3,973 research outputs found

    Inferring the magnetic field vector in the quiet Sun. II. Interpreting results from the inversion of Stokes profiles

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    In a previous paper, we argued that the inversion of Stokes profiles applied to spectropolarimetric observations of the solar internetwork yield unrealistically large values of the inclination of the magnetic field vector (γ\gamma). This is because photon noise in Stokes QQ and UU are interpreted by the inversion code as valid signals, that leads to an overestimation of the transverse component BB_\perp, thus the inclination γ\gamma. However, our study was based on the analysis of linear polarization signals that featured only uncorrelated noise. In this paper, we develop this idea further and study this effect in Stokes QQ and UU profiles that also show correlated noise. In addition, we extend our study to the three components of the magnetic field vector, as well as the magnetic filling factor α\alpha. With this, we confirm the tendency to overestimate γ\gamma when inverting linear polarization profiles that, although non-zero, are still below the noise level. We also establish that the overestimation occurs mainly for magnetic fields that are nearly vertical γ20deg\gamma \lesssim 20\deg. This indicates that a reliable inference of the inclination of the magnetic field vector cannot be achieved by analyzing only Stokes II and VV. In addition, when inverting Stokes QQ and UU profiles below the noise, the inversion code retrieves a randomly uniform distribution of the azimuth of the magnetic field vector ϕ\phi. To avoid these problems, we propose only inverting Stokes profiles for which the linear polarization signals are sufficiently above the noise level. However, this approach is also biased because, in spite of allowing for a very accurate retrieval of the magnetic field vector from the selected Stokes profiles, it selects only profiles arising from highly inclined magnetic fields.Comment: Accepted for publication in Astronomy and Astrophysics. 14 pages. 7 color figure

    Inferring the magnetic field vector in the quiet Sun. III. Disk variation of the Stokes profiles and isotropism of the magnetic field

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    We have studied the angular distribution of the magnetic field vector in the solar internetwork employing high-quality data (noise level σ3×104\sigma \approx 3\times 10^{-4} in units of the quiet-Sun intensity) at different latitudes recorded with the Hinode/SP instrument. Instead of applying traditional inversion codes of the radiative transfer equation to retrieve the magnetic field vector at each spatial point on the solar surface and studying the resulting distribution of the magnetic field vector, we surmised a theoretical distribution function of the magnetic field vector and used it to obtain the theoretical histograms of the Stokes profiles. These histograms were then compared to the observed ones. Any mismatch between them was ascribed to the theoretical distribution of the magnetic field vector, which was subsequently modified to produce a better fit to the observed histograms. With this method we find that Stokes profiles with signals above 2×1032\times 10^{-3} (in units of the continuum intensity) cannot be explained by an isotropic distribution of the magnetic field vector. We also find that the differences between the histograms of the Stokes profiles observed at different latitudes cannot be explained in terms of line-of-sight effects. However, they can be explained by a distribution of the magnetic field vector that inherently varies with latitude. We note that these results are based on a series of assumptions that, although briefly discussed in this paper, need to be considered in more detail in the future.Comment: Accepted for publication in Astronomy and Astrophysics. 14 pages, 8 color figure

    Measurements of Four-Fermion Production via Neutral Elektroweak Currents at LEP

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    Four-fermion production via electroweak neutral currents has been measured by all four LEP collaborations at center-of-mass energies near the Z resonance and for the first time also at energies well above the Z peak. Essentially all possible final states have been covered in four different topologies

    Single and Pair Production of Neutral Electroweak Gauge Bosons at LEP

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    Recent LEP results on single and pair production of neutral electroweak gauge bosons are reviewed. QED and Electroweak gamma-e Compton scattering at LEP covers gamma-e center-of-mass energies sqrt{shat} in the range from about 20 GeV to 170 GeV, and leads to single production of on-shell gamma, off-shell gamma*, and Z bosons, also known as ``Zee'' process. The latter two final states have been observed for the first time by the OPAL collaboration, while the measurement of the scattered on-shell gamma's by L3 represents the highest energies at which QED Compton scattering has been studied so far. These processes can be used to set limits on excited electrons. Pair production of gamma* and/or Z at the e+e- center-of-mass energy sqrt{s}=183 GeV has been studied by the DELPHI, L3, and OPAL collaborations. The combination of these experiments yields the first significant measurement of Z pair production. With more statistics at higher energies, interesting limits on anomalous gammaZZ and ZZZ couplings can be derived from this process

    Techniques for Generating Centimetric Drops in Microgravity and Application to Cavitation Studies

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    This paper describes the techniques and physical parameters used to produce stable centimetric water drops in microgravity, and to study single cavitation bubbles inside such drops (Parabolic Flight Campaigns, European Space Agency ESA). While the main scientific results have been presented in a previous paper, we shall herein provide the necessary technical background, with potential applications to other experiments. First, we present an original method to produce and capture large stable drops in microgravity. This technique succeeded in generating quasi-spherical water drops with volumes up to 8 ml, despite the residual g-jitter. We find that the equilibrium of the drops is essentially dictated by the ratio between the drop volume and the contact surface used to capture the drop, and formulate a simple stability criterion. In a second part, we present a setup for creating and studying single cavitation bubbles inside those drops. In addition, we analyze the influence of the bubble size and position on the drop behaviour after collapse, i.e. jets and surface perturbations

    Structural and individual costs of residential aged care services in Australia. The Resource Utilisation and Classification Study: Report 3

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    The Australian Health Services Research Institute (AHSRI), University of Wollongong, was commissioned by the Commonwealth Department of Health (the Department) in August 2017 to undertake the ‘Resource Utilisation and Classification Study’ (RUCS). The RUCS is an important national study commissioned by the Department to inform the development of future funding models for residential aged care in Australia. The purpose of the analysis covered in this report is to identify the drivers of care related costs that are fixed for residential aged care facilities. These are costs that relate to the characteristics of facilities rather than the care needs of individual residents. This study was the second of four separate but interrelated and overlapping studies undertaken to inform the design and implementation strategies for future funding reforms in the Australian residential aged care sector

    Structural and individual costs of residential aged care services in Australia. The Resource Utilisation and Classification Study: Report 3

    Get PDF
    The Australian Health Services Research Institute (AHSRI), University of Wollongong, was commissioned by the Commonwealth Department of Health (the Department) in August 2017 to undertake the ‘Resource Utilisation and Classification Study’ (RUCS). The RUCS is an important national study commissioned by the Department to inform the development of future funding models for residential aged care in Australia. The purpose of the analysis covered in this report is to identify the drivers of care related costs that are fixed for residential aged care facilities. These are costs that relate to the characteristics of facilities rather than the care needs of individual residents. This study was the second of four separate but interrelated and overlapping studies undertaken to inform the design and implementation strategies for future funding reforms in the Australian residential aged care sector
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