394 research outputs found
Discovery of the brightest T dwarf in the northern hemisphere
We report the discovery of a bright (H=12.77) brown dwarf designated SIMP
J013656.5+093347. The discovery was made as part of a near-infrared proper
motion survey, SIMP (Sondage Infrarouge de Mouvement Propre), which uses proper
motion and near-infrared/optical photometry to identify brown dwarf candidates.
A low resolution (lambda/dlambda~40) spectrum of this brown dwarf covering the
0.88-2.35 microns wavelength interval is presented. Analysis of the spectrum
indicates a spectral type of T2.5+/-0.5. A photometric distance of 6.4+/-0.3 pc
is estimated assuming it is a single object. Current observations rule out a
binary of mass ratio ~1 and separation >5 AU. SIMP 0136 is the brightest T
dwarf in the northern hemisphere and is surpassed only by Eps Indi Bab over the
whole sky. It is thus an excellent candidate for detailed studies and should
become a benchmark object for the early-T spectral class.Comment: 4 pages, 3 figures, To be published in November 1, 2006 issue of
ApJL. Following IAU recommendation, the survey acronym (IBIS) was changed to
SIM
An experimental study of how variation in deer density affects vegetation and songbird assemblages of recently harvested boreal forests
Intense browsing by abundant large herbivores can threaten the ecological integrity of ecosystems by inducing modifications in the structure and composition of vegetation that trigger trophic cascades affecting plant and animal communities. We investigated the relationships between density of white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)), forest succession after clear-cut, and songbird communities on Anticosti Island, Quebec, Canada. We hypothesized that lower deer densities would alter the trajectory of forest succession after clear-cutting and lead to a rapid recovery of habitat attributes favorable to songbirds associated with a dense complex shrub layer. Six years after establishing a controlled browsing experiment (0, 7.5, 15, and >27 deer·kmâ2) in recent clearcuts, reducing deer densities â€7.5 deer·kmâ2 initiated the restoration of balsam fir (Abies balsamea (L.) Mill.) forests and increased the regeneration of paper birch (Betula papyrifera Marshall). Increasing birch ground cover from 10% to 20% increased songbird total abundance, species richness, and diversity by 17%, 39%, and 31%, respectively. Alder Flycatcher (Empidonax alnorum Brewster, 1895) was only present at â€7.5 deer·kmâ2 and strongly associated with birch regeneration. The regeneration of browse-resistant plants such as white spruce (Picea glauca (Moench) Voss) in some areas at high deer density favored the maintenance of many shrub-dependent songbirds but also species usually associated with forest canopy. Active management of deer populations in Canadian harvested boreal forests will mitigate losses in vegetation and songbirds caused by over-browsing.Le broutement intensif par de nombreux grands herbivores peut menacer lâintĂ©gritĂ© Ă©cologique dâĂ©cosystĂšmes en
induisant des modifications de la structure et de la composition de la végétation qui déclenchent des cascades trophiques
ayant des incidences sur les communautés végétales et animales. Nous nous sommes penchés sur les liens entre la densité
du cerf de Virginie (Odocoileus virginianus (Zimmermann, 1780)), la succession forestiĂšre aprĂšs la coupe Ă blanc et les
communautĂ©s dâoiseaux chanteurs sur lâĂźle dâAnticosti (QuĂ©bec, Canada). Nous avons Ă©mis lâhypothĂšse que de plus faibles
densités de cerfs modifieraient la trajectoire de succession forestiÚre aprÚs une coupe à blanc et mÚneraient au rétablissement
rapide des attributs dâhabitat favorables aux oiseaux chanteurs associĂ©s Ă une strate arbustive complexe et dense. Six ans
aprĂšs lâĂ©tablissement dâune expĂ©rience de broutement contrĂŽlĂ© (0, 7,5, 15 et >27 cerfs·kmâ2) dans des coupes rĂ©centes, la rĂ©duction des densitĂ©s de cerfs Ă â€7,5 cerfs·kmâ2 sâest traduite par le dĂ©but du rĂ©tablissement des forĂȘts de sapin baumier
(Abies balsamea (L.) Mill.) et une régénération accrue du bouleau à papier (Betula papyrifera Marshall). Un passage de la
