A time-step-robust algorithm to compute particle trajectories in 3-D unstructured meshes for Lagrangian stochastic methods

The purpose of this paper is to propose a time-step-robust cell-to-cell integration of particle trajectories in 3-D unstructured meshes in particle/mesh Lagrangian stochastic methods. The main idea is to dynamically update the mean fields used in the time integration by splitting, for each particle, the time step into sub-steps such that each of these sub-steps corresponds to particle cell residence times. This reduces the spatial discretization error. Given the stochastic nature of the models, a key aspect is to derive estimations of the residence times that do not anticipate the future of the Wiener process. To that effect, the new algorithm relies on a virtual particle, attached to each stochastic one, whose mean conditional behavior provides free-of-statistical-bias predictions of residence times. After consistency checks, this new algorithm is validated on two representative test cases: particle dispersion in a statistically uniform flow and particle dynamics in a non-uniform flow

Particle resuspension: challenges and perspectives for future models

International audienceUsing what has become a celebrated catchphrase, Philip W. Anderson once wrote that "more is different" (Science, Vol. 177, Issue 4047, pp. 393-396, 1972). First formulated in the context of condensed matter, this statement carries far beyond the sole limits of solid-state physics. It emphasizes that collective behavior can be more than the mere sum of what happens for elementary constituents or the mere collation of the evolution of each degree of freedom. Said otherwise, complex phenomena can arise out of the interplay between multiple sub-phenomena each of which can be relatively simple. The process of particle resuspension, in which discrete particles adhering on a surface are pulled off and carried away by a fluid flow, is another example involving a web of phenomena pertaining to fluid mechanics, particle dynamics and interface chemistry whose crosseffects create an intricate topic. The purpose of this review is to analyze the physics at play in particle resuspension in order to bring insights into the rich complexity of this common but challenging concern. Following the more-is-different vision, this is performed by starting from a range of practical observations and experimental data. We then work our way through the investigation of the key mechanisms which play a role in the overall process. In turn, these mechanisms reveal an array of fundamental interactions, such as particle-fluid, particle-particle and particle-surface, whose combined effects create the tapestry of current applications. At the core of this analysis are descriptions of these physical phenomena and the different ways through which they are intertwined to build up various models used to provide quantitative assessment of particle resuspension. The physics of particle resuspension implies to hold together processes occurring at extremely different space and time scales and models are key in providing a single vehicle to lead us through such multiscale journeys. This raises questions on what makes up a model and one objective of the present work is to clarify the essence of a modeling approach. In spite of its ubiquitous nature, particle resuspension is still at the early stages of developments. Many extensions need to be worked out and revisiting the art of modeling is not a moot point. The need to consider more complex objects than small and spherical particles and, moreover, to come up with unified descriptions of mono-and multilayer resuspension put the emphasis on solid model foundations if we are to go beyond current limits. This is very much modeling in the making and new ideas are proposed to stimulate interest into this everyday but challenging issue in physics

Intersex related gene expression profiles in clams Scrobicularia plana : molecular markers and environmental application

Intersex, the appearance of female characteristics in male gonads, has been identified in several aquatic species. It is a widespread phenomenon in populations of the bivalve, Scrobicularia plana, from the southwest coast of the U.K. Genes previously identified as differentially expressed (ferritin, testicular haploid expressed gene, THEG, proliferating cell nuclear antigen, PCNA; receptor activated protein kinase C, RACK; cytochrome B, CYB; and cytochrome c oxidase 1, COX1) in intersex clams relative to normal male clams, were selected for characterisation and an environmental survey of the Channel region. Transcripts were significantly differentially expressed at sites with varying intersex incidence and contaminant burdens. Significant correlations between specific gene expressions, key contaminants and sampling locations have been identified, though no single gene was associated with intersex incidence. The results highlight the difficulty in understanding the intersex phenomenon in molluscs where there is still a lack of knowledge on the control of normal reproduction

Identification of Reproduction-Specific Genes Associated with Maturation and Estrogen Exposure in a Marine Bivalve Mytilus edulis

