Analyse diffusiver und intermittierender Suchstrategien mithilfe neuer Monte-Carlo-Algorithmen für allgemeine Reaktions-Diffusionsprobleme

Diese Dissertation beschäftigt sich im ersten Teil mit einer algorithmischen Weiterentwicklung sogenannter First-Passage-Kinetic-Monte-Carlo-Algorithmen. Dabei handelt es sich um effiziente ereignisgesteuerte Algorithmen zur Simulation von Reaktions-Diffusionsproblemen. Es werden allgemeine Methoden zur Lösung von Problemen mit krummlinigen Gebietsrändern und ortsabhängigen Reaktionsraten vorgestellt. Die Anwendung dieser Algorithmen erfordert das Sampeln sogenannter First-Passage-Ereignisse und No-Passage-Ereignisse auf geometrisch einfachen Gebieten. Für die in dieser Arbeit am häufigsten genutzten Gebiete werden sehr effiziente Algorithmen zum Sampeln der zugehörigen Wahrscheinlichkeitsdichten vorgestellt. Im zweiten Teil der Dissertation werden diese Algorithmen genutzt, um unterschiedliche Modelle des Suchens zu studieren: Zum einen wird ein Modell für die Suche von natürlichen Killerzellen nach Target-Zellen in An- und Abwesenheit von Bystander-Zellen und Hindernissen betrachtet, welches in Zusammenarbeit mit Experimentatoren entstanden ist und deren experimentelle Ergebnisse erklärt. Zum anderen werden homogene und inhomogene intermittierende Suchprobleme bezüglich einer optimalen Strategie untersucht. Die Auswahl der Suchszenarien orientiert sich dabei an innerzellulären Such- und Transportproblemen, wie z.B. dem Auffinden eines Bereichs auf der Zellmembran durch einen alternierenden Wechsel von Diffusion im Zytosol und ballistischem Transport entlang des Zytoskeletts. Im zweiten Teil der Dissertation werden diese Algorithmen genutzt, um unterschiedliche Modelle des Suchens zu studieren: Zum einen wird ein Modell für die Suche von natürlichen Killerzellen nach Target-Zellen in An- und Abwesenheit von Bystander-Zellen und Hindernissen betrachtet, welches in Zusammenarbeit mit Experimentatoren entstanden ist und deren experimentelle Ergebnisse erklärt. Zum anderen werden homogene und inhomogene intermittierende Suchprobleme bezüglich einer optimalen Strategie untersucht. Die Auswahl der Suchszenarien orientiert sich dabei an innerzellulären Such- und Transportproblemen, wie z.B. dem Auffinden eines Bereichs auf der Zellmembran durch einen alternierenden Wechsel von Diffusion im Zytosol und ballistischem Transport entlang des Zytoskeletts.The first part of this PhD thesis deals with an algorithmic enhancement of so-called First- Passage-Kinetic-Monte-Carlo-Algorithms, which are efficient event-driven algorithms for solving reaction-diffusion-problems. General methods for handling problems with curvilinear domain walls and spatially varying reaction rates are introduced. Applying these algorithms requires the ability of sampling so-called First-Passage-Events and No-Passage-Events within geometrically simple domains. For the most used domains in this thesis very efficient sampling routines are introduced. In the second part of the PhD thesis these algorithms are used for studying different models of search processes: On the one hand a model for natural killer cells, searching for target cells with and without surrounding bystander cells, are analysed. The model, which has been developed in a research project including experimenters, explains measured results. On the other hand homogeneous and inhomogeneous intermittent search problems are investigated in order to find optimal search strategies. The selection of studied problems is inspired by inner-cellular search and transport problems like locating a certain area on the cell membran by alternating between diffusive motion within the cytosol and ballistic motion along the cytoskeleton

Prävention, Bewertung und Behandlung von Glaskörpertrübungen im Auge. Intraokulare Gesundheit

Die Datei "HH-PAG Mai 2013" ist eine umfangreiche Informationsquelle für Hilfesuchenden über "Prävention, Bewertung und Behandlung von Glaskörpertrübungen", erstellt von betroffenen Patienten für betroffene Patienten. Sie gewährt einen detaillierten Einblick in die Floaterproblematik und in den Krankheitswert der Störung. Die unterschiedlichen Typen und Ausprägungsstärke von Glaskörpertrübungen kommen zur Sprache. Auch auf die Ursachen wird eingegangen. Es wird vorgebracht welche Anforderungen der informierte Patient an eine sorgsame Diagnostik stellt und wie er sich die Aufklärung im Vorfeld einer Pars plana Vitrektomie als Behandlungsmöglichkeit wünscht. Auch dem Thema Prävention wird ein hoher Stellenwert beigemessen. Ein Forderungskatalog bezüglich der Qualität an einer guten augenärztlichen Versorgung rundet das Ganze ab. Mit dem Floaterscreening-Fragebogen wird dem Patienten ein Screeningtool für ein konstruktives Arzt-Patienten-Gespräch in die Hand gegeben. Ziel der Orientierungshilfe ist die Offenlegung eines Dilemmas in der Augenarztpraxis: „vermeintlich“ harmlose Glaskörpertrübungen kontra hoch invasive Vitrektomie als einzige Behandlungsmethode bei schweren Glaskörpertrübungen

