Inst. Theoretische Physik

286 Items

Recent Submissions
Self-assembly and pattern formation of complex active colloids in two dimensions

Liao, Guo-Jun (2021)

In this thesis, we investigate the individual and combined influence of circle swimming and dipole-dipole interactions on the collective behavior of self-propelled colloids in two dimensions. Based on the conventional active Brownian particle model, we construct three extended models where a self-propulsion torque or a permanent point dipole is additionally assigned to each particle. The overda...

Graph Metrics for Network Robustness—A Survey

Oehlers, Milena ; Fabian, Benjamin (2021-04-17)

Research on the robustness of networks, and in particular the Internet, has gained critical importance in recent decades because more and more individuals, societies and firms rely on this global network infrastructure for communication, knowledge transfer, business processes and e-commerce. In particular, modeling the structure of the Internet has inspired several novel graph metrics for asses...

Influence of Sound on Empirical Brain Networks

Sawicki, Jakub ; Schöll, Eckehard (2021-04-22)

We analyze the influence of an external sound source in a network of FitzHugh–Nagumo oscillators with empirical structural connectivity measured in healthy human subjects. We report synchronization patterns, induced by the frequency of the sound source. We show that the level of synchrony can be enhanced by choosing the frequency of the sound source and its amplitude as control parameters for s...

Limitations of the recall capabilities in delay-based reservoir computing systems

Köster, Felix ; Ehlert, Dominik ; Lüdge, Kathy (2020-10-02)

We analyse the memory capacity of a delay-based reservoir computer with a Hopf normal form as nonlinearity and numerically compute the linear as well as the higher order recall capabilities. A possible physical realization could be a laser with external cavity, for which the information is fed via electrical injection. A task-independent quantification of the computational capability of the res...

Steering droplets on substrates using moving steps in wettability

Grawitter, Josua ; Stark, Holger (2021-01-07)

Droplets move on substrates with a spatio-temporal wettability pattern as generated, for example, on light-switchable surfaces. To study such cases, we implement the boundary-element method to solve the governing Stokes equations for the fluid flow field inside and on the surface of a droplet and supplement it by the Cox–Voinov law for the dynamics of the contact line. Our approach reproduces t...

Particle pairs and trains in inertial microfluidics

Schaaf, Christian ; Stark, Holger (2020-08-04)

Staggered and linear multi-particle trains constitute characteristic structures in inertial microfluidics. Using lattice-Boltzmann simulations, we investigate their properties and stability, when flowing through microfluidic channels. We confirm the stability of cross-streamline pairs by showing how they contract or expand to their equilibrium axial distance. In contrast, same-streamline pairs ...

Active open-loop control of elastic turbulence

van Buel, Reinier ; Stark, Holger (2020-09-24)

We demonstrate through numerical solutions of the Oldroyd-B model in a two-dimensional Taylor–Couette geometry that the onset of elastic turbulence in a viscoelastic fluid can be controlled by imposed shear-rate modulations, one form of active open-loop control. Slow modulations display rich and complex behavior where elastic turbulence is still present, while it vanishes for fast modulations a...

Emergent collective dynamics of bottom-heavy squirmers under gravity

Rühle, Felix ; Stark, Holger (2020-05-25)

We present the results of hydrodynamic simulations using the method of multi-particle collision dynamics for a system of squirmer microswimmers moving under the influence of gravity at low Reynolds numbers. In addition, the squirmers are bottom-heavy so that they experience a torque which aligns them along the vertical. The squirmers interact hydrodynamically by the flow fields of a stokeslet a...

Solitary states in adaptive nonlocal oscillator networks

Berner, Rico ; Polanska, Alicja ; Schöll, Eckehard ; Yanchuk, Serhiy (2020-09-28)

In this article, we analyze a nonlocal ring network of adaptively coupled phase oscillators. We observe a variety of frequency-synchronized states such as phase-locked, multicluster and solitary states. For an important subclass of the phase-locked solutions, the rotating waves, we provide a rigorous stability analysis. This analysis shows a strong dependence of their stability on the coupling ...

Irreversibility, heat and information flows induced by non-reciprocal interactions

Loos, Sarah A. M. ; Klapp, Sabine H. L. (2020-12-30)

We study the thermodynamic properties induced by non-reciprocal interactions between stochastic degrees of freedom in time- and space-continuous systems. We show that, under fairly general conditions, non-reciprocal coupling alone implies a steady energy flow through the system, i.e., non-equilibrium. Projecting out the non-reciprocally coupled degrees of freedom renders non-Markovian, one-vari...

Many electrons and the photon field

Buchholz, Florian Konrad Friedrich (2021)

Recent experimental progress in the field of cavity quantum electrodynamics allows to study the regime of strong interaction between quantized light and complex matter systems. Due to the coherent coupling between photons and matter-degrees of freedom, polaritons - hybrid light-matter quasiparticles - emerge, which can significantly influence matter properties and complex process such as chemic...

