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Der vorliegende Text gibt eine Bestandserhebung der bisher stattgefundenen Aktivitäten im E-Learning an der Universität Potsdam wieder, andererseits dient er auch dazu, Potenziale zu sichten und in einem nächstem Schritt daraus Ideen und Vorschläge für eine hochschulweite E-Learning-Strategie abzuleiten. Zielsetzung der Bestandsaufnahme ist es, die relevanten Informationen darzustellen, über den Platz der Universität Potsdam in der hochschulischen E-Learning-Landschaft zu orientieren und den Stand der Entwicklung zu bewerten.
This reference paper describes the sampling and contents of the IZA Evaluation Dataset Survey and outlines its vast potential for research in labor economics. The data have been part of a unique IZA project to connect administrative data from the German Federal Employment Agency with innovative survey data to study the out-mobility of individuals to work. This study makes the survey available to the research community as a Scientific Use File by explaining the development, structure, and access to the data. Furthermore, it also summarizes previous findings with the survey data.
Unstetige Galerkin-Diskretisierung niedriger Ordnung in einem atmosphärischen Multiskalenmodell
(2014)
Die Dynamik der Atmosphäre der Erde umfasst einen Bereich von mikrophysikalischer Turbulenz über konvektive Prozesse und Wolkenbildung bis zu planetaren Wellenmustern. Für Wettervorhersage und zur Betrachtung des Klimas über Jahrzehnte und Jahrhunderte ist diese Gegenstand der Modellierung mit numerischen Verfahren. Mit voranschreitender Entwicklung der Rechentechnik sind Neuentwicklungen der dynamischen Kerne von Klimamodellen, die mit der feiner werdenden Auflösung auch entsprechende Prozesse auflösen können, notwendig. Der dynamische Kern eines Modells besteht in der Umsetzung (Diskretisierung) der grundlegenden dynamischen Gleichungen für die Entwicklung von Masse, Energie und Impuls, so dass sie mit Computern numerisch gelöst werden können. Die vorliegende Arbeit untersucht die Eignung eines unstetigen Galerkin-Verfahrens niedriger Ordnung für atmosphärische Anwendungen. Diese Eignung für Gleichungen mit Wirkungen von externen Kräften wie Erdanziehungskraft und Corioliskraft ist aus der Theorie nicht selbstverständlich. Es werden nötige Anpassungen beschrieben, die das Verfahren stabilisieren, ohne sogenannte „slope limiter” einzusetzen. Für das unmodifizierte Verfahren wird belegt, dass es nicht geeignet ist, atmosphärische Gleichgewichte stabil darzustellen. Das entwickelte stabilisierte Modell reproduziert eine Reihe von Standard-Testfällen der atmosphärischen Dynamik mit Euler- und Flachwassergleichungen in einem weiten Bereich von räumlichen und zeitlichen Skalen. Die Lösung der thermischen Windgleichung entlang der mit den Isobaren identischen charakteristischen Kurven liefert atmosphärische Gleichgewichtszustände mit durch vorgegebenem Grundstrom einstellbarer Neigung zu(barotropen und baroklinen)Instabilitäten, die für die Entwicklung von Zyklonen wesentlich sind. Im Gegensatz zu früheren Arbeiten sind diese Zustände direkt im z-System(Höhe in Metern)definiert und müssen nicht aus Druckkoordinaten übertragen werden.Mit diesen Zuständen, sowohl als Referenzzustand, von dem lediglich die Abweichungen numerisch betrachtet werden, und insbesondere auch als Startzustand, der einer kleinen Störung unterliegt, werden verschiedene Studien der Simulation von barotroper und barokliner Instabilität durchgeführt. Hervorzuheben ist dabei die durch die Formulierung von Grundströmen mit einstellbarer Baroklinität ermöglichte simulationsgestützte Studie des Grades der baroklinen Instabilität verschiedener Wellenlängen in Abhängigkeit von statischer Stabilität und vertikalem Windgradient als Entsprechung zu Stabilitätskarten aus theoretischen Betrachtungen in der Literatur.
