25 research outputs found
3D Coronal Density Reconstruction and Retrieving the Magnetic Field Structure during Solar Minimum
Measurement of the coronal magnetic field is a crucial ingredient in
understanding the nature of solar coronal phenomena at all scales. We employed
STEREO/COR1 data obtained during a deep minimum of solar activity in February
2008 (Carrington rotation CR 2066) to retrieve and analyze the
three-dimensional (3D) coronal electron density in the range of heights from
1.5 to 4 Rsun using a tomography method. With this, we qualitatively deduced
structures of the coronal magnetic field. The 3D electron density analysis is
complemented by the 3D STEREO/EUVI emissivity in the 195 A band obtained by
tomography for the same CR. A global 3D MHD model of the solar corona was used
to relate the reconstructed 3D density and emissivity to open/closed magnetic
field structures. We show that the density maximum locations can serve as an
indicator of current sheet position, while the locations of the density
gradient maximum can be a reliable indicator of coronal hole boundaries. We
find that the magnetic field configuration during CR 2066 has a tendency to
become radially open at heliocentric distances greater than 2.5 Rsun. We also
find that the potential field model with a fixed source surface (PFSS) is
inconsistent with the boundaries between the regions with open and closed
magnetic field structures. This indicates that the assumption of the potential
nature of the coronal global magnetic field is not satisfied even during the
deep solar minimum. Results of our 3D density reconstruction will help to
constrain solar coronal field models and test the accuracy of the magnetic
field approximations for coronal modeling.Comment: Published in "Solar Physics
Tomographic 3D-Modeling of the Solar Corona with FASR
The "Frequency-Agile Solar Radiotelescope" (FASR) litteraly opens up a new
dimension in addition to the 3D Euclidian geometry: the frequency dimension.
The 3D geometry is degenerated to 2D in all images from astronomical
telescopes, but the additional frequency dimension allows us to retrieve the
missing third dimension by means of physical modeling. We call this type of 3D
reconstruction "Frequency Tomography". In this study we simulate a realistic 3D
model of an active region, composed of 500 coronal loops with the 3D geometry
[x(s),y(s),z(s)] constrained by magnetic field extrapolations and the physical
parameters of the density n_e(s) and temperature T_e(s) given by hydrostatic
solutions. We simulate a series of 20 radio images in a frequency range of
f=0.1-10 GHz, anticipating the capabilities of FASR, and investigate what
physical information can be retrieved from such a dataset. We discuss also
forward-modeling of the chromospheric and Quiet Sun density and temperature
structure, another primary goal of future FASR science.Comment: 10 Figure
Visual support for interactive post-interventional assessment of radiofrequency ablation therapy
Percutaneous radiofrequency (RF) ablation is a minimally invasive, image-guided therapy for the treatment of liver tumors. The assessment of the ablation area (coagulation) is performed to verify the treatment success as an essential part of the therapy. Traditionally, pre- and post-interventional CT images are used to visually compare the shape, size, and position of tumor and coagulation. In this work, we present a novel visualization as well as a navigation tool, the so-called tumor map. The tumor map is a pseudo-cylindrical mapping of the tumor surface onto a 2D image. It is used for a combined visualization of all ablation zones of the tumor to allow a reliable therapy assessment. Additionally, the tumor map serves as an interactive tool for intuitive navigation within the 3D volume rendering of the tumor vicinity as well as with familiar 2D viewers