ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Other Sources  (634,596)
Collection
Language
Years
  • 1
    Publication Date: 2020-10-05
    Description: Die Bibliografische Datenbank GeoRef und die Virtuelle Fachbibliothek GEO-LEO eignen sich bei paralleler Nutzung für eine weitgehend erschöpfende Informationsrecherche im Bereich Geowissenschaften. Während GeoRef im Wesentlichen als Nachweisinstrument für Zeitschriftenartikel dient, werden bei GEO-LEO Bibliothekskataloge abgefragt und digitale Volltexte verfügbar gemacht. Der direkte Dokumentzugriff und die Verzeichnung von Webseiten, ein Instrument zur Erkundung von Wissen durch systematische Darstellung von Einzeldisziplinen und eine Publikationsplattform bei GEO-LEO ergänzen sich mit hervorragender Erschließung und großer thematischer Abdeckung bei GeoRef.
    Description: study
    Keywords: 551 ; V 200 ; Geowissenschaften ; Virtuelle Bibliothek ; Literaturdatenbank ; Vergleich ; 38.04
    Language: German
    Type: article_first
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    facet.materialart.
    Unknown
    Universitätsverlag Göttingen
    Publication Date: 2020-10-05
    Description: For about four decades marble has been used as thin veneer cladding. The durability of such thin slabs (mostly 30-40 mm) is satisfactory at most constructions. However, on numerous buildings all over the world, the long-term deformation (expansion, bowing) of some claddings is associated with structural weakening and strength loss which led to an inevitable restoration of the affected facades and to an image problem of marble used as a structural building stone. Up to now, the existing knowledge about the causes for this special kind of marble weathering is mostly restricted to research on Carrara marble and to the effect of individual parameters. This thesis presents the first study of the combined influence of extrinsic (environmental) and intrinsic (material specific) parameters on marble bowing. The respective impact of these factors on the weathering process is elucidated by damage mapping of four different marble facades. The work focuses on the influence of the microfabric on the damage dynamics of veneer marble and particularly considers moisture as an essential climatic parameter. In order to characterize and understand the weathering process, an array of different marble samples had to be studied with regard to their petrographic, rock physical and microstructural properties. Besides both fresh and artificially weathered marble samples this survey also included demounted façade panels from the investigated buildings with varying degrees of pre-deterioration...
    Description: Die seit etwa vier Jahrzehnten dauernde Verwendung von Marmor als dünnplattige Fassadenverkleidung hat weltweit an zahlreichen Gebäuden zu Problemen mit der Langzeitstabilität solcher Fassaden geführt. Das dabei oft auftretende Phänomen des Verbiegens von Marmorplatten geht mit einer Materialentfestigung einher, was langfristig die Sanierung der betroffenen Fassaden zur Folge hat und mittlerweile ein Imageproblem für den Werkstoff Marmor darstellt. Die bislang vorhandenen Kenntnisse zu den Ursachen dieser speziellen Form der Marmorverwitterung beschränken sich meist auf Untersuchungen an Carrara Marmor und auf die Wirkung einzelner Faktoren. In der vorliegenden Arbeit wurde der kombinierte Einfluss von umweltbedingten (extrinsischen) und materialspezifischen (intrinsischen) Parametern untersucht. Ihr Wirkungsgrad wird am Beispiel von vier Schadenskartierungen an Marmorfassaden aufgezeigt. Der Schwerpunkt liegt auf dem Einfluss des Mikrogefüges auf die Schadensdynamik von Fassadenmarmor unter besonderer Berücksichtigung der Feuchtigkeit als essentieller Klimafaktor. Basis für die Charakterisierung und Interpretation des Verwitterungsprozesses ist die Erfassung von petrographischen, gefügekundlichen und petrophysikalischen Eigenschaften an bruchfrischen und künstlich verwitterten Marmorproben sowie an demontierten Fassadenplatten unterschiedlicher Vorschädigung von den untersuchten Marmorfassaden...
    Description: thesis
    Keywords: 551 ; VKB 210 ; VBP 200 ; RVC 810 ; VAE 130 ; ZTI 000 ; VAH 000 ; VKA 170 ; Fassade ; Marmor ; Gefüge 〈Gesteinskunde〉 ; Petrophysik ; Physikalische Verwitterung ; Deformation 〈Geologie〉 ; 38.25 ; 56.47 ; 38.58
    Language: German
    Type: monograph , publishedVersion , monograph
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    facet.materialart.
    Unknown
    Universitätsverlag Göttingen
    Publication Date: 2020-10-05
    Description: Seit nunmehr 20 Jahren findet regelmäßig alle zwei Jahre das Symposium ‚Tektonik — Strukturgeologie — Kristallingeologie‘ (TSK) statt. Die Tagung soll insbesondere jungen Nachwuchswissenschaftlern die Möglichkeit bieten, ihre Ergebnisse zu diskutieren und einem breiten Fachpublikum vorzustellen. Dies ist natürlich besonders attraktiv, wenn auch die ‚alten Hasen‘ der Zunft eifrig dabei sind. In diesem Jahr wird schon TSK 11 — nach Tübingen, Erlangen, Graz, Frankfurt, Salzburg, Freiberg, Freiburg und Aachen nun zum zweiten Mal nach 1994 wieder in Göttingen durchgeführt. Wir freuen uns, auch dieses Mal wieder ein vielseitiges Tagungsprogramm präsentieren zu können. Die vorgestellten Arbeiten befassen sich mit Geländebeobachtungen, Laboranalysen und -experimenten bis hin zu Computermodellierungen. Im Maßstab reichen sie vom submikroskopischen Bereich bis hin zu ganzen Orogenen. Dabei werden sowohl duktile als auch spröde Deformationsprozesse beleuchtet. Regionale Geologie ist ebenso Thema wie auch eher angewandte Fragestellungen. Um die einzelnen Beiträge schnell auffinden zu können, wurden diese alphabetisch nach Erstautoren geordnet. Aus Zeitgründen konnte nur der kleinere Teil der mehr als einhundert eingegangen Beiträge in das Vortragsprogramm aufgenommen werden. Auf parallele Vortragssitzungen haben wir bewusst verzichtet. Besonderen Raum für anregende Diskussionen sollen auch die thematisch zusammengestellten Postersitzungen bieten, für die wir spezielle Zeiten eingeräumt haben. Hierzu werden Poster jeweils vorher im Plenum kurz vorgestellt. Die eingegangenen Manuskripte wurden, wie bei TSK üblich, für die Publikation keinem Gutachterverfahren unterzogen. Daher sind die jeweiligen Autoren allein für den Inhalt verantwortlich. Wir wünschen allen Teilnehmenden anregende Diskussionen und interessante Kontakte sowie einen schönen Aufenthalt in der ‚Stadt, die Wissen schafft‘!
    Description: conference
    Keywords: 551 ; VAE 000 ; VAC 100 ; Tektonik ; Strukturgeologie ; Kristallin ; Kongress ; 38.36 ; 38.37
    Language: German
    Type: anthology , publishedVersion
    Format: 273 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    facet.materialart.
    Unknown
    Univ. Köln
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2020-10-07
    Description: In cosmic ray experiments the arrival directions, among other properties, of cosmic ray particles from detected air shower events are reconstructed. The question of uniformity in the distribution of arrival directions is of large importance for models that try to explain cosmic radiation. In this thesis, methods for the reconstruction of parameters of a dipole-like flux distribution of cosmic rays from a set of recorded air shower events are studied. Different methods are presented and examined by means of detailed Monte Carlo simulations. Particular focus is put on the implications of spurious experimental effects. Modifications of existing methods and new methods are proposed. The main goal of this thesis is the development of the horizontal Rayleigh analysis method. Unlike other methods, this method is based on the analysis of local viewing directions instead of global sidereal directions. As a result, the symmetries of the experimental setup can be better utilised. The calculation of the sky coverage (exposure function) is not necessary in this analysis. The performance of the method is tested by means of further Monte Carlo simulations. The new method performs similarly good or only marginally worse than established methods in case of ideal measurement conditions. However, the simulation of certain experimental effects can cause substantial misestimations of the dipole parameters by the established methods, whereas the new method produces no systematic deviations. The invulnerability to certain effects offers additional advantages, as certain data selection cuts become dispensable.
    Description: thesis
    Keywords: 523 ; TFE 000 ; Kosmische Elektrodynamik {Astrophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: 177 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    facet.materialart.
    Unknown
    Univ. Hamburg
    Publication Date: 2020-10-07
    Description: The main topic of this work is the introduction of time dependence into PHOENIX. This has been achieved for both the radiation field and the matter in the SN Ia model atmosphere. First, time dependence in the radiative transfer equation has been implemented. Two discretization schemes have been used for the implementation of the time derivative. Test calculations have been performed to confirm the correctness of the implementations. The radiation time scale computed with the time dependent radiative transfer is comparable to a simple analytic approach. Perturbations of the inner boundary condition of the atmosphere move through the whole atmosphere. For instance, an atmosphere with a sinusoidally varying inner light bulb leads to an atmosphere where the luminosity varies sinusoidally everywhere. For the next extension of time dependence for the matter, a simple hydrodynamical solver has been implemented. It computes the changes in the energy of an SN Ia atmosphere by considering the homologous expansion, energy transport and the deposition of energy by g -ray emission due to the radioactive decay of 56Ni and 56Co. Test calculations verified that each part of the solver works correctly. The energy deposition heats the atmosphere and increases the observed luminosity, whereas the adiabatic e expansion cools the atmosphere. The energy transport always pushes the temperature structure of the atmosphere towards the radiative equilibrium state ...
    Description: thesis
    Keywords: 523 ; THI 000 ; THU 162 ; Helligkeit von Sternen {Astronomie} ; Supernovae {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 107 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    facet.materialart.
    Unknown
    Univ. Potsdam
    Publication Date: 2020-10-07
    Description: Central stars of planetary nebulae are low-mass stars on the brink of their final evolution towards white dwarfs. Because of their surface temperature of above 25,000 K their UV radiation ionizes the surrounding material, which was ejected in an earlier phase of their evolution. Such fluorescent circumstellar gas is called a "Planetary Nebula". About one-tenth of the Galactic central stars are hydrogen-deficient. Generally, the surface of these central stars is a mixture of helium, carbon, and oxygen resulting from partial helium burning. Moreover, most of them have a strong stellar wind, similar to massive Pop-I Wolf-Rayet stars, and are in analogy classified as [WC]. The brackets distinguish the special type from the massive WC stars.
    Description: thesis
    Keywords: 523 ; TEG 000 ; Kosmogonie {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 102 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    facet.materialart.
    Unknown
    Univ. Bielefeld
    Publication Date: 2020-10-07
    Description: In this thesis we apply methods from statistical physics to stochastic inflation. Those methods, the replica field theory and the Gaussian variational methods, have to our knowledge never been applied before in this context, and allow us to compute the power spectrum of a scalar test field in the most general set-up. It provides a framework to perform calculations in regions of arbitrarily large quantum fluctuations and may also serve as a starting point to address the issue of back reaction. We first give an introduction to cosmological inflation, cosmological perturbation theory and cosmic microwave background anisotropies. Then we explain the idea of stochastic inflation, including some detailed derivations, and give an overview over major progress in this field. This is followed by an introduction to replica field theory, presented in a way directly applicable to stochastic inflation. Our work continues with a detailed calculation of the power spectrum of a scalar test field in a Friedmann Universe. We show the effect of the quantum fluctuations on the spectrum and derive explicit expressions showing its dependence on time and other important parameters. The effect of self-interactions and possible effects on the cosmic microwave background are discussed. We conclude with a summary of our results and give an outlook. One part of our major results has been published in Phys. Rev. D 78, 103501 (2008), where for the first time we present a replica field-theoretical approach to stochastic inflation in which we find a manifestation of the phenomena of so-called dimensional reduction. It implies under certain conditions inevitable infra-red divergencies of correlation functions on large-scales. These conditions are examined in detail in Phys. Rev. D 79, 44009 (2009), where we find that generically for a wide class of circumstances the divergencies are pushed exponentially fast well beyond observable scales ...
