Introduction to high-energy gamma-ray astronomy

The present issue is the first of of a two-volume review devoted to gamma-ray astronomy above 100 MeV which has witnessed considerable progress over the last 20 years. The motivations for research in this area are explained, the follow-on articles of these two thematic issues are introduced and a brief history of the field is given.Comment: 15 pages, 6 figures. Introduction to a two-volume topical issue on Gamma-ray Astronomy above 100 MeV coordinated by the author

New calcium carbonate-based cements for bone reconstruction

The feasibility of calcium carbonate-based cements involving the re-crystallization of metastable calcium carbonate varieties has been demonstrated. Two cement compositions were obtained by mixing either calcium carbonate phases (cement A) or a calcium carbonate and a calcium phosphate phase (cement B) with an aqueous media. These cements set and hardened after 30 minutes and 90 minutes respectively. The final composition of cement A was calcite and aragonite whereas cement B lead to a carbonated apatite analogous to bone mineral. Despite poor mechanical properties the presence of a high carbonate content in the final phase might be of interest to increase the cement resorption rate and to favour its replacement by bone tissue. First assays of implantation performed on fresh anatomical pieces (fresh cadavers) at 37°C revealed important advantages of such cement compositions: easiness of use, rapid setting, good adhesion to bone, very good homogeneity and stability of the cement

Experimental investigations from conventional to high speed milling on a 304-L stainless steel

International audienceLast years analytical or finite element models of milling become more efficient and focus on more physical aspects, nevertheless the milling process is still experimentally unknown on a wide range of use. This paper propose to analyse with accuracy milling operations by investigating the cutting forces values, shape of cutting forces curves obtained for different cutting speeds, and related phenomena as tool wear or tool run-out. These detailed experimental data in milling constitute a suitable experimental basis available to develop predictive machining modelling. All the tests have been conducted on the 304-L stainless steel in many cutting configurations and for different tool geometries. The machinability of the 304-L stainless steel with different tools geometries and configurations in shoulder milling is defined by three working zones: a conventional zone permitting stable cutting (low cutting speed; under 200-250 m.min−1), a dead zone (unfavourable for cutting forces level and cutting stability; between 250 and 450 m.min−1), and a high speed machining zone (high cutting speed; up to 450-500 m.min−1). All the used criteria (cutting forces, chips, wear) confirm the existence of these different zones and a correlation is proposed with cutting perturbations as tool run-out, cutting instability, ploughing, and abrasive wear

Capabilité des micro-fraises en carbure de tungstène à usiner un acier à moule d'injection plastique

La présente étude constitue une approche de l'usinage d'une empreinte de moule d'injection plastique par micro-fraisage. Basée sur des résultats expérimentaux, elle permet de mettre en évidence certains phénomènes liés au procédé. Les résultats présentés résultent de l'usinage d'un acier 42NICrMo16 à l'état trempé avec des micro-fraises en carbure de tungstène revêtu de diamètre 0,5 mm. Ils seront principalement liés aux matériaux et phénomènes d'usure. Néanmoins, des aspects dynamiques de la coupe ainsi que la géométrie de l'outil seront abordés

Segmentation non supervisée d'images par analyse de la connexité Application à la détection de lésions virales sur des images de fond d'oeil

Dans cet article, nous présentons une méthode de segmentation originale basée sur l'analyse de la connexité. Par analyse d'un tableau triangulaire appelé «Pyramide des degrés de connexité normalisés», l'image est décomposée en différents ensembles constitués de pixels connexes dont les niveaux de gris sont homogènes. Cette méthode est utilisée afin de détecter des lésions rétiniennes sur des images de fond d'oeil

Design of a large field-of-view see-through near to eye display with two geometrical waveguides

A novel waveguide near to eye display (WGNED), with new in-coupling and propagation subsystems, is proposed for the first time, to our knowledge, to enlarge the vertical field-of-view (FOV) and the vertical size of the eye box. Two waveguides are stacked—one is for in-coupling and the other for out-coupling. A freeform prism is used to correct the aberrations. These components are combined to form the WGNED. We have simulated such a system; as a result, we show that it achieves a FOV of 30°horizontal (H)×60°vertical (V) and an eye box of about 15  mm (H)×12  mm (V). The modulation transfer function of the system is larger than 0.3 at 33  lp/mm and the distortion is smaller than 5%

Modelling and simulating change in reforesting mountain landscapes using a social-ecological framework

Natural reforestation of European mountain landscapes raises major environmental and societal issues. With local stakeholders in the Pyrenees National Park area (France), we studied agricultural landscape colonisation by ash (Fraxinus excelsior) to enlighten its impacts on biodiversity and other landscape functions of importance for the valley socio-economics. The study comprised an integrated assessment of land-use and land-cover change (LUCC) since the 1950s, and a scenario analysis of alternative future policy. We combined knowledge and methods from landscape ecology, land change and agricultural sciences, and a set of coordinated field studies to capture interactions and feedback in the local landscape/land-use system. Our results elicited the hierarchically-nested relationships between social and ecological processes. Agricultural change played a preeminent role in the spatial and temporal patterns of LUCC. Landscape colonisation by ash at the parcel level of organisation was merely controlled by grassland management, and in fact depended on the farmer's land management at the whole-farm level. LUCC patterns at the landscape level depended to a great extent on interactions between farm household behaviours and the spatial arrangement of landholdings within the landscape mosaic. Our results stressed the need to represent the local SES function at a fine scale to adequately capture scenarios of change in landscape functions. These findings orientated our modelling choices in the building an agent-based model for LUCC simulation (SMASH - Spatialized Multi-Agent System of landscape colonization by ASH). We discuss our method and results with reference to topical issues in interdisciplinary research into the sustainability of multifunctional landscapes

H.E.S.S. observations of gamma-ray bursts in 2003-2007

Very-high-energy (VHE; >~100 GeV) gamma-rays are expected from gamma-ray bursts (GRBs) in some scenarios. Exploring this photon energy regime is necessary for understanding the energetics and properties of GRBs. GRBs have been one of the prime targets for the H.E.S.S. experiment, which makes use of four Imaging Atmospheric Cherenkov Telescopes (IACTs) to detect VHE gamma-rays. Dedicated observations of 32 GRB positions were made in the years 2003-2007 and a search for VHE gamma-ray counterparts of these GRBs was made. Depending on the visibility and observing conditions, the observations mostly start minutes to hours after the burst and typically last two hours. Results from observations of 22 GRB positions are presented and evidence of a VHE signal was found neither in observations of any individual GRBs, nor from stacking data from subsets of GRBs with higher expected VHE flux according to a model-independent ranking scheme. Upper limits for the VHE gamma-ray flux from the GRB positions were derived. For those GRBs with measured redshifts, differential upper limits at the energy threshold after correcting for absorption due to extra-galactic background light are also presented.Comment: 9 pages, 4 tables, 3 figure