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Atmospheric-pressure plasma, generated using a dc power supply, in contact with water was investigated as a green, catalyst-free method for the ammonia synthesis. Stable nitrogen plasmas were generated inside bubbles which were obtained by inserting a dielectric tube with the gas flow into water. A higher production rate was obtained at a higher discharge current, a higher flow rate of nitrogen, and a lower conductivity of water. In addition, the production rate when the water worked as the cathode of the discharge was higher than that with the inverted polarity of the dc power supply. The maximum production rate of similar to 0.98 mu mol min-1 was realized at the optimized discharge condition, which is higher than the literature value obtained using a dc discharge in contact with water (Hawtof et al 2019 Sci. Adv. 5 eaat5778). We also discussed the possible reaction fields for the ammonia synthesis in the experimental condition.

We detected hydrated electrons in a micrometer-size water jet immersed in a low-pressure plasma by laser-induced desolvation. When we irradiated the 2nd, 3rd, and 4th harmonics of Nd:YAG laser pulses to the water jet, we detected the pulsed current which indicated the transport of electrons from the water jet to the plasma. We observed a proportional relationship between the amplitude of the pulsed current and the laser energy, which is consistent with the conversion from hydrated to free electrons by laser-induced desolvation. The amplitude of the pulsed current increased with the negative bias voltage between the plasma and the water jet. The most remarkable result was found in the relationship between the photon energy and the quantum yield of the electron transport. The experimental quantum yield was orders of magnitude higher than that predicted by a Monte Carlo simulation in a low photon energy region, suggesting the possibility that hydrated electrons we detected in the present experiment have much lower hydration energies than well-known hydrated electrons.

In this study, we observed droplet ejection from liquid gallium interacting with an inductively coupled hydrogen plasma. We observed the formation of a bubble in the liquid gallium, and the droplet ejection was synchronized with the burst of the bubble. We examined droplet ejection frequency by varying the ion flux [(0.2 -7.1) x 10(14) cm(-2) s(-1)] , the ion energy (15-215 eV), and the liquid gallium temperature (370 K-500 K). As a result, we found that the droplet ejection frequency increased with the ion flux and the liquid gallium temperature, whereas it decreased with the ion energy. We observed that the inside of the bubble in the liquid gallium was occupied by hydrogen. Furthermore, the amount of hydrogen dissolved in the liquid gallium was dependent on the discharge conditions. On the basis of the experimental results, we have proposed a mechanism for bubble formation and droplet ejection. The key in the mechanism is the supersaturated dissolution of hydrogen due to the ion irradiation.

Transporting patients down stairs by carrying is associated with a particularly high fall risk for patients and the occurrence of back pain among emergency medical technicians. The present study aimed to verify the effectiveness of the Airstretcher device, which was developed to reduce rescuers’ physical burden when transporting patients by dragging along the floor and down stairs. Forty-one paramedical students used three devices to transport a 65-kg manikin down stairs from the 3rd to the 1st floor. To verify the physical burden while carrying the stretchers, ratings of perceived exertion were measured using the Borg CR10 scale immediately after the task. Mean Borg CR10 scores (standard deviation) were 3.6 (1.7), 4.1 (1.8), 5.6 (2.4), and 4.2 (1.8) for the Airstretcher with dragging, Airstretcher with lifting, backboard with lifting, and tarpaulin with lifting conditions, respectively (p < 0.01). Multiple comparisons revealed that the Airstretcher with dragging condition was associated with significantly lower Borg CR10 scores compared with the backboard with lifting condition (p < 0.01). When the analysis was divided by handling position, estimated Borg CR10 values (standard error) for head position were 4.4 (1.3), 2.9 (0.9), 3.2 (0.8), and 4.0 (1.1) for the Airstretcher with dragging, Airstretcher with lifting, backboard with lifting, and tarpaulin with lifting conditions, respectively, after adjusting for participant and duration time (F = 1.4, p < 0.25). The estimated Borg CR10 value (standard error) for toe position in the Airstretcher with dragging condition was 2.0 (0.8), and the scores for the side position were 4.9 (0.4), 6.1 (0.3), and 4.7 (0.4) for the Airstretcher with lifting, backboard with lifting, and tarpaulin with lifting conditions, respectively, after adjusting for participant and duration time (F = 3.6, p = 0.02). Transferring a patient down stairs inside a house by dragging using the Airstretcher may reduce the physical burden for rescuers.

