Controlled Sequential Monte Carlo

Sequential Monte Carlo methods, also known as particle methods, are a popular set of techniques for approximating high-dimensional probability distributions and their normalizing constants. These methods have found numerous applications in statistics and related fields; e.g. for inference in non-linear non-Gaussian state space models, and in complex static models. Like many Monte Carlo sampling schemes, they rely on proposal distributions which crucially impact their performance. We introduce here a class of controlled sequential Monte Carlo algorithms, where the proposal distributions are determined by approximating the solution to an associated optimal control problem using an iterative scheme. This method builds upon a number of existing algorithms in econometrics, physics, and statistics for inference in state space models, and generalizes these methods so as to accommodate complex static models. We provide a theoretical analysis concerning the fluctuation and stability of this methodology that also provides insight into the properties of related algorithms. We demonstrate significant gains over state-of-the-art methods at a fixed computational complexity on a variety of applications

Charged particle identification (PID) for SuperB

The proceedings of the conference will be published in the on-line journal "Proceedings of Science".International audienceCharged particle identification (PID) is a key input for the physics program of the SuperB experiment. In the barrel region, the main detector for K/$\pi$ separation will be the 'Focusing Detector of Internally Reflected Cherenkov light' (FDIRC), the successor of the successful BaBar DIRC, which camera has been completely re-designed. In addition, R&D is ongoing to add a detector on the forward side of SuperB to extend the PID coverage. This innovative time-of-flight detector will use new electronics accurate at the 10-ps level

Charmless hadronic B-decays at BABAR and BELLE

talk on behalf of BaBar and Belle CollaborationsInternational audienc

Analyse d'une conversation: Ouverture du stock de connaissance de la compétence collective

Le travail en groupe s\u27est largement développé ces dernières années. Hier clandestin, il est aujourd\u27hui mis en avant par les responsables d\u27entreprises comme source nouvelle de performance. Etudier la compétence collective, c\u27est, comme le considère Amherdt et al. (2000), s\u27intéresser plus largement à la coordination des activités par des individus lors de situations problématiques. La compétence collective est représentée comme un ensemble de ressources dans lequel vont puiser les acteurs des collectifs mobilisés. Si la compétence collective est un stock de manières d\u27agir, de comportements et de modes de pensé qui évoluent de manières processuelles au gré des interactions successives (fructueuses ou non), nous sommes en droit de nous demander quelles formes concrètes peuvent prendre ces ressources ? et comment sont-elles utilisées pour l\u27action par les acteurs ? Egalement, ces travaux, qui démontrent de manière tout à fait pertinente ce à quoi peut ressembler une compétence collective (représentation partagée, langage opératif commun, confiance), se font par ailleurs plus discrets sur leur dynamique de construction qui est, selon nous, d\u27ordre communicationnelle. En s\u27appuyant à la fois sur les travaux théoriques issus de l\u27approche communicationnelle des organisations (Cooren 2000, Taylor 1993b) et sur une méthodologique d\u27enquête basée le concept de situation (Journé et Raulet-Croset 2008), l\u27article développe l\u27analyse d\u27une conversation entre acteurs d\u27une équipe d\u27exploitants d\u27un important prestataire logistique du secteur de l\u27ameublement. Cette analyse permet d\u27ouvrir ce que nous nommons, en référence aux travaux de Berger et Luckman (1966), le « stock de connaissance » de la compétence collective. Nous démontrons au final que les éléments de ce stock (individus stigmatisés, plaisanteries rituelles, mode d\u27usage des outils de gestion) sont constitués dans et par la dynamique conversationnelle des acteurs. Loin de ne constituer qu\u27une description théorique, l\u27article dégage des éléments permettant d\u27articuler des propositions d\u27animation de ces collectifs