couverture de bouleau de 10 % Ă 20 % sâest traduit par des augmentations de lâabondance totale dâoiseaux chanteurs, de la
richesse spĂ©cifique et de la diversitĂ© de 17 %, 39 % et 31 %, respectivement. Le moucherolle des aulnes (Empidonax alnorum Brewster, 1895) nâĂ©tait prĂ©sent quâĂ des densitĂ©s â€7,5 cerfs·kmâ2 et Ă©tait fortement associĂ© Ă la rĂ©gĂ©nĂ©ration du bouleau. La rĂ©gĂ©nĂ©ration de plantes rĂ©sistantes au broutement, telles que lâĂ©pinette blanche (Picea glauca (Moench) Voss) dans
certaines zones à forte densité de cerfs a favorisé le maintien de nombreux oiseaux chanteurs dépendants des arbustes, mais
Ă©galement dâespĂšces gĂ©nĂ©ralement associĂ©es Ă la canopĂ©e. La gestion active des populations de cerfs dans les forĂȘts borĂ©ales
canadiennes exploitĂ©es attĂ©nuera les pertes de vĂ©gĂ©tation et dâoiseaux chanteurs causĂ©es par le surbroutemen
An electrophysiological investigation of power-amplification in the ballistic mantis shrimp punch
Author Posting. © Faculty for Undergraduate Neuroscience, 2019. This article is posted here by permission of Faculty for Undergraduate Neuroscience for personal use, not for redistribution. The definitive version was published in Journal of Undergraduate Neuroscience Education 17(1), (2019): T12-T19.Mantis shrimp are aggressive, burrowing crustaceans that hunt using one the fastest movements in the natural world. These stomatopods can crack the calcified shells of prey or spear down unsuspecting fish with lighting speed. Their strike makes use of power-amplification mechanisms to move their limbs much faster than is possible by muscles alone. Other arthropods such as crickets and grasshoppers also use power-amplified kicks that allow these animals to rapidly jump away from predator threats. Here we present a template laboratory exercise for studying the electrophysiology of power-amplified limb movement in arthropods, with a specific focus on mantis shrimp strikes. The exercise is designed in such a way that it can be applied to other species that perform power-amplified limb movements (e.g., house crickets, Acheta domesticus) and species that do not (e.g., cockroaches, Blaberus discoidalis). Students learn to handle the animals, make and implant electromyogram (EMG) probes, and finally perform experiments. This integrative approach introduces the concept of power-amplified neuromuscular control; allows students to develop scientific methods, and conveys high-level insights into behavior, and convergent evolution, the process by which different species evolve similar traits.Author GJG declares a commercial interest in the SpikerBox used here as a co-owner in Backyard Brains. Authors ES and SM are employed by Backyard Brains. DJP and GJG were supported by a National Institute of Mental Health (NIMH) Small Business Innovative Research (SBIR) award #R44MH093334. Author KDF is funded by European Commission Marie Sklodowska-Curie Independent Postdoctoral Research Fellowship and the Grass Foundation
The Langevin diffusion as a continuous-time model of animal movement and habitat selection
TM was supported by the Centre for Advanced Biological Modelling at the University of Sheffield, funded by the Leverhulme Trust, award number DS-2014-081.1. The utilisation distribution of an animal describes the relative probability of space use. It is natural to think of it as the long-term consequence of the animal's short-term movement decisions: it is the accumulation of small displacements which, over time, gives rise to global patterns of space use. However, many estimation methods for the utilisation distribution either assume the independence of observed locations and ignore the underlying movement (e.g. kernel density estimation), or are based on simple Brownian motion movement rules (e.g. Brownian bridges). 2. We introduce a new continuous-time model of animal movement, based on the Langevin diffusion. This stochastic process has an explicit stationary distribution, conceptually analogous to the idea of the utilisation distribution, and thus provides an intuitive framework to integrate movement and space use. We model the stationary (utilisation) distribution with a resource selection function to link the movement to spatial covariates, and allow inference about habitat preferences of animals. 