3,134 research outputs found
The Puzzling Frequencies of CEMP and NEMP Stars
We present the results of binary population simulations of carbon- and
nitrogen-enhanced metal-poor (CEMP and NEMP) stars. We show that the observed
paucity of very nitrogen-rich stars puts strong constraints on possible
modifications of the initial mass function at low metallicity.Comment: 3 pages, contribution to "The Origin of the Elements Heavier than
Iron" in honor of the 70th birthday of Roberto Gallino, Torino, Italy,
September 200
Uniformity in association schemes and coherent configurations: cometric Q-antipodal schemes and linked systems
Inspired by some intriguing examples, we study uniform association schemes
and uniform coherent configurations, including cometric Q-antipodal association
schemes. After a review of imprimitivity, we show that an imprimitive
association scheme is uniform if and only if it is dismantlable, and we cast
these schemes in the broader context of certain --- uniform --- coherent
configurations. We also give a third characterization of uniform schemes in
terms of the Krein parameters, and derive information on the primitive
idempotents of such a scheme. In the second half of the paper, we apply these
results to cometric association schemes. We show that each such scheme is
uniform if and only if it is Q-antipodal, and derive results on the parameters
of the subschemes and dismantled schemes of cometric Q-antipodal schemes. We
revisit the correspondence between uniform indecomposable three-class schemes
and linked systems of symmetric designs, and show that these are cometric
Q-antipodal. We obtain a characterization of cometric Q-antipodal four-class
schemes in terms of only a few parameters, and show that any strongly regular
graph with a ("non-exceptional") strongly regular decomposition gives rise to
such a scheme. Hemisystems in generalized quadrangles provide interesting
examples of such decompositions. We finish with a short discussion of
five-class schemes as well as a list of all feasible parameter sets for
cometric Q-antipodal four-class schemes with at most six fibres and fibre size
at most 2000, and describe the known examples. Most of these examples are
related to groups, codes, and geometries.Comment: 42 pages, 1 figure, 1 table. Published version, minor revisions,
April 201
A Novel Protocol-Authentication Algorithm Ruling Out a Man-in-the-Middle Attack in Quantum Cryptography
In this work we review the security vulnerability of Quantum Cryptography
with respect to "man-in-the-middle attacks" and the standard authentication
methods applied to counteract these attacks. We further propose a modified
authentication algorithm which features higher efficiency with respect to
consumption of mutual secret bits.Comment: 4 pages, submitted to the International Journal of Quantum
Information, Proceedings of the meeting "Foundations of Quantum Information",
Camerino, April 200
Practical Quantum Key Distribution with Polarization-Entangled Photons
We present an entangled-state quantum cryptography system that operated for
the first time in a real world application scenario. The full key generation
protocol was performed in real time between two distributed embedded hardware
devices, which were connected by 1.45 km of optical fiber, installed for this
experiment in the Vienna sewage system. The generated quantum key was
immediately handed over and used by a secure communication application.Comment: 5 pages, 3 figure
Extragalactic Planetary Nebulae: tracers of the chemical evolution of nearby galaxies
The study of the chemical composition of Planetary Nebulae in external
galaxies is of paramount importance in the fields of stellar evolution and of
the chemical enrichment history of galaxies. In the last years a number of
spectroscopic studies with 6-8m-class telescopes have been devoted to this
subject improving our knowledge of, among other, the time-evolution of the
radial metallicity gradient in disk galaxies, the chemical evolution of dwarf
galaxies, and the stellar evolution at low metallicity.Comment: 8 pages, 4 figures, Invited Review to IAU Symposium 283, "Planetary
Nebulae: an Eye to the Future", Tenerife, 25-29 July 201
Probing nuclear skins and halos with elastic electron scattering
I investigate the elastic electron scattering off nuclei far from the
stability line. The effects of the neutron and proton skins and halos on the
differential cross sections are explored. Examples are given for the charge
distribution in Sn isotopes and its relation to the neutron skin. The neutron
halo in Li and the proton halo in B are also investigated.
Particular interest is paid to the inverse scattering problem and its
dependence on the experimental precision. These studies are of particular
interest for the upcoming electron ion colliders at the GSI and RIKEN
facilities.Comment: 27 pages, 9 figures, accepted for publication in J. Phys.
The monitoring system for the aerogel Cherenkov counter of the BELLE detector
We report on a design and performances of a monitoring system developed for
the aerogel Cherenkov counters (ACC) of the BELLE detector. The system consists
of blue LEDs, a diffuser box, and optical distributors which distribute the LED
light to the ACC modules. The employed LED (NSPB series) has been observed to
have high reliability on the long term stability and the temprature dependence.
The diffuser box is employed to reduce the intrinsic non-uniformity of the LED
light intensity. The overall performances of the present monitoring system on
uniformity and intensity of the light output have been found to satisfy all the
requirements for the monitoring.Comment: 24 pages, LaTeX, 13 eps figures, to be published in Nucl. Instrum.
and Meth. A. Postscript file (4.5 MB) is available at
http://www-hep.phys.saga-u.ac.jp/~murakami/paper/xxx_accmon.p
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