20,655 research outputs found
Critical Analysis of Non-Nuclear Electron-Density Maxima and the Maximum Entropy Method
Experimental evidence for the existence of non-nuclear maxima in charge densities is questioned. It is shown that the non-nuclear maxima reported for silicon are artifacts of the maximum entropy method that was used to analyze the x-ray diffraction data. This method can be improved by the use of appropriate prior information. We report systematic tests of the improved method leading to the absence of non-nuclear maxima in Si. Likewise, the non-nuclear maxima reported earlier in beryllium are not substantiated.\ud
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The air shower maximum probed by Cherenkov effects from radio emission
Radio detection of cosmic-ray-induced air showers has come to a flight the
last decade. Along with the experimental efforts, several theoretical models
were developed. The main radio-emission mechanisms are established to be the
geomagnetic emission due to deflection of electrons and positrons in Earth's
magnetic field and the charge-excess emission due to a net electron excess in
the air shower front. It was only recently shown that Cherenkov effects play an
important role in the radio emission from air showers. In this article we show
the importance of these effects to extract quantitatively the position of the
shower maximum from the radio signal, which is a sensitive measure for the mass
of the initial cosmic ray. We also show that the relative magnitude of the
charge-excess and geomagnetic emission changes considerably at small observer
distances where Cherenkov effects apply
On the feasibility of RADAR detection of high-energy neutrino-induced showers in ice
In this article we try to answer the question whether the radar detection
technique can be used for the detection of high-energy-neutrino induced
particle cascades in ice. A high-energy neutrino interacting in ice will induce
a particle cascade, also referred to as a particle shower, moving at
approximately the speed of light. Passing through, the cascade will ionize the
medium, leaving behind a plasma tube. The different properties of the
plasma-tube, such as its lifetime, size and the charge-density will be used to
obtain an estimate if it is possible to detect this tube by means of the radar
detection technique. Next to the ionization electrons a second plasma due to
mobile protons induced by the particle cascade is discussed. An energy
threshold for the cascade inducing particle of 4 PeV for the electron plasma,
and 20 PeV for the proton plasma is obtained. This allows the radar detection
technique, if successful, to cover the energy-gap between several PeV and a few
EeV in the currently operating neutrino detectors, where on the low side
IceCube runs out of events, and on the high side the Askaryan radio detectors
begin to have large effective volumes
Massive galaxies with very young AGN
Gigahertz Peaked Spectrum (GPS) radio galaxies are generally thought to be
the young counterparts of classical extended radio sources and live in massive
ellipticals. GPS sources are vital for studying the early evolution of
radio-loud AGN, the trigger of their nuclear activity, and the importance of
feedback in galaxy evolution. We study the Parkes half-Jansky sample of GPS
radio galaxies of which now all host galaxies have been identified and 80% has
their redshifts determined (0.122 < z < 1.539). Analysis of the absolute
magnitudes of the GPS host galaxies show that at z > 1 they are on average a
magnitude fainter than classical 3C radio galaxies. This suggests that the AGN
in young radio galaxies have not yet much influenced the overall properties of
the host galaxy. However their restframe UV luminosities indicate that there is
a low level of excess as compared to passive evolution models.Comment: To appear in the proceedings of "Formation and Evolution of Galaxy
Bulges", IAUS 245; M. Bureau, E. Athanassoula & B. Barbuy, ed
Free radical formation during machining and fracture of polymers
Electron paramagnetic resonance measurements of free radical formation during cutting and grinding of polymer
Monte Carlo calculations of energy depositions and radiation transport. Volume 1 - Validation of COHORT codes
Monte Carlo codes for IBM 7090 digital computer to calculate radiation heating in propellant tanks, and radiation environment about nuclear rocket stag
Constraints and prospects on gravitational wave and neutrino emission using GW150914
The recent LIGO observation of gravitational waves from a binary black hole
merger triggered several follow-up searches from both electromagnetic wave as
well as neutrino observatories. Since in general, it is expected that all
matter has been removed from the binary black hole environment long before the
merger, no neutrino emission is expected from such mergers. Still, it remains
interesting to test this hypothesis. The ratio of the energy emitted in
neutrinos with respect to gravitational waves represents a useful parameter to
constrain the environment of such astrophysical events. In addition to putting
constraints by use of the non-detection of counterpart neutrinos, it is also
possible to consider the diffuse neutrino flux measured by the IceCube
observatory as the maximum contribution from an extrapolated full class of
BBHs. Both methods currently lead to similar bounds on the fraction of energy
that can be emitted in neutrinos. Nevertheless, combining both methods should
allow to strongly constrain the source population in case of a future neutrino
counterpart detection. The proposed approach can and will be applied to
potential upcoming LIGO events, including binary neutron stars and black
hole-neutron star mergers, for which a neutrino counterpart is expected.Comment: 8 pages, 2 figures. In Proceedings of the 35th International Cosmic
Ray Conference (ICRC2017), Busan, Kore
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