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Heterogeneous chemistry of HONO and surface exchange (2013)

Matthias Sörgel

Nitrous acid (HONO) is an important precursor of OH radicals, which are the key oxidizing species in the atmosphere and are therefore called the detergent of the atmosphere. Despite the importance of HONO for atmospheric chemistry and about 30 years of detailed research the exact formation mechanisms of both day- and night-time formation remain unclear. The main formation pathways discussed to date are heterogeneous reactions with nitrogen dioxide as the HONO precursor or microbiological activity in soil. As the ground surface is a major source of HONO, the vertical distribution of HONO is very sensitive to the extent of vertical mixing. Additionally, some uncertainty in comparing laboratory and field measurements might be caused by the not yet clarified role of relative humidity and surface wetness on HONO formation and deposition, respectively. These influences have been investigated in field measurements in the present study. For HONO measurements, LOng Path Absorption Photometers (LOPAPs) have been deployed. During the Diel Oxidant Mechanism In relation to Nitrogen Oxides (DOMINO) campaign, HONO and other reactive trace gases were measured above a pine forest in south west Spain. In line with all recently published work, this study also found a substantial daytime formation of HONO. This so-called additional daytime source or unknown source was found to be slightly correlated (r² = 0.16) with actinic flux. Normalizing this unknown source to nitrogen dioxide mixing ratios improved the correlation (r² = 0.38), which indicates an influence of nitrogen dioxide availability. The coefficient of determination improved further to 0.47 by restricting the data to clear days and rejecting data from advection events. Thus, a fraction of the unknown source might be explained by light-induced nitrogen dioxide conversion but other factors have to be taken into account. Two processes of light-induced nitrogen dioxide conversion, proposed by recent laboratory studies, were shown to be negligible for the semirural conditions during our study. HONO photolysis was found to be the most important primary OH-radical source during DOMINO, contributing 20 % more OH than ozone photolysis integrated over the day. Vertical exchange of HONO was studied at the “Waldstein-Weidenbrunnen” field site of the University of Bayreuth in the Fichtelgebirge Mountains in south east Germany. The simultaneous HONO measurements in and above a forest canopy highlighted the importance of turbulent exchange for the vertical distribution of HONO mixing ratios. The so-called coupling regimes of the forest (with the air layers above) were found to be a very useful micrometeorological concept to study vertical differences of mixing ratios in a forest. They denote which parts of the forest are coupled to the air layer above the canopy and thus take part in turbulent exchange of energy and matter. With this coupling tool it was possible to explain vertical mixing ratio differences by different sources and sinks and the magnitude of the difference by the intensity of vertical exchange. Studying the vertical mixing ratio differences of HONO, an unexpected result was that during late morning and around noon they were close to zero. As the lifetime of HONO below canopy of about 250 to 300 min was a factor of 25 to 30 longer than that above canopy of about 10 min, large mixing ratio differences would have been expected. The lack of these differences could be explained by efficient vertical mixing, which was indicated by a full coupling of the forest or a coupling by sweeps and only intermittent decoupling of the subcanopy during these periods. Around sunset, the whole forest became decoupled from the air layers above. This caused a steep increase in mixing ratio differences up to about 170 ppt due to a faster increase below canopy, indicating local formation below the canopy. HONO and RH are correlated due to their diurnal cycles which are mainly caused by radiation. This diurnal contribution has to be removed from the respective signals in order to extract correlations on other timescales. Singular System Analysis, a tool for time series analysis, has been applied successfully to remove diurnal variations and long-term trends from the HONO and RH time series. Correlations of the higher frequency contributions of the remaining signals were poor but slightly positive. The HONO mixing ratios increase exponentially with RH from about 25 % RH to about 70 % RH. No clear correlation was found between around 70 and 95 % RH. Above 95 % RH, HONO mixing ratios decreased due to HONO uptake in droplets and liquid films. These features are in line with previously proposed mechanisms for interactions of water and HONO on surfaces. The study highlighted the need to assess turbulent transport and surface properties in addition to chemistry for understanding the heterogeneous reactions and processes forming HONO.

