Search

Your search keyword '"University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)"' showing total 222 results
Start Over Author "University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)" Search Limiters Full Text
222 results on '"University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)"'

1. Regularized Contextual Bandits

Author

Fontaine, Xavier, Berthet, Quentin, Perchet, Vianney, Centre de Mathématiques et de Leurs Applications (CMLA), École normale supérieure - Cachan (ENS Cachan)-Centre National de la Recherche Scientifique (CNRS), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Criteo AI Lab, Criteo [Paris], and Fontaine, Xavier

Subjects
FOS: Computer and information sciences, Computer Science - Machine Learning, [MATH.MATH-OC] Mathematics [math]/Optimization and Control [math.OC], Machine Learning (stat.ML), [INFO.INFO-LG] Computer Science [cs]/Machine Learning [cs.LG], [STAT.ML] Statistics [stat]/Machine Learning [stat.ML], Machine Learning (cs.LG), [STAT.ML]Statistics [stat]/Machine Learning [stat.ML], [INFO.INFO-LG]Computer Science [cs]/Machine Learning [cs.LG], Statistics - Machine Learning, Optimization and Control (math.OC), FOS: Mathematics, [MATH.MATH-OC]Mathematics [math]/Optimization and Control [math.OC], Mathematics - Optimization and Control
Abstract

We consider the stochastic contextual bandit problem with additional regularization. The motivation comes from problems where the policy of the agent must be close to some baseline policy which is known to perform well on the task. To tackle this problem we use a nonparametric model and propose an algorithm splitting the context space into bins, and solving simultaneously - and independently - regularized multi-armed bandit instances on each bin. We derive slow and fast rates of convergence, depending on the unknown complexity of the problem. We also consider a new relevant margin condition to get problem-independent convergence rates, ending up in intermediate convergence rates interpolating between the aforementioned slow and fast rates., Comment: AISTATS 2019, 23 pages, 2 figures

Published
2019

2. Large time behavior of the Vlasov-Navier-Stokes system on the torus

Author

Iván Moyano, Ayman Moussa, Daniel Han-Kwan, Centre de Mathématiques Laurent Schwartz (CMLS), Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X), Laboratoire Jacques-Louis Lions (LJLL), Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), and ANR-19-CE40-0004,SALVE,Singularités dans des limites asymptotiques d'équations de Vlasov(2019)

Subjects
Physics, Mechanical Engineering, Dirac (video compression format), 010102 general mathematics, Mathematical analysis, Complex system, Structure (category theory), Mathematics::Analysis of PDEs, Torus, Type (model theory), 01 natural sciences, Exponential function, 010101 applied mathematics, Mathematics (miscellaneous), Distribution function, Mathematics - Analysis of PDEs, FOS: Mathematics, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], 0101 mathematics, Analysis, Energy (signal processing), Analysis of PDEs (math.AP)
Abstract

International audience; We study the large time behavior of Fujita–Kato type solutions to the Vlasov–Navier–Stokes system set on $\T^3 \times \R^3$. Under the assumption that the initial so-called modulated energy is small enough, we prove that the distribution function converges to a Dirac mass in velocity, with exponential rate. The proof is based on the fine structure of the system and on a bootstrap analysis allowing us to get global bounds on moments.

Published
2019

3. Spectral Inequalities for the Schrödinger operator

Author

Lebeau, Gilles, Moyano, Iván, Laboratoire Jean Alexandre Dieudonné (JAD), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), and University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)

Subjects
Mathematics - Analysis of PDEs, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], Mathematics::Spectral Theory
Abstract

In this paper we deal with the so-called "spectral inequalities", which yield a sharp quantification of the unique continuation for the spectral family associated with the Schr\"odinger operator in $ \mathbb{R}^d$ \begin{equation*} H_{g,V} = \Delta_g + V(x), \end{equation*} where $\Delta_g$ is the Laplace-Beltrami operator with respect to an analytic metric $g$, which is a perturbation of the Euclidean metric, and $V(x)$ a real valued analytic potential vanishing at infinity.

Published
2019

4. Quantitative Rates of Convergence to Equilibrium for the Degenerate Linear Boltzmann equation on the Torus

Author

Evans, Josephine, Moyano, Iván, CEntre de REcherches en MAthématiques de la DEcision (CEREMADE), Centre National de la Recherche Scientifique (CNRS)-Université Paris Dauphine-PSL, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), and ANR-17-CE40-0030,EFI,Entropie, flots, inégalités(2017)

Subjects
Mathematics - Analysis of PDEs, Probability (math.PR), FOS: Mathematics, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], FOS: Physical sciences, Mathematical Physics (math-ph), [MATH]Mathematics [math], Mathematical Physics, Mathematics - Probability, Analysis of PDEs (math.AP)
Abstract

We study the linear relaxation Boltzmann equation on the torus with a spatially varying jump rate which can be zero on large sections of the domain. In \cite{BS13} Bernard and Salvarani showed that this equation converges exponentially fast to equilibrium if and only if the jump rate satisfies the geometric control condition of Bardos, Lebeau and Rauch \cite{BLR91}. In \cite{HL15} Han-Kwan and L\'{e}autaud showed a more general result for linear Boltzmann equations under the action of potentials in different geometric contexts, including the case of unbounded velocities. In this paper we obtain quantitative rates of convergence to equilibrium when the geometric control condition is satisfied, using a probabilistic approach based on Doeblin's theorem from Markov chains., Comment: 22 pages

Published
2019
Full Text
View/download PDF

5. (dual-frequency)-dependent dynamic functional connectivity analysis of visual working memory capacity

Author

John Aston, Dominique Dehay, Dudek, Anna E., Jean-Marc Freyermuth, Denes Szucs, Lincoln Colling, Freyermuth, Jean-Marc, University of Cambridge [UK] (CAM), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Institut de Recherche Mathématique de Rennes (IRMAR), AGROCAMPUS OUEST, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-École normale supérieure - Rennes (ENS Rennes)-Centre National de la Recherche Scientifique (CNRS)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), AGH University of Science and Technology [Krakow, PL] (AGH UST), Aix Marseille Université (AMU), Institut de Mathématiques de Marseille (I2M), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-École normale supérieure - Rennes (ENS Rennes)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-INSTITUT AGRO Agrocampus Ouest, and Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)

Subjects
[MATH.MATH-ST]Mathematics [math]/Statistics [math.ST], [MATH.MATH-ST] Mathematics [math]/Statistics [math.ST]
Published
2019

6. Comparison between five acellular oxidative potential measurement assays performed with detailed chemistry on PM10 samples from the city of Chamonix (France)

Author

Calas , Aude, Uzu , Gaëlle, Kelly , Frank, Houdier , Stephan, Martins , Jean, Thomas , Fabrice, Molton , Florian, CHARRON , Aurélie, Dunster , Christina, Oliete , Ana, Jacob , Véronique, Besombes , Jean-Luc, Chevrier , Florie, Jaffrezo , Jean-Luc, Institut des Géosciences de l’Environnement (IGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut de Recherche pour le Développement (IRD)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), MRC -PHE Centre for Environment & Health, Département de Chimie Moléculaire - Chimie Inorganique Redox Biomimétique (DCM - CIRE ), Département de Chimie Moléculaire (DCM), Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Institut Français des Sciences des Transports, de l'Aménagement et des Réseaux (IFSSTAR), IFSSTAR, Laboratoire de Chimie Moléculaire et Environnement (LCME), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry]), Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Département de Chimie Moléculaire - Chimie Inorganique Redox (DCM - CIRE ), Laboratoire Ecologie Fonctionnelle et Environnement (ECOLAB), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Laboratoire Transports et Environnement (IFSTTAR/AME/LTE), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Université de Lyon, Institut des Géosciences de l’Environnement ( IGE ), Institut de Recherche pour le Développement ( IRD ) -Institut polytechnique de Grenoble - Grenoble Institute of Technology ( Grenoble INP ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ) -Université Grenoble Alpes ( UGA ), Département de Chimie Moléculaire - Chimie Inorganique Redox Biomimétique ( DCM - CIRE ), Université Joseph Fourier - Grenoble 1 ( UJF ) -Institut de Chimie Moléculaire de Grenoble (ICMG)-Centre National de la Recherche Scientifique ( CNRS ), Département de Chimie Moléculaire ( DCM ), Université Joseph Fourier - Grenoble 1 ( UJF ) -Centre National de la Recherche Scientifique ( CNRS ) -Université Grenoble Alpes ( UGA ), Institut Français des Sciences des Transports, de l'Aménagement et des Réseaux ( IFSSTAR ), Laboratoire de Chimie Moléculaire et Environnement ( LCME ), Université Grenoble Alpes [Saint Martin d'Hères]-Université Savoie Mont Blanc ( USMB [Université de Savoie] [Université de Chambéry] ), Laboratoire Ecologie Fonctionnelle et Environnement (LEFE), Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), and Université de Toulouse (UT)

Subjects
[ SDE ] Environmental Sciences, [SDE]Environmental Sciences, [CHIM]Chemical Sciences, [ CHIM ] Chemical Sciences, GEOF
Abstract

International audience; Many studies have demonstrated associations between exposure to ambient particulate matter (PM) and adverse health outcomes in humans that can be explained by PM capacity to induce oxidative stress in vivo. Thus, assays have been developed to quantify the oxidative potential (OP) of PM as a more refined exposure metric than PM mass alone. Only a small number of studies have compared different acellular OP measurements for a given set of ambient PM samples. Yet, fewer studies have compared different assays over a year-long period and with detailed chemical characterization of ambient PM. In this study, we report on seasonal variations of the dithiothreitol (DTT), ascorbic acid (AA), electron spin resonance (ESR) and the respiratory tract lining fluid (RTLF, composed of the reduced glutathione (GSH) and ascorbic acid (ASC)) assays over a 1-year period in which 100 samples were analyzed. A detailed PM 10 characterization allowed univariate and multivariate regression analyses in order to obtain further insight into groups of chemical species that drive OP measurements. Our results show that most of the OP assays were strongly intercorrelated over the sampling year but also these correlations differed when considering specific sampling periods (cold vs. warm). All acellular assays are correlated with a significant number of chemical species when considering univariate correlations , especially for the DTT assay. Evidence is also presented of a seasonal contrast over the sampling period with significantly higher OP values during winter for the DTT, AA, GSH and ASC assays, which were assigned to biomass burning species by the multiple linear regression models. The ESR assay clearly differs from the other tests as it did not show seasonal dynamics and presented weaker correlations with other assays and chemical species.

Published
2018

7. Diffusion in small time in incomplete sub-Riemannian manifolds

Author

Bailleul, Ismael, Norris, James, Institut de Recherche Mathématique de Rennes (IRMAR), AGROCAMPUS OUEST, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-École normale supérieure - Rennes (ENS Rennes)-Centre National de la Recherche Scientifique (CNRS)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Apollo - University of Cambridge Repository, INSTITUT AGRO Agrocampus Ouest, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Rennes (ENS Rennes)-Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-École normale supérieure - Rennes (ENS Rennes)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-INSTITUT AGRO Agrocampus Ouest, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), ANR-16-CE40-0020,SINGULAR,Equations aux dérivées partielles singulières(2016), Division of Medical Chemistry and Natural Products, UNC Eshelman School of Pharmacy, and Center for Integrative Chemical Biology and Drug Discovery

Subjects
Mathematics - Differential Geometry, Numerical Analysis, Applied Mathematics, diffusion, Probability (math.PR), sub-Riemannian, [MATH.MATH-PR]Mathematics [math]/Probability [math.PR], Mathematics - Analysis of PDEs, Differential Geometry (math.DG), [MATH.MATH-DG]Mathematics [math]/Differential Geometry [math.DG], heat kernel, FOS: Mathematics, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], [MATH]Mathematics [math], Mathematics - Probability, Analysis, Analysis of PDEs (math.AP)
Abstract

For incomplete sub-Riemannian manifolds, and for an associated second-order hypoelliptic operator, which need not be symmetric, we identify two alternative conditions for the validity of Gaussian-type upper bounds on heat kernels and transition probabilities, with optimal constant in the exponent. Under similar conditions, we obtain the small-time logarithmic asymptotics of the heat kernel, and show concentration of diffusion bridge measures near a path of minimal energy. The first condition requires that we consider points whose distance apart is no greater than the sum of their distances to infinity. The second condition requires only that the operator not be too asymmetric., Comment: Accepted version

Published
2018
Full Text
View/download PDF

8. Fast and stable schemes for non-linear osmosis filtering

Author

Calatroni, L., Morigi, S., Parisotto, S., Recupero, G. A., Morphologie et Images (MORPHEME), Inria Sophia Antipolis - Méditerranée (CRISAM), Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria)-Institut de Biologie Valrose (IBV), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Université Côte d'Azur (UCA)-Signal, Images et Systèmes (Laboratoire I3S - SIS), Laboratoire d'Informatique, Signaux, et Systèmes de Sophia Antipolis (I3S), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Université Côte d'Azur (UCA)-Laboratoire d'Informatique, Signaux, et Systèmes de Sophia Antipolis (I3S), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Dipartimento di Matematica [Bologna], Alma Mater Studiorum Università di Bologna [Bologna] (UNIBO), Department of Applied Mathematics and Theoretical Physics [Cambridge] (DAMTP), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), and University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)

Subjects
Computational Mathematics, Computational Theory and Mathematics, [INFO.INFO-TI]Computer Science [cs]/Image Processing [eess.IV], Modeling and Simulation, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], Mathematics - Numerical Analysis, [MATH.MATH-OC]Mathematics [math]/Optimization and Control [math.OC], 68U10, 94A08, 49K20, 65M05, [MATH.MATH-NA]Mathematics [math]/Numerical Analysis [math.NA]
Abstract

We consider a non-linear variant of the transport-diffusion osmosis model for solving a variety of imaging problems such as shadow/soft-light removal and compact data representation. The non-linear behaviour is encoded in terms of a general scalar function g with suitable properties, which allows to balance the diffusion intensity on the different regions of the image while preventing smoothing artefacts. For the proposed model, conservation properties (intensity and non-negativity) are proved and a variational interpretation is showed for specific choices of g. Upon suitable spatial discretisation, both an explicit and a semi-implicit iterative scheme are considered, for which convergence restrictions and unconditional stability are proved, respectively. To validate the proposed modelling and the computational speed of the numerical schemes considered, we report several results and comparisons for the problem of shadow/light-spot removal and compact data representation, showing that artefact-free and computationally efficient results are obtained in comparison to standard linear and anisotropic models, and state-of-the art approaches., Comment: 25 pages, 14 figures

Published
2023

9. Uniform Stability of a Particle Approximation of the Optimal Filter Derivative

Author

Arnaud Doucet, Sumeetpal S. Singh, Pierre Del Moral, Department of Statistics [Oxford], University of Oxford [Oxford], Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Advanced Learning Evolutionary Algorithms (ALEA), Inria Bordeaux - Sud-Ouest, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria)-Université de Bordeaux (UB)-Centre National de la Recherche Scientifique (CNRS), Institut de Mathématiques de Bordeaux (IMB), Université Bordeaux Segalen - Bordeaux 2-Université Sciences et Technologies - Bordeaux 1-Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux (Bordeaux INP)-Centre National de la Recherche Scientifique (CNRS), Dept of Statistics & Dept of Computer Science, University of British Columbia (UBC), University of Cambridge [UK] (CAM), Inria & Labri, Univ. Bordeaux, Apollo - University of Cambridge Repository, and Université Bordeaux Segalen - Bordeaux 2-Université Sciences et Technologies - Bordeaux 1 (UB)-Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux (Bordeaux INP)-Centre National de la Recherche Scientifique (CNRS)

Subjects
FOS: Computer and information sciences, Control and Optimization, Mathematics - Statistics Theory, Statistics Theory (math.ST), Derivative, sequential Monte Carlo, state-space models, Statistics - Computation, Stability (probability), Methodology (stat.ME), FOS: Mathematics, recursive maximum likelihood, Applied mathematics, Computation (stat.CO), Statistics - Methodology, ComputingMilieux_MISCELLANEOUS, Mathematics, [STAT.AP]Statistics [stat]/Applications [stat.AP], Signal processing, hidden Markov models, Estimation theory, Applied Mathematics, smoothing, Filter (signal processing), Statistics::Computation, [MATH.MATH-PR]Mathematics [math]/Probability [math.PR], Nonlinear system, filter derivative, Particle filter, Smoothing
Abstract

Sequential Monte Carlo methods, also known as particle methods, are a widely used set of computational tools for inference in non-linear non-Gaussian state-space models. In many applications it may be necessary to compute the sensitivity, or derivative, of the optimal filter with respect to the static parameters of the state-space model; for instance, in order to obtain maximum likelihood model parameters of interest, or to compute the optimal controller in an optimal control problem. In Poyiadjis et al. [2011] an original particle algorithm to compute the filter derivative was proposed and it was shown using numerical examples that the particle estimate was numerically stable in the sense that it did not deteriorate over time. In this paper we substantiate this claim with a detailed theoretical study. Lp bounds and a central limit theorem for this particle approximation of the filter derivative are presented. It is further shown that under mixing conditions these Lp bounds and the asymptotic variance characterized by the central limit theorem are uniformly bounded with respect to the time index. We demon- strate the performance predicted by theory with several numerical examples. We also use the particle approximation of the filter derivative to perform online maximum likelihood parameter estimation for a stochastic volatility model.

