Correlations and Renormalization of the Electron-Phonon Coupling in the Honeycomb Hubbard Ladder and Superconductivity in Polyacene

We have performed extensive density matrix renormalization group (DMRG) studies of the Hubbard model on a honeycomb ladder. The band structure (with Hubbard U=0) exhibits an unusual quadratic band touching at half filling, which is associated with a quantum Lifshitz transition from a band insulator to a metal. %SAK as a function of a third-neighbor hopping parameter. For one electron per site, non-zero $U$ drives the system into an insulating state in which there is no pair-binding between added electrons; this implies that superconductivity driven directly by the repulsive electron-electron interactions is unlikely in the regime of small doping, $x\ll 1$. However, the divergent density of states as $x\to 0$, the large values of the phonon frequencies, and an unusual correlation induced enhancement of the electron-phonon coupling imply that lightly doped polyacenes, which approximately realize this structure, are good candidates for high temperature electron-phonon driven superconductivity

Maternal - Neonatal serum selenium and copper levels in Greeks and Albanians

Aim: To evaluate selenium (Se) and copper (Cu) concentrations in Greek and Albanian immigrant mothers and in the cord blood of their newborns. Subjects and methods: From 1118 Greek and 820 Albanian mothers and from the cord blood of their neonates blood was obtained for Se and Cu measurement. Se and Cu concentrations were determined in sera with graphite furnace atomic absorption spectroscopy (GFAAAS) and atomic absorption spectrometry, respectively. In all, 30 days' nutrient intakes were evaluated in both groups. Results: Animal protein, Se and Cu intakes were poor in the Albanians vs the Greeks (P<0.001). Se concentrations in the Greek mothers (68.3 ± 8.5 μg/l) and in their newborns (37.02 ± 8.9 μg/l) were found higher as compared with those in Albanian mothers (37.4 ± 9.9 μg/l) and in their newborns (34.3 ± 9.1 μg/l) (P<0.001). Cu levels were also found higher (P<0.001) in the Greek mothers (1687 ± 353 μg/l) and in their neonates (449 ± 87 μg/l) compared with those in the Albanian mothers (959 ± 318 μg/l) and in their newborns (229 ± 67 μg/l). Additionally, 31.5% of neonates born to Albanian women with Se concentrations less than 28 μg/l had higher Se levels (P<0.01) than their mothers. Conclusions: The low Se and Cu levels evaluated in the Albanian mothers and their newborns could be related to their poor animal protein intake which could be the consequence of their low socioeconomic status. As an effective preventive measure, accurate dietetic strategies to assess the requirements of pregnant immigrant women for trace elements may be planned in Greece. © 2004 Nature Publishing Group. All rights reserved