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Show/Hide Abstract Interactions between hydrology and biogeochemistry within riparian wetlands (2013)
Sven Frei
Interactions between hydrology and biogeochemistry at various spatio-temporal scales are important control mechanisms within terrestrial and aquatic ecosystems and exist among different compartments and transition interfaces. Understanding the fundamental mechanistic couplings between hydrological and biogeochemical processes and how these couplings feed back into ecosystem services and functions is an interdisciplinary challenge that must be addressed especially in the context of humanly mediated climate change. Riparian wetlands, as a transition zone between terrestrial and aquatic ecosystems, occupy large fractions of terrestrial ecosystems and provide important ecohydrological services. Due to their anoxic environments, riparian wetlands are able to store significant amounts of carbon as peat and act as an effective nutrient sink e.g. for sulfur, phosphorous and nitrogen. Riparian wetlands are characterized by highly dynamical interactions between hydrologically controlled transport mechanisms and biogeochemically controlled substrate availability, which governs nutrient cycling as well as the sink and source functions of wetlands. Generally, these interactions and their potential implications on ecosystem functions are only poorly understood. The representation of the tight couplings between hydrology and biogeochemistry in mechanistic models is a very challenging task because they have revealed a complexity which is often beyond the capabilities of current models. The objective of this thesis is to investigate interactions between hydrology and biogeochemistry in riparian wetlands and to understand their potential implications for internal biogeochemical process distributions and solute mobilization. Additionally, one major focus of the thesis is the attempt to represent such fundamental couplings in a process-based, hydrological/biogeochemical modeling approach. To this end, this thesis uses a combination of field and virtual experiments, as well as catchment-scale numerical modeling, performed for the Lehstenbach catchment, which was exemplarily chosen as main study site. Results from the virtual experiments show very complex small-scale hydrological dynamics within the riparian areas. Here, runoff generation processes are strongly influenced by the spatial structure of the wetland-typical micro-topography (hummocks and hollows). Surface flow is episodically generated by a highly dynamical, threshold-controlled process where extended surface flow networks drain large fractions of the wetland's area. During intensive rainstorm events these surface flow networks, which contribute to stream discharge due to a fill and spill mechanism, dominate runoff generation. These fast flow components are characterized by very low residence times (minutes to hours) and once they are activated, the surface flow networks are able to rapidly mobilize large amounts of solutes, like nitrate or dissolved organic carbon (DOC), out of the wetlands by bypassing deeper anoxic layers. The importance of fast flow components for the catchment-scale mobilization of DOC was further confirmed by field investigations and catchment-scale numerical modeling. High frequency measurements of DOC in runoff of the Lehstenbach catchment revealed that DOC export is subject to substantial short term variations at an hourly to daily timescale. During intense rainstorms, DOC concentrations are up to ten times higher (up to 40 mg/L) compared to low flow conditions (~3-5 mg/L). Short term variations together with the dramatic rise of DOC concentrations in runoff during rainstorms can be explained by the episodically activation of fast flow components in the wetland areas. At the catchment-scale, application of a hydraulic mixing-cell (HMC) methodology in combination with numerical modeling has revealed that fast flow components like saturated overland flow are exclusively generated in the wetland areas during intensive rainstorm events. On an annual basis, exemplarily for the hydrological year 2001, the HMC analysis quantified the relative contribution of saturated overland flow related to the total discharge with 19.5%, which highlights the importance of riparian wetlands for catchment-scale runoff generation. Virtual experiments, additionally show that distinct shifts between surface and subsurface flow dominance, as a result of small-scale micro-topographic driven runoff generation in the wetlands, are responsible for very complex three-dimensional subsurface flow patterns showing a wide range of subsurface residence times. To investigate how these micro-topography induced subsurface flow patterns, together with the non-uniform hydrological and biogeogeochemical boundary conditions, affect the internal re-distribution and transformation of redox-sensitive species (like nitrate, sulfate or iron) a coupled hydrological/biogeogeochemical model was developed. In the model, wetland-typical biogeochemical processes are represented in a sequential stream tube approach where redox-sensitive processes are implemented as kinetic reactions. Simulations show the formation of local hot spots for redox-sensitive processes within the subsurface as a result of the complex subsurface flow paths and the transport-limited availability of electron acceptors and donors. Formation of hot spots was simulated for all key reduction processes including iron(III)-/sulfate reduction and denitrification as well as for the corresponding re-oxidation processes. These results offer a new perspective on hydrologically controlled biogeochemical transformation processes in riparian wetlands, which provides a dynamic framework to explain process heterogeneity in wetland soils and variability in process rates over space and time. Findings from this thesis clearly prove how useful interdisciplinary approaches are in understanding processes and mechanisms in ecosystems and how important functions of ecosystems are affected by couplings among those. However, a lot of knowledge gaps still exist in understanding the nature of dependency between water and nutrient cycles across scales and how these interacting cycles feed back into humanly-mediated climate change in ecosystems. Development of new interdisciplinary methodologies and frameworks as well as an integrated way of thinking across the boundaries of the different environmental disciplines is necessary to address the grand challenges associated with climate change.
