TY - JOUR A1 - Zykov, Vladimir A1 - Bordyugov, Grigory A1 - Lentz, Hartmut A1 - Engel, Harald T1 - Hysteresis phenomenon in the dynamics of spiral waves rotating around a hole N2 - Hysteresis in the pinning-depinning transitions of spiral waves rotating around a hole in a circular shaped two- dimensional excitable medium is studied both by use of the continuation software AUTO and by direct numerical integration of the reaction-diffusion equations for the FitzHugh-Nagumo model. In order to clarify the role of different factors in this phenomenon, a kinematical description is applied. It is found that the hysteresis phenomenon computed for the reaction-diffusion model can be reproduced qualitatively only when a nonlinear eikonal equation (i.e. velocity- curvature relationship) is assumed. However, to obtain quantitative agreement, the dispersion relation has to be taken into account. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/01672789 U6 - https://doi.org/10.1016/j.physd.2009.07.018 SN - 0167-2789 ER - TY - JOUR A1 - Zunkovic, Bojan A1 - Prosen, Tomaz T1 - Explicit solution of the Lindblad equation for nearly isotropic boundary driven XY spin 1/2 chain N2 - Explicit solution for the two-point correlation function in a non-equilibrium steady state of a nearly isotropic boundary driven open XY spin 1/2 chain in the Lindblad formulation is provided. A non-equilibrium quantum phase transition from exponentially decaying correlations to long range order is discussed analytically. In the regime of long range order a new phenomenon of correlation resonances is reported, where the correlation response of the system is unusually high for certain discrete values of the external bulk parameter, e.g. the magnetic field. Y1 - 2010 UR - http://iopscience.iop.org/1742-5468/ U6 - https://doi.org/10.1088/1742-5468/2010/08/P08016 SN - 1742-5468 ER - TY - JOUR A1 - Zhu, Jian A1 - Stoyanov, Hristiyan A1 - Kofod, Guggi A1 - Suo, Zhigang T1 - Large deformation and electromechanical instability of a dielectric elastomer tube actuator N2 - This paper theoretically analyzes a dielectric elastomer tube actuator (DETA). Subject to a voltage difference between the inner and outer surfaces, the actuator reduces in thickness and expands in length, so that the same voltage will induce an even higher electric field. This positive feedback may cause the actuator to thin down drastically, resulting in electrical breakdown. We obtain an analytical solution of the actuator undergoing finite deformation when the elastomer obeys the neo-Hookean model. The critical strain of actuation is calculated in terms of various parameters of design. We also discuss the effect of the strain-stiffening on electromechanical behavior of DETAs by using the model of freely joined links. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490186] Y1 - 2010 UR - http://jap.aip.org/ U6 - https://doi.org/10.1063/1.3490186 SN - 0021-8979 ER - TY - JOUR A1 - Zakharova, Anna A1 - Vadivasova, Tatjana A1 - Anishchenko, Vadim S. A1 - Koseska, Aneta A1 - Kurths, Jürgen T1 - Stochastic bifurcations and coherencelike resonance in a self-sustained bistable noisy oscillator N2 - We investigate the influence of additive Gaussian white noise on two different bistable self-sustained oscillators: Duffing-Van der Pol oscillator with hard excitation and a model of a synthetic genetic oscillator. In the deterministic case, both oscillators are characterized with a coexistence of a stable limit cycle and a stable equilibrium state. We find that under the influence of noise, their dynamics can be well characterized through the concept of stochastic bifurcation, consisting in a qualitative change of the stationary amplitude distribution. For the Duffing-Van der Pol oscillator analytical results, obtained for a quasiharmonic approach, are compared with the result of direct computer simulations. In particular, we show that the dynamics is different for isochronous and anisochronous systems. Moreover, we find that the increase of noise intensity in the isochronous regime leads to a narrowing of the spectral line. This effect is similar to coherence resonance. However, in the case of anisochronous systems, this effect breaks down and a new phenomenon, anisochronous-based stochastic bifurcation occurs. Y1 - 2010 UR - http://pre.aps.org/ U6 - https://doi.org/10.1103/Physreve.81.011106 SN - 1539-3755 ER - TY - JOUR A1 - Wu, Ye A1 - Zhou, Changsong A1 - Chen, Maoyin A1 - Xiao, Jinghua A1 - Kurths, Jürgen T1 - Human comment dynamics in on-line social systems N2 - Human comment is studied using data from 'tianya' which is one of the most popular on-line social systems in China. We found that the time interval between two consecutive comments on the same topic, called inter-event time, follows a power-law distribution. This result shows that there is no characteristic decay time on a topic. It allows for very long periods without comments that separate bursts of intensive comments. Furthermore, the frequency of a different ID commenting on a topic also follows a power-law distribution. It indicates that there are some "hubs" in the topic who lead the direction of the public opinion. Based on the personal comments habit, a model is introduced to explain these phenomena. The numerical simulations of the model fit well with the empirical results. Our findings are helpful for discovering regular patterns of human behavior in on-line society and the evolution of the public opinion on the virtual as well as real society. