Late Quaternary climate and environmental reconstruction based on lake and peat sediments from the central southern Cape region of South Africa

This thesis aims at reconstructing environmental and climatic, and particularly hydrological changes in South Africa during the Late Quaternary. Hydrogen isotopes from leaf wax-derived n-alkanes and oxygen isotopes from hemicellulose-derived sugars were analysed in a first step on modern reference material from South Africa in order to evaluate the potential of both biomarker isotopes as well as coupling them in a paleohygrometer for robust paleohydrological reconstruction. In a second step, two sediment archives, i.e., Lake Voёlvlei and the peatland Vankervelsvlei, located at Africa’s southern Cape coast were identified as ideally suited for paleoenvironmental and -climatic reconstruction. Both records have been analysed using a broad multi-proxy approach including well-established sedimentological and geochemical proxies as well as innovative biomarker isotopes and the paleohygrometer approach in high temporal resolution. For the first time in this region, this combination of proxies was used to draw a coherent picture of moisture availability and precipitation sources along South Africa’s southern Cape coast. During the Holocene, hydroclimate variability was driven by contributions from Easterly- and locally-derived precipitation leading to moist conditions and a year-round precipitation regime from ~7.5 to ~5.0 ka and from ~3.0 ka until present day. Drier conditions accompanied by a shift to a winter rainfall regime occurred from ~5.0 to ~3.0 ka. Comparisons with other regional records support these results, but the driving forces behind this climate variability are still subject of considerable debate. On Late Quaternary timescales, low sea level caused the coastline to migrate south of its present position leading to increased continentality and dry conditions during glacial periods. During interglacial periods, the coastline was approximately where it is situated in recent times due to high sea level leading to more humid conditions at Vankervelsvlei

The Transformative Power of Urban Arrival Infrastructures: Berlin’s Refugio and Dong Xuan Center

Migration researchers and urban scholars are increasingly applying infrastructural approaches to analyze the production and organization of urban spaces and migration. While transformative and transforming power seem to be inherent characteristics of infrastructures, studies to date have rarely emphasized this aspect, only placing minimal focus on its importance for understanding the constitution and development of infrastructures and for examining the mobility of migrants. In the current article, we study Berlin’s Refugio, an alternative form of housing for forced migrants, and the city’s Dong Xuan Center (DXC), a Vietnamese hypermarket. We argue that they not only represent infrastructures in which newcomers reach a city, and navigate their trajectories, as well as the obstacles, and opportunities of urban life, but they are also ‘infrastructures of conversion’ that transform material space and the people inhabiting them, and their entanglement with the city. While the DXC and Refugio emerged out of necessity, addressing the lack of economic (DXC) and housing (Refugio) opportunities, they have changed into cultural and economic hubs for migrant communities and beyond. On the one hand, these changes come with multilayered negotiation processes, revealing a complex interplay of interests, actors, and internal hierarchies within the DXC and Refugio. On the other hand, their transformation illustrates the influence of local planning authorities, institutions, and the pressure to culturally and economically exploit their social, spatial, and ‘ethnic’ characteristics. This mesh elucidates the diffuse position of both infrastructures in the urban realm. While their existence and future development is constantly challenged, they simultaneously represent political spaces that prompt institutional logics and questions of immigrant integration

Fullerene als alternative Akzeptoren bei der Transferdotierung von Diamantoberflächen