    Description: thesis
    Keywords: 523 ; TA 100 ; TEC 000 ; Theoretische Grundlagen {Astronomie} ; Kosmologie {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 132 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    facet.materialart.
    Unknown
    Univ. Köln
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 11
    Publication Date: 2021-03-29
    Description: The presented thesis describes the observations of the Galactic center Quintuplet cluster, the spectral analysis of the cluster Wolf-Rayet stars of the nitrogen sequence to determine their fundamental stellar parameters, and discusses the obtained results in a general context.The Quintuplet cluster was discovered in one of the first infrared surveys of the Galactic center region (Okuda et al. 1987, 1989) and was observed for this project with the ESO-VLT near-infrared integral field instrument SINFONI-SPIFFI. The subsequent data reduction was performed in parts with a self-written pipeline to obtain flux-calibrated spectra of all objects detected in the imaged field of view ...
    Description: thesis
    Keywords: 523 ; TIC 000 ; THT 800 ; TIE 662 ; Sternhaufen {Astronomie} ; Massenreiche Sterne {Astronomie} ; Struktur der Milchstrasse {Astronomie}
    Language: German
    Type: monograph , publishedVersion
    Format: 115 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 12
    facet.materialart.
    Unknown
    Univ. Bochum
    Publication Date: 2020-10-07
    Description: Die Dissertation behandelt die Konzepte sowie die Implementierung der operativen Aspekte der Kontrollsoftware des LUCIFER Instruments. Diese ist in vier Schichten aufgeteilt. Die Schnittstelle zwischen Software und Hardware bildet die Control-Schicht. In der Instrument-Schicht sind alle Komponenten des Instruments als Software-Dienste abgebildet und erfüllen die jeweils für diese Komponente notwendigen Aufgaben. In der obersten Schicht sind die wesentlichen Manager-Dienste beheimatet. Durch Beobachtungsskripte ist eine automatische Steuerung von Instrument und Teleskop möglich. Weiterhin wurden die stellaren Populationen im Zentrum von vier Galaxien untersucht. Ein Vergleich mit publizierten Werten für ähnliche Galaxien zeigt keinen signifikanten Trend zu jüngeren Populationen in den Galaxien, die einen Pseudo-Bulge zeigen. Eine Galaxie zeigt deutliche Hinweise auf eine sehr alte stellare Population im Buge, deutlich älter als die Populationen von elliptischen Galaxien.
    Description: thesis
    Keywords: 520 ; TCM 000 ; TIE 400 ; Mathematische und EDV-Verfahren {Astronomie} ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 142 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 13
    facet.materialart.
    Unknown
    Univ. Freiburg (Breisgau)
    Publication Date: 2021-03-29
    Description: Observations of the solar corona show loop-like structures formed by plasma at temperatures of one million degrees and higher. Since the solar surface is much cooler than the corona, a heating mechanism must be responsible for the high temperatures. The dissipation of magnetic fields in the corona could provide such a heating mechanism. However, the process of transforming magnetic energy into thermal energy is still not yet understood in detail. To investigate this process and its impact on the heating of the corona, we employ a three-dimensional magneto-hydrodynamical model. This numerical model synthesizes the temporal evolution of the magnetic field above an Active Region. It includes the solar atmosphere from the photosphere up to the corona. The magnetic field in the corona is braided by foot point motions in the photosphere. This is done imilarly to the braiding through granulation in reality. The stressed agnetic field induces currents which are then dissipated in the corona. This dea is known as the DC model (direct current) and was proposed by Parker in 1972. The model reaches a quasi-stationary state, i.e. the energy input by hotospheric motions is counterbalanced by radiative losses in the optically thin corona. As a result, the described heating process creates and sustains a hot corona with a temperature of one million degrees and higher ...
    Description: thesis
    Keywords: 523 ; TGC 765 ; TGC 800 ; Korona {Astronomie: Sonne} ; Magnetfelder {Astronomie: Sonne}
    Language: English
    Type: monograph , publishedVersion
    Format: 108 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 14
    facet.materialart.
    Unknown
    Univ. Potsdam
    Publication Date: 2021-03-29
    Description: Stellar magnetic fields, as a crucial component of star formation and evolution, evade direct observation at least with current and near future instruments. However investigating whether magnetic fields are generated by a dynamo process or represent relics from the formation process, or whether they show a behavior similar to the sun or something very different, it is essential to investigate their structure and temporal evolution. Fortunately nature provides us with the possibility to indirectly observe surface topologies on distant stars by means of Doppler shift and polarization of light, though not without its challenges. Based on the mentioned effects, the so called Zeeman-Doppler Imaging technique is a powerful method to retrieve magnetic fields from rapid rotating stars based on measurements of spectropolarimetric observations in terms of Stokes profiles. In recent years, a large number of stellar magnetic field distributions could be reconstructed by Zeeman-Doppler Imaging (ZDI). However, the implementation of this method often relies on many approximations because, as an inversion method, it entails enormous computational requirements.
    Description: thesis
    Keywords: 523 ; THR 000 ; TEG 000 ; Elektrische und magnetische Felder {Sterne} ; Kosmogonie {Astronomie}
    Language: German
    Type: monograph , publishedVersion
    Format: 107 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 15
    Publication Date: 2021-03-29
    Description: This work focuses on the distribution of atomic hydrogen in the exosphere of Saturns̉ moon Titan. This work is based on measurements performed by the Hydrogen Deuterium Absorption Cell (HDAC) aboard the Cassini spacecraft, that should directly determine the D/H ratio from the UV emission of atomic hydrogen and deuterium at 121.567 and 121.533 nm, respectively. HDAC measurements were performed on December 26, 2005 during the ninth Titan flyby of the Cassini orbiter. Unfortunately the amount of deuterium in the absorption cell could not be determined. Thus, the purpose, HDAC was designed for could not be achieved. For this reason, HDAC has performed measurements only once. However, the amount of atomic hydrogen in the absorption cell is well known, hence the data using only the hydrogen cell can be used in order to investigate Titans̉ exosphere. This work aims at simulating the HDAC measurements performed in order to investigate Titan’s exosphere, e.g. to determine the distribution of atomic hydrogen. A model of Titan’s exosphere including atomic hydrogen and methane has been developed and the transfer of solar radiation is calculated in order to simulate the HDAC measurements. The radiative transfer is solved using the Monte Carlo method. For the exospheric model, two different atomic hydrogen density distributions were applied, which determine the distribution in the exosphere by different approaches. Density profiles calculated by both models mainly differ in the lower exosphere ...
    Description: thesis
    Keywords: 523 ; TGG 655 ; Saturnmonde {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 171 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 16
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 17
    facet.materialart.
    Unknown
    Univ. Zugl.: Braunschweig
    Publication Date: 2021-03-29
    Description: Seit den 60er Jahren des letzten Jahrhunderts ist Mars immer wieder das Ziel von Raumfahrtmissionen gewesen, um unter anderem nach Wasser auf unserem Nachbarplaneten zu suchen. Nachdem die bisher analysierten Oberflächenmerkmale auf ein Vorhandensein von flüssigem Wasser beim Entstehen der Oberfläche deuten, wurde im Juni 2008 von der Sonde Phoenix erstmals Wassereis unter der Oberfläche direkt nachgewiesen. In dieser Arbeit wird untersucht, wieviel Wasser Mars in den vergangenen 4,5 Milliarden Jahren verloren hat und welche Mechanismen dabei eine Rolle gespielt haben. Bei den nichtthermischen Mechanismen hat insbesondere die Umströmung des Sonnenwindplasmas um die Marsatmosphäre mittels seiner elektromagnetischen Felder entscheidenden Einfluß auf den Verlust planetarer Sauerstoff- und Wasserstoffionen. Dieses Wechselwirkungsszenario wurde mit numerischen Plasmasimulationen untersucht. Das verwendete Hybrid-Modell erfasst vollständig die Ionendynamik durch eine kinetische Beschreibung der Ionen. Die Elektronen werden als massenlose Flüssigkeit modeliert. Eine Reihe von Ergebnissen wird vorgestellt: (a) In Übereinstimmung mit dem ASPERA-3 Experiment auf Mars-Express werden zwei Plasmagrenzschichten und zwar der Bow Shock und die "Ion Composition Boundary" identifiziert. (b) Es wird gezeigt, dass beim Vorbeiflug der Raumsonde Rosetta eine Anomalie des Oberflächenmagnetfeldes registriert wurde ...
    Description: thesis
    Keywords: 523 ; TGC 900 ; TGG 565 ; Solar-terrestrische Erscheinungen {Astronomie} ; Marsatmosphäre {Astronomie}
    Language: German
    Type: monograph , publishedVersion
    Format: 193 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 18
    Publication Date: 2021-03-29
    Description: After the epoch of reionisation the intergalactic medium (IGM) is kept at a high photoionisation level by the cosmic UV background radiation field. Primarily composed of the integrated contribution of quasars and young star forming galaxies, its intensity is subject to spatial and temporal fluctuations. In particular in the vicinity of luminous quasars, the UV radiation intensity grows by several orders of magnitude. Due to an enhanced UV radiation up to a few Mpc from the quasar, the ionised hydrogen fraction significantly increases and becomes visible as a reduced level of absorption in the HI Lyman alpha (Ly-alpha) forest. This phenomenon is known as the proximity effect and it is the main focus of this thesis ...
    Description: thesis
    Keywords: 523 ; TBI 000 ; Ultraviolett-Astronomie
    Language: German
    Type: monograph , publishedVersion
    Format: 94 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 19
    Publication Date: 2021-03-29
    Description: Spectro-astrometry is a technique to obtain information about the structure of an astronomical source on sub-diffraction limited spatial scales down to milli- or micro-arcseconds. The method exploits the shift of the photocentre of a structured source over emission/absorption lines in its spectral energy distribution. Sub-diffraction limited resolution can be achieved because the method only uses wavelength-differential information of longslit spectra. Although spectro-astrometry has already been devised by Bailey (1998) and some studies have been performed to date on different astronomic targets, so far, no systematic analysis of the potential of this technique has been undertaken. The aim of this work was to analyse the potential of the method, develop the tools to exploit this potential and write the software which is needed to perform the analysis procedure. To verify the practical feasibility, observations were done with the VLT/CRIRES facility to demonstrate the capabilities of the method with respect to detecting structures on giant star surfaces. All steps of data reduction were analysed with respect to their influence on the spectro-astrometric quantities and a new method for bad pixel detection was devised and implemented ...
    Description: thesis
    Keywords: 523 ; THT 600 ; THK 000 ; THT 400 ; Riesensterne {Astronomie} ; Spektren und Spektroskopie von Sternen {Astronomie} ; Kalte Sterne {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 109 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 20
    Publication Date: 2021-03-29
    Description: The CERN Axion Solar Telescope (CAST) is searching for solar axions, which could be produced in the core of the Sun via the so-called Primakoff effect. For this purpose, CAST uses a decommissioned LHC prototype magnet. In its magnetic field of 9 Tesla axions could be reconverted into X-ray photons. The magnet is mounted on a structure built to follow the Sun during sunrise and sunset for a total of about 3 hours per day. The analysis of the data acquired during the first phase of the experiment with vacuum in the magnetic field region yielded the best experimental upper limit on the axion-to-photon coupling constant for axion masses up to about 0.02 eV. In order to extend the sensitivity of the experiment to a wider mass range, the CAST experiment continued its search for axions with helium in the magnet bores. In this way it is possible to restore coherence for larger masses. Changing the pressure of the helium gas enables the experiment to scan different axion masses. In the first part of this second phase of CAST, helium-4 has been used and the axion mass region was extended up to 0.4 eV ...
