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The initiation of a marine ice-sheet instability (MISI) is generally discussed from the ocean side of the ice sheet. It has been shown that the reduction in ice-shelf buttressing and softening of the coastal ice can destabilize a marine ice sheet if the bedrock is sloping upward towards the ocean. Using a conceptional flow-line geometry, we investigate the possibility of whether a MISI can be triggered from the direction of the ice divide as opposed to coastal forcing and explore the interaction between connected basins. We find that the initiation of a MISI in one basin can induce a destabilization in the other. The underlying mechanism of basin interaction is based on dynamic thinning and a consecutive motion of the ice divide which induces a thinning in the adjacent basin and a successive initiation of the instability. Our simplified and symmetric topographic setup allows scaling both the geometry and the transition time between both instabilities. We find that the ice profile follows a universal shape that is scaled with the horizontal extent of the ice sheet and that the same exponent of 1/2 applies for the scaling relation between central surface elevation and horizontal extent as in the pure shallow ice approximation (Vialov profile). Altering the central bed elevation, we find that the extent of grounding-line retreat in one basin determines the degree of interaction with the other. Different scenarios of basin interaction are discussed based on our modeling results as well as on a conceptual flux-balance analysis. We conclude that for the three-dimensional case, the possibility of drainage basin interaction on timescales on the order of 1 kyr or larger cannot be excluded and hence needs further investigation.
The strong adhesion of sub-micron sized particles to surfaces is a nuisance, both for removing contaminating colloids from surfaces and for conscious manipulation of particles to create and test novel micro/nano-scale assemblies. The obvious idea of using detergents to ease these processes suffers from a lack of control: the action of any conventional surface-modifying agent is immediate and global. With photosensitive azobenzene containing surfactants we overcome these limitations. Such photo-soaps contain optical switches (azobenzene molecules), which upon illumination with light of appropriate wavelength undergo reversible trans-cis photo-isomerization resulting in a subsequent change of the physico-chemical molecular properties. In this work we show that when a spatial gradient in the composition of trans- and cis- isomers is created near a solid-liquid interface, a substantial hydrodynamic flow can be initiated, the spatial extent of which can be set, e.g., by the shape of a laser spot. We propose the concept of light induced diffusioosmosis driving the flow, which can remove, gather or pattern a particle assembly at a solid-liquid interface. In other words, in addition to providing a soap we implement selectivity: particles are mobilized and moved at the time of illumination, and only across the illuminated area.
Light-driven diffusioosmosis
(2018)
The emergence of microfluidics created the need for precise and remote control of micron-sized objects. I demonstrate how light-sensitive motion can be induced at the micrometer scale by a simple addition of a photosensitive surfactant, which makes it possible to trigger hydrophobicity with light. With point-like laser irradiation, radial inward and outward hydrodynamic surface flows are remotely switched on and off. In this way, ensembles of microparticles can be moved toward or away from the irradiation center. Particle motion is analyzed according to varying parameters, such as surfactant and salt concentration, illumination condition, surface hydrophobicity, and surface structure.
The physical origin of this process is the so-called light-driven diffusioosmosis (LDDO), a phenomenon that was discovered in the framework of this thesis and is described experimentally and theoretically in this work. To give a brief explanation, a focused light irradiation induces a local photoisomerization that creates a concentration gradient at the solid-liquid interface. To compensate for the change in osmotic pressure near the surface, a hydrodynamic flow along the surface is generated. Surface-surfactant interaction largely governs LDDO. It is shown that surfactant adsorption depends on the isomerization state of the surfactant. Photoisomerization, therefore, triggers a surfactant attachment or detachment from the surface. This change is considered to be one of the reasons for the formation of LDDO flow.
These flows are introduced not only by a focused laser source but also by global irradiation. Porous particles show reversible repulsive and attractive interactions when dispersed in the solution of photosensitive surfactant. Repulsion and attraction is controlled by the irradiation wavelength. Illumination with red light leads to formation of aggregates, while illumination with blue light leads to the formation of a well-separated grid with equal interparticle distances, between 2µm and 80µm, depending on the particle surface density. These long-range interactions are considered to be a result of an increase or decrease of surfactant concentration around each particle, depending on the irradiation wavelength. Surfactant molecules adsorb inside the pores of the particles. A light-induced photoisomerization changes adsorption to the pores and drives surfactant molecules to the outside. The concentration gradients generate symmetric flows around each single particle resulting in local LDDO. With a break of the symmetry (i.e., by closing one side of the particle with a metal cap), one can achieve active self-propelled particle motion.
Amour - Passion?
(2005)
Diese Arbeit befasst sich mit der ganzheitlichen Betrachtung der Fluideigenschaften eines unterpermischen Reservoirs am Geothermie Forschungsstandort Groß Schönebeck (GrSk) bei Reservoirbedingungen und im Betrieb der Geothermieanlage. Die Untersuchungen zur Fluidherkunft ergeben, dass es sich um ein konnates Wasser meteorischen Ursprungs ohne den Einfluss der darüberliegenden Zechsteinwässer handelt. Die Ionen und Isotopenverhältnisse im Formationswasser gelöster Komponenten in GrSk belegen einen gemeinsamen Genesepfad mit Wässern anderer Rotliegend-Reservoire des Nordostdeutschen Beckens (NEGB). Die Isotopenverhältnisse von ⁸⁷Sr/⁸⁶Sr ≈ 0,7158 und von δ³⁴SV CDT ≈ 4,1 ‰ des Sulfats weisen auf die Anreicherung des Fluids mit schweren Isotopen durch die Fluid Gestein-Wechselwirkung mit Vulkaniten und Rotliegend Sandsteinen des Unteren Perms hin.
