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Masatomo Iwasa

Publications and source records attributed to Masatomo Iwasa.

5 recordsLinked to original sources
arXiv2011

Phenomenological understanding of aggregation and dispersion of chemotactic cells

We present a simple model that describes the motion of a single chemotactic cell exposed to a traveling wave of the chemoattractant. The model incorporates two types of responses to stimulation by the chemoattractant, i.e., change in polarity and change in motility of the cell. The periodic change in motility is assumed to be induced by the periodic stimulation by the chemoattractant on the basis of previous observations. Consequently, net migration of the cell occurs in a particular direction with respect to wave propagation, which explains the migration of Dictyostelium cells in aggregation processes. The difference between two time delays from the stimulation to the two responses and the wave frequency determined by the frequency of the secretion of the chemoattractant are important parameters that determine the direction of migration and the effective interaction between cells in a population. This result explains the dispersed state of a population of vegetative cells and cells in preaggregation without the assumption of a chemorepellent, and also explains the commencement of the aggregation. The result is extended to a general fact as follows: the temporal oscillation of the magnitude of the random motion for gradient-sensing particles induces spontaneous movement, even when the particles are exposed to a periodic wave of the chemoattractant, which results in the aggregation or dispersion of the particles communicating via their attractant.

physics.bio-ph↗
arXiv2008

The exact probability distribution of saturating states in random sequential adsorption

We consider the non-overlapping irreversible random sequential adsorption (RSA) process on one-dimensional finite line, which is known also as the car parking process. The probability of each coverage in saturating states is analytically and exactly obtained. In the derivation, a new representation of states in RSA process is introduced, which effectively works to make the calculation clear and simple.

cond-mat.stat-mech↗
arXiv2008

Solution of reduced equations derived with singular perturbation methods

For singular perturbation problems in dynamical systems, various appropriate singular perturbation methods have been proposed to eliminate secular terms appearing in the naive expansion. For example, the method of multiple time scales, the normal form method, center manifold theory, the renormalization group method are well known. In this paper, it is shown that all of the solutions of the reduced equations constructed with those methods are exactly equal to sum of the most divergent secular terms appearing in the naive expansion. For the proof, a method to construct a perturbation solution which differs from the conventional one is presented, where we make use of the theory of Lie symmetry group.

nlin.CD↗
arXiv2008

Renormalization group in difference systems

A new singular perturbation method based on the Lie symmetry group is presented to a system of difference equations. This method yields consistent derivation of a renormalization group equation which gives an asymptotic solution of the difference equation. The renormalization group equation is a Lie differential equation of a Lie group which leaves the system approximately invariant. For a 2-D symplectic map, the renormalization group equation becomes a Hamiltonian system and a long-time behaviour of the symplectic map is described by the Hamiltonian. We study the Poincaré-Birkoff bifurcation in the 2-D symplectic map by means of the Hamiltonian and give a condition for the bifurcation.

nlin.CD↗