    Description: thesis
    Keywords: 523 ; TII 100 ; TCE 380 ; Dunkle Materie {Astronomie: Interstellare Materie} ; CCD, Photodetektoren {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
    Format: 266 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 21
    facet.materialart.
    Unknown
    Univ. Hamburg
    Publication Date: 2021-03-29
    Description: This thesis deals with the high-energy emission from young stellar objects, which are on the one hand still actively accreting from their disk, and on the other hand are no longer deeply obscured by their natal cloud. Stars of spectral type B and A are called Herbig Ae/Be (HAeBe) stars in this stage, all stars of later spectral type are termed classical T Tauri stars (CTTS); strictly speaking both types are defined by spectroscopic signatures, which are equivalent to the evolutionary stage described above. In this thesis CTTS and HAeBes are studied through high-resolution X-ray and UV spectroscopy and through detailed physical simulations. Spectroscopic X-ray data is reduced and presented for two targets: The CTTS V4046 Sgr was observed with Chandra for 100 ks, using a high-resolution grating spectrometer. The lightcurve contains one flare and the He-like triplets of Si XIII, Ne IX and O VII indicate high densities in the X-ray emitting regions. The second target is the HAeBe HD 163296, which was observed with XMM-Newton for 130 ks. The lightcurve shows only moderate variability, the elemental abundance follows a pattern, that is usual for active stars. The He-like triplet of O VII exhibits line ratios similar to coronal sources, indicating that neither a high density nor a strong UV-field is present in the region of the X-ray emission ...
    Description: thesis
    Keywords: 523 ; THP 000 ; Thermodynamische Vorgänge in Sternen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 84 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 22
    Publication Date: 2020-10-05
    Description: Bohrlochgeophysikalische Messungen haben seit Jahrzehnten einen festen Platz in der Hydrogeologie und in jüngster zeit auch in der Umweltgeologie. Die meisten Meßverfahren sind vor ihrer Anwendung in diesen Bereichen für die Zwecke der Erföl- und Erfdgaserschließung entwickelt worden. Die Meßeinrichtungen sind daher im Regelfall auch unter ungünstigen Bedingungen (hohe Drücke und Temperaturen, agressive Medien) einsetzbar und eignen sich auch unter den Bedingungen von Altdeponien und anderen Altlasten... Die vorliegende Schrift soll daher nur einen kurzen Überblick über die technischen Möglichkeiten der Meßverfahren geben. Der Schwerpunkt liegt bei der Erörterung der heute im Bereich Hydro- und Umweltgeologie häufig verwendeten Verfahren und ihrer Eignung in der Bearbeitung ingenieurtechnischer Fragestellungen. Hierbei ist insbesondere zu berücksichtigen, daß Planung, ingenieurtechnische Betreuung und Auswertung dieser Messungen im Regelfall nicht in der Hand von speziell geophysikalisch geschulten Fachleuten liegen, sondern von Geologen und Bauingenieuren ohne besondere Vorkenntnisse. Diesen sollen hiermit Anhaltspunkte für den praktischen Einsatz der gängigen Verfahren gegeben werden, aber auch die Grenzen dessen, was der Laie ohne Hinzuziehung eines Geophysikers veranlassen und aussagen kann, aufgezeigt werden...
    Description: manual
    Keywords: 550.28 ; 622.159 ; 550 ; TQG 000 ; VBQ 100 ; VBS 100 ; Geophysikalische Bohrlochmessung ; Methodik, Untersuchungsverfahren und Instrumente ; Methodik, Untersuchungsverfahren und Instrumente ; Bohrlochmessung ; 38.79 ; 38.03 ; 38.86
    Language: German
    Type: monograph , monograph
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 23
    Publication Date: 2021-03-29
    Description: This thesis discusses dust formation in binary systems, in particular for binary systems consisting of a Mira like star and a brown dwarf. A Mira-like star is an intermediate mass star in a late stage of their stellar evolution on the Asymptotic Giant Branch (AGB), and a brown dwarf, is a sub-stellar object with a mass below that necessary to maintain hydrogen-burning nuclear fusion reactions in their cores. In their radial pulsating elevated convective atmospheres, Mira-stars often develop strong stellar winds, which are driven by radiation pressure on the dust and lead to a substantial mass-loss of the star. Stellar winds are of central importance for the development of medium-heavy-AGB stars. Also, they are a reliable source for the production of dust particles and heavy elements for the interstellar medium and the chemical evolution of galaxies. In fact, most stars are in binary or multiple star systems.For a complete description of the processes of dust formation in binary star systems it is necessary to study the perturbative influence of a second star in the vicinity of a AGB-star with a strong stellar wind. This endeavour is embedded in a long standing tradition of scientific investigation of dust formation at the Zentrum für Astronomie und Astrophysik (ZAA) at the Technical University of Berlin...
    Description: thesis
    Keywords: 523 ; THT 900 ; TII 900 ; Doppelsterne {Astronomie} ; Interstellarer Staub {Astronomie: Interstellare Materie}
    Language: English
    Type: monograph , publishedVersion
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 24
    Publication Date: 2021-03-29
    Description: Many stars evolve not alone but along one or more companions. While the evolution of single isolated stars is well predicted by theoretical calculations, close binary systems with their interactions are on the one hand far more difficult to handle, but on the other hand well constrained in their masses and sizes. One mechanism thought to produce such close binaries is the Common Envelope Evolution (CEE). Especially young post CEE binaries show great temperature differences between both components of about a factor 10 at a separation of just a few solar radii. This work focuses on close binary systems with a hot primary component (e.g. a subdwarf O-type star (sdO)) and a much cooler secondary component (e.g. a main-sequence star), which is heavily influenced by external radiation originating from the first. The technique to include external radiation into the stellar atmosphere code PHOENIX, i.e., the deviation of the outer boundary condition and the change in the temperature correction method, is described in detail. To concentrate on the irradiation effect, other difficulties such as asymmetric effects due to tear-drop shaped stars, ongoing mass accretion or shadows of a circumbinary disc, are avoided by selecting pre-cataclysmic variables (pre CVs) out of the class of close binaries as laboratory. The total eclipsing binary system UU~Sagittae is used as an example for massive irradiation and observed spectral features in the optical are fitted ...
    Description: thesis
    Keywords: 523 ; THK 000 ; THT 900 ; Spektren und Spektroskopie von Sternen {Astronomie} ; Doppelsterne {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 100 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 25
    Publication Date: 2021-03-29
    Description: The first extrasolar planet 51 Peg b around the G-type star has been reported in 1995. The planet with few Jupiter masses orbiting its star very closely was detected by measurement of the oscillation in the radial velocity of the host star. In 1999 the first transit, when the planet is eclipsing the host star, of the extrasolar planet HD209458 b was observed with a small ground based photometric telescope. Ever since, new planets in distant systems are continuously being detected with new high precision instruments from the ground and from space. The department of Extrasolar Planets and Atmospheres at Deutsches Zentrum für Luft- und Raumfahrt, Berlin (DLR) is involved in the detection and characterization of extrasolar planets, through participation in the CoRoT space mission. Furthermore, two ground based photometric telescope systems are operated as a ground based support for the space mission CoRoT, dedicated to asteroseismology and to extrasolar planet search with the help of the transit method. The BEST project consists of two small aperture wide field-of-view photometric telescopes devoted to the search for transiting Jupiter-sized extrasolar planets and to the characterization of variable stars in CoRoT target fields...
    Description: thesis
    Keywords: 523 ; THX 100 ; TJ 900 ; TCE 220 ; Detektionsmethoden {Astronomie: Extrasolare Planetensysteme} ; Einzelne Weltraumprojekte ; Bodenständige UV-, Optische und Infrarotteleskope {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 26
    Publication Date: 2021-03-29
    Description: Neutron stars are very dense objects. One teaspoon of their material would have a mass of five billion tons. Their gravitational force is so strong that if an object were to fall from just one meter high it would hit the surface of the respective neutron star at two thousand kilometers per second. In such dense bodies, different particles from the ones present in atomic nuclei, the nucleons, can exist. These particles can be hyperons, that contain non-zero strangeness, or broader resonances. There can also be different states of matter inside neutron stars, such as meson condensates and if the density is height enough to deconfine the nucleons, quark matter. As new degrees of freedom appear in the system, different aspects of matter have to be taken into account.The most important of them being the restoration of the chiral symmetry. This symmetry is spontaneously broken, which is a fact related to the presence of a condensate of scalar quark-antiquark pairs, that for this reason is called chiral condensate. This condensate is present at low densities and even in vacuum. It is important to remember at this point that the modern concept of vacuum is far away from emptiness. It is full of virtual particles that are constantly created and annihilated, being their existence allowed by the uncertainty principle. At very high temperature/density, when the composite particles are dissolved into constituents, the chiral consensate vanishes and the chiral symmetry is restored. To explain how and when chiral symmetry is restored in neutron stars we use a model called non-linear sigma model. This is an effective quantum relativistic model that was developed in order to describe systems of hadrons interacting via meson exchange ...
    Description: thesis
    Keywords: 523 ; THU 400 ; Pulsare, Neutronensterne {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 104 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 27
    Publication Date: 2021-03-29
    Description: Supernovae are known to be the dominant energy source for driving turbulence in the interstellar medium. Yet, their effect on magnetic field amplification in spiral galaxies is still poorly understood. Analytical models based on the uncorrelated-ensemble approach predicted that any created field will be expelled from the disk before a significant amplification can occur. By means of direct simulations of supernova-driven turbulence, we demonstrate that this is not the case. Accounting for vertical stratification and galactic differential rotation, we find an exponential amplification of the mean field on timescales of 100Myr. The self-consistent numerical verification of such a fast dynamo is highly beneficial in explaining the observed strong magnetic fields in young galaxies. We, furthermore, highlight the importance of rotation in the generation of helicity by showing that a similar mechanism based on Cartesian shear does not lead to a sustained amplification of the mean magnetic field. This finding impressively confirms the classical picture of a dynamo based on cyclonic turbulence ...
    Description: thesis
    Keywords: 523 ; THR 000 ; THU 162 ; Elektrische und magnetische Felder {Sterne} ; Supernovae {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 109 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 28
    Publication Date: 2021-03-29
    Description: This thesis deals with the analysis of presolar silicates and oxides by high resolution mass spectrometry and electron microscopy techniques. This stardust was identified by its extreme oxygen isotopic anomalies, which point to nucleosynthetic reactions in stellar interiors, in the carbonaceous chondrite Acfer 094. Isotopic, chemical and mineralogical studies on these stardust grains therefore allow the testing of astrophysical questions on Earth, which are otherwise only accessible by spectroscopy and theoretical models. The class of presolar silicates has been identified only six years ago in 2002, although it was known already from spectroscopic observations that silicates represent the most abundant type of dust in the galaxy. The development of the NanoSIMS was a crucial step in this respect, because this ion probe with its superior spatial resolution of only 50 nm allowed the detection of the typically 300 nm sized presolar silicates. A total of 142 presolar silicates and 20 presolar oxides were identified within Acfer 094, whose matrix therefore contains 163 ± 14 ppm presolar silicates and 26 ± 6 ppm presolar oxides. This is among the highest amounts reported so far for any primitive solar system material. The majority of detected stardust grains derive from asymptotic giant branch stars of 1 2.5 Msun and close-to-solar or slightly lower-than-solar metallicity. However, by measuring the Si isotopic compositions of some enigmatic grains, it could be shown that there is a sub-class of presolar silicates characterized by an extreme enrichment of 17O and a moderate enhancement of 30Si relative to solar, whose origins might be explained by formation in binary stellar systems ...
