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  • Univ. Bremen  (44)
  • Univ. Köln  (35)
  • American Association for the Advancement of Science (AAAS)
  • American Institute of Physics (AIP)
  • Elsevier
  • Ottawa : Geological Survey of Canada
  • English  (80)
  • 2010-2014  (80)
Collection
Keywords
Publisher
Language
Years
Year
  • 1
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    Masses of small bodies (2010)
    Univ. Köln
    Details
    Publication Date: 2020-10-07
    Description: The Radio Science technique enables to estimate the mass and other gravitational parameters of a solar system body from spacecraft observations very precisely. It uses the radio link between ground station and spacecraft. The frequency shift of the radio signal is proportional to the relative velocity change between spacecraft and ground station. If a spacecraft performs a close flyby at a solar system body, the velocity of the spacecraft is changed by the gravitational attraction of the body. If all other contributions on the radio signal are known, the remaining frequency change is solely due to the gravitational attraction. A least square fit can be performed on the frequency residuals to derive from it gravitational parameters. Within this thesis models were developed and merged into a software package with which it is possible to determine the orbit of a spacecraft precisely and to predict accurately the frequency to be observed at a ground station. Models for extracting the frequency shift caused by the propagation of the radio signal through the ionosphere and troposphere of the Earth were incorporated...
    Description: thesis
    Keywords: 522 ; TBC 000 ; TGL 000 ; Radioastronomie ; Interplanetare Materie {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 151 S.
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  • 2
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    Properties of quasistellar objects and their progenitors in the radio and mm wavelength regimes in the context of ULIRG-to-QSO evolution (2010)
    Univ. Köln
    Details
    Publication Date: 2020-10-07
    Description: The thesis at hand presents the results of a study of galaxies with active galactic nuclei (AGN) carried out in the radio and mm wavelength regimes at low and high angular resolutions. The studied objects cover a broad range of mechanisms responsible for powering the engines of the respective galaxies: ULIRGs (UltraLuminous Infrared Galaxies), a product of mergers between galaxies that are supposedly powered by starbursts, AGN or a mixture of the two, and QSOs (quasi-stellar objects) which are powered by AGN. Since ULIRGs and QSOs show similar properties (especially the infrared luminosities), it was proposed that they form the early and late phase of an evolutionary sequence where supposedly ULIRGs are the dust enshrouded progenitors of QSOs. As a prototypical ULIRG, Arp 220 represents an early-to-intermediate phase object in the scheme of the ULIRG-to-QSO evolution. For this object observations at multiple mm wavelengths and angular resolutions with the IRAM Plateau de Bure Interferometer (PdBI) are presented and analyzed. Arp 220 as a whole is studied in CO emission of the more extended structure. Furthermore, Arp 220-East is analyzed in more detail in the CO gas. Indications for emission ~10" towards the south, as well as to the north and to the west of the two nuclei, were found in the low resolution CO(1-0) maps ...
    Description: Zsfassung in dt. und engl. Sprache
    Description: thesis
    Keywords: 523 ; TBC 000 ; TIE 900 ; Radioastronomie ; Sonstige Sternensysteme {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 152 S.
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  • 3
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    Multi-telescope studies of neutron stars (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: Neutron stars are unique stellar remnants with extreme properties, as their density and magnetic field. Their study can be the key to a number of unanswered problems in fundamental physics and astronomy, ranging from stellar evolution to strong field gravity. One of the best ways of studying these objects is with observations at radio wavelengths, the efficiency of which can be vastly improved with the combination of data from multiple radiotelescopes. In this thesis, we use the largest European radiotelescopes for performing high quality studies of the properties of objects belonging into two separate categories of neutron stars, millisecond pulsars and magnetars. In the first part of this thesis, a complete description of the observing systems and calibration procedures for the multiple telescopes used is presented. Specifically, all observations were made with the European Pulsar Timing Array (EPTA) telescopes, which are the Effelsberg 100m radiotelescope in Germany, the Lovell 76m radiotelescope in UK, the Westerbork 94m equivalent synthesis radiotelescope in the Netherlands and the Nanc cay 94m equivalent decimetric radiotelescope in France...
    Description: Zsfassung in dt. und engl. Sprache
    Description: thesis
    Keywords: 523 ; THU 400 ; THK 000 ; TBC 000 ; Pulsare, Neutronensterne {Astronomie} ; Spektren und Spektroskopie von Sternen {Astronomie} ; Radioastronomie
    Language: English
    Type: monograph , publishedVersion
    Format: 152 S.
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  • 4
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    The fate of singularities in quantum cosmology and the application of generalized effective equations to constrained quantum systems (2010)
    Univ. Köln
    Details
    Publication Date: 2020-10-07
    Description: The first part of the thesis is concerned with the fate of singularities in quantum cosmology. The second part addresses the derivation of predictions from quantum cosmology. In the first part, two classes of cosmological models were studied. In the first class of models, the universe evolves to or emerges from a big-rip singularity. Here, energy density, pressure and scale factor diverge after a finite amount of time. This type of singularity arises rather generically in cosmological models with phantom dark energy. For each of these phantom-field models, the corresponding scenario with ordinary scalar field was studied. The scalar field induced a big-bang singularity. The second class of models studied was dominated by a big-brake singularity. At the big brake, the universe evolution comes to a halt due to an infinite deceleration. The motivation behind this choice of models was the occurrence of a singularity at large scale factor. The major question pursued was whether these types of singularity were resolved on the quantum level. If such singularities were resolved in quantum cosmology, this would imply that quantum gravitational effects can occur in the macroscopic universe. After devising classical models that contain the respective singularity, I subjected these models to quantization which was carried out in the geometrodynamical approach. The governing equation is then the WheelerDeWitt equation ...
    Description: Zsfassung in dt. und engl. Sprache
    Description: thesis
    Keywords: 523 ; TEC 800 ; Quantenkosmologie {Astronomie: Kosmologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 228 S.
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  • 5
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    Star-disc encounters in young star clusters (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: According to current knowledge, star formation occurs preferentially in clustered environments. As a byproduct of the star formation process young stars are found to be surrounded by accretion discs that are potential birth places of planets and planetary systems. Located in the hosting cluster, these protoplanetary discs are potentially subject to stellar interactions. These interactions give rise to a fundamental question of clustered star formation: How far does the cluster environment affect the evolution of protoplanetary discs and the formation of planets? The question is addressed in the present investigation in terms of the effect of stellar encounters on stars and their disc in young clusters by combining numerical simulations of isolated star-disc encounters and stellar dynamics of young star clusters. The investigation is composed of three key aspects. First, simulations of a dynamical model of the Orion Nebula Cluster (ONC) show that disc destruction is dominated by encounters with high-mass stars that act as gravitational foci for the lower mass stars in the cluster centre. The massive stars are thus subject to repeated encounters which can lead to a total disc destruction ...
    Description: thesis
    Keywords: 523 ; THX 000 ; TIC 000 ; Extrasolare Planetensysteme {Astronomie: Sterne} ; Sternhaufen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 137 S.
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  • 6
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    The LRS double prism assembly to be flown on the James Webb Space Telescope and host galaxies of active galactic nuclei in the near infrared (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The work presented in my thesis covers two aspects of modern astronomy: Observations and instrumentation. Part I of this thesis addresses the design, the development and the qualification of the Low Resolution Spectroscopy Double Prism Assembly (LRSDPA). From an instrumentational point of view, the purpose of the LRSDPA is to make an integration of two prisms, made of Germanium and Zincsulfide, into the imaging module of the mid infrared instrument of the James Webb Space Telescope possible. My design of the LRSDPA answers to several challenging specifications, joining together available envelope, mechanical, thermal, optical and alignment aspects. Both prisms are mounted separately onto a holder via a semi-kinematic interface. The Aluminium components of the demonstration, qualification and flight model all have been manufactured at the mechanical workshop of the 1st Institute of Physics. As it is demanded of all space equipment, the function and performance of the LRSDPA has to be thoroughly demonstrated. The qualification campaign that was conducted in collaboration with the Centre Spatial de Liège, has just been brought to a successful finish. A brief introduction to the James Webb Space Telescope and its mid infrared instrument are given in Chapters 1 and 2. Chapter 3 then describes in detail the scientific capabilities, the design and the qualification of the LRSDPA. The low resolution spectroscopy mode will provide prism slit spectroscopy at a resolution of R=100 and cover the wavelength range from 5æm-10æm. This mode is particularly aiming at spectroscopic analyses of very low surface brightness objects, such as the first light-emitting galaxies that re-ionized the universe shortly after the big bang ...
    Description: thesis
    Keywords: 522 ; TCE 230 ; TIE 400 ; TBG 000 ; TCE 380 ; Weltraumbasierte UV-, Optische und Infrarotteleskope {Astronomische Instrumente} ; Spektren und Leuchtkraft von Sternsystemen {Astronomie} ; Infrarot-Astronomie ; CCD, Photodetektoren {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
    Format: 146 S.
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  • 7
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    Periodic variability in active galactic nuclei (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: In this doctoral thesis, multi-frequency very long baseline interferometry observations together with multi-frequency total flux-density variability data of compact relativistic jets in active galactic nuclei are presented and analyzed. The main goal of the thesis is to investigate the physical mechanisms in relativistic jets responsible for such phenomena as the co-existence of moving and stationary jet components, jet wiggling and precession. We also aim to study the connection between the structural changes in the relativistic jets and flares in the total flux-density light curves and to find observational evidences for the appearance of a primary perturbation in the base of the jet and its further propagation. In this thesis we also investigate which physical mechanisms are responsible for periodical total flux-density variability and to search for periodicities as a sign of jet precession. In order to study the jet physics we used the multi-frequency very long baseline interferometry technique which gives the highest possible in astronomy resolution. We also compared jet structural changes with single-dish multi-frequency observations spanning more than 30 years together with optical and gamma-ray data. In particular, analysis of the long-term kinematics of two active galactic nuclei S5 1803+784 and 0605-085 shows evidence for jet precession ...
    Description: thesis
    Keywords: 523 ; TBC 000 ; TIE 500 ; Radioastronomie ; Aufbau und Struktur von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 201 S.
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  • 8
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    Star formation conditions in nearby galaxies (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The understanding of gravitational stability of galactic disks against star formation, the interplay of atomic and molecular components of the interstellar medium in a galaxy and its physical conditions, namely temperature and density, are important to gain a deeper insight into star formation. Nearby galaxies like the spiral galaxy M51 or the southern starburst galaxies NGC4945 and Circinus offer excellent opportunities to investigate these topics over a complete galactic disk or parts of the galaxy. A suitable tracer to study the molecular part of the gaseous component of galaxies is the CO molecule. It is the second most abundant molecule after H2 in the interstellar medium, its lower lying transition are excited at typical conditions of molecular clouds and the rotational transitions lie in the radio window. Thus, CO emission can penetrate throughout galactic disks and is observable from the ground. Apart from complementary data from the literature, we use observations of 12CO 21, 12CO 4--3, and 13CO 2--1 in this thesis. Additionally, the [CI] 3P1-3P0 fine structure line was observed to study the physical conditions in the central regions of galaxies. In the first part of this thesis, the nearby spiral galaxy M51 is used as a sample source to investigate the onset of star formation. CO, HI, radio-continuum, dust, and stellar maps of M51 are combined to study star formation rate, the H2/HI transition, the gas-to-dust ratios, the stability of the disk against gravitational collapse, and properties of the giant molecular clouds. Parts of the results have been published in Astronomy and Astrophysics (461,143) in 2007 and are submitted to Astronomy and Astrophysics, 2008 for publication. We use the first complete 12CO 2--1 map of M51 including the companion galaxy NGC5195 observed with HERA at the IRAM-30m telescope to trace the molecular gas. Complementary HI VLA data is used to study the atomic gas distribution and the combined total gas surface density ...
    Description: thesis
    Keywords: 523 ; TEG 000 ; Kosmogonie {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 180 S.
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  • 9
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    LINC-NIRVANA piston control and near-infrared polarization images of the Orion proplyds (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: This thesis is focussed on the development of optimized techniques to overcome limitations of astrophysical observations. The goal is an optimal signal estimation in noisy measurements by the consideration of underlying physical processes. This principle was applied to two different fields in astrophysics: intrumental design and analysis of polarimetric observations. In the observational part of this thesis near-infrared images of young stellar objects in the Orion constellation are studied. Limitations in resolution and sensitivity of current astronomical instruments prohibit the detailed analysis of interesting proto-stellar sources to improve theories of star formation. Radiation from the astronomical targets is not only characterized by its spectral energy, but also by polarization properties. The modeling of typical configurations of star-disk systems and the simulation of their polarization patterns helped to understand and interprete features, that were found in observations. For the case of a proto-stellar systems with both a disk and an envelope analysis techniques were developed, which are based on polarimetric effects of the scattering of light by dust. These techniques substantially improve the sensitivity and resolution and are reliable under different observing conditions. Although the obtained data did not allow investigations of substructures of the circumstellar material, the techniques are suitable to obtain constraints on star formation processes ...
    Description: thesis
    Keywords: 523 ; THK 000 ; Spektren und Spektroskopie von Sternen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 168 S.
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  • 10
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    The near infrared activity of Sagittarius A* (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The meaning of my thesis was to obtain new insights about the supermassive Black Hole in the center of our Milky Way and its accretion flow. The non-thermal radio, X-ray, and near-infrared source Sagittarius A* (Sgr A*) is the electro-magnetic manifestation of the Black Hole. Sgr A* is a unique source to study the accretion onto a very massive compact object as it is the closest galactic nucleus. For this work I conducted observations as well as theoretical computations. The near-infrared camera CONICA in combination with the adaptive optics device NAOS at ESO's Very Large Telescope in Chile were used for the observations. The goal of our group was in particular to find further evidence for a quasi-periodic signal of ~17 minutes in radiation outbursts from Sgr A* that has been reported for the first time in 2003. The radiation outbursts - most often termed `flares' - are periods of ~50 - 130 minutes in which the flux of Sgr A* in the near-infrared rises up to a factor of ten. The quasi-periodic sub-structure thereby manifests itself as sub-flares with a constant separation superimposed on the larger, underlying flare. In 2005 and 2006 we were able to detect a significant periodicity, hence the previous findings are supported ...
