14,950 research outputs found
Finite Temperature QCD Interfaces Out of Equilibrium
The properties of interfaces in non-equilibrium situations are studied by
constructing a density matrix with a space-dependent temperature. The
temperature gradient gives rise to new terms in the equation for the order
parameter. Surface terms induced in effective actions by abrupt temperature
changes provide a natural theoretical framework for understanding the occurence
of both continuous and discontinuous behavior in the order parameter. Monte
Carlo simulation of pure QCD shows both kinds of interfacial behavior.
Perturbation theory predicts a universal profile in the high temperature phase,
which can be tested by Monte Carlo simulation.Comment: 3 pages, contribution to Lattice '94 conference, self-extracting
(revised only to include heplat number in line below
Jet launching from accretion discs in the local approximation
The acceleration of an outflow along inclined magnetic field lines emanating
from an accretion disc can be studied in the local approximation, as employed
in the computational model known as the shearing box. By including the slow
magnetosonic point within the computational domain, the rate of mass loss in
the outflow can be calculated. The accretion rates of mass and magnetic flux
can also be determined, although some effects of cylindrical geometry are
omitted. We formulate a simple model for the study of this problem and present
the results of one-dimensional numerical simulations and supporting
calculations. Quasi-steady solutions are obtained for relatively strong
poloidal magnetic fields for which the magnetorotational instability is
suppressed. In this regime the rate of mass loss decreases extremely rapidly
with increasing field strength, or with decreasing surface density or
temperature. If the poloidal magnetic field in an accretion disc can locally
achieve an appropriate strength and inclination then a rapid burst of ejection
may occur. For weaker fields it may be possible to study the launching process
in parallel with the magnetorotational instability, but this will require
three-dimensional simulations.Comment: 8 pages, 4 figures, to be published in MNRA
Hospital-based alternatives to acute paediatric admission: a systematic review
Objective: To synthesise published evidence of the impacts of introducing hospital-based alternatives to acute paediatric admission.
Design: Systematic review of studies of interventions published in English.
Patients: Children with acute medical problems referred to hospitals.
Interventions: Services provided in a hospital as an alternative to inpatient admission.
Main outcome measures: Admission or discharge, unscheduled returns to hospital, satisfaction of parents and general practitioners, effects on health service activity and costs.
Results: 25 studies were included: one randomised controlled trial, 23 observational or cross-sectional studies and one qualitative study. Many studies were of uncertain quality or were open to significant potential bias. About 40% of children attending acute assessment units in paediatric departments, and over 60% of those attending acute assessment units in A & E departments, do not require inpatient admission. There is little evidence of serious clinical consequences in children discharged from these units, although up to 7% may subsequently return to hospital. There is some evidence that users are satisfied with these services and that they are associated with reductions in inpatient activity levels and certain hospital costs. Evidence about the impact of urgent outpatient clinics is very limited.
Conclusions: Current evidence supports a view that acute paediatric assessment services are a safe, efficient and acceptable alternative to inpatient admission, but this evidence is of limited quantity and quality. Further research is required to confirm that this type of service reorganisation does not disadvantage children and their families, particularly where inpatient services are withdrawn from a hospital
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Can we rehabilitate the guilds? A sceptical re-appraisal
This paper examines recent attempts to rehabilitate pre-modern craft guilds as efficient economic institutions. Contrary to rehabilitation views, craft guilds adversely
affected quality, skills, and innovation. Guild rent-seeking imposed deadweight losses on the economy and generated no demonstrable positive externalities. Industry flourished where
guilds decayed. Despite impairing efficiency, guilds persisted because they redistributed resources to powerful groups. The ârehabilitationâ view of guilds, it concludes, is theoretically
contradictory and empirically untenable
Center Symmetry and Abelian Projection at Finite Temperature
At finite temperature, there is an apparent conflict between Abelian
projection and critical universality. For example, should the deconfinement
transition of an SU(2) gauge theory projected to U(1) lie in the Z(2)
universality class of the parent SU(2) theory or in the U(1) universality
class? I prove that the projected theory lies in the universality class of the
parent gauge theory. The mechanism is shown to be non-local terms in the
projected effective action involving Polyakov loops. I connect this to the
recent work by Dunne et al. on the deconfinement transition in the 2+1
dimensional Georgi-Glashow model.Comment: 3 pages, no figures, Lattice 2002 conference contribution,
Lattice2002(topology
Early discharge of low-risk women from cervical screening
Background: The Scottish Cervical Screening Programme currently offers three-yearly screening to all women between the ages of 20 and 60. However, previous studies have indicated that well-screened women over the age of 50 are likely to be at low risk of cervical neoplasia. This study aimed to explore the implications of discharging these women from screening in a typical area of Scotland.
