1,346 research outputs found
Teleparallel Theories of Gravity: Illuminating a Fully Invariant Approach
Teleparallel gravity and its popular generalization gravity can be
formulated as fully invariant (under both coordinate transformations and local
Lorentz transformations) theories of gravity. Several misconceptions about
teleparallel gravity and its generalizations can be found in the literature,
especially regarding their local Lorentz invariance. We describe how these
misunderstandings may have arisen and attempt to clarify the situation. In
particular, the central point of confusion in the literature appears to be
related to the inertial spin connection in teleparallel gravity models. While
inertial spin connections are commonplace in special relativity, and not
something inherent to teleparallel gravity, the role of the inertial spin
connection in removing the spurious inertial effects within a given frame of
reference is emphasized here. The careful consideration of the inertial spin
connection leads to the construction of a fully invariant theory of
teleparallel gravity and its generalizations. Indeed, it is the nature of the
spin connection that differentiates the relationship between what have been
called good tetrads and bad tetrads and clearly shows that, in principle, any
tetrad can be utilized. The field equations for the fully invariant formulation
of teleparallel gravity and its generalizations are presented and a number of
examples using different assumptions on the frame and spin connection are
displayed to illustrate the covariant procedure. Various modified teleparallel
gravity models are also briefly reviewed.Comment: v2: 72 pages, revised version, references added, matches published
versio
European neonatal intensive care nursing research priorities: an e-Delphi study.
OBJECTIVE: This study aimed to identify and prioritise neonatal intensive care nursing research topics across Europe using an e-Delphi technique. DESIGN: An e-Delphi technique with three questionnaire rounds was performed. Qualitative responses of round one were analysed by content analysis and research statements were generated to be ranged on importance on a scale of 1-6 (not important to most important). SETTING: Neonatal intensive care units (NICUs) in 17 European countries. POPULATION: NICU clinical nurses, managers, educators and researchers (n=75). INTERVENTION: None. MAIN OUTCOME MEASURES: A list of 43 research statements in eight domains. RESULTS: The six highest ranking statements (≥5.0 mean score) were related to prevention and reduction of pain (mean 5.49; SD 1.07), medication errors (mean 5.20; SD 1.13), end-of-life care (mean 5.05; SD 1.18), needs of parents and family (mean 5.04; SD 1.23), implementing evidence into nursing practice (mean 5.02; SD 1.03), and pain assessment (mean 5.02; SD 1.11). The research domains were prioritised and ranked: (1) pain and stress; (2) family centred care; (3) clinical nursing care practices; (4) quality and safety; (5) ethics; (6) respiratory and ventilation; (7) infection and inflammation; and (8) professional issues in neonatal intensive care nursing. CONCLUSIONS: The results of this study might support developing a nursing research strategy for the nursing section of the European Society of Paediatric and Neonatal Intensive Care. In addition, this may promote more European researcher collaboratives for neonatal nursing research
Scalar Field Cosmologies with Barotropic Matter: Models of Bianchi class B
We investigate in detail the qualitative behaviour of the class of Bianchi
type B spatially homogeneous cosmological models in which the matter content is
composed of two non-interacting components; the first component is described by
a barotropic fluid having a gamma-law equation of state, whilst the second is a
non-interacting scalar field (phi) with an exponential potential V=Lambda exp(k
phi). In particular, we study the asymptotic properties of the models both at
early and late times, paying particular attention on whether the models
isotropize (and inflate) to the future, and we discuss the genericity of the
cosmological scaling solutions.Comment: 18 pages, 1 figure, uses revtex and epsf to insert figur
Symmetries in Riemann-Cartan geometries
Riemann-Cartan geometries are metric based geometries admitting a non-zero
torsion tensor. These geometries have been investigated as geometric frameworks
for potential theories in physics including quantum gravity theories and have
many important differences when compared to Riemannian geometries. One notable
difference, is the number of symmetries for a Riemann-Cartan geometry is
potentially smaller than the number of Killing vector fields for the metric. In
this paper we will review the investigation of symmetries in Riemann-Cartan
geometries and the mathematical tools used to determine geometries that admit a
given group of symmetries. As an illustration we will determine all static
spherically symmetric and all stationary spherically symmetric Riemann-Cartan
geometries. Further, we will determine the subclasses of spherically symmetric
Riemann-Cartan geometries that admit a seven-dimensional group of symmetries.Comment: 32 page
Bianchi Type Cosmological Models in Tele-parallel Gravity
Symmetry assumptions on the geometrical framework have provided successful
mechanisms to develop physically meaningful solutions to many problems. In
tele-parallel gravity, invariance of the frame and spin-connection under a
group of motions defines an affine symmetry group. Here, we assume there exists
a three-dimensional group of affine symmetries acting simply transitively on a
spatial hypersurface and that this group of symmetry actions defines our affine
frame symmetry group. We determine the general form of the co-frame and spin
connection for each spatially homogeneous Bianchi type. We then construct the
corresponding field equations for tele-parallel gravity. We show that if
the symmetry group is of Bianchi type A (, , , , or
) then there exists a co-frame/spin connection pair that is consistent with
the antisymmetric part of the field equations of tele-parallel gravity.
For those geometries having a Bianchi type B symmetry group (, , ,
), we find that in general these geometries are inconsistent with the
antisymmetric part of the tele-parallel gravity field equations unless
the theory reduces to an analog of General Relativity with a cosmological
constant.Comment: 28 page
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