    Description: thesis
    Keywords: 522 ; TBG 000 ; THK 000 ; Infrarot-Astronomie ; Spektren und Spektroskopie von Sternen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 125 S.
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  • 11
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    Broadband IF circuits for superconductor isolator superconductor (SIS) mixers for the Heterodyne Instrument for the far infrared on the Herschel Space Observatory and for sideband separating mixers (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: This thesis describes the development and manufacturing of the IF circuits for two different heterodyne receivers used for sub-mm radio astronomy. The first project is the broadband 4-8 GHz IF circuitry for the mixer units for band 2 of the Heterodyne Instrument for the Far Infrared (HIFI). This instrument will be operating onboard of ESA’s Herschel space observatory. The band 2 mixer units for HIFI, built by KOSMA, implement low noise SIS mixers in a very compact, modular design. The complete IF path in the mixer units consist of the mixer block (with the SIS mixer chip) and the bias-T, which is needed to apply a bias voltage to the SIS-junction and to extract the IF signal. The detailed investigation of the IF performance of the mixer block must consider the geometric capacitances of the SIS-junction and the tuning structure as well as the inductance of the bond wires used to establish the contact between the mixer chip and the SMA output connector. The calculations presented in this thesis show that the design can be used for IF frequencies up to 12 GHz. The bias-T, which is implemented in the mixer unit, is a dedicated, new development with high performance and high reliability complying with the special requirements for a spaceborne instrument. These include the survival under high mechanical stress such as vibration during the launch and extensive thermal cycling to cryogenic temperatures during the tests of the mixer unit and the instrument.
    Description: thesis
    Keywords: 522 ; 550 ; TBC 000 ; TCE 230 ; Radioastronomie ; Weltraumbasierte UV-, Optische und Infrarotteleskope {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
    Format: 173 S.
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  • 12
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    Studying martian dust devils by applying pattern recognition algorithms to multi-mission camera images (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: A pattern recognition and classification software was developed to detect dust devils automatically in surface images from Mars. The amount of images taken by spacecraft orbiting Mars is increasing continuously and the expenditure of time is too high to search every image for spatially and temporally highly variable features like dust devils. The pattern recognition method was therefore used to conduct a completely new kind of search for dust devils. Images from the three different Mars missions Viking, Mars Global Surveyor and Mars Express can be processed and for the first time automatically scanned for the desired objects. Viking images including dust devils were used as the database to filter unique dust devil features and the derived parameters built the feature vector. Various Classification methods have been tested resulting in a two-layer perceptron (neural network) as the best classifier. Necessary adjustments and increments complete the software so that it can be applied to Mars Global Surveyor Mars Orbiter Camera (MOC), Mars Express High Resolution Stereo Camera (HRSC) and probably coming images from future missions. It was shown that the standard dust devil is filtered and correctly classified. The two main features, the bright spot representing the dust column and the shadow, must be filterable from the background. Crater rims and hills are the most false-positive objects...
    Description: thesis
    Keywords: 523 ; TGG 545 ; TGG 515 ; TCM 000 ; TCE 380 ; Marsoberfläche {Astronomie} ; Marsbeobachtung, Raumflüge zum Mars {Astronomie} ; Mathematische und EDV-Verfahren {Astronomie} ; CCD, Photodetektoren {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
    Format: 158 S.
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  • 13
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    Dissecting the host galaxies of active galactic nuclei at high angular resolution (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The work presented here is concerned with issues related to the interplay of galaxy structure and the accretion phenomenon onto supermassive black holes (SMBH), i.e. active galactic nuclei (AGN). There is statistical evidence for a coevolution of SMBHs and the galaxy bulges they reside in. The detailed knowledge of the involved physical processes, however, is still far from being satisfactory. In order to test and improve theoretical models of how this coevolution is arising, high angular resolution observations of the host galaxies of AGN are necessary. Imaging and spectroscopy of the innermost region of galaxies have the power to reveal information on the structure, the chemical composition, and the dynamics of stars and gas in the presence of an SMBH, and allow us to separate energetic signatures related either to star formation or to the accretion onto the SMBH. Considering such observations over cosmological distances (redshifts) -- i.e. looking into the past because of the finite light-travel time -- we are also able to assess evolutionary effects on the beforementioned properties ...
    Description: thesis
    Keywords: 523 ; TIE 400 ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 174 S.
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  • 14
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    Cophasing LINC-NIRVANA and molecular gas in low-luminosity QSO host and cluster galaxies (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: This thesis consists of two parts. The first part reports on the development of a fringe tracking system for LINC-NIRVANA, the near-infrared homothetic imaging camera for the Large Binocular Telescope (LBT). LINC-NIRVANA allows for a coherent combination of the light entering the two primary mirrors. The fringe pattern in the focal plane is required to be stable in time to preserve the high spatial frequency information in long exposure images. Atmospheric differential piston causes the position of the fringes to change with time. A fringe tracker is a servo system that measures and corrects for atmospheric differential piston in real-time. In the first part, numerical simulations of atmospheric turbulence are used to investigate the problem of angular anisoplanatism of differential piston. The fringe tracking concept and the top-level requirements are introduced, followed by a presentation of the mechanical design of the system. This design includes a solution for a device that is capable of positioning a detector with high precision within a cryogenic environment. A fitting algorithm determines the amount of differential piston in the point-spread function of a reference target. The performance of this algorithm under different signal-to-noise conditions is investigated. First polychromatic fringes obtained with a testbed interferometer conclude the first part ...
    Description: thesis
    Keywords: 523 ; TII 500 ; Emissionsnebel {Astronomie: Interstellare Materie}
    Language: English
    Type: monograph , publishedVersion
    Format: 186 S.
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  • 15
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    Near- and mid-infrared studies of the galactic center and Sagittarius A* (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The focus of this thesis lies on the analysis and interpretation of near- and mid-infrared images of the Galactic center, with a view to improving the understanding of this region, especially at longer wavelengths. Multi-band (H, K, L and M, i.e. 1.6, 2.1, 3.78 and 4.66æm) photometry of images with a large field of view results in a new L-band calibration which eliminates anomalous color effects found in previous surveys of the Galactic center stellar cluster. The color data obtained indicates that the average extinction toward the region containing the Northern Arm and Sgr A* is lower than previously assumed, confirming the findings of Scoville et al. (2003). The stellar population of the inner few arcseconds is compared to that situated up to approximately 0.5 arcminutes out from the position of Sgr A*, revealing that the extinction does not increase significantly over the entire field of view of the ISAAC instrument (i.e. 70" x 70"). Using the large number of sources (over 500), the M-band extinction is calculated from the average L-M colors, resulting in a higher value than that of the "standard" extinction law of Rieke & Lebofsky (1985). The L-M color is shown to be a useful diagnostic tool in distinguishing hot and cool stars, when more precise methods (e.g. spectroscopy) are not available. The unusual morphology of the bright mid-infrared source IRS 3 is also discussed...
    Description: thesis
    Keywords: 522.683 ; 550 ; TBG 000 ; TIE 400 ; Infrarot-Astronomie ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 117 S.
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  • 16
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    Astrophysical phenomena related to supermassive black holes (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: All projects aim at pushing the limits of our knowledge about the interaction between a galaxy and a supermassive black hole (SMBH) at its center. The development of a new instrument can be as valuable as combining different datasets. I follow both approaches and developed projects which deal with new instrumentation and telescope technology, combine datasets from different wavelengths and resolutions, and incorporate recent theoretical models and predictions, which can be verified empirically. The first two of the six chapters compile astrophysical and technical background of the individual projects, which are presented in the following four chapters. While the first project (Chapter 3) deals with observations of the innermost parsec of our Galaxy, Chapter 4 presents data of the inner kpc of an active galaxy. The subjects of Chapters 5 and 6 are very luminous AGN/host systems, so-called QSOs. Whereas Chapter 5 presents global, spatially unresolved properties of SMBH/host systems, the radio jet, analyzed in the final Chapter 6, combines all size scales. It is investigated from close to its origin out to several kpc. The accretion onto the black hole of the Milky Way (Chapter 3) is extremely inefficient and the SMBH possibly interacts dominantly via tidal forces only. The next discussed system (Chapter 4) is the prototype of moderately luminous Seyfert 2 AGN, NGC 1068. Here a strong local influence of the nuclear X-ray radiation is observed. Chapter 5 deals with the possible global importance of radiative interaction between highly luminous QSO AGN and the host. The radio jet in Chapte 6 definitely shows signs of interaction with the matter of its host several kpc away from the nucleus. Chapters 3-6 include a dedicated introductory and a conclusive section, which put the results obtained in the larger astrophysical context of the observation ...
    Description: thesis
    Keywords: 523 ; TEG 440 ; TIE 662 ; Schwarze Löcher {Astronomie: Kosmogonie} ; Struktur der Milchstrasse {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 147 S.
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  • 17
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    Time varying interaction of Europa's atmosphere ionosphere and its conducting ocean with the Jovian magnetosphere (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: A time-dependent 3D magnetohydrodynamic (MHD) model has been developed to investigate the temporal periodic interaction between Europa and the Jovian magnetosphere. The temporal variations are caused by the periodic variations of the magnetospheric plasma at Europa. As a new feature compared to existing stationary models, periodic induced magnetic fields, caused by electromagnetic induction in a potential subsurface ocean, are included. The MHD-flow problem and the internal induction problem are solved simultaneously by making use of the periodicity and the quasi-stationarity of the problem. The ideal MHD equations have been extended in order to account for the effects of Europa's neutral atmosphere and the internal periodic induced magnetic fields on the plasma interaction. At the beginning of this work, Galileo magnetometer data acquired on four passes by Europa were used to investigate whether a fixed permanent dipole moment is present in the interior of the moon in addition to the induced dipole moment previously identified. We thereby confirm the presence of an inductive response and find that the dipole coefficients of the constant intrinsic field contribute at best in a very minor way to the magnetic field. The induced magnetic fields caused by the time variable plasma interaction are calculated in an interactive process...
    Description: thesis
    Keywords: 523.45 ; 550 ; TGG 605 ; Jupitermonde {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 161 S.
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  • 18
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    Superconducting hot electron bolometers on silicon nitride membranes for terahertz waveguide mixers (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The topic of this work is the development of Hot Electron Bolometer (HEB) mixers on freestanding membrane substrates for terahertz high resolution heterodyne receiver systems. The radio astronomy in the THz frequency spectrum is still in the beginning. At present much effort is put into the development of novel telescopes as well as in detector technologies. This work focuses on the development of THz waveguide detectors with superconducting Hot Electron Bolometer (HEB) mixers. These are primarily aimed for the use in the airborne Stratospheric Observatory For Infrared Astronomy (SOFIA) (1.9 THz) and the Atacama Pathfinder EXperiment (APEX) telescope (1.4 THz) in northern Chile ...
    Description: thesis
    Keywords: 523 ; TBC 000 ; Radioastronomie
    Language: English
    Type: monograph , publishedVersion
    Format: 169 S.
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    Laser ablation ICP-MS in paleoceanography (2010)
    Univ. Bremen
    Details
    Publication Date: 2017-06-09
    Description: The different benthic foraminiferal species (epibenthic as well as endobenthic) colonize wide areas of the ocean floor and are widely used for paleoceanographic reconstructions. To improve these reconstructions, it is an important part in research to continuously develop and refine proxies by e.g. improving measuring techniques as well as introducing other species in paleoceanograhpy. The main focus of the presented thesis is a regional examination of the trace element ratios of the rarely used benthic foraminifer Oridorsalis umbonatus and the investigation of their suitability for paleoceanographic applications. Since O. umbonatus is not very abundant in the sediments, it was necessary . as a prerequisite for such studies . to investigate, whether laser ablation ICP-MS can be used for trace element measurements on benthic foraminifera. Therefore, as a first step, trace elements were measured using laser ablation ICP-MS on a set of modern core top samples collected along a depth transect on the continental slope off Namibia at 25.5.S (320 . 2300m water depth; 2.9. to 10.4.C). The Mg/Ca ratios where than calibrated against bottom water temperatures (BWT). The study demonstrates clearly that benthic foraminiferal trace elements can be reliably measured with the laser ablation technique and that the Mg/Ca ratio of O. umbonatus has the potential to be used as a proxy for BWTs...
    Description: thesis
    Keywords: 579.44 ; 579.44 ; UHG 000 ; VXE 000 ; UHG 000 ; VXE 000 ; Paläoozeanologie ; Protozoa {Paläozoologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 81 S.
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    The effect of acidic polysaccharides on the biogeochemistry of iron in the marine environment (2010)
    Univ. Bremen
    Details
    Publication Date: 2017-06-09
    Description: In the early 1990`s the first IPCC report stated the effect of anthropogenic CO2 emissions on global warming and John Martin`s Iron Hypothesis (Martin and J.H 1990), relating atmospheric dust deposition, a major source of iron to the surface ocean, to the CO2 concentration in the atmosphere and the last ice age, culminating in the well known sentence Give me (half) a tanker of iron and I’ll give you a new ice age!. Since then, several large-scale in situ Fe fertilisation experiments revealed that in large areas of the ocean, the so called high nutrient low chlorophyll (HNLC) areas, phytoplankton growth is partly limited by depleted Fe conditions (Geider et al. 1994; De Baar and Boyed 2000; Boyd et al. 2007). The ocean receives Fe from upwelling, riverine input, melting icebergs, atmospheric dust input, input from anoxic sediments, hydrothermal vents and direct recycling by organisms(Tovar-Sanchez et al. 2007). However, in HNLC regions the Fe input to surface waters is very low resulting in Fe limitation of phytoplankton growth. Fe is an important nutrient for marine phytoplankton (Geider et al. 1994; Falkowski et al. 1998; Morel and Price 2003), being essential in metabolic reactions like the photosynthetic electron transport and the assimilation of nitrogen. It is also required for the synthesis of chlorophyll (Martin et al. 1988; Maldonado et al. 1999) as well as for the functioning of the enzyme superoxide dismutase which inhibits the breakdown of chlorophyll by superoxide radicals (Coale 1991)...
    Description: thesis
    Keywords: 577.14 ; VJE 000 ; VJC 210 ; VJE 000 ; VJC 210 ; Organische Geochemie ; Geochemie des Meerwassers
    Language: English
    Type: monograph , publishedVersion
    Format: 106 S.
