Polarization of stars with debris disks: comparing observations with models

The $Herschel$ Space telescope carried out an unprecedented survey of nearby stars for debris disks. The dust present in these debris disks scatters and polarizes stellar light in the visible part of the spectrum. We explore what can be learned with aperture polarimetry and detailed radiative transfer modelling about stellar systems with debris disks. We present a polarimetric survey, with measurements from the literature, of candidate stars observed by DEBRIS and DUNES $Herschel$ surveys. We perform a statistical analysis of the polarimetric data with the detection of far-infrared excess by $Herschel$ and $Spitzer$ with a sample of 223 stars. Monte Carlo simulations were performed to determine the effects of various model parameters on the polarization level and find the mass required for detection with current instruments. Eighteen stars were detected with a polarization $0.01 \le P \lesssim 0.1$ per cent and $\ge3\sigma_P$, but only two of them have a debris disk. No statistically significant difference is found between the different groups of stars, with, without, and unknown status for far-infrared excess, and presence of polarization. The simulations show that the integrated polarization is rather small, usually $< 0.01$ per cent for typical masses detected by their far-infrared excess for hot and most warm disks. Masses observed in cold disks can produce polarization levels above $0.01$ per cent since there is usually more dust in them than in closer disks. We list five factors which can explain the observed low-polarization detection rate. Observations with high-precision polarimeters should lead to additional constraints on models of unresolved debris disks.Comment: Corrected some quotations and typos and deleted superfluous references. 20 pages, 5 figure

DRC 2 : Dynamically Reconfigurable Computing Circuit based on Memory Architecture

International audienceThis paper presents a novel energy-efficient and Dynamically Reconfigurable Computing Circuit (DRC²) concept based on memory architecture for data-intensive (imaging, …) and secure (cryptography, …) applications. The proposed computing circuit is based on a 10-Transistor (10T) 3-Port SRAM bitcell array driven by a peripheral circuitry enabling all basic operations that can be traditionally performed by an ALU. As a result, logic and arithmetic operations can be entirely executed within the memory unit leading to a significant reduction in power consumption related to the data transfer between memories and computing units. Moreover, the proposed computing circuit can perform extremely-parallel operations enabling the processing of large volume of data. A test case based on image processing application and using the saturating increment function is analytically modeled to compare conventional and DRC²-based approaches. It is demonstrated that DRC²-based approach provides a reduction of clock cycle number of up to 2x. Finally, potential applications and must-be-considered changes at different design levels are discussed

Intrinsic capacity and its association with mortality over 3 years in nursing homes: Results of the SENIOR cohort

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Analyse rétrospective de l’adaptation à la sécheresse chez le douglas

