University of Kaiserslautern
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The fouling behavior on PEEK surfaces during heat transfer
Get PDFFouling in heat exchangers is a major challenge in many industrial processes due to increased
energy costs, environmental pollution and shortened cleaning cycles. One strategy to avoid the
growth of deposits is the use of alternative materials such as polyether ether ketone (PEEK)
instead of the conventionally used stainless steel (SS). In this thesis, the fouling behavior of
PEEK-based heat exchangers is therefore compared qualitatively and quantitatively with SS
heat exchangers. The behavior of crystallization (calcium sulfate) and organic (whey protein
concentrate, WPC) fouling are considered. The experimental studies show that PEEK has a
lower susceptibility to fouling and better cleanability compared to SS under various process
conditions, making it a promising material for preventing fouling. By modeling the fouling
behavior of WPC, a deeper understanding of the process was achieved and predictions were
made for the fouling behavior of non-tested operating conditions. In calcium sulfate solutions,
PEEK exhibited asymptotic fouling behavior, with a fouling factor half that of SS, while talc-filled PEEK (TKT) had higher fouling rates due to increased surface roughness. Cleaning
experiments conirmed the advantage of PEEK over SS, as deposits could be removed more
quickly from the surface compared to SS. PEEK also showed a significant reduction in the
effects of whey protein deposits, with up to a 40 percent reduction of heat resistance compared
to stainless steel. The cause of the reduction in thermal resistance was the removal of the
deposit layer caused by evaporation, so that the thermal resistance remained limited to PEEK
surfaces and longer operating times were possible. Scale-up experiments confirmed that these
results are scalable and showed consistent behavior. A mechanistic and an empirical model
were developed to predict the deposition behavior. Both models were able to predict the
experimental data well. The mechanistic model took into account protein denaturation and
boiling effects and was able to extrapolate from the data better than the empirical model,
even though significant deviations were observed during validation. The empirical model
showed higher accuracy in predicting behavior under untested operating conditions within
the limits of the experimental data compared to the mechanistic model. Symbolic regression
further correlated the model parameters with operating conditions. These results show that
PEEK heat exchangers reduce the costs associated with fouling and improve sustainability,
making them a viable alternative to conventional materials in energy-intensive processes. The
investigations show that PEEK is a competitive alternative to conventional stainless steels and
can contribute to optimize processes
Synaptic integration strategies for sound source localization within an excitation-inhibition circuit
Get PDFExcitatory and inhibitory synapses are major components of interneuronal information processing. A robust interplay between these two types is crucial in the lateral superior olive (LSO). LSO neurons integrate excitatory and inhibitory inputs from the ipsilateral and contralateral ear, respectively. They are remarkably sensitive to interaural level differences (ILDs) and interaural time differences (ITDs), making them well-suited for azimuthal sound source localization. Together with their input neurons from the cochlear nucleus and the medial nucleus of the trapezoid body, LSO neurons form an optimal circuit to investigate the mechanisms underlying behaviorally relevant synaptic integration of excitation and inhibition. The mechanisms by which the relative strength and timing of excitatory and inhibitory inputs are integrated in the LSO are not yet fully understood.
In this study, I examined synaptic integration in LSO neurons in four steps. First, I evaluated excitatory transmission by combining whole-cell voltage-clamp recordings with electrical fiber stimulations in young adult mice. LSO neurons receive up to 40 excitatory inputs, with each input contributing a synaptic weight (SWexc) of 1 nS/input. I used these values, along with four inhibitory inputs of SWinh of 8 nS/input, as canonical synaptic inputs in the LSO circuit. Second, I analyzed the biophysical membrane properties of LSO neurons that underlie synaptic integration. Fast signal integration is enabled by a short membrane time constant and low input resistance along the putative tonotopic axis. Voltage sag behavior and membrane resonances indicate an extension of passive features by active conductances. Suprathreshold responses were observed as biphasic action potentials (APs), likely reflecting compartment-specific activation of voltage-gated sodium channels. Moreover, the AP threshold varied with the slope of stimulation. Third, I employed the dynamic-clamp in conjunction with an input pathway model to study synaptic integration. Upon sinusoidal stimulation, the neurons behaved as coincidence detectors. They transformed a primary-like input pattern with physiological SWexc into onset responses. The onset can be employed for rate-level coding in combination with inhibition. Conversely, the sustained phase does not support rate-based level difference coding, regardless of SWexc and SWinh configurations. The coincidence mechanism creates band-pass filtering during sinusoidal stimulation and sets the highest sensitivity to transient activations. These activations enable robust rate-difference coding and coding of temporal disparities between excitation and inhibition. Fourth, in vivo data from anaesthetized mice showed that LSO neurons are highly sensitive to variations in stimulus transience and can encode these up to high modulation rates. Moreover, integration of ILDs is not impeded by such high modulation rates.