Background: While it is established that vertebrate-like steroids, particularly estrogens (estradiol, estrone) and androgens (testosterone), are present in various tissues of molluscs, it is still unclear what role these play in reproductive endocrinology in such organisms. This is despite the significant commercial shellfishery interest in several bivalve species and their decline. Methodology/Principal Findings: Using suppression subtraction hybridisation of mussel gonad samples at two stages (early and mature) of gametogenesis and (in parallel) following controlled laboratory estrogen exposure, we isolate several differentially regulated genes including testis-specific kinases, vitelline lysin and envelope sequences. Conclusions: The differentially expressed mRNAs isolated provide evidence that mussels may be impacted by exogenous estrogen exposure

A chemical survey of exoplanets with ARIEL

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio

Recherche de biomarqueurs de toxicité liés à l'activité estérase non spécifique et à la résistance multixénobiotique chez divers organismes marins

The atm of this work was to find new non-specifie biomarkers to biomonitor the environmental impact of xénobiotics in marine organisms : the non-specifie esterase activity and the multixenobiotic resistance phenomena (MXR) similar to the multidrug resistance phenomena (MDR). As for the esterase activity, a simple and rapid method based on fluorescent measurements of fluorescein diacetate (FDA) has been developed with unicellular micro-algae : Calothrix sp. , Haslea ostrearia and Prorocentrum micans. This biomarker is very sensitive to many physical and chemical factors such as light intensity, temperature,  salinity, stage of growth and, among the main marine pollutants, to organophosphates and, in a lesser extent, to polycyclic aromatic hydrocarbons (PAH's). Fluorescent measurements using rhodanline B gave results dissimilar to the multidrug resistance phenomena with the algae P. micans.  But western blots using the C219 monoclonal anti body allowed the identification of 3 proteins of 240, 220 kDa and 170 kDa in the musset Mytilus edulis, one of 220 kDa in M galloprovincialis and 2 of 220 and 240 kDa in the oyster Crassostrea gigas. In situ assessment of the MXR-transporter (Pgp) expression leve! in these 3 molluscs along the French coast, using the dot-blot technic, allows the identification of polluted sites with high Pgp expression levet. Theses results indicates that such immunochernical measurements could provide new information about environmental pollution.La recherche de biomarqueurs utilisables pour l'évaluation de la qualité du milieu marin a conduit à étudier deux activités cellulaires sensibles à un ensemble complexe de polluants : l'activité estérasique non spécifique et l'activité de résistance multi-xénobiotique. Concernant l'activité estérasique, une méthodologie simple et rapide a été développée en utilisant des mesures de fluorescence consécutives à la désestérification du diacétate de fluorescéine par les micro-algues Calothrix sp. , Haslea ostrearia et Prorocentrum micans. Ces mesures ont été adaptées à la technique utilisant les microplaques pour laquelle les unicellulaires se sont révélé des supports de choix. Ce biomarqueur est très sensible à de nombreux facteurs physiologiques et, parmi les principaux polluants du milieu marin, sensibles aux organophosphorés et, dans une moindre mesure, aux hydrocarbures polyaromatiques insaturés. Concernant l'activité de résistance multi-xénobiotique, la méthode utilisant les mesures de fluorescence liées à la rhodamine B s'est révélée difficilement utilisable avec les micro-algues. Par contre l'utilisation de l'anticorps C219 a permis de caractériser trois protéines de 240, 220 kDa et 170 ~a chez la moule Mytilus edulis, une de 220 kDa chez M.  galloprovincialis ainsi que deux de 220 kDa 240 kDa chez l'huître Crassostrea gigas. Un test immunologique permettant l'étude in situ d'échantillons de mollusques a ensuite été développé. Quarante-trois stations parmi les lieux de prélèvement du réseau national d'observation ont fait l'objet d'un tel dosage donnant de nouvelles informations sur la qualité du milieu côtier français

Le chabot comme espèce modèle pour évaluer les effets des perturbateurs endocriniens

