Die 100 zuletzt veröffentlichten Dokumente
Vor dem Hintergrund des Klimawandels und der steigenden Bevölkerungsdichte werden Themen wie Nachhaltigkeit und Ernährungssicherheit immer zentraler. Das führt zur erhöhten Bedeutung einer verlässlichen Prozesskontrolle, um Ausschuss aufgrund nicht eingehaltener Spezifikationen oder Vorgaben des Gesetzgebers zu vermeiden. Gerade für kleine und mittelständische Unternehmen ist das von größter Bedeutung, da der dadurch zusätzlich entstehende finanzielle Schaden aufgrund einer sowieso schwierigen wettbewerblichen Situation nicht toleriert werden kann. In dieser Arbeit wurde ein kostengünstiges Mikrocontroller-basiertes portables Photometer entwickelt, das zur Prozesskontrolle in der lebensmittelverarbeitenden Industrie, hier am Beispiel der Weinindustrie, geeignet ist. Messprotokolle für drei Parameter, die Weinfarbe im CIE L*a*b*-Farbraum, das Oxidationspotenzial in Form der Eisenkonzentration und die Kristallstabilität in Form der Calcium- und Kaliumkonzentration wurden erfolgreich in das portable Analysesystem integriert. Die Entwicklungen und Ergebnisse dieser Arbeit unterstreichen die Einsatzfähigkeit des portablen Photometers für aufwändige Messroutinen und in komplexen Matrizes. Das Messgerät bietet damit eine vielversprechende Perspektive für die Implementierung kostengünstiger und dennoch präziser Prozesskontrolle in der Weinindustrie und darüber hinaus.
Normalkraft- und Knicklängenbestimmung von Druckstäben über die Ermittlung von modalen Parametern
(2024)
Das Bauwesen trägt erheblich zu den weltweiten Emissionen von Treibhausgasen bei und steht in einer führenden Rolle, einen geeigneten Beitrag zum Klimaschutz zu leisten. Dazu gehört nicht nur die energetische Sanierung vorhandener Bausubstanz, sondern ebenso die Entwicklung qualifizierter Bewertungs- und Analyseverfahren existierender Tragstrukturen. Diese Arbeit stellt ein dynamisches Verfahren zur Systemidentifikation vor, das Aussagen über die während der Messung vorhandenen Normalkräfte und Lagerungsbedingungen von Druckstäben ermöglicht. Grundlage des Verfahrens ist ein durch vier unabhängige Dreh- und Wegfedern gelagerter Euler-Bernoulli-Balken mit Normalkraftbeanspruchung. Auf Basis einer experimentellen Ermittlung der ersten Eigenkreisfrequenz und Eigenform definiert das vorgestellte Verfahren die Normalkraft und Federsteifigkeiten, welche fortan für einen experimentellen Stabilitätsnachweis herangezogen werden können. Für die Definition der Systemeigenschaften optimiert ein Partikelschwarmalgorithmus die gesuchten Parameter des Grundstabs so lange bis eine bestmögliche Übereinstimmung zwischen den messtechnisch ermittelten und theoretisch errechneten modalen Eigenschaften besteht. Das vorgestellte dynamische Verfahren zur Systemidentifikation wurde anhand von 20 Prüfkörpern der Systemlängen zwischen 2,3975m und 2,545m untersucht. Die Proben wurden senkrecht in einen vorhandenen Prüfrahmen eingebaut. Die untersuchten Prüfkörper bestanden aus fünf unterschiedlichen Stahlprofilen in Kombination mit vier verschiedenen oberen Anschlusstypen. Die Lasteinleitung erfolgte über eine vertikal verschiebliche Führung unterhalb des gelenkig angeschlossenen Prüfkörpers. Für den oberen Anschluss standen ebenfalls ein Gelenkanschluss sowie drei Anschlussprofile unterschiedlicher Biegesteifigkeiten zur Verfügung. Die Untersuchung umfasste über alle Druckstäbe hinweg 117 Belastungsversuche mit Normalkräften zwischen 8,36kN und 178,29kN. Dabei wurden für die Modalanalyse und anschließende Systemidentifikation je nach Anschlusstyp zwölf oder dreizehn gleichmäßig über den Prüfkörper verteilte Messstellen herangezogen. Die Ergebnisse des Identifikationsverfahrens ergeben für die optimierte Druckkraft bei 59 Untersuchungen, also etwa der Hälfte aller Proben, eine Abweichung von unter 10% gegenüber dem mit einer Kraftmessdose ermittelten Vergleichswert.
38 Versuche zeigen Abweichungen von weniger als 5,0%, wobei die geringste Differenz aller Versuche einen Wert von 0,1% demonstriert. Je näher die tatsächliche Last an der Eulerschen Knicklast des Prüfkörpers liegt, desto niedriger werden die messbaren Differenzen. Für Prüfkörper mit einer in den Laborversuchen besonders starken Auslastung der Eulerschen Knicklast zwischen 40% und 45% können die Abweichungen auf eine mittlere Differenz von 5,4% bei einer Standardabweichung von 2,9% reduziert werden. Für die Auswertung der Lagerungsbedingungen wurden die optimierten Federsteifigkeiten in dimensionslose Knicklängenbeiwerte überführt und mithilfe eines statischen Vergleichsverfahrens auf Basis einer experimentellen Verformungsfigur validiert. Grundlage der Auswertung sind die optimierten Drehfedersteifigkeiten des in dieser Arbeit planmäßig variierten oberen Profilanschlusses, wobei auf den Auswertungen der Prüfkörper mit einem Gelenkanschluss am oberen Ende verzichtet wird. Die statistische Auswertung, zusammenfassend je Prüfkörper, ergibt für den Knicklängenbeiwert der dynamischen Untersuchung eine durchschnittliche Abweichung von minimal 0,06% und maximal 5,09% gegenüber dem Wert der statischen Vergleichsuntersuchung. Über alle 15 Druckstäbe hinweg kann eine mittlere Abweichung von 1,56% und dazu korrespondierende Veränderung der Eulerschen Knicklast von -3,05% bis +3,19% ermittelt werden. Abschließend wurden mit dem dynamischen Verfahren fünf ca. 2,20m lange Stützen auf dem Betriebsgelände eines Industrieunternehmens untersucht. Die Stützen sind Elemente einhüftiger Rahmen und dienen zur Abstützung eines Lüftungsrohrs und dem dazugehörigen Laufsteg. Sie werden in der statischen Berechnung als beidseitig gelenkig gelagerte Pendelstäbe idealisiert und besitzen aufgrund vorhandener Einspannungen Lastreserven unklarer Größe. Durch die Anwendung des dynamischen Verfahrens zur Systemidentifikation und dem Ansatz von Drehfedersteifigkeiten konnte die ursprüngliche Grenzlast über alle Stützen hinweg um mindestens 7,1% gesteigert werden.
Die Masterarbeit untersucht die politische Kommunikation und mediale Berichterstattung in Zeiten der Klimakrise am Beispiel der Änderung des Gebäudeenergiegesetzes (GEG). Unter Anwendung einer Framing-Analyse werden die Frames in der politischen Kommunikation und Berichterstattung identifiziert und verglichen, um deren Einfluss auf die Meinungsbildung zu untersuchen. Die Ergebnisse zeigen eine deutliche Diskrepanz zwischen politischer Kommunikation und medialer Berichterstattung sowie eine Tendenz zur Polarisierung und Vereinfachung komplexer Themen. Die Arbeit regt dazu an, eine ausgewogene und neutrale Berichterstattung zu fördern, um eine fundierte Meinungsbildung zu ermöglichen und den Diskurs über wichtige gesellschaftliche Themen zu unterstützen. Die Studie liefert wichtige Erkenntnisse für Politik, Medien und die Öffentlichkeit im Umgang mit der Klimakrise und zeigt die Bedeutung einer transparenten und verständlichen Kommunikation auf.
Gebäude tragen aktuell in Deutschland zu rd. 30 % der Treibhausgasemissionen bei, die reduziert werden sollen. Um dies zu erreichen, werden aktuell unterschiedlichste Ansätze diskutiert, die von der Reduktion der Wärmebedarfe über einen höheren Anteil an Erneuerbaren Energien am Wärmebedarf reichen. Für letzteres müssen das Angebot an Erneuerbaren Energien und der Wärmebedarf durch Speicherung ausgeglichen werden. Neben Pufferspeichern kann auch die Masse des Gebäudes zur Wärmespeicherung genutzt werden. Bei einem hydraulischen System eine thermische Aktivierung – wasserführende Rohre im Bauteil - mit dem Heizsystem verbunden. Da das Bauteil neben den passiv energetischen, statischen und konstruktiven Funktionen auch die aktiven energetischen Funktionen Wärmespeicherung- und -übertragung übernimmt, werden diese als multifunktionale Bauteile (MFB) bezeichnet. Um mit Hilfe der MFB die Treibhausgasemissionen von Gebäuden zu reduzieren, muss deren Temperatur- und Leistungsverlauf in Folge einer Beladung bekannt sein. Im Rahmen dieser Arbeit wird am Beispiel eines repräsentativen Einfamilienhauses mit MFB und Solarthermie gezeigt, dass durch die Ausbildung von Außenwänden als multifunktionale Bauteile die Treibhausgasemissionen im Betrieb von 56 auf 32 t-CO2-Äq., also um 40 %, reduziert werden können. Diese Einsparung ist vorrangig auf die Steigerung des Anteils solarer Wärme am Wärmebedarf auf Grund der MFB zurückzuführen. Wird der gesamte Lebenszyklus des Gebäudes betrachtet, sinken die Emissionen von 86,2 auf 63 t-CO2-Äq., was einer Einsparung von 27 % entspricht. Diesen Einsparungen resultieren in höheren Lebenszykluskosten, welche von 521.000 auf 525.000 €, also um weniger als 1 %, steigen. Bei der Untersuchung von Schichtaufbau, Größe und Orientierung der multifunktionalen Bauteile als Außenwände konnte gezeigt werden, dass die gängigen Aufbauten, Kernaktivierung einer 20 cm dicken Tragschale und Dämmung mit UAW = 0,28 W/(m².K), zu den geringsten Bedarfen an elektrischer Energie führen. Bei der Lage der Aktivierung sollten Außenwände von Räumen ausgewählt werden, die keine nach Süden oder Westen orientierten Fenster aufweisen. Die intendierte zeitversetzte Wärmeabgabe der multifunktionalen Bauteile deckt dann am besten die Heizlast, die im Tagesgang primär durch die Orientierung der Fenster des jeweiligen Raumes beeinflusst wird.Um die multifunktionalen Bauteile mit thermischer Aktivierung in die Baupraxis zu ermöglichen, schließt die Arbeit mit einem Vorschlag zu deren Berücksichtigung in der DIN V 18599.
Der Umgang mit Studienabbruch ist für Hochschulen ein relevantes Thema geworden. Die Frage nach den Ursachen des Studienabbruchs ist Anlass und Ausgangspunkt zur Beschäftigung mit studienbezogener Zeit, welche seit der Bologna-Reform eng mit dem Begriff Workload konnotiert ist. Die Planungskomponente von Workload wird vom Leistungspunktesystem ECTS als organisatorischer Kern der Bologna-Reform getragen und ist eng mit der Studienstruktur, dem Studierverhalten und der Studierbarkeit von Studiengängen verbunden. Studierbarkeit ist dabei u. a. durch die zeitliche Passung der Erfüllung von Anforderungen charakterisiert und formal als Qualitätskriterium von Studiengängen zu verstehen und in Verfahren der Studiengangakkreditierung nachzuweisen. Eine Herausforderung dabei ist die Erfassung des tatsächlichen studentischen Workloads im Vergleich zu den institutionell geplanten zeitlichen Anforderungen eines Studiengangs, denn hierzu bedarf es geeigneter empirischer Verfahren der Workloaderhebung. Ziel der Arbeit ist es, der institutionellen Planungskomponente von Workload die individuelle Entwicklungsperspektive beizulegen und zugleich Chancen und Möglichkeiten der Workloaderfassung zu betrachten. Neben der Darlegung des aktuellen Workload-Forschungsstands werden Determinanten des Workloads abgeleitet und das eigens entwickelte Verfahren „Workloadkurve“ eingeführt, mit dem der Workloadbetrachtung ein ressourcensensibles Erhebungsinstrumente mit individuellen Entwicklungspotenzialen zur Verfügung gestellt wird. Chancen und Möglichkeiten der Workloaderfassung auf individueller Ebene lassen sich z. B. im Feedback zum eigenen Studierhandeln, der Anregung zur Selbstreflexion, aber auch in der Studien- und Lernberatung realisieren. Auf institutioneller Ebene kann die Studiengangentwicklung, die Qualitätssicherung und besonders die Lehrorganisation profitieren, sodass mit der Workloadbetrachtung ein Mehrwert auf unterschiedlichen Ebenen für Studium und Lehre generiert wird.
This thesis addresses several challenges associated with introducing autonomous auxiliary vehicles, e.g., drones or robots, into a logistics system from the perspective of Operations Research. To this end, optimization models are formalized that enable the assessment of potential benefits of integrating such vehicles into last-mile delivery. As the resulting models are computationally challenging, the thesis continuously refines the formulations and develops appropriate algorithms that are capable of producing high-quality solutions with reasonable computational effort. This facilitates effective problem-solving and aids in shaping the design of future delivery fleets, laying the groundwork for future decision support systems. In Operations Research, Mixed-Integer Programming solvers play a pivotal role. As is evident by this thesis, this concerns solving Mixed-Integer Linear Programming formulations directly or integrating parts of them in matheuristic frameworks. This raises the fundamental question if the performance of such solvers can be enhanced in any meaningful way, by adjusting their default algorithmic behavior on a per-instance basis. We trace the roots of this problem to the Algorithm Selection Problem and develop a novel methodology that leverages Machine Learning to formalize a prescriptive optimization problem. By using a tailored Branch & Bound approach, this methodology enables us to effectively compute the (predictably) optimal configuration of a Mixed-Integer Programming solver on a per-instance basis with minimal computational overhead. The potential impact extends beyond specific problem domains, fostering a more comprehensive and synergistic approach to decision-making and optimization.
The primary focus of this work was on exploring the utility of VR and continuous response tracking in psychological experiments. Continuous tracking elucidates the fine-grained dynamics of decision-making. Distributional methods, such as Survival analysis (SA) and my newly developed method, Spatiotemporal Survival Analysis (StSA) served as the primary tool to analyze these responses. Studying the time-course of behavior in classical paradigms can deepen our insight into the cognitive processes, such as working memory and response conflict. This methodology not only sheds new light on classical paradigms but also establishes a groundwork for future research aiming to unravel the complexities of cognitive processes in experimental contexts.
This work also sets out to demonstrate how it is possible to preserve the legacy of prior well established experimental paradigms in VR. In a series of experiments, VR was used to replicate findings in tasks related to visual perception (chapter 4) and working memory (chapters 5 and 6). These experiments demonstrate that, not only can classical results be replicated in VR, but that this technology enables a more fine-grained understanding of human behavior, relying on continuous tracking of response behavior (demonstrated by chapter 5). Finally, this work concludes with remarks on the future of experiments in VR and the utility of Survival Analysis using continuous movement trajectory data.
Mycotoxins are secondary toxic metabolites synthesized by several species of filamentous fungi. Occurrence of hazardous mycotoxins has been studied along the whole food production chain, i.e. in crops and in foods for consumption. In order to protect consumers against an exposure, strategies aimed to reduce and mitigate the occurrence of mycotoxins at pre- and post-harvest stages have been implemented. Furthermore, maximum limits for mycotoxins in major food/feed commodities are set in legislation, and health-based guidance values are derived by scientific advisory committees as basis for assessing risks. Although these strategies and regular monitoring allow for a significant reduction of risks from exposure to mycotoxins, humans continue to be exposed to mycotoxins, in some circumstances at levels exceeding the current health-based guidance values. Therefore, it can be hypothesized that stages in the production of crops and consumer choices of foods are contributors to mycotoxin exposure, but presently not considered. The work presented in this habilitation developed and evaluated new monitoring strategies to investigate this hypothesis.
Soil is the basis for the cultivation and production of crops, but has not been evaluated as source of mycotoxins until now. This is relevant, considering that the soil is the habitat for the inoculum of several mycotoxigenic fungal species and that mycotoxins are ubiquitous in the environment including soil. Next, mycotoxins can be mobilized from soil to plant, which may increase the risk for a contamination of harvested commodities. Evaluation of the soil as a source of mycotoxins should also consider the role of managements and treatments in modern agriculture and how these affect soil physicochemical or biological properties as well as the occurrence and fate of mycotoxins in soils. In addition, some mycotoxins have antimicrobial properties and may thus influence the soil microbiome with the consequence of changes in soil biogeochemical processes and functions.
Current strategies for mycotoxin exposure prevention are restricted to the food production chain, namely from cropping/harvest until retail level. But, food commodities are stored in the households with the possibility that mycotoxins can form by late fungal infection, with a risk for exposure. In this regard, human exposure to mycotoxins is determined by the individual food habits, preferences and lifestyle. Therefore, it is important to identify major sources of mycotoxin exposure in different population groups, and also how the exposure is driven by food preferences and lifestyle, in particular at the household level.
The overall aim of this habilitation is to extend the knowledge on mycotoxins as environmental pollutants by evaluating steps beyond the food production chain that may contribute to mycotoxin-related risks for humans and for the environment. Concretely, this means to conduct monitoring of soils as a source of mycotoxins, and to assess also how alimentary habits and lifestyle may impact on exposure at the consumer level. This entails the design of an integrated monitoring strategy concept which includes unexplored sources and risks for mycotoxin exposure. This habilitation covers 23 published papers and is divided into three main chapters:
(i) Plastic mulching and soil quality indices (chapter 2): In this chapter the impact of mulching systems, namely straw and plastic, on soil physical, chemical and biological properties as well as biogeochemical processes were analysed using the example of asparagus and strawberry crops. The starting point was a literature review on the benefits and potential risks related to the use of plastic mulching in agriculture [chapter 2.1]. This was followed up by field monitoring experiments with a focus on the effects of plastic mulching on soil (micro)organisms [chapter 2.2 and 2.3] and on modifications of soil biogeochemical processes in short- and long-term application [chapter 2.4 and 2.5]. Due to the increasing awareness of the use of plastics in the environment, plastic mulching was also investigated for its contribution to soil plastic pollution [chapter 2.6 - 2.8].
