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Johannes Blaschke

Postdoctoral Researcher, Computational Research Division


Contact Information

Johannes Blaschke
MS 50A-3111
Lawrence Berkeley National Lab
1 Cyclotron Rd.
Berkeley, CA 94720

510-486-6900 (fax)

JPBlaschke@lbl.gov


Affiliation and Research Interests

I am a postdoctoral scholar in the Center for Computational Sciences and Engineering (CCSE) in the Computational Research Division of the Computing Sciences Directorate at the Lawrence Berkeley National Laboratory. I am interested in applying novel (and large-scale) simulation techiniques to broad range of non-equilibrium complex systems. Currently, I am using AMReX and MFIX-Exa to investigate the collective dynamics of hydrodynamically and chemically interacting microswimmers. As well as exploring how coarse-graining techniques can be used to simulate multi-phase granular flows at extremely large scales.


Statistical Physics of Hydrodynamically and Chemically Interacting Microswimmers

The collective dynamics of microorganisms and artificial microswimmers is relevant both to real world applications, as well as for posing fundamental questions in non-equilibrium statistical physics. A striking feature of their collective behavior is that for su ciently strong self-propulsion, they phase-separate into a dense cluster coexisting with a low-density gas-like surrounding. Our research demonstrates that hydrodynamics is essential to the concept of motility-induced phase separation. Here we show that in the mechanical equilibrium a previously neglected hydrodynamic pressure has to be added. Surprisingly the phase coexistence region (binodal) is shifted by the overall mean density. To our knowledge, this is the first example of a phase-separating system where phase coexistence depends on total number of particles. Furthermore, using fully 3-dimensional hydrodynamics simulations, we explore the interplay of sedimentation and activity-induced convection.

Felix Ruehle, Johannes Blaschke, Jan-Timm Kuhr, and Holger Stark. Gravity-induced dynamics of microswimmers in wall proximity. New Journal of Physics, 20, 025003, 2018.

Jan-Timm Kuhr, Johannes Blaschke, Felix Ruehle, and Holger Stark. Collective sedimentation of squirmers under gravity. Soft Matter, 13 7548-7555, 2017.

Johannes Blaschke, Maurice Maurer, Karthik Menon, Andreas Zoettl, and Holger Stark. Phase separation and coexistence of hydrodynamically interacting microswimmers. Soft Matter, 12, 9821-9831, 2016.

Statistical Physics of Brownian Motors far from Equilibrium

Brownian motors are fascinating to statistical physics as they are capable of rectifying fluctuations from a noisy environment. Most studies so far have considered Brownian motors out of equilibrium coupled to an environment which is itself in equilibrium. We explore the impact of the environment deviating from equilibrium for a 1-dimensional Brownian motor for the following cases: 1) an energy (heat) current flows through the bath; 2) the bath is homogeneously externally driven. We find that deviating from a Maxwellian gas reveals a rich range of motor behaviour. We show that recti cation can occur due to a ow of entropy alone, i. e. recti cation occurs even if there is no energy flow to the motor. This constitutes a qualitatively di erent class of Brownian motor, an Entropic motor.

Johannes Blaschke and Juergen Vollmer. Granular Brownian motors: Role of gas anisotropy and inelasticity. Phys. Rev. E , 87, 040201(R), 2013

Nucleation Dynamics of Droplets and Coarsening on Surfaces

The pattern of small droplets formed when liquid vapour condenses on a substrate is also known as a Breath Figure. Breath figures are an essential tool for understanding the mass and heat transport of systems exhibiting condensation. A model introducing a growth process of the droplets (i.e. touching droplets coalesce), as well as two length scales: 1) a smallest droplet size (nucleation); 2) and a largest droplet size (dripping), was analysed numerically. The scaling theory describing the droplet size distribution has been extended to account for these new length scales.

Johannes Blaschke, Tobias Lapp, Bjoern Hof, and Juergen Vollmer. Breath Figures: Nucleation, Growth, Coalescence, and the Size Distribution of Droplets. Phys. Rev. Lett., 109, 068701, 2012.

Publications

Felix Ruehle, Johannes Blaschke, Jan-Timm Kuhr, and Holger Stark. Gravity-induced dynamics of microswimmers in wall proximity. New Journal of Physics, 20, 025003, 2018.

Jan-Timm Kuhr, Johannes Blaschke, Felix Ruehle, and Holger Stark. Collective sedimentation of squirmers under gravity. Soft Matter, 13 7548-7555, 2017.

Johannes Blaschke, Maurice Maurer, Karthik Menon, Andreas Zoettl, and Holger Stark. Phase separation and coexistence of hydrodynamically interacting microswimmers. Soft Matter, 12, 9821-9831, 2016.

Klaus Roeller, Johannes Blaschke, Stephan Herminghaus, and Juergen Vollmer. Arrest of the flow of wet granular matter. Journal of Fluid Mechanics, 738:407–422, December 2013.

Johannes Blaschke and Juergen Vollmer. Granular Brownian motors: Role of gas anisotropy and inelasticity. Phys. Rev. E , 87, 040201(R), 2013

Johannes Blaschke, Tobias Lapp, Bjoern Hof, and Juergen Vollmer. Breath Figures: Nucleation, Growth, Coalescence, and the Size Distribution of Droplets. Phys. Rev. Lett., 109, 068701, 2012.

Paul Martinsen, Johannes Blaschke, Rainer Kuennemeyer, and Robert Jordan. Accelerating Monte Carlo simulations with an NVIDIA® graphics processor. Comput Phys Commun, 180, 1983–1989, 2009.