@inproceedings{64798, abstract = {{Lead-containing piezoelectric ceramics are still the base for today’s ultrasonic transducers used in broad applications. This is partly due to missing powerful lead-free piezoelectric ceramic parts in the commercial market. There has been much research on lead-free materials but developing them into marketable parts seems to be an ongoing process. The actual exemption of ROHS has expired, but as the new exemption has already been requested, ceramic suppliers keep on selling lead containing products. Nevertheless, these should be replaced by lead-free alternatives for environmental and health issues. This contribution focuses on exploring the technological readiness level of lead-free hard piezoceramics for prestressed ultrasonic transducers. A small series of bolted Langevin transducers was set up with standard PZT material and three commercial lead-free variants. Results of the building process from individual ring ceramic characteristics to transducer load tests are presented. The main finding of this study is that the lead-free materials technically can compete with the standard PZT for medium-power applications. Some adaptations in the ultrasonic system must be done: the geometry must be altered to fit resonance frequency, and higher voltages or thinner ceramics are needed to achieve the same vibration level at low load. For reaching same power, the volume of lead-free ceramics must be 1.5 to 3 times larger. As already promoted in literature, mechanical losses at high vibration levels are smaller for the lead-free materials. This might help to argument lead-free piezoelectric materials in some applications. References 1. Directive 2011/65/EU of the European Parliament and of the Council of 8 June 2011 on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment. EUR-Lex Document 02011L0065-20240801. Available online: http://data.europa.eu/eli/dir/2011/65/2024-08-01 (accessed on 24 January 2025). 2. Langevin, P. (1918) Method and Apparatus for Transmitting and Receiving Submarine Elastic Waves Using the Piezoelectric Properties of Quartz. French Patent Office; Patent No. FR505703. 3. Hemsel, T.; Twiefel, J. (2023) Piezoelectric Ultrasonic Power Transducers. In Encyclopedia of Materials: Electronics; Academic Press: Oxford, UK; pp. 276–285. https://doi.org/10.1016/b978-0-12-819728-8.00047-4. 4. ATHENA Technologie Beratung GmbH (2025) Description of Ultrasound Generator. Available online: http://shop.myathena.de/epages/12074748.sf/de_DE/?ObjectPath=/Shops/12074748/Products/AM200 (accessed on 13 January 2025). 5. Littmann, W.; Hemsel, T.; Kauczor, C.; Wallaschek, J.; Sinha, W. (2003) Load-adaptive phase-controller for resonant driven piezoelectric devices. Proc. World Congr. Ultrason. 2003, 48, 547–550. 6. Scheidemann, C., Bornmann, P., Littmann, W., & Hemsel, T. (2025). Lead-Free Ceramics in Prestressed Ultrasonic Transducers. Actuators, 14(2), 55. https://doi.org/10.3390/act14020055 }}, author = {{Scheidemann, Claus and Bornmann, Peter and Littmann, Walter and Hemsel, Tobias}}, keywords = {{lead free piezoelectric ceramics, bolted Langevin transducer, medium power ultrasound.}}, location = {{Vilnius, Lithuania}}, title = {{{Bolted Langevin transducers with leadfree piezoelectric ceramics}}}, year = {{2025}}, } @inproceedings{64800, abstract = {{Intensive ultrasonic cleaning of surfaces by means of a lead-free ultrasonic transducer with focusing sonotrode Ultrasonic cleaning baths are probably a coincidental development: After underwater sonars had already been successfully used to detect submarines before 1920, it was probably observed in this environment that the ultrasonic oscillators not only showed a self-cleaning effect but also cavitation damage. At the beginning of the 1950s, the first ultrasonic cleaning devices finally came onto the market. Today, the range of applications ranges from household appliances for jewellery and eyewear cleaning to classic cleaning baths for metal parts and systems for cleaning highly sensitive electronic components. There is a certain gap in handheld, mobile cleaning equipment. Although devices for spot cleaning of textiles are