We demonstrated that acoustic waves could induce nucleation of both a ${}^4\mathrm{He}$ crystal in superfluid and a superfluid droplet in the crystal in the same temperature range depending on whether an acoustic transducer was covered by the superfluid or the crystal. The temperature dependences of crystal nucleation at and above the melting pressure and that of superfluid droplet nucleation at the melting pressure were investigated systematically by changing the acoustic wave powers. The nucleation processes were monitored by a high-speed camera. Crystals were nucleated above the melting pressure in a metastable superfluid when the sum of the overpressure and the effective overpressure by the acoustic wave reached a threshold value. Crystal nucleation above the melting pressure was effectively induced by acoustic waves at low temperatures and was not induced at all above $800\mathrm{mK}$. Crystal nucleation at the melting pressure was induced when the acoustic wave power exceeded a threshold value. The threshold was temperature independent below $300\mathrm{mK}$ and increased divergently approaching $600\mathrm{mK}$. We saw no sign of nucleation above $600\mathrm{mK}$ even in our maximum acoustic wave power. Superfluid droplet nucleation at the melting pressure was also induced above a threshold power. The threshold was temperature independent at low temperatures with a small maximum at $600\mathrm{mK}$ and decreased with warming at high temperatures. All the behaviors cannot be explained by mere heating, and a possible effect of acoustic radiation pressure on the nucleation is discussed.

An extremely high-sensitivity image sensor has been developed with a combination of an active-matrix high-efficiency electron emission device (HEED) array and a high-gain avalanche rushing amorphous photoconductor (HARP) target. Following the description of the requirements for the use of the electron emitter as an image-sensing probe, the characteristics of a fabricated $640\times 480\text{pixel}$ active-matrix HEED image sensor with a HARP target are presented by image-pickup experiments under a dark condition. The emission current density of the experimental HEED under an active-matrix drive was $4\text{A}/{\text{cm}}^2$ corresponding to a practical level. A clear image observed in the prototype compact camera demonstrates that the surface-emitting HEED is useful for image sensing based on HARP with high sensitivity and sufficient definition.

The electrical conductivity (EC) of minerals found on Earth and throughout the solar system is a fundamental transport property that is used to understand various dynamical phenomena in planetary interiors. High-pressure and high-temperature (P–T) EC measurements are also an important tool for observing phase transitions. Impedance measurements can accurately measure the EC of a nonmetallic sample. In previous measurements under static conditions using a laser-heated diamond-anvil cell (LHDAC), only direct current resistance is measured, but this method overestimates the bulk sample resistance. Moreover, the previous methodology could only be applied to nontransparent samples in an LHDAC using infrared lasers, limiting the range of measurable composition. To the best of our knowledge, no in situ high-P–T EC measurements of transparent materials have been reported using LHDAC techniques. We developed a novel impedance measurement technique under high-P–T conditions in an LHDAC that applies to transparent samples. As a validation, we measured the EC of Mg_0.9Fe_0.1SiO₃ bridgmanite up to 51 GPa and 2000 K and found that the results are consistent with those of previous studies. We also measured the EC values of sodium chloride to compare with those of previous studies, as well as those of cubic boron nitride and zirconia cement to quantify how well they insulate under high P–T conditions. This is the first report of the impedance and EC measurements of transparent minerals in an LHDAC, which allows the measurement of Fe-poor/-free materials, including the major constituents of the interiors of gas giants and icy planets, under extreme conditions.

Semiconductor-based heaters for diamond anvil cells (DACs) have advantages over metal wire heaters in terms of repeated use and the ability to reach higher temperatures. We introduce a cylindrical SiC heater for an externally heated DAC (EHDAC) that works satisfactorily at temperatures up to 1500 K and pressures around 90 GPa. The heater is reusable and inexpensive, and only slight modifications to the DAC are required to fit the heater. Experiments on melting of NaCl and gold are conducted at ambient pressure to test the temperature accuracy of the EHDAC system, and resistance measurements on iodine at high pressures and temperatures are performed to assess the heater assembly. These test runs show that a uniform and accurate temperature can be maintained by the EHDAC assembly, which has potential applications to a variety of transport property measurements.