A radiation-hydrodynamics scheme valid from the transport to the diffusion limit

We present in this paper the numerical treatment of the coupling between hydrodynamics and radiative transfer. The fluid is modeled by classical conservation laws (mass, momentum and energy) and the radiation by the grey moment $M_1$ system. The scheme introduced is able to compute accurate numerical solution over a broad class of regimes from the transport to the diffusive limits. We propose an asymptotic preserving modification of the HLLE scheme in order to treat correctly the diffusion limit. Several numerical results are presented, which show that this approach is robust and have the correct behavior in both the diffusive and free-streaming limits. In the last numerical example we test this approach on a complex physical case by considering the collapse of a gas cloud leading to a proto-stellar structure which, among other features, exhibits very steep opacity gradients.Comment: 29 pages, submitted to Journal of Computational physic

Le mythe de Robinson Crusoé à l’épreuve du monde global: il n’y a pas d’ailleurs. Étude du motif de l’empreinte dans L’Empreinte à Crusoé de Patrick Chamoiseau

De quel ailleurs peut bien nous parler la réécriture contemporaine du mythe de Robinson Crusoé par Patrick Chamoiseau, en 2012, alors que la planète est à la fois menacée par les déséquilibres écologiques et engagée dans une mondialisation des échanges ? L’empreinte à Crusoé est le récit sans aventure d’un homme qui, incapable de se souvenir d’où il vient véritablement, comprend qu’il habite un lieu chargé d’ailleurs. Or, c’est à travers l’empreinte de pas découverte sur la plage que se révèle et se recompose l’identité d’Ogomtemêli et sa place dans le monde. Plus qu’une péripétie, l’empreinte est un motif à partir duquel le naufragé devient la conscience historique et écologique de l’humanité vivant sur une seule et même terre, un lieu-monde dans lequel la relation doit supplanter l’exploitation

The effect of multiple paternity on genetic diversity during and after colonisation

In metapopulations, genetic variation of local populations is influenced by the genetic content of the founders, and of migrants following establishment. We analyse the effect of multiple paternity on genetic diversity using a model in which the highly promiscuous marine snail Littorina saxatilis expands from a mainland to colonise initially empty islands of an archipelago. Migrant females carry a large number of eggs fertilised by 1 - 10 mates. We quantify the genetic diversity of the population in terms of its heterozygosity: initially during the transient colonisation process, and at long times when the population has reached an equilibrium state with migration. During colonisation, multiple paternity increases the heterozygosity by 10 - 300 % in comparison with the case of single paternity. The equilibrium state, by contrast, is less strongly affected: multiple paternity gives rise to 10 - 50 % higher heterozygosity compared with single paternity. Further we find that far from the mainland, new mutations spreading from the mainland cause bursts of high genetic diversity separated by long periods of low diversity. This effect is boosted by multiple paternity. We conclude that multiple paternity facilitates colonisation and maintenance of small populations, whether or not this is the main cause for the evolution of extreme promiscuity in Littorina saxatilis.Comment: 7 pages, 5 figures, electronic supplementary materia

Analytical and numerical stability analysis of Soret-driven convection in a horizontal porous layer

We present an analytical and numerical stability analysis of Soret-driven convection in a porous cavity saturated by a binary fluid. Both the mechanical equilibrium solution and the monocellular flow obtained for particular ranges of the physical parameters of the problem are considered. The porous cavity, bounded by horizontal infinite or finite boundaries, is heated from below or from above. The two horizontal plates are maintained at different constant temperatures while no mass flux is imposed. The influence of the governing parameters and more particularly the role of the separation ratio, characterizing the Soret effect and the normalized porosity, are investigated theoretically and numerically. From the linear stability analysis, we find that the equilibrium solution loses its stability via a stationary bifurcation or a Hopf bifurcation depending on the separation ratio and the normalized porosity of the medium. The role of the porosity is important, when it decreases, the stability of the equilibrium solution is reinforced. For a cell heated from below, the equilibrium solution loses its stability via a stationary bifurcation when the separation ratio >0(Le,), while for 0, while a stationary or an oscillatory bifurcation occurs if mono the monocellular flow loses stability via a Hopf bifurcation. As the Rayleigh number increases, the resulting oscillatory solution evolves to a stationary multicellular flow. For a cell heated from above and <0, the monocellular flow remains linearly stable. We verified numerically that this problem admits other stable multicellular stationary solutions for this range of parameters

A numerical model for multigroup radiation hydrodynamics

We present in this paper a multigroup model for radiation hydrodynamics to account for variations of the gas opacity as a function of frequency. The entropy closure model (M1) is applied to multigroup radiation transfer in a radiation hydrodynamics code. In difference from the previous grey model, we are able to reproduce the crucial effects of frequency-variable gas opacities, a situation omnipresent in physics and astrophysics. We also account for the energy exchange between neighbouring groups which is important in flows with strong velocity divergence. These terms were computed using a finite volume method in the frequency domain. The radiative transfer aspect of the method was first tested separately for global consistency (reversion to grey model) and against a well established kinetic model through Marshak wave tests with frequency dependent opacities. Very good agreement between the multigroup M1 and kinetic models was observed in all tests. The successful coupling of the multigroup radiative transfer to the hydrodynamics was then confirmed through a second series of tests. Finally, the model was linked to a database of opacities for a Xe gas in order to simulate realistic multigroup radiative shocks in Xe. The differences with the previous grey models are discussed.Comment: 27 pages, 11 figures, Accepted for publication in JQSR

