Effect of Photoexcited Electron Dynamics on Photocatalytic Efficiency of Bismuth Tungstate

Photoexcited carrier dynamics of bismuth tungstate (Bi2WO6) photocatalysts was investigated by time-resolved infrared (IR) absorption spectroscopy. Monotonic absorption at the mid-IR region, which is attributable to absorption by photoexcited electrons, was monitored as a function of time delay from the microsecond to millisecond range after photoexcitation. Bi2WO6 particles with different crystalline content were prepared by hydrothermal reaction at several temperatures and used to elucidate the relation between density of photoexcited carriers and steadystate photocatalytic efficiency. Photocatalytic efficiency was tested using two reactions: oxidative decomposition of acetic acid in an aqueous solution (reaction 1) and oxidative decomposition of acetaldehyde in air (reaction 2). Crystallization of Bi2WO6 particles suppressed the fast recombination of photoexcited electrons and holes within 1 μs. In the case of crystallized particles, the density of the photoexcited electron increased with an increase in the crystalline content, and the photocatalytic efficiency for reaction 1 strongly depended on the crystalline content, indicating that photoexcited electrons remaining in the submillisecond time range significantly affect the reaction rate. On the other hand, photocatalytic efficiency for reaction 2 showed a proportional relation with specific surface area rather than crystalline content. The difference in a decisive factor depending on reaction condition is considered to be the slower rate of reaction of photoexcited electrons with molecular oxygen, which might occur within a time range between 200 μs and 3 ms over Bi2WO6

Ionospheric disturbance features in ionograms associated with low-latitude aurorae

Ionospheric disturbance features in ionograms during low-latitude aurorae was studied for two auroral events on 21 October and 17 November, 1989. Large scale periodic traveling ionospheric disturbances were observed by Japanese ionosonde chain with three remarkable wave fronts during the aurora on 21 October 1989. The growing phase of the waves was found from the variations in h\u27F values. This TIDs was estimated to originate from approximately 55-60 degrees in geographic latitude to the northwards of Japan. An increase of foF2 values due to an equatorial anomaly appeared from Okinawa to Akita for the magnetic storms on 21 October 1989. Concerning the spread-F phenomena it was peculiar that the ionospheric scintillations were rather weaker at northern station than southern station for both cases of ionospheric disturbance associated with auroral substorms on 21 October and 17 November, 1989

Uchiage Obba togo santei moderu no Obba-ryo suitei seido kojo ni kansuru kenkyu

This study attempts to enhance the applicability of Integrated Formula of Wave Ovetopping and Runup Modeling (IFORM) for the estimation of wave overtopping discharge on seawalls constructed in shallow water depth. The empirical model describing the relation between overtopping discharge and maximum runup height (Tamada et al., 2010) has been extended based on the detailed re-examination of experimental results by Tamada et al. (2009). The new empirical model is implemented in IFORM in order to improve the prediction accuracy of overtopping discharge for the cases of high crown height. The extended model was validated against additional experimental results conducted by Altomare et al. (2016). The results demonstrate that the performance of the extended IFORM is satisfactory for wide range of conditions.Peer ReviewedPostprint (published version

Solar illumination dependence of the auroral electrojet intensity: Interplay between the solar zenith angle and dipole tilt

The present study investigates the dependence of the local auroral electrojet (AEJ) intensity on solar illumination by statistically examining northward geomagnetic disturbances in the auroral zone in terms of the solar zenith angle χ. It is found that on the dayside, both westward and eastward electrojets (WEJ and EEJ) are more intense for smaller χ, suggesting that the solar extreme ultraviolet‐induced conductance is the dominant factor for the AEJ intensity. On the nightside, in contrast, the χ dependence of the AEJ intensity, if sorted solely by the magnetic local time, apparently depends on the station longitude and hemisphere. However, if additionally sorted by the dipole tilt angle ψ, a consistent pattern emerges. That is, although χ and ψ are correlated, the solar zenith angle and dipole tilt angle have physically different effects on the AEJ intensity. The nightside AEJ, especially the WEJ, tends to be more intense for smaller |ψ|. Moreover, whereas the WEJ is statistically more intense when the ionosphere is dark, the EEJ is more intense when it is sunlit. The preference of the WEJ for the dark ionosphere prevails widely in magnetic local time from premidnight to dawn, and therefore, it cannot be attributed to the previously proposed processes of the preferred monoenergetic or broadband auroral precipitation in the dark ionosphere. Instead, it may be explained, at least morphologically, in terms of the conductance enhancement due to the diffuse auroral precipitation, which is also prevalent from premidnight to dawn and is more intense in the dark hemisphere