TY  - JOUR
A1  - Cramer, Marcus
A1  - Eisert, Jens
T1  - A quantum central limit theorem for non-equilibrium systems : exact local relaxation of correlated states
N2  - We prove that quantum many-body systems on a one-dimensional lattice locally relax to Gaussian states under non- equilibrium dynamics generated by a bosonic quadratic Hamiltonian. This is true for a large class of initial states-pure or mixed-which have to satisfy merely weak conditions concerning the decay of correlations. The considered setting is a proven instance of a situation where dynamically evolving closed quantum systems locally appear as if they had truly relaxed, to maximum entropy states for fixed second moments. This furthers the understanding of relaxation in suddenly quenched quantum many-body systems. The proof features a non-commutative central limit theorem for non-i.i.d. random variables, showing convergence to Gaussian characteristic functions, giving rise to trace-norm closeness. We briefly link our findings to the ideas of typicality and concentration of measure.
Y1  - 2010
UR  - http://iopscience.iop.org/1367-2630
U6  - https://doi.org/10.1088/1367-2630/12/5/055020
SN  - 1367-2630
ER  - 
TY  - JOUR
A1  - Cuzzi, Jeff N.
A1  - Burns, Joseph A.
A1  - Charnoz, Sébastien
A1  - Clark, Roger N.
A1  - Colwell, Josh E.
A1  - Dones, Luke
A1  - Esposito, Larry W.
A1  - Filacchione, Gianrico
A1  - French, Richard G.
A1  - Hedman, Matthew M.
A1  - Kempf, Sascha
A1  - Marouf, Essam A.
A1  - Murray, Carl D.
A1  - Nicholson, Phillip D.
A1  - Porco, Carolyn C.
A1  - Schmidt, Jürgen
A1  - Showalter, Mark R.
A1  - Spilker, Linda J.
A1  - Spitale, Joseph N.
A1  - Srama, Ralf
A1  - Sremcević, Miodrag
A1  - Tiscareno, Matthew Steven
A1  - Weiss, John
T1  - An evolving view of Saturn's dynamic rings
N2  - We review our understanding of Saturn's rings after nearly 6 years of observations by the Cassini spacecraft. Saturn's rings are composed mostly of water ice but also contain an undetermined reddish contaminant. The rings exhibit a range of structure across many spatial scales; some of this involves the interplay of the fluid nature and the self-gravity of innumerable orbiting centimeter- to meter-sized particles, and the effects of several peripheral and embedded moonlets, but much remains unexplained. A few aspects of ring structure change on time scales as short as days. It remains unclear whether the vigorous evolutionary processes to which the rings are subject imply a much younger age than that of the solar system. Processes on view at Saturn have parallels in circumstellar disks.
Y1  - 2010
UR  - http://www.sciencemag.org/
U6  - https://doi.org/10.1126/science.1179118
SN  - 0036-8075
ER  - 
TY  - JOUR
A1  - Eisert, Jens
A1  - Plenio, Martin B.
T1  - Focus on quantum information and many-body theory
N2  - Quantum many-body models describing natural systems or materials and physical systems assembled piece by piece in the laboratory for the purpose of realizing quantum information processing share an important feature: intricate correlations that originate from the coherent interaction between a large number of constituents. In recent years it has become manifest that the cross-fertilization between research devoted to quantum information science and to quantum many- body physics leads to new ideas, methods, tools, and insights in both fields. Issues of criticality, quantum phase transitions, quantum order and magnetism that play a role in one field find relations to the classical simulation of quantum systems, to error correction and fault tolerance thresholds, to channel capacities and to topological quantum computation, to name but a few. The structural similarities of typical problems in both fields and the potential for pooling of ideas then become manifest. Notably, methods and ideas from quantum information have provided fresh approaches to long-standing problems in strongly correlated systems in the condensed matter context, including both numerical methods and conceptual insights.
Y1  - 2010
UR  - http://iopscience.iop.org/1367-2630
U6  - https://doi.org/10.1088/1367-2630/12/2/025001
SN  - 1367-2630
ER  - 
TY  - JOUR
A1  - de Beaudrap, Niel
T1  - On restricted unitary Cayley graphs and symplectic transformations modulo n
N2  - We present some observations on a restricted variant of unitary Cayley graphs modulo n, and implications for a decomposition of elements of symplectic operators over the integers modulo n. We define quadratic unitary Cayley graphs G(n), whose vertex set is the ring Z(n), and where residues a, b modulo n are adjacent if and only if their difference is a quadratic residue. By bounding the diameter of such graphs, we show an upper bound on the number of elementary operations (symplectic scalar multiplications, symplectic row swaps, and row additions or subtractions) required to decompose a symplectic matrix over Z(n). We also characterize the conditions on n for G(n) to be a perfect graph.
Y1  - 2010
UR  - http://www.emis.de/journals/EJC/index.html
SN  - 1077-8926
ER  - 
TY  - JOUR
A1  - de Beaudrap, Niel
T1  - Unitary-circuit semantics for measurement-based computations
N2  - One-way measurement based quantum computations (1WQC) may describe unitary transformations, via a composition of CPTP maps which are not all unitary themselves. This motivates the following decision problems. Is it possible to determine whether a "quantum-to-quantum" 1WQC procedure (having non-trivial input and output subsystems) performs a unitary transformation? Is it possible to describe precisely how such computations transform quantum states, by translation to a quantum circuit of comparable complexity? In this article, we present an efficient algorithm for transforming certain families of measurement-based computations into a reasonable unitary circuit model, in particular without employing the principle of deferred measurement.
Y1  - 2010
UR  - http://ejournals.wspc.com.sg/ijqi/ijqi.shtml
U6  - https://doi.org/10.1142/S0219749910006113
SN  - 0219-7499
ER  - 
TY  - JOUR
A1  - de Beaudrap, Niel
A1  - Ohliger, Matthias
A1  - Osborne, Tobias J.
A1  - Eisert, Jens
T1  - Solving frustration-free spin systems
N2  - We identify a large class of quantum many-body systems that can be solved exactly: natural frustration-free spin-1/2 nearest-neighbor Hamiltonians on arbitrary lattices. We show that the entire ground-state manifold of such models can be found exactly by a tensor network of isometries acting on a space locally isomorphic to the symmetric subspace. Thus, for this wide class of models, real-space renormalization can be made exact. Our findings also imply that every such frustration-free spin model satisfies an area law for the entanglement entropy of the ground state, establishing a novel large class of models for which an area law is known. Finally, we show that our approach gives rise to an ansatz class useful for the simulation of almost frustration-free models in a simple fashion, outperforming mean- field theory.
Y1  - 2010
UR  - http://prl.aps.org/
U6  - https://doi.org/10.1103/Physrevlett.105.060504
SN  - 0031-9007
ER  - 
TY  - JOUR
A1  - de Beaudrap, Niel
A1  - Osborne, Tobias J.
A1  - Eisert, Jens
T1  - Ground states of unfrustrated spin Hamiltonians satisfy an area law
N2  - We show that ground states of unfrustrated quantum spin-1/2 systems on general lattices satisfy an entanglement area law, provided that the Hamiltonian can be decomposed into nearest-neighbor interaction terms that have entangled excited states. The ground state manifold can be efficiently described as the image of a low-dimensional subspace of low Schmidt measure, under an efficiently contractible tree-tensor network. This structure gives rise to the possibility of efficiently simulating the complete ground space (which is in general degenerate). We briefly discuss 'non- generic' cases, including highly degenerate interactions with product eigenbases, using a relationship to percolation theory. We finally assess the possibility of using such tree tensor networks to simulate almost frustration- free spin models.
Y1  - 2010
UR  - http://iopscience.iop.org/1367-2630
U6  - https://doi.org/10.1088/1367-2630/12/9/095007
SN  - 1367-2630
ER  - 
TY  - JOUR
A1  - Mikelskis, Helmut F.
T1  - Physics schoolbooks - their history and future
Y1  - 2010
SN  - 978-3-8309-2018-2
ER  - 
TY  - THES
A1  - Neumeyer, Steffen
T1  - Entwicklung und Evaluation eines Lernortes Praktikum für die Schule
Y1  - 2010
CY  - Potsdam
ER  - 
TY  - THES
A1  - Tambornino, Johannes
T1  - An analysis of the low energy regime of loop quantum gravity
Y1  - 2010
CY  - Potsdam
ER  - 
TY  - THES
A1  - Lara, Lucía Santamaría
T1  - Coalescence of black-hole binaries : from theoretical source models to applications in gravitational-wave astronomy
Y1  - 2010
CY  - Potsdam
ER  - 
TY  - THES
A1  - Krobath, Heinrich
T1  - Binding cooperativity and domain energies of membrane adhesion receptors
Y1  - 2010
CY  - Potsdam
ER  - 
TY  - JOUR
A1  - Blakesley, James C.