known, the cleaning effect is usually low. Due to the directive 2011/65/EU on the restriction of the use of hazardous substances in electrical and electronic equipment (RoHS) [1] lead should no longer be used in technical devices. As today’s standard ceramics for medium and high-power ultrasonic transducers typically contain lead, there is a need to explore the use of lead-free ceramics in this field. Honda [2] already offers a cleaning transducer based on lead-free piezoelectric ceramics, but it is designed to be used in cleaning baths. This article presents the model-based development of a highly innovative ultrasonic cleaner. On the one hand, lead-free piezoelectric ceramics are used, and on the other hand, a special sonotrode has been developed that concentrates the sound in such a way that a strong cavitation and thus cleaning effect is achieved with comparatively low power in a short time. Coupled field finite element method was used to find an appropriate geometry for the focussing sonotrode. The comparison of simulation and measurement results shows that the lead-free piezoceramics used do their job well and can keep up with standard ceramics, but more ceramic volume is needed to achieve same power. An advanced control concept was elaborated to ensure continuous hard cavitation at varying distances between the sonotrode and the part to be cleaned. Cleaning results for different surfaces and contaminations are presented. The concept of the focusing sonotrode shows that a convincing cleaning result can be achieved even with low power and in short time, provided that the oscillation system and control electronics are suitably coordinated. References [1] http://data.europa.eu/eli/dir/2011/65/2024-08-01 [2] https://en.honda-el.co.jp/product/ceramics/lineup/lead_off/lead-off }}, author = {{Hemsel, Tobias and Scheidemann, Claus and Bornmann, Peter and Littmann, Walter and Sextro, Walter}}, location = {{Paderborn, Germany}}, title = {{{Intensive ultrasonic cleaning of surfaces by means of lead-free ultrasonic transducer with focussing sonotrode}}}, year = {{2025}}, } @inproceedings{61755, author = {{Scheidemann, Claus and Hemsel, Tobias and Sextro, Walter}}, location = {{Vilnius, Lithuania}}, title = {{{Time dependent material characteristics of prestressed piezoelectric ceramics in langevin transducers}}}, year = {{2025}}, } @inproceedings{61757, author = {{Scheidemann, Claus and Porzenheim, Julius and Hemsel, Tobias and Sextro, Walter}}, location = {{Paderborn, Germany}}, title = {{{Investigation of the Setting Behaviour of Mechanically Biased Piezoelectric Ultrasonic Transducers}}}, year = {{2025}}, } @inbook{62988, author = {{Amakor, Augustina C. and Berkemeier, Manuel B. and Wohlleben, Meike Claudia and Sextro, Walter and Peitz, Sebastian}}, booktitle = {{Lecture Notes in Computer Science}}, isbn = {{9783032045546}}, issn = {{0302-9743}}, publisher = {{Springer Nature Switzerland}}, title = {{{Surrogate-Assisted Multi-objective Design of Complex Multibody Systems}}}, doi = {{10.1007/978-3-032-04555-3_21}}, year = {{2025}}, } @inproceedings{64812, author = {{Hofmann, Julia and Teutenberg, Dominik and Meschut, Gerson}}, booktitle = {{25. Kolloquium: Gemeinsame Forschung in der Klebtechnik}}, location = {{Köln}}, title = {{{Methodenentwicklung zur numerischen Auslegung von Klebverbindungen mit lackierten Fügeteilen}}}, year = {{2025}}, } @inproceedings{64611, abstract = {{Für die Aufrechterhaltung der natürlichen Ressourcen ist eine effiziente Nutzung dieser essenziell. Vor diesem Hintergrund untersucht das vorliegende Paper die Rolle der Kreislaufwirtschaft als wegweisendes Wirtschaftsmodell, das von der Europäischen Union gefördert wird. Ziel der Kreislaufwirtschaft ist es, den Ressourcenverbrauch und die Abfallproduktion zu minimieren, indem ein kontinuierlicher Kreislauf aus Nutzung, Wiederverwendung und Recycling von Materialien geschaffen wird. Ein zentraler Aspekt dabei ist der Produktentwicklungsprozess (PEP) - ein vielschichtiger Prozess mit zahlreichen Einflussfaktoren und theoretisch unbegrenzten Gestaltungsmöglichkeiten. Diese Vielfalt führt jedoch zu erheblichen Entscheidungsunsicherheiten, die