Integrated size and price optimization for a fashion retailer (2013)

Miriam Kießling

This thesis is the result of a collaboration with a German fashion retailer which lasted for several years. The aim was the development of a decision-support system for the supply of the about 1300 branches in Germany. There are some specialties about the situation at our industrial partner: The branches are supplied by prepackaged size-assortments of a product which we call lot-types. With the objective to economize handling cost, these lot-types are already composed at the respective low-wage country where the article is also produced. The expense at the German central warehouse is further reduced by allowing only four or five different lot-types for the delivery of one product. Moreover, each branch is supplied by a certain quantity of a single lot-type. For the most fashion articles replenishment is not possible. The sales success of a product is a priori unknown. Historical sales data can only be used on a higher aggregation level, e.g., the average historical demand on the commodity group level. Demand estimation is therefore very vague. Under- and oversupplies are unavoidable. Influence over the sales process is possible by marking down prices. To compensate for an oversupply of a product, weekly the price can be reduced to predefined price steps which depend on the starting price of the product. Mark-downs for an article are performed simultaneously for all branches and sizes. Within the cooperation mathematical problem formulations with the aim to minimize measures for the deviation of supply from estimated demand had been developed. In these measures the selling process is not or only very vaguely regarded. Now we include the possibility of marking down prices during the selling time already when deciding on the supply. The result is the two-stage stochastic program ISPO: The so-called first stage decision is the determination of a supply policy. The second stage decision, or recourse, is the decision on mark-downs during the selling time. ISPO yields an expected revenue maximizing supply strategy and corresponding optimal mark-down strategies for the considered scenarios. ISPO it too complex to solve it via standard approaches. Customized methods had to be devised to solve ISPO. On the one side we present an exact solver for benchmarking. On the other side a fast heuristic was developed for practical use at our partner. The basic idea of our exact solver is to enumerate all possible mark-down strategies. With this it is possible to reduce ISPO to a former formulation for the optimization of supply, which can be solved via standard approaches. In practice enumeration of all valid mark-down strategies for the purpose of solving ISPO is for reasons of time impossible. Therefore the idea is extended to a customized Branch&Bound approach. In this context we derived dual bounds for general two-stage stochastic programs which are based on the so-called wait-and-see solution from stochastic programming. We show that in general our bounds are tighter. The heuristic, beginning with a valid second stage decision, determines an optimal first stage decision and alternates between solving the first stage and the second stage until convergence is reached. The optimality gap is small enough to justify a practical use at the industrial partner. In practice the by ISPO proposed mark-down strategies are not applied; instead latest sales figures are exploited. According to these and an updated demand estimation weekly a new optimal mark-down strategy for the remaining selling time of the product is determined. For this purpose we propose an algorithm which relies on dynamic programming and tries to exclude non-optimal solutions a priori by dominance checks. ISPO, more precisely our heuristic approach, together with the weekly adaption of the mark-down strategy forms our decision support system for integrated size and price optimization DISPO. We tested DISPO in a five-month field study, performed as a statistical experiment, at our partner where pairs of similar branches were compared. At one branch of each pair, the test branch, supply and mark-down decisions came from ISPO. With respect to latest sales figures the mark-down decisions were weekly updated via our dynamic programming approach. At the other branch, the control branch, these decisions were not integrated: Supply was determined according to a strategy resulting from a former model that disregarded the selling process and mark-downs were handled manually by our partner. For the branches at which the decisions of ISPO were implemented an average raise of 1.5 percentage points of relative revenue was observed.

THE INDEX THEOREM FOR QUASI-TORI (2013)

Tsz On Mario Chan

The Index theorem for holomorphic line bundles on complex tori asserts that some cohomology groups of a line bundle vanish according to the numbers of negative and positive eigenvalues of the associated hermitian form. In this thesis, this theorem is generalized to quasi-tori, i.e. connected complex abelian Lie groups which are not necessarily compact. In view of the Remmert–Morimoto decomposition of quasi-tori as well as the Künneth formula, it suffices to consider only Cousin-quasi-tori, i.e. quasi-tori which have no non-constant holomorphic functions. The Index theorem is generalized to holomorphic line bundles, both linearizable and non-linearizable, on Cousin-quasi-tori using L2-methods coupled with the Kazama–Dolbeault isomorphism and Bochner–Kodaira formulas.

