doi:http://dx.doi.org/10.1017/psrm.2013.1, Published by Cambridge University Press 2013.

The authors would like to correct a mistake in the expression below.

The mistake is in expression 1. This reads

$${{{\rm{U}}}_{\rm{i}}}\,{\rm{ = }}\,{{{\rm{\ralpha }}}_{\rm{i}}}\,{{{\rm{p}}}_{\rm{i}}}\,{\rm{ + }}\,\mathop{\sum}{{{{\rm{c}}}_{{\rm{ij}}}}\left( {{{{\rm{p}}}_{\rm{i}}}\,{\rm{ - }}\,{{{\rm{p}}}_{\rm{j}}}} \right)\,{\rm{ - }}\,} \left( {{{{\rm{\rkappa }}}_{\rm{i}}}\,{\rm{ - }}\,{\rm{p}}_{{\rm{i}}}^{{\rm{2}}} \,{\rm{ - }}\,{{{\rm{\rphi}}}_{\rm{i}}}{{{\rm{p}}}_{\rm{i}}}} \right){\rm{/}}\,\mathop{\sum}{{{{\rm{g}}}_{{\rm{ij}}}}{{{\rm{p}}}_{\rm{j}}}} $$

Whereas it should have read

$${{{\rm{U}}}_{\rm{i}}}\,{\rm{ = }}\,{{{\rm{\ralpha }}}_{\rm{i}}}\,{{{\rm{p}}}_{\rm{i}}}\,{\rm{ + }}\,\mathop{\sum}{{{{\rm{c}}}_{{\rm{ij}}}}\left( {{{{\rm{p}}}_{\rm{i}}}\,{\rm{ - }}\,{{{\rm{p}}}_{\rm{j}}}} \right)\,{\rm{ - }}\,} \left( {{{{\rm{\rkappa }}}_{\rm{i}}}\,{\rm{p}}_{{\rm{i}}}^{{\rm{2}}} \,{\rm{ - }}\,{{{\rm{\rphi}}}_{\rm{i}}}{{{\rm{p}}}_{\rm{i}}}} \right){\rm{/}}\,\mathop{\sum}{{{{\rm{g}}}_{{\rm{ij}}}}{{{\rm{p}}}_{\rm{j}}}} $$