Published
2015

10. Genetic Depletion or Hyperresponsiveness of Natural Killer Cells Do Not Affect Atherosclerosis Development

Author

Patrick Bruneval, Alain Tedgui, Eric Vivier, Ziad Mallat, Hafid Ait-Oufella, Kazem Zibara, Jérémie Joffre, Andreas Giraud, Megumi Terada, José Vilar, Lynda Zeboudj, Bruno Esposito, Sophie Ugolini, Wared Nour-Eldine, Paris-Centre de Recherche Cardiovasculaire (PARCC - UMR-S U970), Hôpital Européen Georges Pompidou [APHP] (HEGP), Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-Hôpitaux Universitaires Paris Ouest - Hôpitaux Universitaires Île de France Ouest (HUPO)-Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-Hôpitaux Universitaires Paris Ouest - Hôpitaux Universitaires Île de France Ouest (HUPO)-Université Paris Descartes - Paris 5 (UPD5)-Institut National de la Santé et de la Recherche Médicale (INSERM), Laboratory of Stem Cells [Lebanese, Beirut] (ER045-PRASE), Lebanese University [Beirut] (LU), Biology Department [Beirut, Lebanon], Lebanese University [Beirut] (LU)-Faculty of Sciences-I [Beirut, Lebanon], Département d'Anatomopathologie [AP-HP HEGP], Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-Hôpitaux Universitaires Paris Ouest - Hôpitaux Universitaires Île de France Ouest (HUPO)-Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-Hôpitaux Universitaires Paris Ouest - Hôpitaux Universitaires Île de France Ouest (HUPO), Centre d'Immunologie de Marseille - Luminy (CIML), Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU), Department of Medicine [Cambridge, U.K.], Division of Cardiovascular Medicine [Cambridge, U.K.], University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), This work was supported by Inserm, the Fondation pour la Recherche Medicale, CNRS (EV, SU), and Aix-Marseille University (EV, SU)., Paris-Centre de Recherche Cardiovasculaire (PARCC - U970), Hôpital Européen Georges Pompidou [APHP] (HEGP) - Université Paris Descartes - Paris 5 (UPD5) - Institut National de la Santé et de la Recherche Médicale (INSERM), Lebanese University [Beirut], Lebanese University [Beirut] - Faculty of Sciences-I [Beirut, Lebanon], Institut National de la Santé et de la Recherche Médicale (INSERM) - Aix Marseille Université (AMU) - Centre National de la Recherche Scientifique (CNRS), University of Cambridge [UK] (CAM) - University of Cambridge [UK] (CAM), Aix Marseille Université (AMU)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), Mallat, Ziad [0000-0003-0443-7878], and Apollo - University of Cambridge Repository

Subjects
Male, 0301 basic medicine, mice, Physiology, Mice, Transgenic, Inflammation, 030204 cardiovascular system & hematology, Biology, Article, natural killer cells, 03 medical and health sciences, Interleukin 21, 0302 clinical medicine, Immune system, [SDV.MHEP.CSC]Life Sciences [q-bio]/Human health and pathology/Cardiology and cardiovascular system, medicine, Animals, Cells, Cultured, Mice, Knockout, Janus kinase 3, Natural killer T cell, Atherosclerosis, [SDV.MHEP.CSC] Life Sciences [q-bio]/Human health and pathology/Cardiology and cardiovascular system, macrophages, Killer Cells, Natural, Mice, Inbred C57BL, immune system, 030104 developmental biology, medicine.anatomical_structure, inflammation, Immunology, Interleukin 12, Bone marrow, medicine.symptom, Cardiology and Cardiovascular Medicine, Gene Deletion, CD8
Abstract

Rationale: Chronic inflammation is central in the development of atherosclerosis. Both innate and adaptive immunities are involved. Although several studies have evaluated the functions of natural killer (NK) cells in experimental animal models of atherosclerosis, it is not yet clear whether NK cells behave as protective or proatherogenic effectors. One of the main caveats of previous studies was the lack of specificity in targeting loss or gain of function of NK cells. Objectives: We used 2 selective genetic approaches to investigate the role of NK cells in atherosclerosis: (1) Ncr1 iCre/+ R26 lsl− DTA/+ mice in which NK cells were depleted and (2) Noé mice in which NK cells are hyperresponsive. Methods and Results: No difference in atherosclerotic lesion size was found in Ldlr −/− (low-density lipoprotein receptor null) mice transplanted with bone marrow (BM) cells from Ncr1 iCre R26R lsl− DTA , Noé , or wild-type mice. Also, no difference was observed in plaque composition in terms of collagen content, macrophage infiltration, or the immune profile, although Noé chimera had more IFN (interferon)-γ–producing NK cells, compared with wild-type mice. Then, we investigated the NK-cell selectivity of anti–asialoganglioside M1 antiserum, which was previously used to conclude the proatherogenicity of NK cells. Anti–asialoganglioside M1 treatment decreased atherosclerosis in both Ldlr −/− mice transplanted with Ncr1 iCre R26R lsl− DTA or wild-type bone marrow, indicating that its antiatherogenic effects are unrelated to NK-cell depletion, but to CD8 + T and NKT cells. Finally, to determine whether NK cells could contribute to the disease in conditions of pathological NK-cell overactivation, we treated irradiated Ldlr −/− mice reconstituted with either wild-type or Ncr1 iCre R26R lsl− DTA bone marrow with the viral mimic polyinosinic:polycytidylic acid and found a significant reduction of plaque size in NK-cell–deficient chimeric mice. Conclusions: Our findings, using state-of-the-art mouse models, demonstrate that NK cells have no direct effect on the natural development of hypercholesterolemia-induced atherosclerosis, but may play a role when an additional systemic NK-cell overactivation occurs.

Published
2017

11. Lozenge tiling dynamics and convergence to the hydrodynamic equation

Author

Benoit Laslier, Fabio Lucio Toninelli, University of Cambridge [UK] (CAM), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Probabilités, statistique, physique mathématique (PSPM), Institut Camille Jordan [Villeurbanne] (ICJ), École Centrale de Lyon (ECL), Université de Lyon-Université de Lyon-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université Jean Monnet [Saint-Étienne] (UJM)-Institut National des Sciences Appliquées de Lyon (INSA Lyon), Université de Lyon-Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS)-École Centrale de Lyon (ECL), Université de Lyon-Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS), CNRS PICS grant 'Interfaces al ́eatoires discr`etes et dy-namiques de Glauber, and ANR-15-CE40-0020,LSD,Modèles stochastiques en grande dimension pour la physique statistique hors équilibre(2015)

Subjects
Physics, 010102 general mathematics, Probability (math.PR), Inverse, Statistical and Nonlinear Physics, Function (mathematics), 01 natural sciences, Parabolic partial differential equation, Projection (linear algebra), [MATH.MATH-PR]Mathematics [math]/Probability [math.PR], 010104 statistics & probability, Bernoulli's principle, FOS: Mathematics, Heat equation, Differentiable function, 0101 mathematics, Langevin dynamics, Mathematical Physics, ComputingMilieux_MISCELLANEOUS, Mathematics - Probability, Mathematical physics
Abstract

We study a reversible continuous-time Markov dynamics of a discrete $(2+1)$-dimensional interface. This can be alternatively viewed as a dynamics of lozenge tilings of the $L\times L$ torus, or as a conservative dynamics for a two-dimensional system of interlaced particles. The particle interlacement constraints imply that the equilibrium measures are far from being product Bernoulli: particle correlations decay like the inverse distance squared and interface height fluctuations behave on large scales like a massless Gaussian field. We consider a particular choice of the transition rates, originally proposed in [Luby-Randall-Sinclair]: in terms of interlaced particles, a particle jump of length $n$ that preserves the interlacement constraints has rate $1/(2n)$. This dynamics presents special features: the average mutual volume between two interface configurations decreases with time and a certain one-dimensional projection of the dynamics is described by the heat equation. In this work we prove a hydrodynamic limit: after a diffusive rescaling of time and space, the height function evolution tends as $L\to\infty$ to the solution of a non-linear parabolic PDE. The initial profile is assumed to be $C^2$ differentiable and to contain no "frozen region". The explicit form of the PDE was recently conjectured on the basis of local equilibrium considerations. In contrast with the hydrodynamic equation for the Langevin dynamics of the Ginzburg-Landau model [Funaki-Spohn,Nishikawa], here the mobility coefficient turns out to be a non-trivial function of the interface slope., Comment: 35 pages, 7 figures. v3: a few more typos corrected, remark 2.8 added. To appear on Comm. Math. Phys

Published
2017
Full Text
View/download PDF

12. Diffusivity of a random walk on random walks

Author

Serge Cohen, Thibault Espinasse, James Norris, Emmanuel Boissard, Institut de Mathématiques de Toulouse UMR5219 (IMT), Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse - Jean Jaurès (UT2J)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Université Toulouse Capitole (UT Capitole), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut National des Sciences Appliquées (INSA)-Université Toulouse - Jean Jaurès (UT2J), Université de Toulouse (UT)-Université Toulouse III - Paul Sabatier (UT3), and Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Random graph, Discrete mathematics, Heterogeneous random walk in one dimension, Applied Mathematics, General Mathematics, Probability (math.PR), Central limit theorem, Loop-erased random walk, Random element, Random walk, 05C81, 60F05, Computer Graphics and Computer-Aided Design, Graph, [MATH.MATH-PR]Mathematics [math]/Probability [math.PR], Combinatorics, Mathematics::Probability, Lévy flight, FOS: Mathematics, Quantum walk, Mathematics - Probability, ComputingMilieux_MISCELLANEOUS, Software, Self-avoiding walk, Mathematics
Abstract

We consider a random walk Zn1,',ZnK+1∈i¾?K+1 with the constraint that each coordinate of the walk is at distance one from the following one. In this paper, we show that this random walk is slowed down by a variance factor i¾?K2=2K+2 with respect to the case of the classical simple random walk without constraint. © 2014 Wiley Periodicals, Inc. Random Struct. Alg., 47, 267-283, 2015

Published
2014

13. Multimodel climate and variability of the stratosphere

Author

Darryn W. Waugh, Steven Pawson, Paul J. Kushner, N. Butchart, Judith Perlwitz, Hella Garny, Eugene Rozanov, A. J. G. Baumgaertner, Rolando R. Garcia, Kiyotaka Shibata, Lei Wang, John A. Pyle, Veronika Eyring, Kirstin Krüger, Marion Marchand, Scott Osprey, Steven C. Hardiman, Jean-Francois Lamarque, John Austin, Ch. Brühl, Martine Michou, H. Teyssèdre, Paul A. Newman, David A. Plummer, Tetsu Nakamura, Hideharu Akiyoshi, Slimane Bekki, Peter H. Haynes, Sandip Dhomse, Dan Smale, Olaf Morgenstern, Martyn P. Chipperfield, Patrick Jöckel, Martin Dameris, P. Braesicke, Theodore G. Shepherd, W. Tian, Andrew Charlton-Perez, Yousuke Yamashita, Irene Cionni, Michael Sigmond, John F. Scinocca, Met Office Hadley Centre for Climate Change (MOHC), United Kingdom Met Office [Exeter], Department of Meteorology [Reading], University of Reading (UOR), DLR Institut für Physik der Atmosphäre (IPA), Deutsches Zentrum für Luft- und Raumfahrt [Oberpfaffenhofen-Wessling] (DLR), NCAS-Climate [Cambridge], Department of Chemistry [Cambridge, UK], University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Leibniz-Institut für Meereswissenschaften (IFM-GEOMAR), Department of Physics [Toronto], University of Toronto, NASA Goddard Space Flight Center (GSFC), Department of Atmospheric, Oceanic and Planetary Physics [Oxford] (AOPP), University of Oxford, Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado [Boulder]-National Oceanic and Atmospheric Administration (NOAA), National Institute for Environmental Studies (NIES), NOAA Geophysical Fluid Dynamics Laboratory (GFDL), National Oceanic and Atmospheric Administration (NOAA), University Corporation for Atmospheric Research (UCAR), STRATO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Max Planck Institute for Chemistry (MPIC), Max-Planck-Gesellschaft, School of Earth and Environment [Leeds] (SEE), University of Leeds, National Center for Atmospheric Research [Boulder] (NCAR), Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), National Institute of Water and Atmospheric Research [Lauder] (NIWA), Canadian Centre for Climate Modelling and Analysis (CCCma), Environment and Climate Change Canada, Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center (PMOD/WRC), Meteorological Research Institute [Tsukuba] (MRI), Japan Meteorological Agency (JMA), Johns Hopkins University (JHU), Met Office Hadley Centre ( MOHC ), University of Reading ( UOR ), DLR Institut für Physik der Atmosphäre ( IPA ), Deutsches Zentrum für Luft- und Raumfahrt [Oberpfaffenhofen-Wessling] ( DLR ), University of Cambridge [UK] ( CAM ) -University of Cambridge [UK] ( CAM ), Leibniz-Institut für Meereswissenschaften ( IFM-GEOMAR ), NASA Goddard Space Flight Center ( GSFC ), Department of Atmospheric, Oceanic and Planetary Physics [Oxford] ( AOPP ), University of Oxford [Oxford], Cooperative Institute for Research in Environmental Sciences ( CIRES ), University of Colorado Boulder [Boulder]-National Oceanic and Atmospheric Administration ( NOAA ), National Institute for Environmental Studies ( NIES ), NOAA Geophysical Fluid Dynamics Laboratory ( GFDL ), National Oceanic and Atmospheric Administration ( NOAA ), University Corporation for Atmospheric Research ( UCAR ), SHTI - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales ( LATMOS ), Université de Versailles Saint-Quentin-en-Yvelines ( UVSQ ) -Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ) -Université de Versailles Saint-Quentin-en-Yvelines ( UVSQ ) -Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ), Max Planck Institute for Chemistry ( MPIC ), School of Earth and Environment [Leeds] ( SEE ), National Center for Atmospheric Research [Boulder] ( NCAR ), Groupe d'étude de l'atmosphère météorologique ( CNRM-GAME ), Institut national des sciences de l'Univers ( INSU - CNRS ) -Météo France-Centre National de la Recherche Scientifique ( CNRS ), National Institute of Water and Atmospheric Research [Lauder] ( NIWA ), Canadian Centre for Climate Modelling and Analysis ( CCCma ), Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center ( PMOD/WRC ), Meteorological Research Institute [Tsukuba] ( MRI ), Japan Meteorological Agency ( JMA ), Johns Hopkins University ( JHU ), Groupe d'étude de l'atmosphère météorologique (CNRM-GAME), and Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS)

