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Sep 20, 2013
09/13

by
R. Kunert; E. Schoell

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We show that elastic interactions of an array of self-assembled quantum dots in a parent material matrix are markedly distinct from the elastic field created by a single point defect, and can explain the observed abrupt correlation--anticorrelation transition in semiconductor quantum dot stacks. Finite volume effects of the quantum dots are shown to lead to sharper transitions. Our analysis also predicts the inclination angle under which the alignment in successive quantum dot layers occurs in...

Source: http://arxiv.org/abs/cond-mat/0607016v1

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42

Sep 21, 2013
09/13

by
P. Hoevel; E. Schoell

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We show that time-delayed feedback methods, which have successfully been used to control unstable periodic ortbits, provide a tool to stabilize unstable steady states. We present an analytical investigation of the feedback scheme using the Lambert function and discuss effects of both a low-pass filter included in the control loop and non-zero latency times associated with the generation and injection of the feedback signal.

Source: http://arxiv.org/abs/cond-mat/0508367v1

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34

Sep 19, 2013
09/13

by
G. Kiesslich; A. Wacker; E. Schoell

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The low-frequency shot noise properties of two electrostatically coupled semiconductor quantum dot states which are connected to emitter/collector contacts are studied. A master equation approach is used to analyze the bias voltage dependence of the Fano factor as a measure of temporal correlations in tunneling current caused by Pauli's exclusion principle and the Coulomb interaction. In particular, the influence of the Coulomb interaction on the shot noise behavior is discussed in detail and...

Source: http://arxiv.org/abs/cond-mat/0303025v1

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Sep 19, 2013
09/13

by
M. Block; E. Schoell; D. Drasdo

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Based on a cellular automaton model the growth kinetics and the critical surface dynamics of cell monolayers is systematically studied by variation of the cell migration activity, the size of the proliferation zone and the cell cycle time distribution over wide ranges. The model design avoids lattice artifacts and ensures high performance. The monolayer expansion velocity derived from our simulations can be interpreted as a generalization of the velocity relationship for a traveling front in...

Source: http://arxiv.org/abs/physics/0610146v1

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Sep 22, 2013
09/13

by
J. Hizanidis; R. Aust; E. Schoell

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We study the effect of a time-delayed feedback within a generic model for a saddle-node bifurcation on a limit cycle. Without delay the only attractor below this global bifurcation is a stable node. Delay renders the phase space infinite-dimensional and creates multistability of periodic orbits and the fixed point. Homoclinic bifurcations, period-doubling and saddle-node bifurcations of limit cycles are found in accordance with Shilnikov's theorems.

Source: http://arxiv.org/abs/nlin/0702002v2

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Sep 19, 2013
09/13

by
M. Block; B. Schmittmann; E. Schoell

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We propose a new method to control the roughness of a growing surface, via a time-delayed feedback scheme. As an illustration, we apply this method to the Kardar-Parisi-Zhang equation in 1+1 dimensions and show that the effective growth exponent of the surface width can be stabilized at any desired value in the interval [0.25,0.33], for a significant length of time. The method is quite general and can be applied to a wide range of growth phenomena. A possible experimental realization is...

Source: http://arxiv.org/abs/cond-mat/0701171v1

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7.0

Jun 30, 2018
06/18

by
Y. N. Kyrychko; K. B. Blyuss; E. Schoell

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This paper studies the stability of synchronized states in networks where couplings between nodes are characterized by some distributed time delay, and develops a generalized master stability function approach. Using a generic example of Stuart-Landau oscillators, it is shown how the stability of synchronized solutions in networks with distributed delay coupling can be determined through a semi-analytic computation of Floquet exponents. The analysis of stability of fully synchronized and of...

Topics: Nonlinear Sciences, Chaotic Dynamics

Source: http://arxiv.org/abs/1406.5428

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Sep 19, 2013
09/13

by
G. Kiesslich; P. Samuelsson; A. Wacker; E. Schoell

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We theoretically consider charge transport through two quantum dots coupled in series. The corresponding full counting statistics for noninteracting electrons is investigated in the limits of sequential and coherent tunneling by means of a master equation approach and a density matrix formalism, respectively. We clearly demonstrate the effect of quantum coherence on the zero-frequency cumulants of the transport process, focusing on noise and skewness. Moreover, we establish the continuous...

Source: http://arxiv.org/abs/cond-mat/0507403v1

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Sep 19, 2013
09/13

by
V. Flunkert; S. Yanchuk; T. Dahms; E. Schoell

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Stability of synchronization in delay-coupled networks of identical units generally depends in a complicated way on the coupling topology. We show that for large coupling delays synchronizability relates in a simple way to the spectral properties of the network topology. The master stability function used to determine stability of synchronous solutions has a universal structure in the limit of large delay: it is rotationally symmetric around the origin and increases monotonically with the...

