Electromagnetic Manipulation of Individual Nano- and Microparticles

Gegenstand der vorliegenden Dissertation ist die Untersuchung von einzelnen nano- und mikrometergroßen Partikeln, zum Verständnis und zur Entwicklung von neuartigen nanooptischen Elementen, wie Lichtquellen und Sensoren, sowie Strukturen zum Aufsammeln und Leiten von Licht. Neben der Charakterisierung stehen dabei verschiedene Methoden zur elektromagnetischen Manipulation im Vordergrund, die auf eine Kontrolle der Position oder der Geometrie der Partikel ausgerichtet sind. Die gezielten Manipulationen werden verwendet, um vorausgewählte Partikel zu isolieren, modifizieren und transferieren. Dadurch können Partikel zu komplexeren photonischen Systemen kombiniert werden, welche die Funktionalität der einzelnen Bestandteile übertreffen. Der Hauptteil der Arbeit behandelt Experimente mit freischwebenden Partikeln in linearen Paul-Fallen. Durch die räumliche Isolation im elektrodynamischen Quadrupolfeld können Partikel mit reduzierter Wechselwirkung untersucht werden. Neben der spektroskopischen Charakterisierung von optisch aktiven Partikeln (farbstoffdotierte Polystyrol-Nanokügelchen, Cluster aus Nanodiamanten mit Stickstoff-Fehlstellen-Zentren, Cluster aus kolloidalen Quantenpunkten) sowie optischen Resonatoren (plasmonische Silber-Nanodrähte, sphärische Siliziumdioxid-Mikroresonatoren) werden neu entwickelte Methoden zur Manipulation vorgestellt, mit denen sich individuelle Partikel freischwebend kombinieren und elektromagnetisch koppeln sowie aus der Falle auf optischen Fasern zur weiteren Untersuchung bzw. zur Funktionalisierung photonischer Strukturen ablegen lassen. In einem weiteren Teil der Arbeit wird eine Methode zur Manipulation der Geometrie von plasmonischen Nanopartikeln vorgestellt. Dabei werden einzelne Goldkugeln auf einem Deckglas mit einem fokussierten Laserstrahl zum Schmelzen gebracht und verformt. Durch die kontrollierte und reversible Veränderung der Symmetrie lassen sich die lokalisierten Oberflächenplasmonen des Partikels gezielt beeinflußen.The topic of the present thesis is the investigation of single nano- and microsized particles for the understanding and design of novel nanooptical elements as light sources and sensors, as well as light collecting and guiding structures. In addition to particle characterization, the focus is on different methods for electromagnetic particle manipulation aimed at controlling the particle’s position or geometry. The specific manipulations are used for isolation, modification and transfer of preselected particles, enabling combination of particles into more complex photonic systems, which exceed the functionalities of the individual constituents. The main part of this work deals with experiments on levitated particles in linear Paul traps. Due to the spatial isolation in the electrodynamic quadrupole field, particles can be investigated with reduced environmental interaction. In addition to spectroscopic characterization of optically active particles (dye-doped polystyrene nanobeads, clusters of nanodiamonds with nitrogen vacancy defect centers, clusters of colloidal quantum dots) and particles with optical resonances (plasmonic silver nanowires, spherical silica microresonators) new manipulation methods are presented that enable assembly and electromagnetic coupling of individual, levitated particles as well as deposition of particles from the trap on optical fibers for further characterization or functionalization of photonic structures. In a further part of this work a method to manipulate the geometry of plasmonic nanoparticles is presented. Single gold nanospheres on a coverslip are melted and shaped with a focused laser beam. The localized surface plasmons can be influenced specifically by controlled and reversible changes of the particle symmetry

