3,792 research outputs found

    Observations préliminaires sur les insectes nuisibles à l'araza (Eugenia stipitata McVaugh, Myrtaceae), nouvelle culture fruitière en Amazonie

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    L'araza (#Eugenia stipitata McVaugh, #Myrtaceae) est un arbuste fruitier amazonien récemment domestiqué, qui présente un fort potentiel agro-industriel. Afin d'inventorier les insectes nuisibles, des évaluations ont été entreprises entre 1988 et 1992 dans les plantations de trois centres de recherche et dans deux plantations privées, proches d'Iquitos, en Amazonie péruvienne. Neuf espèces nuisibles ont été identifiées dont cinq affectent les fruits, trois sont des défoliateurs et la dernière coupe les rameaux. Quatre de ces espèces sont considérées comme nuisibles : #Anastrepha obliqua, #Conotrachelus eugeniae et #Atractomerus immigrans, qui influent sur la qualité et le volume des fruits récoltés ainsi que #Plectrophoroides impressicollis qui peut détruire totalement les inflorescences. (Résume d'auteur

    Theory of Type-II Superconductors with Finite London Penetration Depth

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    Previous continuum theory of type-II superconductors of various shapes with and without vortex pinning in an applied magnetic field and with transport current, is generalized to account for a finite London penetration depth lambda. This extension is particularly important at low inductions B, where the transition to the Meissner state is now described correctly, and for films with thickness comparable to or smaller than lambda. The finite width of the surface layer with screening currents and the correct dc and ac responses in various geometries follow naturally from an equation of motion for the current density in which the integral kernel now accounts for finite lambda. New geometries considered here are thick and thin strips with applied current, and `washers', i.e. thin film squares with a slot and central hole as used for SQUIDs.Comment: 14 pages, including 15 high-resolution figure

    Unveiling the Active Nucleus of Centaurus A

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    We report new HST WFPC2 and NICMOS observations of the center of the nearest radio galaxy Centaurus A (NGC 5128) and discuss their implications for our understanding of the active nucleus and jet. We detect the active nucleus in the near-IR (K and H) and, for the first time, in the optical (I and V), deriving the spectral energy distribution of the nucleus from the radio to X-rays. The optical and part of the near-IR emission can be explained by the extrapolation of the X-ray power law reddened by A_V~14mag, a value consistent with other independent estimates. The 20pc-scale nuclear disk discovered by Schreier et al. (1998) is detected in the [FeII] 1.64mic line and presents a morphology similar to that observed in Pa alpha with a [FeII]/Pa alpha ratio typical of low ionization Seyfert galaxies and LINERs. NICMOS 3 Pa alpha observations in a 50"x50" circumnuclear region suggest enhanced star formation (~0.3Msun/yr) at the edges of the putative bar seen with ISO, perhaps due to shocks driven into the gas. The light profile, reconstructed from V, H and K observations, shows that Centaurus A has a core profile with a resolved break at ~4" and suggests a black--hole mass of ~10^9 Msun. A linear blue structure aligned with the radio/X-ray jet may indicate a channel of relatively low reddening in which dust has been swept away by the jet.Comment: 19 pages, 13 figures, Astrophysical Journal, in press. High quality figures available at http://www.arcetri.astro.it/~marconi/colpic.htm

    Exact Histogram Specification Optimized for Structural Similarity

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    An exact histogram specification (EHS) method modifies its input image to have a specified histogram. Applications of EHS include image (contrast) enhancement (e.g., by histogram equalization) and histogram watermarking. Performing EHS on an image, however, reduces its visual quality. Starting from the output of a generic EHS method, we maximize the structural similarity index (SSIM) between the original image (before EHS) and the result of EHS iteratively. Essential in this process is the computationally simple and accurate formula we derive for SSIM gradient. As it is based on gradient ascent, the proposed EHS always converges. Experimental results confirm that while obtaining the histogram exactly as specified, the proposed method invariably outperforms the existing methods in terms of visual quality of the result. The computational complexity of the proposed method is shown to be of the same order as that of the existing methods. Index terms: histogram modification, histogram equalization, optimization for perceptual visual quality, structural similarity gradient ascent, histogram watermarking, contrast enhancement