(ii) Occurrence and fate of mycotoxins in agricultural soils (chapter 3): Mycotoxins do occur in soil, but their biosynthesis in situ as well as their persistence are influenced by soil biogeochemical processes related to the structure and function of the soil microbiome. The occurrence and fate of mycotoxins was investigated starting with the development of sensitive methods for the analysis of mycotoxins in soils [chapter 3.1], considering that levels in soils may be of factor hundred lower than concentrations observed in food commodities. Then, suitable sampling strategies were developed to account for the heterogeneous distribution of mycotoxins in soils [chapter 3.2]. Sampling and analytical methods were applied to investigate the occurrence of mycotoxins in soils, exemplified by studies on the use of plastic mulching in agriculture [chapter 3.3 and 3.4]. Since mycotoxin levels in soils reflect only concentrations measured at the time of sampling, without considering spatio-temporal dynamics, a further focus of our studies was to evaluate the biosynthesis and stability (fate) of the mycotoxins in the soil matrix depending on the integrity of the soil microbiome [chapter 3.5 - 3.8].
(iii) Human exposure and biomonitoring (chapter 4): Here, it was evaluated how alimentary habits and lifestyle may contribute to the risk of mycotoxin exposure. Firstly, (bio-) monitoring strategies which include the identification and characterization of suitable biomarkers in biological matrices that are representative of exposure were investigated [chapter 4.1 - 4.4], considering also food intake differences between infants and adults. In the context of sensitive population-groups also an in silico approach was used to model their mycotoxin exposure [chapter 4.5]. Finally, the risk of mycotoxin exposure was evaluated based on alimentary habits and contaminant levels in food commodities, and for lifestyle aspects and awareness on risks from mouldy food [chapter 4.6 and 4.7].
The results of this habilitation provide new insights on so far unexplored sources for mycotoxins with relevance for humans and for the environment. This includes the development and application of suitable sampling and (bio-)monitoring strategies to assess (i) mycotoxin occurrence in agricultural soils and (ii) exposure at the consumer level. This work shows that soil is a source of mycotoxins and that agricultural practices influence the integrity of the soil and consequently in situ mycotoxin concentrations. Then alimentary habits, lifestyle and knowledge on mycotoxins are decisive factors for exposure at the household level. Both aspects are not yet considered in current risk assessment strategies. Therefore, an integrated interdisciplinary model for mycotoxin prevention strategies starting in soil and including also the consumer level is suggested.
Das Ziel der vorliegenden Forschungsarbeit besteht darin, einen Beitrag zur erfolgreichen Gestaltung auf Künstlicher Intelligenz (KI) basierender Services in Produktionsumgebungen zu leisten, der über eine rein technisch-getriebene Entwicklungsperspektive hinausgeht. Dafür wird eine ganzheitliche Betrachtungsperspektive entlang der Ebenen Mensch, Technik und Organisation eingenommen. In einer ersten Analyse wurden Herausforderungen und Erfolgsfaktoren im Zusammenhang mit der Entwicklung, Einführung und dem Betrieb von industriellen KI-basierten Services auf allen Ebenen eines sozio-technischen Systems identifiziert. In einem zweiten Schritt wurden Möglichkeiten zur Stärkung ausgewählter Erfolgsfaktoren oder Lösung spezifischer Herausforderungen definiert, die sowohl menschenzentrierte als auch organisatorische Bereiche betreffen. In anwendungsnahen Forschungsprojekten wurden unter Berücksichtigung der Erfahrungen von Expertinnen und Experten für industrielle KI-Anwendungen zwei Lösungsbereiche ermittelt, die zu einer Optimierung im industriellen Umfeld führen können. Zum einen wurde der Bedarf eines Rollenmodells zur Entwicklung interner KI-basierter Services identifiziert, zum anderen wurde erkannt, dass Ansätze aus dem Bereich Human-Centered Artificial Intelligence (HCAI) ein hohes Potenzial haben, zentrale Herausforderungen der KI-Entwicklung und KI Nutzung im industriellen Kontext zu überwinden. Insbesondere die Anwendung von HCAI Design Prinzipien wird als wertvoll für die industrielle Praxis angesehen. Deutlich wurde aber auch, dass es im breiten Forschungsfeld HCAI einer Kontextualisierung bestehender Ansätze bedarf und eine an die produktionsspezifischen Rahmenbedingungen angepasste Konzeption von Methoden notwendig ist. Auf dieser Erkenntnis aufbauend wurden zwei Modelle konzipiert, die als methodische Unterstützung für primär technisch versierte Entwicklerinnen und Entwickler KI-basierter Services in der Produktion dienen. Dies ist zum einen das „Generische Rollenmodell zur systematischen Entwicklung interner KI basierter Services in der Produktion“ und zum anderen das „Vorgehensmodell zur Nutzung von Design Prinzipien in der ko kreativen Gestaltung menschenzentrierter KI-basierter Services“. Durch die Anwendung der Modelle können zentrale Herausforderungen der KI Entwicklung überwunden und ausgewählte Erfolgsfaktoren gestärkt werden. Das Rollenmodell beschreibt entlang der Entwicklungsphasen eines KI-basierten Services idealtypisch, welche Rollen an der Entwicklung beteiligt werden sollen, welche zentralen Aufgaben die einzelnen Rollen übernehmen und wie intensiv diese in den Entwicklungsprozess eingebunden werden sollen. Das Vorgehensmodell fokussiert die menschenzentrierte Entwicklung KI-basierter Services, indem es durch einen ko-kreativen Ansatz die Anwendung von Design-Prinzipien bei der Gestaltung industrieller KI-basierter Services unterstützt. Beide Modelle fördern die stärkere Einbindung verschiedener Mitarbeitenden, insbesondere auch von Endanwenderinnen und Endanwendern, in den Entwicklungsprozess. Insgesamt trägt die Arbeit dazu bei, industrielle KI basierte Services aus einer ganzheitlichen, menschenzentrierten Perspektive zu betrachten und durch die Anwendung der Modelle die Akzeptanz von KI-basierten Services zu stärken und die Vertrauenswürdigkeit zu erhöhen.
In der vorliegenden Studie wurde ein Verfahren zur Analyse naturwissenschaftlicher Beschreibungen entwickelt und anhand der Beschreibungen von (N = 28) Physiklehramtsstudierenden erprobt.
Im Rahmen der Arbeit wurden Merkmale naturwissenschaftlicher Beschreibungen identifiziert, die bedeutsam für erfolgreiche Erkenntnis- und Problemlöseprozesse sind. Zu den Merkmalen zählen die mittlere Anzahl an Kernaussagen, die Komplexität, der Theoretische Bezug, die Spezifität und die Linearisierung. Zur Untersuchung dieser Merkmale wurde gemäß der qualitativen strukturierenden Inhaltsanalyse nach Mayring (2022) Kategoriensysteme entwickelt. Für die Analyse der identifizierten Merkmale wurden entsprechend der qualitativen strukturierenden Inhaltsanalyse nach Mayring (2022) Kategoriensysteme erstellt. Diese Systeme ermöglichten eine gezielte quantitative Analyse der Beschreibungen von Physiklehramtsstudierenden verschiedener Expertise-Niveaus (u.a. deklarative Modellkompetenz), um Unterschiede in den Beschreibungsmerkmalen herauszuarbeiten. Die Ergebnisse zeigen, dass die Beschreibungen der Studierenden zwar einen hohen theoretischen Bezug aufweisen, sich jedoch in der Anzahl modell-spezifischer Zusammenhänge unterscheiden. Studierende mit einer hohen deklarativen Modellkompetenz formulieren mehr modell-spezifische Zusammenhänge. Dies deckt sich mit Befunden anderer Studien, in denen beobachtet werden konnte, dass Lernende vorwiegend auf einer Oberflächenstruktur beschreiben, wohingegen Expert:innen auf einer Tiefenstruktur beschreiben (Heller & Reif, 1984; Larkin et al., 1980). Ferner deuten die Ergebnisse darauf hin, dass die Transparenz einen positiven Einfluss auf die Formulierung modellspezifischer Zusammenhänge hat.
Diese Masterarbeit analysiert den Einfluss der Organisationskultur auf die Einführung von Agroforstwirtschaftssystemen, als Maßnahme des regenerativen Wirtschaftens, in mittelfränkischen landwirtschaftlichen Betrieben. Trotz vorhandener langfristiger ökolo- gischer und sozialer Perspektiven dominieren kurzfristige ökonomische Gewinne in der Umsetzung. Allerdings wird deutlich, dass Organisationskulturelle Aspekte wie die Grundannahmen über das Wirtschaften, die Natur, den Klimawandel, die Zeit, das Ver- antwortungsgefühl und Selbstverständnis einen wesentlichen Einfluss auf den Hand- lungsdruck zur Implementierung der Agroforstwirtschaftssysteme haben. Hindernisse wie mangelnde Rechtssicherheit, fehlende Honorierung und Skepsis stehen der Imple- mentierung im Weg. Die Arbeit identifiziert verschiedene Ansatzpunkte zur Förderung der Implementierung. Zentral sind dabei die bäuerlichen Werte und Verhaltensweisen, welche in der Organisationskultur der Betriebe verankert sind. Die Ergebnisse haben nicht nur praktische Auswirkungen auf die Landwirtschaft, sondern bieten auch wichtige Erkenntnisse für Organisationen, die regeneratives Wirtschaften etablieren möchten. Die Organisationskultur als zentraler Einflussfaktor, wird dabei eng mit gesellschaftlichen und politischen Denk- und Handlungsweisen verknüpft.
Der Klimawandel ist in vollem Gang und entwickelt sich als zu einer der größten Bedrohungen für die Menschheit. Auch die Landwirtschaft und mit ihr der Weinbau wird dabei vor große Herausforderungen gestellt. Zunehmende Strahlungsintensitäten, Temperaturen und Trockenheit beeinflussen die Zusammensetzung der Trauben und die sensorischen Eigenschaften der Weine. In den frühen 90er Jahren wurde die untypische Alterungsnote (UTA) durch Fehlaromen wie Naphthalin, Bohnerwachs, nasse Wolle, Fuselalkohole oder Akazienblüten charakterisiert. Obwohl 2-Aminoacetophenon (2-AAP) als Marker für die UTA postuliert wurde, ist es lediglich für den "Akazienblüten"-Duft, der in einigen Weinen auftritt, verantwortlich. Die molekulare Basis der anderen sensorischen Aspekte der stressbedingten Fehlaromen blieb jedoch bislang unbekannt.
Um den Grundlagen der UTA zu hinterfragen, wurden in Abschnitt 6.1. und 6.2. akzeptierte und aufgrund von UTA abgelehnte Weine aus der Pfalz gesammelt und sowohl gaschromatographisch als auch sensorisch analysiert. Die Identifikation der Aromastoffe, die zur Differenzierung der Weine beitragen können, erfolgte durch eine gaschromatographische Analyse, die mit Massenspektrometrie gekoppelt war. Zusätzlich zur Aufnahme der Massenspektren und der Messung von Referenzsubstanzen wurde ein GC-Olfaktometrie-System eingesetzt, um die Geruchseindrücke der Aromastoffe zu bestimmen. Am Ende konnten sechs Aromastoffe identifiziert werden, die das durch den Klimawandel negativ beeinflusste Aroma in den Weinen rekonstruieren. Es wurde zum ersten Mal belegt, dass die untypische Alterungsnote, die für eine Beanstandung in der Qualitätsweinprüfung sorgt, nicht nur auf einen Aromastoff oder eine Stoffgruppe zurückzuführen ist. Vielmehr ist es ein Zusammenspiel sowohl aus der erhöhten Konzentration negativwirkender Aromastoffe wie höherer Alkohole und in manchen Fällen 2-AAP als auch dem Fehlen positiver Aromastoffe wie Ethylester.
Im Zuge des Klimawandels treten immer häufiger Sonnenbrandschäden an Weißweintrauben auf, die sowohl zu sensorischen Veränderungen des Weinaromas als auch zu Ertragsverlusten führen können. Um die genauen Auswirkungen der Sonnenbrandstärke auf die Weinqualität zu ermitteln, wurde in Abschnitt 6.3. mit Hilfe eines mobilen Geräts Sonnenbrand im Weinberg erzeugt und das Aroma der resultierenden Weine bewertet. Die Ergebnisse deuten darauf hin, dass leichte Sonnenbrandschäden die Aromaeigenschaften von Weinen verbessern können, indem sie die Bildung von blumigen Terpenen fördern. Hingegen können stärkere Schäden in Form von Verbräunungen zu einer negativen Auswirkung auf das Aroma führen, da sie die Bildung von maskierenden höheren Alkoholen begünstigen. Zudem kann Sonnenbrand zu schweren Ertragseinbußen führen, wenn es zu Sonnenbrandnekrosen oder Botrytis cinerea-Infektionen durch die geschädigte Beerenhaut kommt.
Der letzte Teil der Arbeit umfasste, die in den Abschnitten 6.4., 7.1. und 7.2. diskutierte sensorische und aromachemische Bewertung von möglichen Bekämpfungsstrategien von Sonnenbrand an Trauben im Weinbau und im Keller. Entblätterungsmaßnahmen mit und ohne Kombination mit der Applikation von reflektierenden Schutzpartikeln auf die Traubenzone und Beschattungsnetze zählten zu den weinbaulichen Bekämpfungsmaßnahmen, während im Wein die Anwendung von Schönungsmitteln wie PVPP und Erbsenproteinpräparaten untersucht wurde. Über drei Jahrgänge hinweg lässt sich die Tendenz feststellen, dass eine frühe Entblätterung in Kombination mit der Applikation von reflektierenden Partikeln, insbesondere Fruchtkalk, die am besten bewerteten sensorischen Eigenschaften in den Weinen hervorbringt. Eine frühe Entblätterung der Traubenzone kann zum richtigen Zeitpunkt für genug Sonneneinstrahlung sorgen, um die Bildung positiver Aromastoffe wie Terpene und Ester zu fördern. Außerdem ermöglicht sie eine optimale Anpassung der Rebe an die klimatischen Bedingungen und sorgt für eine verbesserte Luftzirkulation im Bereich der Trauben, um ihre Gesundheit zu gewährleisten. Bei Hitzewellen kann die durch die Entblätterung ungehinderte Sonneneinstrahlung jedoch zu Schäden auf der Traubenhaut führen, weshalb eine künstliche Schattierung oder die Anwendung von lichtreflektierenden Partikeln sinnvoll ist. Die Applikation der Partikel ist dabei leichter zu handhaben, flexibler und kostengünstiger als die Installation von teuren Beschattungsnetzen, die jedoch einen vergleichbaren Effekt erzielen.
Somit wurde durch diese Arbeit nicht nur ein vielfältiger Handlungsrahmen für den Weinbau entwickelt, der geeignet ist, den Anforderungen des sich verschärfenden Klimawandels zu begegnen, sondern auch die molekulare Basis der sensorischen Aspekte der stressbedingten Fehlaromen aufgeklärt.
Nuclear magnetic resonance (NMR) spectroscopy is an excellent tool for reaction and
process monitoring. Process monitoring is often carried out online on flowing samples. Benchtop NMR spectrometers are especially well-suited for these applications because they can be installed close to the studied process. However, it is a challenge to analyze a fast-flowing liquid with NMR spectroscopy because short residence times in the magnetic field of the spectrometer result in inefficient polarization build-up and thus poor signal intensity. This is particularly problematic for benchtop NMR spectrometers because of
their compact design. Therefore, different methods to counteract this prepolarization problem in benchtop NMR spectroscopy were studied experimentally in the present work. Established approaches that were studied gave only poor results at high flow velocities. To overcome this, signal enhancement by Overhauser DNP (ODNP) was used, which is based on polarization transfer from unpaired electron spins to nuclear spins and happens on very short time scales, resulting in high signal enhancements, also in fast-flowing liquids. A corresponding set-up was developed and used for the studies: the line leading to the 1 Tesla benchtop NMR spectrometer first passes a fixed bed of a radical matrix which is placed in a Halbach magnet equipped with a microwave cavity to facilitate the polarization transfer. With this ODNP set-up, excellent results were obtained also for the highest studied flow velocities. This shows that ODNP is an enabler for fast-flow benchtop NMR spectroscopy.
ODNP requires the presence of unpaired electrons in the sample which is usually accomplished by addition of stable radicals. However, radicals affect the nuclear relaxation times and can hamper the NMR detection. This was circumvented by immobilizing radicals in a fixed bed, allowing for the measurement of radical-free samples when using ex situ DNP techniques (DNP build-up and NMR detection happen at different places) with flow-induced separation of the hyperpolarized liquid from the radicals. Therefore, the synthesis of robust and chemically inert immobilized radical matrices is mandatory. This was accomplished by immobilizing the radical glycidyloxy-tetramethylpiperidinyloxyl (GT) with a polyethyleneimine (PEI) linker on the surface of controlled porous glasses (CPG). Both the porosity of the CPGs and also the size of the PEI-linker were varied resulting in a set of distinct radical matrices for continuous-flow ODNP. The study shows that CPGs with PEI linkers provide robust, inert, and efficient ODNP matrices.
Another method to address the prepolarization problem in continuous-flow NMR applications is paramagnetic relaxation enhancement (PRE) by using a T1 relaxation agent. In the present work, a PRE agent was developed that was again based on PEI-grafted CPGs with PEI-linker and GT. Here, the interaction of the studied liquid with this PRE agent significantly accelerates the buildup of nuclear polarization prior to NMR detection, which enables quantitative measurements in continuous-flow benchtop NMR applications. The results show that the flow regime for quantitative measurements can be greatly extended by the use of the synthesized PRE agent.
Pentaisopropylcyclopentadienyl-Komplexe von Pnictogenen, Eisen und Cobalt - Synthese und Reaktivität
(2024)
Diese Dissertation besteht aus zwei Teilen. Der erste Teil handelt über die Synthese neuartiger Pentaisopropylcyclopentadienyl-Komplexe mit Pnictogenen. Die Komplexe der Art [5CpPnCl2] (Pn = P, As, Sb, Bi) wurden in ausgezeichneten Ausbeuten isoliert. Bei der Untersuchung dieser Verbindungen mittels NMR-Spektroskopie wurden sigmatrope Umlagerungen festgestellt. Daraufhin wurden die
Komplexe zusätzlich anhand der Festkörper-NMR-Spektroskopie sowie bei verschiedenen
Temperaturen untersucht. Die Struktur wurde mit Hilfe der Röntgenstrukturanalyse bestimmt und mit DFT-Rechnungen belegt, außerdem wurden die sigmatropen Umlagerungen theoretisch berechnet. Des Weiteren wurden [4CpPCl2] und [Cp´´´AsBr2] synthetisiert und auf ihre Reaktivität untersucht. Dabei wurden unteranderem die Diphophene [5Cp2P2], [4Cp2P2] und ein Disilberkomplex [4Cp2P2Ag2(Lsm)][B12Br12] erhalten. Anhand von [Cp´´´AsX2] (X = F, Cl, Br, I) wurde mittels DFT-Rechnungen der Einfluss des Halogenids auf die Haptizität untersucht.