Methods: A caseâcontrol study of the screening histories of women with and without screen-detected cervical neoplasia between ages 50 and 59 in Lanarkshire was carried out, as well as a cross-sectional study of the prevalence of adequate screening histories among women currently aged 50 in Lanarkshire. Routine screening programme statistics were used to estimate the effects of introducing an early discharge policy.
Results: Women reaching the age of 50 with two recent, consecutive, negative smears had reduced odds of screen-detected neoplasia in the subsequent decade. The estimated odds ratio for all screen-detected neoplasia (CIN 1â3, adenocarcinoma in situ and invasive carcinoma) was 4.4 [95 per cent confidence interval (CI) 1.6â13.2, p = 0.002]. The estimated odds ratio for screen-detected high-grade CIN and invasive squamous carcinoma was 17.0 (95 per cent CI 2.4â243.0, þ = 0.0004). A total of 54.0 per cent (95 per cent CI 47.9â59.9 per cent) of screening participants currently aged 50 fulfilled the definition of adequate screening. Discharging these women might be expected to reduce screening workload by approximately 10 per cent, but those discharged would be at increased risk of neoplasia.
Conclusion: Now that full screening histories are available in all health board areas since 1990, the identification of a low-risk group within the screened population could be the first step towards a screening programme targeted more closely on those with the greatest capacity to benefit
Tidally distorted accretion discs in binary stars
The non-axisymmetric features observed in the discs of dwarf novae in
outburst are usually considered to be spiral shocks, which are the non-linear
relatives of tidally excited waves. This interpretation suffers from a number
of problems. For example, the natural site of wave excitation lies outside the
Roche lobe, the disc must be especially hot, and most treatments of wave
propagation do not take into account the vertical structure of the disc.
In this paper I construct a detailed semi-analytical model of the non-linear
tidal distortion of a thin, three-dimensional accretion disc by a binary
companion on a circular orbit. The analysis presented here allows for vertical
motion and radiative energy transport, and introduces a simple model for the
turbulent magnetic stress. The m=2 inner vertical resonance has an important
influence on the amplitude and phase of the tidal distortion. I show that the
observed patterns find a natural explanation if the emission is associated with
the tidally thickened sectors of the outer disc, which may be irradiated from
the centre. According to this hypothesis, it may be possible to constrain the
physical parameters of the disc through future observations.Comment: 13 pages, 3 figures, to be published in MNRA
Time-dependent quasi-spherical accretion
Differentially rotating, "advection-dominated" accretion flows are considered
in which the heat generated by viscous dissipation is retained in the fluid.
The equations of time-dependent quasi-spherical accretion are solved in a
simplified one-dimensional model that neglects the latitudinal dependence of
the flow. A self-similar solution is presented that has finite size, mass,
angular momentum and energy. This may be expected to be an attractor for the
initial-value problem in which a cool and narrow ring of fluid orbiting around
a central mass heats up, spreads radially and is accreted. The solution
provides some insight into the dynamics of quasi-spherical accretion and avoids
many of the strictures of the steady self-similar solution of Narayan & Yi.
Special attention is given to the astrophysically important case in which the
adiabatic exponent gamma=5/3; even in this case, the flow is found to be
differentially rotating and bound to the central object, and accretion can
occur without the need for powerful outflows.Comment: 6 pages, 3 figures, to be published in MNRA
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