Compound Asterosoma ludwigae Schlirf, 2000 from the Jurassic of the Lusitanian Basin (Portugal): conditional strategies in the behaviour of Crustacea

En este trabajo se describe la icnoespecie Asterosoma ludwigae Schlirf, 2000, que aparece en dos secciones de distinta edad y paleoambiente en el Jurásico de la Cuenca Lusitánica. Las escasas y poco diversifi cadas paleoicnocenosis asociadas a estos icnofósiles, así como los fósiles, indican una oxigenación baja en la interfase agua-sedimento. Por esta razón, se hace hincapié en la importancia paleoecológica de Chondrites en las litofacies que preceden a aquellas con Thalassinoides suevicus y Asterosoma ludwigae (Jurásico Superior de Guincho) o en asociación directa con morfotipos semejantes (Jurásico Inferior de Peniche). En el syn-rift, en las calciturbiditas de fore-reef del Kimmeridgiense-Titónico de la Formación Mem Martins, la paleoicnocenosis exótica con predominio de Asterosoma ludwigae en tres estadios morfoetológicos gradacionales, sugiere una estrategia condicional oportunista forzada para los organismos productores de estas estructuras. Sin embargo, en la Formación “Calcários e margas de Peniche”, contemporánea al post-rifting, Asterosoma se encuentra en paleoicnocenosis que representan condiciones de equilibrio. En ambos casos, existe una relación espacial de proximidad entre Asterosoma ludwigae y las redes de galerías del “grupo S-O-T”, referentes a fodinichnia de posibles crustáceos decápodos.Asterosoma ludwigae Schlirf, 2000 is described in two sections of different age and palaeoenvironment in the Jurassic of the Lusitanian Basin. The scarce and low diversity of palaeoichnocoenoses associated with these trace fossil, as well as body fossils, indicate low oxygenation of sediment levels close to substrate-water interface. Thus, the palaeoecological signifi cance of Chondrites in lithofacies preceding those with Thalassinoides suevicus and Asterosoma ludwigae (Upper Jurassic of Guincho) or in direct association with similar morphotypes (Lower Jurassic of Peniche) is emphasized. In the syn-rift, fore-reef calciturbidites of the Kimmeridgian-to-Tithonian Mem Martins Formation, an exotic palaeoichnocoenosis dominated by Asterosoma ludwigae in three morpho-ethological gradational stages suggests a forced opportunistic, conditional strategy for the trace maker population. However, in the “Calcários e margas de Peniche” Formation, that is coeval with the post-rifting depositional setting, Asterosoma is found in palaeoichnocoenoses representing equilibrium conditions. A close spatial relationship exists, in both cases, between Asterosoma ludwigae and the “S-O-T group” burrow networks referring to fodinichnia of possible decapod crustaceans

Hamiltonian symplectic embedding of the massive noncommutative U(1) Theory

We show that the massive noncommutative U(1) theory is embedded in a gauge theory using an alternative systematic way, which is based on the symplectic framework. The embedded Hamiltonian density is obtained after a finite number of steps in the iterative symplectic process, oppositely to the result proposed using the BFFT formalism. This alternative formalism of embedding shows how to get a set of dynamically equivalent embedded Hamiltonian densities.Comment: 16 pages, no figures, revtex4, corrected version, references additione

Particle Creation by a Moving Boundary with Robin Boundary Condition

We consider a massless scalar field in 1+1 dimensions satisfying a Robin boundary condition (BC) at a non-relativistic moving boundary. We derive a Bogoliubov transformation between input and output bosonic field operators, which allows us to calculate the spectral distribution of created particles. The cases of Dirichlet and Neumann BC may be obtained from our result as limiting cases. These two limits yield the same spectrum, which turns out to be an upper bound for the spectra derived for Robin BC. We show that the particle emission effect can be considerably reduced (with respect to the Dirichlet/Neumann case) by selecting a particular value for the oscillation frequency of the boundary position