Novel role of Ras-GTPase Activating Protein SH3 Domain-Binding Protein G3BP in adhesion and migration of 32D myeloid progenitor cells

Rho GTPases are involved in homing and mobilization of hematopoietic stem and progenitor cells due to their impact on cytoskeleton remodeling. We have previously shown that inhibition of Rho, Rac and Cdc42 clearly impairs adhesion of normal and leukemic hematopoietic progenitor cells (HPC) to fibronectin and migration in a three-dimensional stromal cell model. Here, we identified the Ras GTPase-Activating Protein SH3 Domain-Binding Protein (G3BP) as a target gene of Rho GTPases and analysed its role in regulating HPC motility. Overexpression of G3BP significantly enhanced adhesion of murine 32D HPC to fibronectin and human umbilical vein endothelial cells, increased the proportion of adherent cells in a flow chamber assay and promoted cell migration in a transwell assay and a three-dimensional stromal cell model suggesting a strong impact on the cytoskeleton. Immunofluorescent staining of G3BP-overexpressing fibroblasts revealed a Rho-like phenotype characterized by formation of actin stress fibers in contrast to the Rac-like phenotype of control fibroblasts. This is the first report implicating a role for G3BP in Rho GTPase-mediated signalling towards adhesion and migration of HPC. Our results may be of clinical importance, since G3BP was found overexpressed in human cancers

Efficient kinetic Monte Carlo method for reaction-diffusion processes with spatially varying annihilation rates

We present an efficient Monte Carlo method to simulate reaction-diffusion processes with spatially varying particle annihilation or transformation rates as it occurs for instance in the context of motor-driven intracellular transport. Like Green's function reaction dynamics and first-passage time methods, our algorithm avoids small diffusive hops by propagating sufficiently distant particles in large hops to the boundaries of protective domains. Since for spatially varying annihilation or transformation rates the single particle diffusion propagator is not known analytically, we present an algorithm that generates efficiently either particle displacements or annihilations with the correct statistics, as we prove rigorously. The numerical efficiency of the algorithm is demonstrated with an illustrative example.Comment: 13 pages, 5 figure

Region-Based Template Matching Prediction for Intra Coding

Copy prediction is a renowned category of prediction techniques in video coding where the current block is predicted by copying the samples from a similar block that is present somewhere in the already decoded stream of samples. Motion-compensated prediction, intra block copy, template matching prediction etc. are examples. While the displacement information of the similar block is transmitted to the decoder in the bit-stream in the first two approaches, it is derived at the decoder in the last one by repeating the same search algorithm which was carried out at the encoder. Region-based template matching is a recently developed prediction algorithm that is an advanced form of standard template matching. In this method, the reference area is partitioned into multiple regions and the region to be searched for the similar block(s) is conveyed to the decoder in the bit-stream. Further, its final prediction signal is a linear combination of already decoded similar blocks from the given region. It was demonstrated in previous publications that region-based template matching is capable of achieving coding efficiency improvements for intra as well as inter-picture coding with considerably less decoder complexity than conventional template matching. In this paper, a theoretical justification for region-based template matching prediction subject to experimental data is presented. Additionally, the test results of the aforementioned method on the latest H.266/Versatile Video Coding (VVC) test model (version VTM-14.0) yield an average Bjøntegaard-Delta (BD) bit-rate savings of −0.75% using all intra (AI) configuration with 130% encoder run-time and 104% decoder run-time for a particular parameter selection

On the mechanical quality factors of cryogenic test masses from fused silica and crystalline quartz

Current interferometric gravitational wave detectors (IGWDs) are operated at room temperature with test masses made from fused silica. Fused silica shows very low absorption at the laser wavelength of 1064 nm. It is also well suited to realize low thermal noise floors in the detector signal band since it offers low mechanical loss, i. e. high quality factors (Q factors) at room temperature. However, for a further reduction of thermal noise, cooling the test masses to cryogenic temperatures may prove an interesting technique. Here we compare the results of Q factor measurements at cryogenic temperatures of acoustic eigenmodes of test masses from fused silica and its crystalline counterpart. Our results show that the mechanical loss of fused silica increases with lower temperature and reaches a maximum at 30 K for frequencies of slightly above 10 kHz. The losses of crystalline quartz generally show lower values and even fall below the room temperature values of fused silica below 10 K. Our results show that in comparison to fused silica, crystalline quartz has a considerably narrower and lower dissipation peak on cooling and thus has more promise as a test mass material for IGDWs operated at cryogenic temperatures. The origin of the different Q factor versus temperature behavior of the two materials is discussed.Comment: 11 pages, 2 figures, submitted to Class. Quantum Gra

Humidity Considerations in Filter Testing Based on Analysis of Filters from Gas Turbine Applications

Depth filters used in multistage filter systems adeptly clean the intake air of gas turbines, preventing damage and increasing performance. However, estimation of their service life is based on empirical data and/or standardized testing procedures, e.g., ISO 16890. By applying standardized synthetic test dusts at constant reference humidity, these testing procedures do not reflect application-typical loading conditions. Based on a direct comparison with field data, the influence of temporary exposure to high relative humidity on differential pressure and particle deposit structure is investigated. The results indicate that simulating humidity variations of the ambient atmosphere during filter tests leads to particle deposits, which more accurately reflect the actual behavior during operation