Error threshold in finite populations

A simple analytical framework to study the molecular quasispecies evolution of finite populations is proposed, in which the population is assumed to be a random combination of the constiyuent molecules in each generation,i.e., linkage disequilibrium at the population level is neglected. In particular, for the single-sharp-peak replication landscape we investigate the dependence of the error threshold on the population size and find that the replication accuracy at threshold increases linearly with the reciprocal of the population size for sufficiently large populations. Furthermore, in the deterministic limit our formulation yields the exact steady-state of the quasispecies model, indicating then the population composition is a random combination of the molecules.Comment: 14 pages and 4 figure

Avaliação de impactos ambientais, sociais e econômicos do sistema plantio direto de grãos na Fazenda Rio Grande, Paragominas, PA.

O presente trabalho refere-se à análise de indicadores de impactos ambientais, sociais e econômicos do Sistema Plantio Direto (SPD) de grãos na Fazenda Rio Grande, realizada em setembro de 2010, no município de Paragominas, PA, no âmbito do projeto ?Sistema Plantio Direto: Alternativa de Produção Sustentável para Recuperação de Áreas Alteradas na Amazônia? (MP-02, Embrapa Amazônia Oriental). O estudo de caso empregou o Sistema de Avaliação de Impactos de Inovações Tecnológicas Agropecuárias (Ambitec-Agro), que consiste de um conjunto de indicadores de impactos socioambientais, referentes a critérios de sustentabilidade, na escala do estabelecimento rural. São considerados sete aspectos essenciais de análise: i) Uso de Insumo e Recursos; ii) Qualidade Ambiental; iii) Respeito ao Consumidor; iv) Emprego; v) Renda; vi) Saúde; vii) Gestão e Administração. Os resultados desse estudo explicitam importantes contribuições da tecnologia de plantio direto de grãos adotada na propriedade rural avaliada para o desempenho socioambiental do estabelecimento, com impactos positivos em todos os aspectos de análise. Os manejos realizados na cultura de grãos em SPD favoreceram amplamente os índices relacionados aos indicadores de uso de insumos e recursos, ao melhorar a eficiência das operações com máquinas agrícolas e promover aumentos de produtividade que permitiram importantes reduções na demanda de áreas de cultivo. Esses ganhos de eficiência produtiva garantiram melhorias quanto às emissões de poluentes atmosféricos, redução no risco de contaminação das águas e recomposição da capacidade produtiva dos solos. Uma cuidadosa proteção contra incêndios traz valiosa recuperação das reservas florestais, com ganhos importantes para a conservação da biodiversidade e recomposição de corredores ecológicos. Iniciativas de capacitação dos trabalhadores favoreceram o desempenho do estabelecimento no aspecto relativo ao emprego. Repercussões positivas também foram verificadas nos critérios de desempenho econômico, como geração de renda e valor da propriedade. Significativas melhoras foram observadas no aspecto Gestão e Administração, em virtude das características de dedicação e perfil do responsável ou administrador, que aplica modelos de planejamento das atividades produtivas e de gestão financeira; promove a gestão de resíduos e, especialmente, fomenta o relacionamento institucional. A adoção de melhores práticas de manejo no SPD e a capacitação continuada são iniciativas que explicam o expressivo desempenho socioambiental verificado na Fazenda Rio Grande. Comparativamente a um conjunto de 180 estudos de caso anteriormente realizados, em relação a uma ampla variedade de tecnologias agropecuárias e contextos socioambientais, o índice de desempenho observado posiciona-se entre os 10% mais elevados, atestando as importantes contribuições da tecnologia de plantio direto de grãos, conforme modelo realizado na Fazenda Rio Grande, para o desenvolvimento local sustentável, em uma região submetida a pressões ambientais, como é o caso do Nordeste Paraense.bitstream/item/82537/1/Oriental-BPD86.pd

Yang-Lee zeros for a nonequilibrium phase transition

Equilibrium systems which exhibit a phase transition can be studied by investigating the complex zeros of the partition function. This method, pioneered by Yang and Lee, has been widely used in equilibrium statistical physics. We show that an analogous treatment is possible for a nonequilibrium phase transition into an absorbing state. By investigating the complex zeros of the survival probability of directed percolation processes we demonstrate that the zeros provide information about universal properties. Moreover we identify certain non-trivial points where the survival probability for bond percolation can be computed exactly.Comment: LaTeX, IOP-style, 13 pages, 10 eps figure

Optical energies of AllnN epilayers

Optical energy gaps are measured for high-quality Al1−xInxN-on-GaN epilayers with a range of compositions around the lattice match point using photoluminescence and photoluminescence excitation spectroscopy. These data are combined with structural data to determine the compositional dependence of emission and absorption energies. The trend indicates a very large bowing parameter of 6 eV and differences with earlier reports are discussed. Very large Stokes' shifts of 0.4-0.8 eV are observed in the composition range 0.13<x<0.24, increasing approximately linearly with InN fraction despite the change of sign of the piezoelectric fiel

Renormalization Group Study of Chern-Simons Field Coupled to Scalar Matter in a Modified BPHZ Subtraction Scheme

We apply a soft version of the BPHZ subtraction scheme to the computation of two-loop corrections from an Abelian Chern-Simons field coupled to (massive) scalar matter with a $\lambda(\Phi^\dag\Phi)^2$ and $\nu(\Phi^\dag\Phi)^3$ self-interactions. The two-loop renormalization group functions are calculated. We compare our results with those in the literature.Comment: 15 pages, 7 figures, revtex. To appear in Phys. Rev.

