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Pluripotenz wird durch viele Stammzell-spezifische Transkriptionsfaktoren wie Oct3/4, Nanog und Sox2 sowie deren Funktion in ihrem regulatorischen Netzwerk etabliert und aufrechterhalten. Viele Studien haben gezeigt, wie diese Pluripotenz-assoziierten Faktoren ihre Zielgene regulieren. Dies geschieht durch die Interaktion mit bekannten und unbekannten Interaktionspartnern. In der vorliegenden Arbeit haben wir Zfp819 als einen neuen Pluripotenz-assoziierten Faktor beschrieben und dessen Funktion in pluripotenten Stammzellen untersucht. Im ersten Teil der vorliegenden Arbeit haben wir zwei cDNA-Banken für Yeast two Hybdrid (Y2H)-Assays aus unterschiedlichen pluripotenten Stammzelltypen generiert. Dies hatte zum Ziel, potentielle Interaktionspartner eines Kandidatenproteins zu identifizieren um dadurch Eindrücke über die Funktion des Proteins zu gewinnen. Für die Identifizierung von potentiellen Interaktionspartnern von Zfp819 haben wir die cDNA-Bank aus embryonalen Stammzellen benutzt. Wir konnten 17 putative Interaktionspartner identifizieren und daraus ein hypothetisches „Interaktom“ von Zfp819 generieren. Die Einordnung der putativen Interaktionspartner nach ihrer Gen-Ontologie (GO) ließ vermuten, dass Zfp819 eine Rolle in der Regulation der Transkription, der Aufrechterhaltung der genetischen Integrität und im Zellzyklus bzw. bei der Apoptose spielt. Im zweiten Teil der vorliegenden Arbeit wurde die sehr intensive Expression von Zfp819 in undifferenzierten pluripotenten Zelllinien gezeigt. Desweiteren konnte die Promotorregion von Zfp819 identifiziert werden, und es wurde gezeigt, dass diese mit epigenetischen Mustern ausgestattet ist. Zusätzlich konnten wir Regionen im Zfp819-Gen identifizieren, die für die nukleäre Lokalisation von Zfp819 verantwortlich sind. Desweiteren konnten wir zeigen, dass Zfp819 in der transkriptionellen Repression von spezifischen endogenen, retroviralen Elementen (ERVs) in pluripotenten Zellen eine Rolle spielt. Durch zelluläre und biochemische Studien konnten wir zeigen, dass Zfp819 mit vielen Proteinen interagiert (z.B. Kap1 und Chd4), welche für die Aufrechterhaltung der genomischen Integrität von Bedeutung sind. Tatsächlich resultierte der Verlust von Zfp819 in embryonalen Stammzellen in einer erhöhten Anfälligkeit für DNA-Schäden und in einer verminderten DNA-Reparatur. Zusammenfassend lassen die Identifizierung der Interaktionspartner sowie die Ergebnisse der molekularen und der funktionellen Studien vermuten, dass Zfp819 durch die Unterdrückung von ausgewählten ERVs eine Rolle in der Regulation der genomischen Stabilität von pluripotenten Zellen spielt.

Die vorliegende Arbeit beschäftigt sich mit den Transporteigenschaften defektbehafteter Kohlenstoffnanoröhrchen (CNTs). Als Beispiel werden dabei einfache und doppelte Fehlstellen betrachtet. Der Fokus liegt auf der Berechnung des Transmissionsspektrums und der Leitfähigkeit mit einem schnellen, linear skalierenden rekursiven Greenfunktions-Formalismus, mit dem große Systeme quantenmechanisch behandelt werden können. Als Grundlage wird ein dichtefunktionalbasiertes Tight-Binding-Modell verwendet. Der Einfluss der Defektdichte und des CNT-Durchmessers wird im Rahmen einer statistischen Analyse untersucht. Es wird gezeigt, dass im Grenzfall kleiner Transmission die Leitfähigkeit exponentiell mit der Defektanzahl skaliert. Das System befindet sich im Regime starker Lokalisierung, wobei die Lokalisierungslänge von der Defektdichte und dem CNT-Durchmesser abhängt.

