Effets d'un gradient de lumière sur la croissance en hauteur et morphologie de la cime du sapin baumier

Au Québec, le sapin baumier (Abies balsamea) est un conifère très tolérant à l'ombre. En sous-bois, sa cime est très différente de celle observée en pleine lumière. La disponibilité en lumière semble responsable de ces différences. L'objectif principal de cette recherche était de quantifier la croissance et l'architecture de jeunes sapins baumiers, d'âge moyen de 14 ans, régénérés naturellement, en fonction d'un gradient de disponibilité en lumière. Le pourcentage relatif moyen journalier de lumière photosynthétique (%DFPP: densité du flux de photons photosynthétiques; 400-700nm) a été estimé au-dessus de 98 sapins par des lectures ponctuelles durant une journée complètement nuageuse. Cette technique inédite proposée par Messier et Puttonen ( 1995} a été validée. Sur le site, 16 microsites ont été sélectionnés le long d'un gradient arbitraire d'ouverture du couvert arboré. Les %DFPP ont été calculés à partir de lectures en mesures continues pour une journée complètement nuageuse, complètement ensoleillée et par 3 mesures ponctuelles effectuées durant 3 journées nuageuses à trois différents temps de la journée. Les 3 estimations du %DFPP ont été corrélées de façon positive et linéaire entre elles (r> 0,900; p<0,01) ainsi qu'avec 3 seuils d'intensité lumineuse "sunflecks" {50, 200 et 400 µmolestm2/s). Une lecture ponctuelle durant une journée complètement nuageuse s'avère suffisante pour estimer la disponibilité en lumière d'un microsite. À partir de lectures ponctuelles, la croissance en hauteur des 98 sapins fut corrélée positivement avec le %DFPP (R2= 0,789, p<001). Le nombre de branches nodales, internodales et la masse spécifique (g/mm2) des aiguilles augmentaient avec le %DFPP. Entre 3 et 25% de DFPP, l'architecture des semis passait rapidement d'une forme en parapluie vers un forme de pleine croissance en hauteur. Ce changement de morphologie était causé par la dominance accrue de la croissance apicale sur la croissance moyenne des branches latérales. Les résultats suggèrent un haut degré d'acclimatation des jeunes sapins au bilan radiatif probablement pour maximiser la capture des rayons du soleil et soutenir les exigences énergétiques de la croissance en hauteur

Gianluca Raccagni, The Lombard League (1167-1225)

G. Raccagni, qui enseigne à l’université d’Édimbourg, aborde dans ce livre un thème très classique – voire rebattu – de l’histoire italienne du xiie siècle. Il souligne pourtant d’entrée de jeu une sorte de paradoxe : aucune synthèse actualisée n’était disponible sur le sujet (la dernière synthèse publiée en anglais date de 1866). La Ligue lombarde a en effet bénéficié d’une très grande fortune historiographique depuis le xviiie siècle et a connu un véritable regain d’intérêt en Italie dans l..

Dose to organ at risk and dose prescription in liver SBRT

Stereotactic body radiation therapy (SBRT) is delivered in a curative intent to many primary and secondary tumors.Concerning liver metastasis, SBRT can be safely delivered using one to five fractions. An excellent local control is obtained with doses from 20 to 60[[ce:hsp sp="0.25"/]]Gy. For primary hepatic tumors, results are also good, but the risk of hepatic toxicity related to liver pre-existent pathology must be taken into account. Radiation induced liver disease (RILD) is not frequent in its classical presentation, but modifications of liver enzymes are often observed. Other toxicities of SBRT on the duodenum, small bowel and biliary tract are also described. With respect to contraindications and dose limitations on surrounding structures, SBRT is well tolerated and takes place among curative treatment of liver tumors, as surgery, radiofrequency and embolization

Establishment and dynamics of the balsam fir seedling bank in old forests of northeastern Quebec