The night-sky at the Calar Alto Observatory II: The sky at the near infrared

We present here the characterization of the night sky-brightness at the near-infrared, the telescope seeing, and the fraction of useful time at the Calar Alto observatory. For this study we have collected a large dataset comprising 7311 near-infrared images taken regularly along the last four years for the ALHAMBRA survey (J, H and Ks-bands), together with a more reduced dataset of additional near-infrared images taken for the current study. In addition we collected the information derived by the meteorological station at the observatory during the last 10 years, together with the results from the cloud sensor for the last ~2 years. We analyze the dependency of the near-infrared night sky-brightness with the airmass and the seasons, studying its origins and proposing a zenithal correction. A strong correlation is found between the night sky-brightness in the Ks-band and the air temperature, with a gradient of ~ -0.08 mag per 1 C degree. The typical (darkest) night sky-brightness in the J, H and Ks-band are 15.95 mag (16.95 mag), 13.99 mag (14.98 mag) and 12.39 mag (13.55 mag), respectively. These values show that Calar Alto is as dark in the near-infrared as most of the other astronomical astronomical sites in the world that we could compare with. Only Mauna Kea is clearly darker in the Ks-band. The typical telescope seeing at the 3.5m is ~1.0" when converted to the V-band, being only slightly larger than the atmospheric seeing measured at the same time by the seeing monitor, ~0.9". Finally we estimate the fraction of useful time based on the relative humidity, gust wind speed and presence of clouds. This fraction, ~72%, is very similar to the one derived in Paper I, based on the fraction of time when the extinction monitor is working.Comment: 15 pages, 6 figures, accepted to be published in PAS

Conductance fluctuations and weak localization in chaotic quantum dots

We study the conductance statistical features of ballistic electrons flowing through a chaotic quantum dot. We show how the temperature affects the universal conductance fluctuations by analyzing the influence of dephasing and thermal smearing. This leads us to two main findings. First, we show that the energy correlations in the transmission, which were overlooked so far, are important for calculating the variance and higher moments of the conductance. Second, we show that there is an ambiguity in the method of determination of the dephasing rate from the size of the of the weak localization. We find that the dephasing times obtained at low temperatures from quantum dots are underestimated.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let

Chiral organocatalysts based on lipopeptide micelles for aldol reactions in water

A comprehensive study of the self-assembly in water of a lipopeptide consisting of a sequence of L-proline, L-arginine and L-tryptophan with a hydrocarbon chain has been performed. Fluorescence assays were used to determine the critical aggregation concentration. In situ small-angle X-ray scattering (SAXS) and molecular dynamics simulations showed the presence of spherical micelles with diameters around 6 nm. In agreement with these results, cryo-TEM images showed globular aggregates with diameters ranging from ≈4 nm up to ≈9 nm. Furthermore, the lipopeptide catalytic activity has been tested for the direct aldol reaction between cyclohexanone and p-nitrobenzaldehyde, and we have observed that the self-association of the organocatalyst played a critical role in the enhanced activity. Water affects the selectivity, and poor results are obtained under neat reaction conditions. The location of the catalytic groups at the lipopetide/water solvent interface also endowed unusual selectivity in the catalyzed aldol reactions. Under optimized reaction conditions, high yields (up to >99%), good enantioselectivity (ee up to 85%) and high diastereoselectivity (ds up to 92 : 8) were obtained

The Shape and Scale of Galactic Rotation from Cepheid Kinematics

A catalog of Cepheid variables is used to probe the kinematics of the Galactic disk. Radial velocities are measured for eight distant Cepheids toward l = 300; these new Cepheids provide a particularly good constraint on the distance to the Galactic center, R_0. We model the disk with both an axisymmetric rotation curve and one with a weak elliptical component, and find evidence for an ellipticity of 0.043 +/- 0.016 near the Sun. Using these models, we derive R_0 = 7.66 +/- 0.32 kpc and v_circ = 237 +/- 12 km/s. The distance to the Galactic center agrees well with recent determinations from the distribution of RR Lyrae variables, and disfavors most models with large ellipticities at the solar orbit.Comment: 36 pages, LaTeX, 10 figure