Casimir-Polder shifts on quantum levitation states

An ultracold atom above a horizontal mirror experiences quantum reflection from the attractive Casimir-Polder interaction, which holds it against gravity and leads to quantum levitation states. We analyze this system by using a Liouville transformation of the Schr\"odinger equation and a Langer coordinate adapted to problems with a classical turning point. Reflection on the Casimir-Polder attractive well is replaced by reflection on a repulsive wall and the problem is then viewed as an ultracold atom trapped inside a cavity with gravity and Casimir-Polder potentials acting respectively as top and bottom mirrors. We calculate numerically Casimir-Polder shifts of the energies of the cavity resonances and propose a new approximate treatment which is precise enough to discuss spectroscopy experiments aiming at tests of the weak equivalence principle on antihydrogen. We also discuss the lifetimes by calculating complex energies associated with cavity resonances.Comment: Accepted in PR

Quantum reflection of antihydrogen from a liquid helium film

We study the quantum reflection of ultracold antihydrogen atoms bouncing on the surface of a liquid helium film. The Casimir-Polder potential and quantum reflection are calculated for different thicknesses of the film supported by different substrates. Antihydrogen can be protected from anni- hilation for as long as 1.3s on a bulk of liquid 4He, and 1.7s for liquid 3He. These large lifetimes open interesting perspectives for spectroscopic measurements of the free fall acceleration of antihydrogen. Variation of the scattering length with the thickness of a film of helium shows interferences which we interpret through a Liouville transformation of the quantum reflection problem

High resolution numerical study of the Algiers 2001 flash flood: sensitivity to the upper-level potential vorticity anomaly

From 9 to 11 November 2001, intense cyclogenesis affected the northern coasts of Africa and more particularly the densely populated city of Algiers. During the morning of 10 November, more than 130 mm of precipitation was recorded at Bouzareah and resulted in mudslides which devastated the Bab-el-Oued district. This disaster caused more than 700 casualties and catastrophic damage. Like many other heavy rainstorms in the western Mediterranean, this event was associated with the presence of an upper-level trough materialized by a deep stratospheric intrusion and characterized by high potential vorticity values. In this study, the impact of this synoptic structure on the localization and intensity of the precipitation which affected Algiers is investigated using a potential vorticity (PV) inversion method coupled for the first time with the French non-hydrostatic MESO-NH model. A set of perturbed synoptic environments was designed by slightly modifying the extent and the intensity of the coherent potential vorticity structures in the operational ARPEGE analysis. It is shown that such modifications may have a strong impact on the fine-scale precipitation forecast in the Algiers region, thereby demonstrating the fundamental role played by the potential vorticity anomaly during this exceptional meteorological event

Review of the research knowledge and gaps on fish populations, fisheries and linked ecosystems in the Central Arctic Ocean (CAO)

