Hochschulbibliographie Universität Bremen (hsb)

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Late Quaternary Development of a deep-water Carbonate Mound in the northeast Atlantic
(2003-09-25)
Dorschel, Boris
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Peckmann, Jörn
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Hebbeln, Dierk
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Hebbeln, Dierk
Numerous carbonate mounds have been discovered along the NW European Continental Margin. Many of them are covered by thickets of the ahermatypic corals. To unravel the processes active on the mound, in a case study on Propeller Mound its carbonate budget has been assessed and the mound development has been modelled. In addition benthic foraminiera assemblages have been analysed. Propeller Mound is a ~150m elevated mound in the Porcupine Seabight ca. 90 nautical miles west off South-Ireland. The carbonate budget shows that on Propeller Mound the sediments contain on average >50 wt.-% CaCO3 for the last 175kyrs. In contrast, the sediments from the reference sites off Propeller Mound contain <37 wt.-% CaCO3 for Holocene and <23 wt.-% CaCO3 for glacial sediments. The approximately 30 wt.-% difference between on- and off-mound locations represents the carbonate input due to aragonite added by the corals but extended hiatuses reduce the net long-term CaCO3 accumulation rates on Propeller Mound to ~5% of the off-mound signal. Stable oxygen isotope data, AMS 14C and U/Th ages show that glacial and interglacial sediments were either not deposited or were later eroded on the mound. Instead, almost exclusively interstadial sequences stabilised by loose coral frameworks have been preserved. These sedimentary patterns may be linked to the changing influence of Mediterranean Outflow Water at the mound location. Distinct similarities between benthic foraminiferal assemblages found on-mound with assemblages found in the Mediterranean Sea also point towards a link between MOW and the mound. This interactions result in a spatially and temporally complex sedimentary record on Propeller Mound, impossible to correlate.In contrast to on mound sediments, those deposited in the areas adjacent to Propeller Mound contain more or less continuous records. The discrepancy between on and off-mound sediments imply that at least for the last ~300kyrs Propeller Mound has been shrinking.
Dissertation
599 129
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Darstellung und Untersuchung der photochemischen und photosensibilisierenden Eigenschaften verschieden substituierter Zn(II)-Phthalocyanine
(2006-05-29)
Tsaryova, Olga
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Gabel, Detlef
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Wöhrle, Dieter
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Wöhrle, Dieter
Different zinc(II) phthalocyanines containing o-carboranyl- or dodecahydrododecaborate substituents and zinc(II) phthalocyanines containing electron-donating or withdrawing substituents were prepared. These new tetrasubstituted boronated phthalocyanines were tested for their photocatalytic activities in the photooxidation of citronellol. The singulet oxygen quantum yields of boronated phthalocyanines were measured by using DPBF as chemical quencher. It was seen that o-carboranyl substituted phthalocyanines have higher photocatalytic activities than their not boronated analogues. The investigation of phototoxic properties of boronated phthalocyanines has been carried out on V79 cell. The following properties of the phthalocyanines containing electron-donating or withdrawing substituents were investigated: singlet oxygen quantum yields, photo-oxidative stabilities and photocatalytic activities (photooxidation of (S)-(-)-citronellol). In addition, positions of HOMO/LUMO energy levels of ground states (S0), first excited singlet states (S1) and first excited triplet states (T1) were calculated. Correlations between properties of the investigated compounds were found: relation between HOMO energy levels of S0 and photo-decompositions, photocatalytic activities and photo-decompositions. Singlet oxygen quantum yields are around 0.55 and independent from calculated triplet energies.
Dissertation
190 99
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Advanced Inverse Modeling of Sediment Thermal Diffusion Processes : Reconstructing Temporal Variant Boundary Conditions for the One-Dimensional Heat Equation
(2018-07-05)
Miesner, Frederieke
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Helin, Tapio
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King, Emily
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Lechleiter, Armin
Temperatures in marine sediments are driven by the geothermal heat flow from the Earth's crust and the evolution of the bottom water temperature. Mathematically, the temperature field can be modeled with the heat equation, a Robin boundary condition at the sediment-water interface, and a Neumann condition at the lower boundary. Given the thermal properties of the sediment and a model for the bottom water temperature function the forward problem is well-posed. The inverse problem, i.e. reconstructing the bottom water temperature function from measurements of the sediment temperature, on the other hand is ill-posed; the parameterized model is non-linear but low-dimensional. Different Newton-linke methods, as well as a linear fitting approach with Tikhonov minimization, and a Markov Chain Monte Carlo method are shown and their performances for this problem are compared. The algorithms work differently well on this problem, and regularising methods are not necessarily better. The heuristic linear fitting has the best accuracy in reasonable computing time, while the Markov Chain Monte Carlo method has proven convergence for enlarging ensembles.
