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Transient Physical Effects in Electron Beam Sintering
The extensive use of the electron beam in manufacturing processes like welding or perforating
revealed the high potentials for also using it for solid freeform fabrication. First approaches like
feeding wire into a melt pool have successfully shown the technical feasibility. Among other
features, the electron beam exhibits high scanning speed, high power output, and beam density.
While in laser-based machines the fabrication is working in a stable way, transient physical
effects in the electron beam process can be observed, which still restrict process stability. For
instance, a high power input of the electron beam can result in sudden scattering of the metal
powder. The authors have developed an electron beam freeform fabrication system and examined
the above mentioned effects. Thus, the paper provides methods in order to identify, isolate and
avoid these effects, and to finally realize a reproducible process.Mechanical Engineerin
Centaurus A as the Source of ultra-high energy cosmic rays?
We present numerical simulations for energy spectra and angular distributions
of nucleons above 10^{19} eV injected by the radio-galaxy Centaurus A at a
distance 3.4 Mpc and propagating in extra-galactic magnetic fields in the
sub-micro Gauss range. We show that field strengths B~0.3 micro Gauss, as
proposed by Farrar and Piran, cannot provide sufficient angular deflection to
explain the observational data. A magnetic field of intensity ~1 micro Gauss
could reproduce the observed large-scale isotropy and could marginally explain
the observed energy spectrum. However, it would not readily account for the
E=320 plusminus 93 EeV Fly's Eye event that was detected at an angle 136
degrees away from Cen-A. Such a strong magnetic field also saturates
observational upper limits from Faraday rotation observations and X-ray
bremsstrahlung emission from the ambient gas (assuming equipartition of
energy). This scenario may already be tested by improving magnetic field limits
with existing instruments. We also show that high energy cosmic ray experiments
now under construction will be able to detect the level of anisotropy predicted
by this scenario. We conclude that for magnetic fields B~0.1-0.5 micro Gauss,
considered as more reasonable for the local Supercluster environment, in all
likelihood at least a few sources within ~10 Mpc from the Earth should
contribute to the observed ultra high energy cosmic ray flux.Comment: 7 latex pages, 7 postscript figures included; for related numerical
simulations see also http://www.iap.fr/users/sigl/r2e.htm
Lepton fluxes from atmospheric charm revisited
We update predictions for lepton fluxes from the hadroproduction of charm
quarks in the scattering of primary cosmic rays with the Earth's atmosphere.
The calculation of charm-pair hadroproduction applies the latest results from
perturbative QCD through next-to-next-to-leading order and modern parton
distributions, together with estimates on various sources of uncertainties. Our
predictions for the lepton fluxes turn out to be compatible, within the
uncertainty band, with recent results in the literature. However, by taking
into account contributions neglected in previous works, our total uncertainties
are much larger. The predictions are crucial for the interpretation of results
from neutrino experiments like IceCube, when disentangling signals of neutrinos
of astrophysical origin from the atmospheric background.Comment: 40 pages, 24 figure
Constructing Dirac linear fermions in terms of non-linear Heisenberg spinors
We show that the massive (or massless) neutrinos can be described as special
states of Heisenberg nonlinear spinors. As a by-product of this decomposition a
particularly attractive consequence appears: the possibility of relating the
existence of only three species of mass-less neutrinos to such internal
non-linear structure. At the same time it allows the possibility that neutrino
oscillation can occurs even for massless neutrinos
Prompt neutrinos from atmospheric charm in the general-mass variable-flavor-number scheme
We present predictions for the prompt-neutrino flux arising from the decay of
charmed mesons and baryons produced by the interactions of high-energy cosmic
rays in the Earth's atmosphere, making use of a QCD approach on the basis of
the general-mass variable-flavor-number scheme for the description of charm
hadroproduction at NLO, complemented by a consistent set of fragmentation
functions. We compare the theoretical results to those already obtained by our
and other groups with different theoretical approaches. We provide comparisons
with the experimental results obtained by the IceCube Collaboration in two
different analyses and we discuss the implications for parton distribution
functions.Comment: 43 pages, 21 figures, updated version, to be published in JHE
Search for photons at the Pierre Auger Observatory
The Pierre Auger Observatory has a unique potential to search for ultra-high
energy photons (above ~1 EeV). First experimental limits on photons were
obtained during construction of the southern part of the Observatory.
Remarkably, already these limits have proven useful to falsify proposals about
the origin of cosmic rays, and to perform fundamental physics by constraining
Lorentz violation. A final discovery of photons at the upper end of the
electromagnetic spectrum is likely to impact various branches of physics and
astronomy.Comment: 5 pages, 5 figures. Presented at CRIS 2008, Malfa, Ital
Extremely high energy cosmic rays and the Auger Observatory
Over the last 30 years or so, a handful of events observed in ground-based
cosmic ray detectors seem to have opened a new window in the field of
high-energy astrophysics. These events have energies exceeding 5x10**19 eV (the
region of the so-called Greisen-Zatsepin-Kuzmin spectral cutoff); they seem to
come from no known astrophysical source; their chemical composition is mostly
unknown; no conventional accelerating mechanism is considered as being able to
explain their production and propagation to earth. Only a dedicated detector
can bring in the high-quality and statistically significant data needed to
solve this long-lasting puzzle: this is the aim of the Auger Observatory
project around which a world-wide collaboration is being mobilized.Comment: 14 pages, no figures, Latex, to be published in Proc. of the 7th Int.
Workshop on Neutrino Telescopes (Venice 27/2-1/3 1996
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