arXiv subjects

Hiroyuki Kitahata

Publications and source records attributed to Hiroyuki Kitahata.

49 records · Page 3Linked to original sources

arXiv2018

Interplay between epidermal stem cell dynamics and dermal deformations

We introduce a particle-based model of self-replicating cells on a deformable substrate composed of the dermis and the basement membrane and investigate the relationship between dermal deformations and stem cell pattering on it. We show that our model reproduces the formation of dermal papillae, protuberances directing from the dermis to the epidermis, and the preferential stem cell distributions on the tips of the dermal papillae, which the basic buckling mechanism fails to explain. We argue that cell-type-dependent adhesion strength of the cells to the basement membrane is crucial factors of these patterns.

q-bio.TO↗

arXiv2018

Effective diffusion coefficient including the Marangoni effect

Surface-active molecules supplied from a particle fixed at the water surface create a spatial gradient of the molecule concentration, resulting in Marangoni convection. Convective flow transports the molecules far from the particle, enhancing diffusion. We analytically derive the effective diffusion coefficient associated with the Marangoni convection rolls. The resulting estimated effective diffusion coefficient is consistent with our numerical results and the apparent diffusion coefficient measured in experiments.

nlin.PS↗

arXiv2017

Oscillatory Motion of a Camphor Grain in a One-Dimensional Finite Region

The motion of a self-propelled particle is affected by its surroundings, such as boundaries or external fields. In this paper, we investigated the bifurcation of the motion of a camphor grain, as a simple actual self-propelled system, confined in a one-dimensional finite region. A camphor grain exhibits oscillatory motion or remains at rest around the center position in a one-dimensional finite water channel, depending on the length of the water channel and the resistance coefficient. A mathematical model including the boundary effect is analytically reduced to an ordinary differential equation. Linear stability analysis reveals that the Hopf bifurcation occurs, reflecting the symmetry of the system.

nlin.PS↗

arXiv2017

Relationship between the size of camphor-driven rotor and its angular velocity

We consider a rotor made of two camphor disks glued below the ends of a plastic stripe. The disks are floating on a water surface and the plastic stripe does not touch the surface. The system can rotate around a vertical axis located at the center of the stripe. The disks dissipate camphor molecules. The driving momentum comes from the nonuniformity of surface tension resulting from inhomogeneous surface concentration of camphor molecules around the disks. We investigate the stationary angular velocity as a function of rotor radius $\ell$. For large $\ell$ the angular velocity decreases for increasing $\ell$. At a specific value of $\ell$ the angular velocity reaches its maximum and, for short $\ell$ it rapidly decreases. Such behaviour is confirmed by a simple numerical model. The model also predicts that there is a critical rotor size below which it does not rotate. Within the introduced model we analyze the type of this bifurcation.

nlin.AO↗

arXiv2016

Hydrodynamic collective effects of active proteins in biological membranes

Lipid bilayers forming biological membranes are known to behave as viscous 2D fluids on submicrometer scales; usually they contain a large number of active protein inclusions. Recently, it has been shown [Proc. Nat. Acad. Sci. USA 112, E3639 (2015)] that such active proteins should in- duce non-thermal fluctuating lipid flows leading to diffusion enhancement and chemotaxis-like drift for passive inclusions in biomembranes. Here, a detailed analytical and numerical investigation of such effects is performed. The attention is focused on the situations when proteins are concentrated within lipid rafts. We demonstrate that passive particles tend to become attracted by active rafts and are accumulated inside them.

cond-mat.soft↗

arXiv2015

Oscillation of a Rotating Levitated Droplet: Analysis with a Mechanical Model

A droplet of millimeter-to-centimeter scale can exhibit electrostatic levitation, and such levitated droplets can be used for the measurement of the surface tension of the liquids by observing the characteristic frequency of oscillatory deformation. In the present study, a simple mechanical model is proposed by considering a single mode of oscillation in the ellipsoidal deformation of a levitated rotating droplet. By measuring the oscillation frequency with respect to the rotational speed and oscillation amplitude, it is expected that the accuracy of the surface tension measurement could be improved. Using the proposed model, the dependences of the characteristic frequency of oscillatory deformation and the averaged aspect ratio are calculated with respect to the rotational angular velocity of a rotating droplet. These dependences are found to be consistent with the experimental observations.

