Development of Millimeter Wave Fabry-Pérot Resonator for Simultaneous Electron-Spin and Nuclear Magnetic Resonance Measurement

We report a Fabry-Pérot resonator with spherical and flat mirrors to allow simultaneous electron-spin resonance (ESR) and nuclear magnetic resonance (NMR) measurements that could be used for double magnetic resonance (DoMR). In order to perform simultaneous ESR and NMR measurements, the flat mirror must reflect millimeter wavelength electromagnetic waves and the resonator must have a high Q value (Q?>?3000) for ESR frequencies, while the mirror must simultaneously let NMR frequencies pass through. This requirement can be achieved by exploiting the difference of skin depth for the two frequencies, since skin depth is inversely proportional to the square root of the frequency. In consideration of the skin depth, the optimum conditions for conducting ESR and NMR using a gold thin film are explored by examining the relation between the Q value and the film thickness. A flat mirror with a gold thin film was fabricated by sputtering gold on an epoxy plate. We also installed a Helmholtz radio frequency coil for NMR and tested the system both at room and low temperatures with an optimally thick gold film. As a result, signals were obtained at 0.18 K for ESR and at 1.3 K for NMR. A flat-mirrored resonator with a thin gold film surface is an effective way to locate NMR coils closer to the sample being examined with DoMR.     

Effects of the aluminum concentration on twin boundary motion in pre-strained magnesium alloys

We investigated the effects of Al concentration on the reciprocated motion of twin boundaries in pre-strained Mg-Al-Zn alloys through a combination of applied compression and tension,in-situ electron-backscattering diffraction observations,and high-angle annular dark-field scanning transmission electron microscopy observations.The twin growth was restricted by increased Al concentration,which resulted in the occurrence of smaller-sized twins.The reverse motion of twin boundaries was also restricted,resulting in the formation of higher fractions of secondary twins and 2-5° boundaries during reverse tension.The secondary twins and 2-5° boundaries mainly contributed to the increased ultimate tensile strength of the pre-strained Mg alloys.This effect is more significant in Mg alloys with larger pre-compression.Moreover,the increased amount of the Al solute atoms,rather than the precipitates,mainly contributed to the increased strengthening effect on the twin boundary motion.Our research contributes to development of high-strength Mg alloys by stabilizing twin boundaries.     

In situ high-resolution transmission electron microscopy of photocatalytic reactions by excited electrons in ionic liquid

A transmission electron microscope (TEM) sample for observing photocatalysis in a liquid was prepared by using N,N,N-trimetyl-N-propylammonium-bis(trifluoromethanesulfonyl)imide. The ionic liquid (IL) was used as a reaction solvent. Tetrachloroauric acid was dissolved in the IL as gold ion species. Rutile particles were added in the solution as a photocatalyst. The low vapor pressure of the IL enables a diffusing system in high vacuum of TEM. Rutile particles were UV irradiated in that liquid phase. After 3 h UV irradiation, a gold particle of 8 nm diameter was grown on the TiO2 surface. Photonucleation of Au/TiO2 system was discussed from the high-resolution TEM images.     

Platform design for large-scale artificial market simulation and preliminary evaluation on the K computer

Artificial market simulations have the potential to be a strong tool for studying rapid and large market fluctuations and designing financial regulations. High-frequency traders, that exchange multiple assets simultaneously within a millisecond, are said to be a cause of rapid and large market fluctuations. For such a large-scale problem, this paper proposes a software or computing platform for large-scale and high-frequency artificial market simulations (Plham: /pl\(\Lambda\)m). The computing platform, Plham, enables modeling financial markets composed of various brands of assets and a large number of agents trading on a short timescale. The design feature of Plham is the separation of artificial market models (simulation models) from their execution (execution models). This allows users to define their simulation models without parallel computing expertise and to choose one of the execution models they need. This computing platform provides a prototype execution model for parallel simulations, which exploits the variety in trading frequency among traders, that is, the fact that some traders do not require up-to-date information of markets changing in millisecond order. We evaluated a prototype implementation on the K computer using up to 256 computing nodes.     

