7,169 research outputs found
The Ascending Double-Cone: A Closer Look at a Familiar Demonstration
The double-cone ascending an inclined V-rail is a common exhibit used for
demonstrating concepts related to center-of-mass in introductory physics
courses. While the conceptual explanation is well-known--the widening of the
ramp allows the center of mass of the cone to drop, overbalancing the increase
in altitude due to the inclination of the ramp--there remains rich physical
content waiting to be extracted through deeper exploration. Such an
investigations seems to be absent from the literature. This article seeks to
remedy the omission.Comment: LaTeX, 16 pages, 18 eps figure
VLT near-infrared spectra of hard serendipitous Chandra sources
We present near-infrared long-slit spectra of eight optically-dim X-ray
sources obtained with ISAAC on the Very Large Telescope. Six of the sources
have hard X-ray emission with a significant fraction of the counts emerging
above 2 keV. All were discovered serendipitously in the fields of three nearby
galaxy clusters observed with Chandra, and identified through near-infrared
imaging. The X-ray fluxes lie close to the break in the source counts. Two of
the sources show narrow emission lines, and a third has a broad line. One of
the narrow line-emitting sources has a clear redshift identification at z=2.18,
while the other has a tentative determination based on the highest redshift
detection of He I 10830 at z=1.26. The remainder have featureless spectra to
deep limiting equivalent widths of 20--60 angstroms and line flux approx= 5 x
10^{-17} erg/s/cm^2 in the K-band. High-quality J, H and Ks--band images of the
sources were combined with archival optical detections or limits to estimate a
photometric redshift for six. Two sources show complex double morphology. The
hard sources have spectral count ratios consistent with heavily obscured AGN,
while the host galaxy emits much of the optical and near-infrared flux. The
most likely explanation for the featureless continua is that the line photons
are being scattered or destroyed by optically-thick gas and associated dust
with large covering fractions.Comment: Replaced in response to problems with the PDF version of Fig 4 at
arxiv.org, but not at the mirror sites (lanl.gov, soton.ac.uk). No content
change
Automated Top View Registration of Broadcast Football Videos
In this paper, we propose a novel method to register football broadcast video
frames on the static top view model of the playing surface. The proposed method
is fully automatic in contrast to the current state of the art which requires
manual initialization of point correspondences between the image and the static
model. Automatic registration using existing approaches has been difficult due
to the lack of sufficient point correspondences. We investigate an alternate
approach exploiting the edge information from the line markings on the field.
We formulate the registration problem as a nearest neighbour search over a
synthetically generated dictionary of edge map and homography pairs. The
synthetic dictionary generation allows us to exhaustively cover a wide variety
of camera angles and positions and reduce this problem to a minimal per-frame
edge map matching procedure. We show that the per-frame results can be improved
in videos using an optimization framework for temporal camera stabilization. We
demonstrate the efficacy of our approach by presenting extensive results on a
dataset collected from matches of football World Cup 2014
WISE view of Narrow-Line Seyfert 1 galaxies: mid-infrared color and variability
We present the color and flux variability analysis at 3.4 {\mu}m (W1-band)
and 4.6 {\mu}m (W 2-band) of 492 narrow-line Seyfert 1 (NLSy1) galaxies using
archival data from the Wide-field Infrared Survey Explorer (WISE). In the WISE
color-color, (W1 - W2) versus (W2 - W3) diagram, ~58% of the NLSy1 galaxies of
our sample lie in the region occupied by the blazar category of active galactic
nuclei (AGN). The mean W1 - W2 color of candidate variable NLSy1 galaxies is
mag. The average amplitude of variability is
mag in long-term (multi-year) with no difference in variability between W1 and
W2-bands. The W1 - W2 color of NLSy1 galaxies is anti-correlated with the
relative strength of [O III] to H{\beta}, strongly correlated with continuum
luminosity, black hole mass, and Eddington ratio. The long-term amplitude of
variability shows weak anti-correlation with the Fe II strength, continuum
luminosity and Eddington ratio. A positive correlation between color as well as
the amplitude of variability with the radio power at 1.4 GHz was found for the
radio-detected NLSy1 galaxies. This suggests non-thermal synchrotron
contribution to the mid-infrared color and flux variability in radio-detected
NLSy1 galaxies.Comment: 10 pages; Accepted for publication in MNRA
On a sperm whale Physeter macrocephalus washed ashore at Irumeni (Palk Bay) near Mandapam
A female sperm whale Physeter macrocephalus Linnaeus (Fig. 1) measuring 4 m, weighing 1.5 t was washed ashore in dead condition at Irumeni (Palk Bay) near Mandapam on 10-11- 2000. The length at birth of a sperm whale is about 4 meters, hence it mav be in-ferred that the present
whale is a new born baby
Accretion disc-corona and jet emission from the radio-loud narrow-line Seyfert 1 galaxy RX J1633.3+4719
We perform X-ray/ultraviolet (UV) spectral and X-ray variability studies of
the radio-loud narrow-line Seyfert 1 (NLS1) galaxy RX J1633.3+4719 using
XMM-Newton and Suzaku observations from 2011 and 2012. The 0.3-10 keV spectra
consist of an ultrasoft component described by an accretion disc blackbody
(kT_in = 39.6^{+11.2}_{-5.5} eV) and a power law due to the thermal
Comptonization ({\Gamma} = 1.96^{+0.24}_{-0.31}) of the disc emission. The disc
temperature inferred from the soft excess is at least a factor of 2 lower than
that found for the canonical soft excess emission from radio-quiet NLS1s. The
UV spectrum is described by a power law with photon index 3.05^{+0.56}_{-0.33}.
The observed UV emission is too strong to arise from the accretion disc or the
host galaxy, but can be attributed to a jet. The X-ray emission from RX
J1633.3+4719 is variable with fractional variability amplitude =13.5 per cent. In contrast to radio-quiet active galactic nuclei
(AGN), X-ray emission from the source becomes harder with increasing flux. The
fractional rms variability increases with energy and the rms spectrum is well
described by a constant disc component and a variable power-law continuum with
the normalization and photon index being anticorrelated. Such spectral
variability cannot be caused by variations in the absorption and must be
intrinsic to the hot corona. Our finding of possible evidence for emission from
the inner accretion disc, jet and hot corona from RX J1633.3+4719 in the
optical to X-ray bands makes this object an ideal target to probe the disc-jet
connection in AGN.Comment: 12 pages, 11 figures, 3 tables, Published in MNRA
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