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  • 21
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    Mg-Ca, B-Ca and U-Ca in shells of benthic foraminifers (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Mg/Ca ratios in benthic foraminiferal shells are frequently used in paleoceanographic studies to estimate past bottom water temperatures. Apart from temperature, other factors may exert additional influences on foraminiferal Mg/Ca. These include the Mg/Ca ratio of seawater, partial dissolution of shell calcite, salinity, physiological effects, and, probably of capital importance, the carbonate chemistry of seawater. In this context, the seperate effects of temperature and seawater carbonate chemistry on the magnesium incorporation into benthic foraminideral calcite are unraveled and quantified in this thesis...
    Description: thesis
    Keywords: 579.44 ; 579.44 ; 560 ; VXE 000 ; VJE 220 ; VXE 000 ; VJE 220 ; Protozoa {Paläozoologie} ; Geochemie der Fauna
    Language: English
    Type: monograph , publishedVersion
    Format: 88 S.
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  • 22
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    Quantitative estimation of aerobic diagenetic overprint of palaeoproductivity signals (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Organic-walled dinoflagellate cysts, oxidation, degradation, organic matter. - Species-selective aerobic decomposition affects fossil organic-walled dinoflagellate cyst (dinocyst) records and hence dinocyst-based interpretations of primary productivity and oceanographic conditions. However, since the recognition of dinocyst species sensitive and resistant to oxic degradation (S- and R-cysts, respectively) it has become apparent that R-cysts may still serve as reliable productivity and oceanographic conditions proxies. On the other hand S-cysts provide a way to quantify aerobic degradation of organic matter (OM) and past bottom-water O2 concentrations. OM degradation plays a key role in global carbon cycling and is important for global climate change. Therefore dinocysts are a valuable tool for estimating the rate of diagenetic process. Questions concerning species-selective aerobic degradation still remain and will be adressed here. To obtain information on the rate of S-cyst decomposition, the relationship between S-cyst degradation and O2 concentrations, and the aerobic degradation of extinct dinocyst species, a natural exposure experiment has been conducted and studies of both Quaternary and pre-Quaternary material from sediment cores were executed. The exposure experiment was conducted in the natural setting of the Eastern Mediterranean. During a 15 month exposure period to oxic water masses, concentrations of S-cysts (Brigantedinium spp. and Echinidinium granulatum) decreased by 24 to 57%. However, taxa such as Nematosphaeropsis labyrinthus, Echinidinium aculeatum, Operculodinium israelianum and Impagidinium aculeatum demonstrated a slight increase in concentration, indicating resistance to aerobic degradation. These results show that even short-term exposure to oxygen may cause considerable changes in the dinocyst assemblage ...
    Description: thesis
    Keywords: 560 ; VVA 560 ; VXE 000 ; VVA 560 ; VXE 000 ; Aktuopaläontologie ; Protozoa {Paläozoologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 159 S.
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  • 23
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    Distribution and transportation pathways of marine particulate matter off Northwest Africa (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Marine snow, underwater cameras, particle flux, aggregation, suspended particulate matter, particle transport. - This study focusses on the vertical distribution and transportation pathways of marine particles off NW-Africa with aid of optical methodologies. A profiling camera system and a remotely operated vehicle (ROV) was used for in-situ observations on the distribution, transport processes and sinking behaviour of marine particulate matter. Between the regional areas of investigation Cape Blanc, Dakhla and Cape Bojador significant differences could be observed with respect to distribution and transportation patterns. These differences are primarily related to the different primary production conditions between the investigation areas. Primary production is the most important factor for the abundance of particulate matter, where highest particle concentrations in the entire water column were seen off Cape Blanc. Next to primary production, water depth, currents and density gradients are factors influencing the particle distribution patterns. With respect to the prevailing transport processes, the Cape Blanc region is characterised by vertically orientated transport patterns. In addition to the continuous supply of large, relatively fast sinking particle aggregates a sinking event could be documented for the first time in-situ in the water column. These events deliver huge amounts of particulate matter from the ocean surface ...
    Description: thesis
    Keywords: 551
    Language: English
    Type: monograph , publishedVersion
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  • 24
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    Sedimentary and stratal patterns in jurassic successions of western Madagascar (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Madagascar; Jurassic; Karoo; Gondwana; Breakup; Rift; Microfauna; Macrofauna; Ammonites; Indian Ocean. - The breakup of Gondwana along the former East African Orogen is widely interpreted to have lasted from the Late Palaeozoic to the Callovian. The present study indicates that the Permian-Triassic or Karoo phase of rifting was not responsible for the separation of East- and West-Gondwana, since that rift system failed in the Late Triassic. Instead the breakup of Gondwana occurred in the Late Liassic. The pre-rift phase in the Morondava Basin is represented by the Karoo deposits, and the syn-rift phase is recorded by Toarcian marine shales, locally overlain by Aalenian sandstones. A major Early Bajocian unconformity is interpreted as the breakup unconformity. The initial post-rift or drift phase is represented by the Bajocian-Bathonian carbonates, marls and sandstones of coastal plain environment and a coastal barrier/lagoon complex. During the Bathonian the siliciclastic shoreface system moved basinward. Callovian-Early Kimmeridgian shales with interbedded iron-oolites represent ...
    Description: thesis
    Keywords: 551 ; VAE 500 ; VDB 100 ; VEQ 300 ; Geotektonische Entwicklung der Erdkruste {Geologie} ; Gondwana ; Madagaskar {Geologie}
    Language: English
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    Biogeochemie gelöster Kohlenhydrate in der Arktis (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551.9 ; VJE 200 ; VJC 210 ; Geochemie Lebender Materie ; Geochemie des Meerwassers
    Language: English
    Type: monograph , publishedVersion
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  • 26
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    Production and preservation of calcareous dinoflagellate cysts in the modern Arabian Sea (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 560 ; VYF 200 ; Pyrrophyceae {Paläobotanik}
    Language: English
    Type: monograph , publishedVersion
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  • 27
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    Late Quaternary environmental history of Taylor Valley, southern Victoria Land, Antarctica, reconstructed by a multidisciplinary study of lake sediments (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: In the unglaciated areas of Antarctica, lake sediments act as archives of the regional environmental and climatic history. In most cases, the records are restricted to the Holocene. Amongst the few exceptions are lakes in the McMurdo Dry Valleys, southern Victoria Land, which are known to have remained mostly ice-free during the Last Glacial Maximum. Within the scope of an U.S.-American-German expedition in austral summer 2002/2003, several sediment cores were recovered from the three major lakes in the Taylor Valley: lakes Fryxell, Hoare, and Bonney. In order to reconstruct the late Quaternary regional environmental and climate history, sedimentological, biogeochemical, mineralogical, and chronological investigations were conducted on the sediment sequences recovered from Lake Hoare (core Lz1020) and East Lake Bonney (core Lz1023) within the scope of this thesis. Sediment cores from Lake Hoare with a maximum length of 2.3 m mainly consist of coarse-grained material and penetrate back into the late Weichselian, when Taylor Valley was occupied by the large proglacial Lake Washburn. This lake was dammed by the advanced Ross Sea ice sheet at the valley outlet and was mainly fed by meltwater of the ice sheet. During the Pleistocene-Holocene transition, enhanced evaporation led to a significant lake level drop of Lake Washburn ...
    Description: thesis
    Keywords: 551 ; 550 ; TWC 500 ; VDI 200 ; VAU 000 ; VEY 200 ; VBN 500 ; VBL 500 ; Klimaschwankungen und Klimaänderungen im Quartär ; Quartär ; Paläolimnologie {Geologie} ; Antarktis {Geologie} ; Geochronologie einzelner Regionen im allgemeinen ; Geologische Bohrungen in einzelnen Regionen
    Language: English
    Type: monograph , publishedVersion
    Format: 121 S.
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    The late Quaternary environmental and climatic history of North-East Greenland, inferred from coastal lakes (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: Eleven lakes and ponds and three lacustrine sediment sequences from coastal East and North-East Greenland were studied for recent hydrological and phytoplankton characteristics and for palaeolimnology, respectively. The limnological survey of lakes and ponds from Store Koldewey in summer 2003 revealed cold, monomictic, thermally unstratified, alkaline and likely oligotrophic water bodies. The diatom phytoplankton, present in six lakes and dominated by four species, varied distinctly between the lakes. The results give information about the recent status of the ecology of these High Arctic freshwater bodies. The sediment sequences were investigated for their chronology, changes in physical and biogeochemical properties, macro- and microfossils, grain-size distribution and in the case of one sequence for its elemental profiles using XRF. The palaeolimnological studies address different time intervals at various temporal resolutions with particular attention to the latitudinal differences of late Quaternary climatic and environmental changes along the coast of East and North-East Greenland. The results include information about the Late Weichselian ice-front environments on southern Store Koldewey with information about the temporal and spatial evolution of the Greenland Ice Sheet margin west of the island ...
    Description: thesis
    Keywords: 551 ; 550 ; TWC 500 ; VDI 200 ; VAU 000 ; VEY 110 ; VBN 500 ; VBL 500 ; Klimaschwankungen und Klimaänderungen im Quartär ; Quartär ; Paläolimnologie {Geologie} ; Grönland {Geologie} ; Geochronologie einzelner Regionen im allgemeinen ; Geologische Bohrungen in einzelnen Regionen
    Language: English
    Type: monograph , publishedVersion
    Format: 148 S.
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    An adaptive shallow water model on the sphere (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: This thesis describes the adaptive shallow water model PLASMA-FEMmE. It solves on the sphere the shallow water equations, the prototype for partial differential equations in atmospheric modeling, using a semi-implicit semi-Lagrangian time step and linear finite elements. Both statically and dynamically adapted grids created by the grid generator amatos are investigated. The results are compared with those of the predecessor model FEMmE that uses a static uniform grid. The outcome demonstrates the capability of the chosen approach as well as its limits. Grid adaptation can easily be achieved with amatos. No reflexions at the grid interfaces are observed. Though in one test case instabilities are released at the grid interfaces. The numerical errors are reduced without a considerable enhancement of the computational effort in another test case with a well-known analytical solution. In respect to the conservation properties the results are more complicated. Mass conservation can be achieved in one test case with an appropriate static grid. In case of complex flow regimes all conservation properties are weakened during the simulation using dynamic grid adaptation...
    Description: thesis
    Keywords: 532.5 ; 551.46 ; 550 ; Meteorologische Modelle ; Fluiddynamik {Geophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: 135 S.
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    Evaluation and application of GPS and altimetry data over central Dronning Maud Land, Antarctica (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: The polar ice sheets are unique paleoclimatic archives and play an important role in recent and future climate. The melting of the big freshwater reservoirs will not only increase the global sea level, but will also influence the ocean currents. Therefore, it will be of particular interest to improve the currently available numeric climate models to achieve more accurate statements about climatic change and its consequences. In this work, the evaluation and the different applications of GPS and altimetry data will be described in respect to enhance models. The antarctic area of investigation, Dronning Maud Land (DML), is of particular interest for German polar research, because both the overwintering station Neumayer and the summer station Kohnen are located within it. In the surroundings of these two stations, highly accurate kinematic GPS measurement were made, which will be the basis for the digital elevation model presented here. Because these data are spatially limited, they are supplemened with remotely sensed data. For this purpose, two airborne altimetry data sets and spaceborne laser altimetry data of the Ice, Cloud, and land Elevation Satellite (ICESat) are used...
    Description: thesis
    Keywords: 551.312 ; 551 ; 550 ; TWC 600 ; VAR 980 ; TQI 000 ; TSY 200 ; Geophysikalische Satellitenfernerkundung ; Antarktis {Geophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: 140 S.
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    Assessing the fidelity of the marine sedimentary magnetic record (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Marine sediments, diagenesis, anoxic environments, paleomagnetism, low-temperature magnetism, magnetic Fe-Ti-Oxides. - Magnetic particles usually occur in very minor concentrations in igneous and sedimentary rocks, soils, volcanic ashes, dusts and even in living organisms. Many of these magnetic grains are capable of carrying a stable permanent magnetization and therefore act as recorders of the recent and ancient Earth's magnetic field. Thus paleomagnetism refers to the study of this remanent magnetization in sedimentary and volcanic rocks through time. From this magnetization, directional intensity information can be recovered concerning the geomagnetic field that prevailed at the sample location at the time of the rock formation. The magnetic parameter on which such paleomagnetic studies are based is the natural remanent magnetization (NRM). In continental margin regions the remanence acquisition process is often complicated by post-depositional modifications of the original magnetic material. After deposition magnetic minerals can be altered or new magnetic phases can be formed. Consequently the original NRM might be obscured or even fully erased. The process of diagenesis and authigenesis may thus seriously compromise paleomagnetic interpretation. Therefore our knowledge of the geomagnetic field behavior based on sediment records from continental margin regions remains limited. To obtain fully reliable information about the geomagnetic field or paleoenvironmental conditions from continental margin regions, the effect of early diagenetic processes occurring after deposition of the sediment must be understood in detail.
    Description: thesis
    Keywords: 551.4686 ; 538.727 ; 550 ; TOT 320 ; VKB 380 ; TSZ 100 ; Paläomagnetismus {Geophysik} ; Sedimente bestimmter Regionen ; Atlantischer Ozean {Geophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: 113 S.
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    Methane oxidation and carbon assimilation in marine sediments (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Anaerobe Oxidation of Methane, AOM, methanotrophy, stable isotope labeling, stable isotope probing, carbon assimilation, flow-through columns, ANME, Seep-SRB, Gullfaks, Tommeliten. - Anaerobic oxidation of methane (AOM) performed by consortia of methanotrophic archaea (ANME) and sulfate reducing bacteria (SRB) is the major sink of methane in marine sediments. This thesis describes methane consumption at two of the most active North Sea cold seeps (Gullfaks, Tommeliten), their microbial community and the resulting lipid biomarker patterns. Experiments in flow-through setups are presented, focusing on physiological parameters of AOM activity such as different methane and sulfate concentrations and on the tolerance of AOM to starvation periods. The roles of inorganic carbon (DIC) and methane as carbon sources for the microbial community performing AOM were examined combining stable isotope probing and lipid biomarker analyses. For archaea substantial uptake of carbon from DIC and methane was found, indicting a novel carbon assimilation pathway. Biomass from SRB was exclusively labeled by DIC indicating a methane dependent, but autotrophic growth consortial SRB.