This report presents a review of the research knowledge and gaps on fish populations, fisheries and linked ecosystems in the Central Arctic Ocean (CAO). The CAO comprises the deep basins of the Arctic Ocean beyond the shelf break, which largely overlap with the High Seas of the Arctic Ocean, i.e. the marine areas outside the Exclusive Economic Zones (EEZs) of the Arctic coastal nations. The authors of the report are members of the European Fisheries Inventory in the Central Arctic Ocean (EFICA) Consortium. This study was funded by the European Commission as an EU contribution to the international cooperation within the Agreement to Prevent Unregulated High Seas Fisheries in the Central Arctic Ocean. The report contains desk-based research, using scientific research data bases as well as any available research performed by the EFICA Consortium partners and EU institutions or others. In Chapters 2-8 the authors review the literature and identify specific knowledge gaps. The gap analyses involve comparisons of actual knowledge with desired knowledge on the fish stocks of the CAO to be able to evaluate possibilities for future sustainable fisheries in the area. Chapter 1 is an introductory chapter, and Chapter 9 presents a holistic gap analysis based on Chapters 2-8 and recommendations for research priorities and the next steps. The critical gap analysis highlights that the knowledge gaps for the CAO are enormous and obstruct any quantitative analyses of its fish stocks. This agrees with the conclusions from the Fifth FiSCAO Report (FiSCAO 2018). While data for the physical environment in the CAO (oceanography, bottom topography and ice-cover dynamics) would be sufficient for fish stock modelling and assessment, there is a massive lack of biological and ecological data. The CAO is not a closed system and some aspects of the shelf seas are of high relevance for the CAO, notably connectivity of fish stocks and fish species moving north with climate warming. Scientific research and monitoring programs are established in the shelf seas, and new data are constantly being produced. Fish stock data are available from scientific projects and monitoring programs for some of the shelf seas (Barents Sea, Bering Sea, and to a lesser extent for the Beaufort Sea and the Chukchi Sea). Data exist also for the Russian shelf seas (Kara Sea, Laptev Sea, East Siberian Sea), but these data are not internationally available, while for the areas north of Canada/Greenland data are missing; they do not exist because of the severe ice conditions there. More data from all shelf seas may be hidden in reports that are not publicly accessible. We recommend to make current knowledge generally available by translating key publications and identification of valuable data reports. Research priorities comprise the collection and analysis of primary data in the CAO, and – to a limited extent – from adjacent waters through collaborations with other Signatories of the Agreement (e.g. on population genetics). Further research priorities include an evaluation of ecosystem vulnerability, social-ecological analyses, i.e. recognizing the close and often complex interactions between humans and nature, and recommendations for governance of the CAO. Fulfilling the 14 specific research priorities mentioned in Chapter 9 to “sufficient knowledge available” could enable the potential, future application of an Ecosystem Approach to Management for the CAO

The Dynamics of Ecosystems, Biodiversity Management and Social Institutions at High Northern Latitudes

Ecosystems at high latitudes are highly dynamic, influenced by a multitude of large-scale disturbances. Due to global change processes these systems may be expected to be particularly vulnerable, affecting the sustained production of renewable wood resources and abundance of plants and animals on which local cultures depend. In this paper, we assess the implications of new understandings of high northern latitude ecosystems and what must be done to manage systems for resilience. We suggest that the focus of land management should shift from recovery from local disturbance to sustaining ecosystem functions in the face of change and disruption. The role of biodiversity as insurance for allowing a system to reorganize and develop during the disturbance and reorganization phases needs to be addressed in management and policy. We emphasize that the current concepts of ecological reserves and protected areas need to be reconsidered to developp dynamic tools for sustainable management of ecosystems in face of change. Characteristics of what may be considered as customary reserves at high latitudes are often consistent with a more dynamic view of reserves. We suggest new directions for addressing biodiversity management in dynamic landscapes at high latitudes, and provide empirical examples of insights from unconventional perspectives that may help improve the potential for sustainable management of biodiversity and the generation of ecosystem services

Delamination of pipeline steels: determination of an anisotropic cleavage criterion

Cette étude concerne l’effet de l’anisotropie de la rupture par clivage appliquée à deux tôles d’acier faiblement allié, ferrito-bainitiques, pour gazoducs. La rupture de la tôle par délaminage est étudiée en fonction de la microstructure et du chargement mécanique, afin d’optimiser les propriétés de ces aciers et notamment leur résilience mesurée par essais Battelle et Charpy. Des essais mécaniques ont été effectués sur des mini-éprouvettes axisymétriques entaillées, dimensionnées à cette intention et prélevées dans les directions principales de la tôle, y compris dans la direction travers court. Des essais de traction ont permis de tracer une courbe de transition ductile-fragile sur ces éprouvettes entaillées, dans une gamme de températures comprise entre +20°C et -140°C. Les mécanismes de rupture et les sites d’amorçage de la rupture par clivage ont été identifiés au microscope électronique à balayage. L’analyse mécanique de ces essais a été menée aux différentes températures, le comportement mécanique étant identifié sur éprouvettes lisses sollicitées dans les mêmes directions que les éprouvettes entaillées. Des simulations par éléments finis des essais sur éprouvettes entaillées ont été effectuées afin d’analyser les champs de contrainte et de déformation à rupture et d’en extraire une valeur de contrainte critique de clivage, en fonction de la direction de sollicitation. L’impact du modèle de comportement choisi (critère de plasticité isotrope ou non) sur la valeur de la contrainte critique de clivage a été évalué. Le critère de rupture proposé tient compte des paramètres microstructuraux des aciers étudiés