Kyoto University
研究内容
My research area is the statistical physics of complex soft condensed materials. Soft materials contain various length and time scales, which couple together in a complicated manner. Therefore we do not have one unique method to analyze them. Starting from microscopic (for example atomic) systems is not always efficient. As a result, we need to combine number of methods or sometimes create new ways to find essential route to the reality. 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 contain most of industrial products, and sustain our comfortable lives.
My interests are how to describe these complicated systems in a simple way. Although these systems contain various time and length scales, most of the scales are slaved by a few slow and mesoscopic variables. This makes problems very clear and tractable. To perform this reduction, physical imaginations is often needed. I use simulations not only for comparison with theories and experiments but also to obtain the imaginations. We employ mainly theoretical (analytical and numerical) methods to study these problems. On the other hand, I am not confined to theoretical methods and I did study with experimental techniques, such as the fluorescent microscopy aSat, 21.01.2012rs are one of representations in soft materials. My research focuses on folding transition of single semiflexible polymers. In the polymer physics, various properties of flexible polymers, which have no bending rigidity, are discussed. On the other hand, the understandings of semiflexible polymers are still developing in spite of the fact that semiflexible polymers have important features of folding into organized structures. This is important because in biological systems, DNA molecules and proteins have well-organized structures and they are closely related with their functions. Therefore we have studied with atomic force microscopy the conformation of DNA molecules, especially long so that we can discuss statistical properties of single molecules. It has been clarified that such long DNA molecules make transitions into folded states with condensing agents, and we therefore investigated the effect of the specific binding with DNA on the folding transition using the intercalating molecules. We have also considered theoretically the phase transition of semiflexible polymers between the elongated coiled state and the folded states, and found that the effect of bending rigidity changes qualitative feature of the transition by coupling of density and orientational order of degree of freedoms.
On the other hand, semiflexible polymers at nonequilibrium state are far less understood even though most of the biological and chemical systems are far from equilibrium. We have studied semiflexible polymers under external mechanical loading and unloading, and folding kinetics of them. We performed simulations of mechanical unfolding and refolding and found that there is large hysteresis in this cycle. These results were analyzed with phenomenological scaling approach and the two-variable model in more general way. The scaling approach was applied for the folding and unfolding kinetics of single semiflexible polymers and compared with simulations.