A1  - Clubb, Helen S.
A1  - Greenham, Neil C.
T1  - Temperature-dependent electron and hole transport in disordered semiconducting polymers : analysis of energetic disorder
N2  - We have used space-charge limited current measurements to study the mobility of holes and electrons in two fluorene-based copolymers for temperatures from 100 to 300 K. Interpreting the results using the standard analytical model produced an Arrhenius-type temperature dependence for a limited temperature range only and mobility was found to be apparently dependent on the thickness of the polymer film. To improve on this, we have interpreted our data using a numerical model that takes into account the effects of the carrier concentration and energetic disorder on transport. This accounted for the thickness dependence and gave a more consistent temperature dependence across the full range of temperatures, giving support to the extended Gaussian disorder model for transport in disordered polymers. Furthermore, we find that the same model adequately describes both electron and hole transport without the need to explicitly include a distribution of electron traps. Room-temperature mobilities were found to be in the region of 4 x 10(-8) and 2 x 10(- 8) cm(2) V-1 s(-1) in the limit of zero field and zero carrier density with disorders of 110+/-10 and 100+/-10 meV for polymers poly{9,9-dioctylfluorene-co-bis[N,N'-(4-butylphenyl)]bis(N, N'-phenyl-1,4-phenylene)diamine} and poly(9,9-dioctylfluorene-co-benzothiadiazole), respectively.
Y1  - 2010
UR  - http://prb.aps.org/
U6  - https://doi.org/10.1103/Physrevb.81.045210
SN  - 1098-0121
ER  - 
TY  - JOUR
A1  - Boedeker, Hendrik Ulrich
A1  - Beta, Carsten
A1  - Frank, Till D.
A1  - Bodenschatz, Eberhard
T1  - Quantitative analysis of random ameboid motion
N2  - We quantify random migration of the social ameba Dictyostelium discoideum. We demonstrate that the statistics of cell motion can be described by an underlying Langevin-type stochastic differential equation. An analytic expression for the velocity distribution function is derived. The separation into deterministic and stochastic parts of the movement shows that the cells undergo a damped motion with multiplicative noise. Both contributions to the dynamics display a distinct response to external physiological stimuli. The deterministic component depends on the developmental state and ambient levels of signaling substances, while the stochastic part does not.
Y1  - 2010
UR  - http://iopscience.iop.org/0295-5075/
U6  - https://doi.org/10.1209/0295-5075/90/28005
SN  - 0295-5075
ER  - 
TY  - JOUR
A1  - Bordyugov, Grigory
A1  - Fischer, Nils
A1  - Engel, Harald
A1  - Manz, Niklas
A1  - Steinbock, Oliver
T1  - Anomalous dispersion in the Belousov-Zhabotinsky reaction : experiments and modeling
N2  - We report results on dispersion relations and instabilities of traveling waves in excitable systems. Experiments employ solutions of the 1,4-cyclohexanedione Belousov-Zhabotinsky reaction confined to thin capillary tubes which create a pseudo-one-dimensional system. Theoretical analyses focus on a three-variable reaction-diffusion model that is known to reproduce qualitatively many of the experimentally observed dynamics. Using continuation methods, we show that the transition from normal, monotonic to anomalous, single-overshoot dispersion curves is due to an orbit flip bifurcation of the solitary pulse homoclinics. In the case of "wave stacking", this anomaly induces attractive pulse interaction, slow solitary pulses, and faster wave trains. For "wave merging", wave trains break up in the wake of the slow solitary pulse due to an instability of wave trains at small wavelength. A third case, "wave tracking" is characterized by the non-existence of solitary waves but existence of periodic wave trains. The corresponding dispersion curve is a closed curve covering a finite band of wavelengths.
Y1  - 2010
UR  - http://www.sciencedirect.com/science/journal/01672789
U6  - https://doi.org/10.1016/j.physd.2009.10.022
SN  - 0167-2789
ER  - 
TY  - JOUR
A1  - Balaž, Antun
A1  - Vidanovic, Ivana
A1  - Bogojević, Aleksandar
A1  - Pelster, Axel
T1  - Ultra-fast converging path-integral approach for rotating ideal Bose-Einstein condensates
N2  - A recently developed efficient recursive approach for analytically calculating the short-time evolution of the one-particle propagator to extremely high orders is applied here for numerically studying the thermodynamical and dynamical properties of a rotating ideal Bose gas of Rb-87 atoms in an anharmonic trap. At first, the one-particle energy spectrum of the system is obtained by diagonalizing the discretized short-time propagator. Using this, many-boson properties such as the condensation temperature, the ground-state occupancy, density profiles, and time-of-flight absorption pictures are calculated for varying rotation frequencies. The obtained results improve previous semiclassical calculations, in particular for smaller particle numbers. Furthermore, we find that typical time scales for a free expansion are increased by an order of magnitude for the delicate regime of both critical and overcritical rotation.
Y1  - 2010
UR  - http://www.sciencedirect.com/science/journal/03759601
U6  - https://doi.org/10.1016/j.physleta.2010.01.034
SN  - 0375-9601
ER  - 
TY  - JOUR
A1  - Barthel, Thomas
A1  - Kliesch, Martin
A1  - Eisert, Jens
T1  - Real-space renormalization yields finite correlations
N2  - Real-space renormalization approaches for quantum lattice systems generate certain hierarchical classes of states that are subsumed by the multiscale entanglement renormalization Ansatz (MERA). It is shown that, with the exception of one spatial dimension, MERA states are actually states with finite correlations, i.e., projected entangled pair states (PEPS) with a bond dimension independent of the system size. Hence, real-space renormalization generates states which can be encoded with local effective degrees of freedom, and MERA states form an efficiently contractible class of PEPS that obey the area law for the entanglement entropy. It is further pointed out that there exist other efficiently contractible schemes violating the area law.
Y1  - 2010
UR  - http://prl.aps.org/
U6  - https://doi.org/10.1103/Physrevlett.105.010502
SN  - 0031-9007
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  - 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  - 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  - Senthilkumar, Dharmapuri Vijayan
A1  - Muruganandam, Paulsamy
A1  - Lakshmanan, Muthusamy
T1  - Scaling and synchronization in a ring of diffusively coupled nonlinear oscillators
N2  - Chaos synchronization in a ring of diffusively coupled nonlinear oscillators driven by an external identical oscillator is studied. Based on numerical simulations we show that by introducing additional couplings at (mN(c) + 1)-th oscillators in the ring, where m is an integer and N-c is the maximum number of synchronized oscillators in the ring with a single coupling, the maximum number of oscillators that can be synchronized can be increased considerably beyond the limit restricted by size instability. We also demonstrate that there exists an exponential relation between the number of oscillators that can support stable synchronization in the ring with the external drive and the critical coupling strength epsilon(c) with a scaling exponent gamma. The critical coupling strength is calculated by numerically estimating the synchronization error and is also confirmed from the conditional Lyapunov exponents of the coupled systems. We find that the same scaling relation exists for m couplings between the drive and the ring. Further, we have examined the robustness of the synchronous states against Gaussian white noise and found that the synchronization error exhibits a power-law decay as a function of the noise intensity indicating the existence of both noise-enhanced and noise-induced synchronizations depending on the value of the coupling strength epsilon. In addition, we have found that epsilon(c) shows an exponential decay as a function of the number of additional couplings. These results are demonstrated using the paradigmatic models of Rossler and Lorenz oscillators.
Y1  - 2010
UR  - http://pre.aps.org/
U6  - https://doi.org/10.1103/Physreve.81.066219
SN  - 1539-3755
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  - 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  - 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  - Hamann, Wolf-Rainer
T1  - Stellar winds from hot low-mass stars
N2  - Stellar winds appear as a persistent feature of hot stars, irrespective of their wide range of different luminosities, masses, and chemical composition. Among the massive stars, the Wolf-Rayet types show considerably stronger mass loss than the O stars. Among hot low-mass stars, stellar winds are seen at central stars of planetary nebulae, where again the hydrogen-deficient stars show much stronger winds than those central stars with "normal" composition. We also studied mass-loss from a few extreme helium stars and sdOs. Their mass-loss rate roughly follows the same proportionality with luminosity to the power 1.5 as the massive O stars. This relation roughly marks a lower limit for the mass loss from hot stars of all kinds, and provides evidence that radiation pressure on spectral lines is the basic mechanism at work. For certain classes of stars the mass-loss rates lie significantly above this relation, for reasons that are not yet fully understood. Mass loss from low-mass stars may affect their evolution, by reducing the envelope mass, and can easily prevent diffusion from establishing atmospheric abundance patterns. In close binary systems, their winds can feed the accretion onto a companion.
