469 research outputs found
Trapping of Spin-0 fields on tube-like topological defects
We have considered the localization of resonant bosonic states described by a
scalar field trapped in tube-like topological defects. The tubes are
formed by radial symmetric defects in dimensions, constructed with two
scalar fields and , and embedded in the dimensional
Minkowski spacetime. The general coupling between the topological defect and
the scalar field is given by the potential .
After a convenient decomposition of the field , we find that the
amplitudes of the radial modes satisfy Schr\"odinger-like equations whose
eigenvalues are the masses of the bosonic resonances. Specifically, we have
analyzed two simple couplings: the first one is for a
fourth-order potential and, the second one is a sixth-order interaction
characterized by % . In both cases the
Schr\"odinger-like equations are numerically solved with appropriated boundary
conditions. Several resonance peaks for both models are obtained and the
numerical analysis showed that the fourth-order potential generates more
resonances than the sixth-order one.Comment: 7 pages, 10 figures, matches version published in Physics Letters
Suppression of two-bounce windows in kink-antikink collisions
We consider a class of topological defects in -dimensions with a
deformed kink structure whose stability analysis leads to a
Schr\"odinger-like equation with a zero-mode and at least one vibrational
(shape) mode. We are interested in the dynamics of kink-antikink collisions,
focusing on the structure of two-bounce windows. For small deformation and for
one or two vibrational modes, the observed two-bounce windows are explained by
the standard mechanism of a resonant effect between the first vibrational and
the translational modes. With the increasing of the deformation, the effect of
the appearance of more than one vibrational mode is the gradual disappearance
of the initial two-bounce windows. The total suppression of two-bounce windows
even with the presence of a vibrational mode offers a counterexample from what
expected from the standard mechanism. For even larger deformation, some
two-bounce windows reappear, but with a non-standard structure.Comment: 13 pages, 6 figure
Ornithogenic soil toposequence on Rata island, Fernando de Noronha archipelago, south atlantic and quaternary paleoclimatic implications.
The formation of highly phosphatized soils on sites of avian activity is a common feature of oceanic islands. We characterized a toposequence of phosphatic soils on Rata Island, to evaluate the soil genesis based on local topographic variations. For this purpose, four soils ranging from the upper hill down to the lowest landscape position on the island, representing a range of parent materials (basalt and calcareous sands), were analyzed. In the lowest landscape position a shallow Entisol was identified, strongly influenced by birds and marine sprays (Litholic Neosol), developed on " karstified" Pleistocene calcarenites; the three other soils in the upper part of the toposequence are Ornithogenic Inceptsols (Cambisols), ranging from a deep Cambisol profile on Basalt lava to intermediate Cambisols on mixed colluvial sediments of the basalt/calcareous. The lowermost Litholic Neosol is associated with a rugged landscape with strong calcarenite dissolution and karstification, related to a former wetter climate. The soil phosphatization is clearly an inherited process of the Late Quaternary age, when climate conditions were different. Initial weathering took place in the last interglacial period, under wetter conditions during which the Tertiary basalts were strongly weathered, leaving corestones in a saprolitic, oxidized mass. In the late Pleistocene, a gentle surface distributed these weathering products along the pediment slopes as colluvial materials, whereas in the coastal areas aeolian processes formed large sand dunes composed of reworked calcareous sands from marine sources during a time of very low sea level. During this time, widespread bird activity accounted for secondary apatite formation on the surface of calcareous oolites. Finally, the Holocene warming was accompanied by increasing sea level, enhanced tropical weathering, Fe and Al mobility and variscite formation superimposed on degraded Ca-phosphates, forming two phase phosphatic aggregates
Kink scattering in the presence of geometric constrictions
We investigate kink-antikink collisions in a model characterized by two
scalar fields in the presence of geometric constrictions. The model includes an
auxiliary function that modifies the kinematics associated with one of the two
fields. An important fact is that one of the fields can be solved
independently, being responsible for changing the internal structure of the
second one. We performed several collisions and observed the presence of
resonance windows for small values of the parameters. Furthermore, we have been
able to show the alternation between the appearance of oscillating pulses, as
well as the annihilation and formation of kink-antikink pairs when the
geometric constriction is more pronounced. The study of kink dynamics in models
with geometric constrictions is connected with issues of interest such as
domain wall formation and magnetization at the manometric scale.Comment: 30 pages, 17 figures, final version to be published in JHE
False vacuum decay in kink scattering
In this work we consider kink-antikink and antikink-kink collisions in a
modified model with a false vacuum characterized by a dimensionless
parameter . The usual model is recovered for .
We investigate the regime where the kink in the presence of false
vacuum can be understood as a small deformation of the standard kink for the
model. We show that the attractive interaction between the
kink-antikink pair leads to a rich scattering pattern, in some cases delaying
considerably the false vacuum decay.Comment: 16 pages, 17 figure
Neural Online Filtering Based on Preprocessed Calorimeter Data
Aiming at coping with LHC high event rate, the ATLAS collaboration has been designing a sophisticated three-level online triggering system. A significant number of interesting events decays into electrons, which have to be identified from a huge background noise. This work proposes a high-efficient L2 electron / jet discrimination algorithm based on artificial neural processing fed from preprocessed calorimeter information. The feature extraction part of the proposed system provides a ring structure for data description. Energy normalization is later applied to the rings, making the proposed system usable for a broad energy spectrum. Envisaging data compaction, Principal Component Analysis and Principal Component of Discrimination are compared in terms of both compaction rates and classification efficiency. For the pattern recognition section, an artificial neural network was employed. The proposed algorithm was able to achieve an electron detection efficiency of 96% for a false alarm of 7%
Hydrodynamic limit for a boundary driven stochastic lattice gas model with many conserved quantities
We prove the hydrodynamic limit for a particle system in which particles may
have different velocities. We assume that we have two infinite reservoirs of
particles at the boundary: this is the so-called boundary driven process. The
dynamics we considered consists of a weakly asymmetric simple exclusion process
with collision among particles having different velocities
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