Source: http://arxiv.org/abs/1009.6120v2

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Sep 22, 2013
09/13

by
H. Sprekeler; G. Kiesslich; A. Wacker; E. Schoell

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Due to the Fermi-Dirac statistics of electrons the temporal correlations of tunneling events in a double barrier setup are typically negative. Here, we investigate the shot noise behavior of a system of two capacitively coupled quantum dot states by means of a Master equation model. In an asymmetric setup positive correlations in the tunneling current can arise due to the bunching of tunneling events. The underlying mechanism will be discussed in detail in terms of the current-current...

Source: http://arxiv.org/abs/cond-mat/0309027v1

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40

Sep 18, 2013
09/13

by
Y. N. Kyrychko; K. B. Blyuss; E. Schoell

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This paper studies the effects of distributed delay coupling on the dynamics in a system of non-identical coupled Stuart-Landau oscillators. For uniform and gamma delay distribution kernels, conditions for amplitude death are obtained in terms of average frequency, frequency detuning and parameters of the coupling, including coupling strength and phase, as well as the mean time delay and the width of the delay distribution. To gain further insight into the dynamics inside amplitude death...

Source: http://arxiv.org/abs/1209.0133v1

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Sep 22, 2013
09/13

by
N. B. Janson; A. G. Balanov; E. Schoell

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Time--delayed feedback is exploited for controlling noise--induced motion in coherence resonance oscillators. Namely, under the proper choice of time delay, one can either increase or decrease the regularity of motion. It is shown that in an excitable system, delayed feedback can stabilize the frequency of oscillations against variation of noise strength. Also, for fixed noise intensity, the phenomenon of entrainment of the basic oscillation period by the delayed feedback occurs. This allows...

Source: http://arxiv.org/abs/cond-mat/0309226v2

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Sep 22, 2013
09/13

by
H. Sprekeler; G. Kiesslich; A. Wacker; E. Schoell

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Tunneling through two vertically coupled quantum dots is studied by means of a Pauli master equation model. The observation of double peaks in the current-voltage characteristic in a recent experiment is analyzed in terms of the tunnel coupling between the quantum dots and the coupling to the contacts. Different regimes for the emitter chemical potential indicating different peak scenarios in the tunneling current are discussed in detail. We show by comparison with a density matrix approach...

Source: http://arxiv.org/abs/cond-mat/0309696v1

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Sep 19, 2013
09/13

by
B. Hauschildt; N. B. Janson; A. Balanov; E. Schoell

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We investigate feedback control of the cooperative dynamics of two coupled neural oscillators that is induced merely by external noise. The interacting neurons are modelled as FitzHugh-Nagumo systems with parameter values at which no autonomous oscillations occur, and each unit is forced by its own source of random fluctuations. Application of delayed feedback to only one of two subsystems is shown to be able to change coherence and timescales of noise induced oscillations either in the given...

Source: http://arxiv.org/abs/nlin/0610007v1

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33

Sep 22, 2013
09/13

by
A. Carpio; L. L. Bonilla; A. Wacker; E. Schoell

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In weakly coupled, current biased, doped semiconductor superlattices, domain walls may move upstream against the flow of electrons. For appropriate doping values, a domain wall separating two electric field domains moves downstream below a first critical current, it remains stationary between this value and a second critical current, and it moves upstream above. These conclusions are reached by using a comparison principle to analyze a discrete drift-diffusion model, and validated by numerical...

Source: http://arxiv.org/abs/cond-mat/0003258v1

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Sep 18, 2013
09/13

by
M. A. Dahlem; G. Hiller; A. Panchuk; E. Schoell

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We study the nonlinear dynamics of two delay-coupled neural systems each modelled by excitable dynamics of FitzHugh-Nagumo type and demonstrate that bistability between the stable fixed point and limit cycle oscillations occurs for sufficiently large delay times and coupling strength. As the mechanism for these delay-induced oscillations we identify a saddle-node bifurcation of limit cycles.

Source: http://arxiv.org/abs/0803.2352v1

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39

Sep 18, 2013
09/13

by
E. Schoell; G. Hiller; P. Hoevel; M. A. Dahlem

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The influence of time delay in systems of two coupled excitable neurons is studied in the framework of the FitzHugh-Nagumo model. Time-delay can occur in the coupling between neurons or in a self-feedback loop. The stochastic synchronization of instantaneously coupled neurons under the influence of white noise can be deliberately controlled by local time-delayed feedback. By appropriate choice of the delay time synchronization can be either enhanced or suppressed. In delay-coupled neurons,...