Y1  - 2010
UR  - http://www.springerlink.com/content/100241
U6  - https://doi.org/10.1007/s10509-010-0344-8
SN  - 0004-640X
ER  - 
TY  - JOUR
A1  - Gross, David
A1  - Eisert, Jens
T1  - Quantum computational webs
N2  - We discuss the notion of quantum computational webs: These are quantum states universal for measurement-based computation, which can be built up from a collection of simple primitives. The primitive elements-reminiscent of building blocks in a construction kit-are (i) one-dimensional states (computational quantum wires) with the power to process one logical qubit and (ii) suitable couplings, which connect the wires to a computationally universal web. All elements are preparable by nearest-neighbor interactions in a single pass, of the kind accessible in a number of physical architectures. We provide a complete classification of qubit wires, a physically well-motivated class of universal resources that can be fully understood. Finally, we sketch possible realizations in superlattices and explore the power of coupling mechanisms based on Ising or exchange interactions.
Y1  - 2010
UR  - http://pra.aps.org/
U6  - https://doi.org/10.1103/Physreva.82.040303
SN  - 1050-2947
ER  - 
TY  - JOUR
A1  - Gross, David
A1  - Liu, Yi-Kai
A1  - Flammia, Steven T.
A1  - Becker, Stephen
A1  - Eisert, Jens
T1  - Quantum state tomography via compressed sensing
N2  - We establish methods for quantum state tomography based on compressed sensing. These methods are specialized for quantum states that are fairly pure, and they offer a significant performance improvement on large quantum systems. In particular, they are able to reconstruct an unknown density matrix of dimension d and rank r using O(rdlog(2)d) measurement settings, compared to standard methods that require d(2) settings. Our methods have several features that make them amenable to experimental implementation: they require only simple Pauli measurements, use fast convex optimization, are stable against noise, and can be applied to states that are only approximately low rank. The acquired data can be used to certify that the state is indeed close to pure, so no a priori assumptions are needed.
Y1  - 2010
UR  - http://prl.aps.org/
U6  - https://doi.org/10.1103/Physrevlett.105.150401
SN  - 0031-9007
ER  - 
TY  - JOUR
A1  - Gross, David
A1  - Mueller, Markus
A1  - Colbeck, Roger
A1  - Dahlsten, Oscar C. O.
T1  - All reversible dynamics in maximally nonlocal theories are trivial
N2  - A remarkable feature of quantum theory is nonlocality ( Bell inequality violations). However, quantum correlations are not maximally nonlocal, and it is natural to ask whether there are compelling reasons for rejecting theories in which stronger violations are possible. To shed light on this question, we consider post-quantum theories in which maximally nonlocal states ( nonlocal boxes) occur. We show that reversible transformations in such theories are trivial: they consist solely of local operations and permutations of systems. In particular, no correlations can be created; nonlocal boxes cannot be prepared from product states and classical computers can efficiently simulate all such processes.
Y1  - 2010
UR  - http://prl.aps.org/
U6  - https://doi.org/10.1103/Physrevlett.104.080402
SN  - 0031-9007
ER  - 
TY  - JOUR
A1  - Gvaramadze, Vasily V.
A1  - Kniazev, Alexei Y.
A1  - Hamann, Wolf-Rainer
A1  - Berdnikov, Leonid N.
A1  - Fabrika, Sergei Nikolaevich
A1  - Valeev, Azamat F.
T1  - A new Wolf-Rayet star and its circumstellar nebula in Aquila
N2  - We report the discovery of a new Wolf-Rayet star in Aquila via detection of its circumstellar nebula (reminiscent of ring nebulae associated with late WN stars) using the Spitzer Space Telescope archival data. Our spectroscopic follow-up of the central point source associated with the nebula showed that it is a WN7h star (we named it WR121b). We analysed the spectrum of WR 121b by using the Potsdam Wolf-Rayet model atmospheres, obtaining a stellar temperature of similar or equal to 50 kK. The stellar wind composition is dominated by helium with similar to 20 per cent of hydrogen. The stellar spectrum is highly reddened [E(B - V) = 2.85 mag]. Adopting an absolute magnitude of M-v = 5.7, the star has a luminosity of log L/L-circle dot = 5.75 and a mass-loss rate of 10(-4.7)M(circle dot)yr(-1), and resides at a distance of 6.3 kpc. We searched for a possible parent cluster of WR 121b and found that this star is located at similar or equal to 1 degrees from the young star cluster embedded in the giant HII region W43 (containing a WN7+a/OB? star - WR121a). We also discovered a bow shock around the O9.5III star ALS 9956, located at similar or equal to 0 degrees.5 from the cluster. We discuss the possibility that WR121b and ALS 9956 are runaway stars ejected from the cluster in W43.
Y1  - 2010
UR  - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=0035-8711
U6  - https://doi.org/10.1111/j.1365-2966.2009.16126.x
SN  - 0035-8711
ER  - 
TY  - JOUR
A1  - Senthilkumar, Dharmapuri Vijayan
A1  - Kurths, Jürgen
T1  - Characteristics and synchronization of time-delay systems driven by a common noise
N2  - We investigate the characteristics of time-delay systems in the presence of Gaussian noise. We show that the delay time embedded in the time series of time-delay system with constant delay cannot be estimated in the presence noise for appropriate values of noise intensity thereby forbidding any possibility of phase space reconstruction. We also demonstrate the existence of complete synchronization between two independent identical time-delay systems driven by a common noise without explicitly establishing any external coupling between them.
Y1  - 2010
UR  - http://www.springerlink.com/content/1951-6355
U6  - https://doi.org/10.1140/epjst/e2010-01273-4
SN  - 1951-6355
ER  - 
TY  - JOUR
A1  - Stich, Michael
A1  - Beta, Carsten
T1  - Control of pattern formation by time-delay feedback with global and local contributions
N2  - We consider the suppression of spatiotemporal chaos in the complex Ginzburg-Landau equation by a combined global and local time-delay feedback. Feedback terms are implemented as a control scheme, i.e., they are proportional to the difference between the time-delayed state of the system and its current state. We perform a linear stability analysis of uniform oscillations with respect to space-dependent perturbations and compare with numerical simulations. Similarly, for the fixed-point solution that corresponds to amplitude death in the spatially extended system, a linear stability analysis with respect to space-dependent perturbations is performed and complemented by numerical simulations.
Y1  - 2010
UR  - http://www.sciencedirect.com/science/journal/01672789
U6  - https://doi.org/10.1016/j.physd.2010.05.001
SN  - 0167-2789
ER  - 
TY  - THES
A1  - Klasczyk, Benjamin
T1  - Interactions of ions with membranes
Y1  - 2010
CY  - Potsdam
ER  - 
TY  - THES
A1  - Fix, Dmitri
T1  - Lokalkorrosion auf Aluminium: Nicht-invasive in-situ-Observation von Lochkorrosion
Y1  - 2010
CY  - Potsdam
ER  - 
TY  - BOOK
A1  - Föhlisch, Alexander
T1  - Phasenübergänge und Ultrakurzzeitdynamik : Antrittsvorlesung 2010-05-12
N2  - Föhlisch wird in seinem Vortrag die großen Zukunftsthemen der Mensch streifen: Energie, Umwelt und Struktur der Materie. Die Komplexität ihrer elementaren Prozesse erfordert die komplementäre Betrachtung der damit verbundene Dimensionen von Energie, Zeit und Raum. Dies lässt sich inzwischen mit Synchrotronstrahlungsquellen in größter Präision darstellen.
Y1  - 2010
UR  - http://info.ub.uni-potsdam.de/multimedia/show_projekt.php?projekt_id=63
PB  - Univ.-Bibl.
