179 research outputs found
Living analytics methods for the social web
[no abstract
The accretion disk in the post period-minimum cataclysmic variable SDSS J080434.20+510349.2
This study of SDSS0804 is primarily concerned with the double-hump shape in
the light curve and its connection with the accretion disk in this bounce-back
system. Time-resolved photometric and spectroscopic observations were obtained
to analyze the behavior of the system between superoutbursts. A geometric model
of a binary system containing a disk with two outer annuli spiral density waves
was applied to explain the light curve and the Doppler tomography. Observations
were carried out during 2008-2009, after the object's magnitude decreased to
V~17.7(0.1) from the March 2006 eruption. The light curve clearly shows a
sinusoid-like variability with a 0.07 mag amplitude and a 42.48 min
periodicity, which is half of the orbital period of the system. In Sept. 2010,
the system underwent yet another superoutburst and returned to its quiescent
level by the beginning of 2012. This light curve once again showed a
double-humps, but with a significantly smaller ~0.01mag amplitude. Other types
of variability like a "mini-outburst" or SDSS1238-like features were not
detected. Doppler tomograms, obtained from spectroscopic data during the same
period of time, show a large accretion disk with uneven brightness, implying
the presence of spiral waves. We constructed a geometric model of a bounce-back
system containing two spiral density waves in the outer annuli of the disk to
reproduce the observed light curves. The Doppler tomograms and the
double-hump-shape light curves in quiescence can be explained by a model system
containing a massive >0.7Msun white dwarf with a surface temperature of
~12000K, a late-type brown dwarf, and an accretion disk with two outer annuli
spirals. According to this model, the accretion disk should be large, extending
to the 2:1 resonance radius, and cool (~2500K). The inner parts of the disk
should be optically thin in the continuum or totally void.Comment: 12 pages, 15 figures, accepted for publication in A&
Personalized Event-Based Surveillance and Alerting Support for the Assessment of Risk
In a typical Event-Based Surveillance setting, a stream of web documents is
continuously monitored for disease reporting. A structured representation of
the disease reporting events is extracted from the raw text, and the events are
then aggregated to produce signals, which are intended to represent early
warnings against potential public health threats.
To public health officials, these warnings represent an overwhelming list of
"one-size-fits-all" information for risk assessment. To reduce this overload,
two techniques are proposed. First, filtering signals according to the user's
preferences (e.g., location, disease, symptoms, etc.) helps reduce the
undesired noise. Second, re-ranking the filtered signals, according to an
individual's feedback and annotation, allows a user-specific, prioritized
ranking of the most relevant warnings.
We introduce an approach that takes into account this two-step process of: 1)
filtering and 2) re-ranking the results of reporting signals. For this,
Collaborative Filtering and Personalization are common techniques used to
support users in dealing with the large amount of information that they face.Comment: International Meeting on Emerging Diseases and Surveillance. IMED
2011 - Poster Session - Vienna, Austria. February 4-7, 201
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