ABSTRACT
A method of systematically enumerating homogeneous (i.e. symmetry-related) packings of equal cylinders is developed. 19 three-way packings with axes parallel to <100> and 40 four-way packings with axes parallel to <111> are described. Cubic 6-, 12- and 24-way packings are possible and examples are given with axes parallel to <210> and <421>.
ABSTRACT
A tiling of space by tiles that have all hexagonal faces and are infinite in one direction is described. The tiling is simple (four tiles meet at each vertex, three at each edge and two at each face) and carries a 4-connected net whose vertices are the lattice complex S* with symmetry Ia(-)3d. The tiling is closely related to the densest cubic cylinder packing, Gamma. It is shown that the other invariant cubic lattice complexes unique to Ia(-)3d (Y** and V*) are also related to the same cylinder packing.
ABSTRACT
Six packings of symmetry-related cylinders, with cylinder axes in invariant positions (coordinates completely determined by symmetry), are described. Two have axes along <100> and four have axes along <111>. It is shown that there can be no cubic cylinder packing with axes along <110>. Earlier errors concerning the numbers of such packings and their symmetries are corrected.
ABSTRACT
Paramagnetic shifts have been observed for the first time in rare-earth zeolites; the 29Si MAS NMR spectra of rare-earth ion-exchanged low silica X show a large range of isotropic chemical shifts that can be attributed to Fermi contact interactions with the lanthanide electronic moments.