CY  - Potsdam
ER  - 
TY  - THES
A1  - Schwabedal, Justus Tilmann Caspar
T1  - Phase dynamics of irregular oscillations
N2  - In der vorliegenden Dissertation wird eine Beschreibung der Phasendynamik irregulärer Oszillationen und deren Wechselwirkungen vorgestellt. Hierbei werden chaotische und stochastische Oszillationen autonomer dissipativer Systeme betrachtet. Für eine Phasenbeschreibung stochastischer Oszillationen müssen zum einen unterschiedliche Werte der Phase zueinander in Beziehung gesetzt werden, um ihre Dynamik unabhängig von der gewählten Parametrisierung der Oszillation beschreiben zu können. Zum anderen müssen für stochastische und chaotische Oszillationen diejenigen Systemzustände identifiziert werden, die sich in der gleichen Phase befinden. Im Rahmen dieser Dissertation werden die Werte der Phase über eine gemittelte Phasengeschwindigkeitsfunktion miteinander in Beziehung gesetzt. Für stochastische Oszillationen sind jedoch verschiedene Definitionen der mittleren Geschwindigkeit möglich. Um die Unterschiede der Geschwindigkeitsdefinitionen besser zu verstehen, werden auf ihrer Basis effektive deterministische Modelle der Oszillationen konstruiert. Hierbei zeigt sich, dass die Modelle unterschiedliche Oszillationseigenschaften, wie z. B. die mittlere Frequenz oder die invariante Wahrscheinlichkeitsverteilung, nachahmen. Je nach Anwendung stellt die effektive Phasengeschwindigkeitsfunktion eines speziellen Modells eine zweckmäßige Phasenbeziehung her. Wie anhand einfacher Beispiele erklärt wird, kann so die Theorie der effektiven Phasendynamik auch kontinuierlich und pulsartig wechselwirkende stochastische Oszillationen beschreiben. Weiterhin wird ein Kriterium für die invariante Identifikation von Zuständen gleicher Phase irregulärer Oszillationen zu sogenannten generalisierten Isophasen beschrieben: Die Zustände einer solchen Isophase sollen in ihrer dynamischen Entwicklung ununterscheidbar werden. Für stochastische Oszillationen wird dieses Kriterium in einem mittleren Sinne interpretiert. Wie anhand von Beispielen demonstriert wird, lassen sich so verschiedene Typen stochastischer Oszillationen in einheitlicher Weise auf eine stochastische Phasendynamik reduzieren. Mit Hilfe eines numerischen Algorithmus zur Schätzung der Isophasen aus Daten wird die Anwendbarkeit der Theorie anhand eines Signals regelmäßiger Atmung gezeigt. Weiterhin zeigt sich, dass das Kriterium der Phasenidentifikation für chaotische Oszillationen nur approximativ erfüllt werden kann. Anhand des Rössleroszillators wird der tiefgreifende Zusammenhang zwischen approximativen Isophasen, chaotischer Phasendiffusion und instabilen periodischen Orbits dargelegt. Gemeinsam ermöglichen die Theorien der effektiven Phasendynamik und der generalisierten Isophasen eine umfassende und einheitliche Phasenbeschreibung irregulärer Oszillationen.
N2  - Many natural systems embedded in a complex surrounding show irregular oscillatory dynamics. The oscillations can be parameterized by a phase variable in order to obtain a simplified theoretical description of the dynamics. Importantly, a phase description can be easily extended to describe the interactions of the system with its surrounding. It is desirable to define an invariant phase that is independent of the observable or the arbitrary parameterization, in order to make, for example, the phase characteristics obtained from different experiments comparable. In this thesis, we present an invariant phase description of irregular oscillations and their interactions with the surrounding. The description is applicable to stochastic and chaotic irregular oscillations of autonomous dissipative systems. For this it is necessary to interrelate different phase values in order to allow for a parameterization-independent phase definition. On the other hand, a criterion is needed, that invariantly identifies the system states that are in the same phase. To allow for a parameterization-independent definition of phase, we interrelate different phase values by the phase velocity. However, the treatment of stochastic oscillations is complicated by the fact that different definitions of average velocity are possible. For a better understanding of their differences, we analyse effective deterministic phase models of the oscillations based upon the different velocity definitions. Dependent on the application, a certain effective velocity is suitable for a parameterization-independent phase description. In this way, continuous as well pulse-like interactions of stochastic oscillations can be described, as it is demonstrated with simple examples. On the other hand, an invariant criterion of identification is proposed that generalizes the concept of standard (Winfree) isophases. System states of the same phase are identified to belong to the same generalized isophase using the following invariant criterion: All states of an isophase shall become indistinguishable in the course of time. The criterion is interpreted in an average sense for stochastic oscillations. It allows for a unified treatment of different types of stochastic oscillations. Using a numerical estimation algorithm of isophases, the applicability of the theory is demonstrated by a signal of regular human respiration. For chaotic oscillations, generalized isophases can only be obtained up to a certain approximation. The intimate relationship between these approximate isophase, chaotic phase diffusion, and unstable periodic orbits is explained with the example of the chaotic \roes oscillator. Together, the concept of generalized isophases and the effective phase theory allow for a unified, and invariant phase description of stochastic and chaotic irregular oscillations.
T2  - Phasendynamik irregulärer Oszillationen
KW  - Phasendynamik
KW  - Stochastische Oszillationen
KW  - Chaotische Oszillationen
KW  - Phasenkopplung
KW  - Zeitreihenanalyse
KW  - phase dynamics
KW  - stochastic oscillations
KW  - chaotic oscillations
KW  - phase coupling
KW  - time series analysis
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-50115
ER  - 
TY  - THES
A1  - Ahnert, Karsten
T1  - Compactons in strongly nonlinear lattices
T1  - Kompaktonen in stark nichtlinearen Gittern
N2  - In the present work, we study wave phenomena in strongly nonlinear lattices. Such lattices are characterized by the absence of classical linear waves. We demonstrate that compactons – strongly localized solitary waves with tails decaying faster than exponential – exist and that they play a major role in the dynamics of the system under consideration. We investigate compactons in different physical setups. One part deals with lattices of dispersively coupled limit cycle oscillators which find various applications in natural sciences such as Josephson junction arrays or coupled Ginzburg-Landau equations. Another part deals with Hamiltonian lattices. Here, a prominent example in which compactons can be found is the granular chain. In the third part, we study systems which are related to the discrete nonlinear Schrödinger equation describing, for example, coupled optical wave-guides or the dynamics of Bose-Einstein condensates in optical lattices. Our investigations are based on a numerical method to solve the traveling wave equation. This results in a quasi-exact solution (up to numerical errors) which is the compacton. Another ansatz which is employed throughout this work is the quasi-continuous approximation where the lattice is described by a continuous medium. Here, compactons are found analytically, but they are defined on a truly compact support. Remarkably, both ways give similar qualitative and quantitative results. Additionally, we study the dynamical properties of compactons by means of numerical simulation of the lattice equations. Especially, we concentrate on their emergence from physically realizable initial conditions as well as on their stability due to collisions. We show that the collisions are not exactly elastic but that a small part of the energy remains at the location of the collision. In finite lattices, this remaining part will then trigger a multiple scattering process resulting in a chaotic state.
N2  - In der hier vorliegenden Arbeit werden Wellenphänomene in stark nichtlinearen Gittern untersucht. Diese Gitter zeichnen sich vor allem durch die Abwesenheit von klassischen linearen Wellen aus. Es wird gezeigt, dass Kompaktonen – stark lokalisierte solitäre Wellen, mit Ausläufern welche schneller als exponentiell abfallen – existieren, und dass sie eine entscheidende Rolle in der Dynamik dieser Gitter spielen. Kompaktonen treten in verschiedenen diskreten physikalischen Systemen auf. Ein Teil der Arbeit behandelt dabei Gitter von dispersiv gekoppelten Oszillatoren, welche beispielsweise Anwendung in gekoppelten Josephsonkontakten oder gekoppelten Ginzburg-Landau-Gleichungen finden. Ein weiterer Teil beschäftigt sich mit Hamiltongittern, wobei die granulare Kette das bekannteste Beispiel ist, in dem Kompaktonen beobachtet werden können. Im dritten Teil werden Systeme, welche im Zusammenhang mit der Diskreten Nichtlinearen Schrödingergleichung stehen, studiert. Diese Gleichung beschreibt beispielsweise Arrays von optischen Wellenleitern oder die Dynamik von Bose-Einstein-Kondensaten in optischen Gittern. Das Studium der Kompaktonen basiert hier hauptsächlich auf dem numerischen Lösen der dazugehörigen Wellengleichung. Dies mündet in einer quasi-exakten Lösung, dem Kompakton, welches bis auf numerische Fehler genau bestimmt werden kann. Ein anderer Ansatz, der in dieser Arbeit mehrfach verwendet wird, ist die Approximation des Gitters durch ein kontinuierliches Medium. Die daraus resultierenden Kompaktonen besitzen einen im mathematischen Sinne kompakten Definitionsbereich. Beide Methoden liefern qualitativ und quantitativ gut übereinstimmende Ergebnisse. Zusätzlich werden die dynamischen Eigenschaften von Kompaktonen mit Hilfe von direkten numerischen Simulationen der Gittergleichungen untersucht. Dabei wird ein Hauptaugenmerk auf die Entstehung von Kompaktonen unter physikalisch realisierbaren Anfangsbedingungen und ihre Kollisionen gelegt. Es wird gezeigt, dass die Wechselwirkung nicht exakt elastisch ist, sondern dass ein Teil ihrer Energie an der Position der Kollision verharrt. In endlichen Gittern führt dies zu einem multiplen Streuprozess, welcher in einem chaotischen Zustand endet.
