Review on Experimental and Theoretical Investigations of Ultra-Short Pulsed Laser Ablation of Metals with Burst Pulses

Laser processing with ultra-short double pulses has gained attraction since the beginning of the 2000s. In the last decade, pulse bursts consisting of multiple pulses with a delay of several 10 ns and less found their way into the area of micromachining of metals, opening up completely new process regimes and allowing an increase in the structuring rates and surface quality of machined samples. Several physical effects such as shielding or re-deposition of material have led to a new understanding of the related machining strategies and processing regimes. Results of both experimental and numerical investigations are placed into context for different time scales during laser processing. This review is dedicated to the fundamental physical phenomena taking place during burst processing and their respective effects on machining results of metals in the ultra-short pulse regime for delays ranging from several 100 fs to several microseconds. Furthermore, technical applications based on these effects are reviewed

Migrations- und Integrationsprozesse in Europa. Vergemeinschaftung oder nationalstaatliche Lösungswege?

Hunger U, Aybek CM, Ette A, Michalowski I. Migrations- und Integrationsprozesse in Europa. Vergemeinschaftung oder nationalstaatliche Lösungswege? In: Hunger U, Aybek CM, Ette A, Michalowski I, eds. Migrations- und Integrationsprozesse in Europa. Vergemeinschaftung oder nationalstaatliche Lösungswege?. Wiesbaden: VS; 2008: 7-13

Kooperation statt Harmonisierung: Konsequenzen europäischer Governance für die Europäisierung der deutschen Rückkehr- und Abschiebungspolitik

Ette A, Kreienbrink A. Kooperation statt Harmonisierung: Konsequenzen europäischer Governance für die Europäisierung der deutschen Rückkehr- und Abschiebungspolitik. In: Hunger U, Aybek CM, Ette A, Michalowski I, eds. Migrations- und Integrationsprozesse in Europa. Vergemeinschaftung oder nationalstaatliche Lösungswege?. Wiesbaden: VS; 2008: 51-74

The Influence of Composition and Microstructure of the Cathode on the Impedance Response in Lithium-Sulfur Batteries

Lithium-sulfur batteries represent one of the most promising candidates for next-generation batteries due to their high specific energy density. Nonetheless, this battery chemistry is also facing obstacles such as the polysulfide-shuttle effect and the insulative nature of sulfur. In attempt to counteract these undesirable effects, several cathode-focused approaches were examined in the scientific community, including the infiltration and confinement of the active material in a conductive carbon host material or utilizing covalently bound sulfur within a polymeric backbone. However, these concepts also alter the known redox-mechanisms of lithium-sulfur cell chemistry as polysulfide dissolution is suppressed. In this work, various cathode systems including sulfur-carbon composite and sulfurized polyacrylonitrile (SPAN) are studied comprehensively by means of electrochemical impedance spectroscopy. Symmetrical two- or three-electrode cell arrangement is employed in order to analyze cathodic mechanisms without anode-induced or asymmetry artifacts. Transmission line models characteristic of porous electrodes have been implemented to understand the contribution of the different processes to the impedance of these cathodes. The influence of parameters such as microstructure of these cathodes, in particular porosity, on the impedance response is discussed in detail. Moreover, the investigation of impedance evolution upon various states of charge allows the identification of the highly diverse underlying processes related to the cathode, specifically a range of charge transfer mechanisms including quasi-solid-state and polysulfide-based redox reactions

Lokale Bürgerschaft. Kämpfe um politische Rechte und Mitgliedschaft von Migranten in Spanien

Fauser M. Lokale Bürgerschaft. Kämpfe um politische Rechte und Mitgliedschaft von Migranten in Spanien. In: Hunger U, Aybek CM, Ette A, Michalowski I, eds. Migrations- und Integrationsprozesse in Europa ; Vergemeinschaftung oder nationalstaatliche Lösungswege?. Wiesbaden: VS, Verl. für Sozialwiss.; 2008: 287-306

Data-Driven Prediction and Uncertainty Quantification of Process Parameters for Directed Energy Deposition

Laser-based directed energy deposition using metal powder (DED-LB/M) offers great potential for a flexible production mainly defined by software. To exploit this potential, knowledge of the process parameters required to achieve a specific track geometry is essential. Existing analytical, numerical, and machine-learning approaches, however, are not yet able to predict the process parameters in a satisfactory way. A trial-&-error approach is therefore usually applied to find the best process parameters. This paper presents a novel user-centric decision-making workflow, in which several combinations of process parameters that are most likely to yield the desired track geometry are proposed to the user. For this purpose, a Gaussian Process Regression (GPR) model, which has the advantage of including uncertainty quantification (UQ), was trained with experimental data to predict the geometry of single DED tracks based on the process parameters. The inherent UQ of the GPR together with the expert knowledge of the user can subsequently be leveraged for the inverse question of finding the best sets of process parameters by minimizing the expected squared deviation between target and actual track geometry. The GPR was trained and validated with a total of 379 cross sections of single tracks and the benefit of the workflow is demonstrated by two exemplary use cases