Bose-Einstein condensation of metastable helium: some experimental aspects

We describe our recent realization of BEC using metastable helium. All detection is done with a micruchannel plate which detects the metastables or ions coming from the trapped atom cloud. This discussion emphasizes some of the diagnostic experiments which were necessary to quantitatively analyse our results.Comment: 5 pages, 3 figure

Prediction of intervertebral disc mechanical response to axial load using isotropic and fiber reinforced FE models

International audienc

Ionization rates in a Bose-Einstein condensate of metastable Helium

We have studied ionizing collisions in a BEC of He*. Measurements of the ion production rate combined with measurements of the density and number of atoms for the same sample allow us to estimate both the 2 and 3-body contributions to this rate. A comparison with the decay of the number of condensed atoms in our magnetic trap, in the presence of an rf-shield, indicates that ionizing collisions are largely or wholly responsible for the loss. Quantum depletion makes a substantial correction to the 3-body rate constant.Comment: 4 pages, 3 figure

Getting the elastic scattering length by observing inelastic collisions in ultracold metastable helium atoms

We report an experiment measuring simultaneously the temperatureand the flux of ions produced by a cloud of triplet metastablehelium atoms at the Bose-Einstein critical temperature. The onsetof condensation is revealed by a sharp increase of the ion fluxduring evaporative cooling. Combining our measurements withprevious measurements of ionization in a pure BEC,we extract an improved value of the scattering length$a=11.3^{+2}_{-1}$ nm. The analysis includes corrections takinginto accountthe effect of atomic interactions on the criticaltemperature, and thus an independent measurement of the scatteringlength would allow a new test of these calculations

Pair correlations of scattered atoms from two colliding Bose-Einstein Condensates: Perturbative Approach

We apply an analytical model for anisotropic, colliding Bose-Einstein condensates in a spontaneous four wave mixing geometry to evaluate the second order correlation function of the field of scattered atoms. Our approach uses quantized scattering modes and the equivalent of a classical, undepleted pump approximation. Results to lowest order in perturbation theory are compared with a recent experiment and with other theoretical approaches.Comment: 9 pages, 3 figure

Study and comparison of results of experimental and numerical solutions for hydraulic analogy

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.The hydraulic analogy existing between the propagation of wavelets at the free surface flow of a liquid and the propagation of acoustic waves in a compressible gas is used to study aerodynamics problems with phenomena at flow around solids at supersonic velocities and aeroacoustic phenomena in supersonic divergent jets. In particular, water level fluctuations, which are proportional to pressure fluctuations in the gas, are measured with an optical fiber and special measuring apparatus. Investigations are carried out on a convergent-divergent (de Laval) nozzle. This phenomenon is linked to the existence of shock-cells in supersonic jets, which are formed in the output of the nozzle. These experimental results will be compared with the results from numerical solution and will be obtained from our own program and from the commercial program CFD Fluent.cs201

Risk Factor Analysis of Bird Beak Occurrence after Thoracic Endovascular Aortic Repair

ObjectivesThe aim was to analyze the role played by anatomy and stent graft in the incidence of incomplete apposition to aortic arch.MethodsBetween 2007 and 2014 data including available and suitable computed tomographic angiography (CTA) imaging of patients who had undergone thoracic endovascular aortic repair were reviewed. The study included 80 patients (65 men, 54 ± 21 years) treated for traumatic aortic rupture (n = 27), thoracic aortic aneurysm (n = 15), type B aortic dissection (n = 24), penetrating aortic ulcer (n = 5), intramural hematoma (n = 2), aorto-oesophageal fistula (n = 2), and aortic mural thrombus (n = 5). Pre- and post-operative CTA images were analyzed to characterize bird beak in terms of length and angle, and to calculate aortic angulation within a 30 mm range at the proximal deployment zone.ResultsBird beak configuration was detected in 46 patients (57%): mean stent protrusion length was 16 mm (range: 8–29 mm) and mean bird beak angle was 20° (range: 7–40°). The bird beak effect was significantly more frequent after traumatic aortic rupture treatment (p = .05) and in landing zone 2 (p = .01). No influence of either stent graft type or generation, or degree of oversizing was observed (p = .29, p = .28, p = .81 respectively). However, the mean aortic angle of patients with bird beak was higher in the Pro-form group than that in the Zenith TX2 group (62° vs. 48°, p = .13). Multivariate analysis identified the aortic angle of the deployment zone as the unique independent risk factor of malapposition (HR = 1.05, 95% CI 1–1.10, p = .005). The cutoff value of 51° was found to be predictive of bird beak occurrence with a sensitivity of 58% and a specificity of 85%.ConclusionsAssessment of proximal landing zone morphology to avoid deployment zones generating an aortic angle of over 50° can be recommended to improve aortic curvature apposition with the current available devices

Using ion production to monitor the birth and death of a metastable helium Bose-Einstein condensate

We discuss observations of the ion flux from a cloud of trapped metastable helium atoms. Both Bose-Einstein condensates and thermal clouds were investigated. The ion flux is compared to time-of-flight observations of the expanded cloud. We show data concerning BEC formation and decay, as well as measurements of two- and three-body ionization rate constants. We also discuss possible improvements and extensions of our results.Comment: 14 pages, 9 figures, submitted to Journal of Optics B (special issue, cold quantum gases

Relations between Au / Sn-W mineralizations and late hercynian granite: Preliminary results from the Schistose Domain of Galicia-Trás-os-Montes Zone, Spain

International audienceAu and W-Sn mineralization of the Schistose Domain of Galicia-Trás-os-Montes are spatially related to late hercynian granites. The Bruès (Au) and the Mina Soriana W-(Sn) deposits are studied. Both show some similarities and are assumed to form in the same tectonic and metamorphic context, on top of the granites. The role of the granite as a source for mineralizing fluids and rheological control for vein emplacement is re-adressed and discussed