498 research outputs found
Enhanced response of the regular networks to local signals in presence of a fast impurity
We consider an array of inductively coupled Josephson junctions with a fast
impurity (a junction with a smaller value of critical current), and study the
consequences of imposing a small amplitude periodic signal at some point in the
array. We find that when external signal is imposed at the impurity, the
response of the array is boosted and a small amplitude signal can be detected
throughout the array. When the signal is imposed elsewhere, minor effects is
seen on the dynamics of the array. The same results have been also seen in
presence of a single fast spiking neuron in a chain of diffusively coupled
FitzHugh-Nagumo neurons.Comment: 6 pages, 5 figures, arXiv admin note: substantial text overlap with
arXiv:1108.460
Non-linear effects in hopping conduction of single-crystal La_{2}CuO_{4 + \delta}
The unusual non-linear effects in hopping conduction of single-crystal
La_{2}CuO_{4 + \delta} with excess oxygen has been observed. The resistance is
measured as a function of applied voltage U (10^{-3} V - 25 V) in the
temperature range 5 K 0.1 V) the
conduction of sample investigated corresponds well to Mott's variable-range
hopping (VRH). An unusual conduction behavior is found, however, in low voltage
range (approximately below 0.1 V), where the influence of electric field and
(or) electron heating effect on VRH ought to be neglected. Here we have
observed strong increase in resistance at increasing U at T < 20 K, whereas at
T > 20 K the resistance decreases with increasing U. The magnetoresistance of
the sample below 20 K has been positive at low voltage and negative at high
voltage. The observed non-Ohmic behavior is attributable to inhomogeneity of
the sample, and namely, to the enrichment of sample surface with oxygen during
the course of the heat treatment of the sample in helium and air atmosphere
before measurements. At low enough temperature (below 20 K) the surface layer
with increased oxygen concentration is presumed to consist of disconnected
superconducting regions (with T_{c} about 20 K) in poor-conducting matrix. The
results obtained demonstrate that transport properties of cuprate oxides may be
determined in essential degree by structural or stoichimetric inhomogeneities.
This should be taken into account at evaluation of "quality" of
high-temperature superconductors on the basis of transport properties
measurements.Comment: 12 pages, REVTex, 11 Postscript figures, To be published in Fizika
Nizkikh Temperatur (published by AIP as Low Temperature Physics
Filament tension and phase-locked drift of meandering scroll waves
Rotating scroll waves are self-organising patterns which are found in many
oscillating or excitable systems. Here we show that quasi-periodic (meandering)
scroll waves, which include the rotors that organise cardiac arrhythmias,
exhibit filament tension when averaged over the meander cycle. With strong
filament curvature or medium thickness gradients, however, scroll wave dynamics
are governed by phase-locked drift instead of filament tension. Our results are
validated in computational models of cycloidal meander and a cardiac tissue
model with linear core.Comment: accepted for publication in Physical Review Letters (December 2017
Analytical and Numerical Study of the Impact of Methanogenic Bacteria on Gas Composition in Underground Hydrogen Storages
Unlike natural gas, hydrogen gas mixtures stored in underground reservoirs undergo active chemical transformations under the influence of methanogenic microorganisms inhabiting in porous reservoirs. They lead to reduction of hydrogen and carbon dioxide concentrations and increase methane concentration. This chemical activity coupled with bacterial dynamics and gas/water flow through porous medium causes the phenomenon of self-organization such as the occurrence of autowave spatial structures, whose dynamics is characterized by a multiplicity of scenarios and bifurcations between them. In this paper we continue to develop the qualitative theory of self-organization in underground hydrogen storage, for more complicated
cases that include the mechanism of chemotaxis, which is one of the main types of bacterial movement, and takes into account the flow of both phases. The analysis of scenarios is based on the model of two-phase compositional flow coupled with population dynamics
Helicoidal instability of a scroll vortex in three-dimensional reaction-diffusion systems
We study the dynamics of scroll vortices in excitable reaction-diffusion
systems analytically and numerically. We demonstrate that intrinsic
three-dimensional instability of a straight scroll leads to the formation of
helicoidal structures. This behavior originates from the competition between
the scroll curvature and unstable core dynamics. We show that the obtained
instability persists even beyond the meander core instability of
two-dimensional spiral wave.Comment: 4 pages, 5 figures, revte
Evolution of spiral and scroll waves of excitation in a mathematical model of ischaemic border zone
Abnormal electrical activity from the boundaries of ischemic cardiac tissue
is recognized as one of the major causes in generation of ischemia-reperfusion
arrhythmias. Here we present theoretical analysis of the waves of electrical
activity that can rise on the boundary of cardiac cell network upon its
recovery from ischaemia-like conditions. The main factors included in our
analysis are macroscopic gradients of the cell-to-cell coupling and cell
excitability and microscopic heterogeneity of individual cells. The interplay
between these factors allows one to explain how spirals form, drift together
with the moving boundary, get transiently pinned to local inhomogeneities, and
finally penetrate into the bulk of the well-coupled tissue where they reach
macroscopic scale. The asymptotic theory of the drift of spiral and scroll
waves based on response functions provides explanation of the drifts involved
in this mechanism, with the exception of effects due to the discreteness of
cardiac tissue. In particular, this asymptotic theory allows an extrapolation
of 2D events into 3D, which has shown that cells within the border zone can
give rise to 3D analogues of spirals, the scroll waves. When and if such scroll
waves escape into a better coupled tissue, they are likely to collapse due to
the positive filament tension. However, our simulations have shown that such
collapse of newly generated scrolls is not inevitable and that under certain
conditions filament tension becomes negative, leading to scroll filaments to
expand and multiply leading to a fibrillation-like state within small areas of
cardiac tissue.Comment: 26 pages, 13 figures, appendix and 2 movies, as accepted to PLoS ONE
2011/08/0
INTRAVITAL AND POST-MORTEM DIAGNOSIS OF MYOCARDIAL INFARCTION: URGENT CARDIOLOGY DEPARTMENT LETHAL CASES ANALYSIS
To estimate an accuracy of methods of myocardial infarction diagnostics (ECC, echocardiography, biomarkers) 41 case history reports of patients with Q(+) and Q(-) myocardial infarction and lethal outcome were analyzed. ECG and echocardiography were proved to be most accurate in case of anterior (67 % and 67 %), lateral (71 % and 67 %) and inferior (46 % and 79%) localizations of myocardial infarction. Interventricular septum and posterior localizations were not detected on ECG (0%). Complete coincidence of ECG and echocardiography with autopsy results was detected only in 4 %. CPC and CPC-МВ levels were elevated in 97%, troponins were positive in 70 %. Risk factors of lethal outcome in case of myocardial infarction include sex (male), comorbid pathology (arterial hypertension, cerebrovascular disease, diabetes mellitus type 2), complications (rhythm disorders, cardiogenic shock, congestive heart failure), absence of thrombolytic therapy and its inefficacy. Myocardial infarction hypo- and hyperdiagnosis were detected
Size-Dependent Transition to High-Dimensional Chaotic Dynamics in a Two-Dimensional Excitable Medium
The spatiotemporal dynamics of an excitable medium with multiple spiral
defects is shown to vary smoothly with system size from short-lived transients
for small systems to extensive chaos for large systems. A comparison of the
Lyapunov dimension density with the average spiral defect density suggests an
average dimension per spiral defect varying between three and seven. We discuss
some implications of these results for experimental studies of excitable media.Comment: 5 pages, Latex, 4 figure
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