die Umsetzung von Kreislaufwirtschaftsprinzipien erschweren können. Um diese Herausforderungen zu adressieren, wird ein methodischer Prozess vorgestellt, der eine systematische Klassifizierung im Zusammenhang mit umliegenden Bauteilen ermöglicht. Die Methodik basiert auf einer strukturierten Bewertung von Bauteilen hinsichtlich ihrer Relevanz für die Kreislaufwirtschaft. Dabei werden zentrale Aspekte wie Wiederverwendbarkeit, Recyclingfähigkeit und Ressourceneffizienz berücksichtigt, darunter: • Handelt es sich um ein Gebrauchs- oder Verbrauchsprodukt? • Ist das Bauteil eine Wiederverwendung oder eine Neufertigung? • Ist das Bauteil standardisiert, zugekauft oder individuell ausgerichtet? • Welche primäre Funktion nimmt das Bauteil ein? Diese strukturierte Klassifizierung unterstützt die Entscheidungsfindung bereits früh im PEP. Sie ermöglicht es Produktentwickelnden, Potenziale für die Kreislaufwirtschaft frühzeitig zu erkennen und gezielt nachhaltige Maßnahmen zu ergreifen. Die entwickelte Methodik bildet somit eine Grundlage für die Integration kreislaufwirtschaftlicher Prinzipien in den Entwicklungsprozess. Insbesondere im Kontext moderner Anforderungen des Mobility Management zeigt sich ihr Potenzial, nachhaltige Innovationen gezielt zu fördern und die Umsetzung der Kreislaufwirtschaft in der industriellen Praxis zu erleichtern.}}, author = {{Rohde, Katharina and Ott, Manuel and Budde, Finn Lukas and Mozgova, Iryna}}, booktitle = {{Solving Conflicts on the Way to Sustainable Mobility: Technische und betriebswirtschaftliche Aspekte}}, editor = {{Proff, Heike}}, location = {{Duisburg}}, publisher = {{Springer Nature Meteor}}, title = {{{Optimierung modularer Produkte für die Mobilität: Ein Klassifizierungsrahmen für zirkuläre Produkte}}}, year = {{2025}}, } @inproceedings{64804, abstract = {{Das Ultraschallschweißen ist in der Verpackungs-, Halbleiter- und Automobilindustrie weit verbreitet. Neben dem Schweißen von Blechen bietet es die Möglichkeit, Folien oder Hülsen zu verschweißen. Konventionelle Schweißsysteme arbeiten mit Längs- oder Biegeschwingungen, deren Hauptanteil in der Schweißebene liegt. Der orthogonale Anteil verursacht zusätzliche Belastungen im Schweißgut. Bei der Verwendung von Torsionsschwingungen wird die orthogonale Komponente der Schwingung nahezu eliminiert. In diesem Beitrag wird ein System vorgestellt, bei dem die Torsionsschwingung durch tangentiale Polarisation der Piezokeramiken erzeugt wird. Der Transducer ist axial oberhalb des Schweißpunktes platziert, sodass die Normalkraft momentfrei aufgebracht wird. Das Schweißwerkzeug weicht beim Schweißvorgang daher seitlich nicht aus. Zudem wird das Schweißen an schwer zugänglichen Positionen vereinfacht, da der Systemaufbau deutlich schlanker ist als konventionelle Ultraschallschweißsysteme. Die Auslegung des Torsionsschwingsystems stellt eine Herausforderung dar. Insbesondere muss die Lagerung des Schwingers betrachtet werden, da diese die Normalkraft übertragen und zugleich die Schwingung nicht beeinträchtigen soll. Der Schweißprozess bewirkt eine Verschiebung von Schwingungsknoten und Resonanzfrequenzen. Im Rahmen des Vortrags wird ein Finite-Elemente-Simulationsmodell vorgestellt, das in Kombination mit einem Lastmodell das Systemverhalten während des Schweißprozesses abbildet. Die Geometrie des Transducers wurde schrittweise so angepasst, dass die Schwingamplitude im Lagerungspunkt minimiert wird. }}, author = {{Dohmen, Markus Daniel and Bornmann, Peter and Littmann, Walter and Hemsel, Tobias and Sextro, Walter}}, title = {{{Modellgestützte Optimierung eines Ultraschall-Torsionsschweißsystems}}}, year = {{2025}}, } @article{64824, abstract = {{(1) Background: As digitalisation transforms society, digital competences are increasingly essential. Yet students’ digital competences often vary significantly, largely influenced by socio-economic background. Some schools—termed “resilient schools”—effectively counter these disadvantages and foster high digital competence. This study investigates the prevalence of such schools and examines how they differ from others. (2) Methods: Drawing on representative ICILS 2023 data, quantitative