Physics-based derivation of a formula for the mutual depolarization of two post-like field emitters

Recent analyses of the field enhancement factor (FEF) from multiple emitters have revealed that the depolarization effect is more persistent with respect to the separation between the emitters than originally assumed. It has been shown that, at sufficiently large separations, the fractional reduction of the FEF decays with the inverse cube power of separation, rather than exponentially. The behavior of the fractional reduction of the FEF encompassing both the range of technological interest $0<c/h\lesssim5$ ($c$ being the separation and $h$ is the height of the emitters) and $c\rightarrow\infty$, has not been predicted by the existing formulas in field emission literature, for post-like emitters of any shape. In this letter, we use first principles to derive a simple two-parameter formula for fractional reduction that can be of interest for experimentalists to modeling and interpret the FEF from small clusters of emitters or arrays in small and large separations. For the structures tested, the agreement between numerical and analytical data is $\sim1\%$

On the Integrability and Chaos of an N=2 Maxwell-Chern-Simons-Higgs Mechanical Model

We apply different integrability analysis procedures to a reduced (spatially homogeneous) mechanical system derived from an off-shell non-minimally coupled N=2 Maxwell-Chern-Simons-Higgs model that presents BPS topological vortex excitations, numerically obtained with an ansatz adopted in a special - critical coupling - parametric regime. As a counterpart of the regularity associated to the static soliton-like solution, we investigate the possibility of chaotic dynamics in the evolution of the spatially homogeneous reduced system, descendant from the full N=2 model under consideration. The originally rich content of symmetries and interactions, N=2 susy and non-minimal coupling, singles out the proposed model as an interesting framework for the investigation of the role played by (super-)symmetries and parametric domains in the triggering/control of chaotic behavior in gauge systems. After writing down effective Lagrangian and Hamiltonian functions, and establishing the corresponding canonical Hamilton equations, we apply global integrability Noether point symmetries and Painleveproperty criteria to both the general and the critical coupling regimes. As a non-integrable character is detected by the pair of analytical criteria applied, we perform suitable numerical simulations, as we seek for chaotic patterns in the system evolution. Finally, we present some Comments on the results and perspectives for further investigations and forthcoming communications.Comment: 18 pages, 5 figure

Produção de palha e forragem por espécies anuais e perenes em sucessão à soja.

O objetivo deste trabalho foi avaliar a produção de palha e de forragem por forrageiras anuais e perenes implantadas em sucessão à cultura da soja, e seus efeitos sobre a produtividade de grãos da cultura no próximo cultivo. O delineamento experimental utilizado foi o de blocos ao acaso, com parcelas subdivididas (crescimento livre e sob cortes sucessivos), com quatro repetições. Foram avaliadas oito forrageiras em dois municípios de Mato Grosso do Sul. A produção de palha e forragem foi avaliada em 2005 e 2006, nas espécies Urochloa ruziziensis; U. decumbens; U. brizantha cv. Marandu e Xaraés; Panicum maximum cv. Tanzânia e Mombaça, P. maximum x P. infestans cv. Massai; Pennisetum americanum cv. BRS 1501; e Sorghum bicolor cv. Santa Elisa. As forrageiras foram semeadas mecanicamente após a colheita da soja, em 1/4/2005 e 24/3/2006, em São Gabriel do Oeste, e em 20/3/2005 e 13/3/2006, em Dourados. Sorgo, U. brizantha cv. Xaraés e P. maximum cv. Tanzânia apresentaram características como elevada produtividade, alta qualidade da forragem e facilidade de controle, favoráveis para produção tanto de forragem quanto de palha. Urochloa ruziziensis e U. decumbens apresentaram melhor desempenho para a produção de palha. O cultivo das espécies forrageiras em sucessão à soja não afeta a produtividade da cultura.The objective of this work was to evaluate forage and straw production, of annual and perennial forage implanted in succession to soybean, and their effects on crop grain yield in the following season. The experimental design was in randomized blocks with four replicates, in a split-plot arrangement (free growth and successive cuts). Eight forages were evaluated in two municipalities of the state of Mato Grosso do Sul, Brazil. Straw and forage production was evaluated in 2005 and 2006, in the following species: Urochloa ruziziensis, U. decumbens; U. brizantha cv. Marandu and Xaraés; Panicum maximum cv. Tanzânia and Mombaça, P. maximum x P. infestans cv. Massai, Pennisetum americanum cv. BRS 1501, and Sorghum bicolor cv. Santa Elisa. Forages were planted mechanically, after the soybean crop harvest on 4/1/2005 and 3/24/2006, in São Gabriel do Oeste, and 3/20/2005 and 3/13/2006, in Dourados. Sorghum, U. brizantha cv. Xaraés and P. maximum cv. Tanzânia characteristics, such as high productivity, high forage quality and easiness in control, were favorable for production of both forage and straw. Urochloa ruziziensis and U. decumbens showed better performance for straw production. Forage cultivation in soybean succession does not affect crop yield

