Effect of Dynamical Coulomb Correlations on the Fermi Surface of Na_0.3CoO_2

The t2g quasi-particle spectra of Na_0.3CoO_2 are calculated within the dynamical mean field theory. It is shown that as a result of dynamical Coulomb correlations charge is transfered from the nearly filled e_g' subbands to the a_1g band, thereby reducing orbital polarization among Co t2g states. Dynamical correlations therefore stabilize the small e_g' Fermi surface pockets, in contrast to angle-resolved photoemission data, which do not reveal these pockets.Comment: 4 pages, to appear in PR

Fenologia reprodutiva de espécies vegetais da Floresta Ombrófila Mista do Paraná, Brasil.

(Reproductive phenology of plant species of Mixed Ombrophilous Forest in Paraná, Brazil). The Mixed Ombrophilous Forest (FOM) or Araucaria Forest, vegetation that occupies regions with a highly seasonal climate subject to frost, used to cover 40% of Paraná State. Nowadays, however, there is less than 1% of advanced and well conserved FOM covering this State. This study presents the reproductive phenological patterns (flowering and fruiting) of the plant species found in FOM fragments located in three municipalities of Paraná State in order to subside restoration activities. Monthly phenological observations in 543 individuals of 145 species, representing several life forms (71 trees, 52 bushes, 18 vines and four epiphytes) were conducted between January 2004 and December 2005 employing the activity index. Flowering was recorded mainly between September and December, with a peak in October and November (68 species), followed by fruiting, which was concentrated between December and April, peaking in February (61 species). During the coldest months (June to August), the number of species with flowers or fruits was very low, with less than five species per phenophase. The availability of araucaria (Araucaria angustifolia (Bertol.) Kuntze) seeds varied between the years, but usually occurred between April and September. Significant correlations between phenophases and some abiotic factors, especially day length and temperature, were found. Therefore, plant species of the FOM proved to be highly seasonal, with periods of high and low flowering and fruiting activity, as consequence of the climatic seasonality, characteristic of the study region

Damage caused by brown-capuchin monkeys to nine Pinus species and the implications for forest management.

Danos causados por Sapajus nigritus a plantios de pínus são comuns no sul e sudeste do Brasil. Para avaliar a susceptibilidade ao ataque desses primatas, foi calculada a porcentagem média de árvores com danos em parcelas de inventário contínuo de nove espécies de Pinus spp. tropicais e temperado em plantios de quatro empresas nos estados do Paraná e Santa Catarina. Os resultados indicaram preferência por P. taeda e P greggii, com cerca de 97% das árvores com danos. No que diz respeito às espécies menos susceptíveis, P. patula e P. palustris com poucas árvores com danos (0.01%) ou não apresentaram danos. Outras espécies de Pinus variaram de 1.4 a 11.8% de árvores com danos. A preferência de macacos-prego por plantios de P. taeda é particularmente preocupante, já que é a espécie mais plantada no Sul do Brasil. No entanto, outras espécies que sofrem pouco ou nenhum dano, poderiam ser usadas como espécies alternativas, que possibilitem a diversificação de culturas e abre novas perspectivas para melhoria e engenharia genética do Pinus, de acordo com as necessidades dos diferentes produtores. Recomenda-se, no entanto, que essas estratégias sejam combinas com a recuperação de florestas nativas, uma vez que os danos estão associados a baixa qualidade dos fragmentos de florestas nativas no entorno dos plantios

Surface vs. bulk Coulomb correlations in photoemission spectra of perovskites

Recent photoemission spectra of the perovskite series Sr$_x$Ca$_{1-x}$VO$_3$ revealed strong modifications associated with surface contributions. To study the effect of Coulomb correlations in the bulk and at the surface the quasi-particle spectra are evaluated using the dynamical mean field theory. It is shown that as a result of the reduced coordination number of surface atoms correlation effects are stronger at the surface than in the bulk, in agreement with experiment.Comment: 4 pages 3 figure

Danos provocados por macaco-prego em povoamentos de pinus spp.

Editores técnicos: Marcílio José Thomazini, Elenice Fritzsons, Patrícia 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

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 $J_{H}$ 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 $U$ 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

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 $GW$ 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.