112,238 research outputs found
Interpretation of Hanle effect measurements in the Solar Corona: promises and difficulties
No full textInternational audienceAfter having recalled the main features of the Hanle effect, and of its application to coronal lines, the promises and difficulties of the measurement interpretation in terms of magnetic field vector diagnostics, will be investigated, based on Bommier, V., Leroy, J.L., and Sahal-Bréchot, S., 1981, A&A, 100, 231, and in the light of the new instrumentation presently available or in project, as well as data-driven modeling present possibilities. The feasibility of measuring the Coronal magnetic field by interpretation of the Zeeman effect observed in the infrared, will also be investigated
Risk Aversion and the Value of Risk to Life
No full textThis paper argues for an alternative methodology to estimate the value of risk to life. By relaxing the assumption of additive separability, we introduce risk aversion with respect to the length of life and show that the extended model better fits available data. This is crucial for the extrapolation stage that the evaluation of life-saving programs systematically requires. Current practice, we show, puts too little weight on the young. Our correction surpasses in magnitude that introduced by the switch from the notion of number of lives saved to the notion of years of life saved.value of statistical life; lifecycle behavior; cost-benefit analysis
XTAT: A New Multilevel-Multiline Polarized Radiative Transfer Code with PRD
No full textInternational audienceThis work is intended to the interpretation of the so-called "Second Solar Spectrum" (Stenflo 1996), which is the spectrum of the linear polarization formed by scattering and observed close to the solar internal limb. The lines are also optically thick, and the problem is to solve in a coherent manner, the statistical equilibrium of the atomic density matrix and the polarized radiative transfer in the atmosphere. Following Belluzzi & Landi Degl'Innocenti (2009), 30 % of the solar visible line linear polarization profiles display the M-type shape typical of coherent scattering effect in the far wings. A new theory including both coherent (Rayleigh) and resonant scatterings was developed by Bommier (1997a,b). Raman scattering was later added (Bommier 1999, SPW2). In this theory, which is straightly derived from the Schrödinger equation for the atomic density matrix, the radiative line broadening appears as a non-Markovian process of atom-photon interaction. The collisional broadening is included. The Rayleigh (Raman) scattering appears as an additional term in the emissivity from the fourth order of the atom-photon interaction perturbation development. The development is pursued and finally summed up, leading to a non-perturbative final result. In this formalism, the use of redistribution functions is avoided. The published formalism was limited to the two-level atom without lower level alignment. But most of the solar lines are more complex. We will present how the theory has to be complemented for multi-level atom modeling, including lower level alignment. The role of the collisions as balancing coherent and resonant scatterings is fully taken into account. Progress report will be given about the development of a new code for the numerical iterative solution of the statistical equilibrium and polarized radiative transfer equations, for multi-level atoms and their multi-line spectrum. Fine and hyperfine structures, and Hanle, Kemp (Kemp et al. 1984), Zeeman, incomplete Paschen-Back effects, are included. Doppler redistribution is fully taken into account, by solving the statistical equilibrium for each velocity class of the atoms. In the presentation, a particular attention will be devoted to the depolarizing collisions and their rate estimation
Mortality, Time Preference and Life-Cycle Models
No full textThis paper introduces a life-cycle model where impatience, instead of being driven by an exogenous discount function, results from the combination of risk aversion and mortality risks. Opting for such a formulation provides novel views on the impact of longevity extension on welfare, saving behavior and capital accumulation. In particular, we show that longevity extension may have much larger impacts on capital accumulation and equilibrium rate of interest than is usually thought. Moreover, we show that the adherence to the additive life cycle model introduced by Yaari (1965)may lead to significantly overstimating the welfare gains due to mortality risk reduction.