    Description: thesis
    Keywords: 551.9
    Language: English
    Type: monograph , publishedVersion
    Format: 153 S.
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    Seafloor seepage in the Black Sea (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Black Sea, seafloor seepage, mud volcanoes, seeps, fluid migration, gas hydrates, diapirs. - The Black Sea is the worldwide largest anoxic basin with thick gas rich sediments facilitating seafloor seepage, which is widely distributed along the continental slopes of the Black Sea. In two areas, the Sorokin Trough off Crimea and at the continental slope off Batumi (Georgia), the distribution, structure and evolution of two different vent systems and their relation to fluid migration pathways and gas/gas hydrate occurrences have been investigated by means of high resolution multichannel seismic data. In both regions, the distribution of seafloor seepage is controlled by fluid migration along permeable pathways associated with diapiric uplift in the subsurface. In the Sorokin Trough, seepage is expressed by intensive material upflow and the formation of mud volcanoes; offshore Batumi, gas seeps with low material flux dominate. In the Sorokin Trough, most mud volcanoes are associated with near-subsurface mud diapirs. The great morphological variability of the mud volcanoes reflects different driving mechanisms, which depend on the availability of permeable fluid migration pathways and the depositional environment. A 3D seismic dataset images the detailed three-dimensional ...
    Description: thesis
    Keywords: 551.466 ; 550 ; TSZ 100 ; VAT 300 ; VEZ 120 ; TQC 600 ; Atlantischer Ozean {Geophysik} ; Geologie des Meeresboden ; Randmeere {Geologie} ; Tiefseeseismik {Geophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: 154 S.
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    Development of a novel balloon-borne optical sonde for the measurement of ozone and other stratospheric trace gases (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Ozone, balloon-borne measurements, atmospheric trace gases, concentration profiles, climate change. - In the frame of this work, a new small-size balloon-borne sonde was developed. A miniature grating spectrometer in the sonde measures simultaneously the solar spectral irradiance at a wide wavelength range from 200 to 850. As a first application, ozone profiles have been determined by measuring the changes in the spectral irradiance, caused by ozone absorption in the Huggins band. The wide spectral coverage of the spectrometer offers the possibility for measurements of other trace gases which absorb within the wavelength range, e.g. NO2 and BrO. The low weight of the new sonde (1.7 kg), the moderate price, and the autonomous portable telemetry system makes it a very versatile tool for satellite validation and for case studies, which requires a high number of launches. The newly developed sonde works well without temperature stabilisation, even so the spectrometer experiences rather large temperature changes (15 - 20 K) during the ascent through the atmosphere. Laboratory measurements were performed in ...
    Description: thesis
    Keywords: 551.5 ; 551.8 ; 550
    Language: English
    Type: monograph , publishedVersion
    Format: 148 S.
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    A new algorithm to retrieve the sea ice concentration using weather-corrected 85 GHz SSM/I measurements (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Sea ice is a very important component of the climate system. While the Arctic sea ice extent has retreated during the past 20 years, it has remained constant in the Antarctic. In order to better understand the role of sea ice in the climate system in the context of global warming currently used coupled Atmosphere-Ocean Global Circulation Models have to be improved. This requires to know the sea ice concentration C for a long period for both hemispheres and at the best possible spatial resolution. Currently used methods to obtain C like the NASA Team (NT) algorithm are based on data acquired by the Special Sensor Microwave/Imager (SSM/I) at 19 and 37GHz. The SEA LION (SL) algorithm presented here allows to infer C from the polarization P at 85GHz taking advantage of the higher spatial resolution at this frequency. However, the decrease of P caused by the weather influence leads to an overestimation of C. Therefore, P is corrected using a radiative transfer model and atmospheric data taken from Numerical Weather Prediction models and/or derived from SSM/I measurements. The various sea ice and snow properties are considered calculating monthly sea ice tie points. The average standard deviation of C derived with the SL algorithm is 12% for C 〈 50% and below 5% for C 〉 90%. The SL ice edge agrees within 10km with the one evident in VIS/IR images. The SL ice concentration gradient across the marginal ice zone (MIZ) agrees much better with the one evident in SAR images compared to results of the NT algorithm. Using the higher spatial resolution at 85GHz the SL algorithm allows to detect smaller open water areas than known algorithms. A major limitation of the SL algorithm arises from the quality of atmospheric data needed for the weather correction. A spatial resolution of these data lower than the 85GHz SSM/I channels and/or a time lag larger than half an hour between both data sets can cause relative errors above 100%, particulary in the cloud-covered parts of the MIZ.
    Description: thesis
    Keywords: 550.28 ; 551.31 ; 550 ; TWH 500 ; TWC 100 ; Einfluss von Eis {Klimatologie} ; Instr. Ergebn. zu Klimaänderungen und Klimaschwankungen
    Language: English
    Type: monograph , publishedVersion
    Format: 186 S.
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    Remote sensing of the Northwest African upwelling and its production dynamics (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Carbon export; SeaWiFS; variability; upwelling; Atlantic Ocean; chlorophyll filament; SeaWiFS; SST. - The North Atlantic off NW Africa is characterized by the trade wind induced upwelling of cold and nutrient rich waters. As one of most strongest eastern boundary upwelling areas it is marked by low sea surface temperature and high bio-production, both subject to strong seasonal and interannual variations.Satellite measurements of sea surface temperature (SST) and chlorophyll-a (Chl-a) in the upper water-column were used to (a) recognize the upwelling of deep water and its distribution and mixing in the surface, (b) identify the development of phytoplankton blooms and (c) provide further insights in the characteristics of its variations.Measurements of surface Chl-a were compared to deep-sea fluxes of organic carbon in order to determine the relationship between both parameters and to further calculate the export of Corg and the export variation strength.The off-shore extension of SST-defined upwelling from 1988 through 1999 between 18ʿ and 25ʿN shows maxima in January and May/June with an average area of 140,000 km2 (standard deviation of 20,000 km2). Minima in August exhibit an extension of 43,000 km2 (15,000 km2 standard deviation). A correlation between ...
    Description: thesis
    Keywords: 910 ; UKB 100 ; Nordatlantik {Regionale Ozeanologie}
    Language: English
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    Potential of millimeter- and submillimeter-wave satellite observations for hydrometeor studies (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The distribution of hydrometeors is highly variable in space and time, since it is the result of a complex chain of processes with scales from microphysical (1e-6 m) to synoptical (1e3 m). It is a challenging task to observe these highly variable atmospheric constituents on a global scale with a temporal and spatial resolution sufficient for numerical weather prediction (NWP) and hydrological purposes. This study investigates the potential of the millimeter- and submillimeter-wavelength range on space-borne sensors for hydrometeor and surface precipitation rate observations. The approach is based on simulations with cloud resolving models (CRMs) coupled to a radiative transfer (RT) model. The simulations are performed for mid-latitude cases covering a broad band of precipitation events such as heavy convective and light stratiform winter precipitation. Realistic atmospheric conditions were simulated with two mesoscale CRMs: the Meso-scale NonHydrostatic model (Meso-NH) on a 10 km and the COSMO-DE (COnsortium for Small-scale MOdeling-DEutschland) on a 2.8 km horizontal resolution. When calculating brightness temperatures for satellite observations with the one-dimensional radiative transfer model MWMOD (MicroWave MODel), the detailed cloud microphysics and the three-dimensional fields of temperature, humidity, and pressure of the CRMs are considered in the calculation of the interaction parameters ...
    Description: thesis
    Keywords: 551.5 ; TUA 800 ; TUA 850 ; Radarmeteorologie ; Satellitenmeteorologie
    Language: English
    Type: monograph , publishedVersion
    Format: 138 S.
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    The H_1n+3 + H2 isotopic system (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: Dense cold molecular clouds reckoned to be stellar nurseries are the scene of an extreme molecular deuteration. Despite the cosmic D/H ratio of 10^{-5}, molecular species in prestellar cores are observed to contain nearly as much deuterium as hydrogen. This astonishing deuterium enrichment promoted by low temperatures is the work of H3+. It is the key species which unlocks the deuterium from its HD reservoir via reactions like H3+ + HD -〉 H2D+ + H_2 and drags it further to other species in successive reactions. For this reason, the H3+ + H2 isotopic system is outstandingly critical for the astrochemistry of cold environments. However, its understanding is yet incomplete and insufficient. This thesis thus focuses on the H3+ + H2 isotopic system from a theoretical, experimental and astronomical point of view giving a particular look into the role of nuclear spins...
    Description: thesis
    Keywords: 523 ; TJM 000 ; Kosmochemie {Weltraumforschung}
    Language: English
    Type: monograph , publishedVersion
    Format: 202 S.
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    Antarctic ice sheet expansions in the Middle Miocene and Pliocene (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: This study focuses on the interactions between climate and ice sheets in order to obtain a better understanding of the processes involved. Two periods in the geological past are explored; the Middle Miocene and the mid-Pliocene. For both periods, foraminiferal oxygen-isotope records from deep-sea sediment cores as well as stratigraphical data, suggest a global sea-level lowering. The magnitude of these reductions in sea level indicate large-scale ice-sheet build-up. However, the origin of these events and even the geographic locations of the ice sheets, are still under discussion. The ice sheet-climate model developed in this study provides a tool to test some of the hypotheses brought forward to explain the ice-sheet expansion events. It describes the Antarctic ice sheet and is forced by a climate component based on energy and mass balances. Further more, the model computes the oxygen-isotopic composition of the ice-sheet, thereby providing the possibility to compare numerical results directly to deep-sea sediment records. Numerical experiments focus on the interactions between atmospheric CO2, temperature, ice volume (sea-level equivalent) and the isotopic composition of sea water...
    Description: thesis
    Keywords: 551.69 ; 551 ; 550 ; TWC 600 ; VAR 980 ; Paläoklimatologie ; Antarktis {Glazialgeologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 137 S.
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    Palaeoenvironmental evolution of the Tunisian carbonate platform margin (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: The Late BarremianLate Aptian interval was characterised by several major changes in the ocean/climate system related to the onset of the Mid-Cretaceous greenhouse world. North Africansedimentary deposits offer excellent archives of the ecological changes on the southern Tethyscontinental margin during this time interval. In the present phD thesis sedimentology, palaeontology,biostratigraphy, chemostratigraphy, and geochemistry are combined to reconstruct the palaeoenvironmental evolution and sea-level changes of the Tunisian carbonate platform margin.Respect is paid to major palaeoceanographic and palaeoclimatic events including the late Early Aptian Oceanic Anoxic Event 1a (OAE 1a) and two time intervals associated with widespread carbonate platform drowning in the early- and mid-Late Aptian. The last chapter deals with the cephalopod fauna of the platform margin. Results of the detailed regional investigations are compared to global marine palaeoenvironments and discussed in a broad geological context...
    Description: thesis
    Keywords: 551.77 ; 551 ; 550 ; TWC 600 ; VKB 372 ; VEN 130 ; VDH 300 ; Paläoklimatologie ; Karbonatische Sedimentgesteine ; Tunesien {Geologie} ; Kreide
    Language: English
    Type: monograph , publishedVersion
    Format: 160 S.
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  • 41
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    Enhanced analysis of stratified climate archives through upgrade of Laser Ablation Inductively Coupled Plasma Quadrupole to Time of Flight Mass Spectrometry? (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: ICP-MS, Time of Flight, laser ablation, solid and liquid samples, ice cores, Antarctica, mineral dust, trace element analysis. - The analysis of the inorganic composition of climatic archives provides proxies for climate reconstruction. For many applications commercially available inductively coupled plasma quadrupole mass spectrometry (ICP-Q-MS) systems are used for investigations. One aim of this thesis was to test the laser ablation (LA)-ICP-Q-MS method for the analysis of different sample matrices (polar ice cores, bivalves, frozen lake sediment cores). The main limitation of LA-ICP-Q-MS measurements is the number of analysed isotopes, especially for point scan analysis of embedded particles in the ice matrix and the analysis of growth bands of bivalve shells. Analysing as many isotopes as possible is of interest to deduce e.g. the corresponding source region of embedded particles in the ice matrix. The quasi-simultaneous detection of several isotopes of transient signals is realised in ICP-Time of Flight-MS (ICP-TOF-MS) systems. The applicability of the newly developed ICP-TOF-MS system for ice core analysis in climatic research was explored in this thesis. With the present experimental setup the analysis of trace elements in ice core samples is only possible for liquid samples. The accuracy and precision compares to well established ICP-Q-MS systems. Using the Aridus II as sample introduction system the signal sensitivity was 2-10 times lower for the ICP-TOF-MS compared to ICP-Q-MS systems. Calibration studies and investigation of reference materials showed that the calibration range is limited to an order of magnitude of about 10exp4 to 10exp5 except for m/z ratios between 23 amu and 72 amu where it is even lower. The observed ...
    Description: thesis
    Keywords: 551.6 ; VJA 240 ; TWC 100 ; TWC 500 ; VAR 980 ; Spektroskopische Verfahren {Geochemie} ; Instr. Ergebn. zu Klimaänderungen und Klimaschwankungen ; Klimaschwankungen und Klimaänderungen im Quartär ; Antarktis {Glazialgeologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 185 S.
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  • 42
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    Sediment dynamics of megaslides along the Svalbard continental margin and the relation to paleoenvironmental changes and climate history (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Slope stability, submarine slides, Svalbard, Arctic Ocean, Sophia Basin. - With increasing interest in slope stability issues on continental shelves the causes and trigger mechanism of submarine slides get more and more into the scientific focus. Within the ESF EUROMARGINS project 'Slope Stabilities on Europe's passive continental Margin' (SPACOMA) sediment dynamics of megaslides along the passive continental margin north of Svalbard have been investigated. The study concentrated on identification and sedimentological characterisation of megafailure events, their dating and interpretation in relation to paleoceanography and climate history of the Svalbard archipelago. Integrated interpretation of multibeam bathymetric, sediment-penetrating acoustic (PARASOUND) and seismic data shows a multiple slope failure on the northern European continental margin, north of Spitsbergen. One huge submarine slide has been identified which was first described by Cherkis et al. (1999) - the Yermak Slide (later named Hinlopen/Yermak Megaslide). The extent of the Hinlopen/Yermak Megaslide has been revised based on new acoustic and detailed bathymetric data. Details from the side's internal structure give evidence for one main slide event followed by repeated minor events. The first slide event occurred during MIS 3 around 30 cal. kyr. BP and was characterised by highly dynamic and rapid evacuation of ca. 1.250 kmÃÂđ of sediment from the lower to the upper part of the shelf slope. During this megaslide event, headwalls up to 1600 m have been created and ca. 1150 kmÃÂđ material from hemipelagic sediments and from the lower preexisting trough mouth fan has been entrained and transported into the semi-enclosed Sophia Basin. This megaslide was followed by a secondary evacuation of debris material to the Nansen Basin accomplished by funnelling of the debris through the Littke Channel between Polarstern Seamount and the adjacent continental slope. The main slide debris is overlain by a set of fining-upwards sequences as evidence for the associated suspension cloud and ...
