6,969 research outputs found
Tributes to Professor Cyril A. Fox, Jr.
Cy Fox often forgets that he was supposed to be “only” an academic. For three decades, as he helped thousands of law students through the intricacies of the Rule in Shelley’s Case, or watched them calculate a “life in being plus twenty one years” for the Rule Against Perpetuities, he failed to appreciate that law school was supposed to be an amalgam of theory and confusion, not the place for his teaching law students about helping real people solve real life problems
A New Generalized Harmonic Evolution System
A new representation of the Einstein evolution equations is presented that is
first order, linearly degenerate, and symmetric hyperbolic. This new system
uses the generalized harmonic method to specify the coordinates, and
exponentially suppresses all small short-wavelength constraint violations.
Physical and constraint-preserving boundary conditions are derived for this
system, and numerical tests that demonstrate the effectiveness of the
constraint suppression properties and the constraint-preserving boundary
conditions are presented.Comment: Updated to agree with published versio
Item Wording and Internal Consistency of a Measure of Cohesion: The Group Environment Questionnaire
A common practice for counteracting response acquiescence in psychological measures has been to employ both negatively and positively worded items. However, previous research has highlighted that the reliability of measures can be affected by this practice (Spector, 1992). The purpose of the present study was to examine the effect that the presence of negatively worded items has on the internal reliability of the Group Environment Questionnaire (GEQ). Two samples (N = 276) were utilized, and participants were asked to complete the GEQ (original and revised) on separate occasions. Results demonstrated that the revised questionnaire (containing all positively worded items) had significantly higher Cronbach α values for three of the four dimensions of the GEQ. Implications, alternatives, and future directions are discussed
Conceptualising the policy practice and behavioural research relationship
BackgroundPolicy is frequently identified in the behavioural nutrition and physical activity research literature as a necessary component of effective research and practice. The purpose of this commentary is to promote a dialogue to contribute towards the further development of conceptual understandings and theories of the relationship between policy practice and behavioural research and how these two activities might work synergistically to improve public health outcomes.MethodsDrawing on policy and public health literature, this commentary presents a a conceptual model of the interaction and mediation between nutrition and physical activity-relevant policy and behavioural nutrition and physical activity research, environments, behaviours and public health implications. The selling of food in school canteens in several Australian states is discussed to illustrate components of the relationship and the interactions among its components.ResultsThe model depicts a relationship that is interdependent and cyclic. Policy contributes to the relationship through its role in shaping environmental and personal-cognitive determinants of behaviours and through these determinants it can induce behaviour change. Behavioural research describes behaviours, identifies determinants of behaviour change and therefore helps inform policy development and monitor and evaluate its impact.ConclusionThe model has implications for guiding behavioural research and policy practice priorities to promote public health outcomes. In particular, we propose that policy practice and behavioural research activities can be strengthened by applying to each other the theories from the scientific disciplines informing these respective activities. Behavioural science theories can be applied to help understand policy-making and assist with disseminating research into policy and practice. In turn, policy science theories can be applied to support the \u27institutionalisation\u27 of commitments to ongoing behavioural research.<br /
Black hole evolution by spectral methods
Current methods of evolving a spacetime containing one or more black holes
are plagued by instabilities that prohibit long-term evolution. Some of these
instabilities may be due to the numerical method used, traditionally finite
differencing. In this paper, we explore the use of a pseudospectral collocation
(PSC) method for the evolution of a spherically symmetric black hole spacetime
in one dimension using a hyperbolic formulation of Einstein's equations. We
demonstrate that our PSC method is able to evolve a spherically symmetric black
hole spacetime forever without enforcing constraints, even if we add dynamics
via a Klein-Gordon scalar field. We find that, in contrast to
finite-differencing methods, black hole excision is a trivial operation using
PSC applied to a hyperbolic formulation of Einstein's equations. We discuss the
extension of this method to three spatial dimensions.Comment: 20 pages, 17 figures, submitted to PR
Illness perceptions of leprosy-cured individuals in Surinam with residual disfigurements – “I am cured, but still I am ill”
