1,516 research outputs found
The antinucleon-nucleon quasi-bound states: J/psi and atomic evidence
The measurements of J/psi decays into photon, proton and antiproton show a
strong enhancement at the proton-antiproton threshold not seen in the decays
into neutral pion, proton and antiproton. What is the nature of this
enhancement? A natural interpretation can be performed in terms of a classical
model of nucleon-antinucleon interactions based on G-parity transformation. The
observed proton-antiproton structure is the consequence of the strong
attraction in the singlet S-wave state related predominantly to pion exchanges.
Similar attractions generate near threshold: an isospin-zero virtual (or
quasi-bound) state in singlet S-wave, an isospin-one quasi-bound state in
triplet P-wave with total angular momentum one and an isospin-zero resonance in
triplet P-wave with total angular momentum zero. These P-wave structures find
support in the antiproton-atomic data.Comment: 7 pages, 3 eps figures. Invited talk (S. Wycech) to the International
Conference on Low Energy Antiproton Physics (LEAP05), May 16-22, 2005,
Bonn-Juelich, Germany, to appear in AIP series of conference proceeding
Antiproton-Proton Channels in J/psi Decays
The recent measurements by the BES Collaboration of J/psi decays into a
photon and a proton-antiproton pair indicate a strong enhancement at the
proton-antiproton threshold not observed in the decays into a neutral pion and
a proton-antiproton pair. Is this enhancement due to a proton-antiproton
quasi-bound state or a baryonium? A natural explanation follows from a
traditional model of proton-antiproton interactions based on G-parity
transformation. The observed proton-antiproton structure is due to a strong
attraction in the 1S0 state, and possibly to a near-threshold quasi-bound state
in the 11S0 wave.Comment: 6 pages, 5 figures. The antiproton-proton pair being in isospin one
in the J/Psi decay into neutral pion-antiproton-proton, the antiproton-proton
1P1 and 3S1 waves have been replaced by the 31P1 and 33S1 ones and Figs. 1
and 2 have been replaced accordingly. Conclusions are unchanged. Most of the
content of the paper is published in Phys. Rev. C72, 011001 (2005
On the structure of the X(1835) baryonium
The measurement by the BES collaboration of J/psi -> gamma p pbar decays
indicates an enhancement at the p-pbar threshold. In another experiment BES
finds a peak in the invariant mass of pi-mesons produced in the possibly
related decay J/psi -> gamma pi+ pi- eta'. Using a semi-phenomenological
potential model which describes all the N-Nbar scattering data, we show that
the explanation of both effects may be given by a broad quasi-bound state in
the spin and isospin singlet S wave. The structure of the observed peak is due
to an interference of this quasi-bound state with a background amplitude and
depends on the annihilation mechanism.Comment: 7 pages, 7 figures, this version corresponds to the published paper
in Phys. Rev. C: minor corrections done and in section 5 suggestions of
experiments to confirm the link of the X(1835) to the antiproton-proton
syste
Incentive Mechanisms for Internet Congestion Management: Fixed-Budget Rebate versus Time-of-Day Pricing
Mobile data traffic has been steadily rising in the past years. This has
generated a significant interest in the deployment of incentive mechanisms to
reduce peak-time congestion. Typically, the design of these mechanisms requires
information about user demand and sensitivity to prices. Such information is
naturally imperfect. In this paper, we propose a \emph{fixed-budget rebate
mechanism} that gives each user a reward proportional to his percentage
contribution to the aggregate reduction in peak time demand. For comparison, we
also study a time-of-day pricing mechanism that gives each user a fixed reward
per unit reduction of his peak-time demand. To evaluate the two mechanisms, we
introduce a game-theoretic model that captures the \emph{public good} nature of
decongestion. For each mechanism, we demonstrate that the socially optimal
level of decongestion is achievable for a specific choice of the mechanism's
parameter. We then investigate how imperfect information about user demand
affects the mechanisms' effectiveness. From our results, the fixed-budget
rebate pricing is more robust when the users' sensitivity to congestion is
"sufficiently" convex. This feature of the fixed-budget rebate mechanism is
attractive for many situations of interest and is driven by its closed-loop
property, i.e., the unit reward decreases as the peak-time demand decreases.Comment: To appear in IEEE/ACM Transactions on Networkin
Radio and X-ray study of two multi-shell Supernova Remnants: Kes79 and G352.7-0.1
We investigate two multi-shell galactic supernova remnants (SNRs), Kes79 and
G352.7-0.1, to understand the causes of such morphology. The research was
carried out based on new and reprocessed archival VLA observations and
XMM-Newton archival data. The surrounding was investigated based on data
extracted from the HI Canadian Galactic Plane Survey, the 13^CO Galactic Ring
Survey and the HI Southern Galactic Plane Survey. The present study revealed
