306,056 research outputs found
El Camino de Santiago (observaciones sobre el mito del "Plus Ultra" en un cuento de Alejo Carpentier)
El relato histórico de Alejo Carpentier "El Camino de Santiago" narra la historia de un soldado español del siglo XVI, Juan, que emprende una peregrinación a Santiago de Compostela. A partir de Amberes, en el insurgente Flandes, pierde su camino y llega finalmente a Sevilla y América, donde su destino será cumplido. Mediante la vinculación de Amberes a Sevilla demuestra que ambas ciudades están conectadas -aunque en formas muy diferentes- con el mito del Plus ultra. Como es bien sabido, este lema adorna las armas de la corona castellana, pero sus orígenes se encuentran en el estado de Borgoñona del siglo XV. Santiago de Compostela simboliza el non "Plus ultra" del "finis terrae" en Galicia, el mito de "Plus ultra" llega desde Amberes a Sevilla y va a cruzar el Atlántico en el comienzo de una nueva edad, que no puede cerrarse más con los símbolos de las columnas de Hércules. El peregrino no muy suelto a su manera, La Vía Láctea, El Camino de Santiago, siempre lleva a uno de los muchos Santiagos en todo el mundo.Alejo Carpentier's historical tale El Camino de Santiago tells the story of the XVIth century spanish soldier Juan, who undertakes a pilgrimage to Santiago de Compostela. Starting from Antwerp in the insurgent Flanders he looses his way and finally comes to Sevilla and America, where his destiny will be fulfilled. By linking Antwerp to Sevilla he shows that both cities are connected -although in quite different ways- with the myth of the plus ultra. As is well known, this lema adorns the arms of the Castillan crown, but it's origins are to be found in the Burgundian state of the XVth century. If Santiago de Compostela symbolizes the non plus ultra of thefinis terrae in Galicia, the myth of the plus ultra is brought from Antwerp to Sevilla and it will cross the Atlantic at the beginng of a new age, which cannot be closed up anymore in the symbols of Her- cules' Columns. The pilgrim does not really loose his way. The Milky Way, El Camino de Santiago, will always lead him to one of the many Santiagos all over the world.notPeerReviewe
Quark-meson coupling model for finite nuclei
A Quark-Meson Coupling (QMC) model is extended to finite nuclei in the
relativistic mean-field or Hartree approximation. The ultra-relativistic quarks
are assumed to be bound in non-overlapping nucleon bags, and the interaction
between nucleons arises from a coupling of vector and scalar meson fields to
the quarks. We develop a perturbative scheme for treating the spatial
nonuniformity of the meson fields over the volume of the nucleon as well as the
nucleus. Results of calculations for spherical nuclei are given, based on a fit
to the equilibrium properties of nuclear matter. Several possible extensions of
the model are also considered.Comment: 33 pages REVTeX plus 2 postscript figure
Post-Newtonian equation for the energy levels of a Dirac particle in a static metric
We study first the Hamiltonian operator H corresponding to the Fock-Weyl
extension of the Dirac equation to gravitation. When searching for stationary
solutions to this equation, in a static metric, we show that just one invariant
Hermitian product appears natural. In the case of a space-isotropic metric, H
is Hermitian for that product. Then we investigate the asymptotic
post-Newtonian approximation of the stationary Schroedinger equation associated
with H, for a slow particle in a weak-field static metric. We rewrite the
expanded equations as one equation for a two-component spinor field. This
equation contains just the non-relativistic Schroedinger equation in the
gravity potential, plus correction terms. Those "correction" terms are of the
same order in the small parameter as the "main" terms, but are numerically
negligible in the case of ultra-cold neutrons in the Earth's gravity.Comment: 12pt LaTeX, 17 pages. v2: version accepted for publication in
Phys.Rev.D: comments on scalar product changed, using a recent paper;
discussion of PN expansions simplified (no change of units any more);
numerical estimates for ultra-cold neutrons in the Earth's gravit
Transverse Expansion and High Azimuthal Asymmetry at RHIC
Rapid 3+1D transverse plus Bjorken collective expansion in collisions
at ultra-relativistic energies is shown to reduce substantially the azimuthal
asymmetry resulting from jet quenching. While the azimuthal asymmetry in
non-central collisions, reported by STAR at
RHIC, can be accounted for by spatially anisotropic jet energy loss through a
1+1D expanding gluon plasma with , we show that if rapid
transverse collective expansion of the plasma is assumed, then the asymmetry
due to jet quenching may be reduced below the observed level. Possible
implications of this effect are discussed.Comment: Journal version: 1 figure added, references added. 6 pages, 4 figure
Ultra-wide-field retinal imaging in the management of non-infectious retinal vasculitis.
BACKGROUND: The purpose of this study is to describe and quantify the benefit of ultra-wide-field imaging and fluorescein angiography (FA) in the management of non-infectious retinal vasculitis. In this prospective observational cohort series, patients with non-infectious retinal vasculitis were evaluated and enrolled by four investigators from the Divisions of Retina and Ocular Immunology at the Wilmer Eye Institute. In each patient, disease activity and the need for management changes were assessed, based on clinical examination with or without standard (60°) imaging and then with the addition of ultra-wide-field pseudo-color scanning laser ophthalmoscope (SLO) images and FA using the Optos ultra-wide-field SLO (Optos Panoramic 200MA™, Optos PLC, Dunfermline, Scotland, UK). A standardized questionnaire was completed by each investigator at the time of the clinical evaluation.The primary outcome was the percentage of patients whose management was changed by clinical examination and standard FA, compared with clinical examination plus ultra-wide-field imaging. The secondary outcome was the percentage of patients whose disease was determined to be active based on each modality.
