Exemplar Causality as similitudo aequivoca in Peter Auriol

The aim of this paper is to discuss the theory of exemplary causality of Peter Auriol (1280-1322). Until at least the late 13th century, medieval authors claim that the world is orderly and intelligible because God created it according to the models existing eternally in his mind (i.e. divine ideas). Auriol challenges the view of his predecessors and contemporaries. He argues that assuming divine ideas amounts to assuming multiplicity in God and therefore questioning the principle of his absolute simplicity. To avoid this problem, he develops a system that enables him to account for God’s knowledge of creatures (both as individuals and as species) and hence to preserve the theological principle of providence, but at the same time allows him to reject divine ideas as intermediaries for creation. In Auriol’s theory of exemplary causality, divine essence is the only object of God’s knowledge and thus the only exemplar for creation. God’s cognitive act is directed exclusively towards his own essence. However, he knows creatures through multiple connotations, i.e. the multiple ways divine essence is connotated when God knows himself. But these connotations play no role in creation, because imitability is only proper to divine essence. To explain how an object can be the only exemplar for the creation of many different creatures, Auriol has to rethink the concept of imitability and develop a new model of exemplary causality enabling him to account for the relationship between God and his creatures. The traditional model was that of analogy: a cause produces an effect which is partly similar and partly different from it. Auriol relies on the concept of equivocity. He argues that it is unnecessary to assume a particular similarity between a cause and its effect. Quite the contrary: for an object to be the exemplar of multiple different things, it is necessary that it should not be similar to any of them. The concept of aequivocatio allows Auriol to reject the traditional model of creation. Aequivocatio does not entail a resemblance between idea and ideatum. There is no contradiction, then, in claiming that a single object (divine essence) is in an equivocal way (aequivoce) the exemplary cause of multiple different objects. This is Auriol’s new theory of divine exemplarism: the theory of similitudo aequivoca

From the atmosphere to the circumstellar environment in cool evolved stars

We discuss and illustrate contributions that optical interferometry has made on our current understanding of cool evolved stars. We include red giant branch (RGB) stars, asymptotic giant branch (AGB) stars, and red supergiants (RSGs). Studies using optical interferometry from visual to mid-infrared wavelengths have greatly increased our knowledge of their atmospheres, extended molecular shells, dust formation, and winds. These processes and the morphology of the circumstellar environment are important for the further evolution of these stars toward planetary nebulae (PNe) and core-collapse supernovae (SNe), and for the return of material to the interstellar medium.Comment: To appear in the Book of the VLTI School 2013, held 9-21 Sep 2013 Barcelonnette (France), "What the highest angular resolution can bring to stellar astrophysics?", Ed. Millour, Chiavassa, Bigot, Chesneau, Meilland, Stee, EAS Publications Series (2015

Tomography of silicate dust around M-type AGB stars I. Diagnostics based on dynamical models

The heavy mass loss observed in evolved asymptotic giant branch stars is usually attributed to a two-step process: atmospheric levitation by pulsation-induced shock waves, followed by radiative acceleration of newly formed dust grains. Detailed wind models suggest that the outflows of M-type AGB stars may be triggered by photon scattering on Fe-free silicates with grain sizes of about 0.1 - 1 $\mu$m. Due to the low grain temperature, these Fe-free silicates can condense close to the star, but they do not produce the characteristic mid-IR features that are often observed in M-type AGB stars. However, it is probable that the silicate grains are gradually enriched with Fe as they move away from the star, to a degree where the grain temperature stays below the sublimation temperature, but is high enough to produce emission features. We investigate whether differences in grain temperature in the inner wind region, which are related to changes in the grain composition, can be detected with current interferometric techniques, in order to put constraints on the wind mechanism. To investigate this we use radial structures of the atmosphere and wind of an M-type AGB star, produced with the 1D radiation-hydrodynamical code DARWIN. The spectral energy distribution is found to be a poor indicator of different temperature profiles and therefore is not a good tool for distinguishing different scenarios of changing grain composition. However, spatially resolved interferometric observations have promising potential. They show signatures even for Fe-free silicates (found at 2-3 stellar radii), in contrast to the spectral energy distribution. Observations with baselines that probe spatial scales of about 4 stellar radii and beyond are suitable for tracing changes in grain composition, since this is where effects of Fe enrichment should be found.Comment: Accepted for publication in Section 8. Stellar atmospheres of Astronomy and Astrophysics. The official date of acceptance is 07/09/2017. 9 pages, 7 figures, 4 figures in appendi

Polarimetric Radar Target Decomposition and Classification

The polarization transformation properties of radar target characterize the radar scattering phenomena according to the theory introduced by E. Kennaugh, J. R. Huynen and S. R. Cloude. For this reason airborne and spaceborne polarimetric SAR are currently emergent technologies useful for providing maximum available information for application on remote sensing. The measurable quantities in the linear polarization basis have strong variability as function of the target aspect angle given the presence of strong disturbance effects like multiplicative noise. For this reason and given the difficult interpretation of the scattering coefficients in linear polarization basis, many authors have proposed several target decomposition theorems in order to give a likelihood interpretation of the observed phenomena. Target decomposition theorems have shown the basis for developing target classification and remote sensing inversion studies. In this Philosophy Doctoral dissertation the Einstein's photon circular polarization special unitary basis is used extensively in order to develop several lossless and sufficient target decomposition theorems providing orientation invariant parameters stressing the proper number of degrees of freedom of each case. Respectively the five novel target decomposition theorems proposed in this Dissertation are proven useful for: a) extracting the characteristic parameters of a coherent field, b) characterizing the statistics of a random field, c) decomposing the main features of a reciprocal deterministic target vector, d) modeling the degrees of freedom of a random reciprocal target, e) assessing the features of circular polarization dual coherent radar. The quantum theory of radar target scattering has been introduced by analyzing qualitatively the photon spin transformation properties of some elemental targets. Two Unsupervised Classification schemes based on the inner Hermitian product have been proposed generalizing the Cameron's approach to not symmetric and random targets. A Supervised Classification scheme based on the Cloude-Pottier eigen-features has been proposed for the identification of man-made target. A relationship of equivalence for the estimation of the coherency matrices of random target is also proved. Results have been validated via an extensive use of airborne and spaceborne fully polarimetric, simulated dual coherent radar and some anechoic chamber data sets. The new parameters proposed in this Ph. D. dissertation and the wide number of classes proposed are useful for assessing the advantages of fully polarimetric system versus dual coherent radar radiating circular polarization