Evanescent straight tapered-fiber coupling of ultra-high Q optomechanical micro-resonators in a low-vibration helium-4 exchange-gas cryostat

We developed an apparatus to couple a 50-micrometer diameter whispering-gallery silica microtoroidal resonator in a helium-4 cryostat using a straight optical tapered-fiber at 1550nm wavelength. On a top-loading probe specifically adapted for increased mechanical stability, we use a specifically-developed "cryotaper" to optically probe the cavity, allowing thus to record the calibrated mechanical spectrum of the optomechanical system at low temperatures. We then demonstrate excellent thermalization of a 63-MHz mechanical mode of a toroidal resonator down to the cryostat's base temperature of 1.65K, thereby proving the viability of the cryogenic refrigeration via heat conduction through static low-pressure exchange gas. In the context of optomechanics, we therefore provide a versatile and powerful tool with state-of-the-art performances in optical coupling efficiency, mechanical stability and cryogenic cooling.Comment: 8 pages, 6 figure

Searching for Very High Energy Emission from Pulsars Using the High Altitude Water Cherenkov (HAWC) Observatory

There are currently over 160 known gamma-ray pulsars. While most of them are detected only from space, at least two are now seen also from the ground. MAGIC and VERITAS have measured the gamma ray pulsed emission of the Crab pulsar up to hundreds of GeV and more recently MAGIC has reported emission at $\sim2$ TeV. Furthermore, in the Southern Hemisphere, H.E.S.S. has detected the Vela pulsar above 30 GeV. In addition, non-pulsed TeV emission coincident with pulsars has been detected by many groups, including the Milagro Collaboration. These GeV-TeV observations open the possibility of searching for very-high-energy (VHE, > 100GeV) pulsations from gamma-rays pulsars in the HAWC field of view.Comment: Presented at the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands. See arXiv:1508.03327 for all HAWC contribution

Les ressorts territoriaux de la gestion de l'eau sont-ils gages d'efficacité environnementale ? Analyse des dimensions territorialisées et territorialisantes des dispositifs de gestion des eaux dans la vallée de la Drôme (1980-2011)

National audienceLes dispositifs de Contrat de rivière et de Schéma d’Aménagement et de Gestion des Eaux font partie des nouveaux modes d’action publique faisant le pari d’un gain d’efficacité par leur territorialisation. En matière environnementale, cette efficacité repose sur la capacité des gestionnaires de l’eau à transformer les pratiques responsables des atteintes aux milieux aquatiques et à obtenir pour ce faire des marges et moyens d’action. Si, dans les dernières décennies, la politique française de l’eau s’est territorialisée, dans la mesure où elle est modelée par les spécificités locales, elle possède également une dimension territorialisante, dans le sens où elle conforte, défait ou modifie les territorialités existantes. Cette recherche pose l’hypothèse que l’efficacité environnementale de ces dispositifs de gestion locale des eaux dépend de la manière dont les acteurs qui les mettent en place se saisissent de leurs dimensions territoriales. Elle explore les stratégies territoriales déployées dans l’élaboration et la mise en ½uvre des projets de gestion de l’eau. Elle identifie et qualifie les différents ressorts territoriaux mobilisés et analyse leurs implications en termes de modification des représentations et des pratiques des usagers de l’eau et in fine de l’état environnemental des ressources et des milieux aquatiques. La démonstration s’appuie sur le cas empirique de la vallée de la Drôme, qui offre une intéressante perspective diachronique sur trois décennies avec la mise en ½uvre de deux contrats de rivière puis d’un SAGE, aujourd’hui en cours de révision. Les résultats de la recherche portent sur les mécanismes et les conditions par lesquels la gestion territoriale de l’eau peut être gage d’efficacité environnementale. Des facteurs déterminants sont mis en évidence : (i) la mise en synergie des projets de développement territorial avec ceux de la gestion de l’eau ; (ii) l’activation de ressorts territoriaux de type identitaire et (iii) les intentions et les capacités d’action de la gestion intentionnelle de l’eau. Les structures intercommunales présentent de bonnes dispositions pour activer et mobiliser les ressorts territoriaux de la gestion de l’eau en raison : (i) de leur taille moyenne et de leur position intermédiaire, qui leur permettent d’obtenir les moyens d’actions et les marges de man½uvre nécessaires à leurs projets auprès des partenaires supra-locaux tout en créant et conservant la confiance des usagers de l’eau et (ii) de leur double compétence en matière de développement territorial et dans le domaine environnemental. Au sein de ces structures, les binômes élu/ agent de développement constituent les moteurs d’activation des ressorts territoriaux de la gestion durable de l’eau

Comparison of Quadratic- and Median-Based Roughness Penalties for Penalized-Likelihood Sinogram Restoration in Computed Tomography

We have compared the performance of two different penalty choices for a penalized-likelihood sinogram-restoration strategy we have been developing. One is a quadratic penalty we have employed previously and the other is a new median-based penalty. We compared the approaches to a noniterative adaptive filter that loosely but not explicitly models data statistics. We found that the two approaches produced similar resolution-variance tradeoffs to each other and that they outperformed the adaptive filter in the low-dose regime, which suggests that the particular choice of penalty in our approach may be less important than the fact that we are explicitly modeling data statistics at all. Since the quadratic penalty allows for derivation of an algorithm that is guaranteed to monotonically increase the penalized-likelihood objective function, we find it to be preferable to the median-based penalty