Schlucken ist ein lebensnotwendiger Prozess, dessen Diagnose und Therapie eine enorme Herausforderung bedeutet. Die Erkennung und Beurteilung von Schlucken und Schluckstörungen erfordert den Einsatz von technisch aufwendigen Verfahren, wie Videofluoroskopie (VFSS) und fiberoptisch-endoskopische Schluckuntersuchung (FEES), die eine hohe Belastung für die Patienten darstellen. Beide Verfahren werden als Goldstandard in der Diagnostik von Schluckstörungen eingesetzt. Die Durchführung obliegt in der Regel ärztlichem Personal. Darüber hinaus erfordert die Auswertung des Bildmaterials der Diagnostik eine ausreichend hohe Erfahrung. In der Therapie findet neben den klassischen Therapiemethoden, wie z.B. diätetische Modifikationen und Schluckmanöver, auch zunehmend die funktionelle Elektrostimulation Anwendung. Ziel der vorliegenden Dissertationsschrift ist die Evaluation eines im Verbundprojekt BigDysPro entwickelten Bioimpedanz (BI)- und Elektromyographie (EMG)-Messsystems. Es wurde geprüft, ob sich das BI- und EMG-Messsystem eignet, sowohl in der Diagnostik als auch in der Therapie als eigenständiges Messsystem und im Rahmen einer Schluckneuroprothese eingesetzt zu werden. In verschiedenen Studien wurden gesunde Probanden für die Überprüfung der Reproduzierbarkeit (Intra-und Interrater-Reliabilität), der Unterscheidbarkeit von Schluck- und Kopfbewegungen und der Beeinflussung der Biosignale (BI, EMG) durch verschiedene Faktoren (Geschlecht der Probanden, Leitfähigkeit, Konsistenz und Menge der Nahrung) untersucht. Durch zusätzliche Untersuchungen mit Patienten wurde einerseits der Einfluss der Elektrodenart geprüft. Andererseits wurden parallel zur BI- und EMG-Messung auch endoskopische (FEES) und radiologische Schluckuntersuchungen (VFSS) durchgeführt, um die Korrelation der Biosignale mit der Bewegung anatomischer Strukturen (VFSS) und mit der Schluckqualität (FEES) zu prüfen. Es wurden 31 gesunde Probanden mit 1819 Schlucken und 60 Patienten mit 715 Schlucken untersucht. Die Messkurven zeigten einen typischen, reproduzierbaren Signalverlauf, der mit anatomischen und funktionellen Änderungen während der pharyngalen Schluckphase in der VFSS korrelierte (r > 0,7). Aus dem Bioimpedanzsignal konnten Merkmale extrahiert werden, die mit physiologischen Merkmalen eines Schluckes, wie verzögerter laryngealer Verschluss und Kehlkopfhebung, korrelierten und eine Einschätzung der Schluckqualität in Übereinstimmung mit der FEES ermöglichten. In den Signalverläufen der Biosignale konnten signifikante Unterschiede zwischen Schluck- und Kopfbewegungen und den Nahrungsmengen und -konsistenzen nachgewiesen werden. Im Gegensatz zur Nahrungsmenge und -konsistenz zeigte die Leitfähigkeit der zu schluckenden Nahrung, das Geschlecht der Probanden und die Art der Elektroden keinen signifikanten Einfluss auf die Messsignale. Mit den Ergebnissen der Evaluation konnte gezeigt werden, dass mit dem BI- und EMG-Messsystem ein neuartiges und nicht-invasives Verfahren zur Verfügung steht, das eine reproduzierbare Darstellung der pharyngalen Schluckphase und ihrer Veränderungen ermöglicht. Daraus ergeben sich vielseitige Einsatzmöglichkeiten in der Diagnostik, z.B. Langzeitmessung zur Schluckfrequenz und Einschätzung der Schluckqualität, und in der Therapie, z.B. der Einsatz in einer Schluckneuroprothese oder als Biofeedback zur Darstellung des Schluckes, von Schluckstörungen.
