603,500 research outputs found

    Annual report, 1960

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    Dynamic structure selection and instabilities of driven Josephson lattice in high-temperature superconductors

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    We investigate the dynamics of the Josephson vortex lattice in layered high-Tc_{c} superconductors at high magnetic fields. Starting from coupled equations for superconducting phases and magnetic field we derive equations for the relative displacements [phase shifts] between the planar Josephson arrays in the layers. These equations reveal two families of steady-state solutions: lattices with constant phase shifts between neighboring layers, starting from zero for a rectangular configuration to π\pi for a triangular configuration, and double-periodic lattices. We find that the excess Josephson current is resonantly enhanced when the Josephson frequency matches the frequency of the plasma mode at the wave vector selected by the lattice structure. The regular lattices exhibit several kinds of instabilities. We find stability regions of the moving lattice in the plane lattice structure - Josephson frequency. A specific lattice structure at given velocity is selected uniquely by boundary conditions, which are determined by the reflection properties of electromagnetic waves generated by the moving lattice. With increase of velocity the moving configuration experiences several qualitative transformations. At small velocities the regular lattice is stable and the phase shift between neighboring layers smoothly decreases with increase of velocity, starting from π\pi for a static lattice. At the critical velocity the lattice becomes unstable. At even higher velocity a regular lattice is restored again with the phase shift smaller than π/2\pi/2. With increase of velocity, the structure evolves towards a rectangular configuration.Comment: 28 pages, 12 figures, submitted to Phys. Rev.

    Calendar, 1956

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    DroughtScape- Winter 2018

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    CONTENTS Year in review: Drought eased in California, developed in Northern Plains......... 2 Quarterly Summary: Drought creeps across the country.............. 3 Annual impact summary: A year of wildfires.......... 4 Quarterly impact summary: Drought expands in Texas, Colorado............ 6 Drought and water crisis book updated............... 8 U.S. Drought Monitor available in Spanish........... 9 Study shows cities step up when drought occurs............... 10 New staff at the NDMC............. 11 Drought Summit in photos.............. 1

    Science and Engineering Labor Force

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    [Excerpt] Like most developed economies, the United States increasingly depends on a technically skilled workforce, including scientists and engineers. Workers for whom knowledge and skill in S&E are central to their jobs have an effect on the economy and the wider society that is disproportionate to their numbers: they contribute to research and development, increased knowledge, technological innovation, and economic growth. Moreover, the knowledge and skills associated with science and engineering have diffused across occupations and become more important in jobs that are not traditionally associated with S&E

    DroughtScape- Spring 2017

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    CONTENTS Drought center helps islands reduce drought vulnerability.......... 2 2017 sees above-average precipitation, warmer temps.......... 3 California pulls out of drought............. 4 After tech transfer, training Tunisia launches first drought map............... 6 Drought center releases 2016 annual report.............. 7 Book chapter focuses on drought and health................ 8 U2U wraps up, brings useful tools to farmers...............9 Survey finds drought info leads to better decisions.............. 1
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