TY - GEN A1 - Federici, S. A1 - Pohl, Martin A1 - Ruppel, J. A1 - Telezhinsky, Igor O. A1 - Hofmann, Werner A1 - Martinez, M. A1 - Knapp, J. T1 - Design concepts for the Cherenkov Telescope Array CTA BT - an advanced facility for ground-based high-energy gamma-ray astronomy T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1325 KW - ground based gamma ray astronomy KW - next generation Cherenkov telescopes KW - design concepts Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-430149 SN - 1866-8372 VL - 32 IS - 1325 ER - TY - GEN A1 - Todt, Helge Tobias A1 - Peña, Miriam A1 - Zühlke, Julia A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer A1 - Gräfener, Götz T1 - Weak emission line central stars of planetary nebulae T2 - Planetary Nebulae: an Eye to the Future N2 - To understand the evolution and morphology of planetary nebulae, a detailed knowledge of their central stars is required. Central stars that exhibit emission lines in their spectra, indicating stellar mass-loss allow to study the evolution of planetary nebulae in action. Emission line central stars constitute about 10 % of all central stars. Half of them are practically hydrogen-free Wolf-Rayet type central stars of the carbon sequence, [WC], that show strong emission lines of carbon and oxygen in their spectra. In this contribution we address the weak emission-lines central stars (wels). These stars are poorly analyzed and their hydrogen content is mostly unknown. We obtained optical spectra, that include the important Balmer lines of hydrogen, for four weak emission line central stars. We present the results of our analysis, provide spectral classification and discuss possible explanations for their formation and evolution. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 462 KW - stars: AGB and post-AGB KW - stars: Wolf-Rayet KW - stars: abundances Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-413775 ER - TY - JOUR A1 - Stoyanov, Hristiyan A1 - Kollosche, Matthias A1 - Risse, Sebastian A1 - McCarthy, Denis N. A1 - Kofod, Guggi T1 - Elastic block copolymer nanocomposites with controlled interfacial interactions for artificial muscles with direct voltage control JF - Soft matter N2 - Soft, physically crosslinking, block copolymer elastomers were filled with surface-treated nanoparticles, in order to evaluate the possibility for improvement of their properties when used as soft dielectric actuators. The nanoparticles led to improvements in dielectric properties, however they also reinforced the elastomer matrix. Comparing dielectric spectra of composites with untreated and surface-treated particles showed a measurable influence of the surface on the dielectric loss behaviour for high filler amounts, strongly indicating an improved host-guest interaction for the surface-treated particles. Breakdown strength was measured using a test bench and was found to be in good agreement with the results from the actuation measurements. Actuation responses predicted by a model for prestrained actuators agreed well with measurements up to a filler amount of 20%(vol). Strong improvements in actuation behaviour were observed, with an optimum near 15%(vol) nanoparticles, corresponding to a reduction in electrical field of 27% for identical actuation strains. The use of physically crosslinking elastomer ensured the mechanical properties of the matrix elastomer were unchanged by nanoparticles effecting the crosslinking reaction, contrary to similar experiments performed with chemically crosslinking elastomers. This allows for a firm conclusion about the positive effects of surface-treated nanoparticles on actuation behavior. Y1 - 2011 U6 - https://doi.org/10.1039/c0sm00715c SN - 1744-683X SN - 1744-6848 VL - 7 IS - 1 SP - 194 EP - 202 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Filimon, Marlena A1 - Kopf, Ilona A1 - Schmidt, Dietrich A. A1 - Bruendermann, Erik A1 - Rühe, Jürgen A1 - Santer, Svetlana A1 - Havenith, Martina T1 - Local chemical composition of nanophase-separated polymer brushes JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Using scattering scanning nearfield infrared microscopy (s-SNIM), we have imaged the nanoscale phase separation of mixed polystyrene-poly(methyl methacrylate) (PS-PMMA) brushes and investigated changes in the top layer as a function of solvent exposure. We deduce that the top-layer of the mixed brushes is composed primarily of PMMA after exposure to acetone, while after exposure to toluene this changes to PS. Access to simultaneously measured topographic and chemical information allows direct correlation of the chemical morphology of the sample with topographic information. Our results demonstrate the potential of s-SNIM for chemical mapping based on distinct infrared absorption properties of polymers with a high spatial resolution of 80 nm x 80 nm. Y1 - 2011 U6 - https://doi.org/10.1039/c0cp02756a SN - 1463-9076 VL - 13 IS - 24 SP - 11620 EP - 11626 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Belova, Valentina A1 - Shchukin, Dmitry G. A1 - Gorin, Dmitry A. A1 - Kopyshev, Alexey A1 - Moehwald, Helmuth T1 - A new approach to nucleation of cavitation bubbles at chemically modified surfaces JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Cavitation at the solid surface normally begins with nucleation, in which defects or assembled molecules located at a liquid-solid interface act as nucleation centers and are actively involved in the evolution of cavitation bubbles. Here, we propose a simple approach to evaluate the behavior of cavitation bubbles formed under high intensity ultrasound (20 kHz, 51.3 W cm (2)) at solid surfaces, based on sonication of patterned substrates with a small roughness (less than 3 nm) and controllable surface energy. A mixture of octadecylphosphonic acid (ODTA) and octadecanethiol (ODT) was stamped on the Si wafer coated with different thicknesses of an aluminium layer (20-500 nm). We investigated the growth mechanism of cavitation bubble nuclei and the evolution of individual pits (defects) formed under sonication on the modified surface. A new activation behavior as a function of Al thickness, sonication time, ultrasonic power and temperature is reported. In this process cooperativity is introduced, as initially formed pits further reduce the energy to form bubbles. Furthermore, cavitation on the patterns is a controllable process, where up to 40-50 min of sonication time only the hydrophobic areas are active nucleation sites. This study provides a convincing proof of our theoretical approach on nucleation. Y1 - 2011 U6 - https://doi.org/10.1039/c1cp20218a SN - 1463-9076 VL - 13 IS - 17 SP - 8015 EP - 8023 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Lachmuth, Susanne A1 - Durka, Walter A1 - Schurr, Frank Martin T1 - Differentiation of reproductive and competitive ability in the invaded range of Senecio inaequidens the role of genetic Allee effects, adaptive and nonadaptive evolution JF - New phytologist : international journal of plant science N2 - Genetic differentiation in the competitive and reproductive ability of invading populations can result from genetic Allee effects or r/K selection at the local or range-wide scale. However, the neutral relatedness of populations may either mask or falsely suggest adaptation and genetic Allee effects. In a common-garden experiment, we investigated the competitive and reproductive ability of invasive Senecio inaequidens populations that vary in neutral genetic diversity, population age and field vegetation cover. To account for population relatedness, we analysed the experimental results with 'animal models' adopted from quantitative genetics. Consistent with adaptive r/K differentiation at local scales, we found that genotypes from low-competition environments invest more in reproduction and are more sensitive to competition. By contrast, apparent effects of large-scale r/K differentiation and apparent genetic Allee effects can largely be explained by neutral population relatedness. Invading populations should not be treated as homogeneous groups, as they may adapt quickly to small-scale environmental variation in the invaded range. Furthermore, neutral population differentiation may strongly influence invasion dynamics and should be accounted for in analyses of common-garden experiments. KW - animal models KW - biological invasions KW - genetic Allee effects KW - interspecific competition KW - life history evolution KW - nonadaptive evolution KW - r and K selection KW - reproduction Y1 - 2011 U6 - https://doi.org/10.1111/j.1469-8137.2011.03808.x SN - 0028-646X VL - 192 IS - 2 SP - 529 EP - 541 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Straube, Arthur V. A1 - Pikovskij, Arkadij T1 - Pattern formation induced by time-dependent advection JF - Mathematical modelling of natural phenomena N2 - We study pattern-forming instabilities in reaction-advection-diffusion systems. We develop an approach based on Lyapunov-Bloch exponents to figure out the impact of a spatially periodic mixing flow on the stability of a spatially homogeneous state. We deal with the flows periodic in space that may have arbitrary time dependence. We propose a discrete in time model, where reaction, advection, and diffusion act as successive operators, and show that a mixing advection can lead to a pattern-forming instability in a two-component system where only one of the species is advected. Physically, this can be explained as crossing a threshold of Turing instability due to effective increase of one of the diffusion constants. KW - pattern formation KW - reaction-advection-diffusion equation Y1 - 2011 U6 - https://doi.org/10.1051/mmnp/20116107 SN - 0973-5348 VL - 6 IS - 1 SP - 138 EP - 148 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Douce, Laurent A1 - Suisse, Jean-Moise A1 - Guillon, Daniel A1 - Taubert, Andreas T1 - Imidazolium-based liquid crystals a modular platform for versatile new materials with finely tuneable properties and behaviour JF - Liquid crystals : an international journal of science and technology N2 - Ionic liquid Crystals constitute highly versatile materials that have drawn much interest these past few years in the fields of academic research and industrial development. In this respect, the present article is intended as an update of K. Binnemans review published in 2005, but focusing exclusively on the imidazolium cation - the most widely studied. Herein, imidazolium-containing thermotropic liquid crystalline materials will be sorted by molecular structure (mono-, bis-, poly-imidazolium compounds, with symmetrical and non-symmetrical structures) and discussed. Their physico-chemical properties will be exposed in order to adduce the relevancy and potential of the imidazolium platform in various fields of research. KW - imidazolium KW - liquid crystal KW - ionic liquid Y1 - 2011 U6 - https://doi.org/10.1080/02678292.2011.610474 SN - 0267-8292 VL - 38 IS - 11-12 SP - 1653 EP - 1661 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - JOUR A1 - Schewe, Jacob A1 - Levermann, Anders A1 - Meinshausen, Malte T1 - Climate change under a scenario near 1.5 degrees C of global warming: monsoon intensification, ocean warming and steric sea level rise JF - Earth system dynamics N2 - We present climatic consequences of the Representative Concentration Pathways (RCPs) using the coupled climate model CLIMBER-3 alpha, which contains a statistical-dynamical atmosphere and a three-dimensional ocean model. We compare those with emulations of 19 state-of-the-art atmosphere-ocean general circulation models (AOGCM) using MAGICC6. The RCPs are designed as standard scenarios for the forthcoming IPCC Fifth Assessment Report to span the full range of future greenhouse gas (GHG) concentrations pathways currently discussed. The lowest of the RCP scenarios, RCP3-PD, is projected in CLIMBER-3 alpha to imply a maximal warming by the middle of the 21st century slightly above 1.5 degrees C and a slow decline of temperatures thereafter, approaching today's level by 2500. We identify two mechanisms that slow down global cooling after GHG concentrations peak: The known inertia induced by mixing-related oceanic heat uptake; and a change in oceanic convection that enhances ocean heat loss in high latitudes, reducing the surface cooling rate by almost 50%. Steric sea level rise under the RCP3-PD scenario continues for 200 years after the peak in surface air temperatures, stabilizing around 2250 at 30 cm. This contrasts with around 1.3 m of steric sea level rise by 2250, and 2 m by 2500, under the highest scenario, RCP8.5. Maximum oceanic warming at intermediate depth (300-800 m) is found to exceed that of the sea surface by the second half of the 21st century under RCP3-PD. This intermediate-depth warming persists for centuries even after surface temperatures have returned to present-day values, with potential consequences for marine ecosystems, oceanic methane hydrates, and ice-shelf stability. Due to an enhanced land-ocean temperature contrast, all scenarios yield an intensification of monsoon rainfall under global warming. Y1 - 2011 U6 - https://doi.org/10.5194/esd-2-25-2011 SN - 2190-4979 SN - 2190-4987 VL - 2 IS - 1 SP - 25 EP - 35 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Robinson, Alexander A1 - Calov, Reinhard A1 - Ganopolski, Andrey T1 - Greenland ice sheet model parameters constrained using simulations of the Eemian Interglacial JF - Climate of the past : an interactive open access journal of the European Geosciences Union N2 - Using a new approach to force an ice sheet model, we performed an ensemble of simulations of the Greenland Ice Sheet evolution during the last two glacial cycles, with emphasis on the Eemian Interglacial. This ensemble was generated by perturbing four key parameters in the coupled regional climate-ice sheet model and by introducing additional uncertainty in the prescribed "background" climate change. The sensitivity of the surface melt model to climate change was determined to be the dominant driver of ice sheet instability, as reflected by simulated ice sheet loss during the Eemian Interglacial period. To eliminate unrealistic parameter combinations, constraints from present-day and paleo information were applied. The constraints include (i) the diagnosed present-day surface mass balance partition between surface melting and ice discharge at the margin, (ii) the modeled present-day elevation at GRIP; and (iii) the modeled elevation reduction at GRIP during the Eemian. Using these three constraints, a total of 360 simulations with 90 different model realizations were filtered down to 46 simulations and 20 model realizations considered valid. The paleo constraint eliminated more sensitive melt parameter values, in agreement with the surface mass balance partition assumption. The constrained simulations resulted in a range of Eemian ice loss of 0.4-4.4m sea level equivalent, with a more likely range of about 3.7-4.4m sea level if the GRIP delta O-18 isotope record can be considered an accurate proxy for the precipitation-weighted annual mean temperatures. Y1 - 2011 U6 - https://doi.org/10.5194/cp-7-381-2011 SN - 1814-9324 VL - 7 IS - 2 SP - 381 EP - 396 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Hundertmark, Michaela A1 - Dimova, Rumiana A1 - Lengefeld, Jan A1 - Seckler, Robert A1 - Hincha, Dirk K. T1 - The intrinsically disordered late embryogenesis abundant protein LEA18 from Arabidopsis thaliana modulates membrane stability through binding and folding JF - Biochimica et biophysica acta : Biomembranes N2 - Intrinsically disordered proteins (IDPs) constitute a substantial part of cellular proteomes. late embryogenesis abundant (LEA) proteins are mostly predicted to be IDPs associated with dehydration tolerance in many plant, animal and bacterial species. Their functions, however, are largely unexplored and also their structure and interactions with potential target molecules have only recently been experimentally investigated in a small number of proteins. Here, we report on the structure and interactions with membranes of the Pfam LEA_1 protein LEA18 from the higher plant Arabidopsis thaliana. This functionally uncharacterized positively charged protein specifically aggregated and destabilized negatively charged liposomes. Isothermal titration calorimetry showed binding of the protein to both charged and uncharged membranes. LEA18 alone was largely unstructured in solution. While uncharged membranes had no influence on the secondary structure of LEA18, the protein partially folded into beta-sheet structure in the presence of negatively charged liposomes. These data suggest that LEA18 does not function as a membrane stabilizing protein, as suggested for other LEA proteins. Instead, a possible function of LEA18 could be the composition-dependent modulation of membrane stability, e.g., during signaling or vesicle-mediated transport. KW - Intrinsically disordered protein KW - Late embryogenesis abundant protein KW - Membrane stability KW - Protein-membrane interaction KW - Protein folding Y1 - 2011 U6 - https://doi.org/10.1016/j.bbamem.2010.09.010 SN - 0005-2736 VL - 1808 IS - 1 SP - 446 EP - 453 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Schenk, Paul A1 - Hamilton, Douglas P. A1 - Johnson, Robert E. A1 - McKinnon, William B. A1 - Paranicas, Chris A1 - Schmidt, Jürgen A1 - Showalter, Mark R. T1 - Plasma, plumes and rings saturn system dynamics as recorded in global color patterns on its midsize icy satellites JF - Icarus : international journal of solar system studies N2 - New global maps of the five inner midsize icy saturnian satellites, Mimas, Enceladus, Tethys, Dione, and Rhea, have been constructed in three colors (UV, Green and near-IR) at resolutions of 1 km/pixel. The maps reveal prominent global patterns common to several of these satellites but also three major color features unique to specific satellites or satellite subgroups. The most common features among the group are first-order global asymmetries in color properties. This pattern, expressed on Tethys, Dione and Rhea, takes the form of a similar to 1.4-1.8 times enhancement in redness (expressed as IR/UV ratio) of the surface at the center of the trailing hemisphere of motion, and a similar though significantly weaker IR/UV enhancement at the center of the leading hemisphere. The peak in redness on the trailing hemisphere also corresponds to a known decrease in albedo. These double hemispheric asymmetries are attributable to plasma and E-ring grain bombardment on the trailing and leading hemispheres, respectively, for the outer three satellites Tethys, Dione and Rhea, whereas as E-ring bombardment may be focused on the trailing hemisphere of Mimas due to its orbital location interior to Enceladus. The maps also reveal three major deviations from these basic global patterns. We observe the previously known dark bluish leading hemisphere equatorial band on Tethys but have also discovered a similar band on Mimas. Similar in shape, both features match the surface patterns expected for irradiation of the surface by incident MeV electrons that drift in a direction opposite to the plasma flow. The global asymmetry on Enceladus is offset similar to 40 degrees to the west compared to the other satellites. We do not consider Enceladus in detail here, but the global distribution of bluish material can be shown to match the deposition pattern predicted for plume fallback onto the surface (Kempf, S., Beckmann, U., Schmidt, S. [2010]. Icarus 206, 446-457. doi:10.1016/j.icarus.2009.09.016). E-ring deposition on Enceladus thus appears to mask or prevent the formation of the lenses and hemispheric asymmetries we see on the other satellites. Finally, we