77 research outputs found
Machine-learning identification of galaxies in the WISExSuperCOSMOS all-sky catalogue
The two currently largest all-sky photometric datasets, WISE and SuperCOSMOS,
were cross-matched by Bilicki et al. (2016) (B16) to construct a novel
photometric redshift catalogue on 70% of the sky. Galaxies were therein
separated from stars and quasars through colour cuts, which may leave
imperfections because of mixing different source types which overlap in colour
space. The aim of the present work is to identify galaxies in the
WISExSuperCOSMOS catalogue through an alternative approach of machine learning.
This allows us to define more complex separations in the multi-colour space
than possible with simple colour cuts, and should provide more reliable source
classification. For the automatised classification we use the support vector
machines learning algorithm, employing SDSS spectroscopic sources cross-matched
with WISExSuperCOSMOS as the training and verification set. We perform a number
of tests to examine the behaviour of the classifier (completeness, purity and
accuracy) as a function of source apparent magnitude and Galactic latitude. We
then apply the classifier to the full-sky data and analyse the resulting
catalogue of candidate galaxies. We also compare thus produced dataset with the
one presented in B16. The tests indicate very high accuracy, completeness and
purity (>95%) of the classifier at the bright end, deteriorating for the
faintest sources, but still retaining acceptable levels of 85%. No significant
variation of classification quality with Galactic latitude is observed.
Application of the classifier to all-sky WISExSuperCOSMOS data gives 15 million
galaxies after masking problematic areas. The resulting sample is purer than
the one in B16, at a price of lower completeness over the sky. The automatic
classification gives a successful alternative approach to defining a reliable
galaxy sample as compared to colour cuts.Comment: 12 pages, 15 figures, accepted for publication in A&A. Obtained
catalogue will be included in the public release of the WISExSuperCOSMOS
galaxy catalogue available from http://ssa.roe.ac.uk/WISExSCO
A rate equation approach to cavity mediated laser cooling
The cooling rate for cavity mediated laser cooling scales as the Lamb-Dicke
parameter eta squared. A proper analysis of the cooling process hence needs to
take terms up to eta^2 in the system dynamics into account. In this paper, we
present such an analysis for a standard scenario of cavity mediated laser
cooling with eta << 1. Our results confirm that there are many similarities
between ordinary and cavity mediated laser cooling. However, for a weakly
confined particle inside a strongly coupled cavity, which is the most
interesting case for the cooling of molecules, numerical results indicate that
even more detailed calculations are needed to model the cooling process
accurately.Comment: 15 pages, 10 figures, minor corrections, PRA (in press
Tracing dark energy with quasars
The nature of dark energy, driving the accelerated expansion of the Universe,
is one of the most important issues in modern astrophysics. In order to
understand this phenomenon, we need precise astrophysical probes of the
universal expansion spanning wide redshift ranges. Quasars have recently
emerged as such a probe, thanks to their high intrinsic luminosities and, most
importantly, our ability to measure their luminosity distances independently of
redshifts. Here we report our ongoing work on observational reverberation
mapping using the time delay of the Mg II line, performed with the South
African Large Telescope (SALT).Comment: 3 pages, 2 figures, submitted as PTA proceeding
The mass of the black hole in RE J1034+396
The black hole mass measurement in active galaxies is a challenge,
particularly in sources where the reverberation method cannot be applied. We
aim to determine the black hole mass in a very special object, RE J1034+396,
one of the two AGN with QPO oscillations detected in X-rays, and a single
bright AGN with optical band totally dominated by starlight. We fit the stellar
content using the code starlight, and the broad band disk contribution to
optical/UV/X-ray emission is modeled with optxagnf. We also determine the black
hole mass using several other independent methods. Various methods give
contradictory results. Most measurements of the blacc hole mass are in the
range 1.e6-1.e7 Msun, and the measurements based on dynamics give higher values
than measurements based on Hbeta and Mg II emission lines.Comment: A&A, in pres
Concentrating Energy by Measurement
In a recent article [A. Kurcz et al., Phys. Rev. A 81, 063821 (2010)] we predicted an energy concentrating mechanism in composite quantum systems. Its result is a non-zero stationary state photon emission rate even in the absence of external driving. Here we discuss the possible origin of the predicted effect. We attribute it to the presence of a non-trivial interaction between different system components and to repeated environment-induced photon measurements
Long-term multi-source precipitation estimation with high resolution (RainGRS Clim)
This paper explores the possibility of using multi-source
precipitation estimates for climatological applications. A data-processing
algorithm (RainGRS Clim) has been developed to work on precipitation
accumulations such as daily or monthly totals, which are significantly
longer than operational accumulations (generally between 5 min and 1 h). The
algorithm makes the most of additional opportunities, such as the
possibility of complementing data with delayed data, access to high-quality data
that are not operationally available, and the greater efficiency of the
algorithms for data quality control and merging with longer accumulations.
Verification of the developed algorithms was carried out using monthly
accumulations through comparison with precipitation from manual rain gauges.
As a result, monthly accumulations estimated by RainGRS Clim were found to
be significantly more reliable than accumulations generated operationally.
This improvement is particularly noticeable for the winter months, when
precipitation estimation is much more difficult due to less reliable radar
estimates.</p
The Interspersed Spin Boson Lattice Model
We describe a family of lattice models that support a new class of quantum
magnetism characterized by correlated spin and bosonic ordering [Phys. Rev.
Lett. 112, 180405 (2014)]. We explore the full phase diagram of the model using
Matrix-Product-State methods. Guided by these numerical results, we describe a
modified variational ansatz to improve our analytic description of the
groundstate at low boson frequencies. Additionally, we introduce an
experimental protocol capable of inferring the low-energy excitations of the
system by means of Fano scattering spectroscopy. Finally, we discuss the
implementation and characterization of this model with current circuit-QED
technology.Comment: Submitted to EPJ ST issue on "Novel Quantum Phases and Mesoscopic
Physics in Quantum Gases
A cavity-mediated collective quantum effect in sonoluminescing bubbles
This paper discusses a collective quantum effect which might play an important role in sonoluminescence experiments. We suggest that it occurs during the final stages of the collapse phase and enhances the heating of the particles inside the bubble
Ecology and Contaminant Exposure of Lake Calumet Black-Crowned Night Herons: Population Levels and Nesting Ecology: Final Report
Illinois Department of Natural Resources, Wildlife Preservation Grantunpublishednot peer reviewedOpe
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