'Flying Plasmons': Fabry-P\`erot Resonances in Levitated Silver Nanowires

Plasmonic nano structures such as wire waveguides or antennas are key building blocks for novel highly integrated photonics. A quantitative understanding of the optical material properties of individual structures on the nanoscale is thus indispensable for predicting and designing the functionality of complex composite elements. In this letter we study propagating surface plasmon polaritons in single silver nanowires isolated from its environment by levitation in a linear Paul trap. Symmetry-breaking effects, e.g., from supporting substrates are completely eliminated in this way. Illuminated with white light from a supercontinuum source, Fabry-P\`erot-like resonances are observed in the scattering spectra obtained from the ends of the nanowires. The plasmonic nature of the signal is verified by local excitation and photon collection corresponding to a clean transmission measurement through a Fabry-P\`erot resonator. A numerical simulation is used to compute the complex effective refractive indices of the nanowires as input parameter for a simple Fabry-P\`erot model, which nicely reproduces the measured spectra despite the highly dispersive nature of the system. Our studies pave the way for quantitative characterization of nearly any trappable plasmonic nano object, even of fragile ones such as droplets of liquids or molten metal and of nearly any nanoresonator based on a finite waveguide with implications for modeling of complex hybrid structures featuring strong coupling or lasing. Moreover, the configuration has the potential to be complemented by gas sensors to study the impact of hot electrons on catalytic reactions nearby plasmonic particles

Wissen und Naturkatastrophen: einige Überlegungen zum Thema Nichtwissen und ein empirisches Beispiel

"Ausgehend von der These, dass das Hochwasser 2002 den kollektiven Erfahrungshorizont überstieg, wird der Frage nachgegangen, auf Grundlage welcher Wissensbestände und Handlungsressourcen betroffene soziale Gruppen mit der Gefahr umgegangen sind und welche Auswirkungen dies auf ihre Verwundbarkeit hatte. Dabei wird zunächst auf katastrophensoziologische und geographische Theorien rekurriert. Sowohl das katastrophensoziologische Theorem FAKKEL (Clausen) als auch sozialgeographische Konzeptionen von Verwundbarkeit (Blaikie u.a.) betrachten Faktoren sozialer Ungleichheit als zentrale Verwundbarkeitsdeterminanten. Es ist jedoch zu berücksichtigen, dass das FAKKEL-Theorem als makrosoziologische Fassung von Katastrophen gedacht ist und der Verwundbarkeitsansatz dem Kontext von 'Entwicklungsländern' entstammt. Daher ist zu hinterfragen, inwiefern sie auf moderne Industriegesellschaften anwendbar sind. Nahezu konträr argumentieren Theoretiker reflexiver Modernisierung (Giddens, Beck). Sie konstatieren, dass sich traditionelle Handlungskonstellationen und -routinen auflösen und durch stärker wissensabhängige und -vermittelte Strukturen ersetzt werden. Daraus ergeben sich zwei weitere Fragen: Treffen diese Überlegungen auch auf den Umgang mit Hochwassergefahren zu? Welche Auswirkungen hat der postulierte Modernisierungsprozess auf die Verwundbarkeit verschiedener Gruppen? Um diese Fragen zu beantworten, wird auf empirische Daten einer Haushaltsbefragung sowie narrative Interviews im Rahmen des EU-Projekts FLOODsite zurückgegriffen und gezeigt, dass verschiedene lokale Milieus in Bezug auf das Hochwasser 2002 unterschiedlich verwundbar waren. Es lassen sich zum einen verletzlichkeits- und schadensmindernde Handlungsstrategien identifizieren, die mit dem Konzept der 'reflexiven Modernisierung' beschrieben werden können. Zum anderen - und quantitativ bedeutsamer - sind traditionale Milieus auszumachen, die im Fall des Hochwassers 2002 verwundbarer waren als andere. Ihr Handeln wurde wesentlich dadurch beeinflusst, dass das Ausmaß des Ereignisses auf der Basis überkommener Wissensbestände so nicht antizipierbar war. Abschließen wird der Vortrag mit Reflexionen über die praktischen Implikationen der Ergebnisse." (Autorenreferat

