7,213 research outputs found
Practice pointer: Using the new UK-WHO growth charts
The new UK growth charts for children aged 0-4 years (designed using data from the new WHO standards) describe the optimal pattern of growth for all children, rather than the prevailing pattern in the UK (as with previous charts).
The new charts are suitable for all ethnic groups and set breast feeding as the norm.
UK children match the new charts well for length and height, but after age 6 months fewer children will be below the 2nd centile for weight or show weight faltering, and more will be above the 98th centile.
The new charts look different: they have a separate preterm section, no lines between 0 and 2 weeks, and the 50th percentile is no longer emphasised.
The charts give clear instructions on gestational correction, and there is a new chart for infants born before 32 weeks’ gestation.
The instructions advise on when and how to measure and when a measurement or growth pattern is outside the normal range.
The charts include a “look-up” tool for determining the body mass index centile from height and weight centiles without calculation and aid for predicting adult height.
The charts and supporting educational materials can be downloaded from www.growthcharts.rcpch.ac.u
Asymptotic Behaviour of Inhomogeneous String Cosmologies
The asymptotic behaviour at late times of inhomogeneous axion-dilaton
cosmologies is investigated. The space-times considered here admit two abelian
space-like Killing vectors. These space-times evolve towards an anisotropic
universe containing gravitational radiation. Furthermore, a peeling-off
behaviour of the Weyl tensor and the antisymmetric tensor field strength is
found. The relation to the pre-big-bang scenario is briefly discussed.Comment: 15 pages, Late
Distances in inhomogeneous quintessence cosmology
We investigate the properties of cosmological distances in locally
inhomogeneous universes with pressureless matter and dark energy
(quintessence), with constant equation of state. We give exact solutions for
angular diameter distances in theempty beam approximation. In this hypothesis,
the distance-redshift equation is derived fron the multiple lens-plane theory.
The case of a flat universe is considered with particular attention. We show
how this general scheme makes distances degenerate with respect to w_X and the
smoothness parameters, alpha, accounting for the homogeneously distributed
fraction of energy of the i-components. We analyse how this degeneracy
influences the critical redshift where the angular diameter distance takes its
maximum, and put in evidence future prospects for measuring the smoothness
parameter of the pressureless matter, alpha_M.Comment: 24 pages, 9 ps figure
Towards gravitationally assisted negative refraction of light by vacuum
Propagation of electromagnetic plane waves in some directions in
gravitationally affected vacuum over limited ranges of spacetime can be such
that the phase velocity vector casts a negative projection on the time-averaged
Poynting vector. This conclusion suggests, inter alia, gravitationally assisted
negative refraction by vacuum.Comment: 6 page
Evolution of magnetic fields through cosmological perturbation theory
The origin of galactic and extra-galactic magnetic fields is an unsolved
problem in modern cosmology. A possible scenario comes from the idea of these
fields emerged from a small field, a seed, which was produced in the early
universe (phase transitions, inflation, ...) and it evolves in time.
Cosmological perturbation theory offers a natural way to study the evolution of
primordial magnetic fields. The dynamics for this field in the cosmological
context is described by a cosmic dynamo like equation, through the dynamo term.
In this paper we get the perturbed Maxwell's equations and compute the energy
momentum tensor to second order in perturbation theory in terms of gauge
invariant quantities. Two possible scenarios are discussed, first we consider a
FLRW background without magnetic field and we study the perturbation theory
introducing the magnetic field as a perturbation. The second scenario, we
consider a magnetized FLRW and build up the perturbation theory from this
background. We compare the cosmological dynamo like equation in both scenarios
A Riemann-Hilbert Problem for an Energy Dependent Schr\"odinger Operator
\We consider an inverse scattering problem for Schr\"odinger operators with
energy dependent potentials. The inverse problem is formulated as a
Riemann-Hilbert problem on a Riemann surface. A vanishing lemma is proved for
two distinct symmetry classes. As an application we prove global existence
theorems for the two distinct systems of partial differential equations
for suitably restricted,
complementary classes of initial data
- …