共查询到20条相似文献,搜索用时 15 毫秒
1.
Rühle V Ziebert F Peter R Zimmermann W 《The European physical journal. E, Soft matter》2008,27(3):243-251
The dynamical interaction between filaments and motor proteins is known for their propensity to self-organize into spatio-temporal
patterns. Since the filaments are polar in the sense that motors define a direction of motion on them, the system can display
a spatially homogeneous polar-filament orientation. We show that the latter anisotropic state itself may become unstable with
respect to inhomogeneous fluctuations. This scenario shares similarities with instabilities in planarly aligned nematic liquid
crystals: in both cases the wave vector of the instability may be oriented either parallel or oblique to the polarity axis.
However, the encountered instabilities here are long-wave instead of short-wave and the destabilizing modes are drifting ones
due to the polar symmetry. Additionally a nonpropagating transverse instability is possible. The stability diagrams related
to the various wave vector orientations relative to the polarity axis are determined and discussed for a specific model of
motor-filament interactions. 相似文献
2.
S. Bottin J. Lega 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):299-308
We show that a nonlinear gradient term can be used to tune the width of pulse-like solutions to a generalized quintic Ginzburg-Landau
equation. We investigate the dynamics of these solutions and show that weakly turbulent patches can persist for long times.
Analogies with turbulent spots in plane Couette flows are discussed.
Received: 29 May 1997 / Revised: 16 March 1998 / Accepted: 30 April
1998 相似文献
3.
P. Bot I. Mutabazi 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):141-155
The dynamics of defects in a pattern of traveling inclined rolls has been investigated. Two regimes were identified in the
neighborhood of defects: a diffusive regime, with a negative phase diffusion coefficient, and a coalescence regime in which
the phase gradient diverges in time following a power law behavior. The observed periodic nucleation of defects is related
to the frequency inhomogeneity induced by the disymmetry of the wave amplitude. Amplitude holes have been observed in the
secondary modulated pattern.
Received 23 February 1999 and Received in final form 26 May 1999 相似文献
4.
5.
B. Andreotti P. Claudin S. Douady 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):321-339
Almost fifty years of investigations of barchan dunes morphology and dynamics is reviewed, with emphasis on the physical understanding
of these objects. The characteristic quantities measured on the field (shape, size, velocity) and the physical problems they
rise are presented. Then, we review the dynamical mechanisms explaining the formation and the propagation of dunes. In particular
a complete and original approach of the sand transport over a flat sand bed is proposed and discussed. We conclude on open
problems by outlining future research directions.
Received 22 December 2001 / Received in final form 31 May 2002 Published online 31 July 2002 相似文献
6.
B. Andreotti P. Claudin S. Douady 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):341-352
We present in this paper a simplification of the dune model proposed by Sauermann et al. which keeps the basic mechanisms but allows analytical and parametric studies. Two kinds of purely propagative two dimensional
solutions are exhibited: dunes and domes. The latter, by contrast to the former, do not present a slip face. Their shape and
velocity can be predicted as a function of their size. We recover that dune profiles are not scale invariant (small dunes
are flatter than the large ones), and that the inverse of the velocity grows almost linearly with the dune size. We furthermore
get the existence of a critical mass below which no dune solution exists. It rises the problem of dune nucleation: how can
dunes appear if any bump below this minimal mass gets eroded and disappears? The linear stability analysis of a flat sand
bed shows that it is unstable at large wavelengths: dune can in fact nucleate from a small sand mass if the proto-dune is
sufficiently long.
Received 22 December 2001 / Received in final form 31 May 2002 Published online 31 July 2002 相似文献
7.