KW  - Gitterdynamik
KW  - Hamilton
KW  - Compacton
KW  - Soliton
KW  - granulare Kette
KW  - Lattice dynamics
KW  - Hamiltonian
KW  - Compacton
KW  - Soliton
KW  - Granular chain
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-48539
ER  - 
TY  - THES
A1  - Kralemann, Björn Christian
T1  - Die Rekonstruktion invarianter Phasenmodelle aus Daten
T1  - Reconstructing invariant phase models from data
N2  - Ziel dieser Arbeit ist die Überwindung einer Differenz, die zwischen der Theorie der Phase bzw. der Phasendynamik und ihrer Anwendung in der Zeitreihenanalyse besteht: Während die theoretische Phase eindeutig bestimmt und invariant unter Koordinatentransformationen bzw. gegenüber der jeweils gewählten Observable ist, führen die Standardmethoden zur Abschätzung der Phase aus gegebenen Zeitreihen zu Resultaten, die einerseits von den gewählten Observablen abhängen und so andererseits das jeweilige System keineswegs in eindeutiger und invarianter Weise beschreiben. Um diese Differenz deutlich zu machen, wird die terminologische Unterscheidung von Phase und Protophase eingeführt: Der Terminus Phase wird nur für Variablen verwendet, die dem theoretischen Konzept der Phase entsprechen und daher das jeweilige System in invarianter Weise charakterisieren, während die observablen-abhängigen Abschätzungen der Phase aus Zeitreihen als Protophasen bezeichnet werden. Der zentrale Gegenstand dieser Arbeit ist die Entwicklung einer deterministischen Transformation, die von jeder Protophase eines selbsterhaltenden Oszillators zur eindeutig bestimmten Phase führt. Dies ermöglicht dann die invariante Beschreibung gekoppelter Oszillatoren und ihrer Wechselwirkung. Die Anwendung der Transformation bzw. ihr Effekt wird sowohl an numerischen Beispielen demonstriert - insbesondere wird die Phasentransformation in einem Beispiel auf den Fall von drei gekoppelten Oszillatoren erweitert - als auch an multivariaten Messungen des EKGs, des Pulses und der Atmung, aus denen Phasenmodelle der kardiorespiratorischen Wechselwirkung rekonstruiert werden. Abschließend wird die Phasentransformation für autonome Oszillatoren auf den Fall einer nicht vernachlässigbaren Amplitudenabhängigkeit der Protophase erweitert, was beispielsweise die numerischen Bestimmung der Isochronen des chaotischen Rössler Systems ermöglicht.
N2  - The aim of this work is to bridge the gap between the theoretical description of the phase dynamics of coupled oscillators and the application of the theory to model reconstruction from time series analysis. In the theory, the phase of a self-sustained oscillator is defined in an unambiguous way, whereas the standard techniques used to estimate phases from given time series provide observabledependent results, so that generally these estimates deviate from the true phase. To stress this crucial issue, we term the observable-dependent phase-like variables as protophases. The main goal of this work is to develop a deterministic transformation from arbitrary protophases to the true, unique phase of the selfsustained oscillator. This approach allows us to obtain an invariant description of coupled oscillators and of their interaction. The application of the transformation and its efficiency are illustrated by means of numerical examples, as well as by the reconstruction of phase models of the cardiorespiratory interaction from multivariate time series of ECG, pulse and respiration. Next, the transformation from protophases to phases is extended for the case of three coupled oscillators. Finally, we go beyond the phase approximation and extend the phase transformation for autonomous oscillators to the case when the amplitude dynamics cannot be neglected. This technique for example allows us to compute numerically the isochrones of the chaotic Roessler system.
KW  - nichtlineare Dynamik
KW  - selbsterhaltende Oszillatoren
KW  - Phase
KW  - Protophase
KW  - Invarianz
KW  - nonlinear Dynamics
KW  - self-sustained Oscillators
KW  - Phase
KW  - Protophase
KW  - Invariance
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-45057
ER  - 
TY  - JOUR
A1  - Schwabedal, Justus T. C.
A1  - Pikovskij, Arkadij
T1  - Effective phase description of noise-perturbed and noise-induced oscillations
N2  - An effective dynamical description of a general class of stochastic phase oscillators is presented. For this, the effective phase velocity is defined either by the stochastic phase oscillators invariant probability density or its first passage times. Using the first approach the effective phase exhibits the correct frequency and invariant distribution density, whereas the second approach models the proper phase resetting curve. The discrepancy of the effective models is most pronounced for noise-induced oscillations and is related to non-monotonicity of the stochastic phase variable due to fluctuations.
Y1  - 2010
U6  - https://doi.org/10.1140/epjst/e2010-01271-6
SN  - 1951-6355
ER  - 
TY  - JOUR
A1  - Schwabedal, Justus T. C.
A1  - Pikovskij, Arkadij
T1  - Effective phase dynamics of noise-induced oscillations in excitable systems
N2  - We develop an effective description of noise-induced oscillations based on deterministic phase dynamics. The phase equation is constructed to exhibit correct frequency and distribution density of noise-induced oscillations. In the simplest one-dimensional case the effective phase equation is obtained analytically, whereas for more complex situations a simple method of data processing is suggested. As an application an effective coupling function is constructed that quantitatively describes periodically forced noise-induced oscillations.
Y1  - 2010
UR  - http://link.aps.org/doi/10.1103/PhysRevE.81.046218
U6  - https://doi.org/10.1103/Physreve.81.046218
SN  - 1539-3755
ER  - 
TY  - JOUR
A1  - Baibolatov, Yernur
A1  - Rosenblum, Michael
A1  - Zhanabaev, Zeinulla Zh.
A1  - Pikovskij, Arkadij
T1  - Complex dynamics of an oscillator ensemble with uniformly distributed natural frequencies and global nonlinear coupling
N2  - We consider large populations of phase oscillators with global nonlinear coupling. For identical oscillators such populations are known to demonstrate a transition from completely synchronized state to the state of self-organized quasiperiodicity. In this state phases of all units differ, yet the population is not completely incoherent but produces a nonzero mean field; the frequency of the latter differs from the frequency of individual units. Here we analyze the dynamics of such populations in case of uniformly distributed natural frequencies. We demonstrate numerically and describe theoretically (i) states of complete synchrony, (ii) regimes with coexistence of a synchronous cluster and a drifting subpopulation, and (iii) self-organized quasiperiodic states with nonzero mean field and all oscillators drifting with respect to it. We analyze transitions between different states with the increase of the coupling strength; in particular we show that the mean field arises via a discontinuous transition. For a further illustration we compare the results for the nonlinear model with those for the Kuramoto-Sakaguchi model.
Y1  - 2010
UR  - http://pre.aps.org/
U6  - https://doi.org/10.1103/Physreve.82.016212
SN  - 1539-3755
ER  - 
TY  - JOUR
A1  - Bordyugov, Grigory
A1  - Pikovskij, Arkadij
A1  - Rosenblum, Michael
T1  - Self-emerging and turbulent chimeras in oscillator chains
N2  - We report on a self-emerging chimera state in a homogeneous chain of nonlocally and nonlinearly coupled oscillators. This chimera, i.e., a state with coexisting regions of complete and partial synchrony, emerges via a supercritical bifurcation from a homogeneous state. We develop a theory of chimera based on the Ott-Antonsen equations for the local complex order parameter. Applying a numerical linear stability analysis, we also describe the instability of the chimera and transition to phase turbulence with persistent patches of synchrony.
Y1  - 2010
UR  - http://pre.aps.org/
U6  - https://doi.org/10.1103/Physreve.82.035205
SN  - 1539-3755
ER  - 
TY  - JOUR
A1  - Hennies, Franz
A1  - Pietzsch, Annette
A1  - Berglund, Martin
A1  - Föhlisch, Alexander
A1  - Schmitt, Thorsten
A1  - Strocov, Vladimir
A1  - Karlsson, Hans O.
A1  - Andersson, Joakim
A1  - Rubensson, Jan-Erik
T1  - Resonant inelastic scattering spectra of free molecules with vibrational resolution
N2  - Inelastic x-ray scattering spectra excited at the 1s(-1) pi* resonance of gas phase O-2 have been recorded with an overall energy resolution that allows for well-resolved vibrational progressions. The nuclear wave packet dynamics in the intermediate state is reflected in vibrational excitations of the electronic ground state, and by fine-tuning the excitation energy the dissociation dynamics in the predissociative B' (3) Pi(g) final state is controlled.
Y1  - 2010
UR  - http://prl.aps.org/
U6  - https://doi.org/10.1103/Physrevlett.104.193002
SN  - 0031-9007
ER  - 
TY  - JOUR
A1  - Todt, Helge Tobias
A1  - Pena, Maria A.
