613 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
Universal relationship between crystallinity and irreversibility field of MgB2
The relationship between irreversibility field, Hirr, and crystallinity of
MgB2 bulks including carbon substituted samples was studied. The Hirr was found
to increase with an increase of FWHM of MgB2 (110) peak, which corresponds to
distortion of honeycomb boron sheet, and their universal correlation was
discovered even including carbon substituted samples. Excellent Jc
characteristics under high magnetic fields were observed in samples with large
FWHM of (110) due to the enhanced intraband scattering and strengthened grain
boundary flux pinning. The relationship between crystallinity and Hirr can
explain the large variation of Hirr for MgB2 bulks, tapes, single crystals and
thin films.Comment: 3 pages, 4 figures, to be published in Appl. Phys. Lett. (in press
Conveyance of texture signals along a rat whisker
Neuronal activities underlying a percept are constrained by the physics of sensory signals. In the tactile sense such constraints are frictional stick-slip events, occurring, amongst other vibrotactile features, when tactile sensors are in contact with objects. We reveal new biomechanical phenomena about the transmission of these microNewton forces at the tip of a rat’s whisker, where they occur, to the base where they engage primary afferents. Using high resolution videography and accurate measurement of axial and normal forces at the follicle, we show that the conical and curved rat whisker acts as a sign-converting amplification filter for moment to robustly engage primary afferents. Furthermore, we present a model based on geometrically nonlinear Cosserat rod theory and a friction model that recreates the observed whole-beam whisker dynamics. The model quantifies the relation between kinematics (positions and velocities) and dynamic variables (forces and moments). Thus, only videographic assessment of acceleration is required to estimate forces and moments measured by the primary afferents. Our study highlights how sensory systems deal with complex physical constraints of perceptual targets and sensors
Lyapunov exponent and natural invariant density determination of chaotic maps: An iterative maximum entropy ansatz
We apply the maximum entropy principle to construct the natural invariant
density and Lyapunov exponent of one-dimensional chaotic maps. Using a novel
function reconstruction technique that is based on the solution of Hausdorff
moment problem via maximizing Shannon entropy, we estimate the invariant
density and the Lyapunov exponent of nonlinear maps in one-dimension from a
knowledge of finite number of moments. The accuracy and the stability of the
algorithm are illustrated by comparing our results to a number of nonlinear
maps for which the exact analytical results are available. Furthermore, we also
consider a very complex example for which no exact analytical result for
invariant density is available. A comparison of our results to those available
in the literature is also discussed.Comment: 16 pages including 6 figure
Superconducting order parameter in heavily overdoped : a global quantitative analysis
A systematic analysis of the complex lineshape at of heavily
overdoped BiSrCaCuO is presented. We show that a
coherent component in the quasi-particle excitation is correlated with the
superfluid density throughout the entire doping range and suggest it is a
direct measure of the order parameter of high temperature superconductors.Comment: 4 RevTex4 pages, 4 eps figures (Fig. 3 revised after publication on
PRB
Self-organization in systems of self-propelled particles
We investigate a discrete model consisting of self-propelled particles that
obey simple interaction rules. We show that this model can self-organize and
exhibit coherent localized solutions in one- and in two-dimensions.In
one-dimension, the self-organized solution is a localized flock of finite
extent in which the density abruptly drops to zero at the edges.In
two-dimensions, we focus on the vortex solution in which the particles rotate
around a common center and show that this solution can be obtained from random
initial conditions, even in the absence of a confining boundary. Furthermore,
we develop a continuum version of our discrete model and demonstrate that the
agreement between the discrete and the continuum model is excellent.Comment: 4 pages, 5 figure
The effects of uzu gene on yield and some related characters in barley. I. Pleiotropy of the uzu gene and interaction with genetic background.
Multicentric extra-abdominal desmoid tumors arising in bilateral lower limbs
Extra-abdominal desmoid tumors preferentially affect the shoulders, arms, backs, buttocks, and thighs of young adults. Multicentric occurrence is rather rare but seems to be another distinctive feature of extra-abdominal desmoid tumors. In this article we report a rare case of multicentric extra-abdominal desmoid tumors arising in bilateral lower limbs
Evidence for Nodal superconductivity in SrScFePO
Point contact Andreev reflection spectra have been taken as a function of
temperature and magnetic field on the polycrystalline form of the newly
discovered iron-based superconductor Sr2ScFePO3. A zero bias conductance peak
which disappears at the superconducting transition temperature, dominates all
of the spectra. Data taken in high magnetic fields show that this feature
survives until 7T at 2K and a flattening of the feature is observed in some
contacts. Here we inspect whether these observations can be interpreted within
a d-wave, or nodal order parameter framework which would be consistent with the
recent theoretical model where the height of the P in the Fe-P-Fe plane is key
to the symmetry of the superconductivity. However, in polycrystalline samples
care must be taken when examining Andreev spectra to eliminate or take into
account artefacts associated with the possible effects of Josephson junctions
and random alignment of grains.Comment: Published versio
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