Global Pattern of the Magnetic Field Vectors Above Neutral Lines from 1974 to 1982: Pic-du-Midi Observations of Prominences
No full textInternational audienceThe magnetic field vectors derived from the Hanle effect measured in prominences during the ascending phase and maximum of Cycle XXI have been plotted on the corresponding synoptic maps of the Meudon Observatory. Most of these measurements have been performed in a single line, He I D3. Our previous analysis of 2 lines measurements have already proved that the prominences magnetic field has the Inverse polarity and remains close to the horizontal plane (Bommier et al., 1994, Solar Physics 154, 231; Bommier et al., 1986, A&A 156, 79). We had also found early that the field component along the filament axis shows a remarkable large scale pattern, especially at high latitudes (Leroy et al., 1983, Solar Physics 83, 135). Given the geometry of horizontal Inverse field, we reinvestigate this large scale organization through our complete set of observations (300 prominences). These new maps fully confirm and extend to medium latitudes the law of reversal of the axial field from one prominence band to the adjacent ones. This behavior, together with the Inverse polarity pattern, gives a picture consistent with a North-South global field distorded by the differential rotation
Theoretical study of the collisional depolarization and of the Hanle effect in the line Na I D2 observed on the solar limb
No full textInternational audienceObservations of the Na I D lines polarization in quiet regions near the solar limb have been recently achieved, in particular with THEMIS (Bommier V., Molodij G., 2002, AandA 381, 241). These observations are in very good agreement with a theoretical model developed by Landi Degl'Innocenti (1998, Nature 392, 256, and 1999, "Solar Polarization", K.N. Nagendra and J.O. Stenflo (eds.), ASSL 243, 61). However, this model, based on the existence of atomic polarization in the line lower level, leads to the so-called "Sodium paradox": the existence of this at omic polarization is incompatible with the existence of a magnetic field stronger than 5 mG (except vertical), and also with the existence of collisional depolarization. We have investigated this last point, by using the collisional coefficients recently computed by B. Kerkeni from a quantum chemistry model. We have solved the statistical equilibrium equations for the atomic density matrix in the last scattering approximation, in order to investigate the Na I D2 line polarization formation and destruction at the solar limb. We have obtained that the atomic polarization in the lower level is completely destroyed by the collisions with neutral hydrogen at the line formation depth, which results in a "paradox in the paradox"
Rational Impatience ?
No full textThis paper introduces a life-cycle model where impatience, instead of being driven by an exogenous discount function, results from the combination of risk aversion and mortality risks. Opting for such a formulation provides novel views on the impact of longevity extension on welfare, saving behavior and capital accumulation. In particular, we show that longevity extension may have much larger impacts on capital accumulation and equilibrium rate of interest than is usually thought. Moreover, we show that the adherence to the additive life cycle model introduced by Yaari (1965) may lead to significantly overstimating the welfare gains due to mortality risk reduction.
author-bios-SRD-19-0063.R1 – Supplemental material for The Network Structure of Police Misconduct
No full textSupplemental material, author-bios-SRD-19-0063.R1 for The Network Structure of Police Misconduct by George Wood, Daria Roithmayr and Andrew V. Papachristos in Socius</p
The Quiet Sun Magnetic Field Structure Derived from a Full Vector Determination
No full textInternational audienceThe magnetic field vector of the quiet Sun has been first determined by usual Milne-Eddington inversion of ZIMPOL/THEMIS data. But such an inversion provides the local average field only, i.e. the product of the field strength by the magnetic filling factor. To discriminate between both quantities, an additional method has to be provided. We proposed a direct but approached determination of the filling factor in the spectropolarimetric data themselves. Then we were able to derive the inhomogeneous magnetic field strength (i.e. disambiguated from the filling factor). The methods and results from the ZIMPOL/THEMIS data are now published (Bommier et al. 2009). The present paper is intended to show that the THEMIS/THEMIS data, 10 times more numerous, give the same results, validating thus the THEMIS polarimeter results with the ZIMPOL ones. But the main new result is that finally the inhomogeneous field strength is found clearly dependent on the field inclination angle, thus ruling out the hypothesis of a turbulent field. The corresponding field organization could be: thin scattered vertical tubes of strong field opening and weakening with height (in the photosphere). Thus the weak fields would be horizontally (2D) distributed rather than following their generally admitted 3D turbulent structure. This distribution is not incompatible with the Hanle effect observations, because the Hanle effect is insensitive to the vertical field. The distribution of the thin opening tubes remains to be quantized, but spatial horizontal correlations were observed, which suggests that their size would not be very small with respect to the observation pixel size of 0.2-0.5 arcsec
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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