A1  - Hamann, Wolf-Rainer
A1  - Gräfener, Götz
T1  - The central star of the planetary nebula PB8 : a Wolf-Rayet-type wind of an unusual WN/WC chemical composition
N2  - A considerable fraction of the central stars of planetary nebulae (CSPNe) are hydrogen-deficient. As a rule, these CSPNe exhibit a chemical composition of helium, carbon, and oxygen with the majority showing Wolf-Rayet-like emission line spectra. These stars are classified as CSPNe of a spectral type [WC]. We perform a spectral analysis of CSPN PB 8 with the Potsdam Wolf-Rayet (PoWR) models for expanding atmospheres. The source PB8 displays wind-broadened emission lines from strong mass loss. Most strikingly, we find that its surface composition is hydrogen-deficient, but not carbon-rich. With mass fractions of 55% helium, 40% hydrogen, 1.3% carbon, 2% nitrogen, and 1.3% oxygen, it differs greatly from the 30-50% of carbon which are typically seen in [WC]-type central stars. The atmospheric mixture in PB8 has an analogy in the WN/WC transition type among the massive Wolf-Rayet stars. Therefore we suggest to introduce a new spectral type [WN/WC] for CSPNe, with PB8 as its first member. The central star of PB8 has a relatively low temperature of T-* = 52 kK, as expected for central stars in their early evolutionary stages. Its surrounding nebula is less than 3000 years old, i.e. relatively young. Existing calculations for the post-AGB evolution can produce hydrogen-deficient stars of the [WC] type, but do not predict the composition found in PB8. We discuss various scenarios that might explain the origin of this unique object.
Y1  - 2010
UR  - http://www.aanda.org/
U6  - https://doi.org/10.1051/0004-6361/200912183
SN  - 0004-6361
ER  - 
TY  - THES
A1  - Sánchez-Barriga, Jaime
T1  - A photoemission study of quasiparticle excitations, electron-correlation effects and magnetization dynamics in thin magnetic systems
T1  - Eine Photoemissionsstudie zu Quasiteilchenanregungen, Elektronenkorrelationseffekten und der Magnetisierungsdynamik in dünnen magnetischen Systemen
N2  - This thesis is focused on the electronic, spin-dependent and dynamical properties of thin magnetic systems. Photoemission-related techniques are combined with synchrotron radiation to study the spin-dependent properties of these systems in the energy and time domains. In the first part of this thesis, the strength of electron correlation effects in the spin-dependent electronic structure of ferromagnetic bcc Fe(110) and hcp Co(0001) is investigated by means of spin- and angle-resolved photoemission spectroscopy. The experimental results are compared to theoretical calculations within the three-body scattering approximation and within the dynamical mean-field theory, together with one-step model calculations of the photoemission process. From this comparison it is demonstrated that the present state of the art many-body calculations, although improving the description of correlation effects in Fe and Co, give too small mass renormalizations and scattering rates thus demanding more refined many-body theories including nonlocal fluctuations. In the second part, it is shown in detail monitoring by photoelectron spectroscopy how graphene can be grown by chemical vapour deposition on the transition-metal surfaces Ni(111) and Co(0001) and intercalated by a monoatomic layer of Au. For both systems, a linear E(k) dispersion of massless Dirac fermions is observed in the graphene pi-band in the vicinity of the Fermi energy. Spin-resolved photoemission from the graphene pi-band shows that the ferromagnetic polarization of graphene/Ni(111) and graphene/Co(0001) is negligible and that graphene on Ni(111) is after intercalation of Au spin-orbit split by the Rashba effect. In the last part, a time-resolved x-ray magnetic circular dichroic-photoelectron emission microscopy study of a permalloy platelet comprising three cross-tie domain walls is presented. It is shown how a fast picosecond magnetic response in the precessional motion of the magnetization can be induced by means of a laser-excited photoswitch. From a comparision to micromagnetic calculations it is demonstrated that the relatively high precessional frequency observed in the experiments is directly linked to the nature of the vortex/antivortex dynamics and its response to the magnetic perturbation. This includes the time-dependent reversal of the vortex core polarization, a process which is beyond the limit of detection in the present experiments.
N2  - Diese Dissertation beschäftigt sich mit den elektronischen, spinabhängigen und dynamischen Eigenschaften dünner magnetischer Systeme. Auf dem Photoeffekt basierende Untersuchungsmethoden werden zusammen mit Synchrotronstrahlung eingesetzt, um die spinabhängigen Eigenschaften dieser Systeme im Energie- und Zeitbereich zu untersuchen. Im ersten Teil dieser Arbeit wird mit spin- und winkelaufgelöster Photoemission die Stärke von Elektronenkorrelationseffekten in der spinabhängigen elektonischen Struktur von ferromagnetischerm bcc Fe(110) und hcp Co(0001) untersucht. Die experimentellen Ergebnisse werden verglichen mit theoreteischen Berechnungen im Rahmen der Näherung der Drei-Körper-Streuung und der dynamischen Molekularfeldtheorie, zusammen mit Berechnungen des Photoemissionsprozesses im Rahmen des Ein-Stufen-Modells. Ausgehend von diesem Vergleich wird gezeigt, dass die gegenwärtig fortgeschrittensten Rechnung, obgleich sie die Beschreibung von Korrelationseffekten in Fe und Co verbessern, zu kleine Massenrenormalisierungen und Streuraten ergeben, was zu der Forderung nach verfeinerten Vielteilchentheorien unter Einbeziehung von nichtlokalen Fluktuationen führt. Im zweiten Teil wird unter Kontrolle durch die Photoelektronenspektroskopie im Detail gezeigt, wie Graphen durch chemische Gasphasenabscheidung auf den Übergangsmetall-Oberflächen Ni(111) und Co(0001) aufgebracht und mit einer Monolage Au interkaliert werden kann. Für beide Systeme wird eine lineare E(k)-Dispersion masseloser Dirac-Fermionen im Graphen-pi-Band in der Nähe der Fermi-Energie beobachtet. Spinaufgelöste Photoemission des Graphen-pi-Bandes zeigt, dass die ferromagnetische Polarisation von Graphen/Ni(111) und Graphen/Co(0001) vernachlässigbar ist und dass Graphen/Ni(111) nach Interkalation mit Au eine Spin-Bahn-Aufspaltung aufgrund des Rashba-Effekts zeigt. Im letzten Teil wird eine zeitaufgelöste Studie des Röntgenzirkulardichroismus mit Photoelektronenmikroskopie präsentiert, die an einer Permalloy-Probe durchgeführt wurde, die drei als Stachelwände ausgebildete Domänenwände enthält. Es wird gezeigt, wie eine schnelle magnetische Antwort auf der Pikosekundenskala in der Präzessionsbewegung der Magnetisierung durch einen laserangesteuerten Photoschalter erzeugt werden kann. Durch Vergleich mit einer mikromagnetischen Rechnung wird gezeigt, dass die relativ hohe Präzessionsfrequenz, die im Experiment beobachtet wird, in unmittelbarer Beziehung steht zu den Eigenschaften der Vortex/Antivortex-Dynamik und ihrer Antwort auf die magnetische Störung. Das schließt die zeitabhängige Umkehr der Vortexkernpolarisation ein, einem Vorgang der jenseits der Nachweisgrenze der gegenwärtigen Experimente liegt.
KW  - Spin- und winkelaufgelöste Photoemission
KW  - Photoelektronenmikroskopie
KW  - Eisen
KW  - Kobalt
KW  - Graphen
KW  - Rashba-Effekt
KW  - Spinwellen
KW  - Synchrotronstrahlung
KW  - spin- and angle-resolved photoemission
KW  - photoelectron microscopy
KW  - iron
KW  - cobalt
KW  - graphene
KW  - Rashba effect
KW  - spin waves
KW  - synchrotron radiation
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-48499
ER  - 
TY  - JOUR
A1  - Filimon, Marlena
A1  - Kopf, Ilona
A1  - Ballout, Fuad
A1  - Schmidt, Dietrich A.
A1  - Bruendermann, Erik
A1  - Rühe, Jürgen
A1  - Santer, Svetlana
A1  - Havenith, Martina
T1  - Smart polymer surfaces : mapping chemical landscapes on the nanometre scale
N2  - We show that Scattering Infrared Near-field Microscopy (SNIM) allows chemical mapping of polymer monolayers that can serve as designed nanostructured surfaces with specific surface chemistry properties on a nm scale. Using s- SNIM a minimum volume of 100 nm x 100 nm x 15 nm is sufficient for a recording of a "chemical'' IR signature which corresponds to an enhancement of at least four orders of magnitudes compared to conventional FT-IR microscopy. We could prove that even in cases where it is essentially difficult to distinguish between distinct polymer compositions based solely on topography, nanophase separated polymers can be clearly distinguished according to their characteristic near-field IR response.
