# Universität Stuttgart

Recent publications
Additive manufacturing processes in combination with topology optimization offer great potentials for lightweight design. In this work, the engine mount of a Unmanned Aerial Vehicle (UAV) is topology optimized to minimize weight for a given stiffness. The solutions are carried out taking into account the different material properties of Acrylnitril-Butadien-Styrol-Copolymere (ABS), Polyamide 12 (PA 12), acrylic photopolymer and glass fiber reinforced acrylic photopolymer used for manufacturing. The adapted geometries are then fabricated using Fused Filament Fabrication (FFF), Selective Laser Sintering (SLS) and Stereolithography (SL) to find the most suitable process to produce the weight-optimal solution. In order to validate the simulation results, all parts are tested equally with the same load cases on a customized test rig. The evaluation of the measurements shows that, with one exception, the measured displacements are smaller than the simulation values. By applying a quality criterion, the components made of PA 12 using the FFF process prove to be the weight-to-displacement optimal solution. Compared to the initial design, the topology optimized version saves 40% of mass. In addition, the new design, together with the use of additive manufacturing processes, facilitates the production and assembly of the engine mount.
Targeting costimulatory receptors of the tumor necrosis factor superfamily (TNFSF) to activate T-cells and promote anti-tumor T-cell function have emerged as a promising strategy in cancer immunotherapy. Previous studies have shown that combining two different members of the TNFSF resulted in dual-acting costimulatory molecules with the ability to activate two different receptors either on the same cell or on different cell types. To achieve prolonged plasma half-life and extended drug disposition, we have developed novel dual-acting molecules by fusing single-chain ligands of the TNFSF to heterodimerizing Fc chains (scDuokine-Fc, scDk-Fc). Incorporating costimulatory ligands of the TNF superfamily into a scDk-Fc molecule resulted in enhanced T-cell proliferation translating in an increased anti-tumor activity in combination with a primary T-cell-activating bispecific antibody. Our data show that the scDk-Fc molecules are potent immune-stimulatory molecules that are able to enhance T-cell mediated anti-tumor responses.
Bispecific antibodies have emerged as therapeutic molecules with a multitude of modes of action and applications. Here, we present a novel approach to solve the light-chain problem for the generation of bispecific Ig-like antibodies using the second constant domain of IgE (EHD2) genetically modified to force heterodimerization. This was achieved by introducing a C14S mutation in one domain and a C102S mutation in the other domain, which removed of one of the crossover disulfide bonds. Substituting the CH1 and CL domains of an antigen binding fragment (Fab) with these heterodimerizing EHD2 (hetEHD2) domains resulted in Fab-like building blocks (eFab). These eFabs were used to generate different bispecific antibodies of varying valency and molecular composition employing variable domains with different specificities and from different origins. Formats included bivalent bispecific IgG-like molecules (eIgs) and Fc-less Fab-eFab fusion proteins, as well as tri- and tetravalent Fab-eIg fusion proteins. All proteins, including bispecific antibodies for dual receptor targeting and for retargeting of T cells, efficiently assembled into functional molecules. Furthermore, none of the hetEHD2-comprising molecules showed binding to the two Fcε receptors and are thus most likely do not induce receptor cross-linking and activation. In summary, we established the eIg technology as a versatile and robust platform for the generation of bispecific antibodies of varying valency, geometry, and composition, suitable for numerous applications.Abbreviations: antibody drug conjugate (ADC), acute lymphocytic leukemia (ALL), constant domain of IgE (Cε), receptor of Cε (CεRI or CεRII), cluster of differentiation (CD), constant domain of heavy chain (CH), constant domain of light chain (CL), (single-chain) diabody ((sc)Db), diabody-immunoglobulin (Db-Ig), dynamic light scattering (DLS), Fragment antigen-binding (Fab), Fab with hetEHD2 (eFab), Fab-EHD2 with T121G in chain 1 and S10I in chain 2 (EFab), bispecific Ig domain containing hetEHD2 (eIg), extracellular domain (ECD), epidermal growth factor receptor 1, 2, 3 (EGFR, HER2, HER3), heavy chain domain 2 of IgE (EHD2), EHD2 domain with C102S (EHD2-1), EHD2 domain with C14S and N39Q (EHD2-2), (human or mouse) fragment crystalline ((hu or mo)Fc), heavy chain (HC), heterodimerized second domain of IgE (hetEHD2), high molecular weight (HMW), immunoglobulin (Ig), light chain (LC), liquid chromatography-mass spectrometry (LC-MS), mesenchymal epithelial transition factor (MET), heavy chain domain 2 of IgM (MHD2), peripheral blood mononuclear cell (PBMC), prolactin receptor (PRLP), Stokes radius (RS), single-chain Fragment variable (scFv), tumor necrosis factor (TNF), TNF receptor 2 (TNFR2), single-chain TNF-related apoptosis-inducing ligand (scTRAIL), variable domain of heavy chain (VH), variable domain of light chain (VL).