    Description: thesis
    Keywords: 551.307 ; 551.69 ; 551 ; Nordatlantische Polarinseln {Geologie} ; Sedimente bestimmter Regionen ; Sonstige Sedimentationsprozesse ; Paläoklimatologie
    Language: English
    Type: monograph , publishedVersion
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    Retrieval of surface emissivity of sea ice and temperature profiles over sea ice from passive microwave radiometers (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Sea ice, surface emissivity, emitting layer temperature, temperature profile, microwave radiometry. - Polar regions play a key role in the global climate. The information on atmospheric parameters in these regions is sparse. Among the polar surfaces, sea ice varies in extent and physical properties with region and season and so does the surface emissivity. In the present study a method to retrieve the emissivity is applied over two selected regions in the Arctic, one covered by first-year ice and the other by multiyear ice and it investigates the application of them in the improvement of temperature profile retrieval ver sea ice. The retrieval of surface emissivity is done by combining simulated brightness temperatures with the satellite measured brightness temperature. In order to determine the surface emissivity of sea ice, the observations of the microwave instruments amsu (Advanced Microwave Sounding Unit) and amsr-e (Advanced Microwave Scanning Radiometer- Earth Observing System) are used. Determination of emissivity requires the knowledge of the temperature of the emitting layer. The penetration depth of microwaves in sea ice varies between millimeters and decimeters depending on the frequency and micro-physical structure. A year-round observation of temperature profiles of sea ice from the Surface Heat Budget of the Arctic Ocean (sheba) campaign at a first-year and a multiyear ice site is used to derive a set of coefficients a and b to linearly relate ...
    Description: thesis
    Keywords: 551.343 ; VAQ 990 ; VAQ 100 ; Meereis {Glaziologie} ; Gletscheruntersuchungen im Allgemeinen
    Language: English
    Type: monograph , publishedVersion
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    Water vapor in the tropical upper troposphere (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: Wasserdampf ist eines der wichtigsten atmosphärischen Spurengase. Sein Einfluss auf das Klima, die Chemie und den Energiehaushalt ist bedeutend. Von besonderem Interesse ist dabei die Wasserdampfverteilung in der oberen Troposphäre insbesondere in den Tropen. Die wichtigste Wasserdampfquelle für die tropische obere Troposphäre ist tropische Konvektion. Ihr wirkt das grossräumige Absinken entgegen, das seine Ursache sowohl in der Dynamik als auch im Strahlungshaushalt hat. Es gleicht die konvektive Aufwärtsbewegung aus und transportiert dabei relativ trockene Luft nach unten. Über den Netto-Effekt dieser beiden Prozesse ist wenig bekannt, vorallem wegen eines Mangels an zuverlässigen Messungen in dieser Region. In dieser Arbeit werden der Wasserdampfgehalt und die Mechanismen, die für die Wasserdampfverteilung in der oberen tropischen Troposphäre verantwortlich sind, mithilfe einer grossen Menge an in-situ Feuchtemessungen untersucht. Die Messungen wurden auf Linienflugzeugen im Rahmen des EU Projektes MOZAIC durchgeführt (Measurements of Ozone and Water Vapor by Airbus In-Service AirCraft; Messungen von Ozon und Wasserdampf auf Airbus Linienflugzeugen). Eine Klimatologie der gemessenen Parameter über dem tropischen Atlantik zeigt, dass die Feuchte auf allen zeitlichen und räumlichen Skalen sehr variabel ist. Die bimodale Verteilung der Feuchte in den Tropen unterscheidet sich ausserdem deutlich von der Verteilung in den Sub-Tropen oder mittleren Breiten...
    Description: thesis
    Keywords: 551.5 ; 550 ; TVB 100 ; TVL 100
    Language: English
    Type: monograph , publishedVersion
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    Atmospheric parameter retrieval from UV-vis-NIR limb scattering measurements (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: The hyperspectral UV-vis-NIR spectrometer SCIAMACHY will be launched aboard the European satellite Envisat. Its limb measurements will provide vertically resolved profiles of trace gases and other atmospheric parameters. No retrieval algorithms and radiative transfer models have been established for these measurements yet.In this thesis, a unique, fast radiative transfer model for UV-vis-NIR limb radiances has been developed, implemented, and validated. It takes into account the sphericity of the atmosphere and up to two orders of scattering and surface reflection. The weighting functions for all parameters are calculated from analytical formulae. A realistic instrument model with field-of-view integration and signal-to-noise computation and retrieval algorithms have also been implemented. All have been combined in the new program package SCIARAYS. The package has been applied for the characterisation of the limb measurements in several ways:The simulated weighting functions agree well with those due to full multiple scattering. Thus they may be used to calculate theoretical precision estimates and averaging kernels. In conformance with this, test retrievals with approximate weighting functions converge correctly. Therefore, the approximate weighting functions of SCIARAYS are well suited for retrievals from SCIAMACHYś limb measurements.Detailed theoretical retrieval precisions have been calculated for SCIAMACHYś trace gas targets. The conclusion is that a UV-vis-NIR limb sensor like SCIAMACHY is well suited for studying the vertical structure of the stratosphere and also of the upper troposphere above cloud top.Further investigations show that the vertical resolution of retrievals from SCIAMACHYś limb measurements can be improved beyond its geometrical limits. As a trade-off for better vertical resolution, the retrieval precision gets worse. Thus O3 profile features with 1km vertical extent will be detectable with a precision of 20-30%.
    Description: thesis
    Keywords: 551.5 ; 550.28 ; 550 ; TUA 850 ; TQI 000 ; TVA 210 ; Satellitenmeteorologie ; Geophysikalische Satellitenfernerkundung ; Chemische Zusammensetzung der Atmosphäre {Meteorologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 247 S.
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    Pedogenic carbonates as a proxy for palaeo-CO2 in the Palaeozoic atmosphere (2010)
    Elsevier
    Details
    Publication Date: 2021-03-29
    Description: According to a model by Cerling (1991, 1999), the carbon isotope composition of calcretes should depend on the soil type and the CO2-concentration in the atmosphere. We have tested Cerling’s model by investigating 14 Palaeozoic sections with soil profiles. A large number of carbonate types of different genetic origin exist in the localities examined. Comparing the Palaeozoic samples with recent and subrecent calcretes, it can be demonstrated that anhedral, cryptocrystalline (〈10 μm) and subhedral microcrystalline (10 - 40 μm) carbonates are clearly of pedogenic origin. Crystals of larger size with a poikilotopic texture are of groundwater or burial diagenetic origin. Macro- and micromorphological features, typical of recent calcretes, occur in several soil profiles, but thin section microscopy reveals a strong diagenetic overprint of most pedogenic carbonates. Time equivalent sections with comparable soil types (protosols, calcisols and vertisols) show large variations in carbon isotope composition. On the other hand, different carbonate generations at one site do not differ much. Therefore Palaeozoic calcretes appear to be unsuitable for a deduction of the Palaeozoic CO2-concentration.
    Description: German Research Foundation (DFG)
    Description: research
    Keywords: 551.9 ; 552.5 ; VKB 350 ; VJJ 110 ; VCA 300 ; VKB 332 ; VKA 300 ; VKB 371 ; VEA 000 ; VKB 372 ; Lithogenese {Sedimentologie} ; Geochemie der Stabilen Isotopen ; Paläozoische Geologie ; Sedimentationsbedingungen ; Petrogenese ; Klastische Sedimentgesteine ; Europa insgesamt {Geologie} ; Karbonatische Sedimentgesteine ; Kohlenstoffkreislauf ; C-isotope ; Jungpaläozoikum ; Paläopedologie ; Kalkkruste ; CO2 ; calcrete ; carbon cycle ; upper Paleozoic ; paleosol ; C-13/C-12 ; Europa ; paläoklima ; Europe ; 38.41 ; 38.61 ; 38.32
    Language: English
    Type: article
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    Mass distribution at the galactic centre (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: In the framework of this PhD thesis, the study of the distribution of an extended mass close to the super-massive black hole (SMBH) at the centre of our Galaxy is addressed using observational data and theoretical modelling. The main emphasize is on establishing a distinction between the fraction of dark mass present in the form of a black hole and that in an extended form. Despite the significant observational and theoretical progress in the understanding of SMBHs in the last ten years, the formation of SMBHs and the interplay with their host galaxy are still poorly understood. The work presented here extends our understanding of the dynamics in the vicinity of the SMBH. Already in 1974, it was proposed that the radio source SgrA* could be a SMBH. With observations during the following years, it became more clear that the centre of our Galaxy hides an amount of dark mass close to 3 million solar masses. However, the strongest evidence for the existence of a SMBH, was only after it became possible to trace for the first time stellar orbits of fast moving stars, the so-called S-stars, around SgrA*. This was achievable using the SHARP near-infrared speckle camera at la Silla in Chile as well as the near-infrared camera NAOS/CONICA at the Very Large Telescope (VLT) at Paranal in Chile.
    Description: thesis
    Keywords: 523 ; TEG 000 ; TIC 000 ; TEG 440 ; Kosmogonie {Astronomie} ; Sternhaufen {Astronomie} ; Schwarze Löcher {Astronomie: Kosmogonie}
    Language: English
    Type: monograph , publishedVersion
    Format: 122 S.
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  • 48
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    Design and analysis of a broadband SIS-mixer for the Heterodyne Instrument for the Far Infrared (HIFI) on the Herschel Space Observatory (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: In this thesis the design and analysis of SIS-mixers (SIS: superconductor-isolator-superconductor) for the use as low-noise and broad-band detectors in the submm-region for astronomical observations is described. The SIS-mixers have been developed for the frequency band 2 (636-802 GHz) of the Heterodyne Instrument for the Far Infrared (HIFI) on ESA’s space-observatory Herschel. The required performance baseline has been defined by the HIFI-consortium in terms of the estimated noise temperature contribution of the mixer to be 110 K at 636 GHz and 150 K at 802 GHz. In the frequency region between 80 GHz and 900 GHz Heterodyne SIS mixers are established as the best devices for low noise mixing with a high spectral resolution (mixing of the signal radiation with local oscillator, LO). For the HIFI band 2 mixers, the technology of Nb/Al-Al2O3/Nb-junctions has been used with junction areas of 0.5-1.0 um2, a target value for the current density jc of 15 kA/cm2 and a gap-voltage of 2.75-2.77 mV. For the compensation of the SIS-junction’s intrinsic capacitance and the optimized power coupling to the tunnel junction, two types of matching circuits have been theoretically modelled and experimentally studied: (1) three-step transformer single junction devices and (2) double-junction devices. This has been done for two material combinations: for an all-superconductive micro strip NbTiN/SiO2/Nb, and for the superconductor/normal-conductor combination NbTiN/SiO2/Al...
    Description: thesis
    Keywords: 523 ; TBG 000 ; TCE 230 ; Infrarot-Astronomie ; Weltraumbasierte UV-, Optische und Infrarotteleskope {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
    Format: 183 S.
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    Development of a wide bandwidth array acousto optical spectrometer for the Herschel Satellite Mission (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The Herschel satellite observatory will explore the universe at far-infrared, submillimetre, and millimetre wavelengths. This regime of the electromagnetic spectrum is difficult to observe, because water vapour in the Earth’s atmosphere absorbs the signals of almost all the astronomical sources. With the 3.5m telescope (the largest ever placed aboard a spacecraft), it will be possible to observe various atomic and molecular lines with exceptionally high spatial resolution. The receiver system employs the heterodyne technique, and the spectral information is obtained by means of real-time spectrometers. Within this thesis, the requirements, specifications, design concept, and development of a wide bandwidth array acousto-optical spectrometer (WBS) is discussed...
    Description: thesis
    Keywords: 523 ; TC 200 ; TBG 000 ; Astronomische Beobachtungen vom Weltraum aus ; Infrarot-Astronomie
    Language: English
    Type: monograph , publishedVersion
    Format: 177 S.
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  • 50
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    Development of ultrathin niobium nitride and niobium titanium nitride films for THz hot-electron bolometers (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The main focus of this work is the development of ultrathin NbN and NbTiN films. A reproducible and reliable deposition process for ultrathin NbN and NbTiN films for the use in phonon-cooled HEB devices was established. The ultrathin films were deposited on silicon (Si) substrates and on 2æm Si3N4 membranes by DC reactive magnetron sputtering. A method for the precise control of the nitrogen partial pressure by monitoring the target voltage has been introduced to deposit high quality, ultrathin NbN (3-4nm, Tc=8.5 K) and NbTiN (4-5nm, Tc=8K) films. Substrate heating of at least 600ʿC during the deposition is essential for the fabrication of ultrathin NbN and NbTiN films on Si substrates and Si3N4 membranes. The fabrication process required for HEB devices to be used in a quasi-optical mixer was developed. The ultrathin film was patterned by electron beam lithography (EBL), resulting in bolometer devices that measure areas of about 0.4 æm x 4 æm. The nature of the contact determines the interface transparency between the bolometer and the contact structure. Different cleaning processes have been performed and the influence on the contact resistance has been instigated. A better interface transparency gives less RF losses and could improve the HEB sensitivity and local oscillator (LO) requirement ...
    Description: thesis
    Keywords: 523 ; TBC 000 ; Radioastronomie
    Language: English
    Type: monograph , publishedVersion
    Format: 165 S.