Subjects
quasi-biennial oscillation, Atmospheric Science, polar night jet, 010504 meteorology & atmospheric sciences, Soil Science, Aquatic Science, Sudden stratospheric warming, 010502 geochemistry & geophysics, Oceanography, Atmospheric sciences, 01 natural sciences, Geochemistry and Petrology, Polar vortex, Earth and Planetary Sciences (miscellaneous), General circulation model, Southern Hemisphere, Stratosphere, 0105 earth and related environmental sciences, Earth-Surface Processes, Water Science and Technology, [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph], Ecology, Polar night, Northern Hemisphere, Paleontology, Forestry, Jet stream, stratospheric warmings, Geophysics, [ PHYS.PHYS.PHYS-AO-PH ] Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph], 13. Climate action, Space and Planetary Science, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, Climatology, Environmental science, Polar, Dynamik der Atmosphäre, Stratospheric climate
Abstract

The stratospheric climate and variability from simulations of sixteen chemistry-climate models is evaluated. On average the polar night jet is well reproduced though its variability is less well reproduced with a large spread between models. Polar temperature biases are less than 5 K except in the Southern Hemisphere (SH) lower stratosphere in spring. The accumulated area of low temperatures responsible for polar stratospheric cloud formation is accurately reproduced for the Antarctic but underestimated for the Arctic. The shape and position of the polar vortex is well simulated, as is the tropical upwelling in the lower stratosphere. There is a wide model spread in the frequency of major sudden stratospheric warnings (SSWs), late biases in the breakup of the SH vortex, and a weak annual cycle in the zonal wind in the tropical upper stratosphere. Quantitatively, "metrics" indicate a wide spread in model performance for most diagnostics with systematic biases in many, and poorer performance in the SH than in the Northern Hemisphere (NH). Correlations were found in the SH between errors in the final warming, polar temperatures, the leading mode of variability, and jet strength, and in the NH between errors in polar temperatures, frequency of major SSWs, and jet strength. Models with a stronger QBO have stronger tropical upwelling and a colder NH vortex. Both the qualitative and quantitative analysis indicate a number of common and long-standing model problems, particularly related to the simulation of the SH and stratospheric variability. Copyright 2011 by the American Geophysical Union.

Published
2016

14. Hydrodynamic limit equation for a lozenge tiling Glauber dynamics

Author

Benoît Laslier, Fabio Lucio Toninelli, University of Cambridge [UK] (CAM), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Institut Camille Jordan [Villeurbanne] (ICJ), École Centrale de Lyon (ECL), Université de Lyon-Université de Lyon-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université Jean Monnet [Saint-Étienne] (UJM)-Institut National des Sciences Appliquées de Lyon (INSA Lyon), Université de Lyon-Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS), Probabilités, statistique, physique mathématique (PSPM), and Université de Lyon-Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS)-École Centrale de Lyon (ECL)

Subjects
Physics, Nuclear and High Energy Physics, Markov chain, Plane (geometry), Probability (math.PR), 010102 general mathematics, Mathematical analysis, FOS: Physical sciences, Statistical and Nonlinear Physics, Hamming distance, Mathematical Physics (math-ph), 01 natural sciences, Parabolic partial differential equation, Square (algebra), [MATH.MATH-PR]Mathematics [math]/Probability [math.PR], Nonlinear system, 0103 physical sciences, FOS: Mathematics, 010307 mathematical physics, Limit (mathematics), 0101 mathematics, Balanced flow, ComputingMilieux_MISCELLANEOUS, Mathematics - Probability, Mathematical Physics
Abstract

We study a reversible continuous-time Markov dynamics on lozenge tilings of the plane, introduced by Luby et al. Single updates consist in concatenations of $n$ elementary lozenge rotations at adjacent vertices. The dynamics can also be seen as a reversible stochastic interface evolution. When the update rate is chosen proportional to $1/n$, the dynamics is known to enjoy especially nice features: a certain Hamming distance between configurations contracts with time on average and the relaxation time of the Markov chain is diffusive, growing like the square of the diameter of the system. Here, we present another remarkable feature of this dynamics, namely we derive, in the diffusive time scale, a fully explicit hydrodynamic limit equation for the height function (in the form of a non-linear parabolic PDE). While this equation cannot be written as a gradient flow w.r.t. a surface energy functional, it has nice analytic properties, for instance it contracts the $\mathbb L^2$ distance between solutions. The mobility coefficient $\mu$ in the equation has non-trivial but explicit dependence on the interface slope and, interestingly, is directly related to the system's surface free energy. The derivation of the hydrodynamic limit is not fully rigorous, in that it relies on an unproven assumption of local equilibrium., Comment: 31 pages, 8 figures. v2: typos corrected, some proofs clarified. To appear on Annales Henri Poincare

Published
2016

15. A note on dimers and T-graphs

Author

Berestycki, Nathanael, Laslier, Benoît, Ray, Gourab, University of Cambridge [UK] (CAM), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), and Laslier, Benoit

Subjects
[MATH.MATH-PR]Mathematics [math]/Probability [math.PR], [MATH.MATH-PR] Mathematics [math]/Probability [math.PR], Probability (math.PR), FOS: Mathematics, Mathematics - Combinatorics, Combinatorics (math.CO), Mathematics - Probability
Abstract

The purpose of this note is to give a succinct summary of some basic properties of T-graphs which arise in the study of the dimer model. We focus in particular on the relation between the dimer model on the heaxgonal lattice with a given slope, and the behaviour of the uniform spanning tree on the associated T-graph. Together with the main result of the companion paper \cite{BLR16}, the results here show Gaussian free field fluctuations for the height function in some dimer models.

Published
2016
Full Text
View/download PDF

16. On a Bubble algorithm for the cubic Nonlinear Schrödinger equation

Author

Faou, Erwan, Le Henaff, Yoann, Raphaël, Pierre, Multi-scale numerical geometric schemes (MINGUS), École normale supérieure - Rennes (ENS Rennes)-Inria Rennes – Bretagne Atlantique, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria)-Institut de Recherche Mathématique de Rennes (IRMAR), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-École normale supérieure - Rennes (ENS Rennes)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut Agro Rennes Angers, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut Agro Rennes Angers, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), Institut de Recherche Mathématique de Rennes (IRMAR), Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), and PI ERC/UKRI advanced grant SWAT,Associated team INRIA-University of Cambridge: Bubbles

Subjects
Mathematics - Analysis of PDEs, Soliton, FOS: Mathematics, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], Bubbles, numerical Dirac-Frenkel, Schrödinger, dynamical system, 35C08, 65M22, 37M15, 35Q41, Analysis of PDEs (math.AP)
Abstract

Based on very recent and promising ideas, stemming from the use of bubbles, we discuss an algorithm for the numerical simulation of the cubic nonlinear Schr{\"o}dinger equation with harmonic potential (cNLS) in any dimension, that could easily be extended to other polynomial nonlinearities. This algorithm consists in discretizing the initial function as a sum of modulated complex gaussian functions (the bubbles), each one having its own set of parameters, and then updating the parameters according to cNLS. Numerically, we solve exactly the linear part of the equation and use the Dirac-Frenkel-MacLachlan principle to approximate the nonlinear part. We then obtain a grid free algorithm in any dimension whose efficiency compared with spectral methods is illustrated by numerical examples.

Published
2023

17. Simple regret for infinitely many armed bandits

Author

Alexandra Carpentier, Valko, M., Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Sequential Learning (SEQUEL), Inria Lille - Nord Europe, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria)-Centre de Recherche en Informatique, Signal et Automatique de Lille - UMR 9189 (CRIStAL), Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS), and ANR-14-CE24-0010,ExTra-Learn,Extraction et transfert de connaissances dans l'apprentissage par renforcement(2014)

Subjects
FOS: Computer and information sciences, Computer Science::Machine Learning, Computer Science - Learning, Statistics::Machine Learning, [STAT.ML]Statistics [stat]/Machine Learning [stat.ML], Statistics - Machine Learning, [INFO.INFO-IR]Computer Science [cs]/Information Retrieval [cs.IR], Machine Learning (stat.ML), Machine Learning (cs.LG)
Abstract

We consider a stochastic bandit problem with infinitely many arms. In this setting, the learner has no chance of trying all the arms even once and has to dedicate its limited number of samples only to a certain number of arms. All previous algorithms for this setting were designed for minimizing the cumulative regret of the learner. In this paper, we propose an algorithm aiming at minimizing the simple regret. As in the cumulative regret setting of infinitely many armed bandits, the rate of the simple regret will depend on a parameter $\beta$ characterizing the distribution of the near-optimal arms. We prove that depending on $\beta$, our algorithm is minimax optimal either up to a multiplicative constant or up to a $\log(n)$ factor. We also provide extensions to several important cases: when $\beta$ is unknown, in a natural setting where the near-optimal arms have a small variance, and in the case of unknown time horizon., Comment: in 32th International Conference on Machine Learning (ICML 2015)

Published
2015

18. Stochastic Primal Dual Hybrid Gradient Algorithm with Adaptive Step-Sizes

Author

Chambolle, Antonin, Delplancke, Claire, Ehrhardt, Matthias, Schönlieb, Carola-Bibiane, Tang, Junqi, CEntre de REcherches en MAthématiques de la DEcision (CEREMADE), Université Paris Dauphine-PSL, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Méthodes numériques pour le problème de Monge-Kantorovich et Applications en sciences sociales (MOKAPLAN), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Dauphine-PSL, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Inria de Paris, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria), EDF R&D (EDF R&D), EDF (EDF), Department of Mathematical Sciences [Bath], University of Bath [Bath], Department of Applied Mathematics and Theoretical Physics [Cambridge] (DAMTP), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), School of Mathematics [Birmingham], University of Birmingham [Birmingham], MJE acknowledges support from the EPSRC (EP/S026045/1, EP/T026693/1, EP/V026259/1) and the Leverhulme Trust (ECF-2019-478)., and CBS acknowledges support from the Philip Leverhulme Prize, the Royal Society Wolfson Fellowship, the EPSRC advanced career fellowship EP/V029428/1, EPSRC grants EP/S026045/1 and EP/T003553/1, EP/N014588/1, EP/T017961/1, the Wellcome Innovator Awards 215733/Z/19/Z and 221633/Z/20/Z, the European Union Horizon 2020 research and innovation programme under the Marie Skodowska-Curie grant agreement No. 777826 NoMADS, the Cantab Capital Institute for the Mathematics of Information and the Alan Turing Institute.

Subjects
47N10, 49J40, 65D18, 65K10, 90C06, 90C15, 90C25, 92C55, 94A08, Optimization and Control (math.OC), FOS: Mathematics, [MATH]Mathematics [math], Mathematics - Optimization and Control
Abstract

In this work we propose a new primal-dual algorithm with adaptive step-sizes. The stochastic primal-dual hybrid gradient (SPDHG) algorithm with constant step-sizes has become widely applied in large-scale convex optimization across many scientific fields due to its scalability. While the product of the primal and dual step-sizes is subject to an upper-bound in order to ensure convergence, the selection of the ratio of the step-sizes is critical in applications. Up-to-now there is no systematic and successful way of selecting the primal and dual step-sizes for SPDHG. In this work, we propose a general class of adaptive SPDHG (A-SPDHG) algorithms, and prove their convergence under weak assumptions. We also propose concrete parameters-updating strategies which satisfy the assumptions of our theory and thereby lead to convergent algorithms. Numerical examples on computed tomography demonstrate the effectiveness of the proposed schemes., 28 pages, 8 figures

Published
2023

19. SCOTCH and SODA: A Transformer Video Shadow Detection Framework

Author

Liu, Lihao, Prost, Jean, Zhu, Lei, Papadakis, Nicolas, Liò, Pietro, Schönlieb, Carola-Bibiane, Aviles-Rivero, Angelica I, Department of Applied Mathematics and Theoretical Physics [Cambridge] (DAMTP), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Institut de Mathématiques de Bordeaux (IMB), Université Bordeaux Segalen - Bordeaux 2-Université Sciences et Technologies - Bordeaux 1 (UB)-Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux (Bordeaux INP)-Centre National de la Recherche Scientifique (CNRS), Electronic and Computer Engineering Department [Hong Kong] (ECE), Hong Kong University of Science and Technology (HKUST), and European Project: 777826,NoMADS(2018)

Subjects
FOS: Computer and information sciences, Computer Vision and Pattern Recognition (cs.CV), Computer Science - Computer Vision and Pattern Recognition, [INFO.INFO-CV]Computer Science [cs]/Computer Vision and Pattern Recognition [cs.CV]
Abstract

Shadows in videos are difficult to detect because of the large shadow deformation between frames. In this work, we argue that accounting for shadow deformation is essential when designing a video shadow detection method. To this end, we introduce the shadow deformation attention trajectory (SODA), a new type of video self-attention module, specially designed to handle the large shadow deformations in videos. Moreover, we present a new shadow contrastive learning mechanism (SCOTCH) which aims at guiding the network to learn a unified shadow representation from massive positive shadow pairs across different videos. We demonstrate empirically the effectiveness of our two contributions in an ablation study. Furthermore, we show that SCOTCH and SODA significantly outperforms existing techniques for video shadow detection. Code is available at the project page: https://lihaoliu-cambridge.github.io/scotch_and_soda/, Accepted to CVPR 2023

Published
2022

20. Microscopic observation of two-level systems in a metallic glass model

Author

Felix C. Mocanu, Ludovic Berthier, Simone Ciarella, Dmytro Khomenko, David R. Reichman, Camille Scalliet, Francesco Zamponi, Laboratoire de physique de l'ENS - ENS Paris (LPENS), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Département de Physique de l'ENS-PSL, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Systèmes Désordonnés et Applications, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Département de Physique de l'ENS-PSL, Laboratoire Charles Coulomb (L2C), Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM), Dipartimento di Fisica [Roma La Sapienza], Università degli Studi di Roma 'La Sapienza' = Sapienza University [Rome] (UNIROMA), Columbia University [New York], Department of Applied Mathematics and Theoretical Physics [Cambridge] (DAMTP), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), ANR-10-EQPX-0029,EQUIP@MESO,Equipement d'excellence de calcul intensif de Mesocentres coordonnés - Tremplin vers le calcul petaflopique et l'exascale(2010), and European Project: 723955,GlassUniversality

Subjects
[PHYS.PHYS.PHYS-COMP-PH]Physics [physics]/Physics [physics]/Computational Physics [physics.comp-ph], General Physics and Astronomy, FOS: Physical sciences, [PHYS.COND.CM-DS-NN]Physics [physics]/Condensed Matter [cond-mat]/Disordered Systems and Neural Networks [cond-mat.dis-nn], Disordered Systems and Neural Networks (cond-mat.dis-nn), [PHYS.COND.CM-SM]Physics [physics]/Condensed Matter [cond-mat]/Statistical Mechanics [cond-mat.stat-mech], Physical and Theoretical Chemistry, Computational Physics (physics.comp-ph), Condensed Matter - Disordered Systems and Neural Networks, Physics - Computational Physics
Abstract