Show/Hide Abstract Tibet Plateau Atmosphere-Ecology-Glaciology Cluster Joint Kobresia Ecosystem Experiment: Documentation of the second Intensive Observation Period, Summer 2012 in KEMA, Tibet (2013)
Tobias Biermann
Experiment documentation of the second joined Kobresia ecosystem experiment conducted by the Atmosphere-Ecology-Glaciology Cluster within DFG SPP 1372 (Tibetan Plateau)in Kema, Tibet, China. The report provides background information about the field side, conducted measurements and participants.
Show/Hide Abstract Über lasergeheizte kolloidale Goldnanopartikel in Polymerlösungen (2013)
Florian Schwaiger
Im Rahmen dieser Arbeit wurden verschiedene Aspekte untersucht, die im Zusammenhang mit photothermischen Effekten durch absorbierende Goldkollide in binären Polymerlösungen stehen. Dabei kamen neben den experimentellen Untersuchungen durch Hellfeld- und Phasenkontrastmikroskopie in Verbindung mit lokalen Laserheizungen und Methoden der CCD-Einzelteilchenverfolgung auch numerische Verfahren zur Lösung von Differentialgleichungen zum Einsatz. Das durch Absorption von Laserlicht erzeugte Temperaturfeld isolierter Goldnanopartikel wurde analytisch und die Abweichungen vom Idealfall eines unendlich ausgedehnten Mediums homogener Wärmeleitung mit Comsol für spezielle Geometrien und Grenzfälle berechnet. Nach diesen Untersuchungen in isothermen Systemen wurde dann die Käfigbildung um geheizte Goldkolloide in Polymerlösungen untersucht. Zur theoretischen Beschreibung des System Polystyrol/Toluol wurde der Soret-Koeffizient als Funktion der Konzentration, Molmasse und Temperatur parametrisiert. Dabei wurden neben Literaturwerten für die Molmassenabhängigkeit auch eigene Messungen der Transportkoeffizienten für die Temperatur- und Konzentrationsabhängigkeit verwendet. Die Parametrisierung des Soret-Koeffizienten reproduziert in den essentiellen Grenzfällen großer und kleiner Konzentrationen die erwarteten Skalengesetze und das Verschwinden der Molmassenabhängigkeit. Das durch den Soret-Effekt hervorgerufene Konzentrationsfeld konnte dann durch die numerische Integration der erweiterten Diffusionsgleichung berechnet werden. Aufgrund der komplexen Temperatur-, Konzentrations- und Molmassenabhängigkeit dieses Prozesses stehen die Selbstverstärkung und Schwächung der Konzentrationsabreicherung im Wettbewerb. Die Konzentration in der nahen Umgebung der Heizquelle kann, in Abhängigkeit von der Gleichgewichtskonzentration und der Molmasse, stark reduziert oder sogar auf praktisch Null reduziert werden. Die Konzentration für verschiedene Parameter wie Abstand, Molmasse und Oberflächentemperatur wurden berechnet und visualisiert. Der Soret-Koeffizient des Systems Pullulan/Wasser weist temperaturabhängig einen Nulldurchgang auf. Dadurch entstehen komplizierte Szenarien zur Strukturbildung. Das Konzentrationsfeld wurde numerisch berechnet und diskutiert. Im Gegensatz zum Konzentrationsfeld von PS/Toluol ist es für Pullulan/Wasser nicht mehr monoton, sondern zeigt neben eines starken Ausbleichens in der unmittelbaren Umgebung des Kolloids ein Konzentrationsmaximum oberhalb der Gleichgewichtskonzentration auf. Da die Dynamik eingebetteter Goldkolloide von der lokalen Viskosität abhängt, wurden zwei Szenarien im System PS/Toluol diskutiert: bei hohen Polymerkonzentrationen, wo die Lösung in die Nähe des Glasübergangs kommt, sorgen sowohl die Abreicherung des Polymers als auch die dadurch bedingte Vergrößerung des Abstandes zur Glastemperatur für eine Abnahme der Viskosität. Dieser Effekt ist mit einer abschwächenden Rückkopplung verbunden und die Polymerkonzentration auf der Teilchenoberfläche bleibt endlich, unabhängig von der Molmasse im Hochpolymer-Regime. Das zweite Szenario beschreibt die Viskosität von