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Scaffolding self-regulated problem solving: the influence of content-independent metacognitive prompts on students’ general problem-solving skills
(2025-06-11) Jasper, Leonie; Melle, Insa
The ability to solve problems is considered a key competence in today’s society. However, solving domain-specific problems, such as those in chemistry, places high demands on students. Effective problem solving requires metacognitive strategies and their corresponding ‘cold’ executive functions, namely working memory and cognitive flexibility, which many students struggle with. To support students, we developed a web-based tool, ChemApro, designed to scaffold problem-solving processes by providing content-independent metacognitive prompts. The tool was used over several weeks in seven schools with N = 153 participating students (M age = 15.63, SD = 0.79) in grades 10 and 11. Among other things, the study focuses on ChemApro’s effect on students’ general problem-solving skills, and on how students perceive the tool in terms of its attractiveness and usability. In line with the study results, the use of ChemApro was descriptively associated with greater improvements in the treatment group’s problem-solving skills compared to the corresponding baseline, particularly among those students with a lower cognitive level. However, the mixed ANOVA did not reveal significant interaction effects between group and time, although trends in the low cognitive level group approached significance. Additionally, students rated the tool’s attractiveness and usability as moderate.
Scalable aggregation of demand side flexibilities in power systems
(2026) Öztürk, Emrah; Faulwasser, Timm; Palzer, Stefan
Die zunehmende Integration erneuerbarer Energien und die steigende Stromnachfrage stellen moderne Stromnetze vor erhebliche Herausforderungen. Eine zentrale Schwierigkeit besteht darin, das Gleichgewicht zwischen schwankender Energieerzeugung und wachsender Nachfrage aufrechtzuerhalten. Gleichzeitig werden immer mehr Flexibilitäten wie Batteriespeicher, thermostatgesteuerte Lasten und Elektrofahrzeuge in das System integriert, die ein großes Potenzial für netzstabilisierende Dienste bieten.
Um einen sicheren und effizienten Netzbetrieb zu gewährleisten, wird in der Literatur die Aggregation als Lösungsansatz diskutiert. Dabei wird die Flexibilität verschiedener Geräte genutzt, um an Energiemärkten teilzunehmen. Der Aggregator kennt als einzige Entität die Systemdetails und hat die Betriebsautorität über die Geräte der Vertragsverbraucher, was den Datenschutz gewährleistet.
Eine Herausforderung bei der aggregationsbasierten Steuerung ist jedoch die genaue Quantifizierung der aggregierten Flexibilität. Die Flexibilität eines Geräts kann durch die Menge seiner potenziellen Lastprofile dargestellt werden, und die aggregierte Flexibilität mehrerer Geräte durch die Addition dieser individuellen Flexibilitätsmengen. Da die Mengenaddition jedoch nicht effizient berechenbar ist, wurden in der Literatur verschiedene Approximationsmethoden vorgeschlagen.
Diese Dissertation untersucht das Konzept der aggregationsbasierten Betriebsführung und dessen Potenzial zur Bereitstellung von Regelleistung- und Zusatzdiensten. Zunächst werden moderne Approximationsstrategien analysiert und in einem Benchmark miteinander verglichen, um deren Schwächen aufzuzeigen. Auf dieser Basis wird eine eckpunktbasierte innere Approximation vorgeschlagen, um die Mängel bestehender Methoden zu überwinden. Dieser Ansatz wird auf Batteriespeichersysteme sowie auf konvexe Speichermodelle ausgeweitet, die eine Vielzahl praktikabler Geräte abbilden können.
Abschließend wird eine effiziente Disaggregationsstrategie vorgestellt, die keine Online-Optimierung erfordert. Die entwickelten numerischen Verfahren werden als Open-Source-Python-Toolbox bereitgestellt und mit modernen Methoden hinsichtlich Rechenzeit und Genauigkeit verglichen.
Das Hauptziel der Dissertation ist es, Algorithmen zu entwickeln, die es Forschern und Fachkräften aus der Industrie ermöglichen, die Flexibilität mehrerer Geräte in realen Anwendungsfällen genau und effizient zu aggregieren.
Amtliche Mitteilungen der Technischen Universität Dortmund, Nr. 5/2026
(Technische Universität Dortmund, 2026-02-20)
Frictional behaviour of coated carbide tools and AISI 316L when using translational and rotatory relative movement considering dry and lubricated conditions
(2024-04-12) Volke, Pascal; Courbon, Cédric; Krumme, Erik; Saelzer, Jannis; Rech, Joel; Biermann, Dirk
In machining, tool temperatures and thus tool wear are significantly influenced by frictional behaviour. Friction tests are used to determine the friction coefficient depending on relative speed, which serves as basis for parameterising friction models as input data for chip formation simulations. Therefore, this paper represents investigations towards the frictional behaviour of uncoated and coated (TiN, TiAlN) carbide tools when using two different relative movements (translational and rotary) and cooling lubricant conditions. In dry conditions, the investigations show insignificant influence of different engagement surfaces and testing kinematics on resulting friction. In lubricated conditions, three different friction coefficient sections were observed.
From frequency-dependent models to frequency-independent enriched continua for mechanical metamaterials
(2024-02-23) Rizzi, Gianluca; d'Agostino, Marco Valerio; Voss, Jendrik; Bernardini, Davide; Neff, Patrizio; Madeo, Angela
Mechanical metamaterials have recently gathered increasing attention for their uncommon mechanical responses enabling unprecedented applications for elastic wave control. Many research efforts are driven towards the conception of always new metamaterials’ unit cells that, due to local resonance or Bragg-Scattering phenomena, may produce unorthodox macroscopic responses such as band-gaps, cloaking, focusing, channeling, negative refraction, etc. To model the mechanical response of large samples made up of these base unit cells, so-called homogenization or upscaling techniques come into play trying to establish an equivalent continuum model describing these macroscopic metamaterials’ characteristics. A rather common approach is to assume a priori that the target continuum model is a classical linear Cauchy continuum featuring the macroscopic displacement as the only kinematical field. This implies that the parameters of such continuum models (density and/or elasticity tensors) must be considered to be frequency-dependent to capture the complex response of the considered mechanical systems in the frequency domain. These frequency-dependent models can be useful to describe some of the aforementioned macroscopic metamaterials’ properties, yet, they suffer some drawbacks such as featuring negative masses and/or elastic coefficients in some frequency ranges which are close to resonance frequencies of the underlying microstructure. This implies that the considered Cauchy continuum is not positive-definite for all the considered frequencies. In this paper, we present a procedure, based on the definition of extra kinematical variables (with respect to displacement alone) and through the use of the inverse Fourier transform in time, to convert a frequency-dependent model into an enriched continuum model of the micromorphic type. All the parameters of the associated enriched model are constant (i.e., frequency-independent) and the model itself remains positive-definite for all the considered frequency ranges. The response of the frequency-dependent model and the associated micromorphic model coincide in the frequency domain, in particular when looking at the dispersion curves. Moreover, the micromorphic (frequency-independent) model results to be well defined both in time- and in the frequency-domain, while the Cauchy (frequency-dependent) model can only exist in the frequency domain This paper aims to build a bridge between the upscaling techniques usually found in the literature and our persuasion that macroscopic continua of the micromorphic type should be used to model metamaterials’ response at the macroscopic scale.