secondary analyses—including descriptive statistics, t-tests, and multiple regression—were conducted. Following the identification of resilient schools, in-depth analyses focus on those countries with substantial proportions of resilient schools above 10 percent (Austria, Italy, and Portugal), as these countries seem to have effective strategies to foster school resilience. (3) Results: The findings highlight considerable cross-national variation, indicating that school resilience is context-dependent. Resilient schools consistently emphasise student learning-related factors—such as ICT-related attitudes and educational aspirations—while the influence of home environments is less pronounced than in other schools. (4) Conclusions: Strengthening student learning-related factors appears to be crucial for building digital resilience. These insights can inform policy and practice aimed at fostering educational equity and closing the digital divide, particularly in socio-economically disadvantaged contexts.}}, author = {{Niemann, Jan and Eickelmann, Birgit and Drossel, Kerstin}}, issn = {{2227-7102}}, journal = {{Education Sciences}}, number = {{7}}, publisher = {{MDPI AG}}, title = {{{Overcoming Digital Inequalities—Identification and Characterisation of Digitally Resilient Schools in Different Countries Using ICILS 2023 Data}}}, doi = {{10.3390/educsci15070898}}, volume = {{15}}, year = {{2025}}, } @unpublished{57235, author = {{Weiler, David and Burde, Jan-Philipp and Costan, Kasim and Große-Heilmann, Rike Isabel and Kulgemeyer, Christoph and Lässer, Armin and Riese, Josef and Schubatzky, Thomas}}, booktitle = {{Lernen, lehren und forschen im Schülerlabor. Gesellschaft Für Didaktik Der Chemie Und Physik Jahrestagung 2024 in Bochum}}, title = {{{Bedürfnisse von Lehrkräften zu digitalen Medien adressieren! }}}, year = {{2025}}, } @inproceedings{56337, author = {{Knickenberg, Margarita and Hoya, Fabian and Hellmich, Frank}}, publisher = {{Universität Mannheim}}, title = {{{Wahrnehmung und Effekte elterlichen Feedbacks auf die Lesemotivation und -leistung von Grundschulkindern. Vortrag im Rahmen des Symposiums „Lernen durch Feedback von Lehrpersonen, Eltern und Schüler:innen“ (Sebastian Röhl & Fabian Hoya) auf der 12. Tagung der Gesellschaft für Empirische Bildungsforschung (GEBF). Thema: „Bildung als Schlüssel für gesellschaftliche Herausforderungen: Interdisziplinäre Beiträge aus der Bildungsforschung“}}}, year = {{2025}}, } @inproceedings{56336, author = {{Löper, Marwin Felix and Hellmich, Frank}}, publisher = {{Universität Mannheim}}, title = {{{ Determinanten für prosoziales Verhalten und Einstellungen von Grundschulkindern gegenüber Peers mit emotional-sozialem Förderbedarf. Vortrag auf der 12. Tagung der Gesellschaft für Empirische Bildungsforschung (GEBF). Thema: „Bildung als Schlüssel für gesellschaftliche Herausforderungen: Interdisziplinäre Beiträge aus der Bildungsforschung“}}}, year = {{2025}}, } @article{34807, abstract = {{Let $M$ be a compact, real analytic manifold and $G$ be the Lie group of all real-analytic diffeomorphisms of $M$, which is modelled on the (DFS)-space ${\mathfrak g}$ of real-analytic vector fields on $M$. We study flows of time-dependent real-analytic vector fields on $M$ which are integrable functions in time, and their dependence on the time-dependent vector field. Notably, we show that the Lie group $G$ is $L^1$-regular in the sense that each $[\gamma]$ in $L^1([0,1],{\mathfrak g})$ has an evolution which is an absolutely continuous $G$-valued function on $[0,1]$ and smooth in $[\gamma]$. As tools for the proof, we develop several new results concerning $L^p$-regularity of infinite-dimensional Lie groups, for $1\leq p\leq \infty$, which will be useful also for the discussion of other classes of groups. Moreover, we obtain new results concerning the continuity and complex analyticity of non-linear mappings on open subsets of locally convex direct limits.