Im Fokus dieser Diplomarbeit steht ein korreliertes Anderson Modell. Unser Modell beschreibt kurzreichweitige Einzelplatzpotentiale, wobei negative Korrelationen zugelassen werden. Für dieses korrelierte Modell wird mittels der fraktionalen Momentenmethode im Falle genügend großer Unordnung exponentieller Abfall der Greenschen Funktion bewiesen. Anschließend wird daraus für den nicht korrelierten Spezialfall Anderson Lokalisierung bewiesen. / This thesis (diploma) is devoted to a correlated Anderson model. Our model describes short range single site potentials, whereby negative correlations become certified. For this correlated model exponential decay of the Greens' function is proven in the case sufficient large disorder according to the fractional moment method. Subsequently, we prove Anderson localization for the not correlated special case.

Die Fahrzeuglokalisierung ist im Bereich der Fahrerassistenzsysteme von entscheidender Bedeutung und Voraussetzung fur verschiedene Anwendungen der Robotik, wie z.B. Navigation oder Kollisionsvermeidung fur fahrerlose Transportsysteme (FTS). In dieser Arbeit wird ein Verfahren zur Lokalisierung mittels Landmarken vorgestellt, die eine Orientierung bezuglich einer Karte ermoglichen. Dabei werden der Erweiterte- Kalman-Filter und der Partikel-Filter fur diese Aufgabe untersucht und verglichen. Ein Schwerpunkt dieser Betrachtungen stellt dabei der Partikel-Filter dar. Die besondere Problematik der Initialisierung wird ausfuhrlich fur beide Filter dargestellt. Simulationen und Versuche zeigen, dass sich der Partikel-Filter fur eine robuste Lokalisierung der Fahrzeugposition verwenden lasst. Im Vergleich dazu kann der Erweiterte-Kalman-Filter nur im begrenzten Maße eingesetzt werden. / The localization of vehicles is of vital importance in the field of driver assistance systems and a requirement of different applications for robotics, i.e. navigation or collision avoidance for automatic guided vehicle systems. In this thesis an approach for localization by means of landmarks is introduced, which enables an orientation regarding a map. The extended Kalman filter and the particle filter are analyzed and compared. The main focus for this consideration is on the particle filter. The problematic for initialization is discussed in detail for both filters. Simulations and tests prove that the particle filter is suitable for robust localization of the vehicle position. Compared to this, the extended Kalman filter can only be used to a certain extend.

Movement of motor proteins along cytoskeletal filaments is fundamental for various cellular processes ranging from muscle contraction over cell division and flagellar movement to intracellular transport. Not surprisingly, the impairment of motility was shown to cause severe diseases. For example, a link between impaired intracellular transport and neurodegenerative diseases, such as Alzheimer’s, has been established. There, the movement of kinesin-1, a neuronal motor protein transporting vesicles along microtubules toward the axonal terminal, is thought to be strongly affected by roadblocks leading to malfunction and death of the nerve cell. Detailed information on how the motility of kinesin-1 deteriorates in the presence of roadblocks and whether the motor has a mechanism to circumvent such obstructions is scarce. In this thesis, kinesin-1 motility was studied in vitro in the presence of rigor kinesin-1 mutants, which served as permanent roadblocks, under controlled single-molecule conditions. The 25 nm wide microtubule track, consisting of 13 individual protofilaments, resembles a multi-lane environment for transport by processive kinesin-1 motors. The existence of multiple traffic-lanes, allows kinesin-1 to utilize different paths for cargo transport and potentially also for the circumvention of roadblocks. However, direct observation of motor encounters with roadblocks has been intricate in the past, mainly due to limitations in both, spatial and temporal resolution. These limitations, intrinsic to fluorescent probes commonly utilized to report on the motor positions, originate from a low rate of photon generation (low brightness) and a limited photostability (short observation time). Thus, studying kinesin-1 encounters with microtubule-associated roadblocks requires alternative labels, which explicitly avoid the shortcomings of fluorescence and consequently allow for a higher localization precision. Promising candidates for replacing fluorescent dyes are gold nanoparticles (AuNPs), which offer an enormous scattering cross-section due to plasmon resonance in the visible part of the optical spectrum. Problematic, however, is their incorporation into conventionally used (fluorescence) microscopes, because illumination and scattered light have the same wavelength and cannot be separated spectrally. Therefore, an approach based on total internal reflection (TIR) utilizing a novel parabolically shaped quartz prism for illumination was developed within this thesis. This approach provided homogenous and spatially invariant illumination profiles in combination with a convenient control over a wide range of illumination angles. Moreover, single-molecule fluorescence as well as single-particle scattering were detectable with high signal-to-noise ratios. Importantly, AuNPs with a diameter of 40 nm provided sub-nanometer localization accuracies within millisecond integration times and reliably reported on the characteristic 8 nm stepping of individual kinesin-1 motors moving along microtubules. These results highlight the potential of AuNPs to replace fluorescent probes in future single-molecule experiments. The newly developed parabolic prism-type TIR microscope is expected to strongly facilitate such approaches in the future. To study how the motility of kinesin-1 is affected by permanent roadblocks on the microtubule lattice, first, conventional objective-type TIRF microscopy was applied to GFP-labeled motors. An increasing density of roadblocks caused the mean velocity, run length, and dwell time to decrease exponentially. This is explained by (i) the kinesin-1 motors showing extended pausing phases when confronted with a roadblock and (ii) the roadblocks causing a reduction in the free path of the motors. Furthermore, kinesin-1 was found to be highly sensitive to the crowdedness of microtubules as a roadblock decoration as low as 1 % sufficed to significantly reduce the landing rate. To study events, where kinesin-1 molecules continued their runs after having paused in front of a roadblock, AuNPs were loaded onto the tails of the motors. When observing the kinesin-1 motors with nanometer-precision, it was interestingly found that about 60 % of the runs continued by movements to the side, with the left and right direction being equally likely. This finding suggests that kinesin-1 is able to reach to a neighboring protofilament in order to ensure ongoing transportation. In the absence of roadblocks, individual kinesin-1 motors stepped sideward with a much lower, but non-vanishing probability (0.2 % per step). These findings suggest that processive motor proteins may possess an intrinsic side stepping mechanism, potentially optimized by evolution for their specific intracellular tasks.

