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

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

CONSTRUCTION ON EXPANSIVE SOILS: CASE OF ROAD SECTION SÉHOUÈ-MASSI

The expansive soils are some soils able to move after loading or water movement; thus, precocious degradations are observed on the structures that are built on them. The present study based on the Sèhouè-Massi section of the Akassato-Bohicon road that is a part of the RNIE N°2 in Benin. The previous work done on the soil of this road section showed that it is on aexpansive clay formation. After had analyzed the auscultation and the geotechnical study results, a road inverse structure appropriate to the traffic was propose

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

Unveiled optical properties of tetrapyrollic pigments in cryogenic environments

An unexpected phenomenon was revealed in the laser induced fluorescence spectra of free-base (H₂Pc) and zinc (ZnPc) phthalocyanines trapped in rare gas and nitrogen matrices under a moderate increase in the laser intensity. In all matrices the intensity of an emission band near 755 nm increased drastically when pumping the S₁←S₀ transition. This observation was assigned to stimulated emission in a four-level scheme involving a vibronic transition from the lowest electronic state to a vibrational level of the ground state. In the present work, we expose new similar results obtained with porphyrin molecules, i.e. tetra-benzoporphin (TBP). With free-base H₂TBP, stimulated emission was observed in Ar or N₂ matrices, but not in Xe matrices. A possible reason could be a fast inter-system crossing rate due to the heavy atom effect induced by Xe. We also report the observation of persistent burnt spectral holes, although the low efficiency of this process is not competitive with stimulated emission and no decrease of the stimulated emission with time was observed. With ZnTBP, no stimulated emission could be recorded; however the appearance of rather strong phosphorescence was noticed. Similar studies focusing on the stimulated emission phenomenon is that they should allow new insights into site effects and site selectivity

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

Microwave studies of the fractional Josephson effect in HgTe-based Josephson junctions

The rise of topological phases of matter is strongly connected to their potential to host Majorana bound states, a powerful ingredient in the search for a robust, topologically protected, quantum information processing. In order to produce such states, a method of choice is to induce superconductivity in topological insulators. The engineering of the interplay between superconductivity and the electronic properties of a topological insulator is a challenging task and it is consequently very important to understand the physics of simple superconducting devices such as Josephson junctions, in which new topological properties are expected to emerge. In this article, we review recent experiments investigating topological superconductivity in topological insulators, using microwave excitation and detection techniques. More precisely, we have fabricated and studied topological Josephson junctions made of HgTe weak links in contact with two Al or Nb contacts. In such devices, we have observed two signatures of the fractional Josephson effect, which is expected to emerge from topologically-protected gapless Andreev bound states. We first recall the theoretical background on topological Josephson junctions, then move to the experimental observations. Then, we assess the topological origin of the observed features and conclude with an outlook towards more advanced microwave spectroscopy experiments, currently under development.Comment: Lectures given at the San Sebastian Topological Matter School 2017, published in "Topological Matter. Springer Series in Solid-State Sciences, vol 190. Springer