3,096 research outputs found
Asymptotic properties of the development of conformally flat data near spatial infinity
Certain aspects of the behaviour of the gravitational field near null and
spatial infinity for the developments of asymptotically Euclidean, conformally
flat initial data sets are analysed. Ideas and results from two different
approaches are combined: on the one hand the null infinity formalism related to
the asymptotic characteristic initial value problem and on the other the
regular Cauchy initial value problem at spatial infinity which uses Friedrich's
representation of spatial infinity as a cylinder. The decay of the Weyl tensor
for the developments of the class of initial data under consideration is
analysed under some existence and regularity assumptions for the asymptotic
expansions obtained using the cylinder at spatial infinity. Conditions on the
initial data to obtain developments satisfying the Peeling Behaviour are
identified. Further, the decay of the asymptotic shear on null infinity is also
examined as one approaches spatial infinity. This decay is related to the
possibility of selecting the Poincar\'e group out of the BMS group in a
canonical fashion. It is found that for the class of initial data under
consideration, if the development peels, then the asymptotic shear goes to zero
at spatial infinity. Expansions of the Bondi mass are also examined. Finally,
the Newman-Penrose constants of the spacetime are written in terms of initial
data quantities and it is shown that the constants defined at future null
infinity are equal to those at past null infinity.Comment: 24 pages, 1 figur
Climbing the African energy ladder::internal and external factors influencing household demand for improved cookstoves and modern fuels in sub-Saharan Africa
Brouwer, R. [Promotor]Beukering, P.J.H. van [Copromotor
Can one detect a non-smooth null infinity?
It is shown that the precession of a gyroscope can be used to elucidate the
nature of the smoothness of the null infinity of an asymptotically flat
spacetime (describing an isolated body). A model for which the effects of
precession in the non-smooth null infinity case are of order is
proposed. By contrast, in the smooth version the effects are of order .
This difference should provide an effective criterion to decide on the nature
of the smoothness of null infinity.Comment: 6 pages, to appear in Class. Quantum Gra
Initial data sets for the Schwarzschild spacetime
A characterisation of initial data sets for the Schwarzschild spacetime is
provided. This characterisation is obtained by performing a 3+1 decomposition
of a certain invariant characterisation of the Schwarzschild spacetime given in
terms of concomitants of the Weyl tensor. This procedure renders a set of
necessary conditions --which can be written in terms of the electric and
magnetic parts of the Weyl tensor and their concomitants-- for an initial data
set to be a Schwarzschild initial data set. Our approach also provides a
formula for a static Killing initial data set candidate --a KID candidate.
Sufficient conditions for an initial data set to be a Schwarzschild initial
data set are obtained by supplementing the necessary conditions with the
requirement that the initial data set possesses a stationary Killing initial
data set of the form given by our KID candidate. Thus, we obtain an algorithmic
procedure of checking whether a given initial data set is Schwarzschildean or
not.Comment: 16 page
Mindfulness as substitute for transformational leadership
Purpose Transformational leaders spark the intrinsic motivation of employees, thereby stimulating their extra-role performance. However, not all employees are lucky enough to have a transformational leader. The purpose of this paper is to investigate to what extent mindfulness can function as a substitute for transformational leadership. By being attentive to and aware of what is taking place in the present, mindfulness provides employees with a source of intrinsic motivation that lies within the person, thereby possibly making employees less dependent on transformational leadership. Design/methodology/approach An online survey was used to collect data of 382 employees working in diverse sectors in the Netherlands. Findings Moderated mediation analyses indicated that mindfulness partly compensates for a low levels of transformational leadership in fostering intrinsic motivation and in turn extra-role performance, thereby providing evidence for the substitutes for leadership theory. Moreover, the findings extend previous research on the contribution of mindfulness to in-role performance by showing its additional value for intrinsic motivation and extra-role performance. Research limitations/implications Despite the use of validated measures and the presence of an interaction effect, common-source bias cannot be out ruled completely. Practical implications - Since mindfulness can be developed, the results suggest a training intervention to make employees less dependent on their leaders for their motivation. Originality/value This paper is the first to show that mindful people are more resilient against the absence of transformational leadership. Given the frequent changes in management layers in organizations, knowledge about resources for individual resilience and self-management is sorely needed
Painleve-Gullstrand Coordinates for the Kerr Solution
We construct a coordinate system for the Kerr solution, based on the zero
angular momentum observers dropped from infinity, which generalizes the
Painleve-Gullstrand coordinate system for the Schwarzschild solution. The Kerr
metric can then be interpreted as describing space flowing on a (curved)
Riemannian 3-manifold. The stationary limit arises as the set of points on this
manifold where the speed of the flow equals the speed of light, and the
horizons as the set of points where the radial speed equals the speed of light.
A deeper analysis of what is meant by the flow of space reveals that the
acceleration of free-falling objects is generally not in the direction of this
flow. Finally, we compare the new coordinate system with the closely related
Doran coordinate system.Comment: 6 pages; v2: new section, matches final published version; v3: sign
error in the expression of the function delta correcte
Micro-macro multilevel latent class models with multiple discrete individual-level variables
An existing micro-macro method for a single individual-level variable is extended to the multivariate situation by presenting two multilevel latent class models in which multiple discrete individual-level variables are used to explain a group-level outcome. As in the univariate case, the individual-level data are summarized at the group-level by constructing a discrete latent variable at the group level and this group-level latent variable is used as a predictor for the group-level outcome. In the first extension, that is referred to as the Direct model, the multiple individual-level variables are directly used as indicators for the group-level latent variable. In the second extension, referred to as the Indirect model, the multiple individual-level variables are used to construct an individual-level latent variable that is used as an indicator for the group-level latent variable. This implies that the individual-level variables are used indirectly at the group-level. The within- and between components of the (co)varn the individual-level variables are independent in the Direct model, but dependent in the Indirect model. Both models are discussed and illustrated with an empirical data example
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