9,449 research outputs found
A point mass in an isotropic universe: III. The region
McVittie's solution of Einstein's field equations, representing a point mass
embedded into an isotropic universe, possesses a scalar curvature singularity
at proper radius . The singularity is space-like and precedes, in the
expanding case, all other events in the space-time. It is shown here that this
singularity is gravitationally weak, and the possible structure of the region
is investigated. A characterization of this solution which does not
involve asymptotics is given.Comment: Revtex, 11pp. To appear in Class.Quant.Grav. Paper II appeared as
Class. Quant. Grav. 16 (1999) 122
Health-related quality of life in the WA HIV Cohort: 2008
Quality of life (QOL) is an important outcome of HIV treatment and a priority in the management of HIV. A new Patient-Reported Outcomes (PRO) questionnaire to measure the QOL in people living with HIV/AIDS (PLWHA) from different cultures and language groups has been developed. The instrument, PROQOL-HIV, has undergone psychometric validation in 791 individuals from 8 countries including 99 people from the WA HIV Cohort Study
Expansion-induced contribution to the precession of binary orbits
We point out the existence of new effects of global spacetime expansion on
local binary systems. In addition to a possible change of orbital size, there
is a contribution to the precession of elliptic orbits, to be added to the
well-known general relativistic effect in static spacetimes, and the
eccentricity can change. Our model calculations are done using geodesics in a
McVittie metric, representing a localized system in an asymptotically
Robertson-Walker spacetime; we give a few numerical estimates for that case,
and indicate ways in which the model should be improved.Comment: revtex, 7 pages, no figures; revised for publication in Classical and
Quantum Gravity, with minor changes in response to referees' comment
Odd-parity perturbations of self-similar Vaidya spacetime
We carry out an analytic study of odd-parity perturbations of the
self-similar Vaidya space-times that admit a naked singularity. It is found
that an initially finite perturbation remains finite at the Cauchy horizon.
This holds not only for the gauge invariant metric and matter perturbation, but
also for all the gauge invariant perturbed Weyl curvature scalars, including
the gravitational radiation scalars. In each case, `finiteness' refers to
Sobolev norms of scalar quantities on naturally occurring spacelike
hypersurfaces, as well as pointwise values of these quantities.Comment: 28 page
Radiant measurement accuracy of micrometeors detected by the Arecibo 430 MHz dual-beam radar
International audiencePrecise knowledge of the angle between the meteor vector velocity and the radar beam axis is one of the largest source of errors in the Arecibo Observatory (AO) micrometeor observations. In this paper we study ~250 high signal-to-noise ratio (SNR) meteor head-echoes obtained using the dual-beam 430 MHz AO Radar in Puerto Rico, in order to reveal the distribution of this angle. All of these meteors have been detected first by the radar first side lobe, then by the main beam and finally seen in the side lobe again. Using geometrical arguments to calculate the meteor velocity in the plane perpendicular to the beam axis, we find that most of the meteors are travelling within ~15° with respect to the beam axis, in excellent agreement with previous estimates. These results suggest that meteoroids entering the atmosphere at greater angles may deposit their meteoric material at higher altitudes explaining at some level the missing mass inconsistency raised by the comparisson of meteor fluxes derived from satellite and radar observations. They also may be the source of the observed high altitude ions and metallic layers observed by radars and lidars respectively
Patient reactions to a web-based cardiovascular risk calculator in type 2 diabetes: a qualitative study in primary care.
Use of risk calculators for specific diseases is increasing, with an underlying assumption that they promote risk reduction as users become better informed and motivated to take preventive action. Empirical data to support this are, however, sparse and contradictory
Bulk and surface energetics of lithium hydride crystal: benchmarks from quantum Monte Carlo and quantum chemistry
We show how accurate benchmark values of the surface formation energy of
crystalline lithium hydride can be computed by the complementary techniques of
quantum Monte Carlo (QMC) and wavefunction-based molecular quantum chemistry.
To demonstrate the high accuracy of the QMC techniques, we present a detailed
study of the energetics of the bulk LiH crystal, using both pseudopotential and
all-electron approaches. We show that the equilibrium lattice parameter agrees
with experiment to within 0.03 %, which is around the experimental uncertainty,
and the cohesive energy agrees to within around 10 meV per formula unit. QMC in
periodic slab geometry is used to compute the formation energy of the LiH (001)
surface, and we show that the value can be accurately converged with respect to
slab thickness and other technical parameters. The quantum chemistry
calculations build on the recently developed hierarchical scheme for computing
the correlation energy of a crystal to high precision. We show that the
hierarchical scheme allows the accurate calculation of the surface formation
energy, and we present results that are well converged with respect to basis
set and with respect to the level of correlation treatment. The QMC and
hierarchical results for the surface formation energy agree to within about 1
%.Comment: 16 pages, 4 figure
Supporting direct care workers in dementia care: effects of a psycho-educational intervention
YesAn experimental study using a pre-posttest control group design was conducted to assess the effects of a person-centred care based psycho-educational intervention on direct care workers’ stress, burnout and job satisfaction. The intervention aimed to develop person-centred care competences and tools for stress management. Four aged care facilities were randomly assigned to a psycho-educational or an education-only intervention (control). Data were collected from fifty-six direct care workers (female, mean age 44.72±9.02) through measurements of burnout (Maslach Burnout Inventory), job satisfaction (Minnesota Satisfaction Questionnaire-short form) and stress (Perceived Stress Scale) and focus-group interviews. Results showed significant positive effects in emotional exhaustion (p=0.029) and positive but no significant effects in stress and job satisfaction. According to qualitative data, the experimental group perceived enhanced group cohesion, emotional management and self-care awareness. Psycho-educational interventions may contribute to reduce direct care workers’ burnout. Further work is needed to determine the extent of its benefits.Portuguese Foundation for Science and Technolog
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