847 research outputs found
Experimental realization of a relativistic fluxon ratchet
We report the observation of the ratchet effect for a relativistic flux
quantum trapped in an annular Josephson junction embedded in an inhomogeneous
magnetic field. In such a solid state system mechanical quantities are
proportional to electrical quantities, so that the ratchet effect represents
the realization of a relativistic-flux-quantum-based diode. Mean static voltage
response, equivalent to directed fluxon motion, is experimentally demonstrated
in such a diode for deterministic current forcing both in the overdamped and in
the underdamped dynamical regime. In the underdamped regime, the recently
predicted phenomenon of current reversal is also recovered in our fluxon
ratchet.Comment: 4 pages, 6 figures. To appear in PHYSICA
Impact of tissue microstructure on a model of cardiac electromechanics based on MRI data
Cardiac motion is a vital process as it sustains the pumping of blood in the body. For this reason motion abnormalities are often associated with severe cardiac pathologies. Clinical imaging techniques, such as MRI, are powerful in assessing motion abnormalities but their connection with pathology often remains unknown.

Computational models of cardiac motion, integrating imaging data, would thus be of great help in linking tissue structure (i.e. cells organisation into fibres and sheets) to motion abnormalities and to pathology. Current models, though, are not able yet to correctly predict realistic cardiac motion in the healthy or diseased heart.

Our hypothesis is that a more realistic description of tissue structure within an electromechanical model of the heart, with structural information extracted from data rather than mathematically defined, and a more careful definition of tissue material properties, would better represent the high heterogeneity of cardiac tissue, thus improving the predictive power of the model
Common features of vortex structure in long exponentially shaped Josephson junctions and Josephson junctions with inhomogeneities
We study vortex structure in three different models of long Josephson
junctions: exponentially shaped Josephson junction and Josephson junctions with
resistor and shunt inhomogeneities in barrier layer. Numerical calculations of
the possible magnetic flux distributions and corresponding bifurcation curves
have done. For these three models the critical curves ``critical
current-magnetic field'' are constructed. We develop an idea of the equivalence
of exponentially shaped Josephson junction and rectangular junction with
distributed inhomogeneity and demonstrate that at some parameters of shunt and
resistor inhomogeneities at the ends of the junction the corresponding critical
curves are very close to the exponentially shaped one.Comment: Presented for M2S, Dresden, July 9-14, 200
Speed limit to the Abrikosov lattice in mesoscopic superconductors
We study the instability of the superconducting state in a mesoscopic
geometry for the low pinning material MoGe characterized by a large
Ginzburg-Landau parameter. We observe that in the current driven switching to
the normal state from a nonlinear region of the Abrikosov flux flow, the mean
critical vortex velocity reaches a limiting maximum velocity as a function of
the applied magnetic field. Based on time dependent Ginzburg-Landau simulations
we argue that the observed behavior is due to the high velocity vortex dynamics
confined on a mesoscopic scale. We build up a general phase diagram which
includes all possible dynamic configurations of Abrikosov lattice in a
mesoscopic superconductor.Comment: 7 pages, 6 figure
Nonlinear current-voltage characteristics due to quantum tunneling of phase slips in superconducting Nb nanowire networks
We report on the transport properties of an array of N about 30
interconnected Nb nanowires, grown by sputtering on robust porous Si
substrates. The analyzed system exhibits a broad resistive transition in zero
magnetic field, H, and highly nonlinear V(I) characteristics as a function of H
which can be both consistently described by quantum tunneling of phase slips.Comment: accepted for publication on Appl. Phys. Let
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