574 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
A self-learning case and rule-based reasoning algorithm for intelligent technology evaluation and selection [Abstract]
This research programme proposes to fulfill the existing gap in knowledge by providing an experience-oriented decision algorithm to solve technology selection problems based on cases and expert’s experience. The approach adopts historical case-based data to extract rules through the ID3 rule induction algorithm. The decision model integrates a rule induction approach in a rule-based knowledge system and database management system to support automated knowledge mining and usage. The adoption of a pair-wise comparison algorithm within the similarity index assists in relating the importance of the criteria within the knowledgebases reasoner. A series of historical and new solutions are presented in a scoring index based on the requirements of a new case
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