Coexisting density-wave and superconducting states along with the large anomalous Hall effect in the absence of local magnetism remain intriguing and enigmatic features of the AV 3 Sb 5 kagome metals (A = K, Rb, Cs). Here, we demonstrate via optical spectroscopy and density-functional calculations that low-energy dynamics of KV 3 Sb 5 is characterized by unconventional localized carriers, which are strongly renormalized across the density-wave transition and indicative of electronic correlations. Strong phonon anomalies are prominent not only below the density-wave transition, but also at high temperatures, suggesting an intricate interplay of phonons with the underlying electronic structure. We further propose the star-of-David and tri-hexagon (inverse star-of-David) configurations for the density-wave order in KV 3 Sb 5 . These configurations are strongly reminiscent of p -wave states expected in the Hubbard model on the kagome lattice at the filling level of the van Hove singularity. The proximity to this regime should have intriguing and far-reaching implications for the physics of KV 3 Sb 5 and related materials.
Globally, food crops production has been challenged by the impacts of climate change. Climate change scholars have argued that rural dwellers, particularly smallholder farmers who engage in food crops production, suffer the most due to their low capacity to adapt. A growing body of knowledge also suggests that local practices serve as safeguards, that enable smallholder farmers to lessen their vulnerability in food crops production. However, limited scholarly insight has been advanced about sustainable food production via the use of local practices. Through the mixed research approach, the study contributes to local practices and climate adaptation debates by examining the various local practices of smallholder farmers, the challenges they encounter with the use of such practices and the possibility for sustainable food crops production in the future in Ghana. The findings suggest that smallholders encounter multiple drawbacks in attempt to utilize local practices to adapt food crops production to climate change including the advent of modern farming inputs/practices. Even when multiple local practices (the planting of multiple crops’ varieties, switching between crops and livestock rearing, reducing cultivatable land size) are utilized, only the increment in farm size, the use of income/remittances of rural–urban migrants to support food crops production, and early cultivation offered some possibilities of sustaining improvement in food crops production for the future. Therefore, the study concluded that local practices are not necessarily panaceas for sustaining food crops production under climate change. The study recommended that further studies pay attention to the sustainability of local practices under climate change.
The family of room temperature atomic scale magnetometers is currently limited to nitrogen-vacancy centers in diamond. However, nitrogen-vacancy centers are insensitive to strong off-axis magnetic fields. In this work, we show that the well-known TR12 radiative defect in diamond, exhibits strong optically detected magnetic resonance (ODMR) signal under optical saturation. We also demonstrate that the spin system responsible for the magnetic resonance is an excited triplet state that can be coherently controlled at room temperature on a single defect level. The high optically detected magnetic resonance contrast, which is maintained even for strong off-axis magnetic fields, suggests that TR12 centers can be used for vector magnetometry even at high field.