Der zweite Teil behandelt die Synthese von Eisen- und Cobaltverbindungen mit den sperrigen 5Cp-Liganden. Zunächst wurden Verbindungen [5CpM(acac)], [5CpMX]2 und [5CpMN(TMS)2] (M = Fe, Co; X = Cl, Br, I) hergestellt. Ausgehen von diesen wurden neuartige N-heterocyclische Carbenkomplexe der Art [5CpMX(NHC)] synthetisiert. Die Struktur der NHC-Komplexe sowie der Acetylacetonatkomplexe wurde mittels DFT-Berechnungen ermittelt und mit den Strukturparametern aus den XRD-Messungen verglichen. Zusätzlich dazu wurde der elektronische Zustand dieser Komplexe ermittelt, in Falle aller Cobaltverbindungen ist es der low-spin-Zustand und im Falle der Eisenverbindungen des Typs [5CpFe(acac)] ist es der high-spin-Zustand. Bei den [5CpMX(NHC)] ist es der Triplett-Zustand (M3).
Die regelmäßige Anwesenheit in der Schule ist entscheidend für den schulischen Erfolg und die soziale Integration der Schülerinnen und Schüler. Diese Arbeit untersucht das Problem gravierender Fehlzeiten, die zu schulischen Misserfolgen und abgebrochenen Bildungswegen führen können. Solche Fehlzeiten erschweren den Eintritt ins Erwerbsleben und erhöhen den Bedarf an staatlichen Transferleistungen. Zudem erhöhen sie das Risiko für psychische und physische Erkrankungen sowie die Neigung zur Kriminalität. Diese Arbeit beleuchtet, inwiefern Organisationentwicklung (OE) zur Reduktion von Schulabsentismus an der Konrad-Adenauer-Schule, einer berufsbildenden Schule in Kriftel, Hessen, beitragen kann. Die Schule hat seit der Corona-Pandemie steigende Absentismuszahlen verzeichnet und bereits Maßnahmen wie ein konsequentes Fehlzeitenmanagement eingeführt. Durch den mäeutischen Ansatz der OE und unter Einbeziehung von Konzepten wie der Neuen Autorität von Haim Omer wird ein Ansatz zur Reduktion von Absentismus entwickelt. Die Arbeit untersucht, wie unter Einbeziehung der Schulbelegschaft Maßnahmen erarbeitet werden können, die Schulkarrieren fördern und im besten Fall zum Abschluss bringen.
Regular school attendance is crucial for academic success and social integration of students. This thesis examines the issue of significant absenteeism leading to academic failure and school dropouts. Such absenteeism hampers entry into the workforce and increases reliance on state welfare. It also raises the risk of mental and physical illnesses and a tendency towards criminal behavior. This work explores how organizational development (OD) can contribute to reducing absenteeism at the Konrad-Adenauer School, a vocational school in Kriftel, Hesse. The school has seen a rise in absenteeism since the COVID-19 pandemic and has implemented measures such as strict absence management. Using the maieutic approach of OD and incorporating concepts like Haim Omer's New Authority, a strategy to reduce absenteeism is developed. The study investigates how measures can be created with the involvement of school staff to support and ideally complete educational careers.
Im Bauwesen sind in vielen Bereichen Nachweise erforderlich, um die Leistungen von Bauteilen, Systemen oder des Gebäudes zu bescheinigen. Brandschutznachweise können dabei in zwei unterschiedlichen Bereichen angefertigt werden. So können Brandrisiken, -gefahren oder -verläufe Bestandteil solcher Nachweise sein, aber auch Personenströme oder die allgemeine Erfüllung der Schutzziele durch die vorhandenen oder vorgesehenen Maßnahmen. Damit die Nachweisverfahren ein größtmögliches Maß an Genauigkeit bieten, müssen diese die Abläufe von Bränden und deren Wirkung auf die Bauteile und Baustoffe so genau wie möglich berücksichtigen. Jedes Nachweisverfahren ist daher mit den neuen Erkenntnissen über Brandverläufe und Temperaturentwicklungen zu validieren. Die Art der Nachweisführung ist dabei ebenso vielfältig wie der Gegenstand, für den diese erfolgt.
Die aktuellen Nachweismöglichkeiten für raumabschließende Holztafelbauteile anhand additive Berechnungsverfahren, wie sie in der DIN EN 1995-1-2:2010 aufgeführt sind, schließen, wie auch die Muster-Richtlinie über brandschutztechnische Anforderungen an Bauteile und Außenwandbekleidungen in Holzbauweise, eine Ausführung von Holztafelbauteilen in Gebäudeklasse 5 Objekten nicht mit ein. Daher sind aktualisierte Nachweismethoden erforderlich, die die Feuerwiderstandsdauer eines Holzrahmenbauteils mit großer Genauigkeit bis zu einer Feuerwiderstandsdauer von min. 90 Minuten aufzeigen können. Hierfür wurde im Rahmen dieser Arbeit das Nachweisverfahren der schichtweisen Bauteilsimulation entwickelt. Dieses beschreibt FEM-basierte, thermisch-transiente Simulationen, die über die grafische Benutzeroberfläche des Simulationsprogrammes ausgeführt werden können. Dabei werden die erforderlichen Schutz- und Isolationszeiten jeder Bauteilschicht einzeln ermittelt und anschließend unter Berücksichtigung einer Vorerwärmung durch vorangegangene Schichten aufaddiert. Validiert wurde das Verfahren anhand durchgeführter Brandversuche. Die Genauigkeiten des neuen Simulationsverfahren übertreffen dabei die der untersuchten Berechnungsverfahren deutlich. Zur sicheren Anwendung wird am Ende dieser Arbeit ein Leitfaden zur Durchführung der schichtweisen Bauteilsimulation aufgeführt.
Riparian areas are an important transition zone in freshwater systems, connecting and regulating both aquatic and terrestrial systems. They are characterized by a high diversity and are important for conservation. However, riparian areas are frequently under stress from human activities. Two of these stressors are agricultural activity and introduction of invasive plant species. One example of the impact of agriculture is pollution with heavy metals such as copper. Copper is commonly used as a fungicide in agriculture and can be introduced into riparian areas via flooding events via streams in areas previously unaffected by pollution. There, copper is toxic to animals, plants and microorganisms at high concentrations, damaging DNA, enzymes, cell membranes and chloroplasts. This leads to a reduction in growth and reproduction of the affected organisms, potentially disrupting the ecosystems. Invasive alien plants are another major cause of biodiversity loss in animals, plants and microorganisms. This can negatively affect entire ecosystems above as well as belowground, leading to alterations of resources and ecosystem functions. Especially soil fungi are important for ecosystem functions. For example by forming symbiotic interactions with plants, which can be disrupted by plant invasion and copper pollution. Two common invasive plant species in riparian areas are Fallopia japonica and Impatiens glandulifera. They frequently invade stands of the native Urtica dioica. The aim of this project was to investigate the impact of these two plant invaders, especially of F. japonica, on native soil communities further modified by copper pollution. This was done in two parts: a field study, investigating the impact of the invasive plants on soil properties, invertebrates, fungi and activity and a mesocosm experiment under the influence of copper pollution, comparing the impact of copper on plants, soil invertebrates, microorganisms and activity depending on the presence of a native or invasive plant species. Under field conditions, plant invasion mainly reduced the diversity of fungi directly associated with the plants but not the biomass of fungi. Direct impacts on soil invertebrates were also observed. In the mesocosms, microbial biomass was reduced under the invasive plant and no impact on invertebrates was observed. Similarly, the soil activity was not affected in the field but was strongly reduced by the presence of F. japonica in the mesocosms. These results align with the enemy release hypothesis, indicating that these invasive species, especially F. japonica, may be less associated with fungal parasites in the invasive range, allowing them to perform better than native species. These findings also indicate that these invaders have various and contrasting impacts on belowground systems, making their effects highly context-dependent and site-specific. Copper pollution inhibited growth in both F. japonica and U. dioica. Urtica dioica seemed to be more sensitive to copper pollution compared to the invasive plant. In the soil, copper pollution further amplified the reduction of soil activity by the invasive plant and had variable effects on invertebrates and microbial biomass. This indicates that F. japonica may gain an advantage against the commonly occurring U. dioica, especially in polluted areas. The negative impact of copper pollution on soil functions could therefore be amplified by facilitating invasion by F. japonica, which also negatively impacts soil functions. Therefore, disturbances by agricultural activity, one major source of copper pollution, could have an even stronger impact across much wider distances and in previously undisturbed areas.
Product manufacturing is performed in a massively automated and increasingly customized manner.
However, overall production speed is limited by automation of inspection since each product has to ensure the required quality.
A widespread and often-used quality assurance method is visual surface inspection.
Automated surface inspection relies on an inspection plan and defect recognition algorithms.
Both inspection planning and defect recognition algorithms development heavily rely on the availability of representative image data containing various product surface textures and imperfections showing a wide variety of possible surface responses to different viewing and lighting conditions.
Due to the advancements in manufacturing, defects in products occur rarely, with different frequencies of appearance, followed by a subjective and laborious annotation process.
Further, since the surface texture is often not relevant to product performance and thus not controlled, products with different surface textures are not treated as different product samples and thus not provided.
Motivated by aforementioned problems, this work introduces the following contributions: (1) image synthesis requirements for industrial quality inspection and a novel realistic image synthesis pipeline satisfying those requirements (Chapter 4), (2) texture synthesis requirements for industrial quality inspection and a procedural approach to parameterized surface texture modeling incorporating domain knowledge (Chapter 5) and (3) defect synthesis requirements for industrial quality inspection as well as a procedural approach to parameterized defect modeling (Chapter 6).
The contributions presented in this thesis, make it possible to obtain, in a controllable and automated manner, the required amount of image data, containing realistic and varying surface textures resembling machining surfaces as well as diversified geometrical defects with automated, pixel-precise annotations (Chapters 7,8).
The presented contributions enable the inspection planning and development of machine vision algorithms for defect recognition to be performed completely virtually, by inspection planning experts, without computer graphics knowledge.
Machine learning and artificial intelligence are pivotal pillars in the area of
computer vision, especially object detection and classification. They support
or replace conventional methods such as morphological operators or manual
surveillance. These models, tailored and trained for various use cases, typically possess a vast number of trainable parameters to cover a wide range of scenarios.
However, their sizes have reached a point where classical computers struggle
to train them efficiently, both in terms of time and computational resources.
Moreover, the data itself is becoming increasingly detailed and thus larger. In
our case, we are dealing with 2D or 3D image data, specifically gray value
images.
One promising avenue to mitigate computational demands is quantum computing.
With properties like superposition, entanglement, and other quantum
mechanical properties, there exists a theoretical advantage over classical methods.
In this doctoral thesis, we aim to investigate the practical utility of quantum
hardware in several application scenarios.
The first part of our study focuses on encoding classical image data into
quantum states. To design quantum algorithms, we must first transform image
information, represented as gray values, into quantum states. This step is
crucial and a main part for the development of quantum algorithms. Image
information is converted into quantum states through methods like basis encoding,
amplitude encoding, or phase encoding. We contribute to this field by
enhancing a phase encoding method called Flexible Representation of Quantum
Images (FRQI). This contribution is included in our two papers [1, 2] and in
Chapter 4 in this thesis. Our approach reduces the number of so called CXoperations
and consequently the errors observed on current quantum hardware.
We also evaluate the scalability in terms of feasibility and usability on existing
hardware.
We adapted our research for the following parts of the thesis based on the
results of the first part. We can not encode and retrieve large images on current
quantum devices. Either we simulate the quantum hardware as in the second
part of this thesis, reduce the image size, or use hybrid approaches as in the
other parts of this thesis.
In the second part, we concentrate on amplitude encoding, with Quantum
Probability Image Encoding (QPIE), and apply the Quantum Fourier Transform
(QFT) to the quantum states. We can detect the orientation of objects in images
with this approach by using additional post-processing methods. We compare
the results of the QFT with those of the Fast Fourier Transform (FFT) and
demonstrate that, at least on the simulator, we get the same results as with the
classical method (see Chapter 5).
The third part of the study is about edge detection of objects in gray value
images. We use the idea of a quantum artificial neuron as the core building block
of our algorithm (see [3] and Chapter 6). In this part, our primary focus is on
the algorithm’s robustness in the face of current hardware limitations. To tailor
it further to the current hardware, we developed six variations of the algorithm
with the aim of reducing the number of quantum circuits. We compare the
results of the six variations. Our adaption of the algorithm allows to examine
image sizes that were previously unattainable by quantum algorithms on existing
quantum hardware.
In the fourth part, we focus on hybrid algorithms in the form of quantum
transfer learning. Drawing from the experiences of the first part regarding the
practical usability of current hardware, quantum transfer learning offers a way
to circumvent these limitations by keeping some parts of the algorithm classical
while executing other parts on quantum hardware. Our algorithm demonstrates
its utility in detecting small cracks with a thickness of approximately one or
two pixels in concrete samples (see [4] and Chapter 7). We highlight differences
between simulators and current quantum computers and demonstrate the capability
to detect the cracks in the images with the current quantum hardware.
Tropical dry forests are crucial for climate adaptation, economic development, and poverty alleviation, offering vital ecosystem services. However, this understudied, and inadequately protected biome faces severe threats like deforestation and land-use changes and is often overlooked in national policies. This neglect poses risks to services like clean water provision, diverse habitats, and climate change mitigation. Changes in land use within these forests impact environmental conditions, causing reduced biodiversity and vegetation restructuring. The regeneration process relies on abiotic factors and natural soil recovery. In this dissertation, I investigated the role of two keystone organism groups—Biological soil crusts ('biocrusts') and leaf-cutting ants (LCA)—in dry forest regeneration. These ecosystem engineers can enhance topsoil quality, introduce essential nutrients and water, and influence plant germination and growth, thereby potentially affecting dry forest regeneration. My primary objectives were to determine the relevance of biocrusts in the Caatinga dry forest, their interaction with LCA, as well as both of their provision of essential ecosystem services, and their response to chronic anthropogenic disturbance. I employed various techniques to document biocrust diversity, and distribution, along with the abiotic environment alterations caused by biocrusts and LCA.
Biocrusts, diverse components in the Caatinga dry forest, were present in various successional stages, including agricultural fields, regenerating areas, and old-growth forests. Dominated by cyanobacteria, their coverage depended on factors like leaf-litter burial, disturbance levels, soil stability, seasonality, and the presence/ activity of LCA nests. A balance between vascular plant cover and disturbance pressure was also crucial for biocrust distribution. Both biocrusts and LCA impacted key abiotic factors for dry forest resilience but with significantly differing ecological consequences and reactions to anthropogenic disturbances. Biocrusts, by reducing water infiltration, promoted runoff, fostering small-scale source-sink patterns, benefiting vascular vegetation. They enhanced soil fertility and provided erosion protection, with older biocrusts exhibiting more significant positive effects. Anthropogenic disturbance disrupted biocrust succession, limiting their services and leading to negative feedback loops. LCA nests increased compaction, and reduced water infiltration, potentially hindering forest regeneration. These physico-hydrological barriers persisted, especially in disturbed areas, impacting forest dynamics and resilience for years, even after colony death. Adverse effects of LCA on water availability and soil resistance escalated with anthropogenic disturbance, though LCA refuse had the potential to mitigate some negative soil property changes.
Both biocrusts and LCA act as edaphic ecosystem engineers in the Caatinga dry forest, impacting vascular plants through their abiotic influence. A greenhouse experiment demonstrated the positive effects of both organisms on plant germination, development, and survival across various functional groups. This dissertation also showed for the first time that LCA can accelerate germination time. These facilitative effects are attributed to improved soil conditions, including enhanced water availability and nutrient richness. Given species-specific responses and the prevalence of LCA nests and biocrust coverage in regenerating areas, their activities likely play a pivotal role in shaping successional trajectories and regeneration dynamics in dry forests. This underscores the significant potential of both ecosystem engineers in influencing the regeneration and resilience of tropical dry forests.
In summary, in the human-modified landscapes of the Caatinga, biocrusts and LCA act as ecosystem engineers, influencing vital soil properties. Biocrusts protect degraded soils and facilitate plant establishment, while the impact of LCA depends on the nest structure. These engineers play a crucial role in dry forest regeneration and sustainability. However, climate change and land degradation pose significant threats to both ecosystems and engineers, impacting their effects diametrically. This research enhances understanding of the biome's functioning, regeneration, and resilience, providing insights for sustainable management, restoration, and conservation to support biodiversity and human well-being.
Das Fachgebiet Stadtsoziologie der RPTU Kaiserslautern-Landau hat im Jahr 2022 eine teilstandardisierte Befragung der 50- bis 75-jährigen Einwohner:innen von sieben Modellkommunen durchgeführt. Urbane, suburbane und ländliche Kom-munen aus drei Bundesländern wurden ausgewählt. Dieser „Steckbrief“ für die Verbandsgemeinde Kusel-Altenglan beinhaltet die Ergebnisse für die zentralen so-ziodemografischen, sozialstrukturellen und wohnungsbezogenen Merkmale der Babyboomer (53- bis 67-jährigen).
Die Ergebnisse bilden einen kleinen Ausschnitt der Befragung zum Wohnen, der Wohnumgebung, der Freizeitgestaltung und digitaler Affinität der älteren Men-schen und vor allem der Babyboomer-Kohorte in den Kommunen. Insgesamt wur-den über 5.000 Menschen befragt. Eingebettet ist die Umfrage in das Projekt „Ageing Smart – Räume intelligent gestalten“, das die geburtenstarken Jahrgänge 1955 bis 1969 ("Babyboomer") adressiert. Mit dem sukzessiven Übergang der Babyboomer in den Ruhestand sind die Gesellschaft und insbesondere die Kommunen gefordert, ange-messene Angebote zum Wohnen und für Betätigungsmöglichkeiten zu entwickeln.
Das Projekt wird durch die Carl-Zeiss-Stiftung sowie von der RPTU Kaiserslautern-Landau von 04/2021 bis 03/2026 gefördert. Zehn Fachgebiete der RPTU Kaiserslautern-Landau führen das Projekt gemeinsam mit dem Fraunhofer IESE und dem Deutschen For-schungszentrum für Künstliche Intelligenz (DFKI) durch.
