8,625 research outputs found
Nonlinear physics of electrical wave propagation in the heart: a review
The beating of the heart is a synchronized contraction of muscle cells
(myocytes) that are triggered by a periodic sequence of electrical waves (action
potentials) originating in the sino-atrial node and propagating over the atria and
the ventricles. Cardiac arrhythmias like atrial and ventricular fibrillation (AF,VF)
or ventricular tachycardia (VT) are caused by disruptions and instabilities of these
electrical excitations, that lead to the emergence of rotating waves (VT) and turbulent
wave patterns (AF,VF). Numerous simulation and experimental studies during the
last 20 years have addressed these topics. In this review we focus on the nonlinear
dynamics of wave propagation in the heart with an emphasis on the theory of pulses,
spirals and scroll waves and their instabilities in excitable media and their application
to cardiac modeling. After an introduction into electrophysiological models for action
potential propagation, the modeling and analysis of spatiotemporal alternans, spiral
and scroll meandering, spiral breakup and scroll wave instabilities like negative line
tension and sproing are reviewed in depth and discussed with emphasis on their impact
in cardiac arrhythmias.Peer ReviewedPreprin
Lagrangian study of surface transport in the Kuroshio Extension area based on simulation of propagation of Fukushima-derived radionuclides
Lagrangian approach is applied to study near-surface large-scale transport in
the Kuroshio Extension area using a simulation with synthetic particles
advected by AVISO altimetric velocity field. A material line technique is
applied to find the origin of water masses in cold-core cyclonic rings pinched
off from the jet in summer 2011. Tracking and Lagrangian maps provide the
evidence of cross-jet transport. Fukushima derived caesium isotopes are used as
Lagrangian tracers to study transport and mixing in the area a few months after
the March of 2011 tsunami that caused a heavy damage of the Fukushima nuclear
power plant (FNPP). Tracking maps are computed to trace the origin of water
parcels with measured levels of Cs-134 and Cs-137 concentrations collected in
two R/V cruises in June and July 2011 in the large area of the Northwest
Pacific. It is shown that Lagrangian simulation is useful to finding the
surface areas that are potentially dangerous due to the risk of radioactive
contamination. The results of simulation are supported by tracks of the surface
drifters which were deployed in the area
Competing mechanisms of stress-assisted diffusivity and stretch-activated currents in cardiac electromechanics
We numerically investigate the role of mechanical stress in modifying the
conductivity properties of the cardiac tissue and its impact in computational
models for cardiac electromechanics. We follow a theoretical framework recently
proposed in [Cherubini, Filippi, Gizzi, Ruiz-Baier, JTB 2017], in the context
of general reaction-diffusion-mechanics systems using multiphysics continuum
mechanics and finite elasticity. In the present study, the adapted models are
compared against preliminary experimental data of pig right ventricle
fluorescence optical mapping. These data contribute to the characterization of
the observed inhomogeneity and anisotropy properties that result from
mechanical deformation. Our novel approach simultaneously incorporates two
mechanisms for mechano-electric feedback (MEF): stretch-activated currents
(SAC) and stress-assisted diffusion (SAD); and we also identify their influence
into the nonlinear spatiotemporal dynamics. It is found that i) only specific
combinations of the two MEF effects allow proper conduction velocity
measurement; ii) expected heterogeneities and anisotropies are obtained via the
novel stress-assisted diffusion mechanisms; iii) spiral wave meandering and
drifting is highly mediated by the applied mechanical loading. We provide an
analysis of the intrinsic structure of the nonlinear coupling using
computational tests, conducted using a finite element method. In particular, we
compare static and dynamic deformation regimes in the onset of cardiac
arrhythmias and address other potential biomedical applications
Double step structure and meandering due to the many body interaction at GaN(0001) surface in N-rich conditions
Growth of gallium nitride on GaN(0001) surface is modeled by Monte Carlo
method. Simulated growth is conducted in N-rich conditions, hence it is
controlled by Ga atoms surface diffusion. It is shown that dominating four-body
interactions of Ga atoms can cause step flow anisotropy. Kinetic Monte Carlo
simulations show that parallel steps with periodic boundary conditions form
double terrace structures, whereas initially V -shaped parallel step train
initially bends and then every second step moves forward, building regular,
stationary ordering as observed during MOVPE or HVPE growth of GaN layers.
These two phenomena recover surface meandered pair step pattern observed, since
1953, on many semiconductor surfaces, such as SiC, Si or GaN. Change of terrace
width or step orientation particle diffusion jump barriers leads either to step
meandering or surface roughening. Additionally it is shown that step behavior
changes with the Schwoebel barrier height. Furthermore, simulations under
conditions corresponding to very high external particle flux result in
triangular islands grown at the terraces. All structures, emerging in the
simulations, have their corresponding cases in the experimental results.Comment: 25 pages, 8 figure
Spiral-wave dynamics in a mathematical model of human ventricular tissue with myocytes and Purkinje fibers
We present systematic numerical studies of the possible effects of the coupling of human endocardial and Purkinje cells at cellular and two-dimensional tissue levels. We find that the autorhythmic-activity frequency of the Purkinje cell in a composite decreases with an increase in the coupling strength; this can even eliminate the autorhythmicity. We observe a delay between the beginning of the action potentials of endocardial and Purkinje cells in a composite; such a delay increases as we decrease the diffusive coupling, and eventually a failure of transmission occurs. An increase in the diffusive coupling decreases the slope of the action-potential-duration-restitution curve of an endocardial cell in a composite. By using a minimal model for the Purkinje network, in which we have a two-dimensional, bilayer tissue, with a layer of Purkinje cells on top of a layer of endocardial cells, we can stabilize spiral-wave turbulence; however, for a sparse distribution of Purkinje-ventricular junctions, at which these two layers are coupled, we can also obtain additional focal activity and many complex transient regimes. We also present additional effects resulting from the coupling of Purkinje and endocardial layers and discuss the relation of our results to the studies performed in anatomically accurate models of the Purkinje network
Vernal Pool: A Participatory Art Project About Place + Precipitation
Produced by Karen Miranda Abel with Jessica Marion Barr, Vernal Pool is an immersive, elemental water installation created as a participatory, contemplative inquiry into our transitory interrelationships with water and landscape. From November 2013 to April 2014, 114 individuals across Canada and abroad gathered snow samples as a form of extrinsic artistic practice about place and precipitation. With the arrival of spring, the reservoir of melted snow was convened for four days at Toronto’s historic Gladstone Hotel to create Vernal Pool
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