Superpixels are the results of an image oversegmentation. They are an established intermediate level image representation and used for various applications including object detection, 3d reconstruction and semantic segmentation. While there are various approaches to create such segmentations, there is a lack of knowledge about their properties. In particular, there are contradicting results published in the literature. This thesis identifies segmentation quality, stability, compactness and runtime to be important properties of superpixel segmentation algorithms. While for some of these properties there are established evaluation methodologies available, this is not the case for segmentation stability and compactness. Therefore, this thesis presents two novel metrics for their evaluation based on ground truth optical flow. These two metrics are used together with other novel and existing measures to create a standardized benchmark for superpixel algorithms. This benchmark is used for extensive comparison of available algorithms. The evaluation results motivate two novel segmentation algorithms that better balance trade-offs of existing algorithms: The proposed Preemptive SLIC algorithm incorporates a local preemption criterion in the established SLIC algorithm and saves about 80 % of the runtime. The proposed Compact Watershed algorithm combines Seeded Watershed segmentation with compactness constraints to create regularly shaped, compact superpixels at the even higher speed of the plain watershed transformation. Operating autonomous systems over the course of days, weeks or months, based on visual navigation, requires repeated recognition of places despite severe appearance changes as they are for example induced by illumination changes, day-night cycles, changing weather or seasons - a severe problem for existing methods. Therefore, the second part of this thesis presents two novel approaches that incorporate superpixel segmentations in place recognition in changing environments. The first novel approach is the learning of systematic appearance changes. Instead of matching images between, for example, summer and winter directly, an additional prediction step is proposed. Based on superpixel vocabularies, a predicted image is generated that shows, how the summer scene could look like in winter or vice versa. The presented results show that, if certain assumptions on the appearance changes and the available training data are met, existing holistic place recognition approaches can benefit from this additional prediction step. Holistic approaches to place recognition are known to fail in presence of viewpoint changes. Therefore, this thesis presents a new place recognition system based on local landmarks and Star-Hough. Star-Hough is a novel approach to incorporate the spatial arrangement of local image features in the computation of image similarities. It is based on star graph models and Hough voting and particularly suited for local features with low spatial precision and high outlier rates as they are expected in the presence of appearance changes. The novel landmarks are a combination of local region detectors and descriptors based on convolutional neural networks. This thesis presents and evaluates several new approaches to incorporate superpixel segmentations in local region detection. While the proposed system can be used with different types of local regions, in particular the combination with regions obtained from the novel multiscale superpixel grid shows to perform superior to the state of the art methods - a promising basis for practical applications.