    Los insectos plaga del camu camu (Myrciaria dubia H.B.K.) y del araza (Eugenia stipitata Mc Vaugh) identificacion y control

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    Le camu camu (#Myrciaria dubio H.B.K.) et l'araza (#Eugenia stipitata Mc Vaugh) sont des cultures nouvelles en Amazonie péruvienne. Dans ce travail sont citées 21 espèces d'insectes nuisibles au camu camu, parmi lesquelles 6 espèces doivent être considérées comme des ravageurs économiquement importants, ce sont : #Austrotachardiella sp, #Ceroplastes sp., #Conotrachelus sp.1., #Dysmicoccus brevipes Cock, #Tuthillia cognata Hodk. y #Xylosandrus compactus Heichh. Sur araza 9 espèces ont été répertoriées, dont 4 sont des ravageurs importants : #Anastrepha obliqua Macq., #Atractomerus immigrans Clark, #Conotrachelus sp. 2 y #Plectrophoroides impressicollis Chevr. Quelques espèces nouvelles pour la science ont été décrites récemment ou sont en cours d'étude. On donne les premières informations sur les espèces dont la biologie et l'écologie n'étaient pas connues, ainsi que des méthodes de contrôle adaptées au système de gestion des plantations. (Résumé d'auteur

    On the algebraic invariant curves of plane polynomial differential systems

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    We consider a plane polynomial vector field P(x,y)dx+Q(x,y)dyP(x,y)dx+Q(x,y)dy of degree m>1m>1. To each algebraic invariant curve of such a field we associate a compact Riemann surface with the meromorphic differential ω=dx/P=dy/Q\omega=dx/P=dy/Q. The asymptotic estimate of the degree of an arbitrary algebraic invariant curve is found. In the smooth case this estimate was already found by D. Cerveau and A. Lins Neto [Ann. Inst. Fourier Grenoble 41, 883-903] in a different way.Comment: 10 pages, Latex, to appear in J.Phys.A:Math.Ge

    Infrared Constraints on AGN Tori Models

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    This work focuses on the properties of dusty tori in active galactic nuclei (AGN) derived from the comparison of SDSS type 1 quasars with mid-Infrared (MIR) counterparts and a new, detailed torus model. The infrared data were taken by the Spitzer Wide-area InfraRed Extragalactic (SWIRE) Survey. Basic model parameters are constraint, such as the density law of the graphite and silicate grains, the torus size and its opening angle. A whole variety of optical depths is supported. The favoured models are those with decreasing density with distance from the centre, while there is no clear tendency as to the covering factor, ie small, medium and large covering factors are almost equally distributed. Based on the models that better describe the observed SEDs, properties such as the accretion luminosity, the mass of dust, the inner to outer radius ratio and the hydrogen column density are computed.Comment: 4 pages, 4 figures, to appear in "Infrared Diagnostics of Galaxy Evolution", ASP Conference Series, Pasadena, 14-16 November 200

    A Rigourous Treatment of the Lattice Renormalization Problem of F_B

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    The BB-meson decay constant can be measured on the lattice using a 1/mb1/m_b expansion. To relate the physical quantity to Monte Carlo data one has to know the renormalization coefficient, ZZ, between the lattice operators and their continuum counterparts. We come back to this computation to resolve discrepancies found in previous calculations. We define and discuss in detail the renormalization procedure that allows the (perturbative) computation of ZZ. Comparing the one-loop calculations in the effective Lagrangian approach with the direct two-loop calculation of the two-point BB-meson correlator in the limit of large bb-quark mass, we prove that the two schemes give consistent results to order αs\alpha_s. We show that there is, however, a renormalization prescription ambiguity that can have sizeable numerical consequences. This ambiguity can be resolved in the framework of an O(a)O(a) improved calculation, and we describe the correct prescription in that case. Finally we give the numerical values of ZZ that correspond to the different types of lattice approximations discussed in the paper.Comment: 27 pages, 2 figures (Plain TeX, figures in an appended postscript file
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