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  • Open Access German
    Authors: 
    Vogeler, Georg;
    Publisher: BoD
    Country: Germany

    Starting from the observation that the existing models of digital scholarly editions can be expressed in many technologies, this paper goes beyond the simple opposition of ‘XML’ and ‘graph’, It studies the implicit context of the technologies as applied to digital scholarly editions: embedded mark-up in XML/TEI trees, graph representa- tions in RDF, and stand-off annotation as realised in annotation tools widely used for information extraction. It describes the affordances of the encoding methods offered. It takes as a test case the “assertive edition” (Vogeler 2019), in which the text is considered in a double role: as palaeographical and linguistic phenomenon, and as a representation of information. It comes to the conclusion that the affordances of XML help to detect sequential and hierarchical properties of a text, while those of RDF best cover the representation of knowledge as semantic networks of statements. The relationship between them can be expressed by the metaphor of ‘layers’, for which stand-off annotation technologies seem to be best fitted. However, there is no standardised technical formalism to create stand-off annotations beyond graphical tools sharing interface elements. The contribution concludes with the call for the acceptance of the advantages of each technology, and for efforts to be made to discuss the best way to combine these technologies.

  • Open Access English
    Authors: 
    Salverda, Tijo; Hollington, Andrea; Kloß, Sinah; Schneider, Nina; Tappe, Oliver;
    Publisher: Global South Studies Center Cologne
    Country: Germany
  • Open Access German
    Authors: 
    Häp, Nicole;
    Country: Germany

    Das Ziel der vorliegenden Arbeit war die Verifizierung der Hypothese, dass die Hybridbrücken, die von Poly(carbasulfanen) als Vernetzer im Vulkanisationsprozess gebildet werden, für die erhöhte Reversionsstabilität der Vulkanisate verantwortlich sind. Dies wurde erreicht anhand der quantitativen und qualitativen Auswertung zeitabhängiger Modellvulkanisate von DMB als Modellolefin mit verschiedenen Vernetzern: Cyclooctaschwefel, dem bereits bekannten Poly(tetrathio-1,2-ethandiyl) [(CH2)2-S4]p und einem neuen Poly(carbasulfan) [varioC4-Sx-varioC4-Sy]p als Vernetzer. Die quantitative Erfassung der Vulkanisationsprodukte erfolgte durch RP-HPLC und 1H-NMR-Spektroskopie. Durch Anwendung quantitativer 13C{1H}-NMR-Spektroskopie (1,4-Dichlorbenzol wurde als interner Standard verwendet) wurden für die bei der Modellvulkanisation entstehenden Bis(2,3-dimethyl-2-buten-1-yl)sulfane (dmb-Sx-dmb) die Eichfaktoren ihrer RP-HPLC-Methode bestimmt. Die chemische Verschiebung besonders des g-Kohlenstoffatoms hängt von der Schwefelkettenlänge ab. Diese spezielle Eigenschaft erlaubte es, die Konzentrationen der einzelnen in einem Gemisch vorliegenden Sulfane mit Kettenlängen von x = 2 bis x = 14 zu bestimmen. [varioC4-Sx-varioC4-Sy]p wurde in zwei Schritten zunächst aus 1,3-Butadien und Rohsulfan H2Sx, dann im Autoklaven durch Umsetzung des Primärproduktes mit Schwefel und Schwefelwasserstoff synthetisiert. Neben der Bildung von 10 % Cyclooctaschwefel zeigte die Charakterisierung ein Polymer aus 1,2-, 1,3- und 2,3﷓Alkandiyleinheiten mit verbrückenden Schwefelketten unterschiedlicher Länge. Die im Modellvulkanisat mit dem oben genannten Vernetzer erhaltenen Produkte wurden mittels GPC- und semi-präparativen RP-HPLC separiert. Neben schwefelverbrückten und beschleunigerhaltigen Komponenten wurden 20 neue Moleküle, die Hybridbrücken enthalten, identifiziert und NMR-spektroskopisch charakterisiert. Mehr als die Hälfte der Vulkanisationsprodukte bestehen aus hybridvernetzten Verbindungen, was gut mit den Modellvulkanisaten mit [(CH2)2-S4]p als Vernetzer vergleichbar ist. Beide Poly(carbasulfane) zeichneten sich im Rheometertest durch erhöhte Reversionsstabilität aus, was sich in den Ergebnissen der zeitabhängiger Modellvulkanisationen widerspiegelt. Die Vulkanisationsgeschwindigkeiten waren leicht langsamer als die der Schwefelvulkanisate, da die Polymere erst abgebaut werden müssen. Die Schwefelkettenlänge bei den Hybrid- wie auch bei den Schwefelbrücken war bereits zu Beginn der Vulkanisation im Vergleich zu denen reiner Schwefelvulkanisate deutlich kürzer, so dass ein stabiles Netzwerk entstand und Reversionsprozesse kaum zu beobachten waren. Da die Hybridbrücke jedoch wenigstens zwei Schwefelsegmente besitzt, bleibt ihre Flexibilität auch mit wenigen Schwefelatomen erhalten und gewährleistet somit neben Reversionsstabilität gute dynamische Eigenschaften der Vulkanisate.