The low-temperature quasi-universal behavior of amorphous solids has been attributed to the existence of spatially-localized tunneling defects found in the low-energy regions of the potential energy landscape. Computational models of glasses can be studied to elucidate the microscopic nature of these defects. Recent simulation work has demonstrated the means of generating stable glassy configurations for models that mimic metallic glasses using the swap Monte Carlo algorithm. Building on these studies, we present an extensive exploration of the glassy metabasins of the potential energy landscape of a variant of the most widely used model of metallic glasses. We carefully identify tunneling defects and reveal their depletion with increased glass stability. The density of tunneling defects near the experimental glass transition temperature appears to be in good agreement with experimental measurements., 17 pages, 12 figures

Published
2022

21. Nonexplosion criteria for relativistic diffusions

Author

Jacques Franchi, Ismael Bailleul, Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Institut de Recherche Mathématique Avancée (IRMA), Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS), Agence Nationale de la Recherche, n° ANR-09-BLAN-0364-01, et EPSRC grant EP/E01772X/1., I. Bailleul - J. Franchi, and ProbaGeo, ANR-09-BLAN-0364-01,ProbaGeo, ANR-09-BLAN-0364-01

Subjects
Statistics and Probability, 83C99, General relativity, 83C10, Lorentz transformation, FOS: Physical sciences, nonexplosion criterion, Curvature, 01 natural sciences, Volume growth, 010104 statistics & probability, symbols.namesake, Mathematics::Probability, FOS: Mathematics, Covariant transformation, 0101 mathematics, Mathematical Physics, Mathematical physics, Mathematics, Primary 58J65, secondary 53C50, 83C10, 83C99, Probability (math.PR), 53C50, 010102 general mathematics, Subriemannian minimal time, Mathematical Physics (math-ph), 58J65, Physics::History of Physics, Manifold, Non-explosion criterion, [MATH.MATH-PR]Mathematics [math]/Probability [math.PR], Relativistic diffusions, symbols, Statistics, Probability and Uncertainty, Mathematics - Probability, Stochastic completeness
Abstract

Some general Lorentz covariant operators, associated to the so-called \Theta (or \Xi)-relativistic diffusions and making sense in any Lorentzian manifold, have been introduced by Franchi and Le Jan [Comm. Pure Appl. Math. 60 (2007) 187-251], Franchi and Le Jan [Curvature diffusions in general relativity (2010). Unpublished manuscript]. Only a few examples have been studied so far. We provide in this work some nonexplosion criteria for these diffusions, which can be used in generic cases., Comment: Published in at http://dx.doi.org/10.1214/11-AOP672 the Annals of Probability (http://www.imstat.org/aop/) by the Institute of Mathematical Statistics (http://www.imstat.org)

Published
2012

22. Online allocation and homogeneous partitioning for piecewise constant mean-approximation

Author

Maillard, Odalric-Ambrym, Carpentier, Alexandra, Montanuniversität Leoben (MUL), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), and Maillard, Odalric-Ambrym

Subjects
Active sampling, Histograms, [INFO.INFO-LG]Computer Science [cs]/Machine Learning [cs.LG], [STAT.ML]Statistics [stat]/Machine Learning [stat.ML], [STAT.TH] Statistics [stat]/Statistics Theory [stat.TH], [MATH.MATH-ST]Mathematics [math]/Statistics [math.ST], [INFO.INFO-LG] Computer Science [cs]/Machine Learning [cs.LG], [STAT.TH]Statistics [stat]/Statistics Theory [stat.TH], Multi-armed bandits, [MATH.MATH-ST] Mathematics [math]/Statistics [math.ST], [STAT.ML] Statistics [stat]/Machine Learning [stat.ML]
Abstract

22; In the setting of active learning for the multi-armed bandit, where the goal of a learner is to estimate with equal precision the mean of a finite number of arms, recent results show that it is possible to derive strategies based on finite-time confidence bounds that are competitive with the best possible strategy. We here consider an extension of this problem to the case when the arms are the cells of a finite partition P of a continuous sampling space X \subset \Real^d. Our goal is now to build a piecewise constant approximation of a noisy function (where each piece is one region of P and P is fixed beforehand) in order to maintain the local quadratic error of approximation on each cell equally low. Although this extension is not trivial, we show that a simple algorithm based on upper confidence bounds can be proved to be adaptive to the function itself in a near-optimal way, when |P| is chosen to be of minimax-optimal order on the class of \alpha-Hölder functions.

Published
2012

23. Some discussions of D. Fearnhead and D. Prangle's Read Paper 'Constructing summary statistics for approximate Bayesian computation: semi-automatic approximate Bayesian computation'

Author

Christophe Andrieu, Simon Barthelme, Nicolas Chopin, Julien Cornebise, Arnaud Doucet, Mark Girolami, Ioannis Kosmidis, Ajay Jasra, Anthony Lee, Jean-Michel Marin, Pierre Pudlo, Christian Robert, Mohammed Sedki., Singh, Sumeetpal S., Department of Mathematics [Bristol], University of Bristol [Bristol]-University Walk, Technische Universität Berlin (TU), Centre de Recherche en Économie et Statistique (CREST), Ecole Nationale de la Statistique et de l'Analyse de l'Information [Bruz] (ENSAI)-École polytechnique (X)-École Nationale de la Statistique et de l'Administration Économique (ENSAE Paris)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Traitement et Communication de l'Information (LTCI), Télécom ParisTech-Institut Mines-Télécom [Paris] (IMT)-Centre National de la Recherche Scientifique (CNRS), Dept of Statistics & Dept of Computer Science, University of British Columbia (UBC), Department of Statistical Science, University College of London [London] (UCL), Department of Computing [London], Biomedical Image Analysis Group [London] (BioMedIA), Imperial College London-Imperial College London, Department of Statistics [Oxford], University of Oxford [Oxford], Institut de Mathématiques et de Modélisation de Montpellier (I3M), Centre National de la Recherche Scientifique (CNRS)-Université Montpellier 2 - Sciences et Techniques (UM2)-Université de Montpellier (UM), CEntre de REcherches en MAthématiques de la DEcision (CEREMADE), Centre National de la Recherche Scientifique (CNRS)-Université Paris Dauphine-PSL, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut Universitaire de France (IUF), Ministère de l'Education nationale, de l’Enseignement supérieur et de la Recherche (M.E.N.E.S.R.), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), and Robert, Christian

Subjects
stat.CO, Methodology (stat.ME), FOS: Computer and information sciences, [STAT.ME] Statistics [stat]/Methodology [stat.ME], stat.ME, [STAT.CO]Statistics [stat]/Computation [stat.CO], [STAT.CO] Statistics [stat]/Computation [stat.CO], [STAT.ME]Statistics [stat]/Methodology [stat.ME], Statistics - Computation, Computation (stat.CO), Statistics - Methodology
Abstract

This report is a collection of comments on the Read Paper of Fearnhead and Prangle (2011), to appear in the Journal of the Royal Statistical Society Series B, along with a reply from the authors., 10 pages

Published
2012

24. A Historical Law of Large Numbers for the Marcus-Lushnikov Process

Author

Stéphanie Jacquot, Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), INRIA Bordeaux - Sud-Ouest, and SESSION 03 : Processus de branchement en dynamique des populations

Subjects
Statistics and Probability, 60B10, Distribution (number theory), Smoluchowski coagulation equation, tightness, 01 natural sciences, Combinatorics, 010104 statistics & probability, symbols.namesake, 60J25, Law of large numbers, 60B05, Statistical physics, Limit (mathematics), coupling, Physics::Chemical Physics, 0101 mathematics, Marcus-Lushnikov process on trees, Mathematics, Particle system, limit measure on trees, 010102 general mathematics, Empirical distribution function, [MATH.MATH-PR]Mathematics [math]/Probability [math.PR], symbols, Particle, historical trees, 60F15, Tree (set theory), Statistics, Probability and Uncertainty
Abstract

The Marcus-Lushnikov process is a finite stochastic particle system, in which each particle is entirely characterized by its mass. Each pair of particles with masses $x$ and $y$ merges into a single particle at a given rate $K(x,y)$. Under certain assumptions, this process converges to the solution to the Smoluchowski coagulation equation, as the number of particles increases to infinity. The Marcus-Lushnikov process gives at each time the distribution of masses of the particles present in the system, but does not retain the history of formation of the particles. In this paper, we set up a historical analogue of the Marcus-Lushnikov process (built according to the rules of construction of the usual Markov-Lushnikov process) each time giving what we call the historical tree of a particle. The historical tree of a particle present in the Marcus-Lushnikov process at a given time t encodes information about the times and masses of the coagulation events that have formed that particle. We prove a law of large numbers for the empirical distribution of such historical trees. The limit is a natural measure on trees which is constructed from a solution to the Smoluchowski coagulation equation.

Published
2010

25. Prospects for GRB Science with the Fermi Large Area Telescope

Author

R. M. Kippen, Brenda Dingus, Sinéad McGlynn, Takashi Shimokawabe, Carmelo Sgrò, E. Moretti, Jonathan Granot, F. Kuehn, J. P. Norris, M. N. Mazziotta, P. D. Smith, R. E. Hughes, Nicola Omodei, M. Kuss, James Chiang, J. J. Russell, Felix Ryde, Jeffrey D. Scargle, P. Lubrano, N. Gehrels, E. Do Couto E Silva, P. Spinelli, Guido Barbiellini, Ryo Yamazaki, F. Longo, Brian L Winer, G. Bogaert, V. Pelassa, S. Cutini, V. Connaughton, F. Piron, Robert D. Preece, Matthew G. Baring, Takeshi Nakamori, Gerald J. Fishman, T. Kamae, N. Giglietto, Masanori Ohno, M. Razzano, P. M. Saz Parkinson, David L. Band, M. Olivo, Johann Cohen-Tanugi, F. de Palma, Magnus Axelsson, A. Galli, Gloria Spandre, Julie McEnery, Luca Baldini, Sylvain Guiriec, J. Bonnel, Elisabetta Bissaldi, M. Battelino, Denis Bastieri, Ronaldo Bellazzini, M. Stamatikos, N. Komin, Department of Zoology, University of Gothenburg (GU), CNR Institute of Atmospheric Sciences and Climate (ISAC), Consiglio Nazionale delle Ricerche (CNR), Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Leprince-Ringuet (LLR), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS), Joint Center for Astrophysics/Physics Department University of Maryland, University of Maryland [College Park], University of Maryland System-University of Maryland System, Laboratoire de Physique Théorique et Astroparticules (LPTA), Université Montpellier 2 - Sciences et Techniques (UM2)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Bureau d'Économie Théorique et Appliquée (BETA), Institut National de la Recherche Agronomique (INRA)-Université de Strasbourg (UNISTRA)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Hansen Experimental Physics Laboratory (HEPL), Stanford University [Stanford], Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), Stanford Linear Accelerator Center (SLAC), Institut d'Informatique et de Mathématiques Appliquées de Grenoble (IMAG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut National Polytechnique de Grenoble (INPG)-Centre National de la Recherche Scientifique (CNRS), Department of Chemistry [Waterloo], University of Waterloo [Waterloo], Statistical Laboratory (DPMMS), University of Cambridge [UK] (CAM), Istituto Nazionale di Fisica Nucleare, Sezione di Trieste (INFN, Sezione di Trieste), National Institute for Nuclear Physics (INFN), Lunar and Planetary Laboratory [Tucson] (LPL), University of Arizona, NASA Goddard Space Flight Center (GSFC), Center for Research and Exploration in Space Science and Technology [GSFC] (CRESST), Stockholm Observatory Department of Astronomy, Stockholm University, Istituto Nazionale di Fisica Nucleare [Pisa] (INFN), Istituto Nazionale di Fisica Nucleare (INFN), Dipartimento di Fisica [Trieste], Università degli studi di Trieste = University of Trieste, Department of Physics and Astronomy [Houston], Rice University [Houston], Istituto Nazionale di Fisica Nucleare, Sezione di Padova (INFN, Sezione di Padova), Dipartimento di Fisica 'G. Galilei', Università degli Studi di Padova = University of Padua (Unipd), Department of Physics, Royal Institute of Technology (KTH), Max-Planck-Institut für Extraterrestrische Physik (MPE), Stanford University, SLAC National Accelerator Laboratory (SLAC), Hansen Experimental Physics Lab [Stanford] (HEPL), University of Alabama in Huntsville (UAH), Agenzia Spaziale Italiana (ASI), Istituto Nazionale di Fisica Nucleare, sezione di Bari (INFN, sezione di Bari), Dipartimento di Fisica 'M. Merlin' dell'Università e del Politecnico di Bari, Politecnico di Bari, Los Alamos National Laboratory (LANL), NASA Marshall Space Flight Center (MSFC), Istituto di Astrofisica Spaziale e Fisica cosmica - Roma (IASF-Roma), Istituto Nazionale di Astrofisica (INAF), University of Maryland System, Centre for Astrophysics Research [Hatfield], University of Hertfordshire [Hatfield] (UH), Department of Physics, Ohio State University, Laboratoire Aimé Cotton (LAC), Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Institut de Recherches sur les lois Fondamentales de l'Univers (IRFU), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, Istituto Nazionale di Fisica Nucleare, Sezione di Perugia (INFN, Sezione di Perugia), Tokyo Institute of Technology [Tokyo] (TITECH), Department of Physics [Tokyo], Rikkyo University [Tokyo], Department of Physics and Astronomy [Denver], University of Denver, Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency [Sagamihara] (JAXA), Santa Cruz Institute for Particle Physics (SCIPP), University of California [Santa Cruz] (UC Santa Cruz), University of California (UC)-University of California (UC), NASA Ames Research Center (ARC), Center for Cosmology & AstroParticle Physics, Ohio State University [Columbus] (OSU), Department of Physics, The Ohio State University, Hiroshima Astrophysical Science Center, Hiroshima University, Department of Physical Sciences [Higashi-Hiroshima], The Fermi LAT Collaboration acknowledges support from a number of agencies and institutes for both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support from the Istituto Nazionale di Astrofisica in Italy for science analysis during the operations phase is also gratefully acknowledged., Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Université de Lorraine (UL)-Université de Strasbourg (UNISTRA)-Institut National de la Recherche Agronomique (INRA)-Centre National de la Recherche Scientifique (CNRS), D. L., Band, M., Axelsson, L., Baldini, BARBIELLINI AMIDEI, Guido, M. G., Baring, D., Bastieri, M., Battelino, R., Bellazzini, Bissaldi, Elisabetta, G., Bogaert, J., Bonnell, J., Chiang, J., Cohen Tanugi, V., Connaughton, S., Cutini, F. d., Palma, B. L., Dingu, E. D. E., Silva, G., Fishman, A., Galli, N., Gehrel, N., Giglietto, J., Granot, S., Guiriec, R. E., Hughe, T., Kamae, N., Komin, F., Kuehn, M., Ku, Longo, Francesco, P., Lubrano, R. M., Kippen, M. N., Mazziotta, J. E., Mcenery, S., Mcglynn, Moretti, Elena, T., Nakamori, J. P., Norri, M., Ohno, M., Olivo, N., Omodei, V., Pelassa, F., Piron, R., Preece, M., Razzano, J. J., Russell, F., Ryde, P. M. S., Parkinson, J. D., Scargle, C., Sgro, T., Shimokawabe, P. D., Smith, G., Spandre, P., Spinelli, M., Stamatiko, B. L., Winer, and R., Yamazaki

