Effects of reduced discrete coupling on filament tension in excitable media

Wave propagation in the heart has a discrete nature, because it is mediated by discrete intercellular connections via gap junctions. Although effects of discreteness on wave propagation have been studied for planar traveling waves and vortexes (spiral waves) in two dimensions, its possible effects on vortexes (scroll waves) in three dimensions are not yet explored. In this article, we study the effect of discrete cell coupling on the filament dynamics in a generic model of an excitable medium. We find that reduced cell coupling decreases the line tension of scroll wave filaments and may induce negative filament tension instability in three-dimensional excitable lattices.Peer Reviewe

Collective motion and nonequilibrium cluster formation in colonies of gliding bacteria

We characterize cell motion in experiments and show that the transition to collective motion in colonies of gliding bacterial cells confined to a monolayer appears through the organization of cells into larger moving clusters. Collective motion by non-equilibrium cluster formation is detected for a critical cell packing fraction around 17%. This transition is characterized by a scale-free power-law cluster size distribution, with an exponent $0.88\pm0.07$, and the appearance of giant number fluctuations. Our findings are in quantitative agreement with simulations of self-propelled rods. This suggests that the interplay of self-propulsion of bacteria and the rod-shape of bacteria is sufficient to induce collective motion

Scientific Visualization for Atmospheric Data Analysis in Collaborative Virtual Environments

The three year European research project CROSS DRIVE (Collaborative Rover Operations and Planetary Science Analysis System based on Distributed Remote and Interactive Virtual Environments) started in January 2014. The research and development within this project is motivated by three use case studies: landing site characterization, atmospheric science and rover target selection. Currently the implementation for the second use case is in its final phase. Here, the requirements were generated based on the domain experts input and lead to development and integration of appropriate methods for visualization and analysis of atmospheric data. The methods range from volume rendering, interactive slicing, iso-surface techniques to interactive probing. All visualization methods are integrated in DLR’s Terrain Rendering application. With this, the high resolution surface data visualization can be enriched with additional methods appropriate for atmospheric data sets. This results in an integrated virtual environment where the scientist has the possibility to interactively explore his data sets directly within the correct context. The data sets include volumetric data of the martian atmosphere, precomputed two dimensional maps and vertical profiles. In most cases the surface data as well as the atmospheric data has global coverage and is of time dependent nature. Furthermore, all interaction is synchronized between different connected application  instances, allowing for collaborative sessions between distant experts

Bose-Fermi mixtures in 1D optical superlattices

The zero temperature phase diagram of binary boson-fermion mixtures in two-colour superlattices is investigated. The eigenvalue problem associated with the Bose-Fermi-Hubbard Hamiltonian is solved using an exact numerical diagonalization technique, supplemented by an adaptive basis truncation scheme. The physically motivated basis truncation allows to access larger systems in a fully controlled and very flexible framework. Several experimentally relevant observables, such as the matter-wave interference pattern and the condensatefraction, are investigated in order to explore the rich phase diagram. At symmetric half filling a phase similar to the Mott-insulating phase in a commensurate purely bosonic system is identified and an analogy to recent experiments is pointed out. Furthermore a phase of complete localization of the bosonic species generated by the repulsive boson-fermion interaction is identified. These localized condensates are of a different nature than the genuine Bose-Einstein condensates in optical lattices.Comment: 18 pages, 9 figure

Structural motifs of 2-(2-fluoro-phenyl)-ethylamine conformers

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Vibronic and vibrational spectra of 2-(2-fluoro-phenyl)-ethylamine (2-FPEA) conformers were measured in a molecular beam by resonant two-photon ionization (R2PI), ultraviolet-ultraviolet hole burning (UV-UV HB) spectroscopy, and ionization-loss stimulated Raman spectroscopy (ILSRS). The measured ILSR spectral signatures in the survey spectra of the amino group region and in the broad spectral range revealed the presence of five different conformers, which were confirmed by the HB spectra. The determination of the structures of the conformers of 2-FPEA was assisted by quantum chemical calculations of the torsional potential energy surface and of the scaled harmonic Raman spectra. Comparison of the measured ILSR spectra with the calculated Raman spectra allowed us to identify one gauche structure with the ethylamino side chain folded toward the fluorine atom, two gauche structures with the ethylamino side chain folded to the opposite side and two anti conformers with extended tails. The effect of fluorination on the spectra and on the stability and structures of these species is discussed

Nonlinear Analysis of the Eckhaus Instability: Modulated Amplitude Waves and Phase Chaos with Non-zero Average Phase Gradient

We analyze the Eckhaus instability of plane waves in the one-dimensional complex Ginzburg-Landau equation (CGLE) and describe the nonlinear effects arising in the Eckhaus unstable regime. Modulated amplitude waves (MAWs) are quasi-periodic solutions of the CGLE that emerge near the Eckhaus instability of plane waves and cease to exist due to saddle-node bifurcations (SN). These MAWs can be characterized by their average phase gradient $\nu$ and by the spatial period P of the periodic amplitude modulation. A numerical bifurcation analysis reveals the existence and stability properties of MAWs with arbitrary $\nu$ and P. MAWs are found to be stable for large enough $\nu$ and intermediate values of P. For different parameter values they are unstable to splitting and attractive interaction between subsequent extrema of the amplitude. Defects form from perturbed plane waves for parameter values above the SN of the corresponding MAWs. The break-down of phase chaos with average phase gradient $\nu$ > 0 (``wound-up phase chaos'') is thus related to these SNs. A lower bound for the break-down of wound-up phase chaos is given by the necessary presence of SNs and an upper bound by the absence of the splitting instability of MAWs.Comment: 24 pages, 14 figure