6,047 research outputs found
Classification and Ranking of Fermi LAT Gamma-ray Sources from the 3FGL Catalog using Machine Learning Techniques
We apply a number of statistical and machine learning techniques to classify
and rank gamma-ray sources from the Third Fermi Large Area Telescope (LAT)
Source Catalog (3FGL), according to their likelihood of falling into the two
major classes of gamma-ray emitters: pulsars (PSR) or Active Galactic Nuclei
(AGN). Using 1904 3FGL sources that have been identified/associated with AGN
(1738) and PSR (166), we train (using 70% of our sample) and test (using 30%)
our algorithms and find that the best overall accuracy (>96%) is obtained with
the Random Forest (RF) technique, while using a logistic regression (LR)
algorithm results in only marginally lower accuracy. We apply the same
techniques on a sub-sample of 142 known gamma-ray pulsars to classify them into
two major subcategories: young (YNG) and millisecond pulsars (MSP). Once more,
the RF algorithm has the best overall accuracy (~90%), while a boosted LR
analysis comes a close second. We apply our two best models (RF and LR) to the
entire 3FGL catalog, providing predictions on the likely nature of {\it
unassociated} sources, including the likely type of pulsar (YNG or MSP). We
also use our predictions to shed light on the possible nature of some gamma-ray
sources with known associations (e.g. binaries, SNR/PWN). Finally, we provide a
list of plausible X-ray counterparts for some pulsar candidates, obtained using
Swift, Chandra, and XMM. The results of our study will be of interest for both
in-depth follow-up searches (e.g. pulsar) at various wavelengths, as well as
for broader population studies.Comment: Accepted by Ap
Oxygen isotope equilibrium in brachiopod shell fibres in the context of biological control
No abstract available
Expressed sequence tag survey of gene expression in the scab mite Psoroptes ovis--allergens, proteases and free-radical scavengers
Bayesian analysis of Friedmannless cosmologies
Assuming only a homogeneous and isotropic universe and using both the 'Gold'
Supernova Type Ia sample of Riess et al. and the results from the Supernova
Legacy Survey, we calculate the Bayesian evidence of a range of different
parameterizations of the deceleration parameter. We consider both spatially
flat and curved models. Our results show that although there is strong evidence
in the data for an accelerating universe, there is little evidence that the
deceleration parameter varies with redshift.Comment: 7 pages, 3 figure
Radio-quiet and radio-loud pulsars: similar in Gamma-rays but different in X-rays
We present new Chandra and XMM-Newton observations of a sample of eight
radio-quiet Gamma-ray pulsars detected by the Fermi Large Area Telescope. For
all eight pulsars we identify the X-ray counterpart, based on the X-ray source
localization and the best position obtained from Gamma-ray pulsar timing. For
PSR J2030+4415 we found evidence for an about 10 arcsec-long pulsar wind
nebula. Our new results consolidate the work from Marelli et al. 2011 and
confirm that, on average, the Gamma-ray--to--X-ray flux ratios (Fgamma/Fx) of
radio-quiet pulsars are higher than for the radio-loud ones. Furthermore, while
the Fgamma/Fx distribution features a single peak for the radio-quiet pulsars,
the distribution is more dispersed for the radio-loud ones, possibly showing
two peaks. We discuss possible implications of these different distributions
based on current models for pulsar X-ray emission.Comment: Accepted for publication in The Astrophysical Journal; 12 pages, 3
figures, 2 table
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Challenges of ultra large scale integration of biomedical computing systems
The NCRI Informatics Initiative is overseeing the implementation of an informatics
framework for the UK cancer research community. The framework advocates an integrated
multidisciplinary method of working between scientific and medical communities. Key to this
process is community adoption of high quality acquisition, storage, sharing and integration of
diverse data elements to improve knowledge of the causes, prevention and treatment of
cancer. The integration of the complex data and meta-data used by these multiple
communities is a significant challenge and there are technical, resource-based and
sociological issues to be addressed. In this paper we review progress aimed at establishing
the framework and outline key challenges in ultra large scale integration of biomedical
computing systems
Probing CDM cosmology with the Evolutionary Map of the Universe survey
The Evolutionary Map of the Universe (EMU) is an all-sky survey in
radio-continuum which uses the Australian SKA Pathfinder (ASKAP). Using galaxy
angular power spectrum and the integrated Sachs-Wolfe effect, we study the
potential of EMU to constrain models beyond CDM (i.e., local
primordial non-Gaussianity, dynamical dark energy, spatial curvature and
deviations from general relativity), for different design sensitivities. We
also include a multi-tracer analysis, distinguishing between star-forming
galaxies and galaxies with an active galactic nucleus, to further improve EMU's
potential. We find that EMU could measure the dark energy equation of state
parameters around 35\% more precisely than existing constraints, and that the
constraints on and modified gravity parameters will improve up to
a factor with respect to Planck and redshift space distortions
measurements. With this work we demonstrate the promising potential of EMU to
contribute to our understanding of the Universe.Comment: 15 pages (29 with references and appendices), 6 figures and 10
tables. Matches the published version. Minimal changes from previous versio
Laboratory studies in ultraviolet solar physics
The research activity comprised the measurement of basic atomic processes and parameters which relate directly to the interpretation of solar ultraviolet observations and to the development of comprehensive models of the component structures of the solar atmosphere. The research was specifically directed towards providing the relevant atomic data needed to perform and to improve solar diagnostic techniques which probe active and quiet portions of the solar chromosphere, the transition zone, the inner corona, and the solar wind acceleration regions of the extended corona. The accuracy with which the physical conditions in these structures can be determined depends directly on the accuracy and completeness of the atomic and molecular data. These laboratory data are used to support the analysis programs of past and current solar observations (e.g., the Orbiting solar Observatories, the Solar Maximum Mission, the Skylab Apollo Telescope Mount, and the Naval Research Laboratory's rocket-borne High Resolution Telescope and Spectrograph). In addition, we attempted to anticipate the needs of future space-borne solar studies such as from the joint ESA/NASA Solar and Heliospheric Observatory (SOHO) spacecraft. Our laboratory activities stressed two categories of study: (1) the measurement of absolute rate coefficients for dielectronic recombination and electron impact excitation; and (2) the measurement of atomic transition probabilities for solar density diagnostics. A brief summary of the research activity is provided
Parkinson's Law Quantified: Three Investigations on Bureaucratic Inefficiency
We formulate three famous, descriptive essays of C.N. Parkinson on
bureaucratic inefficiency in a quantifiable and dynamical socio-physical
framework. In the first model we show how the use of recent opinion formation
models for small groups can be used to understand Parkinson's observation that
decision making bodies such as cabinets or boards become highly inefficient
once their size exceeds a critical 'Coefficient of Inefficiency', typically
around 20. A second observation of Parkinson - which is sometimes referred to
as Parkinson's Law - is that the growth of bureaucratic or administrative
bodies usually goes hand in hand with a drastic decrease of its overall
efficiency. In our second model we view a bureaucratic body as a system of a
flow of workers, which enter, become promoted to various internal levels within
the system over time, and leave the system after having served for a certain
time. Promotion usually is associated with an increase of subordinates. Within
the proposed model it becomes possible to work out the phase diagram under
which conditions bureaucratic growth can be confined. In our last model we
assign individual efficiency curves to workers throughout their life in
administration, and compute the optimum time to send them to old age pension,
in order to ensure a maximum of efficiency within the body - in Parkinson's
words we compute the 'Pension Point'.Comment: 15 pages, 5 figure
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