103,299 research outputs found
Tracking Table Tennis Balls in Real Match Scenes for Umpiring Applications
Judging the legitimacy of table tennis services presents many challenges where technology can be judiciously applied to enhance decision-making. This paper presents a purpose-built system to automatically detect and track the ball during table-tennis services to enable precise judgment over their legitimacy in real-time. The system comprises a suite of algorithms which adaptively exploit spatial and temporal information from real match video sequences, which are generally characterised by high object motion, allied with object blurring and occlusion. Experimental results on a diverse set of table-tennis test sequences corroborate the system performance in facilitating consistently accurate and efficient decision-making over the validity of a service
The Fundamentals of Radar with Applications to Autonomous Vehicles
Radar systems can be extremely useful for applications in autonomous vehicles. This paper seeks to show how radar systems function and how they can apply to improve autonomous vehicles. First, the basics of radar systems are presented to introduce the basic terminology involved with radar. Then, the topic of phased arrays is presented because of their application to autonomous vehicles. The topic of digital signal processing is also discussed because of its importance for all modern radar systems. Finally, examples of radar systems based on the presented knowledge are discussed to illustrate the effectiveness of radar systems in autonomous vehicles
Study of Globular Cluster M53: new variables, distance, metallicity
We study the variable star content of the globular cluster M53 to compute the
physical parameters of the constituting stars and the distance of the cluster.
Covering two adjacent seasons in 2007 and 2008, new photometric data are
gathered for 3048 objects in the field of M53. By using the OIS method and
subsequently TFA, we search for variables in the full sample by using DFT and
BLS methods. We select variables based on the statistics related to these
methods combined with visual inspections. We identified 12 new variables (2 RR
Lyrae stars, 7 short periodic stars - 3 of them are SX Phe stars - and 3
long-period variables). No eclipsing binaries were found in the present sample.
Except for the 3 (hitherto unknown) Blazhko RR Lyrae stars, no multiperiodic
variables were found. We showed that after proper period shift, the PLC
relation for the first overtone RR Lyrae sample tightly follows the one spanned
by the fundamental stars. Furthermore, the slope is in agreement with the one
derived from other clusters. Based on the earlier Baade-Wesselink calibration
of the PLC relations, the derived reddening-free distance modulus of M53 is
16.31 +/- 0.04 mag, corresponding to a distance modulus of 18.5 mag for the
Large Magellanic Cloud. From the Fourier parameters of the RRab stars we
obtained an average iron abundance of -1.58 +/- 0.03. This is ~0.5 dex higher
than the overall abundance of the giants as given in the literature and derived
in this paper from the three-color photometry of giants. We suspect that the
source of this discrepancy (observable also in other, low-metallicity clusters)
is the want of sufficient number of low-metallicity objects in the calibrating
sample of the Fourier method.Comment: Accepted for publication in Astronomy & Astrophysics. The paper
contains 5 tables and 13 figure
AGN feedback works both ways
Simulations of galaxy growth need to invoke strong negative feedback from
active galactic nuclei (AGN) to suppress the formation of stars and thus
prevent the over-production of very massive systems. While some observations
provide evidence for such negative feedback, other studies find either no
feedback, or even positive feedback, with increased star formation associated
with higher AGN luminosities. Here we report an analysis of several hundred AGN
and their host galaxies in the Chandra Deep Field South using X-ray and radio
data for sample selection. Combined with archival far infrared data as a
reliable tracer of star formation activity in the AGN host galaxies, we find
that AGN with pronounced radio jets exhibit a much higher star formation rate
than the purely X-ray selected ones, even at the same X-ray luminosities. This
difference implies that positive AGN feedback plays an important role, too, and
therefore has to be accounted for in all future simulation work. We interpret
this to indicate that the enhanced star formation rate of radio selected AGN
arises because of jet-induced star formation, as is hinted by the different jet
powers among our AGN samples, while the suppressed star formation rate of X-ray
selected AGN is caused by heating and photo-dissociation of molecular gas by
the hot AGN accretion disc.Comment: 21 pages, 9 figures, 3 tables, accepted for publication by Ap
Comparison and contrast in perceptual categorization
People categorized pairs of perceptual stimuli that varied in both category membership and pairwise similarity. Experiments 1 and 2 showed categorization of 1 color of a pair to be reliably contrasted from that of the other. This similarity-based contrast effect occurred only when the context stimulus was relevant for the categorization of the target (Experiment 3). The effect was not simply owing to perceptual color contrast (Experiment 4), and it extended to pictures from common semantic categories (Experiment 5). Results were consistent with a sign-and-magnitude version of N. Stewart and G. D. A. Brown's (2005) similarity-dissimilarity generalized context model, in which categorization is affected by both similarity to and difference from target categories. The data are also modeled with criterion setting theory (M. Treisman & T. C. Williams, 1984), in which the decision criterion is systematically shifted toward the mean of the current stimuli
Reference-less detection, astrometry, and photometry of faint companions with adaptive optics
We propose a complete framework for the detection, astrometry, and photometry
of faint companions from a sequence of adaptive optics corrected short
exposures. The algorithms exploit the difference in statistics between the
on-axis and off-axis intensity. Using moderate-Strehl ratio data obtained with
the natural guide star adaptive optics system on the Lick Observatory's 3-m
Shane Telescope, we compare these methods to the standard approach of PSF
fitting. We give detection limits for the Lick system, as well as a first guide
to expected accuracy of differential photometry and astrometry with the new
techniques. The proposed approach to detection offers a new way of determining
dynamic range, while the new algorithms for differential photometry and
astrometry yield accurate results for very faint and close-in companions where
PSF fitting fails. All three proposed algorithms are self-calibrating, i.e.
they do not require observation of a calibration star thus improving the
observing efficiency.Comment: Astrophysical Journal 698 (2009) 28-4
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