Structural analysis of nanoparticles by small angles X-ray scattering (2013)

Christophe N. Rochette

The objective of this work was to analyze nano-scaled particles by the combination of small angle x-ray scattering (SAXS), electron microscopy (TEM and cryo-TEM) and dynamic light scattering (DLS). Two systems with totally di_erent morphologies and compositions have been investigated: spherical particles of calcium-phosphate-protein complexes and hamburgers of semi-crystalline polybutadiene/polyethylene nanoparticles. The study of the calcium-phosphate-protein complexes consisted in looking for the influence of a protein, Fetuin-A, also called ahsg, onto the calci_cation at early stage. For the purpose, calcium and phosphate ions were mixed with or without the presence of Fetuin-A in a buffr solution of pH=7.4. In a first step, DLS measurements were realized to better appreciate the effect of the total weight percentage of Ca2+ and PO43- ions. These experiments, withtout addition of ahsg, demonstrated that for a lower weight fraction, the particles formed are smaller. Studies with addition of Fetuin-A affected the calcification during the first minute of this process. The early formation of calcium phosphate complexes has been successfully followed by TR-SAXS. A very fast nucleation of nanoparticles within 1 second has been detected. For the first time, the role of the glycoprotein Fetuin-A at the very early stage of calcification has been qualitatively highlighted: ahsg inhibits the aggregation of calcium phosphate particles. Thus, Fetuin-A plays an important role in the fetal serum in the pre-formation of the skeleton of Vertebrates. This study demonstrated that a physiological concentration of this glycoprotein (15 µM) is suffcient to completely inhibit the aggregation of calcium phosphate particles. Freely suspended nanoparticles of syndiotactic polybutadiene have been studied. By using the combination of cryo-TEM and SAXS, it has been shown that they consist of remarkably thin polymer crystalline lamella. Different models have been compared in order to theoretically fit the experimental SAXS data: homogeneous and heterogeneous (two and three different electron densities within one particle) nanoparticles. The presence of amorphous and crystalline polybutadiene has been demonstrated by the X-ray diffraction. The necessity of using an additional layer of SDS for the modeling is explained by the abundancy of SDS added after the synthesis of the polybutadiene particles (weight ratio ca. 1:1) and by the modeling of the SAXS theoretical intensities which were not sufficient without taking into account the presence of SDS. After the formation of semi-crystalline nanoparticles of PE, these new nanoparticles open a new route to the synthesis of nanopolymers of interesting physico-chemical properties such as semi-conductors or photovoltaic compounds. Finally, in contrast to recent literature on bulk polyethylene (PE), this thesis investigated freely suspended nanoparticles of PE. As suggested by Weber and coworkers, the combination of SAXS and cryo-TEM has been used for this study. The structure of individual PE nanocrystals has been determined in detail and an improved model of the form factor (SAXS) has been developped in close collaboration with Priv.-Doz. Dr. Ludger Harnau. The second part of this thesis mainly deals with the annealing of these PE particles. For the first time, it is shown that the effect of the annealing process results in a doubling of the crystalline layer of the PE nanoparticles. This behaviour could be traced back to the unlooping of the PE chains. In addition, a linear relationship between the reciprocal of the crystalline layer and the annealing temperature has been experimentally drawn. This line was predicted by the Gibbs-Thomson equation according to the literature. This result is important because it allows controlling the crystalline thickness and physical properties of the system, by the temperature.

Soil erosion and conservation potential of row crop farming in mountainous landscapes of South Korea (2013)