This study examines balsam fir (Abies balsamea (L.) Mill.) recruitment in old fir stands. Studying the regeneration of these stands is essential to understand the regeneration dynamic of the species in the absence of standdestroying disturbances. The objectives were (1) to obtain substrate-seedling associations for different age-classes and according to the presence or absence of adventitious roots; (2) to evaluate the contribution of the seed rain to seedling recruitment; (3) to re-examine age structures using the most appropriate method that minimizes estimation errors due to the presence of adventitious roots. A total of 90 quadrats (1 m2) were established along transects. In each quadrat, subtrates were characterized (type and topography) and their area was estimated. All balsam fir seedlings (<50 cm tall) present in the quadrats were located, harvested whole (root and shoot), and described (age, height, presence of adventitious roots, etc). Fir seedlings were strongly associated with woody mounds covered with thin mats of mixed mosses and Pleurozium shreberi (Bird.) Mitt. but negatively associated with flat topography particularly dominated by Hylocomium splendens (Hedw.) B.S.G. The presence of adventitious root is related to seedling age more than substrate type or topography. The age structure is in agreement with seed production and disturbance regime

Fortification with mushroom flour (Pleurotus ostreatus (Jacq.) P. Kumm) and substitution of wheat flour by cassava flour in bread-making: Nutritional and technical implications in eastern DR Congo

peer reviewedBackground: The import of wheat flour is the major driver for the high prices and low use of bakery products in nonproducing tropical countries such as the Democratic Republic of Congo (DRC). These products' high prices worsen the risk of malnutrition and food insecurity among rural and resource-poor populations. This study aimed at substituting the imported wheat flour with less expensive local cassava flour fortified with oyster mushroom flour in order to mitigate the nutritional crisis in the region. Methodology: Series of experiments were conducted by substituting wheat flour with cassava flour at proportions of 10-25% to find the optimal combination. In addition, oyster mushroom flour (2.5-10%) was added to the composite flour to compensate for nutrient deficiencies of cereals and tuber crops. The overall aim was to identify the optimal wheat-cassava-mushroom combination, improving the nutritional value of breads while keeping their physicochemical and organoleptic properties. Results: Results showed that 0-10% mushroom flour increased bread protein from 19.63 to 22.66%. Besides, 7.5% mushroom flour allowed rising the bread calories from 311.8 to 354.5 kcal, and the dry matter from 77.33 to 87.86%. The wheat substitution for cassava fortified with mushroom flour negatively affected the bread volume, color and taste (p < 0.001). However, other organoleptic features remained unchanged. The different breads were microbiologically stable for bacteria, but susceptible to fungal attacks. Conclusion: This study recommended 5-15-80% and 10-10-80% mushroom-cassava-wheat composite flour for better bakery results, good consistency and high protein and energy contents, for improving the nutritional status of populations in the tropical non-wheat producing regions such as DRC. Efforts are necessary to improve the taste and color of the mushroom-fortified bread to increase its uptake and competitiveness in the local markets

A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope

Globular clusters with their large populations of millisecond pulsars (MSPs) are believed to be potential emitters of high-energy gamma-ray emission. Our goal is to constrain the millisecond pulsar populations in globular clusters from analysis of gamma-ray observations. We use 546 days of continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to study the gamma-ray emission towards 13 globular clusters. Steady point-like high-energy gamma-ray emission has been significantly detected towards 8 globular clusters. Five of them (47 Tucanae, Omega Cen, NGC 6388, Terzan 5, and M 28) show hard spectral power indices $(0.7 < \Gamma <1.4)$ and clear evidence for an exponential cut-off in the range 1.0-2.6 GeV, which is the characteristic signature of magnetospheric emission from MSPs. Three of them (M 62, NGC 6440 and NGC 6652) also show hard spectral indices $(1.0 < \Gamma < 1.7)$, however the presence of an exponential cut-off can not be unambiguously established. Three of them (Omega Cen, NGC 6388, NGC 6652) have no known radio or X-ray MSPs yet still exhibit MSP spectral properties. From the observed gamma-ray luminosities, we estimate the total number of MSPs that is expected to be present in these globular clusters. We show that our estimates of the MSP population correlate with the stellar encounter rate and we estimate 2600-4700 MSPs in Galactic globular clusters, commensurate with previous estimates. The observation of high-energy gamma-ray emission from a globular cluster thus provides a reliable independent method to assess their millisecond pulsar populations that can be used to make constraints on the original neutron star X-ray binary population, essential for understanding the importance of binary systems in slowing the inevitable core collapse of globular clusters.Comment: Accepted for publication in A&A. Corresponding authors: J. Kn\"odlseder, N. Webb, B. Pancraz