The topic of this thesis is the fullerene induced surface conductivity on hydrogen terminated diamond. This novel doping mechanism is described here for the first time. It relies on the high electron affinity of the fullerenes on the one side and on the low ionization energy of hydrogen terminated diamond of only 4.2 eV which is the smallest of all common semiconductors on the other side. Fluorofullerenes C60F18, C60F36 and C60F48 were used as well as common backyball C60. To this end the successive deposition of fullerenes using an electron beam evaporator and the evaluation of the fullerene layer thickness with sub monolayer precision by X-ray photoelectron spectroscopy was achieved. The characterization of fullerenes using photoemission spectroscopy gives information about composition and purity of the material. The C1s signature of the fluorofullerenes consists of two spectral lines separated by a chemical shift. This allowed the verification of the stoichiometry of the evaporated molecules with a deviation of ± 1 F atom. The C1s core level spectra show a varying splitting of these peaks depending on the degree of fluorination from 2.2 eV for C60F48, 2.4 eV for C60F36 culminating in 3.0 eV for C60F18. This result could be attributed to the geometrical structure of the molecules. Both the loss spectrum and the valence band spectrum show in particular for the highly symmetric C60 characteristic structures, due to molecular orbitals that appear well separated on account of the large degeneracy of states. This again can be used for the clear identification of these molecules. A systematic investigation of C60, C60F18, C60F36 and C60F48 as transfer dopants on hydrogenated diamond has been performed. Thereby, electrons from hydrogenated diamond are transferred to the fullerenes leaving a subsurface hole layer behind that gives a pronounced conductivity. The doping efficiency increases with F content and reaches unity for C60F48, corresponding to the continuous rise in electron affinity. Whereas C60F48 acts as a surface acceptor even in molecular form, for C60 the formation of the solid fullerite phase is required to yield a sufficiently high electron affinity (≈ 4.1 eV) and correspondingly low activation energy for electron transfer out of the diamond. p−type surface transfer doping of hydrogen terminated diamond by fullerenes leads to sheet conductivities in the range of 10−4−10−5 S that are comparable to or even higher than those observed for the atmosphere induced surface conductivity of hydrogenated diamond. The doping efficiency can be quantitatively understood by considering the energy levels of diamond and the adsorbate layers and evaluating the hole density in diamond and the electron density in the adsorbate layer in thermal equilibrium. For C60, the doping mechanism is more accurately described as a charge exchange in an extreme type II heterojunction. On the other hand a molecular surface acceptor model that takes the degeneracy of holes and the electric field caused by charge separation into account has been performed for the case of C60F48 in excellent agreement with experimental results. Using in situ Hall Effect measurements of air, C60, and C60F48 induced conductivity the sign of the charge carriers that dominate the transport properties was determined. Independent of the kind of adsorbate, it could be confirmed that holes in the valence band of diamond are responsible for the surface conductivity on hydrogenated diamond. At ambient temperature the hole mobility µ as a function of the induced charge carrier density p between p = 5 • 1010 cm−2 and p = 3 • 1013 cm−2 was measured. A maximum of the mobility of 130 − 150 cm2V −1s−1 occurs for p = 2 • 1011 cm−2. Temperature dependent Hall measurements between 77 and 350 K show a non−activated, constant charge carrier density on all examinated samples, independently of the kind of adsorbates. On the other hand, both the conductivity and the mobility exhibit temperature dependence, varying with the charge carrier concentration. A not ideal activated transport in inversion layers with strong localization has been considered to explain the experimental results. An essential part of this thesis addressed the investigation and the improvement of the thermal stability of the fullerene layers. The thermal stability of the fullerene induced surface conductivity in vacuum is governed by the loss of dopant molecules through sublimation. C60F48 and C60F36 are molecules with high vapour pressures and a sizeable desorption rate is observed already at room temperature. C60F18 and C60 have lower vapour pressures and sublime at about 200 °C. In order to extend the thermal stability of these compounds and thus the surface conductivity to higher temperatures three different strategies were investigated. The first uses diverse dielectric layers as protective coatings, namely SiO, CaF2, and Si3N4. These dielectric layers do indeed improve the thermal stability. However, the improvement is limited to temperatures below 250 °C: at T = 300 °C the surface conductivity induced by C60F48 is only 0.1 % of its initial value even with protection. An entirely different stabilization mechanism was detected for C60. Here prolonged exposure to air and light leads to the oxidation of C60 and an oxygen mediated polymerization. A controlled polymerization of C60 layers on diamond in pure oxygen atmosphere and UV light was systematically investigated by photoemission spectroscopy. This process lowers the vapour pressure sufficiently without impairing the doping efficiency for C60 on diamond to maintain a surface conductivity in the 10−5 S range up to 500 °C in vacuo. Also, C60F48 molecules can be linked by oxygen radicals, even though with lower efficiency, due to the reduced number of  −bonds. In order to achieve the covalent attachment of C60F48 to a hydrogen terminated diamond surface a process for controlled partially hydrolisation was developed. Functionalization with hydroxyl groups could be achieved by using a remote water vapour plasma at room temperature for a few seconds as demonstrated by photoelectron spectroscopy. Prolonged water plasma exposure, however, as well as annealing at temperatures above 200 °C destroys the O−H groups again by converting them into ether and ketone configurations. A chemical shift of the O1s signal by 0.5 eV after evaporation of C60F48 confirms the successful attachment of the molecules to the hydrogen terminated diamond surface via hydroxyl functionalization. The covalent attachment seems to be stable up to 200 °C in vacuum. However, the fluorofullerene cages themselves show a significant decomposition at this temperature. Whereas the fluorofullerenes can be used as extremely efficient dopands, the advantage of C60 lies in its excellent thermal stability. It remains to be seen, if polymerized, coated C60 layers can lead to the fabrication of diamond based electronic devices.Der zentrale Gegenstand dieser Arbeit war die fullereninduzierte Oberflächenleitfähigkeit von wasserstoffabgesättigten Diamantoberflächen. Neben dem Standardfulleren C60 kamen die fluorierten Modifikationen C60F18, C60F36 und C60F48 zum Einsatz. Es gelang die kontrollierte