Physik - Open Access LMU - Teil 01/02

Diffusion-limited reactions are studied in detail on the classical coalescing process. We demonstrate how, with the aid of a recent renormalization group approach, fluctuations can be integrated systematically. We thereby obtain an exact relation between the microscopic physics (lattice structure and particle shape and size) and the macroscopic decay rate in the law of mass action. Moreover, we find a strong violation of the law of mass action. The corresponding term in the kinetic equations originates in longwavelength fluctuations and is a universal function of the macroscopic decay rate.

Microbes providing public goods are widespread in nature despite running the risk of being exploited by

free-riders. However, the precise ecological factors supporting cooperation are still puzzling. Following

recent experiments, we consider the role of population growth and the repetitive fragmentation of

populations into new colonies mimicking simple microbial life-cycles. Individual-based modeling reveals

that demographic fluctuations, which lead to a large variance in the composition of colonies, promote

cooperation. Biased by population dynamics these fluctuations result in two qualitatively distinct regimes of

robust cooperation under repetitive fragmentation into groups. First, if the level of cooperation exceeds a

threshold, cooperators will take over the whole population. Second, cooperators can also emerge from a

single mutant leading to a robust coexistence between cooperators and free-riders. We find frequency and

size of population bottlenecks, and growth dynamics to be the major ecological factors determining the

regimes and thereby the evolutionary pathway towards cooperation.

Die Aufgaben und Übungen beziehen sich auf das Buch:

, das im Hochschulnetz der LMU abrufbar ist unter der URL: http://dx.doi.org/10.1007/978-3-642-05098-5

Min-protein oscillations in Escherichia coli are characterized by the remarkable robustness with which spatial patterns dynamically adapt to variations of cell geometry. Moreover, adaption, and therefore proper cell division, is independent of temperature. These observations raise fundamental questions about the mechanisms establishing robust Min oscillations, and about the role of spatial cues, as they are at odds with present models. Here, we introduce a robust model based on experimental data, consistently explaining the mechanisms underlying pole-to-pole, striped, and circular patterns, as well as the observed temperature dependence of the oscillation period. Contrary to prior conjectures, the model predicts that MinD and cardiolipin domains are not colocalized. The transient sequestration of MinE and highly canalized transfer of MinD between polar zones are the key mechanisms underlying oscillations. MinD channeling enhances midcell localization and facilitates stripe formation, revealing the potential optimization process from which robust Min-oscillations originally arose.

Solution-based self-assembly of quasi-one-dimensional semiconductor nanostructures (nanowires) from quasi-zero-dimensional (quantum dots) colloidal nanocrystal building blocks has proven itself as a powerful and flexible preparation technique. Polycrystalline CdTe nanowires self-assembled from light-emitting thiol-capped CdTe nanocrystals are the focus of this Feature Article. These nanowires represent an interesting model system for quantum dot solids, where electronic coupling between the individual nanocrystals can be optically accessed and controlled. We provide a literature-based summary of the formation mechanism and the morphology-related aspects of self-assembled CdTe nanowires, and highlight several fundamental and application-related optical properties of these nanostructures. These include fundamental aspects of polarization anisotropies in photoluminescence excitation and emission, the electronic coupling between individual semiconductor nanocrystals constituting the nanowires, and more applied, waveguiding properties of CdTe nanowire bundles and anti-Stokes photoluminescence in a prototypical structure of co-axial nanowires. The optical properties of self-assembled CdTe nanowires considered here render them potential candidates for photonic nanoscale devices.