243 research outputs found
Isospin Fluctuations from a Thermally Equilibrated Hadron Gas
Partition functions, multiplicity distributions, and isospin fluctuations are
calculated for canonical ensembles in which additive quantum numbers as well as
total isospin are strictly conserved. When properly accounting for
Bose-Einstein symmetrization, the multiplicity distributions of neutral pions
in a pion gas are significantly broader as compared to the non-degenerate case.
Inclusion of resonances compensates for this broadening effect. Recursion
relations are derived which allow calculation of exact results with modest
computer time.Comment: 10 pages, 5 figure
The Quark-Gluon Plasma in a Finite Volume
The statistical mechanics of quarks and gluons are investigated within the
context of the canonical ensemble. Recursive techniques are developed which
enforce the exact conservation of baryon number, total isospin, electric
charge, strangeness, and color. Bose and Fermi-Dirac statistics are also
accounted for to all orders. The energy, entropy and particle number densities
are shown to be significantly reduced for volumes less than 5 cubic fm.Comment: 8 pages, 3 figure
Balance Functions, Correlations, Charge Fluctuations and Interferometry
Connections between charge balance functions, charge fluctuations and
correlations are presented. It is shown that charge fluctuations can be
directly expressed in terms of a balance functions under certain assumptions.
The distortion of charge balance functions due to experimental acceptance is
discussed and the effects of identical boson interference is illustrated with a
simple model.Comment: 1 eps figure included. 5 pages in revtex
Saving Lives â an epic quest to promote an evidence-based approach for preventing healthcare-associated infections in the National Health Service in England
Since its inception more than half a century ago, the National Health Service has continued to transform and improve the health and wellbeing of the Nation. Now treating a million people every 36 hours, the NHS provides an unprecedented range of clinical interventions that can mend accidental damage, prevent, identify and manage or cure disease, and prolong quality life. However, hospital care and healthcare interventions are always associated with potential hazards, including the risk of acquiring an infection during care. Those patients most at risk are often the most vulnerable and chronically ill in our society and they and their families suffer needlessly because healthcare-associated infections are largely preventable. During the last decade, the Richard Wells Research Centre (RWR) in the Faculty of Health and Human Sciences at University of West London (formally Thames Valley university) has collaborated with the Department of Health and a variety of other governmental organisations and professional societies to develop an evidence-based approach to preventing healthcare-associated infections. This article describes the impact of our work and our journey in partnerships to support sustainable improvements in patient care, enhance patient safety and ultimately save lives
Light cluster production in intermediate energy heavy-ion collisions induced by neutron-rich nuclei
The coalescence model based on nucleon distribution functions from an
isospin-dependent transport model is used to study the production of light
clusters such as deuteron, triton, and He from heavy-ion collisions
induced by neutron-rich nuclei at intermediate energies. It is found that the
emission time of light clusters depends on their masses. For clusters with the
same momentum per nucleon, heavier ones are emitted earlier. Both the yield and
energy spectrum of light clusters are sensitive to the density dependence of
nuclear symmetry energy, with more light clusters produced in the case of a
stiff symmetry energy. On the other hand, effects due to the stiffness of the
isoscalar part of nuclear equation of state and the medium dependence of
nucleon-nucleon cross sections on light cluster production are unimportant. We
have also studied the correlation functions of clusters, and they are affected
by the density dependence of nuclear symmetry energy as well, with the stiff
symmetry energy giving a stronger anti-correlation of light clusters,
particularly for those with large kinetic energies. Dependence of light cluster
production on the centrality and incident energy of heavy ion collisions as
well as the mass of the reaction system is also investigated.Comment: Revised version, typos corrected and discussions added, 14 pages, 15
figures, 1 table, REVTeX4.
Hadronic freeze-out following a first order hadronization phase transition in ultrarelativistic heavy-ion collisions
We analyze the hadronic freeze-out in ultra-relativistic heavy ion collisions
at RHIC in a transport approach which combines hydrodynamics for the early,
dense, deconfined stage of the reaction with a microscopic non-equilibrium
model for the later hadronic stage at which the hydrodynamic equilibrium
assumptions are not valid. With this ansatz we are able to self-consistently
calculate the freeze-out of the system and determine space-time hypersurfaces
for individual hadron species. The space-time domains of the freeze-out for
several hadron species are found to be actually four-dimensional, and differ
drastically for the individual hadrons species. Freeze-out radii distributions
are similar in width for most hadron species, even though the Omega-baryon is
found to be emitted rather close to the phase boundary and shows the smallest
freeze-out radii and times among all baryon species. The total lifetime of the
system does not change by more than 10% when going from SPS to RHIC energies.Comment: 11 pages, 4 eps-figures included, revised versio
Sensitivity of HBT interferometry to the microscopic dynamics of freeze-out
We study the HBT interferometry of ultra-relativistic nuclear collisions
using a freezeout model in which free pions emerge in the course of the last
binary collisions in the hadron gas. We show that the HBT correlators of both
identical and non-identical pions change with respect to the case of
independent pion production. Practical consequences for the design of the event
generator with the built in Bose-Einstein correlations are discussed. We argue
that the scheme of inclusive measurement of the HBT correlation function does
not require the symmetrization of the multi-pion transition amplitudes
(wave-functions).Comment: 22 pages, 3 epsf figures, RevTe
Early collective expansion: Relativistic hydrodynamics and the transport properties of QCD matter
Relativistic hydrodynamics for ideal and viscous fluids is discussed as a
tool to describe relativistic heavy-ion collisions and to extract transport
properties of the quark-gluon plasma from experimentally measured hadron
momentum spectra.Comment: Review article, 54 pages, 25 figure
Planck early results. XXVI. Detection with Planck and confirmation by XMM-Newton of PLCK G266.6-27.3, an exceptionally X-ray luminous and massive galaxy cluster at z ~ 1
Planck early results. IX. XMM-Newton follow-up for validation of Planck cluster candidates
We present the XMM-Newton follow-up for confirmation of Planck cluster candidates. Twenty-five candidates have been observed to date using
snapshot (âŒ10 ks) exposures, ten as part of a pilot programme to sample a low range of signal-to-noise ratios (4 < S/N < 6), and a further 15 in a
programme to observe a sample of S/N > 5 candidates. The sensitivity and spatial resolution of XMM-Newton allows unambiguous discrimination
between clusters and false candidates. The 4 false candidates have S/N †4.1. A total of 21 candidates are confirmed as extended X-ray sources.
Seventeen are single clusters, the majority of which are found to have highly irregular and disturbed morphologies (about âŒ70%). The remaining
four sources are multiple systems, including the unexpected discovery of a supercluster at z = 0.45. For 20 sources we are able to derive a redshift
estimate from the X-ray Fe K line (albeit of variable quality). The new clusters span the redshift range 0.09 <⌠z <⌠0.54, with a median redshift
of z ⌠0.37. A first determination is made of their X-ray properties including the characteristic size, which is used to improve the estimate of
the SZ Compton parameter, Y500. The follow-up validation programme has helped to optimise the Planck candidate selection process. It has also
provided a preview of the X-ray properties of these newly-discovered clusters, allowing comparison with their SZ properties, and to the X-ray
and SZ properties of known clusters observed in the Planck survey. Our results suggest that Planck may have started to reveal a non-negligible
population of massive dynamically perturbed objects that is under-represented in X-ray surveys. However, despite their particular properties, these
new clusters appear to follow the Y500âYX relation established for X-ray selected objects, where YX is the product of the gas mass and temperature
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