Universität Stuttgart
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Item Open Access Anti-adhesive surfaces inspired by bee mandible surfaces(2023) Saccardi, Leonie; Schiebl, Jonas; Balluff, Franz; Christ, Ulrich; Gorb, Stanislav N.; Kovalev, Alexander; Schwarz, OliverPropolis, a naturally sticky substance used by bees to secure their hives and protect the colony from pathogens, presents a fascinating challenge. Despite its adhesive nature, honeybees adeptly handle propolis with their mandibles. Previous research has shown a combination of an anti-adhesive fluid layer and scale-like microstructures on the inner surface of bee mandibles. Our aim was to deepen our understanding of how surface energy and microstructure influence the reduction in adhesion for challenging substances like propolis. To achieve this, we devised surfaces inspired by the intricate microstructure of bee mandibles, employing diverse techniques including roughening steel surfaces, creating lacquer structures using Bénard cells, and moulding resin surfaces with hexagonal patterns. These approaches generated patterns that mimicked the bee mandible structure to varying degrees. Subsequently, we assessed the adhesion of propolis on these bioinspired structured substrates. Our findings revealed that on rough steel and resin surfaces structured with hexagonal dimples, propolis adhesion was significantly reduced by over 40% compared to unstructured control surfaces. However, in the case of the lacquer surface patterned with Bénard cells, we did not observe a significant reduction in adhesion.Item Open Access Data-informed reconstruction of a bipennate muscle’s aponeurosis and its fibre distribution for performing continuum-mechanical simulations(2025) Ranjan, Animesh; Avci, Okan; Röhrle, OliverAlternatives to Diffusion-Tensor-Imaging tractography methods for determining fibre orientation fields in skeletal muscle include Laplacian flow simulations. Such methods require flux boundary conditions (BCs) at the tendons and/or along the inner aponeuroses, which can significantly influence the gradients of the resulting Laplacian flow. Herein, we propose a novel method based on solving the 3D steady-state thermal heat equations to determine the fibre architecture in a bi-pennate muscle, specifically the m. rectus femoris . Additionally, we propose a semi-automated algorithm that provides the geometrical representation of the anterior aponeurosis, which, along with the thermal-based fibre field, is particularly well suited for Finite Element (FE) simulations. The semi-automated reconstruction of the aponeurosis shows a good correlation with manual segmentation, yielding a dice coefficient (DSC) of 0.83. The metamodel-based approach resulted in fluxes with a mean angular deviation of 14.25∘±10.36∘and a fibre inclination from the muscle’s longitudinal axis of 0.44∘±4.48∘. Comparing the mechanical output of the same m. rectus femoris muscle geometry informed by the two respective fibre architectures showed that the most significant contributing factor was the relative fibre inclination. Compared to the standard deviation in the undeformed configuration ( 0.44∘±4.48∘), the standard deviation of relative fibre inclination during passive stretching at low applied loads, for instance, at 30%of the maximum applied load, showed a significant decrease ( 0.49∘±2.24∘). Similarly, at maximum isometric contraction, the relative fibre inclinations at 10%initial fibre pre-stretch are 0.19∘±1.23∘, indicating a drop in standard deviation from the undeformed configuration ( 0.44∘±4.48∘). The current study demonstrates that despite the initial deviations in fibre orientations and relative fibre inclinations, thermal flux-based fibre orientations not only exhibit comparable results to DTI-based fibre tractography for the macroscopic analysis of the m. rectus femoris but also result in homogeneous stretch fields and improved numerical convergence. The proposed methods may be applied to determine inner aponeuroses of other bi- or multi-pennate muscles, enabling efficient in-silico computations of the musculoskeletal system.Item Open Access Analytic free-energy expression for the 2D-Ising model and perspectives for battery modeling(2023) Markthaler, Daniel; Birke, Kai PeterAlthough originally developed to describe the magnetic behavior of matter, the Ising model represents one of the most widely used physical models, with applications in almost all scientific areas. Even after 100 years, the model still poses challenges and is the subject of active research. In this work, we address the question of whether it is possible to describe the free energy A of a finite-size 2D-Ising model of arbitrary size, based on a couple of analytically solvable 1D-Ising chains. The presented novel approach is based on rigorous statistical-thermodynamic principles and involves modeling the free energy contribution of an added inter-chain bond DAbond(b, N) as function of inverse temperature b and lattice size N. The identified simple analytic expression for DAbond is fitted to exact results of a series of finite-size quadratic N N-systems and enables straightforward and instantaneous calculation of thermodynamic quantities of interest, such as free energy and heat capacity for systems of an