Biomedical subjects

Makoto Tsubota

Publications and source records attributed to Makoto Tsubota.

10 recordsLinked to original sources

PubMed2006

Thermal dissipation in quantum turbulence.

The microscopic mechanism of thermal dissipation in quantum turbulence is numerically studied by solving the coupled system involving the Gross-Pitaevskii equation and the Bogoliubov-de Gennes equation. At low temperatures, the obtained dissipation does not work at scales greater than the vortex core size. However, as the temperature increases, dissipation works at large scales and it affects the vortex dynamics. We successfully obtain the mutual friction coefficients of the vortex in dilute Bose-Einstein condensates dynamics as functions of temperature.

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PubMed2006

Phase separation of a fast rotating boson-fermion mixture in the lowest-Landau-level regime.

By minimizing the coupled mean-field energy functionals, we investigate the ground-state properties of a rotating atomic boson-fermion mixture in a two-dimensional parabolic trap. At high angular frequencies in the mean-field lowest-Landau-level regime, quantized vortices enter the bosonic condensate, and a finite number of degenerate fermions form the maximum-density-droplet state. As the boson-fermion coupling constant increases, the maximum density droplet develops into a lower-density state associated with the phase separation, revealing characteristics of a Landau-level structure.

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PubMed2005

Kolmogorov spectrum of superfluid turbulence: numerical analysis of the Gross-Pitaevskii equation with a small-scale dissipation.

The energy spectrum of superfluid turbulence is studied numerically by solving the Gross-Pitaevskii equation. We introduce the dissipation term which works only in the scale smaller than the healing length to remove short wavelength excitations which may hinder the cascade process of quantized vortices in the inertial range. The obtained energy spectrum is consistent with the Kolmogorov law.

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PubMed2004

Vortex molecules in coherently coupled two-component Bose-Einstein condensates.

A vortex molecule is predicted in rotating two-component Bose-Einstein condensates whose internal hyperfine states are coupled coherently by an external field. A vortex in one component and one in the other are connected by a domain wall of the relative phase, constituting a "vortex molecule," which features a nonaxisymmetric (pseudo)spin texture with a pair of merons. The binding mechanism of the vortex molecule is discussed based on a generalized nonlinear sigma model and a variational ansatz. The anisotropy of vortex molecules is caused by the difference in the scattering lengths, yielding a distorted vortex-molecule lattice in fast rotating condensates.

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PubMed2004

Multiple domain formation induced by modulation instability in two-component Bose-Einstein condensates.

The dynamics of multiple domain formation caused by the modulation instability of two-component Bose-Einstein condensates in an axially symmetric trap are studied by numerically integrating the coupled Gross-Pitaevskii equations. The modulation instability induced by the intercomponent mean-field coupling occurs in the out-of-phase fluctuation of the wave function and leads to the formation of multiple domains that alternate from one domain to another, where the phase of one component jumps across the density dips where the domains of the other exist. This behavior is analogous to a soliton train, which explains the origin of the long lifetime of the spin domains observed by Miesner et al. [Phys. Rev. Lett. 82, 2228 (1999)]].

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PubMed2003

Vortex phase diagram in rotating two-component Bose-Einstein condensates.

We investigate the structure of vortex states in rotating two-component Bose-Einstein condensates with equal intracomponent but varying intercomponent-coupling constants. A phase diagram in the intercomponent-coupling versus rotation-frequency plane reveals rich equilibrium structures of vortex states. As the ratio of intercomponent to intracomponent couplings increases, the interlocked vortex lattices undergo phase transitions from triangular to square, to double-core lattices, and eventually develop interwoven "serpentine" vortex sheets with each component made up of chains of singly quantized vortices.

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PubMed2003

Kelvin-wave cascade on a vortex in superfluid 4He at a very low temperature.

A study by computer simulation is reported of the behavior of a quantized vortex line at a very low temperature when there is continuous excitation of low-frequency Kelvin waves. There is no dissipation except by phonon radiation at a very high frequency. It is shown that nonlinear coupling leads to a net flow of energy to higher wave numbers and to the development of a simple spectrum of Kelvin waves that is insensitive to the strength and frequency of the exciting drive. The results are likely to be relevant to the decay of turbulence in superfluid 4He at very low temperatures.

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PubMed2003

Rotating superfluid turbulence.

Almost all studies of vortex states in helium II have been concerned with either ordered vortex arrays or disordered vortex tangles. This work numerically studies what happens in the presence of both rotation (which induces order) and thermal counterflow (which induces disorder). We find a new statistically steady state in which the vortex tangle is polarized along the rotational axis. Our results are used to interpret an instability that was discovered experimentally by Swanson et al. [Phys. Rev. Lett. 50, 190 (1983)]] and the vortex state beyond the instability that has been unexplained until now.

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PubMed2002

Energy spectrum of superfluid turbulence with no normal-fluid component.

The energy of superfluid turbulence without the normal fluid is studied numerically under the vortex filament model. Time evolution of the Taylor-Green vortex is calculated under the full nonlocal Biot-Savart law. It is shown that for k<2pi/l the energy spectrum is very similar to the Kolmogorov's -5/3 law which is the most important statistical property of the conventional turbulence, where k is the wave number of the Fourier component of the velocity field and l is the average intervortex spacing. The vortex length distribution converges to a scaling property reflecting the self-similarity of the tangle.

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PubMed2002

Gene expression of MMP8 and MMP13 during embryonic development of bone and cartilage in the rat mandible and hind limb.

Matrix metalloproteinases (MMPs) 8 and 13 comprise the collagenase subfamily in rats and mice, and only MMP13 has been implicated in degradation of the collagenous matrices during development of bone and cartilage. On the hypothesis that MMP8 is also involved in bone and cartilage development, the present study was designed to investigate gene expression of MMP8 in rat embryonic mandibles and hind limbs. Expression of MMP8 was examined with in situ hybridization and RT-PCR and was compared with that of MMP13. Osteoblastic and chondrocytic cells expressing collagenous matrix molecules were identified using in situ hybridization for collagen Types I and II. The results demonstrated that MMP8 is expressed by osteoblastic progenitors, differentiated osteoblasts, osteocytes, and chondrocytes in the growth plate for the first time. Furthermore, the expression of MMP8 is much broader than that of MMP13, for which expression is confined to differentiated phenotypes of osteoblastic and chondrocytic lineage.

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