81 research outputs found
A new wrinkle on the enhancon
We generalize the basic enhancon solution of Johnson, Peet and Polchinski by
constructing solutions without spherical symmetry. A careful consideration of
boundary conditions at the enhancon surface indicates that the interior of the
supergravity solution is still flat space in the general case. We provide some
explicit analytic solutions where the enhancon locus is a prolate or oblate
sphere.Comment: 19 pages, no figure
Many worlds in one
A generic prediction of inflation is that the thermalized region we inhabit
is spatially infinite. Thus, it contains an infinite number of regions of the
same size as our observable universe, which we shall denote as \O-regions. We
argue that the number of possible histories which may take place inside of an
\O-region, from the time of recombination up to the present time, is finite.
Hence, there are an infinite number of \O-regions with identical histories up
to the present, but which need not be identical in the future. Moreover, all
histories which are not forbidden by conservation laws will occur in a finite
fraction of all \O-regions. The ensemble of \O-regions is reminiscent of
the ensemble of universes in the many-world picture of quantum mechanics. An
important difference, however, is that other \O-regions are unquestionably
real.Comment: 9 pages, 2 figures, comments and references adde
De Sitter and Schwarzschild-De Sitter According to Schwarzschild and De Sitter
When de Sitter first introduced his celebrated spacetime, he claimed,
following Schwarzschild, that its spatial sections have the topology of the
real projective space RP^3 (that is, the topology of the group manifold SO(3))
rather than, as is almost universally assumed today, that of the sphere S^3.
(In modern language, Schwarzschild was disturbed by the non-local correlations
enforced by S^3 geometry.) Thus, what we today call "de Sitter space" would not
have been accepted as such by de Sitter. There is no real basis within
classical cosmology for preferring S^3 to RP^3, but the general feeling appears
to be that the distinction is in any case of little importance. We wish to
argue that, in the light of current concerns about the nature of de Sitter
space, this is a mistake. In particular, we argue that the difference between
"dS(S^3)" and "dS(RP^3)" may be very important in attacking the problem of
understanding horizon entropies. In the approach to de Sitter entropy via
Schwarzschild-de Sitter spacetime, we find that the apparently trivial
difference between RP^3 and S^3 actually leads to very different perspectives
on this major question of quantum cosmology.Comment: 26 pages, 8 figures, typos fixed, references added, equation numbers
finally fixed, JHEP versio
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Rethinking research in breast-feeding: a critique of the evidence base identified in a systematic review of interventions to promote and support breast-feeding
OBJECTIVE
To appraise critically the relevance and value of the evidence base to promote and support the duration of breast-feeding, with a specific focus on disadvantaged groups.
DESIGN
A systematic review was conducted of intervention studies relevant to enhancing the duration of breast-feeding; topics included public health, public policy, clinical issues, and education, training and practice change. A systematic search was conducted. Eighty studies met the inclusion criteria. Data were systematically extracted and analysed. Full results and recommendations are reported elsewhere. Here a critique of the evidence base – topics, quality and gaps – is reported.
RESULTS
Many studies were substantially methodologically flawed, with problems including small sample sizes, inconsistent definitions of breast-feeding and lack of appropriate outcomes. Few were based on relevant theory. Only a small number of included studies (10%) were conducted in the UK. Very few targeted disadvantaged subgroups of women. No studies of policy initiatives or of community interventions were identified. There were virtually no robust studies of interventions to prevent and treat common clinical problems, or of strategies related to women's health issues. Studies of health professional education and practice change were limited. Cost-effectiveness studies were rare.
CONCLUSIONS
Policy goals both in the UK and internationally support exclusive breast-feeding until 6 months of age. The evidence base to enable women to continue to breast-feed needs to be strengthened to include robust evaluations of policies and practices related to breast-feeding; a step change is needed in the quality and quantity of research funded
The Development of multi-axial creep damage constitutive equations for 0.5Cr0.5Mo0.25V ferritic steel at 590.DEG.C..
Within the framework of a phenomenological approach a set of multi-axial creep damage constitutive equations for 0.5Cr0.5Mo0.25V ferritic steel at 590°C is developed in which a new formulation is employed. The deficiency of the previous formulation and the need for improvement became apparent after a critical review of the development of creep damage constitutive equations for 316 stainless steel(1). The need for improvement was further underpinned by a call for modification of the constitutive equations(36). Recently, a specific formulation was proposed and validated(2)-(4). This paper reports the latest developments of the multi-axial creep constitutive equations for 0.5Cr0.5Mo0.25V ferritic steel at 590°C including: 1) the fundamental requirement; 2) formulation; 3) validation; and 4) conclusion. It systematically shows the suitability of this new set of constitutive equations and the incapability of the previous ones. Furthermore, it contributes knowledge to the methodolog
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