Sebastian Arnhold

Soils play an essential role for mankind because they provide fundamental ecosystem services required for human life, primarily for the production of food by providing the environment for plant growth. However, soils worldwide became highly threatened by human induced degradation, especially as a consequence of accelerated erosion by water during recent decades. In consideration of climate change and an increasing food demand of a rising population, there is an urgent need to conserve the soil resources by implementing effective erosion control measures for agricultural production. The effective implementation of those measures strongly depends on the specific conditions of particular regions and requires the analysis of the existing farming systems and their capability for erosion control. Objective of this thesis is the analysis of the major agricultural practices applied for row crop cultivation in mountainous watersheds of South Korea with respect to water erosion and the identification of their conservation potential. Our first two studies analyze the subsurface flow processes, the runoff patterns, and the associated erosion rates of the widely applied plastic covered ridge-furrow system (plastic mulch), and our third study investigates the impact of herbicide applications on erosion associated with conventional and organic farming. To analyze the flow processes induced by the plastic mulch cultivation, we conducted four irrigation experiments on potato fields that represent a smooth surface, uncovered ridges, and plastic covered ridges with and without a developed crop canopy. With an automatic sprinkler, we irrigated small plots with a dye tracer solution of Brilliant Blue and potassium iodide, collected surface runoff, and excavated soil profiles to visualize the subsurface flow patterns, which were subsequently analyzed by image index functions. We found that the ridge-furrow system, especially when ridges are covered with plastic, decreased infiltration and generated high amounts of surface runoff, whereas a developed crop canopy increased infiltration due to interception and stem flow. The analyses of the subsurface flow patterns show that the plastic covered ridge-furrow system induces preferential infiltration in furrows and planting holes due to its topography and the impermeable covers, but that the impact on flow processes in the soils is relatively small compared to the impact on runoff generation. To identify the patterns of overland flow and the erosion rates associated with the plastic mulch system, we installed runoff collectors to monitor runoff and sediment transport of two potato fields with concave and convex topographies, and we applied the EROSION 3D model to compare the plastic covered ridge-furrow system to uncovered ridges and a smooth surface. We found that plastic mulch cultivation considerably increases soil erosion compared to uncovered ridges as a consequence of high amounts of surface runoff. Our results show that the ridge-furrow system concentrated overland flow on the concave field, resulting in severe gully erosion, but prevented flow accumulation and reduced erosion on the convex field, which demonstrates that the effect of this cultivation strategy is primarily controlled by the field topography and its orientation. To analyze the effects of conventional and organic farming on water erosion, we measured multiple vegetation parameters of crops and weeds of conventional and organic farms cultivating bean, potato, radish, and cabbage, and we simulated long-term soil loss rates with the Revised Universal Soil Loss Equation (RUSLE). We found that organic farming reduced erosion for radish, as a result of an increased weed biomass due to the absence of herbicides, but that it increased erosion for potato due to lower crop coverage, presumably as a consequence of crop-weed competition or herbivory associated with the absence of agricultural chemicals. Although we demonstrated that a developed weed cover in the furrows can potentially decrease the erosion risk for row crops, our results show that the average annual erosion rates of both farming systems exceed by far any tolerable soil loss. In consideration of the generally high soil loss found in our studies, we conclude that the applied farming practices are not capable for effective erosion control and soil conservation in this region. However, based on our findings, we could identify possible modifications of those practices that can help to reduce the risk of erosion in the future. We recommend perforated plastic covers for ridges to reduce runoff generation, and the orientation of the ridge-furrow system along the contours or towards field edges to prevent flow accumulation and gully formation. Additionally, we suggest residue mulching of furrows to protect the soil surface from overland flow, and the cultivation of winter cover crops after harvest to maintain a better soil cover throughout the year.

Flow and transport processes as affected by tillage management under monsoonal conditions in South Korea (2013)

