Yasuo Hasegawa

Monte Carlo simulation of light transmission through living tissues

To analyze the fundamental characteristics of light transmitted through living tissues, we used the Monte Carlo method to trace the paths of the rays incident upon slabs of particles. The slabs contained either (i) two types of scattering particles in a solution or (ii) one type of particle with pigment added to the solution. Temporal analyses of the transmittance have illustrated that the differences in the optical density among the slabs having different absorption coefficients with the same scattering coefficient vary linearly with time. Also, their gradients have been shown to be proportional to the differences in the absorption coefficients, thus verifying the microscopic Beer-Lambert law in highly scattering media when temporally resolved measurement is used.

Simulation of fan-beam-type optical computed-tomography imaging of strongly scattering and weakly absorbing media.

Numerical simulations of the transmission of a light impulse through strongly scattering and weakly absorbing slab media and of fan-beam-type optical computed-tomography imaging for cylindrical media are presented. A hybrid calculation scheme of scattering by the Monte Carlo method is employed to obtain the temporal variation of transmittance of the light impulse through the media. A set of projection data is provided by temporally extrapolating the difference in the optical density between the absorbing object and the nonabsorbing reference to the shortest time of flight. For the case of identical scattering between the object and reference, the reconstructed image of the difference in the absorption coefficient has better accuracy and spatial resolution than those images by the time-gating method.

Simulation of time-resolved optical computer tomography imaging

A new method of data processing is presented for a time-resolved optical computer tomography (CT) imaging of a strongly scattering and weakly absorbing medium, similar to a living body. A fundamental experiment and a numerical calculation of time-resolved spectroscopy are conducted to validate the proposed temporally extrapolated absorbance concept. A numerical simulation shows a possibility of a new method of time-resolved optical CT imaging. A reference cylinder is filled with a uniformly scattering medium, and an object cylinder has a weakly absorbing portion in addition to the uniform scattering in the reference cylinder. The extrapolated values of the difference in the absorbance to the shortest time of flight reduce to the line integrals of the difference in the absorption coefficient along the incident beam lines. By this process, the information of the weak absorption is extracted from the signals subject to the strong scattering, and the extrapolated values provide a set of projection data for a conventional filtered back projection of the CT reconstruction algorithm. The reconstructed image reproduces the difference in the absorption coefficient between the object and the reference with a reasonable accuracy and spatial resolution. This type of image describing the absorption change is useful to noninvasive diagnostics of the oxygen metabolism inside bodies.

An Automated Impedance Estimation Method in Low-Voltage Distribution Network for Coordinated Voltage Regulation

Internode line impedance values are essential information for achieving coordinated voltage regulation with distributed energy devices. However, in a low-voltage distribution system, these values are difficult to acquire, especially when the devices are installed in an ad hoc manner by individual users. This paper proposes a novel method for automated impedance estimation based on practically available parameters at the terminal nodes. The distributed energy devices measure and transmit the terminal parameters to a host device. Then, the host device estimates the line impedances based on its impedance model and the collected parameters. For practical implementation, the proposed method is built under several assumptions. For example, it is assumed that the phases of terminal voltages are not synchronized owing to communication latency. Instead, only the magnitude value is incorporated during the impedance estimation. The proposed method is verified via a simulation that assumes a realistic environment.

Electrode Behavior of Hydrogen Reduction in LiCl‐KCl Melt. Voltammetric Analysis

Hydrogen reduction in molten alkali halide is an important process for the development of thermally regenerative fuel cells using hydrogen and lithium. Hydrogen reduction in LiCl-KCI eutectic melt was studied by the potential-sweep method with Ni, Fe, Co, and Cu electrodes. A reaction model, which considers not only a surface redox process but also the behavior of absorbed hydrogen in the electrode, is proposed. Based on this model, I-E curves are numerically calculated and fitted with experimental voltammograms. A good agreement is obtained between calculated and experimental data in the reversible region, and the validity of this model is demonstrated for Ni, Fe, and Cu electrodes. The Henrys constant for hydrogen in the melt and the diffusion constant were determined from the calculations as follows: {kappa}{sub H} = 5.68 x 10{sup {minus}12} mol/cm{sup 3} Pa, D{sub H{sub 2}} = 3.18 x 10{sup {minus}5} cm{sup 2}/s at 723 K.