Together, my results provide a mechanistic rationale for the synaptic integration underlying the high perceptual acuity of sound source localization with transient sound signals
Riemannian shape optimization of thin elastic shells using isogeometric analysis
Get PDFIn this thesis, we consider the optimal shape design of thin elastic shells based on a model of Koiter's type, whose shape can be described by a surface embedded in three-dimensional Euclidean space. We regard the set of unparametrized embeddings of the surface as an infinite-dimensional Riemannian shape manifold and perform numerical optimization in this setting using the Riemannian shape gradient. Non-uniform rational B-splines (NURBS) are employed to discretize the shell and numerically solve the equations that govern its mechanical behavior via isogeometric finite element analysis (IGA). The aim is to develop and implement new numerical methods for solving shape optimization problems constrained by partial differential equations (PDEs) that take the inherent geometric structure of shape spaces into account and make use of the integration of finite element analysis (FEA) with technologies from computer-aided design (CAD). In contrast to existing methods based on the Riemannian framework, we investigate the use of geodesic retractions instead of linear updates on shape spaces of planar curves and surfaces for the gradient descent method. We demonstrate our proposed approach and numerical methods mainly on the computation of minimal surfaces, the compliance minimization of thin elastic shell structures under static load and fixed area constraint, as well as the identification of parameters for a model of Earth's lithosphere in the context of geoscientific applications.In dieser Arbeit wird die Formoptimierung von dünnen elastischen Koiter-Schalen behandelt, dessen Form durch eine in den dreidimensionalen euklidischen Raum eingebettete Fläche beschrieben werden kann. Wir betrachten die Menge aller nichtparametrisierten Einbettungen der Fläche als eine unendlichdimensionale Riemann'sche Formmannigfaltigkeit und führen in diesem Rahmen unter Verwendung des Riemann'schen Formgradients eine numerische Formoptimierung durch. Nicht-uniforme rationale B-splines (NURBS) werden eingesetzt, um die Schale anhand von isogeometrischer Analysis (IGA) zu diskretisieren und die partiellen Differentialgleichungen (PDEs), die das mechanische Verhalten des Festkörpers festlegen, numerisch zu lösen. Das Ziel ist es, neuartige numerische Verfahren für die PDE-beschränkte Optimierung von Formen zu entwickeln und zu implementieren, die die inhärente geometrische Struktur von Riemann'schen Formräumen in Betracht ziehen. Dabei werden Technologien aus dem rechnerunterstütztem Konstruieren (CAD) mit der Finite-Elemente-Analysis (FEA) integriert. Im Gegensatz zu bestehenden Methoden, die auf dem Riemann'schen Modell basieren, wird die Verwendung einer geodätischen Retraktion statt einer linearen Iterationsvorschrift für das Gradientenverfahren auf Formräumen von ebenen Kurven und Flächen untersucht. Der vorgeschlagene Ansatz wird insbesondere auf die Berechnung von Minimalflächen und die Minimierung der Nachgiebigkeit von dünnen elastischen Schalen unter statischer Belastung und mit festem Flächeninhalt angewandt. Darüber hinaus werden im geowissenschaftlichen Anwendungsbereich Parameter in einem mathematischen Modell für die Lithosphäre der Erde geschätzt
Abschlussbericht: CyberTech – Advanced Systems Engineering für die Arbeitsgestaltung von Cyber-technischen Systemen
Get PDFDas vom BMBF geförderte Verbundforschungsprojekt CyberTech adressiert die wachsende Komplexität moderner Produktentwicklungsprozesse, die durch steigende Softwareanteile, zunehmende Vernetzung und verkürzte Innovationszyklen geprägt sind. Ziel des Projekts war die Entwicklung und Erprobung eines integrativen Ansatzes für Advanced Systems Engineering (ASE), der die Dimensionen Mensch, Technik und Organisation nach dem MTO-Prinzip ganzheitlich verbindet. Im Mittelpunkt stand die Frage, wie cyber-technische Systeme künftig effizient, nachvollziehbar und menschzentriert entwickelt werden können.