    Description: thesis
    Keywords: 523 ; TJM 000 ; TII 900 ; THQ 000 ; Kosmochemie {Weltraumforschung} ; Interstellarer Staub {Astronomie: Interstellare Materie} ; Kernreaktionen in Sternen; Astrochemie {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 142 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 29
    facet.materialart.
    Unknown
    Univ. Bochum
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 523 ; TEG 000 ; THT 800 ; Kosmogonie {Astronomie} ; Massenreiche Sterne {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 131 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 30
    facet.materialart.
    Unknown
    Univ. Köln
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 31
    facet.materialart.
    Unknown
    Univ. Freiburg (Breisgau)
    Publication Date: 2021-03-29
    Description: The solar surface outside sunspots and active regions, i.e., the quiet Sun, shows the ubiquitous pattern of granulation in the photosphere. The quiet solar photosphere harbors small-scale magnetic structures inside and between granules. This thesis presents thermodynamic properties of the small-scale magnetic flux concentrations in the quiet Sun using high spatial and temporal resolution observations along with numerical simulations. Spectral line profiles of the Fe I 630 nm pair and Ca II H were used to trace the photospheric and chromospheric layers of the magnetic elements. In the presence of magnetic field spectral lines split and are polarized via the Zeeman effect. The difference of a spectral line profile, measured in left and right circular polarized light, is a Stokes-V profile with two lobes. In the absence of any gradients of velocity or magnetic field along the line of sight, Stokes-V profiles are anti-symmetric. The different area of the two lobes, the Stokes-V area asymmetry, provides information about the gradients of the magnetic and velocity fields along the line of sight. Comparing high resolution spectropolarimetric data with synthetic maps of a 3D MHD simulation, we found several magnetic elements in the photosphere showing a central region of negative Stokes-V area asymmetry surrounded by a peripheral region with larger positive asymmetry ...
    Description: thesis
    Keywords: 523 ; TGC 745 ; TGC 755 ; TGC 800 ; Photosphäre {Astronomie: Sonne} ; Chromosphäre {Astronomie: Sonne} ; Magnetfelder {Astronomie: Sonne}
    Language: English
    Type: monograph , publishedVersion
    Format: 146 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 32
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 523 ; TCE 500 ; TFE 000 ; TVM 610 ; TVB 420 ; Sonstige Instrumente {Astronomische Instrumente} ; Kosmische Elektrodynamik {Astrophysik} ; Luftelektrische Beobachtungs- und Meßverfahren {Meteorologie} ; Aeronomie {Meteorologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 165 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 33
    Publication Date: 2021-03-29
    Description: The Sun is a star, which due to its proximity has a tremendous influence on Earth. Since its very first days mankind tried to "understand the Sun", and especially in the 20th century science has uncovered many of the Sun's secrets by using high resolution observations and describing the Sun by means of models. As an active star the Sun's activity, as expressed in its magnetic cycle, is closely related to the sunspot numbers. Flares play a special role, because they release large energies on very short time scales. They are correlated with enhanced electromagnetic emissions all over the spectrum. Furthermore, flares are sources of energetic particles. Hard X-ray observations (e.g., by NASA's RHESSI spacecraft) reveal that a large fraction of the energy released during a flare is transferred into the kinetic energy of electrons. However the mechanism that accelerates a large number of electrons to high energies (beyond 20 keV) within fractions of a second is not understood yet.
    Description: thesis
    Keywords: 523 ; TGC 560 ; TGC 440 ; Eruptionen, Flares {Astronomie: Sonne} ; Korpuskelstrahlung {Sonne}
    Language: English
    Type: monograph , publishedVersion
    Format: 122 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 34
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 523 ; TCE 320 ; Photometer, Polarimeter, spektroskopische Instrumente {Astronomische Instrumente}
    Language: German
    Type: monograph , publishedVersion
    Format: 79 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 35
    Publication Date: 2021-03-29
    Description: We investigate the double-peak profile of the emission of powerful cosmic non-thermal radiation sources with dominant magnetic field self-generation like TeV blazars. Therefore, we assume a flare to occur in the emission knot due to the uniform instantaneous injection of monoenergetic ultra-relativistic electrons via a relativistic pick-up process. The electrons are subjected to a linear or nonlinear synchrotron radiation cooling and the synchrotron photons are multiple Thomson scattered off their generating electrons (SSC process). We work out the differences between single and multiple instantaneous injections of monoenergetic relativistic electrons. This is of great interest, because it is very likely that injections into the plasmoids occur repeatedly, so that this would explain the short-time energy variability of blazars. We also compute for the first time the nonlinear SSC radiation quantities using a Thomson limit approximation and the full Klein-Nishina cross section.
    Description: thesis
    Keywords: 523 ; TIE 900 ; Sonstige Sternensysteme {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 84 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 36
    Publication Date: 2021-03-29
    Description: Das Antarctic Muon And Neutrino Detector Array (AMANDA) ist ein Cherenkov Detektor, der sich im Gletscher der Antarktis am Südpol befindet. Wir präsentieren die Analyse von Daten, die in den Jahren 2000 bis 2004 gesammelt wurden, die einer effektiven Detektorlaufzeit von 1001 Tagen entsprechen. Die Suche zielt auf den Nachweis von elektomagnetische und hadronische Teilchenschauern, so gennante Kaskaden, die durch Elektron- und Tauneutrinowechselwirkung produziert werden können. Die hadronischen Kaskaden können auch über neutrale Ströme Wechselwirkung von Neutrinos aller Arten produziert werden. Der Kaskadenkanal hat einige Vorteile in der Suche nach einem diffusen Fluss von astrophysikalischen Neutrinos. Durch die gute Energieauflösung des AMANDA Detektors kann man zwischen einem harten astrophysikalische Spektrum und einem weichen atmosphärischen Spektrum unterscheiden. Außerdem ist der atmosphärischen Elektronneutrinos Fluss um eine Gößenordnung kleiner als der atmosphärische Myonneutrinofluss. Der Untergrund von atmosphärischem Myonen aus Luftschauern kann unterdrückt werden, weil diese als Spuren im Detektor erscheinen und leicht zu identifizieren sind...
    Description: thesis
    Keywords: 539.7215 ; 523 ; 550 ; TBN 000 ; TCE 500 ; Neutrino-Astronomie ; Sonstige Instrumente {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 37
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 38
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 39
    Publication Date: 2021-03-29
    Description: This dissertation presents a comprehensive description of the stability of asteroid orbits in the Edgeworth-Kuiper belt taking the 3:5, 4:7 and 1:2 mean motion resonance with Neptune as example. Further emphasis is given to the numerical computability of the Lyapunov time of asteroids. Starting with a general description of rounding and approximation errors in numerical computations, the growth of these errors within numerical integrations is estimated. These, partly machine-dependent errors influence the calculated trajectory of the asteroid as well as the derived Lyapunov time. Different hardware architectures and integration methods were used to investigate the influence on the computed Lyapunov time. As a measure of this dependence a computability index ê is defined. Furthermore it is shown, that the general structure of phase space is robust against these changes...
    Description: thesis
    Keywords: 523.44 ; 550 ; TDG 400 ; TGG 900 ; Bahnbestimmung von Himmelskörpern {Astronomie: Himmelsmechanik} ; Planetoide {Astronomie}
    Language: German
    Type: monograph , publishedVersion
    Format: 121 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 40
    facet.materialart.
    Unknown
    Univ. Braunschweig
    Publication Date: 2021-03-29
    Description: The thesis deals with the investigation of the plasma environment of Venus using data of the ASPERA-4 (Analyzer of Space Plasmas and Energetic Atoms) experiment onboard the Venus Express (VEX) spacecraft as well as a 3D hybrid code in order to study the solar wind - atmosphere interaction of an unmagnetized planet. (1) Data Analysis: By using data from the ion and electron spectrometers, the shapes and average locations of the plasma boundaries (bow shock, upper and lower boundary of the mantle region) around the planet are determined. Additionally, the variation of the terminator bow shock position is analyzed as a function of the solar wind dynamic pressure and solar EUV flux. It is demonstrated that the shock location is insensitive to the upstream ram pressure and that the changes in the solar EUV radiation are too small over the period of the VEX observations to analyze solar activity dependence.
    Description: thesis
    Keywords: 523 ; TGE 585 ; TGG 220 ; Magnetosphären, Magnetismus, Ionosphären {Astronomie} ; Atmosphäre {Astronomie: Venus}
    Language: English
    Type: monograph , publishedVersion
    Format: 126 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 41
    facet.materialart.
    Unknown
    Univ. Köln
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 42
    facet.materialart.
    Unknown
    Univ. Bochum
    Publication Date: 2021-03-29
    Description: This work deals with the search for substructures in four nearby galaxies (NGC 300, NGC 7793, M 33, M 83) in which it is possible to resolve single stars in their outer parts.The search is based on the photometry of wide field imaging data. This photometry is further analysed by the use of classical methods (colour-magnitude-diagrams, star counts) and by the use of data-mining tools (fuzzy c-means clustering). Finally, it could be shown that three out of four galaxies show signs of substructure. In NGC 300 the analysis of the red-giant-branch stars revealed a truncation in the outer parts, while in NGC 7793 hints for a tidal stream or spiral arm were found. In case of M 83 it was possible to recover an already known surface brightness arc first seen on old photographic plates.
    Description: thesis
    Keywords: 523 ; TIE 400 ; TIE 500 ; Spektren und Leuchtkraft von Sternsystemen {Astronomie} ; Aufbau und Struktur von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 151 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 43
    Publication Date: 2021-03-29
    Description: Die Arbeit beschreibt die Analyse von Beobachtungen zweier Sonnenflecken in zweidimensionaler Spektro-Polarimetrie. Die Daten wurden mit dem Fabry-Pérot-Interferometer der Universität Göttingen am Vakuum-Turm-Teleskop auf Teneriffa erfasst. Von der aktiven Region NOAA 9516 wurde der volle Stokes-Vektor des polarisierten Lichts in der Absorptionslinie bei 630,249 nm in Einzelaufnahmen beobachtet, und von der aktiven Region NOAA 9036 wurde bei 617,3 nm Wellenlänge eine 90-minütige Zeitserie des zirkular polarisierten Lichts aufgezeichnet. Aus den reduzierten Daten werden Ergebniswerte für Intensität, Geschwindigkeit in Beobachtungsrichtung, magnetische Feldstärke sowie verschiedene weitere Plasmaparameter abgeleitet. Mehrere Ansätze zur Inversion solarer Modellatmosphären werden angewendet und verglichen. Die teilweise erheblichen Fehlereinflüsse werden ausführlich diskutiert. Das Frequenzverhalten der Ergebnisse und Abhängigkeiten nach Ort und Zeit werden mit Hilfe der Fourier- und Wavelet-Transformation weiter analysiert.
    Description: thesis
    Keywords: 523 ; TGC 520 ; TGC 100 ; Sonnenflecken {Astronomie} ; Sonnenbeobachtung {Astronomie}
    Language: German
    Type: monograph , publishedVersion
    Format: 117 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 44
    facet.materialart.
