33,205 research outputs found

    Ecology and structure of Drosophyllum lusitanicum (l.) Links populations in the south-west of the Iberian Peninsula

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    Ecolog√≠a y estructura de poblaciones de Drosophyllum lusitanicum (L.) Link en el suroeste de la Pen√≠nsula Ib√©rica. Drosophyllum lusitanicum es una planta aut√≥gama y nautoc√≥rica cuyo tama√Īo y estructura de poblaci√≥n han sido estudiados en dos √°reas del suroeste de la Pen√≠nsula Ib√©rica. Su car√°cter cenol√≥gico se documenta mediante una tabla fitosociol√≥gica sint√©tica basada en inventarios ya publicados y datos nuevos. En la Sierra de Monchique (Portugal) se cartograf√≠an 21 poblaciones cuyo tama√Īo medio es de 165 individuos. Sin embargo, en el Campo de Gibraltar (Espa√Īa), se encontr√≥ la poblaci√≥n de mayor tama√Īo, con varios miles de individuos en la Sierra del Aljibe. Aqu√≠ se estudi√≥ el tama√Īo de las plantas, el di√°metro de la roseta basal y el grado de lignificaci√≥n de 700 individuos, lo que se utiliz√≥ como indicador indirecto de la estructura de edades de 19 poblaciones.Drosophyllum lusitanicum tiene un cierto car√°cter pionero. Se presenta mayoritariamente en los brezales aclarados de Ericion umbellatae (Stauracantho-Drosophylletum, Querco lusitanicae-Stauracanthetum, Genisto tridentis-Stauracanthetum, etc.). Es capaz de colonizar medios alterados, como cunetas de carreteras y cortafuegos, y es un ap√≥fito en las comunidades basales de Drosophyllo-[Stauracanthenion], siendo adem√°s esta especie favorecida por los frecuentes incendios de la zona. En los alcornocales abiertos de Myrto-Quercetum suberis y en los brezales densos de Erica australis predominan los individuos grandes, siendo √©stas poblaciones maduras. Finalmente, se aportan algunos datos poco conocidos de su reproducci√≥n y ecolog√≠a que indican la necesidad de un mayor esfuerzo para la conservaci√≥n del √°rea portuguesa estudiada

    Too Much to Lose, or More to Gain? Should Sweden Join the Euro?

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    This paper considers the costs and benefits of Sweden joining the European Economic and Monetary Union (EMU). We pay particular attention to the costs of abandoning the krona in terms of a loss of monetary policy independence. For this purpose, we apply a cointegrated VAR framework to examine the degree of monetary independence that the Sveriges Riksbank enjoys. Our results suggest that Sweden has in fact relatively little to lose from joining EMU, at least in terms of monetary independence. We complement our analysis by looking into other criteria affecting the cost-benefit calculus of monetary integration, which, by and large, support our positive assessment of Swedish EMU membership

    Chinese Monetary Policy and the Dollar Peg

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    This paper investigates to what extent Chinese monetary policy is constrained by the dollar peg. To this end, we use a cointegration framework to examine whether Chinese interest rates are driven by the Fed's policy. In a second step, we estimate a monetary model for China, in which we include also other monetary policy tools besides the central bank interest rate, namely reserve requirement ratios and open market operations. Our results suggest China has been relatively successful in isolating its monetary policy from the US policy and that the interest rate tool has not been effectively made use of. We therefore conclude that by employing capital controls and relying on other instruments than the interest rate China has been able to exert relatively autonomous monetary policy

    Calculation of Hydrogenic Bethe Logarithms for Rydberg States

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    We describe the calculation of hydrogenic (one-loop) Bethe logarithms for all states with principal quantum numbers n <= 200. While, in principle, the calculation of the Bethe logarithm is a rather easy computational problem involving only the nonrelativistic (Schroedinger) theory of the hydrogen atom, certain calculational difficulties affect highly excited states, and in particular states for which the principal quantum number is much larger than the orbital angular momentum quantum number. Two evaluation methods are contrasted. One of these is based on the calculation of the principal value of a specific integral over a virtual photon energy. The other method relies directly on the spectral representation of the Schroedinger-Coulomb propagator. Selected numerical results are presented. The full set of values is available at quant-ph/0504002.Comment: 10 pages, RevTe

    Does Corticothalamic Feedback Control Cortical Velocity Tuning?

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    The thalamus is the major gate to the cortex and its contribution to cortical receptive field properties is well established. Cortical feedback to the thalamus is, in turn, the anatomically dominant input to relay cells, yet its influence on thalamic processing has been difficult to interpret. For an understanding of complex sensory processing, detailed concepts of the corticothalamic interplay need yet to be established. To study corticogeniculate processing in a model, we draw on various physiological and anatomical data concerning the intrinsic dynamics of geniculate relay neurons, the cortical influence on relay modes, lagged and nonlagged neurons, and the structure of visual cortical receptive fields. In extensive computer simulations we elaborate the novel hypothesis that the visual cortex controls via feedback the temporal response properties of geniculate relay cells in a way that alters the tuning of cortical cells for speed.Comment: 31 pages, 7 figure

    Multiplicity distribution and source deformation in full-overlap U+U collisions

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    We present a full Monte Carlo simulation of the multiplicity and eccentricity distributions in U+U collisions at sqrt(s) = 200 A GeV. While unavoidable trigger inefficiencies in selecting full-overlap U+U collisions cause significant modifications of the multiplicity distribution shown in PRL94, 132301 (2005), a selection of source eccentricities by cutting the multiplicity distribution is still possible.Comment: 4 pages. Corrected error in Eq. (4), recalculated Figs. 2-4 and added Fig. 5 and more discussion. As a result of correcting this error, the spectator cut for a useful definition of "full-overlap" collisions had to be tightened by a factor 10, to the 0.5% of events with the lowest number of spectator
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