Innerhalb der Säule Mensch wurden ein ASE-spezifisches Kompetenzmodell, Maßnahmen zur Förderung agiler Lernkulturen sowie moderne Lernformate einschließlich eines universitären Lehr- und Lernlabors entwickelt. Die Säule Technik fokussierte die Gestaltung digitaler Zwillinge, die Integration von Sensordaten in Simulationsmodelle, ein ASE-Reifegradmodell sowie Methoden zur domänenübergreifenden Interoperabilität und Traceability. In der Säule Organisation entstanden ein agiles Vorgehensmodell für MBSE, ein generisches Informationsmodell zur Gestaltung durchgängiger Digital Threads sowie Ansätze für KI-basierte Entwicklungsassistenz zur Unterstützung der Systemmodellierung und Normkonformitätsprüfung. Der Abschlussbericht fasst die genannten Ergebnisse zusammen und bietet somit einen Leitfaden zur Einführung von ASE in der industriellen Praxis und skizziert zugleich künftige Forschungsbedarfe für resiliente, vernetzte und menschorientierte Engineering-Prozesse
Kollegiale Beratung als Beitrag zur Weiterentwicklung beruflicher Identität von Pflegekräften
Get PDFDer beruflichen Pflege in Deutschland kann ein Identitätsproblem konstatiert werden. Dies resultiert mitunter daraus, dass die in den letzten Jahren durchgeführten Ausbildungsreformen jeweils mit grundlegenden Veränderungen des Berufs- und Pflegeverständnisses einhergingen, die sich nicht nur auf das Handeln in der Praxis auswirken, sondern auch die im Rahmen der beruflichen Sozialisation verinnerlichten Haltungen maßgeblich prägen. In der vorliegenden Arbeit wird untersucht, inwieweit kollegiale Beratung einen Beitrag zur Weiterentwicklung der individuellen und kollektiven pflegeberuflichen Identität leisten kann, um den negativen Auswirkungen dieser Identitätsproblematik entgegenzuwirken und das Potenzial der Heterogenität zu nutzen.Professional nursing in Germany can be said to have an identity problem. This is partly due to the fact that the training reforms carried out in recent years have been accompanied by fundamental changes in the understanding of the profession and nursing, which not only affect practice but also have a significant impact on the attitudes internalised during professional socialisation. This paper examines the extent to which collegial counselling can contribute to the further development of individual and collective professional nursing identity in order to counteract the negative effects of this identity problem and exploit the potential of heterogeneity
Can AI-generated news reduce hostile media perceptions? Findings from two experiments
Get PDFIntroduction: The current debate regarding artificial intelligence (AI) raises the
question of whether AI-generated news articles on controversial topics can
reduce news consumers’ hostile media perceptions (HMP). In addition, there is
a debate about people’s prior attitudes toward AI and how it influences people’s
perceptions of AI-generated news articles.
Methods: Based on the theoretical foundation of the MAIN model and the
Hostile Media Phenomenon, we conducted two preregistered experimental
studies in the United States (N = 1,197). All subjects were presented with a news
article on a divisive and polarizing topic (gun regulation), but we systematically
varied the supposed author of the article (human journalist, AI-generated, AI and
human journalist working together).