  • Publication . Other literature type . Part of book or chapter of book . 1995
    Open Access
    Authors: 
    Frank Damm; F.-P. Heider; G. Wambach;
    Publisher: Springer Berlin Heidelberg
    Country: Germany

    This paper describes the development and implementation of the MPQS factoring algorithm using multiple hypercubes customised to a MIMD parallel computer. The computationally most expensive steps ran on a Parsytec machine consisting of 1024 Inmos T805 microprocessors. General 100 decimal digit numbers can be factored in 1-2 days.

  • Open Access German
    Authors: 
    Sewerin, Sebastian;
    Country: Germany

    Although the comparative study of environmental politics and policy dates back well into the 1970s, it has never featured prominently within comparative politics generally. Against a background of mounting environmental pressures, most notably climate change, this low profile seems puzzling. As Steinberg and VanDeveer (2012) point out, building bridges between comparative environmental politics and the broader field of comparative politics is an important task for current research. This dissertation seeks to contribute to this linkage by revisiting the issue of cross-national environmental performance, focusing on climate performance. By addressing both the outcome and the output dimension of national climate performance, this thesis engages with two central issues of comparative politics: (i) the effect of political institutions on performance and (ii) policy change. Thus, it also contributes to broader research into the capacity of political systems to deal with complex longterm political problems. This dissertation attempts to make six major conceptual, methodological, and analytical contributions: 1) the thesis presents a conceptualization of general environmental performance based on the “planetary boundaries” approach; 2) it provides a theoretical framework for policy output and develops a measurement for its assessment; 3) it argues that actor constellations of specific environmental problems need to be considered to strengthen theoretical arguments about the effects of political institutions; 4) it argues that entire policy portfolios rather than (a set of) individual policy instruments need to be considered for assessing policy change; 5) it analyses the effect of political institutions on climate performance; 6) and it analyses policy change in climate mitigation and the role of policy innovations in altering policy portfolios.

  • Open Access English
    Authors: 
    Valdau, Yury;
    Country: Germany

    Total cross section of the pp->K+nSigam+ reaction, recently published by the COSY11 collaboration, exhibit surprisingly high value violating isospin considerations, and, together with other data, indicates a threshold anomaly. Dedicated measurements of the Sigma+ production cross section have been performed at the ANKE magnetic spectrometer, employing a previously developed method of the cross section determination, based on the analysis of three simultaneously measured spectra. The total cross section measured with ANKE at five energies close to threshold of the reaction, are two orders of magnitude smaller than reported by COSY11 and do not contradict isospin relations. The analysis procedure as well as extracted total cross sections for the Lambda, Sigma0 and Sigma+ hyperons are presented in the thesis.

