Dense granular flow around a penetrating object: Experiments and hydrodynamic model

We present in this Letter experimental results on the bidimensional flow field around a cylinder penetrating into dense granular matter together with drag force measurements. A hydrodynamic model based on extended kinetic theory for dense granular flow reproduces well the flow localization close to the cylinder and the corresponding scalings of the drag force, which is found to not depend on velocity, but linearly on the pressure and on the cylinder diameter and weakly on the grain size. Such a regime is found to be valid at a low enough "granular" Reynolds number.Comment: 5 pages, 4 figure

Particle flux in the Rainbow hydrothermal vent field (Mid-Atlantic Ridge): Dynamics, mineral and biological composition

In order to provide information about the export and the distribution of hydrothermal particulate material to the surrounding deep ocean, four moorings were deployed in the vicinity of the hydrothermal Rainbow vent field (Mid-Atlantic Ridge, 36°14′N, 2250 m depth). The first mooring was a sediment trap with a current meter deployed at 2 m from a chimney of the Rainbow vent field and 1.5 m above the bottom (a.b.) for 16 days. It represented the reference for the initial composition of particles produced by the vent. The total mean mass particle flux (6.9 g m-2 d-1) was distinctly higher than the flux measured at the shallower hydrothermal vents on the MAR segment. This particulate flux showed a high temporal variation at the scale of a few days and was characterized by a high concentration of sulphur (17.2%) and copper (3.5%) and a very low concentration of organic carbon (0.14%). Several hundred bivalve larvae belonging to the hydrothermal mytilid Bathymodiolus azoricus were collected in this trap at the beginning of the experiment. The density of larvae decreased strongly at the end, indicating a patchiness distribution or a discontinuous reproduction of this species. The other three moorings, including sediment traps, current-meters and thermistor chains, were deployed for 304 days at different distances and altitudes from the Rainbow vent field. The mean speed of the current in the rift valley was low (6 cm s-1) and was oriented toward the north. The total mean particle mass flux measured with the five sediment traps varied little, from 10.6 to 25.0 mg m m-2 d-1, and displayed temporal variations which are typical of deep-sea environments with seasonal changes in the overlying production. However, in the trap at 500 m from the vents 150 m a.b., the presence of the hydrothermal plume can be observed: the sulphur, iron and copper concentrations of particles were significantly higher compared to the particles sampled in the pelagic reference trap. The plume composition was about 50% hydrothermal particles and 50% pelagic particles and its upper limit reached 300 m a.b. at this distance. In the traps at 1000 m from the vents, the elemental composition of particles was similar to the pelagic particles and we assume that these traps were not in the plume during the experiment. The zooplankton obtained in the long-term trap samples revealed high density variations in relation to the distance from the vent site. The nutrient enrichment around the hydrothermal area and the abundance of free living bacteria explain these variations in zooplankton density

The Nexus Land-Use model, approach articulating biophysical potentials and economic dynamics to model competition for land-use

International audienceInteractions between food demand, biomass energy and forest preservation are driving both food prices and land-use changes. This study presents a new model called Nexus Land-Use which describes these interactions through a representation of agricultural intensification. The model combine biophysics and economics to calculate crop yields, food prices, and resulting pasture and cropland areas within 12 inter-connected regions. The representation of cropland production systems relies on a biomass production function derived from the crop yield response function to inputs and a spatially explicit distribution of potential crop yields prescribed from the Lund-Postdam-Jena global vegetation model for managed Land (LPJmL). The economic principles governing decisions about land-use and intensification are adapted from the Ricardian rent theory, assuming cost minimisation. The land-use modelling approach described in this paper makes it possible to explore interactions among different types of demand for biomass, including indirect effects on land-use change resulting from international trade. Yield variations induced by the possible expansion of croplands on less suitable lands are modelled by using regional land area distributions of potential yields, and a boundary between intensive and extensive production. Idealized scenarios exploring the impact of forest preservation policies or rising energy price on agricultural intensification are presented

Nautilia abyssi sp. nov., a thermophilic, chemolithoautotrophic, sulfur-reducing bacterium isolated from an East Pacific Rise hydrothermal vent

