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Organisationseinheit der BAM
This thesis deals with the development of a novel optical fiber sensing scheme based on geometric phase for sensing strain and its application to seismology. Interference of two coherent frequency offset electromagnetic waves gives rise to a geometric phase in the resulting beat signal. The existence of this phase was recently reported along with requisite conditions for its existence. This thesis proposes to detect and use this geometric phase in the context of distributed and dynamic fiber optic strain sensing, also known as distributed acoustic sensing (DAS). In the first part, I devise a novel DAS hardware setup capable of detecting the geometric phase considering that its measurement methods require the measurement of beam intensities and the beat signal’s envelope. The geometric phase is a function of relative intensity and polarisation state of two interfering beams. Therefore, its measurement is verified by determining its relation on these quantities using a polarisation scrambler and a piezoelectric transducer, inline an optical fiber. It is a fundamental study that has implications in coherent optical communication and novel sensing mechanisms.
The second part involves using the geometric phase in DAS for measurement of strain. I attempt to replace the traditionally measured dynamic phase in a DAS setup with the geometric phase. This is made possible by the fact that the geometric and dynamic phases are reportedly coupled over every beat period such that their sum remains constant. However, the spatial resolution for geometric phase is lower as it is measured per beat period. I determine an equivalence for the two phases empirically as well as optimum test parameters such as the required frequency offset between the interfering beams. The advantages offered by the use of geometric phase are demonstrated; geometric phase can be measured even when the two interfering beams have non-identical polarisation states, unlike the traditionally measured dynamic phase. Moreover, it does not require phase unwrapping and is therefore free from unwrapping errors.
In the third and final part, the setup, after optimisation, is tested in the field to detect seismic waves travelling on the surface of the Earth in response to a set of blasts carried out at a test-site. The surface waves are used for the characterisation of the structure and material properties of the first tens of meters of the Earth with applications in earthquake monitoring, resource exploration and infrastructure planning.
In short, this study is the first of its kind to measure geometric phase in beat signal of light using optical fiber medium and to measure strain with it, for which a novel hardware setup and a novel sensing mechanism is designed and tested in addition to its application in real-world seismology measurements.
Antimicrobial resistance (AMR) is a global health problem. It is well known that antibiotics can drive evolutionary processes that underlie antimicrobial resistance (AMR) evolution and spread in clinical and environmental settings. In contrast, less is known about the effects of antimicrobial substances that are used as biocides (i.e. disinfectants and preservatives) on AMR evolution and spread. Biocides are present in various settings, interacting with diverse microbial communities. Therefore, it is crucial to evaluate their role in the evolution and dissemination of antimicrobial resistance. Biocides occur in a wide range of concentrations in various environmental settings. By examining how the various concentrations affect selection mechanisms, we gain insights into potential developments related to antimicrobial resistance. The aim of this PhD thesis is to investigate the effects of biocides on processes underlying resistance evolution. Specifically, the work focused on key mechanisms for resistance spread, resistance evolution, and the effect of selection pressures on evolved resistance mechanisms. The thesis is structured around three major objectives: (i) to determine the effect of biocides on the evolution of resistance by affecting the rate of occurrence of de novo mutations, (ii) to determine the effect of biocides on the spread of resistance genes by modifying the rate of horizontal gene transfer (HGT) processes, and (iii) to investigate the selective drivers of the emergence of antimicrobial resistance in adaptive laboratory evolution (ALE) experiments. De-novo mutations are spontaneous mutations that occur at a certain rate in microorganisms. The effect of biocides at subinhibitory environmentally relevant concentrations on the mutation rate in Acinetobacer baylyi, Bacillus subtilis and Escherichia coli was assessed with the fluctuation assay. The results showed that biocides