This paper is build around the stationary anisotropic Stokes and Navier-Stokes systems with an $$L^\infty$$ L ∞ -tensor coefficient satisfying an ellipticity condition in terms of symmetric matrices in $${\mathbb {R}}^{n\times n}$$ R n × n with zero matrix traces. We analyze, in $$L^2$$ L 2 -based Sobolev spaces, the non-homogeneous boundary value problems of Dirichlet-transmission type for the anisotropic Stokes and Navier-Stokes systems in a compressible framework in a bounded Lipschitz domain with a transversal Lipschitz interface in $${\mathbb {R}}^n$$ R n , $$n\ge 2$$ n ≥ 2 ( $$n=2,3$$ n = 2 , 3 for the nonlinear problems). Thus, the interface intersects transversally the boundary of the Lipschitz domain and divides the domain into two Lipschitz sub-domains. First, we use a mixed variational approach to prove the well-posedness of linear problems related to the anisotropic Stokes system. Then we show the existence of a weak solution to the Dirichlet and Dirichlet-transmission problems for the nonlinear anisotropic Navier-Stokes system. This is done by implementing the Leray-Schauder fixed point theorem and using various results and estimates from the linear case, as well as the Leray-Hopf and some other norm inequalities. Explicit conditions for uniqueness of solutions to the nonlinear problems are also provided.
Organic–inorganic hybrid halide perovskites are widely considered to be one the most promising material in photovoltaic technology, the use of this semiconductor as absorbent layer in solar cells has attracted considerable interest due to their excellent properties. It has been reported that the incorporation of potassium ion is a powerful strategy to tune the perovskites properties, notwithstanding there has been some disagreement regarding the role of this monovalent alkali metal within the perovskite structure. Here, we investigated the impact of K⁺ on the film properties and photovoltaic performance in double cation perovskite solar cells Cs0.1FA0.9PbI3. Our results show that K⁺ intervenes in the crystallization process inducing the extraction of non-reactive PbI2 from the bulk, resulting in a notable enhancement in morphology and reduced non-radiative recombination. The solar cells fabricated with 3% of K⁺ content achieve a PCE of 19.3%, showing a significative improvement in Jsc, Voc and stability values compared with control devices.
Any 6-dimensional strict nearly Kähler manifold is Einstein with positive scalar curvature. We compute the coindex of the metric with respect to the Einstein–Hilbert functional on each of the compact homogeneous examples. Moreover, we show that the infinitesimal Einstein deformations on F1,2=SU(3)/T2 are not integrable into a curve of Einstein metrics.
We consider two cantilevered beams undergoing frictional impacts at the free end. The beams are designed to be of similar geometry so that they have distinct but close natural frequencies. Under harmonic base excitation near the primary resonance with the higher-frequency fundamental bending mode, the system shows a strongly modulated non-periodic response. The purpose of this work is to analyze to what extent the non-periodic vibro-impact dynamics can be predicted. To this end, we use a recently developed modeling and simulation approach. The approach relies on component mode synthesis, the massless boundary concept and an appropriate time stepping scheme. Unilateral contact and dry friction are modeled as set-valued laws and imposed locally within the spatially resolved contact area. A linear model updating is carried out based on the natural frequencies and damping ratios identified in the regime without impacts. The nonlinear simulation of the steady-state response to forward and backward stepped sine excitation is compared against measurements. The results are in very good agreement, especially in the light of the uncertainty associated with the observed material loss in the contact region and the nonlinear behavior of the clamping.
We consider the common problem setting of an elastic sphere impacting on a flexible beam. In contrast to previous studies, we analyze the modal energy distribution induced by the impact, having in mind the particular application of impact vibration absorbers. Also, the beam is analyzed in the clamped–clamped configuration, in addition to the free–free configuration usually considered. We demonstrate that the designed test rig permits to obtain well-repeatable measurements. The measurements are confronted with predictions obtained using two different approaches, state-of-the-art Finite Element Analysis and a recently developed computational approach involving a reduced-order model. The innovative aspect of the latter approach is to achieve a massless contact boundary using component mode synthesis, which reduces the mathematical model order and numerical oscillations. We show that the novel computational approach reduces the numerical effort by 3–4 orders of magnitude compared to state-of-the-art Finite Element Analysis, without compromising the excellent agreement with the measurements.
A quota-based approach can help grid operators deal with congestions in distribution grids in a non-discriminatory way for customers. The quota limits the maximum feed-in or consumption of a group of flexibility providing units (FPU) within a grid cluster. The novel iterative quota calculation (IQC) method is introduced in this paper. In this approach, the maximal active power limits of the FPU are constantly adapted, and the feasible operating region (FOR) of the grid is computed. The quota is computed from the resulting FORs after ensuring that the FPU operation cannot cause grid instability. The proposed method is compared to a previously developed static approach in a real LV grid. Results show the benefits of adding reactive power to the quota calculation, especially in distribution grids with inadequate reactive power compensation.
