4,589 research outputs found
Liberating the NHS; commissioning, outsourcing and a new politics debate
In the short months following the result of the UK 2010 General election,
a new Government White Paper has been released entitled: Equity and
Excellence: Liberating the NHS (Department of Health (DH), 2010a). It strives
to distance itself from previous health-care proposals (DH, 2009), yet if the
initiatives of this latest paper are combined against previous initiatives,
also using high impact declarative terms, such as competition and choice,
it is clear that little has changed and more important principles than saving
money are at risk
Cosmic String Power Spectrum, Bispectrum and Trispectrum
We use analytic calculations of the post-recombination gravitational effects
of cosmic strings to estimate the resulting CMB power spectrum, bispectrum and
trispectrum. We place a particular emphasis on multipole regimes relevant for
forthcoming CMB experiments, notably the Planck satellite. These calculations
use a flat sky approximation, generalising previous work by integrating string
contributions from last scattering to the present day, finding the dominant
contributions to the correlators for multipoles l > 50. We find a well-behaved
shape for the string bispectrum (without divergences) which is easily
distinguishable from the inflationary bispectra which possess significant
acoustic peaks. We estimate that the nonlinearity parameter characterising the
bispectrum is approximately f_NL \sim -20 (given present string constraints
from the CMB power spectrum. We also apply these unequal time correlator
methods to calculate the trispectrum for parrallelogram configurations, again
valid over a large range of angular scales relevant for WMAP and Planck, as
well as on very small angular scales. We find that, unlike the bispectrum which
is suppressed by symmetry considerations, the trispectrum for cosmic strings is
large. Our current estimate for the trispectrum parameter is tau_NL \sim 10^5,
which may provide one of the strongest constraints on the string model as
estimators for the trispectrum are developed
Recommended from our members
Effective classroom practice: a mixed-method study of influences and outcomes: a research paper
This brief paper reports findings from a two-year research project, funded by the ESRC, which identified, described and analyzed variation in effective primary and secondary school teachers’ classroom practice. The study also explored these practices in relation to different school contexts and teachers’ professional life phases in order to draw out relevant implications for policy and practice
A critical commentary on management science in relation to reforms following institutional National Health Service failures
Aim(s): A discussion paper on the United Kingdom (UK) National Health Service (NHS) market reforms. Background: NHS market reforms reliance on management science methods introduced a fundamental shift in measuring care for commissioning purposes rather than what actually counts such as putting patients first, maintaining a generosity of purpose and social philosophy. Evaluation: A number of key reports are discussed in relation to NHS market reforms and management science. Key issues: NHS market reforms were influenced through a close alliance between policy makers, the department of health, free market think tanks and management consultancies. The timing of reforms coincided with reports on NHS failings and the evolution of measurement methods to focus on finance. Conclusions: The balance in favour of measurement practises is of concern. Management science methods are criticised in the Francis report yet promoted as the solution to some of the key findings; why may be explained by the close alliance. Implications for Nursing Management: A return to principles of management involving consensus, trust, involvement in which a shared vision and a can do, hands on approach to management would be valued in the drive to promote quality care and use management science methods to this end
General CMB and Primordial Trispectrum Estimation
We present trispectrum estimation methods which can be applied to general
non-separable primordial and CMB trispectra. We present a general optimal
estimator for the connected part of the trispectrum, for which we derive a
quadratic term to incorporate the effects of inhomogeneous noise and masking.
We describe a general algorithm for creating simulated maps with given
arbitrary (and independent) power spectra, bispectra and trispectra. We propose
a universal definition of the trispectrum parameter , so that the
integrated bispectrum on the observational domain can be consistently compared
between theoretical models. We define a shape function for the primordial
trispectrum, together with a shape correlator and a useful parametrisation for
visualizing the trispectrum. We derive separable analytic CMB solutions in the
large-angle limit for constant and local models. We present separable mode
decompositions which can be used to describe any primordial or CMB bispectra on
their respective wavenumber or multipole domains. By extracting coefficients of
these separable basis functions from an observational map, we are able to
present an efficient estimator for any given theoretical model with a
nonseparable trispectrum. The estimator has two manifestations, comparing the
theoretical and observed coefficients at either primordial or late times. These
mode decomposition methods are numerically tractable with order
operations for the CMB estimator and approximately order for the general
primordial estimator (reducing to order in both cases for a special class
of models). We also demonstrate how the trispectrum can be reconstructed from
observational maps using these methods.Comment: 38 pages, 9 figures. In v2 Figures 4-7 are altered slightly and some
extra references are included in the bibliography. v3 matches version
submitted to journal. Includes discussion of special case
Rapid Separable Analysis of Higher Order Correlators in Large Scale Structure
We present an efficient separable approach to the estimation and
reconstruction of the bispectrum and the trispectrum from observational (or
simulated) large scale structure data. This is developed from general CMB
(poly-)spectra methods which exploit the fact that the bispectrum and
trispectrum in the literature can be represented by a separable mode expansion
which converges rapidly (with terms). With an
effective grid resolution (number of particles/grid points
), we present a bispectrum estimator which requires only
operations, along with a
corresponding method for direct bispectrum reconstruction. This method is
extended to the trispectrum revealing an estimator which requires only operations. The complexity in
calculating the trispectrum in this method is now involved in the original
decomposition and orthogonalisation process which need only be performed once
for each model. However, for non-diagonal trispectra these processes present
little extra difficulty and may be performed in
operations. A discussion of how the methodology may be applied to the
quadspectrum is also given. An efficient algorithm for the generation of
arbitrary nonGaussian initial conditions for use in N-body codes using this
separable approach is described. This prescription allows for the production of
nonGaussian initial conditions for arbitrary bispectra and trispectra. A brief
outline of the key issues involved in parameter estimation, particularly in the
non-linear regime, is also given
Universal Non-Gaussian Initial Conditions for N-body Simulations
In this paper we present the implementation of an efficient formalism for the
generation of arbitrary non-Gaussian initial conditions for use in N-body
simulations. The methodology involves the use of a separable modal approach for
decomposing a primordial bispectrum or trispectrum. This approach allows for
the far more efficient generation of the non-Gaussian initial conditions
already described in the literature, as well as the generation for the first
time of non-separable bispectra and the special class of diagonal-free
trispectra. The modal approach also allows for the reconstruction of the
spectra from given realisations, a fact which is exploited to provide an
accurate consistency check of the simulations.Comment: 7 pages, 3 figure
Microscopic Surface Structure of Liquid Alkali Metals
We report an x-ray scattering study of the microscopic structure of the
surface of a liquid alkali metal. The bulk liquid structure factor of the
eutectic K67Na33 alloy is characteristic of an ideal mixture, and so shares the
properties of an elemental liquid alkali metal. Analysis of off-specular
diffuse scattering and specular x-ray reflectivity shows that the surface
roughness of the K-Na alloy follows simple capillary wave behavior with a
surface structure factor indicative of surface induced layering. Comparison of
thelow-angle tail of the K67Na33 surface structure factor with the one measured
for liquid Ga and In previously suggests that layering is less pronounced in
alkali metals. Controlled exposure of the liquid to H2 and O2 gas does not
affect the surface structure, indicating that oxide and hydride are not stable
at the liquid surface under these experimental conditions.Comment: 12 pages, 3 figures, published in Phys. Rev.
- …