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Yasui Laboratory

Plasma sterilization technology of nutrient solution

 Plasma will become extremely effective for environmental technologies if it can be used as an alternative to agrochemicals.

 Plant factories have attracted attention because they can provide pesticide?free vegetables and cultivate them regardless of the weather. Hence, the construction of plant factories in renovated factories and buildings is increasing. In plant factories, the nutrient film technique (NFT), in which small amounts of nutrient solution are circulated, has been promoted owing to its effective utilization of resources and environmental safety. However, the spread of pathogenic bacteria in a circulating nutrient solution, which causes widespread plant destruction, is unavoidable.

 The main application of our research is the sterilization of bacteria in plant factories.

 We have been developing a new solution?based plasma generation technique that uses surface discharge and have examined the applicability of sterilization in plant factories. By generating the plasma in solution, the active species in the plasma can act directly on the pathogenic bacteria.

 We reported the ability of this plasma technology to sterilize the microconidia of Fusarium oxysporum, and also we clarified the effect of plasma irradiation on the physicochemical properties of the nutrient solution.

 We have been investigation the sterilization mechanism and developing the plasma sterilization system in the plant factory.

Fig.1 Plant factories and plasma

Decomposition of PFCs and recycling of Fluorine

 Fluorocarbons and perfluoro compounds (PFCs) contribute to global warming and are used in large quantities in the semiconductor industry, which must reduce the emission of these gases to the atmosphere in order to achieve the requirements of the Kyoto Protocol.

 In the semiconductor industry, voluntary reduction goals for PFCs were set at the World Semiconductor Council held in April 1999 and ongoing reduction efforts have been made. However, since hydrofluorocarbons (HFCs) and PFCs are used in critical processes, including chamber cleaning and etching during the manufacturing of semiconductors such as LCDs and solar panels, the consumption of these chemicals increases every year. Therefore, in spite of the reduction efforts, the emission of fluorocarbons and PFCs has increased in recent years.

 We had developed a new dry-type off-gas treatment system for recycling fluorine from perfluoro compounds present in off-gases from the semiconductor industry.

 We have been developing new type of plasma technologies for treatment of PFCs.
Fig.2 Experimental setup

Fig.3 Fluorite(Prity: over 97%)

Fig.4 Fluorite(Prity: 99.95%)

Lightning surge phenomenon and protection

 In recent years, because of global warming, the frequency of local lightning flashes with heavy rain has increased in Japan. In the modern information society in Japan, the risk posed by lightning surges has increased for home electronics and telecommunication equipment. Special facilities such as data centers, computer centers, and hospitals with operating rooms require an extremely static electromagnetic environment. These facilities are expected to maintain this environment even in conditions of lightning strikes or electrical noise.

 We are researching and developing the following subjects in relation to lightning protection.

● Overvoltage analysis of grounding lines inside building directly struck by lightning.
● Analysis of overvoltage caused by a lightning strike on a traction substation’s grounding system.
● Analysis model of the transient ground resistance of the plate-shaped ground electrode.
● Development of construction technology of an Insulated-cable-type Down conductor.
● Observation of lightning current in the soil by rocket-triggered lightning.
● Detector for measuring lightning current in the ground.
● Lightning risk management of electric and electronic systems.
Fig.5 Lightning surge