Quatre enquêtes de terrain menées auprès de 3 000 personnes dans deux pays d'Afrique du Nord (Maroc Tunisie) et deux du Sud du Sahara (Tchad, Togo), à partir d’un questionnaire commun avec des ...adaptations locales, posent un jalon dans une réflexion sur les rapports que ces publics entretiennent aujourd’hui avec les films en Afriques. L’analyse permet de rendre compte des oeuvres vues, par quels moyens dans différents contextes, et de questionner les usages, les sociabilités qu’ils suscitent, les cultures de films qui en découlent, etc. Il s’agit ainsi d’interroger le statut du film dans le jeu de l’offre et de la demande de productions audiovisuelles dans les pays concernés, la place de la production locale sur des marchés longtemps dominés par les productions audiovisuelles occidentales. Ce volume est un approfondissement des premiers résultats d’enquête publiés dans Regarder des films en Afriques (Presses universitaires du Septentrion, 2017).
Tree seedling establishment and growth were studied in experimental canopy gaps to assess the effect of heterogeneity of regeneration microsites within and among gaps in mature conifer forests. ...Seedlings were studied for two years in closed-canopy areas and in recently created gaps ranging in size from 40 to 2000 m2 in four stands of mature (90-140 yr) and old-growth ($>$400 yr) Douglas-fir forest in the western Cascade Range of central Oregon and southern Washington, USA. We examined the relative importance of substrate type, shade from logs and shade cloth, density of understory vegetation, gap size, and forest age on the success of Pacific silver fir (Abies amabilis), Douglas-fir (Pseudotsuga menziesii), and western hemlock (Tsuga heterophylla). Seedlings originating from seed sown on experimental microsites were compared with seedlings regenerating naturally on a range of microsites. Seedling establishment was greater on decayed wood than on forest floor or mineral soil in closed-canopy areas, particularly for Tsuga. Differences in establishment among substrates declined with increasing gap size, although establishment on the forest floor tended to be low in portions of large gaps exposed to direct solar radiation. In exposed areas, shade from woody debris and shade cloth facilitated establishment for all species, while shade from understory vegetation aided the establishment of Pseudotsuga but not that of Tsuga. Establishment in shaded portions of gaps declined with vegetation and shade-cloth cover. Seedling size increased with gap size, decreased with level of shade, and tended to be greatest on forest floor and lowest on decayed wood. Establishment and growth of the different species was related to differences in seed mass and tolerance of environmental extremes. Heterogeneity at the seedling scale ($<$10 cm) often overrode larger-scale environmental gradients ($>$2 m) associated with gap size and within-gap position. Thus the gap partitioning hypothesis, which emphasizes gap size and within-gap position, may be too simple to account for the role of microsite heterogeneity and species' regeneration traits on the development of mature forests.
We report on the measurement of the beam spin asymmetry in the deeply virtual Compton scattering off 4He using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab using a 6 GeV ...longitudinally polarized electron beam incident on a pressurized 4He gaseous target. We detail the method used to ensure the exclusivity of the measured reactions, in particular the upgrade of CLAS with a radial time projection chamber to detect the low-energy recoiling 4He nuclei and an inner calorimeter to extend the photon detection acceptance at forward angles. Our results confirm the theoretically predicted enhancement of the coherent (e4 He $~\to~e'p'γ'X')$ asymmetries exhibit a 30% suppression. From the coherent data, we were able to extract, in a model-independent way, the real and imaginary parts of the only 4He Compton form factor, $\cal H_A$, leading the way toward 3D imaging of the partonic structure of nuclei.
We report on the measurement of the beam spin asymmetry in the deeply virtual Compton scattering off $^4$He using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab using a 6 GeV ...longitudinally polarized electron beam incident on a pressurized $^4$He gaseous target. We detail the method used to ensure the exclusivity of the measured reactions, in particular the upgrade of CLAS with a radial time projection chamber to detect the low-energy recoiling $^4$He nuclei and an inner calorimeter to extend the photon detection acceptance at forward angles. Our results confirm the theoretically predicted enhancement of the coherent ($e^4$He$~\to~e'$$^4$He$'\gamma'$) beam spin asymmetries compared to those observed on the free proton, while the incoherent ($e^4$He$~\to~e'$p$'\gamma'$X$'$) asymmetries exhibit a 30$\%$ suppression. From the coherent data, we were able to extract, in a model-independent way, the real and imaginary parts of the only $^4$He Compton form factor, $\cal H_A$, leading the way toward 3D imaging of the partonic structure of nuclei.
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