93 search hits
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Loess-like and palaeosol sediments from Lanzarote (Canary Islands/Spain) —Indicators of palaeoenvironmental change during the Late Quaternary
(2009)
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Hans von Suchodoletz
Peter Kühn
Ulrich Hambach
Michael Dietze
Ludwig Zöller
Dominik Faust
- On Lanzarote (Canary Islands) Quaternary Saharan dust and weathered local volcanic material were trapped in Miocence to Pliocene valleys dammed by younger volcanic edifices. These sediments show sequences of alternating reddish/clayey and loess-like yellowish/silty material. In order to investigate if reddish/clayey layers contain material derived from local pedogenesis and if so, which pedogenetic processes were active, we performed sedimentological, micromorphological and environmental magnetic analyses. The analyses demonstrate that these layers contain material derived from local soils. These soils were characterised by clay formation, rubefication and the formation of superparamagnetic particles during periods of enhanced soil moisture. Thus, they can serve as natural archives in order to reconstruct the terrestrial palaeoclimatic history of Lanzarote. The distribution of soil material in the profiles shows that cold periods of the Late Quaternary were characterised by more humid conditions than today. Using palaeontological remains and a comparison with recent soils on Tenerife, we can roughly estimate maximal palaeoprecipitation values during more humid periods.
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Existence Results for Plasma Physics Models Containing a Fully Coupled Magnetic Field
(2009)
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Martin Seehafer
- The present thesis concern is the initial value problem for three nonlinear systems of partial differential equations: the Vlasov-Darwin system, the Vlasov-Poisswell system and a version of the latter which is called the modified Vlasov-Poisswell system. These equations belong to kinetic theory, which has proved useful when describing large particle systems in different areas of physics such as kinetic theory of gases, the formation of stellar structures or plasma physics. In the present thesis equations originating in plasma physics are considered which describe the evolution of the time dependent density function f(t,x,v) (t - time, x – position, v - particle velocity) of a large ensemble of charged particles in the (x,v)-phase space influenced by the electromagnetic field created by the particles and when neglecting collisions. The focus of the investigation is on existence and uniqueness questions for solutions of the initial value problem, i.e., it is asked whether there exists a solution f of the system under consideration such that f(t=0)=f0 where f0 is a prescribed initial datum. In order to answer this question further properties of solutions such as energy and charge conservation or decay rates must be taken into account. An important issue is, whether - if necessary under additional hypotheses or by weakening the concept of solution - global solutions, i.e., solutions existing for all t>=0, may be obtained. The most important results are a theorem about local existence and uniqueness of classical solutions of the Vlasov-Poisswell system, a global existence result for weak solutions of the modified Vlasov-Poisswell system, and a global existence theorem for classical solutions of the Vlasov-Darwin system under the assumption of smallness of the initial.
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Multi-View Reconstruction of Unknown Objects in the Presence of Known Occlusions
(2009)
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Stefan Kuhn
Dominik Henrich
- We present a general method for reconstructing unknown objects (e.g. humans) within a known environment (e.g. tables, racks, robots) which usually has occlusions. These occlusions have to be considered since parts of the unknown objects might be hidden in some or even all camera views. Besides grayscale and color cameras also depth sensors are considered. In order to avoid cluttered reconstructions, plausibility checks are used to eliminate reconstruction artifacts which actually do not contain any unknown object. One application is a supervision/surveillance system for safe human/robot-coexistence and –cooperation. Experiments for a voxel-based implementation are given.
