Activity wave

Furthermore, under certain conditions (e.g. local unidirectional block) it is possible that the activation wavefront is delayed and encounters areas already repolarized. This may result in a circulating wave-front (= reentrant circuit reentrant arrhythmia), from which centrifugal activation waves originate and elicit life-threatening ventricular fibrillation. 

This work includes simulation of the activation wave front [7, 33, 34]. This is heavily influenced by cardiac ultra-structure, with preferential conduction along the fiber-sheet axes and the result corresponds well with that obtained from multielectrode recording from dog hearts in situ. Accurate reconstruction of the depolar-... 

Figure 59. Potential-titne curves measured at two different positions along a metal wire during (a) Fe dissolution in 1 N H2SO4, (b) Au corrosion in 1 N HCl/2 N NaCl, (c) Zn dissolution in 4 N NaOH, (d) Activity wave of Fe in 12 N HNO3 with successive repassivation and (e) passivation wave during Co dissolution in 1.3 M Cr03 + 1 N HCl with successive reactivation. The distance between the potential probes corresponds to the distance given under each curve. (After Franck, reprinted with permission from VCH Publishers.)...

When a quasi-one-dimensional ribbon was used as the working electrode (see Fig. 57), the activation waves emerged at the same time at the two edges of the ribbon and increased their velocity while traveling toward the center. The positions of the leading fronts as a function of time are shown in Fig. 62(b). 

Figure 62. Single autonomous oscillation during Co dissolution, (a) Total current vs. time, (b) Position of the leading edges of the activation waves vs. time. (Reprinted with permission from R. D. Otterstedt, P. J. Plath, N. 1. Jaeger, and J. L. Hudson, Phys. Rev. E 54, 3744, 1996. Copyright 1996, American Physical Society.)...

Cheer, A., J.P. Vincent, R. Nuccitelli G. Oster. 1987. Cortical activity in vertebrate eggs. I The activation wave. J. Theor. Biol 124 377-404. 

We have already noted above that in analyzing excitable systems one has, more often than not, to deal with a parabolic equation with a nonlinear source. In this section we will concern ourselves with an excitable medium of a different type, where the signals are transmitted in the neuron network not by the local currents but by the nervous impulses traveling along the axons. The propagation speed of the activity wave will, if this transmission mode is possible at all, depend not only on the signal transmission speed but also on the other characteristics of nerve cells such as cell body capacitance, conductance, etc. 

Figure 15. Graphic illustration of the solution of the equation for activity wave propagation speed. Straight lines correspond to left-hand side of Eq. (83), curve lines represent right-hand side of the Equation. A finite-memory neuron net (g > 0) B infinite memory neuron net (g = 0). The dashed lines represent the left-hand portion of Eq. (83) at sufficiently large

In contrast, epicardial potentials accurately mirror details of the electrical events within the myocardium with high resolution. This property is demonstrated below by our eccentric spheres model simulations. In these simulations, when two activation waves in the anterior part of a spherical myocardium are separated by less than 100°, two discrete maxima arise on the epicardium, whereas a single broad maximum appears on the body surface. For a separation greater than 100°, two discrete maxima are apparent on the body surface as well (see Figure 10). Note, however, that the fact that the single surface potential max-... 

Figure 10. Comparison of body surface (A) and epicardial (B) potentials originating from two discrete activation wave fronts located in the myocardium. The central angles of the two activation waves are 10°. The separation between the wave fronts is 1-40°, 11-80°, 111-120°. The geometry is illustrated by the cross section of the model in the left upper corner of each graph.

It is recognized that floods originating from dam failures could be increased by flood waves due to landshdes into rivers and reservoirs, which could result from severe precipitation. Floods caused by dam failures should generally be combined with an appropriate flood due to other causes (see below) to obtain the controlhng flood. The appropriate coincident wind wave activity (wave set-up and wave runup) should be superimposed on the flood still water level that has been determined. 

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