Sabín J Prieto G Ruso JM Hidalgo-Alvarez R Sarmiento F 《The European physical journal. E, Soft matter》2006,20(4):401-408
Dynamic light scattering and electrophoretic mobility measurements have been used to characterize the size, size distribution
and zeta potentials (ζ-potentials) of egg yolk phosphatidylcholine (EYPC) liposomes in the presence of monovalent ions ( Na+ and K+). To study the stability of liposomes the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory has been extended by introducing
the hydrated radius of the adsorbed ions onto the liposome surfaces. The decrease of liposome size is explained on the basis
of the membrane impermeability to some ions which generate osmotic forces, which leads to evacuate water from liposome inside. 相似文献
8.
The role of thermodiffusive generation of concentration fluctuations via the Soret effect, their contribution to the buoyancy forces that drive convection, the advective mixing effect of the latter, and the diffusive homogenisation are compared and elucidated for oscillatory convection. Numerically obtained solutions of the field equations in the form of spatially extended relaxed traveling waves, of standing waves, and of the transient growth of standing waves and their transition to traveling waves are discussed as well as spatially localized convective states of traveling waves that are surrounded by the quiescent fluid. 相似文献
9.
For an ordered array of critical volatile wetting droplets the formation of a super lattice by an Ostwald-ripening-like competition
process is considered. The underlying diffusion problem is treated within a quasistatic approximation and to first order in
the inverse droplets distance. The approach is rather general but a square lattice and a triangular lattice are studied explicitly.
Dispersion relations for the super lattice growth of these arrays are calculated.
Received 29 November 1999 and Received in final form 15 February 2000 相似文献
10.
11.
Motivated by the cytoskeleton of eukaryotic cells, we develop a general framework for describing the large-scale dynamics
of an active filament network. In the cytoskeleton, active cross-links are formed by motor proteins that are able to induce
relative motion between filaments. Starting from pair-wise interactions of filaments via such active processes, our framework
is based on momentum conservation and an analysis of the momentum flux. This allows us to calculate the stresses in the filament
network generated by the action of motor proteins. We derive effective theories for the filament dynamics which can be related
to continuum theories of active polar gels. As an example, we discuss the stability of homogenous isotropic filament distributions
in two spatial dimensions. 相似文献
12.
E. Plaut L. Pastur R. Ribotta 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):283-297
We study experimentally the evolution of thermoconvection in a laterally extended planar nematic layer, at zero or weak stabilizing
magnetic field. As the applied thermal gradient is increased, a cascade of symmetry breakings occurs, towards structures of
increasing spatial complexity, and ultimately towards oscillating states. The patterns are characterized optically, and simple
models for the distortion of the vertical (out of plane) component of the director field are proposed.
Received: 1st December 1997 / Revised: 25 May 1998 / Accepted: 2 June 1998 相似文献
13.
A. Lange M. Schröter M.A. Scherer A. Engel I. Rehberg 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):475-484
The temporal evolution of a water-sand interface driven by gravity is experimentally investigated. By means of a Fourier analysis
of the evolving interface the growth rates are determined for the different modes appearing in the developing front. To model
the observed behavior we apply the idea of the Rayleigh-Taylor instability for two stratified fluids. Carrying out a linear
stability analysis we calculate the growth rates from the corresponding dispersion relations for finite and infinite cell
sizes. Based on the theoretical results the viscosity of the suspension is estimated to be approximately 100 times higher
than that of pure water, in agreement with other experimental findings.
Received: 12 December 1997 / Revised: 23 March 1998 / Accepted: 28
April 1998 相似文献
14.