Y1  - 2010
UR  - http://www.rsc.org/Publishing/Journals/sm/index.asp
U6  - https://doi.org/10.1039/C0sm00098a
SN  - 1744-683X
ER  - 
TY  - JOUR
A1  - Chinaglia, Dante Luis
A1  - Gregorio, Rinaldo
A1  - Stefanello, Josiani Cristina
A1  - Altafim, Ruy Alberto Pisani
A1  - Wirges, Werner
A1  - Wang, Feipeng
A1  - Gerhard, Reimund
T1  - Influence of the solvent evaporation rate on the crystalline phases of solution-cast poly(vinylidene fluoride) films
N2  - The influence of the solvent-evaporation rate on the formation of of. and P crystalline phases in solution-cast poly(vinylidene fluoride) (PVDF) films was systematically investigated. Films were crystallized from PVDF/N,N- dimethylformamide solutions with concentrations of 2.5, 5.0, 10, and 20 wt % at different temperatures. During crystallization, the solvent evaporation rate was monitored in situ by means of a semianalytic balance. With this system, it was possible to determine the evaporation rate for different concentrations and temperatures of the solution under specific ambient conditions (pressure, temperature, and humidity). Fourier-Transform InfraRed spectroscopy with Attenuated Total Reflectance revealed the P-phase content in the PVDF films and its dependence on previous evaporation rates. Based on the relation between the evaporation rate and the PVDF phase composition, a consistent explanation for the different amounts of P phase observed at the upper and lower sample surfaces is achieved. Furthermore, the role of the sample thickness has also been studied. The experimental results show that not only the temperature but also the evaporation rate have to be controlled to obtain the desired crystalline phases in solution-cast PVDF films.
Y1  - 2010
UR  - http://www3.interscience.wiley.com/cgi-bin/jhome/30035
U6  - https://doi.org/10.1002/App.31488
SN  - 0021-8995
ER  - 
TY  - JOUR
A1  - Flores Suárez, Rosaura
A1  - Ganesan, Lakshmi Meena
A1  - Wirges, Werner
A1  - Gerhard, Reimund
A1  - Mellinger, Axel
T1  - Imaging liquid crystals dispersed in a ferroelectric polymer matrix by means of thermal-pulse tomography
N2  - A new arrangement of the optical elements in a Thermal-Pulse-Tomography (TPT) setup allows to scan micrometer structures in composite and heterogeneous samples such as polymer-dispersed liquid crystals (PDLCs). The non-destructive TPT technique allows the determination of three-dimensional profiles of polarization and space charge in dielectrics. The samples under study were 12 mu m thick films of a copolymer of vinylidene fluoride with trifluoroethylene P(VDF- TrFE) (65/35) with embedded liquid-crystal droplets. The poling process was performed in direct contact well above the coercive field of the copolymer. The 3D map obtained from scanning with a 10 mu m wide spot shows elliptically shaped areas with liquid-crystal droplets. Considering the droplets as oblate spheroids, their major axis lies in the x-y plane, while their minor axis in the z direction measures 0.5 mu m or more. This result is in good agreement with scanning electron micrographs. It is believed that the major axis is overestimated due to imaging of liquid-crystal clusters.
Y1  - 2010
UR  - http://ieeexplore.ieee.org/servlet/opac?punumber=94
U6  - https://doi.org/10.1109/TDEI.2010.5539683
SN  - 1070-9878
ER  - 
TY  - JOUR
A1  - Greco, Tonino
A1  - Wang, Feipeng
A1  - Wegener, Michael
T1  - Multifunctional silver poly(vinylidene fluoride) nanocomposites : nanoparticle synthesis, film processing, and structural characterization
N2  - Scope of this work was the synthesis of homogeneously dispersed silver nanoparticles in the ferroelectric polymer poly(vinylidene fluoride) (PVDF) and the study of the resulting properties affecting both the electro-active matrix and the optically-active nanofiller. In the nanocomposites surface plasmon resonances can be tuned across the UV- vis to the NIR spectral range. From IR spectra and DSC measurements it is concluded that the - to -phase transformation is observed and no degradation of the polymer matrix occurs. Finally, electrical poling was performed in order to investigate the influence of the embedded silver particles on the polarization behavior of the ferroelectric polymer.
Y1  - 2010
UR  - http://www.informaworld.com/openurl?genre=journal&issn=0015-0193
U6  - https://doi.org/10.1080/00150193.2010.482896
SN  - 0015-0193
ER  - 
TY  - JOUR
A1  - Fang, Peng
A1  - Qiu, Xunlin
A1  - Wirges, Werner
A1  - Gerhard, Reimund
A1  - Zirkel, Larissa
T1  - Polyethylene-naphthalate (PEN) ferroelectrets : cellular structure, piezoelectricity and thermal stability
N2  - Cellular polyethylene-naphthalate (PEN) ferroelectrets are useful as soft and flexible electromechanical transducer materials. Improved cellular PEN foams are prepared by means of a "voiding + inflation + stretching" process and investigated with respect to their structure and their applications-relevant properties. It is found that most of the cellular voids have heights below 8 mu m. The polymer walls do not allow sufficient gas exchange between the voids and the ambient atmosphere, when the cellular films are exposed to atmospheric pressures between a millibar and a few bars. As expected for ferroelectrets, a threshold voltage for charging is observed: A reasonable piezoelectric coefficient d(33) is only found when the charging voltage is higher than 4 kV. Furthermore, d(33) increases with charging voltage and reaches saturation at approximately 8 kV. Annealing after charging or charging at elevated temperatures may enhance the thermal stability of the PEN ferroelectrets. The d(33) of properly annealed samples is stable up to the respective annealing temperatures, but the annealing process reduces the piezoelectric activity of charged ferroelectret films to some extent. Samples charged at suitable elevated temperatures show much better thermal stability than those charged at room temperature, but the charging temperature should be limited to values below the material's glass-transition temperature T-g. Furthermore, the relevant elastic modulus c(33) of PEN ferroelectrets may decrease upon thermal treatment.
Y1  - 2010
UR  - http://ieeexplore.ieee.org/servlet/opac?punumber=94
U6  - https://doi.org/10.1109/TDEI.2010.5539678
SN  - 1070-9878
ER  - 
TY  - THES
A1  - Fang, Peng
T1  - Preparation and investigation of polymer-foam films and polymer-layer systems for ferroelectrets
T1  - Präparation und Untersuchung von Polymerschaumfolien und Polymerschichtsystemen für Ferroelektrete
N2  - Piezoelectric materials are very useful for applications in sensors and actuators. In addition to traditional ferroelectric ceramics and ferroelectric polymers, ferroelectrets have recently become a new group of piezoelectrics. Ferroelectrets are functional polymer systems for electromechanical transduction, with elastically heterogeneous cellular structures and internal quasi-permanent dipole moments. The piezoelectricity of ferroelectrets stems from linear changes of the dipole moments in response to external mechanical or electrical stress. Over the past two decades, polypropylene (PP) foams have been investigated with the aim of ferroelectret applications, and some products are already on the market. PP-foam ferroelectrets may exhibit piezoelectric d33 coefficients of 600 pC/N and more. Their operating temperature can, however, not be much higher than 60 °C. Recently developed polyethylene-terephthalate (PET) and cyclo-olefin copolymer (COC) foam ferroelectrets show slightly better d33 thermal stabilities, but usually at the price of smaller d33 values. Therefore, the main aim of this work is the development of new thermally stable ferroelectrets with appreciable piezoelectricity. Physical foaming is a promising technique for generating polymer foams from solid films without any pollution or impurity. Supercritical carbon dioxide (CO2) or nitrogen (N2) are usually employed as foaming agents due to their good solubility in several polymers. Polyethylene propylene (PEN) is a polyester with slightly better properties than PET. A “voiding + inflation + stretching” process has been specifically developed to prepare PEN foams. Solid PEN films are saturated with supercritical CO2 at high pressure and then thermally voided at high temperatures. Controlled inflation (Gas-Diffusion Expansion or GDE) is applied in order to adjust the void dimensions. Additional biaxial stretching decreases the void heights, since it is known lens-shaped voids lead to lower elastic moduli and therefore also to stronger piezoelectricity. Both, contact and corona charging are suitable for the electric charging of PEN foams. The light emission from the dielectric-barrier discharges (DBDs) can be clearly observed. Corona charging in a gas of high dielectric strength such as sulfur hexafluoride (SF6) results in higher gas-breakdown strength in the voids and therefore increases the piezoelectricity. PEN foams can exhibit piezoelectric d33 coefficients as high as 500 pC/N. Dielectric-resonance spectra show elastic moduli c33 of 1 − 12 MPa, anti-resonance frequencies of 0.2 − 0.8 MHz, and electromechanical coupling factors of 0.016 − 0.069. As expected, it is found that PEN foams show better thermal stability than PP and PET. Samples charged at room temperature can be utilized up to 80 − 100 °C. Annealing after charging or charging at elevated temperatures may improve thermal stabilities. Samples charged at suitable elevated temperatures show working temperatures as high as 110 − 120 °C. Acoustic measurements at frequencies of 2 Hz − 20 kHz show that PEN foams can be well applied in this frequency range. Fluorinated ethylene-propylene (FEP) copolymers are fluoropolymers with very good physical, chemical and electrical properties. The charge-storage ability of solid FEP films can be significantly improved by adding boron nitride (BN) filler particles. FEP foams are prepared by means of a one-step procedure consisting of CO2 saturation and subsequent in-situ high-temperature voiding. Piezoelectric d33 coefficients up to 40 pC/N are measured on such FEP foams. Mechanical fatigue tests show that the as-prepared PEN and FEP foams are mechanically stable for long periods of time. Although polymer-foam ferroelectrets have a high application potential, their piezoelectric properties strongly depend on the cellular morphology, i.e. on size, shape, and distribution of the voids. On the other hand, controlled preparation of optimized cellular structures is still a technical challenge. Consequently, new ferroelectrets based on polymer-layer system (sandwiches) have been prepared from FEP. By sandwiching an FEP mesh between two solid FEP films and fusing the polymer system with a laser beam, a well-designed uniform macroscopic cellular structure can be formed. Dielectric resonance spectroscopy reveals piezoelectric d33 coefficients as high as 350 pC/N, elastic moduli of about 0.3 MPa, anti-resonance frequencies of about 30 kHz, and electromechanical coupling factors of about 0.05. Samples charged at elevated temperatures show better thermal stabilities than those charged at room temperature, and the higher the charging temperature, the better is the stability. After proper charging at 140 °C, the working temperatures can be as high as 110 − 120 °C. Acoustic measurements at frequencies of 200 Hz − 20 kHz indicate that the FEP layer systems are suitable for applications at least in this range.
