5,081 research outputs found
Isotropic cosmological singularities 1: Polytropic perfect fluid spacetimes
We consider the conformal Einstein equations for polytropic perfect fluid
cosmologies which admit an isotropic singularity. For the polytropic index
gamma strictly greater than 1 and less than or equal to 2 it is shown that the
Cauchy problem for these equations is well-posed, that is to say that solutions
exist, are unique and depend smoothly on the data, with data consisting of
simply the 3-metric of the singularity. The analogous result for gamma=1 (dust)
is obtained when Bianchi type symmetry is assumed.Comment: LaTeX, 43 pages, no figures, submitted to Ann. Phy
Can a nudge keep you warm? Using nudges to reduce excess winter deaths: insight from the Keeping Warm in Later Life Project (KWILLT)
Nudges are interventions that aim to change people's behaviour through changing the environment in which they choose rather than appealing to their reasoning. Nudges have been proposed as of possible use in relation to health-related behaviour. However, nudges have been criticized as ethically dubious because they bypass peoples reasoning and (anyway) are of little help in relation to affecting ill-health that results from social determinants, such as poverty. Reducing the rate of excess winter deaths (EWDs) is a public health priority; however, EWD seems clearly to be socially determined such that nudges arguably have little role. This article defends two claims: (i) nudges could have a place in tackling even the heavily socially determined problem of EWD. We draw on evidence from an empirical study, the Keeping Warm in Later Life Project (KWILLT), to argue that in some cases the risk of cold is within the personâs control to some extent such that environmental modifications to influence behaviour such as nudges are possible. (ii) Some uses of behavioural insights in the form of nudges are acceptable, including some in the area of EWD. We suggest a question-based framework by which to judge the ethical acceptability of nudges
On the Weyl Curvature Hypothesis
The Weyl curvature hypothesis of Penrose attempts to explain the high
homogeneity and isotropy, and the very low entropy of the early universe, by
conjecturing the vanishing of the Weyl tensor at the Big-Bang singularity.
In previous papers it has been proposed an equivalent form of Einstein's
equation, which extends it and remains valid at an important class of
singularities (including in particular the Schwarzschild, FLRW, and isotropic
singularities). Here it is shown that if the Big-Bang singularity is from this
class, it also satisfies the Weyl curvature hypothesis.
As an application, we study a very general example of cosmological models,
which generalizes the FLRW model by dropping the isotropy and homogeneity
constraints. This model also generalizes isotropic singularities, and a class
of singularities occurring in Bianchi cosmologies. We show that the Big-Bang
singularity of this model is of the type under consideration, and satisfies
therefore the Weyl curvature hypothesis.Comment: 10 pages, slides at
http://www.sciencedirect.com/science/article/pii/S000349161300171
Analyticity of strictly static and strictly stationary, inheriting and non-inheriting Einstein-Maxwell solutions
Following the technique of M\"uller-zum-Hagen, refs [1,2], we show that
strictly static and strictly stationary solutions of the Einstein-Maxwell
equations are analytic in harmonic coordinates. This holds whether or not the
Maxwell field inherits the symmetry.Comment: 11 pages; to appear in Gen.Rel.Gra
Trace metals in common marine foods of the Pacific Coast
Trace metal analysis of 23 species of common Pacific Coast marine foods revealed high cadmium values for Bent-nosed clams (Macoma nasuta), Bay mussels (Mytilus edulis), Bay oysters (Osrtrea lurida), Pacific oysters (Crassostrea gigas), and Littleneck clams (Protothaca staminea). Metals were found to concentrate in the gills, heart, and visceral mass of all 10 species of bivalve mollusks examined. Swordfish (Xiphias gladius) and Salmon (Oncorhynchus tshawytscha) demonstrated the highest cadmium values for fish flesh
The geometry of the Toda equation
I show that solutions of the SU(infinity) Toda field equation generating a
fixed Einstein-Weyl space are governed by a linear equation on the
Einstein-Weyl space. From this, obstructions to the existence of Toda solutions
generating a given Einstein-Weyl space are found. I also give a classification
of Einstein-Weyl spaces arising from the Toda equation in more than one way.
This classification coincides with a class of spaces found by Ward and hence
clarifies some of their properties. I end by discussing the simplest examples.Comment: AMS-LaTeX 11 pages; minor changes to title, keywords and reference
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