OPUS Online Publikationen der Universität Stuttgart
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Fluctuation theorems for non-Gaussian processes and disordered baths : quantum and classical
No full textNon-Gaussian noise is omnipresent in systems where the central-limit theorem is inapplicable. We investigate the stochastic thermodynamics of small systems described by a general Kramers-Moyal equation with both Gaussian and non-Gaussian white noise, obtaining detailed and integral fluctuation relations for non-equilibrium entropy production in the small-noise regime. These results extend to phase space, where we examine whether the integral fluctuation theorem holds for Markovian non-Gaussian noises and characterize their non-equilibrium thermodynamics. These theoretical results manifest in inhomogeneous environments with finite-range system-bath coupling, where finite correlation lengths induce non-Gaussian Markovian noise via higher-order terms in the Kramers-Moyal equation; analytical solutions for the overdamped harmonic oscillator in this regime explicitly demonstrate non-Gaussian diffusion and non-trivial steady-state statistics. Building on these findings, we numerically study a driven system with localized bath interactions, including overdamped or underdamped particles in dragged harmonic potentials, where systematically reducing the interaction range leads to two main effects: dramatic enhancement of non-Gaussian signatures accompanied by strong suppression of mean entropy production. Finally, in the overdamped regime, we further discuss a generalized detailed-balance condition that defines a dynamic structure factor for the environment’s non-Gaussian density fluctuations, making it directly measurable in scattering experiment
Closing the carbon cycle in plasma‐based CO2 splitting : a techno‐economic perspective
No full textThis techno‐economic analysis examines the impact of CO₂ capture energy and capital costs on plasma‐based power‐to‐liquid (PtL) systems, identifying strategies to minimize the net production costs (NPC) for synthetic fuels. Three future development scenarios were defined. One, focusing on high efficiencies, reaches NPC of 2.9 EUR L-1 of marine diesel. The approach of prioritizing high CO2 conversion results in costs of 3.7 EUR L-1. A more balanced approach between efficiency and conversion achieves an NPC of 2.6 EUR L-1. Further NPC reductions are possible by sourcing lower‐cost renewable electricity, reducing the NPC further to a minimum of 1.6 EUR L-1. These findings underscore that direct air capture (DAC) cost‐efficiency and process integration improvements are essential for scalable, economically viable CO₂ utilization in PtL processes.Projekt DEA
Utilizing liquid crystalline polymers as a reinforcement phase in the fused filament fabrication with conventional polymers
No full textUsing thermotropic liquid crystalline polymers (LCP) in fused filament fabrication (FFF) facilitates the production of highly anisotropic parts that exhibit a high tensile strength and Young´s modulus in the printing direction. This work investigates, for the first time, an approach where the LCP (reinforcing phase) and a conventional polymer (matrix) are printed using two separate printer nozzles. This contrasts with the existing approach in literature, where both components are blended during filament extrusion and subsequently printed with a single printer nozzle. A polyamide 6/66 copolymer (CoPA), a polycarbonate (PC), and a polyetherketoneketone (PEKK) serve as conventional matrix polymers. Due to their chemical structure, a good compatibility is expected between each of these polymers with the LCP. Composite tensile samples are printed with 14, 23, and 30 vol.% LCP and subsequently characterized by uniaxial tensile testing. The highest Young's modulus of 6.8 GPa is achieved in PC/LCP samples with 30 vol.% LCP. In contrast, the highest tensile strength of 126 MPa is obtained in PEKK/LCP tensile samples with 30 vol.% LCP, after an additional thermal annealing at elevated temperatures. The main failure mechanism for all composites is an LCP pull‐out, indicating a poor adhesion between the LCP and the matrix polymers.Deutsche Forschungsgemeinschaf
Insights into decoupled solar energy conversion and charge storage in a 2D covalent organic framework for solar battery function
