors are involved in experimentation and the production of results. From these findings, consensus statements were collectively elaborated in qualitative and quantitative registers. Once acknowledged by the scientific community, these consensus statements became shareable knowledge. We propose that this renewed interdisciplinarity associating the human and social sciences with agronomic and biological sciences in collaboration with stakeholders produces actionable knowledge that mobilises and engages winegrowers to conceive and implement sustainable viticulture on a transnational scale

Impact des pratiques agricoles sur l'état biologique du sol : SIPANEMA, un outil d'aide à la décision basé sur les nématodes

La caractérisation des nématodes des sols renseigne sur différentes fonctionnalités du sol, et en raison de cette qualité, les nématodes sont utilisés comme indicateurs biologiques des écosystèmes terrestres depuis les années 1990. Par ailleurs, parmi les nématodes présents dans le sol, certains sont phytoparasites, bio-agresseurs des racines, bien connus en agriculture et pour lesquels un contrôle rigoureux est requis sous peine de perte de production. Pour évaluer qualitativement et quantitativement la présence de ces organismes dans les parcelles agricoles, il est nécessaire de réaliser des analyses d'échantillons de sol en laboratoire. Afin d'avoir une première évaluation théorique, un outil de simulation de l'effet des pratiques sur les nématodes des sols nommé SIPANEMA (Scénarios d'impacts des pratiques agricoles sur l'état biologique du sol) a été développé. Le moteur de calcul de l'outil utilise des données scientifiques issues de 2 bases de données : (1) des résultats d'une méta-analyse qui quantifie l'impact des pratiques agricoles (labour, pesticides, fertilisation, rotation, diversité végétale) sur la nématofaune et (2) Nemabase (Université de Davis, USA) qui synthétise les données scientifiques spécifiques pour les nématodes phytoparasites. SIPANEMA simule deux risques : le risque sur le fonctionnement biologique (RFB) et le risque de pression parasitaire due aux nématodes phytoparasites (RPP) à partir de la description des pratiques et de la diversité végétale présente sur la parcelle considérée renseignées par l'utilisateur de l'application en ligne. Cet outil innovant permet de sensibiliser les professionnels de l'agriculture sur les rôles joués par les nématodes et sur les effets des pratiques mises en oeuvre dans des parcelles agricoles, d'identifier les parcelles à risque fort aussi bien en termes de perte de biodiversité que de pression phytoparasitaire, de hiérarchiser les parcelles pour des efforts de suivi de symptômes ou de diagnostic faunistique, et propose de simuler l'effet de changements de pratiques

Influence of cumulative surgical experience on the outcome of poor-grade patients with ruptured intracranial aneurysm.

International audienceBACKGROUND:The expansion of endovascular techniques for intracranial aneurysms has led to a global decrease in vascular neurosurgery activity. This situation might impact neurosurgeons' level of expertise, even though they all might have to deal with this surgically challenging pathology. In that context, we wanted to assess the impact of cumulative surgical experience on the outcome of patients with poor-grade subarachnoid haemorrhage (SAH) and intracerebral haemorrhage (ICH) treated by microsurgery.METHODS:Sixty-seven patients who underwent surgery for a ruptured aneurysm with SAH and ICH, and a WFNS scale of IV/V, were included. Surgeries were performed by five surgeons, whose experience was judged by the total number of aneurysm surgeries performed. The outcome was assessed by three indicators: intraoperative rupture (IOR), early mortality, and the modified Rankin Scale at last follow-up. The time of IOR was reported on an IOR score. The correlation between surgical experience and outcome was assessed by linear regression. Nonlinear regression was used to assess the correlation of the data with a learning curve model.RESULTS:The analysis showed an influence of surgical experience on intraoperative rupture, with no effect on long-term outcome. No influence was found on early mortality. Increased surgical experience seems to reduce IOR during aneurysm dissection and clip repositioning. Intraoperative rupture data fit Wright's learning curve model.CONCLUSION:This study suggests a direct impact of cumulative experience on the course of ruptured aneurysm surgery and pleads for the use of training and simulation programmes dedicated to neurovascular surgery