This is an author manuscript that has been accepted for publication in International Journal of Systematic and Evolutionary Microbiology, copyright Society for General Microbiology, but has not been copy-edited, formatted or proofed. Cite this article as appearing in International Journal of Systematic and Evolutionary Microbiology. This version of the manuscript may not be duplicated or reproduced, other than for personal use or within the rule of 'Fair Use of Copyrighted Materials' (section 17, Title 17, US Code), without permission from the copyright owner, Society for General Microbiology. The Society for General Microbiology disclaims any responsibility or liability for errors or omissions in this version of the manuscript or in any version derived from it by any other parties. The final copy-edited, published article, which is the version of record, can be found at http://mic.sgmjournals.org, and is freely available without a subscription.International audienceA novel strictly anaerobic, thermophilic, sulfur-reducing bacterium, designated PH1209(T), was isolated from an East Pacific Rise hydrothermal vent (1 degrees N) sample and studied using a polyphasic taxonomic approach. Cells were Gram-negative, motile rods (approx. 1.60 x 0.40 microm) with a single polar flagellum. Strain PH1209(T) grew at temperatures between 33 and 65 degrees C (optimum 60 degrees C), from pH 5.0 to 8.0 (optimum 6.0-6.5), and between 2 and 4 % (w/v) NaCl (optimum 3 %). Cells grew chemolithoautotrophically with H(2) as an energy source, S(0) as an electron acceptor and CO(2) as a carbon source. Strain PH1209(T) was also able to use peptone and yeast extract as carbon sources. The G+C content of the genomic DNA was 35 mol%. Phylogenetic analyses based on 16S rRNA gene sequencing showed that strain PH1209(T) fell within the order Nautiliales, in the class Epsilonproteobacteria. Comparative 16S rRNA gene sequence analysis indicated that strain PH1209(T) belonged to the genus Nautilia and shared 97.2 and 98.7 % 16S rRNA gene sequence identity, respectively, with the type strains of Nautilia lithotrophica and Nautilia profundicola. It is proposed, from the polyphasic evidence, that the strain represents a novel species, Nautilia abyssi sp. nov.; the type strain is PH1209(T) (=DSM 21157(T)=JCM 15390(T))

Plongée dans le sable

National audienceComprendre la manière dont un matériau composé de grains s'écoule a des répercussions dans des situations pratiques très variées : transport de sable ou de graviers dans le génie civil, mélange de poudres dans les industries pharmaceutiques et cosmétiques, stockage de céréales dans le secteur agroalimentaire. Dans la nature, la formation de cratères d'impacts météoritiques ou encore la locomotion animale dans les zones désertiques sont des exemples parmi d'autres où des matériaux granulaires s'écoulent autour d'un obstacle. Une approche de type " hydrodynamique " permet-elle de décrire ces écoulements de grains ? En quoi sont-ils fondamentalement différents d'un fluide simple

Taxe carbone : recyclage des recettes et double dividende, Note pour le Conseil économique pour le développement durable - n°4

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Simulating the dynamics of epiphytic diatom metacommunity in stream environments contaminated with heavy metals

International audienceHeavy-metal pollution may drive succession in freshwater diatom communities towards more pollution tolerant species, resulting in an increased tolerance of communities but also in loss of species diversity. Using models is the best way to have a fast and robust estimation of natural-community evolution to study efficiently the microorganism community dynamics in freshwater environments. However until nowadays, no ecotoxicological study dealing with modeling diatom dynamics in heavy-metal contaminated stream environments was established. A means of considering population level in ecotoxicology is the "demographic" methodology. It consists of introducing effects of pollutants on demographic parameters into models of population dynamics. When the study deals with several species belonging to a same group, the community must be considered. And when several communities are considered, some processes emerge like spontaneous migration, non-spontaneous migration or "actions at distance". So modeling species-structured communities with matrix methods can be applied to spatial fragmented populations. The dimensions of these models describing real systems (demography, migrations) increase with the number of spatial patches and the number of species considered, which have dissuaded all scientists to work on stream diatom communities. Our work aimed to integrate pollutant effects in such a multi-region model with two different time scales. We developed a model of a theoretical river network based upon the catchment basin of the Vienne river located in the Limousin region (France) with low autoecological variations. We have selected 8 diatom species adnated to one of the most common macrophyte in the limousin rivers, Myriophyllum alterniflorum (Haloragaceae) and two heavy metals (copper and cadmium) as the toxic compounds. These metals were chosen because they are common pollutants of stream environments and they have a high toxicity associated with a strong potential for bioaccumulation. Furthermore, their persistence in aquatic systems lead to their registration on the European Union's blacklist of harmful substances since many years. Our theoretical river network consists of 6 asymmetric levels and 14 patches. The patch distribution among the levels is based on the geography of the 14 studied in situ localities. This allows a better comprehension of the ecotoxicological impacts of heavy metals on macrophyte-associated diatom communities. Our multi-area model considers toxicity in terms of survival and colonization reduction through dose-response curves established from our in situ data. We hypothesized that the maximum heavy-metal concentrations (measured in situ in each studied locality) are discharged when the pollution occurs. Species composition, spatial distribution, demographic and migration processes were taken into account to estimate community responses to this really realistic scenario of pollutant discharge. As a breakthrough, our results highlight that in cadmium-polluted areas, diatom migrations play here an important role in the survival of three species: Achnanthes microcephala, Cocconeis placentula and Navicula simplex. This study brings important information for health environmental projects which must considered not only the pollution frequency but also the sustainability of the biological substrate for periphyton

