Lift-off dynamics in a simple jumping robot

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 $f_0$. Two distinct jumping modes emerge: a simple jump which is optimal above $f_0$ is achievable with a squat maneuver, and a peculiar stutter jump which is optimal below $f_0$ 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

Thermodynamic effects on cryogenic cavitating flow in an orifice

Temperature depression in a cavitating orifice flow was experimentally investigated with liquid nitrogen in order to clarify the influence of turbulent flow around a bubble on thermodynamic effects on cavitation. The temperature began to decrease at the outlet of the orifice when the cavitation number decreased below 0. Moreover, the temperature depression became larger as the cavitation number became smaller. In addition, the temperature depression also became greater as the flow velocity became lower when the cavitation numbers were equal. Based on theoretical considerations and experimental results, the difference of temperature depression can be considered to be caused by the enhancement of thermal transport around bubbles due to the turbulent flow. In addition, if thermal transport is enhanced as mentioned above, the temperature in the area where the cavitation collapses can become higher than that upstream of the orifice due to the temporary breakdown of the heat balance between the inception and collapse of cavity bubbles.http://deepblue.lib.umich.edu/bitstream/2027.42/84237/1/CAV2009-final36.pd

Suppression of bone marrow-derived microglia in the amygdala improves anxiety-like behavior induced by chronic partial sciatic nerve ligation in mice

大脳辺縁系の一部である扁桃体は，不快情動の形成において重要な役割を担っている．我々は，神経障害性疼痛の慢性期に扁桃体中心核に集積する骨時由来ミクログリアが IL-1βを分泌して神経細胞に作用することで，慢性疼痛における不快情動の形成に関与することを明らかにした

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

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

Search for the Θ+\Theta^{+} pentaquark via the π−p→K−X\pi^-p\to K^-X reaction at 1.92 GeV/cc

The $\Theta^+$ pentaquark baryon was searched for via the $\pi^-p\to K^-X$ reaction in a missing-mass resolution of 1.4 MeV/$c^2$(FWHM) at J-PARC. $\pi^-$ meson beams were incident on the liquid hydrogen target with the beam momentum of 1.92 GeV/$c$. No peak structure corresponding to the $\Theta^+$ mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2$^{\circ}$ to 15$^{\circ}$ in the laboratory frame was obtained to be 0.26 $\mu$b/sr in the mass region of 1.51$-$1.55 GeV/$c^2$.The upper limit of the $\Theta^+$ decay width using the effective Lagrangian approach was obtained to be 0.72 MeV/$c^2$ and 3.1 MeV/$c^2$ for $J^P_{\Theta}=1/2^+$ and $J^P_{\Theta}=1/2^-$, respectively.Comment: 5 pages, 3 figures, 1 tabl