Decay resistance against Coriolus versicolor in Sessile oak ( Quercus petraea Liebl.): analysis of the between-tree variability and correlations with extractives, tree growth and other basic wood properties

Abstract : Weight loss due to fungus Coriolus versicolor has been measured on 614 samples according to the NF EN 113 norm. Up to eight samples were cut at breast height (two opposite radii×four radial positions in heartwood) from 82 mature sessile oaks ( Quercus petraea Liebl.) originating from contrasting regions, silvicultural schedules and site qualities in France. The following points are addressed in the paper: (i) contribution to the total variability for weight loss of the effects "tree”, "position in the tree”, as well as their interaction; (ii) percentage of wood samples and trees in each of the five classes of natural durability defined by the norm NF EN 350-2; (iii) test of the effects of region, silvicultural schedule and site quality on weight loss and evaluating their contribution to the total variation; and (iv) correlations at tree level between weight loss and several traits related to tree growth and basic wood properties (density, swelling, grain angle, multiseriate wood rays characteristics, extractives content). The results are discussed with a view to aid the forest manager as well as the log/wood user to take advantage of the high level of between-tree variability observed as natural durability against C. versicolo

Levels of cafestol, kahweol, and related diterpenoids in wild species of the coffee plant coffea

Abstract Specific fatty acids and sterols in food composites from seven countries were analyzed. In the 1960s, groups of 8 to 49 men from 16 cohorts, ages 40–59 years and living in the United States, Finland, the Netherlands, Italy, Greece, the former Yugoslavia, or Japan recorded their food intake. In 1987, we collected food composites representing the average food intake per cohort sample in the 1960s. The foods were transported to the Netherlands, pooled, and centrally analyzed for energy, total fat, 42 fatty acids, cholesterol, and four plant sterols. The fat content ranged from 12% of total daily energy in the Tanushimaru, Japan, cohort to 50% in the U.S. cohort sample, and the polyunsaturated to saturated fat ratio ranged from 0.17 in the east Finland cohort to 1.2 in Tanushimaru. The amount oftransfatty acids with 16 or 18 carbon atoms varied between 0.2 g/day in Corfu, Greece, and 8.6 g/day in Zutphen, Netherlands, and that of -linolenic acid between 0.8 g/day in Rome and 2.5 g/day in east Finland. The sum of eicosapentaenoic and docosahexanoic acid ranged from 0.1 (U.S. railroad) to 2.0 g/day (Ushibuka, Japan), and phytosterols from 170 (U.S. railroad) to 358 mg/day (Corfu, Greece). Thus the intake of various fatty acids and sterols with potential relevance for coronary heart disease occurrence varied 10-fold or more between cohorts. Our data can be used to generate new hypotheses about the causes of differences in incidence of diseases between countries

Évaluation des risques écologiques causés par des matériaux de dragage: roposition d'une approche adaptée aux dépôts en gravière en eau

