4,081 research outputs found
Positioning systems in Minkowski space-time: Bifurcation problem and observational data
In the framework of relativistic positioning systems in Minkowski space-time,
the determination of the inertial coordinates of a user involves the {\em
bifurcation problem} (which is the indeterminate location of a pair of
different events receiving the same emission coordinates). To solve it, in
addition to the user emission coordinates and the emitter positions in inertial
coordinates, it may happen that the user needs to know {\em independently} the
orientation of its emission coordinates. Assuming that the user may observe the
relative positions of the four emitters on its celestial sphere, an
observational rule to determine this orientation is presented. The bifurcation
problem is thus solved by applying this observational rule, and consequently,
{\em all} of the parameters in the general expression of the coordinate
transformation from emission coordinates to inertial ones may be computed from
the data received by the user of the relativistic positioning system.Comment: 10 pages, 7 figures. The version published in PRD contains a misprint
in the caption of Figure 3, which is here amende
Neutrinos from supernovae: experimental status and perspectives
I discuss the state of the art in the search for neutrinos from galactic
stellar collapses and the future perspectives of this field. The implications
for the neutrino physics of a high statistics supernova neutrino burst
detection by the network of detectors operating around the world are also
reviewed.Comment: 19 pages, 12 figures. Extended version of talk given at IInd
International Workshop on Matter, Anti-Matter and Dark Matter, Trento
(Italy), 29-30 October 2001. A reduced version will appear in Int. J. of Mod.
Phys.
DAMA detection claim is still compatible with all other DM searches
We show that the annual modulation signal observed by DAMA can be reconciled
with all other negative results from dark matter searches with a conventional
halo model for particle masses around 5 to 9 GeV. We also show which particular
dark matter stream could produce the DAMA signal.Comment: Talk given at TAUP2005, Sept. 10-14 2005, Zaragoza (Spain). 3 pages,
4 figure
Rainich theory for type D aligned Einstein-Maxwell solutions
The original Rainich theory for the non-null Einstein-Maxwell solutions
consists of a set of algebraic conditions and the Rainich (differential)
equation. We show here that the subclass of type D aligned solutions can be
characterized just by algebraic restrictions.Comment: 12 pages; v2: appendix with notatio
Education Deans: Challenges and Stress
Abstract:
This study explored issues facing deans within higher education, specifically deans of doctoral granting schools/colleges of education. The study explored key challenges/issues and related stress education deans experience at research universities
A physical application of Kerr-Schild groups
The present work deals with the search of useful physical applications of
some generalized groups of metric transformations. We put forward different
proposals and focus our attention on the implementation of one of them.
Particularly, the results show how one can control very efficiently the kind of
spacetimes related by a Generalized Kerr-Schild (GKS) Ansatz through
Kerr-Schild groups. Finally a preliminar study regarding other generalized
groups of metric transformations is undertaken which is aimed at giving some
hints in new Ans\"atze to finding useful solutions to Einstein's equations.Comment: 18 page
On the degrees of freedom of a semi-Riemannian metric
A semi-Riemannian metric in a n-manifold has n(n-1)/2 degrees of freedom,
i.e. as many as the number of components of a differential 2-form. We prove
that any semi-Riemannian metric can be obtained as a deformation of a constant
curvature metric, this deformation being parametrized by a 2-for
Condroblastoma de astrágalo: localización inusual
Se expone 1 caso de un condroblastoma de astrágalo en 1 paciente de 17 años.
Esta tumoración, definida como tal en 1942 por Jaffe y Lichtenstein, presenta un comportamiento
benigno que responde al tratamiento mediante curetaje e injerto óseo de la cavidad. A pesar de
este comportamiento benigno se hace mención a la posibilidad de metástasis pulmonares y a la
agresividad local en algunos casos.A 17-year-old man with chondroblastoma of the talus is reported. This tumor described
in 1942 by Jaffe and Lichtenstein has a benign behavior and a good response to surgical
treatment by curetage of the cavity and bone graft. In certain cases local aggresivity and lung metastasis
has been described
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