207 research outputs found
What Happened to the Beverly Caribou Herd after 1994?
The Beverly herd was one of the first large migratory herds of barren-ground caribou (Rangifer tarandus groenlandicus) defined in northern Canada on the basis of annual return of breeding females to traditional calving grounds near Beverly Lake in Nunavut. In 1994, herd size was estimated at 276 000 ± 106 600 (SE) adult caribou, but monitoring was minimal from 1994 to 2007. The next calving ground survey in 2002 revealed that caribou densities had dropped by more than half since 1994; annual surveys following from 2007 to 2009 demonstrated an extreme decline in numbers of calving cows, and by 2011, no newborn calves were seen there. We examine two possible explanations for the declining use of the traditional Beverly calving grounds from 1994 until their abandonment by 2011. One explanation is that a true numerical decline in herd size occurred, driven in at least the later stages by low cow survival and poor calf productivity, which led the remaining Beverly cows to switch to the neighbouring Ahiak calving ground 250 km to the north in 2007 â 09 and join that herd. An alternative explanation is that the decline on the traditional Beverly calving grounds was largely due to a distributional shift to the north of the Beverly herd that may have begun in the mid-1990s. We suggest that the former explanation is the more likely and that the Beverly herd no longer exists as a distinct herd. We acknowledge that gaps in monitoring of Beverly and Ahiak caribou hamper definitive evaluation of the Beverly herdâs fate. The large size sometimes achieved by barren-ground caribou herds is not a guarantee of persistence; monitoring shortfalls may hamper management actions to address declines.La harde de caribous de Beverly a Ă©tĂ© lâune des premiĂšres grandes hardes migratoires de caribous de la toundra (Rangifer tarandus groenlandicus) dĂ©finies dans le nord du Canada en fonction du retour annuel des femelles reproductrices aux lieux de mise bas traditionnels situĂ©s prĂšs du lac Beverly, au Nunavut. En 1994, la taille de la harde Ă©tait Ă©valuĂ©e Ă 276 000 ± 106 600 (ES) caribous adultes, mais de 1994 Ă 2007, la surveillance a Ă©tĂ© minime. Le prochain recensement relatif aux mises bas a Ă©tĂ© rĂ©alisĂ© en 2002, et celui-ci a rĂ©vĂ©lĂ© que les densitĂ©s de caribous avaient chutĂ© de plus de la moitiĂ© depuis 1994. De 2007 Ă 2009, des recensements annuels ont permis de constater le dĂ©clin prononcĂ© du nombre de femelles en vĂȘlage, si bien que vers 2011, on nâa aperçu aucun nouveau-nĂ©. Nous nous penchons sur deux possibilitĂ©s pouvant expliquer le dĂ©clin de lâutilisation des lieux de mise bas traditionnels de Beverly de 1994 jusquâĂ lâabandon de ces lieux vers 2011. Une explication veut quâil y ait eu une chute rĂ©elle du nombre de membres de la harde attribuable, tout au moins vers la fin, au faible taux de survie des femelles et au faible taux de productivitĂ© des veaux, ce qui a menĂ© le reste des femelles reproductrices de Beverly Ă opter pour le lieu de mise bas environnant dâAhiak, Ă 250 km au nord entre 2007 et 2009, et Ă joindre cette harde. Lâautre explication veut que le dĂ©clin enregistrĂ© aux lieux de mise bas traditionnels de Beverly soit grandement attribuable Ă la dĂ©rivation de la rĂ©partition vers le nord de la harde de Beverly, dĂ©rivation qui aurait pu commencer vers le milieu des annĂ©es 1990. Nous suggĂ©rons que la premiĂšre explication est plus plausible et que la harde de Beverly nâexiste plus en tant que harde distincte. Nous reconnaissons que le manque de surveillance des caribous de Beverly et dâAhiak a empĂȘchĂ© de connaĂźtre de maniĂšre dĂ©finitive le sort de la harde de Beverly. Parfois, la grande taille des hardes de caribous de la toundra nâest pas un gage de longĂ©vitĂ©. Les manques en matiĂšre de surveillance peuvent porter atteinte aux mesures de gestion Ă prendre pour contrer les dĂ©clins
Have geographical influences and changing abundance led to sub-population structure in the Ahiak caribou herd, Nunavut, Canada?