Une procédure d'évaluation des risques pour l'écosystème aquatique engendrés par un dépôt de matériaux de dragage dans une gravière type a été élaborée, et testée avec des échantillons de sédiments d'un canal du Nord-Est de la France. La procédure comporte une étape d'évaluation sommaire des risques, à partir de quotients des concentrations mesurées par les critères de danger correspondants, et une étape d'évaluation détaillée où des essais de toxicité et de lixiviation en colonnes sont mis en œuvre. Le scénario testé retient trois hypothèses, qui concernent (a) les effets sur les peuplements d'invertébrés benthiques, représentés notamment par Hyalella azteca et Chironomus riparius, (b) les effets sur les peuplements d'organismes pélagiques, représentés par Chlorella vulgaris, Ceriodaphnia dubia, et Brachionus calyciflorus, et (c) la pollution de la nappe alluviale associée. Différentes modalités d'exposition (essais normalisés, microcosmes) ont été testées. Dans le contexte particulier des trois sédiments étudiés, ces hypothèses se sont avérées plus ou moins discriminantes, la pollution de la nappe étant la plus sensible. Des améliorations de la procédure doivent être envisagées qui concernent à la fois la formulation des hypothèses (risques à court et long terme sur les organismes pélagiques), et les protocoles d'essai, tant pour les organismes du sédiment (rôle de la nourriture notamment) que pour les essais de lixiviation en colonnes.When contaminated by metals or synthetic organic compounds, dredged sediments may have negative impacts on receiving ecosystems. Therefore, there is a need for an operational risk assessment approach. Such a framework is proposed for dredged material deposits in open gravel quarries, which is a rather common means of disposal in France. The first step of the assessment relies upon chemical characterisation of the sediments; the resulting concentrations are divided by "probable effect concentrations" and pooled together, in order to calculate a global hazard quotient. According to the value of this quotient, several decisions can be taken: (a) undertake a detailed risk assessment, (b) dispose of the materials without further constraints, or (c) in case of uncertainty, do some biological testing (with Hyalella azteca and Chironomus riparius) in order to allow decisions. The second step is a detailed ecological risk assessment. Three different assessment endpoints have been proposed, which are (1) the deposit should have no effect on the structure and abundance of benthic invertebrates in the quarry, (2) it should have no long term effect on pelagic species, and (3) it should not cause groundwater pollution, as such quarries are in fact cross sections of shallow alluvial groundwater aquifers. A fourth assessment endpoint should be introduced, regarding health risks for recreational uses, including fishing, but this endpoint was not implemented in the current version of the approach. The analysis phase includes aquatic bioassays (bacteria - Metplate TM-, algae, microcrustaceans Ceriodaphnia dubia, rotifers Brachionus calyciflorus), and leaching assays in columns under ascendant flow.The proposed approach was tested with 3 sediments from a canal located in the north-eastern region of France. Microcosm assays were introduced in parallel to the proposed tests, in order to explore alternatives to standardised bioassays. According to their hazard quotient, the 3 sediments showed a contamination gradient; one of them should not have entered the detailed risk assessment phase, while another would have been further tested with H. azteca and C. riparius. In that case, this latter sediment would not have entered the detailed phase either, as it was not toxic to these species. However, the detailed risk assessment approach was applied to the three sediments, so as to test completely the relevance of the framework.The three sediments were not significantly toxic to either C. riparius or H. azteca. However, some effects were observed in microcosms, including genotoxicity to molluscs. In this case, no risk characterisation could be made. Pore waters extracted from the three sediments were not toxic or slightly toxic to bacteria, algae, and C. dubia; an EC10 value could be determined only for B. calyciflorus. Therefore, due to exposure calculations, it seems there is a risk to pelagic species. However, as 3 bioassays out of 4 were negative or inconclusive, a refinement step would seem to be necessary. The highest concentrations of cadmium, copper, chromium, nickel and zinc were measured in the first lixiviates of the most contaminated sediment. Yet, even in that case, the total extracted fraction remained less than 10% of the total load. This fraction was below 1% for the other sediments, whatever the metal. Maximum concentrations and predicted concentrations at 1 year were compared to drinking water standards. This comparison showed a real risk of degrading groundwater quality for that most contaminated sediment, and a transient risk due to cadmium and nickel for the following one on the contamination gradient.Considering these results, the design of the first step of the proposed assessment approach may be discussed, as one sediment which would not have been assessed in depth according to its hazard quotient did show a risk to pelagic species. This discrepancy underlines the fact that some sediment toxicity may exist below the lowest threshold. As it would be unrealistic to enter systematically into detailed risk assessments, the proposed thresholds in the decision diagram must be pragmatic compromises rather than absolutely safe boundaries. Moreover, protocol improvements are needed for sediment toxicity bioassays. Chronic endpoints are preferable, as they are more sensitive and more relevant. Another issue is related to the role of additional food: not adding food may increase the apparent toxicity, but the sediment organic content, which is an alternative food source, may also be a contaminant carrier. Furthermore, the second assessment endpoint (risk to pelagic species) should be reformulated, as it includes in fact two different questions. Short-term risks related to the deposition phase could be assessed with standardised bioassays like C. dubia survival and reproduction and algal growth, while longer term risks related to contaminant diffusion could be assessed with microcosms. Genotoxic effects were observed at rather high levels, as compared to published results. This result stresses the interest of introducing sensitive and early markers in the risk assessment process, although their real meaning for ecosystems is not yet fully elucidated. Finally, the leaching tests in columns are not completely satisfactory, as the column filling implies that one must first dry the sediments, which will alter their structure. Other application trials along with field validation studies should be carried out prior to the introduction of this scenario in operational or regulatory frameworks

A summary of new predictive high frequency thermo-vibrational models in porous media

In this chapter, we consider the effect of mechanical vibration on the onset of convection in porous media. The porous media is saturated either by a pure fluid or by a binary mixture. The importance of transport model on stability diagrams are presented and discussed. The stability threshold for the Darcy-Brinkman case in the RaTc-R and kc-R diagrams are presented (where RaTc, kc and R are the critical Rayleigh number, the critical wave number and the vibration parameters respectively). It is shown that there is a significant deviation from the Darcy model. In the thermo-solutal case with the Soret effect, the influence of vibration on the reduction of multi-cellular convection is emphasized. A new analytical relation for obtaining the threshold of mono-cellular convection is derived. This relation shows how the separation factor Ψ is related to controlling parameters of the problem, Ψ = f (R, ε*, Le) when the wave number k -> 0. The importance of vibrational parameter definition is highlighted and it is shown how, by using a proper definition for vibrational parameter, we may obtain compact relationship. It is also shown how this result may be used to increase components separation