Ultrasonic probing of the elastic properties of PMMA bead packings and their rearrangement during pressure sintering

Ultrasound transmission in PMMA spherical bead packings is investigated during the sintering process under stress. Velocity and amplitude measurements of coherent longitudinal waves are performed to monitor the evolution of the elastic properties of the solid frame from noncohesive packing to sintered granular material. Comparison between the experimental velocity data and the prediction by a contact model [Digby, J. Appl. Mech. 48, 803, (1981)] reveals the crucial role of the bonding effect on the mechanical behavior of granular compacts. By using the correlation technique of acoustic speckles, we also observe the important rearrangements in granular packings before the onset of sintering.Comment: to be published in Powder Technology, 8 pages, 8 figure

Sound pulse broadening in stressed granular media

International audienceThe pulse broadening and decay of coherent sound waves propagating in disordered granular media are investigated. We find that the pulse width of these compressional waves is broadened when the disorder is increased by mixing the beads made of different materials. To identify the responsible mechanism for the pulse broadening, we also perform the acoustic attenuation measurement by spectral analysis and the numerical simulation of pulsed sound wave propagation along one-dimensional disordered elastic chains. The qualitative agreement between experiment and simulation reveals a dominant mechanism by scattering attenuation at the high-frequency range, which is consistent with theoretical models of sound wave scattering in strongly random media via a correlation length

Organisation socio-spatiale et structuration régionale de l’Outaouais

L'organisation socio-spatiale de l'Outaouais se caractérise par une juxtaposition d'éléments dont l'interdépendance est faible. Cette faiblesse se révèle bien à l'étude des comportements différenciés de migration. Cette réalité s'oppose aux efforts des divers organismes politico-administratifs cherchant à intégrer la région dans un ensemble cohérent. Cela impose une compréhension du dynamisme des éléments locaux qui constituent un passage obligé de toute politique d'aménagement et de développement régional.The socio-spatial organization of the Outaouais region is characterized by a juxtaposition of elements, the interdependence of which is weak. This weakness can be revealed, for example, by a study of the migration behaviour. To this reality is opposed the integration objective supported by political organisms at the regional level. However, this opposition can be resolved by a better understanding of local dynamisms at the roots of any political intervention

Déterminants et inégalités d’utilisation des services obstétricaux essentiels dans les pays à revenu faible et intermédiaire

