Collective excitations of a trapped degenerate Fermi gas

We evaluate the small-amplitude excitations of a spin-polarized vapour of Fermi atoms confined inside a harmonic trap. The dispersion law $\omega=\omega_{f}[l+4n(n+l+2)/3]^{1/2}$ is obtained for the vapour in the collisional regime inside a spherical trap of frequency $\omega_{f}$, with $n$ the number of radial nodes and $l$ the orbital angular momentum. The low-energy excitations are also treated in the case of an axially symmetric harmonic confinement. The collisionless regime is discussed with main reference to a Landau-Boltzmann equation for the Wigner distribution function: this equation is solved within a variational approach allowing an account for non-linearities. A comparative discussion of the eigenmodes of oscillation for confined Fermi and Bose vapours is presented in an Appendix.Comment: 14 pages, no figures, accepted for publication in Eur.Phys.Jour.

Bose-Einstein condensation in inhomogeneous Josephson arrays

We show that spatial Bose-Einstein condensation of non-interacting bosons occurs in dimension d < 2 over discrete structures with inhomogeneous topology and with no need of external confining potentials. Josephson junction arrays provide a physical realization of this mechanism. The topological origin of the phenomenon may open the way to the engineering of quantum devices based on Bose-Einstein condensation. The comb array, which embodies all the relevant features of this effect, is studied in detail.Comment: 4 pages, 5 figure

Radial solitons in armchair carbon nanotubes

Radial solitons are investigated in armchair carbon nanotubes using a generalized Lennard-Jones potential. The radial solitons are found in terms of moving kink defects whose velocity obeys a dispersion relation. Effects of lattice discreteness on the shape of kink defects are examined by estimating the Peierls stress. Results suggest that the typical size for an unpinned kink phase is of the order of a lattice spacing.Comment: 11 pages, 3(eps) figure

Electron-phonon interaction on bundled structures: Static and transport properties

We study the small-polaron problem of a single electron interacting with the lattice for the Holstein model in the adiabatic limit on a comb lattice hen the electron-phonon interaction acts only on the base sites. The ground state properties can be easily deduced from the ones of a linear chain with a appropriate rescaling of the coupling constant. On the other hand, the dynamical properties, that involve the complete spectrum of the system, present an "exotic" behavior. In the weak coupling limit the Drude weight (zero-frequency-conductivity) is enhanced with respect to its free-case value, contrary to the linear chain case, where for every finite value one has suppression of the Drude peak. More interestingly, the loss of coherent electron motion and the polaronic localization of the carrier occurs for different coupling values. Thus for intermediate coupling, a different phase appears with large kinetic energy and no coherent motion. RI Capone, Massimo/A-7762-200

Comparison between active and passive biomonitoring strategies for the assessment of genotoxicity and metal bioaccumulation in Echinogammarus veneris (Crustacea: Amphipoda)

The aim of this study was to investigate the relevance and the robustness of active and passive approaches used in freshwater biomonitoring with the ecologically relevant gammarid amphipod Echinogammarus veneris. To assess the contaminant bioavailability in two rivers of Latium (Central Italy), we measured the genotoxic potential in haemocytes by comet assay and metal bioaccumulation in tissues by analytical methods. We adopted an active strategy of exposure in situ and a passive method of sampling in situ. In the first case, the gammarids were exposed in cages in several sampling sites selected along two rivers, while in the sampling in situ, individuals were collected directly in the same sampling sites and then analyzed. The results indicate that the comet assay carried out on haemocytes from caged individuals proved to be a sensitive tool for freshwater genotoxicity monitoring. However, the sampling in situ is more appropriate for a realistic understanding of the presence of trace metal in E. veneris