@article {CarlsonLS88,
	title = {Frustration in modulated phases - ripples and boojums},
	journal = {Europhysics Letters},
	volume = {5},
	year = {1988},
	pages = {327-331},
	author = {Carlson, J. M. and Langer, S. A. and Sethna, J. P.}
}
