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Figure 1
Nomenclature for a toroidally bent wafer. The thickness of the wafer is d. The origin O of the Cartesian coordinate system (x, y, z) and the polar coordinates (r, ϕ) are located at the midplane of the crystal in the z direction.

IUCrJ
Volume 8| Part 1| January 2021| Pages 102-115
ISSN: 2052-2525
https://doi.org/10.1107/S2052252520014165