Estimating underwater light regime under spatially heterogeneous sea ice in the Arctic

Abstract: The vertical diffuse attenuation coefficient for downward plane irradiance (Kd ) is an apparent optical property commonly used in primary production models to propagate incident solar radiation in the water column. In open water, estimating Kd is relatively straightforward when a vertical profile of measurements of downward irradiance, Ed, is available. In the Arctic, the ice pack is characterized by a complex mosaic composed of sea ice with snow, ridges, melt ponds, and leads. Due to the resulting spatially heterogeneous light field in the top meters of the water column, it is difficult to measure at single-point locations meaningful Kd values that allow predicting average irradiance at any depth. The main objective of this work is to propose a new method to estimate average irradiance over large spatially heterogeneous area as it would be seen by drifting phytoplankton. Using both in situ data and 3D Monte Carlo numerical simulations of radiative transfer, we show that (1) the large-area average vertical profile of downward irradiance, Ed(z), under heterogeneous sea ice cover can be represented by a single-term exponential function and (2) the vertical attenuation coefficient for upward radiance (KLu), which is up to two times less influenced by a heterogeneous incident light field than Kd in the vicinity of a melt pond, can be used as a proxy to estimate Ed(z) in the water column

Time to Switch to Second-line Antiretroviral Therapy in Children With Human Immunodeficiency Virus in Europe and Thailand.

Background: Data on durability of first-line antiretroviral therapy (ART) in children with human immunodeficiency virus (HIV) are limited. We assessed time to switch to second-line therapy in 16 European countries and Thailand. Methods: Children aged <18 years initiating combination ART (≥2 nucleoside reverse transcriptase inhibitors [NRTIs] plus nonnucleoside reverse transcriptase inhibitor [NNRTI] or boosted protease inhibitor [PI]) were included. Switch to second-line was defined as (i) change across drug class (PI to NNRTI or vice versa) or within PI class plus change of ≥1 NRTI; (ii) change from single to dual PI; or (iii) addition of a new drug class. Cumulative incidence of switch was calculated with death and loss to follow-up as competing risks. Results: Of 3668 children included, median age at ART initiation was 6.1 (interquartile range (IQR), 1.7-10.5) years. Initial regimens were 32% PI based, 34% nevirapine (NVP) based, and 33% efavirenz based. Median duration of follow-up was 5.4 (IQR, 2.9-8.3) years. Cumulative incidence of switch at 5 years was 21% (95% confidence interval, 20%-23%), with significant regional variations. Median time to switch was 30 (IQR, 16-58) months; two-thirds of switches were related to treatment failure. In multivariable analysis, older age, severe immunosuppression and higher viral load (VL) at ART start, and NVP-based initial regimens were associated with increased risk of switch. Conclusions: One in 5 children switched to a second-line regimen by 5 years of ART, with two-thirds failure related. Advanced HIV, older age, and NVP-based regimens were associated with increased risk of switch

Devenir des étudiants ayant présenté une première inscription en troisième cycle de médecine générale à la faculté de Clermont-Ferrand en 1999, 2002 et 2006

Enquête menée auprès de 122 étudiants retenus parmi les 134 ayant présenté une première inscription en troisième cycle de médecine générale en 1999, 2002 et 2006 par l'envoi d'un questionnaire (composé de 22 chapitres), s'intéressant à la formation, la FMC, aux modes d'exercice et aux motivations des MG. L'étude se termine par une évaluation de la satisfaction et des projets éventuels. Les 86 réponses obtenues ont permis de montrer : 1) la confirmation de la féminisation de la médecine ; 2) l'apparition d'une égalisation du rapport homme femme dans le choix du salariat ; 3) l'augmentation de la fréquence du regroupement médical en libéral (avec l'apparition des maisons de santé pluridisciplinaires), ce qui facilite la ruralisation de l'exercice, améliorant le plateau technique ; 4 ) une réorganisation du temps de travail en libéral, qui respecte mieux la qualité de vie privée.CLERMONT FD-BCIU-Santé (631132104) / SudocSudocFranceF

Accurate experimental determination of the complex elastic tensor of anisotropic materials of unknown orientation using ultrasonic transmitted bulk waves

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Study of ultrasonic characterization and propagation in austenitic welds: The MOSAICS project

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Straightforward preparation of polymers based on oligodimethylsiloxane and alkylamine

International audienceNovel oligodimethylsiloxane-based polymers with alkyl side chain were synthesized in bulk by step-growth polymerization between alpha,omega-glycidyl ether oligodimethylsiloxanes and a monoalkylamine in the absence of catalyst and at temperatures ranging between 80 and 180 degrees C. Matrix assisted laser desorption ionization time of flight results attested for the high reactivity of the amine functions with the glycidyl groups and revealed that the main polymer structure was (A2B2)n type with alkyl moieties as dangling chains. No etherification was observed during the reaction even at high temperatures and the nature of the end groups strongly depended on the molar ratio between glycidyl and amine functions. Polymerization reactions were followed by 1H NMR and the kinetics of the glycidyl-amine reaction pointed out the dependence of temperature, molar ratio, and the molar mass of the oligodimethylsiloxane. High conversion rates were obtained, especially with the lowest molecular weight oligodimethylsiloxane. An optimized kinetic model derived from the Horie's model was discussed and permitted to correctly fit the experimental data

3D modelling of ultrasonic testing in austenitic welds

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Validation of an ultrasonic characterization technique for anisotropic materials: comparison of experiments with beam propagation modelling

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