Spiral Waves in Media with Complex Excitable Dynamics

The structure of spiral waves is investigated in super-excitable reaction-diffusion systems where the local dynamics exhibits multi-looped phase space trajectories. It is shown that such systems support stable spiral waves with broken symmetry and complex temporal dynamics. The main structural features of such waves, synchronization defect lines, are demonstrated to be similar to those of spiral waves in systems with complex-oscillatory dynamics.Comment: to appear in International Journal of Bifurcation and Chao

On a family of integrable systems on S2S^2 with a cubic integral of motion

We discuss a family of integrable systems on the sphere $S^2$ with an additional integral of third order in momenta. This family contains the Coryachev-Chaplygin top, the Goryachev system, the system recently discovered by Dullin and Matveev and two new integrable systems. On the non-physical sphere with zero radius all these systems are isomorphic to each other.Comment: LaTeX, 8 page

Comment on ``Theory of Spinodal Decomposition''

I comment on a paper by S. B. Goryachev [PRL vol 72, p.1850 (1994)] that presents a theory of non-equilibrium dynamics for scalar systems quenched into an ordered phase. Goryachev incorrectly applies only a global conservation constraint to systems with local conservation laws.Comment: 2 pages LATeX (REVTeX macros), no figures. REVISIONS --- more to the point. microscopic example added, presentation streamlined, long-range interactions mentioned, to be published in Phys. Rev. Let

187^{187}Re(\gamm,n) cross section close to and above the neutron threshold

The neutron capture cross section of the unstable nucleus $^{186}$Re is studied by investigating the inverse photodisintegration reaction $^{187}$Re($\gamma$,n). The special interest of the {\it s}-process branching point $^{186}$Re is related to the question of possible {\it s}-process contributions to the abundance of the {\it r}-process chronometer nucleus ^{187}$Re. We use the photoactivation technique to measure photodisintegration rates. Our experimental results are in good agreement with two different statistical model calculations. Although the cross sections predicted by both models for the inverse reaction$^{186}$Re(n,$\gamma$) is too low to remove the overproduction of$^{186}$Os; the two predicted neutron-capture cross sections differ by a factor of 2.4; this calls for future theoretical study.Comment: Phys. Rev. C, in pres

The s-process branching at 185W

The neutron capture cross section of the unstable nucleus 185W has been derived from experimental photoactivation data of the inverse reaction 186W(gamma,n)185W. The new result of sigma = (687 +- 110) mbarn confirms the theoretically predicted neutron capture cross section of 185W of sigma = 700 mbarn at kT = 30 keV. A neutron density in the classical s-process of n_n = (3.8 +0.9 -0.8} * 1e8 cm-3 is derived from the new data for the 185W branching. In a stellar s-process model one finds a significant overproduction of the residual s-only nucleus 186Os.Comment: ApJ, in pres