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Research

My interest

My ultimate goal for my research is understanding the way living structures are made up.

If I say living structures, many people will imagine life on earth, say animals, plants, and so on. But what I mean with living structures also includes nations, societies, and relationships with friends in more familiar things. They have small units that behave independently and also almost randomly. However, through local interactions between such active units, mass of such units behaves as if it has other intention, and it has distinct order. I'd like to understand mechanisms and underlying universality that promotes such structure formation.

To consider such phenomena especially from a view standpoint of physics, statistical mechanics and thermodynamics are key field. Statistical mechanics can be said to be a field which succeeded in predicting the collective behavior of simple and ideal units, such as molecules. One key for this success is that extraordinary larger number of units constitutes a group. Another field, thermodynamics, puts observation of macroscopic physical quantity as a start point. It is with dare to ignore internal details, and succeed in finding a relation between these macroscopic observable. 

These field in common assumes that a system is in a thermal equilibrium condition. This is strikingly useful concept/approximation. However, the unit which constitutes living structure is under continuous input of energy, and many are not in a thermal equilibrium situation. Moreover, in many cases, it has also input of constituents particles. Such a system us called as nonequilibrium open system, or far from equilibrium system.

In a nonequilibrium open system, the concept of a thermal equilibrium can be used only locally. So the understanding of a nonequilibrium open system is still on-going. On the other hand in a nonequilibrium open system, a various phenomenon with amazingly beautiful pattern formation occurs, as well as in human societies. 

I am using the technique of the both sides of an experiment and theory to understand this nonequilibrium open system, and aim to unveil the physical side of a life process.


Research Interest

Chemo-mechanical energy transduction in isothermal condition.

Living organisms transduce chemical energy into mechanical energy efficiently without changing it into thermal energy. This is really remarkable considering that we, human being, need to burn fossil fuels to acquire the energy for everyday life. The understanding of the mechanism of this chemo-mechanical energy transduction is of high interest, not only from academic viewpoints, but also from practical reasons. My approach to this fascinating phenomenon is not to use living things directly, but rather to construct simple chemical model systems that have the same features as living organisms and analyze it.

Systems showing solutal Marangoni effect

When some molecules are adsorbed on to an interface between 2 phases, the interfacial tension of this interface is generally weakened. Especially, molecules that strongly adsorb on interfaces is called surfactant. This sounds a little difficult, but dish detergent, which we usually use, is one of the common examples of surfactant. Because each surfactant molecule has oil-friendly part (non-polar part) and water-friendly part (polar part), it accumulates at an interface to become an agent for each phase.
Here, if there is inhomogeneous surfactant distribution, there occurs sear stress to make flows that reduce this inhomogeneity. This phenomenon is called solutal Marangoni effect (Please check solutal Marangoni page (under construction) ). This solutal Marangoni effect is one of chemo-mechanical energy transduction systems under isothermal condition. Through analysis of this system, I want to reveal physics of chemo-mechanical energy transduction.

Oil/Water system (Oil Worm)

In a coexisting system of aqueous phase contains cationic surfactant, organic phase contains iodine and glass substrate, oil/water interface moves spontaneously. This is interesting not only because a real-space model of chemo-mechanical energy transduction system, but also because this system is under energy input with large noise.
(More including movies)
Phys. Rev. Lett., 94, 068301 (2005)

Spontaneous Motion of Alcohol Droplet on Water

An alcohol droplet put on an air-water surface moves spontaneously resulting from the concentration gradient of an alcohol (Pentanol) on air-water surface. Since an alcohol droplet is deformable, the alcohol droplet takes characteristic shape coupled with the mode of motion. We have analyzed the mode of motion is determined by its size, and concluded that it is the result of the competition between the local driving of interface and interfacial tension which tries to maintain its interface to be minimum.

Movie Page from Mr. Ken Nagai
Phys. Rev. E, 71, 065301 (2005)

Emergence of spatio-temporal order

In far-from-equilibrium system, there appear various order which includes spatial ones and temporal ones. Such kind of order or pattern can be recognized as a primitive model for the living things. Life phenomena also create spatio-temporal patterns by using the flow of matters, chemicals or heats. Therefore, I believe the research on this field will shed lights on the physical aspect of life phenomena.

Fellowships

JSPS KAKENHI(Grant-in-aid for Young Scientists (B)), 24740287
Grant-in-aid for Research Activity Start-up, 23840019
Research fellowship from the Japan Society for the Promotion of Science (JSPS) for Young Scientists (DC1)(Apr. 2006 - Mar. 2009)
Research fellowship from the Japan Society for the Promotion of Science (JSPS) for Young Scientists (PD)(Apr. 2009 - Mar. 2012)


Publication

Please check Laboratory website.

Presentation(in English)

Please check Laboratory website.