18,417 research outputs found
Sparse Coding for Event Tracking and Image Retrieval
Comparing regions of images is a fundamental task in both similarity based object tracking as well as retrieval of images from image datasets, where an exemplar image is used as the query. In this thesis, we focus on the task of creating a method of comparison for images produced by NASA’s Solar Dynamic Observatory mission. This mission has been in operation for several years and produces almost 700 Gigabytes of data per day from the Atmospheric Imaging Assembly instrument alone. This has created a massive repository of high-quality solar images to analyze and categorize. To this end, we are concerned with the creation of image region descriptors that are selective enough to differentiate between highly similar images yet compact enough to be compared in an efficient manner, while also being indexable with current indexing technology. We produce such descriptors by pooling sparse coding vectors produced by spanning learned basis dictionaries. Various pooled vectors are used to describe regions of images in event tracking, entire image descriptors for image comparison in content based image retrieval, and as region descriptors to be used in a content based image retrieval system on the SDO AIA image pipeline
Neutrino oscillations
In the last decades, a very important breakthrough has been brought in the
elementary particle physics by the discovery of the phenomenon of the neutrino
oscillations, which has shown neutrino properties beyond the Standard Model.
But a full understanding of the various aspects of the neutrino oscillations is
far to be achieved. In this paper the theoretical background of the neutrino
oscillation phenomenon is described, referring in particular to the
paradigmatic models. Then the various techniques and detectors which studied
neutrinos from different sources are discussed, starting from the pioneering
ones up to the detectors still in operation and to those in preparation. The
physics results are finally presented adopting the same research path which has
crossed this long saga. The problems not yet fixed in this field are discussed,
together with the perspectives of their solutions in the near future
Ellerman Bombs at high resolution: I. Morphological evidence for photospheric reconnection
High-resolution imaging-spectroscopy movies of solar active region NOAA 10998
obtained with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish 1-m
Solar Telescope show very bright, rapidly flickering, flame-like features that
appear intermittently in the wings of the Balmer H-alpha line in a region with
moat flows and likely some flux emergence. They show up at regular H-alpha
blue-wing bright points that outline magnetic network, but flare upward with
much larger brightness and distinct "jet" morphology seen from aside in the
limbward view of these movies. We classify these features as Ellerman bombs and
present a morphological study of their appearance at the unprecedented spatial,
temporal, and spectral resolution of these observations. The bombs appear along
magnetic network with footpoint extents up to 900km. They show apparent travel
away from the spot along the pre-existing network at speeds of about 1 km/s.
The bombs flare repetitively with much rapid variation at time scales of
seconds only, in the form of upward jet-shaped brightness features. These reach
heights of 600-1200km and tend to show blueshifts; some show bi-directional
Doppler signature, and some seem accompanied with an H-alpha surge. They are
not seen in the core of H-alpha due to shielding by overlying chromospheric
fibrils. The network where they originate has normal properties. The morphology
of these jets strongly supports deep-seated photospheric reconnection of
emergent or moat-driven magnetic flux with pre-existing strong vertical network
fields as the mechanism underlying the Ellerman bomb phenomenon.Comment: 13pages, 10 figures, 2 tables. Accepted for publication in the
Astrophysical Journa
Automated LASCO CME catalog for solar cycle 23: are CMEs scale invariant?
In this paper we present the first automatically constructed LASCO CME
catalog, a result of the application of the Computer Aided CME Tracking
software (CACTus) on the LASCO archive during the interval September 1997 -
January 2007. We have studied the CME characteristics and have compared them
with similar results obtained by manual detection (CDAW CME catalog). On
average CACTus detects less than 2 events per day during solar minimum up to 8
events during maximum, nearly half of them being narrow (< 20 degrees).
Assuming a correction factor, we find that the CACTus CME rate is surprisingly
consistent with CME rates found during the past 30 years. The CACTus statistics
show that small scale outflow is ubiquitously observed in the outer corona. The
majority of CACTus-only events are narrow transients related to previous CME
activity or to intensity variations in the slow solar wind, reflecting its
turbulent nature. A significant fraction (about 15%) of CACTus-{\it only}
events were identified as independent events, thus not related to other CME
activity. The CACTus CME width distribution is essentially scale invariant in
angular span over a range of scales from 20 to 120 degrees while previous
catalogues present a broad maximum around 30 degrees. The possibility that the
size of coronal mass outflows follow a power law distribution could indicate
that no typical CME size exists, i.e. that the narrow transients are not
different from the larger well-defined CMEs.Comment: 13 pages. ApJ, accepte
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