  • Open Access German
    Authors: 
    Seidel, Marc;
    Country: Germany

    A new 3D time domain CSEM forward modeling code TDcustEM built upon the recently published open-source frequency domain code custEM and the open-source finite element toolbox FEniCS is presented. The transformation of the frequency domain data provided by custEM is performed by a Fast Hankel Transform using 80 digital filter coefficients. 3D edge-based tetrahedral meshes generated by TetGen facilitate the calculation of syn- thetic data using topography, arbitrary source geometries and complex subsurface structures. To ensure precision and reliability of the new algorithm, calculated results of different CSEM setups and electromagnetic field components are cross-validated against analytic solutions as well as 1D and 3D time domain modeling codes. Certain modeling studies are conducted regarding possible interpolation and extrapola- tion techniques to reduce the number of necessary frequencies and therefore the compu- tational runtime, which is still an issue of convolutional time domain CSEM approaches. Additional modeling studies showed the importance of precise receiver positioning for measuring the horizontal components of the time derivative of the magnetic field. As the present thesis is embedded in the Collaborative Research Centre 806 – Our Way to Europe, three sedimentary deposits in the East African Rift Valley were subject to mul- tidimensional TEM surveys in the framework of this project. Common 1D (EMUPLUS) as well as laterally and spatially constrained (AarhusInv) in- version techniques were applied to the TEM field data. Sediment thicknesses as well as stratigraphic sequences of the investigated sedimentary basins were derived. An extensive 3D modeling study of one of the target areas representing a volcanically-formed basin including topography was performed using the newly developed TDcustEM code.

  • Open Access English
    Authors: 
    Sieger, Dirk;
    Country: Germany

    Somitogenesis is the key developmental process, which divides the vertebrate body axis into segmentally repeated structures. These structures are called somites. Somites derive from the unsegmented presomitic mesoderm (PSM) that flanks the notochord to both sides. A prepatterning process, taking place in the PSM, is necessary to allow the exact spatial and temporal formation of the somites. The prepatterning is achieved by a clock and wavefront mechanism. The clock consists of the Delta-Notch (D-N) pathway, building up a genetic circuit with several cyclically expressed h/E(spl)/hey-related genes while the wave front is created by a FGF gradient, showing its highest expression in the posterior PSM. Disturbance of the clock or the mediator of the wavefront (her13.2) results in a disruption of cyclic gene expression and posterior somite border formation, while anterior somites are still formed. On the level of Delta-Notch signalling it is not clear if the escaped anterior somites are formed due to redundancy, since there are at least four notch and four delta homologues in zebrafish. Furthermore it is not known if Notch signalling is transmitted via the canonical way through Su(H) during somitogenesis or if an alternative way is used. Since there appears to be only one complete Su(H) homologue in zebrafish, the function of this gene was analyzed using morpholino oligonucleotides. The knockdown of Su(H) leads to a clear disruption of cyclic gene expression, comparable to effects in previously described D-N mutants. Beyond this, posterior somite defects were detected while anterior somites were still formed, implying that their formation is not due to redundancy between different delta or notch genes. Performing the Su(H) knockdown in the fss/tbx24 mutant it could be shown that D-N signalling is necessary for the creation and synchronization of cyclic gene expression. These results clearly suggest that the canonical way of Notch signalling is used during somitogenesis. To further specify the prepatterning process two newly identified her genes, her11 and her12, were analyzed during somitogenesis. It turned out that both genes are dynamically expressed in the PSM and are differentially regulated by D-N signalling. Functional studies suggest that her11 interacts with her1 and her7 and is involved in the fine tuning of cyclic gene expression while her12 seems to be involved in somite border formation and cyclic gene expression. It was recently shown that the D-N driven Her1 protein and the FGF activated Her13.2 protein form heterodimers in vitro. To proof a combinatorial function also in vivo, both genes were knocked down individually and in combination. The combined knockdown leads to distinct additional effects, namely the break down of cyclic gene expression right from the start and a disruption of anterior somite formation. This suggests clearly a combinatorial role for both genes in vivo during early somitogenesis.

