Research

Droplet motion in chemical gradients

In this project, I investigate the motion of phase separated droplets in a gradient of a third chemical species. I identify two different propulsion mechanisms:

• Diffusiophoresis (basically the motion due to diffusion of material onto and off the droplet)

• Hydrodynamic flows induced by surface tension gradients

The mechanism of diffusiophoresis is quite well understood and is dominant in high viscosity environments (diffusion dominates). On the other hand, the mechanism by which the gradients in the surface tension arises is not clear.

Currently, I am using field based simulations and analytical techniques to find the relevant mechanisms that drive advective propulsion.

In the future, I want to incorporate activity in the form of chemical conversion reactions to explain the collective motion of actively driven droplets and compare to experiments done in the Lab of Eric Dufresne at Cornell.

Multistability of active droplets

In this project, we investigate how droplet size can be controlled by active chemical reactions and hydrodynamic effects. Using numerical simulations of a binary mixture that phase separates and undergoes reactions, we identify three different dynamical regimes: Small droplets are dominated by coalescence due to hydrodynamic advection, then transition to an Ostwald ripening regime dominated by diffusion, and finally exhibit size control by active chemical reactions. 

We can estimate the final droplet size analytically. However, our simulations reveal various final sizes indicating that the system is multistable. These metastable states can be explored by the system if advection and reactions are strong enough.

See the Poster on this topic!

Response function of ERK-signaling in HeLa cells

Supervised by Kazuhiro Aoki at the NIBB in Okazaki, Japan, we measured the transfer function of the EGFR-Ras-ERK signaling pathway in HeLa cells by way of ERK-KTR, a biosensor visualizing ERK activity by translocation to the nucleus, while activating ERK at different levels of the signaling pathway with optogenetic techniques.

We found oscillating ERK activity as a reaction to single short excitations of the pathway.  The final goal will be to extract a minimal network model of the pathway by means of data regression.

See the Poster on this topic!

Free energy principle of the brain

As part of a small interdisciplinary research group, supported by the German Academic Scholarship Foundation, we explore the utility of a Unified Theory of the Brain based on the Free Energy Principle (Karl Friston, 2010).

Supervised by Michael Kohl, we explored the theory and applications of the Free Energy Principle (FEP) through Literature and discussions with leading experts in the fields of neuroscience, computer science and philosophy. We particularly focused on the potential applicability of this abstract concept to laboratory experiments and evaluated its practical usefulness.

Topological defects in ferromagnetic superconductors (Master thesis)

In this project, supervised by Alexei Vagov and Vollrath Martin Axt, I developed a theory of coexisting ferromagnetism and superconductivity in materials such as P-doped EuFe2As2. 

I analyzed the formation of patterns in the magnetization of such materials, using linear stability and methods from nonlinear analysis like Amplitude equations.

Finally, I was able to predict the existence and motion of topological Y-shaped defects in the magnetization-stripe-pattern that were subsequently found in experiments. I analyzed their velocity and connected it to important material parameters.

Temperature dependence of surface plasmon dispersion (Bachelor thesis)

In this project, supervised by Vollrath Martin Axt, I explored the dispersion of surface plasmon polaritons. These are quasi-particles, arising from a coupling between electromagnetic waves and collective electron motion at the interface of a (semi-)conductor.

I solved Maxwell's equation coupled to the electronic response function for different simple surface geometries and found that a temperature increase leads to an increased group velocity for small wave-lengths and an increased damping. We also found that for certain geometries (wave-guides), we can achieve a group velocity of zero for very large wave-lengths, that are excitable with light or quantum emitters.

View my bachelor thesis!

Granular impact in microgravity

This project, lead by Kai Huang, aimed to understand the impact characteristics of projectiles shot into granular matter, specifically under microgravity conditions. It also highlights methods to measure the trajectory of the projectile, without relying on optical imaging. Instead we used an IMU (Inertial Measurement Unit) that recorded tri-axial acceleration and angular velocity data.

As a student I developed analysis software to integrate the acceleration and angular velocity data to obtain the trajectory. Subsequently, I analyzed the IMU data from projectiles shot into granular matter in microgravity conditions (Drop Tower Bremen).