326 research outputs found
About coherent structures in random shell models for passive scalar advection
A study of anomalous scaling in models of passive scalar advection in terms
of singular coherent structures is proposed. The stochastic dynamical system
considered is a shell model reformulation of Kraichnan model. We extend the
method introduced in \cite{DDG99} to the calculation of self-similar instantons
and we show how such objects, being the most singular events, are appropriate
to capture asymptotic scaling properties of the scalar field. Preliminary
results concerning the statistical weight of fluctuations around these optimal
configurations are also presented.Comment: 4 pages, 2 postscript figures, submitted to PR
Tuning the atomic and domain structure of epitaxial films of multiferroic BiFeO3
Recent works have shown that the domain walls of room-temperature
multiferroic BiFeO3 (BFO) thin films can display distinct and promising
functionalities. It is thus important to understand the mechanisms underlying
domain formation in these films. High-resolution x-ray diffraction and
piezo-force microscopy, combined with first-principles simulations, have
allowed us to characterize both the atomic and domain structure of BFO films
grown under compressive strain on (001)-SrTiO3, as a function of thickness. We
derive a twining model that describes the experimental observations and
explains why the 71o domain walls are the ones commonly observed in these
films. This understanding provides us with a new degree of freedom to control
the structure and, thus, the properties of BiFeO3 thin films.Comment: RevTeX; 4 two-column pages; 4 color figures. Figure 2b does not seem
to display well. A proper version can be found in the source fil
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