N2  - Piezoelektrische Materialien haben große technische und wirtschaftliche Bedeutung für Anwendungen in Sensoren und Aktuatoren. Neben den traditionellen ferroelektrischen Keramiken und Polymeren bilden Ferroelektrete eine neue Gruppe der Piezoelektrika. Ferroelektrete sind reversible funktionelle Polymersysteme zur Umwandlung von elektrischer in mechanische Energie und umgekehrt. Sie zeichnen sich aus durch eine elastische zelluläre Struktur mit internen quasi-permanenten Dipolen. Der Mechanismus der Piezoelektrizität in Ferroelektreten wird dominiert von der Änderung der einzelnen Dipolmomente bei Einwirkung einer äußeren mechanischen Kraft. Insbesondere zelluläres Polypropylene (PP) war in den vergangenen zwei Jahrzehnten Gegenstand intensiver Forschung und Entwicklung im Hinblick auf die grundlegenden Eigenschaften und Anwendungen von Ferroelektreten. Einige bereits erhältliche kommerzielle Produkte nutzen die in geladenem zellulären PP erreichbaren hohen piezoelektrischen d33-Koeffizienten von 600 pC/N und mehr, sind aber durch eine relativ geringe maximale Betriebstemperatur von ungefähr 60 °C eingeschränkt. Die kürzlich entwickelten Ferroelektrete aus zellulärem Polyethylenterephthalat (PET) und zellulären Cyclo-Olefin-Copolymeren (COC) zeigen eine bessere Temperaturbeständigkeit (vor allem COC), allerdings gewöhlich auf Kosten von geringeren d33-Koeffizienten. Das Ziel der vorliegenden Arbeit ist es, temperaturbeständige Ferroelektrete mit für den Markt geeigneten piezoelektrischen Eigenschaften zu entwickeln. Physikalisches Schäumen ist eine beliebte Methode, um besonders reine Polymerschäume herzustellen. Häufig werden, wegen ihrer guten Löslichkeit in vielen Polymeren, Kohlenstoffdioxid (CO2) und Stickstoff (N2) im superkritischen Zustand als Treibmittel eingesetzt. Der Polyester Polyethylennaphtalat (PEN) hat ähnliche Eigenschaften wie PET, ist jedoch temperaturbeständiger. Ein Dreistufenprozess (Schäumen, Aufblähen und Strecken) wurde entwickelt, um PEN-Schäume für hochwertige Ferroelektrete herzustellen. Ungeschäumte PEN-Folien werden mit superkritischem CO2 unter hohem Druck gesättigt und anschließend unter geringem Druck bei Temperaturen nahe der Glastemperatur geschäumt. Um die Hohlräume zu vergrößern, wird der Schaum anschließend mittels Gasdiffusionsexpansion (GDE) aufgebläht. Nach zusätzlichem biaxialen Verstrecken erhält man die optimalen linsenförmigen Zellen, welche zu einer minimalen mechanischen Steifigkeit und einem maximalen piezoelektrischen d33-Koeffizienten des Ferroelektrets führen. Sowohl Korona- als auch Kontaktaufladung werden an zellulärem PEN erfolgreich eingesetzt. Die Lichtemission der dielektrisch behinderten Entladungen (DBDs) kann klar beobachtet werden. Korona-Aufladung in Gasen mit hohen dielektrischen Durchbruchsfestigkeiten, wie z.B. Schwefelhexafluorid (SF6), ermöglicht es, das Paschen-Durchbruchsfeld in den Hohlräumen und damit die erzielbare interne Ladungsdichte zu erhöhen. Dadurch können für zelluläres PEN piezoelektrische d33-Koeffizienten bis zu 500 pC/N erzielt werden. Piezoelektrischen Resonanzmessungen der Ferroelektrete liefern Steifigkeiten c33 im Bereich von 1 – 12 MPa, Antiresonanzfrequenzen von 0.2 – 0.8 MHz und elektromechanische Kopplungsfaktoren zwischen 0.016 und 0.069. PEN-Ferroelektrete zeigen eine bessere Temperaturstabilität als solche aus PP und PET. Der Anwendungsbereich von unbehandeltem PEN reicht bis etwa 80 – 100°C, jener von getemperten oder bei 120°C geladenen Proben bis etwa 110 – 120 °C. Akustische Messungen im Frequenzbereich von 2 Hz – 20 kHz zeigen die Eignung von PEN-Ferroelektretwandlern für Luftschallanwendungen. Fluoriertes Ethylen-Propylen (FEP) ist ein Fluorpolymer mit sehr guten physikalischen, chemischen und elektrischen Eigenschaften. Die Ladungsspeichereigenschaften von ungeschäumtem FEP können durch die Beimengung von Bornitrid deutlich verbessert werden. In dieser Arbeit wird zelluläres FEP mittels eines einstufigen Prozesses, dem schon erwähnten Schäumen mit überkritischem CO2, hergestellt. Die geladenen FEP-Proben weisen d33-Koeffizienten von bis zu 40 pC/N auf. Ermüdungstests zeigen eine sehr gute mechanische Stabilität von PEN- und FEP-Ferroelektreten. Zelluläre Polymerferroelektrete haben großes Potenzial für Anwendungen, und die Suche nach geeigneten zellulären Morphologien ist eng verknüpft mit dem technischen Aufwand ihrer Herstellung. Alternativ wurden Ferroelektrete mit Sandwich-Strukturen aus FEP-Folien entwickelt. Durch Laserverschmelzen eines FEP-Foliengitters mit zwei umgebenden FEP-Folien wird eine definierte, einheitliche zelluläre Struktur gebildet. Aus dielektrischen Resonanzspektren können effektive piezoelektrische d33-Koeffizienten bis zu 350 pC/N, effektive mechanische Steifigkeiten um 0.3 MPa, Antiresonanzfrequenzen um 30 kHz und elektromechanische Kopplungsfaktoren von etwa 0.05 abgeleitet werden. Proben, welche bei erhöhter Temperatur geladen werden, zeigen höhere Ladungsstabilitäten. Nach geeigneter Aufladung bei 140 °C kann die Arbeitstemperatur bis auf 110 – 120 °C gesteigert werden. Akustische Messungen im Frequenzbereich von 2 Hz – 20 kHz zeigen die Eignung von FEP-Sandwich-Strukturen für Luftschallanwendungen.
KW  - Elektroaktive Materialien
KW  - Ferroelektret
KW  - Piezoelektrizität
KW  - Polymerschaum
KW  - Polymerfilm
KW  - Electroactive material
KW  - ferroelectret
KW  - piezoelectricity
KW  - polymer foam
KW  - polymer film
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-48412
ER  -