1. Alexander, J., Gardner, R., Jones, C.K.R.T.: A topological invariant arising in the stability analysis of travelling waves. J. Reine Angew. Math. 410, 167–212 (1990)
2. Aronson, D.G.: Density-dependent interaction–diffusion systems. In: Stewart, W.E., Ray, W.H., Conley, C.C. (eds.) Dynamics and Modelling of Reactive Systems, vol. 44 of Publication of the Mathematics Research Center, University of Wisconsin, pp. 161–176. Academic Press, New York (1980)
3. Aronson, D.G.: The role of diffusion in mathematical population biology: Skellam revisited. In: Capasso, V., Grosso, E., Paveri-Fontana, S.L. (eds.) Mathematics in Biology and Medicine, vol. 57 of Lecture Notes in Biomathematics, pp. 2–6. Springer, Berlin (1985)
4. Balslev, E., Gamelin, T.W.: The essential spectrum of a class of ordinary differential operators. Pac. J. Math. 14(3), 755–776 (1964)
5. Ben-Jacob, E., Cohen, I., Levine, H.: Cooperative self-organization of microorganisms. Adv. Phys. 49(4), 395–554 (2000)