Electrical activity induced by nitric oxide in canine colonic circular muscle.

Nitric oxide generates slow electrical oscillations (SEOs) in cells near the myenteric edge of the circular muscle layer, which resemble slow waves generated by interstitial cells of Cajal (ICCs) at the submucosal edge of this muscle. The properties of SEOs were studied to determine whether these events are similar to slow waves. Rapid frequency membrane potential oscillations (MPOs; 16 +/- 1 cycles/min and 9.6 +/- 0.2 mV) were recorded from control muscles near the myenteric edge. Sodium nitroprusside (0.3 microM) reduced MPOs and initiated SEOs (1.3 +/- 0.3 cycles/min and 13.4 +/- 1.4 mV amplitude). SEOs were abolished by the guanylate cyclase inhibitor 1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxaline-1-one (10 microM). MPOs were abolished by nifedipine (1 microM), whereas SEO frequency increased and the amount of depolarization decreased. BAY K 8644 (1 microM) prolonged SEOs and reduced their frequency. SEOs were abolished by Ni(2+) (0.5 mM), low Ca(2+) solution (0.1 mM Ca(2+)), cyclopiazonic acid (10 microM), and the mitochondrial uncouplers antimycin (10 microM) and carbonyl cyanide p-trifluoromethoxyphenylhydrazone (1 microM). Oligomycin (10 microM) was without effect. These effects are similar to those described for colonic slow waves. Our results suggest that nitric oxide-induced SEOs are similar in mechanism to slow waves, an activity not previously thought to be generated by myenteric pacemakers.

Study of the intergrain interaction potential and associated instability of dust-lattice plasma oscillations in the presence of ion flow

A comprehensive study of the Debye-Huckel repulsive and ion wakefield induced attractive potentials around a dust grain is presented, including ion flow. It is found that the modified interaction potential (especially the attractive wakefield force) can cause instability of linear dust oscillations propagating in a dusty plasma crystal composed of dust grains in a horizontal arrangement suspended in the sheath region near a conducting wall (electrode). The dependence of dust lattice modes on the ion flow is studied, revealing instability of dust lattice modes for certain values of the ion flow speed. (C) 2003 Elsevier B.V. All rights reserved.

On the origin of the forward peak and backward oscillations in the F + H2(v = 0) to HF(v' = 2) + H reaction

We present a semiclassical complex angular momentum (CAM) analysis of the forward scattering peak which occurs at a translational collision energy around 32 meV in the quantum mechanical calculations for the F + H2(v = 0, j = 0) ? HF(v' = 2, j' = 0) + H reaction on the Stark–Werner potential energy surface. The semiclassical CAM theory is modified to cover the forward and backward scattering angles. The peak is shown to result from constructive/destructive interference of the two Regge states associated with two resonances, one in the transition state region and the other in the exit channel van der Waals well. In addition, we demonstrate that the oscillations in the energy dependence of the backward differential cross section are caused by the interference between the direct backward scattering and the decay of the two resonance complexes returning to the backward direction after one full rotation.

Modulated wavepackets associated with longitudinal dust grain oscillations in a dusty plasma crystal

The nonlinear amplitude modulation of longitudinal dust lattice waves (LDLWs) propagating in a dusty plasma crystal is investigated in a continuum approximation. It is shown that long wavelength LDLWs are modulationally stable, while shorter wavelengths may be unstable. The possibility for the formation and propagation of different envelope localized excitations is discussed. It is shown that the total grain displacement bears a (weak) constant displacement (zeroth harmonic mode), due to the asymmetric form of the nonlinear interaction potential. The existence of asymmetric envelope localized modes is predicted. The types and characteristics of these coherent nonlinear structures are discussed. (C) 2004 American Institute of Physics.

Nonlinear theory of solitary waves associated with longitudinal particle motion in lattices - Application to longitudinal grain oscillations in a dust crystal

The nonlinear aspects of longitudinal motion of interacting point masses in a lattice are revisited, with emphasis on the paradigm of charged dust grains in a dusty plasma (DP) crystal. Different types of localized excitations, predicted by nonlinear wave theories, are reviewed and conditions for their occurrence (and characteristics) in DP crystals are discussed. Making use of a general formulation, allowing for an arbitrary (e.g. the Debye electrostatic or else) analytic potential form phi(r) and arbitrarily long site-to-site range of interactions, it is shown that dust-crystals support nonlinear kink-shaped localized excitations propagating at velocities above the characteristic DP lattice sound speed v(0). Both compressive and rarefactive kink-type excitations are predicted, depending on the physical parameter values, which represent pulse- (shock-)like coherent structures for the dust grain relative displacement. Furthermore, the existence of breather-type localized oscillations, envelope-modulated wavepackets and shocks is established. The relation to previous results on atomic chains as well as to experimental results on strongly-coupled dust layers in gas discharge plasmas is discussed.

Standing wave oscillations in an electrocatalytic reaction

Experimental standing wave oscillations of the interfacial potential across an electrode have been observed in the electrocatalytic oxidation of formic acid on a Pt ring working electrode. The instantaneous potential distribution was monitored by means of equispaced potential microprobes along the electrode. The oscillatory standing waves spontaneously arose from a homogeneous stationary state prior to a Hopf bifurcation if the reference electrode was placed close to the working electrode. Reduced electrolyte concentrations resulted in aperiodic potential patterns, while the presence of a sufficiently large ohmic resistance completely suppressed spatial inhomogeneities. The experimental findings confirm numerical predictions of a reaction-migration formalism: under the chosen geometry, a long-range negative potential coupling between distant points across the ring electrode can lead to oscillatory potential domains of distinct phase. It is further shown that the occurrence of oscillatory standing waves can be rationalized as the electrochemical equivalent of Turing's second bifurcation (wave bifurcation). In the presence of an external resistance, the coupling becomes positive throughout and leads to spatial synchronization.

Prediction of limit cycle oscillations under uncertainty using a Harmonic Balance method

The Harmonic Balance method is an attractive solution for computing periodic responses and can be an alternative to time domain methods, at a reduced computational cost. The current paper investigates using a Harmonic Balance method for simulating limit cycle oscillations under uncertainty. The Harmonic Balance method is used in conjunction with a non-intrusive polynomial-chaos approach to propagate variability and is validated against Monte Carlo analysis. Results show the potential of the approach for a range of nonlinear dynamical systems, including a full wing configuration exhibiting supercritical and subcritical bifurcations, at a fraction of the cost of performing time domain simulations.