7 results
The Atlantic Meridional Overturning Circulation as productivity regulator of the North Atlantic Subtropical Gyre
- Sílvia Nave, Susana Lebreiro, Elisabeth Michel, Catherine Kissel, Maria Ondina Figueiredo, Abel Guihou, António Ferreira, Laurent Labeyrie, Ana Alberto
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- Journal:
- Quaternary Research / Volume 91 / Issue 1 / January 2019
- Published online by Cambridge University Press:
- 14 November 2018, pp. 399-413
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Spatially extensive and intense phytoplankton blooms observed off Iberia, in satellite pictures, are driven by significant nutrient supply by upper-ocean vertical mesoscale activity rather than by horizontal advection by coastal upwelling. Productivity of oligotrophic regions is still poorly depicted by discrete instrumental and model data sets. The paleoproductivity reconstructions of these areas represent the mean productivity over long periods, bringing new insights into the total biomass fluxes. Here, we present paleoproductivity records from the oceanic Tore Seamount region, covering the period from 140 to 60 ka. They show higher nutrient supplies during Termination II, Marine Oxygen Isotope Stage (MIS) 4, MIS 6, and warming transitions of the MIS 5 sub-stages. The highest nutrient content (higher productivity) in phase with tracers of bottom-water ventilation (benthic δ13C,231Pa/230Th) establishes a strong linkage with variability of Southern Ocean-sourced waters. Low productivity and ventilation over warm sub-stages of MIS 5 respond instead to North Atlantic Deep Water. Assuming that the Tore Seamount is representative of oligotrophic regions, the glacial-interglacial relationship observed between paleoproductivity and Atlantic Meridional Overturning Circulation strength opens new insights into the importance of estimating the total biomass in these regions. The subtropical gyres might play a considerable role in the carbon cycle over (sub-)glacial-interglacial time scales than previously thought.
Silicified plant megafossils from the upper Turonian of Vienne, western France
- Bernard Gomez, Véronique Daviero-Gomez, Géraldine Garcia, Laurent Caner, Anaïs Boura, Abel Barral, Patrice Cantinolle, Xavier Valentin
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- Journal:
- Earth and Environmental Science Transactions of The Royal Society of Edinburgh / Volume 108 / Issue 4 / December 2017
- Published online by Cambridge University Press:
- 29 November 2018, pp. 449-457
- Print publication:
- December 2017
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A new locality with silicified permineralised plant megafossils is reported from the upper Turonian of Colombiers, Vienne, western France. The plant fossil assemblage consists of Geinitzia reichenbachii (Geinitz) Hollick et Jeffrey and ‘Lomatopteris' superstes Saporta. Whilst G. reichenbachii is a worldwide widespread Cretaceous conifer, ‘L.' superstes is reported in western France for the first time. The latter fossil shows bipinnately compound leaf, marginal teeth, one thick primary vein, pinnate secondary veins and faint, reticulate, narrower veins. Besides its fern-like gross morphology, these characters indicate that it most likely belongs to angiosperms and eudicots. The formation of silicified nodules bearing such fossils from the Cenomanian to the Coniacian of western France was previously attributed to the secondary silicification of limestones during Cenozoic climatic weathering episodes. However, based on both petrography and preservation evidence, we demonstrate that it was an endogenic process contemporaneous to the earliest stages of fossil diagenesis created by palaeoenvironmental and climatic conditions.
Frequency selection by feedback control in a turbulent shear flow
- Vladimir Parezanović, Laurent Cordier, Andreas Spohn, Thomas Duriez, Bernd R. Noack, Jean-Paul Bonnet, Marc Segond, Markus Abel, Steven L. Brunton
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- Journal:
- Journal of Fluid Mechanics / Volume 797 / 25 June 2016
- Published online by Cambridge University Press:
- 18 May 2016, pp. 247-283
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Many previous studies have shown that the turbulent mixing layer under periodic forcing tends to adopt a lock-on state, where the major portion of the fluctuations in the flow are synchronized at the forcing frequency. The goal of this experimental study is to apply closed-loop control in order to provoke the lock-on state, using information from the flow itself. We aim to determine the range of frequencies for which the closed-loop control can establish the lock-on, and what mechanisms are contributing to the selection of a feedback frequency. In order to expand the solution space for optimal closed-loop control laws, we use the genetic programming control (GPC) framework. The best closed-loop control laws obtained by GPC are analysed along with the associated physical mechanisms in the mixing layer flow. The resulting closed-loop control significantly outperforms open-loop forcing in terms of robustness to changes in the free-stream velocities. In addition, the selection of feedback frequencies is not locked to the most amplified local mode, but rather a range of frequencies around it.
