A stainless steel container, filled with 1 g of water and sealed with a copper plug, was repeatedly heated and cooled over an appropriate temperature range (temperature cycles). Negative pressures, although scattered, increased with temperature cycle repetition through two stages. The cavitation history effect persisted for continued temperature cycles after renewal of only the water. The authors found two efficient means of raising the negative pressure by the cavitation history effect: (i) a high repetition rate of the conditioning cycles and (ii) using a sealing metal melted and cast under vacuum. Aided by these means, negative pressure was raised to -87 bar at 49 degrees C after 392 cycles repeated over a period of one week, while the maximum value of -76 bar at 46 degrees C was attained after a total of 850 cycles continued for over a month. The results can be interpreted by the gas-trapping crevice model supplemented with a working assumption that crevices on the metal surface are supplied with gas from sources in the metal bulk. A more recent maximum value of -125 bar at 47 degrees C, the highest value ever reported for water in a metal tube, supports the assumption.

The authors made a stainless steel tube with a copper plug to study the effects of cavitation history on negative pressure for a system of water in a metal Berthelot tube. The water and the copper plug were pre-treated for air purging. The system was alternatively heated and cooled over appropriate temperature ranges many times. In the Berthelot method, the negative pressure generated with failing temperature becomes highest just before cavitation for a single heating and cooling procedure (one temperature cycle). Negative pressures for respective temperature cycles, though scattered, exhibited an increasing trend through two stages, a steep stage for earlier cycles and a gradual stage for later cycles. A similar effect of the cavitation history persisted even in a series of temperature cycles after exchanges of water, so long as the same plug was used for sealing. The negative pressure -76 atm (-7.7 MPa), which is higher than the values ever reported for water in a metal tube, developed at 46 degrees C through two water exchanges after a total of 850 temperature cycles. The two-stage increase was considered to be caused by the successive fading of the weaker cavitation nuclei in the system.

The authors made an automatic temperature cycle repeater (ATCR), which could repeat the successive heating and cooling procedure of a metal Berthelot tube over the appropriate temperature range (temperature cycle) required for the generation of negative pressure. By operating the ATCR, they observed trends in negative pressure for water contained in a stainless steel tube, which enabled them to study the effect of the degassing pretreatment of the sealing material. Using a plug made from Ni degassed at 500 degrees C for 30 h under a vacuum of 10-6 Torr, the negative pressure was raised to -125 bar at 47 degrees C after a total of 3800 temperature cycles, which is the highest level ever reported for water in a metal tube; it is notable because it was raised for about a gram of water in contact with rough metal surfaces. The result supports the working assumption that the generation of a high negative pressure in a metal tube is limited by the supply of gas from sources in the bulk to crevices on the surface. The generally accepted gas-trapping crevice model should be supplemented with this working assumption.

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According to research firms, employee engagement in Japan is extremely low compared with that in other countries. This is a major problem for Japanese companies, and they are implementing various measures to improve their employee engagement. However, this is a relatively new concept with no clear definition, and it is also unclear whether the concept of employee engagement fits the corporate culture of Japanese companies and the characteristics of Japanese people. Taking this point as a problem, and based on previous research on employee engagement and the current study, the authors concluded that a theoretical system suitable for Japan, different from the Western concept of social exchange theory, might be necessary to define employee engagement in Japan.