Message in a Bottle: Unveiling the Magneto-Ionic Complexity of AGNs through the Stokes QU-Fitting Technique

Here, I overview one of the available techniques for the analysis of broad-band spectropolarimetric data, the Stokes QU-fitting. Since broad-band receivers have been installed at most radio facilities, the collection of radio data, both the total intensity and the linear polarization, is revealing interesting features in their spectra. The polarized light, and therefore its properties, i.e. the fractional polarization p and the polarized angle χ, are now finally well sampled in wide wavelength ranges. The new complex behaviors revealed by the data can be studied using the Stokes QU-fitting, which consists of modeling the Stokes parameters Q and U using wavelength-dependent analytical models, available in the literature. This technique provides a very good diagnostic of the nature and structure of the magnetized plasma, with the possibility to identify complex structures, internal or external, of the source of study. A summary of the available and most used models describing the polarization behavior, is presented. Moreover, some of the most significant observational works which use this technique are also summarized.

Corrosion performance and degradation mechanism of a bi-metallic aluminum structure processed by wire-arc additive manufacturing

An Al-5Mg alloy (AA5083) block, deposited over an AA6061 substrate by wire-arc additive manufacturing, was electrochemically tested along two different cross-sectional planes by cyclic polarization in 3.5 wt.% NaCl. The deposited layers and the interlayer boundaries showed similar polarization behavior regardless of the cross-sectional direction. The corrosion of both the substrate and the deposited layers was mainly attributed to the presence of relatively coarse intermetallic Al(Fe, Mn)Si particles. In the substrate, corrosion was governed by deep crevices along the interfaces of directionally aligned Al(Fe, Mn)Si particles with the Al matrix. The deposited layers and the interlayer boundaries showed pitting around numerous Al(Fe, Mn)Si particles and/or Al(Fe, Mn, Cr, Ti)Si at the interlayer boundaries, which were much finer compared to those of the substrate. The abundance of the fine precipitates and their intergranular location caused surface material removal, which was more extensive along the interlayer boundaries. The perpendicular z-y and z-x planes of the deposited block did not show significant differences in anodic polarization behavior. Differences were more distinct in the case of cathodic polarization. Some anisotropy in polarization behavior was noted through the thickness of the z-y plane that complies with the obtained tensile behavior.