Large scale numerical investigation of excited states in poly(phenylene)

A density matrix renormalisation group scheme is developed, allowing for the first time essentially exact numerical solutions for the important excited states of a realistic semi-empirical model for oligo-phenylenes. By monitoring the evolution of the energies with chain length and comparing them to the experimental absorption peaks of oligomers and thin films, we assign the four characteristic absorption peaks of phenyl-based polymers. We also determine the position and nature of the nonlinear optical states in this model.Comment: RevTeX, 10 pages, 4 eps figures included using eps

Theory of the first-order isostructural valence phase transitions in mixed valence compounds YbIn_{x}Ag_{1-x}Cu_{4}

For describing the first-order isostructural valence phase transition in mixed valence compounds we develop a new approach based on the lattice Anderson model. We take into account the Coulomb interaction between localized f and conduction band electrons and two mechanisms of electron-lattice coupling. One is related to the volume dependence of the hybridization. The other is related to local deformations produced by f- shell size fluctuations accompanying valence fluctuations. The large f -state degeneracy allows us to use the 1/N expansion method. Within the model we develop a mean-field theory for the first-order valence phase transition in YbInCu_{4}. It is shown that the Coulomb interaction enhances the exchange interaction between f and conduction band electron spins and is the driving force of the phase transition. A comparison between the theoretical calculations and experimental measurements of the valence change, susceptibility, specific heat, entropy, elastic constants and volume change in YbInCu_{4} and YbAgCu_{4} are presented, and a good quantitative agreement is found. On the basis of the model we describe the evolution from the first-order valence phase transition to the continuous transition into the heavy-fermion ground state in the series of compounds YbIn_{1-x}Ag_{x}Cu_{4}. The effect of pressure on physical properties of YbInCu_{4} is studied and the H-T phase diagram is found.Comment: 17 pages RevTeX, 9 Postscript figures, to be submitted to Phys.Rev.

Mapping and Assessment of forest Ecosystem and Their Services. Applications and guidance for decision making in the framework of MAES

The aim of this report is to illustrate by means of a series of case studies the implementation of mapping and assessment of forest ecosystem services in different contexts and geographical levels. Methodological aspects, data issues, approaches, limitations, gaps and further steps for improvement are analysed for providing good practices and decision making guidance. The EU initiative on Mapping and Assessment of Ecosystems and their Services (MAES), with the support of all Member States, contributes to improve the knowledge on ecosytem services. MAES is one of the building-block initiatives supporting the EU Biodiversity Strategy to 2000

Yield and fruit quality of apple from conventional and organic production systems Rendimento e qualidade de maçãs em pomares conduzidos nos sistemas convencional e orgânico de produção

The objective of this study was to assess the yield and fruit quality of apple produced with a conventional and an organic production systems in Southern Brazil. The orchards consisted of alternate rows from 10 to 12-year old 'Royal Gala' and 'Fuji' apple trees on M.7 rootstocks, grown as slender spindles, on 4x6 m spacing. Eighteen apple trees of each cultivar and management system were randomly selected and assessed for nutrition, flowering, fruit set, yield, and fruit quality during two growing seasons (2002/2003 and 2003/2004). The organic management system resulted in lower concentrations of K, Mg, and N in leaves and fruits, and in smaller fruits for both cultivars, and lower fruit yield for 'Fuji' than from the conventional production system. For both cultivars, fruits from the organic orchard harvested at commercial maturity had a more yellowish skin background color, higher percentage of blush in the fruit skin, higher soluble solids content, higher density, higher flesh firmness, and higher severity of russet than fruits from the conventional orchard. Fruit from the organic orchard had lower titratable acidity in 'Royal Gala', and higher incidence of moldy core and lower incidence of watercore in 'Fuji', than fruit from the conventional orchard. A non-trained sensory panel detected no significant differences for fruit attributes of taste, flavor and texture between fruit from the production systems for either cultivar.<br>O objetivo deste estudo foi avaliar o rendimento e a qualidade de frutos em pomares de macieira, nos sistemas convencional e orgânico de produção no Sul do Brasil. Os pomares consistiram de filas alternadas de plantas com 10 a 12 anos de idade das cultivares Royal Gala e Fuji, sobre porta-enxerto M.7, conduzidas com líder central, em espaçamento de 4x6 m. Dezoito plantas de cada cultivar e sistema de manejo foram marcadas aleatoriamente e avaliadas quanto à nutrição, floração, frutificação efetiva, rendimento e qualidade de frutos, em dois anos agrícolas (2002/2003 e 2003/2004). O sistema orgânico apresentou menores concentrações de K, Mg e N nas folhas e frutos, frutos de menor tamanho em ambas as cultivares e menor rendimento de frutos na cultivar Fuji. Em ambas as cultivares, frutos do pomar orgânico na maturação comercial apresentaram cor de fundo da casca mais amarelada, maior percentagem de coloração vermelha, maior teor de sólidos solúveis totais, maior densidade, maior firmeza de polpa e maior severidade de "russet" do que frutos do pomar convencional. No pomar orgânico, 'Royal Gala' apresentou a menor acidez titulável e 'Fuji' a maior incidência de podridão carpelar e menor incidência de pingo-de-mel. Não foram detectadas diferenças significativas quanto ao sabor, aroma e textura dos frutos entre sistemas de produção, em ambas as cultivares