定義： Polymetallic nodules, also called manganese nodules, are rock concretions on the sea bottom formed of concentric layers of iron and manganese hydroxides around a core. Nodules vary in size from tiny particles visible only under a microscope to large pellets more than 20 centimetres (8 in) across. However, most nodules are between 5 and 10 cm in diameter.
定義： Drag swimmers use a cyclic motion where they push water back in a power stroke, and return their limb forward in the return or recovery stroke. When they push water directly backwards, this moves their body forward, but as they return their limbs to the starting position, they push water forward, which will thus pull them back to some degree, and so opposes the direction that the body is heading. This opposing force is called drag. The return-stroke drag causes drag swimmers to employ different strategies than lift swimmers. Reducing drag on the return stroke is essential for optimizing efficiency.
定義： Component found in mineralized skeletal tissue, (a specialized form of biogenic tissue in which the extracellular matrix is mineralized, and which functions in mechanical and structural support.)
定義： Hard framework, internal or external, which supports and protects softer parts of plant, animal or unicellular organism, and to which muscles usually attach in animals, includes skeletons (derived from Lawrence, 2005).
