Direct observation of homogeneous cavitation in nanopores

We report on the evaporation of hexane from porous alumina and silicon membranes. These membranes contain billions of independent nanopores tailored to an ink-bottle shape, where a cavity several tens of nanometers in diameter is separated from the bulk vapor by a constriction. For alumina membranes with narrow enough constrictions, we demonstrate that cavity evaporation proceeds by cavitation. Measurements of the pressure dependence of the cavitation rate follow the predictions of the bulk, homogeneous, classical nucleation theory, definitively establishing the relevance of homogeneous cavitation as an evaporation mechanism in mesoporous materials. Our results imply that porous alumina membranes are a promising new system to study liquids in a deeply metastable state.Comment: 14 pages , 4 figures. Source files also contain Supplemental Material (Doebele_HomogeneousCavitationMembranes_SM.pdf

Evaporation process in porous silicon: cavitation vs pore-blocking

International audienceWe have measured sorption isotherms for helium and nitrogen in wide temperature ranges and for a series of porous silicon samples, both native samples and samples with reduced pore mouth so that the pores have an ink-bottle shape. Combining volumetric measurements and sensitive optical techniques, we show that, at high temperature, homogeneous cavitation is the relevant evaporation mechanism for all samples. At low temperature, the evaporation is controlled by meniscus recession, the detailed mechanism being dependent on the pore length and on the mouth reduction. Native samples and samples with ink-bottle pores shorter than one micrometer behave as an array of independent pores. In contrast, samples with long ink-bottle pores exhibit long-range correlations between pores. In this latter case, evaporation takes place by a collective percolation process and not by heterogeneous cavitation as previously proposed. The variety of evaporation mechanisms points to porous silicon being an anisotropic three dimensional pore network rather than an array of straight independent pores

Shift in Herders' Territorialities from Regional to Local Scale: The Political Ecology of Pastoral Herding in Western Burkina Faso

International audienceIn Burkina Faso, livestock sedentarization programmes are still at the top of policy makers’ agendas and at the heart of their discourse, despite huge changes in land cover, land use and territorialities in rural areas. This paper contributes to the literature on the impact of livestock policies targeting the sedentarization of pastoralism in sub-Saharan Africa by specifically highlighting the territorial consequences of such policies. This paper suggests that policies directed at improving livestock governance in a context of climate change and changes in land cover and land tenure need to focus on securing pastoralists’ reticular territories, which are made up of corridors and numerous areas of pastureland, rather than on creating disconnected state ranches

Baby MIND detector first physics run

International audienceBaby MIND is a Magnetized Iron Neutrino Detector, serving as a downstream magnetized muon range detector for WAGASCI on the T2K beam line in Japan. The first physics run of Baby MIND together with other WAGASCI sub-detectors took place in the period from November 2019 to February 2020 (T2K run10), where a total of $4.8 \times 10^{20}$ Protons on target (POT) was delivered. Preliminary results showing Baby MIND data quality, detector performance and examples of neutrino interactions on iron during the first physics run are presented