324 research outputs found
Ferromagnetic resonance with a magnetic Josephson junction
We show experimentally and theoretically that there is a coupling via the
Aharonov-Bohm phase between the order parameter of a ferromagnet and a singlet,
s-wave, Josephson supercurrent. We have investigated the possibility of
measuring the dispersion of such spin waves by varying the magnetic field
applied in the plane of the junction and demonstrated the electromagnetic
nature of the coupling by the observation of magnetic resonance side-bands to
microwave induced Shapiro steps.Comment: 6 pages, 5 figure
Transport properties of clean and disordered Josephson junction arrays
We investigate the influence of quantum fluctuations and weak disorder on the
vortex dynamics in a two-dimensional superconducting
Berezinskii-Kosterlitz-Thouless system. The temperature below which quantum
fluctuations dominate the vortex creep is determined, and the transport in this
quantum regime is described. The crossover from quantum to classical regime is
discussed and the quantum correction to the classical current-voltage relation
is determined. It is found that weak disorder can effectively reduce the
critical current as compared to that in the clean system.Comment: 4 pages, 2 figure
Carrier drift velocity and edge magnetoplasmons in graphene
We investigate electron dynamics at the graphene edge by studying the
propagation of collective edge magnetoplasmon (EMP) excitations. By timing the
travel of narrow wave-packets on picosecond time scales around exfoliated
samples, we find chiral propagation with low attenuation at a velocity which is
quantized on Hall plateaus. We extract the carrier drift contribution from the
EMP propagation and find it to be slightly less than the Fermi velocity, as
expected for an abrupt edge. We also extract the characteristic length for
Coulomb interaction at the edge and find it to be smaller than for soft,
depletion edge systems.Comment: 5 pages, 3 figures of main text and 6 pages, 6 figures of
supplemental materia
Understanding Linkages Between Public Participation and Management of Protected Areas – Case Study of Serbia
Distribution of velocities and acceleration for a particle in Brownian correlated disorder: inertial case
We study the motion of an elastic object driven in a disordered environment
in presence of both dissipation and inertia. We consider random forces with the
statistics of random walks and reduce the problem to a single degree of
freedom. It is the extension of the mean field ABBM model in presence of an
inertial mass m. While the ABBM model can be solved exactly, its extension to
inertia exhibits complicated history dependence due to oscillations and
backward motion. The characteristic scales for avalanche motion are studied
from numerics and qualitative arguments. To make analytical progress we
consider two variants which coincide with the original model whenever the
particle moves only forward. Using a combination of analytical and numerical
methods together with simulations, we characterize the distributions of
instantaneous acceleration and velocity, and compare them in these three
models. We show that for large driving velocity, all three models share the
same large-deviation function for positive velocities, which is obtained
analytically for small and large m, as well as for m =6/25. The effect of small
additional thermal and quantum fluctuations can be treated within an
approximate method.Comment: 42 page
Failure Analysis of the Tower Crane Counterjib
Failures of the cranes' structural parts unavoidably lead to serious damages or total collapses; these accidents are often followed by very high financial losses and possibly serious injuries or crane-related fatalities. The objective of this research was to identify the causes that led to the failure of the hammerhead tower crane (x1425C) counteijib. The crane is used for assembly works at the hydropower dam. The counteijib collapse resulted from a gusset plate failure and caused such significant damage of the whole crane structure that the crane was dismantled and removed from operation. The study of the accident includes: (1) Identification of the stress-state, where a FEM model is developed to provide a useful tool for studying stress analysis; (2) Laboratory investigations are conducted in order to define the chemical composition and mechanical properties of the material, the tensile properties, hardness, impact toughness, as well as the metallographic analyses. The analysis of the obtained results showed that the principal reasons behind the gusset plate failure originated from design and fabrication faults. The working stress was higher than the allowable one. Also, impact toughness was too low and the fabrication of welds was incorrect
Phase dynamics of ferromagnetic Josephson junctions
We have investigated the classical phase dynamics of underdamped
ferromagnetic Josephson junctions by measuring the switching probability in
both the stationary and nonstationary regimes down to 350 mK. We found the
escape temperature to be the bath temperature, with no evidence of additional
spin noise. In the nonstationary regime, we have performed a pump-probe
experiment on the Josephson phase by increasing the frequency of the junction
current bias. We show that an incomplete energy relaxation leads to dynamical
phase bifurcation. Bifurcation manifests itself as premature switching,
resulting in a bimodal switching distribution. We directly measure the phase
relaxation time by following the evolution of the bimodal switching
distribution when varying the bias frequency. Numerical simulations account for
the experimental values of the phase relaxation time.Comment: 4 pages, 3 figure
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