  • Open Access English
    Authors: 
    Hilgers, Alexandra;
    Country: Germany

    The study is concerned with the reconstruction of dune formation and reactivation by means of optically stimulated luminescence (OSL) dating of dunes developed throughout the last 20,000 years in the central part of the so-called "European Sand Belt" (ESB) in northeast Germany and adjacent areas in Poland. In order to create a data set with regional validity dune sites in five different study areas are investigated which are located in the Elbe-, the Glogow-Baruth-, and in the Torun-Eberswalde-ice marginal valleys and in the glacio-lacustrine basins of the "Ueckermuender Heide" and "Altdarss" area. In total 183 sediment samples from aeolian, fluvial, glacio-fluvial and glacio-lacustrine deposits were sampled at twenty different sites. Fundamental questions were, if several phases of aeolian activity and periods of stabilisation and soil development could be defined and if similarities or differences regarding their intensity, beginning and ending exist on a regional scale. The summary of OSL ages allows conclusions regarding climate driven phases of aeolian activity during the Late Glacial and Late Holocene man made dune remobilisation in accordance with the settlement history. The study demonstrates that by application of a consistent methodical approach to a large data set, OSL dating has the potential to resolve the dune record of the last 20,000 years in northeastern Germany into individual phases of dune sand deposition. The conclusions drawn from this study provide new information for both, the application of OSL dating and the interpretation of the aeolian record of the study area.

  • Open Access German
    Authors: 
    Schmitz, Jessica;
    Country: Germany

    Der Einfluss von Kohlenhydratstoffwechsel und Akklimatisierungsprozessen an Hochlicht-Bedingungen wurde anhand von A. thaliana Doppelmutanten mit Defekten im Tages- und Nachtexport von Photoassimilaten untersucht. Hierzu wurde eine kürzlich identifizierte Mutante mit vollständigem Funktionsverlust des Triosephosphat/Phosphat Translokators (TPT; tpt-2) sowohl in den Hintergrund von (1) Mutanten mit einer deutlich beeinträchtigten Stärkebiosynthese in Blättern (AGPase, adg1-1; plastidäre Phosphoglukomutase, pgm1; Phosphoglukoseisomerase, pgi1-1) als auch in (2) Mutanten mit Defekten im Stärkeabbau (Glukan Wasser Dikinase, sex1-3) bzw. im Export von Stärkeabbauprodukten (Maltoseexporter, mex1-2) eingekreuzt. Die erstaunlicherweise überlebensfähigen Doppelmutanten zeigten eine starke Wachstumsretardierung und mit Ausnahme der sex1-3/tpt-2 Doppelmutante einen Photosynthesephänotyp. Dieser war charakterisiert durch eine verminderte Photosyntheseeffizienz und eine stark erhöhte Grundfluoreszenz. Daher wurden diese Doppelmutanten auch als „Hoch-Chlorophyll-Fluoreszenz“ (HCF) Mutanten definiert. Es wurde festgestellt, dass der HCF Phänotyp nur unter Hochlichtbedingungen ausgebildet wurde, während die Doppelmutanten unter Schwachlichtbedingungen phänotypisch vom Wildtyp nicht zu unterscheiden waren. In der adg1-1/tpt-2 Doppelmutante führte eine Anzucht im Hochlicht zu einer dramatischen Veränderung der Gehalte von Photosynthese assoziierten Proteinen. Die plastomkodierten zentralen Untereinheiten von beiden Photosystemen waren stark verringert, während die kernkodierten Lichtsammelkomplexe weder auf transkriptioneller noch auf Proteinebene eine Veränderung zeigten. Die Ursache der stark erhöhten Grundfluoreszenz konnte auf eine Ablösung der Lichtsammelkomplexe von den Photosynthesezentren zurückgeführt werden. Die erhöhte Fluoreszenz der ungebundenen Lichtsammelkomplexe wurde im Licht durch den Prozess der „Hoch Energie“ Löschung in Form von Wärme abgestrahlt. Dieser Prozess kann als protektiver Mechanismus interpretiert werden und wurde in dieser Form bisher noch nicht beschrieben. Es wird postuliert, dass die beobachteten Veränderungen im Zusammenhang mit einer fehlerhaften Hochlicht-Akklimatisierung aufgrund einer veränderten retrograden Signalgebung stehen. Aus der Analyse von genomweiter Expressionsdaten konnte abgeleitet werden, dass Veränderungen der Lichtintensität dennoch perzipiert werden und zu einer Modulation der chloroplastidären Genexpression führen. Fütterung mit exogener Saccharose führte zu einer Revertierung des HCF- sowie des Wachstumsphänotyps im Hochlicht. Daher wird die Rolle Zucker-abhängiger Signalwege bei der Hochlicht-Akklimatisierung diskutiert und ein Modell postuliert, wie es zu einer regulatorischen Funktion des Kohlenhydratstoffwechsels kommen kann.

