Local correlation functional for electrons in two dimensions

We derive a local approximation for the correlation energy in two-dimensional electronic systems. In the derivation we follow the scheme originally developed by Colle and Salvetti for three dimensions, and consider a Gaussian approximation for the pair density. Then, we introduce an ad-hoc modification which better accounts for both the long-range correlation, and the kinetic-energy contribution to the correlation energy. The resulting functional is local, and depends parametrically on the number of electrons in the system. We apply this functional to the homogeneous electron gas and to a set of two-dimensional quantum dots covering a wide range of electron densities and thus various amounts of correlation. In all test cases we find an excellent agreement between our results and the exact correlation energies. Our correlation functional has a form that is simple and straightforward to implement, but broadly outperforms the commonly used local-density approximation

Density-based mixing parameter for hybrid functionals

A very popular ab-initio scheme to calculate electronic properties in solids is the use of hybrid functionals in density functional theory (DFT) that mixes a portion of Fock exchange with DFT functionals. In spite of their success, a major problem still remains, related to the use of one single mixing parameter for all materials. Guided by physical arguments that connect the mixing parameter to the dielectric properties of the solid, and ultimately to its band gap, we propose a method to calculate this parameter from the electronic density alone. This method is able to cut significantly the error of traditional hybrid functionals for large and small gap materials, while retaining a good description of structural properties. Moreover, its implementation is simple and leads to a negligible increase of the computational time.Comment: submitte

The Ultrasensitivity of Living Polymers

Synthetic and biological living polymers are self-assembling chains whose chain length distributions (CLDs) are dynamic. We show these dynamics are ultrasensitive: even a small perturbation (e.g. temperature jump) non-linearly distorts the CLD, eliminating or massively augmenting short chains. The origin is fast relaxation of mass variables (mean chain length, monomer concentration) which perturbs CLD shape variables before these can relax via slow chain growth rate fluctuations. Viscosity relaxation predictions agree with experiments on the best-studied synthetic system, alpha-methylstyrene.Comment: 4 pages, submitted to Phys. Rev. Let

Investigating interaction-induced chaos using time-dependent density functional theory

Systems whose underlying classical dynamics are chaotic exhibit signatures of the chaos in their quantum mechanics. We investigate the possibility of using time-dependent density functional theory (TDDFT) to study the case when chaos is induced by electron-interaction alone. Nearest-neighbour level-spacing statistics are in principle exactly and directly accessible from TDDFT. We discuss how the TDDFT linear response procedure can reveal the mechanism of chaos induced by electron-interaction alone. A simple model of a two-electron quantum dot highlights the necessity to go beyond the adiabatic approximation in TDDFT.Comment: 8 pages, 4 figure

Trigo-mourisco na alimentação de frangos de corte.

Trigo-mourisco (Fagopyrum esculentum, Moench) em rações de frangos de corte. Linhagem Hubbard. Delineamento experimental inteiramente casualizado

Sistema agroflorestal em área de pequeno produtor na região do Tapajós, Estado do Pará: avaliação após doze anos de implantado.

bitstream/item/63497/1/Oriental-Doc99.PD

Structure, growth and production of a remarkably abundant population of the common goby, Pomatoschistus microps (Actinopterygii: Gobiidae)

The common goby, Pomatoschistus microps, is a relevant species from estuarine food webs, playing important roles as predator of polychaetes and crustaceans and as prey for larger fishes and crustaceans. The Minho estuary (NW Portugal) is a relatively wellpreserved and productive system. To assess the population structure and production of P. microps in this estuary, monthly samples were undertaken in three different areas along an estuarine gradient in the lower estuary. The density of P. microps varied considerably among seasons and sampling stations, with higher densities occurring in summer and autumn. The lowest densities were found closer to the sea. In general, the density of females was higher than the density of males in all sampling stations, while juveniles were more abundant within a salt marsh area. Compared with other European estuaries, our data showed a remarkable higher density and production values of P. microps. This may be related to the high freshwater input and the low salinities found in this estuary. In addition, we hypothesize that the lower density of the sympatric species P. minutus and the high availability of bivalve shells observed in the Minho estuary may have also contributed to the present results, once P. minutus and P. microps often display a diet overlap and the bivalve shells are crucial for the common goby reproduction.This research was supported by a grant from Iceland, Liechtenstein and Norway through the EEA Financial Mechanism and the Norwegian Financial Mechanism. A.T. Souza has a PhD grant (SFRH/BD/ 71232/2010) from the Fundação para a Ciência e a Tecnologia (Portugal). I. Martins was financed for CIÊNCIA 2007 and the project INPACTAR PTDC/MAR/111537/2009; FCT; COMPETE; QREN; UE

Efeitos do estresse salino na germinação, emergência e estabelecimento da plântula de cajueiro anão precoce.

Objetivou-se com este trabalho avaliar os efeitos da salinidade em três estádios de desenvolvimento (ED) da plântula de cajueiro anão-precoce, a saber, germinação, emergência e estabelecimento da plântula, tentando estabelecer uma relação entre o desenvolvimento e o acúmulo de íons nos tecidos da plântula. Para isso, castanhas do clone CCP-06 de cajueiro anão precoce foram semeadas em bandejas de plástico contendo vermiculita umedecida com água destilada (0,0 dS m-1) ou soluções de NaCl com condutividades elétricas variando entre 3,0 e 18,0 dS m-1 e mantidas em casa de vegetação. Determinaram-se a percentagem de plântulas que alcançaram os ED estudados e o tempo e a velocidade com que isso ocorreu, assim como a matéria seca dos cotilédones e eixo embrionário e os teores de Na+, K+ e Cl- do eixo embrionário. A salinidade retardou o desenvolvimento das plântulas nos ED correspondentes à emergência e estabelecimento, entretanto apenas neste último ED é que a percentagem final de plântulas foi reduzida, acompanhada pela inibição da depleção das reservas cotiledonares e decréscimo da massa seca do eixo embrionário. Em todos os ED, os teores de Na+ e Cl- aumentaram com a salinidade, mas isso foi mais pronunciado nas plântulas estabelecidas, nas quais houve redução dos teores de K+. Os resultados obtidos sugerem que as plântulas de cajueiro anão precoce são mais sensíveis à salinidade durante a etapa de estabelecimento e que os efeitos deletérios desse estresse são mediados, pelo menos em parte, pelo acúmulo excessivo de íons Na+ e Cl- na plântula