...

Subscript "0'' denotes the starting epoch of integration.

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... radii

Effective radius correspond to a sphere of the same projected area, which changes from $\pi R_{\rm a}^2$to $\pi R_{\rm a}\cdot R_{\rm b} = \pi (1-s)\cdot R_{\rm a}^2$according to the spin-axis orientation. Thus, we approximate the effective radius by a mean value of circles radii whose areas correspond to maximum and minimum projected areas of ellipsoidal nucleus, respectively.

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