Replica Conditional Sequential Monte Carlo

We propose a Markov chain Monte Carlo (MCMC) scheme to perform state inference in non-linear non-Gaussian state-space models. Current state-of-the-art methods to address this problem rely on particle MCMC techniques and its variants, such as the iterated conditional Sequential Monte Carlo (cSMC) scheme, which uses a Sequential Monte Carlo (SMC) type proposal within MCMC. A deficiency of standard SMC proposals is that they only use observations up to time $t$ to propose states at time $t$ when an entire observation sequence is available. More sophisticated SMC based on lookahead techniques could be used but they can be difficult to put in practice. We propose here replica cSMC where we build SMC proposals for one replica using information from the entire observation sequence by conditioning on the states of the other replicas. This approach is easily parallelizable and we demonstrate its excellent empirical performance when compared to the standard iterated cSMC scheme at fixed computational complexity.Comment: To appear in Proceedings of ICML '1

Observational Test of Coronal Magnetic Field Models I. Comparison with Potential Field Model

Recent advances have made it possible to obtain two-dimensional line-of-sight magnetic field maps of the solar corona from spectropolarimetric observations of the Fe XIII 1075 nm forbidden coronal emission line. Together with the linear polarization measurements that map the azimuthal direction of the coronal magnetic field, these coronal vector magnetograms now allow for direct observational testing of theoretical coronal magnetic field models. This paper presents a study testing the validity of potential-field coronal magnetic field models. We constructed a theoretical coronal magnetic field model of active region AR 10582 observed by the SOLARC coronagraph in 2004 by a global potential field extrapolation of the synoptic map of Carrington Rotation 2014. Synthesized linear and circular polarization maps from thin layers of the coronal magnetic field model above the active region along the line of sight are compared with the observed maps. We found that reasonable agreement occurs from layers located just above the sunspot of AR 10582, near the plane of the sky. This result provides the first observational evidence that potential field extrapolation can yield a reasonable approximation of the magnetic field configuration of the solar corona for simple and stable active regions.Comment: 25 pages, 11 figures. ApJ in pres

Stochastic Cahn-Hilliard equation with double singular nonlinearities and two reflections

We consider a stochastic partial differential equation with two logarithmic nonlinearities, with two reflections at 1 and -1 and with a constraint of conservation of the space average. The equation, driven by the derivative in space of a space-time white noise, contains a bi-Laplacian in the drift. The lack of the maximum principle for the bi-Laplacian generates difficulties for the classical penalization method, which uses a crucial monotonicity property. Being inspired by the works of Debussche, Gouden\`ege and Zambotti, we obtain existence and uniqueness of solution for initial conditions in the interval $(-1,1)$. Finally, we prove that the unique invariant measure is ergodic, and we give a result of exponential mixing

Pertinence d'une méthode de prédétermination des crues basée sur la simulation stochastique de pluies horaires.

International audienceExtreme events are rarely observed, so their analysis is generally based on observations of more frequent values. The relevance of flood frequency analysis (FFA) method depends on its capability to estimate the frequency of extreme values with reasonable accuracy using extrapolation. A FFA method based on stochastic simulation of flood event is assessed based on its reliability and stability. For such an assessment, different training/testing decompositions are performed for a set of data from more than 1,000 gauging stations. We showed that the method enables relevant "predictive" estimates, e.g. by assigning correct return periods to the record values that are systematically absent in calibration data sets. The model is also highly stable vis-a-vis the sampling. This characteristic is linked to the use of regional statistical rainfall data and a simple rainfall-runoff model that requires calibrating only one parameterLes événements extrêmes sont par nature rarement observés, c'est pourquoi leur estimation est généralement basée sur l'observation de valeurs plus courantes. La pertinence d'une méthode de prédétermination des événements extrêmes dépend donc de sa capacité à raisonnablement extrapoler les distributions de fréquences vers les valeurs extrêmes. Dans cette étude, une méthode de prédétermination de crues basée sur la simulation de scénarios de pluies horaires, est évaluée sur sa capacité à produire des estimations justes et stables. Cette évaluation s'appuie sur différents tests d'échantillonnage sur les périodes de calage et de validation, appliqués sur un jeu de données conséquent (plus de 1000 stations). Nous montrons que la méthode est capable de fournir une estimation pertinente sur les événements extrêmes bien que ceux-ci soit systématiquement ôtés de la période de calage. La méthode montre aussi une grande stabilité face à l'échantillonnage. Cette caractéristique est liée à l'utilisation d'une information statistique régionale sur la pluie et à la simplicité de la modélisation hydrologique paramétrée par un seul paramètre

