All static spherically symmetric anisotropic solutions of Einstein's equations

An algorithm recently presented by Lake to obtain all static spherically symmetric perfect fluid solutions, is extended to the case of locally anisotropic fluids (principal stresses unequal). As expected, the new formalism requires the knowledge of two functions (instead of one) to generate all possible solutions. To illustrate the method some known cases are recovered.Comment: 8 pages Latex. To appear in Phys. Rev. D. New reference added. Some references correcte

The spacetime outside a source of gravitational radiation: The axially symmetric null fluid

We carry out a study of the exterior of an axially and reflection symmetric source of gravitational radiation. The exterior of such a source is filled with a null fluid produced by the dissipative processes inherent to the emission of gravitational radiation, thereby representing a generalization of the Vaidya metric for axially and reflection symmetric spacetimes. The role of the vorticity, and its relationship with the presence of gravitational radiation is put in evidence. The spherically symmetric case (Vaidya) is, asymptotically, recovered within the context of the $1+3$ formalism.Comment: 11 pages Latex. arXiv admin note: text overlap with arXiv:1609.02841. Typos corrected, to appear in Eur. Phys. J.

The Effects of Being Subject to the Colombian Apprenticeship Contract on Manufacturing Firm Performance

This paper evaluates the intent to treat local average treatment effects of the Colombian apprenticeship contract on manufacturing firm dynamics taking advantage of an exogenous variation generated by the 2002 labor reform and the regulation design. This evaluation is appealing because very little is known about the effects of apprenticeship policies on firm dynamics in developing countries. Moreover, although this regulation has been in place for years it has not been evaluated. Results using a regression discontinuity design which compares small firms subject to the regulation to those that are not, shows positive effects on output per worker (10 log points), total factor productivity (3 log points) and the share of exported sales (2 percentage points). It also shows a negative effect on the average wage bill of directly hired workers (9 log points). These results suggest that small firms which became subject to the regulation adjusted their labor force more efficiently, thus increasing productivity but did not share these gains with workers through higher wages.Centro de Estudios Distributivos, Laborales y Sociales (CEDLAS