Quantum-mechanical interference in charge exchange between hydrogen and graphene-like surfaces.

The neutral to negative charge fluctuation of a hydrogen atom in front of a graphene surface is calculated by using the Anderson model within an infinite intra atomic Coulomb repulsion approximation. We perform an ab initio calculation of the Anderson hybridization function that allows investigation of the effect of quantum-mechanical interference related to the Berry phase inherent to the graphene band structure. We find that consideration of the interaction of hydrogen on top of many C atoms leads to a marked asymmetry of the imaginary part of the hybridization function with respect to the Fermi level. Consequently, Fano factors larger than one and strongly dependent on the energy around the Fermi level are predicted. Moreover, the suppression of the hybridization for energies above the Fermi level can explain the unexpected large negative ion formation measured in the scattering of protons by graphite-like surfaces.

Localized description of surface energy gap effects in the resonant charge exchange between atoms and surfaces.

The resonant charge exchange between atoms and surfaces is described by considering a localized atomistic view of the solid within the Anderson model. The presence of a surface energy gap is treated within a simplified tight-binding model of the solid, and a proper calculation of the Hamiltonian terms based on a LCAO expansion of the solid eigenstates is performed. It is found that interference terms jointly with a surface projected gap maximum at the Γ point and the Fermi level inside it, lead to hybridization widths negligible around the Fermi level. This result can explain experimental observations related to long-lived adsorbate states and anomalous neutral fractions of low energy ions in alkali/Cu(111) systems.

[Functional ability in people above 80 years old]. / Capacidad funcional en mayores de 80 años.

OBJECTIVE: To discover the functional capacity (CF) for population over 80 years assing to an health center. DESIGN: This was an observational crossover study, using OARS questionary. SETTING: An urban health center. PATIENTS AND OTHER PARTICIPANTS: A sex and residence proportional sample of aged 80 and over was taken from 1986 census registry. MEASUREMENTS AND MAIN RESULTS: To asses functional capacity we used ADL (Activities of daily living) dimension from OARS questionry. It's composed of 14 items, seven for basic activities of daily living (AVDb) and seven for instrumental activities (AVDi). We considered severe incapacity if the aged had some difficulty in one AVDb at lest; moderate incapacity if the showed only a trouble in some AVDi, and good CF if didn't show the least difficulty in any item. The 42.2% of aged had severe incapacity, 26% of population had got good CF. The most incapacity was watched in house-works and cooking; in the AVDb were sphincters and control and cleaniless corporal. CONCLUSIONS: Functional capacity in population aged in the zone is lightly inferior to the other studies, however the ages chosen aren't comparable absolutely. We find differences in functional capacity between sex, the results are better for men. Population aged who is living in institutions have mainly CF moderate, and the married are more good functional capacity than singles or widows.