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  • 51
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    Merger dynamics and stellar populations in the host galaxies of the quasi-stellar objects I Zw 1 and 3C 48 (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The thesis focuses on two case studies of the host galaxies of the quasi-stellar objects (QSOs) I Zw 1 and 3C 48. The studies are motivated by the hypothesis that ultra-luminous infrared galaxies (ULIRGs) might represent the early stage of QSO evolution (Sanders et al. 1988). According to this hypothesis, galaxy mergers and interactions trigger gas inflow which is followed by starburst activity and by the formation of an active nucleus. As likely transitionary objects between the ultra-luminous infrared stage and the QSO stage, I Zw 1 and 3C 48 are promising candidates to investigate the active nucleus, the starburst, and the merger properties as the essential links between all stages of the proposed evolutionary sequence. The case study of I Zw 1 has an observational focus and is based on near-infrared (NIR) imaging and spectroscopy, carried out with ISAAC (Infrared Spectrometer and Array Camera) at the Very Large Telescope of the European Southern Observatory (ESO) on Cerro Paranal in Chile. The two-armed spiral host galaxy of I Zw 1 shows two bright knots in the north and in the west of the optical disk region, respectively. Here, the new ISAAC spectra indicate that the northern object is a projected foreground star, as previously assumed but recently challenged. In the surroundings of the western source, the ISAAC J-band image displays tidal features. This gives further support for the scenario that I Zw 1 is presently in a minor merger process with this source. The new spectra and the NIR colors of the western source indicate an old stellar population. The host of I Zw 1 is analyzed in a one-dimensional structural decomposition into bulge, disk, and halo components, which results in mean J-band mass-to-light ratios ...
    Description: thesis
    Keywords: 523 ; THS 000 ; TIE 900 ; TIE 400 ; Sternpopulationen {Astronomie} ; Sonstige Sternensysteme {Astronomie} ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 123 S.
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    High resolution multi-wavelength study of active galaxies (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: This PhD thesis presents a study of active galaxies carried out from cm- to mm-wavelengths with high angular resolution. The mechanism of the activity in these objects is supposed to be strongly correlated with the accretion of matter onto a super-massive black hole in their centres. One approach to increase the understanding of these highly interesting sources is to observe and analyse the molecular gas. The characteristics of its distribution and dynamics are indispensible diagnostic tools to investigate the accretion processes at different angular scales. A second approach is the study of emission originating in the direct vicinity of the black hole, such as non-thermal radio emission. To account for different activity levels, five objects were chosen ranging from nearby, Low Luminosity Active Galaxies (LLAGs; NGC3718 at z=0.003 and NGC1068 at z=0.004) to higher redshifted, High LAGs (HLAGs; HE1029-1831 at z=0.039, 3C48 at z=0.367, and Q0957+561 at z=1.414). The first two sources are part of the NU(clei of)-GA(laxy) project, that aims at analysing the distribution and kinematics of the molecular gas at high angular resolution/sensitivity in a sample of 30 nearby LLAGs. HE1029-1831 is part of a complementary sample of nearby HLAGs with similar aims. All sources were observed in carbon-monoxide (CO), known to be a good molecular gas tracer, with the IRAM Plateau de Bure Interferometer (PdBI) providing high sensitivity and high angular resolution. CO emission was detected in all five galaxies. In NGC3718, the molecular gas disk, having roughly two hundred million solar masses, is highly warped. The distribution of the gas reveals large scale asymmetries witnessing a possible tidal tail interaction with a close companion, and as well small scale asymmetries most likely tracing accretion onto the nucleus ...
    Description: thesis
    Keywords: 523 ; TIE 400 ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 207 S.
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    Global modeling of comets: nucleus, neutral and ionized coma of comets 67P/Churyumov-Gerasimenko and 46P/Wirtanen (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: Models of the thermal behavior of a cometary nucleus, the evolution of the neutral gas coma, the ionized cometary coma and of the interaction of the cometary plasma with the solar wind are studied in this work. The general aim is to develop a global model of the comet and its environment in order to characterize the physical conditions around comets 67P/Churyumov-Gerasimenko and 46P/Wirtanen with respect to the heliocentric distance. The results also provide estimates of the effects of the cometary environment on the radio science investigations experiment (RSI) aboard the spacecraft Rosetta. After the launch that is scheduled for February 2004, the Rosetta mission is planned to encounter comet 67P/Churyumov-Gerasimenko and accompany it on its orbit. Comet 46P/Wirtanen has been the original target comet, but serves now as back-up target due to the postponement of the Rosetta launch in January 2003. The model of the heat diffusion within the cometary nucleus is one-dimensional. A grid of one-dimensional models is distributed over the nucleus in order to determine the temperature distribution and the sublimation characteristics of the comet on the whole surface of the comet. A heat balance equation is applied as boundary condition on the surface. Many parameters that have to be accounted for in a heat diffusion model are not precisely known to date. The variation of these parameters within reasonable limits yields a wide range of possible results. The heat diffusion within the cometary nucleus is derived from an energy conservation equation that includes heat conduction through the porous cometary material and heat convection due to the transport of latent heat by the gas phase within the nucleus. Model results are evaluated by a comparison of modeled and observed global gas production rates ...
    Description: thesis
    Keywords: 523 ; TGL 280 ; TC 200 ; Einzelne Kometen {Astronomie} ; Astronomische Beobachtungen vom Weltraum aus
    Language: English
    Type: monograph , publishedVersion
    Format: 153 S.
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    Oceanic anoxic event (OAE) 1b (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: Während der Kreide wurden zahlreiche Störungen des globalen Kohlenstoffkreislaufes aufgezeichnet. Diese Störungen führten zu organisch reichen Ablagerungen, den sogenannten ozeanischen anoxischen Ereignissen (OAEs). Der OAE 1b, abgelagert in der Unteren Kreide, ist einer dieser bedeutenden CO2- Störungen und wird mit der Sedimentation von Schwarzschiefern in Verbindung gebracht. Beschrieben wurde OAE 1b in Ablagerungen des Unteren Albs für die Regionen des Nord- und Zentral Atlantiks sowie im westlichen Einzugsbereich der Tethys und wird deshalb als überregionaler Schwarzschiefer beschrieben. OAE 1b ist assoziiert mit einer abrupten Verschiebung zu ausgeprägt negativen Werten innerhalb zahlreicher Kohlenstoffisotopenreservoirs. Negative Piks in den Kohlenstoffisotopen wurden ebenfalls für das OAE im Toarcium und das OAE 1a im Frühen Apt beschrieben und werden in Zusammenhang mit spontaner Freisetzung von Methan aus marinen Gashydraten gebracht. In dieser hier präsentierten Studie wurden hochauflösende geochemische Profile von zwei paläogeographisch getrennten und klimatisch differenzierten Gebieten (Mazagan Plateau DSDP Site 545 und dem Vokontischen Becken) erstellt. Der Beginn der Sedimentation und der Abschluss fallen zeitgleich mit den negativen Isotopen Piks für beide Untersuchungsgebiete einher. Auffallend ist ein plötzlicher Anstieg der Meeresoberflächentemperatur um 3 ʿC, gemessen an der tropisch gelegenen Site 545 mit dem TEX86 Temperaturproxie, zeitgleich mit dem negativen Piks in den Kohlenstoffisotopen zu Beginn des OAE 1b ...
    Description: Zsfassung in dt. und engl. Sprache
    Description: thesis
    Keywords: 551 ; VJI 000 ; VDH 310 ; VJB 313 ; VKB 380 ; Geochemische Kreislaufmodelle ; Unterkreide ; Geochemie der Sedimente ; Sedimente bestimmter Regionen
    Language: English
    Type: monograph , publishedVersion
    Format: 135 S.
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    Microbial ecology of anaerobic carbon mineralization in Namibian shelf sediments (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Carbon, Upwelling, Namibia, shelf, sediments. - This PhD thesis is an essential component of the 'Namibia Gas' (NAMIBGAS) project, which aims to improve the understanding of the rate and fluxes of hydrogen sulfide and methane to the sediment surface and into the water column on the Namibian shelf, which is one of the most productive upwelling systems on Earth. Organic matter degradation in the sediment drives hydrogen sulfide production, the maintenance of anoxia, and methane formation. Therefore, the primary aims of the thesis are to study carbon transformation processes within the sediment, determine the reactivity of organic carbon in the sediment and, investigate the control of microbial community structure and activity by the amount and accessibility of carbon sources. The emphasis is on linking microbial community structure (identity) to their function (activity) to provide new insights into the microbial ecology that controls carbon turnover in these upwelling sediments. By studying the stepwise degradation of organic carbon a complete process overview of organic carbon mineralization could be obtained. Firstly, the diagenetic transformation of dissolved organic carbon (DOC), in particular dissolved carbohydrates, was studied by using both biogeochemical methods and molecular techniques. The bulk sediment composition, pore water chemistry, polysaccharide hydrolysis rates, 35S-sulfate reduction rates, and the abundance of active bacteria involved in the initial and terminal processes of organic carbon degradation within the top 15 cm of the sediment from two sampling stations were determined (Chapter 2). Secondly, the diversity of bacteria from the same ...
    Description: thesis
    Keywords: 551 ; VAT 270 ; VGE 500 ; Flachsee-Sedimente {Geologie} ; Biomineralisation
    Language: English
    Type: monograph , publishedVersion
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    High-resolution climate reconstruction for the holocene based on growth chronologies of the bivalve Arctica Islandica from the North Sea (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: High-resolution climate reconstruction, North Sea, annual banded proxy, Arctica islandica. - Until now, there has been no published documentation of North Sea year-to-year climate variability during the last 8000 to 10000 years. High-resolution instrumental time series of climatic and environmental data for the North Sea and the adjacent North Atlantic are only available for the last decades or a century at best. Long term paleoclimatic reconstructions in higher latitudes have been predominantly undertaken using land-based annually banded archives, such as trees, varves, glaciers, and speleothems. A suitable long-term environmental archive with annual may be provided by CaCO3-skeletons of long-lived marine invertebrates. This study evaluates whether recent and subfossil shells of the long-lived bivalve Arctica islandica from the North Sea carry feasible information on Holocene climatic and oceanographic conditions. I compared modern shells of Arctica islandica from two very different habitats, a near-coastal shallow site (German Bight) and a northerly, more central, deep site (Fladen Ground). From the latter, subfossil shells were analysed, also. This study demonstrates that Arctica from both sites provides suitable archives of marine environmental conditions in the form of (i) variations in annual shell ...
    Description: thesis
    Keywords: 560 ; TWC 500 ; VAR 990 ; VXM 200 ; VZZ 120 ; Klimaschwankungen und Klimaänderungen im Quartär ; Meeresräume {Glazialgeologie} ; Lamellibranchiata {Paläozoologie} ; Randmeere {Paläontologie}
    Language: English
    Type: monograph , publishedVersion
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    The role of mesozooplankton grazing in the biogeochemical cycle of silicon in the Southern Ocean (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Calanus simillimus, Rhincalanus gigas, grazing, biogeochemistry, biogenic silica. - The role of copepod grazing, particularly of Calanus simillimus and Rhincalanus gigas, in the biogeochemical cycles of silicon (Si) and carbon (C) in the Antarctic Circumpolar Current (ACC) of the Southern Ocean is investigated. The two grazers show differences in feeding behavior before and in response to a diatom bloom stimulated by in situ iron fertilization. The continuously high feeding activity of C. simillimus on diatoms is conducive to enhance the export of primary produced C and Si. The grazing impact of this key species is high enough to influence population dynamics in the microplankton communities of the ACC. In the pre-bloom situation, R. gigas fulfils most of its carbon requirement through grazing on detritus and thereby effectively reduces the vertical fecal flux produced by C. simillimus. It is proposed that a Copepod-Retention-System for organic material is put in place by the copepod community under High Nutrient Low Chlorophyll (HNLC) conditions. Prey switching by R. gigas from detritus to diatoms in the bloom situation lifts the grazing check on the detritus flux and enables loss of particulate C and Si from the surface layer with fast sinking fecal pellets. Results from dissolution experiments indicate that the enclosure of biogenic silica (BSi) in copepod fecal pellets prevents the dissolution of diatom frustules. Diatoms submitted to grazing of copepods and krill (Euphausia superba) dissolved 4 to 26 times slower than un-grazed controls.
    Description: thesis
    Keywords: 560 ; VJE 220 ; Geochemie der Fauna
    Language: English
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    Magmatic and volcanological evolution of the Desertas rift zone (Madeira Archipelago, NE Atlantic) (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Volcanology, volcanic rift zones, Madeira, fluid inclusions, thermobarometry, geochemistry, geochronology. - Madeira and the Desertas Islands show two well-developed volcanic rift zones which intersect near the eastern tip of Madeira (São Lourenço peninsula). To examine a possible genetic link, volcanic structures, rock ages and rock compositions were investigated at the Desertas and São Lourenço. Barometric data derived from fluid inclusions and clinopyroxene-melt compositions indicate fractionation at multiple levels within the mantle beneath the rift zones, followed by temporary magma stagnation within the crust. Depths of crustal stagnation beneath São Lourenço and the Desertas differ significantly, and there is no evidence for a shallow magma reservoir feeding both rifts. This suggests that Madeira and the Desertas have separated magma supply systems. 40Ar/39Ar age determinations revealed that Desertas volcanism lasted from 〉5.1 to 1.9 Ma overlapping in age with the shield phase of Madeira. Eruptive quiescence between 4 and 2.5 Ma at São Lourenço coincides with the main period of volcanism on the Desertas. Major and trace elements and ...
    Description: thesis
    Keywords: 551 ; VAD 600 ; VAD 700 ; VAE 840 ; VEF 139 ; Paläovulkanismus {Geologie} ; Regionaler Vulkanismus {Geologie} ; Rifts {Geologie} ; Balearen un Pityusen {Geologie}
    Language: English
    Type: monograph , publishedVersion
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    Modeling physical and biological processes in Antarctic sea ice (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VAQ 990 ; Meereis {Glaziologie}
    Language: English
    Type: monograph , publishedVersion
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    Seasonal dynamics and characterization of coccolithophore export production in two major upwelling regions (2010)
    Univ. Bremen
    Details
    Publication Date: 2020-10-05
    Description: Coccolithophores, a major group of the nanophytoplankton, belong to the class Prymnesiophyceae.The cells of coccolithophores are typically surrounded by layer(s) of calcium carbonate plates, the coccoliths. Certain coccolithophores can be assigned to particular water masses or to photic zone characteristics and, therefore, single species as well as whole assemblages can be used as oceanographical indicators for the present and the past. Due to their ocean wide distribution, their large contribution to the fine grained carbonate ooze of the deep sea, their ability to photosynthesize and to calcificate they play an important role in the global carbon cycle...
