In the original publication of Gerard and Jing,Reference Gerard and Jing1 the a and b designations of Figure 2 were placed in a manner that could have been misinterpreted. A corrected version of Figure 2 is above to avoid ambiguity.
![](https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20201216055102004-0935:S2159685920000099:S2159685920000099_fig2.png?pub-status=live)
The publisher apologizes for this error.