3. Standard approximation techniques can be used to derive the pseudo-likelihood of the Langevin diffusion movement model, and to estimate habitat preference and movement parameters from tracking data. We investigate the performance of the method on simulated data, and discuss its sensitivity to the time scale of the sampling. We present an example of its application to tracking data of Steller sea lions (Eumetopias jubatus). 4. Due to its continuous-time formulation, this method can be applied to irregular telemetry data. The movement model is specified using a habitat-dependent utilisation distribution, and it provides a rigorous framework to estimate long-term habitat selection from correlated movement data. The Langevin movement model can be approximated by linear model, which allows for very fast inference. Standard tools such as residuals can be used for model checking.PostprintPeer reviewe
Species indicators of ecosystem recovery after reducing large herbivore density: Comparing taxa and testing species combinations
Indicator species have been used successfully for estimating ecosystem integrity, but comparative studies for defining optimal taxonomic group remain scarce. Furthermore, species combinations may constitute more integrative tools than single species indicators, but case studies are needed to test their efficiency. We used Indicator Species Analysis, which statistically determines the association of species to one or several groups of sites, to obtain indicators of ecosystem recovery after various deer density reductions. We used five taxonomic groups: plants, carabid beetles, bees, moths and songbirds. To test whether species combinations could complement single indicator species, we used plants as a model taxon and examined the indicator value of joint occurrence of two or three plant species. Our study relies on experimental controlled browsing enclosures established for six years on Anticosti Island (Quebec). Four levels of deer density (0, 7.5 and 15 deer kmâ2 and natural densities between 27 and 56 deer kmâ2) were studied in two vegetation cover types (uncut forests and cut-over areas), in a full factorial design for a total of eight experimental treatments. For all taxa but bees, we tested 54 treatment groups consisting in one specific density or in a sequence of two or more consecutive deer densities in one or both cover types (ten groups for bees, sampled only in cut-over areas). We found 12 plants, 11 moths and one songbird to be single species indicators of ecosystem conditions obtained under 12 different treatment groups. Six treatment groups were indicated by plants and six different ones by moths, of which one group was also identified by a songbird species. Moths were thus worth the extra sampling effort, especially since the groups they indicated were more treatment-specific (mainly one or two deer density treatments). We tested the same 54 treatment groups for plant species combinations represented by two or three co-occurring species. Plant combinations efficiently complemented plant singletons for detecting ecosystem conditions obtained under various deer densities. In fact, although singletons were highly predictive, 17 additional treatment groups were identified exclusively with two- and three-species combinations, some being more treatment-specific. Our findings show that plants and moths provide complementary indicators of ecosystem conditions under various deer densities, and that computing species combinations increases our capacity to monitor ecosystem recovery after reducing herbivore densities.Funding was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC)-Produits forestiers Anticosti Industrial Chair to SDC, the MinistĂšre des Ressources Naturelles et de la Faune du QuĂ©bec, the Canadian Forest Service of Natural Resources Canada and an NSERC scholarship to MB and NSERC DG to MP and SP. We are grateful to the Centre de la Science de la BiodiversitĂ© du QuĂ©bec and Centre dâĂ©tudes nordiques for scholarships
Spectroscopy, MOST Photometry, and Interferometry of MWC 314: Is it an LBV or an interacting binary?
