6,412 research outputs found
Extragalactic Radio Continuum Surveys and the Transformation of Radio Astronomy
Next-generation radio surveys are about to transform radio astronomy by
discovering and studying tens of millions of previously unknown radio sources.
These surveys will provide new insights to understand the evolution of
galaxies, measuring the evolution of the cosmic star formation rate, and
rivalling traditional techniques in the measurement of fundamental cosmological
parameters. By observing a new volume of observational parameter space, they
are also likely to discover unexpected new phenomena. This review traces the
evolution of extragalactic radio continuum surveys from the earliest days of
radio astronomy to the present, and identifies the challenges that must be
overcome to achieve this transformational change.Comment: To be published in Nature Astronomy 18 Sept 201
CERES: Clouds and the Earth's Radiant Energy System
This brochure gives a brief description of the science research that is being done with data from the Clouds and Earth's Radiant Energy System (CERES) instrument flying onboard NASA's Terra satellite. It also contains information about some of the data products and technical specifications. Educational levels: Undergraduate lower division, Undergraduate upper division, Graduate or professional
Global Optimization for Future Gravitational Wave Detectors' Sites
We consider the optimal site selection of future generations of gravitational
wave detectors. Previously, Raffai et al. optimized a 2-detector network with a
combined figure of merit. This optimization was extended to networks with more
than two detectors in a limited way by first fixing the parameters of all other
component detectors. In this work we now present a more general optimization
that allows the locations of all detectors to be simultaneously chosen. We
follow the definition of Raffai et al. on the metric that defines the
suitability of a certain detector network. Given the locations of the component
detectors in the network, we compute a measure of the network's ability to
distinguish the polarization, constrain the sky localization and reconstruct
the parameters of a gravitational wave source. We further define the
`flexibility index' for a possible site location, by counting the number of
multi-detector networks with a sufficiently high Figure of Merit that include
that site location. We confirm the conclusion of Raffai et al., that in terms
of flexibility index as defined in this work, Australia hosts the best
candidate site to build a future generation gravitational wave detector. This
conclusion is valid for either a 3-detector network or a 5-detector network.
For a 3-detector network site locations in Northern Europe display a comparable
flexibility index to sites in Australia. However for a 5-detector network,
Australia is found to be a clearly better candidate than any other location.Comment: 30 pages, 23 figures, 2 table
Detection and Classification of Obstacles for Autonomous Vessels Using Machine Learning
Desenvolvimento de um sistema capaz de realizar a deteção e classificação de obstáculos de vários tipos que possam ser sujeitos de colisões e resultar em danos para a embarcação ou até na destruição total do mesmo. O sistema é também capaz da deteção da linha do horizonte para estimar a distância relativa dos objetos detetados à posição atual da embarcação. As deteções são conseguidas recorrendo a técnicas de Deep Learning, nomeadamente usando CNNs, para a deteção dos obstaculos e linha do horizonte.Development of a system capable of obstacle detection and classification of various types that may be subject of collisions and result in damages to the ship or even its own total loss. The system is also capable of detection the horizon line, to estimate the relative distance of the detected objects to the vehicle current position. This is achieved throught Deep Learning techniques, namely by the use of Convolutional Neural Networks
The ANTARES Collaboration: Contributions to ICRC 2017 Part II: The multi-messenger program
Papers on the ANTARES multi-messenger program, prepared for the 35th
International Cosmic Ray Conference (ICRC 2017, Busan, South Korea) by the
ANTARES Collaboratio
A Bayesian Approach to the Detection Problem in Gravitational Wave Astronomy
The analysis of data from gravitational wave detectors can be divided into
three phases: search, characterization, and evaluation. The evaluation of the
detection - determining whether a candidate event is astrophysical in origin or
some artifact created by instrument noise - is a crucial step in the analysis.
The on-going analyses of data from ground based detectors employ a frequentist
approach to the detection problem. A detection statistic is chosen, for which
background levels and detection efficiencies are estimated from Monte Carlo
studies. This approach frames the detection problem in terms of an infinite
collection of trials, with the actual measurement corresponding to some
realization of this hypothetical set. Here we explore an alternative, Bayesian
approach to the detection problem, that considers prior information and the
actual data in hand. Our particular focus is on the computational techniques
used to implement the Bayesian analysis. We find that the Parallel Tempered
Markov Chain Monte Carlo (PTMCMC) algorithm is able to address all three phases
of the anaylsis in a coherent framework. The signals are found by locating the
posterior modes, the model parameters are characterized by mapping out the
joint posterior distribution, and finally, the model evidence is computed by
thermodynamic integration. As a demonstration, we consider the detection
problem of selecting between models describing the data as instrument noise, or
instrument noise plus the signal from a single compact galactic binary. The
evidence ratios, or Bayes factors, computed by the PTMCMC algorithm are found
to be in close agreement with those computed using a Reversible Jump Markov
Chain Monte Carlo algorithm.Comment: 19 pages, 12 figures, revised to address referee's comment
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