75 research outputs found
Functional Analysis of Spontaneous Cell Movement under Different Physiological Conditions
Cells can show not only spontaneous movement but also tactic responses to
environmental signals. Since the former can be regarded as the basis to realize
the latter, playing essential roles in various cellular functions, it is
important to investigate spontaneous movement quantitatively at different
physiological conditions in relation to cellular physiological functions. For
that purpose, we observed a series of spontaneous movements by Dictyostelium
cells at different developmental periods by using a single cell tracking
system. Using statistical analysis of these traced data, we found that cells
showed complex dynamics with anomalous diffusion and that their velocity
distribution had power-law tails in all conditions. Furthermore, as development
proceeded, average velocity and persistency of the movement increased and as
too did the exponential behavior in the velocity distribution. Based on these
results, we succeeded in applying a generalized Langevin model to the
experimental data. With this model, we discuss the relation of spontaneous cell
movement to cellular physiological function and its relevance to behavioral
strategies for cell survival.Comment: Accepted to PLoS ON
Scaling law in target-hunting processes
We study the hunting process for a target, in which the hunter tracks the
goal by smelling odors it emits. The odor intensity is supposed to decrease
with the distance it diffuses. The Monte Carlo experiment is carried out on a
2-dimensional square lattice. Having no idea of the location of the target, the
hunter determines its moves only by random attempts in each direction. By
sorting the searching time in each simulation and introducing a variable to
reflect the sequence of searching time, we obtain a curve with a wide plateau,
indicating a most probable time of successfully finding out the target. The
simulations reveal a scaling law for the searching time versus the distance to
the position of the target. The scaling exponent depends on the sensitivity of
the hunter. Our model may be a prototype in studying such the searching
processes as various foods-foraging behavior of the wild animals.Comment: 7 figure
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
A Stochastic Description of Dictyostelium Chemotaxis
Chemotaxis, the directed motion of a cell toward a chemical source, plays a key role in many essential biological processes. Here, we derive a statistical model that quantitatively describes the chemotactic motion of eukaryotic cells in a chemical gradient. Our model is based on observations of the chemotactic motion of the social ameba Dictyostelium discoideum, a model organism for eukaryotic chemotaxis. A large number of cell trajectories in stationary, linear chemoattractant gradients is measured, using microfluidic tools in combination with automated cell tracking. We describe the directional motion as the interplay between deterministic and stochastic contributions based on a Langevin equation. The functional form of this equation is directly extracted from experimental data by angle-resolved conditional averages. It contains quadratic deterministic damping and multiplicative noise. In the presence of an external gradient, the deterministic part shows a clear angular dependence that takes the form of a force pointing in gradient direction. With increasing gradient steepness, this force passes through a maximum that coincides with maxima in both speed and directionality of the cells. The stochastic part, on the other hand, does not depend on the orientation of the directional cue and remains independent of the gradient magnitude. Numerical simulations of our probabilistic model yield quantitative agreement with the experimental distribution functions. Thus our model captures well the dynamics of chemotactic cells and can serve to quantify differences and similarities of different chemotactic eukaryotes. Finally, on the basis of our model, we can characterize the heterogeneity within a population of chemotactic cells
Directional properties of an array of sound receivers positioned in an impedance screen recess
Inversely correlated cycles in speed and turning in an ameba: an oscillatory model of cell locomotion.
Previous biophysical models of ameboid crawling have described cell movement in terms of a persistent random walk. Speed and orientation were treated in the latter model as independent and temporally homogeneous stochastic processes. We show here that, at least in the case of Dictyostelium discoideum, both speed control and reorientation processes involve a deterministic, periodic component. We also show that the processes are synchronized and negatively correlated, as was suggested by earlier findings. That is, increased turning correlates with periods of slow movement. Therefore, previous models are inconsistent with the behavior of cells. Using a heuristic approach, we have developed a mathematical model that describes the statistical properties of the cell's velocity and movement of its centroid. Our observations and the model are consistent with the phenomenological description of ameboid motility as a cyclic process of pseudopod extension and retraction
Helmholtz equation solutions corresponding to multiple roots of the dispersion equation for a waveguide with impedance walls
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