nlin.PS↗

arXiv2015

General Criteria for Determining Rotation or Oscillation in a Two-dimensional Axisymmetric System

A self-propelled particle in a two-dimensional axisymmetric system, such as a particle in a central force field or confined in a circular region, may show rotational or oscillatory motion. These motions do not require asymmetry of the particle or the boundary, but arise through spontaneous symmetry breaking. We propose a generic model for a self-propelled particle in a two-dimensional axisymmetric system. A weakly nonlinear analysis establishes criteria for determining rotational or oscillatory motion.

nlin.PS↗

arXiv2012

Drift instability in the motion of a fluid droplet with a chemically reactive surface driven by Marangoni flow

We theoretically derive the amplitude equations for a self-propelled droplet driven by Marangoni flow. As advective flow driven by surface tension gradient is enhanced, the stationary state becomes unstable and the droplet starts to move. The velocity of the droplet is determined from a cubic nonlinear term in the amplitude equations. The obtained critical point and the characteristic velocity are well supported by numerical simulations.

cond-mat.soft↗

arXiv2011

Spontaneous motion of a droplet coupled with a chemical wave

We propose a novel framework for the spontaneous motion of a droplet coupled with internal dynamic patterns generated in a reaction-diffusion system. The spatio-temporal order of the chemical reaction gives rise to inhomogeneous surface tension and results in self-propulsion driven by the surrounding flow due to the Marangoni effect. Numerical calculations of internal patterns together with theoretical results of the flow fields at low Reynolds number well reproduces the experimental results obtained using a droplet of Belousov-Zhabotinsky (BZ) reaction medium.

cond-mat.soft↗

arXiv2005

Chemo-Sensitive Running Droplet

Chemical control of the spontaneous motion of a reactive oil droplet moving on a glass substrate under an aqueous phase is reported. Experimental results show that the self-motion of an oil droplet is confined on an acid-treated glass surface. The transient behavior of oil-droplet motion is also observed with a high-speed video camera. A mathematical model that incorporates the effect of the glass surface charge is built based on the experimental observation of oil-droplet motion. A numerical simulation of this mathematical model reproduced the essential features concerning confinement within a certain chemical territory of oil-droplet motion, and also its transient behavior. Our results may shed light on physical aspects of reactive spreading and a chemotaxis in living things.

nlin.AO↗

arXiv2005

Mode Selection in the Spontaneous Motion of an Alcohol Droplet

An alcohol (pentanol) droplet exhibits spontaneous agitation on an aqueous solution, driven by a solutal Marangoni effect. We found that the droplet's mode of motion is controlled by its volume. A droplet with a volume of less than $0.1 μ\rm{l}$ shows irregular translational motion, whereas intermediate-sized droplets of $0.1-200 μ\rm{l}$ show vectorial motion. When the volume is above $300 μ\rm{l}$, the droplet splits into smaller drops. These experimental results regarding mode selection are interpreted in terms of the wave number selection depending on the droplet volume.

nlin.AO↗

arXiv2005

Dynamics of micrometer-scale phase separation in a polymer mixture upon laser irradiation

Ten $μ$m -sized droplets in an aqueous-two-phase system (water/ polyethylene-glycol (PEG)/ dextran) dissapear upon irradiation with a focused YAG laser. The interface of the dextran-rich droplet broadens, indicating smoothing of the concentration profile, whereas, the PEG-rich droplet shrinks and disappears. These phenomena can be described in terms of the Ginzburg-Landau free energy, by considering the laser-induced dielectric potential.

cond-mat.other↗

arXiv2005

Slowing and stopping of chemical waves in a narrowing canal

The propagation of a chemical wave in a narrow, cone-shaped glass capillary was investigated. When a chemical wave propagates from the wider end to the narrower end, it slows, stops, and then disappears. A phenomenological model that considers the surface effect of the glass is proposed, and this model reproduces the experimental trends.

nlin.PS↗