Hideharu Takahashi

Intra- and inter-atomic optical transitions of Fe, Co, and Ni ferrocyanides studied using first-principles many-electron calculations

We have investigated the electronic structures and optical properties of Fe, Co, and Ni ferrocyanide nanoparticles using first-principles relativistic many-electron calculations. The overall features of the theoretical absorption spectra for Fe, Ni, and Co ferrocyanides calculated using a first-principles many-electron method well reproduced the experimental one. The origins of the experimental absorption spectra were clarified by performing a configuration analysis based on the many-electron wave functions. For Fe ferrocyanide, the experimental absorption peaks originated from not only the charge-transfer transitions from Fe2+ to Fe3+ but also the 3d-3d intra-transitions of Fe3+ ions. In addition, the spin crossover transition of Fe3+ predicted by the many-electron calculations was about 0.24 eV. For Co ferrocyanide, the experimental absorption peaks were mainly attributed to the 3d-3d intra-transitions of Fe2+ ions. In contrast to the Fe and Co ferrocyanides, Ni ferrocyanide showed that the absorption p...

Velocity Profile Measurements in Two-Phase Flow using Multi-wave Sensors

Two-phase flow has been recognized as one of the most important phenomena in fluid dynamics. In addition, gas-liquid two-phase flow appears in various industrial fields such as chemical industries and power generations. In order to clarify the flow structure, some flow parameters have been measured by using many effective measurement techniques. The velocity profile as one of the important flow parameter, has been measured by using ultrasonic velocity profile (UVP) technique. This technique can measure velocity distributions along a measuring line, which is a beam formed by pulse ultrasounds. Furthermore, a multi-wave sensor can measure the velocity profiles of both gas and liquid phase using UVP method. In this study, two types of multi-wave sensors are used. A sensor has cylindrical shape, and another one has square shape. The piezoelectric elements of each sensor have basic frequencies of 8 MHz for liquid phase and 2 MHz for gas phase, separately. The velocity profiles of air-water bubbly flow in a vertical rectangular channel were measured by using these multi-wave sensors, and the validation of the measuring accuracy was performed by the comparison between the velocity profiles measured by two multi-wave sensors.

Visualization of Dispersed Phase Flow in Centrifugal Extractor Using Taylor-Couette Vortex Flow

For studying the designs and running operations of an extractor which uses Taylor-Couette vortex flow, we focused on a metal extraction system as one of the extraction models of heat generating nuclides and observed the flow patterns of dispersed phase by dyeing the phase in the extractor, and we investigated the effects of hydrophobic coating applied to the inner cylinder surface on the flow characteristics. Moreover, for the quantitative measurement and analysis of the flow field, we evaluated the applicability of Ultrasonic Velocity Profiler (UVP) to flow field measurement. Thorough these visualization methods of dispersed phase in a centrifugal extractor using Taylor-Couette vortex flow, we examined the relation between flow field and extraction characteristics of the extractor.Copyright

Ultrasonic Measurement of Velocity Profile on Bubbly Flow Using Fast Fourier Transform (FFT) Technique

In two-phase bubbly flow, measurement of liquid and bubble velocity is a necessity to understand fluid characteristic. The conventional ultrasonic velocity profiler (UVP), which has been known as a nonintrusive measurement technique, can measure velocity profile of liquid and bubble simultaneously by applying a separation technique for both phases (liquid and bubble) and transparent test section is unnecessary. The aim of this study was to develop a new technique for separating liquid and bubble velocity data in UVP method to measure liquid and bubble velocity profiles separately. The technique employs only single resonant frequency transducer and a simple UVP system. An extra equipment is not required. Fast Fourier Transform (FFT) based frequency estimator paralleled with other signal processing techniques, which is called as proposed technique, was proposed to measure liquid and bubble velocity separately. The experimental facility of two-phase bubbly flow in the vertical pipe was constructed. Firstly, the Doppler frequency estimation by using the FFT technique was evaluated in single-phase liquid flow. Results showed that FFT technique showed a good agreement with autocorrelation and maximum likelihood estimator. Then, separation of liquid and bubble velocity was demonstrated experimentally in the two-phase bubbly flow. The proposed technique confirmed that liquid and bubble velocity could be measured efficiently.

Effects of NH4+, K+, Mg2+, and Ca2+ on the Cesium Adsorption/Desorption in Binding Sites of Vermiculitized Biotite

The reversibility of cesium adsorption in contaminated soil is largely dependent on its interaction with micaceous minerals, which may be greatly influenced by various cations. Herein, we systematically investigated the effects of NH4+, K+, Mg2+, and Ca2+ on the adsorption/desorption of Cs+ into different binding sites of vermiculitized biotite (VB). Original VB was initially saturated by NH4+, K+, or Mg2+; we then evaluated the adsorption of Cs+ on three treated VBs, and the desorption by extraction with NH4+, K+, Mg2+, or Ca2+ was further evaluated. Our structural analysis and Cs+ extractability determinations showed that NH4+ and K+ both collapsed the interlayers of VB, resulting in the dominant adsorption of Cs+ to external surface sites on which Cs+ was readily extracted by NH4+, K+, Mg2+, or Ca2+ irrespective of their species, whereas Mg2+ maintained the VB with expanded interlayers, leading to the overwhelming adsorption of Cs+ in collapsed interlayer sites on which the Cs+ desorption was difficult and varied significantly by the cations used in extraction. The order of Cs+ extraction ability from the collapsed interlayers was K+ ≫ Mg2+ ≈ Ca2+ ≫ NH4+. These results could provide important insights into Cs migration in soil and its decontamination for soil remediation.

Cultivation of the photosynthesis microorganism in a Taylor-Couette Vortex Flow with a small aspect ratio

This study focuses on the dynamics of the Taylor-Couette Vortex Flow (TVF) in a photo-bioreactor in which CO2 is changed to O2 with high efficiency by the photosynthesis ability of micro algae. Stirring by means of a screw propeller is generally used for a simple agitation. However, the problem is that there exists a very high shearing flow region just near the propeller, which causes the destruction of the alga cell by the shearing force. In contrast, the TVF mixing is expected to reduce such a local and random shearing force because of their column of steady and orderly vortices. In this study, the relationship between the microorganism growth rate and the flow structures in dilute suspensions of a TVF is investigated and the flow characteristics are measured by using an ultrasonic velocity profiler with a small aspect ratio of 3.

The Effect of Magnetic Field on Magnetotactic Bacteria Behaviors

The motion of magnetotactic bacteria was observed using an optical darkfield microscopy. The images were taken using video cameras, and measured by image processing techniques. In our experiment, it was found that the bacteria motion was found to follow to magnetic field frequency within some range. The observation results indicate the possibility of the bacteria behavior control by magnetic field.