828 research outputs found
Comparison of Josephson vortex flow transistors with different gate line configurations
We performed numerical simulations and experiments on Josephson vortex flow
transistors based on parallel arrays of YBa2Cu3O(7-x) grain boundary junctions
with a cross gate-line allowing to operate the same devices in two different
modes named Josephson fluxon transistor (JFT) and Josephson fluxon-antifluxon
transistor (JFAT). The simulations yield a general expression for the current
gain vs. number of junctions and normalized loop inductance and predict higher
current gain for the JFAT. The experiments are in good agreement with
simulations and show improved coupling between gate line and junctions for the
JFAT as compared to the JFT.Comment: 3 pages, 6 figures, accept. for publication in Appl. Phys. Let
Temperature dependence of the nitrogen-vacancy magnetic resonance in diamond
The temperature dependence of the magnetic resonance spectra of
nitrogen-vacancy (NV-) ensembles in the range of 280-330 K was studied. Four
samples prepared under different conditions were studied with NV-
concentrations ranging from 10 ppb to 15 ppm. For all of these samples, the
axial zero-field splitting (ZFS) parameter, D, was found to vary significantly
with temperature, T, as dD/dT = -74.2(7) kHz/K. The transverse ZFS parameter,
E, was non-zero (between 4 and 11 MHz) in all samples, and exhibited a
temperature dependence of dE/(EdT) = -1.4(3) x 10^(-4) K^(-1). The results
might be accounted for by considering local thermal expansion. The observation
of the temperature dependence of the ZFS parameters presents a significant
challenge for room-temperature diamond magnetometers and may ultimately limit
their bandwidth and sensitivity.Comment: 5 pages, 2 figures, 1 tabl
Fluctuations and oscillations in a simple epidemic model
We show that the simplest stochastic epidemiological models with spatial
correlations exhibit two types of oscillatory behaviour in the endemic phase.
In a large parameter range, the oscillations are due to resonant amplification
of stochastic fluctuations, a general mechanism first reported for
predator-prey dynamics. In a narrow range of parameters that includes many
infectious diseases which confer long lasting immunity the oscillations persist
for infinite populations. This effect is apparent in simulations of the
stochastic process in systems of variable size, and can be understood from the
phase diagram of the deterministic pair approximation equations. The two
mechanisms combined play a central role in explaining the ubiquity of
oscillatory behaviour in real data and in simulation results of epidemic and
other related models.Comment: acknowledgments added; a typo in the discussion that follows Eq. (3)
is corrected
Two-dimensional macroscopic quantum dynamics in YBCO Josephson junctions
We theoretically study classical thermal activation (TA) and macroscopic
quantum tunneling (MQT) for a YBCO Josephson junction coupled with an LC
circuit. The TA and MQT escape rate are calculated by taking into account the
two-dimensional nature of the classical and quantum phase dynamics. We find
that the MQT escape rate is largely suppressed by the coupling to the LC
circuit. On the other hand, this coupling leads to the slight reduction of the
TA escape rate. These results are relevant for the interpretation of a recent
experiment on the MQT and TA phenomena in YBCO bi-epitaxial Josephson
junctions.Comment: 9 pages, 2 figure
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