RESUMO
Routine ultraviolet imaging of the Sun's upper atmosphere shows the spectacular manifestation of solar activity; yet, we remain blind to its main driver, the magnetic field. Here, we report unprecedented spectropolarimetric observations of an active region plage and its surrounding enhanced network, showing circular polarization in ultraviolet (Mg ii h & k and Mn i) and visible (Fe i) lines. We infer the longitudinal magnetic field from the photosphere to the very upper chromosphere. At the top of the plage chromosphere, the field strengths reach more than 300 G, strongly correlated with the Mg ii k line core intensity and the electron pressure. This unique mapping shows how the magnetic field couples the different atmospheric layers and reveals the magnetic origin of the heating in the plage chromosphere.
RESUMO
Understanding many physical processes in the solar atmosphere requires determination of the magnetic field in each atmospheric layer. However, direct measurements of the magnetic field in the Sun's corona are difficult to obtain. Using observations with the Coronal Multi-channel Polarimeter, we have determined the spatial distribution of the plasma density in the corona and the phase speed of the prevailing transverse magnetohydrodynamic waves within the plasma. We combined these measurements to map the plane-of-sky component of the global coronal magnetic field. The derived field strengths in the corona, from 1.05 to 1.35 solar radii, are mostly 1 to 4 gauss. Our results demonstrate the capability of imaging spectroscopy in coronal magnetic field diagnostics.
RESUMO
Following coronary angioplasty and stent implantation, restenosis remains common and its outcome difficult to predict. We set out to determine the diagnostic accuracy of electron-beam computed tomography (EBCT) for the non-invasive detection of stent obstruction. In a prospective, blinded investigation, we included 152 coronary artery segments in 117 patients treated with a stent implant. All segments were evaluated by a dynamic EBCT study that depicted contrast bolus passage distal to the stent and a CT angiographic study of the entire coronary arteries. It was found that delayed contrast enhancement in the distal segment correlated with angiographic stent obstruction (Spearman's rank correlation, P=0.008), while all other indicators of stent occlusion did not correlate with angiographic diagnosis. However, direct comparison of patients with obstruction of less vs. more than 75% of luminal diameter did not yield any statistically significant differences of distal enhancement delay, and for the detection of >90% occlusion, the sensitivity was 72% at a specificity of 60%. Although delayed contrast enhancement distal to the stent upon EBCT did correlate with angiographical obstruction, the correlation did not suffice to appear clinically satisfactory.
