Ricci Collineations for Non-Degenerate, Diagonal and Spherically Symmetric Ricci Tensors

The expression of the vector field generator of a Ricci Collineation for diagonal, spherically symmetric and non-degenerate Ricci tensors is obtained. The resulting expressions show that the time and radial first derivatives of the components of the Ricci tensor can be used to classify the collineation, leading to 64 families. Some examples illustrate how to obtain the collineation vector

Early Geometrical Thinking in the Environment of Patterns, Mosaics and Isometries

This book discusses the learning and teaching of geometry, with a special focus on kindergarten and primary education. It examines important new trends and developments in research and practice, and emphasizes theoretical, empirical and developmental issues. Further, it discusses various topics, including curriculum studies and implementation, spatial abilities and geometric reasoning, as well as the psychological roots of geometrical thinking and teacher preparation in geometry education. It considers these issues from historical, epistemological, cognitive semiotic and educational points of view in the context of students' difficulties and the design of teaching and curricula

Thermal conductivity of high- T c superconductors

This paper reviews existing data on the thermal conductivity of high- T c superconductors. Included are discussions of pristine polycrystalline high- T c ceramics, single crystal specimens, and high- T c materials structurally modified by substitution or by radiation damage. The thermal conductivity of high- T c superconductors is compared with that of conventional superconductors, and dramatic differences are found between the two families. Mechanisms of thermal conductivity applicable to high- T c perovskites are discussed and implications for theories of high- T c superconductivity are noted.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45121/1/10948_2004_Article_BF00617463.pd