No full textDecoupling solar energy conversion and storage in a single material offers a great advantage for off-grid applications. Herein, we disclose a two-dimensional naphthalenediimide (NDI)-based covalent organic framework (COF) exhibiting remarkable solar battery performance when used as a photoanode. Light-induced radicals are stabilized within the framework for several hours, offering on-demand charge extraction for electrical energy production. Our study reveals mechanistic insights into the long-term charge stabilization using optical spectroscopy and (photo)electrochemical measurements, in conjunction with density functional theory (DFT) simulations. Among several solvents, water provides the best dielectric screening and energetically favorable proton exchange to stabilize photoinduced radicals for more than 48 h without the need for additional metal cations. This study provides fundamental insights into the optoionic charge storage mechanism in NDI-COF, while introducing a highly tunable, nanoporous material platform that surpasses related materials, such as carbon nitrides, metal–organic frameworks (MOFs), or metal oxides, in terms of charge storage capacity. This study opens new perspectives for the design of optoionic charge-storing materials and the direct storage of solar energy to overcome the intermittency of solar irradiation.Alexander von Humboldt-StiftungDeutsche ForschungsgemeinschaftMax-Planck-Gesellschaf
Voltage balancing of a Pi-type multilevel converter for charging electrocaloric capacitors
No full textElectrocaloric solid state heat pumps provide a sustainable solution for cooling and heating systems powered by electricity. The electrocaloric effect is a reversible temperature change when the electric field changes in multilayer capacitors made of special dielectric functional materials. It can be transferred into an efficient solid-state heat pump system but requires highly efficient power electronics. High efficiency has already been achieved with multilevel converters with ideal capacitive loads. However, when operating with real, lossy and non-linear electrocaloric components as a load, the internal buffer voltages drift away due to uneven charge distribution across the capacitors. The main idea of this paper is to investigate and solve the unbalancing problem with a purely software-based control technique: Intentional unsymmetrical level-skipping can effectively charge or discharge the buffer voltage. The new balancing operation is experimentally demonstrated with a four-level Pi-type GaN-based multilevel converter, hysteretic current control for zero voltage switching, and an electrocaloric ceramic capacitive load (10µF, 120V, 0.5Hz system frequency). The 4 level balancing operation reduced the power loss by 24% (compared to 2 level), and enabled continuous operation with stabilized buffer voltages
Electrostatic all-passive force clamping of charged nanoparticles
No full textIn the past decades, many techniques have been explored for trapping microscopic and nanoscopic objects, but the investigation of nano-objects under arbitrary forces and conditions remains nontrivial. One fundamental case concerns the motion of a particle under a constant force, known as force clamping . Here, we employ metallic nanoribbons embedded in a glass substrate in a capacitor configuration to generate a constant electric field on a charged nanoparticle in a water-filled glass nanochannel. We estimate the force fields from Brownian trajectories over several micrometers and confirm the constant behavior of the forces both numerically and experimentally. Furthermore, we manipulate the diffusion and relaxation times of the nanoparticles by tuning the charge density on the electrode. Our highly compact and controllable setting allows for the trapping and force-clamping of charged nanoparticles in a solution, providing a platform for investigating nanoscopic diffusion phenomena.Max-Planck-GesellschaftAlexander von Humboldt-Stiftun
Data-driven quality assurance of the dry fibre tape laying process
No full textThe aerospace industry faces significant challenges in producing carbon fibre composite structures due to the high costs and manual labour involved. To address the increasing demand for these materials, novel automated production technologies are needed. This dissertation focuses on the Automated Dry Fibre Tape Placement (DFTP) process, a promising method for cost-efficient production of composite parts. However, the lack of a reliable quality assurance system remains a significant barrier to its widespread industry adoption.
