A signal transfer link includes a first plasmonic coupler, and a second plasmonic coupler spaced apart from the first plasmonic coupler to form a gap. The tank also includes a sensor for detecting fire or smoke in the above-ground storage tank and a mass of fire extinguishing materials and a dispenser for dispensing the fire extinguishing materials inwardly across the top of the storage tank upon sensing a fire within the tank. The device causes the atrial septum to deform and push the anterior leaflet of the mitral valve in a posterior direction for reducing mitral valve regurgitation. These two stages, buffer stage and cross-coupled differential pair stage, are both very fast operating stages. According to the above structure of the present invention, there can be provided a silicon nitride wear resistant member and a method of manufacturing the member having a high strength and a toughness property, and particularly excellent in sliding characteristics.