Inst. Theoretische Physik

154 Items

Recent Submissions
Simulating the complex cell design of Trypanosoma brucei and its motility

Alizadehrad, Davod ; Krüger, Timothy ; Engstler, Markus ; Stark, Holger (2015)

The flagellate Trypanosoma brucei, which causes the sleeping sickness when infecting a mammalian host, goes through an intricate life cycle. It has a rather complex propulsion mechanism and swims in diverse microenvironments. These continuously exert selective pressure, to which the trypanosome adjusts with its architecture and behavior. As a result, the trypanosome assumes a diversity of compl...

Theory of multidimensional spectroscopy and excitation transfer processes in nanostructures

Specht, Judith Felicitas (2018)

Advances in the manufacturing of semiconductor-based hybrid nanostructures draws attention towards possible optoelectronic and quantum computational applications. The present work develops theoretical models to study the coherent couplings and excitation transfer mechanisms in nanostructures and aims at a microscopic understanding of the underlying Coulomb-mediated processes, thus, laying the f...

Multi-chimera States in the Leaky Integrate-and-Fire Model

Tsigkri-DeSmedt, N.D. ; Hizanidis, J. ; Hövel, Philipp ; Provata, A. (2015)

We study the dynamics of identical leaky integrate-and-fire neurons with symmetric non-local coupling. Upon varying control parameters (coupling strength, coupling range, refractory period) we investigate the system's behaviour and highlight the formation of chimera states. We show that the introduction of a refractory period enlarges the parameter region where chimera states appear and affects...

Synchronization and waves in confined complex active media

Totz, Jan Frederik (2018)

The aim of this thesis is the study and characterization of a number of self-organized patterns with potential relevance to biological systems and beyond. To this end we utilize the well-established oscillating Belousov-Zhabotinsky (BZ) reaction in chemical experiments as well as numerical simulations of the underlying model equations on graphics cards. The first part of this thesis features e...

Gravity-induced dynamics of a squirmer microswimmer in wall proximity

Rühle, Felix ; Blaschke, Johannes ; Kuhr, Jan-Timm ; Stark, Holger (2018-02-07)

We perform hydrodynamic simulations using the method of multi-particle collision dynamics and a theoretical analysis to study a single squirmer microswimmer at high Péclet number, which moves in a low Reynolds number fluid and under gravity. The relevant parameters are the ratio α of swimming to bulk sedimentation velocity and the squirmer type β. The combination of self-propulsion, gravitation...

Physical minimal models of amoeboid cell motility

Kulawiak, Dirk Alexander (2017)

Cell locomotion plays an important role in many biological processes such as the immune system, embryonic development, or cancer metastasis. In these examples, cells interact with their environments or coordinate their movements with other cells, creating collective behavior. In this thesis, we utilize minimal modeling to investigate single and collective cell motility in three different settin...

Quantum light driven many level systems in the weak and strong coupling limits

Chatraee Azizabadi, Shahabedin (2017)

We propose a possibility to study the quantum light excitation of atomic systems. To confine our study, we limit the configuration to two and four level emitters as target systems. Source and target are coupled via unidirectional waveguide. We numerically implement the cascaded formalism and use the source-target approach. Herein, we focus on continuous excitation scenarios where the source s...

Multidimensional high harmonic spectroscopy

Serbinenko, Valeriya (2017)

Multidimensional high harmonic spectroscopy is a cutting-edge technique for studying the effect of the intense low-frequency laser fields on atoms and molecules. The high energy photons, emitted by a particle as a result of the interaction with the strong laser field, carry the information about the processes in atoms and molecules, which lead to the emission. Multidimensional character of the te...

Quantum control of light and matter fields in the nonlinear regime

Naumann, Nicolas Ludwig (2017)

In this thesis three different approaches to control the quantum statistics in nanoscopic devices are investigated. In the first part of the thesis, mechanical oscillations in solid state devices are manipulated by an external laser to show bistabilities, coherent amplification, and enhanced damping. The dynamics is controlled by the frequency of the external laser. This study is performed in a...

Identical emitters, collective effects and dissipation in quantum optics

Gegg, Michael (2017)

In this thesis a formalism for indistinguishable multi-level quantum emitters in quantum master equations is developed. The complexity of the approach scales only polynomially in the number of quantum emitters. Complexity here means the number of coupled equations or rather the dimension of the Liouville space. This approach opens new possibilities for calculating open quantum systems. The meth...

