The Medicare Physician Group Practice Demonstration: Lessons Learned on Improving Quality and Efficiency in Health Care

Discusses the experiences of ten large practices earning performance payments for improving the quality and cost-efficiency of health care delivered to Medicare fee-for-service beneficiaries

Equation-free implementation of statistical moment closures

We present a general numerical scheme for the practical implementation of statistical moment closures suitable for modeling complex, large-scale, nonlinear systems. Building on recently developed equation-free methods, this approach numerically integrates the closure dynamics, the equations of which may not even be available in closed form. Although closure dynamics introduce statistical assumptions of unknown validity, they can have significant computational advantages as they typically have fewer degrees of freedom and may be much less stiff than the original detailed model. The closure method can in principle be applied to a wide class of nonlinear problems, including strongly-coupled systems (either deterministic or stochastic) for which there may be no scale separation. We demonstrate the equation-free approach for implementing entropy-based Eyink-Levermore closures on a nonlinear stochastic partial differential equation.Comment: 7 pages, 2 figure

Star Formation and AGN Activity in Galaxy Clusters from z=1−2z=1-2: a Multi-wavelength Analysis Featuring HerschelHerschel/PACS

We present a detailed, multi-wavelength study of star formation (SF) and AGN activity in 11 near-infrared (IR) selected, spectroscopically confirmed, massive ($\gtrsim10^{14}\,\rm{M_{\odot}}$) galaxy clusters at $1<z<1.75$. Using new, deep $Herschel$/PACS imaging, we characterize the optical to far-IR spectral energy distributions (SEDs) for IR-luminous cluster galaxies, finding that they can, on average, be well described by field galaxy templates. Identification and decomposition of AGN through SED fittings allows us to include the contribution to cluster SF from AGN host galaxies. We quantify the star-forming fraction, dust-obscured SF rates (SFRs), and specific-SFRs for cluster galaxies as a function of cluster-centric radius and redshift. In good agreement with previous studies, we find that SF in cluster galaxies at $z\gtrsim1.4$ is largely consistent with field galaxies at similar epochs, indicating an era before significant quenching in the cluster cores ($r<0.5\,$Mpc). This is followed by a transition to lower SF activity as environmental quenching dominates by $z\sim1$. Enhanced SFRs are found in lower mass ($10.1< \log \rm{M_{\star}}/\rm{M_{\odot}}<10.8$) cluster galaxies. We find significant variation in SF from cluster-to-cluster within our uniformly selected sample, indicating that caution should be taken when evaluating individual clusters. We examine AGN in clusters from $z=0.5-2$, finding an excess AGN fraction at $z\gtrsim1$, suggesting environmental triggering of AGN during this epoch. We argue that our results $-$ a transition from field-like to quenched SF, enhanced SF in lower mass galaxies in the cluster cores, and excess AGN $-$ are consistent with a co-evolution between SF and AGN in clusters and an increased merger rate in massive haloes at high redshift.Comment: 26 pages, 14 figures, 6 tables with appendix, accepted for publication in the Astrophysical Journa

Branes on the Brane

We show that four-dimensional N=2 ungauged Einstein-Maxwell supergravity can be embedded on the Randall-Sundrum 3-brane, as a consistent Kaluza-Klein reduction of five-dimensional N=4 gauged supergravity. In particular, this allows us to describe four-dimensional Reissner-Nordstrom black holes within the Randall-Sundrum scenario. Using earlier results on the embedding of five-dimensional N=4 gauged supergravity in ten dimensions, we can then describe the four-dimensional Einstein-Maxwell supergravity on the 3-brane, and its solutions, from a type IIB viewpoint. We also show that the minimal ungauged supergravities in D=5 and D=6 can be consistently embedded in the half-maximally supersymmetric gauged supergravities in D=6 and D=7 respectively. These allow us to construct solutions including BPS black holes and strings living in "Randall-Sundrum 4-branes," and BPS self-dual strings living in "Randall-Sundrum 5-branes." We can also lift the embeddings to ten-dimensional massive type IIA and D=11 supergravity respectively. In particular, we obtain a solution describing the self-dual string living in the world-volume of an M5-brane, which can be viewed as an open membrane ending on the M5-brane.Comment: Latex, 19 pages. Comments added and typos correcte

The evolution of dust-obscured star formation activity in galaxy clusters relative to the field over the last 9 billion years