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Transport Processes of Reactive Trace Gases in the Atmospheric Boundary Layer
(2009)
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Jens-Christopher Mayer
- Transport of trace gases within the atmospheric boundary layer plays a key role in feedback processes between the earth’s surface and the atmosphere and consequently in ecosystem budgets of carbon and nitrogen (among many more). For a correct quantification of the exchange between surface and atmosphere, it is crucial to understand the transport processes involved and to determine limitations of the presently available measurement techniques in order to apply the right technique with respect to the currently active transport processes. This dissertation focuses on three topics: (a) The analysis of effects of vertical transport mechanisms on surface measurements of trace gases, (b) the appropriate choice of an experimental setup to assess specific measurement errors of moving measurement systems and (c) the application of a series of measurement techniques for surface fluxes of reactive trace gases to determine their degree of agreement and to assess potential source of deviations. To study the impact of vertical transport mechanisms on surface trace gas measurements, this thesis presents a comprehensive set of measurements at the surface and within the atmospheric boundary layer (by tethered balloon). It enables the attribution of a recurrent negative excursion of ozone mixing ratios in the morning hours at a mountain summit to a very efficient vertical transport by free convection. It has been shown that, due to the rapid vertical transport, a layer of approximately 20 m thickness developed at the equilibrium height of the free convection, being located within the residual layer. It had a chemical composition similar to the air close to the ground while being surrounded by residual layer air masses. Hence, very strong gradients of the chemical composition were found within the residual layer. Evidence was found, that such a transport occurs rather frequently at this location, affecting at least 18 % of the days between April and September. To assess measurement errors introduced by the application of scanning methods as compared to gradient approaches, a higher temporal resolution of the vertical profiles was needed. Because of limitation inherent to a tethered balloon, an elevator based profiling system was installed, providing a temporal resolution of 10 minutes with a maximum ceiling of 100 m. Prior to the investigation of transport processes, the proper functioning of correction algorithms for the so-called dynamical error was investigated under real atmospheric conditions. This dynamical error is inherent to all moving measurement systems and arises from the non-zero response time of the deployed sensors. It has been shown that existing algorithms as well as one developed by the authors reliably balance the dynamical error. Furthermore it has been demonstrated, that the elevator data correlate with reference data at fixed levels with coefficients of determination being always greater than 0.992 at every level (10, 20, 40, 60, 80, 98 m). To evaluate the applicability of different flux measurement techniques for the determination of surface fluxes of reactive trace gases, three different approaches were compared. In order to determine surface fluxes of trace gases, a new modification of the modified Bowen ratio method was used. In this modification, the measurements of sensible heat flux and of the gradients were horizontally separated. This allowed the simultaneous measurement of the fluxes of various trace gases without creating errors due to flow distortion by bulky inlet systems. Surface emission fluxes of nitric oxide were found to be in the range 0.02 – 0.15 nmol m-2 s-1 (night/day), nitrogen dioxide fluxes varied around 0.1 nmol m-2 s-1 (deposition) with slightly positive values in the early afternoon, indicating emission. Ozone deposition fluxes ranged from close to zero to about 6 nmol m 2 s-1. A laboratory parameterization of biogenic soil emission fluxes of nitric oxide from incubated soil samples yielded values from 0.025 nmol m-2 s-1 to 0.12 nmol m-2 s-1 for environmental conditions encountered during the field campaign. This was in excellent agreement with the fluxes from field observations. Besides the comparison of field fluxes with laboratory data, a case study (1 night) comparison of carbon dioxide and ozone fluxes between two field methods was done. Results from the modified Bowen ratio method have been compared to fluxes derived from the integral boundary layer budget method. Both methods yielded similar mean carbon dioxide fluxes during the night. In contrast, ozone fluxes deviated between both methods. This deviation was attributed to chemical in-situ loss of ozone during night time within the profile being integrated by the budget method.