Results and Discussion: In both studies exposure to the AI-generated news
article significantly reduced participants’ HMP. However, the effect was only
detected for individuals with negative and moderate prior attitudes toward
AI. Individuals with positive AI attitudes did not benefit from AI-generated
articles. AI-assisted news reporting showed very limited effects (only in Study
2). Furthermore, we examined if HMP predict online engagement. While Study
1 showed no effects on online engagement, Study 2 revealed that exposure to
an AI-generated news article indirectly increased online engagement (intention
to share a news article with friends and family). Implications for communication
and journalism are discussed
Textilrecycling: Die Bedeutung geschlossener Kreisläufe für die Transformation der Bekleidungsindustrie
Get PDFDie globale Textil- und Bekleidungsindustrie steht angesichts wachsender Abfallmengen, hoher Ressourcennachfrage und linearer Produktionsmuster vor tiefgreifenden Transformationszwängen. Die Masterarbeit untersucht die Rolle des Textilrecyclings als zentralen Baustein einer zirkulären Wirtschaft und analysiert, wie aus textilen Abfallströmen nachhaltige Wertschöpfung generiert werden kann. Fallstudien aus Ghana, Vietnam, Pakistan und dem italienischen Textildistrikt Prato zeigen bestehende Strukturen, Engpässe und Entwicklungspotenziale auf globaler Ebene. Abschließend werden Zukunftsperspektiven skizziert, die verdeutlichen, welche technologischen Innovationen, politischen Maßnahmen und infrastrukturellen Voraussetzungen notwendig sind, um geschlossene textile Kreisläufe im industriellen Maßstab zu realisieren
Droplet Condensation on Superhydrophobic Graphite Composites
Get PDFHeat exchangers play a crucial role in the chemical industry, where efficient heat management is essential for maintaining process control, reducing operational costs, and conserving energy.
A considerable portion of the energy used in chemical production is associated with the heating and cooling of process fluids. Traditionally, metals such as stainless steel have been employed in heat exchanger construction due to their high thermal conductivity and mechanical robustness. However, their application is often limited by disadvantages such as high weight, high material cost, and susceptibility to corrosion in aggressive chemical environments. Polymers have emerged as a promising alternative, particularly when reinforced with thermally conductive fillers. These materials combine chemical resistance, low weight, and ease of manufacturing. In this thesis, thermally conductive graphite-filled polymer composites were modified to create superhydrophobic surfaces. This was achieved through a combination of microscale structuring via thermal imprinting, nanostructuring using metal oxide nanostructures (MONSTRs), and subsequent functionalization with fatty acid coatings such as stearic and lauric acid. The resulting surfaces were systematically characterized to evaluate their wetting behavior, condensation dynamics, and heat transfer performance under varying relative humidity conditions.
Experimental results showed that the surface-modified composites achieved contact angles exceeding 170◦ with contact angle hysteresis below 5◦, demonstrating effective superhydrophobicity.
Condensation experiments revealed enhanced droplet shedding and significantly higher heat transfer coefficients compared to stainless steel and its filmwise condensation. Furthermore, droplet size distributions were determined from high-resolution imaging and compared with predictions from a population balance model based on the frameworks of Wang et al. [1] and Tancon et al. [2]. While good agreement was found in droplet size distribution, discrepancies
in predicted heat fluxes were observed, primarily due to the presence of non-condensable gases (NCGs) in humid air, which are not fully captured by existing models.
These findings underscore the potential of surface-engineered polymer composites to enhance condensation-driven heat transfer and highlight the need for advanced modeling approaches that incorporate the effects of NCGs. The results provide valuable insights into the potential of surface-engineered polymer composites for condensation-based heat transfer enhancement
Accelerating Computation of Stable Merge Tree Edit Distances using Parameterized Heuristics
Get PDFIn this paper, we present a novel heuristic algorithm for the stable but NP-complete deformation-based edit distance on merge trees.
Our key contribution is the introduction of a user-controlled look-ahead parameter that allows to trade off accuracy and computational cost.
We achieve a fixed parameter tractable running time that is polynomial in the size of the input but exponential in the look-ahead value.
This extension unlocks the potential of the deformation-based edit distance in handling saddle swaps, while maintaining feasible computation times.
Experimental results demonstrate the computational efficiency and effectiveness of this approach in handling specific perturbations
Picky elements, subnormalisers, and character correspondences
Get PDFWe gather evidence on a new local-global conjecture of Moret\'o and
Rizo on values of irreducible characters of finite groups. For this we study subnormalisers and picky elements in finite groups of Lie type and determine them in many cases, for unipotent elements as well as for semisimple elements of prime power order. We also discuss subnormalisers of unipotent and semisimple elements in connected and disconnected reductive linear algebraic groups