665 research outputs found

    Lift-off dynamics in a simple jumping robot

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    We study vertical jumping in a simple robot comprising an actuated mass-spring arrangement. The actuator frequency and phase are systematically varied to find optimal performance. Optimal jumps occur above and below (but not at) the robot's resonant frequency f0f_0. Two distinct jumping modes emerge: a simple jump which is optimal above f0f_0 is achievable with a squat maneuver, and a peculiar stutter jump which is optimal below f0f_0 is generated with a counter-movement. A simple dynamical model reveals how optimal lift-off results from non-resonant transient dynamics.Comment: 4 pages, 4 figures, Physical Review Letters, in press (2012

    Photoproduction of Lambda(1405) and Sigma^{0}(1385) on the proton at E_\gamma = 1.5-2.4 GeV

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    Differential cross sections for γpK+Λ(1405)\gamma p \to K^+\Lambda(1405) and γpK+Σ0(1385)\gamma p \to K^+\Sigma^0(1385) reactions have been measured in the photon energy range from 1.5 to 2.4 GeV and the angular range of 0.8<cos(Θ)<1.00.8<\cos(\Theta)<1.0 for the K+K^+ scattering angle in the center-of-mass system. This data is the first measurement of the Λ(1405)\Lambda(1405) photoproduction cross section. The lineshapes of \LamS measured in Σ+π\Sigma^+\pi^- and Σπ+\Sigma^-\pi^+ decay modes were different with each other, indicating a strong interference of the isospin 0 and 1 terms of the Σπ\Sigma\pi scattering amplitudes. The ratios of \LamS production to \SigS production were measured in two photon energy ranges: near the production threshold (1.5<Eγ<2.01.5<E_\gamma<2.0 GeV) and far from it (2.0<Eγ<2.42.0 <E_\gamma<2.4 GeV). The observed ratio decreased in the higher photon energy region, which may suggest different production mechanisms and internal structures for these hyperon resonances
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