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Kuduru - Musikmachen ohne Führerschein
(2009)
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Nadine Siegert
- Im diesem Artikel möchte ich einen ersten wissenschaftlichen Versuch unternehmen, die musikalische Kultur des Kuduru und seine Bedeutung sowohl in der angolanischen Hauptstadt als auch in der - vielfach als Vorort Luandas wahrgenommenen - zweiten Produktionsstätte Lissabon zu beleuchten. Kuduru als rein elektronische Musik ist derzeit tatsächlich als einzigartig für Afrika zu bewerten - abgesehen von einigen südafrikanischen Kwaito-Stücken gibt es keine nur mit Computertechnologie generierte Populärmusik. In den populären Jugendkulturen anderer afrikanischer Metropolen ist vielmehr lokaler Hip Hop und Reggae dominant. Die vielfach an zeitgenössische Musikentwicklungen herangetragene Kritik der Homogenisierung und Amerikanisierung durch globale Einflüsse lässt sich im Fall der Kuduru-Szene kaum bestätigen. Zwar handelt es sich hier um elektronische Musik, die sich musikalisch westlichen Musikkulturen annähert und mit diesen kreuzt, jedoch haben wir es nicht mit einer Rave-Kultur zu tun, wie sie in den urbanen Zentren Europas im Zusammenhang mit Techno- und Housemusik seit den späten 1980er Jahren entstanden ist. Im Kuduru geht es nicht um ´kollektive Tanzekstase, oder ´unreflektierte Spaß- und Partykultur, Elemente die als charakteristisch für die Rave-Kultur der 1990er Jahre gelten. Kuduru und seine Performance sind vielmehr individualistisch angelegt. Zwar findet, wie auch in anderen Bereichen elektronischer Musikkultur, eine Art Nivellierung der Hierarchiestrukturen statt, vor allem über den offenen Austausch von Daten und Informationen (sog. open-content) sowie eine starke Vernetzung über die so genannte ´virtuelle Kulturrealität, das Internet. Gleichzeitig gibt es Kuduru aber auch ganz manifest in der Kulturrealität vor Ort. Hier wird Starkult betrieben und Machtpositionen zwischen den besten Musikern, DJs und Tänzern werden ausgehandelt.
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Functional Nanostructures from well-defined Block Copolymers: Stimuli-responsive Membranes, Multicompartment Micelles, and Interpolyelectrolyte Complexes
(2009)
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Felix Schacher
- In dieser Arbeit werden die Synthese, die Charakterisierung und die Selbstaggregation von Blockco- und Terpolymeren sowohl des AB- als auch des ABC-Typs beschrieben. Lebende anionische Polymerisation wurde herangezogen, um wohldefinierte Materialien zu erhalten. Diese wurden anschließend verwendet um Nanostrukturen mit definierten Funktionalitäten herzustellen. In einem ersten Ansatz wurden fünf Serien von Polybutadien-block-poly(2-vinylpyridin)-block-poly(tert-butylmethacrylat) (BVT) Blockterpolymeren synthetisiert. Daraufhin wurden deren Eigenschaften in Dünnfilmen untersucht. Die Zielsetzung bestand darin, mikrophasenseparierte Strukturen herzustellen und diese als mögliche Vorstufen zur Herstellung schaltbarer Komposit-Membranen zu verwenden. Dazu wurden Dünnfilme (Dicke unter 100 nm) durch Aufschleudern auf eine Oberfläche (z.B. Silizium) aufgebracht und der Prozess der Selbstanordnung durch nachfolgendes Quellen und Tempern im kontrollierten Lösungsmitteldampf beschleunigt. Auf diese Weise gelangen intensive Untersuchungen an Modellsystemen. Außerdem wurde das morphologische Verhalten derartiger BVT-Terpolymere sorgfältig analysiert und mit den jeweiligen Volumenstrukturen verglichen. Mittels einer anderen Strategie, nämlich