This paper demonstrates the estimation of vibrational temperatures of N-2 and CO2 in low-pressure plasmas by threshold ionization mass spectrometry. The principle for the estimation is the decrease in the ionization potential by the vibrational excitation. We observed that the threshold ionization curves of N-2 and CO2, which were measured using a quadrupole mass spectrometer with an energy-variable electron beam, shifted toward the low-energy side, when they were sampled from the plasmas. We constructed a model which assumed a Boltzmann distribution for the population densities of vibrational excited states and the same cross sections of electron impact ionization for vibrational excited states except the shifts of the threshold energies. The vibrational temperatures were estimated by fitting the experimental threshold ionization curves with the model.

We have shown that measuring the surface tension is a useful scheme to examine the plasma–liquid interface in real-time. The surface tension was measured using a method based on the dispersion relation of an acoustic capillary wave excited on the water surface. The surface tension gradually increased with time, when the water surface was irradiated with the outside region of the spatial afterglow of an atmospheric-pressure plasma. The Marangoni effect associated with the localized increase in the surface tension was observed during the plasma irradiation. The surface tension decreased after the termination of the discharge. A correlation was found between the transient decrease in the surface tension and the variation of the OH radical density in the gas phase. No increase in the surface tension was observed in the solution containing a trapping agent for liquid-phase OH radicals. These experimental results suggest that OH radicals act to increase the surface tension. However, the behavior of the surface tension cannot be explained perfectly by considering only the action of OH radicals.

We have developed a new method to detect solvated (hydrated) electrons at the plasma-water interface. The method is based on laser-induced desolvation followed by the release of free electrons into the plasma. We employed an atmospheric-pressure dc glow discharge, in which the water surface worked as the cathode, in the experiment. When the region just below the water cathode was irradiated with a pulsed laser beam, we observed the pulsed increase in the discharge current. The increase in the discharge current was caused by the release of free electrons, which were produced from hydrated electrons by the laser-induced desolvation. The pulsed increase in the discharge current was sensitive to the laser wavelength. We compared the relationship between the pulsed increase and the laser wavelength with the distribution of the solvation energy of hydrated electrons using Monte Carlo simulation on the transport of free electrons in water. As a result, it was concluded that hydrated electrons produced under the experimental conditions were located at a distance of 7-15 nm from the plasma-water interface.

We investigated oxidation-reduction reactions on the surface of water jet immersed in a low-pressure inductively coupled helium plasma. The electrical potential of the water jet was floating, and no electrical current was supplied from the plasma to the water jet. We observed the productions of molecular hydrogen and molecular oxygen. We also observed negligible consumption of water vapor in the gas phase, suggesting that the productions of hydrogen and oxygen were not owing to the conversion from water vapor. When we employed silver nitrate solution instead of pure water, we observed the decrease in the production rate of hydrogen, whereas the production rate of oxygen was the same in pure water and silver nitrate solution. In addition, we found the synthesis of silver particulates in the silver nitrate solution, indicating the competition between the reductions of H+ and Ag+. Thus, the experimental results reveal the simultaneous oxidation and reduction at the same plasma-liquid interface.

We have shown that measuring the surface tension is a useful scheme to examine the plasma–liquid interface in real-time. The surface tension was measured using a method based on the dispersion relation of an acoustic capillary wave excited on the water surface. The surface tension gradually increased with time, when the water surface was irradiated with the outside region of the spatial afterglow of an atmospheric-pressure plasma. The Marangoni effect associated with the localized increase in the surface tension was observed during the plasma irradiation. The surface tension decreased after the termination of the discharge. A correlation was found between the transient decrease in the surface tension and the variation of the OH radical density in the gas phase. No increase in the surface tension was observed in the solution containing a trapping agent for liquid-phase OH radicals. These experimental results suggest that OH radicals act to increase the surface tension. However, the behavior of the surface tension cannot be explained perfectly by considering only the action of OH radicals.

We investigated the vibrational temperature of molecular nitrogen in the downstream of helicon-wave excited helium and argon-based plasmas. It was confirmed by optical emission spectroscopy that the major part of the helium plasma was at a recombining state and it had an ultralow electron temperature of approximately 0.1 eV. In spite of the ultralow electron temperature, the vibrational temperature of molecular nitrogen, which was added into the helium plasma, was higher than that in the argon-based plasma at an ionizing state with an electron temperature of 1.7 eV. According to the relationship between the rate coefficient of electron impact vibrational excitation and the electron temperature, the higher vibrational temperature in the helium plasma is not attributable to the more efficient vibrational excitation. Therefore, the higher vibrational temperature is owing to the less efficient destruction of vibrational excited states in the helium plasma with the ultralow electron temperature.