647 research outputs found
Why charges go to the surface: a generalized Thomson problem
We study a generalization of a Thomson problem of n particles confined to a
sphere and interacting by a 1/r^g potential. It is found that for g \le 1 the
electrostatic repulsion expels all the charges to the surface of the sphere.
However for g>1 and n>n_c(g) occupation of the bulk becomes energetically
favorable. It is curious to note that the Coulomb law lies exactly on the
interface between these two regimes
On a possible photon origin of the most-energetic AGASA events
In this work the ultra high energy cosmic ray events recorded by the AGASA
experiment are analysed. With detailed simulations of the extensive air showers
initiated by photons, the probabilities are determined of the photonic origin
of the 6 AGASA events for which the muon densities were measured and the
reconstructed energies exceeded 10^20 eV. On this basis a new, preliminary
upper limit on the photon fraction in cosmic rays above 10^20 eV is derived and
compared to the predictions of exemplary top-down cosmic-ray origin models.Comment: 3 pages, 1 figure, 2 tables; presented at XIII ISVHECRI, Pylos,
Greec
Leptospiroses et lésions oculaires chez le Chien
Rossi Paul, Kolochine-Erber B., Berujon J. Leptospiroses et lésions oculaires chez le Chien. In: Bulletin de l'Académie Vétérinaire de France tome 106 n°8, 1953. pp. 451-455
Plasma Magnetosphere Formation Around Oscillating Magnetized Neutron Stars
The notion of death line of rotating pulsars is applied to model of
oscillating neutron stars. It is shown that the magnetosphere of typical
non-rotating oscillating stars may not contain secondary plasma to support the
generation of radio emission in the region of open field lines of plasma
magnetosphere.Comment: Accepted for publication in Astrophysics & Space Scienc
Simulation of Ultra-High Energy Photon Propagation in the Geomagnetic Field
The identification of primary photons or specifying stringent limits on the
photon flux is of major importance for understanding the origin of ultra-high
energy (UHE) cosmic rays. We present a new Monte Carlo program allowing
detailed studies of conversion and cascading of UHE photons in the geomagnetic
field. The program named PRESHOWER can be used both as an independent tool or
together with a shower simulation code. With the stand-alone version of the
code it is possible to investigate various properties of the particle cascade
induced by UHE photons interacting in the Earth's magnetic field before
entering the Earth's atmosphere. Combining this program with an extensive air
shower simulation code such as CORSIKA offers the possibility of investigating
signatures of photon-initiated showers. In particular, features can be studied
that help to discern such showers from the ones induced by hadrons. As an
illustration, calculations for the conditions of the southern part of the
Pierre Auger Observatory are presented.Comment: 41 pages, 9 figures, added references in introduction, corrected
energy in row 1 of Table 3, extended caption of Table
Crystalline Order on a Sphere and the Generalized Thomson Problem
We attack generalized Thomson problems with a continuum formalism which
exploits a universal long range interaction between defects depending on the
Young modulus of the underlying lattice. Our predictions for the ground state
energy agree with simulations of long range power law interactions of the form
1/r^{gamma} (0 < gamma < 2) to four significant digits. The regime of grain
boundaries is studied in the context of tilted crystalline order and the
generality of our approach is illustrated with new results for square tilings
on the sphere.Comment: 4 pages, 5 eps figures Fig. 2 revised, improved Fig. 3, reference
typo fixe
Dysregulation of the intrinsic apoptotic pathway mediates megakaryocytic hyperplasia in myeloproliferative neoplasms
published_or_final_versio
Characteristics of geomagnetic cascading of ultra-high energy photons at the southern and northern sites of the Pierre Auger Observatory
Cosmic-ray photons above 10^19 eV can convert in the geomagnetic field and
initiate a preshower, i.e. a particle cascade before entering the atmosphere.
We compare the preshower characteristics at the southern and northern sites of
the Pierre Auger Observatory. In addition to a shift of the preshower patterns
on the sky due to the different pointing of the local magnetic field vectors,
the fact that the northern Auger site is closer to the geomagnetic pole results
in a different energy dependence of the preshower effect: photon conversion can
start at smaller energies, but large conversion probabilitites (>90%) are
reached for the whole sky at higher energies compared to the southern Auger
site. We show how the complementary preshower features at the two sites can be
used to search for ultra-high energy photons among cosmic rays. In particular,
the different preshower characteristics at the northern Auger site may provide
an elegant and unambiguous confirmation if a photon signal is detected at the
southern site.Comment: 25 pages, 14 figures, minor changes, conclusions unchanged, Appendix
A replaced, accepted by Astroparticle Physic
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