Deposition der Fullerene und die Bestimmung der Bedeckung mit Hilfe der Photoemissionsspektroskopie bis in den Submonolagenbereich. Die Charakterisierung der Fullerene mittels Photoemission liefert unter anderem wichtige Erkenntnisse über die Zusammensetzung und die Reinheit des verwendeten Materials. Anhand von C1s Spektren kann die Stöchiometrie der aufgedampften Fluorofullerene mit einer Unsicherheit von einem F−Atom bestimmt werden. Die C1s Rumpfniveauspektren zeigen eine von der Höhe der Fluorierung abhängige Aufspaltung zwischen der chemisch verschobenen C1s Linie (C2−C−F) und dem nicht verschobenen C1s Peak (C3−C) von 2,2 eV bei C60F48 über 2,4 eV bei C60F36 bis hin zu 3,0 eV bei C60F18. Die Unterschiede können auf die geometrische Struktur der Moleküle zurückgeführt werden. Insbesondere für das hochsymmetrische C60 zeigen das Elektronenverlust-spektrum und das Valenzbandspektrum wegen der hohen Entartung der Zustände wohl separierte Strukturen, die zur eindeutigen Identifizierung dieses Moleküls genutzt werden können. Weiterhin wurde eine systematische Untersuchung der Fullerene C60, C60F18, C60F36 und C60F48 als Akzeptoren auf wasserstoffterminiertem Diamant durchgeführt. Wegen der Zunahme der Elektronenaffinität der Fullerene mit steigendem Fluorgehalt nimmt auch ihre Dotiereffizienz kontinuierlich zu und erreicht für C60F48 den Wert eins. Während es sich bei C60F48 um einen rein molekularen Akzeptor handelt, führt bei C60 erst die Ausbildung der Festkörperphase zu einer für die Transferdotierung ausreichend hohen Elektronenaffinität (≈ 4,1 eV) und somit zu einer niedrigen Aktivierungsenergie für den Elektronentransfer aus dem Diamant. Die p−typ Dotierung der Oberfläche durch die Fullerenmoleküle führt zu Leitfähigkeitswerten, die vergleichbar oder im Falle von C60F48 sogar höher ausfallen, als dies bei der luftinduzierten Oberflächenleitfähigkeit der Fall ist. Durch die Analyse der Energieniveaus von Diamant und der auf der Oberfläche adsorbierten Fullerene konnte ein quantitatives Verständnis der Transferdotierung erreicht werden. Dazu wurden die Löcherdichte im Diamantvalenzband und die Elektronenkonzentration in der Adsorbatschicht im thermodynamischen Gleichgewicht berechnet. Im Falle von C60 wird die Transferdotierung am besten durch den Ladungsaustausch in einem extremen Typ−II Heteroübergang beschrieben. Dagegen zeigt das molekulare Modell, welches die Löcherentartung im Diamantvalenzband und das durch die Ladungsseparation auf der Oberfläche entstehende elektrische Feld berücksichtigt, für die C60F48−Akzeptoren eine hervorragende Übereinstimmung mit den experimentellen Ergebnissen. Im Rahmen der in situ Hall−Effekt Messungen an der luft−, C60−, und C60F48−induzierten Leitfähigkeit wurde das Vorzeichen der dominanten Ladungsträger beim Transport bestimmt. Es hat sich unabhängig von der Art den Adsorbaten bestätigt, dass stets Löcher im Diamantvalenzband für die Oberflächenleitfähigkeit auf einem H−terminierten Diamant verantwortlich sind. Ferner wurde bei Raumtemperatur die Löcherbeweglichkeit µ als Funktion der induzierten Ladungsträgerdichte p im Bereich zwischen p = 5 • 1010 cm−2 und p = 3 • 1013 cm−2 gemessen. Bei p = 2 • 1011 cm−2 wird ein Maximum der Beweglichkeit von 130 − 150 cm2V −1s−1 beobachtet. Bei den temperaturabhängigen Messungen zwischen 77 und 350 K wurde auf allen untersuchten Proben, unabhängig von der Art der Adsorbate, eine nicht aktivierte, konstante Ladungsträgerdichte festgestellt. Dagegen zeigen sowohl die Leitfähigkeit als auch die Beweglichkeit im selben Temperaturbereich eine mit der Höhe der Ladungsträgerkonzentration variierende Abhängigkeit von der Temperatur. Für die luftinduzierte Oberflächenleitfähigkeit finden auch andere Forschungsgruppen entsprechende Ergebnisse. Als Modell wird unter anderen der „nicht ideale“ aktivierte Transport in Inversionsschichten mit starker Lokalisierung diskutiert. Ein wesentlicher Teil dieser Arbeit widmete sich der Untersuchung und der Verbesserung der thermischen Eigenschaften von aufgedampften Fullerenschichten. Die Temperaturbeständigkeit der fullereninduzierten Oberflächenleitfähigkeit ist im Vakuum durch die Sublimation der Dotiermoleküle begrenzt. Während C60F48 und C60F36 relativ hohe Dampfdrücke aufweisen, die bereits bei Raumtemperatur zu beträchtlichen Sublimationsraten führen, haben C60F18 und C60 niedrigere Dampfdrücke und sublimieren erst bei 200 °C. Um die thermische Stabilität dieser Molekülschichten und somit der Oberflächenleitfähigkeit zu erhöhen, wurden drei unterschiedliche Strategien verfolgt. Als erstes wurde die Passivierung der Oberfläche mit verschiedenen Dielektrika, nämlich SiO, CaF2 und Si3N4, untersucht. Es ergab sich dabei eine klare Verbesserung der Temperaturbeständigkeit, obgleich nur für Temperaturen unter 250 °C. Nach Anlassen auf 300 °C lag die C60F48−induzierte Leitfähigkeit unter 0,1 % ihres Ausgangswertes und zwar unabhängig von der verwendeten Passivierungs-schicht. Ein völlig anderer Mechanismus der thermischen Stabilisierung von C60 wurde bei Proben, die gleichzeitig der Luft und der Laborbeleuchtung ausgesetzt waren, beobachtet. Dabei werden die Fullerenschichten durch Sauerstoffradikale oxidiert, wodurch sich ein durch O−Brücken verknüpftes Polymernetzwerk bildet. Eine kontrollierte Polymerisation von C60−Schichten wurde in einer reinen Sauerstoffatmosphäre in Kombination mit UV−Licht systematisch mit der Photoemissionsspektroskopie untersucht. Dieser Prozess führt zu einer signifikanten Absenkung des Dampfdruckes, ohne dabei die Dotiereffizienz der C60−Schicht wesentlich zu verändern, so dass die Oberflächenleitfähigkeit selbst nach Anlassen der Proben auf 500 °C unverändert im Bereich von 10−5 S bleibt. Auch C60F48−Moleküle können durch Sauerstoffbrücken miteinander verknüpft werden, wenngleich dies, wegen der niedrigeren Anzahl der  −Bindungen, mit weitaus geringerer Effizienz geschieht. Um eine kovalente Anbindung von C60F48 auf einem wasserstoffabgesättigten Diamanten zu erreichen, wurde eine Methode zur partiellen Hydrolysierung der Oberfläche entwickelt. Durch den kontrollierten Einsatz von Wasserdampfplasma im Remote−Modus bei Raumtemperatur konnte eine OH−Funktionalisierung der Diamantoberfläche erzielt werden. Dagegen führt eine längere Plasma−Expositionszeit, genauso wie das Anlassen der Proben auf Temperaturen über 200 °C, zur Umwandlung der Hydroxyl−Gruppen in Ether− bzw. Kethon−Konfigurationen. Die Photoemissionsanalyse zeigte nach dem Aufdampfen von C60F48 auf eine OH−funktionalisierte Oberfläche eine chemische Verschiebung der O−Linie um 0,5 eV, und bestätigte damit eine erfolgreiche kovalente Anbindung der Moleküle. Diese ist bis etwa 200 °C im Vakuum stabil, wogegen die Fluorofullerenkäfige bei diesen Temperaturen eine klare Degradation aufweisen. Während also die Fluorofullerene eine hocheffiziente Alternative zur luftinduzierten Leitfähigkeit darstellen, zeigt C60 darüber hinaus eine beeindruckende thermische Stabilität. Es bleibt abzuwarten, ob in naher Zukunft der Einsatz von polymerisierten, passivierten C60−Schichten zu einem wesentlichen Fortschritt bei der Herstellung von Bauelementen auf Basis der auf Diamant induzierten Oberflächenleitfähigkeit führt