Subjects
[PHYS.ASTR.HE]Physics [physics]/Astrophysics [astro-ph]/High Energy Astrophysical Phenomena [astro-ph.HE], [PHYS.ASTR.IM]Physics [physics]/Astrophysics [astro-ph]/Instrumentation and Methods for Astrophysic [astro-ph.IM], gamma rays: bursts, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Fermi satellite, Astrophysics, 7. Clean energy, 01 natural sciences, High Energy Gamma-ray Astronomy, law.invention, Telescope, law, 0103 physical sciences, 010306 general physics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Bursts, Spacecraft, business.industry, [SDU.ASTR.HE]Sciences of the Universe [physics]/Astrophysics [astro-ph]/High Energy Astrophysical Phenomena [astro-ph.HE], Detector, Gamma rays, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Afterglow, [SDU.ASTR.IM]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Instrumentation and Methods for Astrophysic [astro-ph.IM], Space and Planetary Science, Gamma-ray Bursts, business, Gamma-ray burst, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Fermi Gamma-ray Space Telescope
Abstract

The LAT instrument on the Fermi mission will reveal the rich spectral and temporal gamma-ray burst phenomena in the > 100 MeV band. The synergy with Fermi's GBM detectors will link these observations to those in the well explored 10-1000 keV range; the addition of the > 100 MeV band observations will resolve theoretical uncertainties about burst emission in both the prompt and afterglow phases. Trigger algorithms will be applied to the LAT data both onboard the spacecraft and on the ground. The sensitivity of these triggers will differ because of the available computing resources onboard and on the ground. Here we present the LAT's burst detection methodologies and the instrument's GRB capabilities., Accepted by ApJ

Published
2009

26. A stochastic min-driven coalescence process and its hydrodynamical limit

Author

Anne-Laure Basdevant, Clément Rau, Philippe Laurençot, James Norris, Modélisation aléatoire de Paris X (MODAL'X), Université Paris Nanterre (UPN), Institut de Mathématiques de Toulouse UMR5219 (IMT), Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse - Jean Jaurès (UT2J)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Université Toulouse Capitole (UT Capitole), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut National des Sciences Appliquées (INSA)-Université Toulouse - Jean Jaurès (UT2J), Université de Toulouse (UT)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS), Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), and Institut National des Sciences Appliquées (INSA)-Université Fédérale Toulouse Midi-Pyrénées-Institut National des Sciences Appliquées (INSA)-Université Toulouse - Jean Jaurès (UT2J)-Université Toulouse III - Paul Sabatier (UT3)

Subjects
Statistics and Probability, Stochastic modelling, stochastic coalescence, 82C22, 60K35, 60H10, 34A34, 34C11, Binary number, 01 natural sciences, hydrodynamical limit, 010104 statistics & probability, 82C22, 60K35, 60H10, 34A34, 34C11, FOS: Mathematics, Statistical physics, 0101 mathematics, Mathematics, Coalescence (physics), Probability (math.PR), 010102 general mathematics, Time evolution, [MATH.MATH-PR]Mathematics [math]/Probability [math.PR], min-driven clustering, Statistics, Probability and Uncertainty, Mathematics - Probability
Abstract

International audience; A stochastic system of particles is considered in which the sizes of the particles increase by successive binary mergers with the constraint that each coagulation event involves a particle with minimal size. Convergence of a suitably renormalised version of this process to a deterministic hydrodynamical limit is shown and the time evolution of the minimal size is studied for both deterministic and stochastic models.

Published
2009

27. Multiple coexisting states of liquid rope coiling

Author

Daniel Bonn, Herbert E. Huppert, Neil M. Ribe, Mehdi Habibi, Mark A. Hallworth, Institut de Physique du Globe de Paris (IPGP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), Institute of Theoretical Geophysics [Cambridge] (ITG), Department of Applied Mathematics and Theoretical Physics [Cambridge] (DAMTP), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Department of Earth Sciences [Cambridge, UK], University of Cambridge [UK] (CAM), Institute for Advanced Studies in Basic Sciences, Institute for advanced Studies in Basic Sciences, Laboratoire de Physique Statistique de l'ENS (LPS), Université Paris Diderot - Paris 7 (UPD7)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Fédération de recherche du Département de physique de l'Ecole Normale Supérieure - ENS Paris (FRDPENS), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Institut des Neurosciences Cellulaires et Intégratives (INCI), Université Louis Pasteur - Strasbourg I-Centre National de la Recherche Scientifique (CNRS), University of Amsterdam Van der Waals-Zeeman Institute (VAN DER WAALS-ZEEMAN INSTITUTE), University of Amsterdam [Amsterdam] (UvA), Institute of Theoretical Geophysics, Department of Applied Mathematics and Theoretical Physics, Fédération de recherche du Département de physique de l'Ecole Normale Supérieure - ENS Paris (FRDPENS), Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Institute for Advanced Studies in Basic Sciences (IASBS), Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), and Soft Matter (WZI, IoP, FNWI)

Subjects
Physics, [PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Mechanics of the fluids [physics.class-ph], Mechanical Engineering, Bending, Viscous liquid, Condensed Matter Physics, Rotation, 01 natural sciences, Instability, String (physics), 010305 fluids & plasmas, Gravitation, Classical mechanics, Mechanics of Materials, 0103 physical sciences, Life Science, [PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph], Atomic physics, 010306 general physics, Falling (sensation), ComputingMilieux_MISCELLANEOUS, Rope
Abstract

A thin ‘rope’ of viscous fluid falling from a sufficient height onto a surface forms a series of regular coils. Here we investigate theoretically and experimentally a curious feature of this instability: the existence of multiple states with different frequencies at a fixed value of the fall height. Using a numerical model based on asymptotic ‘thin rope’ theory, we determine curves of coiling frequency Ω vs. fall height H as functions of the fluid viscosity ν, the diameter d of the injection hole, the volumetric injection rate Q, and the acceleration due to gravity g. In addition to the three coiling modes previously identified (viscous, gravitational and inertial), we find a new multivalued ‘inertio-gravitational’ mode that occurs at heights intermediate between gravitational and inertial coiling. In the limit when the rope is strongly stretched by gravity and Π1 ≡ (ν 5 /gQ 3 ) 1/5 � 1, inertio-gravititational coiling occurs in the height range O(Π −1/6 1 ) H (g/ν 2 ) 1/3 O(Π −5/48 1 ). The frequencies of the individual branches are proportional to (g/H) 1/2 , and agree closely with the eigenfrequencies of a whirling liquid string with negligible resistance to bending and twisting. The number of coexisting branches scales as Π 5/32 1 . The predictions of the numerical model are in excellent agreement with laboratory experiments performed by two independent groups using different apparatus and working fluids. The experiments further show that interbranch transitions in the inertio-gravitational regime occur via an intermediate state with a ‘figure of eight’ geometry that changes the sense of rotation of the coiling.

Published
2006

28. Semidefinite programming lower bounds on the squashed entanglement

Author

Fawzi, Hamza, Fawzi, Omar, Department of Applied Mathematics and Theoretical Physics [Cambridge] (DAMTP), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Laboratoire de l'Informatique du Parallélisme (LIP), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut National de Recherche en Informatique et en Automatique (Inria)-Centre National de la Recherche Scientifique (CNRS), Traitement optimal de l'information avec des dispositifs quantiques (QINFO), Inria Grenoble - Rhône-Alpes, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria)-École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Université Grenoble Alpes (UGA)-Inria Lyon, Institut National de Recherche en Informatique et en Automatique (Inria), European Project: 851716,ERC-2019-STG,AlgoQIP(2021), Fawzi, Omar, and Beyond Shannon: Algorithms for optimal information processing - AlgoQIP - 2021-01-01 - 2025-12-31 - 851716 - VALID

Subjects
Quantum Physics, [PHYS.QPHY]Physics [physics]/Quantum Physics [quant-ph], Physics::Space Physics, FOS: Physical sciences, TheoryofComputation_GENERAL, Quantum Physics (quant-ph), [PHYS.QPHY] Physics [physics]/Quantum Physics [quant-ph], Physics::Geophysics
Abstract

The squashed entanglement is a widely used entanglement measure that has many desirable properties. However, as it is based on an optimization over extensions of arbitrary dimension, one drawback of this measure is the lack of good algorithms to compute it. Here, we introduce a hierarchy of semidefinite programming lower bounds on the squashed entanglement., 10 pages, comments welcome

Published
2022

29. Large deviations for the Yang-Mills measure on a compact surface

Author

James Norris, Thierry Lévy, Département de Mathématiques et Applications - ENS Paris (DMA), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)

Subjects
Surface (mathematics), Mathematics - Differential Geometry, High Energy Physics::Lattice, FOS: Physical sciences, Yang–Mills existence and mass gap, 01 natural sciences, Measure (mathematics), General Relativity and Quantum Cosmology, High Energy Physics::Theory, Large deviation principle, Simple (abstract algebra), [MATH.MATH-MP]Mathematics [math]/Mathematical Physics [math-ph], Mathematics::Quantum Algebra, 0103 physical sciences, FOS: Mathematics, Limit (mathematics), 0101 mathematics, Sobolev connections, Yang-Mills measure, Mathematical Physics, Mathematics, MSC 60F10, 81T13, 58D20, 010102 general mathematics, Mathematical analysis, Probability (math.PR), Statistical and Nonlinear Physics, Mathematical Physics (math-ph), [MATH.MATH-PR]Mathematics [math]/Probability [math.PR], Nonlinear Sciences::Exactly Solvable and Integrable Systems, Differential Geometry (math.DG), [MATH.MATH-DG]Mathematics [math]/Differential Geometry [math.DG], Large deviations theory, 010307 mathematical physics, Rate function, Energy (signal processing), Mathematics - Probability
Abstract

We prove the first mathematical result relating the Yang-Mills measure on a compact surface and the Yang-Mills energy. We show that, at the small volume limit, the Yang-Mills measures satisfy a large deviation principle with a rate function which is expressed in a simple and natural way in terms of the Yang-Mills energy.

Published
2004
Full Text
View/download PDF

30. Modelling Incentives for Collaboration in Mobile Ad Hoc Networks

Author

Richard J. Gibbens, Jon Crowcroft, Frank Kelly, Sven Östring, Inria Sophia Antipolis-Méditerranée / I3s, Service Ist, Computer Laboratory [Cambridge], University of Cambridge [UK] (CAM), Statistical Laboratory [Cambridge], Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)-Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), and Session 04 : Game models for cooperation in Ad-hoc networks (T. Basar)

Subjects
Delay-tolerant networking, Computer Networks and Communications, Computer science, Wireless ad hoc network, 02 engineering and technology, [INFO.INFO-MC]Computer Science [cs]/Mobile Computing, [INFO.INFO-NI]Computer Science [cs]/Networking and Internet Architecture [cs.NI], [INFO.INFO-MC] Computer Science [cs]/Mobile Computing, [INFO.INFO-PF] Computer Science [cs]/Performance [cs.PF], Computer Science::Networking and Internet Architecture, 0202 electrical engineering, electronic engineering, information engineering, Vehicular ad hoc network, Adaptive quality of service multi-hop routing, [INFO.INFO-NI] Computer Science [cs]/Networking and Internet Architecture [cs.NI], business.industry, 020206 networking & telecommunications, Mobile ad hoc network, Ad hoc wireless distribution service, [INFO.INFO-PF]Computer Science [cs]/Performance [cs.PF], Optimized Link State Routing Protocol, Hardware and Architecture, Geocast, Modeling and Simulation, 020201 artificial intelligence & image processing, Telecommunications, business, Software, Computer network
Abstract

International audience; This paper explores a model for the operation of an ad hoc mobile network. The model incorporates incentives for users to act as transit nodes on multi-hop paths and to be rewarded with their own ability to send trafic. The paper explores consequences of the model by means of fluid-level simulations of a network and illustrates the way in which network resources are allocated to users according to their geographical position.

Published
2003

31. Device-independent lower bounds on the conditional von Neumann entropy

Author

Brown, Peter, Fawzi, Hamza, Fawzi, Omar, Laboratoire de l'Informatique du Parallélisme (LIP), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut National de Recherche en Informatique et en Automatique (Inria)-Centre National de la Recherche Scientifique (CNRS), Traitement optimal de l'information avec des dispositifs quantiques (QINFO), Inria Grenoble - Rhône-Alpes, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria)-École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Université Grenoble Alpes (UGA)-Inria Lyon, Institut National de Recherche en Informatique et en Automatique (Inria), Department of Applied Mathematics and Theoretical Physics [Cambridge] (DAMTP), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), European Project: 851716,ERC-2019-STG,AlgoQIP(2021), Fawzi, Omar, and Beyond Shannon: Algorithms for optimal information processing - AlgoQIP - 2021-01-01 - 2025-12-31 - 851716 - VALID

Subjects
Quantum Physics, [PHYS.QPHY]Physics [physics]/Quantum Physics [quant-ph], FOS: Physical sciences, [INFO]Computer Science [cs], [INFO] Computer Science [cs], Quantum Physics (quant-ph), [PHYS.QPHY] Physics [physics]/Quantum Physics [quant-ph], Computer Science::Cryptography and Security
Abstract

The rates of several device-independent (DI) protocols, including quantum key-distribution (QKD) and randomness expansion (RE), can be computed via an optimization of the conditional von Neumann entropy over a particular class of quantum states. In this work we introduce a numerical method to compute lower bounds on such rates. We derive a sequence of optimization problems that converge to the conditional von Neumann entropy of systems defined on general separable Hilbert spaces. Using the Navascu\'es-Pironio-Ac\'in hierarchy we can then relax these problems to semidefinite programs, giving a computationally tractable method to compute lower bounds on the rates of DI protocols. Applying our method to compute the rates of DI-RE and DI-QKD protocols we find substantial improvements over all previous numerical techniques, demonstrating significantly higher rates for both DI-RE and DI-QKD. In particular, for DI-QKD we show a minimal detection efficiency threshold which is within the realm of current capabilities. Moreover, we demonstrate that our method is capable of converging rapidly by recovering all known tight analytical bounds up to several decimal places. Finally, we note that our method is compatible with the entropy accumulation theorem and can thus be used to compute rates of finite round protocols and subsequently prove their security., Comment: 21 (+8) pages, 4 (+2) figures. V2: improved numerics and restructured article

Published
2022

32. Climate change penalty and benefit on surface ozone: a global perspective based on CMIP6 earth system models

Author

Prodromos Zanis, Dimitris Akritidis, Steven Turnock, Vaishali Naik, Sophie Szopa, Aristeidis K Georgoulias, Susanne E Bauer, Makoto Deushi, Larry W Horowitz, James Keeble, Philippe Le Sager, Fiona M O’Connor, Naga Oshima, Konstantinos Tsigaridis, Twan van Noije, Aristotle University of Thessaloniki, Met Office Hadley Centre for Climate Change (MOHC), United Kingdom Met Office [Exeter], University of Leeds, NOAA Geophysical Fluid Dynamics Laboratory (GFDL), National Oceanic and Atmospheric Administration (NOAA), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Modélisation du climat (CLIM), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), NASA Goddard Institute for Space Studies (GISS), NASA Goddard Space Flight Center (GSFC), Japan Meteorological Agency (JMA), Department of Chemistry [Cambridge, UK], University of Cambridge [UK] (CAM), NCAS-Climate [Cambridge], University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Royal Netherlands Meteorological Institute (KNMI), Center for Climate Systems Research [New York] (CCSR), Columbia University [New York], P Z, D A and A K G would like acknowledge the funding from the Action titled 'National Network on Climate Change and its Impacts—CLIMPACT' which is implemented under the sub-project 3 of the project 'Infrastructure of national research networks in the fields of Precision Medicine, Quantum Technology and Climate Change', funded by the Public Investment Program of Greece, General Secretary of Research and Technology/Ministry of Development and Investments. S T would like to acknowledge the UK-China Research and Innovation Partnership Fund through the Met Office Climate Science for Service Partnership (CSSP) China as part of the Newton Fund. M D and N O were supported by the Japan Society for the Promotion of Science KAKENHI (Grant Numbers: JP18H03363, JP18H05292, JP19K12312, and JP20K04070), the Environment Research and Technology Development Fund (JPMEERF20202003 and JPMEERF20205001) of the Environmental Restoration and Conservation Agency of Japan, the Arctic Challenge for Sustainability II (ArCS II), Program Grant Number JPMXD1420318865, and a grant for the Global Environmental Research Coordination System from the Ministry of the Environment, Japan (MLIT1753). J K was financially supported by NERC through NCAS (Grant No. R8/H12/83/003). FMO was supported by the Met Office Hadley Centre Climate Programme funded by BEIS and Defra (Grant No. GA01101) and the EU Horizon 2020 Research Programme CRESCENDO project (Grant No. 641816)., and European Project: 641816,H2020,H2020-SC5-2014-two-stage,CRESCENDO(2015)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, penalty, climate change, surface ozone, Renewable Energy, Sustainability and the Environment, benefit, Public Health, Environmental and Occupational Health, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, CMIP6, General Environmental Science, ESMs
Abstract