Cluster-based reduced-order modelling of a mixing layer
- Eurika Kaiser, Bernd R. Noack, Laurent Cordier, Andreas Spohn, Marc Segond, Markus Abel, Guillaume Daviller, Jan Östh, Siniša Krajnović, Robert K. Niven
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- Journal:
- Journal of Fluid Mechanics / Volume 754 / 10 September 2014
- Published online by Cambridge University Press:
- 06 August 2014, pp. 365-414
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We propose a novel cluster-based reduced-order modelling (CROM) strategy for unsteady flows. CROM combines the cluster analysis pioneered in Gunzburger’s group (Burkardt, Gunzburger & Lee, Comput. Meth. Appl. Mech. Engng, vol. 196, 2006a, pp. 337–355) and transition matrix models introduced in fluid dynamics in Eckhardt’s group (Schneider, Eckhardt & Vollmer, Phys. Rev. E, vol. 75, 2007, art. 066313). CROM constitutes a potential alternative to POD models and generalises the Ulam–Galerkin method classically used in dynamical systems to determine a finite-rank approximation of the Perron–Frobenius operator. The proposed strategy processes a time-resolved sequence of flow snapshots in two steps. First, the snapshot data are clustered into a small number of representative states, called centroids, in the state space. These centroids partition the state space in complementary non-overlapping regions (centroidal Voronoi cells). Departing from the standard algorithm, the probabilities of the clusters are determined, and the states are sorted by analysis of the transition matrix. Second, the transitions between the states are dynamically modelled using a Markov process. Physical mechanisms are then distilled by a refined analysis of the Markov process, e.g. using finite-time Lyapunov exponent (FTLE) and entropic methods. This CROM framework is applied to the Lorenz attractor (as illustrative example), to velocity fields of the spatially evolving incompressible mixing layer and the three-dimensional turbulent wake of a bluff body. For these examples, CROM is shown to identify non-trivial quasi-attractors and transition processes in an unsupervised manner. CROM has numerous potential applications for the systematic identification of physical mechanisms of complex dynamics, for comparison of flow evolution models, for the identification of precursors to desirable and undesirable events, and for flow control applications exploiting nonlinear actuation dynamics.
Contributors
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- By Ted Abel, Antoine Adamantidis, Karla V. Allebrandt, Simon N. Archer, Amelie Baud, Michel Billiard, Carlos Blanco-Centurion, Diane B. Boivin, Ethan Buhr, Matthew E. Carter, Nicolas Cermakian, Jennifer H.K. Choi, S.Y. Christin Chong, Chiara Cirelli, Marc Cuesta, Thomas Curie, Yves Dauvilliers, Luis de Lecea, Derk-Jan Dijk, Stephane Dissel, Annette C. Fedson, Jonathan Flint, Marcos G. Frank, Paul Franken, Ying-Hui Fu, Thorarinn Gislason, David Gozal, Devon A. Grant, Hakon Hakonarson, Makoto Honda, Hyun Hor, Christer Hublin, Peng Jiang, Takashi Kanbayashi, Jaakko Kaprio, Andrew Kasarskis, Leila Kheirandish-Gozal, RodaRani Konadhode, Michael Lazarus, Meng Liu, Michael March, Mark F. Mehler, Keivan Kaveh Moghadam, Valérie Mongrain, Charles M. Morin, Benjamin M. Neale, Seiji Nishino, Allan I. Pack, Dheeraj Pelluru, Rosa Peraita-Adrados, Giuseppe Plazzi, David A. Prober, Louis J. Ptáček, Irfan A. Qureshi, David M. Raizen, John J. Renger, Till Roenneberg, Elizabeth J. Rossin, Takeshi Sakurai, Paul Salin, Karen D. Schilli, Eva C. Schulte, Laurent Seugnet, Paul J. Shaw, Priyattam J. Shiromani, Patrick Sleiman, Mehdi Tafti, Joseph S. Takahashi, Matthew S. Thimgan, Katsushi Tokunaga, Giulio Tononi, Fred W. Turek, Yoshihiro Urade, Hans P.A. Van Dongen, Juliane Winkelmann, Christopher J. Winrow
- Edited by Paul Shaw, Mehdi Tafti, Michael J. Thorpy
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- Book:
- The Genetic Basis of Sleep and Sleep Disorders
- Published online:
- 05 November 2013
- Print publication:
- 24 October 2013, pp xi-xiv
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2 - Application of genetic epidemiology to dissecting host susceptibility/resistance to infection illustrated with the study of common mycobacterial infections
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- By Alexandre Alcaïs, Human Genetics of Infectious Diseases, Necker Medical School, University René Descartes, Laurent Abel, Human Genetics of Infectious Diseases, Necker Medical School, University René Descartes
- Edited by Richard Bellamy, Kintampo Health Research Centre, Ghana
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- Book:
- Susceptibility to Infectious Diseases
- Published online:
- 14 August 2009
- Print publication:
- 22 December 2003, pp 7-44
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Summary
INTRODUCTION
In the general context of genetic dissection of complex traits, genetics of human infectious diseases present the following several advantages and specificities: (1) there is a known causative agent which is absolutely required to become infected and to get the disease, but generally not sufficient stressing the importance of the host background; (2) environmental factors influencing the risk of infection are generally known and can be taken into account in the analysis when they are accurately measured; (3) there is a strong orientation in the choice of candidate genes based on the function of the gene and its known role in the response to the studied pathogen and/or on mouse–human chromosome homology exploiting the identification of murine resistance loci; and (4) the identification of major genes involved in the response to a given infectious pathogen takes advantage of the opportunity to study several complementary traits related to this pathogen. Among these traits are clinical phenotypes which are usually binary (affected/unaffected) but can take into account time to onset of the disease (e.g., time of progression to AIDS for HIV-infected patients), biological phenotypes measuring infection which can be either quantitative (e.g., infection intensities measured by fecal egg counts in schistosomiasis) or binary (HIV seropositive/seronegative), and immunological phenotypes measuring the immune response (antibody or cytokine levels, skin test response, etc.) more or less specific to a given antigen.