Lösungen mit langen Ketten im halb-verdünnten Bereich. Dort findet man Selbstverstärkung aufgrund des zunehmenden Soret-Koeffizienten und das Polymer kann auch schon für moderate Temperaturerhöhungen vollständig von der Oberfläche verdrängt werden. Es konnte weiterhin gezeigt werden, dass sich Goldnanopartikel als Markierungen eignen, um über ein einzelnes, geheiztes Kolloid thermooptisch induzierte Netzwerkdeformationen mittels Lichtmikroskopie sichtbar zu machen. Auf Zeitskalen des Experiments, in denen das verschlaufte, transiente Polymernetzwerk bestehen bleibt und die Kolloide daher in den Netzwerkmaschen praktisch immobil sind, kann durch Einzelteilchenverfolgung die Verschiebung der Kolloide mit dem Deformationsfeld des Netzwerkes korreliert werden. In realistischen Geometrien nimmt die Verschiebung aufgrund der Randbedingungen mit steigendem Abstand zwar (in erster Näherung linear) ab, bleibt aber langreichweitig. Die Modellierung dieser Geometrie erfolgte über die Vorstellung zweier impermeabler konzentrischer Kugeln. Trotz dieses recht einfachen Modells konnte eine gute Übereinstimmung zwischen Messung und numerisch berechneten Verschiebungen gefunden werden.
Show/Hide Abstract The Re-implementation of Sharia in Northern Nigeria and the Education of Muslim Women 1999-2007 (2013)
Chikas Danfulani
This study investigates the impact of the re-implementation of Sharia on the education of Muslim women between 1999 and 2007, in four states in northern Nigeria namely, Zamfara, Kano, Bauchi and Kaduna. The study fills the research gap in the description of the status of women with respect to education under the Sharia dispensation re-introduced in 1999. Before this era, scholarly works have documented the state of female education in northern Nigeria; however, none deals directly with post re-implementation and its impact on Muslim women’s education. This period is particularly interesting because it coincides with the return of the country to democratic rule after a string of military rules. Using interviews with Sharia proponents, school administrators, women and reports from Sharia Commissions in these states, the work establishes that while Zamfara and Kano States underwent transformations in the educational sector as a result of the programs introduced by the Sharia governments, the changes in the educational domain in Bauchi and Kaduna were exceedingly triggered by the return of democracy in Nigeria after decades of military rule. The results arrived at in this study reveal interesting facets of the relationship between Sharia and the education of Muslim women. The research shows that proponents of Sharia used the premise (also supported by verses from the Qur’an and Prophet Mohammed’s teachings) that education is an important part of Islam to which both males and females have equal rights, to sell the Islamic-based educational programs introduced by the Sharia regime. Using religion to promote these programs, the predominantly male Sharia bodies, mitigate the often tough cultural practices and religious dogmas that have prevented women from having full access to formal, western education. However, the type of education offered to women under these Sharia programs is a hybrid of formal education and Islamic education which pays strict attention to such cultural and religious practices like the wearing of the hijab, the separation of males and females in schools, the teaching of practical, home craft skills such as knitting and baking to the women. So, instead of the education taking women out of the home domain in which they have been restricted in the past, it rather further maintains them while providing them access to formal education which they will hardly use in any public career.
