Une nouvelle méthode multi-élément non-intrusive basée sur la clusterisation agglorémative capable d'approcher les systèmes dynamiques bifurcatifs

International audienceA multi-element non-intrusive generalised polynomial chaos method is developed to approximate state variable of a bifurcative dynamical system. It rely on a partitioning of the stochastic space along discon-tinuities of any shapes, efficient even when the discontinuities are running partially, and allowing the use of a low degree of approximation. An agglomerative clustering method is implemented in a space defined by the values of the quantity of interest (QOI) and of its derivatives with respect to the stochastic parameters. The stochastic space is first properly sampled. Then, at every instant, several partitions of the stochastic space are tested and the best one is selected as the one minimizing the maximum of the cross-validation errors of the local surrogate models. Once the local models are obtained and the sto-chastic space is correctly sliced, a neural network classifier is learned to determine in which element a sample is for further evaluations at the considered instant. The method uses the same samples for the space partitioning and for the training of the local models with regression thus reducing the computational cost. The long-time integration problem is countered and the stochastic space can be split according to the discontinuity induced by the potential bifurcation. The results of the method are advantageously compared to those obtained with the direct use of a Gradient Tree Boosting algorithm at every instant and the classical Pseudo projection method for a system leading to a bifurcation

Pertinent spatio-temporal scale of observation to understand suspended sediment yield control factors in the Andean region : the case of the Santa River (Peru)

Hydro-sedimentology development is a great challenge in Peru due to limited data as well as sparse and confidential information. This study aimed to quantify and to understand the suspended sediment yield from the west-central Andes Mountains and to identify the main erosion-control factors and their relevance. The Tablachaca River (3132 km(2)) and the Santa River (6815 km(2)), located in two adjacent Andes catchments, showed similar statistical daily rainfall and discharge variability but large differences in specific suspended-sediment yield (SSY). In order to investigate the main erosion factors, daily water discharge and suspended sediment concentration (SSC) datasets of the Santa and Tablachaca rivers were analysed. Mining activity in specific lithologies was identified as the major factor that controls the high SSY of the Tablachaca (2204 t km(2) yr(-1)), which is four times greater than the Santa's SSY. These results show that the analysis of control factors of regional SSY at the Andes scale should be done carefully. Indeed, spatial data at kilometric scale and also daily water discharge and SSC time series are needed to define the main erosion factors along the entire Andean range

Effect of Embedded Dexamethasone in Cochlear Implant Array on Insertion Forces in an Artificial Model of Scala Tympani

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Impact of an Acinetobacter baumannii outbreak on kidney events in a burn unit: A targeted machine learning analysis

International audienceBackground: Multidrug-resistant (MDR) bacteria outbreaks represent a major threat in intensive care units. Patients may then be exposed to drug-related direct toxicity during such outbreaks. The objective of this study was to explore the impact of an outbreak of imipenem-resistant Acinetobacter baumannii (IR-AB) on renal outcomes.Methods: We performed a before-and-after observational study in a French burn intensive care unit during an IR-AB outbreak: a 13-month period before (period A, October 2013-October 2014) and a 13-month period after outbreak control (period B, December 2014-December 2015). A total of 409 patients were included, 195 during period A and 214 during period B. The main endpoint was major adverse kidney events at day 90 (MAKE 90). Secondary endpoints were acute kidney injury (AKI) and persistent renal dysfunction.Results: Incidence of MAKE 90 was 15.9% during period A versus 11.2% during period B (P = .166) and AKI 28.2% versus 18.7% (P = .023). The use of colistin was associated with renal outcomes in univariate analysis. After adjustment of potential confounding factors using a targeted Machine Learning Analysis (ie, IR-AB-related infection, septic shock, severity scores, other nephrotoxics, chronic kidney disease, serum creatinine at admission, Staphylococcus aureus), colistin remained associated with the risk of MAKE and AKI (relative risk = 2.909, 95% confidence interval [CI] [1.364, 6.204], P = .006 for MAKE 90, and relative risk = 2.14, 95% CI [1.52, 3.02], P<.0001 for AKI).Conclusions: The episode of IR-AB outbreak was associated with an increased risk of kidney events, which appears to be driven by the use of colistin

Contributing factors and outcomes of burn-associated cholestasis

International audienceBackground & AimsCholestasis often occurs after burn injuries. However, the prevalence of cholestasis and its effect on outcomes in patients with severe burn injuries are unknown. The aim of this study was to describe the course and the burden of cholestasis in a cohort of severely burned adult patients.MethodsWe investigated the relationship between burn-associated cholestasis (BAC) and clinical outcomes in a retrospective cohort of patients admitted to our unit for severe burn injuries between 2012 and 2015. BAC was defined as an increased level of serum alkaline phosphatase (ALP) ≥1.5x the upper limit of normal (ULN) with an increased level of gamma-glutamyltransferase (GGT) ≥3x ULN, or as an increased level of total bilirubin ≥2x ULN.ResultsA total of 214 patients were included: 111 (52%) patients developed BAC after a median (IQR) stay of 9 (5–16) days. At 90 days, the mortality rate was 20%, including 34 and 9 patients with and without BAC (p <0.001), respectively, which corresponded to a 2.5-fold higher (95% CI 1.2–5.2, p = 0.012) risk of 90-day mortality for patients with BAC. After being adjusted for severity of illness, patients with BAC, hyperbilirubinemia and without elevated ALP and GGT levels had a hazard ratio of 4.51 (95% CI 1.87–10.87) for 90-day mortality. BAC was associated with the severity of the burn injury, shock and bacteraemia. BAC was present in 38 (51%) patients at discharge, and 7 (18%) patients had secondary sclerosing cholangitis. These patients maintained elevated levels of ALP and GGT that were 5.8x (1.7–15) the ULN and 11x the ULN (4.5–22), respectively, 20 months (3.5–35) after discharge.ConclusionBAC is prevalent among patients with severe burn injuries and is associated with worse short-term outcomes, especially when total bilirubin levels were increased without elevated ALP and GGT levels. BAC survivors are at risk of developing sclerosing cholangitis.Lay summaryCholestasis is common after burn injuries and is associated with burn severity, sepsis, organ failure and mortality. Patients with hyperbilirubinemia without elevated alkaline phosphatase and gamma-glutamyltransferase levels after the burn injury have a poor prognosis. Patients with burn-associated cholestasis may develop sclerosing cholangitis and secondary biliary cirrhosis