A mutual reference shape based on information theory

International audienceIn this paper, we propose to consider the estimation of a refer-ence shape from a set of different segmentation results using both active contours and information theory. The reference shape is defined as the minimum of a criterion that benefits from both the mutual information and the joint entropy of the input segmentations and called a mutual shape. This energy criterion is here justified using similarities between informa-tion theory quantities and area measures, and presented in a continuous variational framework. This framework brings out some interesting evaluation measures such as the speci-ficity and sensitivity. In order to solve this shape optimization problem, shape derivatives are computed for each term of the criterion and interpreted as an evolution equation of an active contour. Some synthetical examples allow us to cast the light on the difference between our mutual shape and an average shape. Our framework has been considered for the estimation of a mutual shape for the evaluation of cardiac segmentation methods in MRI

Le partage de la ressource en eau sur la Durance en 2050 : vers une évolution du mode de gestion des grands ouvrages duranciens ?

Congrès SHF: Water Tensions in Europe and in the Mediterranean: water crisis by 2050?, Paris, FRA, 08-/10/2015 - 09/10/2015International audienceUne vision prospective de la gestion de l'eau du bassin de la Durance et des territoires alimentés par ses eaux à l'horizon 2050 a été élaborée, appuyée par une chaine de modèles incluant des représentations du climat, de la ressource naturelle, des demandes en eau et du fonctionnement des grands ouvrages hydrauliques (Serre-Ponçon, Castillon et Sainte-Croix), sous contraintes de respect des débits réservés, de cotes touristiques dans les retenues et de restitution d'eau stockée pour des usages en aval. Cet ensemble, validé en temps présent, a été alimenté par des projections climatiques et paramétré pour intégrer les évolutions du territoire décrites par des scénarios de développement socio-économique avec une hypothèse de conservation des règles de gestion actuelles. Les résultats suggèrent à l'horizon 2050 : une hausse de la température moyenne de l'air impactant l'hydrologie de montagne ; une évolution incertaine des précipitations ; une réduction des stocks de neige et une fonte avancée dans l'année qui induisent une réduction des débits au printemps ; une diminution de la ressource en eau en période estivale ; une diminution de la demande globale en eau à l'échelle du territoire, cette demande étant fortement conditionnée par les scénarios territoriaux élaborés ici ; la satisfaction des demandes en eau en aval des ouvrages considérées comme prioritaires, au détriment de la production d'énergie en hiver (flexibilité moindre en période de pointe) et du maintien de cotes touristiques en été ;une diminution de la production d'énergie due notamment à la réduction des apports en amont des ouvrages hydroélectriques

Characterization of primary human hepatocytes, HepG2 cells, and HepaRG cells at the mRNA level and CYP activity in response to inducers and their predictivity for the detection of human hepatotoxins

In the pharmaceutical industry, improving the early detection of drug-induced hepatotoxicity is essential as it is one of the most important reasons for attrition of candidate drugs during the later stages of drug development. The first objective of this study was to better characterize different cellular models (i.e., HepG2, HepaRG cells, and fresh primary human hepatocytes) at the gene expression level and analyze their metabolic cytochrome P450 capabilities. The cellular models were exposed to three different CYP450 inducers; beta-naphthoflavone (BNF), phenobarbital (PB), and rifampicin (RIF). HepG2 cells responded very weakly to the different inducers at the gene expression level, and this translated generally into low CYP450 activities in the induced cells compared with the control cells. On the contrary, HepaRG cells and the three human donors were inducible after exposure to BNF, PB, and RIF according to gene expression responses and CYP450 activities. Consequently, HepaRG cells could be used in screening as a substitute and/or in complement to primary hepatocytes for CYP induction studies. The second objective was to investigate the predictivity of the different cellular models to detect hepatotoxins (16 hepatotoxic and 5 nonhepatotoxic compounds). Specificity was 100% with the different cellular models tested. Cryopreserved human hepatocytes gave the highest sensitivity, ranging from 31% to 44% (depending on the donor), followed by lower sensitivity (13%) for HepaRG and HepG2 cells (6.3%). Overall, none of the models under study gave desirable sensitivities (80–100%). Consequently, a high metabolic capacity and CYP inducibility in cell lines does not necessarily correlate with a high sensitivity for the detection of hepatotoxic drugs. Further investigations are necessary to compare different cellular models and determine those that are best suited for the detection of hepatotoxic compounds

On the visual detection of non-natural records in streamflow time series: challenges and impacts

Large datasets of long-term streamflow measurements are widely used to infer and model hydrological processes. However, streamflow measurements may suffer from what users can consider anomalies, i.e. non-natural records that may be erroneous streamflow values or anthropogenic influences that can lead to misinterpretation of actual hydrological processes. Since identifying anomalies is time consuming for humans, no study has investigated their proportion, temporal distribution, and influence on hydrological indicators over large datasets. This study summarizes the results of a large visual inspection campaign of 674 streamflow time series in France made by 43 evaluators, who were asked to identify anomalies falling under five categories, namely, linear interpolation, drops, noise, point anomalies, and other. We examined the evaluators' individual behaviour in terms of severity and agreement with other evaluators, as well as the temporal distributions of the anomalies and their influence on commonly used hydrological indicators. We found that inter-evaluator agreement was surprisingly low, with an average of 12 % of overlapping periods reported as anomalies. These anomalies were mostly identified as linear interpolation and noise, and they were more frequently reported during the low-flow periods in summer. The impact of cleaning data from the identified anomaly values was higher on low-flow indicators than on high-flow indicators, with change rates lower than 5 % most of the time. We conclude that the identification of anomalies in streamflow time series is highly dependent on the aims and skills of each evaluator, which raises questions about the best practices to adopt for data cleaning.</p

