101 research outputs found
Large-scale collective properties of self-propelled rods
We study, in two space dimensions, the large-scale properties of collections
of constant-speed polar point particles interacting locally by nematic
alignment in the presence of noise. This minimal approach to self-propelled
rods allows one to deal with large numbers of particles, revealing a
phenomenology previously unseen in more complicated models, and moreover
distinctively different from both that of the purely polar case (e.g. the
Vicsek model) and of active nematics.Comment: Submitted to Phys. Rev. Let
Optimal cellular mobility for synchronization arising from the gradual recovery of intercellular interactions
Cell movement and intercellular signaling occur simultaneously during the
development of tissues, but little is known about how movement affects
signaling. Previous theoretical studies have shown that faster moving cells
favor synchronization across a population of locally coupled genetic
oscillators. An important assumption in these studies is that cells can
immediately interact with their new neighbors after arriving at a new location.
However, intercellular interactions in cellular systems may need some time to
become fully established. How movement affects synchronization in this
situation has not been examined. Here we develop a coupled phase oscillator
model in which we consider cell movement and the gradual recovery of
intercellular coupling experienced by a cell after movement, characterized by a
moving rate and a coupling recovery rate respectively. We find (1) an optimal
moving rate for synchronization, and (2) a critical moving rate above which
achieving synchronization is not possible. These results indicate that the
extent to which movement enhances synchrony is limited by a gradual recovery of
coupling. These findings suggest that the ratio of time scales of movement and
signaling recovery is critical for information transfer between moving cells.Comment: 18 single column pages + 1 table + 5 figures + Supporting Informatio
Self-propelled particles with fluctuating speed and direction of motion
We study general aspects of active motion with fluctuations in the speed and
the direction of motion in two dimensions. We consider the case in which
fluctuations in the speed are not correlated to fluctuations in the direction
of motion, and assume that both processes can be described by independent
characteristic time-scales. We show the occurrence of a complex transient that
can exhibit a series of alternating regimes of motion, for two different
angular dynamics which correspond to persistent and directed random walks. We
also show additive corrections to the diffusion coefficient. The characteristic
time-scales are also exposed in the velocity autocorrelation, which is a sum of
exponential forms.Comment: to appear in Phys. Rev. Let
Emergence of a non-scaling degree distribution in bipartite networks: a numerical and analytical study
We study the growth of bipartite networks in which the number of nodes in one
of the partitions is kept fixed while the other partition is allowed to grow.
We study random and preferential attachment as well as combination of both. We
derive the exact analytical expression for the degree-distribution of all these
different types of attachments while assuming that edges are incorporated
sequentially, i.e., a single edge is added to the growing network in a time
step. We also provide an approximate expression for the case when more than one
edge are added in a time step. We show that depending on the relative weight
between random and preferential attachment, the degree-distribution of this
type of network falls into one of four possible regimes which range from a
binomial distribution for pure random attachment to an u-shaped distribution
for dominant preferential attachment
Constructing a Stochastic Model of Bumblebee Flights from Experimental Data
PMCID: PMC3592844This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Spontaneous Segregation of Self-Propelled Particles with Different Motilities
We study mixtures of self-propelled and passive rod-like particles in two
dimensions using Brownian dynamics simulations. The simulations demonstrate
that the two species spontaneously segregate to generate a rich array of
dynamical domain structures whose properties depend on the propulsion velocity,
density, and composition. In addition to presenting phase diagrams as a
function of the system parameters, we investigate the mechanisms driving
segregation. We show that the difference in collision frequencies between
self-propelled and passive rods provides a driving force for segregation, which
is amplified by the tendency of the self-propelled rods to swarm or cluster.
Finally, both self-propelled and passive rods exhibit giant number fluctuations
for sufficient propulsion velocities.Comment: 8 pages, 6 figures, 5 movies available on Data Conservancy; added
references, replaced supplemental figure, added smaller movie
Dielectric breakdown model for conductor-loaded and insulator-loaded composite materials
In the present work we generalize the dielectric breakdown model to describe dielectric breakdown patterns in both conductor-loaded and insulator-loaded composites. The present model is an extension of a previous one [F. Peruani et al., Phys. Rev. E 67, 066121 (2003)] presented by the authors to describe dielectric breakdown patterns in conductor-loaded composites. Particles are distributed at random in a matrix with a variable concentration p. The generalized model assigns different probabilities P(i,k!i8,k8) to breakdown channel formation according to particle characteristics. Dielectric breakdown patterns are characterized by their fractal dimension D and the parameters of the Weibull distribution. Studies are carried out as a function of the fraction of inhomogeneities, p.Instituto de Investigaciones FisicoquÃmicas Teóricas y AplicadasUniversidad de Buenos Aire
Periodic and Quasiperiodic Motion of an Elongated Microswimmer in Poiseuille Flow
We study the dynamics of a prolate spheroidal microswimmer in Poiseuille flow
for different flow geometries. When moving between two parallel plates or in a
cylindrical microchannel, the swimmer performs either periodic swinging or
periodic tumbling motion. Although the trajectories of spherical and elongated
swimmers are qualitatively similar, the swinging and tumbling frequency
strongly depends on the aspect ratio of the swimmer. In channels with reduced
symmetry the swimmers perform quasiperiodic motion which we demonstrate
explicitely for swimming in a channel with elliptical cross section
On the duality between interaction responses and mutual positions in flocking and schooling.
Recent research in animal behaviour has contributed to determine how alignment, turning responses, and changes of speed mediate flocking and schooling interactions in different animal species. Here, we propose a complementary approach to the analysis of flocking phenomena, based on the idea that animals occupy preferential, anysotropic positions with respect to their neighbours, and devote a large amount of their interaction responses to maintaining their mutual positions. We test our approach by deriving the apparent alignment and attraction responses from simulated trajectories of animals moving side by side, or one in front of the other. We show that the anisotropic positioning of individuals, in combination with noise, is sufficient to reproduce several aspects of the movement responses observed in real animal groups. This anisotropy at the level of interactions should be considered explicitly in future models of flocking and schooling. By making a distinction between interaction responses involved in maintaining a preferred flock configuration, and interaction responses directed at changing it, our work provides a frame to discriminate movement interactions that signal directional conflict from interactions underlying consensual group motion
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