438 research outputs found
Competition of crystal field splitting and Hund's rule coupling in two-orbital magnetic metal-insulator transitions
Competition of crystal field splitting and Hund's rule coupling in magnetic
metal-insulator transitions of half-filled two-orbital Hubbard model is
investigated by multi-orbital slave-boson mean field theory. We show that with
the increase of Coulomb correlation, the system firstly transits from a
paramagnetic (PM) metal to a {\it N\'{e}el} antiferromagnetic (AFM) Mott
insulator, or a nonmagnetic orbital insulator, depending on the competition of
crystal field splitting and the Hund's rule coupling. The different AFM Mott
insulator, PM metal and orbital insulating phase are none, partially and fully
orbital polarized, respectively. For a small and a finite crystal
field, the orbital insulator is robust. Although the system is nonmagnetic, the
phase boundary of the orbital insulator transition obviously shifts to the
small regime after the magnetic correlations is taken into account. These
results demonstrate that large crystal field splitting favors the formation of
the orbital insulating phase, while large Hund's rule coupling tends to destroy
it, driving the low-spin to high-spin transition.Comment: 4 pages, 4 figure
Danos provocados por macaco-prego em povoamentos de pinus spp.
Editores tĂ©cnicos: MarcĂlio JosĂ© Thomazini, Elenice Fritzsons, PatrĂcia Raquel Silva, Guilherme Schnell e Schuhli, Denise Jeton Cardoso, Luziane Franciscon. EVINCI. Resumos
Photoemission Beyond the Sudden Approximation
The many-body theory of photoemission in solids is reviewed with emphasis on
methods based on response theory. The classification of diagrams into loss and
no-loss diagrams is discussed and related to Keldysh path-ordering
book-keeping. Some new results on energy losses in valence-electron
photoemission from free-electron-like metal surfaces are presented. A way to
group diagrams is presented in which spectral intensities acquire a
Golden-Rule-like form which guarantees positiveness. This way of regrouping
should be useful also in other problems involving spectral intensities, such as
the problem of improving the one-electron spectral function away from the
quasiparticle peak.Comment: 18 pages, 11 figure
Experimental study exploring the factors that promote rib fragility in the elderly
Rib fractures represent a common injury type due to blunt chest trauma, affecting hospital stay and mortality especially in elderly patients. Factors promoting rib fragility, however, are little investigated. The purpose of this in vitro study was to explore potential determinants of human rib fragility in the elderly. 89 ribs from 13 human donors (55\u201399 years) were loaded in antero-posterior compression until fracture using a material testing machine, while surface strains were captured using a digital image correlation system. The effects of age, sex, bone mineral density, rib level and side, four global morphological factors (e.g. rib length), and seven rib cross-sectional morphological factors (e.g. cortical thickness, determined by \u3bcCT), on fracture load were statistically examined using Pearson correlation coefficients, Mann\u2013Whitney U test as well as Kruskal\u2013Wallis test with Dunn-Bonferroni post hoc correction. Fracture load showed significant dependencies (p < 0.05) from bone mineral density, age, antero-posterior rib length, cortical thickness, bone volume/tissue volume ratio, trabecular number, trabecular separation, and both cross-sectional area moments of inertia and was significantly higher at rib levels 7 and 8 compared to level 4 (p = 0.001/0.013), whereas side had no significant effect (p = 0.989). Cortical thickness exhibited the highest correlation with fracture load (r = 0.722), followed by the high correlation of fracture load with the area moment of inertia around the longitudinal rib cross-sectional axis (r = 0.687). High correlations with maximum external rib surface strain were detected for bone volume/tissue volume ratio (r = 0.631) and trabecular number (r = 0.648), which both also showed high correlations with the minimum internal rib surface strain (r = 12 0.644/ 12 0.559). Together with rib level, the determinants cortical thickness, area moment of inertia around the longitudinal rib cross-sectional axis, as well as bone mineral density exhibited the largest effects on human rib fragility with regard to the fracture load. Sex, rib cage side, and global morphology, in contrast, did not affect rib fragility in this study. When checking elderly patients for rib fractures due to blunt chest trauma, patients with low bone mineral density and the mid-thoracic area should be carefully examined
Self-energy and lifetime of Shockley and image states on Cu(100) and Cu(111): Beyond the GW approximation of many-body theory
We report many-body calculations of the self-energy and lifetime of Shockley
and image states on the (100) and (111) surfaces of Cu that go beyond the
approximation of many-body theory. The self-energy is computed in the framework
of the GW\Gamma approximation by including short-range exchange-correlation
(XC) effects both in the screened interaction W (beyond the random-phase
approximation) and in the expansion of the self-energy in terms of W (beyond
the GW approximation). Exchange-correlation effects are described within
time-dependent density-functional theory from the knowledge of an adiabatic
nonlocal XC kernel that goes beyond the local-density approximation.Comment: 8 pages, 5 figures, to appear in Phys. Rev.
