1,702 research outputs found
Ab initio calculations of the dynamical response of copper
The role of localized -bands in the dynamical response of Cu is
investigated, on the basis of {\em ab initio} pseudopotential calculations. The
density-response function is evaluated in both the random-phase approximation
(RPA) and a time-dependent local-density functional approximation (TDLDA). Our
results indicate that in addition to providing a polarizable background which
lowers the free-electron plasma frequency, d-electrons are responsible, at
higher energies and small momenta, for a double-peak structure in the dynamical
structure factor. These results are in agreement with the experimentally
determined optical response of copper. We also analyze the dependence of
dynamical scattering cross sections on the momentum transfer.Comment: 4 pages, 4 figures, to appear in Phys. Rev.
A Rare Presentation of Invasive Tuberculosis of the Central Nervous System in an Immunocompetent Patient in a Nonendemic Country.
We herein report a rare case of a 25-year-old immunocompetent male patient with disseminated tuberculosis of central nervous system (CNS), first presenting as multiple cerebral lesions with no meningeal involvement. Subsequent diagnostic workup disclosed extensive peritoneal involvement. A broad differential diagnosis was considered, including neoplastic and infectious diseases. The diagnosis was confirmed with positive PCR result for Mycobacterium tuberculosis in the biopsied mesenteric tissue. The patient was started on tuberculostatic regimen with favorable outcome. No acquired or hereditary immunodeficiency was documented. Disseminated tuberculosis in immunocompetent individuals is extremely rare. Genetic susceptibility factors have been reported in individuals with extensive forms of the disease and a high index of suspicion is required, as observed in our case.info:eu-repo/semantics/publishedVersio
Feshbach-resonance-induced atomic filamentation and quantum pair correlation in atom-laser-beam propagation
We study the propagation of an atom laser beam through a spatial region with
a magnetic field tuned to a Feshbach resonance. Tuning the magnetic field below
the resonance produces an effective focusing Kerr medium that causes a
modulational instability of the atomic beam. Under appropriate circumstances,
this results in beam breakup and filamentation seeded by quasi-particle
fluctuations, and in the generation of correlated atomic pairs
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