Das Europäische Parlament ist zweifelsohne die mächtigste parlamentarische Versammlung auf supranationaler Ebene. Das provoziert die Frage, wie Entscheidungen in diesem Parlament gefällt werden und wie sie begründet werden können. Darin liegt das Hauptanliegen dieser Arbeit, die zur Beantwortung dieser Frage auf soziologische Ansätze der Erklärung sozialen Handelns zurückgreift und damit einen neuen Zugang zur Beobachtung parlamentarischen Handelns schafft. Dabei arbeitet sie heraus, wie wichtig es ist, bei der Analyse politischer Entscheidungsprozesse zu beachten, wie politische Probleme von Akteuren interpretiert und gegenüber Verhandlungspartnern dargestellt werden. An den Fallbeispielen der Entscheidungsprozesse zur Dienstleistungsrichtlinie, zur Chemikalien-Verordnung REACH und dem TDIP (CIA)-Ausschuss in der Legislaturperiode 2004–2009, wird der soziale Mechanismus dargestellt, der hinter Einigungen im Europäischen Parlament steckt. Kultur als Interpretation der Welt wird so zum Schlüssel des Verständnisses politischer Entscheidungen auf supranationaler Ebene.
Herein, we report the chain-growth tin-free room temperature polymerization method to synthesize n-type perylene diimide-dithiophene-based conjugated polymers (PPDIT2s) suitable for solar cell and transistor applications. The palladium/electron-rich tri-tert-butylphosphine catalyst is effective to enable the chain-growth polymerization of anion-radical monomer Br-TPDIT-Br/Zn to PPDIT2 with a molecular weight up to Mw ≈ 50 kg mol−1 and moderate polydispersity. This is the second example of the polymerization of unusual anion-radical aromatic complexes formed in a reaction of active Zn and electron-deficient diimide-based aryl halides. As such, the discovered polymerization method is not a specific reactivity feature of the naphthalene-diimide derivatives but is rather a general polymerization tool. This is an important finding, given the significantly higher maximum external quantum efficiency that can be reached with PDI-based copolymers (32–45%) in all-polymer solar cells compared to NDI-based materials (15–30%). Our studies revealed that PPDIT2 synthesized by the new method and the previously published polymer prepared by step-growth Stille polycondensation show similar electron mobility and all-polymer solar cell performance. At the same time, the polymerization reported herein has several technological advantages as it proceeds relatively fast at room temperature and does not involve toxic tin-based compounds. Because several chain-growth polymerization reactions are well-suited for the preparation of well-defined multi-functional polymer architectures, the next target is to explore the utility of the discovered polymerization in the synthesis of end-functionalized polymers and block copolymers. Such materials would be helpful to improve the nanoscale morphology of polymer blends in all-polymer solar cells.
Formation of a Eu(III) borate solid species from a weak Eu(III) borate complex in aqueous solution
(2014)
In the presence of polyborates (detected by 11B-NMR) the formation of a weak Eu(III) borate complex (lg β11 ∼ 2, estimated) was observed by time-resolved laser-induced fluorescence spectroscopy (TRLFS). This complex is a precursor for the formation of a solid Eu(III) borate species. The formation of this solid in solution was investigated by TRLFS as a function of the total boron concentration: the lower the total boron concentration, the slower is the solid formation. The solid Eu(III) borate was characterized by IR spectroscopy, powder XRD and solid-state TRLFS. The determination of the europium to boron ratio portends the existence of pentaborate units in the amorphous solid.