Das Fachgebiet Stadtsoziologie der RPTU Kaiserslautern-Landau hat im Jahr 2022 eine teilstandardisierte Befragung der 50- bis 75-jährigen Einwohner:innen von sieben Modellkommunen durchgeführt. Urbane, suburbane und ländliche Kom-munen aus drei Bundesländern wurden ausgewählt. Dieser „Steckbrief“ für die Verbandsgemeinde Nieder-Olm beinhaltet die Ergebnisse für die zentralen sozio-demografischen, sozialstrukturellen und wohnungsbezogenen Merkmale der Baby-boomer (53- bis 67-jährigen).
Die Ergebnisse bilden einen kleinen Ausschnitt der Befragung zum Wohnen, der Wohnumgebung, der Freizeitgestaltung und digitaler Affinität der älteren Men-schen und vor allem der Babyboomer-Kohorte in den Kommunen. Insgesamt wur-den über 5.000 Menschen befragt. Eingebettet ist die Umfrage in das Projekt „Ageing Smart – Räume intelligent gestalten“, das die geburtenstarken Jahrgänge 1955 bis 1969 ("Babyboomer") adressiert. Mit dem sukzessiven Übergang der Babyboomer in den Ruhestand sind die Gesellschaft und insbesondere die Kommunen gefordert, ange-messene Angebote zum Wohnen und für Betätigungsmöglichkeiten zu entwickeln.
Das Projekt wird durch die Carl-Zeiss-Stiftung sowie von der RPTU Kaiserslautern-Landau von 04/2021 bis 03/2026 gefördert. Zehn Fachgebiete der RPTU Kaiserslautern-Landau führen das Projekt gemeinsam mit dem Fraunhofer IESE und dem Deutschen For-schungszentrum für Künstliche Intelligenz (DFKI) durch.
Babyboomer in Mannheim - Soziodemografische, sozialstrukturelle und wohnungsbezogene Merkmale
(2024)
Das Fachgebiet Stadtsoziologie der RPTU Kaiserslautern-Landau hat im Jahr 2022 eine teilstandardisierte Befragung der 50- bis 75-jährigen Einwohner:innen von sieben Modellkommunen durchgeführt. Urbane, suburbane und ländliche Kom-munen aus drei Bundesländern wurden ausgewählt. Dieser „Steckbrief“ für die Stadt Mannheim beinhaltet die Ergebnisse für die zentralen soziodemografischen, sozialstrukturellen und wohnungsbezogenen Merkmale der Babyboomer (53- bis 67-jährigen).
Die Ergebnisse bilden einen kleinen Ausschnitt der Befragung zum Wohnen, der Wohnumgebung, der Freizeitgestaltung und digitaler Affinität der älteren Men-schen und vor allem der Babyboomer-Kohorte in den Kommunen. Insgesamt wur-den über 5.000 Menschen befragt. Eingebettet ist die Umfrage in das Projekt „Ageing Smart – Räume intelligent gestalten“, das die geburtenstarken Jahrgänge 1955 bis 1969 ("Babyboomer") adressiert. Mit dem sukzessiven Übergang der Babyboomer in den Ruhestand sind die Gesellschaft und insbesondere die Kommunen gefordert, ange-messene Angebote zum Wohnen und für Betätigungsmöglichkeiten zu entwickeln.
Das Projekt wird durch die Carl-Zeiss-Stiftung sowie von der RPTU Kaiserslautern-Landau von 04/2021 bis 03/2026 gefördert. Zehn Fachgebiete der RPTU Kaiserslautern-Landau führen das Projekt gemeinsam mit dem Fraunhofer IESE und dem Deutschen Forschungszentrum für Künstliche Intelligenz (DFKI) durch.
Babyboomer in Kaiserslautern - Soziodemografische, sozialstrukturelle und wohnungsbezogene Merkmale
(2024)
Das Fachgebiet Stadtsoziologie der RPTU Kaiserslautern-Landau hat im Jahr 2022 eine teilstandardisierte Befragung der 50- bis 75-jährigen Einwohner:innen von sieben Modellkommunen durchgeführt. Urbane, suburbane und ländliche Kom-munen aus drei Bundesländern wurden ausgewählt. Dieser „Steckbrief“ für die Stadt Kaiserslautern beinhaltet die Ergebnisse für die zentralen soziodemografi-schen, sozialstrukturellen und wohnungsbezogenen Merkmale der Babyboomer (53- bis 67-jährigen).
Die Ergebnisse bilden einen kleinen Ausschnitt der Befragung zum Wohnen, der Wohnumgebung, der Freizeitgestaltung und digitaler Affinität der älteren Men-schen und vor allem der Babyboomer-Kohorte in den Kommunen. Insgesamt wur-den über 5.000 Menschen befragt. Eingebettet ist die Umfrage in das Projekt „Ageing Smart – Räume intelligent gestalten“, das die geburtenstarken Jahrgänge 1955 bis 1969 ("Babyboomer") adressiert. Mit dem sukzessiven Übergang der Babyboomer in den Ruhestand sind die Gesellschaft und insbesondere die Kommunen gefordert, ange-messene Angebote zum Wohnen und für Betätigungsmöglichkeiten zu entwickeln.
Das Projekt wird durch die Carl-Zeiss-Stiftung sowie von der RPTU Kaiserslautern-Landau von 04/2021 bis 03/2026 gefördert. Zehn Fachgebiete der RPTU Kaiserslautern-Landau führen das Projekt gemeinsam mit dem Fraunhofer IESE und dem Deutschen Forschungszentrum für Künstliche Intelligenz (DFKI) durch.
Babyboomer im Geisaer Land - Soziodemografische, sozialstrukturelle und wohnungsbezogene Merkmale
(2024)
Das Fachgebiet Stadtsoziologie der RPTU Kaiserslautern-Landau hat im Jahr 2022 eine teilstandardisierte Befragung der 50- bis 75-jährigen Einwohner:innen von sieben Modellkommunen durchgeführt. Urbane, suburbane und ländliche Kommunen aus drei Bundesländern wurden ausgewählt. Dieser „Steckbrief“ für das Geisaer Land beinhaltet die Ergebnisse für die zentralen soziodemografischen, sozialstrukturellen und wohnungsbezogenen Merkmale der Babyboomer (53- bis 67-jährigen).
Die Ergebnisse bilden einen kleinen Ausschnitt der Befragung zum Wohnen, der Wohnumgebung, der Freizeitgestaltung und digitaler Affinität der älteren Menschen und vor allem der Babyboomer-Kohorte in den Kommunen. Insgesamt wurden über 5.000 Menschen befragt. Eingebettet ist die Umfrage in das Projekt „Ageing Smart – Räume intelligent gestalten“, das die geburtenstarken Jahrgänge 1955 bis 1969 ("Babyboomer") adressiert. Mit dem sukzessiven Übergang der Babyboomer in den Ruhestand sind die Gesellschaft und insbesondere die Kommunen gefordert, angemessene Angebote zum Wohnen und für Betätigungsmöglichkeiten zu entwickeln.
Das Projekt wird durch die Carl-Zeiss-Stiftung sowie von der RPTU Kaiserslautern-Landau von 04/2021 bis 03/2026 gefördert. Zehn Fachgebiete der RPTU Kaiserslautern-Landau führen das Projekt gemeinsam mit dem Fraunhofer IESE und dem Deutschen Forschungszentrum für Künstliche Intelligenz (DFKI) durch.
Babyboomer in Remshalden - Soziodemografische, sozialstrukturelle und wohnungsbezogene Merkmale
(2024)
Das Fachgebiet Stadtsoziologie der RPTU Kaiserslautern-Landau hat im Jahr 2022 eine teilstandardisierte Befragung der 50- bis 75-jährigen Einwohner:innen von sieben Modellkommunen durchgeführt. Urbane, suburbane und ländliche Kom-munen aus drei Bundesländern wurden ausgewählt. Dieser „Steckbrief“ für Rems-halden beinhaltet die Ergebnisse für die zentralen soziodemografischen, sozial-strukturellen und wohnungsbezogenen Merkmale der Babyboomer (53- bis 67-jährigen).
Die Ergebnisse bilden einen kleinen Ausschnitt der Befragung zum Wohnen, der Wohnumgebung, der Freizeitgestaltung und digitaler Affinität der älteren Men-schen und vor allem der Babyboomer-Kohorte in den Kommunen. Insgesamt wur-den über 5.000 Menschen befragt. Eingebettet ist die Umfrage in das Projekt „Ageing Smart – Räume intelligent gestalten“, das die geburtenstarken Jahrgänge 1955 bis 1969 ("Babyboomer") adressiert. Mit dem sukzessiven Übergang der Babyboomer in den Ruhestand sind die Gesellschaft und insbesondere die Kommunen gefordert, ange-messene Angebote zum Wohnen und für Betätigungsmöglichkeiten zu entwickeln.
Das Projekt wird durch die Carl-Zeiss-Stiftung sowie von der RPTU Kaiserslautern-Landau von 04/2021 bis 03/2026 gefördert. Zehn Fachgebiete der RPTU Kaiserslautern-Landau führen das Projekt gemeinsam mit dem Fraunhofer IESE und dem Deutschen For-schungszentrum für Künstliche Intelligenz (DFKI) durch.
Reaktive Strömungen sind ein wichtiger Bestandteil vieler umwelttechnischer und industrieller Prozesse und ein Forschungsgegenstand in vielen Bereichen. Ein Beispiel eines solchen Prozesses ist die Reinigung von Abgasen eines Verbrennungsmotors in der Automobilindustrie. Hierzu werden Katalysatoren und poröse Filter benutzt. In allen Forschungsbereichen wird mathematische Modellierung und Simulation eingesetzt, die es ermöglicht, die Effizienz des zu entwickelnden Prozesses oder Produkts zu steigern und Daten zu erhalten, die für theoretische oder experimentelle Forschungsmethoden unzugänglich sind. Numerische Algorithmen zur Simulation reaktiver Strömungen werden seit Jahrzehnten entwickelt und haben in vielen Bereichen ihre Leistungsfähigkeit bei der Lösung angewandter Industrie- und Umweltprobleme bewiesen. Die Klasse der reaktiven Strömungen und insbesondere die der reaktiven Strömungen auf der Porenskala ist aber sehr reichhaltig, und es gibt keinen allgemeinen Algorithmus, der für alle Strömungen dieser Art effizient ist. Eine Anpassung der Algorithmen für bestimmte Klassen von Problemen ist erforderlich. In dieser Arbeit liegt der Schwerpunkt auf der Entwicklung effizienter Algorithmen zur porenskaligen Simulation von Prozessen in katalytischen Filtern. Ein besonderes Merkmal dieser Filter ist, dass das Filtermaterial ein inertes, undurchlässiges Grundgerüst und nanoporöse aktive (Washcoat) Partikel enthält, in denen die Reaktionen stattfinden. Der Stofftransport findet innerhalb der Poren statt und in den Washcoat-Partikeln kann der Transport durch Konvektion (oft vernachlässigt) und Diffusion beschrieben werden. Die mathematischen Modelle basieren auf einer Konvektions-Diffusions-Reaktions-Gleichung oder Systemen solcher Gleichungen. Zu den größten Herausforderungen bei der Lösung solcher Probleme gehören die Nichtlinearitäten der reaktiven Terme und die Heterogenität des Strömungsfeldes, die durch die Heterogenität der porösen Medien verursacht wird. Letzteres bedeutet, dass in ein und derselben Materialprobe schnelle und langsame Zonen koexistieren, was bedeutet, dass sich die Art der maßgeblichen Gleichungen lokal ändert. Letzteres impliziert, dass nicht einfach Algorithmen für parabolische oder hyperbolische Probleme ausgewählt werden können. Die Algorithmen sollten für jede Art von Strömung robust sein oder sich an die Änderung der Art der Gleichungen anpassen können. Darüber hinaus kann die Eigenschaft ausgenutzt werden, dass der Washcoat (in dem die Reaktionen stattfinden und den Algorithmen eine wesentliche Änderung auferlegen) nur einen begrenzten Teil des Rechengebiets einnimmt. All dies motiviert dazu, die Klasse der Splitting-Verfahren erneut zu untersuchen, an die betrachtete Klasse von Problemen anzupassen und ihre Stabilität und Leistung numerisch zu untersuchen. Dies ist das Hauptthema der Dissertation. Die Steigerung der Rechenleistung und sich ändernde Rechnerarchitekturen erfordern eine Überarbeitung der bisherigen Softwareimplementierung und der bisher verwendeten Datenstrukturen. Ein weiteres Ziel dieser Arbeit ist daher die Entwicklung von Softwarelösungen, die die Simulation reaktiver Strömungen für hochdimensionale Probleme ermöglichen. Zur reaktiven Strömungssimulation auf der Porenskala wurden verschiedene Methoden verwendet. Die Arbeit konzentrierte sich auf zwei allgemeine Methodenklassen: Splitting-Algorithmen und implizit-explizite Schemata. Zum Vergleich werden vollständig implizite Algorithmen verwendet. Eine Reihe von Benchmark-Geometrien und chemischen Reaktionen, deren Komplexität von einfachen 1D- und linearen Fällen bis hin zu CT-Scan-basierten echten Filterdomänen und echten nichtlinearen komplexen chemischen Reaktionen reichte, wurden berücksichtigt und untersucht. Die vorliegende Arbeit zeigt, dass für alle betrachteten Fälle durch die Nutzung von Splitting-Verfahren für den (schwachen) Transport- und den Reaktionsterm, Verbesserungen in Bezug auf Speichernutzung und Konvergenzgeschwindigkeit erzielt werden können.
Ein Großteil der elektrischen Energie wird zum Betrieb von Pumpen benötigt. Bei drehzahlkonstanten Pumpen werden als Antrieb oft Käfigläufer-Asynchronmotoren (ASM) eingesetzt, die direkt an das Drehstromnetz angeschlossen sind. ASM sind günstig und robust, ihre Effizienz wird jedoch durch die prinzipbedingten Rotorverluste begrenzt. Um höchsten Effizienzanforderungen zu genügen, bieten daher verschiedene Hersteller permanentmagneterregte Line-Start (PMLS) Motoren an, die den Vorteil der Netzanlauffähigkeit mit einem hohen Wirkungsgrad verbinden. Die hierbei verwendeten Seltenen-Erd-Magnetmaterialien verursachen jedoch hohe Anschaffungskosten.
Als Alternative werden in dieser Arbeit PMLS-Motoren in Ferrittechnik vorgestellt. Ferritmagnete zeichnen sich durch ihre geringen Anschaffungskosten und eine gute Verfügbarkeit ihrer Bestandteile aus, sind jedoch im Hinblick auf ihre magnetischen Eigenschaften Seltenen-Erd-Magneten unterlegen. Diese Nachteile müssen über einen geschickten Motoraufbau kompensiert werden.
Zur Entwicklung geeigneter Motoren werden zunächst analytische Modelle für das stationäre und das transiente Betriebsverhalten physikalisch hergeleitet und ihre mathematische Behandlung erläutert. Im stationären Modell wird die Eisensättigung über einen nichtlinearen magnetischen Kreis und die Motorerwärmung über ein thermisches, drehzahlabhängiges Netzwerk berücksichtigt. Die Güte der Modelle wird durch entsprechende FEM-Simulationen überprüft. Mit diesen Modellen werden zwei Funktionsmuster ausgelegt, wobei der Schutz der Ferritmagnete vor Entmagnetisierung beim Hochlauf im Fokus steht. Die so ausgelegten Motoren werden messtechnisch untersucht und die Mess- mit den Simulationsergebnissen abgeglichen. Ein abschließender Konzeptvergleich rundet die Arbeit ab.
Das Fachgebiet Stadtsoziologie der RPTU Kaiserslautern-Landau hat im Jahr 2022 eine teilstandardisierte Befragung der 50- bis 75-jährigen Einwohner:innen von sieben Modellkommunen durchgeführt. Urbane, suburbane und ländliche Kommunen aus drei Bundesländern wurden ausgewählt. Dieser „Steckbrief“ für die Stadt Jena beinhaltet die Ergebnisse für die zentralen soziodemografischen, sozialstrukturellen und wohnungsbezogenen Merkmale der Babyboomer (53- bis 67-jährigen).
Die Ergebnisse bilden einen kleinen Ausschnitt der Befragung zum Wohnen, der Wohnumgebung, der Freizeitgestaltung und digitaler Affinität der älteren Menschen und vor allem der Babyboomer-Kohorte in den Kommunen. Insgesamt wurden über 5.000 Menschen befragt. Eingebettet ist die Umfrage in das Projekt „Ageing Smart – Räume intelligent gestalten“, das die geburtenstarken Jahrgänge 1955 bis 1969 ("Babyboomer") adressiert. Mit dem sukzessiven Übergang der Babyboomer in den Ruhestand sind die Gesellschaft und insbesondere die Kommunen gefordert, angemessene Angebote zum Wohnen und für Betätigungsmöglichkeiten zu entwickeln.
Das Projekt wird durch die Carl-Zeiss-Stiftung sowie von der RPTU Kaiserslautern-Landau von 04/2021 bis 03/2026 gefördert. Zehn Fachgebiete der RPTU Kaiserslautern-Landau führen das Projekt gemeinsam mit dem Fraunhofer IESE und dem Deutschen Forschungszentrum für Künstliche Intelligenz (DFKI) durch.
Comparative analysis of scalar fields in scientific visualization often involves distance functions on topological abstractions. This paper focuses on the merge tree abstraction (representing the nesting of sub- or superlevel sets) and proposes the application of the unconstrained deformation-based edit distance. Previous approaches on merge trees often suffer from instability: small perturbations in the data can lead to large distances of the abstractions. While some existing methods can handle so-called vertical instability, the unconstrained deformation-based edit distance addresses both vertical and horizontal instabilities, also called saddle swaps. We establish the computational complexity as NP-complete, and provide an integer linear program formulation for computation. Experimental results on the TOSCA shape matching ensemble provide evidence for the stability of the proposed distance. We thereby showcase the potential of handling saddle swaps for comparison of scalar fields through merge trees.
Comparative visualization of scalar fields is often facilitated using similarity measures such as edit distances. In this paper, we describe a novel approach for similarity analysis of scalar fields that combines two recently introduced techniques: Wasserstein geodesics/barycenters as well as path mappings, a branch decomposition-independent edit distance. Effectively, we are able to leverage the reduced susceptibility of path mappings to small perturbations in the data when compared with the original Wasserstein distance. Our approach therefore exhibits superior performance and quality in typical tasks such as ensemble summarization, ensemble clustering, and temporal reduction of time series, while retaining practically feasible runtimes. Beyond studying theoretical properties of our approach and discussing implementation aspects, we describe a number of case studies that provide empirical insights into its utility for comparative visualization, and demonstrate the advantages of our method in both synthetic and real-world scenarios. We supply a C++ implementation that can be used to reproduce our results.
