1,012 research outputs found
Switching times in long-overlap Josephson junctions subject to thermal fluctuations and non-Gaussian noise sources
We investigate the superconducting lifetime of long current-biased Josephson
junctions, in the presence of Gaussian and non-Gaussian noise sources. In
particular, we analyze the dynamics of a Josephson junction as a function of
the noise signal intensity, for different values of the parameters of the
system and external driving currents. We find that the mean lifetime of the
superconductive state is characterized by nonmonotonic behavior as a function
of noise intensity, driving frequency and junction length. We observe that
these nonmonotonic behaviours are connected with the dynamics of the junction
phase string during the switching towards the resistive state. An important
role is played by the formation and propagation of solitons, with two different
dynamical regimes characterizing the dynamics of the phase string. Our analysis
allows to evidence the effects of different bias current densities, that is a
simple spatially homogeneous distribution and a more realistic inhomogeneous
distribution with high current values at the junction edges. Stochastic
resonant activation, noise enhanced stability and temporary trapping phenomena
are observed in the system investigated.Comment: 16 pages, 9 figures, Physical Review B, in pres
Effects of L\'evy noise on the dynamics of sine-Gordon solitons in long Josephson junctions
We numerically investigate the generation of solitons in current-biased long
Josephson junctions in relation to the superconducting lifetime and the voltage
drop across the device. The dynamics of the junction is modelled with a
sine-Gordon equation driven by an oscillating field and subject to an external
non-Gaussian noise. A wide range of -stable L\'evy distributions is
considered as noise source, with varying stability index and asymmetry
parameter . In junctions longer than a critical length, the mean
switching time (MST) from superconductive to the resistive state assumes a
values independent of the device length. Here, we demonstrate that such a value
is directly related to the mean density of solitons which move into or from the
washboard potential minimum corresponding to the initial superconductive state.
Moreover, we observe: (i) a connection between the total mean soliton density
and the mean potential difference across the junction; (ii) an inverse behavior
of the mean voltage in comparison with the MST, with varying the junction
length; (iii) evidences of non-monotonic behaviors, such as stochastic resonant
activation and noise enhanced stability, of MST versus the driving frequency
and noise intensity for different values of and ; (iv) finally,
these non-monotonic behaviors are found to be related to the mean density of
solitons formed along the junction.Comment: 24 pages, 8 figures, submitted to J. Stat. Mech.: Theory Exp. arXiv
admin note: text overlap with arXiv:1406.481
Sine-Gordon breathers generation in driven long Josephson junctions
We consider a long Josephson junction excited by a suitable external
ac-signal, in order to generate control and detect breathers. Studying the
nonlinear supratransmission phenomenon in a nonlinear sine-Gordon chain
sinusoidally driven, Geniet and Leon explored the bifurcation of the energy
transmitted into the chain and calculated a threshold for the
external driving signal amplitude, at which the energy flows into the system by
breathers modes. I numerically study the continuous sine-Gordon model,
describing the dynamics of the phase difference in a long Josephson junction,
in order to deeply investigate the "continuous limit" modifications to this
threshold. Wherever the energy flows into the system due to the nonlinear
supratransmission, a peculiar breather localization areas appear in a parameters space. The emergence of these areas depends on the damping
parameter value, the bias current, and the waveform of driving external signal.
