82,165 research outputs found
Radio detection of cosmic rays: present and future
Digital radio detection of cosmic rays has made tremendous progress over the
past decade. It has become increasingly clear where the potential --- but also
the limitations --- of the technique lie. In this article, we discuss roads
that could be followed in future radio detection efforts and try to evaluate
the associated prospects and challenges.Comment: Contribution to the Proceedings of the UHECR2014 conference,
Springdale, UT; to be published in JPS Conf. Pro
Physics, Astrophysics and Cosmology with Gravitational Waves
Gravitational wave detectors are already operating at interesting sensitivity
levels, and they have an upgrade path that should result in secure detections
by 2014. We review the physics of gravitational waves, how they interact with
detectors (bars and interferometers), and how these detectors operate. We study
the most likely sources of gravitational waves and review the data analysis
methods that are used to extract their signals from detector noise. Then we
consider the consequences of gravitational wave detections and observations for
physics, astrophysics, and cosmology.Comment: 137 pages, 16 figures, Published version
<http://www.livingreviews.org/lrr-2009-2
A personal, distributed exposimeter: procedure for design, calibration, validation, and application
This paper describes, for the first time, the procedure for the full design, calibration, uncertainty analysis, and practical application of a personal, distributed exposimeter (PDE) for the detection of personal exposure in the Global System for Mobile Communications (GSM) downlink (DL) band around 900 MHz (GSM 900 DL). The PDE is a sensor that consists of several body-worn antennas. The on-body location of these antennas is investigated using numerical simulations and calibration measurements in an anechoic chamber. The calibration measurements and the simulations result in a design (or on-body setup) of the PDE. This is used for validation measurements and indoor radio frequency (RF) exposure measurements in Ghent, Belgium. The main achievements of this paper are: first, the demonstration, using both measurements and simulations, that a PDE consisting of multiple on-body textile antennas will have a lower measurement uncertainty for personal RF exposure than existing on-body sensors; second, a validation of the PDE, which proves that the device correctly estimates the incident power densities; and third, a demonstration of the usability of the PDE for real exposure assessment measurements. To this aim, the validated PDE is used for indoor measurements in a residential building in Ghent, Belgium, which yield an average incident power density of 0.018 mW/m(2)
Point source generation of chiral fields:measures of near- and far-field optical helicity
To consider the relationship between different measures of chirality in an optical field, the simplest case is considered: direct spontaneous emission of circularly polarized light by a point source. In the electromagnetic fields radiated from a suitably chiral source, such as a low-symmetry chiral molecule undergoing radiative decay, optical helicity is exhibited in the extent of a difference in left- and right-handed circular polarization components. There are several practical measures for quantifying the emergence of ensuing optical helicity, exhibiting different forms of dependence on the properties of the emitter and the positioning of a detector. By casting each measure in terms of an irreducible helicity density, connections and distinctions can be drawn between results expressible in either classical or quantum form
Ground-based detectors in very-high-energy gamma-ray astronomy
Following the discovery of the cosmic rays by Victor Hess in 1912, more than
70 years and numerous technological developments were needed before an
unambiguous detection of the first very-high-energy gamma-ray source in 1989
was made. Since this discovery the field on very-high-energy gamma-ray
astronomy experienced a true revolution: A second, then a third generation of
instruments were built, observing the atmospheric cascades from the ground,
either through the atmospheric Cherenkov light they comprise, or via the direct
detection of the charged particles they carry. Present arrays, 100 times more
sensitive than the pioneering experiments, have detected a large number of
astrophysical sources of various types, thus opening a new window on the
non-thermal Universe. New, even more sensitive instruments are currently being
built; these will allow us to explore further this fascinating domain. In this
article we describe the detection techniques, the history of the field and the
prospects for the future of ground-based very-high-energy gamma-ray astronomy.Comment: 21 pages, 13 figure
Time domain analysis of switching transient fields in high voltage substations
Switching operations of circuit breakers and disconnect switches generate transient currents propagating along the substation busbars. At the moment of switching, the busbars temporarily acts as antennae radiating transient electromagnetic fields within the substations. The radiated fields may interfere and disrupt normal operations of electronic equipment used within the substation for measurement, control and communication purposes. Hence there is the need to fully characterise the substation electromagnetic environment as early as the design stage of substation planning and operation to ensure safe operations of the electronic equipment. This paper deals with the computation of transient electromagnetic fields due to switching within a high voltage air-insulated substation (AIS) using the finite difference time domain (FDTD) metho
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