Delocalization of slowly damped eigenmodes on Anosov manifolds

We look at the properties of high frequency eigenmodes for the damped wave equation on a compact manifold with an Anosov geodesic flow. We study eigenmodes with spectral parameters which are asymptotically close enough to the real axis. We prove that such modes cannot be completely localized on subsets satisfying a condition of negative topological pressure. As an application, one can deduce the existence of a "strip" of logarithmic size without eigenvalues below the real axis under this dynamical assumption on the set of undamped trajectories.Comment: 28 pages; compared with version 1, minor modifications, add two reference

\epsilon-regularity for systems involving non-local, antisymmetric operators

We prove an epsilon-regularity theorem for critical and super-critical systems with a non-local antisymmetric operator on the right-hand side. These systems contain as special cases, Euler-Lagrange equations of conformally invariant variational functionals as Rivi\`ere treated them, and also Euler-Lagrange equations of fractional harmonic maps introduced by Da Lio-Rivi\`ere. In particular, the arguments presented here give new and uniform proofs of the regularity results by Rivi\`ere, Rivi\`ere-Struwe, Da-Lio-Rivi\`ere, and also the integrability results by Sharp-Topping and Sharp, not discriminating between the classical local, and the non-local situations

Effects of Different Imaging Models on Least-Squares Image Reconstruction Accuracy in Photoacoustic Tomography

In the classic formulation of photoacoustic tomography (PAT), two distinct descriptions of the imaging model have been employed for developing reconstruction algorithms. We demonstrate that the numerical and statistical properties of unweighted least-squares reconstruction algorithms associated with each imaging model are generally very different. Specifically, some PAT reconstruction algorithms, including many of the iterative algorithms previously explored, do not work directly with the raw measured pressure wavefields, but rather with an integrated data function that is obtained by temporally integrating the photoacoustic wavefield. The integration modifies the statistical distribution of the data, introducing statistical correlations among samples. This change is highly significant for iterative algorithms, many of which explicitly or implicitly seek to minimize a statistical cost function. In this work, we demonstrate that iterative reconstruction by least-squares minimization yields better resolution-noise tradeoffs when working with the raw pressure data than with the integrated data commonly employed. In addition, we demonstrate that the raw-data based approach is less sensitive to certain deterministic errors, such as dc offset errors

Management and orientation of geriatric patients admitted to emergencies for a fall: results of the French prospective OREGoN cohort study

Falls in older adults are a frequent reason for admission to the emergency department, associated with greater morbidity and mortality risks, and justify specialized geriatric expertise. Our objective was to determine i) the number of older fallers admitted to the emergency department for a serious fall, and ii) the proportion of those who were referred to a geriatrician in the following 12 months. METHODS: We included all patients aged 75 and over admitted to the emergency department of the University hospital of Angers, France, for a fall between 1st October and 1st November 2015. The consensual criteria proposed by the French national authority for health (2009) were used to define serious falls. RESULTS: Of the 214 older fallers admitted to the emergency department, 213 (99.5%) had at least one severity criterion for the fall. Only 40 older patients (18.7%) were referred to a geriatrician during the following 12 months. They exhibited more frequently a post-fall syndrome (p=0.007), more than 3 fall risk factors (p <0.001), and took more often an anticoagulant (p=0.032) than those who had not been referred to a geriatrician. CONCLUSIONS: Although almost all older fallers admitted to the emergency room had experienced a serious fall, only a minority of them received a geriatric assessment in the following year

Enhancing high-order harmonic generation in light molecules by using chirped pulses

One of the current challenges in high-harmonic generation is to extend the harmonic cutoff to increasingly high energies while maintaining or even increasing the efficiency of the high-harmonic emission. Here we show that the combined effect of down-chirped pulses and nuclear dynamics in light molecules allows one to achieve this goal, provided that long enough IR pulses are used to allow the nuclei to move well outside the Franck-Condon region. We also show that, by varying the duration of the chirped pulse or by performing isotopic substitution while keeping the pulse duration constant, one can control the extension of the harmonic plateauWe gratefully acknowledge fruitful discussions with Y.Mairesse. This work has been accomplished with a generous allocation of computer time from Mare Nostrum BSC and CCC-UAM and has been partially supported by the European Research Council Advanced Grant No. XCHEM 290853, MINECO Project No. FIS2013-42002-R, ERA-Chemistry Project No. PIM2010EEC-00751, European Grant No. MC-ITN CORINF, European COST Action XLIC CM1204, and the CAM project NANOFRONTMAG. R. E. F. S. acknowledges FCT—Fundação para a Ciência e Tecnologia, Portugal, Grant No. SFRH/BD/84053/201

Cryogenic properties of optomechanical silica microcavities

We present the optical and mechanical properties of high-Q fused silica microtoroidal resonators at cryogenic temperatures (down to 1.6 K). A thermally induced optical multistability is observed and theoretically described; it serves to characterize quantitatively the static heating induced by light absorption. Moreover the influence of structural defect states in glass on the toroid mechanical properties is observed and the resulting implications of cavity optomechanical systems on the study of mechanical dissipation discussed.Comment: 4 pages, 3 figure