Water activity in lamellar stacks of lipid bilayers: “Hydration forces” revisited R. Leite Rubim, B. B. Gerbelli, K. Bougis, C. L. Pinto de Oliveira, L. Navailles, F. Nallet and E. Andreoli de Oliveira Eur. Phys. J. E, 39 1 (2016) 3 Published online: 25 January 2016 DOI: 10.1140/epje/i2016-16003-0