observe a chain of discrete bluish splotches along the equator of Rhea. Unlike the equatorial bands of Tethys and Mimas, these splotches form a very narrow great circle <= 10-km wide (north-to-south) and appear to be related to surface disruption, exposing fresh, bluish ice on older crater rims. This feature is unique to Rhea and may have formed by impact onto its surface of orbiting material. KW - Satellites, Surfaces KW - Saturn, Satellites KW - Saturn, Rings KW - Enceladus KW - Satellites, Composition KW - Magnetospheres Y1 - 2011 U6 - https://doi.org/10.1016/j.icarus.2010.08.016 SN - 0019-1035 VL - 211 IS - 1 SP - 740 EP - 757 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - Koenig, Tobias A1 - Goldenberg, Leonid M. A1 - Kulikovska, Olga A1 - Kulikovsky, Lazar A1 - Stumpe, Joachim A1 - Santer, Svetlana T1 - Reversible structuring of photosensitive polymer films by surface plasmon near field radiation JF - Soft matter N2 - We report on the fabrication and characterisation of a novel type of hybrid azo-modified photosensitive polymer film with a nanoscale metallic structuring integrated into the substrate. The metal structures permit to generate surface plasmon near fields when irradiated by UV-light from the rear without directly illuminating the polymer. This allows establishment of a localized, complex-shape intensity distribution at sub-wavelength resolution with a corresponding impact on the photosensitive polymer. The possibilities of exploiting this setup are manifold. We find that just by using the change of polarization of the incident light as means of control, the topography can be driven to change between various patterns reversibly. These results are confirmed by numerical simulations and compared with in situ recorded topography changes. Y1 - 2011 U6 - https://doi.org/10.1039/c0sm01164a SN - 1744-683X VL - 7 IS - 9 SP - 4174 EP - 4178 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Kollosche, Matthias A1 - Stoyanov, Hristiyan A1 - Laflamme, Simon A1 - Kofod, Guggi T1 - Strongly enhanced sensitivity in elastic capacitive strain sensors JF - Journal of materials chemistry N2 - Strain sensors based on dielectric elastomer capacitors function by the direct coupling of mechanical deformations with the capacitance. The coupling can be improved by enhancing the relative permittivity of the dielectric elastomer. Here, this is carried out through the grafting of conducting polymer (poly-aniline) to the elastomer backbone, leading to molecular composites. An enhancement in capacitance response of 46 times is observed. This could help to extend the possible range of miniaturization towards even smaller device features. Y1 - 2011 U6 - https://doi.org/10.1039/c0jm03786a SN - 0959-9428 VL - 21 IS - 23 SP - 8292 EP - 8294 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Seiss, Martin A1 - Spahn, Frank T1 - Hydrodynamics of saturn's dense rings JF - Mathematical modelling of natural phenomena N2 - The space missions Voyager and Cassini together with earthbound observations revealed a wealth of structures in Saturn's rings. There are, for example, waves being excited at ring positions which are in orbital resonance with Saturn's moons. Other structures can be assigned to embedded moons like empty gaps, moon induced wakes or S-shaped propeller features. Furthermore, irregular radial structures are observed in the range from 10 meters until kilometers. Here some of these structures will be discussed in the frame of hydrodynamical modeling of Saturn's dense rings. For this purpose we will characterize the physical properties of the ring particle ensemble by mean field quantities and point to the special behavior of the transport coefficients. We show that unperturbed rings can become unstable and how diffusion acts in the rings. Additionally, the alternative streamline formalism is introduced to describe perturbed regions of dense rings with applications to the wake damping and the dispersion relation of the density waves. KW - granular gas KW - instabilities KW - hydrodynamics KW - planetary rings Y1 - 2011 U6 - https://doi.org/10.1051/mmnp/20116409 SN - 0973-5348 SN - 1760-6101 VL - 6 IS - 4 SP - 191 EP - 218 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Martin, Maria A. A1 - Winkelmann, Ricarda A1 - Haseloff, M. A1 - Albrecht, Tanja A1 - Bueler, Ed A1 - Khroulev, C. A1 - Levermann, Anders T1 - The Potsdam parallel ice sheet model (PISM-PIK) - Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union N2 - We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for bed topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-shelf basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine ice sheet model. Y1 - 2011 U6 - https://doi.org/10.5194/tc-5-727-2011 SN - 1994-0416 VL - 5 IS - 3 SP - 727 EP - 740 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Winkelmann, Ricarda A1 - Martin, Maria A. A1 - Haseloff, Monika A1 - Albrecht, Torsten A1 - Bueler, Ed A1 - Khroulev, C. A1 - Levermann, Anders T1 - The Potsdam parallel ice sheet model (PISM-PIK) - Part 1: Model description JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union N2 - We present the Potsdam Parallel Ice Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA) dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid-scale representation of calving front motion (Albrecht et al., 2011) and a physically-motivated calving law based on horizontal spreading rates. The model is tested in experiments from the Marine Ice Sheet Model Intercomparison Project (MISMIP). A dynamic equilibrium simulation of Antarctica under present-day conditions is presented in Martin et al. (2011). Y1 - 2011 U6 - https://doi.org/10.5194/tc-5-715-2011 SN - 1994-0416 VL - 5 IS - 3 SP - 715 EP - 726 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Sepp, T. A1 - Tempel, E. A1 - Gramann, M. A1 - Nurmi, P. A1 - Haupt, Michael T1 - Studying the patterns of the universe JF - Baltic astronomy N2 - The SDSS galaxy catalog is one of the best databases for galaxy distribution studies. The SDSS DR8 data is used to construct the galaxy cluster catalog. We construct the clusters from the calculated luminosity density field and identify denser regions. Around these peak regions we construct galaxy clusters. Another interesting question in cosmology is how observable galaxy structures are connected to underlying dark matter distribution. To study this we compare the SDSS DR7 galaxy group catalog with galaxy groups obtained from the semi-analytical Millennium N-Body simulation. Specifically, we compare the group richness, virial radius, maximum separation and velocity dispersion distributions and find a relatively good agreement between the mock catalog and observations. This strongly supports the idea, that the dark matter distribution and galaxies in the semi-analytical models and observations are very closely linked. KW - galaxies: groups, clusters KW - cosmology: dark matter, large-scale structure of the Universe Y1 - 2011 SN - 1392-0049 VL - 20 IS - 2 SP - 309 EP - 312 PB - Institute of Theoretical Physics and Astronomy CY - Moletai ER - TY - JOUR A1 - Zhirov, O. V. A1 - Pikovskij, Arkadij A1 - Shepelyansky, Dima L. T1 - Quantum vacuum of strongly nonlinear lattices JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We study the properties of classical and quantum strongly nonlinear chains by means of extensive numerical simulations. Due to strong nonlinearity, the classical dynamics of such chains remains chaotic at arbitrarily low energies. We show that the collective excitations of classical chains are described by sound waves whose decay rate scales algebraically with the wave number with a generic exponent value. The properties of the quantum chains are studied by the quantum Monte Carlo method and it is found that the low-energy excitations are well described by effective phonon modes with the sound velocity dependent on an effective Planck constant. Our results show that at low energies the quantum effects lead to a suppression of chaos and drive the system to a quasi-integrable regime of effective phonon modes. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevE.83.016202 SN - 1539-3755 VL - 83 IS - 1 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Lemr, Karel A1 - Cernoch, A. A1 - Soubusta, Jan A1 - Kieling, Konrad A1 - Eisert, Jens A1 - Dusek, M. T1 - Experimental implementation of the optimal linear-optical controlled phase gate JF - Physical review letters N2 - We report on the first experimental realization of optimal linear-optical controlled phase gates for arbitrary phases. The realized scheme is entirely flexible in that the phase shift can be tuned to any given value. All such controlled phase gates are optimal in the sense that they operate at the maximum possible success probabilities that are achievable within the framework of postselected linear-optical implementations with vacuum ancillas. The quantum gate is implemented by using bulk optical elements and polarization encoding of qubit states. We have experimentally explored the remarkable observation that the optimum success probability is not monotone in the phase. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevLett.106.013602 SN - 0031-9007 VL - 106 IS - 1 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Mari, Andrea A1 - Kieling, Konrad A1 - Nielsen, B. Melholt A1 - Polzik, E. S. A1 - Eisert, Jens T1 - Directly estimating nonclassicality JF - Physical review letters N2 - We establish a method of directly measuring and estimating nonclassicality-operationally defined in terms of the distinguishability of a given state from one with a positive Wigner function. It allows us to certify nonclassicality, based on possibly much fewer measurement settings than necessary for obtaining complete tomographic knowledge, and is at the same time equipped with a full certificate. We find that even from measuring two conjugate variables alone, one may infer the nonclassicality of quantum mechanical modes. This method also provides a practical tool to eventually certify such features in mechanical degrees of freedom in opto-mechanics. The proof of the result is based on Bochner's theorem characterizing classical and quantum characteristic functions and on semidefinite programming. In this joint theoretical-experimental work we present data from experimental optical Fock state preparation. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevLett.106.010403 SN - 0031-9007 VL - 106 IS - 1 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Mizuno, Yosuke A1 - Pohl, Martin A1 - Niemiec, Jacek A1 - Zhang, Bing A1 - Nishikawa, Ken-Ichi A1 - Hardee, Philip E. T1 - Magnetic-field amplification by turbulence in a relativistic shockpropagating through an inhomogeneous medium JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We perform two-dimensional relativistic magnetohydrodynamic simulations of a mildly relativistic shock propagating through an inhomogeneous medium. We show that the postshock region becomes turbulent owing to preshock density inhomogeneity, and the magnetic field is strongly amplified due to the stretching and folding of field lines in the turbulent velocity field. The amplified magnetic field evolves into a filamentary structure in two-dimensional simulations. The magnetic energy spectrum is flatter than the Kolmogorov spectrum and indicates that a so-called small-scale dynamo is occurring in the postshock region. We also find that the amount of magnetic-field amplification depends on the direction of the mean preshock magnetic field, and the timescale of magnetic-field growth depends on the shock strength. KW - gamma-ray burst: general KW - magnetohydrodynamics (MHD) KW - methods: numerical KW - relativistic processes KW - shock waves KW - turbulence Y1 - 2011 U6 - https://doi.org/10.1088/0004-637X/726/2/62 SN - 0004-637X VL - 726 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Kalbitz, Rene A1 - Frübing, Peter A1 - Gerhard, Reimund A1 - Taylor, D. M. T1 - Stability of polarization in organic ferroelectric metal-insulator-semiconductor structures JF - Applied physics letters N2 - Dielectric measurements have been carried out on all-organic metal-insulator-semiconductor structures with the ferroelectric polymer poly(vinylidenefluoride-trifluoroethylene) as the gate insulator. It is shown that the polarization states remain stable after poling with accumulation and depletion voltage. However, negative charge trapped at the semiconductor-insulator interface during the depletion cycle masks the negative shift in flatband voltage expected during the sweep to accumulation voltages. Y1 - 2011 U6 - https://doi.org/10.1063/1.3543632 SN - 0003-6951 VL - 98 IS - 3 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Schiefele, Juergen A1 - Henkel, Carsten T1 - Bosonic enhancement of spontaneous emission near an interface JF - Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics N2 - We show how the spontaneous emission rate of an excited two-level atom placed in a trapped Bose-Einstein condensate of ground-state atoms is enhanced by bosonic stimulation. This stimulation depends on the overlap of the excited matter-wave packet with the macroscopically occupied condensate wave function, and provides a probe of the spatial coherence of the Bose gas. The effect can be used to amplify the distance-dependent decay rate of an excited atom near an interface. KW - Bose-Einstein condensation KW - Correlation function KW - Bosonic stimulation KW - Superradiance KW - Spontaneous decay KW - Cavity-quantum electrodynamics Y1 - 2011 U6 - https://doi.org/10.1016/j.physleta.2010.11.058 SN - 0375-9601 VL - 375 IS - 3 SP - 680 EP - 684 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Gogolin, Christian A1 - Müller, Markus P. A1 - Eisert, Jens T1 - Absence of thermalization in nonintegrable systems JF - Physical review letters N2 - We establish a link between unitary relaxation dynamics after a quench in closed many-body systems and the entanglement in the energy eigenbasis. We find that even if reduced states equilibrate, they can have memory on the initial conditions even in certain models that are far from integrable. We show that in such situations the equilibrium states are still described by a maximum entropy or generalized Gibbs ensemble, regardless of whether a model is integrable or not, thereby contributing to a recent debate. In addition, we discuss individual aspects of the thermalization process, comment on the role of Anderson localization, and collect and compare different notions of integrability. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevLett.106.040401 SN - 0031-9007 VL - 106 IS - 4 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Fiehler, Katja A1 - Bannert, Michael M. A1 - Bischoff, Matthias A1 - Blecker, Carlo A1 - Stark, Rudolf A1 - Vaitl, Dieter A1 - Franz, Volker H. A1 - Roesler, Frank T1 - Working memory maintenance of grasp-target information in the human posterior parietal cortex JF - NeuroImage : a journal of brain function N2 - Event-related functional magnetic resonance imaging was applied to identify cortical areas involved in maintaining target information in working memory used for an upcoming grasping action. Participants had to grasp with their thumb and index finger of the dominant right hand three-dimensional objects of different size and orientation. Reaching-to-grasp movements were performed without visual feedback either immediately after object presentation or after a variable delay of 2-12 s. The right inferior parietal cortex demonstrated sustained neural activity throughout the delay, which overlapped with activity observed during encoding of the grasp target. Immediate and delayed grasping activated similar motor-related brain areas and showed no differential activity. The results suggest that the right inferior parietal cortex plays an important functional role in working memory maintenance of grasp-related information. Moreover, our findings confirm the assumption that brain areas engaged in maintaining information are also involved in encoding the same information, and thus extend previous findings on working memory function of the posterior parietal cortex in saccadic behavior to reach-to-grasp movements. Y1 - 2011 U6 - https://doi.org/10.1016/j.neuroimage.2010.09.080 SN - 1053-8119 VL - 54 IS - 3 SP - 2401 EP - 2411 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - Mellinger, Axel A1 - Mellinger, Olena T1 - Breakdown threshold of dielectric barrier discharges in ferroelectrets where Paschen's law fails JF - IEEE transactions on dielectrics and electrical insulation N2 - The piezoelectric activity of charged cellular foams (so-called ferroelectrets) is compared against simulations based on a multi-layer electromechanical model and Townsend's model of Paschen breakdown, with the distribution of void heights determined from scanning electron micrographs. While the calculated space charge hysteresis curves are in good agreement with experimental data, the onset of piezoelectric activity is observed at significantly higher electric fields than predicted by Paschen's law. One likely explanation is that the commonly accepted Paschen curve for electric breakdown in air poorly describes the critical electric field for dielectric barrier discharges in micrometer-size cavities. KW - Ferroelectrets KW - dielectric barrier discharges KW - piezoelectricity KW - Paschen's law Y1 - 2011 U6 - https://doi.org/10.1109/TDEI.2011.5704491 SN - 1070-9878 VL - 18 IS - 1 SP - 43 EP - 48 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - JOUR A1 - Qiu, Xunlin A1 - Gerhard, Reimund A1 - Mellinger, Axel T1 - Turning polymer foams or polymer-film systems into ferroelectrets dielectric barrier discharges in voids JF - IEEE transactions on dielectrics and electrical insulation N2 - Polymer foams and void-containing polymer-film systems with internally charged voids combine large piezoelectricity with mechanical flexibility and elastic compliance. This new class of soft materials (often called ferro-or piezoelectrets) has attracted considerable attention from science and industry. It has been found that the voids can be internally charged by means of dielectric barrier discharges (DBDs) under high electric fields. The charged voids can be considered as man-made macroscopic dipoles. Depending on the ferroelectret structure and the pressure of the internal gas, the voids may be highly compressible. Consequently, very large dipole-moment changes can be induced by mechanical or electrical stresses, leading to large piezoelectricity. DBD charging of the voids is a critical process for rendering polymer foams piezoelectric. Thus a comprehensive exploration of DBD charging is essential for the understanding and the optimization of piezoelectricity in ferroelectrets. Recent studies show that DBDs in the voids are triggered when the internal electric field reaches a threshold value according to Townsend's model of Paschen breakdown. During the DBDs, charges of opposite polarity are generated and trapped at the top and bottom internal surfaces of the gas-filled voids, respectively. The deposited charges induce an electric field opposite to the externally applied one and thus extinguish the DBDs. Back discharges may eventually be triggered when the external voltage is reduced or turned off. In order to optimize the efficiency of DBD charging, the geometry (in particular the height) of the voids, the type of gas and its pressure inside the voids are essential factors to be considered and to be optimized. In addition, the influence of the plasma treatment on the internal void surfaces during the DBDs should be taken into consideration. KW - Ferroelectret KW - piezoelectret