    Unknown
    Univ. Bielefeld
    Publication Date: 2021-03-29
    Description: Despite the glorious successes of modern cosmology, our understanding of the cosmic substitution is still limited to a tiny fraction (a few per cents only). Accelerated expansion of the Universe, caused by the mysterious dark energy is currently the most severe crisis in cosmology, even in physics. In this dissertation, we argue that light may be shed on this crisis by means of the cosmological backreaction mechanism in the averaging problem in inhomogeneous and anisotropic space-time. Due to the non-commutation of temporal evolution and spatial averaging, the averaged Einstein tensor as the function of the perturbed metric is not trivially equal to the Einstein tensor of the averaged metric. Consequently, inhomogeneities and anisotropies (cosmic structures) influence the evolution of the background Universe. In order to obtain the quantitative information of this mechanism, we combine Buchert's non-perturbative framework with cosmological perturbation theory, calculate the relevant averaged physical observables up to third order in the comoving synchronous gauge (both temporal and spatial dependence) and discuss their gauge dependence. With the help of an integrability condition, the leading higher order contributions follow from the lower order calculations. We demonstrate that the leading contributions to all the averaged physical observables under consideration are specified completely on the boundary of the averaged domain. For any finite domain, these surface terms are nonzero in general, and thus backreaction is for real.
    Description: thesis
    Keywords: 523 ; TEC 000 ; Kosmologie {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 130 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 45
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 46
    facet.materialart.
    Unknown
    Univ. Dortmund
    Publication Date: 2021-03-29
    Description: The presented thesis describes an unfolding method whose principle is to determine the probability that a certain set of events has a certain range of energy. Unfolding methods are not related to the analyzed data and one is interested in the extent to which the unfolding solution encapsulates the unfolding variables in the data. For this purpose, new factors have been defined. These factors enable the use of the unfolding methods for obtaining information about the unfolding variables in the data, independent of the unfolding solutions. Amongst others, this information determines whether the unfolding variables exist in the data after applying standard (analysis) cuts or additional ones. This opens the way to study the effects of different cuts on the data and how they will change the content of the unfolding variables in the data. Additionally, the unfolding method is applied to three special AGN: Markarian 421, Markarian 501 and PKS 2155304. The obtained spectra follow the results of already established methods, and in most of the cases (Markarian 501 and PKS 2155304) the spectra could be extended to higher and/or lower energies.
    Description: thesis
    Keywords: 523 ; TCM 000 ; TIE 900 ; Mathematische und EDV-Verfahren {Astronomie} ; Sonstige Sternensysteme {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 120 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 47
    facet.materialart.
    Unknown
    Univ. Berlin
    Publication Date: 2021-03-29
    Description: Magnetic cataclysmic variables, also called AM Her stars or 'polars', are close binaries with mass transfer (accretion), consisting of a late-type main-sequence star (commonly called secondary)and a more massive white dwarf with a strong magnetic field. The late-type star is losing mass to the white dwarf. The overflowing matter firstly follows a ballistic trajectory and is then captured by the magnetic field of the white dwarf and guided along the field lines onto the white dwarf. The released gravitational energy is radiated away in all wavelength ranges from infra-red to X-ray. The observed light of an AM Her system is composed of the contributions from the stellar components and the contributions of the accretion column and the accretion region on the white dwarf. The last two components are not only depending on the actual mass transfer rate but also from the spatial orientation of the magnetic field. Since the white dwarf is locked in synchronous rotation, this leads to emission that varies with orbital phase. The decomposition of the observed light from an AM Her system makes it possible to analyse the different components within this system...
    Description: thesis
    Keywords: 523 ; THK 000 ; Spektren und Spektroskopie von Sternen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 140 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 48
    Publication Date: 2021-03-29
    Description: Photogrammetrie, Mars Express, digitale Bildzuordnung
    Description: thesis
    Keywords: 523 ; TGG 515 ; TGE 100 ; Marsbeobachtung, Raumflüge zum Mars {Astronomie} ; Planetenbeobachtung {Astronomie}
    Language: German
    Type: monograph , publishedVersion
    Format: 137 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 49
    Publication Date: 2021-03-29
    Description: Die vorliegende Dissertation untersucht, ob heiße und expandierende Gasstrukturen gravitativ an ihre Galaxie gebunden sind (Ausfluss) oder ob sie das Gravitationspotential der Galaxie verlassen können (galaktischer Wind). Galaktische Winde, d.h. Massenverlust für die Galaxie und Anreicherung des intergalaktischen Mediums haben direkte Auswirkungen auf die Entwicklung von Galaxien und Galaxienhaufen. Spektroskopische Untersuchungen des neutralen und ionisierten Wasserstoffs wurden in einer Auswahl von vier nahen irregulären Zwerggalaxien durchgeführt. In allen vier Galaxien wurden expandierende Gasstrukturen gefunden und ihre Expansionsgeschwindigkeiten vermessen. Aus Dunkle Materie Halo Modellen wurde das Gravitationspotential der Galaxien abgeschätzt. Dadurch konnte gezeigt werden, dass das Gas in allen Fällen gravitativ gebunden bleibt. Dieses Ergebnis ist in Übereinstimmung mit hydrodynamischen Simulationen und legt nahe, dass galaktische Winde in masseärmeren Galaxien zu finden sind.
    Description: thesis
    Keywords: 523 ; TII 500 ; Emissionsnebel {Astronomie: Interstellare Materie}
    Language: English
    Type: monograph , publishedVersion
    Format: 136 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 50
    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
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 51
    facet.materialart.
    Unknown
    Univ. Bayreuth
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 523 ; THE 000 ; Bewegung von Sternen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 85 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 52
    Publication Date: 2021-03-29
    Description: Beim Ras-RasGAP-Komplex ist die Hydrolyse des Guanosintriphosphats stark beschleunigt im Vergleich zu Ras allein. Dies wird hauptsächlich durch den Argininfinger R789 verursacht, der direkt zur Triphosphatgruppe zeigt. QM/MM-Simulationen wurden durchgeführt, bei denen das Triphosphat quantenmechanisch mithilfe der DFT behandelt wurde, während der Proteinkomplex und die Wasserumgebung klassisch beschrieben wurden. Im Vergleich zu Ras sind beim Ras-RasGAP-Komplex die entscheidende Elektronenverschiebung, die Bindungsverlängerung und die Verdrillung hin zu einer ekliptischen gamma-beta-Orientierung wesentlich stärker ausgeprägt. Der Argininfinger interagiert durch Verdrängung von Wassermolekülen aus der Bindenische. Das resultierende verstärkte elektrische Feld katalysiert den Bindungsbruch. Eine hypothetische Protonierung des beta-Phosphats führt zum Bindungsbruch. Nach Abschluss der Hydrolyse sind die Schwingungen des Mono- und Diphosphats über Dipol-Dipol-Wechselwirkung gekoppelt.
    Description: thesis
    Keywords: 523 ; TIE 400 ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 149 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 53
    Publication Date: 2021-03-29
    Description: The term "stellar activity" summarizes a number of phenomena on the stellar surface and in the stellar atmosphere. The origin of many of these phenomena are changes in the structure of the stellar magnetic field. While it is possible to directly observe different forms of activity on the Sun in great detail, this remains impossible for other stars. However, by analyzing the spectra of these stars, information about their activity can be obtained. This thesis addresses two aspects of activity: First, the X-ray emission from the positions of A-type stars and a possible mechanism to produce these X-rays and second, the chromospheric activity in the spectral range from late A- to late K-type stars. Since the dynamo, which is responsible for the activity of solar-like stars, emerges in the range of late A- to early F-type stars, this spectral range is of special interest for the understanding of the activity phenomena. To study the X-ray activity of A-type stars, their optical positions as given in the Bright Star Catalogue were compared with the positions of the X-ray sources listed in the ROSAT catalogs. The matching criteria for the ROSAT All-Sky Survey data were 90 arcseconds, 36 arcseconds for the pointing observations with the PSPC and 18 arcseconds for HRI data. Those stars which could be associated with X-ray sources were tested for indications of hidden late-type companions. Variations in the radial velocity, the proper motion, and the light curve were interpreted as signs for binarity...
    Description: thesis
    Keywords: 523 ; THP 000 ; THN 400 ; Thermodynamische Vorgänge in Sternen {Astronomie} ; Sternatmosphären {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 54
    Publication Date: 2021-03-29
    Description: Die Natur der dunklen Materie ist nach wie vor ungeklart und stellt eine der fundamentalsten Fragen der aktuellen Kosmologie dar. In vielen verschiedenen Experimenten wird versucht, diese Teilchen, die sogenannten WIMPs (aus dem Englischen: Weakly Interacting Massive Particles), nachzuweisen. In einigen Modellen der dunklen Materie wird vorhergesagt, dass sehr hochenergetische -Strahlung durch Annihilation der WIMPs in konzentrierten Ansammlungen dunkler Materie produziert wird. Im Rahmen der vorliegenden Arbeit wurden anhand von Beobachtungen im Energiebereich von 100 GeV bis 100 TeV mit dem System abbildender Cherenkov-Teleskope des H.E.S.S.-Experiments (aus dem Englischen: High Energy Stereoscopic System) verschiedene Objekte untersucht, ob die gemessene Strahlung ihren Ursprung in der Annihilation von Teilchen dunkler Materie haben konnte. Das Zentrum unserer Galaxie ist ein in der Literatur viel diskutierter Bereich, in dem sehr hochenergetische -Strahlung aus Annihilation dunkler Materie entstehen konnte. Es wurde mit H.E.S.S. sehr hochenergetische -Strahlung aus dieser Richtung nachgewiesen. Es wird aber gezeigt, dass die gemessene Strahlung aus der Richtung des galaktischen Zentrums nicht ausschlie lich von dunkler Materie erzeugt wird. Daher wurde zusatzlich untersucht, welche Aussagen mit der Hypothese getro en werden konnen, dass nur ein Anteil aus dieser Strahlung besteht. Es konnten interessante Einschrankungen auf das Dichtepro l der hypothetischen DM-Ansammlung gewonnen werden; ein Dichtepro l nach Moore kann fur viele Parametersatze der untersuchten Modelle ausgeschlossen werden. Auf den Wirkungsquerschnitt der Annihilation kann keine relevante Einschrankung erzielt werden..
    Description: thesis
    Keywords: 523 ; 550 ; TII 100 ; TIE 650 ; Dunkle Materie {Astronomie: Interstellare Materie} ; Milchstrasse {Astronomie}
    Language: German
    Type: monograph , publishedVersion
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 55
    facet.materialart.
    Unknown
    Univ. Bochum
    Publication Date: 2021-03-29
    Description: Diese Dissertation untersucht, ob die Dynamik von Galaxien in Einklang mit den Ergebnissen aus CDM (cold dark matter) Simulationen ist. Im Wesentlichen wurden 19 Galaxien hinsichtlich Abweichungen von kreisförmigen Bewegungen analysiert. Diese nicht-kreisförmigen Bewegungen werden von den Simulationen vorhergesagt, um das lang bestehende cusp/core Problem zu erklären. Es konnte jedoch gezeigt werden, dass die Abweichungen von den kreisförmigen Bewegungen zu klein sind, um die Ergebnisse von CDM Simulationen mit den Beobachtungen in Einklang zu bringen. Große nicht-kreisförmige Bewegungen finden sich vor allem in den Zentren von massereichen Galaxien und Balkengalaxien. Dies lässt jedoch vermuten, dass diese Bewegungen durch baryonische Materie hervorgerufen werden und nicht durch den DM Halo. Die vorliegende Dissertation unterstreicht die Notwendigkeit, die CDM Simulationen zu verändern, bzw. alternative Lösungen zu CDM Modellen zu suchen.
    Description: thesis
    Keywords: 523 ; TII 100 ; Dunkle Materie {Astronomie: Interstellare Materie}
    Language: English
    Type: monograph , publishedVersion
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 56
    facet.materialart.
    Unknown
    Univ. Potsdam
    Publication Date: 2021-03-29
    Description: The intergalactic medium is kept highly photoionised by the intergalactic UV background radiation field generated by the overall population of quasars and galaxies. In the vicinity of sources of UV photons, such as luminous high-redshift quasars, the UV radiation field is enhanced due to the local source contribution. The higher degree of ionisation is visible as a reduced line density or generally as a decreased level of absorption in the Lyman alpha forest of neutral hydrogen. This so-called proximity effect has been detected with high statistical significance towards luminous quasars. If quasars radiate rather isotropically, background quasar sightlines located near foreground quasars should show a region of decreased Lyman alpha absorption close to the foreground quasar. Despite considerable effort, such a transverse proximity effect has only been detected in a few cases...
