435 research outputs found
A statistical multiresolution approach for face recognition using structural hidden Markov models
This paper introduces a novel methodology that combines the multiresolution feature of the discrete wavelet transform (DWT) with the local interactions of the facial structures expressed through the structural hidden Markov model (SHMM). A range of wavelet filters such as Haar, biorthogonal 9/7, and Coiflet, as well as Gabor, have been implemented in order to search for the best performance. SHMMs perform a thorough probabilistic analysis of any sequential pattern by revealing both its inner and outer structures simultaneously. Unlike traditional HMMs, the SHMMs do not perform the state conditional independence of the visible observation sequence assumption. This is achieved via the concept of local structures introduced by the SHMMs. Therefore, the long-range dependency problem inherent to traditional HMMs has been drastically reduced. SHMMs have not previously been applied to the problem of face identification. The results reported in this application have shown that SHMM outperforms the traditional hidden Markov model with a 73% increase in accuracy
A detailed radio study of the energetic, nearby, and puzzling GRB 171010A
We present the results of an intensive multi-epoch radio frequency campaign
on the energetic and nearby GRB 171010A with the Karl G. Janksy Very Large
Array and Arcminute Microkelvin Imager Large Array. We began observing GRB
171010A a day after its initial detection, and were able to monitor the
temporal and spectral evolution of the source over the following weeks. The
spectra and their evolution are compared to the canonical theories for
broadband GRB afterglows, with which we find a general agreement. There are,
however, a number of features that are challenging to explain with a simple
forward shock model, and we discuss possible reasons for these discrepancies.
This includes the consideration of the existence of a reverse shock component,
potential microphysical parameter evolution and the effect of scintillation
Rapid radio flaring during an anomalous outburst of SS Cyg
The connection between accretion and jet production in accreting white dwarf binary systems, especially dwarf novae, is not well understood. Radio wavelengths provide key insights into the mechanisms responsible for accelerating electrons, including jets and outflows. Here, we present densely sampled radio coverage, obtained with the Arcminute MicroKelvin Imager Large Array, of the dwarf nova SS Cyg during its 2016 February anomalous outburst. The outburst displayed a slower rise (3 dmag-1) in the optical than typical ones and lasted for more than three weeks. Rapid radio flaring on time-scales <1 h was seen throughout the outburst. The most intriguing behaviour in the radio was towards the end of the outburst where a fast, luminous ('giant'), flare peaking at ~20 mJy and lasting for 15 min was observed. This is the first time that such a flare has been observed in SS Cyg and insufficient coverage could explain its non-detection in previous outbursts. These data, together with past radio observations, are consistent with synchrotron emission from plasma ejection events as being the origin of the radio flares. However, the production of the giant flare during the declining accretion rate phase remains unexplained within the standard accretion-jet framework and appears to be markedly different to similar patterns of behaviour in X-ray binaries
Century-of-Information Research – a Strategy for Research and Innovation in the Century of Information
The QUIJOTE experiment: project overview and first results
QUIJOTE (Q-U-I JOint TEnerife) is a new polarimeter aimed to characterize the
polarization of the Cosmic Microwave Background and other Galactic and
extragalactic signals at medium and large angular scales in the frequency range
10-40 GHz. The multi-frequency (10-20~GHz) instrument, mounted on the first
QUIJOTE telescope, saw first light on November 2012 from the Teide Observatory
(2400~m a.s.l). During 2014 the second telescope has been installed at this
observatory. A second instrument at 30~GHz will be ready for commissioning at
this telescope during summer 2015, and a third additional instrument at 40~GHz
is now being developed. These instruments will have nominal sensitivities to
detect the B-mode polarization due to the primordial gravitational-wave
component if the tensor-to-scalar ratio is larger than r=0.05.Comment: To appear in "Highlights of Spanish Astrophysics VIII", Proceedings
of the XI Scientific Meeting of the Spanish Astronomical Society, Teruel,
Spain (2014
AMI-LA Observations of the SuperCLASS Super-cluster
We present a deep survey of the SuperCLASS super-cluster - a region of sky
known to contain five Abell clusters at redshift - performed using
the Arcminute Microkelvin Imager (AMI) Large Array (LA) at 15.5GHz. Our
survey covers an area of approximately 0.9 square degrees. We achieve a nominal
sensitivity of Jy beam toward the field centre, finding 80
sources above a threshold. We derive the radio colour-colour
distribution for sources common to three surveys that cover the field and
identify three sources with strongly curved spectra - a high-frequency-peaked
source and two GHz-peaked-spectrum sources. The differential source count (i)
agrees well with previous deep radio source count, (ii) exhibits no evidence of
an emerging population of star-forming galaxies, down to a limit of 0.24mJy,
and (iii) disagrees with some models of the 15GHz source population.
