651 research outputs found
A Measurement of the Cosmic Ray Spectrum and Composition at the Knee
The energy spectrum and primary composition of cosmic rays with energy
between and 3\times10^{16}\unit{eV} have been studied using
the CASA-BLANCA detector. CASA measured the charged particle distribution of
air showers, while BLANCA measured the lateral distribution of Cherenkov light.
The data are interpreted using the predictions of the CORSIKA air shower
simulation coupled with four different hadronic interaction codes.
The differential flux of cosmic rays measured by BLANCA exhibits a knee in
the range of 2--3 PeV with a width of approximately 0.5 decades in primary
energy. The power law indices of the differential flux below and above the knee
are and .
We present our data both as a mean depth of shower maximum and as a mean
nuclear mass. A multi-component fit using four elemental species shows the same
composition trends given by the mean quantities, and also indicates that QGSJET
and VENUS are the preferred hadronic interaction models. We find that an
initially mixed composition turns lighter between 1 and 3 PeV, and then becomes
heavier with increasing energy above 3 PeV.Comment: 25 pages, 10 figures. Submitted to Astroparticle Physic
Large Scale Magnetic Fields and the Number of Cosmic Ray Sources above 10^(19) eV
We present numerical simulations for the two-point correlation function and
the angular power spectrum of nucleons above 10^{19} injected by a discrete
distribution of sources following a simple approximation to the profile of the
Local Supercluster. We develop a method to constrain the number of sources
necessary to reproduce the observed sky distribution of ultra-high energy
cosmic rays, as a function of the strength of the large scale cosmic magnetic
fields in the Local Supercluster. While for fields B < 0.05 micro Gauss the
Supercluster source distribution is inconsistent with the data for any number
of sources, fields of strength B~0.3 micro Gauss could reproduce the observed
data with a number of sources around 10.Comment: 10 latex pages, 17 postscript figures include
Ultra-High Energy Cosmic Rays from Neutrino Emitting Acceleration Sources?
We demonstrate by numerical flux calculations that neutrino beams producing
the observed highest energy cosmic rays by weak interactions with the relic
neutrino background require a non-uniform distribution of sources. Such sources
have to accelerate protons at least up to 10^{23} eV, have to be opaque to
their primary protons, and should emit the secondary photons unavoidably
produced together with the neutrinos only in the sub-MeV region to avoid
conflict with the diffuse gamma-ray background measured by the EGRET
experiment. Even if such a source class exists, the resulting large
uncertainties in the parameters involved in this scenario does currently not
allow to extract any meaningful information on absolute neutrino masses.Comment: 6 pages, 4 figures, RevTeX styl
New onshore insights into the role of structural inheritance during Mesozoic opening of the Inner Moray Firth Basin, Scotland
The Inner Moray Firth Basin (IMFB) forms the western arm of the North Sea trilete rift system that initiated mainly during the Late Jurassic–Early Cretaceous with the widespread development of major NE–SW-trending dip-slip growth faults. The IMFB is superimposed over the southern part of the older Devonian Orcadian Basin. The potential influence of older rift-related faults on the kinematics of later Mesozoic basin opening has received little attention, partly owing to the poor resolution of offshore seismic reflection data at depth. New field observations augmented by drone photography and photogrammetry, coupled with U–Pb geochronology, have been used to explore the kinematic history of faulting in onshore exposures along the southern IMFB margin. Dip-slip north–south- to NNE–SSW-striking Devonian growth faults are recognized that have undergone later dextral reactivation during NNW–SSE extension. The U–Pb calcite dating of a sample from the synkinematic calcite veins associated with this later episode shows that the age of fault reactivation is 130.99  ±  4.60 Ma (Hauterivian). The recognition of dextral-oblique Early Cretaceous reactivation of faults related to the underlying and older Orcadian Basin highlights the importance of structural inheritance in controlling basin- to sub-basin-scale architectures and how this influences the kinematics of IMFB rifting
New onshore insights into the role of structural inheritance during Mesozoic opening of the Inner Moray Firth Basin, Scotland
The Inner Moray Firth Basin (IMFB) forms the western arm of the North Sea trilete rift system that initiated mainly during the Late Jurassic–Early Cretaceous with the widespread development of major NE–SW-trending dip-slip growth faults. The IMFB is superimposed over the southern part of the older Devonian Orcadian Basin. The potential influence of older rift-related faults on the kinematics of later Mesozoic basin opening has received little attention, partly owing to the poor resolution of offshore seismic reflection data at depth. New field observations augmented by drone photography and photogrammetry, coupled with U–Pb geochronology, have been used to explore the kinematic history of faulting in onshore exposures along the southern IMFB margin. Dip-slip north–south- to NNE–SSW-striking Devonian growth faults are recognized that have undergone later dextral reactivation during NNW–SSE extension. The U–Pb calcite dating of a sample from the synkinematic calcite veins associated with this later episode shows that the age of fault reactivation is 130.99  ±  4.60 Ma (Hauterivian). The recognition of dextral-oblique Early Cretaceous reactivation of faults related to the underlying and older Orcadian Basin highlights the importance of structural inheritance in controlling basin- to sub-basin-scale architectures and how this influences the kinematics of IMFB rifting
Ultra-High Energy Neutrino Fluxes and Their Constraints
Applying our recently developed propagation code we review extragalactic
neutrino fluxes above 10^{14} eV in various scenarios and how they are
constrained by current data. We specifically identify scenarios in which the
cosmogenic neutrino flux, produced by pion production of ultra high energy
cosmic rays outside their sources, is considerably higher than the
"Waxman-Bahcall bound". This is easy to achieve for sources with hard injection
spectra and luminosities that were higher in the past. Such fluxes would
significantly increase the chances to detect ultra-high energy neutrinos with
experiments currently under construction or in the proposal stage.Comment: 11 pages, 15 figures, version published in Phys.Rev.
