Redefining Performance Evaluation Tools for Real-Time QRS Complex Classification Systems

International audienceIn a heartbeat classification procedure, the detection of QRS complex waveforms is necessary. In many studies, this heartbeat extraction function is not considered: the inputs of the classifier are assumed to be correctly identified. This paper aims to redefine classical performance evaluation tools in entire QRS complex classification systems and to evaluate the effects induced by QRS detection errors on the performance of a heartbeat classification processing (normal vs abnormal). Performance statistics are given and discussed considering the MIT/BIH database records that are replayed on a real-time classification system imposed of the classical detector proposed by Hamilton & Tompkins, followed by a neural network classifier. This study shows that a classification accuracy of 96.72% falls to 94.90% when a drop of 1.78% error rate is introduced in the detector quality. This corresponds an increase of about 50% bad classifications

Radio emission of extensive air shower at CODALEMA: Polarization of the radio emission along the v*B vector

Cosmic rays extensive air showers (EAS) are associated with transient radio emission, which could provide an efficient new detection method of high energy cosmic rays, combining a calorimetric measurement with a high duty cycle. The CODALEMA experiment, installed at the Radio Observatory in Nancay, France, is investigating this phenomenon in the 10^17 eV region. One challenging point is the understanding of the radio emission mechanism. A first observation indicating a linear relation between the electric field produced and the cross product of the shower axis with the geomagnetic field direction has been presented (B. Revenu, this conference). We will present here other strong evidences for this linear relationship, and some hints on its physical origin.Comment: Contribution to the 31st International Cosmic Ray Conference, Lodz, Poland, July 2009. 4 pages, 8 figures. v2: Typo fixed, arxiv references adde

Geomagnetic origin of the radio emission from cosmic ray induced air showers observed by CODALEMA

The new setup of the CODALEMA experiment installed at the Radio Observatory in Nancay, France, is described. It includes broadband active dipole antennas and an extended and upgraded particle detector array. The latter gives access to the air shower energy, allowing us to compute the efficiency of the radio array as a function of energy. We also observe a large asymmetry in counting rates between showers coming from the North and the South in spite of the symmetry of the detector. The observed asymmetry can be interpreted as a signature of the geomagnetic origin of the air shower radio emission. A simple linear dependence of the electric field with respect to vxB is used which reproduces the angular dependencies of the number of radio events and their electric polarity.Comment: 9 pages, 15 figures, 1 tabl

FAN : étude d'antennes en réseau au foyer du radiotélescope de Nançay

Communications consultables sur http://ursi-france.institut-telecom.frInternational audienceLe NRT (Nançay Radio Telescope) est l'un des trois radiotélescopes "single-dish" de la classe des 100m dans le monde. De nouvelles techniques observationnelles ainsi que des besoins scientifiques nouveaux pour de grands relevés aveugles ont émergés ces dernières années, et doivent utiliser des grands champs de vue. En particulier, la technologie des réseaux d'antennes au foyer est au cœur des recherches et développements de préparation à SKA. Nous présentons le projet FAN (Focal Array at Nançay) qui consiste en l'étude et la réalisation d'un premier prototype d'antenne à réseau phasé installé au foyer du NRT, qui utilise une chaîne de réception et d'acquisition développée par les laboratoires LAL /IN2P3 et SPP/IRFU/CEA. L'antenne est utilisée pour des observations de test depuis la fin 2010. Le système FAN et son fonctionnement sont décrits, ainsi que la méthode de calibration et les premiers résultats obtenus

Two RFI Mitigation Experiments With The Embrace Demonstrator

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RFI Mitigation in Radio Astronomy: an Overview

National audienceRadio astronomy is a passive service and is equipped to observe extremely weak signals from outer space. The sensitivity of current state-of-the-art telescopes is over ten orders of magnitude higher than in most communications systems. Although radio telescopes are best located in relatively remote areas, astronomical observations may be still hampered by man-made radio frequency interference (RFI). In this paper we will consider different interference mitigation options. After a quick overview of techniques already implemented in current radio telescopes, we will focus on the innovative possibilities induced by the new generation of radio telescopes. In particular, phased array architecture can lead to interesting spatial filtering approaches. Examples on real data from LOFAR and from Nançay radio telescopes will be shown

Exploration of the Potential of the Radio-Detection Technique for the Detection of High-Energy Gamma Rays

International audienceThe radio detection of atmospheric particle showers initiated by ultra-high energy cosmic rays is today a proven technique that allows to reconstruct their properties (direction of arrival, energy, nature). Among the precursors of this method, the CODALEMA experiment installed at the Nançay radio-astronomy Observatory has contributed to several major technological innovations relevant for the radio detection technique (autonomous triggering, hybrid reconstruction, very wide frequency bands) and its high-performance antennas are also used on the NenuFAR radio telescope in Nançay. We propose to exploit the unique environment of the Nan\c cay Observatory through the CODALEMA experiment and the NenuFAR radio-telescope to explore the possibilities of radio-detection of atmospheric showers initiated by very high energy photons. The central idea is to phase a large set of antennas (several tens) in the direction of known sources emitting gamma (catalogs H.E.S.S., MAGIC, VERITAS, Fermi-LAT ...) to significantly increase the sensitivity of detection and to use the triggering capabilities on ultra fast transients controlled within the framework of CODALEMA. This would make it possible to observe the sources with a useful cycle close to 100 %. We present here the intended instrumental scheme as well as the expected signal level and some first results obtained on the observation of cosmic ray air showers with NenuFAR

Radio emission of extensive air shower at CODALEMA: Polarization of the radio emission along the v*B vector

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