636 research outputs found
Integrated out-of-hours care arrangements in England: observational study of progress towards single call access via NHS Direct and impact on the wider health system
Objectives: To assess the extent of service integration achieved within general practice cooperatives and NHS Direct sites participating in the Department of Health’s national “Exemplar Programme” for single call access to out-of-hours care via NHS Direct. To assess the impact of integrated out-of-hours care arrangements upon general practice cooperatives and the wider health system (use of emergency departments, 999 ambulance services, and minor injuries units).
Design: Observational before and after study of demand, activity, and trends in the use of other health services.
Setting: Thirty four English general practice cooperatives with NHS Direct partners (“exemplars”) of which four acted as “case exemplars”. Also 10 control cooperatives for comparison.
Main Outcome Measures: Extent of integration achieved (defined as the proportion of hours and the proportion of general practice patients covered by integrated arrangements), patterns of general practice cooperative demand and activity and trends in use of the wider health system in the first year.
Results: Of 31 distinct exemplars 21 (68%) integrated all out-of-hours call management by March 2004. Nine (29%) established single call access for all patients. In the only case exemplar where direct comparison was possible, cooperative nurse telephone triage before integration completed a higher proportion of calls with telephone advice than did NHS Direct afterwards (39% v 30%; p<0.0001). The proportion of calls completed by NHS Direct telephone advice at other sites was lower. There is evidence for transfer of demand from case exemplars to 999 ambulance services. A downturn in overall demand for care seen in two case exemplars was also seen in control sites.
Conclusion: The new model of out-of-hours care was implemented in a variety of settings across England by new partnerships between general practice cooperatives and NHS Direct. Single call access was not widely implemented and most patients needed to make at least two telephone calls to contact the service. In the first year, integration may have produced some reduction in total demand, but this may have been accompanied by shifts from one part of the local health system to another. NHS Direct demonstrated capability in handling calls but may not currently have sufficient capacity to support national implementation
Hyperons and massive neutron stars: vector repulsion and SU(3) symmetry
With the discovery of massive neutron stars such as PSR J1614-2230, the
question has arisen whether exotic matter such as hyperons can exist in the
neutron star core. We examine the conditions under which hyperons can exist in
massive neutron stars. We consistently investigate the vector meson-hyperon
coupling, going from SU(6) quark model to a broader SU(3) symmetry. We propose
that the maximum neutron star mass decreases linearly with the strangeness
content f_s of the neutron star core as M_max(f_s) = M_max(0) - 0.6 M_solar
(f_s/0.1), which seems to be independent of the underlying nuclear equation of
state and the vector baryon-meson coupling scheme. Thus, pulsar mass
measurements can be used to constrain the hyperon fraction in neutron stars.Comment: 13 pages, 10 figure
Computation of Neutron Star Structure Using Modern Equation of State
Using the modern equations of state derived from microscopic calculations, we
have calculated the neutron star structure. For the neutron star, we have
obtained a minimum mass about which is nearly independent
of the equation of state, and a maximum mass between and
which is strongly dependent on the equation of state. It
is shown that among the equations of state of neutron star matter which we have
used, the stiffest one leads to higher maximum mass and radius and lower
central density. It is seen that the given maximum mass for the Reid-93
equation of state shows a good consistency with the accurate observations of
radio pulsars. We have indicated that the thickness of neutron star crust is
very small compared to the predicted neutron star radius.Comment: 16 pages, 6 figure
The effect of neutrinos on the initial fireballs in gamma-ray bursts
We investigate the fate of very compact, sudden energy depositions that may
lie at the origin of gamma-ray bursts. Following on from the work of Cavallo
and Rees (1978), we take account of the much higher energies now believed to be
involved. The main effect of this is that thermal neutrinos are present and
energetically important. We show that these may provide sufficient cooling to
tap most of the explosion energy. However, at the extreme energies usually
invoked for gamma-ray bursts, the neutrino opacity suffices to prevent dramatic
losses, provided that the heating process is sufficiently fast. In a generic
case, a few tens of percent of the initial fireball energy will escape as an
isotropic millisecond burst of thermal neutrinos with a temperature of about 60
MeV, which is detectable for nearby gamma-ray bursts and hypernovae. For
parameters we find most likely for gamma-ray burst fireballs, the dominant
processes are purely leptonic, and thus the baryon loading of the fireball does
not affect our conclusions.Comment: 10 pages, 4 figures. To be submitted to MNRA
Isospin-rich nuclei in neutron star matter
Stability of nuclei beyond the drip lines in the presence of an enveloping
gas of nucleons and electrons, as prevailing in the inner crust of a neutron
star, is studied in the temperature-dependent Thomas-Fermi framework. A
limiting asymmetry in the isospin space beyond which nuclei cannot exist
emerges from the calculations. The ambient conditions like temperature, baryon
density and neutrino concentration under which these exotic nuclear systems can
be formed are studied in some detail.Comment: Submitted to Phy. Rev. C: Revtex version of manuscript 22 pages and
10 PS-files for figure
Equation of state and phase transitions in asymmetric nuclear matter
The structure of the 3-dimension pressure-temperature-asymmetry surface of
equilibrium of the asymmetric nuclear matter is studied within the thermal
Thomas-Fermi approximation. Special attention is paid to the difference of the
asymmetry parameter between the boiling sheet and that of the condensation
sheet of the surface of equilibrium. We derive the condition of existence of
the regime of retrograde condensation at the boiling of the asymmetric nuclear
matter. We have performed calculations of the caloric curves in the case of
isobaric heating. We have shown the presence of the plateau region in caloric
curves at the isobaric heating of the asymmetric nuclear matter. The shape of
the caloric curve depends on the pressure and is sensitive to the value of the
asymmetry parameter. We point out that the experimental value of the plateau
temperature T \approx 7 MeV corresponds to the pressure P = 0.01 MeV/fm^3 at
the isobaric boiling.Comment: 6 pages, 6 figures, submitted to Phys. Rev.