Advanced search in
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arrow_drop_down
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Include:
7,009 Research products, page 1 of 701
  • Open Access German
    Authors: 
    Vogeler, Georg;
    Publisher: BoD
    Country: Germany

    Starting from the observation that the existing models of digital scholarly editions can be expressed in many technologies, this paper goes beyond the simple opposition of ‘XML’ and ‘graph’, It studies the implicit context of the technologies as applied to digital scholarly editions: embedded mark-up in XML/TEI trees, graph representa- tions in RDF, and stand-off annotation as realised in annotation tools widely used for information extraction. It describes the affordances of the encoding methods offered. It takes as a test case the “assertive edition” (Vogeler 2019), in which the text is considered in a double role: as palaeographical and linguistic phenomenon, and as a representation of information. It comes to the conclusion that the affordances of XML help to detect sequential and hierarchical properties of a text, while those of RDF best cover the representation of knowledge as semantic networks of statements. The relationship between them can be expressed by the metaphor of ‘layers’, for which stand-off annotation technologies seem to be best fitted. However, there is no standardised technical formalism to create stand-off annotations beyond graphical tools sharing interface elements. The contribution concludes with the call for the acceptance of the advantages of each technology, and for efforts to be made to discuss the best way to combine these technologies.

  • Open Access English
    Authors: 
    Salverda, Tijo; Hollington, Andrea; Kloß, Sinah; Schneider, Nina; Tappe, Oliver;
    Publisher: Global South Studies Center Cologne
    Country: Germany
  • Open Access German
    Authors: 
    Häp, Nicole;
    Country: Germany

    Das Ziel der vorliegenden Arbeit war die Verifizierung der Hypothese, dass die Hybridbrücken, die von Poly(carbasulfanen) als Vernetzer im Vulkanisationsprozess gebildet werden, für die erhöhte Reversionsstabilität der Vulkanisate verantwortlich sind. Dies wurde erreicht anhand der quantitativen und qualitativen Auswertung zeitabhängiger Modellvulkanisate von DMB als Modellolefin mit verschiedenen Vernetzern: Cyclooctaschwefel, dem bereits bekannten Poly(tetrathio-1,2-ethandiyl) [(CH2)2-S4]p und einem neuen Poly(carbasulfan) [varioC4-Sx-varioC4-Sy]p als Vernetzer. Die quantitative Erfassung der Vulkanisationsprodukte erfolgte durch RP-HPLC und 1H-NMR-Spektroskopie. Durch Anwendung quantitativer 13C{1H}-NMR-Spektroskopie (1,4-Dichlorbenzol wurde als interner Standard verwendet) wurden für die bei der Modellvulkanisation entstehenden Bis(2,3-dimethyl-2-buten-1-yl)sulfane (dmb-Sx-dmb) die Eichfaktoren ihrer RP-HPLC-Methode bestimmt. Die chemische Verschiebung besonders des g-Kohlenstoffatoms hängt von der Schwefelkettenlänge ab. Diese spezielle Eigenschaft erlaubte es, die Konzentrationen der einzelnen in einem Gemisch vorliegenden Sulfane mit Kettenlängen von x = 2 bis x = 14 zu bestimmen. [varioC4-Sx-varioC4-Sy]p wurde in zwei Schritten zunächst aus 1,3-Butadien und Rohsulfan H2Sx, dann im Autoklaven durch Umsetzung des Primärproduktes mit Schwefel und Schwefelwasserstoff synthetisiert. Neben der Bildung von 10 % Cyclooctaschwefel zeigte die Charakterisierung ein Polymer aus 1,2-, 1,3- und 2,3﷓Alkandiyleinheiten mit verbrückenden Schwefelketten unterschiedlicher Länge. Die im Modellvulkanisat mit dem oben genannten Vernetzer erhaltenen Produkte wurden mittels GPC- und semi-präparativen RP-HPLC separiert. Neben schwefelverbrückten und beschleunigerhaltigen Komponenten wurden 20 neue Moleküle, die Hybridbrücken enthalten, identifiziert und NMR-spektroskopisch charakterisiert. Mehr als die Hälfte der Vulkanisationsprodukte bestehen aus hybridvernetzten Verbindungen, was gut mit den Modellvulkanisaten mit [(CH2)2-S4]p als Vernetzer vergleichbar ist. Beide Poly(carbasulfane) zeichneten sich im Rheometertest durch erhöhte Reversionsstabilität aus, was sich in den Ergebnissen der zeitabhängiger Modellvulkanisationen widerspiegelt. Die Vulkanisationsgeschwindigkeiten waren leicht langsamer als die der Schwefelvulkanisate, da die Polymere erst abgebaut werden müssen. Die Schwefelkettenlänge bei den Hybrid- wie auch bei den Schwefelbrücken war bereits zu Beginn der Vulkanisation im Vergleich zu denen reiner Schwefelvulkanisate deutlich kürzer, so dass ein stabiles Netzwerk entstand und Reversionsprozesse kaum zu beobachten waren. Da die Hybridbrücke jedoch wenigstens zwei Schwefelsegmente besitzt, bleibt ihre Flexibilität auch mit wenigen Schwefelatomen erhalten und gewährleistet somit neben Reversionsstabilität gute dynamische Eigenschaften der Vulkanisate.