Das im Formationswasser bei Reservoirbedingungen gelöste Gas (Gas/Wasser ≤ 2 bei STP) enthält Stickstoff (δ¹⁵NAir ≈ 0,6 ‰) und thermogenes Methan (δ¹³CV-PDB ≈ - 18 ‰) aus organischen Karbonablagerungen (Kerogen Typ - III Kohlen) hoher Reife. Die Isotopenverhältnisse der Edelgase belegen eine krustale Herkunft des Gasgemisches. Die berechnete Verweilzeit τ (⁴He) der Gase im Reservoir liegt zwischen 275 und 317 Ma und überschreitet damit bei gegebener Konzentration von Mutternukliden im Reservoirgestein das allgemein angenommene Zeitalter der Sedimentgruppe. Das lässt sich durch eine Zuwanderung von Gasen aus älteren Sedimentfolgen erklären.
Die Veränderungen der physikochemischen Fluidparameter während des Anlagenbetriebs sind hauptsächlich temperaturbedingt. Bei stabilen Produktionsbedingungen und einer Temperatur von ca. 100 °C stabilisieren sich auch die Fluideigenschaften. Bei In situ Bedingungen übertage beträgt die Dichte ρ = 1,1325 ± 0,0002 g ∙ mL⁻¹, das Redoxpotential Eh = -105,5 ± 1,3 mV und der pH = 6,61 ± 0,002. Die relative Zusammensetzung der Gasphase bei stabilen Produktionsbedingungen zeigt dagegen eine geringe Erhöhung des Stickstoffanteils sowie des Anteils der Kohlenwasserstoffe (Ethan, Propan, usw.) und Abnahme des relativen Methananteils im Laufe des Betriebs.
Die quantitative Untersuchung der sekundären mineralischen Ausfällungen im Fluid mittels sequentieller Extraktion zeigte, dass Schwermetalle als eine Hauptkomponente der Fluidfestphase größtenteils in Verbindung mit organischen Molekülen vorliegen. Experimente zum Einfluss organischer Verbindungen unterschiedlicher Substanzklassen auf eine Mobilisierung der Schwermetalle aus dem Reservoirgestein ergaben, dass die Verbindungen wie Fettsäuren und PAK (polyzyklische aromatische Kohlenwasserstoffe) die Freisetzung von Kupfer, Nickel, Chrom und Blei verhindern bzw. zu derer Immobilisierung beitragen. Im Gegensatz dazu wird die Mobilität von Zink in Anwesenheit von diesen Verbindungen erhöht. Niedermolekulare Monocarbonsäuren und stickstoffhaltige Heteroaromaten tragen, mit Ausnahme von Blei, zur Freisetzung bzw. Mobilisierung von Schwermetallen aus dem Reservoirgestein bei.
Die gewonnenen Erkenntnisse dieser Arbeit bestätigen das Risiko massiver Ausfällungen auf der kalten Seite der Geothermieanlage bei Inbetriebnahme des Kraftwerks, wenn keine an den Fluidchemismus angepassten Präventionsmethoden eingesetzt werden. Die Isotopenzusammensetzung der Fluidkomponenten sowie geringfügige Schwankungen der Gaszusammensetzung im kontinuierlichen Anlagenbetrieb lässt eine Kommunikation des unterpermischen Reservoirs mit dem darunter liegenden Oberkarbon vermuten, was eine nachträgliche Veränderung der Fluidzusammensetzung beim Dauerbetrieb der Anlage bedeuten kann.
- Sichtbarer Translator - Jan Assmanns Translationsmodell - Inhaltliche Parallelen zwischen Migration und Translation im erweiterten Übersetzungskonzept - Ein bewohnbarer „dritter Raum“? - Produktives ‚Dazwischen‘ - Migrationsliteratur als Medium kultureller Übersetzung - Poetik der Migration. Die aktuellen literaturwissenschaftlichen ‚Befunde‘ - Nahtstelle: Migration/Translation - Rhetorik - Metaphorik - Denkfiguren - Ambivalente Differenz
In March 2010, the project CoCoCo (incipient COntinent-COntinent COllision) recorded a 650 km long amphibian N-S wide-angle seismic profile, extending from the Eratosthenes Seamount (ESM) across Cyprus and southern Turkey to the Anatolian plateau. The aim of the project is to reveal the impact of the transition from subduction to continent-continent collision of the African plate with the Cyprus-Anatolian plate. A visual quality check, frequency analysis and filtering were applied to the seismic data and reveal a good data quality. Subsequent first break picking, finite-differences ray tracing and inversion of the offshore wide-angle data leads to a first-arrival tomographic model. This model reveals (1) P-wave velocities lower than 6.5 km/s in the crust, (2) a variable crustal thickness of about 28 - 37 km and (3) an upper crustal reflection at 5 km depth beneath the ESM. Two land shots on Turkey, also recorded on Cyprus, airgun shots south of Cyprus and geological and previous seismic investigations provide the information to derive a layered velocity model beneath the Anatolian plateau and for the ophiolite complex on Cyprus. The analysis of the reflections provides evidence for a north-dipping plate subducting beneath Cyprus. The main features of this layered velocity model are (1) an upper and lower crust with large lateral changes of the velocity structure and thickness, (2) a Moho depth of about 38 - 45 km beneath the Anatolian plateau, (3) a shallow north-dipping subducting plate below Cyprus with an increasing dip and (4) a typical ophiolite sequence on Cyprus with a total thickness of about 12 km. The offshore-onshore seismic data complete and improve the information about the velocity structure beneath Cyprus and the deeper part of the offshore tomographic model. Thus, the wide-angle seismic data provide detailed insights into the 2-D geometry and velocity structures of the uplifted and overriding Cyprus-Anatolian plate. Subsequent gravity modelling confirms and extends the crustal P-wave velocity model. The deeper part of the subducting plate is constrained by the gravity data and has a dip angle of ~ 28°. Finally, an integrated analysis of the geophysical and geological information allows a comprehensive interpretation of the crustal structure related to the collision process.
