Issei Nakamura
McMaster University
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Featured researches published by Issei Nakamura.
Soft Matter | 2012
Issei Nakamura; Zhen-Gang Wang
We develop a self-consistent field theory for salt-doped diblock copolymers, such as polyethylene oxide (PEO)–polystyrene with added lithium salts. We account for the inhomogeneous distribution of Li+ ions bound to the ion-dissolving block, the preferential solvation energy of anions in the different block domains, the translational entropy of anions, the ion-pair equilibrium between polymer-bound Li+ and anion, and changes in the χ parameter due to the bound ions. We show that the preferential solvation energy of anions provides a large driving force for microphase separation. Our theory is able to explain many features observed in experiments, particularly the systematic dependence in the effective χ-parameter on the radius of the anions, the observed linear dependence in the effective χ on salt concentration, and increase in the domain spacing of the lamellar phase due to the addition of lithium salts. We also examine the relationship between two definitions of the effective χ parameter, one based on the domain spacing of the ordered phase and the other based on the structure factor in the disordered phase. We argue that the latter is a more fundamental measure of the effective interaction between the two blocks. We show that the ion distribution and the electrostatic potential profile depend strongly on the dielectric contrast between the two blocks and on the ability of the Li+ to redistribute along the backbone of the ion-dissolving block.
Journal of Physical Chemistry B | 2010
Hidekazu Ishitobi; Issei Nakamura; Norihiko Hayazawa; Zouheir Sekkat; Satoshi Kawata
Three-dimensional molecular orientations of single fluorescence molecules in polymeric thin films were measured by focused azimuthally and radially polarized light, in which we found that the fluorescence intensity was dependent on the depth position of the molecule with respect to the film surface. We found that the fluorescence intensity for a molecule which is 80 nm deep in the film excited by radial polarization is appreciably larger when compared with the fluorescence intensity for a molecule which is also excited by radial polarization but which is closer to the polymer/air interface, a feature which leads to different fluorescence intensities, under excitation by radial polarization, for molecules with the same polar orientation but with different depths inside the film. We also found that the variation of fluorescence intensity from a molecule inside an 80 nm film in radial polarization is appreciably larger compared with one in azimuthal polarization. These findings were confirmed by comparing experiments using different thickness films with theoretically calculated electric field distributions.
Journal of Physical Chemistry B | 2014
Issei Nakamura
We studied the thermodynamic properties of ion solvation in polymer blends and block copolymer melts and developed a dipolar self-consistent field theory for polymer mixtures. Our theory accounts for the chain connectivity of polymerized monomers, the compressibility of the liquid mixtures under electrostriction, the permanent and induced dipole moments of monomers, and the resultant dielectric contrast among species. In our coarse-grained model, dipoles are attached to the monomers and allowed to rotate freely in response to electrostatic fields. We demonstrate that a strong electrostatic field near an ion reorganizes dipolar monomers, resulting in nonmonotonic changes in the volume fraction profile and the dielectric function of the polymers with respect to those of simple liquid mixtures. For the parameter sets used, the spatial variations near an ion can be in the range of 1 nm or larger, producing significant differences in the solvation energy among simple liquid mixtures, polymer blends, and block copolymers. The solvation energy of an ion depends substantially on the chain length in block copolymers; thus, our theory predicts the preferential solvation of ions arising from differences in chain length.
Soft Matter | 2013
Issei Nakamura; Zhen-Gang Wang
We illustrate the effects of dielectric inhomogeneity on the statistical properties of polyelectrolytes in solution, by a lattice Monte Carlo simulation that combines the bond fluctuation model with a local algorithm for computing the electrostatic interactions. Our model accounts for the difference in the dielectric properties between the polymer backbone and the solvent. Taking the coil–globule transition of a single polyelectrolyte chain in solvent as an example, we show that the chain conformation and the degree of counterion condensation are substantially affected by the dielectric contrast.
Progress of Theoretical Physics | 2001
Issei Nakamura; Veljko Dmitrasinovic
We apply a self-consistent relativistic mean-field variational “Gaussian functional” (or Hartree) approximation to the linear σ model with spontaneously and explicitly broken chiral O(4) symmetry. We set up the self-consistency, or “gap” and the Bethe-Salpeter equations. We check and confirm the chiral Ward-Takahashi identities, among them the Nambu-Goldstone theorem and the (partial) axial current conservation [CAC], both in and away from the chiral limit. With explicit chiral symmetry breaking, we confirm the Dashen relation for the pion mass and partial CAC. We solve numerically the gap and Bethe-Salpeter equations, discuss the solutions’ properties and the particle content of the theory.
Journal of the Physical Society of Japan | 2015
Yuichiro Manabe; T. Wada; Yuichi Tsunoyama; Hiroo Nakajima; Issei Nakamura; Masako Bando
We present a novel model to estimate biological effects caused by artificial radiation exposure, Whack-a-mole (WAM) model. It is important to take account of the recovery effects during the time course of the cellular reactions. The inclusion of the dose-rate dependence is essential in the risk estimation of low dose radiation, while nearly all the existing theoretical models relies on the total dose dependence only. By analyzing the experimental data of the relation between the radiation dose and the induced mutation frequency of 5 organisms, mouse, drosophila, chrysanthemum, maize and tradescantia, we found that all the data can be reproduced by WAM model. Most remarkably, a scaling function, which is derived from WAM model, consistently accounts for the observed mutation frequencies of 5 organisms. This is the first rationale to account for the dose rate dependence as well as to give a unified understanding of a general feature of organisms.
Journal of the Physical Society of Japan | 2014
Yuichiro Manabe; Issei Nakamura; Masako Bando
We develop a kinetic reaction model for cells having irradiated DNA molecules due to ionizing radiation exposure. Our theory simultaneously accounts for the time-dependent reactions of the DNA damage, the DNA mutation, the DNA repair, and the proliferation and apoptosis of cells in a tissue with a minimal set of model parameters. In contrast to existing theories for radiation exposition, we do not assume the relationships between the total dose and the induced mutation frequency. Our theory provides a universal scaling function that reasonably explains the mega-mouse experiments in Ref.[W. L. Russell and E. M. Kelly, Proc. Natl. Acad. Sci. USA. {\bf 79} (1982) 542.] with different dose rates. Furthermore, we have estimated the effective dose rate, which is biologically equivalent to the ionizing effects other than those caused by artificial irradiation. This value is
Journal of Physical Chemistry B | 2011
Issei Nakamura; An-Chang Shi
1.11 \times 10^{-3} ~\rm{[Gy/hr]}
Journal of Chemical Physics | 2010
Issei Nakamura; An-Chang Shi
, which is significantly larger than the effect caused by natural background radiation.
Journal of Physical Chemistry B | 2017
Lijun Liu; Issei Nakamura
Polymer-polymer complexation in solvent is studied using an extension of the self-consistent field theory. The model polymers are capable of forming ladder-like duplex structures. The duplex formation occurs with an abrupt change of entropy, resulting in a first-order transition. Moreover, the complexation can be stabilized by solvent-polymer interactions, instead of the usual specific binding interactions. Various types of unconventional phase diagrams are predicted. For example, phase separation with decreasing χ-parameter between duplex polymer and solvent can be induced, leading to a lower critical solution temperature (LCST) behavior. Multiphase coexistence points at which two, three, or four phases coexist are also obtained. Under certain conditions a homogeneous phase becomes unstable when the polymer chain length is decreased, in contrast to the standard Flory-Huggins theory.