affected mutation rates in a species and substance dependent matter. The bisbiguanide chlorhexidine digluconate, the quaternary ammonium compound didecyldimethylammonium chloride, the metal copper, the pyrethroid-insecticide permethrin, and the azole-fungicide propiconazole increase mutation rates in E. coli, whereas no increases were identified for B. subtilis and A. baylyi. Horizontal gene transfer refers to diverse mechanisms that mediate the transfer of mobile genetic elements between microorganisms. This work focused on conjugation and transformation. Conjugation is a process whereby a conjugative plasmid is transferred from a donor cell to a recipient cell. Transformation is a process whereby exogenous donor DNA is taken up into a recipient cell and integrated into the recipient’s’ genome. The effects of subinhibitory environmentally relevant biocide concentrations on the conjugation rate of E. coli and the transformation rate of the naturally competent organisms A. baylyi in were assessed. The results showed that benzalkonium chloride (BAC), chlorhexidine and permethrin increased conjugation in E. coli, while none of the biocides increased transformation rates in A. baylyi. To further understand the molecular mechanisms underlying the effects on mutation and conjugation rates, I investigated the induction of the RpoS-mediated general stress and the RecA-linked SOS response upon biocide exposure. The results show a link between the general stress and the SOS response with increased rates of mutation and conjugation, but not for all biocides. One major approach to study the evolutionary response of bacteria to antimicrobials are ALE experiments with growth at subinhibitory concentrations linked to serial subculturing over many generations. Such experiments have been used to study resistance evolution to antibiotics and biocides. However, previous work showed that adaptation to biocide stress may be mediated by different evolutionary drivers. Here, I investigated the contributions of evolution for increased survival as opposed to improved growth in ALE experiments with E. coli exposed to subinhibitory BAC concentrations. Two distinct evolutionary treatments selecting for survival only or survival and growth led to specific evolutionary adaptations apparent in the phenotypes and genotypes of the evolved populations. Populations growing in the presence of BAC evolved increased fitness in the presence of BAC associated with higher resistance to BAC and cross-resistance to antibiotics, while this was not the case for populations evolving for increased survival only. Genotypic characterization by whole genome sequencing of the evolved populations revealed parallelism in mutated genes among replicate populations and distinct differences across treatments. Treatments selecting for survival and growth showed mutations in stress response related genes (hslO and tufA), while selection for survival led to mutations in genes for metabolic regulation (cyaA) and cellular structure (flagella fliJ). In summary, this thesis shows that biocides affect AMR evolution and emphasizes the importance of understanding of how biocides impact the molecular and evolutionary process that underlie AMR evolution.
In der Wissenschaft und Technik gibt es verschiedene Gründe, um auf Basis geeigneter Modelle in die Zukunft schauen zu wollen, beispielsweise um zu bewerten, ob ein Bauteil auch noch deutlich länger verwendet werden kann als eigentlich einmal vorgesehen. Eine Methode dieses zu tun, basiert auf dem Zeit-Temperatur-Äquivalenz-Prinzip, welches besagt, dass ein Zustand oder eine Materialeigenschaft gleichwertig bei verschiedenen Zeit-Temperatur-Kombinationen auftritt oder erreicht werden kann. Höhere Temperaturen verkürzen in der Regel die Dauer und umgekehrt. In den letzten Jahrzehnten hat sich ein umfangreiches Methodenspektrum für unterschiedliche Werkstoffe und Anwendungsgebiete entwickelt, sodass die Identifikation einer geeigneten Methode für einen konkreten Anwendungsfall oder neue Materialien eine Herausforderung darstellt. These: „Fortschrittlich wäre, existierende Methoden zusammenzuführen, methodenspezifische Vorteile zu kombinieren, um mit geringerem Aufwand ein geeignetes Prognosemodell zu entwickeln.“
