1,136 research outputs found
Non-topological solitons in field theories with kinetic self-coupling
We investigate some fundamental features of a class of non-linear
relativistic lagrangian field theories with kinetic self-coupling. We focus our
attention upon theories admitting static, spherically symmetric solutions in
three space dimensions which are finite-energy and stable. We determine general
conditions for the existence and stability of these non-topological soliton
solutions. In particular, we perform a linear stability analysis that goes
beyond the usual Derrick-like criteria. On the basis of these considerations we
obtain a complete characterization of the soliton-supporting members of the
aforementioned class of non-linear field theories. We then classify the family
of soliton-supporting theories according to the central and asymptotic
behaviors of the soliton field, and provide illustrative explicit examples of
models belonging to each of the corresponding sub-families. In the present work
we restrict most of our considerations to one and many-components scalar
models. We show that in these cases the finite-energy static spherically
symmetric solutions are stable against charge-preserving perturbations,
provided that the vacuum energy of the model vanishes and the energy density is
positive definite. We also discuss briefly the extension of the present
approach to models involving other types of fields, but a detailed study of
this more general scenario will be addressed in a separate publication.Comment: 5 pages, 1 figure, revtex4, minor corrections adde
Thermodynamics of weakly measured quantum systems
We consider continuously monitored quantum systems and introduce definitions
of work and heat along individual quantum trajectories that are valid for
coherent superpositions of energy eigenstates. We use these quantities to
extend the first and second laws of stochastic thermodynamics to the quantum
domain. We illustrate our results with the case of a weakly measured driven
two-level system and show how to distinguish between quantum work and heat
contributions. We finally employ quantum feedback control to suppress detector
backaction and determine the work statistics.Comment: 6 pages, 3 figure
Effects of nest and nest site characteristics on Humboldt penguins’ breeding success at Punta San Juan, Peru: Implications for conservation
Populations of Humboldt penguins (Spheniscus humboldti) in Peru began declining significantly in the 19th century because of industrial guano mining and a later increase in fishing. Guano mining changed the features of the penguins’ breeding habitat by eliminating the substrate where this species excavated their burrows. We analyzed the effects of nest and nest site characteristics and monitoring methodologies on Humboldt penguins’ breeding performance at Punta San Juan, Peru. We used a binomial generalized linear mixed model with random intercept to tests for differences in the probability of successfully raising at least one fledgling and also tested for differences in the number of fledglings produced among nests with different characteristics. We identified nests (including artificial nests) and classified them by nest cover (covered or uncovered), nest site habitat (cliff tops and beaches or caves) and nest substrate (guano or other substrate). We also assessed the impact of invasive and noninvasive nest monitoring methodologies on breeding performance. We included year and breeding season as random effects to account for environmental oscillation between and within years. Our results showed that the combination of guano substrate with noninvasive nest monitoring and nest cover were best correlated with penguin breeding success (increased probability of success and number of successful fledglings). The mean number of fledglings produced changed significantly between years and breeding seasons. In a separate analysis, breeding success of artificial nests was similar to natural covered or uncovered nests. Artificial nests in guano substrates were more successful than artificial nests in other substrates. Breeding success between habitats was similar. Our results show that nest and nest site characteristics affect Humboldt penguins’ breeding performance. Management decisions regarding penguins breeding habitat can affect the conservation of Humboldt penguins. An experiment is required to disentangle the effects of monitoring methodology and substrate on Humboldt’s penguins’ breeding performance, but as cautionary measures we recommend careful nest monitoring and avoiding guano extraction from penguins’ breeding sites
Estratigrafía de Sr y evolución sedimentaria de los depósitos marinos del Mioceno temprano en el antepaís del norte de la Cuenca Austral (o Magallanes), Argentina
