principal axis

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Related to Principle axis: centre of curvature

principal axis

In optics, a line that passes through the optical center or nodal point of a lens perpendicular to the surface of the lens.
See also: axis
References in periodicals archive ?
The object is a cube with magnetization, [M.sub.s], exchange stiffness parameter, A, and magnetocrystalline anisotropy constant [K.sub.u] = 0.1 X 1/2 [[micro].sub.o][M.sup.2.sub.s], with the easy direction parallel to a principle axis of the cube.