Gas diffusion in zeolite beds: PFG NMR evidence for different tortuosity factors in the Knudsen and bulk regimesS. Vasenkov, O. Geir and J. KärgerEur. Phys. J. E, 12 (2003) 35-38DOI: https://doi.org/10.1140/epjed/e2003-01-009-1