Jana Lasser

Geophysical Pattern Formation in Salt Playa

For a long time I have been interested in the quantitative research of complex structures emerging from simple building blocks and rules. For my bachelor's and master's thesis I mainly worked with biological transport networks whereas for my PhD thesis I will focus in network-like patterns that emerge on the surfaces of deserts due to dynamical processes in the soil.

NET: past and current projects

During my undergraduate studies I developed a framework called NET (network extraction tool) that is especially tailored for the extraction of graphs from images of networks. The access to the network in graph-representation opens a vast range of possibilities for quantitative analysis. The up-to-date version of NET can be found at https://github.com/JanaLasser/network_extraction.

The development of a data analysis tool has allowed me to collaborate with many experimentalists who kindly supplied me with images to analyze. The projects I am currently involved in using NET are

  • Quantitative analysis and phenotyping of Drosophila tracheoles (Collaboration with Sara Sigurbjornsdottir and the Leptin Lab at EMBL Heidelberg).
  • Topological phenotypes in leaf vascular networks (Collaboration with Eleni Katifori at University of Pennsilvanya).
  • Analysis of morphological cell boundary changes in Drosophila larvae during growth (Collaboration with Fred Wolf at MPIDS Goettingen).
  • Pedestrian flow through the old city of Jerusalem (Collaboration with Marc Timme at MPIDS Goettingen).
  • Tracking of bubbles in microfluidics experiments (Collaboration with Laura Stricker and Marcin Makowski at MPIDS Goettingen).
  • Extending and adapting NET to different datasets and keeping the software up to date.

PhD project: Salt polygons on Salt Playa and crack patterns in permafrost soils

For my PhD thesis I (at least partly) turned my back on software development and started to work experimentally. The goal is to understand the mechanisms that drive pattern formation on the surface of deserts (salt or permafrost). The work involves experiments to understand the onset of pattern formation and scaling of the spatial frequency of the emerging patterns with control parameters.

At first I will concentrate on salt polygons in deserts and maybe extend experiments and numerical simulations to perma-frost soils at a later point.

For the experiments we use Hele-Shaw cells filled with sand and salt water. We investigate the behaviour of the convection and crystallizing salt on the surface at different sand grain sizes and evaporation rates.

On the other hand I also develop a numerical model of the dynamics happening in the ground. We suspect the salt polygons emerge due to convection of salt water under the surface. Therefore the goal is to develop an efficient, heavily parallelized solver for the involved advection-diffusion equations which supports crystallization of salt. As a starting point I use simulations used to describe CO2 sequestration which rely on a stream-function/ vorticity approach and make use of the horizontal periodicity of the problem. I hope to be able to accurately describe the experimental setup with the simulations and reproduce and predict results from the experiment.

For the future, field trips in collaboration with Jo Nield at the university of Southampton to investigate the time development of salt polygons in nature are planned. During these trips we want to create high-resolution laser scans of the desert surface to characterize the three-dimensional patterns.

To connect the theoretical and experimental work with my previous experience in network formation and analysis, I also plan to analyze satellite images of patterns in deserts on earth and mars. I hope to find network characteristics that allow me to classify networks into groups or distinguish between them.

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