Abstract: A method of reducing a nitrogen oxide content in gas is disclosed. In this method, subject gas containing nitrogen oxide is supplied to a gas passage of a surface discharger to decompose the nitrogen oxide content in the gas into nitrogen gas.

Abstract: A method for opening, closing and rotating a rigid marine sail, which comprises the steps of: selectively opening, closing and rotating, in response to a wind velocity and a wind direction, a rigid sail comprising at least two sail portions which are fitted in front of a mast rotatable around the vertical axis thereof substantially in parallel with said axis, and which are selectively pivotably movable between the opened position and the closed position relative to the mast: the method being characterized by: smoothing a plurality of wind velocity signals and a plurality of wind direction signals from a wind velocity/wind direction meter, by a calculating device at prescribed intervals of time; determining opening and closing of the at least two sail portions by the calculating device on the basis of smoothed wind velocity signals and smoothed wind direction signals; automatically selectively opening or closing the at least two sail portions by an opening/closing device in response to the determination; deter

Abstract: A rigid marine sail has a rigid left sail portion and a rigid right sail portion, both of which are pivotally secured to a mast on a ship so as to be pivotable about one common pivot axis which extends substantially parallel to the mast of the ship. The common pivot axis is spaced ahead of the mast with respect to the direction of intended movement of the ship. The left and right sail portions are foldable to an operable position by pivoting them about the common pivot axis and are also foldable to a streamlined folded inoperable position by being pivoted about the one common pivot axis, the left and right sail portions being substantially parallel to each other and closely facing each other when they are in their streamlined folded inoperable positions. A shroud is provided ahead of the common pivot axis with respect to the direction of movement of the ship. When the left and right sail portions are in their folded inoperable position, the shroud spans a gap between them to reduce air resistance.