Energy cascade and the four-fifths law in superfluid turbulence

The 4/5-law of turbulence, which characterizes the energy cascade from large to small-sized eddies at high Reynolds numbers in classical fluids, is verified experimentally in a superfluid 4He wind tunnel, operated down to 1.56 K and up to R_lambda ~ 1640. The result is corroborated by high-resolution simulations of Landau-Tisza's two-fluid model down to 1.15 K, corresponding to a residual normal fluid concentration below 3 % but with a lower Reynolds number of order R_lambda ~ 100. Although the K\'arm\'an-Howarth equation (including a viscous term) is not valid \emph{a priori} in a superfluid, it is found that it provides an empirical description of the deviation from the ideal 4/5-law at small scales and allows us to identify an effective viscosity for the superfluid, whose value matches the kinematic viscosity of the normal fluid regardless of its concentration.Comment: 6 pages, 7 figure

Investigation of intermittency in superfluid turbulence

International audienceThis paper reports new experimental and simulation velocity data for superfluid steady turbulence above 1 K. We present values for the scaling exponent of the absolute value of velocity-increment structure functions. In both experiments and simulations, they evidence that intermittency occurs in superfluid flows in a quite comparable way to classical turbulence. In particular, the deviation from Kolmogorov 1941 keeps the same strength as we cross the superfluid transition. To the best of our knowledge, this is the first confirmation of the superfluid 4He experimental results from Maurer et al. EPL 1998 and the first numerical evidence of intermittency in superfluid turbulence

Gestion prédictive d'un micro-réseau résidentiel

International audienceDans cet article est présentée une stratégie de gestion prédictive destinée au pilotage des systèmes de production et de stockage d'énergie d'un micro-réseau résidentiel. Ainsi, un habitat d'une surface de 190 m2, situé dans le sud de la France et qu'il est possible d'équiper de panneaux solaires photovoltaïques, d'une éolienne à axe vertical et de batteries, a été modélisé. Une tarification dynamique a également été considérée. Cette stratégie tient compte des états actuel et futur du réseau électrique ainsi que des interactions entre ce dernier et le micro-réseau. L'objectif est ici de favoriser l'auto-consommation d'énergie, tout en minimisant l'impact négatif de la production locale sur le réseau électrique. Les résultats obtenus en simulation démontrent notamment que le recours à un système de stockage électrique, piloté grâce à la stratégie proposée, permet d'optimiser l'interaction avec le réseau électrique. Enfin, l'auto-consommation est favorisée par le mix-énergétique considéré

Turbulent velocity spectra in superfluid flows

International audienceWe present velocity spectra measured in three cryogenic liquid 4He steady flows: grid and wake flows in a pressurized wind tunnel capable of achieving mean velocities up to 5 m/s at temperatures above and below the superfluid transition, down to 1.7 K, and a "chunk" turbulence flow at 1.55 K, capable of sustaining mean superfluid velocities up to 1.3 m/s. Depending on the flows, the stagnation pressure probes used for anemometry are resolving from one to two decades of the inertial regime of the turbulent cascade. We do not find any evidence that the second order statistics of turbulence below the superfluid transition differ from the ones of classical turbulence, above the transition

Etudes de systèmes d'anticoïncidence pour les missions spatiales X et Gamma, Simbol-X, IXO et Astro-H

L'astronomie X permet de comprendre et d'explorer les phénomènes les plus énergétiques de notre univers. Les performances scientifiques des futures missions X nécessitent un détecteur avec un niveau très faible de fond, et sa réduction devient un enjeu majeur pour l'obtention de hautes performances des télescopes spatiaux. Cela implique des simulations approfondies et des systèmes de rejet efficaces. Il nécessite également une très bonne connaissance des détecteurs qui seront protégés. Durant ma thèse, j'ai acquis une forte expérience en participant à la conception, les tests et l'optimisation de la protection active et passive de la mission Simbol-X, un téléscope spatial franco-italien dédié à l'observation des rayons X, dans la gamme d'énergie 0,1 à 80 keV. Ce blindage est composé de scintillateurs plastiques et de fibres optiques collées sur celui-ci et d'une lecture par photomultiplicateur multi-anode. J'étais également responsable d'effectuer les essais de performance des détecteurs et de simulations avec les logiciels Monte-Carlo GEANT4 et SLitrani. Le projet Simbol-X a cessé en Mars 2009. Considérant que notre travail sur Simbol-X peut être étendu à d'autres missions X, nous avons suivi une R&D CNES sur l'étude des systèmes de rejet de fond en vue du télescope IXO/HXI, dont le système d'anticoïncidence est constitué d'un cristal de BGO lu par un photodiode. J'ai également participé à la conception et aux tests du modèle de laboratoire de ce système, refroidi grâce à un système Peltier. J'ai également contribué à l'étude d'un cristal de LaBr3, un nouveau type de détecteur scintillant, qui semble très prometteur pour les futurs systèmes de réduction de fond.X-ray astronomy allows us to understand and explore the most energetic phenomena in the Universe. The scientific performances of future hard X-ray missions necessitate a very low detector background reduction is thus a main issue for obtaining high performance space telescopes. This implies thorough background simulations, and efficient rejection systems. It necessitates also a very good knowledge of the detectors to be shielded. During my PHD, I got a strong experience on these issues by participating to the conception, tests and optimization of the active and passive shielding of the Simbol-X mission, a French-Italian space telescope dedicated to observe the X-ray sky, in the 0.1 to 80 keV energy band. This shielding is made of plastic scintillators with optical fibers glued on it and readout by multi-anode photomultiplier. I was also responsible of performing the detectors performance tests and the consequent simulations with the GEANT4 and SLitrani Monte-Carlo simulation software. The Simbol-X project has stopped in March 2009. Considering that our work on Simbol-X may be naturally extended to other X-ray missions, we have followed up with a CNES R&D project on the study of background rejection systems mainly in view the IXO/HXI telescope, whose anticoincidence is constituted by BGO blocks readout by APD diods. During my PHD, I have then also participated to the conception and test of the laboratory model of this anticoincidence, cooled down to -20C thanks to a Peltier system. I have also contributed to the study of LaBr3 detectors, a new kind of scintillating detector, which seems very promising for future background reduction systems.PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