Marianne Ruidisch

A sustainable agriculture, which provides enough yields to satisfy the food demand and minimizes the impacts on ecosystem services such as provision of high water quality, is challenging especially in monsoon regions. In this thesis, plastic mulched ridge cultivation (RTpm) under monsoonal conditions and its impact on flow processes and nitrate transport was investigated. On hillslopes, we monitored surface and subsurface flow processes in four plastic mulched potato fields using a network of tensiometers, FDR sensors, runoff collectors and flow dividers as well as Brilliant Blue FCF tracer experiments. The obtained datasets were used to calibrate the process-based models HYDRUS 2/3D and EROSION 3D in order to quantify drainage water fluxes, surface runoff and erosion rates of RTpm compared to ridge tillage without coverage (RT) and conventional flat tillage (CT). In a flat terrain, N fate under fertilizer rates at 50, 150, 250 and 350 kg NO3− ha−1 was investigated in a plastic mulched radish field using suction lysimeters, tensiometers and a 15N tracer experiment. We used datasets of nitrate concentrations and matric potentials to calibrate a water flow and solute transport model using the numerical code HydroGeoSphere. RTpm affects soil water dynamics dominantly during dry periods, when ridge soil was drier compared to furrow soil caused by the protective plastic coverage and root water uptake in ridges. Hence, pressure head gradients induced lateral flow from furrows to ridges. Under monsoonal conditions, soil was fully saturated and down slope lateral flow occurred in the coarse textured topsoil. The dye tracer experiments showed that matrix flow dominated in the sandy topsoil. Lateral funnel flow above the tillage pan was the prominent preferential flow path. Unexpectedly, macropore flow in deeper soil horizons was not detected. The field and modeling studies revealed that surface runoff was substantially increased under RTpm compared to RT and CT. However, the field topography primarily controlled surface runoff and erosion rates. The concavity of the field led to flow accumulation and high erosion losses in the center of the field, while a convex shape resulted in less soil erosion. NO3− leaching was found to be the prominent pathway especially during the early season. Furthermore, the biomass production did not significantly differ between NO3− fertilizer rates of 150 to 350 kg ha−1. Hence, we recommend NO3− fertilizer application of 150 kg ha−1, a better fertilizer placement and split applications. We simulated whether the given recommendations on fertilizer best management practices (FBMPs) decreased NO3− leaching amounts. Compared to RT under conventional fertilization in ridges and furrows, the simulations showed that NO3− leaching can be considerably reduced up to 82% by combining RTpm, fertilizer placement only in ridges and split applications with a total fertilizer NO3− amount of 150 kg ha−1. Based on these findings, the impact of RTpm on flow and transport processes has to be evaluated differently depending on terrain complexity. In a flat terrain, where surface runoff processes are absent or minimal, RTpm has several advantages. Beside functions such as weed control, and earlier plant emergence due to higher temperatures, plastic mulching decreases drainage water and NO3− leaching. Thus, RTpm enhances nutrient retention below the plastic mulch and reduces NO3− groundwater contamination risk. On slopes, where precipitation contributes substantially to surface runoff, RTpm even increases runoff, soil erosion and surface leaching of agrochemicals into aquatic systems. This thesis provides several recommendations, aiming to minimize environmental impacts and to decrease costs of fertilizer and herbicide inputs. To reduce surface runoff and soil erosion at sloped fields, we suggest applying perforated plastic mulch and a ridge configuration following contours of the field. Furthermore, we recommend omitting application of herbicides in furrows to allow weed growth, which slows down runoff processes. These suggestions would increase infiltration and subsurface flow processes automatically become more important. However, absent preferential flow to deeper soil layers indicated a low groundwater contamination risk. Since funnel flow above the tillage pan was found to be the most important preferential flow path, we propose the establishment of riparian buffer zones. This would also help to reduce the discharge of sediments and fertilizers via surface runoff into the streams. Finally, FBMPs such as fertilizer placement only in ridges and split applications were found to decrease nitrate leaching considerably. Hence, we suggest applying FBMPs with impermeable plastic mulch in flat terrain, while on hill slopes FBMPs should be applied with perforated plastic mulch. To reduce the leaching and erosion risk after harvest when the plastic mulched ridges are removed, we recommend cultivating cover crops.

