TY - JOUR A1 - Gross, Thilo A1 - Feudel, Ulrike T1 - Generalized models as a universal approach to the analysis of nonlinear dynamical systems N2 - We present a universal approach to the investigation of the dynamics in generalized models. In these models the processes that are taken into account are not restricted to specific functional forms. Therefore a single generalized models can describe a class of systems which share a similar structure. Despite this generality, the proposed approach allows us to study the dynamical properties of generalized models efficiently in the framework of local bifurcation theory. The approach is based on a normalization procedure that is used to identify natural parameters of the system. The Jacobian in a steady state is then derived as a function of these parameters. The analytical computation of local bifurcations using computer algebra reveals conditions for the local asymptotic stability of steady states and provides certain insights on the global dynamics of the system. The proposed approach yields a close connection between modelling and nonlinear dynamics. We illustrate the investigation of generalized models by considering examples from three different disciplines of science: a socioeconomic model of dynastic cycles in china, a model for a coupled laser system and a general ecological food web Y1 - 2006 UR - http://pre.aps.org/ U6 - https://doi.org/10.1103/Physreve.73.016205 SN - 1539-3755 ER - TY - JOUR A1 - Beyvers, Stephanie A1 - Ohtsuki, Y A1 - Saalfrank, Peter T1 - Optimal control in a dissipative system : vibrational excitation of CO/Cu(100) by IR pulses N2 - The question as to whether state-selective population of molecular vibrational levels by shaped infrared laser pulses is possible in a condensed phase environment is of central importance for such diverse fields as time-resolved spectroscopy, quantum computing, or "vibrationally mediated chemistry." This question is addressed here for a model system, representing carbon monoxide adsorbed on a Cu(100) surface. Three of the six vibrational modes are considered explicitly, namely, the CO stretch vibration, the CO-surface vibration, and a frustrated translation. Optimized infrared pulses for state-selective excitation of "bright" and "dark" vibrational levels are designed by optimal control theory in the framework of a Markovian open-system density matrix approach, with energy flow to substrate electrons and phonons, phase relaxation, and finite temperature accounted for. The pulses are analyzed by their Husimi "quasiprobability" distribution in time-energy space. Y1 - 2006 UR - http://jcp.aip.org/ U6 - https://doi.org/10.1063/1.2206593 SN - 0021-9606 ER - TY - JOUR A1 - Evans, Nicholas R. A1 - Devi, Lekshmi Sudha A1 - Mak, Chris S. K. A1 - Watkins, Scott E. A1 - Pascu, Sofia I. A1 - Köhler, Anna A1 - Friend, Richard H. A1 - Williams, Charlotte K. A1 - Holmes, Andrew B. T1 - Triplet energy back transfer in conjugated polymers with pendant phosphorescent iridium complexes N2 - The nature of Dexter triplet energy transfer between bonded systems of a red phosphorescent iridium complex 13 and a conjugated polymer, polyfluorene, has been investigated in electrophosphorescent organic light-emitting diodes. Red- emitting phosphorescent iridium complexes based on the [Ir(btp)2(acac)]fragment (where btp is 2-(2 '- benzo[b]thienyl)pyridinato and acac is acetylacetonate) have been attached either directly (spacerless) or through a - (CH2)(8)-chain (octamethylene-tethered) at the 9-position of a 9-octylfluorene host. The resulting dibromo- functionalized spacerless (8) or octamethylene-tethered (12) fluorene monomers were chain extended by Suzuki polycondensations using the bis(boronate)-terminated fluorene macromonomers 16 in the presence of end-capping chlorobenzene solvent to produce the statistical spacerless (17) and octamethylene-tethered ( 18) copolymers containing an even dispersion of the pendant phosphorescent fragments. The spacerless monomer 12 adopts a face-to-face conformation with a separation of only 3.6 angstrom between the iridium complex and fluorenyl group, as shown by X-ray analysis of a single crystal, and this facilitates intramolecular triplet energy transfer in the spacerless copolymers 17. The photo- and electroluminescence efficiencies of the octamethylene-tethered copolymers 18 are double those of the spacerless copolymers 17, and this is consistent with suppression of the back transfer of triplets from the red phosphorescent iridium complex to the polyfluorene backbone in 18. The incorporation of a -(CH2)(8)- chain between the polymer host and phosphorescent guest is thus an important design principle for achieving higher efficiencies in those electrophosphorescent organic light-emitting diodes for which the triplet energy levels of the host and guest are similar Y1 - 2006 UR - http://pubs.acs.org/journal/jacsat U6 - https://doi.org/10.1021/Ja0584267 SN - 0002-7863 ER - TY - JOUR A1 - Yang, X. H. A1 - Jaiser, Frank A1 - Klinger, S A1 - Neher, Dieter T1 - Blue polymer electrophosphorescent devices with different electron-transporting oxadiazoles N2 - We report that the performances of blue polymer electrophosphorescent devices are crucially depending on the choice of the electron transporting material incorporated into the emissive layer. Devices with 