Infobrief FBK 72/24
(2024)
World2Go – Der digitale Botanische Garten mit handlungsorientierten Stationen im Klassenzimmer
(2024)
Im Rahmen der vorliegenden Dissertation sind zwei Geobotanik-Boxen konzipiert worden, die sich nahtlos in einen interdisziplinären Unterricht der beiden naturwissenschaftlichen Fächer Erdkunde und Biologie integrieren lassen. Die Geobotanik-Boxen basieren auf einem digital gestützten Lernzirkel, der sich thematisch mit den Anpassungsstrategien von Pflanzen an die tropische und subtropische Klimazone beschäftigt, der den Schüler*innen adressatengerechte Hinweise und Aufgaben zur Verfügung stellt und gleichzeitig das analoge Experimentieren und Durchführen von Versuchen ermöglicht. Dadurch sollen sowohl das digitale Lernen als auch naturwissenschaftliche Arbeitsweisen bei den Schüler*innen der Klassenstufen 5-13 gefordert und gefördert werden.
Begleitet wird der Einsatz der beiden Geobotanik-Boxen von einer zweigleisigen Studie, die sich sowohl auf die Schüler*innen als auch die Lehrer*innen bezieht. Durch ein quantitatives Forschungsdesign (Fragebogen für die Schüler*innen) soll zum einen herausgefunden werden, ob ein digitaler Lernzirkel in den Schulunterricht integriert werden kann, und zum anderen ein Überblick geschaffen werden, welchen Umgang die Schüler*innen mit digitalen Medien bereits erlernt haben. Der Schwerpunkt der Forschung befindet sich im zweiten Teilbereich der Studie. Hier werden die Lehrkräfte, die an dem Projekt „World2Go“ teilgenommen haben, in Interviews zum Lernzirkel und dem Einsatz von digitalen Medien im Unterricht befragt.
Da im Zuge des Projektes auch eine Lehrer*innenfort- und -weiterbildung konzipiert werden soll, die sich an den Wünschen und Bedürfnissen der Lehrkräfte orientiert, werden auch diese beiden Bereiche in den Interviews abgedeckt. Gestützt durch die Ergebnisse aus beiden Forschungsbereichen, beabsichtigt diese Arbeit die Entwicklung einer Lehrer*innenfort- und -weiterbildung. Diese Bildungsmaßnahme hat zum Ziel, einerseits das Projekt „World2Go“ vorzustellen und Lehrkräften die Integration der Geobotanik-Boxen in ihren Unterricht zu erleichtern und andererseits die Erkenntnisse aus der projektbezogenen Forschung aufzugreifen, um Lehrkräften die Gestaltung eines digital gestützten Unterrichts zu erleichtern.
In the first part of this thesis, the synthesis of several molecularly imprinted polymers (MIPs) and non imprinted polymers (NIPs) and the characterization of their ability to bind glyphosate and AMPA in the aqueous enviroment is described. These polymers are to be used as concentrators in a mobile water monitoring system, and were developed in the framework of the EU-funded Interreg V project „WaterPollutionSensor“. They were produced using block copolymerization of different functional monomers and crosslinkers in various ratios. Phenylphosphonic acid was used as template. For comparison, homopolymers containing only the crosslinkers were also synthesized and all polymers were referend against the commerically available MIP Affinimip® from Affinisep.
The composition of the polymers was determined using elemental analysis. Brunauer–Emmett–Teller (BET) and scanning electron microscope (SEM) measurements were carried out to characterize the polymer morphology. The most polymers showed a specific surface between 100 – 400 m2g-1, which is typical for MIPs. The adsorption and elution behavior of the polymers was investigated using NMR and UV/Vis in modified batch and flow experiments. While the polymers based on DMAPMA showed very good adsorption for glyphosate and AMPA, the polymers based on ATH were suitable for both adsorption and elution. The polymers based on EGDMA and ATH showed an imprinting effect while the crosslinker TAHT formed attractive interactions with glyphosate and AMPA and therefore no imprinting effect was observed. The results obtained provided insight into structural parameters that influenced the adsorption properties.
In the secound project of this thesis, two bis(cyclopeptides) (BCP) isomers containing a photo-switchable linker were successfully synthesized and isolated. The successful synthesis of both products was confirmed using NMR, elemental analysis, ESI and MALDI mass spectrometry. In cooperation with the Wezenberg group, the switching and binding properties of the two BCPs were analyzed using NMR, ESI and ITC. These experiments showed that both BCPs bind strongly to sulfate anions in DMSO with a 1:1 stoichiometry for the Z and a 2:2 stoichiometry for the E isomer. The high stability of these both sulfate complexes prevented switching from one complex to the other by light. Switching could be achieved by additionally changing the protonation state of the anion using an acid/base mediated stimulus, since hydrogen sulfate is less strongly bound by both isomers.
Intelligent formal methods
(2022)
Information technology has become an indispensable part of our daily lives, with a significant proportion of our everyday activities relying on the safe and reliable operation of computer systems. One promising approach to ensuring these critical properties is the use of so-called formal methods, a broad range of rigorous, mathematical techniques for specifying, developing, and verifying hardware, software, cyber-physical systems, and artificial intelligence. Unlike traditional quality assurance approaches, such as testing, formal methods offer the unique ability to provide formal proof of the absence of errors, a trait particularly desirable in the context of today's ubiquitous safety-critical systems. However, this advantage comes at a cost: formal methods require extensive training, often assume idealized or limited settings, and typically demand substantial computational resources.
Inspired by the vision of artificial intelligence, this work seeks to automate formal methods and dramatically expand their applicability. To achieve this goal, we develop a novel, innovative type of formal method that combines inductive techniques from machine learning with deductive techniques from logic. We name this new approach "intelligent formal methods" and apply it to three fundamental areas: software verification, hardware and software synthesis, and the generation of formal specifications.
Objective. Gradient-based optimization using algorithmic derivatives can be a useful technique to improve engineering designs with respect to a computer-implemented objective function. Likewise, uncertainty quantification through computer simulations can be carried out by means of derivatives of the computer simulation. However, the effectiveness of these techniques depends on how 'well-linearizable' the software is. In this study, we assess how promising derivative information of a typical proton computed tomography (pCT) scan computer simulation is for the aforementioned applications. Approach. This study is mainly based on numerical experiments, in which we repeatedly evaluate three representative computational steps with perturbed input values. We support our observations with a review of the algorithmic steps and arithmetic operations performed by the software, using debugging techniques. Main results. The model-based iterative reconstruction (MBIR) subprocedure (at the end of the software pipeline) and the Monte Carlo (MC) simulation (at the beginning) were piecewise differentiable. However, the observed high density and magnitude of jumps was likely to preclude most meaningful uses of the derivatives. Jumps in the MBIR function arose from the discrete computation of the set of voxels intersected by a proton path, and could be reduced in magnitude by a 'fuzzy voxels' approach. The investigated jumps in the MC function arose from local changes in the control flow that affected the amount of consumed random numbers. The tracking algorithm solves an inherently non-differentiable problem. Significance. Besides the technical challenges of merely applying AD to existing software projects, the MC and MBIR codes must be adapted to compute smoother functions. For the MBIR code, we presented one possible approach for this while for the MC code, this will be subject to further research. For the tracking subprocedure, further research on surrogate models is necessary.
We discuss the dynamics of the formation of a Bose polaron when an impurity is injected into a weakly interacting one-dimensional Bose condensate. While for small impurity-boson couplings this process can be described within the Froehlich model as generation, emission and binding of Bogoliubov phonons, this is no longer adequate if the coupling becomes strong. To treat this regime we consider a mean-field approach beyond the Froehlich model which accounts for the backaction to the condensate, complemented with Truncated Wigner simulations to include quantum fluctuation. For the stationary polaron we find a periodic energy-momentum relation and non-monotonous relation between impurity velocity and polaron momentum including regions of negative impurity velocity. Studying the polaron formation after turning on the impurity-boson coupling quasi-adiabatically and in a sudden quench, we find a very rich scenario of dynamical regimes. Due to the build-up of an effective mass, the impurity is slowed down even if its initial velocity is below the Landau critical value. For larger initial velocities we find deceleration and even backscattering caused by emission of density waves or grey solitons and subsequent formation of stationary polaron states in different momentum sectors. In order to analyze the effect of quantum fluctuations we consider a trapped condensate to avoid 1D infrared divergencies. Using Truncated Wigner simulations in this case we show under what conditions the influence of quantum fluctuations is small.
European crayfish species are considered keystone in freshwater ecosystems. As such, their conservation is of paramount importance to prevent biodiversity decline and loss of ecosystem function. Unfortunately, today, European crayfish species are among the most threatened crayfish species worldwide. An especially relevant threat is represented by the invasive pathogen Aphanomyces astaci. This oomycete, native of North America, has been one of the main causes of crayfish population declines across Europe since its first introduction 150 years ago, to the point of causing the local extinction of many populations. Over the years, several introductions of A. astaci strains into Europe took place through translocation of infected North American crayfish, and were followed by mass mortalities across European crayfish populations. However, in the past 20 years, more and more reports emerged of European crayfish populations surviving A. astaci infections or being latently infected with the pathogen. The survival of infected crayfish can be ascribed to both increased resistance of some crayfish populations and decreased virulence of some A. astaci strains. As the relationship between host and pathogen in Europe is changing, it is imperative to gain insights on what shapes these changes to understand the implications for the long-term coexistence of crayfish and A. astaci in Europe. With this thesis, I focused on the virulence of A. astaci, looking for mechanisms, patterns and determinants underlying the pathogen’s virulence variability. In particular, by characterising the virulence of several A. astaci strains, I identified two possible different mechanisms of loss of virulence. I revealed that A. astaci’s virulence variability is not linked to variation of in vitro growth and sporulation, traits classically associated with a pathogen’s virulence. Based on these results, I suggest that the pathogen’s virulence determinants are likely its “virulence effectors”, of which A. astaci genome is enriched. Additionally, with the present work I provided transcriptomic evidence of coevolution between A. astaci and European crayfish. I showed that the haplogroups based on the canonical mitochondrial markers, often used to assess A. astaci’s virulence to inform management actions, do not differ for some of their characterising phenotypical traits, including virulence. Finally, after experimental characterisation of virulence and assessment of its likely phenotypical determinants, i.e., sporulation and growth, the next and more comprehensive step to study the pathogen’s virulence is through genomic approaches. To this aim, I provided key data for future comparative genomic studies, i.e., highly complete genome assemblies based on Nanopore (3) and Illumina reads (11). These data can be exploited in several ways, from building a pangenome of the species to a genome-wide association study (GWAS), that can offer a much deeper understanding of A. astaci’s virulence and adaptability. In particular, the identification of the loci associated with virulence through a GWAS has the potential to be revolutionary for the management of A. astaci, as it can become the basis to create a genomic tool to quickly and accurately assess the virulence of newly introduced strains, directing management actions towards the more dangerous strains.
We report the experimental implementation of dynamical decoupling on a small, non-interacting ensemble of up to 25 optically trapped, neutral Cs atoms. The qubit consists of the two magnetic-insensitive Cs clock states \(\vert F = 3, m_F = 0\rangle\) and \(\vert F = 4, m_F = 0\rangle\), which are coupled by microwave radiation. We observe a significant enhancement of the coherence time when employing Carr-Purcell-Meiboom-Gill (CPMG) dynamical decoupling. A CPMG sequence with ten refocusing pulses increases the coherence time of 16.2(9) ms by more than one order of magnitude to 178(2) ms. In addition, we make use of the filter function formalism and utilise the CPMG sequence to measure the background noise floor affecting the qubit coherence, finding a power-law noise spectrum \(1/\omega^\alpha\) with \(\mathit{\alpha} = 0.89(2)\). This finding is in very good agreement with an independent measurement of the noise in the intensity of the trapping laser. Moreover, the measured coherence evolutions also exhibit signatures of low-frequency noise originating at distinct frequencies. Our findings point toward noise spectroscopy of engineered atomic baths through single-atom dynamical decoupling in a system of individual Cs impurities immersed in an ultracold 87Rb bath.
Olive mill wastewater (OMW) is a by-product of olive oil extraction and its disposal on soil has been associated with significant environmental challenges, including toxic effects on soil organisms and quality of groundwater due to its high phenolic content. Recent studies focusing on the dynamics of OMW degradation in soil are handling the environmental conditions as main factors influencing the fate and transport of polyphenols in the soil-water system. The understanding of seasonal-dependent phenol leaching from OMW-treated soil remained elusive, as field studies are hindered by spatial variability and complex environmental dynamics. Therefore, controlled lysimeter experiments were conducted to investigate the leaching and transport mechanisms of OMW-derived phenolic compounds in soil.
This thesis presents the results of an 18-week lysimeter experiment conducted in a laboratory setting, aimed at monitoring and comprehending the distribution and leaching of OMW-derived phenolic compounds in soil after OMW application. The experiment spanned four seasonal simulation phases, including two winter, one spring, and one summer, under semi-arid climate Tunisian conditions. The effects of OMW on soil leachates properties, soil water repellency, and soil water retention capacity were assessed.
The soil leachates exhibited varying degrees of recovery across the different simulation phases. However, persistent salinity in the leachates and high soil water repellency at the top treated OMW-soils were recorded. The findings revealed also that OMW application changed the pore size distribution in treated OMW-soils. Most of the OMW-derived phenols were immobilized in the upper 5 cm of the soil. Notably, soluble phenolic compounds exhibited the formation of coarser pores for the sake of fine pores, suggesting that OMW- organic carbon played a crucial role in controlling the depth-dependent transport mechanisms of OMW within the soil matrix.
In conclusion, this study provides valuable insights into the fate and impact of OMW-derived phenolic compounds in soil. It emphasizes the significance of conducting OMW applications with careful irrigation practices and thorough phenol leaching surveys to minimize the risk of potential groundwater contamination. Additionally, more experiments are warranted to investigate the sorption capacity of the soil during and after OMW application and its influence on the stability of soluble phenolic compounds
in soils.
Thermo-optic interaction significantly differs from the usual particle-particle interactions in physics, as it is retarded in time. A prominent platform for realising this kind of interaction are photon Bose–Einstein condensates, which are created in dye-filled microcavities. The dye solution continually absorbs and re-emits these photons, causing the photon gas to thermalize and to form a Bose–Einstein condensate. Because of a non-ideal quantum efficiency, these cycles heat the dye solution, creating a medium that provides an effective thermo-optic photon–photon interaction. So far, only a mean-field description of this process exists. This paper goes beyond by working out a quantum mechanical description of the effective thermo-optic photon–photon interaction. To this end, the self-consistent modelling of the temperature diffusion builds the backbone of the modelling. Furthermore, the manyfold experimental timescales allow for deriving an approximate Hamiltonian. The resulting quantum theory is applied in the perturbative regime to both a harmonic and a box potential for investigating its prospect for precise measurements of the effective photon–photon interaction strength.
Although photon Bose–Einstein condensates have already been used for studying many interesting effects, the precise role of the photon–photon interaction is not fully clarified up to now. In view of this, it is advantageous that these systems allow measuring both the intensity of the light leaking out of the cavity and its spectrum at the same time. Therefore, the photon–photon interaction strength can be determined once via analysing the condensate broadening and once via examining the interaction-induced modifications of the cavity modes. As the former method depends crucially on the concrete shape of the trapping potential and the spatial resolution of the used camera, interferometric methods promise more precise measurements. To this end, the present paper works out the impact of the photon–photon interaction upon the cavity modes. A quantum mechanical description of the photon–photon interaction, including the thermal cloud, builds the theoretical backbone of the method. An exact diagonalisation approach introduced here exposes how the effective photon–photon interaction modifies both the spectrum and the width of the photon gas. A comparison with a variational approach based on the Gross–Pitaevskii equation quantifies the contribution of the thermal cloud in the respective applications.
Surface roughness plays a critical role and has effects in, e.g. fluid dynamics or contact mechanics. For example, to evaluate fluid behavior at different roughness properties, real-world or numerical experiments are performed. Numerical simulations of rough surfaces can speed up these studies because they can help collect more relevant information. However, it is hard to simulate rough surfaces with deterministic or structured components in current methods. In this work, we present a novel approach to simulate rough surfaces with a Gaussian process (GP) and a noise model because GPs can model structured and periodic elements. GPs generalize traditional methods and are not restricted to stationarity so they can simulate a wider range of rough surfaces. In this paper, we summarize the theoretical similarities of GPs with auto-regressive moving-average processes and introduce a linear process view of GPs. We also show examples of ground and honed surfaces simulated by a predefined model. The proposed method can also be used to fit a model to measurement data of a rough surface. In particular, we demonstrate this to model turned profiles and surfaces that are inherently periodic.
An important tool for the functional characterization of technical surfaces are envelope estimation techniques. This paper describes a new method for generating profile envelope lines based on a simplified beam-surface contact model with intuitive parameterization. The method is closely related to spline filters and shares some of their positive characteristics such as smoothness and robustness against isolated outliers. Unlike spline filters, the proposed method does not calculate mean lines, but envelope lines. Several examples of calculated profile envelopes of sintered surfaces are shown and a comparison with morphological methods, the state-of-the-art method for envelope estimation, is presented.
The Born–Fock theorem is one of the most fundamental theorems of quantum mechanics and forms the basis for reliable and efficient navigation in the Hilbert space of a quantum system with a time-dependent Hamiltonian by adiabatic evolution. In the absence of level crossings, i.e. without degeneracies, and under adiabatic time evolution all eigenstates of the Hamiltonian keep their energetic order, labeled by a conserved integer quantum number. Thus, controlling the eigenstates of the Hamiltonian and their energetic order in asymptotic limits allows one to engineer a perfect adiabatic transfer between a large number of initial and target states. The fidelity of the state transfer is only limited by adiabaticity and the selection of target states is controlled by the integer invariant labeling the order of eigenstates. We show here, for the example of a finite superlattice Wannier-Stark ladder, i.e. a one-dimensional lattice with alternating hopping amplitudes and constant potential gradient, that such an adiabatic control of eigenstates can be used to induce perfectly quantized single-particle transport across a pre-determined number of lattice sites. We dedicate this paper to the memory of our late friend and colleague Bruce Shore, who was an expert in adiabatic processes and taught us much about this field.
