Biomedical subjects

Yasuya Nakayama

Publications and source records attributed to Yasuya Nakayama.

4 recordsLinked to original sources

PubMed2006

Direct numerical simulations of electrophoresis of charged colloids.

We propose a numerical method to simulate electrohydrodynamic phenomena in charged colloidal dispersions. This method enables us to compute the time evolutions of colloidal particles, ions, and host fluids simultaneously by solving Newton, advection-diffusion, and Navier-Stokes equations so that the electrohydrodynamic couplings can be fully taken into account. The electrophoretic mobilities of charged spherical particles are calculated in several situations. The comparisons with approximation theories show quantitative agreements for dilute dispersions without any empirical parameters; however, our simulation predicts notable deviations in the case of dense dispersions.

Colloids↗

PubMed2005

Simulation method to resolve hydrodynamic interactions in colloidal dispersions.

A computational method is presented to resolve hydrodynamic interactions acting on solid particles immersed in incompressible host fluids. In this method, boundaries between solid particles and host fluids are replaced with a continuous interface by assuming a smoothed profile. This enabled us to calculate hydrodynamic interactions both efficiently and accurately, without neglecting many-body interactions. The validity of the method was tested by calculating the drag force acting on a single cylindrical rod moving in an incompressible Newtonian fluid. This method was then applied in order to simulate sedimentation process of colloidal dispersions.

Journal Article↗

PubMed2003

Intermittency and exponent field dynamics in developed turbulence.

Spatiotemporal dynamics of intermittency in association with coarse-grained energy-dissipation rate fluctuations is discussed. This is done first by phenomenologically constructing the probability density for exponent field fluctuations that is introduced to characterize the energy-dissipation rate field, and then by proposing the Langevin dynamics derived with the projection-operator method on the basis of the Navier-Stokes equation. With a Gaussian approximation for exponent fluctuations, spatiotemporal correlation functions for coarse-grained energy-dissipation rate fluctuations are explicitly obtained.

Journal Article↗

PubMed2002

Scaling hypothesis leading to generalized extended self-similarity in turbulence.

A scaling hypothesis leading to generalized extended self-similarity (GESS) for velocity structure functions, valid for intermediate scales in isotropic, homogeneous turbulence, is proposed. By introducing an effective scale ŕ, monotonically depending on the physical scale r, with the use of the large deviation theory, the asymptotic forms of the probability densities for the velocity differences u(r) and for the coarse-grained energy-dissipation rate fluctuations epsilon(r), compatible with this GESS, are proposed. The probability density for epsilon(r) is shown to have the form P(r)(epsilon) approximately equal to epsilon(-1)(ŕ/L)(S(ŕ)[z(ŕ)](epsilon))) with z(ŕ)(epsilon)=ln(epsilon/epsilon(L))/ln(L/ŕ), where L and epsilon(L) are the stirring scale and the coarse-grained energy-dissipation rate over the scale L. The concave function S(ŕ)(z), the spectrum, plays the central role of the present approach. Comparing the results with numerical and experimental data, we explicitly obtain the fluctuation spectra S(ŕ)(z).

Journal Article↗