arXiv subjects

E. Schoell

Publications and source records attributed to E. Schoell.

29 records · Page 2Linked to original sources

arXiv2006

Classifying the expansion kinetics and critical surface dynamics of growing cell populations

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 the Fisher-Kolmogorov-Petrovskii-Piskounov (FKPP) equation that is frequently used to model tumor growth phenomena by continuum models. The critical surface dynamics corresponds to the Kardar-Parisi-Zhang (KPZ) universality class for all parameters and model variations studied. While the velocity agrees quantitatively with experimental observations by Bru et al, the critical surface dynamics is in contrast to their interpretation as generic molecular-beam-epitaxy-like growth.

physics.bio-ph↗

arXiv2006

Noise-induced cooperative dynamics and its control in coupled neuron models

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 subsystem, or globally. It is also able to induce or to suppress stochastic synchronization under certain conditions.

nlin.CD↗

arXiv2006

Strain-controlled correlation effects in self-assembled quantum dot stacks

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 dependence on the material anisotropy.

cond-mat.mtrl-sci↗

arXiv2005

Control of unstable steady states by time-delayed feedback methods

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.

cond-mat.other↗

arXiv2005

Counting statistics and decoherence in coupled quantum dots

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 transition from the coherent to the incoherent tunneling limit in all cumulants of the transport process and compare this with decoherence described by a dephasing voltage probe model.

cond-mat.mes-hall↗

arXiv2004

Delayed feedback as a means of control of noise-induced motion

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 one to steer the timescales of noise-induced motion by changing the time delay.

cond-mat.stat-mech↗

arXiv2003

Coulomb effects in tunneling through a quantum dot stack

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 that the interplay of coherent and incoherent effects in the stationary current can be fully described by this approach.

cond-mat.mes-hall↗

arXiv2003

Positive Correlations in Tunneling through coupled Quantum Dots

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 correlation function and the frequency-dependent Fano factor.

cond-mat.mes-hall↗

arXiv2003

Shot noise of coupled semiconductor quantum dots

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 predictions for future experiments will be given. Furthermore, we propose a mechanism for negative differential conductance and investigate the related super-Poissonian shot noise.

cond-mat.mes-hall↗

arXiv2002

Shot Noise in Tunneling through a Quantum Dot Array

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 analytical expression.

cond-mat↗

arXiv2000

Wavefronts may move upstream in doped semiconductor superlattices

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 simulations. Possible experimental realizations are suggested.

cond-mat.mes-hall↗