This work presents an analysis of the effect of climate change on surface ozone discussing the related penalties and benefits around the globe from the global modelling perspective based on simulations with five CMIP6 (Coupled Model Intercomparison Project Phase 6) Earth System Models. As part of AerChemMIP (Aerosol Chemistry Model Intercomparison Project) all models conducted simulation experiments considering future climate (ssp370SST) and present-day climate (ssp370pdSST) under the same future emissions trajectory (SSP3-7.0). A multi-model global average climate change benefit on surface ozone of −0.96 ± 0.07 ppbv °C−1 is calculated which is mainly linked to the dominating role of enhanced ozone destruction with higher water vapour abundances under a warmer climate. Over regions remote from pollution sources, there is a robust decline in mean surface ozone concentration on an annual basis as well as for boreal winter and summer varying spatially from −0.2 to −2 ppbv °C−1, with strongest decline over tropical oceanic regions. The implication is that over regions remote from pollution sources (except over the Arctic) there is a consistent climate change benefit for baseline ozone due to global warming. However, ozone increases over regions close to anthropogenic pollution sources or close to enhanced natural biogenic volatile organic compounds emission sources with a rate ranging regionally from 0.2 to 2 ppbv C−1, implying a regional surface ozone penalty due to global warming. Overall, the future climate change enhances the efficiency of precursor emissions to generate surface ozone in polluted regions and thus the magnitude of this effect depends on the regional emission changes considered in this study within the SSP3_7.0 scenario. The comparison of the climate change impact effect on surface ozone versus the combined effect of climate and emission changes indicates the dominant role of precursor emission changes in projecting surface ozone concentrations under future climate change scenarios.

Published
2022

33. A subpolynomial-time algorithm for the free energy of one-dimensional quantum systems in the thermodynamic limit

Author

Fawzi, Hamza, Omar, Fawzi, Scalet, Samuel, Department of Applied Mathematics and Theoretical Physics [Cambridge] (DAMTP), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Traitement optimal de l'information avec des dispositifs quantiques (QINFO), Inria Grenoble - Rhône-Alpes, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria)-École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Université Grenoble Alpes (UGA)-Inria Lyon, Institut National de Recherche en Informatique et en Automatique (Inria), European Project: 851716,ERC-2019-STG,AlgoQIP(2021), and Apollo - University of Cambridge Repository

Subjects
Quantum Physics, One-dimensional quantum systems, Physics and Astronomy (miscellaneous), Statistical Mechanics (cond-mat.stat-mech), Theory of computation → Design and analysis of algorithms, FOS: Physical sciences, Mathematical Physics (math-ph), Theory of computation → Quantum complexity theory, Atomic and Molecular Physics, and Optics, Theory of computation → Quantum information theory, [PHYS.QPHY]Physics [physics]/Quantum Physics [quant-ph], Free energy, Quantum Physics (quant-ph), Condensed Matter - Statistical Mechanics, Mathematical Physics
Abstract

We introduce a classical algorithm to approximate the free energy of local, translation-invariant, one-dimensional quantum systems in the thermodynamic limit of infinite chain size. While the ground state problem (i.e., the free energy at temperature T = 0) for these systems is expected to be computationally hard even for quantum computers, our algorithm runs for any fixed temperature T > 0 in subpolynomial time, i.e., in time O((1/ε)^c) for any constant c > 0 where ε is the additive approximation error. Previously, the best known algorithm had a runtime that is polynomial in 1/ε where the degree of the polynomial is exponential in the inverse temperature 1/T. Our algorithm is also particularly simple as it reduces to the computation of the spectral radius of a linear map. This linear map has an interpretation as a noncommutative transfer matrix and has been studied previously to prove results on the analyticity of the free energy and the decay of correlations. We also show that the corresponding eigenvector of this map gives an approximation of the marginal of the Gibbs state and thereby allows for the computation of various thermodynamic properties of the quantum system., LIPIcs, Vol. 251, 14th Innovations in Theoretical Computer Science Conference (ITCS 2023), pages 49:1-49:6

Published
2022
Full Text
View/download PDF

34. Bragg's additivity rule and core and bond model studied by real-time TDDFT electronic stopping simulations: The case of water vapor

Author

Fabrizio Cleri, Bin Gu, Emilio Artacho, Jorge Kohanoff, Fabiana Da Pieve, Daniel Muñoz-Santiburcio, Nanjing University of Information Science and Technology (NUIST), Queen's University [Belfast] (QUB), Universidad Politécnica de Madrid (UPM), Royal Belgian Institute for Space Aeronomy, Ikerbasque - Basque Foundation for Science, Donostia International Physics Center (DIPC), University of the Basque Country/Euskal Herriko Unibertsitatea (UPV/EHU), Theory of Condensed Matter Group (TCM), Cavendish Laboratory, University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Physique - IEMN (PHYSIQUE - IEMN), Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Université catholique de Lille (UCL)-Université catholique de Lille (UCL)-Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Université catholique de Lille (UCL)-Université catholique de Lille (UCL), This work has received funding from the Research Executive Agency under the EU’s Horizon 2020 Research and Innovation program ESC2RAD (grant ID 776 410). We are grateful for computational support from the UK national high performance computing service, ARCHER, for which access was obtained via the UKCP consortium and funded by EPSRC grant ref EP/P022561/1. This work benefited from networking activities carried out within the EU funded COST Action TUMIEE (CA17126) and represents a contribution to it., COST Action TUMIEE, and European Project: 776410,H2020,H2020-COMPET-2017,ESC2RAD(2018)

Subjects
Chemical Physics (physics.chem-ph), Materiales, Radiation, Bragg's additivity rule, Física, FOS: Physical sciences, Rt-TDDFT simulation, Physics - Medical Physics, Physics - Chemical Physics, Medical Physics (physics.med-ph), Electronic stopping power, Core and bond contributions, [CHIM.RADIO]Chemical Sciences/Radiochemistry
Abstract

The electronic stopping power ($S_e$) of water vapor (H$_2$O), hydrogen (H$_2$) and oxygen (O$_2$) gases for protons in a broad range of energies, centered in the Bragg peak, was calculated using real-time time-dependent density functional theory (rt-TDDFT) simulations with Gaussian basis sets. This was done for a kinetic energy of incident protons ($E_k$) ranging from 1.56 keV/amu to 1.6 MeV/amu. $S_e$ was calculated as the average over geometrically pre-sampled short ion trajectories. The average $S_e(E_k)$ values were found to rapidly converge with 25-30 pre-sampled, 2 nm-long ion trajectories. The rt-TDDFT $S_e(E_k)$ curves were compared to experimental and SRIM data, and used to validate the Bragg's Additivity Rule (BAR). Discrepancies were analyzed in terms of basis set effects and omitted nuclear stopping at low energies. At variance with SRIM, we found that BAR is applicable to our rt-TDDFT simulations of $\mathrm{2H_2+O_2}$ $\mathrm{\rightarrow 2H_2O}$ without scaling for $E_k>40$ keV/amu. The hydrogen and oxygen Core and Bond (CAB) contributions to electronic stopping were calculated and found to be slightly smaller than SRIM values as a result of a red-shift in our rt-TDDFT $S_e(E_k)$ curves and a re-distribution of weights due to some bond contributions being neglected in SRIM., 15 pages 5 figures, 1 table

Published
2022

35. Plumes in rotating fluid and their transformation into tornados

Author

Sylvain Joubaud, Daphné Lemasquerier, Bruce R. Sutherland, Morris Flynn, M. Le Bars, Paul Linden, Thierry Dauxois, Yongxing Ma, Daria Frank, C. Pacary, Timothée Jamin, University of Alberta, Department of Applied Mathematics and Theoretical Physics [Cambridge] (DAMTP), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Institut de Recherche sur les Phénomènes Hors Equilibre (IRPHE), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique de l'ENS Lyon (Phys-ENS), École normale supérieure de Lyon (ENS de Lyon)-Université de Lyon-Centre National de la Recherche Scientifique (CNRS), ANR-17-CE30-0003,DisET,Démêler la turbulence d'ondes de la turbulence tourbillonnaire : le défi des fluides stratifiés et en rotation(2017), Department of Physics, University of Alberta, Edmonton, AB T6G 2E1, Canada, University of Alberta, Edmonton, Department of Civil and Environmental Engineering, University of Alberta, Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)-École Centrale de Marseille (ECM), École normale supérieure - Lyon (ENS Lyon)-Centre National de la Recherche Scientifique (CNRS)-Université Claude Bernard Lyon 1 (UCBL), and Université de Lyon-Université de Lyon

Subjects
Rotation period, Entrainment (hydrodynamics), 010504 meteorology & atmospheric sciences, Turbulence, Mechanical Engineering, Mechanics, Condensed Matter Physics, Rotation, 01 natural sciences, 010305 fluids & plasmas, Vortex, Plume, Physics::Geophysics, Rossby number, Physics::Fluid Dynamics, Mechanics of Materials, 0103 physical sciences, Tornadogenesis, [PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph], Geology, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences
Abstract

International audience; Through laboratory experiments and numerical simulations, we examine the evolution of buoyant plumes as they are influenced by background rotation in a uniform density ambient fluid. The source Rossby number is sufficiently large that rotation does not directly affect the plume at early times. However, on a time scale of the order of half a rotation period, the plume becomes deflected from the vertical axis. For some experiments and simulations, the deflection persists and the flow precesses about the vertical axis. In other cases, shortly after being deflected, the plume laminarizes near the source to form a near-vertical columnar vortex, which we refer to as a ‘tornado’. Tornado formation occurs in some experiments and not in others even if the source and background rotation parameters are identical. However, their formation is more likely if the plumes are ‘lazy’. Simulations reveal that this is a consequence of the competing dynamics that occurs on comparable time scales. As a consequence of entrainment, vertical vorticity builds up within the plume reducing the Rossby number and suppressing vertical motion at distances progressively closer to the source. Meanwhile, the swirl (the ratio of the azimuthal to vertical flow) around the vicinity of the source increases, which tends to suppress three-dimensional turbulence in the near-source flow. Although the former process ultimately acts to deflect the plume off axis, in some instances, the swirl around the source succeeds in laminarizing the flow, resulting in tornado formation.

Published
2021

36. Propagation of smallness and spectral estimates

Author

Burq, Nicolas, Moyano, Iván, Analyse, Géométrie et Modélisation (AGM - UMR 8088), Centre National de la Recherche Scientifique (CNRS)-CY Cergy Paris Université (CY), Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), and University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)

Subjects
Mathematics - Analysis of PDEs, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP]
Abstract

The purpose of this article is to show that the spectral projector estimates for Laplace operators can be deduced from Logunov-Malinnikova's Propagation of smallness estimates for harmonic functions [11, 10, 9]. The main point is to pass from the local estimates obtained in [4] (on a compact manifold) to global estimates. We also state classical consequences in terms of observability and control for heat equations, which are direct consequences of these spectral projector estimates..

Published
2021

37. Exact fluctuating hydrodynamics of active lattice gases—typical fluctuations

Author

Tal Agranov, Sunghan Ro, Vivien Lecomte, Yariv Kafri, Laboratoire Interdisciplinaire de Physique [Saint Martin d’Hères] (LIPhy), Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel, Technion - Israel Institute of Technology [Haifa], Department of Applied Mathematics and Theoretical Physics [Cambridge] (DAMTP), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), and Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)

Subjects
Statistics and Probability, Collective behavior, [PHYS.MPHY]Physics [physics]/Mathematical Physics [math-ph], Lattice (group), FOS: Physical sciences, Condensed Matter - Soft Condensed Matter, 01 natural sciences, 010305 fluids & plasmas, Critical point (thermodynamics), Phase (matter), 0103 physical sciences, Statistical physics, [PHYS.COND.CM-SM]Physics [physics]/Condensed Matter [cond-mat]/Statistical Mechanics [cond-mat.stat-mech], 010306 general physics, Condensed Matter - Statistical Mechanics, ComputingMilieux_MISCELLANEOUS, Physics, Statistical Mechanics (cond-mat.stat-mech), Statistical and Nonlinear Physics, Renormalization group, 3. Good health, Active matter, Thermodynamic limit, Soft Condensed Matter (cond-mat.soft), Ising model, Statistics, Probability and Uncertainty
Abstract

We extend recent results on the exact hydrodynamics of a system of diffusive active particles displaying a motility-induced phase separation to account for typical fluctuations of the dynamical fields. By calculating correlation functions exactly in the homogeneous phase, we find that two macroscopic length scales develop in the system. The first is related to the diffusive length of the particles and the other to the collective behavior of the particles. The latter diverges as the critical point is approached. Our results show that the critical behavior of the model in one dimension belongs to the universality class of a mean-field Ising model, both for static and dynamic properties, when the thermodynamic limit is taken in a specified manner. The results are compared to the critical behavior exhibited by the ABC model. In particular, we find that in contrast to the ABC model the density large deviation function, at its Gaussian approximation, does not contain algebraically decaying interactions but is of a finite, macroscopic, extent which is dictated by the diverging correlation length., Comment: 17 pages, 6 figures

Published
2021

38. Training in the use of intrapartum electronic fetal monitoring with cardiotocography: Systematic review and meta-analysis

Author

Tim Draycott, Mary Dixon-Woods, Guillaume Lamé, Isla Kuhn, Sarah Kelly, Clare Oliver-Williams, Sarah King, Elisa Liberati, Patrick Redmond, Jenni Burt, Cathy Winter, THIS Institute (The Healthcare Improvement Studies Institute), Department of Public Health and Primary Care, University of Cambridge, Department of Public Health and Primary Care, University of Cambridge-Department of Public Health and Primary Care, University of Cambridge, University of Cambridge [UK] (CAM), King‘s College London, Independent Consultant, Dept of Public Health and Primary Care, University of Cambridge [UK] (CAM)-MRC Center for Nutritional Epidemiology and Cancer Prevention and Survival, Homerton College, University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Laboratoire Génie Industriel (LGI), CentraleSupélec-Université Paris-Saclay, PROMPT Maternity Foundation, Southmead Hospital, Bristol, University of Bristol [Bristol], Kelly, S [0000-0002-1114-2456], Redmond, P [0000-0002-3929-2018], King, S [0000-0002-0637-7672], Oliver-Williams, C [0000-0002-3573-2426], Lamé, G [0000-0001-9514-1890], Liberati, E [0000-0003-4981-1210], Kuhn, I [0000-0002-2292-6053], Winter, C [0000-0002-8066-7061], Draycott, T [0000-0002-1825-4864], Dixon-Woods, M [0000-0002-5915-0041], Burt, J [0000-0002-0037-274X], Apollo - University of Cambridge Repository, Oliver‐Williams, C [0000-0002-3573-2426], and Dixon‐Woods, M [0000-0002-5915-0041]

