4,877 research outputs found
Chronic pain detection from resting-state raw EEG signals using improved feature selection
We present an automatic approach that works on resting-state raw EEG data for
chronic pain detection. A new feature selection algorithm - modified Sequential
Floating Forward Selection (mSFFS) - is proposed. The improved feature
selection scheme is rather compact but displays better class separability as
indicated by the Bhattacharyya distance measures and better visualization
results. It also outperforms selections generated by other benchmark methods,
boosting the test accuracy to 97.5% and yielding a test accuracy of 81.4% on an
external dataset that contains different types of chronic painComment: 9 pages, 4 figures, journal submissio
Optical/IR counterpart to the resolved X-ray jet source CXO J172337.5-373442 and its distance
We present results of observations in the optical to mid-infrared wavelengths
of the X-ray source CXO J172337.5-373442, which was serendipitously discovered
in the Chandra images and was found to have a fully resolved X-ray jet. The
observations include a combination of photometry and spectroscopy in the
optical using ground-based telescopes and mid-infrared photometry using
Spitzer. We detect the optical/IR counterpart of CXO J172337.5-373442 and
identify it to be a G9-V star located at a distance of 334+-60~pc. Comparable
values of the hydrogen column densities determined independently from the
optical/IR observations and X-ray observations indicate that the optical source
is associated with the X-ray source. Since the X-ray luminosity can not be
explained in terms of emission from a single G9-V star, it is likely that CXO
J172337.5-373442 is an accreting compact object in a binary system. Thus, CXO
J172337.5-373442 is the nearest known resolved X-ray jet from a binary system,
which is not a symbiotic star. Based on the existing X-ray data, the nature of
the compact object can not be confirmed. However the low luminosity of the
X-ray point source, 7.1x10^{30} Lsun combined with estimates of the age of the
jet and a lack of detection of bright outburst, suggests that the X-ray jet was
launched during extreme quiescence of the object. The measured low X-ray
luminosity of the jet suggests the likelihood of such jets being more
ubiquitous than our current understanding.Comment: Accepted for publication in MNRA
Dynamics of Laterally Propagating Flames in X-ray Bursts. I. Burning Front Structure
We investigate the structure of laterally-propagating flames through the
highly-stratified burning layer in an X-ray burst. Two-dimensional
hydrodynamics simulations of flame propagation are performed through a rotating
plane-parallel atmosphere, exploring the structure of the flame. We discuss the
approximations needed to capture the length and time scales at play in an X-ray
burst and describe the flame acceleration observed. Our studies complement
other multidimensional studies of burning in X-ray bursts.Comment: Submitted to Ap
New X-ray observations of the Geminga pulsar wind nebula
Previous observations of the middle-aged pulsar Geminga with XMM-Newton and
Chandra have shown an unusual pulsar wind nebula (PWN), with a 20" long central
(axial) tail directed opposite to the pulsar's proper motion and two 2' long,
bent lateral (outer) tails. Here we report on a deeper (78 ks) Chandra
observation and a few additional XMM-Newton observations of the Geminga PWN.
The new Chandra observation has shown that the axial tail, which includes up to
three brighter blobs, extends at least 50" (i.e., 0.06 d_{250} pc) from the
pulsar. It also allowed us to image the patchy outer tails and the emission in
the immediate vicinity of the pulsar with high resolution. The PWN luminosity,
L_{0.3-8 keV} ~ 3\times 10^{29} d_{250}^2 erg/s, is lower than the pulsar's
magnetospheric luminosity by a factor of 10. The spectra of the PWN elements
are rather hard (photon index ~ 1). Comparing the two Chandra images, we found
evidence of PWN variability, including possible motion of the blobs along the
axial tail. The X-ray PWN is the synchrotron radiation from relativistic
particles of the pulsar wind; its morphology is connected with the supersonic
motion of Geminga. We speculate that the outer tails are either (1) a sky
projection of the limb-brightened boundary of a shell formed in the region of
contact discontinuity, where the wind bulk flow is decelerated by shear
instability, or (2) polar outflows from the pulsar bent by the ram pressure
from the ISM. In the former case, the axial tail may be a jet emanating along
the pulsar's spin axis, perhaps aligned with the direction of motion. In the
latter case, the axial tail may be the shocked pulsar wind collimated by the
ram pressure.Comment: 16 pages, including 6 figures; minor changes in the text; typos
corrected; published in Ap
Boosted Random ferns for object detection
© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this paper we introduce the Boosted Random Ferns (BRFs) to rapidly build discriminative classifiers for learning and detecting object categories. At the core of our approach we use standard random ferns, but we introduce four main innovations that let us bring ferns from an instance to a category level, and still retain efficiency. First, we define binary features on the histogram of oriented gradients-domain (as opposed to intensity-), allowing for a better representation of intra-class variability. Second, both the positions where ferns are evaluated within the sliding window, and the location of the binary features for each fern are not chosen completely at random, but instead we use a boosting strategy to pick the most discriminative combination of them. This is further enhanced by our third contribution, that is to adapt the boosting strategy to enable sharing of binary features among different ferns, yielding high recognition rates at a low computational cost. And finally, we show that training can be performed online, for sequentially arriving images. Overall, the resulting classifier can be very efficiently trained, densely evaluated for all image locations in about 0.1 seconds, and provides detection rates similar to competing approaches that require expensive and significantly slower processing times. We demonstrate the effectiveness of our approach by thorough experimentation in publicly available datasets in which we compare against state-of-the-art, and for tasks of both 2D detection and 3D multi-view estimation.Peer ReviewedPostprint (author's final draft
Fluid dynamics on ultrastatic spacetimes and dual black holes
We show that the classification of shearless and incompressible stationary
fluid flows on ultrastatic manifolds is equivalent to classifying the
isometries of the spatial sections. For a flow on R x S this leaves only
one possibility, since on the 2-sphere all Killing fields are conjugate to each
other, and it is well-known that the gravity dual of such a (conformal) fluid
is the spherical KNAdS black hole. On the other hand, in R x H the
situation is more complicated, since the isometry group of H admits
elliptic, parabolic and hyperbolic elements. One might thus ask what the
gravity duals of the flows corresponding to these three different cases are.
Answering this question is one of the scopes of this paper. In particular we
identify the black hole dual to a fluid that is purely translating on the
hyperbolic plane. Although this lies within the Carter-Plebanski (CP) class, it
has never been studied in the literature before, and represents thus in
principle a new black hole solution in AdS. For a rigidly rotating fluid in
R x H (holographically dual to the hyperbolic KNAdS solution), there is
a certain radius where the velocity reaches the speed of light, and thus the
fluid can cover only the region within this radius. Quite remarkably, it turns
out that the boundary of the hyperbolic KNAdS black hole is conformal to
exactly that part of R x H in which the fluid velocity does not exceed the
speed of light. We extend these results to establish a precise mapping between
possible flows on ultrastatic spacetimes (with constant curvature spatial
sections) and the parameter space of the CP solution. Finally, we show that the
alternative description of the hyperbolic KNAdS black hole in terms of
fluid mechanics on R x S or on flat space is dynamical and consists of a
contracting or expanding vortex.Comment: 43 pages, many figures. v2: Final version to appear in JHE
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