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We have studied ultrafast dynamics of thin films of LaCoO$_3$ and La$_{0.5}$Sr$_{0.5}$CoO$_3$ with femtosecond pump-probe ellipsometry in the energy range of 1.6-3.4 eV. We have observed a large pump-induced transfer of spectral weight in LaCoO$_3$ that corresponds to an insulator-to-metal transition. The photo-induced metallic state initially relaxes via a fast process with a decay constant of about 200 fs. Both LaCoO$_3$ and La$_{0.5}$Sr$_{0.5}$CoO$_3$ exhibit a significant secondary transient structure in the 1-30 ps range. Results of measurements on films with different thicknesses demonstrate that it corresponds to a propagation of an acoustic strain pulse. On timescales longer than 100 ps, heat diffusion to the substrate takes place that can be modelled with a bi-exponential decay., Comment: 8 pages, 4 figures

In this paper we develop explicitly the general Statistical Thermodynamics formalism to study of systems restricted to lie on revolution surfaces, particularly we derive the virial state equation of sphere and torus. A model to study the thermodynamical properties of macromolecules on biological membranes is constructed., Comment: in Spanish

We use the Self Consisten Generalized Langevin Equation theory (SCGLE) to study the dynamic arrest transitions of a system of three species of hard sphere colloidal system in the size ratio 1:3:9. We find that the inclusion of the smallest species has a depletion effect that drives the system to a second glass-liquid-glass re-entrance in a similar way that the inclusion of a small species in an otherwise monodisperse system leads to a (first) re-entrance. And we also find that the new glass after the second reentrance has very small localization length. Additionally we compare the kinetic phase diagram of a binary hard sphere mixture with size asymmetry 1:5, obtained with Mode Coupling Theory (MCT) and SCGLE theory and exhibit the significant differences between the two theories.