Interactive rhythms across species: The evolutionary biology of animal chorusing and turn-taking

The study of human language is progressively moving toward comparative and interactive frameworks, extending the concept of turn‐taking to animal communication. While such an endeavor will help us understand the interactive origins of language, any theoretical account for cross‐species turn‐taking should consider three key points. First, animal turn‐taking must incorporate biological studies on animal chorusing, namely how different species coordinate their signals over time. Second, while concepts employed in human communication and turn‐taking, such as intentionality, are still debated in animal behavior, lower level mechanisms with clear neurobiological bases can explain much of animal interactive behavior. Third, social behavior, interactivity, and cooperation can be orthogonal, and the alternation of animal signals need not be cooperative. Considering turn‐taking a subset of chorusing in the rhythmic dimension may avoid overinterpretation and enhance the comparability of future empirical work

Kinetic step bunching during surface growth

We study the step bunching kinetic instability in a growing crystal surface characterized by anisotropic diffusion. The instability is due to the interplay between the elastic interactions and the alternation of step parameters. This instability is predicted to occur on a vicinal semiconductor surface Si(001) or Ge(001) during epitaxial growth. The maximal growth rate of the step bunching increases like $F^{4}$, where $F$ is the deposition flux. Our results are complemented with numerical simulations which reveals a coarsening behavior on the long time for the nonlinear step dynamics.Comment: 4 pages, 6 figures, submitted to PR

Effect of step stiffness and diffusion anisotropy on the meandering of a growing vicinal surface

We study the step meandering instability on a surface characterized by the alternation of terraces with different properties, as in the case of Si(001). The interplay between diffusion anisotropy and step stiffness induces a finite wavelength instability corresponding to a meandering mode. The instability sets in beyond a threshold value which depends on the relative magnitudes of the destabilizing flux and the stabilizing stiffness difference. The meander dynamics is governed by the conserved Kuramoto-Sivashinsky equation, which display spatiotemporal coarsening.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Lett. (February 2006

Numerical modeling of periodic pumping tests in wells penetrating a heterogeneous aquifer

This study investigated how to utilize multiple frequency components of pressure data from periodic pulse tests to estimate the intra-well permeability and compressibility distribution and also the presence of heterogeneities in a real field case. Periodic well testing is a technique in which injection or production pulses of a fluid are applied to a well in a periodic fashion. One of its main advantages is that ongoing operations do not have to be interrupted during the test as the superposed harmonic components can be identified using Fourier analysis. Further, modeling calculations are much faster than calculations in the time domain as no time-stepping is required and only the frequencies observed in the test need to be evaluated. We applied an earlier developed numerical code in the frequency domain to evaluate periodic-test results in a shallow aquifer and obtained a good match between data and calculations. The interpreted formation heterogeneity is in line with the local geology. Joints of various orientations constitute the main hydraulic conduits of the tested subsurface but they do not directly connect the wells. Thus communication between the wells has to be established through low-permeability features. The interwell periodic testing has corroborated the geological understanding of the aquifer and helped understanding the fluid flow pattern

Anisotropic dynamics of a vicinal surface under the meandering step instability

We investigate the nonlinear evolution of the Bales-Zangwill instability, responsible for the meandering of atomic steps on a growing vicinal surface. We develop an asymptotic method to derive, in the continuous limit, an evolution equation for the two-dimensional step flow. The dynamics of the crystal surface is greatly influenced by the anisotropy inherent to its geometry, and is characterized by the coarsening of undulations along the step direction and by the elastic relaxation in the mean slope direction. We demonstrate, using similarity arguments, that the coalescence of meanders and the step flow follow simple scaling laws, and deduce the exponents of the characteristic length scales and height amplitude. The relevance of these results to experiments is discussed.Comment: 10 pages, 7 figures; submitted to Phys. Rev.