Dynamical change under slowly changing conditions: the quantum Kruskal–Neishtadt–Henrard theorem
(2022)
Adiabatic approximations break down classically when a constant-energy contour splits into separate contours, forcing the system to choose which daughter contour to follow; the choices often represent qualitatively different behavior, so that slowly changing conditions induce a sudden and drastic change in dynamics. The Kruskal–Neishtadt–Henrard (KNH) theorem relates the probability of each choice to the rates at which the phase space areas enclosed by the different contours are changing. This represents a connection within closed-system mechanics, and without dynamical chaos, between spontaneous change and increase in phase space measure, as required by the Second Law of Thermodynamics. Quantum mechanically, in contrast, dynamical tunneling allows adiabaticity to persist, for very slow parameter change, through a classical splitting of energy contours; the classical and adiabatic limits fail to commute. Here we show that a quantum form of the KNH theorem holds nonetheless, due to unitarity.
Experimental observation of a dissipative phase transition in a multi-mode many-body quantum system
(2022)
Dissipative phase transitions are a characteristic feature of open systems. One of the paradigmatic examples for a first order dissipative phase transition is the driven nonlinear single-mode optical resonator. In this work, we study a realization with an ultracold bosonic quantum gas, which generalizes the single-mode system to many modes and stronger interactions. We measure the effective Liouvillian gap of the system and find evidence for a first order dissipative phase transition. Due to the multi-mode nature of the system, the microscopic dynamics is much richer and allows us to identify a non-equilibrium condensation process.
Individual quantum emitters form a fundamental building block for emerging quantum technologies. Collective effects of emitters, such as superradiance, might improve the performance of applications even further. When scaling materials to larger sizes, however, the optical density of states is modified by the surrounding material, and the collective coupling in small domains might be covered by transitions to bulk properties due to the presence of multiple collectively emitting domains, which inhomogeneously add. Here, we probe the optical properties of nitrogen vacancy centers in agglomerates of nanodiamonds. We quantify the transition from individual emitters to bulk emission by fluorescence lifetime measurements, and find a transition to occur on a length scale of \(\sim \!3\) wavelengths around the emitter. While our lifetime measurements are consistent with superradiant decay, the second-order correlation function, which is a standard measure to reveal collective properties, fails to probe collective effects for our case of an ensemble of collectively contributing domains to the emission. Therefore, we propose and apply a new measure to trace collective effects based on the intensity fluctuations of the emitted light. Our work points toward systematically studying collective effects in a scalable solid-state quantum system, and using them for quantum optical applications in agglomerates of highly-doped nanodiamonds.
Within this paper, electro-mechanical long-term tests on a thrust bearing were presented. The effects of an additional electrical load on the bearing raceways and the used lubricant were investigated. Chemical investigations and viscosity measurements were presented, which show the changes in the lubricant. These investigations were compared with the electrical loads and the occurring raceway damage. In addition, a comparison was made with mechanical reference tests. This procedure makes it possible to classify the changes that occur due to the electrical load and to distinguish the effects from each other. The background to these investigations is the increased occurrence of parasitic currents in electric motors, which can lead to damage to machine elements. The phenomena that occur here are new challenges in the development of drive trains
Surface alloys are a highly flexible class of low dimensional materials with the opportunity to tune and control the spin and charge carrier functionalities on the nanoscale. Here, we focus on the atomic and mesoscopic structural details of three distinct binary rare-earth-noble metals (NM) surface alloys by employing scanning tunneling microscopy and low energy electron diffraction. Using Dysprosium as the guest element on fcc(111) NM substrates, we identify the formation of non-commensurate surface alloy superstructures, which lead to homogeneous moiré patterns for DyCu2/Cu(111) and DyAu2/Au(111), while an inhomogeneous one is found for DyAg2/Ag(111). The local structure was analyzed for these samples and the observed differences are discussed in the light of the lattice mismatches of the alloy layer with respect to the underlying substrate. For the particularly intriguing case of a DyAg2 surface alloy, the surface alloy layer does not show a uniform long-range periodic structure, but consists of local hexagonal tiles separated by extended domain walls, which occur likely to relieve the in-plane strain within the DyAg2 surface alloy layer. Our findings clearly demonstrate that surface alloying is an intriguing tool to tailor the local atomic structure as well as the mesoscopic moiré structures of metallic heterostructures.
Spin transport and spin dynamics after femtosecond laser pulse irradiation of iron (Fe) are studied using a kinetic Monte Carlo model. This model simulates spin dependent dynamics by taking into account two interaction processes during nonequilibrium: elastic electron–lattice scattering, where only the direction of the excited electrons changes, and inelastic electron–electron scattering processes, where secondary electrons are generated. An analysis of the spin dependent particle kinetics inside the material shows that a smaller elastic scattering time leads to a larger spatial spread of electrons in the material, whereas generation of secondary electrons extends the time span for superdiffusive transport and increases the spin current density.
Since the advent of experiments with photon Bose–Einstein condensates (phBECs) in dye-filled microcavities in 2010, many investigations have focussed upon the emerging effective photon–photon interaction. Despite its smallness, it can be identified to stem from two physically distinct mechanisms. On the one hand, a Kerr nonlinearity of the dye medium yields a photon–photon contact interaction. On the other hand, a heating of the dye medium leads to an additional thermo-optic interaction, which is both delayed and non-local. The latter turns out to represent the leading contribution to the effective interaction for the current 2D experiments. Here we analyse theoretically how the effective photon–photon interaction increases when the system dimension is reduced from 2D to 1D. To this end, we consider an anisotropic harmonic trapping potential and determine via a variational approach how the properties of the phBEC in general, and both aforementioned interaction mechanisms in particular, change with increasing anisotropy. We find that the thermo-optic interaction strength increases at first linearly with the trap aspect ratio and later on saturates at a certain value of the trap aspect ratio. Furthermore, in the strong 1D limit the roles of both interactions get reversed as the thermo-optic interaction remains saturated and the contact Kerr interaction becomes the leading interaction mechanism. Finally, we discuss how the predicted effects can be measured experimentally.
Photon Bose–Einstein condensates are characterised by a quite weak interaction, so they behave nearly as an ideal Bose gas. Moreover, since the current experiments are conducted in a microcavity, the longitudinal motion is frozen out and the photon gas represents effectively a two-dimensional trapped gas of massive bosons. In this paper we focus on a harmonically confined ideal Bose gas in two dimensions, where the anisotropy of the confinement allows for a dimensional crossover. If the confinement in one direction is strong enough so that this squeezed direction is frozen out, then only one degree of freedom survives and the system can be considered to be quasi-one dimensional. In view of an experimental set-up we work out analytically the thermodynamic properties for such a system with a finite number of photons. In particular, we focus on examining the dimensional information which is contained in the respective thermodynamic quantities.
As shown in recent experiments (Lienhard et al 2020 Phys. Rev. X 10 021031), spin–orbit coupling in systems of Rydberg atoms can give rise to density-dependent Peierls phases in second-order hoppings of Rydberg spin excitations and nearest-neighbor repulsion. We here study theoretically a one-dimensional zig-zag ladder system of such spin–orbit coupled Rydberg atoms at half filling. The second-order hopping is shown to be associated with an effective gauge field, which in mean-field approximation is static and homogeneous. Beyond the mean-field level the gauge potential attains a transverse quantum component whose amplitude is dynamical and linked to density modulations. We here study the effects of this to the possible ground-state phases of the system. In a phase where strong repulsion leads to a density wave, we find that as a consequence of the induced quantum gauge field a regular pattern of current vortices is formed. However also in the absence of density–density interactions the quantum gauge field attains a non-vanishing amplitude. Above a certain critical strength of the second-order hopping the energy gain due to gauge-field induced transport overcomes the energy cost from the associated build-up of density modulations leading to a spontaneous generation of the quantum gauge field.
We investigate small tantalum clusters Tan+, n = 2–4, for their capability to cleave N2 adsorption spontaneously. We utilize infrared photon dissociation (IR-PD) spectroscopy of isolated and size selected clusters under cryogenic conditions within a buffer gas filled ion trap, and we augment our experiments by quantum chemical simulations (at DFT level). All Tan+ clusters, n = 2–4, seem to cleave N2 efficiently. We confirm and extend a previous study under ambient conditions on Ta2+ cluster [Geng et al., Proc. Natl. Acad. Sci. U. S. A. 115, 11680–11687 (2018)]. Our cryo studies and the concomitant DFT simulations of the tantalum trimer Ta3+ suggest cleavage of the first and activation of the second and third N2 molecule across surmountable barriers and along much-involved multidimensional reaction paths. We unravel the underlying reaction processes and the intermediates involved. The study of the N2 adsorbate complexes of Ta4+ presented here extends our earlier study and previously published spectra from (4,m), m = 1–5 [Fries et al., Phys. Chem. Chem. Phys. 23(19), 11345–11354 (2021)], up to m = 12. We confirm the priory published double activation and nitride formation, succeeded by single side-on N2 coordination. Significant red shifts of IR-PD bands from these side-on coordinated μ2-κN:κN,N N2 ligands correlate with the degree of tilting towards the second coordinating Ta center. All subsequently attaching N2 adsorbates onto Ta4+ coordinate in an end-on fashion, and we find clear evidence for co-existence of end-on coordination isomers. The study of stepwise N2 adsorption revealed adsorption limits m(max) of [Tan(N2)m]+ which increase with n, and kinetic fits revealed significant N2 desorption rates upon higher N2 loads. The enhanced absolute rate constants of the very first adsorbate steps kabs(n,0) of the small Ta3+ and Ta4+ clusters independently suggest dissociative N2 adsorption and likely N2 cleavage into Ta nitrides.
We present an IR-PD study of tantalum cluster adsorbate complexes [Tan(N2)m]+, abbreviated (n,m), n = 5–8. We utilize infrared spectroscopy of isolated and size selected clusters as prepared and characterized by a cryogenic tandem ion trap setup, and we augment our experiments with quantum chemical simulations at the level of density functional theory. The cluster adsorbate complexes (n,m) reveal vibrational bands above 2000 cm−1, which indicate end-on coordinated μ1-N2 oscillators, and bands below 2000 cm−1, which indicate side-on μ2-κN:κN,N coordinated ones. We observe a general increase in spectral complexity and an inhomogeneous broadening, mainly towards the red, at certain points of N2 loading m, which originates from an increasingly higher amount of double and triple N2 coordination at Ta sites, eventually at all of them. Other than the small tantalum clusters Tan+, n = 2–4, the IR-PD spectra of the initial N2 adsorbate species (n,1), n = 5–8, provide strong evidence for a lack of spontaneous N2 cleavage. Spontaneous N2 cleavage by Tan+, n = 5–8, seems suppressed. Therefore, the ability of a small Ta cluster to cleave dinitrogen disappears with one more tantalum core atom. The study of stepwise N2 adsorption on size selected Tan+, n = 5–8 clusters revealed adsorption limits m(max) of [Tan(N2)m]+ that are independent of cluster size within this size range. Cryo-adsorption kinetics at 26 K allowed for kinetic fits to consecutive N2 adsorption steps, and the fits revealed significant N2 desorption rates upon higher N2 loads, and the cluster adsorbate complexes eventually reached equilibrium. Some enhanced N2 desorption rates point towards likely adsorbate shell reorganization, and there is also some evidence for the coexistence of isomeric cluster adsorbate complexes.
Finding new energy-efficient methods for exciting magnetization dynamics is one of the key challenges in magnonics. In this work, we present an approach to excite the gyrotropic dynamics of magnetic vortices through the phenomenon of inverse magnetostriction, also known as the Villari effect. We develop an analytical model based on the Thiele formalism that describes the gyrotropic motion of the vortex core including the energy contributions due to inverse magnetostriction. Based on this model, we predict excitations of the vortex core resonances by surface acoustic waves whose frequency is resonant with the frequency of the vortex core. We verify the model's prediction using micromagnetic simulations and show the dependence of the vortex core's oscillation radius on the surface acoustic wave amplitude and the static bias field. Our study contributes to the advancement of energy-efficient magnetic excitations by relying on voltage-induced driven dynamics, which is an alternative to conventional current-induced excitations.
Varactor diodes have been proposed as active tuning elements of reconfigurable metasurfaces in the Ka-band. However, their experimental realization in this frequency range has not been demonstrated yet. We report the implementation of such a reconfigurable intelligent surface (RIS) made of 20 × 20 unit cells. By active tuning of the bias voltage of the varactors, the phase of the backward diffracted wave can be continuously tuned between 0 ° and 180 °. Thus, the phase tuning can be independently controlled for each unit cell. The frequency working range of the RIS is 1.1 GHz (from 30.6 to 31.7 GHz). As an illustration of the practical use, we demonstrate continuous beam steering of microwave radiation at 31 GHz in a defined propagation plane.
Rapid-prototyping of microscopic thermal landscapes in Brillouin light scattering spectroscopy
(2023)
Since temperature and its spatial, and temporal variations affect a wide range of physical properties of material systems, they can be used to create reconfigurable spatial structures of various types in physical and biological objects. This paper presents an experimental optical setup for creating tunable two-dimensional temperature patterns on a micrometer scale. As an example of its practical application, we have produced temperature-induced magnetization landscapes in ferrimagnetic yttrium iron garnet films and investigated them using micro-focused Brillouin light scattering spectroscopy. It is shown that, due to the temperature dependence of the magnon spectrum, spatial temperature distributions can be visualized even for microscale thermal patterns.
The concept of building logically functional networks employing spintronics or magnetic heterostructures is becoming more and more popular today. Incorporating logical segments into a circuit needs physical bonds between the magnetic molecules or clusters involved. In this framework, we systematically study ultrafast laser-induced spin-manipulation scenarios on a closed system of three carbon chains to which three Ni atoms are attached. After the inclusion of spin–orbit coupling and an external magnetic field, different ultrafast spin dynamics scenarios involving spin-flip and long-distance spin-transfer processes are achieved by various appropriately well-tailored time-resolved laser pulses within subpicosecond timescales. We additionally study the various effects of an external magnetic field on spin-flip and spin-transfer processes. Moreover, we obtain spin-dynamics processes induced by a double laser pulse, rather than a single one. We suggest enhancing the spatial addressability of spin-flip and spin-transfer processes. The findings presented in this article will improve our knowledge of the magnetic properties of carbon-based magnetic molecular structures. They also support the relevant experimental realization of spin dynamics and their potential applications in future molecular spintronics devices.
Mass transfer through fluid interfaces is an important phenomenon in industrial applications as well as in naturally occurring processes. In this work, we investigate the mass transfer across vapor–liquid interfaces in binary mixtures using molecular dynamics simulations. We investigate the influence of interfacial properties on mass transfer by studying three binary azeotropic mixtures known to have different interfacial behaviors. Emphasis is placed on the effect of the intermolecular interactions by choosing mixtures with the same pure components but different cross-interactions such that different azeotropic behaviors are obtained. The molar flux is created by utilizing a non-stationary molecular dynamics simulation approach, where particles of one component are inserted into the vapor phase over a short period of time before the system’s response to this insertion is monitored. From a direct comparison of the density profiles and the flux profiles in close proximity to the interface, we analyze the particles’ tendency to accumulate in the interfacial region throughout the different stages of the simulation. We find that for mixtures with strong attractive cross-interactions, the inserted particles are efficiently transported into the liquid phase. For systems with weak attractive cross-interactions, the inserted particles show a tendency to accumulate in the interfacial region, and the flux through the system is lower. The results from this work indicate that the accumulation of particles at the interface can act as a hindrance to mass transfer, which has practical relevance in technical processes.
This paper is concerned with a theoretical analysis of the behavior of optically excited spin currents in bilayer and multilayer systems of ferromagnetic and normal metals. As the propagation, control, and manipulation of the spin currents created in ferromagnets by femtosecond optical pulses is of particular interest, we examine the influence of different thicknesses of the constituent layers for the case of electrons excited several electronvolts above the Fermi level. Using a Monte-Carlo simulation framework for such highly excited electrons, we first examine the spatiotemporal characteristics of the spin current density driven in a Fe layer, where the absorption profile of the light pulse plays an important role. Further, we examine how the combination of light absorption profile, spin-dependent transmission probabilities, and iron layer thickness affects spin current density in a Fe/Au bilayer system. For high-energy electrons studied here, the interface and secondary electron generation have a small influence on spin transport in the bilayer system. However, we find that spin injection from one layer to another is most effective within a certain range of iron layer thicknesses.
Colloidal nanorods based on CdS or CdSe, functionalized with metal particles, have proven to be efficient catalysts for light-driven hydrogen evolution. Seeded CdSe@CdS nanorods have shown increasing performance with increasing rod length. This observation was rationalized by the increasing lifetime of the separated charges, as a large distance between holes localized in the CdSe seed and electrons localized at the metal tip decreases their recombination rate. However, the impact of nanorod length on the electron-to-tip localization efficiency or pathway remained an open question. Therefore, we investigated the photo-induced electron transfer to the metal in a series of Ni-tipped CdSe@CdS nanorods with varying length. We find that the transfer processes occurring from the region close to the semiconductor–metal interface, the rod region, and the CdSe seed region depend in different ways on the rods’ length. The rate of the fastest process from excitonic states generated directly at the interface is independent of the rod length, but the relative amplitude decreases with increasing rod length, as the weight of the interface region is decreasing. The transfer of electrons to the metal tip from excitons generated in the CdS rod region depends strongly on the length of the nanorods, which indicates an electron transport-limited process, i.e., electron diffusion toward the interface region, followed by fast interface crossing. The transfer originating from the CdSe excitonic states again shows no significant length dependence in its time constant, as it is probably limited by the rate of overcoming the shallow confinement in the CdSe seed.
A set of molecular models for the alkali nitrates (LiNO3, NaNO3, KNO3, RbNO3, and CsNO3) in aqueous solutions is presented and used for predicting the thermophysical properties of these solutions with molecular dynamics simulations. The set of models is obtained from a combination of a model for the nitrate anion from the literature with a set of models for the alkali cations developed in previous works of our group. The water model is SPC/E and the Lorentz–Berthelot combining rules are used for describing the unlike interactions. This combination is shown to yield fair predictions of thermophysical and structural properties of the studied aqueous solutions, namely the density, the water activity and the mean ionic activity coefficient, the self-diffusion coefficients of the ions, and radial distribution functions, which were studied at 298 K and 1 bar; except for the density of the solutions of all five nitrates and the activity properties of solutions of NaNO3, which were also studied at 333 K. For calculating the water the activity and the mean ionic activity coefficient, the OPAS (osmotic pressure for the activity of selvents) method was applied. The new models extend an ion model family for the alkali halides developed in previous works of our group in a consistent way.