Climate Change, Coral Reef Ecosystems, and Management Options for Marine Protected Areas

Marine protected areas (MPAs) provide place-based management of marine ecosystems through various degrees and types of protective actions. Habitats such as coral reefs are especially susceptible to degradation resulting from climate change, as evidenced by mass bleaching events over the past two decades. Marine ecosystems are being altered by direct effects of climate change including ocean warming, ocean acidification, rising sea level, changing circulation patterns, increasing severity of storms, and changing freshwater influxes. As impacts of climate change strengthen they may exacerbate effects of existing stressors and require new or modified management approaches; MPA networks are generally accepted as an improvement over individual MPAs to address multiple threats to the marine environment. While MPA networks are considered a potentially effective management approach for conserving marine biodiversity, they should be established in conjunction with other management strategies, such as fisheries regulations and reductions of nutrients and other forms of land-based pollution. Information about interactions between climate change and more “traditional” stressors is limited. MPA managers are faced with high levels of uncertainty about likely outcomes of management actions because climate change impacts have strong interactions with existing stressors, such as land-based sources of pollution, overfishing and destructive fishing practices, invasive species, and diseases. Management options include ameliorating existing stressors, protecting potentially resilient areas, developing networks of MPAs, and integrating climate change into MPA planning, management, and evaluation

Incertitudes sur les changements d'évapotranspiration potentielle : l'importance de la formulation

International audienceAssessing changes in potential evaporation (PE) is crucial in climate change impact studies on water resources. Indeed, PE is still widely used in catchment-scale assessments as input for rainfall-runoff models. Assessing the water balance evolution in a robust way therefore requires to consider and quantify in a comprehensive way the various uncertainties in PE changes. This work attempts to tackle this issue by looking at transient evolutions of PE for the Durance catchment, located in the southern French Alps. This catchment, under both the Alpine and Mediterranean climate influences, already shows periods with water demand – for drinking water, irrigation, and hydropower – close to total water availability. Estimating the evolution of PE together with the associated uncertainty is therefore of major interest for water managers. Transient runs from the ENSEMBLES Stream2 GCMs under the A1B emissions scenario (van der Linden et al., 2009) have been previously downscaled over the Durance catchment by three variants of the K-nearest neighbours resampling approach (Lafaysse et al., 2013): an analog method, a weather type method and a regression-based method. 100 transient runs have been generated from each stochastic downscaling method for all 30 combinations of GCM (4 different structures) and GCM runs (from 1 to 6 runs) selected from the ENSEMBLES project. The specific issue of PE formulation is studied by computing 3000 daily transient evolutions of (1) the reference Penman-Monteith formula calculated from hourly variables derived from the Safran high-resolution reanalysis (Vidal et al., 2010) and (2) the widely used temperature-based formula proposed by Oudin et al. (2005). Results from the 3000 downscaled climate projections show an increase in PE for both formulations, with a substantial dispersion due partly to the GCM structure and run, but mainly to the downscaling method. Moreover, the most important source of uncertainty in PE changes appears to be the choice of formulation. Additionally, the interactions between the downscaling method and the PE formulation seem to play an important role in the overall dispersion. This work shows that PE changes derived in climate change impact studies on water resources should be taken with great care, by considering not only the standard uncertainties (GCM structure, GCM internal variability, downscaling method, local natural variability), but also their combinations with the choice of the PE formulation

Impact of climate change on aquatic ecosystems along the Asse river network

Proceedings of FRIEND-Water 2014, Hanoi, VNM, 07-/10/2014 - 10/10/2014International audienceIntermittent rivers and their ecosystem will have to face climate change during the 21st century, with possible more frequent and more severe droughts leading to changes in biodiversity. The Asse River basin is one of the tributaries of the Durance River basin experiencing dry conditions. A framework was developed to simulate flows and biodiversity richness of intermittent rivers. The approach involves two rainfall-runoff models with distinct structures and a post-processing technique to simulate zero flow events. Perturbed meteorological forcings (downscaled GCM projections and biased resampled observed time series) are considered to study the biological response and intermittence. Results suggest that, by 2050, (i) zero flow events could be more frequent, (2) durations of zero-flows event are expected to increase, and (3) the consequence could be a loss of approximately 2 taxa. Sensitivity analysis demonstrates also that this basin is very sensitive to changes in total precipitation between June and November

Assessment of the SiSPAT SVAT model for irrigation estimation in south-east France

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAUIn this study, we assess the interest of using a Soil – Vegetation – Atmosphere – Transfer model, the SiSPAT (Simple Soil Vegetation Atmosphere Transfer) model, which solves the surface energy balance, for the evaluation of theoretical crop water requirements in south-east France. First the relevance of the model results, when parameterized using information extracted from a soil data base and pedotransfer functions for the estimation of soil hydraulic properties, and when vegetation characteristics are prescribed using available data bases is assessed. We use long term time series of soil water content profiles for this purpose. The results show that evapotranspiration, as simulated by SiSPAT is sensitive to the soil parameter specification leading to large uncertainties in the model results. Then, we present two methods implemented in SiSPAT to compute irrigation requirements. The first option mimics the soil water balance model principles by estimating the irrigation from the available soil water capacity filling. The second option relies on the model physics and estimates the difference between actual transpiration and the value corresponding to a minimal stomatal resistance, i.e. without water stress. Aspersion and drip irrigation can be simulated. Nine crop are chosen for the model evaluation. A comparison with two other water balance models is performed. The three models are consistent with determination coefficient between the simulated annual irrigation generally larger than 0.4. However, differences of the interannual irrigation needs, larger than several 100 mm, are sometimes found, especially for drip irrigation. This work provides a quantification of expected uncertainties when using water balance models or physically-based models for irrigation needs estimation