Slope instabilities in Dolomieu crater, Réunion Island: From seismic signals to rockfall characteristics

International audienceThe seismic signals of hundreds of rockfalls within Dolomieu crater, Piton de la Fournaise volcano, Réunion Island, have been analyzed to investigate a possible link between physical rockfall-generating processes and associated seismic signal features. Moreover, indirect observation of rockfalls via the seismic signals they generate can provide useful data for studying volcanoes and the temporal variations of their structure. An increase in the number of rockfall events and their volumes might be an indicator of structural weakness and deformation of the volcano associated with potential eruptive activity. The study focuses on a 10 month period following the 6 April 2007 crater floor collapse within Dolomieu crater, from May 2007 to February 2008. For granular flows a scaling law is revealed between seismic energy and signal duration. A semiempirical approach based on both analytical analysis and numerical simulation of these flows shows that a similar scaling law exists between the difference of potential energy computed for an event and its propagation times and also emphasizes the effect of local topography on this scaling law. Simulated and observed data were compared to evaluate the proportion of potential energy dissipated in the form of seismic waves and confirm a direct link between the seismic energy and potential energy of a given granular flow. The mean ratio of seismic to potential energy is of the order of 10−4, comparable to the range of values observed in previous studies. A simple method based on these ratios is proposed to estimate the volumes of rockfalls from their seismic signal. Observed seismic energy and the frequency of rockfalls decreased at the beginning of the studied period and reached a stable level in July, thus suggesting a postcollapse relaxation time of Dolomieu crater structure of about 2 months from seismic signal analysis, which is confirmed by deformation data. The total rockfall volume over the study period is estimated to be 1.85 Mm3

La surveillance épidémiologique du risque de cancer

La santé fait partie intégrante du bien être. Certaines maladies bénignes sont faciles à supporter, surtout si elles durent quelques jours seulement. En revanche, d'autres maladies sévères sont lourdes, tant sur le plan individuel que collectif. Le cancer est l'une d'entre elles ; les risques de mortalité sont variables selon l'organe touché, mais, dans tous les cas, une prise en charge par le corps médical s'impose durant des temps longs, souvent plusieurs années. Aussi, des réseaux de surveillance, où médecins et géographes collaborent, ont-ils vu le jour pour mieux cerner les causes de ce fléau ; et, peut-être, en réduire le taux d'incidence1

Kinetics of Palladium(0)‐Allyl Interactions in the Tsuji‐Trost Reaction, derived from Single‐Molecule Fluorescence Microscopy

Single‐molecule (SM) chemistry is devoted to unravel reaction steps which are hidden in cuvette experiments. Controversies about the substrate activation during the Tsuji‐Trost deallylation motivated us to study, on the single‐molecule level, the kinetics of the catalyst precursor Pd(PPh3)4 with our recently designed two‐color fluorescent probes. Photochemical, metal‐free bypass reactions were found and taken into account by the combination of spectrally separated single‐molecule TIRF‐microscopy and state‐of‐the art analysis procedures. Unselective π‐complex formation (KD≈103 M−1) precedes the insertion of the active catalyst into the C−OR bond (RO−=leaving group), indicated by the lacking immediate change of fluorescence color. The formed intermediate then decomposes on a time scale of≥2 – 3 s to the deallylated product

Clay Minerals Mapping from Imaging Spectroscopy

Mapping subsurface clay minerals is an important issue because they have particular behaviors in terms of mechanics and hydrology that directly affects assets laid at the surface such as buildings, houses, etc. They have a direct impact in ground stability due to their swelling capacities, constraining infiltration processes during flooding, especially when moisture is important. So detecting and characterizing clay mineral in soils serve urban planning issues and improve the risk reduction by predicting impacts of subsidence on houses and infrastructures. High-resolution clay maps are thus needed with accurate indications on mineral species and abundances. Clay minerals, known as phyllosilicates, are divided in three main species: smectite, illite, and kaolinite. The smectite group highly contributes to the swelling behavior of soils, and because geotechnical soil analyses are expensive and time-consuming, it is urgent to develop new approaches for mapping clays’ spatial distribution by using new technologies, e.g., ground spectrometer or remote hyperspectral cameras [0.4–2.5 μm]. These technics constitute efficient alternatives to conventional methods. We present in this chapter some recent results we got for characterizing clay species and their abundances from spectrometry, used either from a ground spectrometer or from hyperspectral cameras

Comparison of clinical characteristics and healthcare resource use of pediatric chronic and non-chronic critically ill patients in intensive care units: a retrospective national registry study

Introduction: Chronic critically ill patients (CCI) in pediatric intensive care unit (PICU) are at risk of negative health outcomes, and account for a considerable amount of ICU resources. This study aimed to (a) describe the prevalence of CCI children, (b) compare their clinical characteristics and ICU resources use with non-CCI children, and (c) identify associated risk factors of CCI. Methods: A retrospective national registry study including 2015–2017 data from the eight Swiss PICUs of five tertiary and three regional hospitals, admitting a broad case-mix of medical and surgical patients, including pre- and full-term infants. CCI patients were identified using an adapted definition: PICU length of stay (LOS) ≥8 days and dependence on ≥1 PICU technology. Results: Out of the 12,375 PICU admissions, 982 (8%) were CCI children and compared to non-CCI children, they were younger (2.8 vs. 6.7 months), had more cardiac conditions (24% vs. 12%), and higher mortality rate (7% vs. 2%) (p < 0.001). Nursing workload was higher in the CCI compared to the non-CCI group (22 [17–27]; 21 [16–26] respectively p < 0.001). Factors associated with CCI were cardiac (aOR = 2.241) and neurological diagnosis (aOR = 2.062), surgery (aORs between 1.662 and 2.391), ventilation support (aOR = 2.278), high mortality risk (aOR = 1.074) and agitation (aOR = 1.867). Conclusion: the results confirm the clinical vulnerability and the complexity of care of CCI children as they were defined in our study. Early identification and adequate staffing is required to provide appropriate and good quality care

Slopes instability of the Dolomieu crater in La Reunion from seismological observations and numerical modeling.

