Seminar on the Theory of Complex Systems  Winter Term 2018/2019

Confirmed:

• Thus 29.11.2018   at 14 c.t.
  Silke Bergeler, LMU München
  A Protein Flux-based Mechanism for Midcell Sensing in Bacteria
  

  Intracellular positioning of proteins is important for several vital processes in bacterial cells, including chromosome segregation and cell division. Positioning is typically achieved by protein systems incorporating an ATPase that switches between ADP- and ATP-bound states. In this talk, I will first give a brief overview on protein positioning systems in bacterial cells. Then, I will focus on a specific protein system in the bacterium Myxococcus xanthus that localizes the cell division plane at midcell. In this bacterium, a protein cluster is formed on the chromosome that performs a biased random walk to midcell and positively regulates cell division there [1]. An ATPase, PomZ, is crucial for the cluster dynamics. I will discuss how this protein system can be mathematically described in terms of a stochastic model and reaction-diffusion equations to elucidate on which parameters midcell positioning depends on. A mechanism that involves the fluxes of the ATPase PomZ on the chromosome and the elasticity of the chromosome can explain the experimentally observed cluster dynamics. Interestingly, midcell localization of the cluster turns into oscillatory cluster movement when reducing the diffusion constant of PomZ on the chromosome in our simulations [2].

  1. [1] D. Schumacher, S. Bergeler, A. Harms, J. Vonck, S. Huneke-Vogt, E. Frey and L. Søgaard-Andersen, Dev. Cell 41, 299-314 (2017)
  2. [2] S. Bergeler and E. Frey, PLoS Comp. Biol. 14(8), e1006358 (2018)
• Thu 10.01.19   at 14 c.t.
  Uwe Thiele   University of Münster
  Gradient dynamics models for films of complex fluids and beyond - dewetting, line deposition and biofilms
  

  After briefly reviewing a number of experiments on dewetting and evaporating thin films/drops of simple and complex liquids, I introduce the concept of a gradient dynamics description of the evolution of interface-dominated films and drops on solid substrates. First, the case of films/drops of simple non-volatile liquid is discussed, and illustrated with results on droplet patterns and sliding droplets. As a further example, the diffusion equation is formulated as a gradient dynamics. The obtained elements are combined into a thermodynamically consistent gradient dynamics formulation for films of mixtures and surfactant suspensions [1,2]. Next, such models are employed to investigate the out-of-equilibrium process of the deposition of line patterns at receding contact lines for evaporatively dewetting solutions/suspensions [3] and in Langmuir Blodgett transfer [4]. Finally, I discuss how to combine the presented thin-film dynamics with bioactive elements to obtain models for the osmotic spreading of biofilms growing on moist agars [5]. I conclude with a summary and outlook.

  1. [1] U. Thiele, D. Todorova, H. Lopez, Phys. Rev. Lett. 111, 117801 (2013)
  2. [2] Thiele, U.; Archer, A.Pismen, L., Phys. Rev. Fluids 1, 083903 (2016).
  3. [3] U. Thiele, Advances in Colloid and Interface Science 206, 399-413 (2014).
  4. [4] M.H. Köpf and U. Thiele, Nonlinearity 27, 2711-2734 (2014).
  5. [5] Trinschek, S.; John, K.; Lecuyer, S., Thiele, U., Phys. Rev. Lett. 119, 078003 (2017).
  6. [6] Trinschek, S.; John, K. Thiele, U., Soft Matter 14, 4464-4476 (2018)
• Thus 24.01.19   at 14 c.t.
  Philipp Hansmann, MPI Stuttgart
  Materials beyond the single electron approximation: From oxides to adatoms on silicon
  

  Explaining experimental evidence and guiding the design of new materials for electronic functionality are the two main goals of electronic structure calculations. Due to their ground state sensitivity with respect to external perturbations and rich phase diagrams, correlated electron materials such as transition metal oxides or rare-earth heavy-fermion compounds are promising candidates for future electronic devices. It is for the same reasons, however, that a theoretical description becomes very challenging due to the need of non-perturbative approaches to the quantum many-body problem. The seminar will cover (with equal weight) an introduction to modern methods for the treatment of correlated electron materials as well as selected highlights of recent computations for correlated materials ranging from transition metal oxides to adatom lattices on the (111) surface of silicon.

Confirmed for the Summer Term 2019:

• Koenraad Schalm, Institute Lorentz for Theoretical Physics, Leiden University (Mai 16, 2019)