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Bonn, Germany

von Cube F.,University of Bonn | von Cube F.,Research Center Caesar | Niegemann J.,Karlsruhe Institute of Technology | Matyssek C.,Max Planck Institute of Microstructure Physics | And 4 more authors.
Optical Materials Express | Year: 2011

Scanning transmission electron microscopy in combination with electron energy-loss spectroscopy is a powerful tool for the spatial and spectral characterization of the plasmonic modes of lithographically defined photonic meta-atoms. As an example, we present a size dependence study of the resonance energies of the plasmonic modes of a series of isolated split-ring resonators. Furthermore, we show that the comparison of the plasmonic maps of a split-ring resonator and the corresponding complementary split-ring resonator allows a direct visualization of Babinet's principle. Our experiments are in good agreement with numerical calculations based on a discontinuous Galerkin time-domain approach. © 2011 Optical Society of America. Source

Schulze N.,University of Duisburg - Essen | Graessl M.,University of Duisburg - Essen | Soares A.B.,Bernhard Nocht Institute for Tropical Medicine | Geyer M.,Research Center Caesar | And 2 more authors.
Journal of Cell Science | Year: 2014

The formin FHOD1 (formin homology 2 domain containing protein 1) can act as a capping and bundling protein in vitro. In cells, active FHOD1 stimulates the formation of ventral stress fibers. However, the cellular mechanisms by which this phenotype is produced and the physiological relevance of FHOD1 function are not currently understood. Here, we first show that FHOD1 controls the formation of two distinct stress fiber precursors differentially. On the one hand, it inhibits dorsal fiber growth, which requires the polymerization of parallel bundles of long actin filaments. On the other hand, it stimulates transverse arcs that are formed by the fusion of short antiparallel actin filaments. This combined action is crucial for the maturation of stress fibers and their spatio-temporal organization, and a lack of FHOD1 function perturbs dynamic cell behavior during cell migration. Furthermore, we show that the GTPase-binding and formin homology 3 domains (GBD and FH3) are responsible for stress fiber association and colocalization with myosin. Surprisingly, a version of FHOD1 that lacks these domains nevertheless retains its full capacity to stimulate arc and ventral stress fiber formation. Based on our findings, we propose a mechanism in which FHOD1 promotes the formation of short actin filaments and transiently associates with transverse arcs, thus providing tight temporal and spatial control of the formation and turnover of transverse arcs into mature ventral stress fibers during dynamic cell behavior. © 2014. Published by The Company of Biologists Ltd. Source

Wiedemann U.,University of Bonn | Karapetyan K.,University of Bonn | Dan C.,University of Bonn | Pritzkau D.,University of Bonn | And 3 more authors.
Optics Express | Year: 2010

Applications of subwavelength-diameter optical fibres in nonlinear optics require precise knowledge of the submicrometre fibre waist diameter. We demonstrate a new technique for optical measurement of the diameter based on second-and third-harmonic generation with an accuracy of better than 2%. To generate the harmonic light, inter-modal phase matching must be achieved. We find that the phase-matching condition allows us to unambiguously deduce the fibre diameter from the wavelength of the harmonic light. High-resolution scanning electron microscope imaging is used to verify the results. © 2010 Optical Society of America. Source

Schutt H.H.,University of Tubingen | Schutt H.H.,University of Potsdam | Harmeling S.,Heinrich Heine University Dusseldorf | Macke J.H.,Research Center Caesar | And 5 more authors.
Vision Research | Year: 2016

The psychometric function describes how an experimental variable, such as stimulus strength, influences the behaviour of an observer. Estimation of psychometric functions from experimental data plays a central role in fields such as psychophysics, experimental psychology and in the behavioural neurosciences. Experimental data may exhibit substantial overdispersion, which may result from non-stationarity in the behaviour of observers. Here we extend the standard binomial model which is typically used for psychometric function estimation to a beta-binomial model. We show that the use of the beta-binomial model makes it possible to determine accurate credible intervals even in data which exhibit substantial overdispersion. This goes beyond classical measures for overdispersion-goodness-of-fit-which can detect overdispersion but provide no method to do correct inference for overdispersed data. We use Bayesian inference methods for estimating the posterior distribution of the parameters of the psychometric function. Unlike previous Bayesian psychometric inference methods our software implementation-psignifit 4-performs numerical integration of the posterior within automatically determined bounds. This avoids the use of Markov chain Monte Carlo (MCMC) methods typically requiring expert knowledge. Extensive numerical tests show the validity of the approach and we discuss implications of overdispersion for experimental design. A comprehensive MATLAB toolbox implementing the method is freely available; a python implementation providing the basic capabilities is also available. © 2016 The Authors. Source

Schroder S.,Gladstone | Schroder S.,University of California at San Francisco | Herker E.,Gladstone | Herker E.,Heinrich Pette Institute | And 23 more authors.
Molecular Cell | Year: 2013

Lysine acetylation regulates transcription by targeting histones and nonhistone proteins. Here we report that the central regulator of transcription, RNA polymerase II, is subject to acetylation in mammalian cells. Acetylation occurs at eight lysines within the C-terminal domain (CTD) of the largest polymerase subunit and is mediated by p300/KAT3B. CTD acetylation is specifically enriched downstream of the transcription start sites of polymerase-occupied genes genome-wide, indicating a role in early stages of transcription initiation or elongation. Mutation oflysines or p300 inhibitor treatment causes the loss of epidermal growth-factor-induced expression of c-Fos and Egr2, immediate-early genes with promoter-proximally paused polymerases, but does not affect expression or polymerase occupancy at housekeeping genes. Our studies identify acetylation as a new modification of the mammalian RNA polymerase II required for the induction of growth factor response genes. © 2013 Elsevier Inc. Source

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