MWC 314 is a bright candidate luminous blue variable that resides in a fairly
close binary system, with an orbital period of 60.7530.003 d. We observed
MWC 314 with a combination of optical spectroscopy, broad-band ground- and
space-based photometry, as well as with long baseline, near-infrared
interferometry. We have revised the single-lined spectroscopic orbit and
explored the photometric variability. The orbital light curve displays two
minima each orbit that can be partially explained in terms of the tidal
distortion of the primary that occurs around the time of periastron. The
emission lines in the system are often double-peaked and stationary in their
kinematics, indicative of a circumbinary disc. We find that the stellar wind or
circumbinary disc is partially resolved in the K\prime-band with the longest
baselines of the CHARA Array. From this analysis, we provide a simple,
qualitative model in an attempt to explain the observations. From the
assumption of Roche Lobe overflow and tidal synchronisation at periastron, we
estimate the component masses to be M1 M and M2
M, which indicates a mass of the LBV that is extremely low. In addition
to the orbital modulation, we discovered two pulsational modes with the MOST
satellite. These modes are easily supported by a low-mass hydrogen-poor star,
but cannot be easily supported by a star with the parameters of an LBV. The
combination of these results provides evidence that the primary star was likely
never a normal LBV, but rather is the product of binary interactions. As such,
this system presents opportunities for studying mass-transfer and binary
evolution with many observational techniques.Comment: 26 pages, 7 figures, 5 tables, 2 appendices with 7 additional tables
and 2 additional figures. Accepted for publication in MNRA
Discovery of a Wide Planetary-mass Companion to the Young M3 Star GU Psc
We present the discovery of a comoving planetary-mass companion ~42" (~2000âAU) from a young M3 star, GU Psc, a likely member of the young AB Doradus Moving Group (ABDMG). The companion was first identified via its distinctively red i â z color (>3.5) through a survey made with Gemini-S/GMOS. Follow-up CanadaâFranceâHawaii Telescope/WIRCam near-infrared (NIR) imaging, Gemini-N/GNIRS NIR spectroscopy and Wide-field Infrared Survey Explorer photometry indicate a spectral type of T3.5 ± 1 and reveal signs of low gravity which we attribute to youth. Keck/Adaptive Optics NIR observations did not resolve the companion as a binary. A comparison with atmosphere models indicates T_eff = 1000â1100 K and logâg = 4.5â5.0. Based on evolution models, this temperature corresponds to a mass of 9â13 âM_Jup for the age of ABDMG (70â130 Myr). The relatively well-constrained age of this companion and its very large angular separation to its host star will allow its thorough characterization and will make it a valuable comparison for planetary-mass companions that will be uncovered by forthcoming planet-finder instruments such as Gemini Planet Imager and SPHERE
Colloquium: Mechanical formalisms for tissue dynamics
The understanding of morphogenesis in living organisms has been renewed by
tremendous progressin experimental techniques that provide access to
cell-scale, quantitative information both on theshapes of cells within tissues
and on the genes being expressed. This information suggests that
ourunderstanding of the respective contributions of gene expression and
mechanics, and of their crucialentanglement, will soon leap forward.
Biomechanics increasingly benefits from models, which assistthe design and
interpretation of experiments, point out the main ingredients and assumptions,
andultimately lead to predictions. The newly accessible local information thus
calls for a reflectionon how to select suitable classes of mechanical models.
We review both mechanical ingredientssuggested by the current knowledge of
tissue behaviour, and modelling methods that can helpgenerate a rheological
diagram or a constitutive equation. We distinguish cell scale ("intra-cell")and
tissue scale ("inter-cell") contributions. We recall the mathematical framework
developpedfor continuum materials and explain how to transform a constitutive
equation into a set of partialdifferential equations amenable to numerical
resolution. We show that when plastic behaviour isrelevant, the dissipation
function formalism appears appropriate to generate constitutive equations;its
variational nature facilitates numerical implementation, and we discuss
adaptations needed in thecase of large deformations. The present article
gathers theoretical methods that can readily enhancethe significance of the
data to be extracted from recent or future high throughput
biomechanicalexperiments.Comment: 33 pages, 20 figures. This version (26 Sept. 2015) contains a few
corrections to the published version, all in Appendix D.2 devoted to large
deformation
A Hamiltonianâfree description of single particle dynamics for hopelessly complex periodic systems
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