LE HAVRE-BU Centrale (763512101) / SudocSudocFranceF

Particle resuspension: challenges and perspectives for future models

International audienceUsing what has become a celebrated catchphrase, Philip W. Anderson once wrote that "more is different" (Science, Vol. 177, Issue 4047, pp. 393-396, 1972). First formulated in the context of condensed matter, this statement carries far beyond the sole limits of solid-state physics. It emphasizes that collective behavior can be more than the mere sum of what happens for elementary constituents or the mere collation of the evolution of each degree of freedom. Said otherwise, complex phenomena can arise out of the interplay between multiple sub-phenomena each of which can be relatively simple. The process of particle resuspension, in which discrete particles adhering on a surface are pulled off and carried away by a fluid flow, is another example involving a web of phenomena pertaining to fluid mechanics, particle dynamics and interface chemistry whose crosseffects create an intricate topic. The purpose of this review is to analyze the physics at play in particle resuspension in order to bring insights into the rich complexity of this common but challenging concern. Following the more-is-different vision, this is performed by starting from a range of practical observations and experimental data. We then work our way through the investigation of the key mechanisms which play a role in the overall process. In turn, these mechanisms reveal an array of fundamental interactions, such as particle-fluid, particle-particle and particle-surface, whose combined effects create the tapestry of current applications. At the core of this analysis are descriptions of these physical phenomena and the different ways through which they are intertwined to build up various models used to provide quantitative assessment of particle resuspension. The physics of particle resuspension implies to hold together processes occurring at extremely different space and time scales and models are key in providing a single vehicle to lead us through such multiscale journeys. This raises questions on what makes up a model and one objective of the present work is to clarify the essence of a modeling approach. In spite of its ubiquitous nature, particle resuspension is still at the early stages of developments. Many extensions need to be worked out and revisiting the art of modeling is not a moot point. The need to consider more complex objects than small and spherical particles and, moreover, to come up with unified descriptions of mono-and multilayer resuspension put the emphasis on solid model foundations if we are to go beyond current limits. This is very much modeling in the making and new ideas are proposed to stimulate interest into this everyday but challenging issue in physics

L'état de santé des poissons comme indicateur de la qualité des cours d'eau

International audienceThe assessment of freshwater ecosystem quality is a major regular and societal stake. Based on chemical analysis of environmental pollutants, several effect-based monitoring methodologies are applied. Among them, the measurement of biomarkers in wild fish is a well-documented tool in research activities. During these last few years, this approach was used in wild chubs and roach from Marne and Seine rivers. Response profiles of measured biomarkers allow to highlight disturbances of fish health linked to exposure to environmental pollutants. Similar works were developed around the world. For example, the BEST program assesses environmental quality of large US rivers using a set of biomarkers. Comparison of French and US monitoring activities will be presented but these studies argue for the deployment of effect-based monitoring tools to assess ecotoxicological status of water bodies. Moreover, these tools can be used for fish from small rivers and allow an integrated monitoring of river basins.La surveillance de la qualité des cours d'eau représente un enjeu réglementaire et sociétal important. Essentiellement basée sur l'analyse chimique des polluants environnementaux, différentes méthodologies basées sur la mesure des effets induits par ces contaminants sont de plus en plus utilisées. Parmi celle-ci, la mesure de biomarqueurs chez le poisson est désormais bien documentée par les études de recherche. Au cours des dernières années, ce type d'approche a été mise en oeuvre chez des chevaines et des gardons collectés sur la Marne et la Seine. Les profils de réponse des biomarqueurs permettent de mettre en évidence des perturbations de la santé des poissons en lien avec l'exposition à différents types de polluants. Des approches similaires sont mise en oeuvre dans différents cours d'eau à travers le monde notamment dans le programme américain BEST. La confrontation des approches développées en France et aux Etats-Unis sera présentée mais ces différents travaux montrent l'intérêt de l'approche écotoxicologique dans un contexte de surveillance. De plus, cette approche peut également être appliquée dans des milieux de plus petite taille permettant alors une surveillance intégrée des bassins versants