Structure and physics of solar faculae

Taking into account the effect of roughness (or local departures from sphericity) of the emitting layers in the chromosphere-corona transition zone (CCT) allows one to determine the optical depths of layers responsible for resolved structures in Cii, Ciii, Oiv, and Ovi lines. The result, at the top of the irregularities, is of the order of respectively ₁ 3.5,2.0, 1.6,0.5, and for the bottom of these irregularities, ₂ = 0.7, 0.4, 0.3, 0.25. The characteristic angle of these irregularities is, respectively, of the order of 35 °, 33 °, 35 °, and 41 °. For unresolved structures of Civ and Ovi (already analyzed in the spherical symmetry hypothesis in Paper III), one finds ₁ 0.6; 0.9 and ₂ 0.12; 0.2 in the case of quiet areas; in the case of active areas, the range is broader for Civ and Ovi, from 1.0 to 1.7 for ₁ and from 0.2 to 0.9 for ₂. The values obtained from Ovi are in reasonable agreement with each other for resolved and unresolved structures. And the obtained values of ₁ and ₂ correspond not too badly with the determinations made in Paper III, by methods not exceedingly influenced by the spherical symmetry hypothesis.     

Stellar and extragalactic radiation at the Earth’s surface

Reviving a calculation made by Eddington in the 1920s, and using the most recent and comprehensive databases available on stars and galaxies, including more than 2,500,000 stars and around 20,000 galaxies we have computed their total radiation received at the Earth just outside its atmosphere. This radiation density, if thermalized, would be equivalent to a temperature of 4.212 K. The comparability of this temperature to that of the cosmic microwave background (2.723 K) may either be a pure coincidence or may hold a key to some as yet unknown, aspect of the universe.     

Some considerations from the direct comparison between the observations and the theory of solar disk polarization

Simple considerations of observed variation with wavelength of polarization on the solar disc, computed continuum polarization, and estimated line polarization have led to the following simple conclusions (more qualitative than quantitative); (a) The metal abundances in the photosphere are five times larger than the classical values adopted in the BCA model of the solar photosphere. (b) The depolarization factor k in lines is an increasing function of wavelength. (c) Assuming that k varies as ², an additional polarization (which can be either solar or instrumental) has to be taken into account.     

The effects of non-sphericity in diagnosis of solar and stellar atmospheres

Between the interplanetary medium, filled by winds, magnetic structures, etc., and the interior of stars, opaque, and dominated heavily by the gravitational spherical field, the stellar atmosphere is a place where the true physical equilibrium, on the inside, sufficiently described by the parameters L, M, R, and the chemical composition X, Y, Z, is progressively changing into a situation far for equilibrium, which needs many more parameters to be properly described.The assumption that the equilibrium situation was dominating in the atmosphere has been generally accepted during the first half of this century. Since 1950 or so, we progressively learnt that the thermodynamical equilibrium (TE), and even the local thermodynamical equilibrium (LTE), are far from being actually in existence, that the radiative equilibrium (RE) is not actually perfect, convection, diffusion, magnetism, dissipation processes... playing a non-negligible part in the energy transport, that the hydrostatic equilibrium (HE) is only an approximation, as the convection and the magnetism are affecting the atmospheric layers, that neither the sphericity of atmospheric layers (plane-parallel hypothesis: PP) is achieved, nor the homogeneity of stellar iso- layers. During the 1950s and following decades, we began to suspect these difficulties and their consequences. In this paper, we turn towards a new consequence of the last-mentioned effect: the influence of non-sphericity and inhomogeneity upon the stellar (and solar perhaps) abundances of elements.Dedicated to Cornelis de Jager     

Damping/global energy balance in FE model of bridge foundation lateral response

A global energy analysis is presented of three static unloading–reloading foundation lateral loading cycles, calculated using the nonlinear finite element (FE) program DYNAFLOW. This simulates seismic action on an offshore pier foundation in the Rion-Antirion Bridge in Greece, located in deep-sea water (65 m). A cyclic horizontal force is applied at a height of 30 m to a rigid raft 78 m in width placed on the surface of an idealized 2-layer soil profile consisting of a 3.5 m man-made gravel layer over soft deep natural clay, with elastic vertical steel inclusions reinforcing the soil. Results of the two-dimensional FE run are used for the energy analysis. It is verified that for the three cycles, the sum of energies associated with the external forces and moments, mostly dissipated through hysteresis loops, is about equal to the sum of the total internal energies dissipated or stored in the system. For the smaller loops almost all energy is dissipated in the soil, while for the largest loop about half of the energy is dissipated by horizontal sliding at the raft-soil interface. Global damping ratios obtained from the areas of the horizontal and rocking moment hysteresis loops are about double of those computed from the corresponding static backbone curves using the Masing criterion.     

Foreword

The main objective of this special issue of the Bulletin of Earthquake Engineering is to bring to the earthquake engineering community the outcomes of the research project QUAKER (Quantification and Reduction of Seismic Risk through the Application of Advanced Geotechnical Engineering Techniques) financed by European Commission under contract EVG1-CT-2002-00064.