Spiral wave drift in an electric field and scroll wave instabilities

I present the numerical computation of speed and direction of the drift of a spiral wave in an excitable medium in the presence of an electric field. In contrast to earlier results, the drift speed presents a strong variation close to the parameter value where the drift speed component along the field changes direction. Using a simple phenomenological model and results from a numerical linear stability analysis of scroll waves, I show this behavior can be attributed to a resonance of the meander modes with the translation modes of the spiral wave. Extending this phenomenological model to scroll waves also clarifies the link between the drift and long wavelength instabilities of scroll waves.Comment: Phys Rev E accepte

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

Pattern fluctuations in transitional plane Couette flow

In wide enough systems, plane Couette flow, the flow established between two parallel plates translating in opposite directions, displays alternatively turbulent and laminar oblique bands in a given range of Reynolds numbers R. We show that in periodic domains that contain a few bands, for given values of R and size, the orientation and the wavelength of this pattern can fluctuate in time. A procedure is defined to detect well-oriented episodes and to determine the statistics of their lifetimes. The latter turn out to be distributed according to exponentially decreasing laws. This statistics is interpreted in terms of an activated process described by a Langevin equation whose deterministic part is a standard Landau model for two interacting complex amplitudes whereas the noise arises from the turbulent background.Comment: 13 pages, 11 figures. Accepted for publication in Journal of statistical physic

Secondary instability in the wake of a circular cylinder

Secondary instability of flow past a circular cylinder is examined using highly accurate numerical methods. The critical Reynolds number for this instability is found to be Re_c=188.5. The secondary instability leads to three‐dimensionality with a spanwise wavelength at onset of 4 cylinder diameters. Three‐dimensional simulations show that this bifurcation is weakly subcritical

Parenting interventions for ADHD: a systematic literature review and meta-analysis

Objective. To evaluate the evidence base relating to the effectiveness of parent-administered behavioral interventions for ADHD

The rise of fully turbulent flow

Over a century of research into the origin of turbulence in wallbounded shear flows has resulted in a puzzling picture in which turbulence appears in a variety of different states competing with laminar background flow. At slightly higher speeds the situation changes distinctly and the entire flow is turbulent. Neither the origin of the different states encountered during transition, nor their front dynamics, let alone the transformation to full turbulence could be explained to date. Combining experiments, theory and computer simulations here we uncover the bifurcation scenario organising the route to fully turbulent pipe flow and explain the front dynamics of the different states encountered in the process. Key to resolving this problem is the interpretation of the flow as a bistable system with nonlinear propagation (advection) of turbulent fronts. These findings bridge the gap between our understanding of the onset of turbulence and fully turbulent flows.Comment: 31 pages, 9 figure

Options for Processing Shrimp Landed in South Carolina

Resource /Energy Economics and Policy,

Orbital movement of spiral waves

Spiral waves in active media react to small perturbations as particle-like objects. Here we apply the asymptotic theory to the interaction of spiral waves with a localized inhomogeneity, which leads to a novel prediction: drift of the spiral rotation centre along circular orbits around the inhomogeneity. The stationary orbits have alternating stability and fixed radii, determined by the properties of the bulk medium and the type of inhomogeneity, while the drift speed along an orbit depends on the strength of the inhomogeneity. Direct simulations confirm the validity and robustness of the theoretical predictions and show that these unexpected effects should be observable in experiment

Seasonal Variation of Physical Activity in Community-Living vs. Residential-Dwelling Older Adults

Background and Purpose: Although physical activity (PA) is important for all ages including older adults, participation may be influenced by weather variation and access to programming. Our primary aim was determine if PA participation is influenced by season and place of residence. A secondary aim was to compare objective and subjective measure of PA participation. Methods: Participants included older individuals (age>65) living in a residential retirement community (RR) with access to an on-site fitness facility (n=7) and additional volunteers (n=9) who lived at home and traveled to exercise at a nonresidential community (NR) activities center Accelerometers were used to measure daily PA during the summer and again during the winter. Results: PA for the NR group was higher in the summer (268.4�73.7 min vs. RR=186.8�68.0, p=0.039), but not in the winter (NR=261.8�92.6 min, RR=182.0�72.5, p=0.082). No within-group change in PA was noted from summer to winter for either group (p>0.05). The correlation between subjective and objective measures of PA was low (r=.262). Conclusion: Access to appropriate facilities and programming serves to help older individuals maintain PA levels despite seasonal weather variations. The low correlation between objective and subjective measures suggest a need to re-evaluate methods of tracking PA participation by older adults