For a number of years in certain regions of France the Douglas-fir trees (Pseudotsuga menziesii [Mirb.] Franco) have presented symptoms of withering which have been attributed to drought. Our results show that the hydraulic function of the wood plays a part in the resistance of the Douglas-fir to dry conditions. Narrower cellular conduits, and therefore a greater wood density, contribute to the survival of trees confronted with a period of a marked water deficit. This idea is confirmed by the existence of significant relationships between wood density and hydraulic properties of wood in which the raw sap circulates, and also by the relationships found between the ecological preferences of specimens in their area of origin and the density of their wood in regions of France where they have been introduced. Those coming from dry regions have a tendency to develop wood with characteristics similar to that of trees which have survived drought. While the relationship between wood density and survival has been demonstrated, the differences in the nature of this relationship between different sites show that the mechanisms involved are complex and to a large extent still not understood.Le douglas (Pseudotsuga menziesii [Mirb.] Franco) présente depuis quelques années dans certaines régions de France des symptômes de dépérissement que nous attribuons à la sécheresse. Nos résultats montrent que le fonctionnement hydraulique du bois joue un rôle dans la résistance du douglas à la sécheresse: des conduits cellulaires plus étroits, c'est-à-dire une densité plus élevée, favoriseraient la survie d'arbres confrontés à un épisode de déficit en eau marqué. Cette idée est renforcée par l'existence de relations significatives entre densité du bois et propriétés hydrauliques du bois dans lequel circule la sève brute, et par les relations trouvées entre préférences écologiques de provenances dans leur aire d'origine et densité de leur bois dans les régions d'introduction en France: les provenances issues de régions sèches ont tendance à développer un bois possédant des caractéristiques proches de celles des survivants à la sécheresse. Si la relation densité du bois–survie a bien été mise en évidence, des différences entre sites dans la nature de cette relation montrent que les mécanismes impliqués sont complexes et encore largement incompris.Seit einigen Jahren zeigt die Douglasie (Pseudotsuga menziesii [Mirb.] Franco) in verschiedenen Regionen Frankreichs Absterbeerscheinungen, die wir der Trockenheit zuschreiben. Unsere Untersuchungen belegen, dass das Leitsystem des Holzes bei der Resistenz der Douglasie gegenüber Trockenheit eine Rolle spielt: Engere Gefässe, d.h. eine höhere Holzdichte, würden das Überleben der Bäume in Perioden mit ausgeprägtem Wassermangel begünstigen. Diese Idee wird durch signifikante Zusammenhänge zwischen der Holzdichte und den hydraulischen Eigenschaften des Splintholzes sowie durch die gefundenen Beziehungen zwischen den ökologischen Vorlieben der Provenienzen in ihrer Herkunftsregion und der Dichte ihres Holzes in den Regionen Frankreichs, in denen sie eingebracht wurden, belegt: Herkünfte aus trockenen Regionen haben die Tendenz, ein Holz zu entwickeln, das ähnliche Eigenschaften zeigt wie dasjenige von Bäumen, die Trockenperioden überlebten. Die Beziehung Holzdichte–Überleben konnte zwar klar herausgestellt werden, jedoch zeigen die Unterschiede zwischen den Standorten, dass die Wirkungsmechanismen komplex sind und grösstenteils noch nicht verstanden werden.Estación Experimental Agropecuaria BarilocheFil: Rozenberg, Philippe. INRA. Biologie intégrée pour la valorisation de la diversité des arbres et de la forêt; FranciaFil: Sergent, Anne Sophie. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Instituto de Investigaciones Forestales y Agropecuarias Bariloche; ArgentinaFil: Dalla Salda, Guillermina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche. Área de Recursos Forestales. Grupo de Ecología Forestal; ArgentinaFil: Martinez Meier, Alejandro. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche. Área de Recursos Forestales. Grupo de Ecología Forestal; ArgentinaFil: Marin, Sara. INRA. Biologie intégrée pour la valorisation de la diversité des arbres et de la forêt; FranciaFil: Ruiz Diaz, Manuela. INRA. Biologie intégrée pour la valorisation de la diversité des arbres et de la forêt; FranciaFil: Bastien, Jean-Charles. INRA. Biologie intégrée pour la valorisation de la diversité des arbres et de la forêt; FranciaFil: Sanchez, Leopoldo. INRA. Biologie intégrée pour la valorisation de la diversité des arbres et de la forêt; FranciaFil: Bréda, Nathalie. INRA. Biologie intégrée pour la valorisation de la diversité des arbres et de la forêt; Franci

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in Europe: an overview of management practices

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), one of the most commercially important tree species in western North America and one of the most valuable timber trees worldwide, was introduced to Europe in 1827. It became a major species for afforestation in Western Europe after WWII, currently grows in 35 countries on over 0.83 million ha and is one of the most widespread non-native tree species across the continent. A lower sensitivity to drought makes Douglas-fir a potential alternative to the more drought-sensitive Norway spruce so its importance in Europe is expected to increase in the future. It is one of the fastest growing conifer species cultivated in Europe, with the largest reported dimensions of 2.3 m in diameter and 67.5 m in height. Pure stands have high productivity (up to 20 m3 ha-1a-1) and production (over 1000 m3 ha-1). The species is generally regenerated by planting (initial stocking density from less than 1000 seedlings ha-1 to more than 4000 ha-1), using seedlings of European provenance derived from seed orchards or certified seed stands. As the range of end-uses of its wood is very wide, the rotation period of Douglas-fir is highly variable and ranges between 40 and 120 years. When the production of large sized, knot-free timber is targeted, thinnings are always coupled with pruning up to 6 m. There is an increasing interest in growing Douglas-fir in mixtures and managing stands through close-to-nature silviculture, but the species’ intermediate shade tolerance means that it is best managed through group selection or shelter-wood systems

Ecology, growth and management of black locust (Robinia pseudoacacia L.), a non‑native species integrated into European forests

