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Natsuhiko Yoshinaga

Department of Physics,
Graduate School of Science,
the University of Tokyo,
Room 302, Faculty of Science Bldg. 1
7-3-1 Hongo, Bunkyo-ku
Tokyo, 113-0033 JAPAN

Tel: +81-(0)3-5841-4183
Fax: +81-(0)3-5841-4183

I move from 16th Dec. 2011 to Tohoku University
current address:
(new homepage is here)
Mathematics Unit, WPI Advanced Institute for Materials Research (WPI-AIMR),
Tohoku University Katahira 2-1-1, Aoba-Ku,
Sendai 9808577, Japan
Tel: +81-(0)22-217-6327
Fax: +81-(0)22-217- 5129

E-mail address:
Web page:


Research Interests

      My research area is the statistical physics of "active" soft condensed materials. Soft materials contain various length and time scales correlating in a complicated manner. The importance of this field is that such systems are closely related to biological phenomena, which give us unlimited imagination and intuition. In addition, they are found in most of industrial products sustaining our comfortable lives.

Active Matter -- Self-propelled particles and drops      Biological systems consume energy and exhibit their functions. Among the variety of phenomena, we are particularly interested in cell motility. Interestingly, cells can move without any external force. This is achieved by active force (stress) generation using energy of ATP. The goal of this study is to understand the mechanism of self-propulsion. As a first step, we are now investigating model chemical systems in which particles and drops move spontaneously.

      Thermophoresis is phenomenon of directional motion under temperature gradient. This is similar to electrophoresis under an electric field and osmophoresis (difussiophoresis) under a concentration gradient. It was found back in 1856, though the mechanism, particularly microscopic and mesoscopic aspects, is still less clear despite of intensive studies. We have developed hydrodynamic theory, and investigated flow induced by temperature gradient. This phenomena is strongly dependent on surface properties of objects in phoretic motion.

Deformation induced spontaneous motion
      An important observation for motile cells is that they can deform. Recently, it has been suggested that there is strong correlation between deformation and motion. Although cells are very complex, we believe the essence is shared with artificial model systems which are simpler and exhibit spontaneous motion and deformation. With the aid of hydrodynamics, we are trying to clarify the relation between deformation and motion.

Drift instability of a drop driven by Marangoni flow
     The directional motion of self-propulsion arises either from intrinsic asymmetry of the systems or spontaneous break of rotational symmetry. The latter is related with nonlinear nature of the systems as phase transitions in equilibrium systems. We are now interested in the nonequilibrium phase transition between stationary and moving stales. This has been studied in the field of nonlinear dynamics as drift instability. We have developed hydrodynamics describing this instability for the Marangoni effect.



Biophysics -- Stress Fibers       Stress fibres are key elements of mechanical aspects of cells. Main ingredients are actin filaments, myosin II, and a-actinin. Many other proteins have also been found and considered to function. Our purpose in this study is to model stress fibres as assemble of filaments in nonequilibrium systems.
Polarity pattern
      Actin filaments have polarity, that is, they have plus (barbed) and minus (pointed) ends. Several polarity patterns have been found in cells, for instance (A) graded polarity, (B) alternating polarity, and uniform one. The alternating polarity looks similar to muscle. However, the relation between polarity and mechanical properties are still unknown. We show active stress generated by molecular motors (myosin filaments) determines polarity patterns.

Active polar elasticity

Polymers in Nonequilibrium Systems         Kinetics in soft matter is of importance for understanding of natural phenomena in biological systems and in daily lives. We know empirically shaving gel makes a transition into bubbles by rubbing with our hands. This shear-induced nonequilibrium phase transition involves highly nonlinear and far-from equilibrium equations in physical points of view. Solving these equations and even constituting model equations are accordingly difficult task. It is thus significant challenge as a physicist to work in problems of kinetics in soft materials.
      I focus on kinetics in polymer physics. Even in this particular case, our understanding is quite primitive, while dynamical properties near equilibrium states have been investigated extensively. Recent experiments of single-molecule manipulation open investigations of the kinetics of soft materials including a single semiflexible polymer.

Polymer translocation through a pore

Transition kinetics of a single semiflexible polymer

Polymer stretching

      In living systems, biopolymers such as proteins are, in general, heteropolymers with complicated sequences of amino acids. It is often mentioned that sequences within proteins are relevant for their conformations in the folded states. Therefore, most of studies heretofore conducted have dealt with sequences in heteropolymers which lead to diversity in conformations.

Two-state polymers

Rod-coil copolymers

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2011Hiroyuki Kitahata, Natsuhiko Yoshinaga, Ken H. Nagai, and Yutaka Sumino
"Spontaneous motion of a droplet coupled with a chemical wave"
submitted movies are available here

2010Hong-Ren Jiang, Natsuhiko Yoshinaga, and Masaki Sano
"Active Motion of Janus Particle by Self-thermophoresis in Defocused Laser Beam"
Physical Review Letters, 105, 268302 (2010)
Editor's suggestion and Viewpoint in Physics, 3, 108 (2010) Debut of a hot “fantastic voyager”
movies are available here

Natsuhiko Yoshinaga, Jean-Francois Joanny, Jacques Prost and Pilippe Marcq
"Polarity patterns of stress fibers"
Physical Review Letters, 105, 238103 (2010)

2009 Takahiro Sakaue and Natsuhiko Yoshinaga
"Dynamics of Polymer Decompression: Expansion, Unfolding and Ejection"
Physical Review Letters, 102, 148302 (2009).

Hong-Ren Jiang, Hirofumi Wada, Natsuhiko Yoshinaga, and Masaki Sano
"Manipulation of Colloids by Nonequilibrium Depletion Force in Temperature Gradient"
Physical Review Letters, 102, 208301 (2009).

2008Natsuhiko Yoshinaga, E.I. Kats and A. Halperin
"On the Adsorption of Two-State Polymers"
Macromolecules, 41, 7744-7751 (2008)

Natsuhiko Yoshinaga
"Folding and unfolding transition in a single semiflexible polymer "
Physical Review E, 77, 061805 (2008).

2007Natsuhiko Yoshinaga and Kenichi Yoshikawa
"Core-shell structures in single flexible-semiflexible block copolymers: Finding the free energy minimum for the folding transition"
Journal of Chemical Physics, 127, 044902 (2007).

N. Yoshinaga, D. J. Bicout, E.I. Kats and A. Halperin
"Dynamic Core Shell Structures in Two State Models of Neutral Water Soluble Polymersr"
Macromolecules, 40(6), 2201-2209 (2007)

2006N. Yoshinaga
"Transition kinetics of a single semiflexible polymer"
Progress of Theoretical Physics Supplement, 161, 397-402 (2006).

2005 N. Yoshinaga, K. Yoshikawa and T. Ohta
"Different pathways in mechanical unfolding/folding cycle of a single semiflexible polymer"
European Physical Journal E, 17, 485 (2005).

K. Yoshikawa and N. Yoshinaga
"Novel scenario on the folding transition of a single chain"
Journal of Physics: Condensed Matter, 17, S2817-S2823 (2005).

2002 N. Yoshinaga, K. Yoshikawa and S. Kidoaki
"Multiscaling in a Long Semiflexible Polymer Chain in Two Dimension"
Journal of Chemical Physics, 116, 9926 - 9929 (2002).

2001N. Yoshinaga, T. Akitaya and K. Yoshikawa
“Intercalating Fluorescence Dye YOYO-1 Prevents the Folding Transitionin Giant Duplex DNA”
Biochemical and Biophysical Research Communications, 286, 264-267, (2001).

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