Photoinduced excitation energy transfer and accompanying charge separation are elucidated for a supramolecular system of a single fullerene covalently linked to six pyropheophorbide-a dye molecules. Molecular dynamics simulations are performed to gain an atomistic picture of the architecture and the surrounding solvent. Excitation energy transfer among the dye molecules and electron transfer from the excited dyes to the fullerene are described by a mixed quantum–classical version of the Förster rate and the semiclassical Marcus rate, respectively. The mean characteristic time of energy redistribution lies in the range of 10 ps, while electron transfer proceeds within 150 ps. In between, on a 20 to 50 ps time-scale, conformational changes take place in the system. This temporal hierarchy of processes guarantees efficient charge separation, if the structure is exposed to a solvent. The fast energy transfer can adopt the dye excitation to the actual conformation. In this sense, the probability to achieve charge separation is large enough since any dominance of unfavorable conformations that exhibit a large dye–fullerene distance is circumvented. And the slow electron transfer may realize an averaging with respect to different conformations. To confirm the reliability of our computations, ensemble measurements on the charge separation dynamics are simulated and a very good agreement with the experimental data is obtained.
The synthesis of two novel types of π-expanded coumarins has been developed. Modified Knoevenagel bis-condensation afforded 3,9-dioxa-perylene-2,8-diones. Subsequent oxidative aromatic coupling or light driven electrocyclization reaction led to dibenzo-1,7-dioxacoronene-2,8-dione. Unparalleled synthetic simplicity, straightforward purification and superb optical properties have the potential to bring these perylene and coronene analogs towards various applications.
Two-photon polymerization of hydrogels – versatile solutions to fabricate well-defined 3D structures
(2014)
Hydrogels are cross-linked water-containing polymer networks that are formed by physical, ionic or covalent interactions. In recent years, they have attracted significant attention because of their unique physical properties, which make them promising materials for numerous applications in food and cosmetic processing, as well as in drug delivery and tissue engineering. Hydrogels are highly water-swellable materials, which can considerably increase in volume without losing cohesion, are biocompatible and possess excellent tissue-like physical properties, which can mimic in vivo conditions. When combined with highly precise manufacturing technologies, such as two-photon polymerization (2PP), well-defined three-dimensional structures can be obtained. These structures can become scaffolds for selective cell-entrapping, cell/drug delivery, sensing and prosthetic implants in regenerative medicine. 2PP has been distinguished from other rapid prototyping methods because it is a non-invasive and efficient approach for hydrogel cross-linking. This review discusses the 2PP-based fabrication of 3D hydrogel structures and their potential applications in biotechnology. A brief overview regarding the 2PP methodology and hydrogel properties relevant to biomedical applications is given together with a review of the most important recent achievements in the field.
Werner Mittenzwei’s article of 1967, the title of which coined the term “Brecht-Lukács-Debatte”, is widely considered as a milestone in the development of East German literary criticism towards an “emancipation” from party politics. By placing Mittenzwei’s contribution in the wider context of discussions about the literature of the GDR, within the SED and the writers’ union as well as at international conferences, this article attempts to trace the emergence of “Umfunktionierung” both as a key term and in its official approval by the party.
A new functional luminescent lanthanide complex (LLC) has been synthesized with terbium as a central lanthanide ion and biotin as a functional moiety. Unlike in typical lanthanide complexes assembled via carboxylic moieties, in the presented complex, four phosphate groups are chelating the central lanthanide ion. This special chemical assembly enhances the complex stability in phosphate buffers conventionally used in biochemistry. The complex synthesis strategy and photophysical properties are described as well as the performance in time-resolved Förster Resonance Energy Transfer (FRET) assays. In those assays, this biotin-LLC transferred energy either to acceptor organic dyes (Cy5 or AF680) labelled on streptavidin or to quantum dots (QD655 or QD705) surface-functionalised with streptavidins. The permanent spatial donor–acceptor proximity is assured through strong and stable biotin–streptavidin binding. The energy transfer is evidenced from the quenching observed in donor emission and from a decrease in donor luminescence decay, both associated with simultaneous increase in acceptor intensity and in the decay time. The dye-based assays are realised in TRIS and in PBS, whereas QD-based systems are studied in borate buffer. The delayed emission analysis allows for quantifying the recognition process and for auto-fluorescence-free detection, which is particularly relevant for application in bioanalysis. In accordance with Förster theory, Förster-radii (R0) were found to be around 60 Å for organic dyes and around 105 Å for QDs. The FRET efficiency (η) reached 80% and 25% for dye and QD acceptors, respectively. Physical donor–acceptor distances (r) have been determined in the range 45–60 Å for organic dye acceptors, while for acceptor QDs between 120 Å and 145 Å. This newly synthesised biotin-LLC extends the class of highly sensitive analytical tools to be applied in the bioanalytical methods such as time-resolved fluoroimmunoassays (TR-FIA), luminescent imaging and biosensing.