Help-seeking for mental health problems among older adults with chronic disease: An application of the theory of planned behaviour

Objective: Despite high risk for mental health problems, older adults with chronic diseases underutilise mental health services. This study applied the Theory of Planned Behaviour (TPB) to understand mental health help-seeking intentions among this population and identified factors which influence help-seeking intentions. Method: We conducted a cross-sectional study with a non-clinical sample of 108 older adults aged 65 years or over, living with cardiovascular disease, respiratory disease, and/or type 2 diabetes. TPB variables (attitudes, subjective norms, and perceived behavioural control), intentions to seek help, and additional factors (past help-seeking behaviour, quality of life, and physical health) were assessed using standardised questionnaires. Multiple linear regressions were conducted to identify predictors of help-seeking intentions. Results: 41% of the participants did not intend to seek help, and all three TPB variables were associated with help-seeking intentions. The traditional TPB model accounted for 69.7% of the variance in intentions, and the extended TPB model accounted for an additional 1.6% of the variance. Conclusions: Attitudes and perceived behavioural control have the strongest association with help-seeking intentions among older adults with chronic disease. Further research is needed to identify predictors of mental health help-seeking behaviour and to develop interventions to promote help-seeking in this population. KEY POINTS What is already known about this topic: 1. Older adults aged 65 years or over living with chronic disease are at an increased risk of mental health decline. 2. Older adults underutilise mental health services, and consequently mental health problems often go undiagnosed and untreated in this population. 3. A growing body of research has demonstrated the utility of the Theory of Planned Behaviour in predicting intentions to seek mental health support services. What this topic adds: 1. Most older adults with chronic disease have some intention to seek professional mental health support when needed. 2. Older adults with chronic disease have a high perceived ability to seek professional help. 3. Promoting favourable attitudes towards mental health help-seeking is likely to facilitate the greatest change in help-seeking intentions in the present population