However, our source count is in agreement with recent work that provides an
analytical correction to the source count from the SKADS Simulated Sky,
supporting the suggestion that this discrepancy is caused by an abundance of
flat-spectrum galaxy cores as-yet not included in source population models.Comment: 17 pages, 14 figures, 3 tables. Accepted for publication in MNRA
A Multi-telescope Campaign on FRB 121102: Implications for the FRB Population
We present results of the coordinated observing campaign that made the first
subarcsecond localization of a Fast Radio Burst, FRB 121102. During this
campaign, we made the first simultaneous detection of an FRB burst by multiple
telescopes: the VLA at 3 GHz and the Arecibo Observatory at 1.4 GHz. Of the
nine bursts detected by the Very Large Array at 3 GHz, four had simultaneous
observing coverage at other observatories. We use multi-observatory constraints
and modeling of bursts seen only at 3 GHz to confirm earlier results showing
that burst spectra are not well modeled by a power law. We find that burst
spectra are characterized by a ~500 MHz envelope and apparent radio energy as
high as erg. We measure significant changes in the apparent
dispersion between bursts that can be attributed to frequency-dependent
profiles or some other intrinsic burst structure that adds a systematic error
to the estimate of DM by up to 1%. We use FRB 121102 as a prototype of the FRB
class to estimate a volumetric birth rate of FRB sources Mpc yr, where is the number of bursts per
source over its lifetime. This rate is broadly consistent with models of FRBs
from young pulsars or magnetars born in superluminous supernovae or long
gamma-ray bursts, if the typical FRB repeats on the order of thousands of times
during its lifetime.Comment: 17 pages, 7 figures. Submitted to AAS Journal
A blind detection of a large, complex, Sunyaev--Zel'dovich structure
We present an interesting Sunyaev-Zel'dovich (SZ) detection in the first of
the Arcminute Microkelvin Imager (AMI) 'blind', degree-square fields to have
been observed down to our target sensitivity of 100{\mu}Jy/beam. In follow-up
deep pointed observations the SZ effect is detected with a maximum peak
decrement greater than 8 \times the thermal noise. No corresponding emission is
visible in the ROSAT all-sky X-ray survey and no cluster is evident in the
Palomar all-sky optical survey. Compared with existing SZ images of distant
clusters, the extent is large (\approx 10') and complex; our analysis favours a
model containing two clusters rather than a single cluster. Our Bayesian
analysis is currently limited to modelling each cluster with an ellipsoidal or
spherical beta-model, which do not do justice to this decrement. Fitting an
ellipsoid to the deeper candidate we find the following. (a) Assuming that the
Evrard et al. (2002) approximation to Press & Schechter (1974) correctly gives
the number density of clusters as a function of mass and redshift, then, in the
search area, the formal Bayesian probability ratio of the AMI detection of this
cluster is 7.9 \times 10^4:1; alternatively assuming Jenkins et al. (2001) as
the true prior, the formal Bayesian probability ratio of detection is 2.1
\times 10^5:1. (b) The cluster mass is MT,200 = 5.5+1.2\times 10^14h-1M\odot.
(c) Abandoning a physical model with num- -1.3 70 ber density prior and instead
simply modelling the SZ decrement using a phenomenological {\beta}-model of
temperature decrement as a function of angular distance, we find a central SZ
temperature decrement of -295+36 {\mu}K - this allows for CMB primary
anisotropies, receiver -15 noise and radio sources. We are unsure if the
cluster system we observe is a merging system or two separate clusters.Comment: accepted MNRAS. 12 pages, 9 figure
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