Brief remark on material motion dependence

Muschik, Wolfgang (2013)

Acceleration-sensitive materials have properties which depend on the motion of the material. This motion refers to an arbitrary chosen standard frame of reference and does not depend on observers, which can be changed without changing the material properties. Consequently, one has properly to distinguish between changing the observer and changing the motion of the material. This is achieved by ...

Wie philosophisch dürfen bzw. müssen die Naturwissenschaften sein?

Borzeszkowski, Horst-Heino von (2015)

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Manipulating shear-induced non-equilibrium transitions in colloidal films by feedback control

Vezirov, Tarlan A. ; Gerloff, Sascha ; Klapp, Sabine H. L. (2015)

Using Brownian Dynamics (BD) simulations we investigate non-equilibrium transitions of sheared colloidal films under controlled shear stress sigma(xz). In our approach the shear rate (gamma) over dot is a dynamical variable, which relaxes on a time scale tau(c) such that the instantaneous, configuration-dependent stress sigma(xz)(t) approaches a pre-imposed value. Investigating the dynamics und...

Tunable structures of mixtures of magnetic particles in liquid-crystalline matrices

Peroukidis, Stavros D. ; Lichtner, Ken ; Klapp, Sabine H. L. (2015)

We investigate the self-organization of a binary mixture of similar sized rods and dipolar soft spheres by means of Monte-Carlo simulations. We model interparticle interactions by employing anisotropic Gay-Berne, dipolar and soft-sphere interactions. In the limit of vanishing magnetic moments we obtain a variety of fully miscible liquid crystalline phases including nematic, smectic and lamellar...

Generic model for tunable colloidal aggregation in multidirectional fields

Kogler, Florian ; Velev, Orlin D. ; Hall, Carol K. ; Klapp, Sabine H. L. (2015)

Based on Brownian Dynamics computer simulations in two dimensions we investigate aggregation scenarios of colloidal particles with directional interactions induced by multiple external fields. To this end we propose a model which allows continuous change in the particle interactions from point-dipole-like to patchy-like (with four patches). We show that, as a result of this change, the non-equi...

Effects of magnetic field gradients on the aggregation dynamics of colloidal magnetic nanoparticles

Heinrich, Dirk ; Goñi, Alejandro R. ; Osán, Tristán ; Cerioni, L. M. C. ; Smessaert, Anton ; Klapp, Sabine H. L. ; Faraudo, Jordi ; Pusiol, Daniel Jose ; Thomsen, Christian (2015)

We have used low-field H-1 nuclear-magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) to investigate the aggregation dynamics of magnetic particles in ionic ferrofluids (IFFs) in the presence of magnetic field gradients. At the beginning of the experiments, the measured NMR spectra were broad and asymmetric, exhibiting two features attributed to different dynamical environments o...

Self-assembly of three-dimensional ensembles of magnetic particles with laterally shifted dipoles

Yener, Arzu B. ; Klapp, Sabine H. L. (2016)

We consider a model of colloidal spherical particles carrying a permanent dipole moment which is laterally shifted out of the particles' geometrical centres, i.e. the dipole vector is oriented perpendicular to the radius of the particles. Varying the shift delta from the centre, we analyse ground state structures for two, three and four hard spheres, using a simulated annealing procedure. We al...

The effect of charge separation on the phase behavior of dipolar colloidal rods

Rutkowski, David M. ; Velev, Orlin D. ; Klapp, Sabine H. L. ; Hall, Carol K. (2016)

Colloids with anisotropic shape and charge distribution can assemble into a variety of structures that could find use as novel materials for optical, photonic, electronic and structural applications. Because experimental characterization of the many possible types of multi-shape and multipolar colloidal particles that could form useful structures is difficult, the search for novel colloidal mat...

Dynamics of a bacterial flagellum under reverse rotation

Adhyapak, Tapan Chandra ; Stark, Holger (2016)

To initiate tumbling of an E. coli, one of the helical flagella reverses its sense of rotation. It then transforms from its normal form first to the transient semicoiled state and subsequently to the curly-I state. The dynamics of polymorphism is effectively modeled by describing flagellar elasticity through an extended Kirchhoff free energy. However, the complete landscape of the free energy r...

Orientational order and translational dynamics of magnetic particle assemblies in liquid crystals

Peroukidis, Stavros D. ; Klapp, Sabine H. L. (2016)

Implementing extensive molecular dynamics simulations we explore the organization of magnetic particle assemblies (clusters) in a uniaxial liquid crystalline matrix comprised of rodlike particles. The magnetic particles are modelled as soft dipolar spheres with diameter significantly smaller than the width of the rods. Depending on the dipolar strength coupling the magnetic particles arrange in...