Structure and Dynamics of Dust Clusters: Rotation and Magnetic Fields

Ensembles of charged, micrometer-sized dust particles conned in the sheath of a rf-discharge are typically in a strongly-coupled state and form crystal-like structures (dust clusters). This thesis focuses on the eects of magnetic elds and rotation on the structure and dynamics of dust clusters. Both topics, magnetization and rotation, are linked, since dust structures in the presence of magnetic elds are usually in a rotating state. Furthermore, the Larmor theorem states that the Lorentz force and the Coriolis force are mathematically equivalent and aect the dynamics of dust clusters in a similar way. In order to systematically study the eects of cluster rotation, a dust centrifuge is introduced as a new technique to set dust clusters into rotation. This allows to clearly separate the eects of rotational motion from the in uence of magnetic elds. In a frame of a rotating cluster two pseudo-forces appear: the centrifugal force, which eectively weakens the radial connement of the dust clusters and oers the possibility to probe the dust-dust interaction. Moreover, the Coriolis force, which modies the dynamics of a dust cluster in a similar way as it is expected from a giant magnetic eld. Here, a proof-of-principle is given that the Coriolis force can be used to effctively magnetize a small dust cluster and to study the simultaneous eects of (pseudo) magnetization and strong coupling in a dusty plasma device. The second focus of this thesis lies on the eects of magnetic elds on the dynamics of dust clusters. The mechanism of cluster rotation in the presence of an axial agnetic eld is discussed. It is found that the cluster rotation is accompanied by a co-rotation of the neutral gas column, which can result in an unexpected sense of rotation and magnitude of the rotation frequencies in comparison to an established model of cluster rotation, which is based on a balance of ion and neutral drag force. Furthermore, the dust-dust interaction force is of special interest, which is substantially modied by the ow of ions in the plasma sheath and the formation of ion wakes. Here, the phase-resolved resonance method is introduced to measure the nonreciprocity of the interaction force and the partial decharging of particles in the wake of another with high precision. It turns out that both eects are not independent of each other and that the decharging eect enhances the nonreciprocity of the particle interaction due to a coupling with the external connement. In a further step, the in uence of a strong magnetic eld on the ion-wake-mediated particle interaction force is studied. It is shown for the rst time that a magnetic eld parallel to the ion ow severely reduces the interaction forces, which is in qualitative agreement with linear response calculations predicting a reduction of the wake charge. At last, an alternative approach to reach the realms of fully magnetized dusty plasmas is discussed. Going down in particle size from micrometer-sized dust particles to nanoparticles might allow to produce a dusty plasma, where even the motion of the dust is directly aected by a strong magnetic eld. Here, two important steps towards this aim are made. First, a modied discharge geometry is proposed, which allows to conne dust clouds in a plasma column in the presence of strong magnetic elds. Second, an "Imaging Mie Ellipsometer" is introduced, which provides important parameters, such as the dust size and the dust density, with high spatiotemporal resolution

Linear-response Description of the Series Resistance of Large-area Silicon Solar Cells: Resolving the Difference between Dark and Illuminated Behavior

AbstractDirectly from luminescence images it can be shown that, for constant average injection (lumped dark current) and for not-too-large lateral voltage differences, besides the sign, the current flow direction doesn’t play any role for the voltages present, so the series resistances in the dark and under illumination are the same. This fits to the results of a linear-response based series resistance description, treating lateral voltage differences on large-area silicon solar cells in linear order in the series resistance as deviation from the case of zero resistance. In this approach it is found that for constant lumped dark current, emitter and grid of a large-area solar cell can be described as a passive network. Therefore, no difference occurs in the voltage distribution caused by inward and outward currents except for the sign. This contradicts several literature works reporting a smaller lumped series resistance of silicon solar cells in the dark than under illumination. However, we show that this contradiction is just a result of the series resistance definition applied in the respective works or that it can be the result of unsuitable measurement conditions. In a numerical modeling of a large-area silicon solar cell as a 1D distributed structure, using exactly the same parameters as Araújo et al. [IEEE-TED 33 (3), 391–401 (1986)] but calculating the lumped series resistance from the integrated Joule losses, we obtain completely different results than Araújo et al.: Under short-circuit condition, the series resistance stays constant, and there is no difference between the open-circuit and dark series resistance; the latter show the same dependence on the diode current density

