1,235 research outputs found
Capture of free-flying payloads with flexible space manipulators
A recently developed control system for capturing free-flying payloads with flexible manipulators is discussed. Three essential points in this control system are, calculating optimal path, using a vision sensor for an external sensor, and controlling active vibration. Experimental results are shown using a planar flexible manipulator
Thermal conductivity of quantum magnetic monopoles in the frustrated pyrochlore Yb2Ti2O7
We report low-temperature thermal conductivity of pyrochlore
YbTiO, which contains frustrated spin-ice correlations with
significant quantum fluctuations. In the disordered spin-liquid regime,
exhibits a nonmonotonic magnetic field dependence, which is well
explained by the strong spin-phonon scattering and quantum monopole
excitations. We show that the excitation energy of quantum monopoles is
strongly suppressed from that of dispersionless classical monopoles. Moreover,
in stark contrast to the diffusive classical monopoles, the quantum monopoles
have a very long mean free path. We infer that the quantum monopole is a novel
heavy particle, presumably boson, which is highly mobile in a three-dimensional
spin liquid.Comment: 8 pages, 9 figure
DIRECT NUMERICAL SIMULATION OF FLUIDIZED BED WITH IMMERSED BOUNDARY METHOD
The applicability of the immersed boundary (IB) method, which is one of direct numerical simulations (DNS) for multiphase flow analyses, has been examined to simulate a fluidized bed. The volumetric-force type IB method developed by Kajishima et al. (2001) has been applied in the present work. While particle-fluid interaction force is calculated with the surface integral of fluid stress at the interface between particle and fluid in the standard IB method, the volume integral of interaction force is used in the volumetric-force type IB method. In order to validate the present simulation code, drag force and lift force firstly were calculated with IB method. Then calculated drag coefficients were compared with values estimated with Schiller-Nauman and Ergun equations, while calculated lift coefficients were compared with the previous simulated results. The difference of drag was within approximately 1% except in the range of low Reynolds number. Thus, the accuracy of the present simulation code was confirmed. Next, simulation of fluidized bed was carried out. Since DNS requires a large computer capacity, only 400 particles were used. The particle is 1.0mm in diameter and 2650kg/m3 in density. From the simulated results, concentrated upward stream lines from the bottom wall were observed in some regions. This inhomogeneous flow would be attributed to particulate structure
Successive transition from superconducting to antiferromagnetic phase in (Ca_6(Al, Ti)_4O_y)Fe_2As_2 studied via ^{75}As and ^{27}Al NMR
An unusual successive phase transition from superconducting (SC) to
antiferromagnetic (AF) phases was discovered via ^{75}As and ^{27}Al nuclear
magnetic resonance (NMR) in (Fe_2As_2)(Ca_6(Al, Ti)_4O_y) with four (Al, Ti)O
layers intercalated between FeAs planes. Although the spatially-uniform AF
ordering is clearly visible from ^{27}Al spectra, the ordered moments are very
small and the low-frequency fluctuation is much suppressed, contrary to
existing pnictides with localized magnetic elements. Furthermore, the
temperature (T) dependence of the fluctuation at both nuclei is very similar
throughout the entire temperature range. These facts suggest that some
hybridization between Ti and Fe orbitals induces a uniform electronic state
within FeAs and (Al, Ti)O layers accompanied by the SC and AF transitions. The
iron-based pnictide with Ti-doped blocking layers is the first high-T_c
compound having metallic blocking layers
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