Better prepared but less resilient: the paradoxical impact of frequent flood experience on adaptive behavior and resilience

To better understand factors shaping adaptive behavior and resilience is crucial in designing policy strategies to prepare people for future flooding. The central question of our paper is how frequent flood experience (FFE) impacts adaptive behavior and self-reported resilience. The applied empirical methods are binary logistic and linear regression models using data from a panel dataset including 2462 residents (Germany, state of Saxony). Four main conclusions from the investigations can be drawn. First, more flood-experienced respondents are statistically significantly more likely to have taken precautionary measures in the past. Second, FFE has a statistically significant negative impact on self-reported resilience. Third, the impact of FFE on the capacity to recover and the capacity to resist is statistically significantly non-linear. Fourth, putting together these results reveals the paradox of more flood-experienced respondents being better prepared but feeling less resilient at the same time. It can be concluded that more research is needed to obtain deeper insights into the drivers behind self-reported resilience and that this study can be seen as a piece of the puzzle, taking frequent flood experience as the primary entry point.</p

Assessing cubicle dimensions for finishing bulls based on animal behaviour and cleanliness

Finishing bulls need increasingly large cubicles throughout their growth, and optimal cubicle dimensions may differ from those used for dairy cows. The space requirements of finishing bulls was investigated by observing standing-up and lying-down behaviour, lying duration and number of lying bouts, as well as the cleanliness of cubicles and animals before and after increasing cubicle size at four different points in time. Lying area in the cubicles measured 120 × 70 cm at the start and 185 × 110 cm at the end of the finishing period (approx. at 160 and 550 kg, respectively). Twenty animals kept in four groups were observed at weights of approximately 220, 330, 380 and 500 kg before and after cubicle dimensions were increased. The proportion of standing-up events with more than one head lunge decreased with enlargement of the cubicles (P = 0·01). As cubicle size increased, bulls hit the partition rails less on standing up, except at 220 kg weight where the pattern was inverted (interaction: P = 0·001). Partitions were also hit less on lying down as cubicle size increased, except at 220 kg weight with an inverse pattern (interaction: P = 0·01). The number of exploratory head sweeps before lying down did not change with cubicle enlargement (P > 0·5). Bulls slipped more often with cubicle enlargement, except at 380 kg where the difference was inverted (interaction: P = 0·03). They never fell and never turned around in the cubicles. In general, both animals and cubicles were very clean. On average, lying duration decreased (P < 0·01) while the number of lying bouts tended to increase (P = 0·052) with enlargement of the cubicles but the absolute differences were small. Consequently at each point in time, the smaller cubicles still seemed to provide sufficient lying space for the bulls. If the impacts with the partitions were minor and did not represent a serious welfare concern, as suggested by qualitative observations, the cubicle dimensions used could be considered suitable for housing the type of finishing bulls used in this stud

Managing urban flood resilience through the English planning system: insights from the ‘SuDS-face'

In academic and professional circles, ‘resilience thinking’ has emerged as the dominant paradigm in flood risk management, which emphasizes the need to plan and design cities that can absorb water and replicate natural processes more closely. In this paper, we explore how planners in England are expected to respond to the resilience agenda against the realities in practice, zoning in on the delivery of sustainable (urban) drainage systems (SuDS). Our exploration highlights that, while SuDS are being implemented, they are largely characterized by a ‘bog standard’ design. We found that there are three main institutional factors that are constraining the implementation of SuDS: the lack of legislative backing, the power afforded to private commercial interests in the neoliberalized planning process, compounded by the severe lack of resources in local authorities. What is missing at the moment is SuDS process and design that is flexible, integrated, collaborative and innovative. There are clear implications that, without the necessary institutional support, resilience thinking will remain largely aspirational, and professionals will struggle to gain traction and translate the larger flood resilience policy agenda into England's future climate-resilient places