Permafrost, defined as ground that is frozen for at least two consecutive years, is a distinct feature of the terrestrial unglaciated Arctic. It covers approximately one quarter of the land area of the Northern Hemisphere (23,000,000 km²). Arctic landscapes, especially those underlain by permafrost, are threatened by climate warming and may degrade in different ways, including active layer deepening, thermal erosion, and development of rapid thaw features. In Siberian and Alaskan late Pleistocene ice-rich Yedoma permafrost, rapid and deep thaw processes (called thermokarst) can mobilize deep organic carbon (below 3 m depth) by surface subsidence due to loss of ground ice. Increased permafrost thaw could cause a feedback loop of global significance if its stored frozen organic carbon is reintroduced into the active carbon cycle as greenhouse gases, which accelerate warming and inducing more permafrost thaw and carbon release. To assess this concern, the major objective of the thesis was to enhance the understanding of the origin of Yedoma as well as to assess the associated organic carbon pool size and carbon quality (concerning degradability). The key research questions were:
- How did Yedoma deposits accumulate?
- How much organic carbon is stored in the Yedoma region?
- What is the susceptibility of the Yedoma region's carbon for future decomposition?
To address these three research questions, an interdisciplinary approach, including detailed field studies and sampling in Siberia and Alaska as well as methods of sedimentology, organic biogeochemistry, remote sensing, statistical analyses, and computational modeling were applied. To provide a panarctic context, this thesis additionally includes results both from a newly compiled northern circumpolar carbon database and from a model assessment of carbon fluxes in a warming Arctic.
The Yedoma samples show a homogeneous grain-size composition. All samples were poorly sorted with a multi-modal grain-size distribution, indicating various (re-) transport processes. This contradicts the popular pure loess deposition hypothesis for the origin of Yedoma permafrost. The absence of large-scale grinding processes via glaciers and ice sheets in northeast Siberian lowlands, processes which are necessary to create loess as material source, suggests the polygenetic origin of Yedoma deposits.
Based on the largest available data set of the key parameters, including organic carbon content, bulk density, ground ice content, and deposit volume (thickness and coverage) from Siberian and Alaskan study sites, this thesis further shows that deep frozen organic carbon in the Yedoma region consists of two distinct major reservoirs, Yedoma deposits and thermokarst deposits (formed in thaw-lake basins). Yedoma deposits contain ~80 Gt and thermokarst deposits ~130 Gt organic carbon, or a total of ~210 Gt. Depending on the approach used for calculating uncertainty, the range for the total Yedoma region carbon store is ±75 % and ±20 % for conservative single and multiple bootstrapping calculations, respectively. Despite the fact that these findings reduce the Yedoma region carbon pool by nearly a factor of two compared to previous estimates, this frozen organic carbon is still capable of inducing a permafrost carbon feedback to climate warming. The complete northern circumpolar permafrost region contains between 1100 and 1500 Gt organic carbon, of which ~60 % is perennially frozen and decoupled from the short-term carbon cycle.
