Poisson Geometry in Constrained Systems

Constrained Hamiltonian systems fall into the realm of presymplectic geometry. We show, however, that also Poisson geometry is of use in this context. For the case that the constraints form a closed algebra, there are two natural Poisson manifolds associated to the system, forming a symplectic dual pair with respect to the original, unconstrained phase space. We provide sufficient conditions so that the reduced phase space of the constrained system may be identified with a symplectic leaf in one of those. In the second class case the original constrained system may be reformulated equivalently as an abelian first class system in an extended phase space by these methods. Inspired by the relation of the Dirac bracket of a general second class constrained system to the original unconstrained phase space, we address the question of whether a regular Poisson manifold permits a leafwise symplectic embedding into a symplectic manifold. Necessary and sufficient for this is the vanishing of the characteristic form-class of the Poisson tensor, a certain element of the third relative cohomology.Comment: 41 pages, more detailed abstract in paper; v2: minor corrections and an additional referenc

Avaliação de carbono e nitrogênio em perfis de solos sob diferentes sistemas de uso da terra, em Ponta Grossa, PR.

Em solos agrícolas, os estoques de C e N são afetados pelo uso da terra e pelas práticas de manejo, assim como pela quantidade de resíduos aportados anualmente na superfície do solo. Sistemas agroflorestais ou integrados têm o potencial de aumentar a fertilidade do solo e o sequestro de carbono e reduzir os processos erosivos. O objetivo deste estudo foi avaliar os estoques de C e N em cinco diferentes sistemas de uso da terra, incluindo dois sistemas integrados: sistema integrado lavoura-pecuária (iLP), sistema integrado lavoura-pecuária-floresta (iLPF), plantio de Eucaliptus dunnii (E), lavoura em plantio direto (L) e campo nativo (CN). As maiores diferenças significativas entre os teores de C e N nos diferentes sistemas de uso da terra estão nas camadas até 10 cm de profundidade, embora existam pequenas diferenças nos teores de C nas camadas mais profundas

Elucidating the real-time Ag nanoparticle growth on alpha-Ag2WO4 during electron beam irradiation: experimental evidence and theoretical insights

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORWhy and how Ag is formed when electron beam irradiation takes place on alpha-Ag2WO4 in a vacuum transmission electron microscopy chamber? To find an answer, the atomic-scale mechanisms underlying the formation and growth of Ag on alpha-Ag2WO4 have been investigated by detailed in situ transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) studies, density functional theory based calculations and ab initio molecular dynamics simulations. The growth process at different times, chemical composition, size distribution and element distribution were analyzed in depth at the nanoscale level using FE-SEM, operated at different voltages (5, 10, 15, and 20 kV), and TEM with energy dispersive spectroscopy (EDS) characterization. The size of Ag nanoparticles covers a wide range of values. Most of the Ag particles are in the 20-40 nm range. The nucleation and formation of Ag on alpha-Ag2WO4 is a result of structural and electronic changes in the AgOx (x = 2,4, 6, and 7) clusters used as constituent building blocks of this material, consistent with metallic Ag formation. First principle calculations point out that Ag-3 and Ag-4-fold coordinated centers, located in the sub-surface of the (100) surface, are the most energetically favorable to undergo the diffusion process to form metallic Ag. Ab initio molecular dynamics simulations and the nudged elastic band (NEB) method were used to investigate the minimum energy pathways of these Ag atoms from positions in the first slab layer to outward sites on the (100) surface of alpha-Ag2WO4. The results point out that the injection of electrons decreases the activation barrier for this diffusion step and this unusual behavior results from the presence of a lower energy barrier process.Why and how Ag is formed when electron beam irradiation takes place on alpha-Ag2WO4 in a vacuum transmission electron microscopy chamber? To find an answer, the atomic-scale mechanisms underlying the formation and growth of Ag on alpha-Ag2WO4 have been investigated by detailed in situ transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) studies, density functional theory based calculations and ab initio molecular dynamics simulations. The growth process at different times, chemical composition, size distribution and element distribution were analyzed in depth at the nanoscale level using FE-SEM, operated at different voltages (5, 10, 15, and 20 kV), and TEM with energy dispersive spectroscopy (EDS) characterization. The size of Ag nanoparticles covers a wide range of values. Most of the Ag particles are in the 20-40 nm range. The nucleation and formation of Ag on alpha-Ag2WO4 is a result of structural and electronic changes in the AgOx (x = 2,4, 6, and 7) clusters used as constituent building blocks of this material, consistent with metallic Ag formation. First principle calculations point out that Ag-3 and Ag-4-fold coordinated centers, located in the sub-surface of the (100) surface, are the most energetically favorable to undergo the diffusion process to form metallic Ag. Ab initio molecular dynamics simulations and the nudged elastic band (NEB) method were used to investigate the minimum energy pathways of these Ag atoms from positions in the first slab layer to outward sites on the (100) surface of alpha-Ag2WO4. The results point out that the injection of electrons decreases the activation barrier for this diffusion step and this unusual behavior results from the presence of a lower energy barrier process.17753525359FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORFAPESP [2013/07296-2, 2012/14468-1, 2010/16970-0, 2013/02032-7]CNPq [573636/2008-7, 150753/2013-6]CAPES [088/2013]2010/16970-02012/14468-12013/02032-72013/07296-2573636/2008-7150753/2013-6088/2013The authors are grateful to Prometeo/2009/053 (GeneralitatValenciana), Ministerio de Economia y Competitividad (Spain), CTQ2012-36253-C03-02, Spanish Brazilian program (PHB2009-0065-PC), FAPESP (Project 2013/07296-2) (Project 2012/14468-1) (Project 2010/16970-0), grant (2013/02032-7), CAPES and CNPq (Project 573636/2008-7, Grant 150753/2013-6) and CAPES (Project 088/2013) for financially supporting this research. Most of the calculations were performed using IFGW-UNICAMP computer facilities and the National Center for High Performance Computing in São Paulo (CENAPAD-SP). We also acknowledge the Servei Informática, Universitat Jaume I, for the generous allotment of computer time

Estoque de carbono e fluxo de metano e óxido nitroso em solo sob floresta ombrófila mista.

Resumo

Fitossociologia e desempenho de espécies arbóreas em um sistema agroflorestal sob bases agroecológicas em Dourados, Mato Grosso do Sul.

bitstream/item/69050/1/056-salomao-fitossociologia.pdfPublicado também no Cadernos de Agroecologia, v. 7, n.2, 2012

Seleção de híbridos intraespecíficos de Brachiaria decumbens com base no nível de antibiose à cigarrinha-das-pastagens Notozulia entreriana (Hemiptera: Cercopidae).

Várias espécies de cigarrinhas pertencentes à família Cercopidae constituem as principais pragas de pastagens no Brasil. Quando em altas populações esses insetos podem reduzir a produção e a qualidade da forrageira. Como alternativa de controle, tem-se estimulado a busca por fontes de resistência a esses insetos. No presente ensaio, comparou-se 25 híbridos intraespecíficos de Brachiaria decumbens quanto ao nível de antibiose à cigarrinha Notozulia entreriana. O ensaio foi conduzido em casa de vegetação

Influência de plantas daninhas na qualidade fisiológica de sementes de genótipos de feijão.

Objetivou-se com este trabalho avaliar o efeito de diferentes sistemas de manejo de plantas daninhas (com capina e sem capina) sobre a qualidade fisiológica das sementes de três cultivares de feijão produzidas na região de cerrado