  • Publication . Other literature type . Part of book or chapter of book . 1995
    Open Access
    Authors: 
    Frank Damm; F.-P. Heider; G. Wambach;
    Publisher: Springer Berlin Heidelberg
    Country: Germany

    This paper describes the development and implementation of the MPQS factoring algorithm using multiple hypercubes customised to a MIMD parallel computer. The computationally most expensive steps ran on a Parsytec machine consisting of 1024 Inmos T805 microprocessors. General 100 decimal digit numbers can be factored in 1-2 days.

  • Open Access German
    Authors: 
    Sewerin, Sebastian;
    Country: Germany

    Although the comparative study of environmental politics and policy dates back well into the 1970s, it has never featured prominently within comparative politics generally. Against a background of mounting environmental pressures, most notably climate change, this low profile seems puzzling. As Steinberg and VanDeveer (2012) point out, building bridges between comparative environmental politics and the broader field of comparative politics is an important task for current research. This dissertation seeks to contribute to this linkage by revisiting the issue of cross-national environmental performance, focusing on climate performance. By addressing both the outcome and the output dimension of national climate performance, this thesis engages with two central issues of comparative politics: (i) the effect of political institutions on performance and (ii) policy change. Thus, it also contributes to broader research into the capacity of political systems to deal with complex longterm political problems. This dissertation attempts to make six major conceptual, methodological, and analytical contributions: 1) the thesis presents a conceptualization of general environmental performance based on the “planetary boundaries” approach; 2) it provides a theoretical framework for policy output and develops a measurement for its assessment; 3) it argues that actor constellations of specific environmental problems need to be considered to strengthen theoretical arguments about the effects of political institutions; 4) it argues that entire policy portfolios rather than (a set of) individual policy instruments need to be considered for assessing policy change; 5) it analyses the effect of political institutions on climate performance; 6) and it analyses policy change in climate mitigation and the role of policy innovations in altering policy portfolios.

  • Open Access English
    Authors: 
    Valdau, Yury;
    Country: Germany

    Total cross section of the pp->K+nSigam+ reaction, recently published by the COSY11 collaboration, exhibit surprisingly high value violating isospin considerations, and, together with other data, indicates a threshold anomaly. Dedicated measurements of the Sigma+ production cross section have been performed at the ANKE magnetic spectrometer, employing a previously developed method of the cross section determination, based on the analysis of three simultaneously measured spectra. The total cross section measured with ANKE at five energies close to threshold of the reaction, are two orders of magnitude smaller than reported by COSY11 and do not contradict isospin relations. The analysis procedure as well as extracted total cross sections for the Lambda, Sigma0 and Sigma+ hyperons are presented in the thesis.