We propose a hybrid magnonic-oscillator system based on the combination of a spin transfer auto-oscillator and a magnonic waveguide to open new perspectives for spin-wave based circuits. The system is composed of a spin transfer oscillator based on a vortex state which is dipolarly coupled to a nanoscale spin-wave waveguide with longitudinal magnetization. In its auto-oscillating regime, the oscillator emits coherent spin waves with tunable and controllable frequencies, directions, and amplitudes into the waveguide. We demonstrate the principle of this method using micromagnetic simulations and show that reconfiguration of the system is possible by changing the chirality and polarity of the magnetic vortex. Spin waves are emitted into the waveguide with high non-reciprocity and the preferred direction depends on the core polarity of the vortex. In contrast, different vortex chiralities lead to different amplitudes of the emitted waves. Our findings open up a novel way to design an agile spintronic device for the coherent and tunable generation of propagating spin waves.
Confinement of Bose–Einstein magnon condensates in adjustable complex magnetization landscapes
(2022)
Coherent wave states such as Bose–Einstein condensates (BECs), which spontaneously form in an overpopulated magnon gas even at room temperature, have considerable potential for wave-based computing and information processing at microwave frequencies. The ability to control the transport properties of magnon BECs plays an essential role in their practical use. Here, we demonstrate the spatiotemporal control of the BEC density distribution through the excitation of magnon supercurrents in an inhomogeneously magnetized yttrium iron garnet film. The BEC is created by microwave parametric pumping and probed by Brillouin light scattering spectroscopy. The desired magnetization profile is prepared by heating the film with optical patterns projected onto its surface using a phase-based wavefront modulation technique. Specifically, we observe a pronounced spatially localized magnon accumulation caused by magnon supercurrents flowing toward each other originating in two heated regions. This accumulation effect increases the BEC lifetime due to the constant influx of condensed magnons into the confinement region. The shown approach to manipulate coherent waves provides an opportunity to extend the lifetime of freely evolving magnon BECs, create dynamic magnon textures, and study the interaction of magnon condensates formed in different regions of the sample.
We present a robust, fiber-based endoscope with a silver direct-laser-written structure for radio frequency (RF) emission next to the optical fiber facet. Thereby, we are able to excite and probe a sample, such as nitrogen-vacancy (NV) centers in diamond, with RF and optical signals simultaneously and specifically measure the fluorescence of the sample fully through the fiber. At our targeted frequency range of around 2.9 GHz, the facet of the fiber core is in the near-field of the RF-guiding silver structure, which comes with the advantage of an optimal RF intensity decreasing rapidly with the distance. By creating a silver structure on the cladding of the optical fiber, we achieve the minimal possible distance between an optically excited and detected sample and an antenna structure without affecting the optical performance of the fiber. This allows us to realize a high RF amplitude at the sample’s position when considering an endoscope solution with integrated optical and RF access. The capabilities of the endoscope are quantified by optically detected magnetic resonance (ODMR) measurements of an NV-doped microdiamond that we probe as a practical use case. We demonstrate a magnetic sensitivity of our device of 17.8 nT/Hz when measuring the ODMR exclusively through our fiber and compare the sensitivity to a measurement using a confocal microscope. Moreover, the application of our device is not limited to NV centers in diamonds. Similar endoscope-like devices combining optical excitation and detection with radio frequency or microwave antenna could be used as a powerful tool for measuring a variety of fluorescent particles that have so far only been investigated with bulky and large optical setups. Furthermore, our endoscope points toward precise distance measurements based on Rabi oscillations.
Schlafschwierigkeiten und Insomnie stellen ein gesellschaftlich zunehmendes Phänomen dar. Studierende sind hiervon überdurchschnittlich häufig betroffen, mehr als ein Drittel beklagt eine niedrige Schlafqualität. In diesem Kontext erwiesen sich vor allem achtsamkeitsbasierte Interventionen als hilfreich. Wirksame, neuere Forschungsansätze widmen sich der Untersuchung mobiler Gesundheitsanwendungen. Daran anknüpfend setzt sich die Studie zum Ziel, die Effektivität einer achtsamkeitsbasierten Intervention mittels Meditations-App („7Mind“) in Bezug auf Schlafschwierigkeiten zu evaluieren. Studierende wurden randomisiert der Treatment- oder Wartelisten-Kontrollgruppe zugeordnet. Baseline-Messung, Post-Messung (2 Wochen) und Follow-up-Messung (4 Wochen) wurden mit Selbstberichtfragebogen zu den Variablen Schlafqualität, Insomnie-Schweregrad, Achtsamkeit, Tagesmüdigkeit, Stress und Lebensqualität untersucht. Die Intervention sollte 14 Tage 20 Minuten täglich absolviert werden. Von 53 Studierenden mit Baseline-Messung füllten 35 die Post-Messung und 28 alle Messzeitpunkte aus. Im Anschluss an das Training zeigten sich zwischen den Gruppen signifikante Unterschiede bezüglich der Schlafparameter (p < .001), wohingegen die Achtsamkeit unverändert blieb. Dafür wies letztere eine signifikante Zeit x Gruppe Interaktion auf (p = .018). In Bezug auf den Schlaf ergaben sich hohe Effektstärken, welche auch zum Follow-up-Zeitpunkt persistierten (d= 2.36). Die Variablen Tagesmüdigkeit,
Stress und Lebensqualität waren hochsignifikant mit der Schlafqualität korreliert (p < .001).
Mobile achtsamkeitsbasierte Interventionen stellen eine ökonomische Alternative dar, um Studierende mit Schlafschwierigkeiten zu unterstützen. Zukünftige Schritte inkludieren die Überprüfung über einen längeren Zeitraum und mit einer größeren Reichweite.
Interfacial properties of binary azeotropic mixtures of Lennard-Jones truncated and shifted fluids were studied by molecular dynamics (MD) simulation and density gradient theory (DGT) in combination with an equation of state. Three binary mixtures were investigated, which differ in the energetic cross interaction parameter that yields different types of azeotropic behavior. This study covers a wide temperature and composition range. Mixture A exhibits a heteroazeotrope at low temperatures, which changes to a low-boiling azeotrope at high temperatures, mixture B exhibits a low-boiling azeotrope, and mixture C exhibits a high-boiling azeotrope. The phase behavior and fluid interfacial properties as well as their relation were studied. Vapor–liquid, liquid–liquid, and vapor–liquid–liquid equilibria and interfaces were considered. Density profiles, the surface tension, the interfacial thickness, as well as the relative adsorption and enrichment of the components at the interface were studied. The results obtained from the two independent methods (MD and DGT) are overall in good agreement. The results provide insights into the relation of the phase behavior, particularly the azeotropic behavior, of simple fluid mixtures and the corresponding interfacial properties. Strong enrichment was found for the mixture with a heteroazeotrope in the vicinity of the three-phase equilibrium, which is related to a wetting transition.
We report on the resonant excitation of spin waves in micro-structured magnetic thin films by short-wavelength surface acoustic waves (SAWs). The spin waves as well as the acoustic waves are studied by micro-focused Brillouin light scattering spectroscopy. At low magnetic bias fields, a resonant phonon–magnon conversion is possible, which results in the excitation of short-wavelength spin waves. Using micromagnetic simulations, we verify that during this excitation both energy and linear momentum are conserved and fully transferred from the SAW to the spin wave. This conversion can already be detected after an interaction length of a few micrometers. Thus, our findings pave the way for miniaturized magneto-elastic spin-wave emitters for magnon computing.
We study the influence of transport effects on time- and space-resolved magnetization dynamics in a laser-excited thick nickel film. We explicitly include diffusive heat transport and spin-resolved charge transport as well as Seebeck and Peltier effects and calculate the dynamics of spin-dependent electronic temperatures, chemical potentials, lattice temperatures, and magnetization. We find that transport has an influence on the magnetization dynamics closer to the excited surface as well as in regions deeper than the penetration depth of the laser. We reveal that, for higher absorbed fluences and in the presence of transport, thick magnetic films show a quenching time nearly independent of depth, though the magnitude of quenching is depth-dependent.
We investigate ultrafast spin dynamics due to exchange, electron–phonon and Elliott–Yafet spin-flip scattering in a model with a simple band structure and ferromagnetically coupled electronic sublattices (or more generally, subsystems). We show that this incoherent model of electronic dynamics leads to sublattice magnetization changes in opposite directions after ultrashort-pulse excitation. This prominent feature on an ultrafast timescale is related to a transfer of energy and angular momentum between the subsystems due to exchange scattering. Our calculations illustrate a possible incoherent mechanism that works in addition to the coherent optically induced spin transfer mechanism.
Spin waves in yttrium iron garnet (YIG) nano-structures attract increasing attention from the perspective of novel magnon-based data processing applications. For short wavelengths needed in small-scale devices, the group velocity is directly proportional to the spin-wave exchange stiffness constant λex. Using wave vector resolved Brillouin light scattering spectroscopy, we directly measure λex in Ga-substituted YIG thin films and show that it is about three times larger than for pure YIG. Consequently, the spin-wave group velocity overcomes the one in pure YIG for wavenumbers k > 4 rad/μm, and the ratio between the velocities reaches a constant value of around 3.4 for all k > 20 rad/μm. As revealed by vibrating-sample magnetometry and ferromagnetic resonance spectroscopy, Ga:YIG films with thicknesses down to 59 nm have a low Gilbert damping (α<10−3), a decreased saturation magnetization μ0MS≈20 mT, and a pronounced out-of-plane uniaxial anisotropy of about μ0Hu1≈95 mT, which leads to an out-of-plane easy axis. Thus, Ga:YIG opens access to fast and isotropic spin-wave transport for all wavelengths in nano-scale systems independently of dipolar effects.
In this work, we present a method to microscopically investigate the liquid–vapor interfaces on the bottom side of droplets, which were placed on superhydrophobic structures, so that wetting in the Cassie–Baxter (CB) state occurred. These interfaces are hard to access optically, especially when an opaque substrate material is used, which is usually the case for technical applications. In that case, the menisci have to be observed through the droplet, which substantially deteriorates the imaging quality. Other methods that circumvent these distortions, such as optical coherence tomography, are restricted to a resolution of several micrometers. Confocal or fluorescence microscopy additionally requires a transparent substrate. To measure the liquid–vapor interfaces formed in the Cassie–Baxter state with high accuracy liquid droplets of a monomer solution that chemically reacts to form the elastomer, polydimethylsiloxane was placed on structured surfaces. Because double reentrant structures were used, wetting occurred in the Cassie–Baxter state despite the low surface tension of the monomer solution. After curing, it was possible to remove the solid droplets from the surface and investigate them using confocal microscopy, which provides an excellent height resolution of 10 nm. Test structures such as arrays of stripes and holes with variable spacing or diameter were used to investigate the impact of their geometry on the liquid–vapor interfaces formed in the CB state. Although the maximum height of the menisci on the droplet's bottom side is in the region of several 10 μm, the 10 nm resolution is required to adequately compare their topography with simplified theoretical models.
The magnetic response of a ferromagnet after an ultrafast optical excitation can be connected to the underlying electronic dynamics either via primary excitation processes during the laser pulse or via secondary collision processes. In the latter case, the information on the details of the excitation is lost and, therefore, the electron dynamics can be described using quasi-equilibrium concepts. In this work, we study the effect of the pump photon energy on the ultrafast demagnetization dynamics in ferromagnetic nickel. We find that the magnetization dynamics for similar absorbed energies for a range of pump photon energies are almost identical and depend only on the absorbed energy. This is in stark contrast to characteristic differences in the optically excited electronic distributions, as calculated from the band structure. In addition, the measured fluence-dependent dynamics can be reproduced with a model based on local temperatures. These findings indicate that it is mainly secondary processes that are responsible for the observed demagnetization dynamics.
We present a study of stepwise cryogenic N2 adsorption on size-selected Fen+ (n = 8–20) clusters within a hexapole collision cell held at T = 21–28 K. The stoichiometries of the observed adsorption limits and the kinetic fits of stepwise N2 uptake reveal cluster size-dependent variations that characterize four structural regions. Exploratory density functional theory studies support tentative structural assignment in terms of icosahedral, hexagonal antiprismatic, and closely packed structural motifs. There are three particularly noteworthy cases, Fe13+ with a peculiar metastable adsorption limit, Fe17+ with unprecedented nitrogen phobia (inefficient N2 adsorption), and Fe18+ with an isomeric mixture that undergoes relaxation upon considerable N2 uptake.
Cryo infrared spectroscopy of N2 adsorption onto bimetallic rhodium–iron clusters in isolation
(2021)
We investigated the N2 adsorption behavior of bimetallic rhodium–iron cluster cations [RhiFej(N2)m]+ by means of InfraRed MultiplePhotoDissociation (IR-MPD) spectroscopy in comparison with density functional theory (DFT) modeling. This approach allows us to refine our kinetic results [Ehrhard et al., J. Chem. Phys. (in press)] to enhance our conclusions. We focus on a selection of cluster adsorbate complexes within the ranges of i = j = 3–8 and m = 1–10. For i = j = 3, 4, DFT suggests alloy structures in the case of i = j = 4 of high (D2d) symmetry: Rh–Fe bonds are preferred instead of Fe–Fe bonds or Rh–Rh bonds. N2 adsorption and IR-MPD studies reveal strong evidence for preferential adsorption to Rh sites and mere secondary adsorption to Fe. In some cases, we observe adsorption isomers. With the help of modeling the cluster adsorbate complex [Rh3Fe3(N2)7]+, we find clear evidence that the position of IR bands allows for an element specific assignment of an adsorption site. We transfer these findings to the [Rh4Fe4(N2)m]+ cluster adsorbate complex where the first four N2 molecules are exclusively adsorbed to the Rh atoms. The spectra of the larger adsorbates reveal N2 adsorption onto the Fe atoms. Thus, the spectroscopic findings are well interpreted for the smaller clusters in terms of computed structures, and both compare well to those of our accompanying kinetic study [Ehrhard et al., J. Chem. Phys. (in press)]. In contrast to our previous studies of bare rhodium clusters, the present investigations do not provide any indication for a spin quench in [RhiFej(N2)m]+ upon stepwise N2 adsorption.
Many amphibians and insects have a biphasic life cycle, linking aquatic and terrestrial ecosystems. In temperate wetlands, insect communities are largely dominated by midges, such as non-biting chironomids and mosquitoes. Particularly chironomids and their aquatic larvae play a key role for both aquatic and terrestrial predators, e.g., dragonflies and damselflies (Odonata), birds, riparian spiders and amphibians. Therefore, adverse effects on chironomid larvae induced by pesticides or biocides can have implications on food webs across ecosystem boundaries.
In floodplains of the Upper Rhine Valley in southwest Germany, the biocide Bacillus thuringiensis var. israelensis (Bti) has been applied for over 40 years to reduce nuisance by mass emergence of mosquitoes. Due to its specific mode of action, Bti is presumed to be a more environmentally friendly alternative to non-selective, highly toxic pesticides used in the past. However, research on indirect effects of Bti on non-target organisms inhabiting these wetlands is still relatively scarce. The aim of this thesis was the investigation of direct and indirect effects of Bti on non-target organisms and, consequently, bottom-up effects on aquatic food webs and propagation to the terrestrial ecosystem. Effects were examined in outdoor floodplain pond mesocosms (FPMs) with natural flora and fauna communities.
Benthic macroinvertebrate communities were significantly altered in Bti-treated FPMs, largely due to the reduction of chironomid density by over 40% compared to untreated FPMs. Sampling of exuviae indicated that the emergence of Libellulidae (Odonata) was reduced by Bti, while larger Aeshnidae were not affected. This finding suggested increased intraguild predation (predation of competing predators) in Bti-treated FPMs as a result of decreased prey availability, i.e. chironomid larvae. This conclusion was partly confirmed in food web analyses using stable isotopes of C and N and fatty acids, with Aeshnidae experiencing a slight diet shift towards larger prey (i.e., newts, Aeshnidae) in Bti-treated FPMs. In contrast, the diet proportions of newt larvae were not affected by Bti treatment, but showed a marginal trend in lower omega-6 fatty acid content. Analyses of oxidative stress biomarkers did not reveal any direct effects of Bti on common frog tadpoles under natural climatic conditions.
This thesis emphasizes that adverse effects of Bti on the base of aquatic-terrestrial food webs, i.e., reduction of larval chironomids, can have implications for higher trophic levels and cascade to terrestrial ecosystems. Affected organisms also include species of concern, such as protected Odonata species. In view of the global insect and amphibian decline, the large-scale use of Bti in (partially protected) wetlands should be carefully considered.
We report the N2 cryo adsorption kinetics of selected gas phase mixed rhodium–iron clusters [RhiFej]+ in the range of i = 3–8 and j = 3–8 in 26 K He buffer gas by the use of a cryo tandem RF-hexapole trap–Fourier transform ion cyclotron resonance mass spectrometer. From kinetic data and fits, we extract relative rate constants for each N2 adsorption step and possible desorption steps. We find significant trends in adsorption behavior, which reveal adsorption limits, intermittent adsorption limits, and equilibrium reactions. For those steps, which are in equilibrium, we determine the Gibbs free energies. We conclude on likely ligand shell reorganization and some weakly bound N2 ligands for clusters where multiple N2 adsorbates are in equilibrium. The relative rate constants are transferred to absolute rate constants, which are slightly smaller than the collision rate constants calculated by the average dipole orientation (Langevin) theory. The calculated sticking probabilities increase, in general, with the size of the clusters and decrease with the level of N2 adsorption, in particular, when reaching an adsorption/desorption equilibrium. We receive further evidence on cluster size dependent properties, such as cluster geometries and metal atom distributions within the clusters through the accompanying spectroscopic and computational study on the equiatomic i = j clusters [Klein et al., J. Chem. Phys. 156, 014302 (2022)].