This research develops a comprehensive quality definition for dry fibre tape layups and an inline quality control system for the DFTP process, addressing a significant gap in existing literature, which mainly covers pre-pregs. The first part of the study investigates the impact of common architectural characteristics of dry fibre tape layups, such as gaps, overlaps, and undulations, on the mechanical properties of the final material. A correlation between the sizes and positioning of these characteristics and the material’s knockdown factors was identified through mechanical testing of specimens with controlled architectures, providing critical insights for future design processes and simulations.
In the second part, a novel quality monitoring system was developed, comprising a tape inspection station and an inline monitoring system. The tape inspection station assesses the quality of the raw tape, while the inline monitoring system employs a laser triangulation sensor to detect gaps and overlaps during the laying process. Unlike existing systems that merely detect defects, this system accurately determines the size and position of these features, allowing for a detailed assessment of their severity. The data processing was performed using an expert system based on process knowledge and a deep learning approach utilising a Convolutional Neural Network. The neural network, trained through a transfer learning approach, provided highly accurate real-time results, enabling a closed feedback loop for immediate corrective actions. This method significantly reduces the need for large real scan data sets for training.
The outcomes of this dissertation are a detailed quality definition and an automated, real-time quality monitoring system for the DFTP process. The proposed methods allow the industry to implement high-quality, cost-efficient manufacturing processes for carbon fibre composite parts. This research represents a novel contribution to the field by providing the first system capable of pixel-accurate segmentation of layup scans, enabling informed quality decision-making. Additionally, the transfer learning approach significantly reduces the data requirements for training neural networks, facilitating quicker and more efficient implementation in industrial settings
Erotische Naivität - Darstellung von Jungfräulichkeit in der mittelalterlichen Märendichtung am Beispiel der Mären vom Sperber, Häslein und Gänslein
No full textDie Bachelorarbeit vergleicht die narratologische Darstellung und Bewertung von Jungfräulichkeit und deren Verlust in den Mären vom Sperber, Häslein und Gänslein
Ro(a)d to new functional materials : sustainable isolation of high-aspect-ratio β-chitin microrods from marine algae
No full textHigh-aspect-ratio rod-shaped chitins such as chitin whiskers or chitin nano- and microfibers are particularly promising for a wide range of applications, including electrorheological suspensions, lightweight reinforcement material for biocomposites, biomedical scaffolds, and food packaging. Here, we report the first mild water-based mechanical extraction protocol to isolate β-chitin microrods from the marine algal species Thalassiosira rotula while preserving their structural integrity throughout the process. The resulting microrods could be distributed into two populations based on the fultoportulae from which they are extruded. The rods exhibit typical dimensions of 12.6 ± 4.0 µm in length and 75 ± 21 nm in diameter (outer fultoportulae) or 17.5 ± 4.7 µm in length and 170 ± 39 nm in diameter (central fultoportulae), yielding high aspect ratios of ~168 and ~103 on average, respectively. Due to this environmentally friendly extraction, the high purity of the synthesized chitin, and the renewable algal source, this work introduces a sustainable route to produce pure biogenic β-chitin microrods.Carl Zeiss Foundation for the infrastructure project ChitinFluidGerman Research FoundationEuropean Regional Development Fun
The gut feeling in motion sickness
No full textMotion sickness is a nearly universal response to the unnatural motions that are experienced when traveling by means other than the body’s own faculties; in artificial realities; and in micro- and partial gravity environments. Despite being a known malady since ancient times, its underlying mechanisms, as well as the marked interpersonal variability in susceptibility, remain incompletely understood. While efferent brain-to-body signaling pathways involved in motion sickness have been previously described, recent findings on the functional role of the gut’s (neuro)epithelial cells and microbiome point to a more intricate biological control system than previously appreciated. We examine (afferent) anatomical, hormonal, immune, and extracellular brain-body pathways, and their potential role in motion sickness etiology. This perspective proposes that an additional route may contribute to the pathophysiology of motion sickness, potentially under regulatory influence of the enteric nervous system. Candidate initiators, acting on these pathways, include humoral agents, enteroendocrine cells, and the gut microbiome.Projekt DEA