arbitrary size. This approach is not only interesting from a fundamental perspective with respect to the possible transfer to a 3D-Ising model, but also from an application-driven viewpoint in the context of (Li-ion) batteries where it could be applied to describe intercalation mechanisms.Item Open Access Influence of exoskeleton use on Cardiac Index(2022) Schalk, Marco; Schalk, Ines; Bauernhansl, Thomas; Siegert, Jörg; Schneider, UrsThis study aims to assess the whole-body physiological effects of wearing an exoskeleton during a one-hour standardized work task, utilizing the Cardiac Index (CI) as the target parameter. N = 42 young and healthy subjects with welding experience took part in the study. The standardized and abstracted one-hour workflow consists of simulated welding and grinding in constrained body positions and was completed twice by each subject, with and without an exoskeleton, in a randomized order. The CI was measured by Impedance Cardiography (ICG), an approved medical method. The difference between the averaged baseline measurement and the averaged last 10 min was computed for the conditions with and without an exoskeleton for each subject to result in ∆CIwithout exo and ∆CIwith exo. A significant difference between the conditions with and without an exoskeleton was found, with the reduction in CI when wearing an exoskeleton amounting to 10.51%. This result corresponds to that of previous studies that analyzed whole-body physiological load by means of spiroergometry. These results suggest a strong positive influence of exoskeletons on CI and, therefore, physiological load. At the same time, they also support the hypothesis that ICG is a suitable measurement instrument to assess these effects.Item Open Access Perspectives of biogas plants as BECCS facilities : a comparative analysis of biomethane vs. biohydrogen production with carbon capture and storage or use (CCS/CCU)(2023) Full, Johannes; Hohmann, Silja; Ziehn, Sonja; Gamero, Edgar; Schließ, Tobias; Schmid, Hans-Peter; Miehe, Robert; Sauer, AlexanderThe transition to a carbon-neutral economy requires innovative solutions that reduce greenhouse gas emissions (GHG) and promote sustainable energy production. Additionally, carbon dioxide removal technologies are urgently needed. The production of biomethane or biohydrogen with carbon dioxide capture and storage are two promising BECCS approaches to achieve these goals. In this study, we compare the advantages and disadvantages of these two approaches regarding their technical, economic, and environmental performance. Our analysis shows that while both approaches have the potential to reduce GHG emissions and increase energy security, the hydrogen-production approach has several advantages, including up to five times higher carbon dioxide removal potential. However, the hydrogen bioenergy with carbon capture and storage (HyBECCS) approach also faces some challenges, such as higher capital costs, the need for additional infrastructure, and lower energy efficiency. Our results give valuable insights into the trade-offs between these two approaches. They can inform decision-makers regarding the most suitable method for reducing GHG emissions and provide renewable energy in different settings.Item Open Access A performance and cost overview of selected solid-state electrolytes : race between polymer electrolytes and inorganic sulfide electrolytes(2021) Karabelli, Duygu; Birke, Kai Peter; Weeber, MaxElectrolytes are key components in electrochemical storage systems, which provide an ion-transport mechanism between the cathode and anode of a cell. As battery technologies are in continuous development, there has been growing demand for more efficient, reliable and environmentally friendly materials. Solid-state lithium ion batteries (SSLIBs) are considered as next-generation energy storage systems and solid electrolytes (SEs) are the key components for these systems. Compared to liquid electrolytes, SEs are thermally stable (safer), less toxic and provide a more compact (lighter) battery design. However, the main issue is the ionic conductivity, especially at low temperatures. So far, there are two popular types of SEs: (1) inorganic solid electrolytes (InSEs) and (2) polymer electrolytes (PEs). Among InSEs, sulfide-based SEs are providing very high ionic conductivities (up to 10−2 S/cm) and they can easily compete with liquid electrolytes (LEs). On the other hand, they are much more expensive than LEs. PEs can be produced at less cost than InSEs but their conductivities are still not sufficient for higher performances. This paper reviews the most efficient SEs and compares them in terms of their performances and costs. The challenges associated with the current state-of-the-art electrolytes and their cost-reduction potentials are described.Item Open Access Exploring different extrapolation approaches for the critical temperature of the 2D-Ising model based on exactly solvable finite-sized lattices(2025) Markthaler, Daniel; Birke, Kai PeterThe fact that the Ising model in higher dimensions than 1D features a phase transition at the critical temperature Tcdespite its apparent simplicity is one of the main reasons why it has lost none of its fascination and remains a central benchmark in modeling physical