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Permeability of polydisperse solid foams
No full textInternational audienceThe effect of polydispersity on foam permeability is investigated by numerical simulations. Foam structures are first generated by Laguerre tessellations via the Neper software and relaxed to minimize the surface energy via the Surface Evolver software. The fluid flow and permeability are then calculated by means of pore-network simulations, by considering either fully open-cell foams or foams with randomly selected closed windows. Different configurations of window aperture are used, including identical window aperture size, identical window aperture ratio, or random window aperture ratio. The main results are obtained for the case of foams having identical and uniform window aperture ratios. For such foams and at constant mean pore size, foam permeability is found to strongly increase with the polydispersity degree. The numerical results are employed to discuss the validity of the mean pressure field assumption used to calculate the foam permeability, the effect of small pores, and the definition of an equivalent Kelvin foam size. We show that as long as the fluctuations of the window aperture ratio remain low, foam permeability can be estimated by using the mean pressure field hypothesis. The weak effect of small pores on permeability is related to their small contribution to the overall fluid volume fraction. Finally, various estimations of the equivalent Kelvin foam size based on pore-size distribution are propose
Code Middlenext 2021 : une gouvernance durable tangible
No full textInternational audienceMiddlenext, Code de gouvernement d'entreprise, nouvelle édition, sept. 2021, cahier no 1
CARACTÉRISATION RAPIDE DES BOUES D'ÉPURATION PAR DES MÉTHODES SPECTROSCOPIQUES
No full textInternational audienc
Hammerhead worms everywhere? Modelling the invasion of bipaliin flatworms in a changing climate
No full textInternational audienceAimAlien species introduced into new ecosystems occasionally predate upon or outcompete native species. Land planarians (Geoplanidae) are a family of carnivorous Platyhelminthes among which several species are found outside their native range. Specifically, hammerhead flatworms originate from Asia and Madagascar but have now reached many new locations worldwide through the transport of exotic plants. Because they are predators of earthworms and snails, they are considered a potential threat to native ecosystems. In this context, to anticipate their potential impacts and to inform early preventative actions, it is necessary to know where these species could spread to in future, or where they might already be present but undetected.LocationWorldwide.MethodsHere, we used occurrence records from online databases and climatic and soil variables to model the potential distribution of five hammerhead flatworm species (Bipalium adventitium, B. kewense, B. pennsylvanicum, B. vagum and Diversibipalium multilineatum) that are known to occur outside their native range.ResultsWe demonstrate that precipitation is an important factor determining their distribution, which is in accordance with their known affinity for humidity. We show that some areas have the potential to be invaded by all five species, including regions that are relatively spared so far. This includes the River Plate basin in South America, which already harbours a diverse fauna of native terrestrial flatworms and which appears to also be a potential hotspot for the establishment of alien hammerhead flatworms. According to scenarios of future climate change, two species (B. kewense and B. vagum) that currently have the largest observed global range are predicted to further increase their potential distribution.Main conclusionsThe results we report can be used to provide guidance for monitoring the potential sources of introduction of alien hammerhead flatworms in regions that are suitable, but which are not yet colonized
Predicted changes in the functional structure of earthworm assemblages in France driven by climate change
No full textInternational audienceAimSpecies shift their ranges as a consequence of climate change, hence modifying the structure of local assemblages. This may have important consequences for ecosystem functioning in the case of ecosystem engineers such as earthworms, especially when community restructuring leads to an alteration of their functional diversity. Here, we aimed to model the potential modification of the functional diversity of French earthworm assemblages in a context of climate change.LocationMetropolitan France.MethodsWe fitted boosted regression trees to earthworm data collected using a standardized protocol across France in the 1960s. We used model projections constrained by a macroecological model of species richness to predict the composition of earthworm assemblages in the present and in two scenarios of climate change and two future time periods. We coupled these results with a large set of species traits to calculate predicted changes in functional diversity, which we summarized by ecoregion.ResultsModels predicted a clear decline in functional richness between the period of sampling and nowadays which are expected to continue in the future, with substantial differences depending on ecoregions and on whether species will be able to disperse or not. However, predicted changes in functional evenness and divergence are much weaker, suggesting that climate change will not affect all facets of functional diversity in the same way.Main ConclusionsOur results mostly pointed to a potential reduction of the functional richness of earthworm communities in the future, but this predicted loss of diversity could be weaker if species are able to colonize new suitable sites or to persist in microclimate refugia. There are concerns, though, that these changes lead to an alteration of soil processes and of the ecosystem services they provide
Wavelet methods to study the pointwise regularity of the generalized Rosenblatt process
No full textWe prove that we can identify three types of pointwise behaviour in the regularity of the (generalized) Rosenblatt process. This extends to a non Gaussian setting previous results known for the (fractional) Brownian motion. On this purpose, fine bounds on the increments of the Rosenblatt process are needed. Our analysis is essentially based on various wavelet methods
On the weak invariance principle for ortho-martingale in Banach spaces. Application to stationary random fields
No full textIn this paper, we study the weak invariance principle for stationary ortho-martingales with values in 2-smooth or cotype 2 Banach spaces. Then, with the help of a suitable maximal ortho-martingale approximation, we derive the weak invariance principle for stationary random fields in L 1 under a condition in the spirit of Hannan. As an application, we get an asymptotic result for the L 1-Wasserstein distance between the common distribution function and the corresponding empirical distribution function of stationary random fields
Europan Molecular Indicators of Life Investigation (EMILI) for a Future Europa Lander Mission
No full textInternational audienceThe Europan Molecular Indicators of Life Investigation (EMILI) is an instrument concept being developed for the Europa Lander mission currently under study. EMILI will meet and exceed the scientific and technical/resource requirements of the organic composition analyzer identified as a core instrument on the Lander. EMILI tightly couples two complementary analytical techniques, based on 1) liquid extraction and processing with capillary electrophoresis and 2) thermal and chemical extraction with gas chromatography, to robustly detect, structurally characterize, and quantify the broadest range of organics and other Europan chemicals over widely-varying concentrations. Dual processing and analysis paths enable EMILI to perform a thorough characterization of potential molecular biosignatures and contextual compounds in collected surface samples. Here we present a summary of the requirements, design, and development status of EMILI with projected scientific opportunities on the Europa Lander as well as on other potential life detection missions seeking potential molecular biosignatures in situ