Simulation of time-resolved optical-CT imaging

Simulation of optical-CT imaging has been conducted using the Monte Carlo method to generate projection data for filtered back projection. A reference cylinder of 10 mm diameter is filled with an uniformly scattering medium, and an object cylinder filled with the same scattering medium as the reference has an inner coaxial cylindrical portion with weak absorption. The time-resolved transmittances detected on the line of the incidence for object and the reference provide time- resolved data of the difference in the absorbances between the object and the reference. The difference in the absorbances which is temporally extrapolated to the shortest time of flight present projection data for filtered back projection usually used in CT reconstruction. The resulting reconstructed image reflects the difference in the absorption coefficients between the object and the reference with a satisfactory spatial resolution and accuracy.

Electrode Behavior of Hydrogen Reduction in LiCl-KCl Melt II. AC Impedance Analysis

An ac impedance method was applied to analyze the electrode behavior of hydrogen reduction in a LiCl-KCl eutectic melt containing LiH. Impedance plots of the Co and Cu electrodes were explained by using the Randles-Ershler equivalent circuit. Whereas the impedance plots of Fe and Ni electrodes showed an extraordinary shape due to the effect of the diffusion in the finite-length region and were successfully analyzed using a modified Randles-Ershler equivalent circuit, which took into account the effect of the diffusion of hydrogen atoms in the electrode. This analysis has revealed that both the semi-infinite diffusion of molecular hydrogen in electrolyte and the finite-length diffusion of hydrogen atoms in the electrode are contributing to the reaction at the interface of the electrode.

Time-dependent FEM analysis of photon migration in random media

Time-resolved spectroscopy is expected to be developed for imaging of buried absorbers inside strongly scattering media. It is required to know the temporal behaviors of the reflectance and/or transmittance produced by the propagation of light impulse incident on scattering and absorbing media. The Monte Carlo method (MC) is the most frequently used numerical method, but its computation time is considerably long to obtain the results with a satisfactory accuracy. A faster numerical method is required for analysis of temporal profiles of reflectance and transmittance through random media with complicated configurations. One of the methods to solve the photon diffusion equation numerically is finite element method (FEM). This paper reports the FEM results of temporal profiles of transmittance of light impulse through scattering slabs and cylinders. Time courses of transmittances through homogeneously scattering and absorbing slabs are obtained by FEM and compared with those by MC. The results of cylinders with homogeneous scattering and inhomogeneous absorption coefficients are also presented. Temporal variations of the cross-sectional profiles of the fluence rate generated by impulse incident on a surface are shown by contour plotting, and the effect of the location and size of the localized absorbing volume on the transmittances are discussed.

Electrode Behavior of Hydride Ion in Molten Alkali Chlorides

Electrochemical behavior of hydride ion was studied in three kinds of eutectic melt of alkali chlorides; LiCl-KCl, LiCl-CsCl, and LiCl-KCl-CsCl. The equilibrium potential of H 2 /H - electrode was obtained in these three molten alkali chlorides. The effects of the concentration of H - and the pressure of H 2 on the potential were explained by the Nernst equation. Temperature dependence of the standard electrode potential was approximately expressed by a straight line for these melts over a temperature range from 600 to 773 K. The diffusion coefficients of hydride ion were obtained in these three melts by voltammetric analysis using copper electrode, because hydrogen solubility in copper is very low and the accurate oxidation peak of hydride ion was obtained.

Numerical simulation of cyclic voltammetry for reversible systems with complex stoichiometry

Reversible waves of voltammetry with complex non-unity stoichiometry are studied here based on theory. Numerical simulations were performed for various stoichiometric systems in which coefficients m and q were independently varied from 1 to 4 in a general reaction scheme, mO + ne− ai qR. The calculation results indicate that the peak current function at complex stoichiometry differs from that at simple unity stoichiometry. The relation between the half-wave potential and the formal potential has been partially corrected from that previously reported in the literature. Parameters in the relation between the peak potential and the half-wave potential are unique for each stoichiometric system. The parameter in the relation between the peak potential and the half-peak potential is also presented here.