2,216 research outputs found
New Analyses of Double-Bang Events in the Atmosphere
We use CORSIKA+Herwig simulation code to produce ultra-high energy neutrino
interactions in the atmosphere. Our aim is to reproduce extensive air showers
originated by extragalactic tau-neutrinos. For charged current tau-neutrino
interactions in the atmosphere, beside the air shower originated from the
neutrino interaction, it is expected that a tau is created and may decay before
reaching the ground. That phenomenon makes possible the generation of two
related extensive air showers, the so called Double-Bang event. We make an
analysis of the main characteristics of Double-Bang events in the atmosphere
for mean values of the parameters involved in such phenomenon, like the
inelasticity and tau decay length. We discuss what may happen for the ``out of
the average'' cases and conclude that it may be possible to observe this kind
of event in ultra-high energy cosmic ray observatories such as Pierre Auger or
Telescope Array.Comment: 17 pages, 5 figures, final version to appear in BJ
Ceramic composite bone tissue scaffolds
The repair of broken or diseased bone tissue requires a multitude of strategies ranging from allografts to bone substitutes. Herein we describe a process to create porous all-ceramic scaffolds for bone tissue repair without the need for typical ceramics processing techniques for consolidation (see Figure 1)—a technique that has potential to be used in situ in the operating theatre or in the field. The process uses room temperature and pressure to elicit a reaction within a liquid ceramic precursor to form a silicate-glass binder phase to consolidate bioactive glass frit (of the 45S5 composition). Morphological characterization and mechanical response of the composite scaffolds is reviewed paying credence to design specifications required in biomedical implant materials, such as: formability, structural integrity, porosity, load-bearing capability, bioactivity, and resorbability.
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Measuring cosmological bulk flows via the kinematic Sunyaev-Zeldovich effect in the upcoming cosmic microwave background maps
We propose a new method to measure the possible large-scale bulk flows in the
Universe from the cosmic microwave background (CMB) maps from the upcoming
missions, MAP and Planck. This can be done by studying the statistical
properties of the CMB temperature field at many X-ray cluster positions. At
each cluster position, the CMB temperature fluctuation will be a combination of
the Sunyaev-Zeldovich (SZ) kinematic and thermal components, the cosmological
fluctuations and the instrument noise term. When averaged over many such
clusters the last three will integrate down, whereas the first one will be
dominated by a possible bulk flow component. In particular, we propose to use
all-sky X-ray cluster catalogs that should (or could) be available soon from
X-ray satellites, and then to evaluate the dipole component of the CMB field at
the cluster positions. We show that for the MAP and Planck mission parameters
the dominant contributions to the dipole will be from the terms due to the SZ
kinematic effect produced by the bulk flow (the signal we seek) and the
instrument noise (the noise in our signal). Computing then the expected
signal-to-noise ratio for such measurement, we get that at the 95 % confidence
level the bulk flows on scales >100h^{-1} Mpc can be probed down to the
amplitude of km/sec with the MAP data and down to only 30 km/sec with
the Planck mission.Comment: Astrophysical Journal Letters, in pres
Analysis of Round Off Errors with Reversibility Test as a Dynamical Indicator
We compare the divergence of orbits and the reversibility error for discrete
time dynamical systems. These two quantities are used to explore the behavior
of the global error induced by round off in the computation of orbits. The
similarity of results found for any system we have analysed suggests the use of
the reversibility error, whose computation is straightforward since it does not
require the knowledge of the exact orbit, as a dynamical indicator. The
statistics of fluctuations induced by round off for an ensemble of initial
conditions has been compared with the results obtained in the case of random
perturbations. Significant differences are observed in the case of regular
orbits due to the correlations of round off error, whereas the results obtained
for the chaotic case are nearly the same. Both the reversibility error and the
orbit divergence computed for the same number of iterations on the whole phase
space provide an insight on the local dynamical properties with a detail
comparable with other dynamical indicators based on variational methods such as
the finite time maximum Lyapunov characteristic exponent, the mean exponential
growth factor of nearby orbits and the smaller alignment index. For 2D
symplectic maps the differentiation between regular and chaotic regions is well
full-filled. For 4D symplectic maps the structure of the resonance web as well
as the nearby weakly chaotic regions are accurately described.Comment: International Journal of Bifurcation and Chaos, 201
Does the galaxy correlation length increase with the sample depth?
We have analyzed the behavior of the correlation length, , as a function
of the sample depth by extracting from the CfA2 redshift survey volume--limited
samples out to increasing distances. For a fractal distribution, the value of
would increase with the volume occupied by the sample. We find no linear
increase for the CfA2 samples of the sort that would be expected if the
Universe preserved its small scale fractal character out to the distances
considered (60--100\hmpc). The results instead show a roughly constant value
for as a function of the size of the sample, with small fluctuations due
to local inhomogeneities and luminosity segregation. Thus the fractal picture
can safely be discarded.Comment: Accepted for publication in ApJ
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