1,391 research outputs found
Is Messier 74 a barred spiral galaxy?
No full textWe have obtained ground-based I, J and K
band images of the spiral
galaxy, Messier 74 (NGC 628).
This galaxy has been shown to possess a circumnuclear ring
of star formation from both near-infrared spectroscopy of CO absorption and
sub-millimetre imaging of CO emission. Circumnuclear rings of star formation
are believed to exist only as a result of a bar potential. In this paper we
show evidence for a weak oval distortion in the centre of M 74. We use the
results of Combes & Gerin (1985) to suggest that this weak oval potential
is responsible for the circumnuclear ring of star formation observed in M 74
Cause and effects of the massive star formation in Messier 8 East
No full textContext. Messier 8 (M8), one of the brightest H I
Fatima and the Clementine Thieves by M. Messier
No full textMessier, Mireille. Fatima and the Clementine Thieves. Illustrated by Gabrielle Grimard. Red Deer Press, 2017Fatima helps her grandfather in their clementine orchard every day, caring not only for the trees and their harvest, but also for the spiders that protect the trees from insects. But when elephants ravage the orchard that she and her grandfather rely on, Fatima worries how they will save both the orchard and the elephants. Relying on advice from neighbours, Fatima’s grandfather determines to shoot the elephant mother and two calves, spending his last coins on a gun and ammunition. But Fatima seeks a solution outside human invention and rallies her spider friends to protect the orchard, saving both the orchard and the elephants from destruction.Messier’s Fatima is capable and inventive, driven not only by care for her family but also for the natural world: the spiders, the elephants, and the clementine trees. In a story otherwise populated by men, Fatima is a leader, embracing and befriending spiders who are usually feared or ignored, seeking solutions that will be best for all. Messier ensures that Fatima’s voice fills the pages; though the story is occasionally awkward in its transitions from scene to scene, her joy, her fear, her tenacity, and her words hold this story together. While the treatment of the orchard as the family’s sole livelihood is perhaps simplistic, Messier makes a strong statement about violence, in the end turning a gun into a support for a repaired clementine tree.Grimard’s beautifully warm illustrations are the star here, evoking Fatima’s joy and the grandfather’s devotion to her; the beauty and power of the elephants; and the strength of the smallest creatures, whether little girl or spider. Fatima and the Clementine Thieves is a lovely book that reminds readers how, with compassion and tenacity, someone small can make a powerful difference. Recommended for ages 5-7.Recommended: 3 out of 4 starsReviewer: Katherine SchockKatherine is a high school English teacher currently working on an MLIS at the University of Alberta. Her passion for children’s literature is kindled daily by her two small children and her much larger students. </jats:p
Sugar maple (Acer saccharum Marsh.) growth is influenced by close conspecifics and skid trail proximity following selection harvest
No full textIn this study, we quantified the effects of local neighbourhood competition, light availability, and proximity to skid trails on the growth of sugar maple (Acer saccharum Marsh.) trees following selection harvest. We hypothesized that growth would increase with decreasing competition and increasing light availability, but that proximity to skid trails would negatively affect growth. A total of 300 sugar maples were sampled ∼10 years after selection harvesting in 18 stands in Témiscamingue (Québec, Canada). Detailed tree and skid trail maps were obtained in one 0.4 ha plot per stand. Square-root transformed radial growth data were fitted to a linear mixed model that included tree diameter, crown position, a neighbourhood competition index, light availability (estimated using the SORTIE light model), and distance to the nearest skid trail as explanatory variables. We considered various distance-dependent or -independent indices based on neighbourhood radii ranging from 6 to 12 m. The competition index that provided the best fit to the data was a distance-dependent index computed in a 6 m search radius, but a distance-independent version of the competition index provided an almost equivalent fit to data. Models corresponding to all combinations of main effects were fit to data using maximum likelihood, and weighted averages of parameter estimates were obtained using multimodel inference. All predictors had an influence on growth, with the exception of light. Radial growth decreased with increasing tree diameter, level of competition and proximity to skid trails, and varied among crown positions with trees in suppressed and intermediate positions having lower growth rates than codominants and dominants. Our results indicate that in selection managed stands, the radial growth of sugar maple trees depends on competition from close (≤6 m) conspecific neighbours, and is still affected by proximity to skid trails ∼10 years after harvesting. Such results underscore the importance of minimizing the extent of skid trail networks by careful pre-harvest planning of trail layout. We also conclude that the impact of heterogeneity among individual-tree neighbourhoods, such as those resulting from alternative spatial patterns of harvest, can usefully be integrated into models of post-harvest tree growth
Observations météorologiques faites à Pékin , par le Père Amiot . Mis en ordre par M. Messier,...
No full textAppartient à l’ensemble documentaire : Sinica1Avec mode text
Observational study of hydrocarbons in the bright photodissociation region of Messier 8
No full textAims. Hydrocarbons are ubiquitous in the interstellar medium, but their formation is still not well understood, depending on the physical environment in which they are found. Messier 8 (M8) is host to one of the brightest H I
Observations météorologiques faites à Pékin , par le Père Amiot . Mis en ordre par M. Messier,...
No full textAppartient à l’ensemble documentaire : Sinica1Avec mode text
The White Dwarf Population of Messier 34 (NGC 1039)
No full textWe present observations of the white dwarf population of M34 (NGC 1039), an intermediate-age ( ̃ 250 Myr) open cluster with a turnoff mass of ̃ 4 M☉. White dwarfs in this cluster therefore will fill a current gap in the empirical initial-final mass relation, white dwarfs with initial masses between 4M☉ and 5M☉, a region where some theoretical models predict a change in slope to the relation. Wide-field photometry of the cluster core and two flanking fields is presented. High signal-to-noise spectroscopy from the Keck 10m telescope is used to determine the mass and cooling age of each white dwarf, from which the progenitor mass is determined. We present the revised empirical initial-final mass relation, focusing on the slope and scatter. We also present results from a study in the flanking fields of white dwarf evaporation from the cluster. This work is funded through grant AST-0307492 from the National Science Foundation
Improving tree mortality models by accounting for environmental influences
No full textTree-ring chronologies have been widely used in studies of tree mortality where variables of recent growth act as an indicator of tree physiological vigour. Comparing recent radial growth of live and dead trees thus allows estimating probabilities of tree mortality. Sampling of mature dead trees usually provides death-year distributions that may span over years or decades. Recent growth of dead trees (prior to death) is then computed during a number of periods, whereas recent growth (prior to sampling) for live trees is computed for identical periods. Because recent growth of live and dead trees is then computed for different periods, external factors such as disturbance or climate may influence growth rates and, thus, mortality probability estimations. To counteract this problem, we propose the truncating of live-growth series to obtain similar frequency distributions of the “last year of growth” for the populations of live and dead trees. In this paper, we use different growth scenarios from several tree species, from several geographic sources, and from trees with different growth patterns to evaluate the impact of truncating on predictor variables and their selection in logistic regression analysis. Also, we assess the ability of the resulting models to accurately predict the status of trees through internal and external validation. Our results suggest that the truncating of live-growth series helps decrease the influence of external factors on growth comparisons. By doing so, it reinforces the growth–vigour link of the mortality model and enhances the model’s accuracy as well as its general applicability. Hence, if model parameters are to be integrated in simulation models of greater geographical extent, truncating may be used to increase model robustness
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