Killing spinor data on distorted black hole horizons and the uniqueness of stationary vacuum black holes

We make use of the black hole holograph construction of [I. R\'acz, Stationary black holes as holographs, Class. Quantum Grav. 31, 035006 (2014)] to analyse the existence of Killing spinors in the domain of dependence of the horizons of distorted black holes. In particular, we provide conditions on the bifurcation sphere ensuring the existence of a Killing spinor. These conditions can be understood as restrictions on the curvature of the bifurcation sphere and ensure the existence of an axial Killing vector on the 2-surface. We obtain the most general 2-dimensional metric on the bifurcation sphere for which these curvature conditions are satisfied. Remarkably, these conditions are found to be so restrictive that, in the considered particular case, the free data on the bifurcation surface (determining a distorted black hole spacetime) is completely determined by them. In addition, we formulate further conditions on the bifurcation sphere ensuring that the Killing vector associated to the Killing spinor is Hermitian. Once the existence of a Hermitian Killing vector is guaranteed, one can use a characterisation of the Kerr spacetime due to Mars to identify the particular subfamily of 2-metrics giving rise to a member of the Kerr family in the black hole holograph construction. Our analysis sheds light on the role of asymptotic flatness and curvature conditions on the bifurcation sphere in the context of the problem of uniqueness of stationary black holes. The Petrov type of the considered distorted black hole spacetimes is also determined.Comment: 39 pages, 1 figur

Selective cerebral hypothermia for post-hypoxic neuroprotection in neonates using a solid ice cap

No Abstract. South African Medical Journal Vol. 96(9) (Part 2) 2006: 976-98

Precarious employment amidst global crises:Career shocks, resources and migrants' employability

PurposeThe authors conducted 22 in-depth longitudinal interviews with 11 Hungarian migrant workers in the Dutch logistics sector, before and during the COVID-19 crisis, using thematic analysis and visual life diagrams to interpret them.Design/methodology/approachThis study aims to contribute to conservation of resources theory, by exploring how global crises influence the perceived employability of migrant workers in low-wage, precarious work.FindingsThe authors find that resources are key in how migrants experience the valence of global crises in their careers and perceive their employability. When unforeseen consequences of the COVID-19 crisis coincided with migrants' resource gain spirals, this instigated a positively valenced career shock, leading to positive perceptions of employability. Coincidence with loss spirals led to negative perceptions.Research limitations/implicationsThe authors contribute to careers literature by showing that resources do not only help migrants cope with the impact of career shocks but also directly influence the valence of global crises in their perceived employability and careers.Originality/valueInterestingly, when the COVID-19 crisis did not co-occur with migrants' resource gain and loss spirals, migrants experienced resource stress (psychological strain induced by the threat or actual loss of resources) and no significant change in their perceptions of employability

Testing the assumptions of linear prediction analysis in normal vowels

This paper develops an improved surrogate data test to show experimental evidence, for all the simple vowels of US English, for both male and female speakers, that Gaussian linear prediction analysis, a ubiquitous technique in current speech technologies, cannot be used to extract all the dynamical structure of real speech time series. The test provides robust evidence undermining the validity of these linear techniques, supporting the assumptions of either dynamical nonlinearity and/or non-Gaussianity common to more recent, complex, efforts at dynamical modelling speech time series. However, an additional finding is that the classical assumptions cannot be ruled out entirely, and plausible evidence is given to explain the success of the linear Gaussian theory as a weak approximation to the true, nonlinear/non-Gaussian dynamics. This supports the use of appropriate hybrid linear/nonlinear/non-Gaussian modelling. With a calibrated calculation of statistic and particular choice of experimental protocol, some of the known systematic problems of the method of surrogate data testing are circumvented to obtain results to support the conclusions to a high level of significance

On the non-linear stability of scalar field cosmologies

We review recent work on the stability of flat spatially homogeneous and isotropic backgrounds with a self-interacting scalar field. We derive a first order quasi-linear symmetric hyperbolic system for the Einstein-nonlinear-scalar field system. Then, using the linearized system, we show how to obtain necessary and sufficient conditions which ensure the exponential decay to zero of small non-linear perturbations.JAVK was supported by an EPSRC Advanced Research Fellowship and by a project research grant from the Leverhulme Trust (F/07 476/AI). AA and FM are supported by projects FCT/PTDC/MAT/108921/2008 and CERN/FP/116377/2010 and by CMAT, Univ. Minho, through FCT plurianual funding. AA thanks FCT grant SFRH/BD/48658/2008. FM thanks FCT grant SFRH/BSAB/967/2010