Johannes L. Hörmann

University of Freiburg

livMatS @ FIT

Georges-Köhler-Allee 105

Room 01.030

D-79110 Freiburg

Germany

Experienced research professional specializing in computational modeling for micro- and nanotribology and materials science. Key achievements include:

Established continuum models of rough interfaces using FEM to study solvent concentration variations on rough surfaces.
Developed atomistic models of surfactant adsorption films using MD for Ph.D. research.
Applied machine learning (GPC, GPR) to predict rough surface performance in an entrepreneurial venture.
Co-coordinated proposal writing for the DFG-funded ‘AWEARNESS’ project, employing DFT to study zinc phosphate glasses typically grown as films in tribo-induced decomposition reactions of ZDDP, a common additive in engine oils.
Designed reproducible workflows with well-established Workflow Management Systems (WMS).
Co-developer and maintainer for the dtool & dserver data management ecosystem, a community effort.

Currently serving as Data Steward at the Cluster of Excellence livMatS.

selected publications

Molecular simulations of sliding on SDS surfactant films

Johannes L. Hörmann, Chenxu (刘宸旭) Liu, Yonggang (孟永钢) Meng, and 1 more author

The Journal of Chemical Physics, Jun 2023

Abs DOI

We use molecular dynamics simulations to study the frictional response of monolayers of the anionic surfactant sodium dodecyl sulfate and hemicylindrical aggregates physisorbed on gold. Our simulations of a sliding spherical asperity reveal the following two friction regimes: at low loads, the films show Amonton’s friction with a friction force that rises linearly with normal load, and at high loads, the friction force is independent of the load as long as no direct solid–solid contact occurs. The transition between these two regimes happens when a single molecular layer is confined in the gap between the sliding bodies. The friction force at high loads on a monolayer rises monotonically with film density and drops slightly with the transition to hemicylindrical aggregates. This monotonous increase of friction force is compatible with a traditional plowing model of sliding friction. At low loads, the friction coefficient reaches a minimum at the intermediate surface concentrations. We attribute this behavior to a competition between adhesive forces, repulsion of the compressed film, and the onset of plowing.
dtool and dserver: A flexible ecosystem for findable data

Johannes L. Hörmann, Luis Yanes, Ashwin Vazhappilly, and 5 more authors

PLOS ONE, Jun 2024

Abs DOI

Making data FAIR—findable, accessible, interoperable, reproducible—has become the recurring theme behind many research data management efforts. dtool is a lightweight data management tool that packages metadata with immutable data to promote accessibility, interoperability, and reproducibility. Each dataset is self-contained and does not require metadata to be stored in a centralised system. This decentralised approach means that finding datasets can be difficult. dtool’s lookup server, short dserver, as defined by a REST API, makes dtool datasets findable, hence rendering the dtool ecosystem fit for a FAIR data management world. Its simplicity, modularity, accessibility and standardisation via API distinguish dtool and dserver from other solutions and enable it to serve as a common denominator for cross-disciplinary research data management. The dtool ecosystem bridges the gap between standardisation-free data management by individuals and FAIR platform solutions with rigid metadata requirements.