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E Covas

Publications and source records attributed to E Covas.

2 recordsLinked to original sources
PubMed2001

Influence of noise on scalings for in-out intermittency.

We study the effects of noise on a recently discovered form of intermittency, referred to as in-out intermittency. This type of intermittency, which reduces to on-off in systems with a skew product structure, has been found in the dynamics of maps, (ODE) and (PDE) simulations that have symmetries. It shows itself in the form of trajectories that spend a long time near a symmetric state interspersed with short bursts away from symmetry. In contrast to on-off intermittency, there are clearly distinct mechanisms of approach towards and away from the symmetric state, and this needs to be taken into account in order to properly model the long time statistics. We do this by using a diffusion-type equation with a delay integral boundary condition. This model is validated by considering the statistics of a two-dimensional map with and without the addition of noise.

Journal Article↗
PubMed1999

Multiple forms of intermittency in partial differential equation dynamo models.

We find concrete evidence for the presence of crisis-induced and Pomeau-Manneville type-I intermittencies in an axisymmetric partial differential equation (PDE) mean-field dynamo model. These findings are of potential importance for two different reasons. First, as far as we are aware, this is the first time detailed evidence has been produced for the occurrence of these types of intermittency for such deterministic PDE models. And second, despite the rather idealized nature of these models, the concrete evidence for the occurrence of more than one type of intermittency in such models makes it in principle possible that different types of intermittency may occur in different solar-type stars or even in the same star over different epochs. In this way a multiple intermittency framework may turn out to be of importance in understanding the mechanisms responsible for grand-minima type behavior in the Sun and solar-type stars and in particular in the interpretation of the corresponding observational and proxy evidence.

Journal Article↗