    Description: thesis
    Keywords: 523 ; 550 ; TIE 400 ; TIE 900 ; Sonstige Sternensysteme {Astronomie} ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 144 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 57
    facet.materialart.
    Unknown
    Publication Date: 2021-03-29
    Description: In this thesis we investigate the existence and properties of stationary solutions of the flat Vlasov-Poisson system. This system of partial differential equations can be used as a model of extremely flat astronomical objects and is a combination between the two-dimensional motion of particles and the three-dimensional interaction through their gravitational potential.
    Description: thesis
    Keywords: 523 ; TII 100 ; TIE 500 ; Dunkle Materie {Astronomie: Interstellare Materie} ; Aufbau und Struktur von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 58
    Publication Date: 2021-03-29
    Description: In this work, nonanalytical line profiles for both cool and hot, dense atmospheres are added to the opacity calculations of the multipurpose stellar atmosphere code PHOENIX. Their influence on model atmospheres and synthetic spectra is studied. Model atmospheres are necessary in order to calculate synthetic spectra and to derive reliable stellar parameters. For cool, dense atmospheres, i.e., of objects of spectral type similar to and lower than latetype M, vanderWaals broadening is the most important pressure broadening mechanism. The spectra of these objects below ~1 micro-meter are dominated by alkali resonance lines. The profiles of the alkali resonance lines, especially of Na ID and KI, determine mostly the pseudo continuum in this wavelength range. Up to this work, classical analytical impact approximated alkali near line wing profiles perturbed by H2, He, and HI, which are the dominant perturbing particles, have been applied. In this work, various nonanalytical alkali line profiles, including far line wing and near line wing profiles, for Na I D, Li I, KI, and Rb I are included in order to describe the strong alkali absorption features which are characteristic for latetype dwarfs. For the alkali resonance line profiles, different theoretical approaches were used describing the far and near line wings. Non analytical alkali profiles for the far and near line wings perturbed by H2 and He are provided in the unified semiclassical theory...
    Description: thesis
    Keywords: 523 ; 550 ; THN 400 ; THK 000 ; Sternatmosphären {Astronomie} ; Spektren und Spektroskopie von Sternen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 156 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 59
    Publication Date: 2021-03-29
    Description: Giacconi et al. (1962) discovered a diffuse cosmic X-ray background with rocket experiments when they searched for lunar X-ray emission. Later satellite missions found a spectral peak in the cosmic X-ray background at ~30 keV. Imaging X-ray satellites such as ROSAT (1990-1999) were able to resolve up to 80% of the background below 2 keV into single point sources, mainly active galaxies. The cosmic X-ray background is the integration of all accreting super-massive (several million solar masses) black holes in the centre of active galaxies over cosmic time. Synthesis models need further populations of X-ray absorbed active galaxy nuclei (AGN) in order to explain the cosmic X-ray background peak at ~30 keV. Current X-ray missions such as XMM-Newton and Chandra offer the possibility of studying these additional populations...
    Description: thesis
    Keywords: 523 ; 550 ; TBK 000 ; TIE 900 ; Hochenergieastronomie ; Sonstige Sternensysteme {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 226 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 60
    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
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 61
    facet.materialart.
    Unknown
    Univ. Köln
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 62
    Publication Date: 2021-03-29
    Description: This thesis describes two main projects; the first one is the optimization of a hierarchical search strategy to search for unknown pulsars. This project is divided into two parts; the first part (and the main part) is the semi-coherent hierarchical optimization strategy. The second part is a coherent hierarchical optimization strategy which can be used in a project like Einstein@Home. In both strategies we have found that the 3-stages search is the optimum strategy to search for unknown pulsars. For the second project we have developed a computer software for a coherent Multi-IFO (Interferometer Observatory) search. To validate our software, we have worked on simulated data as well as hardware injected signals of pulsars in the fourth LIGO science run (S4). While with the current sensitivity of our detectors we do not expect to detect any true Gravitational Wave signals in our data, we can still set upper limits on the strength of the gravitational waves signals...
    Description: thesis
    Keywords: 523 ; 550 ; TFA 000 ; Relativistische Astrophysik, Gravitation
    Language: English
    Type: monograph , publishedVersion
    Format: 135 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 63
    Publication Date: 2021-03-29
    Description: The interpretation of thermal neutron star spectra requires extensive data sets of atomic dipole transitions in intensive magnetic fields. For this purpose, the new HFFER method for the fast computation of wave functions, energies, and oscillator strengths of medium-Z atoms and ions at neutron star magnetic field strengths B〉10^7 T is developed in this thesis. The coupled system of Hartree-Fock equations is solved self-consistently with longitudinal wave functions and transversal amplitudes of Landau states up to n=7. In the presented ab-initio procedure the transversal Landau amplitudes are computed by solving the Hartree-Fock-Roothaan equations for each electron. The longitudinal wave functions result from the system of one-dimensional Hartree-Fock equations, which are solved by the finite element method in an apropriate B-spline basis. All algorithms can be implemented in an highly efficient parallel way on a computer cluster. Typically an iron ground state with N=26 electrons is computed on p=N=26 cluster processors using less than 500 seconds of run-time. Numerical calculations are presented for ground states, and different excited states of atoms and ions for nuclear charges Z=2,...,26 and N=2,...,26 electrons. If possible, the new results are compared with previous adiabatic calculations on the one hand, and recent quantum Monte Carlo simulations on the other.
    Description: thesis
    Keywords: 520 ; 550 ; TFG 000 ; Magnetohydrodynamik und Plasma-Astrophysik
    Language: German
    Type: monograph , publishedVersion
    Format: 163 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 64
    facet.materialart.
    Unknown
    Univ. Berlin
    Publication Date: 2021-03-29
    Description: This work covers the dominant aspects of landforms and processes related to the cold-climate (periglacial) and hyperarid environment of Mars and relates the knowledge obtained from terrestrial research to possible Martian analogue landforms. Among the plethora of landforms related to cold-climate environments and subsurface permafrost on Mars, those features have been investigated in detail that are related to the creep of ice and debris at the Martian dichotomy escarpment and the southern-hemispheric impact basins, especially Hellas Planitia, and which have been described controversially as either glacial or periglacial in nature. Structures related to seasonal freeze-thaw cycles on Mars which are generally known as thermal contraction polygons form a second major focus of this work. Research presented on this topic focuses on the northern hemispheric Utopia Planitia area and the south-polar cap of Mars. This work was carried out on the basis of observational and geomorphometrical analyses by utilizing imaging-sensor and topographic data in order to address questions regarding the history, development, and current state of cold-climate landforms on Mars. This work provides new insights with respect to age, composition, source of debris and ice, and the deformational and degradational history of lobate debris aprons and similar landforms. It is shown that processes which led to creep of debris and ice at the northern hemispheric dichotomy boundary are transitional in nature and are not easily categorized using standard definitions commonly used in terrestrial research...
    Description: thesis
    Keywords: 523 ; 550 ; V 600 ; VAR 800 ; TGG 545 ; Grenzgebiete. Beziehungen. Wirkungen. Einflüsse {Geologische Wissenschaften} ; Periglazialerscheinungen ; Marsoberfläche {Astronomie}
    Language: German
    Type: monograph , publishedVersion
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 65
    Publication Date: 2021-03-29
    Description: In der vorliegenden Arbeit werden Methoden der Erdsystemanalyse auf die Untersuchung der Habitabilität terrestrischer Exoplaneten angewandt. Mit Hilfe eines parametrisierten Konvektionsmodells für die Erde wird die thermische Evolution von terrestrischen Planeten berechnet. Bei zunehmender Leuchtkraft des Zentralsterns wird über den globalen Karbonat-Silikat-Kreislauf das planetare Klima stabilisiert. Für eine photosynthetisch-aktive Biosphäre, die in einem bestimmten Temperaturbereich bei hinreichender CO2-Konzentration existieren kann, wird eine Überlebenspanne abgeschätzt. Der Abstandsbereich um einen Stern, in dem eine solche Biosphäre produktiv ist, wird als photosynthetisch-aktive habitable Zone (pHZ) definiert und berechnet. Der Zeitpunkt, zu dem die pHZ in einem extrasolaren Planetensystem endgültig verschwindet, ist die maximale Lebenspanne der Biosphäre. Für Supererden, massereiche terrestrische Planeten, ist sie umso länger, je massereicher der Planet ist und umso kürzer, je mehr er mit Kontinenten bedeckt ist. Für Supererden, die keine ausgeprägten Wasser- oder Landwelten sind, skaliert die maximale Lebenspanne mit der Planetenmasse mit einem Exponenten von 0,14. Um K- und M-Sterne ist die Überlebensspanne einer Biosphäre auf einem Planeten immer durch die maximale Lebensspanne bestimmt und nicht durch das Ende der Hauptreihenentwicklung des Zentralsterns limitiert...
    Description: thesis
    Keywords: 523 ; THX 500 ; THX 500 ; Exoplaneten {Astronomie: Extrasolare Planetensysteme}
    Language: German
    Type: monograph , publishedVersion
    Format: 88 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 66
    facet.materialart.
    Unknown
    Univ. Zugl.: Braunschweig
    Publication Date: 2021-03-29
    Description: Unlike on Earth where 3/4 of the surface is covered by oceans, the Martian surface has rougher topography with greater magnitudes of mountains and valleys. The Martian atmosphere is less dense compared to the terrestrial one. The planetary boundary layer is significantly shallower on Mars than on Earth. These differences indicate that the Martian atmosphere should be very sensitive to the forcing from below. The major mechanism which provides vertical coupling are atmospheric waves generated in the lower atmosphere near the surface. These waves transport the momentum, energy, and heat away from places of their generation in the lower atmosphere. Propagating upward the wave disturbances grow in amplitude, and ultimately break or dissipate. They release the wave energy and momentum to the zonal mean circulation, and thus affect the global transport in the atmosphere of Mars. The main task of this work is to study various physical phenomena which take place in the atmosphere near the surface with an emphasis on the mechanisms of wave generation ...
    Description: thesis
    Keywords: 523 ; TGG 565 ; Marsatmosphäre {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 83 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 67
    Publication Date: 2021-03-29
    Description: The subject of this work is the physical characterization of asteroids, with an emphasis on the thermal inertia of near-Earth asteroids (NEAs). Thermal inertia governs the Yarkovsky effect, a non-gravitational force which significantly alters the orbits of asteroids up to ~20 km in diameter. Yarkovsky-induced drift is important in the assessment of the impact hazard which NEAs pose to Earth. Yet, very little has previously been known about the thermal inertia of small asteroids including NEAs.Observational and theoretical work is reported. The thermal emission of asteroids has been observed in the mid-infrared (5-35 æm) wavelength range using the Spitzer Space Telescope and the 3.0 m NASA Infrared Telescope Facility, IRTF; techniques have been established to perform IRTF observations remotely from Berlin. A detailed thermophysical model (TPM) has been developed and extensively tested; this is the first detailed TPM shown to be applicable to NEA data.