Dissertation
515 228
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Density functional approaches for the interaction of metal oxides with small molecules
(2014-05-07)
Dominguez Garcia, Adriel
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Heine, Thomas
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Frauenheim, Thomas
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Frauenheim, Thomas
The density functional tight-binding (DFTB) and time-dependent DFTB (TD-DFTB) methods are here extended. The incorporation of one-center exchange-like terms in the expansion of multicenter integrals leads to a DFTB scheme in which the fluctuation of the dual density matrix is treated self-consistently. This formalism improves upon hydrogen bond energies of neutral, protonated and hydroxide water clusters as well as of methylimidazole-water complexes. An analogous correction for TD-DFTB leads to marked qualitative and quantitative improvements over the original method. These formalisms are employed to investigate the structural and optical properties of titanium dioxide complexed with nitric oxide and acetaldehyde. Additionally, density functional theory (DFT) and DFTB are employed to investigate the structural and electronic properties of the interfaces between zinc oxide and several organic molecules.
Dissertation
330 151
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Terrigenous climate signals in deep-sea sediments: Insights from the inorganic and organic geochemistry
(2011-12-20)
Kallweit, Wiebke
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Wagner, Thomas
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Zabel, Matthias
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Zabel, Matthias
Terrigenous material is transported to the marine environment in large quantities, mainly by fluvial and eolian transport. Its deposition within the marine sediments provides an archive of Earth s history, past climate conditions, source regions, transport processes, and their variations in time and space. The main objective of this thesis was the documentation of the transport of terrigenous material into the marine environment and the identification of terrigenous material (especially soil organic carbon) in sediments of continental margin systems. These investigations were based on the analysis of the chemical composition as well as specific organic compounds (biomarkers). This thesis contributes to the understanding of the chemical composition of Saharan/Sahelian dust which is deposited in the Atlantic Ocean off NW Africa. It also provides insights into the deposition of terrigenous material on two large deep sea fans in the equatorial Atlantic Ocean during the last ~35 ka.
Dissertation
448 160
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Konzeptbasierte Argumentation in dynamischen Umgebungen
(2010-09-24)
Sprado, Jörn
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Stuckenschmidt, Heiner
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Herzog, Otthein
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Herzog, Otthein
Argumentation systems play an important role when controversial points of views are to be considered in order to make decisions on inconsistent data. In this work a scalable framework for argumentation and decision support is outlined. This framework defines basic arguments and conflicts which refer to conceptual descriptions of the given state of affairs. Based on their meaning and preference relations that adopt specific viewpoints, it is possible to determine efficiently successful explanations depending on these viewpoints. We investigate our approach by examining soccer games, since many observed spatiotemporal behaviours in soccer can be interpreted differently.
Dissertation
400 381
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Suffizienz und Unternehmenskommunikation eine Erkundungsforschung im Kontext ressourcenorientierter Nachhaltigkeit
(2025-09-18)
Heinrich, Anneli Ingeborg
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Müller-Christ, Georg
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Klein, Kristina
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Hagemann, Vera
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Giesenbauer, Bror
Das heutige Konsum- und Wirtschaftsmodell wird mit ökologischen und sozialen Herausforderungen wie Klimawandel und übermäßigem Ressourcenverbrauch in Verbindung gebracht. Ein reduzierter Konsum, also Suffizienz, kann der Übernutzung von Ressourcen und Energie entgegenwirken. Die Dissertation beleuchtet das Phänomen der suffizienz-fördernden Unternehmenskommunikation. Im Rahmen einer Erkundungsforschung mit Systemaufstellungen und mit Hilfe von Methoden qualitativer Sozialforschung wie Fallstudien werden Unternehmen untersucht, die Suffizienz-Botschaften in ihrer Kommunikationspolitik anwenden. Die Untersuchung bringt ein Muster der suffizienz-fördernden Kommunikationspolitik sowie der untersuchten Unternehmen zutage sowie ein Modell der Voraussetzungen suffizienz-fördernder Kommunikationspolitik und Thesen zu der Vereinbarkeit dieser Kommunikationspolitik mit dem Erhalt des Unternehmens. Diese Erkenntnisse dienen dem tieferen Verständnis der Ausgestaltung suffizienz-fördernder Unternehmenskommunikation und der Wesen der Unternehmen, die diese anwenden und sie zeigen Motive und Hemmnisse sowie begünstigende Voraussetzungen für die Umsetzung auf. Dabei liegt ein Augenmerk auf der Fragestellung, wie der Aufruf zu weniger Konsum und der Erhalt des eigenen Unternehmens in Einklang gebracht werden können. Damit liefert diese Arbeit Grundlagen für die weitere Forschung von Suffizienz in der Unternehmenskommunikation und schließt bestehende Forschungslücken.
