Recent Submissions
Exploration-exploitation-based trajectory tracking of mobile robots using Gaussian processes and model predictive control
(2023) Eschmann, Hannes; Ebel, Henrik; Eberhard, Peter
Prozessmodellierung in der additiven Fertigung : Molekulardynamische Simulation als Ansatz zur Optimierung der additiven Qualität
(2023) Müller, Sarah; Klein, Dominic; Öhlschläger, Fabio; Roth, Johannes; Westkämper, Engelbert
Global optimal actuator placement for adaptive structures : new formulation and benchmarking
(2024) Senatore, Gennaro; Virgili, Francesco; Blandini, Lucio
Civil structures are often overdesigned to meet safety and functionality criteria under rare, strong events. Adaptive structures, however, can modify their response through sensing and actuation to satisfy design criteria more efficiently with better material utilization, which results in lower resource consumption and associated environmental impacts. Adaptation is performed through actuators integrated into the structural layout. Several methods exist for optimal actuator placement to control displacements and internal force flow. In discrete systems like trusses and frames, actuator placement is typically a binary assignment. Most existing methods use bilevel and heuristic formulations, leading to suboptimal solutions without proving global optimality. This paper introduces a Mixed Integer Programming (MIP) method that produces global optimum solutions by optimizing both actuator placement and commands. Two objective functions are used: minimizing the number of actuators and minimizing control energy. The optimization considers structural and serviceability limits and control feasibility. An extensive benchmark compares the new formulation’s global optima with solutions from greedy, stochastic, and heuristic methods. Results show that the new method consistently produces higher-quality solutions than all other methods benchmarked in this study.
Editorial - visualizing big culture and history data
(2025) Windhager, Florian; Koch, Steffen; Münster, Sander; Mayr, Eva
Efficacy of personalized feedback in encouraging sustainable washing behavior : evidence from a pilot study in Germany
(2025) Höpfl, Laura; Đula, Ivan; Kiss, Francisco; Walter, Rebecca; Wirzberger, Maria
Introduction: Reducing household energy consumption through behavioral changes is a key strategy in addressing the emissions driving the climate crisis. Behavioral changes in affluent households toward more sustainable practices can have a significant positive impact. Prior research highlighted the role of individual values and motivational factors in shaping sustainable clusters. A more personalized approach toward encouraging the resulting clusters of people to adopt more sustainable strategies seems promising. Such an approach could incorporate aligned feedback, which has been proven to be a powerful mechanism throughout learning processes.
Method: Over 9 weeks, a pilot study with 50 participants investigated the impact of different types of feedback on washing behavior. The within-subjects design included (1) a baseline condition, (2) feedback on energy consumption (kWh), and (3) feedback on monetary costs per cycle (EUR). Data collection encompassed pre- and post-condition surveys, a final comprehensive survey, and a diary-formatted table. The primary objective was to evaluate the potential for individualization. Asynchronous structured interviews were conducted at the end to explore participants' perceptions and washing behaviors.
Results: While we found effects for the feedback manipulation, we found no differences between user clusters in individual washing behaviors. Furthermore, participants qualitatively reported habitual changes, feeling more knowledgeable about the monetary impacts of specific washing programs and temperatures, and wished for a more accessible preset time function. Most participants expressed willingness to switch to a dynamic energy price if it translated to significant cost savings.
Discussion: Our findings may support the notion that individualized behavior change strategies are promising. In general, these strategies should be easily applicable, cost-effective, and promote habits to be exerted regularly. Arising methodological limitations suggest further research in this domain. From an applied perspective, our research provides valuable insights for designing products, services, and regulations by governments and companies, empowering them to develop more effective strategies for reducing energy consumption.
Method: Over 9 weeks, a pilot study with 50 participants investigated the impact of different types of feedback on washing behavior. The within-subjects design included (1) a baseline condition, (2) feedback on energy consumption (kWh), and (3) feedback on monetary costs per cycle (EUR). Data collection encompassed pre- and post-condition surveys, a final comprehensive survey, and a diary-formatted table. The primary objective was to evaluate the potential for individualization. Asynchronous structured interviews were conducted at the end to explore participants' perceptions and washing behaviors.
Results: While we found effects for the feedback manipulation, we found no differences between user clusters in individual washing behaviors. Furthermore, participants qualitatively reported habitual changes, feeling more knowledgeable about the monetary impacts of specific washing programs and temperatures, and wished for a more accessible preset time function. Most participants expressed willingness to switch to a dynamic energy price if it translated to significant cost savings.