Introduction Chaque année, 289 000 femmes décèdent des complications reliées à la grossesse et à l’accouchement, et 2.9 millions de nouveau-nés décèdent avant d’atteindre 28 jours de vie. La quasi-totalité (99%) des décès maternels et néonataux ont cours dans les pays à revenu faible et intermédiaire (PRFI). L’utilisation des services obstétricaux essentiels, incluant l’assistance qualifiée à l’accouchement (AA) et les services postnataux, contribue largement à la réduction de la morbidité et de la mortalité maternelle et néonatale. Il est donc essentiel d’évaluer les déterminants et les inégalités de couverture de ces services, en vue d’informer l’élaboration de politiques et de programmes de santé dans les PRFI. Objectifs 1. Étudier systématiquement les déterminants et inégalités socioéconomiques, géographiques et démographiques dans l’utilisation des services de santé postnataux dans les PRFI. 2. Évaluer l’effet de la politique de subvention des frais aux usagers introduite au Burkina Faso en 2007 sur les taux d’utilisation de l’assistance qualifiée à l’accouchement, en fonction du statut socioéconomique (SSE). Méthodes 1. Nous avons réalisé une revue systématique sur l’utilisation des services postnataux dans les PRFI, en fonction des déterminants socioéconomiques, géographiques et démographiques. Notre étude incluait une méta-analyse de l’utilisation des services selon les quintiles de SSE et le milieu de vie (urbain vs. rural). 2. Nous avons utilisé un devis quasi-expérimental. Les sources de données consistaient en deux sondages représentatifs (n=1408 et n=1403), conduits respectivement en 2008 et 2010 auprès de femmes des districts sanitaires de Houndé et de Ziniaré au Burkina Faso, en plus d’une enquête sur la qualité structurelle des soins offerts dans les centres de santé primaire. Nous avons utilisé des modèles de régression de Poisson, multi-niveaux et segmentés, afin d’évaluer l’effet de la politique de subvention sur les taux d’AA. Nous avons estimé des ratios et différences de taux d’incidence ajustés, en fonction du SSE et du temps écoulé depuis l’introduction de la subvention. Résultats 1. Les estimés de ratio de cotes (RC) agrégés (IC 95%) pour les femmes de SSE élevé (5e quintile ou Q5), Q4, Q3 et Q2 (référence : quintile le plus pauvre, Q1) étaient respectivement : 2.27 (1.75 – 2.93); 1.60 (1.30-1.98); 1.32 (1.12-1.55); et 1.14 (0.96-1.34). La méta-analyse a aussi démontré un gradient d’utilisation des services postnataux entre les femmes urbaines et rurales : RC (IC 95%) = 1.36 (1.01-1.81). L’évaluation narrative a par ailleurs identifié une différence dans la couverture de services selon le niveau d’éducation. 2. Pour les femmes de faible SSE, le taux d’AA était 24% plus élevé (IC 95% : 4-46%) immédiatement après l’introduction de la subvention, en comparaison au taux attendu en l’absence de ladite subvention. L’ampleur de l’effet a diminué dans le temps, correspondant à des estimés (IC 95%) de 22% (3-45%) à 6 mois, 20% (1-43%) à 12 mois, et 17% (-4-42%) à 24 mois après l’introduction de la subvention. La force d’association variait selon les strates de SSE, l’effet le plus prononcé étant observé au sein du SSE le plus faible. Conclusions 1. L’utilisation des services postnataux demeure inéquitable selon le SSE et l’accessibilité géographique aux formations sanitaires dans les PRFI. 2. Notre étude suggère que l’introduction de la subvention des frais aux usagers au Burkina Faso résulte en une augmentation soutenue dans le taux d’assistance qualifiée à l’accouchement, particulièrement chez les femmes de faible SSE. Cette évidence scientifique devrait alimenter l’élaboration de programmes de santé materno-infantile, en plus de guider la planification de politiques et le renforcement des systèmes de santé des PRFI.Background Each year, 289 000 women die from complications related to pregnancy, childbirth or the postnatal period, and 2.9 million newborns decease before reaching 28 days of life. The near totality (99%) of maternal and neonatal deaths occur in low- and middle-income countries (LMICs). Utilization of essential obstetric care services including skilled birth attendance (SBA) and postnatal care (PNC) largely contributes to the reduction of maternal and neonatal morbidity and mortality. There is a strong need to assess the determinants and inequalities in coverage of SBA and PNC services, to inform health policy planning. Objectives 1. Systematically assess the socioeconomic, geographic and demographic inequalities in PNC services utilization in LMICs. 2. Evaluate the effect of Burkina Faso’s 2007 user-fee subsidy policy on SBA rate across socioeconomic status (SES) strata. Methods 1. We conducted a systematic review of the association between PNC services utilization and key determinants, including a meta-analysis of PNC use across socioeconomic status quintiles, and place of residence (urban vs. rural). 2. We used a quasi-experimental design. The data sources were two representative surveys (n=1408 and n=1403) carried out in 2008 and 2010, respectively, of women from Houndé and Ziniaré health districts of Burkina Faso, and a survey of health centres assessing structural quality of care. Multilevel segmented Poisson regression models were used to assess the effect of subsidy on SBA rate. We estimated adjusted rate ratios and rate differences as a function of time and socioeconomic status level. Results 1. The pooled odds ratio (OR) (95% CI) estimates for highest SES women (quintile 5, Q5), Q4, Q3 and Q2 (reference: poorest quintile, Q1) were respectively: 2.27 (1.75 – 2.93); 1.60 (1.30-1.98); 1.32 (1.12-1.55); and 1.14 (0.96-1.34). Meta-analysis also showed a PNC utilization divide between urban and rural women: OR (95% CI) = 1.36 (1.01-1.81). Narrative assessment of studies identified a gradient in PNC coverage across education levels. 2. For low-SES women, immediately upon the introduction of the subsidy policy, the rate of SBA was 24% higher (95% CI: 4-46%) than expected in the absence of subsidy policy introduction. The magnitude of the apparent effect decreased over time, with the corresponding estimates (95% CI) being 22% (3-45%) at 6 months, 20% (1-43%) at 12 months, and 17% (-4-42%) at 24 months after the policy introduction. Furthermore, the magnitude of the association varied across SES strata, with the apparent effect being most pronounced in the low SES stratum. Conclusions 1. PNC utilization remains inequitable across socioeconomic status and geographic access to health facilities in LMICs. 2. Our study suggests that introduction of user fee subsidy in Burkina Faso resulted in sustained increase in the rate of SBA, especially among low-SES women. This evidence should inform maternal and child health programmes and guide health policies and health care systems in LMICs