Im Rahmen einer prospektiven Längsschnittuntersuchung wurde der Berufseinstieg von ÄrztInnen (N = 185) als normatives kritisches Lebensereignis untersucht. Dazu wurden sie insgesamt drei Mal im Abstand von jeweils sechs Monaten im ersten Jahr nach ihrem Studiumsabschluss befragt (T1: in den ersten zwei Wochen nach dem Staatsexamen, T2: kurzzeitig nach dem Berufseinstieg, T3: im Schnitt 9.5 Monate nach dem Berufseinstieg). Die Ergebnisse zeigten zunächst, dass unlängst examinierte Jung-ÄrztInnen, die sich vergleichsweise schlechter auf den Beruf durch das Studium vorbereitet fühlten, ihren bevorstehenden Berufseinstieg negativer bewerteten und schon vor diesem beanspruchter waren. Die Bewertung des Berufseinstiegs vermittelte dabei den Zusammenhang zwischen einer schlechten Vorbereitung und der Beanspruchung. Arbeitsspezifische Copingfunktionalität wiederum pufferte den Zusammenhang zwischen einer schlechten Vorbereitung und der Bewertung des Berufseinstiegs. Das Problem einer als schlecht empfundenen Vorbereitung verdeutlichte sich in der Längsschnittanalyse – sie sagte eine höhere Beanspruchung zum zweiten Messzeitpunkt, d.h. nach dem Berufseinstieg, vorher. In der Untersuchung der Beanspruchungsentwicklung über die drei Messzeitpunkte hinweg fanden sich nur wenige Veränderungen. Es ließ sich zwar eine deutliche Zunahme der mittleren Depressivitäts-Ausprägungen über den Berufseinstieg hinweg herausstellen (T1-T2); auf anderen Beanspruchungsindikatoren zeigte sich jedoch kein direkter Effekt des Arbeitsbeginns bzw. fand sich auch keine Adaptation der Jung-ÄrztInnen an ihre neue Situation im Sinne einer sich verringernden Beanspruchung im weiteren Verlauf (T2-T3). In der Erklärung interindividueller Unterschiede in der Beanspruchung im Untersuchungszeitraum zeigte sich, dass die sich mit dem Berufseinstieg einstellende Arbeitsbelastung zum zweiten und dritten Messzeitpunkt erwartungsgemäß positiv mit Beanspruchung assoziiert war. Die Arbeitsbelastungs-Beanspruchungs-Beziehung bestand jedoch nur im Querschnitt; in der Längsschnittanalyse fand sich kein Effekt der T2-Arbeitsbelastung auf die T3-Beanspruchung. Ausgangsunterschiede in psychischen Ressourcen wirkten einerseits direkt auf die Beanspruchung zu T2, zum Teil moderierten sie aber auch den Zusammenhang zwischen der Arbeitsbelastung und Beanspruchung: Eine höhere Resilienz und die Wahrnehmung sozialer Unterstützung sagten eine geringere Beanspruchung nach dem Berufseinstieg vorher. Jung-ÄrztInnen, die sich durch eine stärkere Arbeitsbelastung auszeichneten, aber über ein funktionaleres Bewältigungsverhalten im Arbeitskontext verfügten, waren kurzzeitig nach dem Berufseinstieg weniger beansprucht als stark arbeitsbelastete Jung-ÄrztInnen mit weniger funktionalem Coping. Verringerungen in den psychischen Ressourcen über den Berufseinstieg hinweg wirkten sich direkt, d.h. per se ungünstig auf die Beanspruchung zum dritten Messzeitpunkt aus. Zudem interagierten sie mit der zu diesem Zeitpunkt bestehenden Arbeitsbelastung in Vorhersage der Beanspruchung. Stärker arbeitsbelastete Jung-ÄrztInnen, deren Copingfunktionalität und Wahrnehmung sozialer Unterstützung vom ersten zum dritten Messzeitpunkt abgenommen hatte, waren am Ende des Untersuchungszeitraums am stärksten beansprucht. Hinsichtlich der Auswirkungen des Berufseinstiegs auf die Persönlichkeit der Jung-ÄrztInnen fanden sich ungünstige Veränderungen: Sowohl die Ausprägungen psychischer Ressourcen (Widerstandsfähigkeit, Wahrnehmung sozialer Unterstützung hinsichtlich der Arbeitstätigkeit) als auch die der Big Five-Faktoren nahmen im Mittel ab. Interindividuelle Unterschiede in den Veränderungen ließen sich auf die Beanspruchung kurzzeitig nach dem Berufseinstieg (T2) bzw. auf deren Entwicklung in den Folgemonaten (T2-T3) zurückführen: Jene Jung-ÄrztInnen, die vergleichsweise stark beansprucht auf den Berufseinstieg reagiert hatten bzw. deren Beanspruchung im weiteren Verlauf zunahm, zeigten entsprechend ungünstige Veränderungen. Die Ergebnisse zusammengefasst verdeutlicht sich folgende Problematik: Jung-ÄrztInnen, die weniger gut, d.h. persönlichkeitsbasiert geschützt den Berufseinstieg absolvieren, reagieren stärker beansprucht und sind dann auch diejenigen, deren Persönlichkeit sich in den ersten Arbeitsmonaten ungünstig verändert. Jung-ÄrztInnen mit geringen psychischen Ressourcen sind folglich nicht nur besonders vulnerabel für die Entwicklung von Beanspruchung angesichts belastender Arbeitsbedingungen, sondern ihre vergleichsweise hohe Beanspruchung bedingt eine weitere Verringerung des Schutz- und Pufferpotenzials ihrer Persönlichkeit. Es kommt zu einer ungünstigen Akzentuierung der ohnehin schon vergleichsweise ressourcenschwachen Persönlichkeit, welche die Vulnerabilität für zukünftige Beanspruchung erhöht. Aus den Ergebnissen lässt sich ein Unterstützungsbedarf junger ÄrztInnen in der sensiblen und wegweisenden Berufseinstiegsphase ableiten. Neben einer Verbesserung ihrer Arbeitsbedingungen stellen eine rechtzeitige Sensibilisierung junger ÄrztInnen für den Arbeitsbelastungs-Beanspruchungs-Zusammenhang, ihre regelmäßige Supervision sowie vor allem aber auch kompetenzorientiertes und ressourcenstärkendes Feedback von den Mentoren und Vorgesetzten die Grundlage dafür dar, dass die Jung-MedizinerInnen selbst gesund bleiben und sie die ärztliche Tätigkeit trotz ihres wohl stets hohen Belastungspotenzials als erfüllend und zufriedenstellend erleben.