    Description: thesis
    Keywords: 523 ; 550 ; TGG 900 ; Planetoide {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 68
    Publication Date: 2021-03-29
    Description: Despite the good consistency of the cosmological standard model with the bulk of present observations, a number of unanticipated features have recently been detected within large-angle data of the Cosmic Microwave Background. Among these features are the anomalous alignments of the quadrupole and octopole with each other, their unexpected alignments with certain astrophysical directions (e.g. equinox, ecliptic) as well as the stubborn lack of angular autocorrelation on scales 〉 60ʿ. We pursue the idea that processes of non-linear structure formation could contribute to the large-scale anomalies via a local Rees-Sciama effect. We find that existing structures are able to produce CMB contributions up to 10^-5. For an axially symmetric setup we show that this effect does induce alignments, albeit not of the same form as extracted from the data, and that yet a Solar system effect seems preferred by the data. Moreover, we address the relationship between the intrinsic alignment of quadrupole and octopole on the one hand and the anomalous angular two-point correlation function on the other hand. We demonstrate the absence of any correlations between them and are able to exclude the joint case at high confidence with respect to recent data. This result enables us to put stringent constraints on any relevant model that exhibits an explicit axial symmetry.
    Description: thesis
    Keywords: 523 ; TBC 000 ; TBC 000 ; Radioastronomie
    Language: English
    Type: monograph , publishedVersion
    Format: 177 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 69
    facet.materialart.
    Unknown
    Univ. Stuttgart
    Publication Date: 2021-03-29
    Description: In this work the dune model introduced by Sauermann et al. (2001) is extended and applied to investigate the formation of different dune shapes on Mars and on Earth as function of wind directionality and sand availability. The formation of sand dunes on Mars under the present atmospheric conditions of the red planet is studied and conclusions about wind speed, migration velocity of dunes and changing wind regimes on Mars are presented. Field measurements of the shape of coastal transverse dunes are presented and the formation of coastal dune fields is explained. Finally, the formation of linear dunes by bimodal wind regimes is calculated. The simulations explain the appearance of exotic bimodal dune shapes in areas of low sand availability on Mars and on Earth.
    Description: thesis
    Keywords: 523 ; 551 ; 550 ; TGG 545 ; VAN 100 ; Marsoberfläche {Astronomie} ; Abspülung {Geologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 171 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 70
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 523 ; 550 ; TH0 000 ; THP 000 ; THT 600 ; Asteroseismologie, Oszillation {Sterne} ; Thermodynamische Vorgänge in Sternen {Astronomie} ; Riesensterne {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 135 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 71
    Publication Date: 2021-03-29
    Description: In der vorliegenden Arbeit wird zunächst eine verallgemeinerte Theorie der relativistischen Weibelinstabilität aufgestellt, indem auf eine Festlegung einer bestimmten Verteilungsfunktion verzichtet wird. Für große Parameterbereiche in anisotropen Plasmen kann die Wachstumsrate in allgemeiner Form bestimmt werden, deren Koeffizienten deutlich einfacher als bisher berechnet werden können. Diese Erleichterung wird anhand von vier Verteilungsfunktionen illustriert; es zeigt sich, dass ein Großteil der Verteilungen zu ähnlichen Ergebnissen führt.Weiterhin kann eine Solitongleichung für ein unmagnetisches Plasma aufgestellt und unter bestimmten Voraussetzungen an die Verteilung der Teilchen gelöst werden; es ergeben sich Verlauf und Stärke der elektromagnetischen Felder. Eine Anwendung findet sich in relativistischen Jets z.B. von Gamma Ray Bursts: Es wird die Strahlung von Elektronen berechnet, welche mit dem Soliton in einem solchen Jet wechselwirken.
    Description: thesis
    Keywords: 520 ; TFG 000 ; Magnetohydrodynamik und Plasma-Astrophysik
    Language: German
    Type: monograph , publishedVersion
    Format: 166 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 72
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 73
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 74
    Publication Date: 2021-03-29
    Description: Astroparticle physics is now entering the very exciting phase in which the efforts to enhance the detection capabilities of our instruments begin to turn out into clear answers. In this context the Pierre Auger Observatory (PAO) has been conceived to study the extensive air showers produced by the primary cosmic rays at energies above 1018eV in their interaction with the Earths̉ atmosphere, in order to solve the mystery of the origin and nature of the highest energy particles.The PAO design combines the most advanced detection techniques and the largest exposure, to provide high data quality together with unprecedented statistics. In addition, two experimental sites, one nearly completed in the southern hemisphere and the other to be built in the northern one will achieve full sky coverage, and the largest exposure ever...
    Description: thesis
    Keywords: 539.7223 ; 522 ; 550 ; TFE 000 ; Kosmische Elektrodynamik {Astrophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: 146 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 75
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 76
    Publication Date: 2021-03-29
    Description: Gravitational waves were predicted by Albert Einstein in 1916 as a consequence of his theory of general relativity. Hulse and Taylor provided indirect experimental evidence of their existence based on the increasing rotation frequency of a pulsar in the binary star system PSR 1913+16. They were awarded with the Nobel price in 1993. The direct detection of gravitational waves is expected to be one of the most exciting advances in physics in the next year...
    Description: thesis
    Keywords: 522 ; TCE 100 ; TCE 500 ; Astrometrische und interferometrische Instrumente ; Sonstige Instrumente {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
    Format: 180 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 77
    Publication Date: 2021-03-29
    Description: We have investigated the implications of isotropically distributed interstellar magnetohydrodynamic plasma waves on the scattering mean free path and the spatial anisotropy of high-energy cosmic rays. We demonstrate a drastic modification of the energy dependence of both cosmic ray transport parameters compared to previous calculations that have assumed that the plasma waves propagate only parallel or antiparallel to the ordered magnetic field (slab turbulence).
    Description: thesis
    Keywords: 539.7223 ; 523 ; 550 ; TFE 000 ; TFG 000 ; Kosmische Elektrodynamik {Astrophysik} ; Magnetohydrodynamik und Plasma-Astrophysik
    Language: English
    Type: monograph , publishedVersion
    Format: 91 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 78
    Publication Date: 2021-03-29
    Description: Mit dem Pierre Auger Experiment wird zur Zeit das größte Luftschauerexperiment betrieben. Es befindet sich noch im Aufbau und die finale Konzeption sieht zwei Detektionsstandorte in den USA und Argentinien vor, um somit volle Himmelsabdeckung zu erlangen. Ziel des Experimentes ist es, die Energie, Art und Herkunft der ultrahoch-energetischen kosmische Strahlung mit zwei komplementäre Nachweistechniken zu untersuchen. Die Detektoranordnung auf der Südhemisphäre besteht zur Zeit (Stand Jul. 2007) aus mehr als 1400 Wasser-Cherenkovdetektoren am Boden (870 g cm-2). Die Fertigstellung des 3000 km2 großen Oberflächendetektorkomplexes ist für Ende 2007 anvisiert mit einer finalen Konfiguration von mehr als 1600 ausgebrachten Tanks. Die Atmosphäre darüber kann mit 24 Fluoreszenz-Teleskopen beobachtet werden, die sich in vier Gebäuden am Rand des Oberflächenkomplexes befinden. In klaren mondlosen Nächten ist es mit dieser Anordnung möglich hybride Messungen von longitudinaler Schauerentwicklung und lateraler Teilchen-Dichteverteilung eines Schauers am Boden durchzuführen. Seit Februar 2007 sind alle Fluoreszenzteleskope in Betrieb...
    Description: thesis
    Keywords: 539.7223 ; 522 ; 550 ; TCE 200 ; Teleskope {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
    Format: 202 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 79
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 80
    Publication Date: 2021-03-29
    Description: In dieser Doktorarbeit wurden im Rahmen des MAGIC Experimentes neue Datenanalysemethoden implementiert, die sich insbesondere fuer die Analyse von Ereignissen niedriger Gammastrahlungsenergie eignen. Die Methoden konnten erfolgreich in Monte Carlo Studien getestet und auf Beobachtungsdaten des Krebsnebels und der extragalaktischen Gammastrahlungsquelle PG1553+113 angewandt werden. Diese Methoden reichen von ''image cleaning'' Techniken und der Nutzung neuer Bildparameter bis zu fortgeschrittenen g/h-Separations- und Energieabschaetzungsverfahren. Zum ersten Mal wurden die Vorteile von Klassifikations- und Regressionsbaeumen in der Gamma-Astrophysik ausgenutzt, um existierende klassische Methoden zu verbessern. Die Analyse - getestet an Monte Carlo Daten - bewies ihre Zuverlaessigkeit bei der Untersuchung der Gammastrahlungsemission des Krebsnebels, wobei ein hochsignifikanter Exzess im Energiebereich unterhalb 100 GeV in nur 1.7 h nachgewiesen werden konnte. Die Analyse von Daten des BL Lac Objekts PG1553+113 ergab signifikante Exzesse fuer Beobachtungen in den Jahren 2005 und 2006. Das kombinierte alpha-Histogramm zeigt ein Signal mit einer Signifikanz, die 8 sigma ueberschreitet...
    Description: thesis
    Keywords: 523 ; TBK 000 ; THT 200 ; Hochenergieastronomie ; Sterne einzelner Spektralklassen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 195 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 81
    Publication Date: 2021-03-29
    Description: Our dynamic Sun manifests its activity by different phenomena: from the 11-year cyclic sunspot pattern to the unpredictable and violent explosions in the case of solar flares. During flares, a huge amount of the stored magnetic energy is suddenly released and a substantial part of this energy is carried by the energetic electrons, considered to be the source of the nonthermal radio and X-ray radiation. One of the most important and still open question in solar physics is how the electrons are accelerated up to high energies within (the observed in the radio emission) short time scales. Because the acceleration site is extremely small in spatial extent as well (compared to the solar radius), the electron acceleration is regarded as a local process. The search for localized wave structures in the solar corona that are able to accelerate electrons together with the theoretical and numerical description of the conditions and requirements for this process, is the aim of the dissertation...
    Description: thesis
    Keywords: 523 ; TGC 765 ; Korona {Astronomie: Sonne}
    Language: English
    Type: monograph , publishedVersion
    Format: 109 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 82
    facet.materialart.
    Unknown
    Univ. Potsdam
    Publication Date: 2021-03-29
    Description: Our Solar system contains a large amount of dust, containing valuable information about our close cosmic environment. If created in a planet's system, the particles stay predominantly in its vicinity and can form extended dust envelopes, tori or rings around them. A fascinating example of these complexes are Saturnian rings containing a wide range of particles sizes from house-size objects in the main rings up to micron-sized grains constituting the E ring. Other example are ring systems in general, containing a large fraction of dust or also the putative dust-tori surrounding the planet Mars. The dynamical life'' of such circumplanetary dust populations is the main subject of our study...
    Description: thesis
    Keywords: 523 ; TGL 800 ; Interplanetarer Staub {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 115, 10 Bl.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 83
    Publication Date: 2021-03-29
    Description: Das Hexapod-Teleskop vereinigt zahlreiche innovative Ideen im Teleskopbau, die von industrieller Seite allerdings nie in einem astronomischen Betrieb getestet wurden. Obwohl die einzelnen Komponenten der Mechanik und Optik alle von höchster Präzision sind, wurde ihr Zusammenspiel weder im Labor noch am Himmel getestet. Die vorliegende Dissertation hat diese Arbeit geleistet und das Teleskop in die unmittelbare Nähe des astronomischen Betriebs gebracht. Erstmalig konnten mit dem Hexapod-Teleskop Sternaufnahmen gemacht und ausgewertet werden.
    Description: thesis
    Keywords: 522 ; TCE 200 ; Teleskope {Astronomische Instrumente}
    Language: German
    Type: monograph , publishedVersion
    Format: 116 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 84
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 85
    Publication Date: 2021-03-29
    Description: Design and performance of waveguide mixers at 1.4 THz and 1.9 THz based on NbTiN phonon-cooled hot electron bolometers (HEB) fabricated on a 2 æm thick Si_3N_4 membrane. The membrane is bonded to a silicon frame in the mixer block using a flip chip process. Simulated RF coupling is compared with experimental results, showing good agreement. Receiver noise temperature measurements show uncorrected values of 1600 K at 1.4 THz and 2100 K at 1.9 THz, both at 1.5 GHz intermediate frequency. Device cooling on the membrane seems not to be problematic. The mixers are used in receivers for SOFIA (GREAT & CONDOR) and APEX (CONDOR).