}}, author = {{Glöckner, Helge}}, journal = {{Nonlinear Analysis}}, title = {{{Lie groups of real analytic diffeomorphisms are L^1-regular}}}, doi = {{10.1016/j.na.2024.113690}}, volume = {{252}}, year = {{2025}}, } @book{57850, author = {{Schneider, Tamara and Weber, Julia }}, isbn = {{9783456862712}}, title = {{{Meine Schwangerschaft - so individuell wie ich! }}}, year = {{2025}}, } @book{54106, author = {{Heise, Tillmann}}, isbn = {{978-3-11-152346-0}}, pages = {{519}}, publisher = {{DeGruyter}}, title = {{{Das ‚andere‘ Europa der Schriftsteller. Ideen, Netzwerke und Schreibweisen des antiliberalen Europa-Diskurses in Deutschland und Österreich (1918–1934) }}}, doi = {{https://doi.org/10.1515/9783111525938}}, volume = {{166}}, year = {{2025}}, } @inproceedings{56298, abstract = {{In the general pattern formation (GPF) problem, a swarm of simple autonomous, disoriented robots must form a given pattern. The robots' simplicity imply a strong limitation: When the initial configuration is rotationally symmetric, only patterns with a similar symmetry can be formed [Yamashita, Suzyuki; TCS 2010]. The only known algorithm to form large patterns with limited visibility and without memory requires the robots to start in a near-gathering (a swarm of constant diameter) [Hahn et al.; SAND 2024]. However, not only do we not know any near-gathering algorithm guaranteed to preserve symmetry but most natural gathering strategies trivially increase symmetries [Castenow et al.; OPODIS 2022]. Thus, we study near-gathering without changing the swarm's rotational symmetry for disoriented, oblivious robots with limited visibility (the OBLOT-model, see [Flocchini et al.; 2019]). We introduce a technique based on the theory of dynamical systems to analyze how a given algorithm affects symmetry and provide sufficient conditions for symmetry preservation. Until now, it was unknown whether the considered OBLOT-model allows for any non-trivial algorithm that always preserves symmetry. Our first result shows that a variant of Go-to-the-Average always preserves symmetry but may sometimes lead to multiple, unconnected near-gathering clusters. Our second result is a symmetry-preserving near-gathering algorithm that works on swarms with a convex boundary (the outer boundary of the unit disc graph) and without holes (circles of diameter 1 inside the boundary without any robots).}}, author = {{Gerlach, Raphael and von der Gracht, Sören and Hahn, Christopher and Harbig, Jonas and Kling, Peter}}, booktitle = {{28th International Conference on Principles of Distributed Systems (OPODIS 2024)}}, editor = {{Bonomi, Silvia and Galletta, Letterio and Rivière, Etienne and Schiavoni, Valerio}}, isbn = {{978-3-95977-360-7}}, issn = {{1868-8969}}, keywords = {{Swarm Algorithm, Swarm Robots, Distributed Algorithm, Pattern Formation, Limited Visibility, Oblivious}}, location = {{Lucca, Italy}}, publisher = {{Schloss Dagstuhl -- Leibniz-Zentrum für Informatik}}, title = {{{Symmetry Preservation in Swarms of Oblivious Robots with Limited Visibility}}}, doi = {{10.4230/LIPIcs.OPODIS.2024.13}}, volume = {{324}}, year = {{2025}}, } @article{58133, author = {{Pramanik, Sudipta and Mileaege, Dennis and Andreiev, Anatolii and Hoyer, Kay-Peter and Schaper, Mirko}}, issn = {{1059-9495}}, journal = {{Journal of Materials Engineering and Performance}}, publisher = {{Springer Science and Business Media LLC}}, title = {{{Effect of Compression Rate and Pore Size Distribution on the Compression Behavior of Additively Manufactured Bio-inspired Fe3Si Microporous Material}}}, doi = {{10.1007/s11665-024-10618-z}}, year = {{2025}}, } @article{58150, author = {{Schryen, Guido and Marrone, Mauricio and Yang, Jack}}, journal = {{Electronic Markets}}, title = {{{Exploring the Scope of Generative AI in Literature Review Development}}}, year = {{2025}}, } @article{56667, author = {{Drechsler, Stephan and Harteis, Christian}}, journal = {{Journal of Education and Learning}}, number = {{2}}, title = {{{A Systematic Review of Learning Opportunities within the Crowdworkers’ Workplace}}}, volume = {{14}}, year = {{2025}}, } @article{58532, author = {{Bullerjahn, Nils}}, journal = {{arXiv}}, title = {{{Error estimates for full discretization by an almost mass conservation technique for Cahn--Hilliard systems with dynamic boundary conditions}}}, doi = {{10.48550/ARXIV.2502.03847}}, year = {{2025}}, }