Structural and vibrational properties of two-dimensional MnxOy\rm Mn_xO_y nanolayers on Pd(100)

Using different experimental techniques combined with density functional based theoretical methods we have explored the formation of interface-stabilized manganese oxide structures grown on Pd(100) at (sub)monolayer coverage. Amongst the multitude of phases experimentally observed we focus our attention on four structures which can be classified into two distinct regimes, characterized by different building blocks. Two oxygen-rich phases are described in terms of MnO(111)-like O-Mn-O trilayers, whereas the other two have a lower oxygen content and are based on a MnO(100)-like monolayer structure. The excellent agreement between calculated and experimental scanning tunneling microscopy images and vibrational electron energy loss spectra allows for a detailed atomic description of the explored models.Comment: 14 pages, 11 figure

Exceptionally strong magnetism in 4d perovskites RTcO3 (R=Ca,Sr,Ba)

The evolution of the magnetic ordering temperature of the 4d3 perovskites RTcO3 (R=Ca,Sr,Ba) and its relation with its electronic and structural properties has been studied by means of hybrid density functional theory and Monte Carlo simulations. When compared to the most widely studied 3d perovskites the large spatial extent of the 4d shells and their relatively strong hybridization with oxygen weaken the tendency to form Jahn-Teller like orbital ordering. This strengthens the superexchange interaction. The resulting insulating G-type antiferromagnetic ground state is characterized by large superexchange coupling constants (26-35 meV) and Neel temperatures (750-1200 K). These monotonically increase as a function of the R ionic radius due to the progressive enhancement of the volume and the associated decrease of the cooperative rotation of the TcO6 octahedra.Comment: 4 pages, 3 figure

Two-spin entanglement distribution near factorized states

We study the two-spin entanglement distribution along the infinite $S=1/2$ chain described by the XY model in a transverse field; closed analytical expressions are derived for the one-tangle and the concurrences $C_r$, $r$ being the distance between the two possibly entangled spins, for values of the Hamiltonian parameters close to those corresponding to factorized ground states. The total amount of entanglement, the fraction of such entanglement which is stored in pairwise entanglement, and the way such fraction distributes along the chain is discussed, with attention focused on the dependence on the anisotropy of the exchange interaction. Near factorization a characteristic length-scale naturally emerges in the system, which is specifically related with entanglement properties and diverges at the critical point of the fully isotropic model. In general, we find that anisotropy rule a complex behavior of the entanglement properties, which results in the fact that more isotropic models, despite being characterized by a larger amount of total entanglement, present a smaller fraction of pairwise entanglement: the latter, in turn, is more evenly distributed along the chain, to the extent that, in the fully isotropic model at the critical field, the concurrences do not depend on $r$.Comment: 14 pages, 6 figures. Final versio

Screened hybrid functional applied to 3d^0-->3d^8 transition-metal perovskites LaMO3 (M=Sc-Cu): influence of the exchange mixing parameter on the structural, electronic and magnetic properties

We assess the performance of the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid density functional scheme applied to the perovskite family LaMO3 (M=Sc-Cu) and discuss the role of the mixing parameter alpha (which determines the fraction of exact Hartree-Fock exchange included in the density functional theory (DFT) exchange-correlation functional) on the structural, electronic, and magnetic properties. The physical complexity of this class of compounds, manifested by the largely varying electronic characters (band/Mott-Hubbard/charge-transfer insulators and metals), magnetic orderings, structural distortions (cooperative Jahn-Teller like instabilities), as well as by the strong competition between localization/delocalization effects associated with the gradual filling of the t_2g and e_g orbitals, symbolize a critical and challenging case for theory. Our results indicates that HSE is able to provide a consistent picture of the complex physical scenario encountered across the LaMO3 series and significantly improve the standard DFT description. The only exceptions are the correlated paramagnetic metals LaNiO3 and LaCuO3, which are found to be treated better within DFT. By fitting the ground state properties with respect to alpha we have constructed a set of 'optimum' values of alpha from LaScO3 to LaCuO3: it is found that the 'optimum' mixing parameter decreases with increasing filling of the d manifold (LaScO3: 0.25; LaTiO3 & LaVO3: 0.10-0.15; LaCrO3, LaMnO3, and LaFeO3: 0.15; LaCoO3: 0.05; LaNiO3 & LaCuO3: 0). This trend can be nicely correlated with the modulation of the screening and dielectric properties across the LaMO3 series, thus providing a physical justification to the empirical fitting procedure.Comment: 32 pages, 29 figure

Relação entre poda verde e o uso de material refletivo com a qualidade de pêssegos ´Eldorado´.

bitstream/item/33532/1/documento-134.pd

A produção do espaço livre público do Parque da Prainha em Vila Velha Espírito Santo: disputa territorial em projetos urbanos

A presente pesquisa trabalha com o objetivo de investigar a produção do espaço livre público do Parque da Prainha, em Vila Velha, Espírito Santo, centralizada no período de 1989, ano de construção do Parque, até 2016, desvelando o processo de construção, demolição e possível reconstrução do Parque. A metodologia utilizada envolveu estudo bibliográfico relativo ao tema relacionado à produção do espaço e ao espaço público, pesquisa documental realizada em arquivos e bibliotecas públicas e entrevistas com pessoas-chave relativas à história de ocupação urbana de Vila Velha, à execução do aterro e ao Parque da Prainha. A investigação se desenvolve por meio da identificação dos agentes sociais que atuam na constante produção do espaço livre público do Parque da Prainha, principalmente a Associação de Moradores; Associação de Empresários; o Grupo Pesqueiro, envolvendo a Cooperativa de Pesca e a Colônia de Pesca, e o Poder Público Municipal e Estadual. As constatações deste estudo revelam que a construção do Parque em 1989 está relacionada às ações da Associação de Moradores, do Grupo de Pesca e do Poder Público Estadual durante a década de 1980. Após 19 anos de funcionamento, o descaso com a manutenção das estruturas do Parque, os problemas apontados pela Associação de Moradores, como a insegurança, e o interesse da Associação de Empresários em construir um parque novo que dê suporte às práticas turísticas e ao turismo de negócios são justificativas que aparecem para fundamentar a demolição do Parque em 2009. Em 2016, passados 7 anos desde a demolição, o Parque não foi reconstruído. Nesse sentido, foram ainda analisados na pesquisa, três projetos arquitetônicos urbanos de reconstrução do Parque da Prainha. Os projetos apresentam um forte viés econômico voltado para o desenvolvimento e para o suporte das atividades turísticas, não apenas aquela vinculada à visitação do sítio histórico ou da atividade religiosa que caracteriza o bairro da Prainha, mas ao fortalecimento do turismo de eventos