1,3-bis[(4-tert- butylphenyl)-1,3,4-oxidiazolyl]phenylene (OXD-7) doped at similar to 40 wt% into a poly(vinylcarbazole) matrix exhibited significantly higher efficiencies than those with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), yielding maximum luminous and power efficiency values of 18.2 Cd/A and 8.8 lm/W, respectively. Time resolved photoluminescence measurements revealed a long lifetime phosphorescence component in layers with PBD, which we assign to significant triplet harvesting by this electron-transporting component. (c) 2006 American Institute of Physics Y1 - 2006 UR - http://scitation.aip.org/getpdf/servlet/ GetPDFServlet?filetype=pdf&id=APPLAB000088000002021107000001&idtype=cvips&doi=10.1063/1.2162693&prog=normal U6 - https://doi.org/10.1063/1.2162693 ER - TY - JOUR A1 - Ostermeyer, Martin A1 - Mudge, Damien A1 - Veitch, Peter John A1 - Munch, Jesper T1 - Thermally induced birefringence in Nd : YAG slab lasers N2 - We study thermally induced birefringence in crystalline Nd:YAG zigzag slab lasers and the associated depolarization losses. The optimum crystallographic orientation of the zigzag slab within the Nd:YAG boule and photoelastic effects in crystalline Nd:YAG slabs are briefly discussed. The depolarization is evaluated using the temperature and stress distributions, calculated using a finite element model, for realistically pumped and cooled slabs of finite dimensions. Jones matrices are then used to calculate the depolarization of the zigzag laser mode. We compare the predictions with measurements of depolarization, and suggest useful criteria for the design of the gain media for such lasers. Y1 - 2006 UR - http://www.opticsinfobase.org/ U6 - https://doi.org/10.1364/AO.45.005368 ER - TY - JOUR A1 - Jechow, Andreas A1 - Raab, Volker A1 - Menzel, Ralf T1 - High cw power using an external cavity for spectral beam combining of diode laser-bar emission N2 - In extension to known concepts of wavelength-multiplexing diode laser arrays, a new external cavity is presented. The setup simultaneously improves the beam quality of each single emitter of a standard 25 emitter broad-area stripe laser bar and spectrally superimposes the 25 beams into one. By using this external resonator in an "off-axis" arrangement, beam qualities of M-slow(2) < 14 and M-fast(2) < 3 with optical powers in excess of 10 W in cw operation are obtained. Y1 - 2006 UR - http://www.opticsinfobase.org/ao/browse.cfm U6 - https://doi.org/10.1364/AO.45.003545 SN - 0003-6935 ER - TY - JOUR A1 - Charron, Eric A1 - Cirone, M. A. A1 - Negretti, Antonio A1 - Schmiedmayer, Jörg A1 - Calarco, Tommaso T1 - Theoretical analysis of a realistic atom-chip quantum gate N2 - We present a detailed, realistic analysis of the implementation of a proposal for a quantum phase gate based on atomic vibrational states, specializing it to neutral rubidium atoms on atom chips. We show how to create a double-well potential with static currents on the atom chips, using for all relevant parameters values that are achieved with present technology. The potential barrier between the two wells can be modified by varying the currents in order to realize a quantum phase gate for qubit states encoded in the atomic external degree of freedom. The gate performance is analyzed through numerical simulations; the operation time is similar to 10 ms with a performance fidelity above 99.9%. For storage of the state between the operations the qubit state can be transferred efficiently via Raman transitions to two hyperfine states, where its decoherence is strongly inhibited. In addition we discuss the limits imposed by the proximity of the surface to the gate fidelity. Y1 - 2006 UR - http://pra.aps.org/ SN - 1050-2947 ER - TY - JOUR A1 - Winterhalder, Matthias A1 - Schelter, B A1 - Kurths, Jürgen A1 - Schulze-Borthage, A A1 - Timmer, Jens T1 - Sensitivity and specificity of coherence and phase synchronization analysis N2 - In this Letter, we show that coherence and phase synchronization analysis are sensitive but not specific in detecting the correct class of underlying dynamics. We propose procedures to increase specificity and demonstrate the power of the approach by application to paradigmatic dynamic model systems. (c) 2006 Elsevier B.V. All rights reserved Y1 - 2006 UR - http://www.sciencedirect.com/science/article/pii/S0375960106004002 ( 11.07.2011] U6 - https://doi.org/10.1016/j.physleta.2006.03.018 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 - Wegener, Michael A1 - Bergweiler, Steffen A1 - Zscherpel, Detlef A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Detection of elliptical oscillations and monopole breathing of organ-pipe bodies with piezoelectric polymer sensors N2 - In this paper, a measuring technique is presented for the detection of radial oscillations of tube walls excited by changes in internal air pressure. On organ pipes, the oscillations were investigated by means of piezoelectric polymer films slightly tensioned around the pipe bodies. Employing sensors with patterned electrodes, the well-known elliptical oscillation of the cross section as well as an additional monopole breathing of the organ-pipe body were detected. For the monopole breathing, a close relationship between the pressure distribution of the air-column resonances inside the pipe and the circumference variations along the pipe was observed Y1 - 2006 ER -