Analyse de fiabilité en modélisation hydrologique: Concepts et applications au modèle pluies-débits GR3

Pour étudier les incertitudes d'un modèle hydrologique, on peut employer l'analyse de fiabilité, méthode couramment utilisée dans le domaine de la résistance des structures et du génie hydraulique. Cet outil peut être transposé dans le domaine hydrologique pour juger de la qualité d'un modèle. Un modèle hydrologique sera fiable si, sur une série de données test, l'ajustement obtenu avec un jeu de paramètres recommandé pour un fonctionnement passe-partout est, selon toute probabilité, d'une qualité proche de l'ajustement idéal correspondant au calage du jeu de paramètres sur l'échantillon test. Ce papier montre comment adapter chacun des concepts de l'analyse de fiabilité en hydrologie et détaille la technique des deux premiers moments afin de calculer explicitement la fiabilité d'un modèle-pluie débit en réalisant un développement limité au voisinage du point de fonctionnement du modèle.Cette approche par analyse de fiabilité est appliquée au modèle GR3 à titre d'illustration pour juger de la pertinence de ce modèle pluie-débit conceptuel à trois paramètres en situation de prédiction des crues à court pas de temps sur un bassin versant situé dans la région de la Côte d'Azur en France . Les résultats numériques obtenus montrent le caractère opérationnel de cette approche très simple. D'autre part, ces calculs de fiabilité mettent en évidence la réponse du modèle à chacun des paramètres. Enfin en mesurant la performance de représentativité d'un modèle selon plusieurs dimensions telles l'erreur quadratique d'ajustement, l'erreur sur le volume de crue prévue ou l'importance de l'écart de pointe de crue, l'analyse de fiabilité peut être naturellement étendue vers une approche multicritère en considérant des probabilités conjointes de satisfaction du modèle sur chacun de ces critères.Reliability analysis is a method for evaluating the risk of failure of a system and this concept is widely used in structure design. The theory can be conveniently transposed to the field of water sciences so as to evaluate the quality of hydrologic models. Hydrological reliability of a model is defined as the probability that there will not be significant different performances between this model, with parameters assessed on the basis of a large sample including various hydrological conditions, and the same model running with ad hoc parameters estimated from the test sample. Consequently a tolerance threshold has to be introduced in reliability analysis for hydrological models. A number of conceptual differences between validation and reliability analysis are reviewed and categorized.This paper shows how to adapt the concepts of reliability to hydrology and gives details of the first two moment technique that can be implemented to compute the reliability of a rainfall runoff model. This technique is based on a Taylor series developed in the neighborhood of the model working point. This simplification allows for an explicit expression of the expectation and the variance of the hydrological model performance as functions of the marginal sensitivity of the criterion and the parameter uncertainties. A Student ratio can be easily computed to evaluate the quality of a hydrological model from a reliability-based point of view.The GR3 model is used to illustrate this technique. A reliability analysis of this three parameter conceptual rainfall-runoff model gives new insight into the performance of the model for short-term flood prediction in the Réal Collobrier river basin located in the French Côte d'Azur. Numerical results show that the reliability analysis approach is very simple and of practical interest. For 16 of the 18 samples used for validation, the GR3 rainfall runoff model proved to be reliable on the basis of the three criteria used in this paper to evaluate the quality of a hydrological model (general quadratic deviation loss of runoffs, flood volume error and flood peak error). Using reliability analysis, contributions of each parameter to the variance of the performance function can be conveniently identified. For the GR3 model and the Réal Collobrier case study, the impacts of each parameter on the model efficiency are as follows:- The contribution of a parameter varies from one criterion to another. This indicates that a parameter originally designed to play a specific role in the modeling of the rainfall runoff transformation process does contribute to the criterion that best describes this function, which confirms the conceptual "good sense" of GR3. - For each criterion, the cross contributions are very low: the GR3 model satisfies the principle of parsimony and each parameter adds something different to the general behavior of GR3. In this case study, the GR3 model exhibits a good balance between complexity and quality for hydrological models.Finally, reliability analysis can provide a multicriteria point of view of the model qualities by changing the various indices of performance. Extension of reliability analysis towards engineering risk would include the estimation of joint probability distributions for these multiple criteria of interest

Analysis of adequacy levels for human resources improvement within primary health care framework in Africa

Human resources in health care system in sub-Saharan Africa are generally picturing a lack of adequacy between expected skills from the professionals and health care needs expressed by the populations. It is, however, possible to analyse these various lacks of adequacy related to human resource management and their determinants to enhance the effectiveness of the health care system. From two projects focused on nurse professionals within the health care system in Central Africa, we present an analytic grid for adequacy levels looking into the following aspects: - adequacy between skills-based profiles for health system professionals, quality of care and service delivery (health care system /medical standards), needs and expectations from the populations, - adequacy between allocation of health system professionals, quality of care and services delivered (health care system /medical standards), needs and expectations from the populations, - adequacy between human resource management within health care system and medical standards, - adequacy between human resource management within education/teaching/training and needs from health care system and education sectors, - adequacy between basic and on-going education and realities of tasks expected and implemented by different categories of professionals within the health care system body, - adequacy between intentions for initial and on-going trainings and teaching programs in health sciences for trainers (teachers/supervisors/health care system professionals/ directors (teaching managers) of schools...). This tool is necessary for decision-makers as well as for health care system professionals who share common objectives for changes at each level of intervention within the health system. Setting this adequacy implies interdisciplinary and participative approaches for concerned actors in order to provide an overall vision of a more broaden system than health district, small island with self-rationality, and in which they operate

The vertebral body growth plate in scoliosis: a primary disturbance of growth?

