Étude d'irradiations électroniques de faible énergie d'hexadécanethiols chimisorbés sur des nanoparticules d'or et des surfaces d'or à basse température

Le domaine des monocouches autoassemblées (SAMs) est bien connu depuis une vingtaine d'année, quoique les phénomènes de bris moléculaire dans un tel environnement compact ne commencent qu'à être étudiés. Ces monocouches sont ordonnées et hautement structurées telles que le démontrent les études de microscopie à effet tunnel (STM) et de spectroscopie infrarouge en réflexion-absorption (IRRAS). Les expériences d'irradiations électroniques de faible énergie sur des SAMs ont démontré un processus résonant d'attachement dissociatif des électrons (DEA) à une énergie spécifique de 10 eV. Les modifications induites par l'impact des électrons sont préférentiellement situées à l'interface film/vide car la proximité du substrat métallique entraîne une relaxation non radiative des états excités anioniques, [RC-H][indice supérieur *-] . On a mesuré un temps de vie de désexcitation de l'état excité de 0,2-0,5 fs pour les méthyles d'une SAM de butanethiols alors qu'il est de 5-10 fs pour les méthyles d'une SAM d'hexadécanethiols. Considérant que le temps de dissociation du lien C-H est d'une durée d'environ 5,2 fs et que le système de relaxation soit en compétition de manière efficace, ceci explique que pour les chaînes plus courtes, la dissociation n'est pas perceptible car aucune modification dans le spectre infrarouge (IR) n'est apparente en fonction de la charge appliquée. Le mécanisme utilisé pour expliquer la diminution des bandes infrarouges est la déshydrogénation, phénomène exothermique d'environ 6 eV lors d'irradiations électroniques de 10 eV."--Résumé abrégé par UMI

Re: Exposure to indoor tanning without burning and melanoma risk by sunburn history

Vogel et al. (1) provide another demonstration that the risk from sunbed use is not limited to skin-sensitive populations and shows increased risk even in those not having experienced sunburns in their lifetimes. It counters the argument frequently put forward by the indoor tanning industry that indoor tanning prevents sunburn and adds further evidence of the carcinogenicity of indoor tanning. We are, however, concerned that those who consider vitamin D as a protective agent for cancer and thus defend sunbed use, might misinterpret the decline in odds ratio for increasing burns and consider that the increasing burns diminished the effect of sunbed use, hence providing “protection.

Conclusion générale - L’agronomie, une construction à poursuivre

Aujourd’hui en France, l’agronomie est enseignée à des milliers d’élèves, d’étudiants ou de professionnels en activité. Pour un certain nombre d’entre eux, elle constitue la base de leur spécialisation de fin d’études et de leur compétence professionnelle. Le terme « agronomie » est utilisé pour spécifier de multiples profils de recrutement, au sein de secteurs d’emploi très variés (recherche, enseignement, développement, agrofourniture, industries agricoles et alimentaires, etc.) qui ont en..

Remerciements

Nous remercions chaleureusement tous les auteurs de chapitres et d’encadrés, qui ont accepté de partager notre engagement dans ce projet et ont enrichi l’éventail d’expériences à partir duquel est construit cet ouvrage. Au-delà du cercle des auteurs, d’autres collègues ont nourri nos réflexions, ou apporté des matériaux précieux, aux différentes étapes de son élaboration. Avant le lancement de la rédaction de l’ouvrage, Pierre Cornu, André Gallais, Frédéric Goulet, Patrick Mayen, Éric Malézi..

Introduction générale - La construction d’une discipline scientifique et technique : récits d’agronomes

À plusieurs reprises lorsque, sous l’impulsion de la société, l’agriculture a dû prendre des orientations nouvelles, on en a appelé à l’agronomie. Ce fut le cas lors de la période dite « de modernisation de l’agriculture » après la Seconde Guerre mondiale. Ce fut à nouveau le cas dans les années 1980, lorsque les inconvénients liés à cette modernisation sont clairement apparus, à côté des bénéfices qu’elle avait apportés. Et de nouveau en ce début de xxie siècle, lorsque les enjeux liés au c..

Simulation of consumer exposure to deoxynivalenol according to wheat crop management and grain segregation: Case studies and methodological considerations

International audienceWe combined agronomic data and a model simulating exposure based on consumption data to assess the impact of crop management and grain segregation procedures on consumer exposure to deoxynivalenol. We used three scenarios of soil tillage at a regional scale and three scenarios of grain segregation for a supply area. The soil tillage scenarios were applied to a range of mean crop contamination levels, with various coefficients representing the degree of tillage. The grain segregation scenarios were applied to two real datasets of DON content distributions. We found that the increase in consumer exposure in response to increases in "risky" crop management practices such as direct-drilling depends largely on mean contamination and on the value of the tillage coefficient. The results for grain segregation procedures showed that exposure was most strongly affected by contamination distributions as the segregation procedure minimising risk differed for the two datasets