With the publication of the European Green Deal, the European Union has committed to reaching carbon neutrality by 2050. The envisaged reductions of direct greenhouse gases emissions are seen as technically feasible, but if a wrong path is pursued, significant unintended impacts across borders, sectors, societies and ecosystems may follow. Without the insights gained from an impact assessment framework reaching beyond the techno-economic perspective, the pursuit of direct emission reductions may lead to counterproductive outcomes in the long run. We discuss the opportunities and challenges related to the creation and use of an integrated assessment framework built to inform the European Commission on the path to decarbonisation. The framework is peculiar in that it goes beyond existing ones in its scope, depth and cross-scale coverage, by use of numerous specialised models and case studies. We find challenges of consistency that can be overcome by linking modelling tools iteratively in some cases, harmonising modelling assumptions in others, comparing model outputs in others. We find the highest added value of the framework in additional insights it provides on the technical feasibility of decarbonisation pathways, on vulnerability aspects and on unintended environmental and health impacts on national and sub-national scale.
We develop new liquidity measures for bond markets. Existing measures suffer from the combination of two effects. First, transaction costs in OTC markets strongly depend on trade size. Second, many bonds trade only scarcely with strongly differing trading volumes. Therefore, changes in average transaction costs often indicate changing trade sizes rather than changing liquidity. We combine full-sample information for the size-cost relation with individual transaction data to eliminate such measurement problems. We find that size-adapted measures make a difference when analyzing liquidity dynamics in the U.S. corporate bond market, liquidity differences between bonds, and the asset pricing implications of liquidity.
Europe and North America have numerous studies on 100% renewable power systems. South America, however, lacks research on zero-carbon energy systems, especially understanding South America as an interconnected region, despite its great renewable energy sources, increasing population, and economic productivity. This work extends the cost-optimization energy planning model LEELO and applies it to South America. This results in the to-date most complete model for planning South America’s power sector, with a high temporal (8760 time steps per year) and spatial (over 40 nodes) resolution, and 30 technologies involved. Besides the base case, we study how varying spatial resolution for South America impacted investment results (43, 30, 16, 1 node). Finally, we also evaluate green hydrogen export scenarios, from 0% to 20% on top of the electricity demand. Our study reveals that South America’s energy transition will rely, in decreasing order, on solar photovoltaic, wind, gas as bridging technology, and also on some concentrated solar power. Storage technologies equal to about 10% of the total installed power capacity would be required, aided by the existing hydropower fleet. Not only is the transition to renewables technically possible, but it is also the most cost-efficient solution: electricity costs are expected to reach 32 €/MWh from the year 2035 onwards without the need for further fossil fuels. Varying the spatial resolution, the most-resolved model (43 nodes) reveals 11% and 6% more costs than the one-node and one-node-per-country (16) models, respectively, with large differences in investment recommendations, especially in concentrated solar and wind power. The difference between 43 and 30 nodes is negligible in terms of total costs, energy storage, and technology mix, indicating that 30 nodes are an adequate resolution for this region. We then use the 30-node model to analyze hydrogen export scenarios. The electricity costs drop, as hydrogen is not only a load but also a flexibility provider. Most green hydrogen is produced in Chile, Argentina, and northeast Brazil. For future work, we propose to do an integrated energy plan, including transport and heat, for the region, as well as modeling local hydrogen demands. This work aims to inform policymakers of sustainable transitions, and the energy community.
Deep penetration laser beam welding is simulated using the mesh-free Lagrangian Smoothed Particle Hydrodynamics (SPH) method. The physical phenomena modeled are the elastic material behavior of the solid phase, the fluid dynamics of the liquid phase including temperature-dependent surface tension, heat transfer by heat conduction, and the phase transitions melting, solidification, and evaporation. The energy input of the laser beam is determined by a ray-tracing scheme that calculates the absorbed irradiance distribution in the capillary. Based on the locally absorbed irradiance, an improved recoil pressure model is introduced and compared with a temperature-dependent model frequently used in the literature. To transfer the momentum of the recoil pressure to the surrounding melt, two boundary conditions based on either dynamically detected boundary particles or surface forces are presented and validated using simple examples. The results show that the recoil pressure is a key factor for the formation of a deep capillary and the acceleration of the melt around the capillary. Comparison of capillary geometry and melt pool size from simulation and experiment shows good agreement for the irradiance-dependent recoil pressure model.