Sozialphilosophie und Geldpolitik bei Friedrich August von Hayek, Walter Eucken, Joseph Alois Schumpeter, Milton Friedman und John Maynard Keynes (2013)

Stephan Balling

Die globale Finanzkrise, die im Frühjahr 2007 begann und im September 2008 durch den Zusammenbruch der Investmentbank Lehman Brothers eskalierte, begann im vierten Quartal 2008 weltweit auf die Realwirtschaft durchzuschlagen. Die deutsche Bundesregierung rechnete damit, dass im Jahr 2009 das Bruttoinlandsprodukt (BIP) um 6 Prozent einbrechen werde – so stark wie nie seit dem Zweiten Weltkrieg. Es kam mit einem BIP-Rückgang von 4,9 Prozent dann zwar nicht ganz so schlimm, aber auch diese Rezession war die stärkste seit 1945. Für diese dramatischen Entwicklungen lieferten Ökonomen im Wesentlichen zwei Erklärungsmuster: Die einen gaben den Zentralbanken die Schuld, sie hätten in den zwei Jahrzehnten vor der Krise zu viel Liquidität geschaffen, die dann zu Preisblasen etwa auf dem amerikanischen Immobilienmarkt führte. Andere machten eine zu schlaffe Regulierung und die Liberalisierung der Finanzmärkte für die Entwicklungen verantwortlich. Vor dem Hintergrund dieser Ereignisse entstand die Idee, nicht nur eine technische Analyse durchzuführen um zu erkennen, welches Erklärungsmuster plausibler sei. Stattdessen sollte analysiert werden, wie sich diese diametral wiedersprechenden Aussagen von Ökonomen ideengeschichtlich erklären lassen. Es erschien nötig, sich ideengeschichtlich mit Sozialphilosophie, der Rolle des Staates in der Wirtschaft sowie dem Wesen des Geldes und des Zinses in den wichtigsten ökonomischen Schriften des 20. Jahrhunderts zu beschäftigen. Dabei sollte es um die Frage gehen, ob bei Ökonomen und Sozialphilosophen zwischen den generellen gesellschafts- und wirtschaftspolitischen Vorstellungen einerseits und den geldpolitischen Vorstellungen andererseits ein Zusammenhang besteht. Diese Frage sollte durch einen Literaturvergleich verschiedener Staats- und Geldtheoretiker geklärt werden, die – bei allen Unterschieden im Detail – für sich das Attribut „liberal“ reklamieren. Die vorliegende Arbeit analysiert folglich die Werke von fünf großen Wirtschafts- und Sozialphilosophen, nämlich von Friedrich August von Hayek als Repräsentant der Österreichischen Schule der Nationalökonomie, Walter Eucken als Vertreter der Freiburger Schule der Ordnungsökonomik, Joseph A. Schumpeter als Vertreter einer Unternehmertheorie, Milton Friedman als Begründer des Monetarismus und John Maynard Keynes als Vertreter einer expansiven Geld- und Fiskalpolitik. Dabei wird ein Zusammenhang des Denkens in Bezug auf allgemeine staatsphilosophische Vorstellungen, wirtschaftspolitische Ziele und die Aufgabe sowie den Instrumentenkasten der Geldpolitik hergestellt. Dabei zeigt sich: Individualistische Vorstellungen über die Gesellschaft gehen mit Präferenzen für eine geringe Tätigkeit des Staates in der Wirtschaft sowie einer weitgehenden, teils sogar völligen Entkopplung der Geldpolitik von politischer Einflussnahme einher. Umgekehrt gehen Vorstellungen, die weniger einem negativen als einem positiven Freiheitsbegriff folgen und dem wirtschaftlichen Erfolg des Kollektivs den Vorzug vor der Freiheit des Einzelnen geben, mit einer stärkeren Rolle des Staates im wirtschaftlichen Koordinations- und Allokationsprozess einher und fordern zugleich eine aktive Rolle der Geldpolitik bei der Steuerung des wirtschaftlichen Prozesses. Daraus ist wiederum zu schließen: Die Forderung nach einer expansiv ausgerichteten Geldpolitik zur Stimulierung von Konjunktur und Wachstum beruht ideengeschichtlich nicht nur auf technischen Überlegungen zur Effizienz, sondern stammt von einer grundsätzlich kollektivistischer – teils sozialistischer – ausgerichteten Grundüberzeugung. Die Argumentation zum Beispiel für oder gegen eine konjunkturstützende Geldpolitik leitet sich nicht nur aus theoretischen ökonomischen Modellen ab, deren Richtigkeit etwa durch empirische Methoden überprüft werden kann. Sie leitet sich auch aus grundsätzlichen Überzeugungen zum Beispiel über den Wert der individuellen Freiheit oder des Schutzes von Eigentumsrechten ab. In der politischen wie in der wissenschaftlich-ökonomischen Diskussion kommt dieser Aspekt allerdings zu kurz.

The origins of olivine fabric transitions and their effects on seismic anisotropy in the upper mantle (2012)

