Zugl.: Graz, Techn. Univ., Diss., 2008

Zugl.: Karlsruhe, Univ., Diss., 2007 / Hergestellt on demand

Zugl.: Erlangen, Nürnberg, Univ., Diss., 2008

Zugl.: Ilmenau, Techn. Univ., Diss., 2010

Zugl.: Ulm, Univ., Diss., 2007

Techn. Hochsch., Diss., 2002--Aachen.

Techn. University, Diss., 2005--Berlin.

Techn. University, Diss., 2005--Darmstadt.

The non-invasive fetal ECG (NIFECG), derived from abdominal surface electrodes, offers novel diagnostic possibilities for prenatal medicine. Despite its straightforward applicability, NIFECG signals are usually corrupted by many interfering sources. Most significantly, by the maternal ECG (MECG), whose amplitude usually exceeds that of the fetal ECG (FECG) by multiple times. The presence of additional noise sources (e.g. muscular/uterine noise, electrode motion, etc.) further affects the signal-to-noise ratio (SNR) of the FECG. These interfering sources, which typically show a strong non-stationary behavior, render the FECG extraction and fetal QRS (FQRS) detection demanding signal processing tasks. In this thesis, several of the challenges regarding NIFECG signal analysis were addressed. In order to improve NIFECG extraction, the dynamic model of a Kalman filter approach was extended, thus, providing a more adequate representation of the mixture of FECG, MECG, and noise. In addition, aiming at the FECG signal quality assessment, novel metrics were proposed and evaluated. Further, these quality metrics were applied in improving FQRS detection and fetal heart rate estimation based on an innovative evolutionary algorithm and Kalman filtering signal fusion, respectively. The elaborated methods were characterized in depth using both simulated and clinical data, produced throughout this thesis. To stress-test extraction algorithms under ideal circumstances, a comprehensive benchmark protocol was created and contributed to an extensively improved NIFECG simulation toolbox. The developed toolbox and a large simulated dataset were released under an open-source license, allowing researchers to compare results in a reproducible manner. Furthermore, to validate the developed approaches under more realistic and challenging situations, a clinical trial was performed in collaboration with the University Hospital of Leipzig. Aside from serving as a test set for the developed algorithms, the clinical trial enabled an exploratory research. This enables a better understanding about the pathophysiological variables and measurement setup configurations that lead to changes in the abdominal signal's SNR. With such broad scope, this dissertation addresses many of the current aspects of NIFECG analysis and provides future suggestions to establish NIFECG in clinical settings.

Sperm cells are guided to the egg by chemoattractants in many species. Sperm cells are propelled in a liquid by the regular beat of their flagellum. In the presence of a concentration gradient of a chemoattractant, they can steer upwards the concentration gradient, a process called chemotaxis. Eggs release chemoattractants to guide the sperm cells to the egg. Sperm chemotaxis is best studied experimentally in the sea urchin. There, specific receptors in the flagellar membrane of the sperm cells are activated upon binding of chemoattractant molecules and trigger a signaling cascade which ultimately changes the activity of the molecular motors which drive the flagellar beat and result in a swimming response. Sea urchin sperm cells swim along circular and helical paths. Sperm cells of the sea urchin and several other species swim along helical paths far from boundary surfaces in the absence of chemoattractant. In a two-dimensional experimental geometry, sperm swimming paths are planar circles. The non-zero curvature of their swimming paths is a direct consequence of an asymmetry of their flagellar beat. In a concentration gradient of chemoattractant, sperm swimming path are drifting circles in two dimensions and bend helices in three dimensions. What is the working mechanism of sperm chemotaxis? In this thesis, we develop a theoretical description of sperm chemotaxis which can be subsumed as follows: While swimming along an approximately circular path in a concentration gradient a sperm cell traces a periodic concentration stimulus from the concentration field that has the frequency of circular swimming. The chemotactic signaling system processes this stimulus and causes a periodic modulation of the curvature of the swimming path which then gives rise to a swimming path which is a drifting circle. The relative direction of the drift with respect to the gradient direction is determined by the phase shift between the stimulus and the curvature oscillations. This picture is in perfect agreement with recent experimental findings. The mechanism is more general and also works in three dimensions for swimming along helical paths. Our results. Our theoretical description of sperm chemotaxis clarifies the concepts underlying sperm chemotaxis. In particular, we derive the role of internal timing of the chemotactic signaling system for sperm chemotaxis. We conclude that sampling a concentration field along circular and helical paths is a robust strategy for chemotaxis that does not require fine-tuning of parameters and which works reliable also in the presence of fluctuations. In a last chapter of this thesis, we discuss sperm chemotaxis in the more general context of an abstract search problem.