Optical Conductivity in Mott-Hubbard Systems

We study the transfer of spectral weight in the optical spectra of a strongly correlated electron system as a function of temperature and interaction strength. Within a dynamical mean field theory of the Hubbard model that becomes exact in the limit of large lattice coordination, we predict an anomalous enhancement of spectral weight as a function of temperature in the correlated metallic state and report on experimental measurements which agree with this prediction in $V_2O_3$. We argue that the optical conductivity anomalies in the metal are connected to the proximity to a crossover region in the phase diagram of the model.Comment: 12 pages and 4 figures, to appear in Phys. Rev. Lett., v 75, p 105 (1995

Oxydation et réduction d´explantats dorsaux et ventraux de gastrulas (amphibiens)

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Recherches sur le rôle des groupes sulfhydriles dans la morphogénèse. I. Action des inhibiteurs des groupes SH sur l'oeuf entier et sur des explantats dorsaux et ventraux chez les amphibiens; implantation de protéines sulfhydrilées. II. Effect de quelques agents oxydants et réducteurs sur le développement d'explantats dorsaux et ventraux de jeunes gastrulas d'amphibiens.

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