Sushant Shekhar

Convecting mantle plays a central role in the thermal and geochemical evolution of the Earth. It provides the principal force responsible for major geological features such as mountains and ocean basins. Plate tectonics and its violent consequences such as earthquakes and volcanoes are all manifestations of the dynamics of the convective mantle. Shearing forces generated by mantle convection leads to lattice preferred orientation (LPO) of the major upper mantle mineral phases. LPO that develops in this way is thought to be the principal cause behind seismic anisotropy in the upper mantle, which can consequently be used to chart convective flow of the mantle. Strong changes in seismic anisotropy occur in the top 300 km of the upper mantle where olivine is the principal mineral. In this study a solid media high pressure deformation apparatus, called the deformation-DIA or D-DIA, has been used to deform aggregates of San Carlos olivine in simple shear geometry at pressures between 3 and 8.5 GPa and temperatures from 1300-1500°C. As part of this project a high pressure and temperature solid-media cubic assembly was developed to facilitate these experiment that employed alumina pistons cut at 45° to shear the sample but minimized cold deformation of the sample by employing initially porous alumina in the sample column. Once stable high pressures and temperature were reached the cubic assembly was deformed by compressing two vertically oriented anvils of the D-DIA, while the four horizontally oriented anvils were maintained at a constant loading force. This assembly shortening led to shearing of the olivine sample. Recovered samples were analyzed for fabric development employing electron backscattered diffraction (EBSD) and microstructure was observed using transmission electron microscopy (TEM). Experiments were performed at each pressure and temperature as a function of strain rate and H2O content. In dry olivine deformation experiments performed at slower strain rates an A-type fabric dominated at all pressures and temperatures, implying deformation by dislocation glide through the (010)[100] slip system. At higher strain rates evidence for the B-type fabric was observed, suggesting increased activity of the (010)[001] slip system at higher stresses. Recrystallization grains size and dislocation densities were used to estimate stresses in the samples and a good correlation was observed between strain rate and estimated flow stresses. Dry experiments from 8.5 GPa and 1500°C exhibited no LPO, which may be an indication for deformation through diffusion accommodated grain boundary sliding at these conditions. No indication was found that pressure influences the dominant slip system in olivine, in contrast to previous studies. It is considered that previously reported incidences of pressure effects can in fact be attributed to the development of higher stresses in experiments performed at higher pressures. Fabrics in H2O bearing olivine deformed at similar conditions revealed the overriding dominance of the C-type fabric, developed through action of the (100)[001] slip system. Variations in pressure, temperature and strain rate had little influence on this fabric development. TEM observations confirmed the presence of dislocations with slip systems consistent with the development of the macroscopic fabrics. Viscoplastic self consistent modeling was employed to understand the development of fabric in the samples and to estimate the relative contributions of variations slip systems to the developed fabrics. These results are used to construct an olivine fabric map which is found to be consistent with some previous studies at lower pressures. It is argued that the decrease in seismic anisotropy observed in the top 300 km of the upper mantle cannot originate from a pressure induced change in the dominant olivine deformation fabric. Instead it is argued that changes in the H2O content of olivine with depth cause a shift in the dominant fabric from A-type to C-type, with a possible excursion through the E-type fabric, dominant slip system (001)[100], which was, however, not observed in this study. Modeling is used to show that this variation in fabric with depth can cause the observed weakening the seismic anisotropy in the upper mantle if the olivine H2O content increases from below 100 ppm at 50 km to 250 ppm at 300 km. Rather than implying an increased in the H2O content of the mantle with depth, however, it is argued that this change in olivine H2O content can be caused by changes in the H2O olivine-pyroxene partition coefficients with depth, for a fixed bulk mantle H2O content of 200 ppm. Similar deformation experiments performed on a peridotite assemblage at 8.5 GPa and 1300°C indicate identical olivine fabrics to those observed in monomineralic experiments at the same conditions. Fabrics for diopside and enstatite were found to be similar to those found in previously performed lower pressure experiments. Experiments on a piezoelectric single crystal of GaPO4 were performed in the D-DIA and 6-ram MAVO press at high pressures in order to measure charge on the crystal developed through the application of deviatoric stresses. Electrical charges were measured through the use of an operational amplifier. Experiments performed at room temperature using a developed cubic assembly were successful in measuring quantifiable electrical charges resulting from the advancement of the deformation anvils by as little as 0.5 µm. Although the piezoelectric constant for this material is not yet calibrated at high pressures, stresses were estimated from the measured charges and measureable values were in the range 4-350 MPa.

Kinetische Untersuchungen der Halogen-Aktivierung einer simulierten Salzpfanne in einer Smogkammer (2013)

Natalja Balzer

Reaktive Halogenverbindungen, insbesondere solche von Br und Cl, spielen eine wichtige Rolle beim atmosphärischen Abbau von Ozon und Kohlenwasserstoffen. Auch beeinflussen sie die Radikalzusammensetzung in der Troposphäre und haben somit eine Auswirkung auf klimarelevante Prozesse. Ziel dieser Arbeit war die Untersuchung der Halogenfreisetzung aus einer künstlichen Salzpfanne bei unterschiedlichen umweltrelevanten Bedingungen, wie relative Feuchte (RF) und Konzentrationen von Stickoxiden und Kohlenwasserstoffen, in einer Smogkammer. Diese Methode wurde in Rahmen dieser Arbeit entwickelt, um diese bislang wenig untersuchte Quelle von Halogenen zu untersuchen. Als Modell für die Salzpfanne wurde eine umweltrelevante Mischung von NaCl mit NaBr verwendet. Kinetische Berechnungen lieferten die zeitlichen Verläufe der Cl-Atome und OH-Radikale aus dem Verbrauch der zugesetzten Kohlenwasserstoffe und der Br-Atome aus dem Ozonverbrauch und UV-Absorptionsmessungen die Verläufe der BrO-Radikale. Während Salzpfannen-Experimenten bei einer mittleren RF von 37 % erreichte die Cl-Konzentration ein Maximum von 5 x104 cm-3. Ein rascherer Ozonabbau wurde bei größerer RF und zugleich höherer BrO-Konzentration beobachtet. Bei den Experimenten in Anwesenheit von sekundären organischen Aerosolen (SOA) verlangsamte sich der Ozonabbau um einen Faktor 16. Das BrO-Mischungsverhältnis erreichte in diesem Fall maximal 0.15 ppb im Vergleich zu Experimenten ohne SOA, bei denen das BrO Mischungsverhältnis 6 ppb erreichte. Nach Einwirkung der aus der Salzpfanne freigesetzten Halogene auf das SOA wurde ein erneutes Partikelwachstum beobachtet. Dies könnte eine Hauptsenke für Halogene in der Atmosphäre darstellen und einen neuen Weg zur Partikelbildung.