Infrared photodissociation (IR-PD) spectra of iron cluster dinitrogen adsorbate complexes [Fen(N2)m]+ for n = 8–20 reveal slightly redshifted IR active bands in the region of 2200–2340 cm−1. These bands mostly relate to stretching vibrations of end-on coordinated N2 chromophores, a μ1,end end-on binding motif. Density Functional Theory (DFT) modeling and detailed analysis of n = 13 complexes are consistent with an icosahedral Fe13+ core structure. The first adsorbate shell closure at (n,m) = (13,12)—as recognized by the accompanying paper on the kinetics of N2 uptake by cationic iron clusters—comes with extensive IR-PD band broadening resulting from enhanced couplings among adjacent N2 adsorbates. DFT modeling predicts spin quenching by N2 adsorption as evidenced by the shift of the computed spin minima among possible spin states (spin valleys). The IR-PD spectrum of (17,1) surprisingly reveals an absence of any structure but efficient non-resonant fragmentation, which might indicate some weakly bound (roaming) N2 adsorbate. The multiple and broad bands of (17,m) for all other cases than (17,1) and (17,7) indicate a high degree of variation in N2 binding motifs and couplings. In contrast, the (17,7) spectrum of six sharp bands suggests pairwise equivalent N2 adsorbates. The IR-PD spectra of (18,m) reveal additional features in the 2120–2200 cm−1 region, which we associate with a μ1,side side-on motif. Some additional features in the (18,m) spectra at high N2 loads indicate a μ1,tilt tilted end-on adsorption motif.
We discuss the realization of a magnonic version of the STImulated-Raman-Adiabatic-Passage (m-STIRAP) mechanism using micromagnetic simulations. We consider the propagation of magnons in curved magnonic directional couplers. Our results demonstrate that quantum-classical analogy phenomena are accessible in magnonics. Specifically, the inherent advantages of the STIRAP mechanism, associated with dark states, can now be utilized in magnonics. Applications of this effect for future magnonic device functionalities and designs are discussed.
Semiconductor multilayer and device fabrication is a complex task in electronics and opto-electronics. Layer dry etching is one of the process steps to achieve a specific lateral device design. In situ and real-time monitoring of etch depth will be necessary if high precision in etch depth is required. Nondestructive optical techniques are the methods of choice. Reflectance anisotropy spectroscopy equipment has been used to monitor the accurate etch depth during reactive ion etching of III/V semiconductor samples in situ and real time. For this purpose, temporal Fabry–Perot oscillations due to the etch-related shrinking thickness of the uppermost layer have been exploited. Earlier, we have already reported an etch-depth resolution of ±16.0 nm. By the use of a quadruple-Vernier-scale measurement and an evaluation protocol, now we even improve the in situ real-time etch-depth resolution by a factor of 20, i.e., nominally down to ±0.8 nm.
Magnonics attracts increasing attention in the view of low-energy computation technologies based on spin waves. Recently, spin-wave propagation in longitudinally magnetized nano-scaled spin-wave conduits was demonstrated, proving the fundamental feasibility of magnonics at the sub-100 nm scale. Transversely magnetized nano-conduits, which are of great interest in this regard as they offer a large group velocity and a potentially chirality-based protected transport of energy, have not yet been investigated due to their complex internal magnetic field distribution. Here, we present a study of propagating spin waves in a transversely magnetized nanoscopic yttrium iron garnet conduit of 50 nm width. Space and time-resolved microfocused Brillouin-light-scattering spectroscopy is employed to measure the spin-wave group velocity and decay length. A long-range spin-wave propagation is observed with a decay length of up to (8.0 ± 1.5) μm and a large spin-wave lifetime of up to (44.7 ± 9.1) ns. The results are supported with micromagnetic simulations, revealing a broad single-mode frequency range and the absence of a mode localized to the edges. Furthermore, a frequency nonreciprocity for counter-propagating spin waves is observed in the simulations and the experiment, caused by the trapezoidal cross section of the structure. The revealed long-distance spin-wave propagation on the nano-scale is particularly interesting for an application in spin-wave devices, allowing for long-distance transport of information in magnonic circuits and low-energy device architectures.
Examination of laminar Couette flow with obstacles by a low-cost particle image velocimetry setup
(2021)
For many technical applications, a detailed analysis of the fluid mechanical properties is necessary, for which computational fluid dynamics (CFD) simulations are used. However, even though flow simulations are becoming faster and more accurate, validation through experimentation is essential. One way of validation is to use Particle Image Velocimetry (PIV), an imaging technique that can visualize the flow field and measure flow velocities. Since the measuring equipment of commercial systems is very expensive, we propose a low-cost PIV setup that is also affordable for small scientific institutions. In addition to the quality of the acquired images, the reliability and comparability between experiment and simulation are also important issues. Therefore, in this work, we compare the image acquisition quality of the proposed low-cost PIV system with two- and three-dimensional CFD simulations for a laminar Couette flow and a laminar flow around square and hexagonal obstacles with very good agreement. In addition, we analyzed the transferability of 2D and 3D CFD simulations with experiments by measuring the velocity field and found that experimentally determined flow velocities often cannot be used to validate idealized (2D) simulations due to the spatial flow that occurs. However, if the non-ideal conditions of the experiment are considered in the (3D) simulation, a good comparability is given and an experimental validation is possible, for which the presented low-cost PIV system is well suitable.
In situ condition monitoring of rotary shaft seals could significantly improve the reliability of future seals in numerous applications. A superficial application of strain gauges capturing the state of deformation could offer a cost-effective retrofit solution for indirect measurements of central operational parameters. Within a simulative investigation of the sealing system, possible sensor positions for determination of the preload as well as the friction torque prevailing in the sealing contact are therefore identified as two parameters directly related to the operating condition. Further investigations of the potential sensor signal with focus on its time-dependent behavior prove the theoretical feasibility of the measurement concepts developed and provide promising prospects for an initial technical implementation.
A building's indoor climate is an essential input variable for a variety of building physics computational models, simulations, and analyses. Precise knowledge of the indoor climate is necessary to minimize the risk of mold or moisture damage and is required to ensure minimum heat insulation standards in buildings. Detailed data are especially necessary for the progressive application of transient calculations, for example, concerning thermal comfort or energy consumption. While the properties of building materials and the (local) outdoor climate are known, only rudimentary information about the dynamic indoor climate is available. Most existing information in the literature about indoor climate is fairly general and forgoes a differentiation between climatic region, occupancy profile, and the utilization of rooms. In this paper, we report on indoor climate measurements in naturally ventilated apartments over a period of 1 year. The measurement results complement the existing data to provide accurate indoor climate data in buildings. The measured values of indoor temperature and relative humidity serve to derive the dew point temperature and moisture load whereby dynamic time-dependent regression functions are determined for these parameters. The evaluations are carried out separately according to room use. The comparison of living rooms and bedrooms indicates a great influence of room use on the indoor climate in residential buildings. The determined indoor climate model can be used for the planning of buildings and simulations. The classification into living rooms and bedrooms makes it possible to take user behavior into account more realistically in building physics simulations. The minimum thermal insulation in residential buildings can also be checked and designed based on realistic data. The prediction interval describes the limits in which residential rooms are free of damage with a high probability. In this way, the indoor climate model describes an approach to examine and evaluate simulation results regarding condensation risk and mold damage in naturally ventilated rooms.
Magnetic heterostructures consisting of single-crystal yttrium iron garnet (YIG) films coated with platinum are widely used in spin-wave experiments related to spintronic phenomena such as the spin-transfer-torque, spin-Hall, and spin-Seebeck effects. However, spin waves in YIG/Pt bilayers experience much stronger attenuation than in bare YIG films. For micrometer-thick YIG films, this effect is caused by microwave eddy currents in the Pt layer. This paper reports that by employing an excitation configuration in which the YIG film faces the metal plate of the microstrip antenna structure, the eddy currents in Pt are shunted and the transmission of the Damon–Eschbach surface spin wave is greatly improved. The reduction in spin-wave attenuation persists even when the Pt coating is separated from the ground plate by a thin dielectric layer. This makes the proposed excitation configuration suitable for injection of an electric current into the Pt layer and thus for application in spintronics devices. The theoretical analysis carried out within the framework of the electrodynamic approach reveals how the platinum nanolayer and the nearby highly conductive metal plate affect the group velocity and the lifetime of the Damon–Eshbach surface wave and how these two wavelength-dependent quantities determine the transmission characteristics of the spin-wave device.
A novel core–shell species for the adsorption-based separation of carbon dioxide (CO2) from methane (CH4) is introduced by hydrothermal synthesis of Ni-MOF-74 on mesoporous spherical Al2O3 carrier substrate. The material was characterized and the shell thickness determined by means of optical and scanning electron microscopy as well as volumetric adsorption and fluid displacement experiments. Kinetic experiments with Ni-MOF-74@Al2O3 core–shell composites carried out at 303.15 K and at pressures up to 10 bar expose remarkably dominating uptake rates for CO2 over CH4. In the contrary Ni-MOF-74@Al2O3 appears to be unselective according to equilibrium data at the same conditions. Dynamic breakthrough experiments of binary CH4/CO2-mixtures (at 303.15 K and 5 bar) prove the prevailing effect of adsorption kinetics and the storage function of the mesoporous core. This statement is supported by a considerable boost in CO2-selectivity and capacity compared to adsorption equilibria measured on pure Ni-MOF-74 by the factor of 55.02 and up to 2.42, respectively.
Surface wetting can be simulated using a phase field approach which describes the continuous liquid-gas transition with the help of an order parameter. In this publication, wetting of non-planar surfaces is investigated based on a phase field model by Diewald et al. [1, 2]. Different scenarios of droplets on rough surfaces are simulated. The static equilibrium for those scenarios is calculated using an Allen-Cahn evolution equation. The influence of the surface morphology on the resulting contact angle is investigated while the width of the phase transition from liquid to gas is varied as a model parameter.
The great flexibility of direct laser writing (DLW) arises from the possibility to fabricate precise three-dimensional structures on very small scales as well as the broad range of applicable materials. However, there is still a vast number of promising materials, which are currently inaccessible requiring the continuous development of novel photoresists. Herein, a new bio-sourced resist is reported that uses the monomeric unit of chitin, N-acetyl-D-glucosamine, paving the way from existing hydrogel resists based on animal carbohydrates to a new class of non-hydrogel ones. In addition, it is shown that the combined use of two photoinitiators is advantageous over the use of a single one. In this approach, the first photoinitiator is a good two-photon absorber at the applied wavelength, while the second photoinitiator exhibits poor two-photon absorbtion abilities, but is better suited for cross-linking of the monomer. The first photoinitiator absorbs the light acting as a sensitizer and transfers the energy to the second initiator, which subsequently forms a radical and initializes the polymerization. This sensitization effect enables a new route to utilize reactive photointiators with a small two-photon absorption cross section for DLW without changing their chemical structure.
Starting from [(η5-cyclopentadienyl)(η6-phenyl)iron(II)]imidazole, dicationic imidazolium salts were prepared by N-alkylation. Reaction of these compounds with basic metal precursors such as mesityl copper(I) or palladium(II) acetate led to mono respectively dicationic transition metal NHC complexes (NHC=N-heterocyclic carbene). Transmetalation using the copper(I) complexes opened up the access to NHC gold(I) compounds. PEPPSI-type NHC complexes of palladium(II) and platinum(II) were prepared by offering a neutral pyridine ligand to the transition metal center. A rhodium(I) NHC complex was accessible by deprotonation of the dicationic imidazolium precursor and subsequent treatment with [(COD)Rh(μ2-Cl)]2 (COD=1,5-cyclooctadiene). The new NHC complexes were investigated by means of NMR spectroscopy, mass spectrometry as well as single crystal X-ray structure analysis. Both, the palladium(II) containing PEPPSI-type and the gold(I) complex, were investigated for their catalytic properties in typical model reactions such as cyclization reactions, Suzuki coupling and cyanation. In addition, a selenium adduct was synthesized in order to study the electronic properties of the underlying ligand backbone. Based on the chemical shift in the 77Se NMR spectrum, it is evident that these NHC ligands possess rather poor π-acidity.
Janus materials are anisotropic nano- and microarchitectures with two different faces consisting of distinguishable or opposite physicochemical properties. In parallel with the discovery of new methods for the fabrication of these materials, decisive progress has been made in their application, for example, in biological science, catalysis, pharmaceuticals, and, more recently, in battery technology. This Minireview systematically covers recent and significant achievements in the application of task-specific Janus nanomaterials as heterogeneous catalysts in various types of chemical reactions, including reduction, oxidative desulfurization and dye degradation, asymmetric catalysis, biomass transformation, cascade reactions, oxidation, transition-metal-catalyzed cross-coupling reactions, electro- and photocatalytic reactions, as well as gas-phase reactions. Finally, an outlook on possible future applications is given.
The folding of newly synthesized polypeptides requires the coordinated action of molecular chaperones. Prokaryotic cells and the chloroplasts of plant cells possess the ribosome-associated chaperone trigger factor, which binds nascent polypeptides at their exit stage from the ribosomal tunnel. The structure of bacterial trigger factor has been well characterized and it has a dragon-shaped conformation, with flexible domains responsible for ribosome binding, peptidyl-prolyl cis–trans isomerization (PPIase) activity and substrate protein binding. Chloroplast trigger-factor sequences have diversified from those of their bacterial orthologs and their molecular mechanism in plant organelles has been little investigated to date. Here, the crystal structure of the plastidic trigger factor from the green alga Chlamydomonas reinhardtii is presented at 2.6 Å resolution. Due to the high intramolecular flexibility of the protein, diffraction to this resolution was only achieved using a protein that lacked the N-terminal ribosome-binding domain. The eukaryotic trigger factor from C. reinhardtii exhibits a comparable dragon-shaped conformation to its bacterial counterpart. However, the C-terminal chaperone domain displays distinct charge distributions, with altered positioning of the helical arms and a specifically altered charge distribution along the surface responsible for substrate binding. While the PPIase domain shows a highly conserved structure compared with other PPIases, its rather weak activity and an unusual orientation towards the C-terminal domain points to specific adaptations of eukaryotic trigger factor for function in chloroplasts.
An improved route for the highly stereoselective synthesis of (Z)-2-oxyenamides is reported. The desired products can be accessed in only three steps from aminoacetaldehyde dimethyl acetal as common, readily available building block in a highly modular fashion. The improved procedure has been applied to the synthesis of various acylated and sufonylated oxyenamides. Mechanistic and theoretical studies provide a conclusive rationale for the observed stereoselectivities.
Scaled boundary isogeometric analysis (SB-IGA) describes the computational domain by proper boundary NURBS together with a well-defined scaling center; see [5]. More precisely, we consider star convex domains whose domain boundaries correspond to a sequence of NURBS curves and the interior is determined by a scaling of the boundary segments with respect to a chosen scaling center. However, providing a decomposition into star shaped blocks one can utilize SB-IGA also for more general shapes. Even though several geometries can be described by a single patch, in applications frequently there appear multipatch structures. Whereas a C0 continuous patch coupling can be achieved relatively easily, the situation becomes more complicated if higher regularity is required. Consequently, a suitable coupling method is inevitably needed for analyses that require global C1 continuity.In this contribution we apply the concept of analysis-suitable G1 parametrizations [2] to the framework of SB-IGA for the C1 coupling of planar domains with a special consideration of the scaling center. We obtain globally C1 regular basis functions and this enables us to handle problems such as the Kirchhoff-Love plate and shell, where smooth coupling is an issue. Furthermore, the boundary representation within SB-IGA makes the method suitable for the concept of trimming. In particular, we see the possibility to extend the coupling procedure to study trimmed plates and shells.The approach was implemented using the GeoPDEs package [1] and its performance was tested on several numerical examples. Finally, we discuss the advantages and disadvantages of the proposed method and outline future perspectives.
Print path-dependent contact temperature dependency for 3D printing using fused filament fabrication
(2022)
This paper focuses on the effects of different time spans and thus different contact temperatures when a molten strand contacts an adjacent already solidified strand in a plane during 3D printing with fused filament fabrication. For this purpose, both the manufacturing parameters and the geometry of the component are systematically varied and the effect on morphology and mechanical properties is investigated. The results clearly show that even with identical printing parameters, the transitions between the individual layers are much more visible with long time spans until fusion and lead to low mechanical properties. In contrast, short spans lead to hardly visible welds and high mechanical properties. Transferring the findings to different component sizes ultimately verifies that the average temperature at the time of contact between the already solidified and the currently deposited strand is decisive for component quality. In order to generate high component qualities, this finding must therefore be taken into account in the future in the path generation strategy, i.e., in so-called slicing.
Methods for predicting Henry's law constants Hij are important as experimental data are scarce. We introduce a new machine learning approach for such predictions: matrix completion methods (MCMs) and demonstrate its applicability using a data base that contains experimental Hij values for 101 solutes i and 247 solvents j at 298 K. Data on Hij are only available for 2661 systems i + j. These Hij are stored in a 101 × 247 matrix; the task of the MCM is to predict the missing entries. First, an entirely data-driven MCM is presented. Its predictive performance, evaluated using leave-one-out analysis, is similar to that of the Predictive Soave-Redlich-Kwong equation-of-state (PSRK-EoS), which, however, cannot be applied to all studied systems. Furthermore, a hybrid of MCM and PSRK-EoS is developed in a Bayesian framework, which yields an unprecedented performance for the prediction of Hij of the studied data set.
Based on conservation of resources theory, this paper examines the mediating mechanisms in the relationship between digital affordances and employee corporate entrepreneurship participation likelihood. Findings from an experimental study with 207 employees show a statistically significant and positive indirect effect of digital affordances on employee corporate entrepreneurship participation likelihood through employee-perceived information technology support for innovation and a statistically significant and—contrary to our expectations—positive indirect effect through employee-perceived work overload. Results are corroborated by insights from in-depth interviews with senior managers. They provide support for digital affordances as action potentials that are associated with resource gains that in turn foster employee corporate entrepreneurship participation likelihood.
Overexpression of the vacuolar sugar transporter TST1 in Arabidopsis leads to higher seed lipid levels and higher total seed yield per plant. However, effects on fruit biomass have not been observed in crop plants like melon, strawberry, cotton, apple, or tomato with increased tonoplast sugar transporter (TST) activity. Thus, it was unclear whether overexpression of TST in selected crops might lead to increased fruit yield, as observed in Arabidopsis. Here, we report that constitutive overexpression of TST1 from sugar beet in the important crop species Camelina sativa (false flax) resembles the seed characteristics observed for Arabidopsis upon increased TST activity. These effects go along with a stimulation of sugar export from source leaves and not only provoke optimised seed properties like higher lipid levels and increased overall seed yield per plant, but also modify the root architecture of BvTST1 overexpressing Camelina lines. Such mutants grew longer primary roots and showed an increased number of lateral roots, especially when developed under conditions of limited water supply. These changes in root properties result in a stabilisation of total seed yield under drought conditions. In summary, we demonstrate that increased vacuolar TST activity may lead to optimised yield of an oil-seed crop species with high levels of healthy ω3 fatty acids in storage lipids. Moreover, since BvTST1 overexpressing Camelina mutants, in addition, exhibit optimised yield under limited water availability, we might devise a strategy to create crops with improved tolerance against drought, representing one of the most challenging environmental cues today and in future.