Source: http://arxiv.org/abs/0809.1025v1

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Sep 21, 2013
09/13

by
V. Flunkert; O. D'Huys; J. Danckaert; I. Fischer; E. Schoell

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We theoretically study chaos synchronization of two lasers which are delay-coupled via an active or a passive relay. While the lasers are synchronized, their dynamics is identical to a single laser with delayed feedback for a passive relay and identical to two delay-coupled lasers for an active relay. Depending on the coupling parameters the system exhibits bubbling, i.e., noise-induced desynchronization, or on-off intermittency. We associate the desynchronization dynamics in the coherence...

Source: http://arxiv.org/abs/0901.4282v2

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95

Jul 20, 2013
07/13

by
B. Fiedler; V. Flunkert; M. Georgi; P. Hoevel; E. Schoell

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We refute an often invoked theorem which claims that a periodic orbit with an odd number of real Floquet multipliers greater than unity can never be stabilized by time-delayed feedback control in the form proposed by Pyragas. Using a generic normal form, we demonstrate that the unstable periodic orbit generated by a subcritical Hopf bifurcation, which has a single real unstable Floquet multiplier, can in fact be stabilized. We derive explicit analytical conditions for the control matrix in...

Source: http://arxiv.org/abs/nlin/0609056v2

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48

Sep 18, 2013
09/13

by
K. B. Blyuss; Y. N. Kyrychko; P. Hoevel; E. Schoell

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We present an analysis of time-delayed feedback control used to stabilize an unstable steady state of a neutral delay differential equation. Stability of the controlled system is addressed by studying the eigenvalue spectrum of a corresponding characteristic equation with two time delays. An analytic expression for the stabilizing control strength is derived in terms of original system parameters and the time delay of the control. Theoretical and numerical results show that the interplay...

Source: http://arxiv.org/abs/1201.5964v1

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42

Sep 18, 2013
09/13

by
Y. N. Kyrychko; K. B. Blyuss; P. Hoevel; E. Schoell

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Spectral properties and transition to instability in neutral delay differential equations are investigated in the limit of large delay. An approximation of the upper boundary of stability is found and compared to an analytically derived exact stability boundary. The approximate and exact stability borders agree quite well for the large time delay, and the inclusion of a time-delayed velocity feedback improves this agreement for small delays. Theoretical results are complemented by a numerically...

Source: http://arxiv.org/abs/1201.5957v1

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36

Sep 18, 2013
09/13

by
Y. N. Kyrychko; K. B. Blyuss; S. J. Hogan; E. Schoell

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This paper studies the effects of a time-delayed feedback control on the appearance and development of spatiotemporal patterns in a reaction-diffusion system. Different types of control schemes are investigated, including single-species, diagonal, and mixed control. This approach helps to unveil different dynamical regimes, which arise from chaotic state or from traveling waves. In the case of spatiotemporal chaos, the control can either stabilize uniform steady states or lead to bistability...

Source: http://arxiv.org/abs/1201.6151v1

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Sep 21, 2013
09/13

by
G. Kiesslich; E. Schoell; T. Brandes; F. Hohls; R. J. Haug

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We show that the intriguing observation of noise enhancement in the charge transport through two vertically coupled quantum dots can be explained by the interplay of quantum coherence and strong Coulomb blockade. We demonstrate that this novel mechanism for super-Poissonian charge transfer is very sensitive to decoherence caused by electron-phonon scattering as inferred from the measured temperature dependence.

Source: http://arxiv.org/abs/0706.1737v3

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Sep 21, 2013
09/13

by
M. T. Greenaway; A. G. Balanov; E. Schoell; T. M. Fromhold

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We show that a tilted magnetic field transforms the structure and THz dynamics of charge domains in a biased semiconductor superlattice. At critical field values, strong coupling between the Bloch and cyclotron motion of a miniband electron triggers chaotic delocalization of the electron orbits, causing strong resonant enhancement of their drift velocity. This dramatically affects the collective electron behavior by inducing multiple propagating charge domains and GHz-THz current oscillations...

Source: http://arxiv.org/abs/0905.3717v2

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Sep 19, 2013
09/13

by
G. Kiesslich; A. Wacker; E. Schoell; A. Nauen; F. Hohls; R. J. Haug

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The shot noise suppression in a sample containing a layer of self-assembled InAs quantum dots has been investigated experimentally and theoretically. The observation of a non-monotonic dependence of the Fano factor on the bias voltage in a regime where only few quantum dot ground states contribute to the tunneling current is analyzed by a master equation model. Under the assumption of tunneling through states without Coulomb interaction this behaviour can be qualitatively reproduced by an...

Source: http://arxiv.org/abs/cond-mat/0209523v1