Subjects
medicine.medical_specialty, Mixed methods, intrapartum, Systematic Reviews, education, MEDLINE, Intervention, PsycINFO, CINAHL, Cochrane Library, [SDV.MHEP.GEO]Life Sciences [q-bio]/Human health and pathology/Gynecology and obstetrics, neonatal, 03 medical and health sciences, 0302 clinical medicine, Fetal heartbeat monitoring, Observational study, medicine, Cardiotocography, Intensive care medicine, Kirkpatrick model, Caesarean, 030219 obstetrics & reproductive medicine, medicine.diagnostic_test, business.industry, Clinical outcome, Obstetrics and Gynecology, Pregnancy, Health personnel, 3. Good health, Meta-analysis, fetal heartrate monitoring, [SDV.SPEE]Life Sciences [q-bio]/Santé publique et épidémiologie, Systematic Review, pregnancy, business, Intrapartum Cardiotocography
Abstract

Background Sub‐optimal classification, interpretation and response to intrapartum electronic fetal monitoring using cardiotocography are known problems. Training is often recommended as a solution, but there is lack of clarity about the effects of training and which type of training works best. Objectives Systematic review of the effects of training healthcare professionals in intrapartum cardiotocography (PROSPERO protocol: CRD42017064525). Search strategy CENTRAL, Cochrane Library, MEDLINE, EMBASE, PsycINFO, British Nursing Database, CINAHL, ERIC, Scopus, Web of Science, ProQuest, grey literature and ongoing clinical trials were searched. Selection criteria Primary studies that reported impact of training healthcare professionals in intrapartum cardiotocography. Title/abstract, full‐text screening and quality assessment were conducted in duplicate. Data collection and analysis Data were synthesised both narratively and using meta‐analysis. Risk of bias and overall quality were assessed with the Mixed Methods Appraisal Tool and GRADE. Main results Sixty‐four studies were included. Overall, training and reporting were heterogeneous, the outcomes evaluated varied widely and study quality was low. Five randomised controlled trials reported that training improved knowledge of maternity professionals compared with no training, but evidence was of low quality. Evidence for the impact of cardiotocography training on neonatal and maternal outcomes was limited, showed inconsistent effects, and was of low overall quality. Evidence for the optimal content and method of delivery of training was very limited. Conclusions Given the scale of harm and litigation claims associated with electronic fetal monitoring, the evidence‐base for training requires improvement. It should address intervention design, evaluation of clinical outcomes and system‐wide contexts of sub‐optimal practice. Tweetable abstract Training in fetal monitoring: systematic review finds little evidence of impact on neonatal outcomes., Tweetable abstract Training in fetal monitoring: systematic review finds little evidence of impact on neonatal outcomes.

Published
2021

39. Quantitative fluid approximation in transport theory: a unified approach

Author

Bouin, Emeric, Mouhot, Clément, CEntre de REcherches en MAthématiques de la DEcision (CEREMADE), Centre National de la Recherche Scientifique (CNRS)-Université Paris Dauphine-PSL, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Université Paris Dauphine-PSL, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Mathematics - Analysis of PDEs, [MATH.MATH-MP]Mathematics [math]/Mathematical Physics [math-ph], FOS: Mathematics, FOS: Physical sciences, General Earth and Planetary Sciences, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], Mathematical Physics (math-ph), Mathematical Physics, Analysis of PDEs (math.AP), General Environmental Science
Abstract

We propose a unified method for the large space-time scaling limit of \emph{linear} collisional kinetic equations in the whole space. The limit is of \emph{fractional} diffusion type for heavy tail equilibria with slow enough decay, and of diffusive type otherwise. The proof is constructive and the fractional/standard diffusion matrix is obtained. The equilibria satisfy a {\em generalised} weighted mass condition and can have infinite mass. The method combines energy estimates and quantitative spectral methods to construct a `fluid mode'. The method is applied to scattering models (without assuming detailed balance conditions), Fokker-Planck operators and Lévy-Fokker-Planck operators. It proves a series of new results, including the fractional diffusive limit for Fokker-Planck operators in any dimension, for which the characterization of the diffusion coefficient was not known, for Lévy-Fokker-Planck operators with general equilibria, and in cases where the equilibrium has infinite mass. It also unifies and generalises the results of ten previous papers with a quantitative method, and our estimates on the fluid approximation error seem novel in these cases.

Published
2021

40. Systematic Literature Reviews: An Introduction

Author

Lame, Guillaume, University of Cambridge [UK] (CAM), THIS Institute (The Healthcare Improvement Studies Institute), Department of Public Health and Primary Care, University of Cambridge, University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), and Guillaume Lamé is supported by the Health Foundation’s grant to the University of Cambridge for The Healthcare Improvement Studies (THIS) Institute. THIS Institute is supported by the Health Foundation - an independent charity committed to bringing about better health and health care for people in the UK.Guillaume Lamé is supported by the Health Foundation’s grant to the University of Cambridge for The Healthcare Improvement Studies (THIS) Institute. THIS Institute is supported by the Health Foundation - an independent charity committed to bringing about better health and health care for people in the UK.

Subjects
[SPI.OTHER]Engineering Sciences [physics]/Other, Research design, Computer science, media_common.quotation_subject, 0211 other engineering and technologies, Public policy, 02 engineering and technology, Scientific evidence, 03 medical and health sciences, 0302 clinical medicine, Design Research, Research methodologies and methods, Quality (business), 030212 general & internal medicine, 33 Built Environment and Design, Evaluation, Design methods, Research question, 40 Engineering, 021106 design practice & management, media_common, Management science, Systematic reviews, General Medicine, 4010 Engineering Practice and Education, 8.4 Research design and methodologies (health services), Systematic review, Work (electrical), Design methodology, Generic health relevance, 8 Health and social care services research, 3303 Design
Abstract

Systematic literature reviews (SRs) are a way of synthesising scientific evidence to answer a particular research question in a way that is transparent and reproducible, while seeking to include all published evidence on the topic and appraising the quality of this evidence. SRs have become a major methodology in disciplines such as public policy research and health sciences. Some have advocated that design research should adopt the method. However, little guidance is available. This paper provides an overview of the SR method, based on the literature in health sciences. Then, the rationale for SRs in design research is explored, and four recent examples of SRs in design research are analysed to illustrate current practice. Foreseen challenges in taking forward the SR method in design research are highlighted, and directions for developing a SR method for design research are proposed. It is concluded that SRs hold potential for design research and could help us in addressing some important issues, but work is needed to define what review methods are appropriate for each type of research question in design research, and to adapt guidance to our own needs and specificities.

Published
2019

41. A finite dimensional approach to Donaldson’s J‑flow

Author

Ruadhaí Dervan, Julien Keller, Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Institut de Mathématiques de Marseille (I2M), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), ANR-14-CE25-0010,EMARKS,Métriques extrémales et K-stabilité(2014), ANR-11-IDEX-0001,Amidex,INITIATIVE D'EXCELLENCE AIX MARSEILLE UNIVERSITE(2011), and Apollo - University of Cambridge Repository

Subjects
Mathematics - Differential Geometry, Statistics and Probability, Pure mathematics, Stability (learning theory), polarisation, Type (model theory), Mathematics - Algebraic Geometry, J-flow, Mathematics::Algebraic Geometry, balanced metrics, FOS: Mathematics, Uniqueness, Complex Variables (math.CV), Algebraic Geometry (math.AG), Mathematics, Energy functional, critical metrics, Mathematics - Complex Variables, Linear system, 4904 Pure Mathematics, K-stability, [MATH.MATH-CV]Mathematics [math]/Complex Variables [math.CV], Chow stability, canonical metrics, Canonical bundle, Differential Geometry (math.DG), projective manifold, Flow (mathematics), [MATH.MATH-DG]Mathematics [math]/Differential Geometry [math.DG], 49 Mathematical Sciences, 14L24, 53C07, 32Q20, 53D50, 53D20, quantization, [MATH.MATH-AG]Mathematics [math]/Algebraic Geometry [math.AG], Geometry and Topology, Statistics, Probability and Uncertainty, Complex manifold, Analysis
Abstract

We define a quantisation of the J-flow over a projective complex manifold. As corollaries, we obtain new proofs of uniqueness of critical points of the J-flow and that these critical points achieve the absolute minimum of an associated energy functional. We show that the existence of a critical point of the J-flow implies the existence of certain canonical metrics, that we call J-balanced metrics. We define a notion of Chow stability for linear systems and relate it to the existence of J-balanced metrics. We also relate the asymptotic Chow stability of a linear system to an analogue of K-semistability that was introduced by Lejmi-Sz\'ekelyhidi, which we call J-semistability. Then, we relate J-semistability to K-stability when one of the polarisation is the canonical bundle. Eventually, this gives new K-stable polarisations of surfaces of general type., Comment: 47 pages; Revised version. To appear in Comm. Anal. Geom

Published
2019

42. From Boltzmann to incompressible Navier–Stokes in Sobolev spaces with polynomial weight

Author

Sara Merino-Aceituno, Marc Briant, Clément Mouhot, Mathématiques Appliquées Paris 5 (MAP5 - UMR 8145), Université Paris Descartes - Paris 5 (UPD5)-Institut National des Sciences Mathématiques et de leurs Interactions (INSMI)-Centre National de la Recherche Scientifique (CNRS), DPMMS/CMS, University of Cambridge [UK] (CAM), Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), and University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM)

Subjects
Polynomial, Boltzmann equation on the Torus, Mathematics::Analysis of PDEs, FOS: Physical sciences, 010103 numerical & computational mathematics, Space (mathematics), Lebesgue integration, Incompressible Navier-Stokes hydrodynamical limit, 01 natural sciences, Physics::Fluid Dynamics, symbols.namesake, Mathematics - Analysis of PDEs, [MATH.MATH-MP]Mathematics [math]/Mathematical Physics [math-ph], FOS: Mathematics, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], QA276, 0101 mathematics, Exponential decay, Mathematical Physics, Mathematics, Applied Mathematics, 010102 general mathematics, Mathematical analysis, Mathematical Physics (math-ph), 16. Peace & justice, Boltzmann equation, Sobolev space, Boltzmann constant, symbols, Knudsen number, Cauchy theory, Analysis, Analysis of PDEs (math.AP)
Abstract

We study the Boltzmann equation on the $d$-dimensional torus in a perturbative setting around a global equilibrium under the Navier-Stokes linearisation. We use a recent functional analysis breakthrough to prove that the linear part of the equation generates a $C^0$-semigroup with exponential decay in Lebesgue and Sobolev spaces with polynomial weight, independently on the Knudsen number. Finally we show a Cauchy theory and an exponential decay for the perturbed Boltzmann equation, uniformly in the Knudsen number, in Sobolev spaces with polynomial weight. The polynomial weight is almost optimal and furthermore, this result only requires derivatives in the space variable and allows to connect to solutions to the incompressible Navier-Stokes equations in these spaces., 30 pages

Published
2018

43. Sensitivity of the Atlantic meridional overturning circulation and climate to tropical Indian Ocean warming

Author

Brady Ferster, Alexey V. Fedorov, Juliette Mignot, Eric Guilyardi, Océan et variabilité du climat (VARCLIM), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Yale University [New Haven], NCAS-Climate [Cambridge], Department of Chemistry [Cambridge, UK], University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), ANR-18-MPGA-0001,ARCHANGE,Changement climatique et Arctique et circulation océanique globale(2018), European Project: 776613,Fighting and adapting to climate change,H2020-EU.3.5.1,EUCP(2017), Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)

Subjects
Atmospheric Science, Water mass, 010504 meteorology & atmospheric sciences, Arctic sea ice, Tropical Atlantic, 010502 geochemistry & geophysics, 01 natural sciences, Sea ice, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography, 0105 earth and related environmental sciences, geography, geography.geographical_feature_category, Global warming, North Atlantic, Arctic ice pack, Indian ocean warming, 13. Climate action, North Atlantic oscillation, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, Climatology, Teleconnections, Environmental science, Climate model, AMOC, North Atlantic Oscillation, Teleconnection
Abstract

International audience; A salient feature of anthropogenic climate change is the enhanced warming of the tropical Indian Ocean (TIO) relative to the tropics. Recent studies show that this warming can remotely modulate the Atlantic meridional overturning circulation (AMOC). Motivated by these results, we systematically study the sensitivity of the AMOC and Atlantic climate to changes in TIO temperature using the latest coupled climate model from the Institut Pierre Simon Laplace (IPSL-CM6A-LR). Ensemble experiments nudging the TIO surface temperatures by-2°C,-1°C, +1°C, and +2°C are conducted. Within a few years after the forcing is imposed, different atmospheric teleconnections begin to drive the AMOC "fast" and "slow" responses, yielding after 150 years an AMOC equilibrium sensitivity of about +9.4 Sv per 1°C of relative TIO warming. A water mass transformation analysis shows that the fast response to TIO warming (on decadal timescales) is largely driven by surface cooling in the Labrador Sea caused by an induced positive North Atlantic Oscillation (NAO)-like mean pattern. By contrast, the slow response (on multi-decadal to centennial timescales) is driven by the gradual advection of positive salinity anomalies from the tropical Atlantic, which predominantly affect the Nordic Seas. The response is non-linear in that a TIO warming strengthens the AMOC through increase in Labrador Sea deep water formation, while a TIO cooling slows down the AMOC via sea ice expansion over the Nordic Seas deep-water formation region, ultimately leading to the AMOC shutdown in the-2ºC-TIO experiment. These results help understand the role of interbasin connections and AMOC drivers in a warming climate.