    Description: thesis
    Keywords: 579.17 ; 577.7 ; 577.15 ; 579.82 ; 560 ; VJI 000 ; VU 000 ; VU 000 ; VJI 000 ; Geobiologie ; Geochemische Kreislaufmodelle
    Language: English
    Type: monograph , publishedVersion
    Format: 151 S.
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    Reconstruction of astronomically forced cyclic and abrupt palaeoecological changes in the upper cretaceous boreal realm based on calcareous dinoflagellate cysts (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 560 ; TWC 600 ; VYF 200 ; VYA 500 ; VWH 300 ; VDH 320 ; Paläoklimatologie ; Pyrrophyceae {Paläobotanik} ; Paläökologie {Paläobotanik} ; Kreide {Stratigraphische Paläontologie} ; Oberkreide
    Language: English
    Type: monograph , publishedVersion
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    Modelling the marine carbonate pump and its implications on the atmospheric CO2 concentration (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: The marine carbonate pump includes the production of calcium carbonate, CaCO3 by marine organisms and its subsequent transport to depth. The balance between carbonate production in surface waters and dissolution and accumulation in sediments influences the surface water CO2 concentration and thus the oceanś capacity to take up atmospheric CO2.Models are developed to investigate on calcium carbonate dissolution in the oceanic water column. Model results yield that dissolution in zooplankton guts contributes a significant portion of the proposed carbonate loss. Dissolution fueled by the respiration of organic matter in marine snow aggregates is very sensitive to the size and settling velocity of the aggregate, which determines the boundary layer thickness and the stability of an undersaturated microenvironment. The constraints set by field data yield that the chemical gradients between the aggregate and the bulk seawater are too small to enable significant carbonate dissolution. Furthermore, the role of the carbonate pump in regulating atmospheric pCO2 on glacial to interglacial timescales is investigated ...
    Description: thesis
    Keywords: 551.9 ; VJI 000 ; Geochemische Kreislaufmodelle
    Language: English
    Type: monograph , publishedVersion
    Format: 132 S.
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    Development and application of 2D and 3D transient electromagnetic inverse solutions based on adjoint Green functions (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: To enhance interpretation capabilities of transient electromagnetic (TEM) methods, a multidimensional inverse solution is introduced, which allows for a explicit sensitivity calculation with reduced computational effort. The main conservation of computational load is obtained by solving Maxwell's equations directly in time domain. This is achieved by means of a high efficient Krylov-subspace technique that is particularly developed for the fast computation of EM fields in the diffusive regime. Traditional modeling procedures for Maxwell's equations yields solutions independently for every frequency or, in the time domain, at a given time through explicit time stepping. Because of this, frequency domain methods are rendered extremely time consuming for multi-frequency simulations. Likewise the stability conditions required by explicit time stepping techniques often result in highly inefficient calculations for large diffusion times and conductivity contrasts. The computation of sensitivities is carried out using the adjoint Green functions approach. For time domain applications, it is realized by convolution of the background electrical field information, originating from the primary signal, with the impulse response of the receiver acting as secondary source. In principle, the adjoint formulation may be extended allowing for a fast gradient calculation without calculating and storing the whole sensitivity matrix but just the gradient of the data residual. This technique, which is also known as migration, is widely used for seismic and, to some extend, for EM methods as well. However, the sensitivity matrix, which is not easily given by migration techniques, plays a central role in resolution analysis and would therefore be discarded ...
    Description: thesis
    Keywords: 550.28 ; 550 ; TQD 000 ; Elektrische Verfahren {Geophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: 233 S.
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  • 64
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    Near-surface sediment structures at cold seeps and their physical control on seepage (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: The major objective of the study is to investigate how near-surface sediment structures and other geological aspects control the nature and occurrence of cold fluid seepage. Mainly high resolution multichannel seismic data and swatch bathymetry data were used to study nearsurface seismostratigraphy, structure and seismic fluid-indicating features in two different fluid seepage provinces: Campeche Knolls, southern Gulf of Mexico and the frontal Makran, offshore Pakistan. The two areas have fundamentally different tectonic settings: The Campeche Knolls, southern Gulf of Mexico represents a passive margin influenced by salt tectonism, while the frontal Makran is the most basinward part of the Makran accretionary prism, characterized by plate subduction, sediment accretion, thrust faulting and development of sediment imbricate slices. However, they share quite a few similarities in shallow sediment structures and fluid seepage patterns...
    Description: thesis
    Keywords: 551.23 ; 553.28 ; 550 ; TSZ 100 ; VAE 880 ; TSZ 200 ; Atlantischer Ozean {Geophysik} ; Passive und aktive Kontinentalränder {Geologie} ; Indischer Ozean {Geophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: 125 S.
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    Differentiation of asteroids in the early solar system from Hf-W systematics (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The first major differentiation in primitive planetesimals is the formation of metal- or metal-sulfide cores. To constrain the time of asteroidal differentiation, meteoritic metals and silicates coexisting with metals were analyzed for Wisotopes and Hf and W concentrations. The study focused on silicate inclusions in non-magmatic IAB iron meteorites and the corresponding metal phases as well as on winonaites and acapulcoites were analyzed. IAB iron meteorites formed by crystallization of metal ponds under low pressure conditions at or near the surface of their asteroidal parent body. The presence of abundant silicate inclusions reflects either incomplete metal-silicate separation or mixing of metal and silicates by impacts. Hafnium-W measurements were performed on magnetic and non-magnetic separates from seven IAB iron meteorites to constrain the exact timing of metal separation, silicate differentiation and metamorphism. IAB metals have a deficit in 182W of - 3.1 ± 0.2 -units (relative to terrestrial standard materials)...
    Description: thesis
    Keywords: 523 ; TGG 900 ; TG 200 ; Planetoide {Astronomie} ; Kosmogonie des Sonnensystems {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 118 S.
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    Deformation and micromechanics of granular materials in shear zones - investigated with the Discrete Element Method (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Deformation, shear zone, granular, micromechanic, numerical model, discrete element method, distinct element method. - This thesis was inspired by the lack of detailed (i.e. particle scale) knowledge concerning deformation processes of mechanically weak sediments, especially intrinsically weak layers on the basal shear plane of submarine landslides. It has been known for some time that many different parameters influence shear strength and localization features. This is true not only for sediments, but also for other kinds of weak layers, such as fault gouge. These parameters include for example mineralogy (e.g. smectite, illite, quartz), sediment composition (clay, silt), sediment structure and texture (microfabric), grain size distribution, excess pore pressure, magnitude of effective stress, and deformation history. However, to date it has not been possible to rank or to quantify the influence of each of these parameters. The main goal of this study is to analyze the influence of some of these parameters and, if possible, rank and quantify them. Standard methods to examine shear strength of sediments and fault gouge are various geotechnical shear experiments. In these, a sample is sheared under defined conditions and resulting coefficient of friction, void ratio change, and other meaningful parameters are analyzed. Unfortunately, it is not possible to 'look' inside a shear box during a test and to analyze grain deformation behaviour on a microscopic scale. Therefore, this study employs a different approach to specifically address the problem of microscopic deformation processes. Here, a numerical modelling technique, the Discrete Element Method (DEM), is used. The DEM is a numerical tool based on the ...
    Description: thesis
    Keywords: 551.8 ; VAE 130 ; VAE 130 ; Geomechanik
    Language: English
    Type: monograph , publishedVersion
    Format: 138 S.
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    Modeling of radiative transfer through a spherical planetary atmosphere (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: During the last years and decades issues related to the physics and chemistry of the Earthś atmosphere have attracted much scientific and public interest. The most important problems are stratospheric ozone loss and the ò̀zone hole ́́above Antarctica, global warming and climate change, and tropospheric air pollution. The understanding of the impact of human activities on the Earthś atmosphere requires measurements on a global scale. These enable the spatial and temporal variability of the atmospheric constituents to be investigated. Recently efforts have been made to establish a global observation system comprising satellite instruments and ground-based networks. To process data supplied by the instruments which belong to the global observation system, the development of radiative transfer models and retrieval algorithms is essential. This thesis contributes to the development of the radiative transfer models and retrieval algorithms intended to interprete measurements of the spectral radiance scattered in the atmosphere or transmitted through the atmosphere in UV-Vis-NIR spectral region performed by a new-generation remote sensing satellite spectrometer SCIAMACHY. In this study, main problems of radiative transfer through a spherical planetary atmosphere compared to a plane-parallel atmosphere are investigated. An efficient spherical radiative transfer model intended to simulate SCIAMACHY limb measurements was developed and validated. The model can also be used for the interpretation of measurements performed by other space-borne instruments as well as to compute air mass factors for ground-based measurements. An approximate approach allowing the simulation of limb measurements to be substantially accelerated was developed and its accuracy was investigated. Furthermore, a numerical radiative transfer model intended to simulate SCIAMACHY occultation measurements was developed and then coupled with an appropriate selected inverse technique.
    Description: thesis
    Keywords: 551.5 ; 550.28 ; 550 ; TQI 000 ; Geophysikalische Satellitenfernerkundung
    Language: English
    Type: monograph , publishedVersion
    Format: 150 S.
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    The sediment record of Lake Ohrid (Albania/Macedonia) (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: This thesis had two primary objectives: One objective was to explore and develop applications of Fourier transform infrared spectroscopy (FTIRS) for the quantification of biogeochemical properties in lake sediment; the other objective was to assess the Lake Ohrid (Albania/Macedonia) sediment record with an emphasis on tephrostratigraphy and inferences of climatic and environmental changes using a 15 m long sediment succession (core Co1202) from the north-eastern part of the lake. Studies presented in this thesis were conducted within the scope of an envisaged deep drilling campaign at Lake Ohrid and therefore represent important preliminary studies. FTIR spectra of lacustrine sediment samples were calibrated to infer concentrations of total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), and biogenic silica (BSi). To test the applicability of the FTIRS technique, site-specific FTIRS calibrations and FTIRS calibrations based on a surface sediment dataset from 94 northern Swedish lakes were constructed. Both approaches demonstrated significant correlations between FTIRS-inferred and conventionally assessed biogeochemical property concentrations, ranging between R2 = 0.79 0.99 for TOC, R2 = 0.85 0.99 for TIC, R2 = 0.62 0.84 for TN, and R2 = 0.68 0.94 for BSi ...
    Description: Zsfassung in dt. und engl. Sprache
    Description: thesis
    Keywords: 551 ; 551 ; 550 ; VKB 380 ; VAU 000 ; TWC 500 ; VEE 600 ; TQG 000 ; Sedimente bestimmter Regionen ; Paläolimnologie {Geologie} ; Klimaschwankungen und Klimaänderungen im Quartär ; Südosteuropa nach politischen Ländern {Geologie} ; Geophysikalische Bohrlochmessungen
    Language: English
    Type: monograph , publishedVersion
    Format: 147 S.
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    Tectonic and magmatic processes along the transform margin of Southern Africa (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Giant shear processes shaped Africa's southern margin during the breakup of the supercontinent Gondwana. They acted along a more than 1000 km long transform fault, whose remnant structure the Agulhas-Falkland Fracture Zone stretches today from the Falkland Plateau to the southeastern margin of Africa. A study of the processes which initiated such a long-offset transform fault and acted during their active phase is essential to understand how this sheared margin developed. Africa’s southern margin is not only one of the best examples to study the sharp continent-ocean-transition zones, the marginal ridge, fracture zone, and basin structures usually associated with transform margins, but it provides the unique opportunity to study how excessive magmatic processes acted which formed a Large Igneous Province at a sheared margin. In this thesis, I use seismic refraction, seismic reflection data and plate-tectonic reconstructions to investigate the structure and dynamics of this margin. These are ideal methods as they lead to high-quality velocity-depth models showing the present-day structure across the margin and provide timing and geometries by means of plate kinematics...
    Description: thesis
    Keywords: 550 ; TSR 000 ; TSZ 200 ; VAE 880 ; VAE 890 ; VER 100 ; VEZ 200 ; Südafrika {Geophysik} ; Indischer Ozean {Geophysik} ; Passive und aktive Kontinentalränder {Geologie} ; Ozeanische Kruste {Tektonik} ; Republik Südafrika {Geologie} ; Indischer Ozean {Geologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 157 S.
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    Joint application of ground-based transient electromagnetics and airborne electromagnetics (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The focus of this thesis lies on the joint application of ground-based and airborne electromagnetic methods for the investigation of a glacial valley. For the first time two different airborne electromagnetic (AEM) surveying methods were employed to determine the resistivity structure of a single geological target: the frequency-domain helicopter-borne electromagnetic (HEM) system operated by the Federal Institute for Geosciences and Natural Resources (BGR), Germany, and the time-domain SkyTEM system developed at the University of Aarhus, Denmark. For verification of the airborne results, ground-based transient electromagnetics (TEM) and 2D resistivity surveying were also performed. The target survey area was the Cuxhaven valley in northern Germany, a significant local groundwater reservoir. The course of this buried valley was revealed by drillings, and the shape determined by reflection seismics along several transects across the valley. Electrical and electromagnetic methods were applied to investigate the structure of the valley fill, consisting of gravel, sand, silt and clay. Here, the extension and the thickness of clay layers are of particular interest. They have a low hydraulic permeability and often serve as protection for underlying aquifers against pollution from the surface ...
    Description: thesis
    Keywords: 550 ; TQD 000 ; TQH 000 ; TSB 000 ; Elektrische Verfahren {Geophysik} ; Aerogeophysik ; Mitteleuropa {Geophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: 125 S.
