Abstract: A screw or a tapping screw, comprising an ultra fine structure steel having ferrite grains of 3 ?m or smaller in average grain size and a nitrided layer on a surface part, wherein a strength is increased, a surface hardness is increased, and the surface hardness and an inside hardness are kept in balance, whereby a novel tapping screw and novel general screws can be provided.

Abstract: In a plant cultivation method, in cultivation of a plurality of plants within a cultivation bed which includes nutritive elements required for growth of the plants, a location adjacent a growing point of the plants is selected to supply gas to the growing point. In a plant cultivation apparatus, a cultivation bed is provided on which a plurality of plants are cultivated. The cultivation bed includes nutritive elements required for growth of the plants. An apparatus body for accommodating the cultivation bed has a gas-supply unit for supplying gas toward a location in the vicinity of a growing point of the plants. A gas-conditioning unit is arranged on the apparatus body for conditioning gas therewithin. An illumination unit for emitting a light to the plants.

Abstract: In a plant culture apparatus, plants being cultured are accommodated in a body. A culture bed is arranged within the body for culturing the plants. An illuminating device is arranged within the body for emitting a light to the plants on the culture bed. A gas-conditioning device is mounted to the body for recirculating gas therethrough. The illuminating device includes a lighting unit for emitting ultraviolet rays to the plants, and a transducing unit arranged below the lighting device for transducing the ultraviolet rays emitted from the lighting unit, to visible radiation. The transducing unit has long-wave absorbability and is formed by a plate element having its entire surface which is coated with phosphor.