31,515 research outputs found
Fermi-Frenet coordinates for space-like curves
We generalize Fermi coordinates, which correspond to an adapted set of
coordinates describing the vicinity of an observer's worldline, to the
worldsheet of an arbitrary spatial curve in a static spacetime. The spatial
coordinate axes are fixed using a covariant Frenet triad so that the metric can
be expressed using the curvature and torsion of the spatial curve. As an
application of Fermi-Frenet coordinates, we show that they allow covariant
inertial forces to be expressed in a simple and physically intuitive way.Comment: 7 page
Germinacao de sementes de leguminosas forrageiras nativas submetidas a tratamentos para a quebra da impermeabilidade do tegumento.
Foi testado o efeito de escarificacao com lixa, do tratamento com acido sulfurico (98o) durante l, 5, 10, 15 e 20 minutos e com agua quente (80oC) durante l, 5,10, 15 e 20 minutos sobre a germinacao das sementes das seguintes leguminosas forrageiras nativas: Stylosanthes capitata, Canavalia obtusifolia, Dioclea lasiophylla, Cratylia floribunda, Calopogonium velutinum e Desmanthus virgatus. O delineamento foi de blocos ao acaso, com tres repeticoes, com 50 sementes por repeticao. Em todas as especies testadas a percentagem de germinacao da testemunha (sem escarificacao) foi muito baixa (0 a 8% aos sete dias e 8 a 16% aos 30 dias) com excecao da C. floribunda (56 e 100% aos 7 e 30 dias). A escarificacao com lixa foi eficiente para S.capitata, C. obtusifolia, C.floribunda e C. velutinum. Os tratamentos com acido sulfurico durante 10, 15 e 20 minutos foram eficazes para D. virgatus (90 a 98% e 94 a 100% de germinacao aos 7 e aos 30 dias) e, durante 5, 10 e 15 minutos foram eficazes para C. floribunda (82 a 92% aos sete dias). Os tratamentos com agua quente so foram eficientes para C. obtusifolia (64 a 90% de germinacao aos 7 e 62 a 100% aos 30 dias). S. capitata teve as mais baixas percentagens de germinacao, em todos os tratamentos, tanto aos 7 como aos 30 dias. C. velutium e D. lasiophylla tiveram germinacao relativamente baixa aos 7 dias, porem bastante aumentada entre o setimo e o trigesimo dia.bitstream/item/40919/1/Bolp50001.pd
Active swarms on a sphere
Here we show that coupling to curvature has profound effects on collective
motion in active systems, leading to patterns not observed in flat space.
Biological examples of such active motion in curved environments are numerous:
curvature and tissue folding are crucial during gastrulation, epithelial and
endothelial cells move on constantly growing, curved crypts and vili in the
gut, and the mammalian corneal epithelium grows in a steady-state vortex
pattern. On the physics side, droplets coated with actively driven microtubule
bundles show active nematic patterns. We study a model of self-propelled
particles with polar alignment on a sphere. Hallmarks of these motion patterns
are a polar vortex and a circulating band arising due to the incompatibility
between spherical topology and uniform motion - a consequence of the hairy ball
theorem. We present analytical results showing that frustration due to
curvature leads to stable elastic distortions storing energy in the band.Comment: 5 pages, 4 figures plus Supporting Informatio
Produção de mudas de tucumanzeiro-do-pará (Astrocaryum vulgare Mart.) por perfilhos.
bitstream/item/68487/1/COM230.pd
Multivariate texture discrimination based on geodesics to class centroids on a generalized Gaussian Manifold
A texture discrimination scheme is proposed wherein probability distributions are deployed on a probabilistic manifold for modeling the wavelet statistics of images. We consider the Rao geodesic distance (GD) to the class centroid for texture discrimination in various classification experiments. We compare the performance of GD to class centroid with the Euclidean distance in a similar context, both in terms of accuracy and computational complexity. Also, we compare our proposed classification scheme with the k-nearest neighbor algorithm. Univariate and multivariate Gaussian and Laplace distributions, as well as generalized Gaussian distributions with variable shape parameter are each evaluated as a statistical model for the wavelet coefficients. The GD to the centroid outperforms the Euclidean distance and yields superior discrimination compared to the k-nearest neighbor approach
Caracterização morfológica de frutos em acessos de pupunheira (Bactris gasipaes var. gasipaes Khunt.)
Publicado também: FRAZÃO, D. A. C.; HOMMA, A. K. O; VIÉGAS, I. de J. M. (Ed.). Contribuição ao desenvolvimento da fruticultura na Amazônia. Belém, PA: Embrapa Amazônia Oriental, 2006. p. 611-617
Soliton surfaces associated with symmetries of ODEs written in Lax representation
The main aim of this paper is to discuss recent results on the adaptation of
the Fokas-Gel'fand procedure for constructing soliton surfaces in Lie algebras,
which was originally derived for PDEs [Grundland, Post 2011], to the case of
integrable ODEs admitting Lax representations. We give explicit forms of the
\g-valued immersion functions based on conformal symmetries involving the
spectral parameter, a gauge transformation of the wave function and generalized
symmetries of the linear spectral problem. The procedure is applied to a
symmetry reduction of the static -field equations leading to the
Jacobian elliptic equation. As examples, we obtain diverse types of surfaces
for different choices of Jacobian elliptic functions for a range of values of
parameters.Comment: 14 Pages, 2 figures Conference Proceedings for QST7 Pragu
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