929 research outputs found
Improved nanopatterning for YBCO nanowires approaching the depairing current
An improved nanopatterning procedure has been developed to obtain YBCO
nanowires with cross sections as small as 50x50 nm^2, protected by an Au
capping layer. To probe the effective role of the Au protecting layer, we have
measured the current-voltage characteristics and the resistive transition in
temperature of the nanowires. Critical current densities up to 10^8 A/cm^2 have
been achieved at T=4.2 K, approaching the theoretical depairing current limit.
The resistance, measured as a function of temperature close to Tc, has been
fitted with a thermal activated phase slip model, including the effect of the
gold layer. The extracted values of the superconducting coherence length and of
the London penetration depth give current densities consistent with the
measured ones. These results cannot be achieved with same nanowires, without
the Au capping layer.Comment: ASC 2012 conference contributio
Collapse of thermal activation in moderately damped Josephson junctions
We study switching current statistics in different moderately damped
Josephson junctions: a paradoxical collapse of the thermal activation with
increasing temperature is reported and explained by interplay of two
conflicting consequences of thermal fluctuations, which can both assist in
premature escape and help in retrapping back into the stationary state. We
analyze the influence of dissipation on the thermal escape by tuning the
damping parameter with a gate voltage, magnetic field, temperature and an
in-situ capacitor.Comment: 4 pages, 4 figure
Anticorrelation between temperature and fluctuations in moderately damped Josephson junctions
We study the influence of dissipation on the switching current statistics of
moderately damped Josephson junctions. Different types of both low- and high-
junctions with controlled damping are studied. The damping parameter of
the junctions is tuned in a wide range by changing temperature, magnetic field,
gate voltage, introducing a ferromagnetic layer or in-situ capacitive shunting.
A paradoxical collapse of switching current fluctuations occurs with increasing
in all studied junctions. The phenomenon critically depends on dissipation
in the junction and is explained by interplay of two counteracting consequences
of thermal fluctuations, which on the one hand assist in premature switching
into the resistive state and on the other hand help in retrapping back to the
superconducting state. This is one of the rare examples of anticorrelation
between temperature and fluctuation amplitude of a physically measurable
quantity.Comment: 17 pages, 20 figure
Dynamics And Control Of Foot-And-Mouth Disease In Endemic Countries: A Pair Approximation Model
The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.jtbi.2014.05.010 © 2014. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/Previous mathematical models of spatial farm-to-farm transmission of foot and mouth disease (FMD) have explored the impacts of control measures such as culling and vaccination during a single outbreak in a country normally free of FMD. As a result, these models do not include factors that are relevant to countries where FMD is endemic in some regions, like long-term waning natural and vaccine immunity, use of prophylactic vaccination and disease re-importations. These factors may have implications for disease dynamics and control, yet few models have been developed for FMD-endemic settings. Here we develop and study an SEIRV (susceptible-exposed-infectious-recovered-vaccinated) pair approximation model of FMD. We focus on long term dynamics by exploring characteristics of repeated outbreaks of FMD and their dependence on disease re-importation, loss of natural immunity, and vaccine waning. We find that the effectiveness of ring and prophylactic vaccination strongly depends on duration of natural immunity, rate of vaccine waning, and disease re-introduction rate. However, the number and magnitude of FMD outbreaks are generally more sensitive to the duration of natural immunity than the duration of vaccine immunity. If loss of natural immunity and/or vaccine waning happen rapidly, then multiple epidemic outbreaks result, making it difficult to eliminate the disease. Prophylactic vaccination is more effective than ring vaccination, at the same per capita vaccination rate. Finally, more frequent disease re-importation causes a higher cumulative number of infections, although a lower average epidemic peak. Our analysis demonstrates significant differences between dynamics in FMD-free settings versus FMD-endemic settings, and that dynamics in FMD-endemic settings can vary widely depending on factors such as the duration of natural and vaccine immunity and the rate of disease re-importations. We conclude that more mathematical models tailored to FMD-endemic countries should be developed that include these factors
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
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