When thawed and reintroduced into the active carbon cycle, the organic matter qualities become relevant. Furthermore, results from investigations into Yedoma and thermokarst organic matter quality studies showed that Yedoma and thermokarst organic matter exhibit no depth-dependent quality trend. This is evidence that after freezing, the ancient organic matter is preserved in a state of constant quality. The applied alkane and fatty-acid-based biomarker proxies including the carbon-preference and the higher-land-plant-fatty-acid indices show a broad range of organic matter quality and thus no significantly different qualities of the organic matter stored in thermokarst deposits compared to Yedoma deposits. This lack of quality differences shows that the organic matter biodegradability depends on different decomposition trajectories and the previous decomposition/incorporation history. Finally, the fate of the organic matter has been assessed by implementing deep carbon pools and thermokarst processes in a permafrost carbon model. Under various warming scenarios for the northern circumpolar permafrost region, model results show a carbon release from permafrost regions of up to ~140 Gt and ~310 Gt by the years 2100 and 2300, respectively. The additional warming caused by the carbon release from newly-thawed permafrost contributes 0.03 to 0.14°C by the year 2100. The model simulations predict that a further increase by the 23rd century will add 0.4°C to global mean surface air temperatures.
In conclusion, Yedoma deposit formation during the late Pleistocene was dominated by water-related (alluvial/fluvial/lacustrine) as well as aeolian processes under periglacial conditions. The circumarctic permafrost region, including the Yedoma region, contains a substantial amount of currently frozen organic carbon. The carbon of the Yedoma region is well-preserved and therefore available for decomposition after thaw. A missing quality-depth trend shows that permafrost preserves the quality of ancient organic matter. When the organic matter is mobilized by deep degradation processes, the northern permafrost region may add up to 0.4°C to the global warming by the year 2300.
Potentiality of nanosized materials has been largely proved but a closer look shows that a significant percentage of this research is related to oxides and metals, while the number drastically drops for metallic ceramics, namely transition metal nitrides and metal carbides. The lack of related publications do not reflect their potential but rather the difficulties related to their synthesis as dense and defect-free structures, fundamental prerequisites for advanced mechanical applications.
The present habilitation work aims to close the gap between preparation and processing, indicating novel synthetic pathways for a simpler and sustainable synthesis of transition metal nitride (MN) and carbide (MC) based nanostructures and easier processing thereafter. In spite of simplicity and reliability, the designed synthetic processes allow the production of functional materials, with the demanded size and morphology.
The goal was achieved exploiting classical and less-classical precursors, ranging from common metal salts and molecules (e.g. urea, gelatin, agar, etc), to more exotic materials, such as leafs, filter paper and even wood. It was found that the choice of precursors and reaction conditions makes it possible to control chemical composition (going for instance from metal oxides to metal oxy-nitrides to metal nitrides, or from metal nitrides to metal carbides, up to quaternary systems), size (from 5 to 50 nm) and morphology (going from mere spherical nanoparticles to rod-like shapes, fibers, layers, meso-porous and hierarchical structures, etc). The nature of the mixed precursors also allows the preparation of metal nitrides/carbides based nanocomposites, thus leading to multifunctional materials (e.g. MN/MC@C, MN/MC@PILs, etc) but also allowing dispersion in liquid media. Control over composition, size and morphology is obtained with simple adjustment of the main route, but also coupling it with processes such as electrospin, aerosol spray, bio-templating, etc. Last but not least, the nature of the precursor materials also allows easy processing, including printing, coating, casting, film and thin layers preparation, etc).
The designed routes are, concept-wise, similar and they all start by building up a secondary metal ion-N/C precursor network, which converts, upon heat treatment, into an intermediate “glass”. This glass stabilizes the nascent nanoparticles during their nucleation and impairs their uncontrolled growth during the heat treatment (scheme 1). This way, one of the main problems related to the synthesis of MN/MC, i.e. the need of very high temperature, could also be overcome (from up to 2000°C, for classical synthesis, down to 700°C in the present cases). The designed synthetic pathways are also conceived to allow usage of non-toxic compounds and to minimize (or even avoid) post-synthesis purification, still bringing to phase pure and well-defined (crystalline) nanoparticles.