Show/Hide Abstract Crystalline-core micelles based on triblock terpolymers with polyethylene middle blocks (2012)
Joachim Schmelz
This thesis is focused on the crystallization-induced structure formation of polyethylene containing triblock terpolymers in organic solvents to surface-compartmentalized worm-like crystalline-core micelles (wCCMs). Obtaining profound knowledge of the parameters controlling the self-assembly process allowed the production of a variety of complex one-dimensional micellar architectures with many potential applications, such as adaptive surfactants. At first, the basic parameters that control the crystallization-induced self-assembly were explored using symmetric polystyrene-block-polyethylene-block-poly(methyl methacrylate) (PS-b-PE-b-PMMA) triblock terpolymers and a PS-b-PE-b-PS triblock copolymer. In good solvents for the PE block, e.g. THF and toluene, the selective formation of wCCMs was observed over a wide range of concentration, applied crystallization temperature and polymer composition. Whereas wCCMs produced by PS-b-PE-b-PS showed a homogeneous PS corona, a patch-like compartmentalization of the corona was observed if the micelles were formed by PS-b-PE-b-PMMA. As THF shows equal solvent quality for both corona blocks, wCCMs with almost alternating PS and PMMA compartments of about 15 nm were observed in this solvent. However, if structure formation was conducted in bad solvents for PE, such as dioxane or dimethylacetamide, spherical micelles with amorphous PE cores were formed already before crystallization. Hence, the subsequent crystallization of PE resulted in spherical CCMs with a patchy or a homogeneous corona depending on the used triblock. These findings allow the highly selective production of stable spherical or worm-like CCMs from the same polymer. As the corona structure of the patchy micelles self-assembled from triblock terpolymers was mainly deduced from transmission electron microscopy (TEM) performed on dried samples, a small-angle neutron scattering (SANS) study was performed in order to elucidate the morphology in solution. Therefore a partly deuterated triblock terpolymer was synthesized and measured at different contrasts to allow the selective detection of the different corona compartments. The resulting SANS curves could be interpreted using a form factor model for core-shell cylinders with alternating PS and PMMA hemishells including interparticle interactions, thus validating the TEM observations. Notably, Janus-type and patchy cylinders can be clearly distinguished using the applied form factor model. Moreover, the controlled formation of wCCMs with tunable corona composition and structure was achieved using the cocrystallization of different triblock copolymers. Via random cocrystallization of PS-b-PE-b-PMMA and PS-b-PE-b-PS the corona morphology could be tuned continuously from a mixed corona at low PMMA content over spherical PMMA patches of increasing number and size to alternating PS and PMMA patches. This approach allows to manufacture wCCMs with predefined corona structure omitting the need to synthesize a new tailor-made triblock terpolymer for every desired morphology. By establishing the controlled crystallization-driven self-assembly of triblock terpolymers with PE middle blocks, it was further possible to prepare wCCMs with predefined average lengths up to 500 nm and length polydispersities as low as Lw/Ln = 1.1. Here, self-assembled spherical CCMs of PS-b-PE-b-PS were used as seeds for the controlled growth of PS-b-PE-b-PS unimers. Upon further addition of PS-b-PE-b-PMMA unimers these grew epitaxially onto the preexisting wCCMs, resulting in triblock co-micelles that consisted of middle blocks with a homogeneous PS corona and outer blocks with alternating PS/PMMA compartments. These structures represent not only the first block co-micelles including blocks with a patchy corona, but also the first ones produced from purely organic block copolymers. In view of application, the ability of patchy wCCMs formed by PS-b-PE-b-PMMA to stabilize interfaces was investigated using pendant-drop tensiometry. The observed reduction of the interfacial tension at the toluene/water interface was significantly higher than that of comparable triblock terpolymer single chains and that of wCCMs with a homogeneous PS corona. Interestingly, the obtained equilibrium interfacial tension equaled that of Janus cylinders with similar dimensions. To explain this unexpected finding the corona chains were proposed to adapt to the interface via selective collapse and shielding of the incompatible part of the corona chains. Studying wCCMs formed by several triblock terpolymers with different compositions, the interfacial activity was found to increase with increasing overall length of the corona chains, and to a certain extent with the molar fraction of PS units in the corona.
