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

The sensitivities of localized surface plasmon resonant sensors can be improved by changing the shape, size, and arrangement of nanosized metal dots on a substrate. In this study, we fabricated nanosized gold structure arrays on a silica substrate by electron beam lithography combined with a liftoff process, and studied their performance as refractive index sensors. We found that the sensitivity of single gold square dot arrays increases with the pitch while the absorbance decreases. On the other hand, both the sensitivity and absorbance of twin gold square dot arrays increase as the gap distance decreases for a particular incident polarization. We discuss the sensitivity of these structures for practical sensor applications.

High-resolution AES (HR-AES) has been used to study the electronic state of Ar + -irradiated graphite in which the increase in the partial charge density caused by the lattice damage has been indicated. At doses of <5 × 10 11 Ar + cm −2 , which was reported as a maximum value to avoid the overlapping cascades, neither plasmon energies nor the work function in highly oriented pyrolytic graphite (