Unsupervised Multi Class Segmentation of 3D Images with Intensity Inhomogeneities

Intensity inhomogeneities in images constitute a considerable challenge in image segmentation. In this paper we propose a novel biconvex variational model to tackle this task. We combine a total variation approach for multi class segmentation with a multiplicative model to handle the inhomogeneities. Our method assumes that the image intensity is the product of a smoothly varying part and a component which resembles important image structures such as edges. Therefore, we penalize in addition to the total variation of the label assignment matrix a quadratic difference term to cope with the smoothly varying factor. A critical point of our biconvex functional is computed by a modified proximal alternating linearized minimization method (PALM). We show that the assumptions for the convergence of the algorithm are fulfilled by our model. Various numerical examples demonstrate the very good performance of our method. Particular attention is paid to the segmentation of 3D FIB tomographical images which was indeed the motivation of our work

Stochastic Modeling of Multiphase Materials Based on Digital Image Data

Multiphase materials combine properties of several materials, which makes them interesting for high-performing components. This thesis considers a certain set of multiphase materials, namely silicon-carbide (SiC) particle-reinforced aluminium (Al) metal matrix composites and their modelling based on stochastic geometry models. Stochastic modelling can be used for the generation of virtual material samples: Once we have fitted a model to the material statistics, we can obtain independent three-dimensional “samples” of the material under investigation without the need of any actual imaging. Additionally, by changing the model parameters, we can easily simulate a new material composition. The materials under investigation have a rather complicated microstructure, as the system of SiC particles has many degrees of freedom: Size, shape, orientation and spatial distribution. Based on FIB-SEM images, that yield three-dimensional image data, we extract the SiC particle structure using methods of image analysis. Then we model the SiC particles by anisotropically rescaled cells of a random Laguerre tessellation that was fitted to the shapes of isotropically rescaled particles. We fit a log-normal distribution for the volume distribution of the SiC particles. Additionally, we propose models for the Al grain structure and the Aluminium-Copper (${Al}_2{Cu}$) precipitations occurring on the grain boundaries and on SiC-Al phase boundaries. Finally, we show how we can estimate the parameters of the volume-distribution based on two-dimensional SEM images. This estimation is applied to two samples with different mean SiC particle diameters and to a random section through the model. The stereological estimations are within acceptable agreement with the parameters estimated from three-dimensional image data as well as with the parameters of the model

Potentials for a women-friendly image of computer science in Germany: A qualitative study on the role of Indian and Chinese doctoral students

Die Bedeutung der Informatik für die Gesellschaft hat stark zugenommen. Diese Entwicklung ist besonders relevant für Frauen aufgrund der weiblichen Konnotation sozialer Aspekte. Dennoch hält sich ein männlich technisches Bild in der Informatik in Deutschland aufrecht. Zugleich verweist vorhandene Forschung auf Potenziale für eine Öffnung dieses Fachbildes über die Positionierungen von Informatiker*innen. Internationale Doktorandinnen, die ein kulturell anderes Verständnis von Frauen in der Informatik haben, geben in dieser Dissertation eine völlig neue Perspektive. Gerade indische und chinesische Doktorandinnen erweisen sich als eine interessante Fokusgruppe: zum einen aufgrund einer, insbesondere in Indien, erhöhten Partizipation von Frauen in der Informatik und zum anderen aufgrund einer zunehmenden Studienmobilität nach Deutschland. Diese Aspekte nahm die vorliegende Dissertation zum Anlass, nach dem Potenzial indischer und chinesischer Doktorandinnen für ein frauenansprechendes Informatikbild in Deutschland zu fragen. Angesichts der Neuheit der Forschungsfrage wurde eine qualitative Studie unter Berücksichtigung intersektionaler Verflechtungen konzipiert, zu der 20 qualitative Interviews mit chinesischen und indischen Doktorandinnen, einer Doktorandin mit indischen Wurzeln und einer indischen Masterstudentin in der Informatik an deutschen Hochschulen durchführt wurden. Die Grounded Theory in Anlehnung an Strauss/Corbin sowie Charmaz stellt den methodologischen Rahmen dar. Den theoretischen Kern bildet Bourdieus Habitus-Theorie. Anhand der untersuchten Erfahrungen der chinesischen und indischen Frauen im voruniversitären Schulkontext, im Übergang zum Bachelor, Master und schließlich zur Promotion wurde zunächst die Entwicklung ihres fachlichen Habitus in der Informatik herausgearbeitet. Auf Grundlage dieser Ergebnisse wurde anschließend ihre Positionierung während der Promotion an deutschen Hochschulen im Hinblick auf Geschlechtereffekte gedeutet. Die Ergebnisse zeigen, dass die Positionierungen indischer und chinesischer Frauen zu einem veränderten Bild der Disziplin und damit zur Geschlechtergleichstellung in der Informatik in Deutschland beitragen können.The importance of computer science for society has grown strongly. This trend is particularly relevant to women due to the female connotation of social aspects. However, a male technical image of computer science in Germany remains stable. At the same time existing research refers to potentials for an opening of this professional image through the positionings of computer scientists. International doctoral students who have culturally different understandings of women in computer science give a completely new perspective in this dissertation. Especially Indian and Chinese doctoral students prove to be an interesting focus group: on the one hand because of an increased participation of women in computer science, particularly in India, and on the other hand because of a growing student mobility to Germany. The present dissertation took these aspects as a motivation to ask for the potentials of Indian and Chinese doctoral students for a women-friendly image of computer science in Germany. Given the novelty of the research question, a qualitative study was designed by considering intersectional interrelations. 20 qualitative interviews with Chinese and Indian doctoral students, one female doctoral student with Indian roots and one Indian female master student in computer science at different German universities were conducted. The Grounded Theory according to Strauss/Corbin and Charmaz represents the methodological frame. The theoretical core is formed by Bourdieu’s habitus theory. By analyzing the experiences of the Chinese and Indian women in the pre-university school context, in the transition to the bachelor, master and finally doctorate, at first, the development of the professional habitus in computer science was worked out. Based on these findings, afterwards, their positioning during the doctorate at a German university was studied with regard to gender effects. The results show that the positionings of Indian and Chinese women can contribute to a modified image of the discipline and thereby to gender equality in computer science in Germany

INTERRUPTED IN-SITU COMPRESSIVE DEFORMATION EXPERIMENTS ON MMC FOAMS IN AN XCT: EXPERIMENTS AND ESTIMATION OF DISPLACEMENT FIELDS

<p>The mechanical properties of a metal-matrix composite foam are investigated by interrupted in-situ compressive deformation experiments within an X-ray computed tomography device (XCT). Each in-situ experiment generates a sequence of reconstructed 3D images of the foam microstructure. From these data, the deformation field is estimated by registring the images corresponding to three consecutive steps. To this end, the generic registration framework of the itk software suite is exploited and combined with several image preprocessing steps. Both segmented (binary) images having just two grey values for foreground (strut structure) and background (pore space) and the result of the Euclidean distance transform (EDT) on pore space and solid phase are used. <br />The estimation quality is evaluated based on a sequence of synthetic data sets, where the foam’s microstructure is modelled by a random Laguerre tessellation. For large deformations, a combination of non-rigid registration for the EDT images and partwise-rigid registration on strongly deformed regions of the binary images, yields surprisingly small estimation errors.</p