International audienceThe intensity of volcanic activity and seasonal rains associated with the instability of the natural slopes has caused many rockfalls in the Dolomieu crater located on top of the volcano Piton de la Fournaise in La Reunion Island. These phenomena, that involve individual blocks up to larger volumes, are expected to be related to the volcanic activity. The unpredictable nature and destructive power of gravitational flows make in-situ measurements extremely difficult. The seismic signal generated by these slope instabilities provides thus a unique tool to trace back these events and retrieve their characteristics (volume, duration, localization, . . . ). The permanent seismic network set on Le Piton de la Fournaise volcano is particularly well suited to the study of seismic signals related to gravitational collapse and of their relation to volcanic activity. Using this network and the new seismic broadband stations recently installed, the seismic signals generated by slope instabilities have been acquired and analyzed. In a first step, signal processing techniques have been developed to distinguish the seismic signal generated by rockfalls from that generated by other seismological events that affect the Piton de la Fournaise Volcano. A localization method has been developed based on inversion of waves arrival time. We focus on the 2006-2007 period, during which the crater has undergone a major collapse. This event has considerably destabilized the Dolomieu crater edges, providing a good opportunity to study the evolution in time of the rockfall activity. Analysis of the seismic signal and simple scaling laws for granular flows made it possible to derive interesting relations between the energy of the seismic waves and the characteristics of rockfalls. The role of the local topography in these relations has been investigated using numerical modeling of dry granular flows and the Digital Elevation Model of the Dolomieu crater constructed by photogrammetric techniques. Good agreement is found between the scaling laws obtained theoretically and those derived from seismic observation providing insight into the effect of the source parameters on the generated seismic signal. The detection methods and the scaling laws developed here provide useful tools for monitoring of rockfall activity, in particular in relation with the volcanic activity. These works were conducted within UNDERVOLC project

Investigation of the interactions of polyvinylpyrrolidone with mixtures of anionic and nonionic surfactants or anionic and zwitterionic surfactants by pulsed field gradient NMR

The interaction of polyvinylpyrrolidone (PVP) with an anionic surfactant (sodium dodecyl sulfate, SDS), a nonionic surfactant (pentaethylene glycol monodecyl ether, C(10)E(5)), and a zwitterionic surfactant (lauryl amido propyl betaine, LAPB) has been investigated by means of pulsed gradient spin-echo NMR (FT-PGSE NMR), allowing self-diffusion coefficients to be determined. The results confirm the strong interaction prevailing in the PVP/SDS system, whereas no association has been observed in the PVP/C(10)E(5) and PVP/LAPB systems. Mixing PVP with two surfactants, namely SDS and C(10)E(5) or SDS and LAPB, results in the formation of ternary aggregates between the polymer and the mixed micelles

SAMCO: Adaptation de la société aux risques en montagne dans un contexte de changement global

National audienceLe projet SAMCO (Society Adaptation for coping with Mountain risks in a global change COntext, 2013-2016) a pour but de développer un ensemble d'outils méthodologiques permettant d'améliorer la résilience des sociétés soumises aux impacts des risques en milieux montagneux. Ces outils visent à mesu-rer la capacité d'adaptation des écosystèmes et des sociétés à partir de l'analyse de cas réels provenant de 3 sites pilotes représentatifs

SAMCO: Society adaptation for coping with mountain risks in a global change context

International audienceThe SAMCO project is intended to contribute to the development of a proactive resilience framework enhancing the overall resilience of societies on the impacts of mountain risks

Plasma Levels of Persistent Organic Pollutants and Risk of Type 2 Diabetes: a Prospective Analysis in the Nurses’ Health Study and Meta-analysis

Background: Prospective data regarding persistent organic pollutants (POPs) and risk of type 2 diabetes (T2D) are limited, and the results for individual POPs are not entirely consistent across studies. Objectives: We prospectively examined plasma POP concentrations in relation to incident T2D and summarized existing evidence in a meta-analysis. Methods: Plasma polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethylene (DDE), and hexachlorobenzene (HCB) concentrations were measured in 1,095 women who were free of diabetes at blood draw in 1989–1990 and participated in two case–control studies in the Nurses’ Health Study. We identified 48 incident T2D cases through 30 June 2008. We conducted a literature search in PubMed and EMBASE through December 2011 to identify prospective studies on POPs in relation to diabetes. We used a fixed-effects model to summarize results. Results: After multivariable adjustment, plasma HCB concentration was positively associated with incident T2D [pooled odds ratio (OR) 3.59 (95% CI: 1.49, 8.64, p$_{trend}$= 0.003) comparing extreme tertiles]. Other POPs were not significantly associated with diabetes. After pooling our results with those of six published prospective studies that included 842 diabetes cases in total, we found that HCB and total PCBs both were associated with diabetes: the pooled ORs were 2.00 (95% CI: 1.13, 3.53; I$^2$= 21.4%, p$_{heterogeneity}$= 0.28) and 1.70 (95% CI: 1.28, 2.27; I$^2$= 16.3%, p$_{heterogeneity}$= 0.30) for HCB and total PCBs, respectively. Conclusions: These findings support an association between POP exposure and the risk of T2D