Für metallische Werkstoffe und Polymere verläuft die Entwicklung von Prognosemodellen mit Zeit-Temperatur-Korrelation seit ca. 1940 parallel und unabhängig voneinander. In diesem Zusammenhang bekannte Methoden sind das Zeit-Temperatur-Superpositionsprinzip und Zeit-Temperatur-Parameter, wie der LARSON-MILLER-Parameter. Die jeweiligen methodischen Ansätze sind in der Regel anwendungs- und materialspezifisch und nur einzelnen Fachartikeln zu entnehmen. Eine zusammenführende thematische Übersicht und Untersuchung existierender Methoden wurden bislang nicht publiziert. Diese Forschungsarbeit verfolgt dahingehend einen neuartigen methodischen Ansatz und zeigt untersuchte Gemeinsamkeiten und Unterschiede als auch Analogien für das Zeit-Temperatur-Superpositionsprinzip und Zeit-Temperatur-Parameter anhand bestimmter Merkmale auf. Dafür wurden verschiedene analytische und grafische Ansätze verwendet. Ferner wird eine zusammenführende Untersuchung anhand eines rheologischen Materialmodells sowie anhand eines praktischen Anwendungsbeispiels gezeigt. Hergeleitet wurde u. a., dass das Prinzip der Zeit-Temperatur-Superposition für sogenanntes thermorheologisch einfaches und komplexes Verhalten konkreten Zeit-Temperatur-Parametern zugeordnet werden können. Und dadurch Verschiebefunktionen nicht nur in Abhängigkeit der Temperatur, sondern auch abhängig vom Zustand untersucht und definiert werden können. Ferner ermöglicht eine Skalierung der Zeit-Temperatur-Parameter auf eine Referenztemperatur physikalisch anschaulichere Auswertungen analog zum Zeit-Temperatur-Superpositionsprinzip. Untersuchungen zeigen, dass sich für einen konkreten Anwendungsfall die geeignetste Zeit-Temperatur-Äquivalenz-Methode aus einer gegenseitigen Abhängigkeit bzw. Kompatibilität einzelner Elemente, wie zugrunde gelegte Daten, Koordinatenachsenskalierung, ermittelte Zeit-Temperatur-Äquivalenz, Masterfunktionsansatz und der geforderten Interpolationsgüte herleitet.
Der gewählte Forschungsansatz und die erzielten Ergebnisse bieten eine Plattform für die weitere Entwicklung von Prognosemodellen auf Basis des Zeit-Temperatur-Äquivalenz-Prinzips, insbesondere im Hinblick auf eine Zusammenführung und Kombination existierender Methoden.
Today’s industrial demands challenge the research and development sector to make advances in the design and properties of materials that can withstand harsh environments. The AlMo0.5NbTa0.5TiZr refractory high-entropy superalloy (RSA), with a remarkable morphological similarity to the γ/γ' microstructure of Ni-based superalloys and promising high-temperature compressive properties, has been considered as a candidate for structural applications. However, additional properties need to be investigated in order to assess the suitability of this alloy for high temperature applications. Therefore, this work investigates the thermodynamic and microstructural stabilities of the RSA at room temperature and between 900 and 1100 °C, and their influence on the mechanical properties. Although it is possible to improve the mechanical properties at 20 °C by tuning the cooling rate, long-term high temperature exposures lead to phase instabilities that negatively influence the creep behavior.
The present Ph.D. thesis provides a comprehensive experimental and theoretical study of the bulging-cracking relationship in laser beam welding of thick unalloyed steel sheets. It focuses on experimentally proving the existence of the bulging region and on developing a coupled multiphysics mathematical framework to analyze its influence on the three critical factors controlling the susceptibility to solidification cracking, namely the thermal, metallurgical, and mechanical factors.
The research employs a novel experimental setup, utilizing a combination of transparent quartz glass and thick unalloyed steel sheet, enabling real-time visualization of the weld pool geometry and confirming the existence of a distinctive bulging region. To deepen the understanding of these experimental insights, an extensive multiphysics mathematical framework was developed and rigorously verified and validated. This framework introduces an innovative approach using Lamé curves for accurately describing complex three-dimensional weld pool geometries, including the bulging region's characteristics. Through analytical solutions and numerical procedures, it facilitates the computation of solidification parameters, which are crucial for understanding the metallurgical aspects of crack formation. The framework also incorporates a mechanical model to assess and evaluate the local stress distribution within the bulging region.
The findings indicate that an elongated, sharply shaped bulging region significantly increases the susceptibility to solidification cracking. This is attributed to its adverse impact on the distribution and local dwell time of liquid metal residing at grain boundaries during solidification, combined with the localized tensile stresses identified in the bulging region.
In essence, this research contributes to the broader understanding of solidification cracking in laser beam welding of thick unalloyed steel sheets, with a particular focus on the bulging region. The insights and methodologies developed in this thesis are valuable for future research and advancements in the application of the laser beam welding technology for joining high-thickness unalloyed steel components.
