1,981 research outputs found
Aggregation of chemotactic organisms in a differential flow
We study the effect of advection on the aggregation and pattern formation in
chemotactic systems described by Keller-Segel type models. The evolution of
small perturbations is studied analytically in the linear regime complemented
by numerical simulations. We show that a uniform differential flow can
significantly alter the spatial structure and dynamics of the chemotactic
system. The flow leads to the formation of anisotropic aggregates that move
following the direction of the flow, even when the chemotactic organisms are
not directly advected by the flow. Sufficiently strong advection can stop the
aggregation and coarsening process that is then restricted to the direction
perpendicular to the flow
Buchbesprechungen
Besprochen werden die beiden folgenden Werke:
(1) Handbuch der Bodenkunde - Grundwerk. Von H. P. Blume , P. Felix-Henningsen, W.R. Fischer, H.-G. Frede, R. Horn u. K. Stahr.
(2) Thienemann, Johannes: Rossitten - drei Jahrzehnte auf der Kurischen Nehrung. Reprint der Ausgabe Melsungen, Neumann-Neudamm von 1930 (3.Aufl.)
From brain to earth and climate systems: Small-world interaction networks or not?
We consider recent reports on small-world topologies of interaction networks
derived from the dynamics of spatially extended systems that are investigated
in diverse scientific fields such as neurosciences, geophysics, or meteorology.
With numerical simulations that mimic typical experimental situations we have
identified an important constraint when characterizing such networks:
indications of a small-world topology can be expected solely due to the spatial
sampling of the system along with commonly used time series analysis based
approaches to network characterization
Absolute instabilities of travelling wave solutions in a Keller-Segel model
We investigate the spectral stability of travelling wave solutions in a
Keller-Segel model of bacterial chemotaxis with a logarithmic chemosensitivity
function and a constant, sublinear, and linear consumption rate. Linearising
around the travelling wave solutions, we locate the essential and absolute
spectrum of the associated linear operators and find that all travelling wave
solutions have essential spectrum in the right half plane. However, we show
that in the case of constant or sublinear consumption there exists a range of
parameters such that the absolute spectrum is contained in the open left half
plane and the essential spectrum can thus be weighted into the open left half
plane. For the constant and sublinear consumption rate models we also determine
critical parameter values for which the absolute spectrum crosses into the
right half plane, indicating the onset of an absolute instability of the
travelling wave solution. We observe that this crossing always occurs off of
the real axis
Hawking Radiation on an Ion Ring in the Quantum Regime
This paper discusses a recent proposal for the simulation of acoustic black
holes with ions. The ions are rotating on a ring with an inhomogeneous, but
stationary velocity profile. Phonons cannot leave a region, in which the ion
velocity exceeds the group velocity of the phonons, as light cannot escape from
a black hole. The system is described by a discrete field theory with a
nonlinear dispersion relation. Hawking radiation is emitted by this acoustic
black hole, generating entanglement between the inside and the outside of the
black hole. We study schemes to detect the Hawking effect in this setup.Comment: 42 pages (one column), 17 figures, published revised versio
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