Study Design and Aims: This was an observational pilot study of the vertebral body growth plates in scoliosis involving high-resolution coronal plane magnetic resonance (MR) imaging and histological examination. One aim of this study was to determine whether vertebral body growth plates in scoliosis demonstrated abnormalities on MR imaging. A second aim was to determine if a relationship existed between MR and histological abnormalities in these vertebral body growth plates. Methods: MR imaging sequences of 18 patients demonstrated the vertebralbody growth plates well enough to detect gross abnormalities/ deficient areas/zones. Histological examination of ten vertebral body growth plates removed during routine scoliosis surgery was performed. Observational histological comparison with MR images was possible in four cases. Results: Four of the 18 MR images demonstrated spines with normal curvature and normal vertebral body growth plates. In 13 scoliotic spines, convex and concave side growth plate deficiencies were observed most frequently at or near the apex of the curve. One MR image demonstrated a 55° kyphosis and no convex or concave side deficiencies. The degree of vertebral body wedging was independent of the presence of vertebral body growth plate deficiency. Histological abnormalities of the vertebral body growth plates were demonstrated in four with MR imaging abnormalities. Conclusion: This study demonstrated MR image abnormalities of scoliotic vertebral body growth plates compared to controls. A qualitative relationship was demonstrated between MR imaging and histological abnormalities. The finding that vertebral body growth plate deficiencies occurred both on the convex and concave sides of the spine, closest to the apical vertebra of the scoliosis curve, implied that they are less likely to be the result of adaptive changes to the physical forces involved in the scoliotic deformity. One explanation is that they represent a primary disturbance of growth

Microguards and micromessengers of the genome

The regulation of gene expression is of fundamental importance to maintain organismal function and integrity and requires a multifaceted and highly ordered sequence of events. The cyclic nature of gene expression is known as ‘transcription dynamics’. Disruption or perturbation of these dynamics can result in significant fitness costs arising from genome instability, accelerated ageing and disease. We review recent research that supports the idea that an important new role for small RNAs, particularly microRNAs (miRNAs), is in protecting the genome against short-term transcriptional fluctuations, in a process we term ‘microguarding’. An additional emerging role for miRNAs is as ‘micromessengers’—through alteration of gene expression in target cells to which they are trafficked within microvesicles. We describe the scant but emerging evidence that miRNAs can be moved between different cells, individuals and even species, to exert biologically significant responses. With these two new roles, miRNAs have the potential to protect against deleterious gene expression variation from perturbation and to themselves perturb the expression of genes in target cells. These interactions between cells will frequently be subject to conflicts of interest when they occur between unrelated cells that lack a coincidence of fitness interests. Hence, there is the potential for miRNAs to represent both a means to resolve conflicts of interest, as well as instigate them. We conclude by exploring this conflict hypothesis, by describing some of the initial evidence consistent with it and proposing new ideas for future research into this exciting topic

Characterization of an Ionization Readout Tile for nEXO

A new design for the anode of a time projection chamber, consisting of a charge-detecting "tile", is investigated for use in large scale liquid xenon detectors. The tile is produced by depositing 60 orthogonal metal charge-collecting strips, 3~mm wide, on a 10~\si{\cm} $\times$ 10~\si{\cm} fused-silica wafer. These charge tiles may be employed by large detectors, such as the proposed tonne-scale nEXO experiment to search for neutrinoless double-beta decay. Modular by design, an array of tiles can cover a sizable area. The width of each strip is small compared to the size of the tile, so a Frisch grid is not required. A grid-less, tiled anode design is beneficial for an experiment such as nEXO, where a wire tensioning support structure and Frisch grid might contribute radioactive backgrounds and would have to be designed to accommodate cycling to cryogenic temperatures. The segmented anode also reduces some degeneracies in signal reconstruction that arise in large-area crossed-wire time projection chambers. A prototype tile was tested in a cell containing liquid xenon. Very good agreement is achieved between the measured ionization spectrum of a $^{207}$Bi source and simulations that include the microphysics of recombination in xenon and a detailed modeling of the electrostatic field of the detector. An energy resolution $\sigma/E$=5.5\% is observed at 570~\si{keV}, comparable to the best intrinsic ionization-only resolution reported in literature for liquid xenon at 936~V/\si{cm}.Comment: 18 pages, 13 figures, as publishe

Sensitivity and discovery potential of the proposed nEXO experiment to neutrinoless double beta decay

The next-generation Enriched Xenon Observatory (nEXO) is a proposed experiment to search for neutrinoless double beta ($0\nu\beta\beta$) decay in $^{136}$Xe with a target half-life sensitivity of approximately $10^{28}$ years using $5\times10^3$ kg of isotopically enriched liquid-xenon in a time projection chamber. This improvement of two orders of magnitude in sensitivity over current limits is obtained by a significant increase of the $^{136}$Xe mass, the monolithic and homogeneous configuration of the active medium, and the multi-parameter measurements of the interactions enabled by the time projection chamber. The detector concept and anticipated performance are presented based upon demonstrated realizable background rates.Comment: v2 as publishe