This research aids to simplify the preparation of MN/MC, making these systems now readily available in suitable amounts both for fundamental and applied science. The prepared systems have been tested (in some cases for the first time) in many different fields, e.g. battery (MnN0.43@C shown a capacity stabilized at a value of 230 mAh/g, with coulombic efficiencies close to 100%), as alternative magnetic materials (Fe3C nanoparticles were prepared with different size and therefore different magnetic behavior, superparamagnetic or ferromagnetic, showing a saturation magnetization value up to 130 emu/g, i.e. similar to the value expected for the bulk material), as filters and for the degradation of organic dyes (outmatching the performance of carbon), as catalysts (both as active phase but also as active support, leading to high turnover rate and, more interesting, to tunable selectivity). Furthermore, with this route, it was possible to prepare for the first time, to the best of our knowledge, well-defined and crystalline MnN0.43, Fe3C and Zn1.7GeN1.8O nanoparticles via bottom-up approaches.
Once the synthesis of these materials can be made straightforward, any further modification, combination, manipulation, is in principle possible and new systems can be purposely conceived (e.g. hybrids, nanocomposites, ferrofluids, etc).
The atmosphere over the Arctic Ocean is strongly influenced by the distribution of sea ice and open water. Leads in the sea ice produce strong convective fluxes of sensible and latent heat and release aerosol particles into the atmosphere. They increase the occurrence of clouds and modify the structure and characteristics of the atmospheric boundary layer (ABL) and thereby influence the Arctic climate.
In the course of this study aircraft measurements were performed over the western Arctic Ocean as part of the campaign PAMARCMIP 2012 of the Alfred Wegener Institute for Polar and Marine Research (AWI). Backscatter from aerosols and clouds within the lower troposphere and the ABL were measured with the nadir pointing Airborne Mobile Aerosol Lidar (AMALi) and dropsondes were launched to obtain profiles of meteorological variables. Furthermore, in situ measurements of aerosol properties, meteorological variables and turbulence were part of the campaign. The measurements covered a broad range of atmospheric and sea ice conditions.
In this thesis, properties of the ABL over Arctic sea ice with a focus on the influence of open leads are studied based on the data from the PAMARCMIP campaign. The height of the ABL is determined by different methods that are applied to dropsonde and AMALi backscatter profiles. ABL heights are compared for different flights representing different conditions of the atmosphere and of sea ice and open water influence. The different criteria for ABL height that are applied show large variation in terms of agreement among each other, depending on the characteristics of the ABL and its history. It is shown that ABL height determination from lidar backscatter by methods commonly used under mid-latitude conditions is applicable to the Arctic ABL only under certain conditions. Aerosol or clouds within the ABL are needed as a tracer for ABL height detection from backscatter. Hence an aerosol source close to the surface is necessary, that is typically found under the present influence of open water and therefore convective conditions. However it is not always possible to distinguish residual layers from the actual ABL. Stable boundary layers are generally difficult to detect.
To illustrate the complexity of the Arctic ABL and processes therein, four case studies are analyzed each of which represents a snapshot of the interplay between atmosphere and underlying sea ice or water surface. Influences of leads and open water on the aerosol and clouds within the ABL are identified and discussed. Leads are observed to cause the formation of fog and cloud layers within the ABL by humidity emission. Furthermore they decrease the stability and increase the height of the ABL and consequently facilitate entrainment of air and aerosol layers from the free troposphere.
Cyanobacteria produce about 40 percent of the world’s primary biomass, but also a variety of often toxic peptides such as microcystin. Mass developments, so called blooms, can pose a real threat to the drinking water supply in many parts of the world. This study aimed at characterizing the biological function of microcystin production in one of the most common bloom-forming cyanobacterium Microcystis aeruginosa.
In a first attempt, the effect of elevated light intensity on microcystin production and its binding to cellular proteins was studied. Therefore, conventional microcystin quantification techniques were combined with protein-biochemical methods. RubisCO, the key enzyme for primary carbon fixation was a major microcystin interaction partner. High light exposition strongly stimulated microcystin-protein interactions. Up to 60 percent of the total cellular microcystin was detected bound to proteins, i.e. inaccessible for standard quantification procedures. Underestimation of total microcystin contents when neglecting the protein fraction was also demonstrated in field samples. Finally, an immuno-fluorescence based method was developed to identify microcystin producing cyanobacteria in mixed populations.
