Spin magnetization of strongly correlated electron gas confined in a two-dimensional finite lattice

The influence of disorder and interaction on the ground state polarization of the two-dimensional (2D) correlated electron gas is studied by numerical investigations of unrestricted Hartree-Fock equations. The ferromagnetic ground state is found to be plausible when the electron number is lowered and the interaction and disorder parameters are suitably chosen. For a finite system at constant electronic density the disorder induced spin polarization is cut off when the electron orbitals become strongly localized to the individual network sites. The fluctuations of the interaction matrix elements are calculated and brought out as favoring the ferromagnetic instability in the extended and weak localization regime. The localization effect of the Hubbard interaction term is discussed.Comment: 7 pages, 9 figure

Coulomb effects on the transport properties of quantum dots in strong magnetic field

We investigate the transport properties of quantum dots placed in strong magnetic field using a quantum-mechanical ' approach based on the 2D tight-binding Hamiltonian with direct Coulomb interaction and the Landauer-B\"{u}ttiker (LB) formalism. The electronic transmittance and the Hall resistance show Coulomb oscillations and also prove multiple addition processes. We identify this feature as the 'bunching' of electrons observed in recent experiments and give an elementary explanation in terms of spectral characteristics of the dot. The spatial distribution of the added electrons may distinguish between edge and bulk states and it has specific features for bunched electrons. The dependence of the charging energy on the number of electrons is discussed for strong and vanishing magnetic field. The crossover from the tunneling to quantum Hall regime is analyzed in terms of dot-lead coupling.Comment: 17 pages,8 figures,Revtex,submitted to Physical Review

Investigation of the Δn = 0 selection rule in Gamow-Teller transitions : The β-decay of 207 Hg

Gamow-Teller β decay is forbidden if the number of nodes in the radial wave functions of the initial and final states is different. This Δn=0 requirement plays a major role in the β decay of heavy neutron-rich nuclei, affecting the nucleosynthesis through the increased half-lives of nuclei on the astrophysical r-process pathway below both Z=50 (for N>82) and Z=82 (for N>126). The level of forbiddenness of the Δn=1ν1g 9/2 →π0g 7/2 transition has been investigated from the β − decay of the ground state of 207 Hg into the single-proton-hole nucleus 207 Tl in an experiment at the ISOLDE Decay Station. From statistical observational limits on possible γ-ray transitions depopulating the π0g 7/2 −1 state in 207 Tl, an upper limit of 3.9×10 −3 % was obtained for the probability of this decay, corresponding to log⁡ft>8.8 within a 95% confidence limit. This is the most stringent test of the Δn=0 selection rule to date

Amperometric biosensor based on the electro-copolymerization of a conductive biotinylated-pyrrole and alginate-pyrrole

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Influence of the culture medium composition on the exopolysaccharides synthesis by Streptococcus sp. IL5 strain

The synthesis of exopolysaccharides was determined for the Streptococcus sp. IL5 strain in MRS and M17 medium, with carbon sources such as glucose, lactose and sucrose. According to the obtained results, by using glucose as carbon source, the highest quantity of exopolysaccharides was obtained, namely of 400 mg l−1. The influence of various glucose concentrations (5, 10, 15, 20%) on exopolysaccharide production was tested. It resulted in that, at a concentration of 15% glucose, a maximum quantity of synthesized exopolysaccharides was obtained. The influence of temperature and of pH on the exopolysaccharide synthesis capacity of the strain was tested as well. From the tests the temperature of 37 °C and pH 7 proved to be the ideal parameters for obtaining a maximum exopolysaccharides quantity. Based on chromatographic methods, the content of synthesized polysaccharide was determined, consisting of 31.87% anhydrous glucose with a degree of polymerization of 36.7%