3,226 research outputs found
Online Learning with Ensembles
Supervised online learning with an ensemble of students randomized by the
choice of initial conditions is analyzed. For the case of the perceptron
learning rule, asymptotically the same improvement in the generalization error
of the ensemble compared to the performance of a single student is found as in
Gibbs learning. For more optimized learning rules, however, using an ensemble
yields no improvement. This is explained by showing that for any learning rule
a transform exists, such that a single student using
has the same generalization behaviour as an ensemble of
-students.Comment: 8 pages, 1 figure. Submitted to J.Phys.
Intraluminal recanalization of long infrainguinal chronic total occlusions using the Crosser system
Purpose: To assess the safety and efficacy of a device for vibrational angioplasty in the
percutaneous intraluminal recanalization of long infrainguinal chronic total occlusions (CTO).
Technique: The Crosser CTO Recanalization System is a mechanical recanalization device
that uses high-frequency vibrational energy to disrupt and channel through fibrocalcific
plaque without harming the vessel wall, thus assisting in the recanalization of an occluded
artery. In 12 diabetic patients (7 men; median age 71 years, range 58–80) with critical limb
ischemia owing to long (median length 26 cm, range 21–32) infrainguinal CTOs resistant to
conventional guidewire techniques, the Crosser CTO Recanalization System was
successful in intraluminally crossing the occlusion in 9 (75%) patients in ,5 minutes
(mean 4:03 minutes). The safety endpoint (distal lumen guidewire position with no vessel
perforation or dissection) was achieved in all successful cases.
Conclusion: In our preliminary experience, the Crosser CTO Recanalization Catheter
decreased crossing time, was safe, and achieved a high rate of intraluminal recanalization
of long infrainguinal CTOs.
J Endovasc Ther. 2009;16:23–27
Key words: critical limb ischemia, chronic total occlusion, percutaneous interventions,
infrainguinal occlusion, intraluminal recanalization, vibrational energ
Identification of gait stability indices for the rehabilitation follow-up of people with transtibial amputation: a preliminary study
Resuming activities of daily living after a lower limb amputation represents a challenge, especially because of the high risk of falling. Thus, rehabilitation initially focuses on stability. Despit..
ON THE APPLICATION OF REMOTE SENSING TIME SERIES ANALYSIS FOR LAND COVER MAPPING: SPECTRAL INDICES FOR CROPS CLASSIFICATION
Abstract. This study aims to introduce a semi-automatic classification workflow for the production of a land use/land cover (LULC) map of the island of Sardinia (Italy) following the CORINE legend schema, and a ground spatial resolution compatible with a scale of 1:25.000. The classification is based on free high-resolution satellite imagery from Sentinel-1 and Sentinel-2 collected in 2020, ancillary data derived from Sardinian Geoportal, Joint Research Centre (JRC) and OpenStreetMap. The LULC map production includes three steps: 1) pixel-based classification, realized with two different approaches, that use i) information derived from existing thematic maps eventually re-coded in case of incoherencies observed between datasets and/or satellite data products, and ii) spectral indices and parameter thresholds defined on the basis of multitemporal analysis; 2) segmentation of Sentinel-1 and 2 annual composites, and pre-labelling of segments with the pixel-based classified map, obtaining the preliminary map; 3) visual inspection procedure in order to confirm, or re-assign, classes to polygons. The accuracy of the preliminary map was tested in a sample area and on specific class of non-irrigated crops through ground truth data collected from a detailed photo-interpretation, estimating 97% of overall accuracy. The results show a great improvement from existing thematic maps in terms of detail, with the possibility of a yearly updating of the map via automatic processes. However, some limitations were found, due to the high fragmentation of Sardinian landscape and the high variety of crop types and agricultural practices, that could affect the efficiency of the classifier
XMM-Newton monitoring of X-ray variability in the quasar PKS 0558-504
We present the temporal analysis of X-ray observations of the radio-loud
Narrow-Line Seyfert 1 galaxy (NLS1) PKS 0558-504 obtained during the XMM-Newton
Calibration and Performance Verification (Cal/PV) phase. The long term light
curve is characterized by persistent variability with a clear tendency for the
X-ray continuum to harden when the count rate increases. Another strong
correlation on long time scales has been found between the variability in the
hard band and the total flux. On shorter time scales the most relevant result
is the presence of smooth modulations, with characteristic time of ~ 2 hours
observed in each individual observation. The short term spectral variability
turns out to be rather complex but can be described by a well defined pattern
in the hardness ratio-count rate plane.Comment: 6 pages, 7 figures, accepted for publication in A&A special issue on
first results from XM
Interstellar Scintillation of the Polarized Flux Density in Quasar, PKS 0405-385
The remarkable rapid variations in radio flux density and polarization of the
quasar PKS 0405-385 observed in 1996 are subject to a correlation analysis,
from which characteristic time scales and amplitudes are derived. The
variations are interpreted as interstellar scintillations. The cm wavelength
observations are in the weak scintillation regime for which models for the
various auto- and cross-correlations of the Stokes parameters are derived and
fitted to the observations. These are well modelled by interstellar
scintillation (ISS) of a 30 by 22 micro-as source, with about 180 degree
rotation of the polarization angle along its long dimension. This success in
explaining the remarkable intra-day variations (IDV)in polarization confirms
that ISS gives rise to the IDV in this quasar. However, the fit requires the
scintillations to be occurring much closer to the Earth than expected according
to the standard model for the ionized interstellar medium (IISM). Scattering at
distances in the range 3-30 parsec are required to explain the observations.
The associated source model has a peak brightness temperature near 2.0
10^{13}K, which is about twenty-five times smaller than previously derived for
this source. This reduces the implied Doppler factor in the relativistic jet,
presumed responsible to 10-20, high but just compatible with cm wavelength VLBI
estimates for the Doppler factors in Active Galactic Nuclei (AGNs).Comment: 43 pages 15 figures, accepted for ApJ Dec 200
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