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  • 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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  • 19
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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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  • 20
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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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  • 21
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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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  • 22
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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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  • 23
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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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  • 24
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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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  • 25
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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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  • 26
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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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  • 27
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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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  • 28
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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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  • 30
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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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  • 31
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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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  • 32
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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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  • 33
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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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    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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  • 35
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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.
    Format: application/pdf
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