We examined the premise that changing abundance and environmental conditions influence the seasonal dispersion and distribution of migratory tundra caribou (Rangifer tarandus groenlandicus). The Ahiak herdâs (north-central Nunavut Territory, Canada) calving shifted from dispersed on islands to gregarious calving on the mainland coast. As abundance further increased, the calving ground elongated east and west such that we proposed a longitudinal climate gradient. As well, the calving groundâs east and west ends are different distances from the tree-line, which dips south closer to Hudson Bay. We proposed that whether caribou winter on the tundra or within boreal forest and the different climate across the long calving ground could contribute to differential survival and productivity such that sub-population structure would result. At the scale of the individual cows (identified through satellite-collars), we did not find inter-annual spatial fidelity to either the western or eastern parts of the calving ground. At the population scale (aerial surveys of calving distribution), we also did not find discontinuities in calving distribution. The spatial association of individual cows during calving compared with their association during the rut was inconsistent among years, but overall, cows that calve together, rut together. At this time and with the available evidence, we could not infer sub-population structure from shifts in dispersion and distribution as influenced by geography and changes in abundance for the Ahiak herd
Geometric representation of interval exchange maps over algebraic number fields
We consider the restriction of interval exchange transformations to algebraic
number fields, which leads to maps on lattices. We characterize
renormalizability arithmetically, and study its relationships with a
geometrical quantity that we call the drift vector. We exhibit some examples of
renormalizable interval exchange maps with zero and non-zero drift vector, and
carry out some investigations of their properties. In particular, we look for
evidence of the finite decomposition property: each lattice is the union of
finitely many orbits.Comment: 34 pages, 8 postscript figure
Delphi survey on conventional conservative treatment of functional posterior shoulder instability
Background: Posterior shoulder instability is caused by structural or functional defects. While the former are mostly treated surgically, physiotherapy is considered the treatment of choice in functional shoulder instability. However, it often has limited success unless very specific and intensive training programs are applied by trained experts. Currently, there is no consensus on the treatment of functional posterior shoulder instability. Objective: To improve treatment of this pathology, a standardized treatment recommendation is required to serve as a guideline for physiotherapy. The aim of this study was to establish expert consensus for treatment recommendations for functional posterior shoulder instability. Design: The Delphi survey technique was employed. Methods: A standardized training program for treatment of functional posterior shoulder instability was developed by a local expert committee. Two rounds of an online Delphi survey were then conducted. The panel of the Delphi survey comprised nine leading scientific experts in the field of functional shoulder instability who treat patients with shoulder-related problems conservatively and operatively. Results: The response rate was 100% and there were no dropouts. The final program consists of three groups of exercises with increasing difficulty. The exercises are mostly easy to perform and focus on the scapula-retracting muscles and the muscles responsible for external rotation of the shoulder. The treatment program should be executed under the supervision of a therapist at the beginning and later may be performed by the patients themselves. Conclusion: Consensus on a new exercise guideline dedicated to the treatment of functional posterior shoulder instability was achieved. This guideline should not only help to treat this challenging pathology but also provide a starting point for further scientific research and ongoing improvement
The interaction studied via femtoscopy in p + Nb reactions at
We report on the first measurement of and correlations via
the femtoscopy method in p+Nb reactions at , studied with the High Acceptance Di-Electron Spectrometer
(HADES). By comparing the experimental correlation function to model
calculations, a source size for pairs of and a slightly
smaller value for of is extracted.
Using the geometrical extent of the particle emitting region, determined
experimentally with correlations as reference together with a source
function from a transport model, it is possible to study different sets of
scattering parameters. The correlation is proven sensitive to
predicted scattering length values from chiral effective field theory. We
demonstrate that the femtoscopy technique can be used as valid alternative to
the analysis of scattering data to study the hyperon-nucleon interaction.Comment: 12 pages, 11 figure
Limit theorems for self-similar tilings
We study deviation of ergodic averages for dynamical systems given by
self-similar tilings on the plane and in higher dimensions. The main object of
our paper is a special family of finitely-additive measures for our systems. An
asymptotic formula is given for ergodic integrals in terms of these
finitely-additive measures, and, as a corollary, limit theorems are obtained
for dynamical systems given by self-similar tilings.Comment: 36 pages; some corrections and improved exposition, especially in
Section 4; references adde
Strange hadron production at SIS energies: an update from HADES
We present and discuss recent experimental activities of the HADES collaboration on open and hidden strangeness production close or below the elementary NN threshold. Special emphasis is put on the feed-down from Ï mesons to antikaons, the presence of the Î(-) excess in cold nuclear matter and the comparison of statistical model rates to elementary p+p data. The implications for the interpretation of heavy-ion data are discussed as well
Impact of the Coulomb field on charged-pion spectra in few-GeV heavy-ion collisions
In nuclear collisions the incident protons generate a Coulomb field which acts on produced charged particles. The impact of these interactions on charged-pion transverse-mass and rapidity spectra, as well as on pionâpion momentum correlations is investigated in Au + Au collisions at = 2.4 GeV. We show that the low-m region (m < 0.2 GeV / c) can be well described with a Coulomb-modified Boltzmann distribution that also takes changes of the Coulomb field during the expansion of the fireball into account. The observed centrality dependence of the fitted mean Coulomb potential energy deviates strongly from a scaling, indicating that, next to the fireball, the non-interacting charged spectators have to be taken into account. For the most central collisions, the Coulomb modifications of the HBT source radii are found to be consistent with the potential extracted from the single-pion transverse-mass distributions. This finding suggests that the region of homogeneity obtained from two-pion correlations coincides with the region in which the pions freeze-out. Using the inferred mean-square radius of the charge distribution at freeze-out, we have deduced a baryon density, in fair agreement with values obtained from statistical hadronization model fits to the particle yields
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