The high light induced microcystin interaction with proteins suggested an impact of the secondary metabolite on the primary metabolism of Microcystis by e.g. modulating the activity of enzymes. For addressing that question, a comprehensive GC/MS-based approach was conducted to compare the accumulation of metabolites in the wild-type of Microcystis aeruginosa PCC 7806 and the microcystin deficient ΔmcyB mutant. From all 501 detected non-redundant metabolites 85 (17 percent) accumulated significantly different in either of both genotypes upon high light exposition. Accumulation of compatible solutes in the ΔmcyB mutant suggests a role of microcystin in fine-tuning the metabolic flow to prevent stress related to excess light, high oxygen concentration and carbon limitation.
Co-analysis of the widely used model cyanobacterium Synechocystis PCC 6803 revealed profound metabolic differences between species of cyanobacteria. Whereas Microcystis channeled more resources towards carbohydrate synthesis, Synechocystis invested more in amino acids. These findings were supported by electron microscopy of high light treated cells and the quantification of storage compounds. While Microcystis accumulated mainly glycogen to about 8.5 percent of its fresh weight within three hours, Synechocystis produced higher amounts of cyanophycin. The results showed that the characterization of species-specific metabolic features should gain more attention with regard to the biotechnological use of cyanobacteria.
Modern microscopic techniques following the stochastic motion of labelled tracer particles have uncovered significant deviations from the laws of Brownian motion in a variety of animate and inanimate systems. Such anomalous diffusion can have different physical origins, which can be identified from careful data analysis. In particular, single particle tracking provides the entire trajectory of the traced particle, which allows one to evaluate different observables to quantify the dynamics of the system under observation. We here provide an extensive overview over different popular anomalous diffusion models and their properties. We pay special attention to their ergodic properties, highlighting the fact that in several of these models the long time averaged mean squared displacement shows a distinct disparity to the regular, ensemble averaged mean squared displacement. In these cases, data obtained from time averages cannot be interpreted by the standard theoretical results for the ensemble averages. Here we therefore provide a comparison of the main properties of the time averaged mean squared displacement and its statistical behaviour in terms of the scatter of the amplitudes between the time averages obtained from different trajectories. We especially demonstrate how anomalous dynamics may be identified for systems, which, on first sight, appear to be Brownian. Moreover, we discuss the ergodicity breaking parameters for the different anomalous stochastic processes and showcase the physical origins for the various behaviours. This Perspective is intended as a guidebook for both experimentalists and theorists working on systems, which exhibit anomalous diffusion.
New porous materials based on covalently connected monomers are presented. The key step of the synthesis is an acetalisation reaction. In previous years we used acetalisation reactions extensively to build up various molecular rods. Based on this approach, investigations towards porous polymeric materials were conducted by us. Here we wish to present the results of these studies in the synthesis of 1D polyacetals and porous 3D polyacetals. By scrambling experiments with 1D acetals we could prove that exchange reactions occur between different building blocks (evidenced by MALDI-TOF mass spectrometry). Based on these results we synthesized porous 3D polyacetals under the same mild conditions.
Picosecond X-ray absorption spectroscopy (XAS) is used to investigate the electronic and structural dynamics initiated by plasmon excitation of 1.8 nm diameter Au nanoparticles (NPs) functionalised with 1-hexanethiol. We show that 100 ps after photoexcitation the transient XAS spectrum is consistent with an 8% expansion of the Au–Au bond length and a large increase in disorder associated with melting of the NPs. Recovery of the ground state occurs with a time constant of ∼1.8 ns, arising from thermalisation with the environment. Simulations reveal that the transient spectrum exhibits no signature of charge separation at 100 ps and allows us to estimate an upper limit for the quantum yield (QY) of this process to be <0.1.