Sabín J Prieto G Ruso JM Sarmiento F 《The European physical journal. E, Soft matter》2007,24(2):201-210
We present a study of the fractal dimension of clusters of large unilamellar vesicles (LUVs) formed by egg yolk phosphatidylcholine
(EYPC), dimyristoylphosphocholine (DMPC) and dipalmitoylphosphocholine (DPPC) induced by Ca2+ . Fractal dimensions were calculated by application of two methods, measuring the angular dependency of the light scattered
by the clusters and following the evolution of the cluster size. In all cases, the fractal dimensions fell in the range from
2.1 to 1.8, corresponding to two regimes: diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation
(RLCA). Whereas DMPC clusters showed a typical transition from the RLCA to the DLCA aggregation, EYPC exhibited an unusual
behaviour, since the aggregation was limited for a higher concentration than the critical aggregation concentration. The behaviour
of DPPC was intermediate, with a transition from the RLCA to the DLCA regimes with cluster sizes depending on Ca2+ concentration. Studies on the reversibility of the aggregates show that EYPC and DPPC clusters can be re-dispersed by dilution
with water. DMPC does not present reversibility. Reversibility is evidence of the existence of secondary minima in the DLVO
potential between two liposomes. To predict these secondary minima, a correction of the DLVO model was necessary taking into
account a repulsive force of hydration. 相似文献
15.
Adhesion between membranes is studied using a phenomenological model, where the inter-membrane distance is coupled to the
concentration of sticker molecules on the membranes. The model applies to both adhesion of two flexible membranes and to adhesion
of one flexible membrane onto a second membrane supported on a solid substrate. We mainly consider the case where the sticker
molecules form bridges and adhere directly to both membranes. The calculated mean-field phase diagrams show an upward shift
of the transition temperature indicating that the lateral phase separation in the membrane is enhanced due to the coupling effect. Hence the possibility of adhesion-induced lateral phase separation is predicted. For a particular
choice of the parameters, the model exhibits a tricritical behavior. We also discuss the non-monotonous shape of the inter-membrane
distance occurring when the lateral phase separation takes place. The inter-membrane distance relaxes to the bulk values with
two symmetric overshoots. Adhesion mediated by other types of stickers is also considered.
Received 12 January 2000 and Received in final form 15 May 2000 相似文献
16.
J. Živković B. Tadić N. Wick S. Thurner 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):255-258
We analyze gene expression time-series data of yeast (S. cerevisiae) measured along two full cell-cycles. We quantify these data by using
q-exponentials, gene
expression ranking and a temporal mean-variance analysis.
We construct gene interaction networks based on correlation coefficients
and study the formation of the corresponding giant components
and minimum spanning trees.
By coloring genes according to their cell function we find
functional clusters in the correlation networks and functional branches
in the associated trees. Our results suggest that a percolation point of functional clusters can be identified on these gene
expression correlation networks. 相似文献
17.
R. Imayama Y. Shiwa 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(3):345-351
We present results of a numerical study of phase separation dynamics of a two-dimensional quenched system which has a small-world
topology, both with and without the conserved order parameter. We examine how the domain coarsening changes with the density
of long-range connections (shortcuts). It is demonstrated that the shortcuts have directly opposite effects, i.e., a speeding
up of the coarsening process of reaching a fully uniform state, and a freezing of the system in a disordered metastable state. 相似文献
18.
P. Fronczak A. Fronczak J. A. Hołyst 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):133-139
We study a model of network with clustering and desired node
degree. The original purpose of the model was to describe optimal
structures of scientific collaboration in the European Union. The
model belongs to the family of exponential random graphs. We show
by numerical simulations and analytical considerations how a very
simple Hamiltonian can lead to surprisingly complicated and
eventful phase diagram. 相似文献
19.
20.
P. Colet D. Walgraef M. San Miguel 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):517-524
We study the nature of the instability of the homogeneous steady states of the subcritical real Ginzburg-Landau equation in
the presence of group velocity. The shift of the absolute instability threshold of the trivial steady state, induced by the
destabilizing cubic nonlinearities, is confirmed by the numerical analysis of the evolution of its perturbations. It is also
shown that the dynamics of these perturbations is such that finite size effects may suppress the transition from convective
to absolute instability. Finally, we analyze the instability of the subcritical middle branch of steady states, and show,
analytically and numerically, that this branch may be convectively unstable for sufficiently high values of the group velocity.
Received 17 December 1998 相似文献