Effects of a nanoscopic filler on the structure and dynamics of a simulated polymer melt and the relationship to ultra-thin films
We perform molecular dynamics simulations of an idealized polymer melt
surrounding a nanoscopic filler particle to probe the effects of a filler on
the local melt structure and dynamics. We show that the glass transition
temperature of the melt can be shifted to either higher or lower
temperatures by appropriately tuning the interactions between polymer and
filler. A gradual change of the polymer dynamics approaching the filler surface
causes the change in the glass transition. We also find that while the bulk
structure of the polymers changes little, the polymers close to the surface
tend to be elongated and flattened, independent of the type of interaction we
study. Consequently, the dynamics appear strongly influenced by the
interactions, while the melt structure is only altered by the geometric
constraints imposed by the presence of the filler. Our findings show a strong
similarity to those obtained for ultra-thin polymer films (thickness nm) suggesting that both ultra-thin films and filled-polymer systems might
be understood in the same context
Anisotropy at the end of the cosmic ray spectrum?
The starburst galaxies M82 and NGC253 have been proposed as the primary
sources of cosmic rays with energies above eV. For energies \agt
10^{20.3} eV the model predicts strong anisotropies. We calculate the
probabilities that the latter can be due to chance occurrence. For the highest
energy cosmic ray events in this energy region, we find that the observed
directionality has less than 1% probability of occurring due to random
fluctuations. Moreover, during the first 5 years of operation at Auger, the
observation of even half the predicted anisotropy has a probability of less
than to occur by chance fluctuation. Thus, this model can be subject
to test at very small cost to the Auger priors budget and, whatever the outcome
of that test, valuable information on the Galactic magnetic field will be
obtained.Comment: Final version to be published in Physical Review
The Saffman-Taylor problem on a sphere
The Saffman-Taylor problem addresses the morphological instability of an
interface separating two immiscible, viscous fluids when they move in a narrow
gap between two flat parallel plates (Hele-Shaw cell). In this work, we extend
the classic Saffman-Taylor situation, by considering the flow between two
curved, closely spaced, concentric spheres (spherical Hele-Shaw cell). We
derive the mode-coupling differential equation for the interface perturbation
amplitudes and study both linear and nonlinear flow regimes. The effect of the
spherical cell (positive) spatial curvature on the shape of the interfacial
patterns is investigated. We show that stability properties of the fluid-fluid
interface are sensitive to the curvature of the surface. In particular, it is
found that positive spatial curvature inhibits finger tip-splitting. Hele-Shaw
flow on weakly negative, curved surfaces is briefly discussed.Comment: 26 pages, 4 figures, RevTex, accepted for publication in Phys. Rev.
Extragalactic Sources for Ultra High Energy Cosmic Ray Nuclei
In this article we examine the hypothesis that the highest energy cosmic rays
are complex nuclei from extragalactic sources. Under reasonable physical
assumptions, we show that the nearby metally rich starburst galaxies (M82 and
NGC 253) can produce all the events observed above the ankle. This requires
diffusion of particles below eV in extragalactic magnetic fields nG. Above eV, the model predicts the presence of
significant fluxes of medium mass and heavy nuclei with small rate of change of
composition. Notwithstanding, the most salient feature of the
starburst-hypothesis is a slight anisotropy induced by iron debris just before
the spectrum-cutoff.Comment: To appear in Phys. Rev. D, reference adde
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