BibTex format
@article{Gibbon:2011:10.1080/03091929.2010.513117,
author = {Gibbon, JD and Holm, DD},
doi = {10.1080/03091929.2010.513117},
journal = {GEOPHYSICAL AND ASTROPHYSICAL FLUID DYNAMICS},
pages = {329--339},
title = {The gradient of potential vorticity, quaternions and an orthonormal frame for fluid particles},
url = {http://dx.doi.org/10.1080/03091929.2010.513117},
volume = {105},
year = {2011}
}