21 research outputs found
Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory
Data from the Pierre Auger Observatory are analyzed to search for
anisotropies near the direction of the Galactic Centre at EeV energies. The
exposure of the surface array in this part of the sky is already significantly
larger than that of the fore-runner experiments. Our results do not support
previous findings of localized excesses in the AGASA and SUGAR data. We set an
upper bound on a point-like flux of cosmic rays arriving from the Galactic
Centre which excludes several scenarios predicting sources of EeV neutrons from
Sagittarius . Also the events detected simultaneously by the surface and
fluorescence detectors (the `hybrid' data set), which have better pointing
accuracy but are less numerous than those of the surface array alone, do not
show any significant localized excess from this direction.Comment: Matches published versio
An upper limit to the photon fraction in cosmic rays above 10^19 eV from the Pierre Auger Observatory
An upper limit of 16% (at 95% c.l.) is derived for the photon fraction in cosmic rays with energies above 10^19 eV, based on observations of the depth of shower maximum performed with the hybrid detector of the Pierre Auger Observatory. This is the first such limit on photons obtained by observing the fluorescence light profile of air showers. This upper limit confirms and improves on previous results from the Haverah Park and AGASA surface arrays. Additional data recorded with the Auger surface detectors for a subset of the event sample, support the conclusion that a photon origin of the observed events is not favoured
Upper limit on the cosmic-ray photon fraction at EeV energies from the Pierre Auger Observatory
From direct observations of the longitudinal development of ultra-high energy
air showers performed with the Pierre Auger Observatory, upper limits of 3.8%,
2.4%, 3.5% and 11.7% (at 95% c.l.) are obtained on the fraction of cosmic-ray
photons above 2, 3, 5 and 10 EeV (1 EeV = 10^18 eV) respectively. These are the
first experimental limits on ultra-high energy photons at energies below 10
EeV. The results complement previous constraints on top-down models from array
data and they reduce systematic uncertainties in the interpretation of shower
data in terms of primary flux, nuclear composition and proton-air
cross-section.Comment: 20 pages, 7 figures, 2 tables. Minor changes. Accepted by
Astroparticle Physic
Dinámica de defectos puntuales en un campo de tensión : Aplicaciones a metales hcp
El objetivo de este trabajo es estudiar la difusión anisotrópica de vacancias e intersticiales a dislocaciones de borde y cavidades esféricas, en un metal de estructura hexagonal compacta (hcp) sometido a tensiones y la potencia de cada uno de estos sumideros en el atrape de defectos puntuales. Entender la dinámica de los defectos puntuales en estos materiales permite predecir su comportamiento bajo irradiación. Se elige la estructura hcp debido a que ha sido poco estudiada en la literatura y, además, el zirconio y sus aleaciones, que tienen esta estructura, son utilizados como materiales para componentes de reactores nucleares por su baja sección eficaz de captura neutrónica. En este trabajo se calculan los perfiles de concentración de defectos alrededor de los sumideros, con un método numérico y un método analítico. Se analizan, también, las implicancias de considerar dos condiciones de contorno, que se representan por distribuciones periódicas o al azar de sumideros. Para preservar la continuidad en el desarrollo de cada tema se explicitan en los Apéndices los detalles de cálculo. También se incluyen, en los Apéndices, los cálculos de los perfiles de concentración de defectos puntuales alrededor de un cilindro hueco y de una esfera hueca, con la aproximación analítica, considerando difusividad isótropa.Facultad de Ciencias Exacta