Fermi Large Area Telescope Constraints on the Gamma-ray Opacity of the Universe

The Extragalactic Background Light (EBL) includes photons with wavelengths from ultraviolet to infrared, which are effective at attenuating gamma rays with energy above ~10 GeV during propagation from sources at cosmological distances. This results in a redshift- and energy-dependent attenuation of the gamma-ray flux of extragalactic sources such as blazars and Gamma-Ray Bursts (GRBs). The Large Area Telescope onboard Fermi detects a sample of gamma-ray blazars with redshift up to z~3, and GRBs with redshift up to z~4.3. Using photons above 10 GeV collected by Fermi over more than one year of observations for these sources, we investigate the effect of gamma-ray flux attenuation by the EBL. We place upper limits on the gamma-ray opacity of the Universe at various energies and redshifts, and compare this with predictions from well-known EBL models. We find that an EBL intensity in the optical-ultraviolet wavelengths as great as predicted by the "baseline" model of Stecker et al. (2006) can be ruled out with high confidence.Comment: 42 pages, 12 figures, accepted version (24 Aug.2010) for publication in ApJ; Contact authors: A. Bouvier, A. Chen, S. Raino, S. Razzaque, A. Reimer, L.C. Reye

Detection of High-Energy Gamma-Ray Emission from the Globular Cluster 47 Tucanae with Fermi

Gamma-Ray Pulsar Bonanza Most of the pulsars we know about were detected through their radio emission; a few are known to pulse gamma rays but were first detected at other wavelengths (see the Perspective by Halpern ). Using the Fermi Gamma-Ray Space Telescope, Abdo et al. (p. 840 , published online 2 July; see the cover) report the detection of 16 previously unknown pulsars based on their gamma-ray emission alone. Thirteen of these coincide with previously unidentified gamma-ray sources, solving the 30-year-old mystery of their identities. Pulsars are fast-rotating neutron stars. With time they slow down and cease to radiate; however, if they are in a binary system, they can have their spin rates increased by mass transfer from their companion stars, starting a new life as millisecond pulsars. In another study, Abdo et al. (p. 845 ) report the detection of gamma-ray emission from the globular cluster 47 Tucanae, which is coming from an ensemble of millisecond pulsars in the cluster's core. The data imply that there are up to 60 millisecond pulsars in 47 Tucanae, twice as many as predicted by radio observations. In a further companion study, Abdo et al. (p. 848 , published online 2 July) searched Fermi Large Area Telescope data for pulsations from all known millisecond pulsars outside of stellar clusters, finding gamma-ray pulsations for eight of them. Their properties resemble those of other gamma-ray pulsars, suggesting that they share the same basic emission mechanism. Indeed, both sets of pulsars favor emission models in which the gamma rays are produced in the outer magnetosphere of the neutron star

Gamma-ray and radio properties of six pulsars detected by the fermi large area telescope

We report the detection of pulsed γ-rays for PSRs J0631+1036, J0659+1414, J0742-2822, J1420-6048, J1509-5850, and J1718-3825 using the Large Area Telescope on board the Fermi Gamma-ray Space Telescope (formerly known as GLAST). Although these six pulsars are diverse in terms of their spin parameters, they share an important feature: their γ-ray light curves are (at least given the current count statistics) single peaked. For two pulsars, there are hints for a double-peaked structure in the light curves. The shapes of the observed light curves of this group of pulsars are discussed in the light of models for which the emission originates from high up in the magnetosphere. The observed phases of the γ-ray light curves are, in general, consistent with those predicted by high-altitude models, although we speculate that the γ-ray emission of PSR J0659+1414, possibly featuring the softest spectrum of all Fermi pulsars coupled with a very low efficiency, arises from relatively low down in the magnetosphere. High-quality radio polarization data are available showing that all but one have a high degree of linear polarization. This allows us to place some constraints on the viewing geometry and aids the comparison of the γ-ray light curves with high-energy beam models