329,091 research outputs found
Impact of anisotropy and fracture density on the approximation of the effective permeability of a fractured rock mass using 2D models
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Radio measurements of the energy and the depth of the shower maximum of cosmic-ray air showers by Tunka-Rex
We reconstructed the energy and the position of the shower maximum of air
showers with energies PeV applying a method using radio
measurements performed with Tunka-Rex. An event-to-event comparison to
air-Cherenkov measurements of the same air showers with the Tunka-133
photomultiplier array confirms that the radio reconstruction works reliably.
The Tunka-Rex reconstruction methods and absolute scales have been tuned on
CoREAS simulations and yield energy and values consistent
with the Tunka-133 measurements. The results of two independent measurement
seasons agree within statistical uncertainties, which gives additional
confidence in the radio reconstruction. The energy precision of Tunka-Rex is
comparable to the Tunka-133 precision of , and exhibits a
uncertainty on the absolute scale dominated by the amplitude calibration of the
antennas. For , this is the first direct experimental
correlation of radio measurements with a different, established method. At the
moment, the resolution of Tunka-Rex is approximately g/cm. This resolution can probably be improved by deploying additional
antennas and by further development of the reconstruction methods, since the
present analysis does not yet reveal any principle limitations.Comment: accepted for publication by JCA
Transverse gradients of azimuthal velocity in a global disk model of the Milky Way
In this paper, we aim to estimate the vertical gradients in the rotational
velocity of the Galaxy. This is carried out in the framework of a global thin
disc model approximation. The predicted gradient values coincide with the
observed vertical fall-off in the rotation curve of the Galaxy. The gradient is
estimated based on a statistical analysis of trajectories of test bodies in the
gravitational field of the disc and in an analytical way using a quasi-circular
orbit approximation. The agreement of the results with the gradient
measurements is remarkable in view of other more complicated, non-gravitational
mechanisms used for explaining the observed gradient values. Finally, we find
that models with a significant spheroidal component give worse vertical
gradient estimates than the simple disc model. In view of these results, we can
surmise that, apart from the central spherical bulge and Galactic halo, the
gross mass distribution in the Galaxy forms a flattened rather than spheroidal
figure.Comment: 11 pages, 18 figures, in v2 added explicit gradient calculation at
z<0.1kpc, reorganized/extended intro and summary, in v3 language correction
Characterizing the contaminating distance distribution for Bayesian supernova cosmology
Measurements of the equation of state of dark energy from surveys of
thousands of Type Ia Supernovae (SNe Ia) will be limited by spectroscopic
follow-up and must therefore rely on photometric identification, increasing the
chance that the sample is contaminated by Core Collapse Supernovae (CC SNe).
Bayesian methods for supernova cosmology can remove contamination bias while
maintaining high statistical precision but are sensitive to the choice of
parameterization of the contaminating distance distribution. We use simulations
to investigate the form of the contaminating distribution and its dependence on
the absolute magnitudes, light curve shapes, colors, extinction, and redshifts
of core collapse supernovae. We find that the CC luminosity function dominates
the distance distribution function, but its shape is increasingly distorted as
the redshift increases and more CC SNe fall below the survey magnitude limit.
The shapes and colors of the CC light curves generally shift the distance
distribution, and their effect on the CC distances is correlated. We compare
the simulated distances to the first year results of the SDSS-II SN survey and
find that the SDSS distance distributions can be reproduced with simulated CC
SNe that are ~1 mag fainter than the standard Richardson et al. (2002)
luminosity functions, which do not produce a good fit. To exploit the full
power of the Bayesian parameter estimation method, parameterization of the
contaminating distribution should be guided by the current knowledge of the CC
luminosity functions, coupled with the effects of the survey selection and
magnitude-limit, and allow for systematic shifts caused by the parameters of
the distance fit.Comment: 17 pages, 5 figures; accepted for publication in the Astrophysical
Journa
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