Plasma–liquid interaction is a critical area of plasma science, mainly because much remains unknown about the physicochemical processes occurring at the plasma–liquid interface. Besides a lot of experimental studies toward the interaction, a few fluid models have also been reported in recent years. However, the interfacial boundary conditions in the models are different and the Henry’s law constants therein are uncertain; hence, the accuracy and robustness of the simulation results are doubtable. In view of this, three 1D fluid models are developed for the interaction between a plasma jet and deionized water, each of which has a unique interfacial boundary condition as reported in the literature. It is found that the density distribution of reactive species is nearly independent of the interfacial boundary conditions in both the gas and liquid phases, except for that in the interfacial gas layer with a thickness of several tens of micrometers above water. The densities of the reactive species with high Henry’s law constants (H > 104) are much different in such gas layers among the interfacial boundary conditions. Moreover, some Henry’s law constants are changed in the models according to their uncertainty reported in the literature, and only the reactive species with low Henry’s law constants (H < 1) have their aqueous densities following the change. These densities are very low in the plasma-activated water. It could be concluded that the simulation of plasma–liquid interaction is generally independent of the interfacial boundary conditions and the uncertainty in Henry’s law constants.

Outside Front Cover: A 3D multicellular tumor spheroid model was used to assess the toxicity of low‐temperature plasma jet treatment in vivo. The results showed that RONS can penetrate through the entire depth of the 3D tumor spheroids, but local apoptosis was observed only on the outermost layer. Further simulation results show that plasma‐induced apoptosis within a tumor depends on the ‘deep’ delivery of the long‐lived RONS rather than the short‐lived RONS. Further details can be found in the article by Hao Zhang, Jishen Zhang, et al. (https://doi.org/10.1002/ppap.201900072).

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The thermodynamic behavior of single molecule-photon cryocooler(SMPC)was described by the study of participating frequency of phonons in light transitions, heat-light converting efficiency and cooling efficiency. The times of heat distribution were taken as a time scale in the investigation of cooling efficiency. The cooling efficiency curve obtained from our theory has the same shape of experiment curves obtained by other researchers. The reason of a bending of cooling efficiency curve appearing in the cooling region was given. The greatest cooling efficiency of SMPC was investigated, and it is obtained that the best wavelength, which results in the greatest cooling efficiency,is located at the point of one fourth exciting band width from the red edge. As a main conclusion, crystal-line materials are the sole kind of promising materials for obtaining the greatest cooling efficiency.