The MobyDick Project: A Mobile Heterogeneous All-IP Architecture
Proceedings of Advanced Technologies, Applications and Market Strategies for 3G (ATAMS 2001). Cracow, Poland: 17-20 June, 2001.This paper presents the current stage of an IP-based architecture for heterogeneous environments, covering UMTS-like W-CDMA wireless access technology, wireless and wired LANs, that is being developed under the aegis of the IST Moby Dick project. This architecture treats all transmission capabilities as basic physical and data-link layers, and attempts to replace all higher-level tasks by IP-based strategies.
The proposed architecture incorporates aspects of mobile-IPv6, fast handover, AAA-control, and Quality of Service. The architecture allows for an optimised control on the radio link layer resources. The Moby dick architecture is currently under refinement for implementation on field trials. The services planned for trials are data transfer and voice-over-IP.Publicad
Acoustic surface plasmons in the noble metals Cu, Ag, and Au
We have performed self-consistent calculations of the dynamical response of
the (111) surface of the noble metals Cu, Ag, and Au. Our results indicate that
the partially occupied surface-state band in these materials yields the
existence of acoustic surface plasmons with linear dispersion at small wave
vectors. Here we demonstrate that the sound velocity of these low-energy
collective excitations, which had already been predicted to exist in the case
of Be(0001), is dictated not only by the Fermi velocity of the two-dimensional
surface-state band but also by the nature of the decay and penetration of the
surface-state orbitals into the solid. Our linewidth calculations indicate that
acoustic surface plasmons should be well defined in the energy range from zero
to meV.Comment: 8 pages, two columns, 7 figures, to appear in Phys. Rev.
Electron rescattering at metal nanotips induced by ultrashort laser pulses
We report on the first investigation of plateau and cut-off structures in
photoelectron spectra from nano-scale metal tips interacting with few-cycle
near-infrared laser pulses. These hallmarks of electron rescattering,
well-known from atom-laser interaction in the strong-field regime, appear at
remarkably low laser intensities with nominal Keldysh parameters of the order
of . Quantum and quasi-classical simulations reveal that a large
field enhancement near the tip and the increased backscattering probability at
a solid-state target play a key role. Plateau electrons are by an order of
magnitude more abundant than in comparable atomic spectra, reflecting the high
density of target atoms at the surface. The position of the cut-off serves as
an in-situ probe for the locally enhanced electric field at the tip apex
Kondo lattice model at half-filling
The single- and two-channel Kondo lattice model consisting of localized spins
interacting antiferromagnetically with the itinerent electrons, are studied
using dynamical mean field theory. As an impurity solver for the effective
single impurity Anderson model we used the exact diagonalization (ED) method.
Using ED allowed us to perform calculations for low temperatures and couplings
of arbitrary large strength. Our results for the single-channel case confirm
and extend the recent investigations. In the two-channel case we find a
symmetry breaking phase transition with increasing coupling strength.Comment: 11 pages, 5 figure
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