Solve two issues in noj: 1. variables passed to np.arccos() could be lareger than 1.0 or less than -1.0 for some combination of R1, R2 and d to cal_overlapping_area_factor. 2. Ct values passed to np.sqrt(1-Ct) could be larger than 1. These two issues both result errors/nan values. Now these variables/values have to pre-treated to avoid such results.