L’aide internationale : comment sortir des débats sur son (in)efficacité ?Enjeux et leçons d’une expérimentation conduite auprès des populations bénéficiaires au Nord Mali

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Load management in multi-energy buildings: a simulation case study

International audienceThis paper presents a comprehensive approach about energy resources management in buildings connected to the electricity grid and equipped with energy production and storage systems. The aim of the work is to find interesting configurations that favour energy self-consumption while minimizing the impact of the local production on the grid. Energy and economic criteria are proposed to evaluate the proposed strategy. A parametric study allowed the local systems to be optimally designed. So, we used first the TRNSYS software to model the thermal behaviour of a single-storey house, inhabited by four persons and equipped with photovoltaic solar panels, a vertical-axis windmill and batteries for electricity storage. The results we obtained in simulation prove that one can design in an optimal way the just-mentioned systems and find configurations that offer a very good compromise between energy self-consumption and renewable energy coverage rate while limiting the negative impact of the local production on the electricity grid

Scintillating anticoincidence detection elements design and tests with muons and protons

International audienceDesign, construction and tests of anticoincidence detection elements are presented. Initially planned to be used as active shielding parts of the anticoincidence detector of the Simbol-X mission, they are aimed to detect cosmic protons and provide veto signal against charged-particle background induced on imaging detectors. The sample is made of a scintillator plate into which grooves are machined and waveshifting fibers glued. The fibers are connected to multianode photomultiplier (PM) tubes. The tubes characteristics have been evaluated for this application. The device has been tested with atmospheric muons that deposit similar energy to that of cosmic protons thanks to a specially designed muon telescope also described in this paper. Tests have also been performed with protons of a tandem accelerator beam line. The response is on average above 10 photoelectrons, which is not complicated to detect, which allows very good detection efficiency as well as very good ability to reject noise. In addition many evolution and performance improvements appear possible

An effective and well-tolerated strategy in recurrent and/or metastatic head and neck cancer: successive lines of active chemotherapeutic agents

BACKGROUND: The combination platinum, 5-fluorouracil (5-FU) and cetuximab is the standard first-line regimen of recurrent and/or metastatic head and neck squamous cell carcinoma (HNSCC). Due to the toxicity of this treatment, alternative therapies are often offered to patients. The aim of this study was to evaluate the overall survival obtained with a first line chemotherapy adapted to patients functional status and the administration of all active drugs within successive lines of chemotherapy. METHODS: This series included a total of 194 patients with recurrent and/or metastatic HNSCC treated from 2006 to 2011 in a single institution where the administration of successive lines of chemotherapies has been the standard clinical approach. Treatment was administered according to clinical practice guidelines. RESULTS: Most patients received at least two treatment lines. Only 11 patients (6%) were treated with a combination of cisplatin, 5-FU and cetuximab in front line, but most patients received at least one platinum-based regimen (n = 154 patients, 78%); 162 (82%) received taxanes, 36 (18%) received 5-FU, 27 (14%) received capecitabine, 67 (34%) received methotrexate and 134 (68%) received cetuximab. The median overall survival was 9.8 months (95% CI: 8.1-11.4 months) and reached 13.1 months among the subgroup of 131 patients eligible for inclusion in a clinical trial. CONCLUSION: The survival outcomes of patients treated in the first-line setting with chemotherapy regimens adapted to their functional status, followed by several subsequent regimens were comparable with published outcomes of patients treated by platinum, 5-FU and cetuximab

Convection at very high Rayleigh number: signature of transition from a micro-thermometer inside the flow

International audienceIn 1991 and 2001, two groups reported a qualitative change in the second order statistics of local temperature fluctuations in Rayleigh-Bénard cells for Rayleigh numbers in the range Ra ~ 10^{12} - 10^{13}. In the second group, this change was accompanied by an abrupt increase of the heat transfer, and these concomitant observations were interpreted as two signatures of the transition to Kraichnan's ''Ultimate Regime'' of convection. In the first group, a second change on temperature statistics was reported at lower Ra but no heat transfer enhancement was found. The 1991 observations have been questioned putting forward a finite size cut-off of the probe . If this finite size argument was valid, it should also hold for the 2001 study, as the probes had the same size (200 microns) and the cell heights used in 1991 and 2001 were respectively 40 and 20 cm. In this case, the only signature of the transition to the Ultimate Regime in the 2001 study would be the increase in heat transfer. To test the finite size argument, we designed a third experiment in a 40 cm-high cell using a specially developed probe 10 times smaller than the ones used previously. A micro-machining process was developed to produce NbN micro-thermometers with temperature-sensitive spot of typical size 20 microns x 1 microns deposited on a poorly conducting glass fiber of diameter 17 microns (or less) and few mm in length. Following the 2001 study, the temperature fluctuations were monitored using the exponent of the increments of the second order structure function. This quantity, which is formally equivalent to the traditional spectral density, provides in practice a more accurate observable thanks to a better immunity to noise. This new experiment shows a heat transfer transition between Ra=10^{12} and 10^{13} and, concomitantly, a qualitative change in the statistics of temperature fluctuations. The nature of this change is very similar to the one reported in 2001 with larger probes. Both present observations are consistent with the 2001 observation