Electrical conductivity of silica nanoparticles deposited on electrodes from colloidal suspension were measured under controlled relative humidity (RH). The electrical conductivity values at 1 kHz increased with increasing RH. Amounts of water adsorbed on silica nanoparticles were measured by quartz crystal microbalance (QCM) and they also increased with increasing RH. An empirical power law relation was observed between the reported surface conductivity and RH data for a silica glass. By applying this relation to the silica nanoparticles, the water film thicknesses are estimated to be from 0.08 nm to 0.23 nm. The corresponding specific surface area (SSA) becomes smaller (102 m 2 g −1) than the reported value (215 m 2 g −1), indicating aggregation of the nanoparticles. In fact, aggregated rod-like structures were observed under electron and laser scanning microscopy. The electrical conduction of deposited silica nanoparticles under various RH can be understood by surface conduction in thin water films adsorbed on the nanoparticles.

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We report on terahertz (THz)-radiation generation from a photoconductive antenna fabricated on a zinc oxide (ZnO) thin film. This ZnO thin film was epitaxially grown on a sapphire single crystal by rf-planar magnetron sputtering. The THz-radiation power from the ZnO thin film did not saturate below 14-kV/cm-biased electric field.

River embankments are earthen structures constructed to protect areas from flooding. If a river embankment collapses, it can cause major damage to human lives; therefore, proper inspection and evaluation are essential to determine the problem areas in river embankments, and repair them if necessary, before any damage occurs. Electrical surveys are a reliable method that has been used widely. Recently, electrical surveys have been used to inspect long structures such as river embankments, highlighting the need for developing non-destructive and less fieldwork electrical survey methods. In this study, we examined a direct current electrical exploration system using polyvinyl alcohol sponge roller electrodes, which are non-destructive and can be moved smoothly without damaging the ground surface. We conducted initial experiments on a test ground in which this new system was towed by an unmanned ground vehicle to perform an electrical survey and compared the results with those obtained using conventional methods that utilize stainless steel electrodes driven into the ground. The results indicate that the direct current electrical survey using the polyvinyl alcohol electrodes yielded almost the same results as those obtained using the stainless steel electrodes. In addition, both methods were tested on a river embankment to investigate the effectiveness of the towed direct current electrical survey. We confirmed that the towed survey method was effective by comparing the resistivity cross-sections and fieldwork required for both survey types.

Landscapes disturbed by shallow landslides present several residual risks. For example, residual soils on sliding surfaces may lead to the re-occurrence of shallow landslides, and landslide deposits on valley floors may introduce multiple hazards associated with river blocking or landslide damming. Despite such risks, few studies have investigated the residual risks following shallow landslides, and thus, no methodology has been established for assessing such risks. In this study, we combined portable cone penetration test (PCPT) and electrical resistivity tomography (ERT) to investigate the post-event risks associated with a landslide scar resulting from the 2018 Hokkaido Eastern Iburi earthquake (HEIE) in Japan. The multi-point PCPT identified the interface between a weak volcanic soil layer and underlying weathered sedimentary rocks. This interface exhibited an abrupt spatial change in resistivity, ranging from 20 to 100 Ωm. The thickness of the residual soil layer was 0.3–3.2 m and that of the landslide deposit exceeded 2.0 m. An infinite-slope stability analysis was performed to predict the re-occurrence of shallow landslides due to a lower intensity earthquake than that of HEIE in this region. Considering the area affected by the HEIE and the physical properties of soil layers, our findings imply a widespread risk of re-occurrence of shallow landslides over an area of 20 km × 20 km. Although the areal coverage of the combined ERT/PCPT method needs to be extended, it is effective for assessing the residual risks associated with shallow landslides.