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/03784371 U6 - https://doi.org/10.1016/j.physa.2010.08.049 SN - 0378-4371 ER - TY - JOUR A1 - Wu, Ye Wu A1 - Zhou, Changsong A1 - Xiao, Jinghua A1 - Kurths, Jürgen A1 - Schellnhuber, Hans Joachim T1 - Evidence for a bimodal distribution in human communication N2 - Interacting human activities underlie the patterns of many social, technological, and economic phenomena. Here we present clear empirical evidence from Short Message correspondence that observed human actions are the result of the interplay of three basic ingredients: Poisson initiation of tasks and decision making for task execution in individual humans as well as interaction among individuals. This interplay leads to new types of interevent time distribution, neither completely Poisson nor power-law, but a bimodal combination of them. We show that the events can be separated into independent bursts which are generated by frequent mutual interactions in short times following random initiations of communications in longer times by the individuals. We introduce a minimal model of two interacting priority queues incorporating the three basic ingredients which fits well the distributions using the parameters extracted from the empirical data. The model can also embrace a range of realistic social interacting systems such as e-mail and letter communications when taking the time scale of processing into account. Our findings provide insight into various human activities both at the individual and network level. Our analysis and modeling of bimodal activity in human communication from the viewpoint of the interplay between processes of different time scales is likely to shed light on bimodal phenomena in other complex systems, such as interevent times in earthquakes, rainfall, forest fire, and economic systems, etc. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/03784371 U6 - https://doi.org/10.1073/pnas.1013140107 SN - 0027-8424 ER - TY - BOOK A1 - Wisotki, Lutz T1 - Galaxien, Schwarze Löcher, Quasare : Antrittsvorlesung 2010-12-08 Y1 - 2010 UR - http://info.ub.uni-potsdam.de/multimedia/show_multimediafile.php?mediafile_id=242 PB - Univ.-Bibl. CY - Potsdam ER - TY - JOUR A1 - Winter, Silvia Maria Giuliatti A1 - Winter, Othon Cabo A1 - Fernandes Guimarães, Ana Helena A1 - Silva, Maria Rita T1 - Exploring S-type orbits in the Pluto-Charon binary system N2 - This work generates, through a sample of numerical simulations of the restricted three-body problem, diagrams of semimajor axis and eccentricity which defines stable and unstable zones for particles in S-type orbits around Pluto and Charon. Since we consider initial conditions with 0 <= e <= 0.99, we found several new stable regions. We also identified the nature of each one of these newly found stable regions. They are all associated to families of periodic orbits derived from the planar circular restricted three-body problem. We have shown that a possible eccentricity of the Pluto-Charon system slightly reduces, but does not destroy, any of the stable regions. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=0035-8711 U6 - https://doi.org/10.1111/j.1365-2966.2010.16302.x SN - 0035-8711 ER - TY - JOUR A1 - Wang, Feipeng A1 - Frübing, Peter A1 - Wirges, Werner A1 - Gerhard, Reimund A1 - Wegener, Michael T1 - Enhanced Polarization in Melt-quenched and Stretched Poly(vinylidene Fluoride-Hexafluoropropylene) Films N2 - beta-phase poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymer films were prepared by uniaxially stretching solution-cast or melt-quenched samples. Different preparation routes lead to different amounts of the crystalline alpha and beta phases in the films, as detected by means of Fourier-transform infrared spectroscopy and X-ray diffractometry. The beta phase is significantly enhanced in melt-quenched and stretched films in comparison to solution-cast and stretched films. This is particularly true for copolymer samples with higher HFP content. The beta- phase enhancement is also observed in ferroelectric-hysteresis experiments where a rather high polarization of 58 mC/ m(2) was found on melt-quenched and stretched samples after poling at electric fields of 140 MV/m. After poling at 160 MV/m, one of these samples exhibited a piezoelectric d(33) coefficient as high as 21 pC/N. An electric-field-induced partial transition from the alpha to the beta phase was also observed on the melt-quenched and stretched samples. This effect leads to a further increase in the applications-relevant dipole polarization. Uniaxially stretched ferroelectric- polymer films are highly anisotropic. Dielectric resonance spectroscopy reveals a strong increase of the transverse piezoelectric d(32) coefficient and a strong decrease of the transverse elastic modulus c(32) upon heating from 20 to 50 degrees C. Y1 - 2010 UR - http://ieeexplore.ieee.org/servlet/opac?punumber=94 U6 - https://doi.org/10.1109/TDEI.2010.5539679 SN - 1070-9878 ER - TY - JOUR A1 - Votruba, Viktor A1 - Feldmeier, Achim A1 - Krticka, Jiri A1 - Kubát, Jiří T1 - Multicomponent stellar wind from hot subdwarfs stars N2 - Stellar wind from hot subdwarf stars is mainly accelerated by the interaction of ultraviolet photospheric radiation with metals, mainly oxygen. Absorbing ions share momentum through Coulombic collisions with the remaining passive part of the plasma (namely protons). We found that in the case of the winds from hot subdwarfs, interactions could be so small that they stop the momentum transfer between the passive bulk of plasma and absorbing ions. As a result wind decouples at a certain point. Y1 - 2010 UR - http://www.springerlink.com/content/100241 U6 - https://doi.org/10.1007/s10509-010-0402-2 SN - 0004-640X ER -