Black locust (Robinia pseudoacacia L.), a species native to the eastern North America, was introduced to Europe probably in 1601 and currently extends over 2.3 × 106 ha. It has become naturalized in all sub-Mediterranean and temperate regions rivaling Populus spp. as the second most planted broadleaved tree species worldwide after Eucalyptus spp. This wide-spreading planting is because black locust is an important multipurpose species, producing wood, fodder, and a source of honey as well as bio-oil and biomass. It is also important for carbon sequestration, soil stabilization and re-vegetation of landfills, mining areas and wastelands, in biotherapy and landscaping. In Europe, black locust is drought tolerant so grows in areas with annual precipitation as low as 500–550 mm. It tolerates dry, nutrient poor soils but grows best on deep, nutrient-rich, well-drained soils. It is a fast-growing tree and the height, diameter and volume growth peak before the age of 20. It mostly regenerates vegetatively by root suckers under a simple coppice system, which is considered the most cost-effective management system. It also regenerates, but less frequently, by stool sprouts. Its early silviculture in production forests includes release cutting to promote root suckers rather than stool shoots, and cleaning-respacing to remove low-quality stems, reduce the number of shoots per stool, and adjust spacing between root suckers. In addition, early, moderate and frequent thinning as well as limited pruning are carried out focusing on crop trees. The species is regarded as invasive in several European countries and its range here is expected to expand under predicted climate changes

Non-Native Forest Tree Species in Europe: The Question of Seed Origin in Afforestation

Non-native forest tree species have been introduced in Europe since the 16th century, but only in the second half of the 20th century the significance of the seed source origin for their economic use was recognized, resulting in the establishment of numerous provenance trials at a national, regional, European and International level, as those led by IUFRO. Breeding programs have also been launched in the continent for the most economically important species. Aim of this work is the formulation of provenance recommendations for planting of five non-native tree species in Europe (Douglas fir, grand fir, Sitka spruce, lodgepole pine and black locust), based on the information obtained from twenty countries, in the frame of the EU FP-1403 NNEXT Cost Action. The survey revealed that official and non-official national recommendations, based on provenance research results, have been elaborated and followed at a different level and extend for the above five species, but only for Douglas fir recommendations exist in almost all the participating to the survey countries. The compilation of provenance recommendations across Europe for each species is presented in the current work. Besides the recommended introduced seed sources, European seed sources are also preferred for planting, due to ease of access and high availability of forest reproductive material. European breeding programs yielding genetic material of high productivity and quality constitute currently the seed source of choice for several species and countries. Consolidation of trial data obtained across countries will allow the joint analysis that is urgently needed to draw solid conclusions, and will facilitate the development of ‘Universal-Response-Functions’ for the species of interest, rendering possible the identification of the genetic material suitable for global change. New provenance trial series that will test seed sources from the entire climatic range of the species, established in sites falling within and outside the environmental envelopes of their natural ranges, are urgently needed to pinpoint and understand the species-specific climate constraints, as well as to correlate functional traits to the seed origin and the environmental conditions of the test sites, so that the selection of suitable forest reproductive material of non-native tree species in the face of climate change can be feasible.publishedVersio

A review of black walnut (Juglans nigra L.) ecology and management in Europe

Black walnut (Juglans nigra L.) is a light-demanding, competition-intolerant, and tall forest tree species, introduced in Europe from North America at the beginning of the seventeenth century. It has an important economic role in Europe for producing wood and fruits, in agroforestry systems, as an ornamental tree for parks and avenues, for rehabilitation/restoration of degraded lands. The best sites for black walnut growth have warm and mild climates, with frequent and well-spread precipitation, and rich, deep, near neutral, well-drained and moist soils. Black walnut is a fast grower in youth and its height and diameter growth reach their peaks before age 30–35 years. It is globally the best known allelopathic species due to the juglone substance present in all parts of black walnut trees. The species is storm-resistant and not affected by any major pest or disease in Europe. It is regenerated by planting or direct seeding on bare land, in monocultures and mixed stands. The management of stands with black walnut, with a rotation period generally up to 80 years, include weeding (mandatory), cleaning-respacing (in dense stands), thinning (mostly from above), high and formative pruning (mandatory), with the aim of producing valuable wood for sliced veneer, solid furniture, flooring/parquet, cabinetry, panelling, sculpture, musical instruments, gunstocks