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![[Figure 1]](ba5148fig1mag.jpg)
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Figure 1
Coordinate system. The x axis is occupied by the X-ray beam and the spindle rotates the crystal (at the origin) about the z axis. The y axis is not shown as it is very nearly perpendicular to the page. The reciprocal-lattice point (relp) of interest is described here by the circle it traces out as the crystal is rotated. Note that it intersects the Ewald sphere twice and that the `penetration speed' is the component of the relp's velocity that is perpendicular to the Ewald sphere surface. The ratio of the `actual speed' to the `penetration speed' is the Lorentz factor. The diffracted ray passes through the point of intersection, but evolves from the center of the Ewald sphere (not the origin!), which is an unfortunate conceptual flaw in Ewald's construction. Nevertheless, the take-off angle (2θ) obtained is the same as that observed in real space. The angles α and κ used in (3) ![[link]](../../../../../../logos/arrows/d_arr.gif) and Appendix C are shown. |
![[Figure 1]](ba5148fig1.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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