Microstructural dependency of thermal expansion and sintering shrinkage in plasma-sprayed zirconia coatings

The effect of microstructure upon thermal expansion and sintering shrinkage in plasma-sprayed zirconia coatings was investigated by an accurate dilatometry. Cut-out samples with different microstructures were prepared from 5.8-mm-thick atmospheric plasma-sprayed (APS) and water-stabilized plasma coatings (WSP). It was quantitatively determined that the samples cut out of different thickness positions had minor differences in microstructure, and these APS samples largely differed from the WSP samples. The thermal expansion behaviors of all the samples coincided after a short annealing time despite their initial structural differences. On the other hand, all the samples showed a significant difference in sintering shrinkages with annealing at 1400 °C. This result was consistent with the theoretical result calculated with Cipitria's sintering model in terms of the relationship between shrinkage and microstructure. It was therefore demonstrated that the initial microstructure, particularly the splat thickness and the inter-splat pore height, exerts a great influence on the sinterability of plasma-sprayed coatings.     

Theoretical study on controllability of quantum state energy in an InGaAs/GaAs quantum dot buried in InGaAs

We theoretically studied the relationship between quantum energy states and structural parameters of an InGaAs/GaAs quantum dot (QD) buried in strained InGaAs, emitting at 1.1 to 1.4 em. The crystal distortion of the buried QD structure in three dimensions was computed based on the three-dimensional finite element method. Under the computed strain fields, the Schr?dinger equation was solved to obtain wavefunctions and eigenenergies. By calculating the dependence on structural parameters, we investigated the controllable range of the ground state energy and the energy separation between the ground state and the first excited state. We found that the energy separation exhibited a maximum value as a function of QD composition, enabling us to identify the composition of the QD structure. The effects of the burying layer composition and QD diameter were also investigated to expand the controllable range of the state energy. We also showed that the wavefunction symmetry was improved by burying the QD in the InGaAs layer. Our results will be useful in developing advanced devices for optical telecommunications and quantum information technology.     

Stacking faults in an epitaxially grown PbTiO3 thick film and their size distribution

The microstructure of an epitaxial PbTiO₃ thick film, grown on a SrRuO₃/SrTiO₃ substrate at 600 °C by pulsed-MOCVD method, was investigated by using transmission electron microscopy. A number of extrinsic or intrinsic stacking faults were observed in the epitaxial PbTiO₃ thick film and they were parallel to the (0 0 1) plane of the PbTiO₃. We also investigated the size distribution of these stacking faults. The width of these stacking faults along the [1 0 0] axis of the PbTiO₃ was very small, ranging from 2 to 13 nm. It was also revealed that the size distribution of stacking faults depends on the position in the film: near the surface, near the substrate, near threading dislocations, and near 90° domain boundaries.     

Possibility of Mg- and Ca-based intermetallic compounds as new biodegradable implant materials

Mg- or Ca-based intermetallic compounds of Mg₂Ca, Mg₂Si, Ca₂Si and CaMgSi are investigated as possible new candidates for biodegradable implant materials, attempting to improve the degradation behavior compared to Mg and Ca alloys. The reactivity of Ca can be indeed reduced by the formation of compounds with Mg and Si, but its reactivity is still high for applications as an implant material. In contrast, Mg₂Si shows a higher corrosion resistance than conventional Mg alloys while retaining biodegradability. In cytotoxicity tests under the severe condition conducted in this study, both pure Mg and Mg₂Si showed relatively high cytotoxicity on preosteoblast MC3T3-E1. However, the cell viability cultured in the Mg₂Si extract medium was confirmed to be better than that in a pure Mg extract medium in all the conditions investigated with the exception of the 10% extract medium, because of the lower corrosion rate of Mg₂Si. The cytotoxicity derived from the Si ion was not significantly detected in the Mg₂Si extract medium in the concentration level of ~ 70 mg/l measured in the present study. For aiming the practical application of Mg₂Si as an implant material, however, its brittle nature must be improved.