Dynamic Front Transitions and Spiral-Vortex Nucleation

This is a study of front dynamics in reaction diffusion systems near Nonequilibrium Ising-Bloch bifurcations. We find that the relation between front velocity and perturbative factors, such as external fields and curvature, is typically multivalued. This unusual form allows small perturbations to induce dynamic transitions between counter-propagating fronts and nucleate spiral vortices. We use these findings to propose explanations for a few numerical and experimental observations including spiral breakup driven by advective fields, and spot splitting

Scroll waves in isotropic excitable media : linear instabilities, bifurcations and restabilized states

Scroll waves are three-dimensional analogs of spiral waves. The linear stability spectrum of untwisted and twisted scroll waves is computed for a two-variable reaction-diffusion model of an excitable medium. Different bands of modes are seen to be unstable in different regions of parameter space. The corresponding bifurcations and bifurcated states are characterized by performing direct numerical simulations. In addition, computations of the adjoint linear stability operator eigenmodes are also performed and serve to obtain a number of matrix elements characterizing the long-wavelength deformations of scroll waves.Comment: 30 pages 16 figures, submitted to Phys. Rev.

Исследование формирования тканево-инженерного конструкта на основе кардиомиоцитов и матрикса различной степени анизотропии и жесткости

In the last decade, in vitro experiments have shown that mechanical properties of the bases could markedly influence the efficacy of differentiation of the induced pluripotent and embryonic stem cells and their development into the mature phenotype. By changing of mechanical, elastic and structural characteristics of the base, it is possible to increase the percentage of stem cells that differentiate to cardiomyocytes. The study was aimed at evaluation of the effects induced by changing physical characteristics of the base on the formation of phenotypic characteristics of cardiac cells. This included the comparison of structural properties of the cultured layer of heart tissue obtained by changing of elasticity and structure of polymeric bases. The results showed significant differences in calcium activity and structural characteristics of cardiomyocytes depending on the base properties, as well as significant variation in the excitation conduction. As long as conduction abnormalities in the heart tissues can often lead to occurrence of life-threatening cardiac arrhythmias, the results can be used to determine patient groups at increased risk of death from heart failure.В экспериментах in vitro в последнее десятилетие было установлено, что механические свойства подложек сильно влияют на эффективность дифференцировки индуцированных плюрипотентных и эмбриональных стволовых клеток и их развития в зрелый фенотип. Меняя механо-эластические и структурные характеристики подложки, можно повышать процентный выход дифференцировки стволовых клеток в кардиомиоциты. Цель данной работы состояла в изучении влияния изменения физических характеристик подложек на формирование фенотипических особенностей сердечных клеток. В задачи входило сравнение структурных свойств культивируемых слоев сердечной ткани, полученных при варьировании эластичности и структуры полимерных подложек. Pезультаты показали значительные различия в кальциевой активности и структурных особенностях кардиомиоцитов в зависимости от свойств подложки, а также существенное варьирование проведения возбуждения. В связи с тем что нарушения проведения в сердечной ткани часто приводят к возникновению опасных сердечных аритмий, полученные данные предполагается использовать для определения группы пациентов с повышенным риском смерти от сердечной недостаточности

Lifetime enhancement of scroll rings by spatiotemporal fluctuations

The dynamics of three-dimensional scroll rings with spatiotemporal random excitability is investigated numerically using the FitzHugh-Nagumo model. Depending on the correlation time and length scales of the fluctuations, the lifetime of the ring filament is enlarged and a resonance effect between the time scale of the scroll ring and the time correlation of the noise is observed. Numerical results are interpreted in terms of a simplified stochastic model derived from the kinematical equations for three-dimensional excitable waves

Lifetime enhancement of scroll rings by spatiotemporal fluctuations

The dynamics of three-dimensional scroll rings with spatiotemporal random excitability is investigated numerically using the FitzHugh-Nagumo model. Depending on the correlation time and length scales of the fluctuations, the lifetime of the ring filament is enlarged and a resonance effect between the time scale of the scroll ring and the time correlation of the noise is observed. Numerical results are interpreted in terms of a simplified stochastic model derived from the kinematical equations for three-dimensional excitable waves

Wave competition in excitable modulated media.

The propagation of an initially planar front is studied within the framework of the photosensitive Belousov-Zhabotinsky reaction modulated by a smooth spatial variation of the local front velocity in the direction perpendicular to front propagation. Under this modulation, the wave front develops several fingers corresponding to the local maxima of the modulation function. After a transient, the wave front achieves a stationary shape that does not necessarily coincide with the one externally imposed by the modulation. Theoretical predictions for the selection criteria of fingers and steady-state velocity are experimentally validated