Rhizodeposition and its effects on C fluxes in the soil (2013)

Johanna Pausch

Organic compounds released from living roots (rhizodeposits) are easily available sources of energy for microorganisms strongly affecting soil organic matter (SOM) dynamics. Although, rhizodeposition is a key driver of microbially mediated processes in the soils, it still remains the most uncertain component of the terrestrial carbon (C) cycle. The input of C through rhizodeposition occurs in temporal and spatial hotspots. The objective of Study 1 was to determine the dynamics of hotspots of recently assimilated C in ryegrass roots. Shoots were 14CO2 pulse labeled and the allocation patterns at increasing time intervals were visualized by phosphor imaging. We could show a quick translocation of assimilated C to the roots. 14C hotspots were detected at the root tips already 6 hours after labeling. The hotspots remained active for at least 2 days. Eleven days after assimilation the hotspots at the tips had disappeared, and the 14C distribution was much more even than after 6 hours and 2 days. Through the availability of rhizodeposits, hotspots create preferred habitats for microbes. Rhizodeposits are an important source of C and energy for microorganisms stimulating their growth and activity. Thereby, roots can influence the rate of native SOM decomposition in the rhizosphere. This rhizosphere priming effect (RPE) was reported to be plant-species specific. Therefore, we hypothesized that also plant inter-species interactions affect the RPE. In Study 2, we used continuous 13CO2 labeling to investigate the RPE of monocultures and mixtures of typical agricultural crops. The RPE was consistently positive for all cultures with an increase of 43% - 136% above the unplanted soil. Of particular interest was the result that plant inter-species interactions between sunflower and wheat significantly reduced the RPE in contrast to mixtures which included soybean as a legume. It was argued that the RPE of the sunflower-wheat mixture was reduced through a more severe competition for nitrogen (N), whereas, due to the N-rich rhizodeposits of the legume and its lower demand for soil mineral N the RPE of the legume containing mixtures remained unaffected. Besides potential plant-specific differences in the quality and quantity of rhizodeposits, also photosynthesis could control root exudation because of the fast transport of recently assimilated C to belowground pools. Taking both factors into account, in Studies 3 and 4 the effect of limited photosynthesis on the distribution of recently assimilated C, of stored C and of N was investigated. Based on 13C, 14C and 15N labeling of a legume and a non-legume we could demonstrate that high C and N demands of regrowing shoots after clipping led to a remobilization of stored C and N to the shoots. Additionally, recently assimilated C was retained in the regrowing shoots. Shading, in contrast, did not induce a remobilization of stored C, since recently assimilated C obviously covered the demand of the shoots with lower growth rates. For both treatments lower amounts of recently assimilated C were observed in the belowground pools emphasizing the importance of the tight coupling of assimilation and belowground processes. Furthermore, different responses of clipping and shading of the legume and the non-legume could be detected for root-derived CO2. The quantitative importance of rhizodeposition at field scale was determined in Study 5. We proposed a new approach for an improved quantification of rhizodeposition under field conditions taking into account the decomposed fraction of rhizodeposits. Based on a 14CO2 pulse labeling experiment under controlled conditions a rhizodeposition-to-root ratio was calculated and was applied to the root biomass of the field. The root biomass C of maize, sampled in July 2009, was 298±64 kg C ha-1. Gross rhizodeposition was 166±53 kg C ha-1. With aging of SOM, the availability of C for microbial decomposition declines. In Study 6 the availability of younger relative to older C sources was assessed. The natural isotope abundances of 13C and 12C of SOM and CO2 were analyzed after a C3 to C4 vegetation change. The contribution of younger C, originating from the belowground C input by maize in the previous year, and that of older C sources, derived from the former C3 vegetation, to SOM and CO2 was determined. Comparing the proportions of younger and older C in SOM with that in CO2, we found that younger C was 7 times more available for microbial decomposition than older C pools. In summary, this thesis extends the understanding of factors affecting rhizodeposition and of processes occurring at the soil-root interface. Furthermore, it presents a new method to quantify gross rhizodeposition at field scale. Although, we could gain insight in temporal changes of the availability of C pools for microbes, the ecological importance of C fluxes in the rhizosphere requires future research on this topic with regard to spatial and temporal predictions.

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