Nobuya Hayashi

Sterilization of Medical Equipment Using Radicals Produced by Oxygen/Water Vapor RF Plasma

The sterilization of medical equipment was performed using low-pressure RF discharge plasma. Oxygen radicals as oxidizing materials for sterilization were produced from oxygen or water vapor. The generation of atomic oxygen and OH radicals was confirmed using the light emission spectra of the plasma. The pressure in the discharge region was varied periodically during inactivation in order to produce radicals effectively and to penetrate the produced radicals into tiny gaps. Medium sheets for microbial detection indicated that the decimal reduction value of active bacillus was 5 and 8 min using oxygen plasma and water vapor plasma with ne=109 cm-3, respectively. Biological indicators clarified that the sterilization of bacilli spores was successful for a treatment time of 90 min.

Generation of Radicals using Discharge inside Bubbles in Water for Water Treatment

Abstract A new method for a water treatment utilizing radicals produced by a discharge inside bubbles in water is proposed. Radicals with short lifetime (atomic oxygen and OH radical) are used effectively for the water purification because those are generated by discharge inside bubbles in water. OH radical production was confirmed by a light emission of the discharge using the spectroscopic technique. Dissolved ozone concentration of about 0.3 mg/1 was obtained when oxygen was used as a bubbling gas. Decolorization process of indigo solution by a discharge inside bubbles in water was investigated.

Growth Enhancement of Radish Sprouts Induced by Low Pressure O2 Radio Frequency Discharge Plasma Irradiation

We studied growth enhancement of radish sprouts (Raphanus sativus L.) induced by low pressure O2 radio frequency (RF) discharge plasma irradiation. The average length of radish sprouts cultivated for 7 days after O2 plasma irradiation is 30–60% greater than that without irradiation. O2 plasma irradiation does not affect seed germination. The experimental results reveal that oxygen related radicals strongly enhance growth, whereas ions and photons do not.

Sterilization of Medical Equipment Using Oxygen Radicals Produced by Water Vapor RF Plasma

A safe and clean method of sterilizing medical equipment is proposed, which uses radicals produced by RF plasma. The plasma source gas for the sterilization is water vapor, which produces hydroxyl radicals upon the RF discharge. The inactivation of bacillus on medical equipment by water vapor plasma at a temperature below 55degC gives a decimal reduction value of 26 min.

Simple method of improving harvest by nonthermal air plasma irradiation of seeds of Arabidopsis thaliana (L.)

We have studied the effects of air nonthermal plasma irradiation of seeds of Arabidopsis thaliana (L.) on their growth from the beginning of cultivation to their harvest. Three minute plasma irradiation of dry seeds resulted in growth acceleration in all the growth stages. Compared with the control, the plasma irradiation led to an 11% shorter harvest period, a 56% increase in total seed weight, a 12% increase in each seed weight, and a 39% increase in seed number.

Ozone Generation Characteristics by Superimposed Discharge in Oxygen-Fed Ozonizer

A superposition type ozonizer has been proposed to achieve relatively high ozone concentration and high ozone generation efficiency. A high-pulsed voltage and a 60 Hz ac voltage are simultaneously applied to the same reaction volume in order to improve the ozone generation yield in a wide discharge gap. The ozone concentration of the superimposed discharge consisting of surface discharge and pulsed corona discharge was approximately two times larger than that obtained by an individual discharge. It was observed that the cross-section of the superimposed discharge extended is observed to be approximately 20% at maximum. The emission intensity of the superimposed discharge shows about two times larger than that of the individual discharge at maximum due to the increased electron temperature. The increment of local electric field in the discharge region causes the superposition effect.

Observation of submicron dust particles trapped in a diffused region of a low pressure radio frequency plasma

Submicron dust particles (Cu, φ 50 nm) were observed to be trapped in an rf plasma at relatively low pressure. The laser light scattering by particles shows the time evolution of the dust particles for several hours after pulsed injection of the particles. The dust particles were localized in the diffused region as a large volume cloud. The suspension mechanism of the dust particles in the diffused plasma was explained by an electrostatic force due to the potential structure. The spatial distribution of the charge of the dust particles was determined by this potential structure. The dispersion relations of the self-excited dust acoustic waves were adopted to confirm the spatial distribution and the time evolution of the charge of the dust particles.

Sterilization Characteristics of Tube Inner Surface Using Oxygen Plasma Produced by AC HV Discharge

Oxygen plasma inside a narrow tube using an AC high-voltage glow discharge at low pressure was produced for the sterilization of the inner surface of a tube. A tube having a length of 500 mm and diameter of 4 mm was sterilized by treatment for 10 min.

Antioxidative activity and growth regulation of Brassicaceae induced by oxygen radical irradiation

The growth regulation characteristics of plants are investigated when plant seeds are irradiated with atmospheric discharge plasma. Enhancement of the germination and lengths of the stem and root of plants are observed after seeding. The total length of the stem and root increases approximately 1.6 times after a cultivation period of 72 h. The growth regulation effect is found to be maintained for 80 h of cultivation after seeding. The growth regulation originates from the change in the antioxidative activity of plant cells induced by active oxygen species generated in the oxygen plasma, which leads to the production of growth factor in plants.

Sterilization characteristics of the surfaces of agricultural products using active oxygen species generated by atmospheric plasma and UV light

Agricultural products were sterilized by irradiation with active oxygen species produced by the combination of atmospheric plasma and UV light in ambient air. It was found that the surfaces of rice and lemons are sterilized after 20 min of irradiation. After the irradiation, the mold spores on the surface, although still viable, become unculturable. Treatment speed using the active oxygen species is higher than that using plasma or UV light alone. Infrared light spectra of the fruits surface indicate that there is no significant damage to the exocarp caused by the active oxygen species.