Coordinates and frames from the causal point of view

Lorentzian frames may belong to one of the 199 causal classes. Of these numerous causal classes, people are essentially aware only of two of them. Nevertheless, other causal classes are present in some well-known solutions, or present a strong interest in the physical construction of coordinate systems. Here we show the unusual causal classes to which belong so familiar coordinate systems as those of Lema{\^{\i}}tre, those of Eddington-Finkelstein, or those of Bondi-Sachs. Also the causal classes associated to the Coll light coordinates (four congruences of real geodetic null lines) and to the Coll positioning systems (light signals broadcasted by four clocks) are analyzed. The role that these results play in the comprehension and classification of relativistic coordinate systems is emphasized.Comment: 5 pages, 1 figure, short communication in A Century of Relativity Physics, Proceedings of the XXVIII Spanish Relativity Meeting ERE-2006, 6-10 September - Oviedo - Spain (AIP Conference Proceedings

Bolivia's Economic Crisis

By any standard, Bolivia's economic crisis in the 1980's has been extraordinary. Like its neighbors. Bolivia suffered from major external shocks, but the extent of economic collapse in the face of these shocks (including a hyperinflation during 1984-85) suggests that internal factors as well as external shocks have been critical to Bolivia's poor economic performance. One major theme of our work is that the recent economic crisis in Bolivia is a reflection of political and economic conflicts in Bolivian society that have undermined the development process throughout this century. While major reforms have been begun by the present government, many of the deepest problems in Bolivian society that contributed to the crisis remain unresolved.