Discussion: Our findings may support the notion that individualized behavior change strategies are promising. In general, these strategies should be easily applicable, cost-effective, and promote habits to be exerted regularly. Arising methodological limitations suggest further research in this domain. From an applied perspective, our research provides valuable insights for designing products, services, and regulations by governments and companies, empowering them to develop more effective strategies for reducing energy consumption.
Interrelations of vegetation growth and water scarcity in Iran revealed by satellite time series
(2022) Behling, Robert; Roessner, Sigrid; Foerster, Saskia; Saemian, Peyman; Tourian, Mohammad J.; Portele, Tanja C.; Lorenz, Christof
Iran has experienced a drastic increase in water scarcity in the last decades. The main driver has been the substantial unsustainable water consumption of the agricultural sector. This study quantifies the spatiotemporal dynamics of Iran’s hydrometeorological water availability, land cover, and vegetation growth and evaluates their interrelations with a special focus on agricultural vegetation developments. It analyzes globally available reanalysis climate data and satellite time series data and products, allowing a country-wide investigation of recent 20+ years at detailed spatial and temporal scales. The results reveal a wide-spread agricultural expansion (27,000 km 2) and a significant cultivation intensification (48,000 km 2). At the same time, we observe a substantial decline in total water storage that is not represented by a decrease of meteorological water input, confirming an unsustainable use of groundwater mainly for agricultural irrigation. As consequence of water scarcity, we identify agricultural areas with a loss or reduction of vegetation growth (10,000 km 2), especially in irrigated agricultural areas under (hyper-)arid conditions. In Iran’s natural biomes, the results show declining trends in vegetation growth and land cover degradation from sparse vegetation to barren land in 40,000 km 2, mainly along the western plains and foothills of the Zagros Mountains, and at the same time wide-spread greening trends, particularly in regions of higher altitudes. Overall, the findings provide detailed insights in vegetation-related causes and consequences of Iran’s anthropogenic drought and can support sustainable management plans for Iran or other semi-arid regions worldwide, often facing similar conditions.
Micro- and nanofabrication of dynamic hydrogels with multichannel information
(2023) Zhang, Mingchao; Lee, Yohan; Zheng, Zhiqiang; Khan, Muhammad Turab Ali; Lyu, Xianglong; Byun, Junghwan; Giessen, Harald; Sitti, Metin
Creating micro/nanostructures containing multi-channel information within responsive hydrogels presents exciting opportunities for dynamically changing functionalities. However, fabricating these structures is immensely challenging due to the soft and dynamic nature of hydrogels, often resulting in unintended structural deformations or destruction. Here, we demonstrate that dehydrated hydrogels, treated by a programmable femtosecond laser, can allow for a robust fabrication of micro/nanostructures. The dehydration enhances the rigidity of the hydrogels and temporarily locks the dynamic behaviours, significantly promoting their structural integrity during the fabrication process. By utilizing versatile dosage domains of the femtosecond laser, we create micro-grooves on the hydrogel surface through the use of a high-dosage mode, while also altering the fluorescent intensity within the rest of the non-ablated areas via a low-dosage laser. In this way, we rationally design a pixel unit containing three-channel information: structural color, polarization state, and fluorescent intensity, and encode three complex image information sets into these channels. Distinct images at the same location were simultaneously printed onto the hydrogel, which can be observed individually under different imaging modes without cross-talk. Notably, the recovered dynamic responsiveness of the hydrogel enables a multi-information-encoded surface that can sequentially display different information as the temperature changes.
Millimeter-wave near-field imaging using multi-mode probes
(2025) Hoffmann, Dennis; Hesselbarth, Jan (Prof. Dr. sc. techn.)
A mmWave near-field imaging concept is presented, which, in addition to purely transversal field components, uses a longitudinal field component to illuminate an object. A prototype at 31 GHz demonstrates, how the additional use of higher-order modes improve the quality of images generated in mmWave near-field imaging.
Mobility support in industrial edge computing for latency critical applications
(2024) Govindaraj, Keerthana; Kirstädter, Andreas (Prof. Dr.-Ing.)
During the last decade, Industry 4.0 has gained increasing attention. Mainly two factors drive this enormous growth, firstly the pressing need for novel use cases in manufacturing industries and secondly the rapid progress of aiding technologies in wireless communication.