Filtros biologicamente ativos por enzimas imobilizadas.

bitstream/CNPDIA/10324/1/PA16_97.pd

Avaliação por Cromatografia Líquida de Alta Eficiência (Hplc) da Interação Atrazina-Carboximetilcelulose.

bitstream/CNPDIA/10488/1/CT38_2000.pd

Restoring observed classical behavior of the carbon nanotube field emission enhancement factor from the electronic structure

Experimental Fowler-Nordheim plots taken from orthodoxly behaving carbon nanotube (CNT) field electron emitters are known to be linear. This shows that, for such emitters, there exists a characteristic field enhancement factor (FEF) that is constant for a range of applied voltages and applied macroscopic fields $F_\text{M}$. A constant FEF of this kind can be evaluated for classical CNT emitter models by finite-element and other methods, but (apparently contrary to experiment) several past quantum-mechanical (QM) CNT calculations find FEF-values that vary with $F_\text{M}$. A common feature of most such calculations is that they focus only on deriving the CNT real-charge distributions. Here we report on calculations that use density functional theory (DFT) to derive real-charge distributions, and then use these to generate the related induced-charge distributions and related fields and FEFs. We have analysed three carbon nanostructures involving CNT-like nanoprotrusions of various lengths, and have also simulated geometrically equivalent classical emitter models, using finite-element methods. We find that when the DFT-generated local induced FEFs (LIFEFs) are used, the resulting values are effectively independent of macroscopic field, and behave in the same qualitative manner as the classical FEF-values. Further, there is fair to good quantitative agreement between a characteristic FEF determined classically and the equivalent characteristic LIFEF generated via DFT approaches. Although many issues of detail remain to be explored, this appears to be a significant step forwards in linking classical and QM theories of CNT electrostatics. It also shows clearly that, for ideal CNTs, the known experimental constancy of the FEF value for a range of macroscopic fields can also be found in appropriately developed QM theory.Comment: A slightly revised version has been published - citation below - under a title different from that originally used. The new title is: "Restoring observed classical behavior of the carbon nanotube field emission enhancement factor from the electronic structure

Modelagem de sistemas para tomada de decisões na pecuária leiteira.

A pecuaria leiteira nacional; Modelagem de sistemas sob o enfoque de negocio; Modelagem de sistemas na agropecuaria; Modelo para avaliacao de dietas de vacas leiteiras

Sorgo para pastejo/corte e cobertura do solo no período de outono/inverno (safrinha) em Mato Grosso do Sul.

Em Mato Grosso do Sul, as principais culturas utilizadas para cobertura de solo na safrinha são o milheto, a aveia e o nabo (Hernani et al., 1995; Machado, 2003). Para pastejo, também são utilizadas essas espécies, com exceção do nabo. Devido ao risco de geadas, as espécies adaptadas ao clima frio, como a aveia e o nabo, são mais utilizadas na região sul do Estado. Na região norte, o milheto e o sorgo são mais produtivos no período de outono, porque o clima, apesar de seco, é quente, favorecendo as espécies tropicais. Em regiões com esta condição, o sorgo é muito utilizado para a produção de grãos, sendo recente sua utilização para a produção de palha e forragem. Pela sua tolerância a déficit hídrico e a baixas temperaturas, a cultura vem ganhando importância econômica no Estado. Este estudo teve como objetivo selecionar genótipos de sorgo para pastejo na safra de outono/inverno, em sucessão a soja.bitstream/item/38771/1/BP-200416.pd

Avaliação do efeito cicatrizante da quitosana por aplicação tópica em ratos.

bitstream/CNPDIA-2009-09/11045/1/DOC29_2007.pd