Early Miocene shallow marine deposits in the region of Lago Posadas-Meseta Belgrano (Argentina) represent part of the “Patagoniense” transgression, an Atlantic marine incursion that flooded large part of Patagonia, including the Austral (foreland) Basin (southern Patagonia). These deposits, referred as El Chacay (Argentina) or Guadal (Chile) formations, and the transition to the overlying Santa Cruz Formation were divided into six facies: subtidal sandbars, shallow marine sandy deposits, muddy shelf deposits, estuarine complex deposits, fluvial channels and fluvial floodplains. These are arranged in a general transgressive-regressive cycle, subdivided into two stratigraphic sequences, separated by a major erosional surface. 87Sr/86Sr ages from shell carbonate in eight oysters yielded an age range of 20.3 to 18.1 Ma for these “Patagoniense” deposits. Correlation with other dated “Patagoniense” sections in southern Patagonia, like those at Lago Argentino or Comodoro Rivadavia, indicates that they belong to a single transgression that flooded several Patagonian basins approximately at the same time. Eustasy, flexural subsidence created by tectonic loading in the adjacent fold-and-thrust belt, and basin floor paleo-topography controlled the duration of the depositional event and the sedimentation style of these shallow marine deposits.Los depósitos marino-someros del Mioceno temprano de la región del Lago Posadas-Meseta Belgano representan parte de la transgresión “Patagoniense”, una incursión marina atlántica que invadió gran parte de la Patagonia, incluyendo la Cuenca de antepaís Austral (Patagonia austral). Estos depósitos, referidos como formaciones El Chacay (Argentina) y Guadal (Chile), y su transición a la suprayacente Formación Santa Cruz, fueron divididos en seis facies: barras submareales, depósitos arenosos marino-someros, depósitos fangosos de plataforma, complejo estuarino, canales fluviales y planicie de inundación. Estas facies muestran un arreglo general transgresivo-regresivo, el que puede ser subdividido en dos secuencias estratigráficas separadas por una superficie erosiva. Resultados de ocho edades 87Sr/86Sr de carbonato tomado de valvas de ostras dieron un rango entre 20,3 Ma y 18,1 Ma para estos depósitos Patagonienses. La correlación con sucesiones equivalentes de edad conocida en la Patagonia Austral, como las del Lago Argentino o Comodoro Rivadavia, indican que estas pertenecen a una misma transgresión que inundó gran parte de la Patagonia aproximadamente al mismo tiempo. La eustacia, la subsidencia flexural creada por carga tectónica en la faja corrida y plegada adyacente, y la paleotopografía del fondo de la cuenca, controlaron la duración del evento depositacional y el estilo de sedimentación estos depósitos marino-someros.Fil: Cuitiño, José Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Ventura Santos, Roberto. Universidade de Brasília; BrasilFil: Alonso Muruaga, Pablo Joaquin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Scasso, Roberto Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentin
Soliton solutions in relativistic field theories and gravitation
We report on some recent results on a class of relativistic lagrangian field
theories supporting non-topological soliton solutions and their applications in
the contexts of Gravitation and Cosmology. We analyze one and many-components
scalar fields and gauge fields.Comment: Latex, 4 pages, 1 figure. Talk given at 30th Spanish Relativity
Meeting (ERE 2007): Relativistic Astrophysics and Cosmology, Puerto de la
Cruz, Tenerife, Spain, 10-14 Sep 200
Screening effects in Relativistic Models of Dense Matter at Finite Temperature
We investigate screening effects of the medium on the potential interaction
between two static 'charges' for different models of dense plasmas in the
one-boson exchange approximation. The potential can exhibit an oscillatory
behavior, which is related to the analytic structure of the corresponding boson
propagators in the complex -plane. We have first revisited the one-pion
exchange in a nuclear medium. In addition to Friedel oscillations, which are
associated to branch cuts in the -plane, there appears another oscillatory
component, which arises from a pole on the pion propagator. This pole is
located appart from the axes, giving rise to an oscillating Yukawa-like
potential. Therefore, we call this phenomenon 'Yukawa oscillations'. This
phenomenon does not appear in the Debye component of the QED screened
potential, even if the coupling constant is artificially increased. We have
also studied a model of QCD quark-gluon plasma. In this case, the one-gluon
propagator also shows this kind of poles. At high densities and/or
temperatures, where one expects perturbative QCD to be valid, the pole shifts
towards large momenta.Comment: Revtex. 9 pages, 9 figure
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