The Covariant Approach to LRS Perfect Fluid Spacetime Geometries

The dynamics of perfect fluid spacetime geometries which exhibit {\em Local Rotational Symmetry} (LRS) are reformulated in the language of a $1+\,3$ "threading" decomposition of the spacetime manifold, where covariant fluid and curvature variables are used. This approach presents a neat alternative to the orthonormal frame formalism. The dynamical equations reduce to a set of differential relations between purely scalar quantities. The consistency conditions are worked out in a transparent way. We discuss their various subcases in detail and focus in particular on models with higher symmetries within the class of expanding spatially inhomogeneous LRS models, via a consideration of functional dependencies between the dynamical variables.Comment: 25 pages, uuencoded/compressed postscript fil

Information Technology Support for Communities of Practice: How Public Defenders Learn about Winning and Losing in Court

The aim of this article is to examine the role of information technologies (IT) in supporting practice and professional identity formation, both major axes for communities of practice. The article uses an ethnographic case study to understand how public defenders learn to improve their court performance. The concept of “communities of practice” helps to illuminate how the attorneys in a public defender’s office share knowledge in order to practice effectively in court. This article presents findings that a community of practice serves as effective scaffolding to support professional development; this is especially true for the practice component. Further, this case study indicates that information technologies, such as listservs, are not very effective social integrators for professionals who work at different sites. In particular, today’s IT forums are most effective when used for sharing technical information about work, and least effective for sharing important cultural meanings about how professionals should approach their work and develop professional identities. This research advances our understanding about the complexity of organizing communities of practice to support professional groups of colleagues and IT-enabled support for various activities