12 - Genetics of human susceptibility to infection and hepatic disease caused by schistosomes
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- By Alain J. Dessein, Immunologie et Génétique des Maladies Parasitaires, Institut National de la Santé et de la Recherche Médicale, Laboratoire de Parasitologie-Mycologie, Faculté de Médecine, Marseille, France, Sandrine Marquet, Immunologie et Génétique des Maladies Parasitaires, Institut National de la Santé et de la Recherche Médicale, Laboratoire de Parasitologie-Mycologie, Faculté de Médecine, Marseille, France, Carole Eboumbou Moukoko, Immunologie et Génétique des Maladies Parasitaires, Institut National de la Santé et de la Recherche Médicale, Laboratoire de Parasitologie-Mycologie, Faculté de Médecine, Marseille, France, Hèlia Dessein, Immunologie et Génétique des Maladies Parasitaires, Institut National de la Santé et de la Recherche Médicale, Laboratoire de Parasitologie-Mycologie, Faculté de Médecine, Marseille, France, Laurent Argiro, Immunologie et Génétique des Maladies Parasitaires, Institut National de la Santé et de la Recherche Médicale, Laboratoire de Parasitologie-Mycologie, Faculté de Médecine, Marseille, France, Sandrine Henri, Immunologie et Génétique des Maladies Parasitaires, Institut National de la Santé et de la Recherche Médicale, Laboratoire de Parasitologie-Mycologie, Faculté de Médecine, Marseille, France, Dominique Hillaire, Immunologie et Génétique des Maladies Parasitaires, Institut National de la Santé et de la Recherche Médicale, Laboratoire de Parasitologie-Mycologie, Faculté de Médecine, Marseille, France, Christophe Chevillard, Immunologie et Génétique des Maladies Parasitaires, Institut National de la Santé et de la Recherche Médicale, Laboratoire de Parasitologie-Mycologie, Faculté de Médecine, Marseille, France, Nasureldin El Wali, Institute of Nuclear Medicine and Molecular Biology, University of Gezira, Wad Medani, Sudan, Mubarak Magzoub, Institute of Nuclear Medicine and Molecular Biology, University of Gezira, Wad Medani, Sudan, Laurent Abel, Génétique Humaine des Maladies Infectieuses, Institut National de la Santé et de la Recherche Médicale, Faculté de Médecine Necker, Paris, Virmondes Rodrigues, Jr, Faculty of Medicine do Triangulo Mineiro, Ubéraba, Brazil, Aluizio Prata, Faculty of Medicine do Triangulo Mineiro, Ubéraba, Brazil, Gachuhi Kimani, Kenya Medical Research Institute, Biomedical Sciences Research Centre, Nairobi, Kenya
- Edited by Richard Bellamy, Kintampo Health Research Centre, Ghana
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- Book:
- Susceptibility to Infectious Diseases
- Published online:
- 14 August 2009
- Print publication:
- 22 December 2003, pp 337-360
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Summary
Schistosome infections cause much suffering in millions of people living in tropical regions of Africa, Asia, and South America (Prata, 1987; Chitsulo et al., 2000). The most severe clinical symptoms affect the kidneys and urinary tract. However, schistosomes also cause various other disorders such as heart failure and neurological diseases. Three species of schistosome are responsible for most human infections (Schistosoma mansoni, Schistosoma japonicum, and Schistosoma haematobium). These species are found in different geographical locations, have different vectors, and cause different symptoms. Schistosomes are multicellular parasites that are disseminated as free swimming larvae (cercariae) in ponds, lakes, and rivers by snails. Humans become infected when they stay in contaminated water for a few minutes. The cercariae penetrate the human skin and develop into male or female adult schistosomes within 5 or 6 weeks. These small worms (Fig. 12.1A) can live in the vascular system of their vertebrate host for 2 to 5 years. Schistosomes do not multiply within their vertebrate host. The female worms, however, lay hundreds of eggs per day in the mesenteric or vesical veins of their host. Most of the symptoms associated with these infections are caused by the inflammation that is induced by the immunogenic and toxic substances produced by the eggs. The chronic cellular reaction that develops around the eggs is organised in a granuloma (Von Lichtenberg, 1962; Warren et al., 1967).