Rezensiertes Werk: Mitterecker, Thomas Josef: Das Erzstift Salzburg im Zweiten Koalitionskrieg : Kämpfe - Besetzung - Folgen / Thomas Josef Mitterecker. - Frankfurt am Main [u.a.] : Lang, 2001. - 138 S. - (Europäische Hochschulschriften ; 914 : Reihe 3, Geschichte und ihre Hilfswissenschaften) Zugl.: Salzburg, Univ., Magisterarbeit, 2000 ISBN 3-631-38420-3
Rezensiertes Werk: Schneider, Thomas Michael: Heeresergänzung und Sozialordnung : Dienstpflichtige, Einsteher und Freiwillige in Württemberg zur Zeit des Deutschen Bundes / Thomas Michael Schneider. - Frankfurt am Main [u.a.] : Lang, 2001. - X, 400 S. : graph. Darst. - ([Europäische Hochschulschriften / 3]: Europäische Hochschulschriften ; Bd. 917 : Reihe 3, Geschichte und ihre Hilfswissenschaften) Zugl.: Münster (Westfalen), Univ., Diss., 2001 ISBN 3-631-38459-9
Rezensiertes Werk: Hagemann, Karen: "Mannlicher Muth und teutsche Ehre" : Nation, Militär und Geschlecht zur Zeit der antinapoleonischen Kriege Preußens / Karen Hagemann. - Paderborn [u.a.] : Schöningh, 2002. - 617 S. : Ill., Kt. - (Krieg in der Geschichte ; Bd. 8) Zugl.: Berlin, Techn. Univ., Habil.-Schr., 2000 ISBN 3-506-74477-1
Software-Fehlerinjektion
(2016)
Fehlerinjektion ist ein essentielles Werkzeug, um die Fehlertoleranz komplexer Softwaresysteme experimentell zu evaluieren.
Wir berichten über das Seminar zum Thema Software-Fehlerinjektion, das am Fachgebiet für Betriebssysteme und Middleware am Hasso-Plattner-Institut der Universität Potsdam im Sommersemester 2015 stattfand.
In dem Seminar ging es darum, verschiedene Fehlerinjektionsansätze und -werkzeuge anzuwenden und hinsichtlich ihrer Anwendbarkeit in verschiedenen Szenarien zu bewerten.
In diesem Bericht werden die studierten Ansätze vorgestellt und verglichen.
rezensiertes Werk: Stephan Dörschel: Fritz Wisten : bis Zum letzten Augenblick : ein jüdisches Theaterleben. - Hentrich & Hentrich : Berlin, 2009. - 112 S. (Jüdische Miniaturen ; 74) ISBN 978-3-938485-85-9
rezensiertes Werk: Schwartz, Yigal: Maamin beli Kenessija : 4 Massot al Aharon Appelfeld. - Tel Aviv : Dvir, 2009.- 181 S.
rezensiertes Werk: Marx, Peter W.:Ein theatralisches Zeitalter : Bürgerliche Selbstinszenierungen um 1900. - Tübingen [u.a.] : A. Francke, 2008. - 429 S. ISBN 978-3-772-08220-7
rezensiertes Werk: Critchfield, Richard D.: From Shakespeare to Frisch: The Provocative Fritz Kortner. - Heidelberg : Synchron, 2008. - 223 S. ISBN 978-3-935025-99-7
Motivation: Corruption is often cited as a central reason why development projects fail. The article tests this claim by assessing whether World Bank projects perform worse in implementation environments with a higher corruption level. The article focuses specifically on bribery between public officials and firms during the procurement of needed goods and services. Approach and Methods: I use data from the World Bank's Enterprise Surveys to avoid the often-criticized corruption perception indices and to allow for an assessment of effects at the subnational level. The analysis builds on an assessment of the performance ratings of 1,228 World Bank projects and covers 87 different countries. Finding: Overall, the article finds a small but statistically significant correlation between the corruption level and project performance. This result indicates that the corruption level of recipient countries should be considered during the design and implementation of projects. Policy Implications: Nonetheless, the relatively small correlation and the low pseudo R-squareds advise not overestimating the relevance of corruption for project performance. At least for the project level, the article finds no indication that corruption is a primary obstacle to aid effectiveness.
