Holstein model in infinite dimensions at half-filling

The normal state of the Holstein model is studied at half-filling in infinite dimensions and in the adiabatic regime. The dynamical mean-field equations are solved using perturbation expansions around the extremal paths of the effective action for the atoms. We find that the Migdal-Eliashberg expansion breaks down in the metallic state if the electron-phonon coupling $\lambda$ exceeds a value of about 1.3 in spite of the fact that the formal expansion parameter $\lambda \omega_0/E_F$ ($\omega_0$ is the phonon frequency, $E_F$ the Fermi energy) is much smaller than 1. The breakdown is due to the appearance of more than one extremal path of the action. We present numerical results which illustrate in detail the evolution of the local Green's function, the self-energy and the effective atomic potential as a function of $\lambda$.Comment: Revtex + 17 postscript figures include

Changes in the chemical and sensorial profile of extra virgin olive oils flavored with herbs and spices during storage

A study is reported on the chemical and sensorial characteristics of extra virgin olive oil flavored with hot pepper, garlic, oregano and rosemary during 7 months of storage. The oils were prepared by addition of the spice oily extracts at three different levels of concentration to an extra virgin olive oil. The following parameters were monitored: acidity, peroxide value (PV), K232, K270, (E)-2-hexenal/hexanal ratio and sensorial characteristics. At the end of the storage, all samples showed PV and K232 values lower than the control, whereas similar values of acidity, K270 and (E)-2-hexenal/hexanal ratio were observed. These results demonstrated that the herb and spice extracts improved the stability of the extra virgin olive oil. Tasters were able to distinguish among the levels of addition, and at the end of the storage, they preferred the oils flavored with 20 g/L of rosemary, 40 g/L of hot pepper, 40 g/L of oregano and 30 g/L of garlic