Scalar field visualization via extraction of symmetric structures

Identifying symmetry in scalar fields is a recent area of research in scientific visualization and computer graphics communities. Symmetry detection techniques based on abstract representations of the scalar field use only limited geometric information in their analysis. Hence they may not be suited for applications that study the geometric properties of the regions in the domain. On the other hand, methods that accumulate local evidence of symmetry through a voting procedure have been successfully used for detecting geometric symmetry in shapes. We extend such a technique to scalar fields and use it to detect geometrically symmetric regions in synthetic as well as real-world datasets. Identifying symmetry in the scalar field can significantly improve visualization and interactive exploration of the data. We demonstrate different applications of the symmetry detection method to scientific visualization: query-based exploration of scalar fields, linked selection in symmetric regions for interactive visualization, and classification of geometrically symmetric regions and its application to anomaly detection.

Direct Characterizing of Densification Mechanisms during Spark Plasma Sintering

Spark plasma sintering (SPS) is a convenient and rapid means of producing dense ceramic compacts. However, the mechanisms responsible for rapid densification have not been identified satisfactorily, with different studies using an indirect approach yielding varied values for the densification parameters. This study involved SPS in high purity nanocrystalline alumina with temperatures ranging from 1173 to 1423K and stresses from 25 to 100MPa. A direct approach, with analyses at a constant density, revealed a stress exponent of similar to 1 and an inverse grain size dependence of similar to 3, consistent with Coble creep process. Whereas the direct approach gives a stress exponent of similar to 1, the indirect approach used previously gives stress exponents ranging from similar to 2.2 to 3.5 with the same data, thereby revealing potentially spurious values of the densification parameters from conventional indirect approaches to characterizing densification. The rapid densification during SPS is related to the finer grain sizes retained with the rapid heating rates and the imposed stress that enhances the driving force for densification.

The Relationship Between Solar Coronal X-Ray Brightness and Active Region Magnetic Fields: A Study Using High-Resolution Hinode Observations

By using high-resolution observations of nearly co-temporal and co-spatial Solar Optical Telescope spectropolarimeter and X-Ray Telescope coronal X-ray data onboard Hinode, we revisit the problematic relationship between global magnetic quantities and coronal X-ray brightness. Co-aligned vector magnetogram and X-ray data were used for this study. The total X-ray brightness over active regions is well correlated with integrated magnetic quantities such as the total unsigned magnetic flux, the total unsigned vertical current, and the area-integrated square of the vertical and horizontal magnetic fields. On accounting for the inter-dependence of the magnetic quantities, we inferred that the total magnetic flux is the primary determinant of the observed integrated X-ray brightness. Our observations indicate that a stronger coronal X-ray flux is not related to a higher non-potentiality of active-region magnetic fields. The data even suggest a slightly negative correlation between X-ray brightness and a proxy of active-region non-potentiality. Although there are small numerical differences in the established correlations, the main conclusions are qualitatively consistent over two different X-ray filters, the Al-poly and Ti-poly filters, which confirms the strength of our conclusions and validate and extend earlier studies that used low-resolution data. We discuss the implications of our results and the constraints they set on theories of solar coronal heating.