14,883 research outputs found

    Finite Temperature QCD Interfaces Out of Equilibrium

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    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

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    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

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    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

    Center Symmetry and Abelian Projection at Finite Temperature

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    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

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    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 case–control 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 1–3, adenocarcinoma in situ and invasive carcinoma) was 4.4 [95 per cent confidence interval (CI) 1.6–13.2, p = 0.002]. The estimated odds ratio for screen-detected high-grade CIN and invasive squamous carcinoma was 17.0 (95 per cent CI 2.4–243.0, þ = 0.0004). A total of 54.0 per cent (95 per cent CI 47.9–59.9 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

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    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
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