über den Nichtlösungsmittel induzierten Phasenseparationsprozess (NIPS), konnten intelligente Ultrafiltrationsmembranen hergestellt werden. Dazu wurden amphiphile Polystyrol-block-poly(N,N-dimethylaminoethylmethacrylat) (PS-b-PDMAEMA) Diblockcopolymere synthetisiert. Konzentrierte Lösungen dieser Materialien wurden mittels einer Rakel in definierten Filmdicken auf Glasplatten aufgetragen. Nach dem Ausfällen der Polymerfilme in einem Wasserbad wurden schaltbare asymmetrische Membranen erhalten. PS bildet die Matrix während PDMAEMA hauptsächlich die Porenwände bedeckt. Das Ansprechen dieser Systeme auf Änderungen des pH-Wertes oder der Umgebungstemperatur wurde auf die Eigenschaften des hydrophilen PDMAEMA Blocks zurückgeführt. Nach ersten Ergebnissen hinsichtlich der Poren dieser Membranen und ihrer Verwendung zur selektiven Filtration von Nanopartikeln unterschiedlicher Größe wurde der Einfluss verschiedener Parameter während der Filmherstellung auf Morphologie und Durchlässigkeit der Membranen untersucht. Neben PS-b-PDMAEMA wurden verschiedene andere Blockcopolymere mit PDMAEMA als zweitem Block hergestellt: PB-b-PDMAEMA, Poly(tert-Butoxystyrol)-block-PDMAEMA sowie Polyethylenoxid-block-PDMAEMA. Im letztgenannten Fall wurde eine neuartige Ein-Topf-Strategie angewandt. Dadurch wurde während der Reaktion direkt von einem Oxoanion-Kettenende auf ein Carbanion-Kettenende gewechselt. Die Kinetik aller DMAEMA-Polymerisationen zeigte, dass der Zusatz von Phosphazen-Base im Falle der Polymerisation von PEO-b-PDMAEMA zu einer deutlich langsameren Reaktionsgeschwindigkeit verglichen mit Polymerisationen in Gegenwart von Alkoxiden führt. Ein dritter Teil dieser Doktorarbeit befasste sich mit der Selbstanordnung von BVT Blockterpolymeren in Lösung. In Aceton, einem selektiven Lösungsmittel für PB, wurden sehr eng verteilte Mizellen mit einem uneinheitlichen Kern gebildet. Sie besaßen einen PB-Kern, eine uneinheitliche Schale aus P2VP sowie eine PtBMA-Corona. Der Mizellkern wurde mit verschiedenen Methoden vernetzt wodurch die Aggregate ohne Strukturveränderung in nicht-selektive Lösungsmittel wie z.B. Dioxan überführt werden konnten. Schließlich wurden an den zuvor gebildeten und charakterisierten Mizellen polymeranaloge Modifikationen durchgeführt. Der PtBMA-Block wurde zu Polymethacrylsäure (MAA) hydrolysiert. Gegebenenfalls wurde zuvor der P2VP-Block durch Quaternisierung mit Methyliodid in einen starken Polyelektrolyten verwandelt. Auf diese Weise wurden amphiphile Blockterpolymere mit entweder einem oder zwei pH-sensitiven Blöcken erhalten. Das Aggregationsverhalten dieser Systeme in Abhängigkeit von pH-Wert und Salzgehalt wurde anschließend untersucht. Mizellen mit einem weichen PB-Kern, einer P2VP-Schale und einer MAA-Corona wurden gebildet. Unter bestimmten Voraussetzungen werden intramizellare Interpolyelektrolytkomplexe (IPECs) gebildet. Daraus resultierten Multikompartiment-Mizellen mit einer uneinheitlichen Schale. Außerdem wurde die IPEC-Bildung dieser Syteme mit entgegengesetzt geladenen Poly(N-methyl-2-vinylpyridinium)-block-polyethylenoxid Diblockcopolymeren untersucht. Es konnte eine weitere Schale durch die elektrostatisch induzierte IPEC-Bildung zwischen PMAA und P2VPq geformt werden. PEO diente als stabilisierende Corona der neu gebildeten Strukturen. Die zeitliche Entwicklung solcher Aggregate wurde weiter untersucht und sternförmige Zwischenzustände konnten identifiziert werden. Abschließend wurde die Bildung von Gold-Nanopartikeln selektiv innerhalb der IPEC-Schale dieser Mizellen demonstriert.
