1,721,006 research outputs found
Cosmic ray bound for models of extragalactic neutrino production
No full textWe obtain the maximum diffuse neutrino intensity predicted by hadronic photoproduction models of the type which have been applied to the jets of active galactic nuclei dr gamma ray bursts. For this, we compare the proton and gamma ray fluxes associated with hadronic photoproduction in extragalactic neutrino sources with the present experimental upper limit on cosmic ray protons and the extragalactic gamma ray background, employing a transport calculation of energetic protons traversing cosmic photon backgrounds. We take into account the effects of the photon spectral shape in the sources on the photoproduction process, cosmological source evolution, the optical depth for cosmic ray ejection, and discuss the possible effects of magnetic fields in the vicinity of the sources. For photohadronic neutrino sources which are optically thin to the emission of neutrons we find that the cosmic ray flux imposes a stronger bound than the extragalactic gamma ray background in the energy range between 10(5) GeV and 10(11) GeV, as previously noted by Waxman and Bahcall [Phys. Rev. D 59, 023002 (1999)]. We also determine the maximum contribution from the jets of active galactic nuclei, using constraints set to their neutron opacity by gamma ray observations. This present upper limit is consistent with the jets of active galactic nuclei producing the extragalactic gamma ray background hadronically, but we point out future observations in the GeV-to-TeV regime could lower this limit. We also briefly discuss the contribution of gamma ray bursts to ultrahigh-energy cosmic rays as it can be inferred from possible observations or limits on their correlated neutrino fluxes
Cosmic ray bound for models of extragalactic neutrino production
No full textWe obtain the maximum diffuse neutrino intensity predicted by hadronic photoproduction models of the type which have been applied to the jets of active galactic nuclei dr gamma ray bursts. For this, we compare the proton and gamma ray fluxes associated with hadronic photoproduction in extragalactic neutrino sources with the present experimental upper limit on cosmic ray protons and the extragalactic gamma ray background, employing a transport calculation of energetic protons traversing cosmic photon backgrounds. We take into account the effects of the photon spectral shape in the sources on the photoproduction process, cosmological source evolution, the optical depth for cosmic ray ejection, and discuss the possible effects of magnetic fields in the vicinity of the sources. For photohadronic neutrino sources which are optically thin to the emission of neutrons we find that the cosmic ray flux imposes a stronger bound than the extragalactic gamma ray background in the energy range between 10(5) GeV and 10(11) GeV, as previously noted by Waxman and Bahcall [Phys. Rev. D 59, 023002 (1999)]. We also determine the maximum contribution from the jets of active galactic nuclei, using constraints set to their neutron opacity by gamma ray observations. This present upper limit is consistent with the jets of active galactic nuclei producing the extragalactic gamma ray background hadronically, but we point out future observations in the GeV-to-TeV regime could lower this limit. We also briefly discuss the contribution of gamma ray bursts to ultrahigh-energy cosmic rays as it can be inferred from possible observations or limits on their correlated neutrino fluxes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Coded-Aperture Timing Measurements of the Crab Pulsar and A0535+26
Full text linkWe report timing observations of the Crab Pulsar and A0535+26 made with the
Caltech imaging gamma-ray telescope, a coded-aperture instrument which
operates in the energy range 30 keV - 10 MeV. Observations of the Crab region
were made in five separate balloon flights during the period H>86-rn89. A0535+26
was detected in its outburst phase during the fifth observation in 1989 April. The
use of coded-aperture instruments for timing and the statistics of the timing
measurements will also be discussed
Cosmic Ray Source Abundances Derived from High Energy Measurements of Fe-Group Nuclei
Full text linkWe examine the cosmic ray source composition of elements from Ar to Ni (18≤ Z≤28) using
data from ~0.l to ~200 GeV /nuc and a cosmic ray propagation code that includes
improved fragmentation cross-sections. By fitting available satellite data over more than
three decades in energy /nuc, including recent HEA0-3 data, we obtain improved source
abundances for Ar, Ca, Cr, Mn, and Ni, and compare these with recent determinations of
the solar composition. We find no evidence for an energy-dependent source composition
below ~20 GeV/nuc, but the data at higher energies deserve further study
Global Representation of the Cross Sections for the Production of Fragments of UH Nuclei
Full text linkWe have examined the fragmentation of relativistic iron, lanthanum, holmium and gold
nuclei with energies between 500 and 1200 MeV/n incident on targets of polyethylene, carbon,
aluminum, copper and lead. We have determined 1,256 elemental partial cross sections for the
production of fragments from interactions in pure target materials. Deduced values have been
found for another 417 cross sections in a hydrogen medium. The dependencies of these cross
sections on energy, mass and charge have been studied. We have generated a seven parameter
global fit to the cross sections for the heavy targets which fits a significant range of the data with
a standard deviation of 7%. We have also generated a similar global fit to the cross sections for
the hydrogen target which fits a slightly smaller range of the data with a standard deviation of
10%. These representations show that weak factorization can apply, but slightly better fits can
be obtained without it. The mean mass losses observed for fragments that have lost a few
protons, show that typically three or more neutrons are lost with each proton, producing
fragment nuclei that must be highly proton rich, and consequently very unstabl
Response of Ionization Chambers and Cherenkov Counters to Relativistic Ultraheavy Nuclei
Full text linkWe have exposed a detector, similar to the one used on the HEAO Heavy
Nuclei Experiment {Binns, et al., 1981) to beams of _(26)Fe, _(57)La, _(61)Ho and
_(79)Au at the LBL Bevalac. We will report on the deviations from z2
scaling for the signals in the ion chambers and the Cherenkov counters
as a function of energy and Z. These deviations are definitely small and
imply an error of less than one charge unit in the charge
determinations used in the Heavy Nuclei Experiment (Binns, et al.,
1989)
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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