12,715 research outputs found

    (63)Cu NQR Evidence for Spatial Variation of Hole Concentration in La(2-x)Sr(x)CuO(4)

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    We report experimental evidence for the spatial variation of hole concentration x_(hole) in the high Tc superconductor La(2-x)Sr(x)CuO(4) (0.04 <= x <= 0.16) by using (63)Cu NQR for (63)Cu isotope enriched samples. We demonstrate that the extent of the spatial variation of the local hole concentration D(x)_(hole) is reflected on (63)1/T1 and deduce the temperature dependence. D(x)_(hole) increases below 500 - 600K, and reaches values as large as D(x)_(hole)/x ~ 0.5 below ~ 150K. We estimate the length scale of the spatial variation in x_(hole) to be R_(hole) >~ 3nm from analysis of the NQR spectrum.Comment: Accepted for publication in Physical Review Letter

    Collective excitations and instability of an optical lattice due to unbalanced pumping

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    We solve self-consistently the coupled equations of motion for trapped particles and the field of a one-dimensional optical lattice. Optomechanical coupling creates long-range interaction between the particles, whose nature depends crucially on the relative power of the pump beams. For asymmetric pumping, traveling density wave-like collective oscillations arise in the lattice, even in the overdamped limit. Increasing the lattice size or pump asymmetry these waves can destabilize the lattice.Comment: 5 pages, minor changes (SI units, new references

    Talk Is Cheap: Getting Serious about Preventing Child Soldiers

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    Talk Is Cheap: Getting Serious about Preventing Child Soldiers

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    Stuxnet and Its Hidden Lessons on the Ethics of Cyberweapons

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    Stuxnet and Its Hidden Lessons on the Ethics of Cyberweapons

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    Review Essay - The War on Terrorism: The Big Picture

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    Caution: Children at War

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    More than Three Laws of Robotics

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    Wired for War: The Robotics Revolution and Conflict in the 21st Centur
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