Lifetime exposure to ambient ultraviolet radiation and the risk for cataract extraction and age-related macular degeneration : the Alienor Study

While exposure to ultraviolet radiation (UVR) is a recognized risk factor for cataract, its association is more controversial with age-related macular degeneration (AMD). We report the associations of lifetime exposure to ambient UVR with cataract extraction and AMD. The Alienor Study is a population-based study of 963 residents of Bordeaux (France), aged 73 years or more. Lifetime exposure to ambient UVR was estimated from residential history and Eurosun satellite-based estimations of ground UVR. It was divided in three groups (lower quartile, intermediate quartiles, upper quartile), using the intermediate quartiles as the reference. Early and late AMD was classified from retinal color photographs. Cataract extraction was defined as absence of the natural lens at slit-lamp. After multivariate adjustment, subjects in the upper quartile of lifetime ambient UVR exposure were at increased risk for cataract extraction (odds ratio [OR] = 1.53; 95% confidence interval [CI], 1.04-2.26; P = 0.03) and for early AMD (OR = 1.59; 95% CI, 1.04-2.44; P = 0.03), by comparison with subjects in the intermediate quartiles. Subjects in the lower quartile of UVR exposure also were at increased risk for early AMD (OR = 1.69; 95% CI, 1.06-2.69; P = 0.03), by comparison with those with medium exposure. Associations of late AMD with UVR exposure was not statistically significant. This study further confirms the increased risk for cataract extraction in subjects exposed to high ambient UVR. Moreover, it suggests that risk for early AMD is increased in subjects exposed to high UVR, but also to low UVR, by comparison with medium exposures

Residential exposure to solar ultraviolet radiation and incidence of childhood hematological malignancies in France

Few studies have investigated the relationship between solar ultraviolet radiation (UV) and childhood hematological malignancies (CHM). This study addresses the associations between residential UV exposure at diagnosis and the incidence of types and subtypes of CHM, by age and gender, in France, over a long period, on the fine scale of the 36,326 Communes that constitute mainland France. The 9,082 cases of acute leukemia and 3,563 cases of lymphoma diagnosed before the age of 15 years from 1990 to 2009 were provided by the French National Registry of Childhood Hematological Malignancies. The incidence of CHM was calculated by Commune, year, age and gender and expressed as the standardized incidence ratio (SIR). UV data from 1988 to 2007 were extracted from the EUROSUN database. The annual daily average UV exposure of the children ranged from 85.5 to 137.8 J/cm2. For each additional 25 J/cm2, there was a significant increase in precursor B-cell acute lymphoblastic leukemia (PBC-ALL) in children aged less than 5 years (SIR 1.18; 95 % CI 1.10–1.27). Further analysis of PBC-ALL in the young children suggested a better fit of models with a threshold, with the risk increasing above 100 J/cm2, for which the SIR was 1.24 (95 % CI 1.14–1.36) for a 25 J/cm2 increase. The results remained stable in analyses stratifying by deprivation index or degree of urbanization of the Communes. The study suggests that higher residential UV exposure may be positively associated with a higher incidence of PBC-ALL in early childhood

Long-term performance of flexible pavement structures in a changing climate

Abstract: Climate changes may cause an increase of precipitation in the Province of Quebec over the next decades. As the performance of flexible pavement structures is closely related to moisture content of soils and aggregates, these structures can be considered vulnerable to climate changes. In order to quantify the effect of future precipitations increase on the pavement service life, this research project was based on a three steps approach: 1) Establishment of a relationship between precipitations and water content in the subgrade layers; 2) Establishment of the relationship between soils water content and soils mechanical properties, quantified with the resilient modulus and the permanent deformation behaviour; 3) Quantification of the effect of increased precipitations on pavement life, based on modification of their mechanical behaviour due to water content increase. For the example considered in this paper, it was found that the service life of pavement structures submitted to future climate may present a service life reaching 0.72 times the service of actual pavement structures. These results vary depending on the soil and damage types considered. Long-term performance of flexible pavement structures in a changing climat

Occupational UV exposure in French outdoor workers

Occupational ultraviolet (UV) exposure was evaluated in a population-based sample in France. A random survey was conducted in 2012 in individuals aged 25 to 69 years. The median daily standard erythemal UV dose (SED) was estimated from exposure time and place and matched to satellite UV records. A total of 889 individuals were exposed to solar UV with highest doses observed among gardeners (1.19 SED), construction workers (1.13 SED), agricultural workers (0.95 SED), and culture/art/social science workers (0.92 SED). Information and communication technology, industry, and transport workers were highly exposed (>0.70 SED). Significant factors associated with high occupational UV exposure were sex (P < 0.0001), phototype (P = 0.0003), and taking lunch outdoors (P < 0.0001). This study identified not only expected occupations with high UV exposure but also unexpected occupations with high exposures. This could serve as a basis for future prevention