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Experimental and theoretical examination of the chemical kinetics of a pollutant coating on porous particles
(2009)
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Radostin Gavrilov
- The persistence in the different compartments and in the atmospheric long-range transportation is important property of pesticides as representatives of the semivolatile substances. These compounds could be distributed dependent on the air pressure as well as the temperature - between gas and particle phase. In an aerosol smog chamber could be simulated the atmospheric degradation of airborne substances through hydroxyl radicals. The smog-chamber was cooled on 2 and -10°C and the degradation kinetic of semivolatile substance (Aldrin) coated on fine quartz particles (Aerosil 380) was researched. The coated Aerosil was mixed with water in ration 1:1000 and the suspension was sprayed into the chamber. Fine agglomerates were formed during the spaying with mean diameter approximately 1 µm. The precursors for the production of hydroxyl radicals were either reacting mixtures of hydrazine and ozone in absence of light source or photolysis of methylntrite. The concentration of hydroxyl radicals was varied over two powers of ten, from approximately 5•105 to 7•107 cm-3. The concentration of that OH–radicals was calculated over the degradation rate of hydrocarbons (n-octane, n-hexane, 2,2,3-trimthylbutane, 2,2-dimethylbutane and 2,2,3,3-tetramethylbutane). The hydrocarbons were cryofocussed in a glass-coated steel capillary at -110°C (using liquid nitrogen and a magnetic valve to control the flow) and analyzed gas chromatographically. Two products (Photoaldrin and Dieldrin) could be detected from the chemical reaction of Aldrin with hydroxyl radicals. A high concentration of the products were produced with additional experiments with coated Aerosil and glass balloons (d = 70 µm, unporous) and production of hydroxyl radicals from the methylnitrite photolysis in an irradiated rotating evaporator. The products were extracted from the carrier material and were identified with GC–MS. Photoaldrin was formed faster than Dieldrin and reacts also faster then Dieldrin. The temperature gradient between the top and the bottom of the smog-chamber was measured. The temperature difference is important for the air mixing of the chamber content. In the presence of a light-source (the fluorescence lamps are under the the smog camber) the temperature difference is 1.0 °C and ensures a fast mixing in the chamber. This difference of the not irradiated chamber is about 0.3 °C and causes a insufficient mixing, that is noticeable through strong fluctuations of the aerosol density. The structure of the aerosol agglomerates was imaged according to the ion etching method with FESEM (Field Emission Scanning Electron Microscopy) in the Fraunhofer-IKTS. The imagines were evaluated in this work with the program “Lince”. A maximum of the agglomerate diameter was obtained by 0,5 µm. The pore size distribution has a maximum by approximately 20 nm diameter. The life-time of Aldrin and respectively the rate constant of the reaction with hydroxyl radicals could be calculated directly from the experiments. The observed rate constant had a dependence on the OH–concentration in approaching form 3.5•10-5•[OH]-0.88 (the function yields a straight in double logarithmic scale). On the basis of the structure of the agglomerates, a mathematical model was applied from the literature in order to take the influence of the agglomerate structure into account. The observed concentration of Aldrin decreases because of the chemical reaction, the radial diffusion from the agglomerate center to the periphery and because of the evaporation of the substance from the agglomerate surface. It is considered also in the model that the concentration of the hydroxyl radicals alters with the penetration in the agglomerate. The penetration depth can not be determined experimentally. This value, as well as the life-time and the diffusion coefficient could be estimated from the experiments. If the experiment is made by low temperature, the evaporation could be neglect. The evaporated part of Aldrin decreases with the increasing OH concentration. The reciprocal life-time or the reaction rate of Aldrin increases linearly with the increase of the OH concentration. The rate constant of the reaction of Aldrin and OH radicals could be calculated from the reaction rate and the OH concentration. The OH rate constant was kOH = 6.2•10-11 ± 1.3•10-11 cm-3s-1. The effective diffusion coefficient was calculated by -10°C and yielded a value of Deff = 4.6•10-11 ± 2.2•10-11 cm2s-1.
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Motility and Force Generation Based on the Dynamics of Actin Gels
(2009)
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Stephan Schmidt
- This thesis explores the force generation of actin gels and their famous pro-pulsion mechanism leading to active motility on the cellular scale. In nature the generation of force and motility is regulated by actin binding proteins and the mesoscopic shape of the gel. Here we controlled an analyzed the effect of both, protein regulation and gel morphology by an in-vitro medium consisting of pu-rified proteins and biomimetic beads with a nucleating surface. Under the con-trolled conditions offered by the medium we analyzed the motion of actin pro-pelled colloids and the forces generated by the expanding actin gels using an AFM-based technique. Besides varying the in-vitro conditions and analyzing the effect on motility and force, we developed a new technique to measure intracellular forces in vivo. Hence, the work is structured in three parts: motility analysis, AFM force measurements (both in vitro) and force measurements in living cells.