KW - dielectric barrier discharge (DBD) KW - effective polarization KW - man-made dipole Y1 - 2011 U6 - https://doi.org/10.1109/TDEI.2011.5704490 SN - 1070-9878 VL - 18 IS - 1 SP - 34 EP - 42 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - JOUR A1 - Rychkov, Dmitry A1 - Kuznetsov, Alexey A1 - Rychkov, Andrey T1 - Electret properties of polyethylene and polytetrafluoroethylene films with chemically modified surface JF - IEEE transactions on dielectrics and electrical insulation N2 - This paper investigates the effect of chemical surface modification of polytetrafluoroethylene (PTFE) and low density polyethylene (LDPE) films on their electret properties. PTFE films were subjected to wet treatment with three different chemicals: orthophosphoric acid, tetrabutyl titanate and tetraethoxysilane. The technique based on the principles of molecular layer deposition (MLD) method was used to modify the surface of LDPE films with phosphorus trichloride vapors. The surfaces of the films were then corona charged, and the electret charge stability was studied by means of isothermal and thermally stimulated surface potential decay. Both PTFE and LDPE films, after the surface treatment, displayed a considerable enhancement in the charge stability compared to the virgin samples. It is important to note that the enhancement of the charge stability was achieved in the positively charged PTFE films, a result important to practical applications. We attribute this effect of charge stabilization to the formation of new energetically deep traps on the modified surface. Decrease in molecular mobility, due to attachment of new chemical structures to the surface macromolecules, may also contribute to the overall growth of the charge stability. KW - Electrets KW - surface treatment KW - charge stability KW - charge carrier processes KW - polytetrafluoroethylene KW - polyethylene Y1 - 2011 U6 - https://doi.org/10.1109/TDEI.2011.5704487 SN - 1070-9878 VL - 18 IS - 1 SP - 8 EP - 14 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - GEN A1 - Gerhard, Reimund T1 - Honoring Professor Gerhard M. Sessler on his 80th Birthday (15th of February 2011) T2 - IEEE transactions on dielectrics and electrical insulation Y1 - 2011 U6 - https://doi.org/10.1109/TDEI.2011.5704485 SN - 1070-9878 VL - 18 IS - 1 SP - 1 EP - 2 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - JOUR A1 - Jordan, Grace A1 - McCarthy, Denis N. A1 - Schlepple, N. A1 - Krissler, Jan A1 - Schroeder, H. A1 - Kofod, Guggi T1 - Actuated micro-optical submount using a dielectric elastomer actuator JF - IEEE ASME transactions on mechatronics N2 - Analysis of the operating characteristics of a dielectric elastomer actuator (DEA) submount for the high-precision positioning of optical components in one dimension is presented. Precise alignment of a single-mode fiber is demonstrated and variation of the sensitivity of the submount motion by changing the bias voltage is confirmed. A comparison of the performance of the DEA submount with a piezoelectric alignment stage is made, which demonstrates that DEAs could present a very attractive, low-cost alternative to currently used manual technologies in overcoming the hurdle of expensive packaging of single-mode optical components. KW - Actuators KW - manufacturing automation KW - optical interconnections KW - packaging KW - position control Y1 - 2011 U6 - https://doi.org/10.1109/TMECH.2010.2089991 SN - 1083-4435 VL - 16 IS - 1 SP - 98 EP - 102 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - JOUR A1 - Abdo, A. A. A1 - Ackermann, Margit A1 - Ajello, M. A1 - Allafort, A. J. A1 - Baldini, L. A1 - Ballet, J. A1 - Barbiellini, G. A1 - Baring, M. G. A1 - Bastieri, D. A1 - Bechtol, K. C. A1 - Bellazzini, R. A1 - Berenji, B. A1 - Blandford, R. D. A1 - Bloom, E. D. A1 - Bonamente, E. A1 - Borgland, A. W. A1 - Bouvier, A. A1 - Brandt, T. J. A1 - Bregeon, Johan A1 - Brez, A. A1 - Brigida, M. A1 - Bruel, P. A1 - Buehler, R. A1 - Buson, S. A1 - Caliandro, G. A. A1 - Cameron, R. A. A1 - Cannon, A. A1 - Caraveo, P. A. A1 - Carrigan, Svenja A1 - Casandjian, J. M. A1 - Cavazzuti, E. A1 - Cecchi, C. A1 - Celik, O. A1 - Charles, E. A1 - Chekhtman, A. A1 - Cheung, C. C. A1 - Chiang, J. A1 - Ciprini, S. A1 - Claus, R. A1 - Cohen-Tanugi, J. A1 - Conrad, Jan A1 - Cutini, S. A1 - Dermer, C. D. A1 - de Palma, F. A1 - do Couto e Silva, E. A1 - Drell, P. S. A1 - Dubois, R. A1 - Dumora, D. A1 - Favuzzi, C. A1 - Fegan, S. J. A1 - Ferrara, E. C. A1 - Focke, W. B. A1 - Fortin, P. A1 - Frailis, M. A1 - Fuhrmann, L. A1 - Fukazawa, Y. A1 - Funk, S. A1 - Fusco, P. A1 - Gargano, F. A1 - Gasparrini, D. A1 - Gehrels, N. A1 - Germani, S. A1 - Giglietto, N. A1 - Giordano, F. A1 - Giroletti, M. A1 - Glanzman, T. A1 - Godfrey, G. A1 - Grenier, I. A. A1 - Guillemot, L. A1 - Guiriec, S. A1 - Hayashida, M. A1 - Hays, E. A1 - Horan, D. A1 - Hughes, R. E. A1 - Johannesson, G. A1 - Johnson, A. S. A1 - Johnson, W. N. A1 - Kadler, M. A1 - Kamae, T. A1 - Katagiri, H. A1 - Kataoka, J. A1 - Knoedlseder, J. A1 - Kuss, M. A1 - Lande, J. A1 - Latronico, L. A1 - Lee, S. -H. A1 - Lemoine-Goumard, M. A1 - Longo, F. A1 - Loparco, F. A1 - Lott, B. A1 - Lovellette, M. N. A1 - Lubrano, P. A1 - Madejski, G. M. A1 - Makeev, A. A1 - Max-Moerbeck, W. A1 - Mazziotta, Mario Nicola A1 - McEnery, J. E. A1 - Mehault, J. A1 - Michelson, P. F. A1 - Mitthumsiri, W. A1 - Mizuno, T. A1 - Moiseev, A. A. A1 - Monte, C. A1 - Monzani, M. E. A1 - Morselli, A. A1 - Moskalenko, I. V. A1 - Murgia, S. A1 - Naumann-Godo, M. A1 - Nishino, S. A1 - Nolan, P. L. A1 - Norris, J. P. A1 - Nuss, E. A1 - Ohsugi, T. A1 - Okumura, A. A1 - Omodei, N. A1 - Orlando, E. A1 - Ormes, J. F. A1 - Paneque, D. A1 - Panetta, J. H. A1 - Parent, D. A1 - Pavlidou, V. A1 - Pearson, T. J. A1 - Pelassa, V. A1 - Pepe, M. A1 - Pesce-Rollins, M. A1 - Piron, F. A1 - Porter, T. A. A1 - Raino, S. A1 - Rando, R. A1 - Razzano, M. A1 - Readhead, A. A1 - Reimer, A. A1 - Reimer, O. A1 - Richards, J. L. A1 - Ripken, J. A1 - Ritz, S. A1 - Roth, M. A1 - Sadrozinski, H. F. -W. A1 - Sanchez, D. A1 - Sander, A. A1 - Scargle, J. D. A1 - Sgro, C. A1 - Siskind, E. J. A1 - Smith, P. D. A1 - Spandre, G. A1 - Spinelli, P. A1 - Stawarz, L. A1 - Stevenson, M. A1 - Strickman, M. S. A1 - Sokolovsky, K. V. A1 - Suson, D. J. A1 - Takahashi, H. A1 - Takahashi, T. A1 - Tanaka, T. A1 - Thayer, J. B. A1 - Thayer, J. G. A1 - Thompson, D. J. A1 - Tibaldo, L. A1 - Torres, F. A1 - Tosti, G. A1 - Tramacere, A. A1 - Uchiyama, Y. A1 - Usher, T. L. A1 - Vandenbroucke, J. A1 - Vasileiou, V. A1 - Vilchez, N. A1 - Vitale, V. A1 - Waite, A. P. A1 - Wang, P. A1 - Wehrle, A. E. A1 - Winer, B. L. A1 - Wood, K. S. A1 - Yang, Z. A1 - Ylinen, T. A1 - Zensus, J. A. A1 - Ziegler, M. A1 - Aleksic, J. A1 - Antonelli, L. A. A1 - Antoranz, P. A1 - Backes, Michael A1 - Barrio, J. A. A1 - Gonzalez, J. Becerra A1 - Bednarek, W. A1 - Berdyugin, A. A1 - Berger, K. A1 - Bernardini, E. A1 - Biland, A. A1 - Blanch Bigas, O. A1 - Bock, R. K. A1 - Boller, A. A1 - Bonnoli, G. A1 - Bordas, Pol A1 - Tridon, D. Borla A1 - Bosch-Ramon, Valentin A1 - Bose, D. A1 - Braun, I. A1 - Bretz, T. A1 - Camara, M. A1 - Carmona, E. A1 - Carosi, A. A1 - Colin, P. A1 - Colombo, E. A1 - Contreras, J. L. A1 - Cortina, J. A1 - Covino, S. A1 - Dazzi, F. A1 - de Angelis, A. A1 - del Pozo, E. De Cea A1 - De Lotto, B. A1 - De Maria, M. A1 - De Sabata, F. A1 - Mendez, C. Delgado A1 - Ortega, A. Diago A1 - Doert, M. A1 - Dominguez, A. A1 - Prester, Dijana Dominis A1 - Dorner, D. A1 - Doro, M. A1 - Elsaesser, D. A1 - Ferenc, D. A1 - Fonseca, M. V. A1 - Font, L. A1 - Lopen, R. J. Garcia A1 - Garczarczyk, M. A1 - Gaug, M. A1 - Giavitto, G. A1 - Godinovi, N. A1 - Hadasch, D. A1 - Herrero, A. A1 - Hildebrand, D. A1 - Hoehne-Moench, D. A1 - Hose, J. A1 - Hrupec, D. A1 - Jogler, T. A1 - Klepser, S. A1 - Kraehenbuehl, T. A1 - Kranich, D. A1 - Krause, J. A1 - La Barbera, A. A1 - Leonardo, E. A1 - Lindfors, E. A1 - Lombardi, S. A1 - Lopez, M. A1 - Lorenz, E. A1 - Majumdar, P. A1 - Makariev, E. A1 - Maneva, G. A1 - Mankuzhiyil, N. A1 - Mannheim, K. A1 - Maraschi, L. A1 - Mariotti, M. A1 - Martinez, M. A1 - Mazin, D. A1 - Meucci, M. A1 - Miranda, J. M. A1 - Mirzoyan, R. A1 - Miyamoto, H. A1 - Moldon, J. A1 - Moralejo, A. A1 - Nieto, D. A1 - Nilsson, K. A1 - Orito, R. A1 - Oya, I. A1 - Paoletti, R. A1 - Paredes, J. M. A1 - Partini, S. A1 - Pasanen, M. A1 - Pauss, F. A1 - Pegna, R. G. A1 - Perez-Torres, M. A. A1 - Persic, M. A1 - Peruzzo, J. A1 - Pochon, J. A1 - Moroni, P. G. Prada A1 - Prada, F. A1 - Prandini, E. A1 - Puchades, N. A1 - Puljak, I. A1 - Reichardt, T. A1 - Reinthal, R. A1 - Rhode, W. A1 - Ribo, M. A1 - Rico, J. A1 - Rissi, M. A1 - Ruegamer, S. A1 - Saggion, A. A1 - Saito, K. A1 - Saito, T. Y. A1 - Salvati, M. A1 - Sanchez-Conde, M. A1 - Satalecka, K. A1 - Scalzotto, V. A1 - Scapin, V. A1 - Schultz, C. A1 - Schweizer, T. A1 - Shayduk, M. A1 - Shore, S. N. A1 - Sierpowska-Bartosik, A. A1 - Sillanpaa, A. A1 - Sitarek, J. A1 - Sobczynska, D. A1 - Spanier, F. A1 - Spiro, S. A1 - Stamerra, A. A1 - Steinke, B. A1 - Storz, J. A1 - Strah, N. A1 - Struebig, J. C. A1 - Suric, T. A1 - Takalo, L. O. A1 - Tavecchio, F. A1 - Temnikov, P. A1 - Terzic, T. A1 - Tescaro, D. A1 - Teshima, M. A1 - Vankov, H. A1 - Wagner, R. M. A1 - Weitzel, Q. A1 - Zabalza, V. A1 - Zandanel, F. A1 - Zanin, R. A1 - Acciari, V. A. A1 - Arlen, T. A1 - Aune, T. A1 - Benbow, W. A1 - Boltuch, D. A1 - Bradbury, S. M. A1 - Buckley, J. H. A1 - Bugaev, V. A1 - Cannon, A. A1 - Cesarini, A. A1 - Ciupik, L. A1 - Cui, W. A1 - Dickherber, R. A1 - Errando, M. A1 - Falcone, A. A1 - Finley, J. P. A1 - Finnegan, G. A1 - Fortson, L. A1 - Furniss, A. A1 - Galante, N. A1 - Gall, D. A1 - Gillanders, G. H. A1 - Godambe, S. A1 - Grube, J. A1 - Guenette, R. A1 - Gyuk, G. A1 - Hanna, D. A1 - Holder, J. A1 - Huang, D. A1 - Hui, C. M. A1 - Humensky, T. B. A1 - Kaaret, P. A1 - Karlsson, N. A1 - Kertzman, M. A1 - Kieda, D. A1 - Konopelko, A. A1 - Krawczynski, H. A1 - Krennrich, F. A1 - Lang, M. J. A1 - Maier, G. A1 - McArthur, S. A1 - McCann, A. A1 - McCutcheon, M. A1 - Moriarty, P. A1 - Mukherjee, R. A1 - Ong, R. A1 - Otte, N. A1 - Pandel, D. A1 - Perkins, J. S. A1 - Pichel, A. A1 - Pohl, M. A1 - Quinn, J. A1 - Ragan, K. A1 - Reyes, L. C. A1 - Reynolds, P. T. A1 - Roache, E. A1 - Rose, H. J. A1 - Rovero, A. C. A1 - Schroedter, M. A1 - Sembroski, G. H. A1 - Senturk, G. D. A1 - Steele, D. A1 - Swordy, S. P. A1 - Tesic, G. A1 - Theiling, M. A1 - Thibadeau, S. A1 - Varlotta, A. A1 - Vincent, S. A1 - Wakely, S. P. A1 - Ward, J. E. A1 - Weekes, T. C. A1 - Weinstein, A. A1 - Weisgarber, T. A1 - Williams, D. A. A1 - Wood, M. A1 - Zitzer, B. A1 - Villata, M. A1 - Raiteri, C. M. A1 - Aller, H. D. A1 - Aller, M. F. A1 - Arkharov, A. A. A1 - Blinov, D. A. A1 - Calcidese, P. A1 - Chen, W. P. A1 - Efimova, N. V. A1 - Kimeridze, G. A1 - Konstantinova, T. S. A1 - Kopatskaya, E. N. A1 - Koptelova, E. A1 - Kurtanidze, O. M. A1 - Kurtanidze, S. O. A1 - Lahteenmaki, A. A1 - Larionov, V. M. A1 - Larionova, E. G. A1 - Larionova, L. V. A1 - Ligustri, R. A1 - Morozova, D. A. A1 - Nikolashvili, M. G. A1 - Sigua, L. A. A1 - Troitsky, I. S. A1 - Angelakis, E. A1 - Capalbi, M. A1 - Carraminana, A. A1 - Carrasco, L. A1 - Cassaro, P. A1 - de la Fuente, E. A1 - Gurwell, M. A. A1 - Kovalev, Y. Y. A1 - Kovalev, Yu. A. A1 - Krichbaum, T. P. A1 - Krimm, H. A. A1 - Leto, Paolo A1 - Lister, M. L. A1 - Maccaferri, G. A1 - Moody, J. W. A1 - Mori, Y. A1 - Nestoras, I. A1 - Orlati, A. A1 - Pagani, C. A1 - Pace, C. A1 - Pearson, R. A1 - Perri, M. A1 - Piner, B. G. A1 - Pushkarev, A. B. A1 - Ros, E. A1 - Sadun, A. C. A1 - Sakamoto, T. A1 - Tornikoski, M. A1 - Yatsu, Y. A1 - Zook, A. T1 - Insights into the high-energy gamma-Ray emission of markarian 501 fromextensive multifrequency observations in the fermi era JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We report on the gamma-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) gamma-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 +/- 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 +/- 0.14, and the softest one is 2.51 +/- 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15-August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size less than or similar to 0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (similar or equal to 10(44) erg s(-1)) constitutes only a small fraction (similar to 10(-3)) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a scenario in which the bulk of the energy dissipation within the dominant emission zone of Mrk 501 is due to relativistic, proton-mediated shocks. We find that the ultrarelativistic electrons and mildly relativistic protons within the blazar zone, if comparable in number, are in approximate energy equipartition, with their energy dominating the jet magnetic field energy by about two orders of magnitude. KW - acceleration of particles KW - BL Lacertae objects: general KW - BL Lacertae objects: individual (Mrk 501) KW - galaxies: active KW - gamma rays: general KW - radiation mechanisms: non-thermal Y1 - 2011 U6 - https://doi.org/10.1088/0004-637X/727/2/129 SN - 0004-637X VL - 727 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Green, Luci M. A1 - Kliem, Bernhard A1 - Wallace, A. J. T1 - Photospheric flux cancellation and associated flux rope formation and eruption JF - Astronomy and astrophysics : an international weekly journal N2 - Aims. We study an evolving bipolar active region that exhibits flux cancellation at the internal polarity inversion line, the formation of a soft X-ray sigmoid along the inversion line and a coronal mass ejection. The aim is to investigate the quantity of flux cancellation that is involved in flux rope formation in the time period leading up to the eruption. Methods. The active region is studied using its extreme ultraviolet and soft X-ray emissions as it evolves from a sheared arcade to flux rope configuration. The evolution of the photospheric magnetic field is described and used to estimate how much flux is reconnected into the flux rope. Results. About one third of the active region flux cancels at the internal polarity inversion line in the 2.5 days leading up to the eruption. In this period, the coronal structure evolves from a weakly to a highly sheared arcade and then to a sigmoid that crosses the inversion line in the inverse direction. These properties suggest that a flux rope has formed prior to the eruption. The amount of cancellation implies that up to 60% of the active region flux could be in the body of the flux rope. We point out that only part of the cancellation contributes to the flux in the rope if the arcade is only weakly sheared, as in the first part of the evolution. This reduces the estimated flux in the rope to similar to 30% or less of the active region flux. We suggest that the remaining discrepancy between our estimate and the limiting value of similar to 10% of the active region flux, obtained previously by the flux rope insertion method, results from the incomplete coherence of the flux rope, due to nonuniform cancellation along the polarity inversion line. A hot linear feature is observed in the active region which rises as part of the eruption and then likely traces out the field lines close to the axis of the flux rope. The flux cancellation and changing magnetic connections at one end of this feature suggest that the flux rope reaches coherence by reconnection immediately before and early in the impulsive phase of the associated flare. The sigmoid is destroyed in the eruption but reforms quickly, with the amount of cancellation involved being much smaller than in the course of its original formation. KW - Sun: activity KW - Sun: coronal mass ejections (CMEs) KW - magnetic fields KW - magnetic reconnection KW - Sun: photosphere KW - Sun: magnetic topology Y1 - 2011 U6 - https://doi.org/10.1051/0004-6361/201015146 SN - 0004-6361 VL - 526 IS - 2 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Fuhrmann, Marcel A1 - Seehafer, Norbert A1 - Valori, Gherardo A1 - Wiegelmann, T. T1 - A comparison of preprocessing methods for solar force-free magnetic field extrapolation JF - Astronomy and astrophysics : an international weekly journal N2 - Context. Extrapolations of solar photospheric vector magnetograms into three-dimensional magnetic fields in the chromosphere and corona are usually done under the assumption that the fields are force-free. This condition is violated in the photosphere itself and a thin layer in the lower atmosphere above. The field calculations can be improved by preprocessing the photospheric magnetograms. The intention here is to remove a non-force-free component from the data. Aims. We compare two preprocessing methods presently in use, namely the methods of Wiegelmann et al. (2006, Sol. Phys., 233, 215) and Fuhrmann et al. (2007, A&A, 476, 349). Methods. The two preprocessing methods were applied to a vector magnetogram of the recently observed active region NOAA AR 10 953. We examine the changes in the magnetogram effected by the two preprocessing algorithms. Furthermore, the original magnetogram and the two preprocessed magnetograms were each used as input data for nonlinear force-free field extrapolations by means of two different methods, and we analyze the resulting fields. Results. Both preprocessing methods managed to significantly decrease the magnetic forces and magnetic torques that act through the magnetogram area and that can cause incompatibilities with the assumption of force-freeness in the solution domain. The force and torque decrease is stronger for the Fuhrmann et al. method. Both methods also reduced the amount of small-scale irregularities in the observed photospheric field, which can sharply worsen the quality of the solutions. For the chosen parameter set, the Wiegelmann et al. method led to greater changes in strong-field areas, leaving weak-field areas mostly unchanged, and thus providing an approximation of the magnetic field vector in the chromosphere, while the Fuhrmann et al. method weakly changed the whole magnetogram, thereby better preserving patterns present in the original magnetogram. Both preprocessing methods raised the magnetic energy content of the extrapolated fields to values above the minimum energy, corresponding to the potential field. Also, the fields calculated from the preprocessed magnetograms fulfill the solenoidal condition better than those calculated without preprocessing. KW - Sun: magnetic topology KW - Sun: atmosphere KW - magnetohydrodynamics (MHD) Y1 - 2011 U6 - https://doi.org/10.1051/0004-6361/201015453 SN - 0004-6361 VL - 526 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Hubrig, Swetlana A1 - Oskinova, Lida A1 - Schoeller, M. T1 - First detection of a magnetic field in the fast rotating runaway Oe star zeta Ophiuchi JF - Astronomische Nachrichten = Astronomical notes N2 - The star zeta Ophiuchi is one of the brightest massive stars in the northern hemisphere and was intensively studied in various wavelength domains. The currently available observational material suggests that certain observed phenomena are related to the presence of a magnetic field. We acquired spectropolarimetric observations of zeta Oph with FORS 1 mounted on the 8-m Kueyen telescope of the VLT to investigate if a magnetic field is indeed present in this star. Using all available absorption lines, we detect a mean longitudinal magnetic field < B(z)>(all) = 141 +/- 45 G, confirming the magnetic nature of this star. We review the X-ray properties of zeta Oph with the aim to understand whether the X-ray emission of zeta Oph is dominated by magnetic or by wind instability processes. KW - stars: mass-loss KW - stars: early-type KW - stars: magnetic field KW - stars: kinematics and dynamics KW - X-rays: stars KW - stars: individual: zeta Ophiuchi Y1 - 2011 U6 - https://doi.org/10.1002/asna.201111516 SN - 0004-6337 VL - 332 IS - 2 SP - 147 EP - 152 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Reiche, Jürgen A1 - Kratz, Karl A1 - Hofmann, Dieter A1 - Lendlein, Andreas T1 - Current status of Langmuir monolayer degradation of polymeric biomaterials JF - The international journal of artificial organs N2 - Langmuir monolayer degradation (LMD) experiments with polymers possessing outstanding biomedical application potential yield information regarding the kinetics of their hydrolytic or enzymatic chain scission under well-defined and adjustable degradation conditions. A brief review is given of LMD investigations, including the author's own work on 2-dimensional (2D) polymer systems, providing chain scission data, which are not disturbed by simultaneously occurring transport phenomena, such as water penetration into the sample or transport of scission fragments out of the sample. A knowledge-based approach for the description and simulation of polymer hydrolytic and enzymatic degradation based on a combination of fast LMD experiments and computer simulation of the water penetration is briefly introduced. Finally, the advantages and disadvantages of this approach are discussed. KW - Monolayer KW - Hydrolytic degradation KW - Enzymatic degradation KW - Biomaterial KW - Degradable polymer Y1 - 2011 U6 - https://doi.org/10.5301/IJAO.2011.6401 SN - 0391-3988 VL - 34 IS - 2 SP - 123 EP - 128 PB - Wichtig CY - Milano ER - TY - JOUR A1 - Hoban, Matty J. A1 - Campbell, Earl T. A1 - Loukopoulos, Klearchos A1 - Browne, Dan E. T1 - Non-adaptive measurement-based quantum computation and multi-party Bell inequalities JF - New journal of physics : the open-access journal for physics N2 - Quantum correlations exhibit behaviour that cannot be resolved with a local hidden variable picture of the world. In quantum information, they are also used as resources for information processing tasks, such as measurement-based quantum computation (MQC). In MQC, universal quantum computation can be achieved via adaptive measurements on a suitable entangled resource state. In this paper, we look at a version of MQC in which we remove the adaptivity of measurements and aim to understand what computational abilities remain in the resource. We show that there are explicit connections between this model of computation and the question of non-classicality in quantum correlations. We demonstrate this by focusing on deterministic computation of Boolean functions, in which natural generalizations of the Greenberger-Horne-Zeilinger paradox emerge; we then explore probabilistic computation via, which multipartite Bell inequalities can be defined. We use this correspondence to define families of multi-party Bell inequalities, which we show to have a number of interesting contrasting properties. Y1 - 2011 U6 - https://doi.org/10.1088/1367-2630/13/2/023014 SN - 1367-2630 VL - 13 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Giewekemeyer, K. A1 - Krueger, S. P. A1 - Kalbfleisch, S. A1 - Bartels, Meike A1 - Beta, Carsten A1 - Salditt, T. T1 - X-ray propagation microscopy of biological cells using waveguides as a quasipoint source JF - Physical review : A, Atomic, molecular, and optical physics N2 - We have used x-ray waveguides as highly confining optical elements for nanoscale imaging of unstained biological cells using the simple geometry of in-line holography. The well-known twin-image problem is effectively circumvented by a simple and fast iterative reconstruction. The algorithm which combines elements of the classical Gerchberg-Saxton scheme and the hybrid-input-output algorithm is optimized for phase-contrast samples, well-justified for imaging of cells at multi-keV photon energies. The experimental scheme allows for a quantitative phase reconstruction from a single holographic image without detailed knowledge of the complex illumination function incident on the sample, as demonstrated for freeze-dried cells of the eukaryotic amoeba Dictyostelium discoideum. The accessible resolution range is explored by simulations, indicating that resolutions on the order of 20 nm are within reach applying illumination times on the order of minutes at present synchrotron sources. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevA.83.023804 SN - 1050-2947 VL - 83 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Mulansky, Mario A1 - Ahnert, Karsten A1 - Pikovskij, Arkadij T1 - Scaling of energy spreading in strongly nonlinear disordered lattices JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - To characterize a destruction of Anderson localization by nonlinearity, we study the spreading behavior of initially localized states in disordered, strongly nonlinear lattices. Due to chaotic nonlinear interaction of localized linear or nonlinear modes, energy spreads nearly subdiffusively. Based on a phenomenological description by virtue of a nonlinear diffusion equation, we establish a one-parameter scaling relation between the velocity of spreading and the density, which is confirmed numerically. From this scaling it follows that for very low densities the spreading slows down compared to the pure power law. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevE.83.026205 SN - 1539-3755 VL - 83 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Pikovskij, Arkadij A1 - Fishman, Shmuel T1 - Scaling properties of weak chaos in nonlinear disordered lattices JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We study the discrete nonlinear Schrodinger equation with a random potential in one dimension. It is characterized by the length, the strength of the random potential, and the field density that determines the effect of nonlinearity. Following the time evolution of the field and calculating the largest Lyapunov exponent, the probability of the system to be regular is established numerically and found to be a scaling function of the parameters. This property is used to calculate the asymptotic properties of the system in regimes beyond our computational power. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevE.83.025201 SN - 1539-3755 SN - 1550-2376 VL - 83 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Kofod, Guggi A1 - Stoyanov, Hristiyan A1 - Gerhard, Reimund T1 - Multilayer coaxial fiber dielectric elastomers for actuation and sensing JF - Applied physics : A, Materials science & processing N2 - A simple dip-coating technique was employed to manufacture coaxial actuators with multiple layers of alternating dielectric and conducting layers. A thin rubber string was coated with an electrode-insulator-electrode structure, giving rise to a thin, fiber-like actuator with coaxial geometry. The process was repeated to achieve a compact multilayer actuator with up to three coaxial dielectric layers. Mechanical and electromechanical characterization of the actuators is presented, showing actuation strains up to 8% and proper voltage-thickness scaling behavior. Also presented is a capacitance vs. extension plot, demonstrating that these structures can be used for compact and accurate capacitive strain sensing. Y1 - 2011 U6 - https://doi.org/10.1007/s00339-010-6066-5 SN - 0947-8396 SN - 1432-0630 VL - 102 IS - 3 SP - 577 EP - 581 PB - Springer CY - New York ER - TY - JOUR A1 - Malic, E. A1 - Weber, C. A1 - Richter, M. A1 - Atalla, V. A1 - Klamroth, Tillmann A1 - Saalfrank, Peter A1 - Reich, Sebastian A1 - Knorr, A. T1 - Microscopic model of the optical absorption of carbon nanotubes functionalized with molecular spiropyran photoswitches JF - Physical review letters N2 - The adsorption of molecules to the surface of carbon nanostructures opens a new field of hybrid systems with distinct and controllable properties. We present a microscopic study of the optical absorption in carbon nanotubes functionalized with molecular spiropyran photoswitches. The switching process induces a change in the dipole moment leading to a significant coupling to the charge carriers in the nanotube. As a result, the absorption spectra of functionalized tubes reveal a considerable redshift of transition energies depending on the switching state of the spiropyran molecule. Our results suggest that carbon nanotubes are excellent substrates for the optical readout of spiropyran-based molecular switches. The gained insights can be applied to other noncovalently functionalized one-dimensional nanostructures in an externally induced dipole field. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevLett.106.097401 SN - 0031-9007 VL - 106 IS - 9 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Montoya, Marisa A1 - Born, Andreas A1 - Levermann, Anders T1 - Reversed North Atlantic gyre dynamics in present and glacial climates JF - Climate dynamics : observational, theoretical and computational research on the climate system N2 - The dynamics of the North Atlantic subpolar gyre (SPG) are assessed under present and glacial boundary conditions by investigating the SPG sensitivity to surface wind-stress changes in a coupled climate model. To this end, the gyre transport is decomposed in Ekman, thermohaline, and bottom transports. Surface wind-stress variations are found to play an important indirect role in SPG dynamics through their effect on water-mass densities. Our results suggest the existence of two dynamically distinct regimes of the SPG, depending on the absence or presence of deep water formation (DWF) in the Nordic Seas and a vigorous Greenland-Scotland ridge (GSR) overflow. In the first regime, the GSR overflow is weak and the SPG strength increases with wind-stress as a result of enhanced outcropping of isopycnals in the centre of the SPG. As soon as a vigorous GSR overflow is established, its associated positive density anomalies on the southern GSR slope reduce the SPG strength. This has implications for past glacial abrupt climate changes, insofar as these can be explained through latitudinal shifts in North Atlantic DWF sites and strengthening of the North Atlantic current. Regardless of the ultimate trigger, an abrupt shift of DWF into the Nordic Seas could result both in a drastic reduction of the SPG strength and a sudden reversal in its sensitivity to wind-stress variations. Our results could provide insight into changes in the horizontal ocean circulation during abrupt glacial climate changes, which have been largely neglected up to now in model studies. Y1 - 2011 U6 - https://doi.org/10.1007/s00382-009-0729-y SN - 0930-7575 VL - 36 IS - 5-6 SP - 1107 EP - 1118 PB - Springer CY - New York ER - TY - JOUR A1 - Kofod, Guggi A1 - Risse, Sebastian A1 - Stoyanov, Hristiyan A1 - McCarthy, Denis N. A1 - Sokolov, Sergey A1 - Krähnert, Ralph T1 - Broad-spectrum enhancement of polymer composite dielectric constant at ultra low volume fractions of silica-supported copper nanoparticles JF - ACS nano N2 - A new strategy for the synthesis of high permittivity polymer composites is demonstrated based on well-defined spatial distribution of ultralow amounts of conductive nanoparticles. The spatial distribution Was realized by immobilizing Cu nanoparticles within the pore system of Alia microspheres, preventing direct contact between individual Cu particles. Both Cu-loaded and unloaded silica microspheres were-then used as fillers in polymer composites prepared with thermoplastic SEBS rubber is the matrix. With a metallic Cu content of about 0.26 vol % In the compoilte, a relative increase of 94% In real permittivity was obtained. No Cu-induced relaxations were observed in the dielectric spectrum within the studied frequency range of 0.1 Hz to 1 MHz. When related to the amount of conductive nanoparticles, the obtained composites achieve the highest broad spectrum enhancement of permittivity ever reported for a polymer based composite. KW - nanocomposite KW - broad-spectrum permittivity enhancement KW - metal nanoparticles KW - uniform spatial arrangement Y1 - 2011 U6 - https://doi.org/10.1021/nn103097q SN - 1936-0851 VL - 5 IS - 3 SP - 1623 EP - 1629 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Kuehn, Sergei A1 - Pingel, Patrick A1 - Breusing, Markus A1 - Fischer, Thomas A1 - Stumpe, Joachim A1 - Neher, Dieter A1 - Elsaesser, Thomas T1 - High-Resolution Near-Field Optical Investigation of Crystalline Domains in Oligomeric PQT-12 Thin Films JF - Advanced functional materials N2 - The structure and morphology on different length scales dictate both the electrical and optical properties of organic semiconductor thin films. Using a combination of spectroscopic methods, including scanning near-field optical microscopy, we study the domain structure and packing quality of highly crystalline thin films of oligomeric PQT-12 with 100 nanometer spatial resolution. The pronounced optical anisotropy of these layers measured by polarized light microscopy facilitates the identification of regions with uniform molecular orientation. We find that a hierarchical order on three different length scales exists in these layers, made up of distinct well-ordered dichroic areas at the ten-micrometer-scale, which are sub-divided into domains with different molecular in-plane orientation. These serve as a template for the formation of smaller needle-like crystallites at the layer surface. A high degree of crystalline order is believed to be the cause of the rather high field-effect mobility of these layers of 10(-3) cm 2 V(-1) s(-1), whereas it is limited by the presence of domain boundaries at macroscopic distances. Y1 - 2011 U6 - https://doi.org/10.1002/adfm.201001978 SN - 1616-301X VL - 21 IS - 5 SP - 860 EP - 868 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Hoffmann, Katrin A1 - Dietzel, Birgit A1 - Schulz, Burkhard A1 - Reck, Guenter A1 - Hoffmann, Angelika A1 - Orgzall, Ingo A1 - Resch-Genger, Ute A1 - Emmerling, Franziska T1 - Combined structural and fluorescence studies of methyl-substituted 2,5-diphenyl-1,3,4-oxadiazoles - Relation between electronic properties and packing motifs JF - Journal of molecular structure N2 - Prerequisite for the rational design of functional organic materials with tailor-made electronic properties is the knowledge of the structure-property relationship for the specific class of molecules under consideration. This encouraged us to systematically study the influence of the molecular structure and substitution pattern of aromatically substituted 1,3,4-oxadiazoles on the electronic properties and packing motifs of these molecules and on the interplay of these factors. For this purpose, seven diphenyl-oxadiazoles equipped with methyl substituents in the ortho- and meta-position(s) were synthesized and characterized. Absorption and fluorescence spectra in solution served here as tools to monitor substitution-induced changes in the electronic properties of the individual molecules whereas X-ray and optical measurements in the solid state provided information on the interplay of electronic and packing effects. In solution, the spectral position of the absorption maximum, the size of Stokes shift, and the fluorescence quantum yield are considerably affected by ortho-substitution in three or four ortho-positions. This results in blue shifted absorption bands, increased Stokes shifts, and reduced fluorescence quantum yields whereas the spectral position and vibrational structure of the emission bands remain more or less unaffected. In the crystalline state, however, the spectral position and shape of the emission bands display a strong dependence on the molecular structure and/or packing motifs that seem to control the amount of dye-dye-interactions. These observations reveal the limited value of commonly reported absorption and fluorescence measurements in solution for a straightforward comparison of spectroscopic results with single X-ray crystallography. This underlines the importance of solid state spectroscopic studies for a better understanding of the interplay of electronic effects and molecular order. KW - Diphenyl-oxadiazoles KW - X-ray structure KW - Packing motif KW - Optical properties KW - Fluorescence quantum yield Y1 - 2011 U6 - https://doi.org/10.1016/j.molstruc.2010.11.071 SN - 0022-2860 VL - 988 IS - 1-3 SP - 35 EP - 46 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Turukina, L. V. A1 - Pikovskij, Arkadij T1 - Hyperbolic chaos in a system of resonantly coupled weakly nonlinear oscillators JF - Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics N2 - We show that a hyperbolic chaos can be observed in resonantly coupled oscillators near a Hopf bifurcation, described by normal-form-type equations for complex amplitudes. The simplest example consists of four oscillators, comprising two alternatively activated, due to an external periodic modulation, pairs. In terms of the stroboscopic Poincare map, the phase differences change according to an expanding Bernoulli map that depends on the coupling type. Several examples of hyperbolic chaos for different types of coupling are illustrated numerically. KW - Coupled oscillators KW - Hyperbolic chaos Y1 - 2011 U6 - https://doi.org/10.1016/j.physleta.2011.02.017 SN - 0375-9601 VL - 375 IS - 11 SP - 1407 EP - 1411 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Prosen, Tomaz T1 - Complexity and nonseparability of classical Liouvillian dynamics JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We propose a simple complexity indicator of classical Liouvillian dynamics, namely the separability entropy, which determines the logarithm of an effective number of terms in a Schmidt decomposition of phase space density with respect to an arbitrary fixed product basis. We show that linear growth of separability entropy provides a stricter criterion of complexity than Kolmogorov-Sinai entropy, namely it requires that the dynamics be exponentially unstable, nonlinear, and non-Markovian. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevE.83.031124 SN - 1539-3755 VL - 83 IS - 3 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Schaefer, Edith A1 - Westendorf, Christian A1 - Bodenschatz, Eberhard A1 - Beta, Carsten A1 - Geil, Burkhard A1 - Janshoff, Andreas T1 - Shape oscillations of dictyostelium discoideum cells on ultramicroelectrodes monitored by impedance analysis JF - Small Y1 - 2011 U6 - https://doi.org/10.1002/smll.201001955 SN - 1613-6810 VL - 7 IS - 6 SP - 723 EP - 726 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Floss, Gereon A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Laser-controlled switching of molecular arrays in an dissipative environment JF - Physical review : B, Condensed matter and materials physics N2 - The optical switching of molecular ensembles in a dissipative environment is a subject of various fields of chemical physics and physical chemistry. Here we try to switch arrays of molecules from a stable collective ground state to a state in which all molecules have been transferred to another stable higher-energy configuration. In our model switching proceeds through electronically excited intermediates which are coherently coupled to each other through dipolar interactions, and which decay incoherently within a finite lifetime by coupling to a dissipative environment. The model is quite general, but parameters are chosen to roughly resemble the all-trans -> all-cis isomerization of an array of azobenzene molecules on a surface. Using analytical and optimal control pulses and the concept of "laser distillation," we demonstrate that for various aggregates (dimers up to hexamers), controlled and complete switching should be possible. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevB.83.104301 SN - 1098-0121 VL - 83 IS - 10 PB - American Physical Society CY - College Park ER -