Aurora on Ganymede

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98774/1/jgra50122.pd

Do Personalized AI Predictions Change Subsequent Decision-Outcomes? The Impact of Human Oversight

Regulators of artificial intelligence (AI) emphasize the importance of human autonomy and oversight in AI-assisted decision-making (European Commission, Directorate-General for Communications Networks, Content and Technology, 2021; 117th Congress, 2022). Predictions are the foundation of all AI tools; thus, if AI can predict our decisions, how might these predictions influence our ultimate choices? We examine how salient, personalized AI predictions affect decision outcomes and investigate the role of reactance, i.e., an adverse reaction to a perceived reduction in individual freedom. We trained an AI tool on previous dictator game decisions to generate personalized predictions of dictators’ choices. In our AI treatment, dictators received this prediction before deciding. In a treatment involving human oversight, the decision of whether participants in our experiment were provided with the AI prediction was made by a previous participant (a ‘human overseer’). In the baseline, participants did not receive the prediction. We find that participants sent less to the recipient when they received a personalized prediction but the strongest reduction occurred when the AI’s prediction was intentionally not shared by the human overseer. Our findings underscore the importance of considering human reactions to AI predictions in assessing the accuracy and impact of these tools as well as the potential adverse effects of human oversight

Observations and modeling of H_2 fluorescence with partial frequency redistribution in giant planet atmospheres

Partial frequency redistribution (PRD), describing the formation of the line profile, has negligible observational effects for optical depths smaller than ~10^3, at the resolving power of most current instruments. However, when the spectral resolution is sufficiently high, PRD modeling becomes essential in interpreting the line shapes and determining the total line fluxes. We demonstrate the effects of PRD on the H_2 line profiles observed at high spectral resolution by the Far-Ultraviolet Spectroscopic Explorer (FUSE) in the atmospheres of Jupiter and Saturn. In these spectra, the asymmetric shapes of the lines in the Lyman (v"- 6) progression pumped by the solar Ly-beta are explained by coherent scattering of the photons in the line wings. We introduce a simple computational approximation to mitigate the numerical difficulties of radiative transfer with PRD, and show that it reproduces the exact radiative transfer solution to better than 10%. The lines predicted by our radiative transfer model with PRD, including the H_2 density and temperature distribution as a function of height in the atmosphere, are in agreement with the line profiles observed by FUSE. We discuss the observational consequences of PRD, and show that this computational method also allows us to include PRD in modeling the continuum pumped H_2 fluorescence, treating about 4000 lines simultaneously.Comment: 17 pages, accepted for publication in Ap