Quantitative Modelling and Perspective Taking: Two Competencies of Decision Making for Sustainable Development

Land use change, natural resource use and climate change are challenging Sustainable Development issues (SDGs 13–15). Fostering the competencies to deal with such issues is one core task for current educational endeavors. Among these competencies, decision-making competencies are central. In detail, we investigate how learners evaluate alternative decision-making options to improve existing competence models. We exemplify our competence modelling approach using the designation of a Marine Protected Area. The cross-sectional sample consists of secondary school students and student teachers (N = 760). Partial Credit modelling shows that quantitative modelling of decision-making options is a different competence dimension than perspective taking if contextualized for Sustainable Development. In quantitative modelling, mathematical modelling is used to evaluate and reflect on decision-making options. Perspective taking covers the ability to consider different normative perspectives on Sustainable Development issues. Both dimensions show plausible (latent) correlations with related constructs within the nomological net, i.e., with qualitative arguing, economic literacy, mathematical competencies, reading competencies and analytical problem solving. Furthermore, person-abilities increase with level of education for both dimensions. The identified competence dimensions quantitative modelling and perspective taking were successfully modelled and shown to be distinct; the resulting measuring instrument is reliable and valid

A Failure-Tolerant Approach for Autonomous Mobile Manipulation in RoboCup@Work

In this paper we summarize how the LUHbots team was able to win the 2015 RoboCup@Work league. We introduce various failure handling concepts, which lead to the robustness necessary to outperform all the other teams. The proposed concepts are based on failure prevention and failure handling

Wohlstand und Wachstum

Die Zweifel wachsen, ob allein die Höhe und der Verlauf des Bruttoinlandsprodukts ausreichen, den Wohlstand einer Gesellschaft zu messen. Um diese Frage zu diskutieren, hatte der Deutsche Bundestag Anfang 2011 eine Enquete-Kommission eingerichtet, die im Frühjahr 2013 ihren Abschlussbericht vorgelegt hat. Dies nahmen die Akademie für Politische Bildung Tutzing und das ifo Institut zum Anlass, unter der Leitung von Dr. Wolfgang Quaisser, Akademie für Politische Bildung Tutzing, und Prof. Dr. Kai Carstensen, ifo Institut am 7. und 8. Juni 2013 eine Fachtagung zu organisieren, um die Ergebnisse zu diskutieren. Einige der dort vorgestellten Vorträge werden hier veröffentlicht

Association Between Maternal Folic Acid Supplementation and Congenital Heart Defects in Offspring in Birth Cohorts From Denmark and Norway

Background: Evidence linking individual‐level maternal folic acid supplementation to offspring risk of congenital heart defects is lacking. We investigated whether folic acid supplementation in early pregnancy reduces offspring risk of heart defects in 2 large birth cohort studies. Methods and Results: Women recruited in early pregnancy within the DNBC (Danish National Birth Cohort), 1996–2003, and MoBa (Norwegian Mother and Child Cohort Study), 2000–2009, were followed until delivery. Information on periconceptional intake of folic acid and other supplements was linked with information on heart defects from national registers. Among 197 123 births, we identified 2247 individuals with heart defects (114/10 000). Periconceptional (4 weeks before through 8 weeks after conception) use of folic acid plus other supplements (54.8%), folic acid only (12.2%), and non–folic acid supplements (5.0%) were compared with no supplement use (28.0%); the adjusted relative risks of heart defects were 0.99 (95% CI, 0.80–1.22), 1.08 (95% CI, 0.93–1.25), and 1.07 (95% CI, 0.97–1.19), respectively. For initiation of folic acid in the preconception period weeks −4 to −1 (33.7%) and the postconception periods 0 to 4 weeks (15.5%), 5 to 8 weeks (17.8%), and 9 to 12 weeks (4.6%), compared with no or late folic acid intake (29.1%), relative risks of heart defect were 1.11 (95% CI, 1.00–1.25), 1.09 (95% CI, 0.95–1.25), 0.98 (95% CI, 0.86–1.12), and 0.97 (95% CI, 0.78–1.20), respectively. Relative risks of severe defects, conotruncal defects, and septal defects showed similar results. Conclusions: Folic acid was not associated with offspring risk of heart defects, including severe defects, conotruncal defects, or septal defects.publishedVersio