Isospin-rich nuclei in neutron star matter
Stability of nuclei beyond the drip lines in the presence of an enveloping
gas of nucleons and electrons, as prevailing in the inner crust of a neutron
star, is studied in the temperature-dependent Thomas-Fermi framework. A
limiting asymmetry in the isospin space beyond which nuclei cannot exist
emerges from the calculations. The ambient conditions like temperature, baryon
density and neutrino concentration under which these exotic nuclear systems can
be formed are studied in some detail.Comment: Submitted to Phy. Rev. C: Revtex version of manuscript 22 pages and
10 PS-files for figure
The Equation of State of Neutron-Star Matter in Strong Magnetic Fields
We study the effects of very strong magnetic fields on the equation of state
(EOS) in multicomponent, interacting matter by developing a covariant
description for the inclusion of the anomalous magnetic moments of nucleons.
For the description of neutron star matter, we employ a field-theoretical
approach which permits the study of several models which differ in their
behavior at high density. Effects of Landau quantization in ultra-strong
magnetic fields ( Gauss) lead to a reduction in the electron
chemical potential and a substantial increase in the proton fraction. We find
the generic result for Gauss that the softening of the EOS caused
by Landau quantization is overwhelmed by stiffening due to the incorporation of
the anomalous magnetic moments of the nucleons. In addition, the neutrons
become completely spin polarized. The inclusion of ultra-strong magnetic fields
leads to a dramatic increase in the proton fraction, with consequences for the
direct Urca process and neutron star cooling. The magnetization of the matter
never appears to become very large, as the value of never deviates from
unity by more than a few percent. Our findings have implications for the
structure of neutron stars in the presence of large frozen-in magnetic fields.Comment: 40 pages, 7 figures, accepted for publication in Ap
Improved Models of Stellar Core Collapse and Still no Explosions: What is Missing?
Two-dimensional hydrodynamic simulations of stellar core-collapse with and
without rotation are presented which for the first time were performed by
solving the Boltzmann equation for the neutrino transport including a
state-of-the-art description of neutrino interactions. Although convection
develops below the neutrinosphere and in the neutrino-heated region behind the
supernova shock, the models do not explode. This suggests missing physics,
possibly with respect to the nuclear equation of state and weak interactions in
the subnuclear regime. However, it might also indicate a fundamental problem of
the neutrino-driven explosion mechanism.Comment: PRL submitted; 3 eps figures, 1 colored, high-quality available upon
reques
A numerical study of the r-mode instability of rapidly rotating nascent neutron stars
The first results of numerical analysis of classical r-modes of {\it rapidly}
rotating compressible stellar models are reported. The full set of linear
perturbation equations of rotating stars in Newtonian gravity are numerically
solved without the slow rotation approximation. A critical curve of
gravitational wave emission induced instability which restricts the rotational
frequencies of hot young neutron stars is obtained. Taking the standard cooling
mechanisms of neutron stars into account, we also show the `evolutionary
curves' along which neutron stars are supposed to evolve as cooling and
spinning-down proceed. Rotational frequencies of stars suffering
from this instability decrease to around 100Hz when the standard cooling
mechanism of neutron stars is employed. This result confirms the results of
other authors who adopted the slow rotation approximation.Comment: 4 pages, 2 figures; MNRAS,316,L1(2000
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