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    Airborne-based geophysical investigation in Dronning Maud Land, Antarctica (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Antarctica represents a key component in the investigation of the geological history and reconstruction of the supercontinents Rodinia and Gondwana. Remnants of the formation and disintegration of these former land masses can be found, although great uncertainties remain in the location of tectonic boundaries beneath the ice sheet of Antarctica due to general lack of outcrops and the limited amount of geological data. Space and airborne measurements are the only possibility to obtain comprehensive spatial data coverage of geophysical data over the extensive large polar areas. Common knowledge of the geological framework displays three major tectonic events which formed Dronning Maud Land (DML): the Grenvillian Orogen (1.1 Ga) build up Rodinia, the Pan-African-Antarctic Orogen (EAAO, 500 Ma) rose in the supercontinent Gondwana and finally the breakup of Gondwanaland, at around 180 Ma...
    Description: thesis
    Keywords: 526.7 ; 559 ; 538.87 ; 550 ; TSY 200 ; Antarktis {Geophysik} ; Aerogeophysik
    Language: English
    Type: monograph , publishedVersion
    Format: 174 S.
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    Crustal structure modelling and interpretation of the East Greenland continental margin between 72°N and 77°N (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Integrated studies of conjugate margins provide important constraints for the sequence of events of synrift tectonic and magmatic processes. The northeast Greenland margin is investigated based on seismic refraction data acquired across the continent ocean transition zone between the Jan Mayen and Greenland fracture zones. Transects of seismic velocity models reveal a clear segmentation of the margin, which is compatible with the potential field data. A crucially important observation is a thick high velocity lower crustal body which clearly decreases northwards. Excessive magmatism is inferred to have occurred during long-term rifting in the south, while reduced syn-rift intrusions account for the norhtern magma-starved margin. Asymmetries and variations across the adjacent and conjugate East Greenland and Norwegian margins, are controversially discussed in terms of the origin of the lower crustal body and magnetic spreading anomalies. Three hypothetical scenarios for the timing and formation of the high velocity lower crustal body are presented. A comprehensive subsidence analysis is established which quantifies the amount of magmatic underplating.
    Description: thesis
    Keywords: 551.136 ; VAE 880 ; TSY 100 ; VBM 000 ; VAE 880 ; TSY 100 ; VBM 000 ; Passive und aktive Kontinentalränder {Geologie} ; Arktis {Geophysik} ; Geologische Interpretation geophysikalischer Beobachtungen
    Language: English
    Type: monograph , publishedVersion
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    Imaging of Cenozoic climatic events and bottom water activities at the northeastern flank of Walvis Ridge: A correlation of seismic data with borehole data measurements (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Seismic, marine, walvis ridge, bottom currents, climatic events. - The history of sedimentation and current activities at the northeastern flank of Walvis Ridge is investigated by a correlation of multichannel seismic data collected during R/V Meteor Cruise M49/1 in early 2001 with borehole measurements of Ocean Drilling Project (ODP) Leg 208. During Meteor Cruise M 49/1 multi-frequency seismic data were collected using two different seismic sources, in a quasi simultaneous mode in order to get best possible penetration and resolution of the sub-surface structures. Walvis Ridge divides the southeastern Atlantic Ocean into two basins, the Angola Basin to the north and the Cape Basin to the south. It is well known as an impassable barrier for bottom waters which separates Antarctic Bottom Waters (AABW) widely distributed in the Cape Basin from North Atlantic Depth Waters (NADW) in the Angola Basin. The sediments of the northeastern flank of Walvis Ridge are characterized by mostly undisturbed sequences of Cenozoic sediments, with varying thickness of ~150 m at the edge of the Angola Basin and ~450 m at the axis of the ridge. A correlation of seismic data with borehole data was accomplished by calculating synthetic seismograms using GRA density measurements of the cores and an averaged velocity model. This 'simple' event modeling allows to assign ages to the seismic reflectors and to identify key horizons/boundaries like the E/O and the K/T boundaries as well as the ELMO event and deposits of the PETM, representing Cenozoic climatic events. The seismic pattern of these target horizons shows similar properties at the different sites indicating their regional distribution. A special static correction in addition to standard seismic processing steps resulted in high quality high resolution deep sea Watergun images. A comparison between the seismic images and the magnetic core ...
    Description: thesis
    Keywords: 551.69 ; 551.462 ; 551 ; 550 ; Tiefseeseismik {Geophysik} ; Atlantischer Ozean {Geophysik} ; Geologische Bohrungen in einzelnen Regionen ; Teilgebiete {Atlantischer Ozean: Geologie} ; Marine Sedimente einzelner Meere und Ozeane {Geologie} ; Paläoklimatologie
    Language: English
    Type: monograph , publishedVersion
    Format: 133 S.
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    Polarimetric remote sensing of land and snow/ice covers with the Spaceborne Microwave Radiometer WindSat (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Microwave remote sensing, polarimetry, radiometer, WindSat, passive. - Measurements from spaceborne microwave radiometers, such as the Scanning Multichannel Microwave Radiometer (SMMR), the Special Sensor Microwave/Imager (SSM/I) and the Advanced Microwave Scanning Radiometer (AMSR), are found to be useful in estimating various earth surface geophysical quantities, e.g. soil moisture and vegetation characteristics over land, snow water equivalent for snow covers and sea ice concentration. All these instruments have measured only the vertical and horizontal polarization component of the brightness temperature (Tb ). WindSat is the first spaceborne radiometer to provide fully polarimetric measurements of the earthÃ
    Description: thesis
    Keywords: 551.5 ; TUA 800 ; TVK 100 ; Radarmeteorologie ; Windmessungen und Beobachtungsergebnisse im Allg. {Meteorologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 122 S.
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    The Phanerozoic thermo-tectonic evolution of northern Mozambique constrained by 40Ar/39Ar, fission track and (U-Th)/He analyses (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Thermochronology, Fission track, (U-Th)/He, 40Ar/39Ar,Mozambique, Gondwana, supercontinent dispersal. - Results of thermochronometric investigations comprising 40Ar/39Ar hornblende and biotite, titanite and apatite fission track (FT) and apatite (U-Th)/He dating on 102 basement rock samples from northern Mozambique record a cooling and denudation history since Early Palaeozoic times. In the north Mozambican sector, these results place new temporal and geometric constraints on the initial rift and subsequent drift configuration during the Gondwana supercontinent dispersal as well as on the post break-up evolution of the sheared margin of central East Africa. Furthermore, they highlight the influence exerted by ductile basement structures of Pan-African age on the loci of tectonically active zone and associated denudation since the Late Palaeozoic. 40Ar/39Ar hornblende and biotite ages range from c. 542 Ma to 456 Ma and c. 448 Ma to 428 Ma, respectively. They record the cooling from the latest Pan-African metamorphic imprint, presumably related to the formation of the Namama Thrust Belt at c. 550-500 Ma, at slow rates of about 11Âʿ 7ÂʿC/Ma from 525ÂʿC to 305ÂʿC in Early to Late Ordovician times. Locally, the thermal influences of syn- to post-tectonic granitoid / pegmatite emplacements at about 500-450 Ma delayed cooling. Widespread basement cooling to 〈 350ãA°C occurred in Late Ordovician to Early Silurian times. The titanite fission track ages fall into two age groups of c. 378 Ma to 327 Ma and c. 284 Ma to 219 Ma. Very slow cooling since the Late Ordovician/Early Silurian at rates of 〈 1ãA°C/Ma to below 275 ãA« 25ãA°C in the Late Devonian/Early Carboniferous is deduced from the older titanite FT ages. It is related to decreasing denudation in ...
    Description: thesis
    Keywords: 551.701 ; 556 ; 551 ; 550 ; VBN 500 ; Geochronologie einzelner Regionen im allgemeinen
    Language: English
    Type: monograph , publishedVersion
    Format: 265 S.
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    Diagenetic imprints on magnetic mineral assemblages in marine sediments (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Diagenesis, Rock magnetism, Marine sediments. - Sediments and sedimentary rocks are important sources for paleomagnetic studies of the geomagnetic field behaviour and of environmental changes. These studies are greatly dependent on the reliable extraction of the detrital magnetic signal. Overprinting of this signal by reductive diagenetic processes, where iron-bearing minerals are dissolved and secondary (magnetic) sulphide minerals form, jeopardizes the validity of such investigations. It is therefore necessary to be aware of the possible presence of diagenetic/authigenic magnetic phases, i.e. greigite, and their influence on the paleomagnetic signal. A chemical remanent magnetisation (CRM) due to these phases can obscure the detrital magnetic signal. It remains to be shown how primary detrital minerals may survive dissolution under these conditions, and by which mechanisms secondary (magnetic) sulphide minerals are formed.
    Description: thesis
    Keywords: 538.7 ; 552.5 ; 550 ; TOT 310 ; VKB 323 ; TOT 310 ; VKB 323 ; Gesteinsmagnetismus {Geophysik} ; Sedimentphysik
    Language: English
    Type: monograph , publishedVersion
    Format: 118 S.
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    Reconstruction of the Phanerozoic tectono-thermal history of central and southern Madagascar, based on fission track thermochronology (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Madagascar, Gondwana, thermochronology. - Titanite and apatite fission track (FT) thermochronology on 127 basement and 18 sedimentary rock samples from central and southern Madagascar record a complex cooling and denudation history since the Early Palaeozoic. Titanite FT analyses gave ages ranging between 483 Ma and 266 Ma. Apatite FT ages vary between 460 Ma and 79 Ma. Samples from Late Carboniferous to Jurassic sediments from the Morondava basin gave apatite FT ages ranging between 462 Ma and 184 Ma. FT data argues for reactivation of several Late Neoproterozoic/Early Cambrian ductile shear zones pre-dating the initial opening of the Morondava basin during the Late Carboniferous. Apatite FT data indicate that the subsequent Mesozoic rift evolution was accompanied with an eastward migration of areas of fast cooling. During Mesozoic times the Morondava basin had a greater eastward extension. Detrital apatite FT data derived from the outcropping Sakoa Group imply that after the Late Carboniferous deposition these rocks were covered by 2-4 km of sedimentary rocks. The final separation of Madagascar and East Africa during the Jurassic influenced mainly samples in southwest Madagascar, where basement regions and also former basin regions were exhumed. Combined Titanite FT and structural data argue for a minor tectono-thermal influence of the Marion hot spot during the Madagascar-India separation. However, apatite FT ages and modelled cooling paths indicate that the break-up during the Cretaceous was associated with a denudation amount of ~4 km crustal section along a narrow stripe parallel to the present eastern continental margin.
    Description: thesis
    Keywords: 551,701 ; 550 ; VBN 500 ; VBN 200 ; VEQ 300 ; VBN 500 ; VBN 200 ; VEQ 300 ; Geochronologie einzelner Regionen im allgemeinen ; Radiometrische Altersbestimmung ; Madagaskar {Geologie}
    Language: English
    Type: monograph , publishedVersion
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    Sediment accumulation and diagenesis in the late quaterary equatorial Atlantic Ocean (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Nonsteady-state Diagenesis, Equatorial Atlantic, Rock-magnetic and Geochemical Multiproxy Approach, XRF Core Scanner, Fe Redox, Magnetite Dissolution. - This thesis investigates 25 Late Quaternary sediment records from the central Equatorial Atlantic by rock magnetic, geochemical and stratigraphical methods. The work was performed in the framework of the Collaborative Research Center 261 ‘The South Atlantic in the Late Quaternary: Reconstruction of Material Budgets and Current Systems’ funded by the Deutsche Forschungsgemeinschaft. The main objective was to analyze and distinguish terrigenous and diagenetic proxysignatures, in particular of rock magnetic parameters. All cores were correlated and dated on basis of their carbonate, iron and rock magnetic records. Magnetite coarsening and partial depletion was observed in glacial organic-rich layers, most intensely during oxygen isotope stages 6, 10 and 12. Non-magnetic and magnetic iron mineral enrichments were found below and at former and active Fe(II) / Fe(III) redox boundaries. Various new proxies quantifying magnetite reduction (ratio of Fe to magnetic susceptibility, ratio of non-ferrimagnetic to total magnetic susceptibility) and authigenesis (ratio of Fe to magnetic susceptibility) were established and found to be highly sensitive indicators of past redox conditions. Comparing these signals with the organic carbon records, it was shown, that rock magnetic, carbon and carbonate records in most parts ...
    Description: thesis
    Keywords: 551.9 ; 538.7 ; 551.46 ; 551 ; 550 ; TOT 320 ; TSZ 100 ; VKB 380 ; VDI 200 ; VEZ 100 ; VAT 240 ; Paläomagnetismus {Geophysik} ; Atlantischer Ozean {Geophysik} ; Sedimente bestimmter Regionen ; Quartär ; Atlantischer Ozean {Geologie} ; Marine Sedimente einzelner Meere und Ozeane {Geologie}
    Language: English
    Type: monograph , publishedVersion
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    Reconstruction of the sedimentary history offshore NW Africa (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: Paleoceanography, Climate, Marine Productivity, Terrigenous Input, High-frequent Cyclicities, LGM, Holocene, XRF Core Scanner. - The goal of this thesis is to reconstruct, with high spatial resolution, the influence of coastal upwelling and terrigeneous input on the magnitude and composition of sediment accumulation off NW Africa, and to investigate how this influence has varied through the last glacial and interglacial periods. To achieve dense coverage for paleoceanographic reconstruction in the investigation area, a large number of sediment cores has been analyzed with rapid and non-destructive core-logging systems. The results of this thesis show that even the small region of the Canary Islands can be separated into several areas, with each reflecting its own sediment characteristics. Recent remote sensing images of chlorophyll concentration reflecting the present upwelling conditions are mirrored by the accumulation rates of the underlying sediment. The variation and distribution of the sediment accumulation rates in the past provides information about paleoceanographic features, such as upwelling conditions and sea-level fluctuations. The contribution of terrigeneous material to the marine sediments can be separated into eolian and a fluvial portions. Three characteristic areas ...
    Description: thesis
    Keywords: 551.46 ; 550.28 ; 550 ; VAT 240 ; TSZ 100 ; VAT 240 ; TSZ 100 ; Marine Sedimente einzelner Meere und Ozeane {Geologie} ; Atlantischer Ozean {Geophysik}
    Language: English
    Type: monograph , publishedVersion
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    Ozone depletion, chlorine activation and water vapor observed in Spitsbergen (2010)
    Univ. Bremen
    Details
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551.5 ; 550 ; TYY 100 ; TVA 210 ; Arktis {Meteorologie und Klimatologie} ; Chemische Zusammensetzung der Atmosphäre {Meteorologie}
    Language: English
    Type: monograph , publishedVersion
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