Zunächst wird der Begriff der Globalisierung konkretisiert, deren Indikatoren beschrieben sowie mögliche Auswirkungen auf Volkswirtschaften diskutiert, bevor dann die Auswirkungen auf die russische Volkswirtschaft genauer betrachtet werden. Dabei wird vor allem die Abhängigkeit von Rohstoffpreisen sowie die Rolle ausländischer Direktinvestitionen herausgestellt und durch verschiedene empirische Erkenntnisse belegt. Ein weiterer Schwerpunkt der Betrachtung stellt die Rolle der Banken, insbesondere auch vor dem Hintergrund der jüngsten Finanzkrise dar. Abschließend werden mögliche Probleme der russischen Volkswirtschaft im Bezug auf die Globalisierung dargestellt und Ansätze zu deren Lösung vorgestellt.
Aufgrund der Bedeutung von Experimenten im physikalischen Erkenntnisprozess, sind diese ein wesentlicher Bestandteil des Physikunterrichts. Um den Einsatz von Experimenten im Physikunterricht zu fördern, sind kompetenzorientiertes Experimentieren und die Reflexion des Einsatzes von Experimenten wichtige Ziele in Lehrkräftebildungsprogrammen. Ablaufmodelle für kompetenzorientiertes Experimentieren unterscheiden typischerweise Phasen der Fragen- und Hypothesenentwicklung, der Planung, der Erforschung und der Schlussfolgerungen. Es ist allerdings unklar, auf welche Weise angehende Physiklehrkräfte Aspekte des kompetenzorientierten Experimentierens in ihrem Unterricht in schulpraktischen Ausbildungsphasen einsetzen, auf welche Weise sie solche Unterrichtsversuche mit Experimentierbezug reflektieren und wie strukturiert (im Sinne der Ablaufmodelle) sie dabei vorgehen.
In der vorliegenden Studie wurde deshalb untersucht, auf welche Weise Praxissemesterstudierende Experimentierprozesse in ihren Unterrichtsversuchen reflektieren. Hierfür wurde betrachtet, zu welchen Anteilen die Experimentierphasen in den Reflexionen adressiert werden. Um weiterhin herauszufinden, mit welcher Qualität die Experimentplanung reflektiert wird und inwiefern sich Vorstrukturierung für die Planungsphase zeigt, wurde diese differenzierter betrachtet. Auf Basis empirischer Vorarbeiten wurde vermutet, dass Fragenentwicklung, Hypothesenbildung und Experimentplanung seltener thematisiert werden als die anderen Teilkompetenzen und dass die Planungsphase hauptsächlich stark vorstrukturierte Elemente enthält, statt den Lernenden Freiräume für selbstständige Planungen zu lassen.
Zur Untersuchung der Fragestellung wurden Kodiermanuale zur Erfassung experimentierbezogener Kompetenzen in schriftlichen Reflexionen entwickelt und validiert. Analysiert wurden 40 Reflexionstexte von 14 Studierenden des Physik-Lehramts im Praxissemester an der Universität Potsdam. Als Untersuchungsmethode wurde die qualitative Inhaltsanalyse genutzt. Die Texte wurden bezüglich der Umsetzung eines Reflexionsmodells und auf das Vorkommen der Teilkompetenzen des Experimentierzyklus untersucht.
Die Ergebnisse bestätigten das geringe Vorkommen der Fragenentwicklung und Hypothesenbildung sowie die tendenziell geschlossenen Planungsinhalte. Zudem konnte festgestellt werden, dass die Planungsphase eher oberflächlich reflektiert und vor allem Arbeitsaufträge wiedergegeben wurden. Allgemein zeigten sich hauptsächlich beschreibende Tendenzen in den Reflexionen und eher wenige Alternativen und Konsequenzen. Aus den Ergebnissen werden Implikationen für die Lehrkräftebildung im Fach Physik abgeleitet. Um die Reflexionskompetenz der angehenden Lehrkräfte zu fördern, sind Hilfestellungen während des Reflexionsprozesses und eine inhaltliche Rückmeldung notwendig. Des Weiteren sollten die angehenden Lehrkräfte für eine ausgewogenere Förderung der Teilkompetenzen in ihrem Unterricht sensibilisiert werden.
Despite general concern that the massive deposits of methane stored under permafrost underground and undersea could be released into the atmosphere due to rising temperatures attributed to global climate change, little is known about the methanogenic microorganisms in permafrost sediments, their role in methane emissions, and their phylogeny. The aim of this thesis was to increase knowledge of uncultivated methanogenic microorganisms in submarine and terrestrial permafrost deposits, their community composition, the role they play with regard to methane emissions, and their phylogeny. It is assumed that methanogenic communities in warmer submarine permafrost may serve as a model to anticipate the response of methanogenic communities in colder terrestrial permafrost to rising temperatures. The compositions of methanogenic communities were examined in terrestrial and submarine permafrost sediment samples. The submarine permafrost studied in this research was 10°C warmer than the terrestrial permafrost. By polymerase chain reaction (PCR), DNA was extracted from each of the samples and analyzed by molecular microbiological methods such as PCR-DGGE, RT-PCR, and cloning. Furthermore, these samples were used for in vitro experiment and FISH. The submarine permafrost analysis of the isotope composition of CH4 suggested a relationship between methane content and in situ active methanogenesis. Furthermore, active methanogenesis was proven using 13C-isotope measurements of methane in submarine permafrost sediment with a high TOC value and a high methane concentration. In the molecular-microbiological studies uncultivated lines of Methanosarcina, Methanomicrobiales, Methanobacteriacea and the Groups 1.3 and Marine Benthic from Crenarchaeota were found in all submarine and terrestrial permafrost samples. Methanosarcina was the dominant group of the Archaea in all submarine and terrestrial permafrost samples. The archaeal community composition, in particular, the methanogenic community composition showed diversity with changes in temperatures. Furthermore, cell count of methanogens in submarine permafrost was 10 times higher than in terrestrial permafrost. In vitro experiments showed that methanogens adapt quickly and well to higher temperatures. If temperatures rise due to climate change, an increase in methanogenic activity can be expected as long as organic material is sufficiently available and qualitatively adequate.
