Abstract

Damages of DNA in tritiated water

Tritium is a radioisotope of hydrogen emitting low energy β-rays in disintegration to ³He. DNA molecules are damaged mainly by β-ray irradiation, and additional damages can be induced by break of chemical bond by nuclear transmutation to inert ³He. Deep knowledges of the mechanisms underlying DNA damages lead to better understanding of biological effects of tritium. This chapter reviews recent experimental and computer simulation activities on quantitative evaluation of damage rates by β-ray irradiation and nuclear transmutation. The rate of DNA double-strand breaks in tritiated water has been examined using a single molecule observation method. The effects of β-ray irradiation were not noticeable at the level of tritium concentration of ～ kBq/cm³, while the irradiation effects were clear at tritium concentrations of ～ MBq/cm³. The factors affecting on the DSB rate are discussed. A new image processing method for the automatic measurement of DNA length using OpenCV and deep learning is also introduced. The effects of tritium transmutation on hydrogen bonds acting between the two main strands of DNA have been examined using molecular dynamics simulations. The study showed that the collapsing of DNA structure by the transmutation can be quantitatively evaluated using the root mean square deviation of atomic positions.

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Monte Carlo Simulations of Liquids --- Wetting and Anomalous Relaxation ---

We develop two typical examples of the Monte Carlo simulations in the study of liquids, one from the macroscopic viewpoint and the other from the microscopic viewpoint. As the former, we investigate wetting phenomena by numerically solving the Navier-Stokes equation and show that the finger instabilities take place as a result of submacroscopic fluctuations. As the latter, we study anomalous relaxation in disordered systems and show that the Cole-Cole form and the Kohlraush law are respectively outcomes of the fractal and non-fractal structures.

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Complex Fluids: Anomalous Relaxation, Percolation and Wetting

Our recent research on complex fluids is reviewed. This article is divided into three parts. The first part is devoted to some theoretical models of the anomalous relaxation observed in various kinds of disordered systems. In the second part, percolation theory, by which disordered systems are also modeled, is focused and, in particular, we report on the determination of percolation threshold with high accuracy. In the last section, we discuss a topic concerning wetting which is an old but developing research area of complex fluids.

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Anomalous Relaxation in Supercooled Liquids

We survey a short history on anomalous relaxation and review experimental results, theoretical and computer simulation analyses on supercooled liquids. We explain our models for anomalous relaxation within one-body picture.

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In Quest of the Mechanisms of Anomalous Relaxation --- Monte Carlo simulations of random walk in spaces of fractal dimension ---

Monte Carlo simulations of random walk in spaces of fractal dimension are performed. We focus our attention on the relaxation processes and show that the complex susceptibility turns out to be Cole-Cole type.

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Chaotic Mixing by Kneading

We study the mixing process of kneading dough experimentally and model it with a simple area-preserving map ("mixing map"). This map is characterized by a parameter r_sm (1/2 r_sm 1), which represents the ratio of "stretching" to "moving", and a map with r_sm=1 corresponds to a baker's transformation. We analyze mixing properties of this map by applying the diagnostics of mixing used by I. Zawadzki and H. Aref (Phys. Fluids A 3, 1405 (1991)). We find that mixing is very efficient at r_sm=1 but degrades rapidly nearby. However at r_sm 3/4 mixing is as efficient as a baker's transformation. Accidentaly, this parameter region r_sm 3/4 is achievable experimentaly.