systems. Building on our previous work, where an approximative analytic free-energy expression for finite 2D-Ising lattices was introduced, we investigate different extrapolation strategies for estimating Tcof the infinite system from exactly solvable small lattices. Finite square lattices of linear dimension N with free and periodic boundary conditions were analyzed, exploiting their exactly accessible density of states to compute the heat capacity profiles C(T). Different approaches were compared, including scaling models for the peak temperature Tmax(N)and an envelope construction across the set of C(T)-profiles. We find that both approaches converge to the same asymptotic value and compare favorably to the established Binder cumulant method. Remarkably, a model for Tmaxwith a single model parameter following an N/(N+1)-law provides robust convergence, with a physical analogy motivating this proportionality. Our findings highlight that surprisingly few, but highly accurate, finite-size results are sufficient to obtain a precise extrapolation.Item Open Access Effects of blood flow restriction on motoneurons synchronization(2025) Taleshi, Mansour; Bubeck, Franziska; Gizzi, Leonardo; Vujaklija, IvanBlood flow restriction (BFR) is a peripheral intervention that induces transient and reversible physiological perturbations. While this intervention offers a unique model to explore neuromuscular responses in multiple contexts, its impact on neural input to motoneurons remains unclear. Here, the influence of BFR on muscle force control, behavior, and neural input to motoneurons during isometric-trapezoidal and isometric-sinusoidal little finger abduction precision tasks has been studied. Sixteen healthy participants performed the tasks under pre-BFR, during BFR, and at two post-BFR conditions. High-density surface electromyography (EMG) was recorded from the abductor digiti minimi muscle, and motor unit spike trains (MUST) were decomposed using blind source separation technique. Coherence between cumulative spike trains (CSTs) of identified motor units was calculated to assess common synaptic input in the delta and alpha frequency bands. As expected, during BFR application, participants reported higher level of discomfort and significant deterioration in force-tracking performance, as measured using root mean square error (RMSE). Following the BFR release, the level of discomfort, along with impaired neuromuscular performance were reduced to pre-BFR condition. Coherence analysis revealed a prominent peak in the alpha band. The mean z-score coherence in the alpha band showed a reduction of 27% for isometric-trapezoidal and 31% for isometric-sinusoidal conditions from pre-BFR to BFR, followed by a rebound post-BFR intervention with increases of 13% and 20%, respectively. In the delta band, coherence values were consistently higher during sinusoidal tasks compared to trapezoidal ones. These findings indicate that brief BFR application led to decrease in motoneuron synchronization and force control precision likely due to desensitization as shown by changes in coherence alpha band.Item Open Access CHEMampere : technologies for sustainable chemical production with renewable electricity and CO2, N2, O2, and H2O(2022) Klemm, Elias; Lobo, Carlos M. S.; Löwe, Armin; Schallhart, Verena; Renninger, Stephan; Waltersmann, Lara; Costa, Rémi; Schulz, Andreas; Dietrich, Ralph‐Uwe; Möltner, Lukas; Meynen, Vera; Sauer, Alexander; Friedrich, K. AndreasThe chemical industry must become carbon neutral by 2050, meaning that process‐, energy‐, and product‐related CO2 emissions from fossil sources are completely suppressed. This goal can only be reached by using renewable energy, secondary raw materials, or CO2 as a carbon source. The latter can be done indirectly through the bioeconomy or directly by utilizing CO2 from air or biogenic sources (integrated biorefinery). Until 2030, CO2 waste from fossil‐based processes can be utilized to curb fossil CO2 emissions and reach the turning point of global fossil CO2 emissions. A technology mix consisting of recycling technologies, white biotechnology, and carbon capture and utilization (CCU) technologies is needed to achieve the goal of carbon neutrality. In this context, CHEMampere contributes to the goal of carbon neutrality with electricity‐based CCU technologies producing green chemicals from CO2, N2, O2, and H2O in a decentralized manner. This is an alternative to the e‐Refinery concept, which needs huge capacities of water electrolysis for a centralized CO2 conversion with green hydrogen, whose demand is expected to rise dramatically due to the decarbonization of the energy sector, which would cause a conflict of use between chemistry and energy. Here, CHEMampere's core reactor technologies, that is, electrolyzers, plasma reactors, and ohmic resistance heating of catalysts, are described, and their technical maturity is evaluated for the CHEMampere platform chemicals NH3, NOx, O3, H2O2, H2, CO, and CxHyOz products such as formic acid or methanol. Downstream processing of these chemicals is also addressed by CHEMampere, but it is not discussed here.Item Open Access Mechatronic control system for a compliant and precise pneumatic rotary drive unit(2019) Stoll, Johannes T.; Schanz, Kevin; Pott, Andreas