Entrainment and deposition of boulders in a gravel bed river

Bedload transport, entrainment of coarse sediment by a river, is inherently a stochastic and intermittent process whose monitoring remains challenging. Here, we propose a new method to characterize bedload transport in the field. Using an uncrewed aerial vehicle (UAV) equipped with a high-resolution camera, we recorded yearly images of a bar of the Grande Rivière des Vieux-Habitants, a gravel bed river located on Basse-Terre Island (Guadeloupe, French West Indies). These images, combined with high-frequency measurements of the river discharge, allow us to monitor the evolution of the population of sediments of a diameter between 0.5 and 0.75 m on the riverbed. Based on this dataset, we estimate the smallest discharge that can move these boulders and calculate the duration of effective transport. We find that the transport of boulders occurs for approximately 10 h yr−1. When plotted as a function of the effective transport time, a given population of boulders decreases exponentially with an effective residence time of approximately 17 h. This exponential decay suggests that the probability of dislodging a grain from the bed is proportional to the number of grains at repose on the bed, an observation consistent with laboratory experiments. Finally, the residence time of bedload particles on a riverbed can be used to evaluate bedload discharge.</p

Vol. 31, No. 5, pp 323-350

Philippe Boutry et Pierre-Antoine Fabre, directeurs d’études avec Dominique Julia, directeur de recherche au CNRS et Claude Langlois, directeur d’études à l’EPHE-Ve section L’histoire religieuse au XXe siècle Compte rendu non communiqué. André Mary, directeur de recherche au CNRS Anthropologie des formes contemporaines du religieux. Les anthropologues et la religion Le séminaire a poursuivi sa réflexion sur le rapport problématique des anthropologues, et de la tradition anthropologique, à la ..

Enseignement supérieur, Recherche, Innovation : en chiffres 2018

Analyse des données de l\u27enseignement supérieur et de la recherche en France, pour la période de 1997 à 2017

Rheological properties of the soft-disk model of two-dimensional foams

The soft-disk model previously developed and applied by Durian [D. J. Durian, Phys. Rev. Lett. 75, 4780 (1995)] is brought to bear on problems of foam rheology of longstanding and current interest, using two-dimensional systems. The questions at issue include the origin of the Herschel-Bulkley relation, normal stress effects (dilatancy), and localization in the presence of wall drag. We show that even a model that incorporates only linear viscous effects at the local level gives rise to nonlinear (power-law) dependence of the limit stress on strain rate. With wall drag, shear localization is found. Its nonexponential form and the variation of localization length with boundary velocity are well described by a continuum model in the spirit of Janiaud et al. [Phys. Rev. Lett. 97, 038302 (2006)]. Other results satisfactorily link localization to model parameters, and hence tie together continuum and local descriptions

Improvement of microwave emissivity parameterization of frozen Arctic soils using roughness measurements derived from photogrammetry

Soil emissivity of Arctic regions is a key parameter for assessing surface properties from microwave brightness temperature (Tb) measurements. Particularly in winter, frozen soil permittivity and roughness are two poorly characterized unknowns that must be considered. Here, we show that after removing snow, the 3D soil roughness can be accurately inferred from in-situ photogrammetry using Structure from Motion (SfM). We focus on using SfM techniques to provide accurate roughness measurements and improve emissivity models parametrization of frozen arctic soil for microwave applications. Validation was performed from ground-based radiometric measurements at 19 and 37 GHz using three different soil emission models: the Wegmüller and Mätzler [1999, TGRS] model (Weg99), the Wang and Choudhury [1981, JGR] model (QNH), and a geometrical optics model (Geo Optics). Measured and simulated brightness temperatures over different tundra and rock sites in the Canadian High Arctic show that Weg99, parametrized with SfM-based roughness and optimized permittivity (ε), yielded an RMSE of 3.1 K (R2=0.71) for all frequencies and polarizations. Our SfM based approach allowed us to measure roughness with 0.1 mm accuracy at 55 locations of different land cover type using a digital camera and metal plates of know dimensions