Dissertation
22 38
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Beyond Magic Realism: the Stuff of Ordinary Lives? Lorene Cary s Rewriting of Beloved
(2014)
Le Fustec, Claude
In the current context of the proliferation of neo-slave narratives, Lorene s Cary The Price of a Child (1995) strikes a rather singular tone. With its title explicitly echoing Toni Morrison s Beloved, Cary s novel and its straightforward realism come as a surprise. As this close intertextual reading of the two novels intends to show, beyond expressing a probable anxiety of influence, Cary s narrative appears to revise major tenets of the African American ethos on which Beloved rests.
Wissenschaftlicher Artikel
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Heft:1
603 156
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From Underspecified Task Descriptions to Robotic Agents Executing Complex Household Activities
(2026-08-25)
Hassouna, Vanessa
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Beetz, Michael
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Lima, Pedro U.
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Beetz, Michael
A household robot asked to prepare breakfast faces a request that is easy to state but difficult to execute. Cutting bread into slices, pouring juice into a glass, spreading butter across toast, and mixing ingredients in a bowl each require physical contact with an object that will be permanently changed. None of these descriptions is executable as stated. The tool, contact site, motion form, force limits, and stopping condition depend on the specific geometry and material of the object at hand. This thesis argues that the gap between what a robot is told to do and what it needs to know to do it correctly is a representational problem. State-changing manipulation cannot be reduced to an action name or a fixed trajectory without losing the conditions that make the action physically correct. The physical correctness of each action is defined by relations between the tool, the manipulated object, the surrounding scene, and the material being changed, and those relations have to be represented explicitly before they can be checked or maintained. The thesis introduces the Object-Anchored Action Template (OAAT), a representation in which manipulation actions are organised as reusable phase structures anchored in the geometry of the manipulated object. Each template makes explicit what the object contributes to the action, which material and structural properties constrain applicability before irreversible contact begins, and which phase invariants are required to hold throughout execution. Missing parameters are resolved at runtime through a layered symbolic grounding process: an action designator names the intended action and declares which slots remain open; the Semantic Digital Twin supplies geometric quantities derived from the current scene; a knowledge graph provides material properties, tool affordances, and technique defaults; and a constraint-based motion controller executes the grounded trajectory while monitoring phase invariants continuously. When a phase invariant is violated, the monitoring layer detects the violation, localises it to the relevant layer, and triggers recovery without modifying the action template. The four primitive families formalised here, separation and division, aggregation and mixing, material transfer, and surface interaction, are developed from observed household instantiations such as cutting, mixing, and pouring and formalised through physical invariants that correspond to image-schematic structures in Hedblom’s ISLFOL. The evaluation tests whether the same templates remain instantiable across robot embodiments, environments, and object instances without structural modification. Eight platforms participate, spanning humanoid robots, mobile manipulators, and a constrained mobile arm platform. Across the full study, 7,693 grounded executions span three environments and four primitive families. That corpus covers all four families in the thesis and includes cutting, mixing, pouring, and surface-interaction trials. The evaluation is systematically seed-controlled across all four primitive families to guarantee matched task conditions globally. To isolate the pure platform-embodiment effect without task-difficulty confounding, the analysis focuses on matched bowl-mixing trials as a primary representative case. Within this subset, object pose, bowl size, environment, and support-surface assignment are held strictly fixed across platforms while only the executing robot varies. This focused bowl-mixing analysis reveals a 72.5 percentage-point spread in success rate under identical task conditions, with TIAGo reaching 97.3% and Stretch trailing at 24.8%. This variance is driven entirely by embodiment because the underlying task seeds are identical. Crucially, no template was rewritten between platforms or across any of the four primitive families; throughout the entire cross-action evaluation, observed failures remained attributable to kinematic constraints, workspace limits, and controller feasibility rather than to the action representation itself. Real-world trials on the PR2 confirm that the same action code transfers from simulation to physical execution across cutting and pouring. Cutting succeeded on bread, cucumber, and zucchini with technique selection driven automatically from material properties; pouring achieved 94.2% success across 120 trials on three container geometries. The result is a grounded action representation that separates reusable phase structure from runtime binding, makes applicability and success conditions explicit, and keeps failures diagnosable at the level where they occur.
Dissertation
5 7
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Theory and Numeric of Spectral Value Sets
(1998-10-02)
Gallestey Alvarez, Eduardo
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Pritchard, Anthony
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Hinrichsen, Diederich
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Hinrichsen, Diederich
Spectral value sets are useful in studying how the spectrum of closed linear operators on infinite dimensional spaces change under the effect of perturbations. They are also important in investigations related to the transient behaviour of linear systems driven by non-normal operators. In the thesis we show that the spectral value sets that can be achieved by perturbations of a given level can be characterized in terms of the norm of certain transfer function. Furthermore, we present an algorithm able to efficiently calculate these sets in the matrix case. In the general (operator!) case finite dimensional approximations of the corresponding transfer function are the natural approach. Thus, we state the approximation problem and solve it under certain conditions. Finally, we apply our approximation results to the robustness analysis of delay equations and of the Orr-Sommerfeld operator.
Dissertation
419 115

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