483 research outputs found
"Spoon-feeding" an AGN
Tidal disruption events (TDEs) occur when a star, passing too close to a
massive black hole, is ripped apart by tidal forces. A less dramatic event
occurs if the star orbits just outside the tidal radius, resulting in a mild
stripping of mass. Thus, if a star orbits a central black hole on one of these
bound eccentric orbits, weaker outbursts will occur recurring every orbital
period. Thanks to five Swift observations, we observed a recent flare from the
close by (92 Mpc) galaxy IC 3599, where a possible TDE was already observed in
December 1990 during the Rosat All-Sky Survey. By light curve modeling and
spectral fitting, we account for all these events as the non-disruptive tidal
stripping of a single star into a 9.5 yr highly eccentric bound orbit. This is
the first example of periodic partial tidal disruptions, possibly spoon-feeding
the central black hole.Comment: 7 pages, 3 figures, to appear in "Swift:10 years of discovery",
Proceedings of Scienc
Consumer guide to competition : a practical handbook
French version available in IDRC Digital Library: Guide du consommateur sur la concurrence : un manuel pratiqu
Concurrence : guide pratique à l'usage des consommateurs
Version anglaise disponible dans la Bibliothèque numérique du CRDI: Consumer guide to competition : a practical handboo
NuQKD: A Modular Quantum Key Distribution Simulation Framework for Engineering Applications
An experimental Quantum Key Distribution (QKD) implementation requires
advanced costly hardware, unavailable in most research environments, making
protocol testing and performance evaluation complicated. Historically, this has
been a major motivation for the development of QKD simulation frameworks, to
allow researchers to obtain insight before proceeding into practical
implementations. Several simulators have been introduced over the recent years.
However, only four are publicly available, only one of which models equipment
imperfections. Currently, no open-source simulator includes all following
capabilities: channel attenuation modelling, equipment imperfections and effect
on key rates, estimation of elapsed time during quantum channel processes, use
of truly random binary sequences for qubits and measurement bases, shared-bit
fraction customization. In this paper, we present NuQKD, an open-source
modular, intuitive simulator, featuring all the above capabilities. NuQKD
establishes communication between two computer terminals, accepts custom inputs
(iterations, raw key size, interception rate etc.) and evaluates the sifted key
length, Quantum Bit Error Rate (QBER), elapsed communication time and more).
NuQKD capabilities include optical fiber and free-space simulation, modeling of
equipment/channel imperfections, bitstrings from True Random Number Generator,
modular design and automated evaluation of performance metrics. We expect NuQKD
to enable convenient and accurate representation of actual experimental
conditions
Multi-scale assessment of distribution and density of procellariiform seabirds within the Northern Antarctic Peninsula marine ecosystem
The Antarctic Peninsula is one of the most rapidly warming regions on earth, and it is likely that the abundance and distribution of marine predators will change as a result.Procellariiform seabirds are highly mobile predators, which target specific habitat characteristics associated with underlying distributions of prey and areas of increased prey availability. We use ship surveys and hurdle models, to estimate the summer distribution and relative density of 11 seabird species within the northern Antarctic Peninsula marine ecosystem. Models differed among species; however, sea surface temperature and depth were frequently associated with seabird occurrence and had the greatest explanatory power across many species. Null models based on observation data were better at predicting seabird density than models that included environmental covariates. This suggests that the main driver of distribution patterns is the broad-scale habitat features, and fine-scale aggregations within these ranges are harder to predict. Our seabird distribution models reflect known habitat associations, species hotspots, and community organization relative to oceanic and coastal marine processes. Application of species distribution models will benefit the assessments of critical habitat and potential responses to climate change and anthropogenic disturbance, which will provide insight into how species may change in polar ecosystems
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