Piloting a Survey-Based Assessment of Transparency and Trustworthiness with Three Medical AI Tools
(2022)
Artificial intelligence (AI) offers the potential to support healthcare delivery, but poorly trained or validated algorithms bear risks of harm. Ethical guidelines stated transparency about model development and validation as a requirement for trustworthy AI. Abundant guidance exists to provide transparency through reporting, but poorly reported medical AI tools are common. To close this transparency gap, we developed and piloted a framework to quantify the transparency of medical AI tools with three use cases. Our framework comprises a survey to report on the intended use, training and validation data and processes, ethical considerations, and deployment recommendations. The transparency of each response was scored with either 0, 0.5, or 1 to reflect if the requested information was not, partially, or fully provided. Additionally, we assessed on an analogous three-point scale if the provided responses fulfilled the transparency requirement for a set of trustworthiness criteria from ethical guidelines. The degree of transparency and trustworthiness was calculated on a scale from 0% to 100%. Our assessment of three medical AI use cases pin-pointed reporting gaps and resulted in transparency scores of 67% for two use cases and one with 59%. We report anecdotal evidence that business constraints and limited information from external datasets were major obstacles to providing transparency for the three use cases. The observed transparency gaps also lowered the degree of trustworthiness, indicating compliance gaps with ethical guidelines. All three pilot use cases faced challenges to provide transparency about medical AI tools, but more studies are needed to investigate those in the wider medical AI sector. Applying this framework for an external assessment of transparency may be infeasible if business constraints prevent the disclosure of information. New strategies may be necessary to enable audits of medical AI tools while preserving business secrets.
We describe a natural construction of deformation quantisation on a compact symplectic manifold with boundary. On the algebra of quantum observables a trace functional is defined which as usual annihilates the commutators. This gives rise to an index as the trace of the unity element. We formulate the index theorem as a conjecture and examine it by the classical harmonic oscillator.
We introduce a natural symmetry condition for a pseudodifferential operator on a manifold with cylindrical ends ensuring that the operator admits a doubling across the boundary. For such operators we prove an explicit index formula containing, apart from the Atiyah-Singer integral, a finite number of residues of the logarithmic derivative of the conormal symbol.
For general elliptic pseudodifferential operators on manifolds with singular points, we prove an algebraic index formula. In this formula the symbolic contributions from the interior and from the singular points are explicitly singled out. For two-dimensional manifolds, the interior contribution is reduced to the Atiyah-Singer integral over the cosphere bundle while two additional terms arise. The first of the two is one half of the 'eta' invariant associated to the conormal symbol of the operator at singular points. The second term is also completely determined by the conormal symbol. The example of the Cauchy-Riemann operator on the complex plane shows that all the three terms may be non-zero.
The index formula for elliptic pseudodifferential operators on a two-dimensional manifold with conical points contains the Atiyah-Singer integral as well as two additional terms. One of the two is the 'eta' invariant defined by the conormal symbol, and the other term is explicitly expressed via the principal and subprincipal symbols of the operator at conical points. In the preceding paper we clarified the meaning of the additional terms for first-order differential operators. The aim of this paper is an explicit description of the contribution of a conical point for higher-order differential operators. We show that changing the origin in the complex plane reduces the entire contribution of the conical point to the shifted 'eta' invariant. In turn this latter is expressed in terms of the monodromy matrix for an ordinary differential equation defined by the conormal symbol.
In the preceding paper we proved an explicit index formula for elliptic pseudodifferential operators on a two-dimensional manifold with conical points. Apart from the Atiyah-Singer integral, it contains two additional terms, one of the two being the 'eta' invariant defined by the conormal symbol. In this paper we clarify the meaning of the additional terms for differential operators.
Using the Riemannian connection on a compact manifold X, we show that the algebra of classical pseudo-differential operators on X generates a canonical deformation quantization on the cotangent manifold T*X. The corresponding Abelian connection is calculated explicitly in terms of the of the exponential mapping. We prove also that the index theorem for elliptic operators may be obtained as a consequence of the index theorem for deformation quantization.
We consider a G-invariant star-product algebra A on a symplectic manifold (M,ω) obtained by a canonical construction of deformation quantization. Under assumptions of the classical Marsden-Weinstein theorem we define a reduction of the algebra A with respect to the G-action. The reduced algebra turns out to be isomorphic to a canonical star-product algebra on the reduced phase space B. In other words, we show that the reduction commutes with the canonical G-invariant deformation quantization. A similar statement in the framework of geometric quantization is known as the Guillemin-Sternberg conjecture (by now completely proved).
We construct a deformation quantization on an infinite-dimensional symplectic space of regular connections on an SU(2)-bundle over a Riemannian surface of genus g ≥ 2. The construction is based on the normal form thoerem representing the space of connections as a fibration over a finite-dimensional moduli space of flat connections whose fibre is a cotangent bundle of the infinite-dimensional gauge group. We study the reduction with respect to the gauge groupe both for classical and quantum cases and show that our quantization commutes with reduction.
We give a construction of an eigenstate for a non-critical level of the Hamiltonian function, and investigate the contribution of Morse critical points to the spectral decomposition. We compare the rigorous result with the series obtained by a perturbation theory. As an example the relation to the spectral asymptotics is discussed.
