Abstract: A method and apparatus for detecting and measuring mechanical movement that is directly or indirectly representative of a physical phenomenon. The method and apparatus involve the use of at least one optical fiber that defines a region of bend having a curvature, the radius of which varies in direct relation with the particular mechanical movement that is induced by the physical phenomenon. Light is introduced into one extremity of the optical fiber and propagates through the fiber where the intensity of the light emitted or radiating from the opposite extremity of the fiber is measured. Differentiation between introduced light and emitted light determines the degree of perturbance caused by the region of bend and is thus representative of the physical phenomenon that alters the radius of curvature at the region of bend.

Abstract: A threaded closure having force-transmitting thread surfaces that face inwardly, whereby the forces acting on a casing wall directly above the closure imposed directly by a pressurized liquid and the forces on the casing wall adjacent to the closure transmitted from the top of the closure and through the closure threads are subtractive.