Die additive Fertigung (AM) metallischer Werkstoffe ist eine Technologie, die zunehmend Gegenstand von Forschungsaktivitäten und industrieller Anwendung ist. Dennoch steht sie noch vor Herausforderungen, um eine breite Nutzung in sicherheitsrelevanten Anwendungen zu erreichen. Die Hauptgründe für die Verzögerung des technologischen Durchbruchs zugunsten von AM-Metallen gegenüber konventionell hergestellten Varianten sind das Fehlen eines tieferen Verständnisses der Prozess-Struktur-Eigenschafts-Beziehungen und die begrenzte Verfügbarkeit von Daten zu den Materialeigenschaften. In diesem Kontext stellt diese Arbeit einen Beitrag sowohl zum Verständnis der Prozess-Struktur-Eigenschafts-Beziehungen als auch zur Verbesserung der Datenlage von 316L dar, einem häufig als Konstruktionswerkstoff in verschiedenen Hochtemperaturbauteilen verwendeten Werkstoff. Die Arbeit legt den Fokus auf die mittels Laser-Pulverbettschmelzen hergestellte Werkstoffvariante, PBF-LB/M/316L. Eine konventionell hergestellte Variante, HR/316L, wurde auch untersucht. Bei PBF-LB/M/316L wurde zusätzlich der Effekt ausgewählter Wärmebehandlungen ausgewertet. Die Untersuchung umfasste die Charakterisierung der mechanischen Eigenschaften und der Verformungs- und Schädigungsmechanismen bei erhöhten Prüftemperaturen bei LCF und Kriechen, wo die Daten und Wissenslage am spärlichsten ist. Außerdem hat die untersuchte PBF-LB/M/316L-Wersktoffvariante einen geringen Porositätsgrad. Somit hat diese Arbeit die Mikrostruktur stärker in den Fokus genommen als die meisten bisher in der Literatur verfügbaren Studien.
Die mechanische Prüfkampagne umfasste Zugversuche zwischen Raumtemperatur und 650 °C, LCF-Versuche zwischen Raumtemperatur und 600 °C sowie Kriechversuche bei 600 °C und 650 °C. In Ermangelung konkreter Richtlinien und Normen wurde die Charakterisierung zumeist anhand der bestehenden internationalen Prüfnormen und Probengeometrien durchgeführt. Aus jedem dieser Prüfverfahren wurden die entsprechenden Festigkeits- und Verformungskennwerte ermittelt. Darüber hinaus wurde mit Hilfe gezielter mikrostruktureller Untersuchungen ein Beitrag zum Verständnis des Zusammenhangs zwischen der Mikrostruktur und den mechanischen Eigenschaften in Bezug auf die Verformungs- und Schädigungsmechanismen geleistet.
Die Dehngrenze von PBF-LB/M/316L ist etwa doppelt so hoch wie die von HR/316L und dieser Trend setzt sich mit ansteigender Prüftemperatur fort. Die Bruchdehnung ist bei allen Prüftemperaturen geringer. PBF-LB/M/316L weist über den größten Teil der Ermüdungslebensdauer vor allem bei Raumtemperatur höhere zyklische Spannungen als HR/316L auf. Ausschließlich bei den kleinsten Dehnungs-schwingbreiten sind die Ermüdungslebensdauer ausgeprägt kürzer. Das Wechselverformungsverhalten von PBF-LB/M/316L ist durch eine Anfangsverfestigung gefolgt von einer kontinuierlichen Entfestigung charakterisiert, welche bis zum Auftreten der zum Versagen führenden Entfestigung stattfindet. Die Kriechbruchzeiten und die Dauer jeder Kriechphase sind bei allen Kombinationen von Prüfparametern bei PBF-LB/M/316 kürzer als bei HR/316L. Die Spannungsabhängigkeit von PBF-LB/M/316L ist im Vergleich zu HR/316L geringer und die Duktilität beim Kriechen kleiner. Die minimale Kriechrate wird bei allen geprüften Parameterkombinationen bei deutlich geringeren Kriechdehnungen erreicht. Eine Wärmebehandlung bei 450 °C / 4 h bewirkt keine wesentliche Änderungen der Mikrostruktur und Zugversuchseigenschaften. Eine zusätzliche Wärmebehandlung bei 900 °C / 1 h verursacht eine Abnahme der Dehngrenze des PBF-LB/M/316L. Diese blieb aber immer noch um den Faktor 1,5x höher als bei HR/316L. Die Verformungsmerkmale wurden kaum davon beeinflusst. Bezüglich des Kriechverhaltens hat die Wärmebehandlung bei 900 °C / 1 h längere sekundäre und tertiäre Kriechstadien bewirkt und die Kriechdehnung hat sich signifikant erhöht. Die Bruchbilder unterscheiden sich generell nicht nur aber vor allem mit ansteigender Prüftemperatur, bei der bei PBF-LB/M/316L oft interkristalline Rissbildung beobachtet wurde. Die Zellstruktur trägt als der Hauptfaktor zu den unterschiedlichen mechanischen Eigenschaften im Vergleich zur HR/316L-Variante bei. Darüber hinaus spielen mutmaßlich die Kornmorphologie, die Stapelfehlerenergie und der Stickstoffgehalt eine Rolle.