Show/Hide Abstract The Watermill Center. A Laboratory for Performance. Robert Wilson's Legacy, hrg. von José Enrique Macián, Sue Jane Stoker und Jörn Weisbrodt, Stuttgart: Daco 2012. (2012)
Ulrike Hartung
Robert Wilson ist ein Theaterkünstler, der etwas geschafft hat, was eine Seltenheit in der Welt des Theaters ist: Er ist – und das lässt sich ohne Übertreibung konstatieren – ein internationaler Superstar, der nicht nur weltweit bekannt ist, sondern der es darüber hinaus vermag, sowohl eine breite Masse an Theaterpublikum zu bedienen als auch ein ebenso weites Feld an wissenschaftlicher Diskussion anzuregen. Wer es sich als Intendant finanziell erlauben kann, Robert Wilson und sein Team – keine seiner Arbeiten wäre denkbar ohne die Unterstützung seiner ihm treu ergebenen Mitarbeiter – für eine Produktion oder auch nur ein Gastspiel zu engagieren, kann davon ausgehen, dass er, zumindest was diese Vorstellungsabende angeht, keine Probleme mit der Auslastung haben wird. [...]
Show/Hide Abstract Daniela Schulz, Wenn die Musik spielt... Der deutsche Schlagerfilm der 1950er bis 1970er Jahre, Bielefeld: Transcript 2012 (2012)
Hans J. Wulff
In vielen Geschichten des deutschen Films steht der Schlagerfilm als lebendiger Beweis für das Zurücktreten jedweden ästhetischen Anspruchs, den Film erfüllen könnte. Stattdessen trete ein flaches Unterhaltungskonzept in den Vordergrund, durchsetzt mit restaurativen Elementen, ablenkend von den Realitäten der Zeit, eskapistischen Neigungen eines kleinbürgerlichen Publikums Vorschub leistend. Es besteht allerdings kein Zweifel daran, dass der Schlagerfilm eines der größten und erfolgreichsten Genres der deutschen Filmproduktion der 1950er bis Mitte der 1970er Jahre gewesen ist. Und doch ist eine Untersuchung des mehrere hundert Filme umfassenden Korpus bis heute ausgeblieben1. Schulz' Kölner Dissertation aus dem Jahre 2011 betritt also Neuland, allein der Mut, sich der so missachteten Gattung anzunehmen, verdient Respekt.
Show/Hide Abstract Silent Sound Art: Performing the Unheard (2012)
Elen Flügge
This article is a reflection on silent sound art, exemplified here by the works of Peter Ablinger and Akio Suzuki, in the context of a partially historical con-sideration of the participatory subject in Installation Art, with a primary focus on artistic movements and selected works from the late 1950s to the early 1970s by John Cage, George Brecht, and La Monte Young.
Show/Hide Abstract Rapporti tra opera e fruitore nelle origini dell’installazione sonora (1900–1966) (2012)
Giacomo Albert
One feature that defines sound installation as a genre is the participation of the user. Upon entering the space of a work, the user assumes an active role. Thereby the work takes on a theatrical and formative dimension: an art initially defined through space reveals its temporality. This essay analyzes the theatrical dimension, that is, the "modal structure," of works up to 1967, the first period of the sound installation genre. Both interactive and non-interactive works are considered. The analysis shows various models of theatricality for the first years of the genre, during which a diversity of origins and genealogy is reflected. What is common to these experiments is that they seek to involve the viewers, a strategy whose roots lie in the aesthetics and experiments of the first half of the twentieth century, but which since 1955 has become conspicuous.
Show/Hide Abstract Gebiete und Karten der neuen Musik erfahren. Über das Klangkunstprojekt sounding D (2012)
Barbara Barthelmes
sounding D ist ein Klangkunstprojekt, das 2010 vom Netzwerk Neue Musik realisiert wurde. Die Arbeit zeichnet sich durch ihren speziellen Charakter von Ortsbestimmtheit aus. Der Klangzug sounding D, angelehnt an John Cages Il treno (1978), fuhr zwei Wochen durch Deutschland und richtete an 15 Stationen Zwischenstopps ein. In jedem Ort, dem per se eine individuelle Klanglichkeit anhaftet, wurden zahlreiche Klangkunstarbeiten oder Musikperformances organisiert. Die im Inneren des Zuges befindliche Klanginstallation Outside In (Blue) von Robin Minard und der während der Fahrt topografisch erschlossene Raum Deutschlands riefen spannende Wechselbeziehungen hervor. Das Ergebnis ist eine Kartografie der zeitgenössischen Musikszene in Deutschland.

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