Published
2021

44. Special macroscopic modes and hypocoercivity

Author

Carrapatoso, Kleber, Dolbeault, Jean, Hérau, Frédéric, Mischler, Stéphane, Mouhot, Clément, Schmeiser, Christian, École polytechnique (X), Centre de Mathématiques Laurent Schwartz (CMLS), École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS), Université Paris Dauphine-PSL, Université Paris sciences et lettres (PSL), CEntre de REcherches en MAthématiques de la DEcision (CEREMADE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Mathématiques Jean Leray (LMJL), Centre National de la Recherche Scientifique (CNRS)-Nantes université - UFR des Sciences et des Techniques (Nantes univ - UFR ST), Nantes Université - pôle Sciences et technologie, Nantes Université (Nantes Univ)-Nantes Université (Nantes Univ)-Nantes Université - pôle Sciences et technologie, Nantes Université (Nantes Univ)-Nantes Université (Nantes Univ), Département de Mathématiques et Informatique - Université de Nantes, Université de Nantes (UN), Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), University of Cambridge [UK] (CAM), University of Vienna [Vienna], ANR-17-CE40-0030,EFI,Entropie, flots, inégalités(2017), ANR-11-LABX-0020,LEBESGUE,Centre de Mathématiques Henri Lebesgue : fondements, interactions, applications et Formation(2011), European Project: 726386,MAFRAN, Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X), Centre National de la Recherche Scientifique (CNRS)-Université Paris Dauphine-PSL, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), and Université de Nantes (UN)-Université de Nantes (UN)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Poincaré-Korn inequality, FOS: Physical sciences, symmetries, hypocoercivity, 82C40, 76P05, 35Q83, 82C70, global conservation laws, special macroscopic modes, Witten-Laplace operator, commutators, Mathematics - Analysis of PDEs, micro/macro decomposition, [MATH.MATH-MP]Mathematics [math]/Mathematical Physics [math-ph], classification of steady states, collision invariant, spectral gap, FOS: Mathematics, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], collision operator, transport operator, linear kinetic equations, Mathematical Physics, partially harmonic potential, rotational invariance, hypoellipticity, 82C40, 76P05, 35Q83, 82C70, Mathematical Physics (math-ph), time-periodic solutions, confinement potential, rotations, local conservation laws, Analysis of PDEs (math.AP)
Abstract

We study linear inhomogeneous kinetic equations with an external confining potential and a collision operator admitting several local conservation laws (local density, momentum and energy). We classify all special macroscopic modes (stationary solutions and time-periodic solutions). We also prove the convergence of all solutions of the evolution equation to such non-trivial modes, with a quantitative exponential rate. This is the first hypocoercivity result with multiple special macroscopic modes with constructive estimates depending on the geometry of the potential., 65 pages, 1 figure

Published
2021

45. Special modes and hypocoercivity for linear kinetic equations with several conservation laws and a confining potential

Author

Carrapatoso, Kleber, Dolbeault, Jean, Hérau, Frédéric, Mischler, Stéphane, Mouhot, Clément, Schmeiser, Christian, École polytechnique (X), Centre de Mathématiques Laurent Schwartz (CMLS), Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X), Université Paris Dauphine-PSL, Université Paris sciences et lettres (PSL), CEntre de REcherches en MAthématiques de la DEcision (CEREMADE), Centre National de la Recherche Scientifique (CNRS)-Université Paris Dauphine-PSL, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Département de Mathématiques et Informatique - Université de Nantes, Université de Nantes (UN), Laboratoire de Mathématiques Jean Leray (LMJL), Centre National de la Recherche Scientifique (CNRS)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN), Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), University of Cambridge [UK] (CAM), and University of Vienna [Vienna]

Subjects
Boltzmann equation, Poincaré inequality, [MATH.MATH-MP]Mathematics [math]/Mathematical Physics [math-ph], micro-macro method, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], hypocoercivity, confining potential, Landau equation, commutator method, weighted Korn inequality
Abstract

41 pages, 1 figure; We study linear inhomogeneous kinetic equations with an external confining potential and a collision operator with several local conservation laws (local density, momentum and energy). We exhibit all equilibria and entropy-maximizing special modes, and we prove asymptotic exponential convergence of solutions to them with quantitative rate. This is the first complete picture of hypocoercivity and quantitative $H$-theorem for inhomogeneous kinetic equations in this setting.

Published
2021

46. Log-transform and the weak Harnack inequality for kinetic Fokker-Planck equations

Author

Jessica Guerand, Cyril Imbert, Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Département de Mathématiques et Applications - ENS Paris (DMA), Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), European Project: 726386,MAFRAN, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), and École normale supérieure - Paris (ENS-PSL)

Subjects
Mathematics - Analysis of PDEs, General Mathematics, FOS: Mathematics, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], Analysis of PDEs (math.AP)
Abstract

This article deals with kinetic Fokker–Planck equations with essentially bounded coefficients. A weak Harnack inequality for nonnegative super-solutions is derived by considering their log-transform and adapting an argument due to S. N. Kružkov (1963). Such a result rests on a new weak Poincaré inequality sharing similarities with the one introduced by W. Wang and L. Zhang in a series of works about ultraparabolic equations (2009, 2011, 2017). This functional inequality is combined with a classical covering argument recently adapted by L. Silvestre and the second author (2020) to kinetic equations.

Published
2021

47. Variational multi-task MRI reconstruction: Joint reconstruction, registration and super-resolution

Author

Carola-Bibiane Schönlieb, Noémie Debroux, Angelica I. Aviles-Rivero, Veronica Corona, Carole Le Guyader, Department of Applied Mathematics and Theoretical Physics (DAMTP), University of Cambridge [UK] (CAM), Department of Pure Mathematics and Mathematical Statistics (DPMMS), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Institut Pascal (IP), Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA)-Institut national polytechnique Clermont Auvergne (INP Clermont Auvergne), Université Clermont Auvergne (UCA)-Université Clermont Auvergne (UCA), Laboratoire de Mathématiques de l'INSA de Rouen Normandie (LMI), Institut national des sciences appliquées Rouen Normandie (INSA Rouen Normandie), Institut National des Sciences Appliquées (INSA)-Normandie Université (NU)-Institut National des Sciences Appliquées (INSA)-Normandie Université (NU), Corona, Veronica [0000-0003-2160-5482], and Apollo - University of Cambridge Repository

Subjects
math.NA, Image Registration, Computer science, media_common.quotation_subject, Physics::Medical Physics, Motion Correction, ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION, MRI Reconstruction, Image registration, Fidelity, CPU time, Health Informatics, Motion (physics), 030218 nuclear medicine & medical imaging, Set (abstract data type), Motion, 03 medical and health sciences, Imaging, Three-Dimensional, 0302 clinical medicine, Image Super-resolution, Image Processing, Computer-Assisted, FOS: Electrical engineering, electronic engineering, information engineering, FOS: Mathematics, [INFO.INFO-IM]Computer Science [cs]/Medical Imaging, Humans, Radiology, Nuclear Medicine and imaging, Computer vision, Mathematics - Numerical Analysis, Representation (mathematics), cs.NA, media_common, ComputingMethodologies_COMPUTERGRAPHICS, Radiological and Ultrasound Technology, business.industry, Image and Video Processing (eess.IV), Numerical Analysis (math.NA), Electrical Engineering and Systems Science - Image and Video Processing, Magnetic Resonance Imaging, Computer Graphics and Computer-Aided Design, Term (time), Task (computing), eess.IV, Computer Vision and Pattern Recognition, Artificial intelligence, business, Algorithms, 030217 neurology & neurosurgery
Abstract

Motion degradation is a central problem in Magnetic Resonance Imaging (MRI). This work addresses the problem of how to obtain higher quality, super-resolved motion-free reconstructions from highly undersampled MRI data. In this work, we present for the first time a variational multi-task framework that allows joining three relevant tasks in MRI: reconstruction, registration and super-resolution. Our framework takes a set of multiple undersampled MR acquisitions corrupted by motion into a novel multi-task optimisation model, which is composed of an L2 fidelity term that allows sharing representation between tasks, super-resolution foundations and hyperelastic deformations to model biological tissue behaviors. We demonstrate that this combination yields significant improvements over sequential models and other bi-task methods. Our results exhibit fine details and compensate for motion producing sharp and highly textured images compared to state of the art methods while keeping low CPU time. Our improvements are appraised on both clinical assessment and statistical analysis.

Published
2021

48. Atlantic ocean ventilation changes across the last deglaciation and their carbon cycle implications

Author

David A. Hodell, Claire Waelbroeck, A. E. Scrivner, E Freeman, Luke C Skinner, N. Vazquez Riveiros, Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences [Cambridge, UK], University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Processus et interactions de fine échelle océanique (PROTEO), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Laboratoire Géodynamique et enregistrement Sédimentaire (LGS), Géosciences Marines (GM), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), ANR-09-BLAN-0347,RETRO(2009), European Project: 339108,EC:FP7:ERC,ERC-2013-ADG,ACCLIMATE(2014), Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU), Laboratoire Géodynamique et enregistrement Sédimentaire - Geosciences Marines (GM-LGS), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Skinner, LC [0000-0002-5050-0244], Hodell, D [0000-0001-8537-1588], Waelbroeck, C [0000-0002-7256-5727], Vazquez Riveiros, N [0000-0001-7513-153X], and Apollo - University of Cambridge Repository

Subjects
Atmospheric Science, air&#8208, 010504 meteorology & atmospheric sciences, sub-01, sea exchange, [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph], Structural basin, deglaciation, 010502 geochemistry & geophysics, Oceanography, 01 natural sciences, law.invention, Carbon cycle, law, carbon cycle, Deglaciation, 14. Life underwater, Stadial, Radiocarbon dating, Younger Dryas, 0105 earth and related environmental sciences, Atlantic hurricane, ventilation, Paleontology, Last Glacial Maximum, 13. Climate action, radiocarbon, AMOC, Geology
Abstract

International audience; Changes in ocean ventilation, controlled by both overturning rates and air‐sea gas exchange, are thought to have played a central role in atmospheric CO2 rise across the last deglaciation. Here, we constrain the nature of Atlantic Ocean ventilation changes over the last deglaciation using radiocarbon and stable carbon isotopes from two depth transects in the Atlantic basin. Our findings broadly cohere with the established pattern of deglacial Atlantic overturning change, and underline the existence of active northern sourced deep‐water export at the Last Glacial Maximum (LGM). We find that the western Atlantic was less affected by incursions of southern‐sourced deep water, as compared to the eastern Atlantic, despite both sides of the basin being strongly influenced by the air‐sea equilibration of both northern and southern deep‐water end‐members. Ventilation at least as strong as modern is observed throughout the Atlantic during the Bølling‐Allerød (BA), implying a “flushing” of the entire Atlantic water column that we attribute to the combined effects of Atlantic meridional overturning circulation (AMOC) reinvigoration and increased air‐sea equilibration of southern sourced deep‐water. This ventilation “overshoot” may have counteracted a natural atmospheric CO2 decline during interstadial conditions, helping to make the BA a “point of no return” in the deglacial process. While the collected data emphasize a predominantly indirect AMOC contribution to deglacial atmospheric CO2 rise, via far field impacts on convection in the Southern Ocean and/or North Pacific during Heinrich Stadial 1 and the Younger Dryas, the potential role of the AMOC in centennial CO2 pulses emerges as an important target for future work.

Published
2021

49. Ocean surface and bottom water conditions, iceberg drift and sediment transport on the North Iceland margin during MIS 3 and MIS 2

Author

Simon T. Belt, Marie-Alexandrine Sicre, Lukas Smik, John T. Andrews, I. N. McCave, Institute of Arctic and Alpine Research (INSTAAR), University of Colorado [Boulder], School of Geography, Earth and Environmental Sciences [Plymouth] (SoGEES), Plymouth University, Variabilité de l'Océan et de la Glace de mer (VOG), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Sorbonne Université (SU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Sorbonne Université (SU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences [Cambridge, UK], University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Institute of Arctic Alpine Research [University of Colorado Boulder] (INSTAAR), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Bristol Biogeochemistry Research Centre, School of Earth Sciences [Bristol], University of Bristol [Bristol]-University of Bristol [Bristol], Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)

Subjects
010506 paleontology, Archeology, sea ice biomarkers, 010504 meteorology & atmospheric sciences, Ice stream, sub-01, [SDE.MCG]Environmental Sciences/Global Changes, IP25, sortable silt, MIS 2 and 3, 01 natural sciences, Sortable silt, Bottom water, [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry, Paleoclimatology, Sea ice, 14. Life underwater, alkenones, Ecology, Evolution, Behavior and Systematics, Holocene, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Drift ice, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Global and Planetary Change, geography, geography.geographical_feature_category, sediment provenance, Alkenones, Sea ice biomarkers, Geology, Iceberg, Sea surface temperature, Oceanography, 13. Climate action, [SDU]Sciences of the Universe [physics], [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, [SDE]Environmental Sciences, Sediment provenance, Iceland Plateau
Abstract

International audience; Radiocarbon dates and marine tephra suggest that the upper 10 m of core MD99-2274 off North Iceland extends from ∼0 to ∼65 ka BP. A multi-proxy sediment and biomarker study at a ∼0.5 ky resolution is used to derive a paleoclimate scenario for this area of the southwestern Nordic Seas, which during the Holocene had intermittent excursions of icebergs and a seasonal cover of drifting sea ice across the site. The sortable silt mean size (S̅S̅) suggests a bottom current (1000 m depth) flow speed maximum to minimum range of ∼8 cm/s during Marine Isotope Stages 2–3, but the data are unreliable for the Holocene. Slow-down in flow speeds may be associated with massive ice and water discharges linked to the Hudson Strait ice stream (H-events) and to melt of icebergs from Greenland in the Nordic seas where convection would have been suppressed. Five pulses of sediment with a distinct felsic component are associated with iceberg transport from E/NE Greenland. Sea ice, open water and sea surface temperature (SST) biomarker proxies (i.e. IP25, HBI III, brassicasterol and alkenones) all point towards near-perennial sea ice cover during MIS 3 and 2, rather than seasonal sea ice or open water conditions. Indeed, our biomarker and sediment data require that the seas north of Iceland experienced a nearly continuous cover of sea ice, together with icebergs calved from ice stream termini, which drifted southward. The cross-correlation of the quartz % records between MD99-2274 and the well-dated core PS2644 in Blosseville Basin indicates significant coherence in the records at a multi-millennial (∼8 ky) timescale. A transition to open ocean conditions is evident from the early Holocene onwards, albeit with the occurrence of some drift ice and icebergs.

Published
2021

50. Reconstructing Holocene landscape and environmental changes at Lago Rogaguado, Bolivian Amazon

Author

Walter Finsinger, Alena Giesche, Umberto Lombardo, Heinz Veit, Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences [Cambridge, UK], University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), Institute of Geography [Bern], University of Bern, Institut des Sciences de l'Evolution de Montpellier (UMR ISEM), École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Montpellier (UM)-Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Centre National de la Recherche Scientifique (CNRS)-Institut de recherche pour le développement [IRD] : UR226, Swiss National Science Foundation (SNF) [200020–141277/1], Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Montpellier (UM)-Institut de recherche pour le développement [IRD] : UR226-Centre National de la Recherche Scientifique (CNRS), and Apollo - University of Cambridge Repository

Subjects
010506 paleontology, Watershed, 010504 meteorology & atmospheric sciences, [SDE.MCG]Environmental Sciences/Global Changes, Climate change, 3705 Geology, Aquatic Science, 01 natural sciences, Sedimentology, Charcoal, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Holocene, 0105 earth and related environmental sciences, Earth-Surface Processes, 15 Life on Land, Sediment, 37 Earth Sciences, 3709 Physical Geography and Environmental Geoscience, 15. Life on land, Sedimentation, [SDE.ES]Environmental Sciences/Environmental and Society, [SDV.BIBS]Life Sciences [q-bio]/Quantitative Methods [q-bio.QM], visual_art, Erosion, visual_art.visual_art_medium, Environmental science, Physical geography, [SDE.BE]Environmental Sciences/Biodiversity and Ecology
Abstract

International audience; We performed geochemical analyses of two lake sediment cores (1.25 and 1.5 m long) from Lago Rogaguado, which is a large (315 km 2) and shallow lake in the Llanos de Moxos, Bolivian Amazon, to investigate Holocene environmental changes based on a multi-proxy dataset (XRF, density, grain size, C:N, and macrocharcoal). One of the two cores provides a history of environmental changes in the Llanos de Moxos from 8100 cal BP until present, which supplements previously published pollen and microscopic charcoal records. Our analyses indicate lake expansion at 5800 cal BP, which may relate to tectonic activity. This was followed by further increasing lake levels, peaking at approximately 1050-400 cal BP, which supports increasingly wetter conditions in the Llanos de Moxos after the mid-Holocene. A fourfold increase in macroscopic charcoal accumulation rate and a more than fivefold increase in sedimentation rates supports anthropogenic fire activity at around 1450 cal BP (500 CE), suggesting that pre-Columbian populations used fire to actively manage the landscape during a period of maximum lake levels around Lago Rogaguado. From 400-100 cal BP, higher C:N, larger grain sizes and peaks in macroscopic charcoal accumulation rates suggest increased watershed erosion associated with increased biomass burning, possibly related to intensified land use. Keywords Bolivian amazon Á Llanos de moxos Á Lake level Á Climate Á Land use change Á Shallow lake

Published
2021

Catalog

Books, media, physical & digital resources
See catalog results