Objective Leprosy has rarely been the subject of health psychology research despite its substantial impact. Our aim was to explore illness perceptions in patients and their health care providers in Surinam. The Common Sense Model (CSM) was the guiding theoretical model. Design Patients with biomedically cured leprosy and their health care providers completed the B-IPQ and took part in semi-structured interviews. The literature on illness perceptions in patients with leprosy was reviewed. Main outcome measures Patients’ B-IPQ scores were compared with samples of patients with other (chronic) illnesses, and with health care providers completing the questionnaire as if they were visibly disfigured patients. Quotations from the semi-structured interviews were used to contextualise the illness perceptions. Results Patients’ B-IPQ scores reflected the chronic nature of leprosy and were comparable with those with other chronic illnesses. Health care providers perceived leprosy to have a greater negative impact than did the patients. Perceived understanding of causes differed considerably between patients and health care providers. Conclusion Leprosy continues to be experienced as an illness with major psychological and social consequences such as stigmatisation, even after biomedical cure. Interventions that target patients, health care providers, and society at large may help reduce perceived shame and stigma. The CSM is a helpful theoretical model in studying this population. </jats:sec
Black hole-neutron star mergers for 10 solar mass black holes
General relativistic simulations of black hole-neutron star mergers have
currently been limited to low-mass black holes (less than 7 solar mass), even
though population synthesis models indicate that a majority of mergers might
involve more massive black holes (10 solar mass or more). We present the first
general relativistic simulations of black hole-neutron star mergers with 10
solar mass black holes. For massive black holes, the tidal forces acting on the
neutron star are usually too weak to disrupt the star before it reaches the
innermost stable circular orbit of the black hole. Varying the spin of the
black hole in the range a/M = 0.5-0.9, we find that mergers result in the
disruption of the star and the formation of a massive accretion disk only for
large spins a/M>0.7-0.9. From these results, we obtain updated constraints on
the ability of BHNS mergers to be the progenitors of short gamma-ray bursts as
a function of the mass and spin of the black hole. We also discuss the
dependence of the gravitational wave signal on the black hole parameters, and
provide waveforms and spectra from simulations beginning 7-8 orbits before
merger.Comment: 11 pages, 11 figures - Updated to match published versio
Controlling the growth of constraints in hyperbolic evolution systems
Motivated by the need to control the exponential growth of constraint violations in numerical solutions of the Einstein evolution equations, two methods are studied here for controlling this growth in general hyperbolic evolution systems. The first method adjusts the evolution equations dynamically, by adding multiples of the constraints, in a way designed to minimize this growth. The second method imposes special constraint preserving boundary conditions on the incoming components of the dynamical fields. The efficacy of these methods is tested by using them to control the growth of constraints in fully dynamical 3D numerical solutions of a particular representation of the Maxwell equations that is subject to constraint violations. The constraint preserving boundary conditions are found to be much more effective than active constraint control in the case of this Maxwell system
Impact of an improved neutrino energy estimate on outflows in neutron star merger simulations
Binary neutron star mergers are promising sources of gravitational waves for
ground-based detectors such as Advanced LIGO. Neutron-rich material ejected by
these mergers may also be the main source of r-process elements in the
Universe, while radioactive decays in the ejecta can power bright
electromagnetic post-merger signals. Neutrino-matter interactions play a
critical role in the evolution of the composition of the ejected material,
which significantly impacts the outcome of nucleosynthesis and the properties
of the associated electromagnetic signal. In this work, we present a simulation
of a binary neutron star merger using an improved method for estimating the
average neutrino energies in our energy-integrated neutrino transport scheme.
These energy estimates are obtained by evolving the neutrino number density in
addition to the neutrino energy and flux densities. We show that significant
changes are observed in the composition of the polar ejecta when comparing our
new results with earlier simulations in which the neutrino spectrum was assumed
to be the same everywhere in optically thin regions. In particular, we find
that material ejected in the polar regions is less neutron rich than previously
estimated. Our new estimates of the composition of the polar ejecta make it
more likely that the color and timescale of the electromagnetic signal depend
on the orientation of the binary with respect to an observer's line-of-sight.
These results also indicate that important observable properties of neutron
star mergers are sensitive to the neutrino energy spectrum, and may need to be
studied through simulations including a more accurate, energy-dependent
neutrino transport scheme.Comment: 19p, 17 figures, Accepted by Phys.Rev.
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