  • Open Access German
    Authors: 
    Seidel, Marc;
    Country: Germany

    A new 3D time domain CSEM forward modeling code TDcustEM built upon the recently published open-source frequency domain code custEM and the open-source finite element toolbox FEniCS is presented. The transformation of the frequency domain data provided by custEM is performed by a Fast Hankel Transform using 80 digital filter coefficients. 3D edge-based tetrahedral meshes generated by TetGen facilitate the calculation of syn- thetic data using topography, arbitrary source geometries and complex subsurface structures. To ensure precision and reliability of the new algorithm, calculated results of different CSEM setups and electromagnetic field components are cross-validated against analytic solutions as well as 1D and 3D time domain modeling codes. Certain modeling studies are conducted regarding possible interpolation and extrapola- tion techniques to reduce the number of necessary frequencies and therefore the compu- tational runtime, which is still an issue of convolutional time domain CSEM approaches. Additional modeling studies showed the importance of precise receiver positioning for measuring the horizontal components of the time derivative of the magnetic field. As the present thesis is embedded in the Collaborative Research Centre 806 – Our Way to Europe, three sedimentary deposits in the East African Rift Valley were subject to mul- tidimensional TEM surveys in the framework of this project. Common 1D (EMUPLUS) as well as laterally and spatially constrained (AarhusInv) in- version techniques were applied to the TEM field data. Sediment thicknesses as well as stratigraphic sequences of the investigated sedimentary basins were derived. An extensive 3D modeling study of one of the target areas representing a volcanically-formed basin including topography was performed using the newly developed TDcustEM code.

  • Open Access English
    Authors: 
    Sieger, Dirk;
    Country: Germany

    Somitogenesis is the key developmental process, which divides the vertebrate body axis into segmentally repeated structures. These structures are called somites. Somites derive from the unsegmented presomitic mesoderm (PSM) that flanks the notochord to both sides. A prepatterning process, taking place in the PSM, is necessary to allow the exact spatial and temporal formation of the somites. The prepatterning is achieved by a clock and wavefront mechanism. The clock consists of the Delta-Notch (D-N) pathway, building up a genetic circuit with several cyclically expressed h/E(spl)/hey-related genes while the wave front is created by a FGF gradient, showing its highest expression in the posterior PSM. Disturbance of the clock or the mediator of the wavefront (her13.2) results in a disruption of cyclic gene expression and posterior somite border formation, while anterior somites are still formed. On the level of Delta-Notch signalling it is not clear if the escaped anterior somites are formed due to redundancy, since there are at least four notch and four delta homologues in zebrafish. Furthermore it is not known if Notch signalling is transmitted via the canonical way through Su(H) during somitogenesis or if an alternative way is used. Since there appears to be only one complete Su(H) homologue in zebrafish, the function of this gene was analyzed using morpholino oligonucleotides. The knockdown of Su(H) leads to a clear disruption of cyclic gene expression, comparable to effects in previously described D-N mutants. Beyond this, posterior somite defects were detected while anterior somites were still formed, implying that their formation is not due to redundancy between different delta or notch genes. Performing the Su(H) knockdown in the fss/tbx24 mutant it could be shown that D-N signalling is necessary for the creation and synchronization of cyclic gene expression. These results clearly suggest that the canonical way of Notch signalling is used during somitogenesis. To further specify the prepatterning process two newly identified her genes, her11 and her12, were analyzed during somitogenesis. It turned out that both genes are dynamically expressed in the PSM and are differentially regulated by D-N signalling. Functional studies suggest that her11 interacts with her1 and her7 and is involved in the fine tuning of cyclic gene expression while her12 seems to be involved in somite border formation and cyclic gene expression. It was recently shown that the D-N driven Her1 protein and the FGF activated Her13.2 protein form heterodimers in vitro. To proof a combinatorial function also in vivo, both genes were knocked down individually and in combination. The combined knockdown leads to distinct additional effects, namely the break down of cyclic gene expression right from the start and a disruption of anterior somite formation. This suggests clearly a combinatorial role for both genes in vivo during early somitogenesis.

