Metal-insulator transition in the one-dimensional Holstein model at half filling

We study the one-dimensional Holstein model with spin-1/2 electrons at half-filling. Ground state properties are calculated for long chains with great accuracy using the density matrix renormalization group method and extrapolated to the thermodynamic limit. We show that for small electron-phonon coupling or large phonon frequency, the insulating Peierls ground state predicted by mean-field theory is destroyed by quantum lattice fluctuations and that the system remains in a metallic phase with a non-degenerate ground state and power-law electronic and phononic correlations. When the electron-phonon coupling becomes large or the phonon frequency small, the system undergoes a transition to an insulating Peierls phase with a two-fold degenerate ground state, long-range charge-density-wave order, a dimerized lattice structure, and a gap in the electronic excitation spectrum.Comment: 6 pages (LaTex), 10 eps figure

Relaxation channels of two-vibron bound states in \alpha-helix proteins

Relaxation channels for two-vibron bound states in an anharmonic alpha-helix protein are studied. It is pointed out that the relaxation originates in the interaction between the dressed anharmonic vibrons and the remaining phonons. This interaction is responsible for the occurrence of transitions between two-vibron eigenstates mediated by both phonon absorption and phonon emission. At biological temperature, it is shown that the relaxation rate does not significantly depends on the nature of the two-vibron state involved in the process. Therefore, the lifetime for both bound and free states is of the same order of magnitude and ranges between 0.1 and 1.0 ps for realistic parameters. By contrast, the relaxation channels strongly depend on the nature of the two-vibron states which is a consequence of the breather-like behavior of the two-vibron bound states.Comment: octobre 2003 - soumis Phys. Rev.

Maternal Protein Malnutrition on Subsequent Generations in the Rat.

Peer Reviewe

Multifractal analysis based on p-exponents and lacunarity exponents

International audienceMany examples of signals and images cannot be modeled by locally bounded functions, so that the standard multifractal analysis, based on the H\"older exponent, is not feasible. We present a multifractal analysis based on another quantity, the p-exponent, which can take arbitrarily large negative values. We investigate some mathematical properties of this exponent, and show how it allows us to model the idea of "lacunarity" of a singularity at a point. We finally adapt the wavelet based multifractal analysis in this setting, and we give applications to a simple mathematical model of multifractal processes: Lacunary wavelet series

A bridge between geometric measure theory and signal processing: Multifractal analysis

International audienceWe describe the main features of wavelet techniques in multifractal analysis, using wavelet bases both as a tool for analysis, and for synthesis. We focus on two promising developments: We introduce the quantile leader method, which allows to put into light nonconcave multifractal spectra; we also test recent extensions of multifractal techniques fitted to functions that are not locally bounded but only belong to an L q space (determination of the q-spectrum)