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Andreas M. Menzel
Collective motion of binary self-propelled particle mixtures
Phys. Rev. E; xx; 2012; yyyyyy
http://www.mpip-mainz.mpg.de/~pleiner/papers/menzel_selfpropelled.pdf
In this study, we investigate the phenomenon of collective motion in binary mixtures of selfpropelled particles. More precisely, we consider two particle species, each of which consisting of pointlike objects that propel with a velocity of constant magnitude. Within each species, the particles try to achieve polar alignment of their velocity vectors, whereas we analyze the cases of preferred polar, antiparallel, as well as perpendicular alignment between particles of different species. Our focus is on the effect that the interplay between the two species has on the threshold densities for the onset of collective motion and on the nature of the solutions above onset. For this purpose, we start from suitable Langevin equations in the particle picture, from which we derive mean field equations of the Fokker-Planck type and finally macroscopic continuum field equations. We perform particle simulations of the Langevin equations, linear stability analyses of the Fokker-Planck and macroscopic continuum equations, and we numerically solve the Fokker-Planck equations. Both, spatially homogeneous and inhomogeneous solutions are investigated, where the latter correspond to stripe-like flocks of collectively moving particles. In general, the interaction between the two species reduces the threshold density for the onset of collective motion of each species. However, this interaction also reduces the spatial organization in the stripe-like flocks. The case that shows the most interesting behavior is the one of preferred perpendicular alignment between different species. There, a competition between polar and truly nematic orientational ordering of the velocity vectors takes place within each particle species. -
M.G. Clerc, S. Coulibaly and D. Laroze
Localized waves in a parametrically driven magnetic nanowire
Europhys. Lett.; xx; 2012; yyyyy
http://www.mpip-mainz.mpg.de/~pleiner/papers/Localized_Waves.pdf
The pattern formation in a magnetic wire forced by a transversal uniform and oscillatory magnetic field is studied. This system is described in the continuous framework by the Landau-Lifshitz-Gilbert equation. We find numerically that the spatio-temporal magnetization field exhibits a family of localized states that connect asymptotically a uniform oscillatory state with an extended wave. Close to the parametrical resonance instability, an amended amplitude equation is derived, which allow us to understand and characterize these localized waves. -
R. Schmitz, S. Yordanov, H.-J. Butt, K. Koynov and B. Duenweg
Studying flow close to an interface by total internal reflection fluorescence cross-correlation spectroscopy: Quantitative data analysis
Physical Review E; 84; 2011; 066306
http://arxiv.org/abs/1109.0205
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O.J. Suarez, L.M. Perez, D. Laroze, and D. Altbir
Magnetostatic interactions in cylindrical nanostructures with non-uniform magnetization
J. Magn. Magn. Mater.; xx; 2012; yyyy
http://www.mpip-mainz.mpg.de/~pleiner/papers/MagCylDL.pdf
Cylindrical magnetic nanostructures, like nanowires or nanotubes, should be used for the new generation of magnetic devices. Therefore, the investigation of inter-element interaction is an intense area of research. In this paper we investigated cylindrical nanostructures with non-uniform magnetization field. We focus on particles with a periodic magnetization function and using Fourier series we reduced the problem to a single integral expression. Analytical expression for both, the self and the interaction magnetostatic energy, are given. These expressions are used to analyze multisegmented tubes, as a function of the number of segments and the distance between particles. -
H.R. Brand, H. Pleiner and D. Svensek
Macroscopic behavior of systems with an axial dynamic preferred direction
Eur. Phys. J. E; 34; 2011; 128
http://www.mpip-mainz.mpg.de/~pleiner/papers/NPunkt.pdf
We present the derivation of the macroscopic equations for systems with an axial dynamic preferred direction. In addition to the usual hydrodynamic variables we introduce the time derivative of the local preferred direction as a new variable and discuss its macroscopic consequences including new cross coupling terms. Such an approach is expected to be useful for a number of systems for which orientational degrees of freedom are important including, for example, the formation of dynamic macroscopic patterns shown by certain bacteria such as Proteus mirabilis. We point out similarities in symmetry between the additional macroscopic variable discussed here, and the magnetization density in magnetic systems as well as the so-called ${\bf \hat l}$ vector in superfluid $^3$He - A. Furthermore we investigate the coupling to a gel-like system for which one has the strain tensor and relative rotations between the new variable and the network as additional macroscopic variables.
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