We compare the star formation (SF) activity in cluster galaxies to the field from z=0.3-1.5 using $Herschel$ SPIRE 250$\mu$m imaging. We utilize 274 clusters from the IRAC Shallow Cluster Survey (ISCS) selected as rest-frame near-infrared overdensities over the 9 square degree Bootes field . This analysis allows us to quantify the evolution of SF in clusters over a long redshift baseline without bias against active cluster systems. Using a stacking analysis, we determine the average star formation rates (SFRs) and specific-SFRs (SSFR=SFR/M$_{\star}$) of stellar mass-limited (M>1.3x10$^{10}$ M$_{\odot}$), statistical samples of cluster and field galaxies, probing both the star forming and quiescent populations. We find a clear indication that the average SF in cluster galaxies is evolving more rapidly than in the field, with field SF levels at z>1.2 in the cluster cores (r<0.5 Mpc), in good agreement with previous ISCS studies. By quantifying the SF in cluster and field galaxies as an exponential function of cosmic time, we determine that cluster galaxies are evolving ~2 times faster than the field. Additionally, we see enhanced SF above the field level at z~1.4 in the cluster outskirts (r>0.5 Mpc). These general trends in the cluster cores and outskirts are driven by the lower mass galaxies in our sample. Blue cluster galaxies have systematically lower SSFRs than blue field galaxies, but otherwise show no strong differential evolution with respect to the field over our redshift range. This suggests that the cluster environment is both suppressing the star formation in blue galaxies on long time-scales and rapidly transitioning some fraction of blue galaxies to the quiescent galaxy population on short time-scales. We argue that our results are consistent with both strangulation and ram pressure stripping acting in these clusters, with merger activity occurring in the cluster outskirts.Comment: 23 pages, 11 figures, 5 tables. Accepted for publication in MNRA

Perceptions of healthcare professionals and managers regarding the effectiveness of GP-led walk-in centres in the UK.

OBJECTIVES: This study aimed to identify the perceptions of healthcare professionals regarding the effectiveness and the impact of a new general practitioner-led (GP-led) walk-in centre in the UK. SETTING: This qualitative study was conducted in a large city in the North of England. In the past few years, there has been particular concern about an increase in the use of emergency department (ED) services provided by the National Health Service and part of the rationale for introducing the new GP-led walk-in centres has been to stem this increase. The five institutes included in the study were EDs, a minor injuries unit, a primary care trust, a GP-led walk-in centre and GP surgeries. PARTICIPANTS: Semistructured interviews were conducted with healthcare providers at an adult ED, an ED at a children's hospital, a minor injuries unit, a GP-led walk-in centre, GPs from surrounding surgeries and GPs. RESULTS: 11 healthcare professionals and managers were interviewed. Seven key themes were identified within the data: the clinical model of the GP-led walk-in centre; public awareness of the services; appropriate use of the centre; the impact of the centre on other services; demand for healthcare services; choice and confusion and mixed views (positive and negative) of the walk-in services. There were discrepancies between the managers and healthcare professionals regarding the usefulness of the GP-led walk-in centre in the current urgent care system. CONCLUSIONS: Participants did not notice declines in the demand for EDs after the GP-led walk-in centre. Most of the healthcare professionals believed that the GP-led walk-in centre duplicated existing healthcare services. There is a need to have a better communication system between the GP-led walk-in centres and other healthcare providers to have an integrated system of urgent care delivery

Matrix exponential-based closures for the turbulent subgrid-scale stress tensor

Two approaches for closing the turbulence subgrid-scale stress tensor in terms of matrix exponentials are introduced and compared. The first approach is based on a formal solution of the stress transport equation in which the production terms can be integrated exactly in terms of matrix exponentials. This formal solution of the subgrid-scale stress transport equation is shown to be useful to explore special cases, such as the response to constant velocity gradient, but neglecting pressure-strain correlations and diffusion effects. The second approach is based on an Eulerian-Lagrangian change of variables, combined with the assumption of isotropy for the conditionally averaged Lagrangian velocity gradient tensor and with the recent fluid deformation approximation. It is shown that both approaches lead to the same basic closure in which the stress tensor is expressed as the matrix exponential of the resolved velocity gradient tensor multiplied by its transpose. Short-time expansions of the matrix exponentials are shown to provide an eddy-viscosity term and particular quadratic terms, and thus allow a reinterpretation of traditional eddy-viscosity and nonlinear stress closures. The basic feasibility of the matrix-exponential closure is illustrated by implementing it successfully in large eddy simulation of forced isotropic turbulence. The matrix-exponential closure employs the drastic approximation of entirely omitting the pressure-strain correlation and other nonlinear scrambling terms. But unlike eddy-viscosity closures, the matrix exponential approach provides a simple and local closure that can be derived directly from the stress transport equation with the production term, and using physically motivated assumptions about Lagrangian decorrelation and upstream isotropy

Turbulence Fluctuations and New Universal Realizability Conditions in Modelling

General turbulent mean statistics are shown to be characterized by a variational principle. The variational functionals, or ``effective actions'', have experimental consequences for turbulence fluctuations and are subject to realizability conditions of positivity and convexity. An efficient Rayleigh-Ritz algorithm is available to calculate approximate effective actions within PDF closures. Examples are given for Navier-Stokes and for a 3-mode system of Lorenz. The new realizability conditions succeed at detecting {\em a priori} the poor predictions of PDF closures even when the classical 2nd-order moment realizability conditions are satisfied.Comment: 4 pages, LaTeX (Version 2.09), 3 figures, Postscript, Submitted to Phys. Rev. Let