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Uwe Karst

Publications and source records attributed to Uwe Karst.

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MIA: A Visual Analytics System for Multimodal Spectral Imaging Data

Hyperspectral bioimaging techniques such as infrared (IR) microscopy and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) produce high-dimensional, spatially resolved datasets that require sophisticated analysis to reveal chemically and anatomically meaningful structures. Existing software solutions are typically modality-specific and cover only parts of the analytical workflow, forcing researchers to transfer data across multiple tools and manually reconcile results. We present MIA (Multiscale Image Analysis), a modality-agnostic visual analysis environment that integrates the full exploratory workflow -- from spectral preprocessing and dimensionality reduction to interactive segmentation and spectral similarity analysis -- within a single, tightly coupled interface. MIA supports hierarchical and landmark-based embeddings to handle datasets of varying scale and complexity, interactive and automatic segmentation with a shared state across all linked views, and multimodal analysis of co-registered datasets from different instruments. We demonstrate the effectiveness of MIA through three use cases drawn from real analytical chemistry workflows: (1) the recovery of biologically meaningful tissue compartments through derivative preprocessing and hierarchical embedding, (2) pigment identification via spectral similarity search with spatial overview, and (3) multimodal tissue characterization combining molecular IR and elemental LA-ICP-MS data. Qualitative feedback from domain expert collaborators confirms that MIA reduces the need for tool-switching and supports analytical insights that are difficult to obtain with existing software.

cs.HC

Suppression of electrical breakdown phenomena in liquid TriMethyl Bismuth based ionization detectors

Organometallic liquids provide good properties for ionization detectors. TriMethyl Bismuth (TMBi) has been proposed as a detector medium with charge and Cherenkov photon readout for Positron Emission Tomography. In this work, we present studies for the handling of TMBi at different electric fields and under different environmental conditions to find applicable configurations for the suppression of electrical breakdowns in TMBi at room temperature. A simple glass cell with two electrodes filled with TMBi was constructed and tested under different operation conditions. Working at the vapour pressure of TMBi at room temperature of about 40 mbar and electric fields of up to 20 kV/cm in presence of a small oxygen contamination we found the formation of a discharge channel in the liquid and a steady increase in the current. Further reduction of pressure by pumping caused the TMBi to boil and a spontaneous combustion. Eliminating the oxygen contamination led the TMBi under the same condition to only decompose. When operating the setup under an argon atmosphere of 1 bar we did not observe breakdowns of the electrical potential up to field strengths of 20 kV/cm. Still, in presence of a small oxygen contamination fluctuating currents in the nA range were observed, but no decomposition or combustion. We conclude from our experiments that TMBi at room temperature in a pure argon atmosphere of 1 bar remains stable against electrical breakdown at least up to electric field strengths of 20 kV/cm, presumably because the formation of gaseous TMBi was prevented.

physics.ins-det