Recent Submissions
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.
Microrobot collectives with reconfigurable morphologies, behaviors, and functions
(2022) Gardi, Gaurav; Ceron, Steven; Wang, Wendong; Petersen, Kirstin; Sitti, Metin
Mobile microrobots, which can navigate, sense, and interact with their environment, could potentially revolutionize biomedicine and environmental remediation. Many self-organizing microrobotic collectives have been developed to overcome inherent limits in actuation, sensing, and manipulation of individual microrobots; however, reconfigurable collectives with robust transitions between behaviors are rare. Such systems that perform multiple functions are advantageous to operate in complex environments. Here, we present a versatile microrobotic collective system capable of on-demand reconfiguration to adapt to and utilize their environments to perform various functions at the air-water interface. Our system exhibits diverse modes ranging from isotropic to anisotrpic behaviors and transitions between a globally driven and a novel self-propelling behavior. We show the transition between different modes in experiments and simulations, and demonstrate various functions, using the reconfigurability of our system to navigate, explore, and interact with the environment. Such versatile microrobot collectives with globally driven and self-propelled behaviors have great potential in future medical and environmental applications.
Slack-based tunable damping leads to a trade-off between robustness and efficiency in legged locomotion
(2023) Mo, An; Izzi, Fabio; Gönen, Emre Cemal; Haeufle, Daniel; Badri-Spröwitz, Alexander
Animals run robustly in diverse terrain. This locomotion robustness is puzzling because axon conduction velocity is limited to a few tens of meters per second. If reflex loops deliver sensory information with significant delays, one would expect a destabilizing effect on sensorimotor control. Hence, an alternative explanation describes a hierarchical structure of low-level adaptive mechanics and high-level sensorimotor control to help mitigate the effects of transmission delays. Motivated by the concept of an adaptive mechanism triggering an immediate response, we developed a tunable physical damper system. Our mechanism combines a tendon with adjustable slackness connected to a physical damper. The slack damper allows adjustment of damping force, onset timing, effective stroke, and energy dissipation. We characterize the slack damper mechanism mounted to a legged robot controlled in open-loop mode. The robot hops vertically and planarly over varying terrains and perturbations. During forward hopping, slack-based damping improves faster perturbation recovery (up to 170%) at higher energetic cost (27%). The tunable slack mechanism auto-engages the damper during perturbations, leading to a perturbation-trigger damping, improving robustness at a minimum energetic cost. With the results from the slack damper mechanism, we propose a new functional interpretation of animals’ redundant muscle tendons as tunable dampers.
Fano interference between collective modes in cuprate high-Tc superconductors
(2023) Chu, Hao; Kovalev, Sergey; Wang, Zi Xiao; Schwarz, Lukas; Dong, Tao; Feng, Liwen; Haenel, Rafael; Kim, Min-Jae; Shabestari, Parmida; Hoang, Le Phuong; Honasoge, Kedar; Dawson, Robert David; Putzky, Daniel; Kim, Gideok; Puviani, Matteo; Chen, Min; Awari, Nilesh; Ponomaryov, Alexey N.; Ilyakov, Igor; Bluschke, Martin; Boschini, Fabio; Zonno, Marta; Zhdanovich, Sergey; Na, Mengxing; Christiani, Georg; Logvenov, Gennady; Jones, David J.; Damascelli, Andrea; Minola, Matteo; Keimer, Bernhard; Manske, Dirk; Wang, Nanlin; Deinert, Jan-Christoph; Kaiser, Stefan
Cuprate high-Tc superconductors are known for their intertwined interactions and the coexistence of competing orders. Uncovering experimental signatures of these interactions is often the first step in understanding their complex relations. A typical spectroscopic signature of the interaction between a discrete mode and a continuum of excitations is the Fano resonance/interference, characterized by the asymmetric light-scattering amplitude of the discrete mode as a function of the electromagnetic driving frequency. In this study, we report a new type of Fano resonance manifested by the nonlinear terahertz response of cuprate high-Tc superconductors, where we resolve both the amplitude and phase signatures of the Fano resonance. Our extensive hole-doping and magnetic field dependent investigation suggests that the Fano resonance may arise from an interplay between the superconducting fluctuations and the charge density wave fluctuations, prompting future studies to look more closely into their dynamical interactions.
The Integrated Policy Package Assessment approach : elaborating ex ante knowledge in the field of urban mobility
(2022) Scheer, Dirk; Dreyer, Marion; Schmidt, Maike; Schmieder, Lisa; Arnold, Annika
Background. In response to climate change challenges, a main policy emphasis is on transitioning the energy system from high- to low-carbon energy supply. The German energy transition is first and foremost based on political decisions and interventions. These decisions need to be assessed ex ante to ensure a good governance approach to energy policies, for which this paper introduces the Integrated Policy Package Assessment approach (IPPA). IPPA consists of four steps: design, assessment, evaluation and discourse.
Results. The results section illustrates the IPPA framework by applying it to urban passenger transport as an example case. First, the design phase was used to elaborate two complementary policy packages each consisting of several policy measures in the transformation pathways of “multi- and inter-modality”, and “alternative drive”. Second, the individual measures of the packages were impact-analysed by a large number of individual impact studies from various disciplines. Synthesizing the individual study results, we developed an impact assessment matrix for impact evaluation. The matrix covers the impact categories: technology development, sector integration, environment, social resonance, and institutional factors. In a further step, the key findings of the impact assessment were reflected and reviewed from the perspectives of various stakeholders and practice experts through a practice-science dialogue on transforming the urban passenger transport system.
Conclusions. The discussion and conclusion sections outline the main findings relating to content and process aspects, when applying the IPPA framework to a policy package in urban transport.
From grassroots to centralization : the development of local and regional governance in the german energy transition
(2023) Fuchs, Gerhard; Fettke, Ulrike
In the process of sustainability and especially electricity transition, the local and regional levels gain a new importance. Both social movements as well as governments from different levels (state, federal) are mobilizing and/or addressing local actors. The way this has been done and the capacities for local actors to have a say in the way transition processes do unfold, however, has changed significantly over the last decades in Germany. The paper will use the example of wind energy projects to analyze how multilevel governance arrangements have changed over time. The main thesis will be that the available repertoires of activities for local actors have become increasingly limited due to increasing policy management activities by state and federal governments. Especially the creation of artificial markets and auctioning devices have severely limited the scope of action for local actors. The article will reconstruct the changes in the multi-level governance structure and assess the effects on the development of wind energy by studying in detail two cases.