Relativistic Positioning Systems: The Emission Coordinates

This paper introduces some general properties of the gravitational metric and the natural basis of vectors and covectors in 4-dimensional emission coordinates. Emission coordinates are a class of space-time coordinates defined and generated by 4 emitters (satellites) broadcasting their proper time by means of electromagnetic signals. They are a constitutive ingredient of the simplest conceivable relativistic positioning systems. Their study is aimed to develop a theory of these positioning systems, based on the framework and concepts of general relativity, as opposed to introducing `relativistic effects' in a classical framework. In particular, we characterize the causal character of the coordinate vectors, covectors and 2-planes, which are of an unusual type. We obtain the inequality conditions for the contravariant metric to be Lorentzian, and the non-trivial and unexpected identities satisfied by the angles formed by each pair of natural vectors. We also prove that the metric can be naturally split in such a way that there appear 2 parameters (scalar functions) dependent exclusively on the trajectory of the emitters, hence independent of the time broadcast, and 4 parameters, one for each emitter, scaling linearly with the time broadcast by the corresponding satellite, hence independent of the others.Comment: 13 pages, 3 figures. Only format changed for a new submission. Submitted to Class. Quantum Gra

Positioning systems in Minkowski space-time: from emission to inertial coordinates

The coordinate transformation between emission coordinates and inertial coordinates in Minkowski space-time is obtained for arbitrary configurations of the emitters. It appears that a positioning system always generates two different coordinate domains, namely, the front and the back emission coordinate domains. For both domains, the corresponding covariant expression of the transformation is explicitly given in terms of the emitter world-lines. This task requires the notion of orientation of an emitter configuration. The orientation is shown to be computable from the emission coordinates for the users of a `central' region of the front emission coordinate domain. Other space-time regions associated with the emission coordinates are also outlined.Comment: 20 pages; 1 figur

Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU

Contains fulltext : 172380.pdf (publisher's version ) (Open Access

Una experiencia de desarrollo profesional del docente universitario de Educación Física a través de una práctica crítica, reflexiva y colaborativa

Presentamos la experiencia realizada por un subgrupo de una red de evaluación formativa en docencia universitaria que desarrolla proyectos de innovación e investigación especialmente enfocados al proceso de convergencia europea. Se explicitan los referentes conceptuales, se describe el contexto de actuación, los participantes y el proceso seguido y se concretan los factores que han caracterizado su aplicación, desarrollo y evaluación. El objetivo es exponer de qué forma, participando en una red interuniversitaria que trabaja a partir de sucesivos ciclos de investigación-acción, se puede contribuir de manera eficaz a la formación y desarrollo profesional del profesorado. La concreción, tanto de los factores facilitadores como de los inconvenientes surgidos en el proceso, define las conclusiones así como las nuevas vías de trabajo.A programme undertaken by a subgroup of a university education evaluation network that carries out innovation and research projects focused on the process of European convergence is presented. The paper explains the programme’s conceptual framework, and describes the context of performance, the participants, the procedure followed, and those factors that have characterised its application, development and assessment. The objective is to show how, by participating in an interuniversity network that works on the basis of successive researchaction cycles, an efficient contribution can be made to the training and professional development of teaching staff. The specification of both facilitating factors and obstacles that arose in the study defines our conclusions as well as new ways to address work