Non-Markovian open quantum many-body system dynamics

Finsterhölzl, Regina Anna (2021)

The study of open quantum systems forms one of the main problems of modern physics. This thesis aims at contributing to this field, and focuses on the investigation of non-Markovian dynamics of open quantum systems. Here, as a special case, quantum many-body systems provide for a rich field of research. With the ability to control them being of essential importance for the development of quantu...

Desynchronization Transitions in Adaptive Networks

Berner, Rico ; Vock, Simon ; Schöll, Eckehard ; Yanchuk, Serhiy (2021-01-15)

Adaptive networks change their connectivity with time, depending on their dynamical state. While synchronization in structurally static networks has been studied extensively, this problem is much more challenging for adaptive networks. In this Letter, we develop the master stability approach for a large class of adaptive networks. This approach allows for reducing the synchronization problem fo...

Multi-particle collision dynamics with a non-ideal equation of state. I

Zantop, Arne W. ; Stark, Holger (2021-01-08)

The method of multi-particle collision dynamics (MPCD) and its different implementations are commonly used in the field of soft matter physics to simulate fluid flow at the micron scale. Typically, the coarse-grained fluid particles are described by the equation of state of an ideal gas, and the fluid is rather compressible. This is in contrast to conventional fluids, which are incompressible f...

Dynamic signatures of mode competition in optically injected high-β lasers

Lingnau, Benjamin ; Schicke, David ; Eichelmann, Marcel ; Lüdge, Kathy (2020-07-28)

In this paper we theoretically investigate the statistical light-emission properties of an optically injected bimodal quantum-dot micropillar laser with high spontaneous emission rates. The nanostructured device is described in terms of a stochastic, semiclassically derived rate equation model. We focus on the stochastic switching dynamics between the two fundamental modes and correlate the res...

Dynamical modes of sheared confined microscale matter

Gerloff, Sascha ; Ortiz-Ambriz, Antonio ; Tierno, Pietro ; Klapp, Sabine H. L. (2020-09-07)

Based on (overdamped) Stokesian dynamics simulations and video microscopy experiments, we study the non equilibrium dynamics of a sheared colloidal cluster, which is confined to a two-dimensional disk. The experimental system is composed of a mixture of paramagnetic and non magnetic polystyrene particles, which are held in the disk by time shared optical tweezers. The paramagnetic particles are...

FitzHugh–Nagumo oscillators on complex networks mimic epileptic-seizure-related synchronization phenomena

Gerster, Moritz ; Berner, Rico ; Sawicki, Jakub ; Zakharova, Anna ; Škoch, Antonín ; Hlinka, Jaroslav ; Lehnertz, Klaus ; Schöll, Eckehard (2020-12-14)

We study patterns of partial synchronization in a network of FitzHugh–Nagumo oscillators with empirical structural connectivity measured in human subjects. We report the spontaneous occurrence of synchronization phenomena that closely resemble the ones seen during epileptic seizures in humans. In order to obtain deeper insights into the interplay between dynamics and network topology, we perfor...

Remote pacemaker control of chimera states in multilayer networks of neurons

Ruzzene, Giulia ; Omelchenko, Iryna ; Sawicki, Jakub ; Zakharova, Anna ; Schöll, Eckehard ; Andrzejak, Ralph G. (2020-11-24)

Networks of coupled nonlinear oscillators allow for the formation of nontrivial partially synchronized spatiotemporal patterns, such as chimera states, in which there are coexisting coherent (synchronized) and incoherent (desynchronized) domains. These complementary domains form spontaneously, and it is impossible to predict where the synchronized group will be positioned within the network. Th...

Quantization of quasinormal modes in dissipative media

Franke, Sebastian Robert (2020)

Light-matter interactions in dissipative nanophotonic or nanoplasmonic systems is a major topic in modern quantum optics and quantum plasmonics. One of the main challenges from the theoretical point of view is to rigorously quantize the light in these systems and to express the electric field operator in terms of discrete photon annihilation and creation operators. This is a highly non-trivial ...

Structural anomalies in brain networks induce dynamical pacemaker effects

Koulierakis, Ioannis ; Verganelakis, Dimitris A. ; Omelchenko, Iryna ; Zakharova, Anna ; Schöll, Eckehard ; Provata, Astero (2020-11-19)

Dynamical effects on healthy brains and brains affected by tumor are investigated via numerical simulations. The brains are modeled as multilayer networks consisting of neuronal oscillators whose connectivities are extracted from Magnetic Resonance Imaging (MRI) data. The numerical results demonstrate that the healthy brain presents chimera-like states where regions with high white matter conce...