In this work, the development of a new molecular building block, based on synthetic peptides derived from decorin, is presented. These peptides represent a promising basis for the design of polymer-based biomaterials that mimic the ECM on a molecular level and exploit specific biological recognition for technical applications. Multiple sequence alignments of the internal repeats of decorin that formed the inner and outer surface of the arch-shaped protein were used to develop consensus sequences. These sequences contained conserved sequence motifs that are likely to be related to structural and functional features of the protein. Peptides representative for the consensus sequences were synthesized by microwave-assisted solid phase peptide synthesis and purified by RP-HPLC, with purities higher than 95 mol%. After confirming the desired masses by MALDI-TOF-MS, the primary structure of each peptide was investigated by 1H and 2D NMR, from which a full assignment of the chemical shifts was obtained. The characterization of the peptides conformation in solution was performed by CD spectroscopy, which demonstrated that using TFE, the peptides from the outer surface of decorin show a high propensity to fold into helical structures as observed in the original protein. To the contrary, the peptides from the inner surface did not show propensity to form stable secondary structure. The investigation of the binding capability of the peptides to Collagen I was performed by surface plasmon resonance analyses, from which all but one of the peptides representing the inner surface of decorin showed binding affinity to collagen with values of dissociation constant between 2•10-7 M and 2.3•10-4 M. On the other hand, the peptides representative for the outer surface of decorin did not show any significant interaction to collagen. This information was then used to develop experimental demonstration for the binding capabilities of the peptides from the inner surface of decorin to collagen even when used in more complicated situations close to possible appications. With this purpose, the peptide (LRELHLNNN) which showed the highest binding affinity to collagen (2•10-7 M) was functionalized with an N-terminal triple bond in order to obtain a peptide dimer via copper(I)-catalyzed cycloaddition reaction with 4,4'-diazidostilbene-2,2'-disulfonic acid. Rheological measurements showed that the presence of the peptide dimer was able to enhance the elastic modulus (G') of a collagen gel from ~ 600 Pa (collagen alone) to ~ 2700 Pa (collagen and peptide dimer). Moreover, it was shown that the mechanical properties of a collagen gel can be tailored by using different molar ratios of peptide dimer respect to collagen. The same peptide, functionalized with the triple bond, was used to obtain a peptide-dye conjugate by coupling it with N-(5'-azidopentanoyl)-5-aminofluorescein. An aqueous solution (5 vol% methanol) of the peptide dye conjugate was injected into a collagen and a hyaluronic acid (HA) gel and images of fluorescence detection showed that the diffusion of the peptide was slower in the collagen gel compared to the HA gel. The third experimental demonstration was gained using the peptide (LSELRLHNN) which showed the lower binding affinity (2.3•10-4 M) to collagen. This peptide was grafted to hyaluronic acid via EDC-chemistry, with a degree of functionalization of 7 ± 2 mol% as calculated by 1H-NMR. The grafting was further confirmed by FTIR and TGA measurements, which showed that the onset of decomposition for the HA-g-peptide decreased by 10 °C compared to the native HA. Rheological measurements showed that the elastic modulus of a system based on collagen and HA-g-peptide increased by almost two order of magnitude (G' = 200 Pa) compared to a system based on collagen and HA (G' = 0.9 Pa). Overall, this study showed that the synthetic peptides, which were identified from decorin, can be applied as potential building blocks for biomimetic materials that function via biological recognition.
One of the most significant current discussions in Astrophysics relates to the origin of high-energy cosmic rays. According to our current knowledge, the abundance distribution of the elements in cosmic rays at their point of origin indicates, within plausible error limits, that they were initially formed by nuclear processes in the interiors of stars. It is also believed that their energy distribution up to 1018 eV has Galactic origins. But even though the knowledge about potential sources of cosmic rays is quite poor above „ 1015 eV, that is the “knee” of the cosmic-ray spectrum, up to the knee there seems to be a wide consensus that supernova remnants are the most likely candidates. Evidence of this comes from observations of non-thermal X-ray radiation, requiring synchrotron electrons with energies up to 1014 eV, exactly in the remnant of supernovae. To date, however, there is not conclusive evidence that they produce nuclei, the dominant component of cosmic rays, in addition to electrons. In light of this dearth of evidence, γ-ray observations from supernova remnants can offer the most promising direct way to confirm whether or not these astrophysical objects are indeed the main source of cosmic-ray nuclei below the knee. Recent observations with space- and ground-based observatories have established shell-type supernova remnants as GeV-to- TeV γ-ray sources. The interpretation of these observations is however complicated by the different radiation processes, leptonic and hadronic, that can produce similar fluxes in this energy band rendering ambiguous the nature of the emission itself. The aim of this work is to develop a deeper understanding of these radiation processes from a particular shell-type supernova remnant, namely RX J1713.7–3946, using observations of the LAT instrument onboard the Fermi Gamma-Ray Space Telescope. Furthermore, to obtain accurate spectra and morphology maps of the emission associated with this supernova remnant, an improved model of the diffuse Galactic γ-ray emission background is developed. The analyses of RX J1713.7–3946 carried out with this improved background show that the hard Fermi-LAT spectrum cannot be ascribed to the hadronic emission, leading thus to the conclusion that the leptonic scenario is instead the most natural picture for the high-energy γ-ray emission of RX J1713.7–3946. The leptonic scenario however does not rule out the possibility that cosmic-ray nuclei are accelerated in this supernova remnant, but it suggests that the ambient density may not be high enough to produce a significant hadronic γ-ray emission. Further investigations involving other supernova remnants using the improved back- ground developed in this work could allow compelling population studies, and hence prove or disprove the origin of Galactic cosmic-ray nuclei in these astrophysical objects. A break- through regarding the identification of the radiation mechanisms could be lastly achieved with a new generation of instruments such as CTA.
Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.
The aim of this paper is to bring together two areas which are of great importance for the study of overdetermined boundary value problems. The first area is homological algebra which is the main tool in constructing the formal theory of overdetermined problems. And the second area is the global calculus of pseudodifferential operators which allows one to develop explicit analysis.
The present thesis is to be brought into line with the current need for alternative and sustainable approaches toward energy management and materials design. In this context, carbon in particular has become the material of choice in many fields such as energy conversion and storage. Herein, three main topics are covered: 1)An alternative synthesis strategy toward highly porous functional carbons with tunable porosity using ordinary salts as porogen (denoted as “salt templating”) 2)The one-pot synthesis of porous metal nitride containing functional carbon composites 3)The combination of both approaches, enabling the generation of highly porous composites with finely tunable properties All approaches have in common that they are based on the utilization of ionic liquids, salts which are liquid below 100 °C, as precursors. Just recently, ionic liquids were shown to be versatile precursors for the generation of heteroatom-doped carbons since the liquid state and a negligible vapor pressure are highly advantageous properties. However, in most cases the products do not possess any porosity which is essential for many applications. In the first part, “salt templating”, the utilization of salts as diverse and sustainable porogens, is introduced. Exemplarily shown for ionic liquid derived nitrogen- and nitrogen-boron-co-doped carbons, the control of the porosity and morphology on the nanometer scale by salt templating is presented. The studies within this thesis were conducted with the ionic liquids 1-Butyl-3-methyl-pyridinium dicyanamide (Bmp-dca), 1-Ethyl-3-methyl-imidazolium dicyanamide (Emim-dca) and 1 Ethyl 3-methyl-imidazolium tetracyanoborate (Emim-tcb). The materials are generated through thermal treatment of precursor mixtures containing one of the ionic liquids and a porogen salt. By simple removal of the non-carbonizable template salt with water, functional graphitic carbons with pore sizes ranging from micro- to mesoporous and surface areas up to 2000 m2g-1 are obtained. The carbon morphologies, which presumably originate from different onsets of demixing, mainly depend on the nature of the porogen salt whereas the nature of the ionic liquid plays a minor role. Thus, a structural effect of the porogen salt rather than activation can be assumed. This offers an alternative to conventional activation and templating methods, enabling to avoid multiple-step and energy-consuming synthesis pathways as well as employment of hazardous chemicals for the template removal. The composition of the carbons can be altered via the heat-treatment procedure, thus at lower synthesis temperatures rather polymeric carbonaceous materials with a high degree of functional groups and high surface areas are accessible. First results suggest the suitability of the materials for CO2 utilization. In order to further illustrate the potential of ionic liquids as carbon precursors and to expand the class of carbons which can be obtained, the ionic liquid 1-Ethyl-3-methyl-imidazolium thiocyanate (Emim-scn) is introduced for the generation of nitrogen-sulfur-co-doped carbons in combination with the already studied ionic liquids Bmp-dca and Emim-dca. Here, the salt templating approach should also be applicable eventually further illustrating the potential of salt templating, too. In the second part, a one-pot and template-free synthesis approach toward inherently porous metal nitride nanoparticle containing nitrogen-doped carbon composites is presented. Since ionic liquids also offer outstanding solubility properties, the materials can be generated through the carbonization of homogeneous solutions of an ionic liquid acting as nitrogen as well as carbon source and the respective metal precursor. The metal content and surface area are easily tunable via the initial metal precursor amount. Furthermore, it is also possible to synthesize composites with ternary nitride nanoparticles whose composition is adjustable by the metal ratio in the precursor solution. Finally, both approaches are combined into salt templating of the one-pot composites. This opens the way to the one-step synthesis of composites with tunable composition, particle size as well as precisely controllable porosity and morphology. Thereby, common synthesis strategies where the product composition is often negatively affected by the template removal procedure can be avoided. The composites are further shown to be suitable as electrodes for supercapacitors. Here, different properties such as porosity, metal content and particle size are investigated and discussed with respect to their influence on the energy storage performance. Because a variety of ionic liquids, metal precursors and salts can be combined and a simple closed-loop process including salt recycling is imaginable, the approaches present a promising platform toward sustainable materials design.
Regulatory focus is a motivational construct that describes humans’ motivational orientation during goal pursuit. It is conceptualized as a chronic, trait-like, as well as a momentary, state-like orientation. Whereas there is a large number of measures to capture chronic regulatory focus, measures for its momentary assessment are only just emerging. This paper presents the development and validation of a measure of Momentary–Chronic Regulatory Focus. Our development incorporates the distinction between self-guide and reference-point definitions of regulatory focus. Ideals and ought striving are the promotion and prevention dimension in the self-guide system; gain and non-loss regulatory focus are the respective dimensions within the reference-point system. Three-survey-based studies test the structure, psychometric properties, and validity of the measure in its version to assess chronic regulatory focus (two samples of working participants, N = 389, N = 672; one student sample [time 1, N = 105; time 2, n = 91]). In two further studies, an experience sampling study with students (N = 84, k = 1649) and a daily-diary study with working individuals (N = 129, k = 1766), the measure was applied to assess momentary regulatory focus. Multilevel analyses test the momentary measure’s factorial structure, provide support for its sensitivity to capture within-person fluctuations, and provide evidence for concurrent construct validity.
Team diversity
(2007)
Team diversity refers to the differences between team members on any attribute that may lead each single member of the group to perceive any other member of the group as being different from the self of this particular member. These attributes and perceptions refer to all dimensions people can differ on, such as age, gender, ethnicity, religious and functional background, personality, skills, abilities, beliefs, and attitudes.
Opritschnina
(2009)