Additive manufacturing (AM) offers significantly greater freedom of design compared to conventional manufacturing processes since the final parts are built layer by layer. This enables metal AM, also known as metal 3D printing, to be utilized for improving efficiency and functionality, for the production of parts with very complex geometries, and rapid prototyping. However, despite many technological advancements made in recent years, several challenges hinder the mass adoption of metal AM. One of these challenges is mechanical anisotropy which describes the dependency of material properties on the material orientation. Therefore, in this work, stainless steel 316L parts produced by laser-based powder bed fusion are used to isolate and understand the root cause of anisotropy in AM parts. Furthermore, an efficient and accurate multiscale numerical framework is presented for predicting the deformation behavior of actual AM parts on the macroscale undergoing large plastic deformations. Finally, a novel constitutive model for the plastic spin is formulated to capture the influence of the microstructure evolution on the material behavior on the macroscale.
The contamination of drinking water with pharmaceuticals represents a severe health risk. In order to monitor the drinking water quality continuously and enable quick countermeasures in case of contamination, novel sensors are required. Here, immunoanalytical methods based on the binding of the analyte to highly selective antibodies can be helpful. In this work, magnetic bead-based immunoassays (MBBAs) have been developed for the detection of two relevant contaminants of drinking water: diclofenac (DCF) and amoxicillin (AMX). In case of the latter, not only the parent drug is of interest in the risk assessment but also its hydrolysis products (HPs). In a comprehensive study, the influence of external factors and intrinsic properties of the water on the rate of hydrolysis was investigated. As the hydrolysis of AMX further impacts the recognition by the antibody, a strategy to analyze samples with unknown hydrolysis degree of AMX was established employing the enzyme β-lactamase in sample preparation. For both analytes, the MBBAs enable the fast quantification with results obtained in less than one hour which represents a major improvement over conventional immunoassays like the enzyme-linked immunosorbent assay (ELISA). Compared to the respective ELISAs with the same antibodies, the MBBAs further exhibit improved analytical parameters such as a broader measurement range and lower limits of detection. Due to the magnetic properties of the beads that serve as a platform for the assays, they are suitable for the mobile and automated detection at the point-of-care. An integrated diagnostic system was designed in which electrochemical detection with chronoamperometry on a microfluidic chip allows for further miniaturization of the system to enable monitoring of the drinking water quality online in water supply pipes at waterworks.