The robustness of generated breathers is checked by introducing into the model
a thermal noise source to mimic the environmental fluctuations. Presented
results allows one to consider a cryogenic experiment for creation and
detection of Josephson breathers.Comment: 8 pages, 3 figure
Heat-transfer fingerprint of Josephson breathers
A sine-Gordon breather enhances the heat transfer in a thermally biased long
Josephson junction. This solitonic channel allows for the tailoring of the
local temperature throughout the system. Furthermore, the phenomenon implies a
clear thermal fingerprint for the breather, and thus a 'non-destructive'
breather detection strategy is proposed here. Distinct breathing frequencies
result in morphologically different local temperature peaks, which can be
identified in an experiment.Comment: 8 pages, 5 figure
Noise-induced, ac-stabilized sine-Gordon breathers: Emergence and statistics
Noisy and ac forcing can cooperatively lead to the emergence of sine-Gordon
breathers robust to dissipation. This phenomenon is studied, for both Neumann
and periodic boundary conditions (NBC and PBC, respectively), at different
values of the main system parameters, such as the noise intensity and the ac
frequency-amplitude pair. In all the considered cases, nonmonotonicities of the
probability of generating only breathers versus the noise strength are
observed, implying that optimal noise ranges for the breather formation process
exist. Within the latter scenarios, the statistics of the breathers' number,
position, and amplitude are analyzed. The number of breathers is found to grow,
on average, with the noise amplitude. The breathers' spatial distribution is
sharply peaked at the system's edges for NBC, whereas it is essentially uniform
for PBC. The average breather amplitude is dictated by the ac
frequency-amplitude pair. Finally, a size analysis shows that the minimum
system length for the generation mechanism is given by the typical breather
half-width (width) in NBC (PBC).Comment: 18 pages, 7 figure
Default Mode Network alterations in alexithymia: An EEG power spectra and connectivity study
Recent neuroimaging studies have shown that alexithymia is characterized by functional alterations in different brain areas [e.g., posterior cingulate cortex (PCC)], during emotional/social tasks. However, only few data are available about alexithymic cortical networking features during resting state (RS). We have investigated the modifications of electroencephalographic (EEG) power spectra and EEG functional connectivity in the default mode network (DMN) in subjects with alexithymia. Eighteen subjects with alexithymia and eighteen subjects without alexithymia matched for age and gender were enrolled. EEG was recorded during 5 min of RS. EEG analyses were conducted by means of the exact Low Resolution Electric Tomography software (eLORETA). Compared to controls, alexithymic subjects showed a decrease of alpha power in the right PCC. In the connectivity analysis, compared to controls, alexithymic subjects showed a decrease of alpha connectivity between: (i) right anterior cingulate cortex and right PCC, (ii) right frontal lobe and right PCC, and (iii) right parietal lobe and right temporal lobe. Finally, mediation models showed that the association between alexithymia and EEG connectivity values was directed and was not mediated by psychopathology severity. Taken together, our results could reflect the neurophysiological substrate of some core features of alexithymia, such as the impairment in emotional awareness
Gastrointestinal symptoms in children: Primary care and specialist interface.
Aims Gastrointestinal symptoms and diseases represent one of the major reasons for paediatricians' requests for specialist consultations and hospital admissions. One fourth of annual medical consultations for children younger than 6 years can be attributed to gastrointestinal symptoms. High-quality guidelines have been validated worldwide to provide clinical recommendations and support healthcare providers' practice. Nevertheless, overall compliance to standards of care is unsatisfactory, and children with gastrointestinal symptoms frequently undergo expensive, useless specialist consultations and laboratory evaluations. The aim of this study is to review the main epidemiological and clinical aspects, together with management strategies, of the most common gastrointestinal symptoms in children, pointing out pitfalls and practical tips in primary care management, and providing correct indications for specialist consultations. Methods For this review, articles published in English from 2000 to January 2018 were identified from the PubMed/Medline (http://www.ncbi.nlm.nih.gov/pubmed/) database and selected on the basis of quality, relevance to the illness and importance in illustrating current management pathways. The search used the following keywords: gastrointestinal symptoms, functional gastrointestinal symptoms, children, primary care, specialist consultations and management. Particular emphasis was placed on evidence-based guidelines and high-quality studies. Results Functional gastrointestinal symptoms have a high impact on the quality of life of children and families and on healthcare costs. A complete medical history and clinical examination are often sufficient to guide the primary care provider in the diagnosis, further workup or referral to a paediatric gastroenterologist. Conclusion Paediatric gastroenterology outpatients' clinics are among the most crowded specialists, and functional gastrointestinal symptoms and disorders are the most frequent reason for counselling. The number of specialist consultations could be reduced if guidelines were applied in primary care settings
Axion field influence on Josephson junction quasipotential
The direct effect of an axion field on Josephson junctions is analyzed
through the consequences on the effective potential barrier that prevents the
junction from switching from the superconducting to the finite-voltage state.
We describe a method to reliably compute the quasipotential with stochastic
simulations, which allows to span the coupling parameter from weakly
interacting axion to tight interactions. As a result, we obtain that the axion
field induces a change in the potential barrier, therefore determining a
significant detectable effect for such a kind of elusive particle.Comment: 12 pages, 3 figure
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