  • Open Access English
    Authors: 
    Hilgers, Alexandra;
    Country: Germany

    The study is concerned with the reconstruction of dune formation and reactivation by means of optically stimulated luminescence (OSL) dating of dunes developed throughout the last 20,000 years in the central part of the so-called "European Sand Belt" (ESB) in northeast Germany and adjacent areas in Poland. In order to create a data set with regional validity dune sites in five different study areas are investigated which are located in the Elbe-, the Glogow-Baruth-, and in the Torun-Eberswalde-ice marginal valleys and in the glacio-lacustrine basins of the "Ueckermuender Heide" and "Altdarss" area. In total 183 sediment samples from aeolian, fluvial, glacio-fluvial and glacio-lacustrine deposits were sampled at twenty different sites. Fundamental questions were, if several phases of aeolian activity and periods of stabilisation and soil development could be defined and if similarities or differences regarding their intensity, beginning and ending exist on a regional scale. The summary of OSL ages allows conclusions regarding climate driven phases of aeolian activity during the Late Glacial and Late Holocene man made dune remobilisation in accordance with the settlement history. The study demonstrates that by application of a consistent methodical approach to a large data set, OSL dating has the potential to resolve the dune record of the last 20,000 years in northeastern Germany into individual phases of dune sand deposition. The conclusions drawn from this study provide new information for both, the application of OSL dating and the interpretation of the aeolian record of the study area.

  • Open Access German
    Authors: 
    Schmitz, Jessica;
    Country: Germany

    Der Einfluss von Kohlenhydratstoffwechsel und Akklimatisierungsprozessen an Hochlicht-Bedingungen wurde anhand von A. thaliana Doppelmutanten mit Defekten im Tages- und Nachtexport von Photoassimilaten untersucht. Hierzu wurde eine kürzlich identifizierte Mutante mit vollständigem Funktionsverlust des Triosephosphat/Phosphat Translokators (TPT; tpt-2) sowohl in den Hintergrund von (1) Mutanten mit einer deutlich beeinträchtigten Stärkebiosynthese in Blättern (AGPase, adg1-1; plastidäre Phosphoglukomutase, pgm1; Phosphoglukoseisomerase, pgi1-1) als auch in (2) Mutanten mit Defekten im Stärkeabbau (Glukan Wasser Dikinase, sex1-3) bzw. im Export von Stärkeabbauprodukten (Maltoseexporter, mex1-2) eingekreuzt. Die erstaunlicherweise überlebensfähigen Doppelmutanten zeigten eine starke Wachstumsretardierung und mit Ausnahme der sex1-3/tpt-2 Doppelmutante einen Photosynthesephänotyp. Dieser war charakterisiert durch eine verminderte Photosyntheseeffizienz und eine stark erhöhte Grundfluoreszenz. Daher wurden diese Doppelmutanten auch als „Hoch-Chlorophyll-Fluoreszenz“ (HCF) Mutanten definiert. Es wurde festgestellt, dass der HCF Phänotyp nur unter Hochlichtbedingungen ausgebildet wurde, während die Doppelmutanten unter Schwachlichtbedingungen phänotypisch vom Wildtyp nicht zu unterscheiden waren. In der adg1-1/tpt-2 Doppelmutante führte eine Anzucht im Hochlicht zu einer dramatischen Veränderung der Gehalte von Photosynthese assoziierten Proteinen. Die plastomkodierten zentralen Untereinheiten von beiden Photosystemen waren stark verringert, während die kernkodierten Lichtsammelkomplexe weder auf transkriptioneller noch auf Proteinebene eine Veränderung zeigten. Die Ursache der stark erhöhten Grundfluoreszenz konnte auf eine Ablösung der Lichtsammelkomplexe von den Photosynthesezentren zurückgeführt werden. Die erhöhte Fluoreszenz der ungebundenen Lichtsammelkomplexe wurde im Licht durch den Prozess der „Hoch Energie“ Löschung in Form von Wärme abgestrahlt. Dieser Prozess kann als protektiver Mechanismus interpretiert werden und wurde in dieser Form bisher noch nicht beschrieben. Es wird postuliert, dass die beobachteten Veränderungen im Zusammenhang mit einer fehlerhaften Hochlicht-Akklimatisierung aufgrund einer veränderten retrograden Signalgebung stehen. Aus der Analyse von genomweiter Expressionsdaten konnte abgeleitet werden, dass Veränderungen der Lichtintensität dennoch perzipiert werden und zu einer Modulation der chloroplastidären Genexpression führen. Fütterung mit exogener Saccharose führte zu einer Revertierung des HCF- sowie des Wachstumsphänotyps im Hochlicht. Daher wird die Rolle Zucker-abhängiger Signalwege bei der Hochlicht-Akklimatisierung diskutiert und ein Modell postuliert, wie es zu einer regulatorischen Funktion des Kohlenhydratstoffwechsels kommen kann.

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