RESULTS: Seventy-one visits from 23 patients were reviewed and analyzed. Based on examination plus ultra-wide-field imaging and ultra-wide-field angiography, disease activity was detected in 48/71 (68%) compared with 32/71 (45%) based on examination and standard FA (P = 0.0095). Based on the clinical examination alone, the decision to alter management was made in 4 of 71 visits (6%), and an additional 3 of 71 (4%) based on simulated standard FA. The addition of ultra-wide-field SLO pseudo-color images altered management in an additional 10/71 visits (14%), and 36/71 (51%) with the addition of ultra-wide-field FA.
CONCLUSIONS: Ultra-wide-field fluorescein imaging and angiography can provide additional information that may be important and relevant in the management of retinal vasculitis
Acceleration and Particle Field Interactions of Cosmic Rays I: Formalism
The acceleration of ultra high energy cosmic rays is conjectured to occur
through various interactions with the electromagnetic fields in different
astrophysical objects, like magnetic matter clumps, besides the well-known
shock and stochastic Fermi mechanisms. It is apparent that the latter are not
depending on the particle's charge, quantitatively. Based on this model, a
considerable portion of the dynamics, that derives a charged particle parallel
to a magnetic field and under the influence of a force
, is assumed to be composed of an acceleration by a non-magnetic
force and a gyromotion along direction,
plus drifts in the direction of . The model and its
formalism are introduced. Various examples for drift motions and accelerating
forces are suggested. The formalism is given in a non-relativistic version.
Obviously, the translation into the relativistic version is standard. In a
forthcoming work, a quantitative estimation of the energy gained by charged
cosmic rays in various astrophysical objects will be evaluated.Comment: 9 pages, 2 EPS figure
TeV gamma rays and cosmic rays from the nucleus of M87, a mis-aligned BL Lac object
The unresolved nuclear region of M87 emits strong non-thermal emission from
radio to X-rays. Assuming this emission to originate in the pc scale jet
aligned at to the line of sight, we interpret this
emission in the context of the Synchrotron Proton Blazar (SPB) model. We find
the observed nuclear jet emission to be consistent with M87 being a mis-aligned
BL Lac Object and predict gamma-ray emission extending up to at least 100 GeV
at a level easily detectable by GLAST and MAGIC, and possibly by VERITAS
depending on whether it is high-frequency or low-frequency peaked. Predicted
neutrino emission is below the sensitivity of existing and planned neutrino
telescopes. Ultra-high energy neutrons produced in pion photoproduction
interactions decay into protons after escaping from the host galaxy. Because
energetic protons are deflected by the intergalactic magnetic field, the
protons from the decay of neutrons emitted in all directions, including along
the jet axis where the Doppler factor and hence emitted neutron energies are
higher, can contribute to the observed ultra-high energy cosmic rays. We
consider the propagation of these cosmic ray protons to Earth and conclude that
M87 could account for the observed flux if the extragalactic magnetic field
topology were favourable.Comment: 17 pages, 6 figures. 3 additional references plus minor changes,
acctepted for publication in Astroparticle Physic
Spectral Control via Multi-Species Effects in PW-Class Laser-Ion Acceleration
Laser-ion acceleration with ultra-short pulse, PW-class lasers is dominated
by non-thermal, intra-pulse plasma dynamics. The presence of multiple ion
species or multiple charge states in targets leads to characteristic
modulations and even mono-energetic features, depending on the choice of target
material. As spectral signatures of generated ion beams are frequently used to
characterize underlying acceleration mechanisms, thermal, multi-fluid
descriptions require a revision for predictive capabilities and control in
next-generation particle beam sources. We present an analytical model with
explicit inter-species interactions, supported by extensive ab initio
simulations. This enables us to derive important ensemble properties from the
spectral distribution resulting from those multi-species effects for arbitrary
mixtures. We further propose a potential experimental implementation with a
novel cryogenic target, delivering jets with variable mixtures of hydrogen and
deuterium. Free from contaminants and without strong influence of hardly
controllable processes such as ionization dynamics, this would allow a
systematic realization of our predictions for the multi-species effect.Comment: 4 pages plus appendix, 11 figures, paper submitted to a journal of
the American Physical Societ
Dynamics and Hadronization at intermediate transverse momentum at RHIC
The ultra-relativistic heavy-ion program at RHIC has shown that at
intermediate transverse momenta (-6 GeV) standard (independent)
parton fragmentation can neither describe the observed baryon-to-meson ratios
nor the empirical scaling of the hadronic elliptic flow () according to
the number of valence quarks. Both aspects find instead a natural explanation
in a coalescence plus fragmentation approach to hadronization. After a brief
review of the main results for light quarks, we focus on heavy quarks showing
that a combined fragmentation and quark-coalescence framework is relevant also
here. Moreover, within relativistic Langevin simulations we find evidence for
the importance of heavy-light resonances in the Quark-Gluon Plasma (QGP) to
explain the strong energy loss and collective flow of heavy-quark spectra as
inferred from non-photonic electron observables. Such heavy-light resonances
can pave the way to a unified understanding of the microscopic structure of the
QGP and its subsequent hadronization by coalescence.Comment: Proceedings of the International Workshop on QCD - Martina Franca
(Italy), June 2007. To be published in AIP. 6 pages, 6 figure
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