Digital Twins are currently investigated as the technological backbone for providing an enhanced understanding and management of existing systems as well as for designing new systems in various domains, e.g., ranging from single manufacturing components such as sensors to large-scale systems such as smart cities. Given the diverse application domains of Digital Twins, it is not surprising that the characterization of the term Digital Twin, as well as the needs for developing and operating Digital Twins are multi-faceted. Providing a better understanding what the commonalities and differences of Digital Twins in different contexts are, may allow to build reusable support for developing, running, and managing Digital Twins by providing dedicated concepts, techniques, and tool support. In this paper, we aim to uncover the nature of Digital Twins based on a systematic mapping study which is not limited to a particular application domain or technological space. We systematically retrieved a set of 1471 unique publications of which 356 were selected for further investigation. In particular, we analyzed the types of research and contributions made for Digital Twins, the expected properties Digital Twins have to fulfill, how Digital Twins are realized and operated, as well as how Digital Twins are finally evaluated. Based on this analysis, we also contribute a novel feature model for Digital Twins from a software engineering perspective as well as several observations to further guide future software engineering research in this area.
The current state of the art approach in the simulation of particle-laden flow in turbomachinery is to handle particle–wall interactions via rebound and erosion models. Rebound models often require a priori parameter tuning to match experimental measurements. Moreover, the actual stochastic nature of the rebound is neglected, and the particle is assumed not to fracture upon impact. However, this affects the resulting particle trajectories and is particularly critical at high (normal) impact velocities, where particles in typical aero engine flow exhibit a high probability of fracture, as illustrated in our previous work. In this work, we propose a method to develop a generalized rebound model which is parameter-free for the user and considers the stochasticity of the rebound. To this end, state of the art methods from function approximation, more precisely, deep dense neural networks are employed. The networks are trained through a supervised learning approach, where the neural network maps the impacting particles’ characteristics to its new particle trajectory after rebound. For this, we present an efficient method to predict probability distributions in a supervised learning context without a priori parameter tuning of known PDFs. In a second step, we extend the network to account for particle fracture, where the particle breakage is based on a fracture probability distribution to determine whether a particle breaks. The performance of the proposed framework is illustrated by the use of experimental measurements of the statistical rebound of sand particles in an erosion test rig specifically designed to match flow and impact conditions (including particle fracture) as well as particle sizes in aero engine compressors.
Many physical processes in the field of rock physics are influenced by the presence of fractures and microcracks. Therefore, intact rock samples are often used for reproducible experimental studies, and cracks are artificially created by various methods. For this, one possibility is the use of thermal treatments. In this work, twelve different thermal treatments are experimentally studied for dry Bianco Carrara marble under ambient conditions. The focus is primarily on the influence of the cooling rate (slow versus fast cooling) in combination with different applied maximum temperatures. This also raises the question of the influence of the specimen size, which has never been systematically investigated in this context before. Therefore, three sizes of cylindrical core samples are investigated to identify a potential specimen size effect. As effective quantities on the core-scale, the bulk volume, the bulk density, and the P- and S-wave velocities, including shear wave splitting, are examined. To obtain a three-dimensional insight into the mechanisms occurring on the micro-scale level, micro X-ray Computed Tomography (μXRCT) imaging is employed. For both cooling conditions, with increasing maximum temperature, the bulk volume increases, the propagation velocities significantly drop, and shear wave splitting increases. This behavior is amplified for fast cooling. The bulk volume increase is related to the initiated crack volume as μXRCT shows. Based on comprehensive measurements, a logarithmic relationship between the relative bulk volume change and the relative change of the ultrasound velocities can be observed. Although there is a size effect for fast cooling, the relationship found is independent of the specimen size. Also the cooling protocol has almost no influence. A model is derived which predicts the relative change of the ultrasound velocities depending on the initiated relative bulk volume change.
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