78,333 research outputs found

    Minimal mechanisms for vegetation patterns in semiarid regions

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    The minimal ecological requirements for formation of regular vegetation patterns in semiarid systems have been recently questioned. Against the general belief that a combination of facilitative and competitive interactions is necessary, recent theoretical studies suggest that, under broad conditions, nonlocal competition among plants alone may induce patterns. In this paper, we review results along this line, presenting a series of models that yield spatial patterns when finite-range competition is the only driving force. A preliminary derivation of this type of model from a more detailed one that considers water-biomass dynamics is also presented. Keywords: Vegetation patterns, nonlocal interactionsComment: 8 pages, 4 figure

    Preface "Nonlinear processes in oceanic and atmospheric flows"

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    Nonlinear phenomena are essential ingredients in many oceanic and atmospheric processes, and successful understanding of them benefits from multidisciplinary collaboration between oceanographers, meteorologists, physicists and mathematicians. The present Special Issue on ``Nonlinear Processes in Oceanic and Atmospheric Flows'' contains selected contributions from attendants to the workshop which, in the above spirit, was held in Castro Urdiales, Spain, in July 2008. Here we summarize the Special Issue contributions, which include papers on the characterization of ocean transport in the Lagrangian and in the Eulerian frameworks, generation and variability of jets and waves, interactions of fluid flow with plankton dynamics or heavy drops, scaling in meteorological fields, and statistical properties of El Ni\~no Southern Oscillation.Comment: This is the introductory article to a Special Issue on "Nonlinear Processes in Oceanic and Atmospheric Flows'', published in the journal Nonlinear Processes in Geophysics, where the different contributions are summarized. The Special Issue itself is freely available from http://www.nonlin-processes-geophys.net/special_issue103.htm

    Helping America's Dual Language Learners Succeed: A Research-based Agenda for Action

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    In the fall of 2014, the Heising-Simons and McKnight Foundations provided support for a National Research Summit on the Early Care and Education of Dual Language Learners (DLLs) in Washington, DC. The goal of the two day summit was to engage and extend the established knowledge base accrued by the Center for Early Care and Educational Research Dual Language Learners (CECER-DLL), while simultaneously informing the future potential efforts by the Heising-Simons and McKnight Foundations specific to the early care and education of dual language learners. Day two centered on the presentation of five McKnight-commissioned papers, the topics of which included: Research Based Models and Best Practices for DLLs across PreK - 3rd gradePerspectives on Assessment of DLLs Development & Learning, PreK - 3Human Resource Development and Support for Those Serving DLLsThe Critical Role of Leaderships in Programs Designed for DLLs, PreK - 3Policy Advances & Levers Related to DLLs in PreK - 3rd gradeThe report attempts to provide a short summary and synthesis of the topics covered in these papers and the discussion generated at the National Summit on Early Care and Education of Dual Language Learners. In addition, a set of recommendations are presented for each topic with regard to the implications drawn from these synthesis and of particular relevance to the supporting foundations' future investment considerations related to DLLs

    The feasibility of inventorying native vegetation and related resources form space photography

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    Photointerpretation of Gemini 4 photographs for inventorying native vegetatio

    Non-localities and Fermi motion corrections in K−K^- atoms

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    We evaluate the p-wave K−NK^-N amplitudes from the chiral Lagrangians and from there construct the p-wave part of the K−K^- nucleus optical potential plus a small s-wave part induced from the elementary p-wave amplitude and the nuclear Fermi motion. Simultaneously, the momentum and energy dependence of the s-wave optical potential, previously developed, are taken into account and shown to generate a small p-wave correction to the optical potential. All the corrections considered are small compared to the leading s-wave potential, and lead to changes in the shifts and widths which are smaller than the experimental errors. A thorough study of the threshold region and low densities is conducted, revealing mathematical problems for which a physical solution is given.Comment: revised version, 28 pages, Latex, 8 postscript figures. Submitted to Nucl. Phys.

    Biological activity in the wake of an island close to a coastal upwelling

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    Hydrodynamic forcing plays an important role in shaping the dynamics of marine organisms, in particular of plankton. In this work we study the planktonic biological activity in the wake of an island which is close to an upwelling region. Our research is based on numerical analysis of a kinematic flow mimicking the hydrodynamics in the wake, coupled to a three-component plankton model. Depending on model parameters different phenomena are described: a) The lack of transport of nutrients and plankton across the wake, so that the influence of upwelling on primary production on the other side of the wake is blocked. b) For sufficiently high vorticity, the role of the wake in facilitating this transport and leading to an enhancement of primary production. Finally c) we show that under certain conditions the interplay between wake structures and biological growth leads to plankton blooms inside mesoscale hydrodynamic vortices that act as incubators of primary production.Comment: 42 pages, 9 figure

    Extraordinary transverse magneto-optical Kerr effect in a superlens

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    It has been shown that a slab of a negative index material can behave as a superlens enhancing the imaging resolution beyond the wavelength limit. We show here that if such a slab possesses in addition some magneto-optical activity, it could act as an ideal optical filter and exhibit an extraordinary transverse magneto-optical Kerr effect. Moreover, we show that losses, which spoil the imaging resolution of these lenses, are a necessary ingredient to observe this effect.Comment: 5 pages, 6 figure

    Plankton blooms in vortices: The role of biological and hydrodynamic time scales

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    We study the interplay of hydrodynamic mesoscale structures and the growth of plankton in the wake of an island, and its interaction with a coastal upwelling. Our focus is on a mechanism for the emergence of localized plankton blooms in vortices. Using a coupled system of a kinematic flow mimicking the mesoscale structures behind the island and a simple three component model for the marine ecosystem, we show that the long residence times of nutrients and plankton in the vicinity of the island and the confinement of plankton within vortices are key factors for the appearance of localized plankton bloomsComment: 29 pages, 9 figure
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