The most prominent use cases that shape the future of manufacturing involve batch-size-one production, predictive maintenance, and AI-based quality monitoring. The devices and applications that majorly constitute these use cases are Augmented Reality devices (AR), Autonomous Guided Vehicle (AGV), and Collaborative Robots (CR). These applications have stringent requirements in terms of the amount of data that needs to be processed and the duration within which it needs to be processed. The devices running these applications are mobile in nature. Therefore, they have a small form factor and are resource constrained. Thus, these applications can be offloaded to computers with high resource availability.
Cloud Computing (CC) has already paved its way into manufacturing to resolve some of the resource and accessibility issues. However, it is not a viable solution for Industry 4.0 applications due to the latency requirements as well as security concerns. Edge Computing (EC) is a novel paradigm proposed to alleviate the latency-related issues in many commercial use cases. Thus, EC is explored in this work for its viability in Industry 4.0 use cases to identify the challenges and examine their practicality in manufacturing infrastructure.
In EC, the computing entities called Edge Servers (ES) are advised to be placed as close as possible to the source of data generation to reduce the latencies involved in communication. Since the backend network infrastructure in factories has limited capacity, and also over-provisioning it is expensive, the placement of ESs centrally at the factory data center creates an extensive load on the network. Therefore, a distributed EC is necessary ideally at the first hop of the communication channel. The first hop is catered by wireless technologies with high data transmission rates, such as 5G.
However, the devices considered in Industry 4.0 use cases are highly mobile and the corresponding applications offloaded are stateful. Thus, to avoid data traffic over the backend network, the application on the ES needs to be migrated to a suitable ES closer to the mobile client.
The downtime experienced during the migration process influences the quality of experience of the clients. Additionally, depending on the number of mobile devices present in the system, the number of migration triggers increases. Accordingly, a new ES needs to be selected for all the clients that experience response time violation. Moreover, the migration triggers need to be orchestrated to avoid congesting the backend network with the migration data.
The state-of-the-art does not offer a complete mobility support solution for Industry 4.0 scenario. Thus, this work makes two major contributions to provide a practical approach for mobility support in industrial edge computing for latency critical applications. Firstly, it proposes a novel stateful migration scheme that reduces the downtime during the migration by a factor of 4−7 compared to an established state-of-the-art migration scheme. Subsequently, an extension of this migration schemed to further reduce the downtime to "zero". Secondly, it proposes a scheduling scheme to orchestrate multiple simultaneous migration triggers, that in turn reduces the total amount of data migrated by 64.15%. All the statements are backed by thorough evaluations done using an NS3-simulation environment.
Observation of ultrafast interfacial Meitner-Auger energy transfer in a Van der Waals heterostructure
(2023) Dong, Shuo; Beaulieu, Samuel; Selig, Malte; Rosenzweig, Philipp; Christiansen, Dominik; Pincelli, Tommaso; Dendzik, Maciej; Ziegler, Jonas D.; Maklar, Julian; Xian, R. Patrick; Neef, Alexander; Mohammed, Avaise; Schulz, Armin; Stadler, Mona; Jetter, Michael; Michler, Peter; Taniguchi, Takashi; Watanabe, Kenji; Takagi, Hidenori; Starke, Ulrich; Chernikov, Alexey; Wolf, Martin; Nakamura, Hiro; Knorr, Andreas; Rettig, Laurenz; Ernstorfer, Ralph
Atomically thin layered van der Waals heterostructures feature exotic and emergent optoelectronic properties. With growing interest in these novel quantum materials, the microscopic understanding of fundamental interfacial coupling mechanisms is of capital importance. Here, using multidimensional photoemission spectroscopy, we provide a layer- and momentum-resolved view on ultrafast interlayer electron and energy transfer in a monolayer-WSe2/graphene heterostructure. Depending on the nature of the optically prepared state, we find the different dominating transfer mechanisms: while electron injection from graphene to WSe2 is observed after photoexcitation of quasi-free hot carriers in the graphene layer, we establish an interfacial Meitner-Auger energy transfer process following the excitation of excitons in WSe2. By analysing the time-energy-momentum distributions of excited-state carriers with a rate-equation model, we distinguish these two types of interfacial dynamics and identify the ultrafast conversion of excitons in WSe2 to valence band transitions in graphene. Microscopic calculations find interfacial dipole-monopole coupling underlying the Meitner-Auger energy transfer to dominate over conventional Förster- and Dexter-type interactions, in agreement with the experimental observations. The energy transfer mechanism revealed here might enable new hot-carrier-based device concepts with van der Waals heterostructures.