Prorocentrum rivalis sp. nov. (Dinophyceae) and its phylogenetic affinities inferred from analysis of a mixed morphological and LSU rRNA data set

International audienceA new freshwater epiphytic Prorocentrum species, Prorocentrum rivalis, from the temperate region of the Haute-Vienne, France, is described. This species is the third freshwater species identified among approximately 60 marine Prorocentrum species. This new species is described using scanning electron microscope and phylogenetic analyses by a polyphasic approach (LSU rRNA sequences combined with 9 morphological characters). The phylogenetic analysis attests that P. rivalis is close to other planktonic freshwater species and the freshwater Prorocentrum clade is evolutionarily derived from an epiphytic freshwater prorocentroid ancestor. The unique marine species in the freshwater clade results from an ecophysiological reversion. P. rivalis differs from other epiphytic taxa by its rarity, its temperate distribution and its ecophysiological needs. The phylogeny confirms also that all planktonic Prorocentrum species are evolutionarily derived from epiphytic/benthic ancestors

Export of deep-sea hydrothermal particles, indigenous thermophilic microorganisms and larvae to the surrounding Ocean

To assess the production and the export of particulate and biological material in deep-sea hydrothermal vents, four moorings with sediment traps and current meters were deployed for 24 days in the Azores Triple Junction (ATJ) region. They were deployed along an axis starting at the base of a hydrothermal vent chimney and ending 1000 m away. The particles sampled at the base of the chimney were characterized by high concentrations in total sulfur (16%) and iron (4%). The particle composition changed drastically with distance from the vent: the sulfur concentration decreased with an increase in clay components. Thermophilic microorganisms were successfully enriched from all the particle samples. Cultured strains were closely related to hydrothermal species, suggesting that viable hydrothermal vent microorganisms can be exported easily from one hydrothermal field to the open ocean. Fauna collected in the trap at the base of the chimney also included the hydrothermal mytilid species Bathymodiolus azoricus (prejuvenile prodissoconch late stage), larval or juvenile polychaetes and two vent gastropod species (Shinkailepas sp. and Phymorhynchus sp.). These organisms were not sampled by the others sediment traps. The most common taxa found in the traps off the vent were polychaetes, euphausiaceans and copepods (harpacticoids, nauplii and calanoids)

The Nexus Land-Use Model, an Approach Articulating Biophysical Potentials and Economic Dynamics to Model

Interactions between food demand, biomass energy and forest preservation are driving both food prices and land-use changes, regionally and globally. This study presents a new model called Nexus Land-Use which describes these interactions through a generic representation of agricultural intensification mechanisms. The Nexus Land-Use model equations combine biophysics and economics into a single coherent framework to calculate crop yields, food prices, and resulting pasture and cropland areas within 12 regions inter-connected with each other by international trade. The representation of cropland and livestock production systems in each region relies on three components: (i) a biomass production function derived from the crop yield response function to inputs such as industrial fertilisers ; (ii) a detailed representation of the livestock production system subdivided into an intensive and an extensive component, and (iii) a spatially explicit distribution of potential (maximal) crop yields prescribed from the Lund-Postdam-Jena global vegetation model for managed Land (LPJmL). The economic principles governing decisions about land-use and intensification are adapted from the Ricardian rent theory, assuming cost minimisation for farmers. The land-use modelling approach described in this paper entails several advantages. Firstly, it makes it possible to explore interactions among different types of demand for biomass for food and animal feed, in a consistent approach, including indirect effects on land-use change resulting from international trade. Secondly, yield variations induced by the possible expansion of croplands on less suitable marginal lands are modelled by using regional land area distributions of potential yields, and a calculated boundary between intensive and extensive production. The model equations and parameter values are first described in detail. Then, idealised scenarios exploring the impact of forest preservation policies or rising energy price on agricultural intensification are described, and their impacts on pasture and cropland areas are investigated