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  • 1
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    Entwicklung und Aufbau eines BWO-basierten 1,9-THz-Lokaloszillatoren für den Heterodynempfänger GREAT (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: Astronomische Beobachtungen im Bereich der THz-Frequenzen geben Aufschluss über die Entwicklung der interstellaren Materie in unserem Universum. Als wichtigste Kühllinie dichter Molekülwolken ist die Detektion des Feinstrukturübergangs von einfach-ionisiertem atomarem Kohlenstoff CII bei der Frequenz von 1,9 THz von fundamentaler Bedeutung. Wünschenswert ist das Studium astronomischer Quellen hinsichtlich ihrer Dynamik, Temperatur und Dichte mit möglichst hoher sowohl räumlicher als auch spektraler Auflösung. Heterodynempfänger sind für diese Aufgabe am besten geeignet. Bei dieser Technologie wird das astronomische Signal mittels eines Lokaloszillatoren (LO) auf eine Zwischenfrequenz von wenigen GHz umgesetzt und dann rauscharm weiterverstärkt. Gegenstand der vorliegenden Arbeit ist die Entwicklung und der Aufbau des LOs für den 1,9 THz Frequenzkanal des Mehrkanalheterodynempfängers German REceiver for Astronomy at THz-Frequencies (GREAT) der auf dem Flugzeugobservatorium Stratospheric Observatory For Infrared Astronomy (SOFIA) zum Einsatz kommen wird. Für den Aufbau des LOs wurde auf eine Kombination zweier THz-Strahlungsquellen bestehend aus einem Rückwärtswellenoszillator (Backward-Wave Oscillator, BWO) und einem Frequenzverdreifacher zurückgegriffen. Dieser Ansatz erforderte die Entwicklung einer astigmatisch-abbildenden Submillimeteroptik, um die Leistungsankopplung zwischen BWO und Frequenzverdreifacher zu verbessern...
    Description: thesis
    Keywords: 522 ; 550 ; TBG 000 ; Infrarot-Astronomie
    Language: German
    Type: monograph , publishedVersion
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  • 2
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    The central parsec of the milky way at 3.8 micrometer (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The central part of the Milky Way is a unique environment where an interplay of different astrophysical phenomena can be studied, starting from the physics of the interstellar medium, stellar physics and star formation, to high energetic processes associated with the accretion onto the supermassive black hole Sgr A*. In this thesis I focus onto the central parsec of the Milky Way, observed at 3.8 micrometer (L'-band) during several epochs from 2002 to 2007. This particular wavelength is interesting because one can observe the (very dense) Galactic stellar nuclear cluster, as well as the thermal component of the interstellar medium which is not visible at shorter near-infrared wavelengths. Our images revealed a high number of very narrow filamentary structures associated with the streamers of gas and dust (called mini-spiral), and sometimes also with stars. We also detected several stellar sources that are barely observable at shorter wavelengths, but well defined in the dust-dominated L'-band. The goal of this thesis was to use multi-epoch observations in order to measure motions of filamentary structures, as well as of those very red stars. The proper motion analysis allows us to come a step further in understanding the real nature of these enigmatic sources. The high-resolution observations were obtained with the NAOS/CONICA Adaptive Optics system at the ESO Very Large Telescope at Paranal, Chile. The first part of the thesis deals with the narrow dust filaments. The analysis of their morphology and proper motions shows that they are (i) probably not due to a projectional effect and (ii) are influenced by other forces than just the gravitational force of the central black hole...
    Description: thesis
    Keywords: 523 ; 550 ; TIE 662 ; Struktur der Milchstrasse {Astronomie}
    Language: German
    Type: monograph , publishedVersion
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  • 3
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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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  • 4
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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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  • 5
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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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  • 6
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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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  • 7
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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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  • 8
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    Karbonat- und Lignitzyklen im Ptolemais-Becken: orbitale Steuerung und suborbitale Variabilität (Spätneogen, NW-Griechenland) (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: Die mio-pliozänen Ablagerungen im NNW SSE streichenden Monastir-Florina-Ptolemais-Kozani/Servia-Graben beherbergen das größte zusammenhängende Braunkohlevorkommen in Bereich des Balkans. Das Becken erstreckt sich von Monastir (F.Y.R.O.M.) im Norden bis hin zur Region von Elassona im Süden (Makedonien/GR). Es umfasst eine Gesamtfläche von ca. 120 kmø. Mittlerweile werden ca. 71 % des elektrischen Energiebedarfs der Hauptstadt Athen durch die Energiegewinnung aus dem MFPK/S-G gedeckt. Diese rhythmisch entwickelten Lignitvorkommen zeigen, neben den bedeutenden wirtschaftlichen Aspekten, ein großes Potential für eine Paläoklima-Analyse des nordöstlichen mediterranen Raums. Das Neogen zeigt einen multiplen Wechsel von Kalt- und Warmzeiten mit vereinzelt deutlich höheren Temperaturen als heute an (Bradley, 1999). Die Ursachen hierfür können u.a. auf Variationen der Erdbahnparameter zurückgeführt werden, welche Schwankungen in der Insolation verursachen und somit das atmosphärisch-ozeanische System steuern. Zeitreihenanalysen belegten bereits in den 70er bis späten 90er Jahren des letzten Jahrhunderts diese Variationen innerhalb mariner (Hays et al., 1976; Imbrie & Imbrie, 1980) und kontinentaler Ablagerungen (Santarelli et al., 1988, van Vugt et al., 1998. Die Ursachen und Steuerungsprozesse dieser Variationen sind von Milankovitch (1920, 1930, 1941) eingehenst diskutiert worden ...
    Description: thesis
    Keywords: 551.69 ; 551 ; 550 ; TSF 300 ; TOT 310 ; VEF 300 ; VKB 372 ; VKB 376 ; VKB 326 ; VDI 110 ; Griechenland und griechische Inseln {Geophysik} ; Gesteinsmagnetismus {Geophysik} ; Griechenland und griechische Inseln {Geologie} ; Karbonatische Sedimentgesteine ; Organogene Sedimentgesteine ; Magnetische Stratigraphie {Sedimentologie} ; Paläogen
    Language: German
    Type: monograph , publishedVersion
    Format: 131 S.
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  • 9
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    Ozon- und Wasserdampfverteilung im polaren Strahlstrom über dem Nordatlantik (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551.5 ; 550 ; TVK 900 ; TYZ 100 ; Vertikale Komponenten der Luftbewegung {Meteorologie} ; Atlantischer Ozean {Meteorologie und Klimatologie}
    Language: German
    Type: monograph , publishedVersion
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  • 10
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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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