3,404 research outputs found
Book Review: Research Methods in Education, 7th Edition
This article reviews the book, “Research Methods in Education” by Louis Cohen, Lawrence Manion, Keith Morrison (Authors)
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
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
Contact seaweeds II: type C
This paper is a continuation of earlier work on the construction of contact
forms on seaweed algebras. In the prequel to this paper, we show that every
index-one seaweed subalgebra of is contact by
identifying contact forms that arise from Dougherty's framework. We extend this
result to include index-one seaweed subalgebras of .
Our methods are graph-theoretic and combinatorial
Classification of contact seaweeds
A celebrated result of Gromov ensures the existence of a contact structure on
any connected, non-compact, odd dimensional Lie group. In general, such
structures are not invariant under left translation. The problem of finding
which Lie groups admit a left-invariant contact structure resolves to the
question of determining when a Lie algebra is contact; that is,
admits a one-form such that
In full generality, this remains an open question; however we settle it for
the important category of the evocatively named seaweed algebras by showing
that an index-one seaweed is contact precisely when it is quasi-reductive.
Seaweeds were introduced by Dergachev and Kirillov who initiated the
development of their index theory -- since completed by Joseph, Panyushev,
Yakimova, and Coll, among others. Recall that a contact Lie algebra has index
one -- but not characteristically so. Leveraging recent work of Panyushev,
Baur, Moreau, Duflo, Khalgui, Torasso, Yakimova, and Ammari, who collectively
classified quasi-reductive seaweeds, our equivalence yields a full
classification of contact seaweeds. We remark that since type-A and type-C
seaweeds are de facto quasi-reductive (by a result of Panyushev), in these
types index one alone suffices to ensure the existence of a contact form
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