Ram extrusion force for a frictional plastic material: model prediction and application to cement paste

the original publication is available at http://www.springerlink.com/content/pn3034u81144458g/International audienceWe developed a model to predict the ram extrusion force of frictional plastic materials such as cement-based pastes. The extrusion of cement-based materials has already been studied, but the interaction between shaping force and paste behaviour still have to be understood. Our model is based on the plastic frictional behaviour of cement-based materials and integrates the physical mechanisms that govern material extrusion flow and extrusion force increase. When the process starts, a pressure gradient is created in the extruder due to wall friction of the paste that is submitted to plug flow. It induces a consolidation of the material. As a result, a large increase of extrusion force appears. A Coulomb law is used to model cement-based materials, which is considered as consolidating granular media. Such modelling is compared with experimental results. Tests were carried out on extrudible cement pastes. Modelling and experimental results are in good agreement

Region-wide glacier mass balances over the Pamir-Karakoram-Himalaya during 1999-2011 (vol 7, pg 1263, 2013)

ISI Document Delivery No.: 273OY Times Cited: 0 Cited Reference Count: 1 Cited References: Gardelle J, 2013, CRYOSPHERE, V7, P1263, DOI 10.5194/tc-7-1263-2013 Gardelle, J. Berthier, E. Arnaud, Y. Kaab, A. 0 COPERNICUS GESELLSCHAFT MBH GOTTINGEN CRYOSPHEREThe recent evolution of Pamir-Karakoram- Himalaya (PKH) glaciers, widely acknowledged as valuable high-altitude as well as mid-latitude climatic indicators, remains poorly known. To estimate the regionwide glacier mass balance for 9 study sites spread from the Pamir to the Hengduan Shan (eastern Himalaya), we compared the 2000 Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) to recent (2008- 2011) DEMs derived from SPOT5 stereo imagery. During the last decade, the region-wide glacier mass balances were contrasted with moderate mass losses in the eastern and central Himalaya (−0.22±0.12mw.e. yr−1 to −0.33±0.14mw.e. yr−1) and larger losses in the western Himalaya (−0.45±0.13mw.e. yr−1). Recently reported slight mass gain or balanced mass budget of glaciers in the central Karakoram is confirmed for a larger area (+0.10±0.16mw.e. yr−1) and also observed for glaciers in the western Pamir (+0.14±0.13mw.e. yr−1). Thus, the "Karakoram anomaly" should be renamed the "Pamir- Karakoram anomaly", at least for the last decade. The overall mass balance of PKH glaciers, −0.14±0.08mw.e. yr−1, is two to three times less negative than the global average for glaciers distinct from the Greenland and Antarctic ice sheets. Together with recent studies using ICESat and GRACE data, DEM differencing confirms a contrasted pattern of glacier mass change in the PKH during the first decade of the 21st century

Caractérisation rhéologique et tribologique d'un matériau viscoplastique à l'aide d'un essai de back-extrusion

National audienceUne nouvelle méthode d'analyse rhéologique et tribologique est développée en exploitant l'écoulement de back-extrusion. L'utilisation des courbes "effort d'extrusion en fonction du déplacement du cylindre intérieur" permet d'identifier les caractéristiques rhéologiques et tribologiques du fluide testé à partir des résultats de tests réalisés avec différentes vitesses de pénétration du cylindre intérieur et différentes configurations géométriques. Dans le cadre de l'étude de fluides complexes incompressibles, tels que les fluides d'Herschell-Bulkley frottant, la méthode aboutit à la construction d'un rhéogramme équivalent tracé à partir d'essais caractérisés par différents taux de déformation moyens. Le comportement tribologique peut être identifié en modifiant les conditions de frottement à la paroi en variant la rugosité des surfaces. La méthode est appliquée aux cas de suspensions concentrées huile/sucre et plasticine. Les comportements rhéologiques et tribologiques sont identifiés et comparés aux résultats obtenus avec la rhéométrie traditionnelle

Termination of Electron Acceleration in Thundercloud by Intra/Inter-cloud Discharge

An on-ground observation program for high energy atmospheric phenomena in winter thunderstorms along Japan Sea has been performed via measurements of gamma-ray radiation, atmospheric electric field and low-frequency radio band. On February 11, 2017, the radiation detectors recorded gamma-ray emission lasting for 75 sec. The gamma-ray spectrum extended up to 20 MeV and was reproduced by a cutoff power-law model with a photon index of $1.36^{+0.03}_{-0.04}$, being consistent with a Bremsstrahlung radiation from a thundercloud (as known as a gamma-ray glow and a thunderstorm ground enhancement). Then the gamma-ray glow was abruptly terminated with a nearby lightning discharge. The low-frequency radio monitors, installed $\sim$50 km away from the gamma-ray observation site recorded leader development of an intra/inter-cloud discharge spreading over $\sim$60 km area with a $\sim$300 ms duration. The timing of the gamma-ray termination coincided with the moment when the leader development of the intra/inter-cloud discharge passed 0.7 km horizontally away from the radiation monitors. The intra/inter-cloud discharge started $\sim$15 km away from the gamma-ray observation site. Therefore, the glow was terminated by the leader development, while it did not trigger the lightning discharge in the present case.Comment: 12 pages, 4 figures, accepted for publication in Geophysical Research Letter