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Evaluation of Modis Products Over Four European Ecological Study Sites
(2009)
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Quoc Dinh Nguyen
- Global vegetation is a key component of the climate system due to its key role in geosphere-biosphere-atmosphere interactions. Understanding these processes is of important for predicting future climate and the future state of terrestrial ecosystems. Land surface properties such as the land cover type and leaf area index (LAI) are used as essential inputs in many hydrological, ecological, and climate models. They are key parameters that describe the functioning of vegetation and are required for modeling vegetation productivity, land surface climatology, global carbon budgets and agricultural outputs as influenced by resource management. Successful modeling of these processes to quantitatively and accurately characterize global dynamics requires definition of these parameters periodically and globally with high accuracy. For this purpose the MODIS-based land surface products were designed and are now regularly available worldwide. Nevertheless, analyses based on MODIS inputs of land cover and LAI must be tested with respect to their reliability, in order that we can trust and use the outputs from simulation models quantifying water and carbon balances at large scale. The purpose of the research reported here is to determine the reliability of the MODIS spectral reflectance, land cover and LAI products for European landscapes which are highly fragmented and not necessarily homogeneous at the 1 km scale characteristic of MODIS products. A stepwise analysis has been carried out for reflectance, land cover and LAI products, comparing results from ground truth data and from high resolution remote sensing images (Landsat) to the coarser scale MODIS information. In this way, the influence of landscape fragmentation on the MODIS products should be clear and advice can be given about how they should be used in land surface modelling efforts. Four European locations were chosen for study; landscapes dominated by deciduous forest at Hesse, France; by coniferous forest at Tharandt, Germany, and by forest and grassland in mountainous terrain in the Berchtesgaden National Park, Germany and in Stubai Valley, Austria. All of these landscapes, however, have a mixture of land use. In order to compare measurements at intensive study plots with MODIS (1 km resolution), it was necessary to build a bridge via remote sensing data derived with Landsat TM (30 m resolution). It was demonstrated that for all study sites, the registration accuracy of Landsat TM images did not deviate by more than half of one pixel, and that the root mean square of error (RMSE) was less than 0.3 pixel when utilizing at least 40 ground control points and nearest-neighbor resampling technique. Comparing Landsat images with aerial photography clearly demonstrated that specific study sites on the ground could be identified and that the measured characteristics could be associated with Landsat pixel properties. The evaluation results showed that the MODIS reflectance product is reasonably accurate (less than 10 % absolute error). Certainly it is appropriate to utilize reflectance data from the two types of satellite images and to use these information in comparative examinations of land cover mapping and leaf area index estimation. The land cover comparison demonstrates that both the scale applied in classifications and the number and type of land use categories that are permitted lead to important shifts in the characterization of land cover when moving from 30 m to 1 km resolution of MODIS. Fragmentation in European landscapes is a fundamental problem encountered in the use of MODIS products. A true representation of the land surface cannot be obtained from the current MODIS land cover classifications at 1 km scale. The use of these descriptors in models describing land surface properties may potentially lead to large errors. Thus, exchange between the land surface and the atmosphere of water and CO2 as estimated by models using MODIS inputs will have a high level of uncertainty, and the results must be considered with caution. The problems in classification that are encountered lead to further difficulties in land surface characterization, since the retrieval of LAI uses land cover as an input variable. At the peak of vegetation development, MODIS LAI appears to strongly underestimate values of the Landsat based maps. During winter, the comparison is even worse, but is not consistent from grassland to deciduous forest and coniferous forest. The results cast doubt on the usefulness of MODIS LAI products as input to continental scale simulation models for carbon and water balances, at least in Europe where land cover is highly modified and fragmented due to centuries of human use and management. Use of the MODIS products in Europe requires that new techniques be considered to search for compatibility in averaging and aggregating information on land cover and reflectance that is used to estimate LAI for large areas. Keywords: Remote sensing; vegetation; MODIS; Landsat; LAI; Land cover classification; reflectance; evaluation.
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Market Acceptance of Cloud Computing - An Empirical Analysis of Market Structure, Price Models and Service Requirements
(2009)
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Lei Han
- As an emerging technology and business paradigm, Cloud Computing embeds fairly large amount of unexplored fields, from technological definition to business models. While the market of Cloud Computing is expected to expand in the near future, few studies of the actual market acceptance of the Cloud Computing services are done. It may be interesting, especially for the Cloud Computing service providers, to know more about the preferences of transaction forms and price models from the users and potential users. From an academic research’s point of view, we want to know whether the development of Cloud Computing market can be explained or even predicted by certain theoretical frameworks.
