A comprehensive analysis of gened relativistic spacetimes which admit a shearfree, irrotational and geodesic time-like coogruence is presented. The equations governing the models for a gened energy-momentum tensor are wrilten down. Coordinates in which the metric of such spacetimes takes on a simplified form are established. The general subwses of 'zero anisotropic stress', 'zero heat-flux vector' and 'two-component Ruids' are investigated. In particular, perfect-fluid Friedmann-Robertson-Walker models and spatially homogeneous models are discussed. Models with a variety of physically relevant energy-momentum tensors are considered. Anisowopic fluid models and viscous fluid models with heat conduction are examined. Also. models with B perfect Ruid plus a magnetic field or with pure radiation. and models with two non-collinw perfect fluids (satisfying a variety of physical conditions) are inwtigated. In particular. models with a (single) perfect Ruid which is tilting with respect to the shem-free, vorticity-free and acceleration-free time-like congruence are discussed.PACS numbers: 0420J. 9880H

Inorganic–organic hybrid materials composed of [O3P–C6H4–SiO3] units and zirconium hydrothermally prepared in the presence of cationic surfactant showed nanoporosity and considerably high specific surface area.

Novel ordered lamellar mesostructure pZrPS-2 was hydrothermally prepared by using zirconium propoxide and 4-(EtO)2OPC6H4Si(OEt)3 (pPPS-E), which was hydrolyzed to organic building units substituted with both siliconate and phosphonate groups, in the presence of Cn TAB and TMAOH. The pZrPS-2 materials were obtained at a Zr/PPS ratio of 2 or higher and the basal spacing was increased by using a longer-chain surfactant (n = 12-18). Removal of the occluded surfactants at 300 °C resulted in retention of the lamellar structure with negligible shrinkage of the interlayer distance. Nitrogen adsorption studies revealed the ordered mesoporous nature of pZrPS-2 with a pore diameter of approximately 2 to 3 nm. The lamellar structure is assumed to be composed of layers that include zirconia-based crystalline nanodomains and interlayer pillars mainly based on PPS units. Although lamellar structures with the same crystalline phase also formed when no surfactant was added or when the meta isomer of PPS was used, no mesoporous materials were obtained except pZrPS-2. A possible schematic model to elucidate these results is also proposed.

PZT thin films were epitaxially grown on (100)Pt/ (100)MgO substrates by CVD under partial oxygen pressure (PO2) from 0.96 to 8.4Torr. The crystal struc ture and microstructure of the films were almost the same as those prepared on MgO substrates irrespective of PO2. However, for films deposited below 1.6Torr of PO2, the existence of PbPt5-7 phase was ascertained by XRD measurement, and the electric leakage between top and bottom electrodes was observed. The X-ray pole figure measurement showed that this PbPt5-7 was epitaxially related to the deposited PZT thin film and the (100)Pt/(100)MgO substrate. The relative dielec tric constant, r, of epitaxially grown Pb(Zr0.5Ti0.5)O3 films was about 300, lower than that of non-oriented film. This phenomenon can be elucidated by the fact that the calculated r of PZT crystals along the c-axis is lower than that perpendicular to the c-axis.

Novel hybrid inorganic–organic mesostructures were hydrothermally prepared from pseudo-boehmite and an organic precursor containing both silanolate and phosphonate groups in the presence of cationic surfactants. The solid-state NMR revealed that aluminum species are mainly connected with phosphonate groups in the formed 2D hexagonal mesostructures.