Development of electrochemical antibody-based and enzymatic assays for mycotoxin analysis in food
(2023)
Electrochemical methods are promising to meet the demand for easy-to-use devices monitoring key parameters in the food industry. Many companies run own lab procedures for mycotoxin analysis, but it is a major goal to simplify the analysis. The enzyme-linked immunosorbent assay using horseradish peroxidase as enzymatic label, together with 3,3',5,5' tetramethylbenzidine (TMB)/H2O2 as substrates allows sensitive mycotoxin detection with optical detection methods. For the miniaturization of the detection step, an electrochemical system for mycotoxin analysis was developed. To this end, the electrochemical detection of TMB was studied by cyclic voltammetry on different screen-printed electrodes (carbon and gold) and at different pH values (pH 1 and pH 4). A stable electrode reaction, which is the basis for the further construction of the electrochemical detection system, could be achieved at pH 1 on gold electrodes. An amperometric detection method for oxidized TMB, using a custom-made flow cell for screen-printed electrodes, was established and applied for a competitive magnetic bead-based immunoassay for the mycotoxin ochratoxin A. A limit of detection of 150 pM (60 ng/L) could be obtained and the results were verified with optical detection. The applicability of the magnetic bead-based immunoassay was tested in spiked beer using a handheld potentiostat connected via Bluetooth to a smartphone for amperometric detection allowing to quantify ochratoxin A down to 1.2 nM (0.5 µg/L). Based on the developed electrochemical detection system for TMB, the applicability of the approach was demonstrated with a magnetic bead-based immunoassay for the ergot alkaloid, ergometrine. Under optimized assay conditions a limit of detection of 3 nM (1 µg/L) was achieved and in spiked rye flour samples ergometrine levels in a range from 25 to 250 µg/kg could be quantified. All results were verified with optical detection. The developed electrochemical detection method for TMB gives great promise for the detection of TMB in many other HRP-based assays. A new sensing approach, based on an enzymatic electrochemical detection system for the mycotoxin fumonisin B1 was established using an Aspergillus niger fumonisin amine oxidase (AnFAO). AnFAO was produced recombinantly in E. coli as maltose-binding protein fusion protein and catalyzes the oxidative deamination of fumonisins, producing hydrogen peroxide. It was found that AnFAO has a high storage and temperature stability. The enzyme was coupled covalently to magnetic particles, and the enzymatically produced H2O2 in the reaction with fumonisin B1 was detected amperometrically in a flow injection system using Prussian blue/carbon electrodes and the custom-made wall-jet flow cell. Fumonisin B1 could be quantified down to 1.5 µM (≈ 1 mg/L). The developed system represents a new approach to detect mycotoxins using enzymes and electrochemical methods.
Concrete is the most important human-made material because it serves as the basis of our built environment. Since the properties of concretes are dominated by their key compound, cement, devising a way to determine the cement’s origin, known as provenancing, is of great importance for answering different provenance-related questions. These questions range from liability issues when damage occurs to concrete-made structures, to forensic investigations where cement particles are found at crime scenes. This thesis showcases the use of isotope techniques to answer these provenance-related questions. Conventional 87Sr/86Sr and 143Nd/144Nd isotope and elemental ratios consisting of Ca, Sr, K, Mn, Mg, and Ti are used as fingerprints for ordinary Portland cement (OPC) provenancing. The first part of this thesis describes research previously conducted in fingerprinting cementitious materials, providing an overview of provenance studies of cement and the main approaches commonly used. In several studies, the origin of clinker for certain locations was determined via different approaches. However, clinker is an intermediate product, which is available only at the production site and therefore, the practical relevance is rather limited. Furthermore, the use of Sr and Nd isotope systems, together with elemental fingerprints are presented as state of the art in the field. Therein, the principal approach for the overall study is sketched. For the second part of the study, a sample preparation technique for Sr isotopes in Portland cement was developed. The aim was to find the most appropriate sample preparation procedure for cement provenancing and selection was realised by comparing the 87Sr/86Sr isotope ratios of differently treated OPCs with those of the corresponding clinkers. Based on these findings, the third part of the study focused on the measurements of Sr and Nd isotope ratios, together with elemental ratios, to establish a reliable technique for OPC provenancing. The outcomes of this final stage are then used to establish a procedure for fingerprinting cements. This becomes possible with the use of Sr and Nd isotope ratios and geochemical profiles. To perform isotope ratio measurements and obtain reliable data, it was necessary to establish a quality control procedure. Thus, an interlaboratory comparison (ILC) was organised to characterise 87Sr/86Sr isotope ratios in geological and industrial reference materials by applying the conventional method for 87Sr/86Sr isotope ratios. As reference material, four cements (VDZ 100a, VDZ 200a, VDZ 300a, IAG OPC-1), one limestone (IAG/CGL ML-3) and one slate (IAG OU-6) were selected, thus covering a wide range of Sr isotope signatures.