that the overall morphology of both SNRs is the result of the mass-loss history
of their respective progenitor stars. Kes79 would be the product of the
gravitational collapse of a massive O9 star evolving near a molecular cloud and
within the precursor's wind-driven bubble, while G352.7-0.1 would be the result
of interactions of the SNR with an asymmetric wind from the progenitor together
with projection effects. No radio point source or pulsar wind nebula was found
associated with the X-ray pulsar CXOU J185238.6+004020 in Kes79. The X-ray
study of G352.7-0.1, on its hand, revealed that most of the thermal X-ray
radiation completely fills in the interior of the remnant and originates in
heated ejecta. Characteristic parameters, like radio flux, radio spectral
index, age, distance, shock velocity, initial energy and luminosity, were
estimated for both SNRs.Comment: 14 pages, 13 figures. Accepted to be published in Astronomy and
Astrophysic
Modélisation, classification et propagation dans des réseaux d'influence
The cognitive map model provides a user a solution to visualize the influences between different notion, and to compute the propagation of influences on a target. Like cognitive maps, our model offers a graphical representation of influences between notions. The distinctive feature of our model is that on a unique support, each notion is precisely defined by conceptual graphs. The combination of operations of cognitive maps and operations of conceptual graphs provides a powerful method to make decision. Firstly, the definition of a notion and the projection provides a solution to compute semantically linked notions. Secondly, original propagations can be computed from such semantically linked notions
The physical interest in kaonic- and antiprotonic-deuterium atoms
Exotic deuterium and helium are discussed. The S, P and D levels of
antiprotonic and kaonic atoms are calculated. Absorptive, subthreshold
antiproton-nucleon amplitudes are extracted from experimental data and compared
to model calculations. The existence of a quasi-bound state in the
antiproton-nucleon system is indicated. In the kaonic atoms some effects of the
Sigma(1385) resonance are evaluated.Comment: 7 pages, 1 eps figure. Invited talk (S. Wycech) to the International
conference on Exotic Atoms, February 21-25, 2005, Vienna, Austria, to appear
in proceedings "Verlag der oesterreichischen Akademie der Wisssenschaften
Un tour d'horizon des approches pour la manipulation des données du web
Le passage au web 2.0 a renforcé le principe selon lequel les données doivent être séparées de leurs présentations. En même temps, le nombre des formats de documents XML a largement évolué sur le web. Les bases de données sont également utilisées pour le fonctionnement des sites. Ces constats impliquent la mise en œuvre d’approches et d’outils associés dédiés à la manipulation des données du web. Certaines de ces approches travaillent directement sur les données, tandis que d’autres se basent sur les schémas de ces mêmes données. L’ingénierie dirigée par les modèles (IDM) forme également une approche candidate à la manipulation des données du web. Dans cet article, nous présentons et comparons les différentes techniques majeures de manipulation de données afin de mettre en exergue leurs avantages et leurs inconvénients pour le problème des données du web
The most complete and detailed X-ray view of the SNR Puppis A
With the purpose of producing the first detailed full view of Puppis A in
X-rays, we carried out new XMM-Newton observations covering the missing regions
in the southern half of the supernova remnant (SNR) and combined them with
existing XMM-Newton and Chandra data. The new images were produced in the
0.3-0.7, 0.7-1.0 and 1.0-8.0 energy bands. We investigated the SNR morphology
in detail, carried out a multi-wavelength analysis and estimated the flux
density and luminosity of the whole SNR. The complex structure observed across
the remnant confirms that Puppis A evolves in an inhomogeneous, probably knotty
interstellar medium. The southwestern corner includes filaments that perfectly
correlate with radio features suggested to be associated with shock/cloud
interaction. In the northern half of Puppis A the comparison with Spitzer
infrared images shows an excellent correspondence between X-rays and 24 and 70
microns emission features, while to the south there are some matched and other
unmatched features. X-ray flux densities of 12.6 X 10^-9, 6.2 X 10^-9, and 2.8
X 10^-9 erg cm^-2 s^-1 were derived for the 0.3-0.7, 0.7-1.0 and 1.0-8.0 keV
bands, respectively. At the assumed distance of 2.2 kpc, the total X-ray
luminosity between 0.3 and 8.0 keV is 1.2 X 10^37 erg s^-1. We also collected
and updated the broad-band data of Puppis A between radio and GeV gamma-ray
range, producing its spectral energy distribution. To provide constraints to
the high-energy emission models, we re-analyzed radio data, estimating the
energy content in accelerated particles to be Umin=4.8 X 10^49 erg and the
magnetic field strength B=26 muG.Comment: Article accepted to be published in the Astronomy and Astrophysics
Main Journa
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