The SuperB Detector

The proceedings of the conference will be published in the on-line journal "Proceedings of Science".International audienceThe SuperB experiment is a next generation Super Flavour Factory expected to accumulate 75ab^-1 of data at the Y(4S) in five years of nominal running. In addition to running data at the Y(4S), SuperB will be able to accumulate data from the psi(3770) up to the Y(6S). A polarized electron beam enables unique physics opportunities at SuperB. We discuss the detector design for this new facility

A Chandra X-ray Study of Cygnus A - II. The Nucleus

We report Chandra ACIS and quasi-simultaneous RXTE observations of the nearby, powerful radio galaxy Cygnus A, with the present paper focusing on the properties of the active nucleus. In the Chandra observation, the hard (> a few keV) X-ray emission is spatially unresolved with a size \approxlt 1 arcsec (1.5 kpc, H_0 = 50 km s^-1 Mpc^-1) and coincides with the radio and near infrared nuclei. In contrast, the soft (< 2 keV) emission exhibits a bi-polar nebulosity that aligns with the optical bi-polar continuum and emission-line structures and approximately with the radio jet. In particular, the soft X-ray emission corresponds very well with the [O III] \lambda 5007 and H\alpha + [N II] \lambda\lambda 6548, 6583 nebulosity imaged with HST. At the location of the nucleus there is only weak soft X-ray emission, an effect that may be intrinsic or result from a dust lane that crosses the nucleus perpendicular to the source axis. The spectra of the various X-ray components have been obtained by simultaneous fits to the 6 detectors. The compact nucleus is detected to 100 keV and is well described by a heavily absorbed power law spectrum with \Gamma_h = 1.52^{+0.12}_{-0.12} (similar to other narrow line radio galaxies) and equivalent hydrogen column N_H (nuc) = 2.0^{+0.1}_{-0.2} \times 10^{23} cm^-2. (Abstract truncated).Comment: To be published in the Astrophysical Journal, v564 January 1, 2002 issue; 34 pages, 11 figures (1 color

Zoom sur la violation de CP à l'occasion des résultats obtenus par les expériences BABAR et BELLE

En août dernier, les expériences BABAR et Belle ont annoncé presque simultanément la découverte d'une « différence spectaculaire entre matière et antimatière ». Cette information a été immédiatement relayée sous forme de communiqués de presse avant d'être présentée à la Conférence Internationale de Physique des Hautes Energies (ICHEP 2004) à Pékin deux semaines plus tard

Hydrogen peroxide metabolism and functions in plants

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordH2 O2 is produced, via superoxide and superoxide dismutase, by electron transport in chloroplasts and mitochondria, plasma membrane NADPH oxidases, peroxisomal oxidases, type III peroxidases and other apoplastic oxidases. Intracellular transport is facilitated by aquaporins and H2 O2 is removed by catalase, peroxiredoxin, glutathione peroxidase-like enzymes and ascorbate peroxidase, all of which have cell compartment-specific isoforms. Apoplastic H2 O2 influences cell expansion, development and defence by its involvement in type III peroxidase-mediated polymer cross-linking, lignification and, possibly, cell expansion via H2 O2 -derived hydroxyl radicals. Excess H2 O2 triggers chloroplast and peroxisome autophagy and programmed cell death. The role of H2 O2 in signalling, for example during acclimation to stress and pathogen defence, has received much attention but the signal transduction mechanisms are poorly-defined. H2 O2 oxidises specific cysteine residues of target proteins to the sulfenic acid form and, similarly to other organisms, this modification could initiate thiol-based redox relays and modify target enzymes, receptor kinases and transcription factors. Quantification of the sources and sinks of H2 O2 is being improved by the spatial and temporal resolution of genetically-encoded H2 O2 sensors such as HyPer and roGFP2-Orp1. These H2 O2 sensors combined with detection of specific proteins modified by H2 O2 will allow deeper understanding of its signalling roles. This article is protected by copyright. All rights reserved.The Biotechnology and Biological Sciences Research Council provided funding for research on hydrogen peroxide signalling (BB/I020004/1 and BB/N001311/1)