    Description: thesis
    Keywords: 523 ; TBG 000 ; Infrarot-Astronomie
    Language: German
    Type: monograph , publishedVersion
    Format: 153 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 86
    Publication Date: 2021-03-29
    Description: Sternentstehung findet im dichten Teil der Molekülwolken des interstellaren Mediums statt. In diesen Gebieten werden die ablaufenden physikalischen und chemischen Prozesse maßgeblich von der Wechselwirkung zwischen der Materie und dem Strahlungsfeld eingebetteter junger Sterne bestimmt. Konsequenz der Bestrahlung mit FUV-Photonen (6eV〈E〈13.6eV) ist die Aufheizung des Staubes und des atomaren bzw. molekularen Gases. Dabei fÓhrt die auf StaubkÒrnern umgesetzte Photonenenergie zur Emission von IR-Kontinuumsstrahlung, wohingegen die vom atomaren bzw. molekularen Gas aufgenommene Energie zu einer Anregung charakteristischer ÃbergÑnge im submm-Bereich fÓhrt. Beobachtbar sind astronomisch relevante Linien wie z.B. CO-RotationsÓbergÑnge, aber auch starke Linienemissionen von HyperfeinstrukturÓbergÑngen von z.B. [OI] und [CII], die im THz-Bereich liegen. Die Verteilung und die IntensitÑten lassen sich mit gÑngigen Modellen Óber so genannte Photonen-dominierte Regionen beschreiben und liefern wichtige Informationen fÓr unser VerstÑndnis Óber z.B. Sternentstehungsgebiete. Mit dem German REceiver for Astronomy at THz-Frequencies (GREAT), einem Einpixel-HeterodynempfÑnger fÓr zwei Frequenzen, wird der Wissenschaft der Zugang zu diesen Linien spektral hochaufgelÒst (R〉10^6) ermÒglicht. Dabei ist zu beachten, dass Frequenzen im Bereich von 1-10THz erdgebunden aufgrund der Absorption des atmosphÑrischen Wassersdampfs nicht beobachtbar sind.
    Description: thesis
    Keywords: 522 ; TJI 000 ; TBG 000 ; Werkstofforschung und Verfahrenstechnik im Weltraum ; Infrarot-Astronomie
    Language: German
    Type: monograph , publishedVersion
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 87
    Publication Date: 2021-03-29
    Description: Observations of the sun are almost always impaired by the turbulent motion of air in Earth's atmosphere. The turbulence would limit the theoretical resolution of modern large telescopes to that of amateur telescopes without additional tools.Today however, high-resolution data of the Sun are necessary to invesitgate its small-scale structure. This structure is likely to be connected to the radially outward increasing temparature distribution of the solar atmosphere. An introduction into further details of this topic that has also been the motivation for this work is presented in Chapt. 1. A theory of atmospheric turbulence that builds the basis for several results of this work is described in Chapt. 2. Here, two modern tools to enhance the resolution of groundbased observations are reviewed, on the one hand adaptive optics (AO) systems and on the other hand speckle interferometry. Until recently, these two techniques were only used separately. In Chapt. 3 the necessary modifications for analytical models of transfer functions are developed that include the changes made by an AO system to the incoming wave front, thus making a combination of AO systems and speckle interferometry possible ...
    Description: thesis
    Keywords: 523 ; TGC 100 ; TGC 740 ; Sonnenbeobachtung {Astronomie} ; Sonnenatmosphäre
    Language: English
    Type: monograph , publishedVersion
    Format: 137 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 88
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 523 ; TGC 800 ; TGC 800 ; Magnetfelder {Astronomie: Sonne}
    Language: English
    Type: monograph , publishedVersion
    Format: 88 Bl.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 89
    facet.materialart.
    Unknown
    Univ. Bochum
    Publication Date: 2021-03-29
    Description: In this work we introduced basic turbulence theory into the framework of the interstellar medium. In many cases turbulence simulations are applied to the interstellar medium (ISM) merely because it is a medium, where extremely high Reynolds numbers are actually realised, and the parameters of the ISM are only taken into account as far as they are needed for the turbulence research. Here, however, we investigated the basic turbulence properties, while at the same time we modelled the properties of the ISM as thoroughly as possible. The important point is that there are many physical processes going on in the ISM, which should be incorporated in the corresponding simulations. These processes reachfrom external influences of the radiation field originating from hot stars to the internal interaction of the particles culminating in the intricate chemistry of the molecular cloud medium. Each of the different phases of the ISM has its own dominant processes to be taken into account for a realistic modelling...
    Description: thesis
    Keywords: 523 ; TII 000 ; Interstellare Materie {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 141 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 90
    Publication Date: 2021-03-29
    Description: I perform and analyse the first ever calculations of rotating stellar iron core collapse in {3+1} general relativity that start out with presupernova models from stellar evolutionary calculations and include a microphysical finite-temperature nuclear equation of state, an approximate scheme for electron capture during collapse and neutrino pressure effects. Based on the results of these calculations, I obtain the to-date most realistic estimates for the gravitational wave signal from collapse, bounce and the early postbounce phase of core collapse supernovae.
    Description: thesis
    Keywords: 523 ; THU 162 ; TFA 000 ; Supernovae {Astronomie} ; Relativistische Astrophysik, Gravitation
    Language: English
    Type: monograph , publishedVersion
    Format: 291 S
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 91
    Publication Date: 2021-03-29
    Description: Sowohl in der Radioastronomie als auch in der Atmosphärenforschung gibt es einen Bedarf für breitbandige Spektrometer mit einer Bandbreite von bis zu 10 GHz und einer moderaten Auflösung. In der Radioastronomie wurde durch die stete Weiterentwicklung der Heterodynempfangssysteme der THz-Bereich für die Beobachtung zugänglich. Dies erfordert bei zahlreichen Beobachtungen, z.B. des galaktischen Zentrums, breitbandige Spektrometer, da die Geschwindigkeitsverteilung von Molekül- und Atomlinien in diesen turbulenten Gebieten sehr hoch ist. Die Auflösung des Spektrometers kann dabei in einen Bereich von 50-100 MHz liegen. Auch in der Atmosphärenforschung werden breitbandige Spektrometer benötigt, um die vollständige Information aus den Flügeln der druckverbreiterten Linienprofile zu gewinnen. Ziel dieser Arbeit war es daher ein Spektrometer zu entwickeln, das die Möglichkeit einer breitbandigen Frequenzanalyse bietet. Dies wird durch die Modulation eines Lasers mit einem externen Phasenmodulator möglich. Der Phasenmodulator kann das Laserlicht mit Frequenzen über 10 GHz modulieren. Zur Frequenzanalyse der so erzeugten Seitenbänder dient ein Fabry-Perot Etalon. Durch die Ausleuchtung des Etalons mit einer Zylinderlinse konnte erreicht werden, dass das vom Etalon erzeugte Ringsystem auf eine Zeile transformiert wird. Dies ermöglicht eine effiziente Ausnutzung des Signallichts. Um die Eigenschaften des in dieser Arbeit entwickelten Spektrometers zu charakterisieren und die Ausleuchtung des Etalons zu optimieren wurde ein Simulationsprogramm entwickelt. Mit Hilfe der Simulation ist es möglich eine Aussage über die Mindestgröße der Apertur des Etalons zu treffen, um die "walk-off" Verluste zu reduzieren. Es konnte zudem an Hand der Simulation gezeigt werden, welchen Einfluss die Ausleuchtung des Etalons auf die Auflösung und Intensitätsverteilung über das gesamte Band hat.
    Description: thesis
    Keywords: 523 ; TCE 320 ; TUD 000 ; Photometer, Polarimeter, spektroskopische Instrumente {Astronomische Instrumente} ; Meteorologische Instrumente
    Language: German
    Type: monograph , publishedVersion
    Format: 97 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 92
    Publication Date: 2021-03-29
    Description: Die H.E.S.S. Kollaboration betreibt ein stereoskopisches System aus vier großen abbildenden Cherenkov-Teleskopen für den Nachweis sehr hochenergetischer Gamma-Strahlung (VHE; 〉 100 GeV). In dieser Arbeit wird über den Nachweis zweier neuer Quellen sehr hochenergetischer Gamma-Strahlung mit den H.E.S.S.-Teleskopen berichtet. Die extragalaktische Quelle 1ES0347-121 gehört zur Klasse der BL Lac Objekte und ist der aktive Kern einer entfernten Galaxie. Detektiert mit einer Signifikanz von mehr als 10 Standard-Abweichungen, ist es die bisher am weitesten entfernte Quelle sehr hochenergetischer Gamma-Strahlung (Rotverschiebung z = 0.1880). Ihr Energiespektrum läßt sich gut durch ein Potenzgesetz mit Photonindex Gamma = 3.08 +/- 0.23_stat +/- 0.1_sys beschreiben. Der integrale Fluss I(E 〉250GeV) entspricht ~2% des Flusses des Krebsnebels. Mit Hilfe des hochenergetische Gamma-Strahlungsspektrum von 1ES 0347-121 werden Einschränkungen auf die Dichte des extragalaktischen diffusen Photonfeldes bestimmt (s. unten). Bei der zweiten Quelle handelt es sich um die ausgehnte Quelle HESS J1023-577, die mit dem jungen, massiven Sternenhaufen Westerlund 2 und dessen Umgebung assoziert wird. Junge und massereichen Sterne strahlen starke Sternenwinde ab, die durch Schockbeschleunigung hochenergetische Teilchen produzieren können. Zum erstenmal konnte eine Quelle sehr hochenergetischer Gamma-Strahlung mit einer solchen Umgebung sicher identifiziert werden. Das Energiespekrum reicht von ~400GeV bis ~20TeV und läßt sich gut durch eine Potenzgesetz mit Photonindex Gamma=2.53 +/- 0.16_stat +/- 0.1_syst beschreiben.
    Description: thesis
    Keywords: 523 ; TIE 400 ; TBK 000 ; TCE 240 ; Spektren und Leuchtkraft von Sternsystemen {Astronomie} ; Hochenergieastronomie ; Röntgen- und Gammateleskope {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
    Format: 123 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 93
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 523 ; THP 000 ; Thermodynamische Vorgänge in Sternen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 76 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 94
    Publication Date: 2021-03-29
    Description: Lambert, cosmological letters, fixed stars, nebulae, island universe, teleology, teleological, enlightenment, enlightened, romanticism, romantic, hypothesis, physical-teleological, speculation, imagination, stability, solar system, cosmology, astronomy, comet, magic, alchemy, pietism, science, arts, philosophy, Newtonian. - Johann Heinrich Lamberts Cosmological Letters was published 1761 in Augsburg. Lambert tried to expose a theory of the structure of the universe as a whole, that is, a theory that was able to involucrate all sorts of observed celestial bodies, like 'fixed stars' und nebulae. Lambert tackles his task mixing two disciplines, which in principle seem to be incompatible: Newtonian physics and teleology. Lambert's speculative and imaginative way to formulate his hypotheses shows resemblances to the way of making science developed during the romantic period, disagreeing with the methods of enlightenment, movement to which Lambert is usually associated. A central aspect of this thesis is to study Lambert's figure in relation to this two traditions, with the finality to deal with the compression of his ideas in depth, in light of the transition between the enlightened vision of the world and the romantic one.
    Description: thesis
    Keywords: 520 ; TA 100 ; TA 400 ; Theoretische Grundlagen {Astronomie} ; Wissenschaftsgeschichte {Astronomie}
    Language: German
    Type: monograph , publishedVersion
    Format: 302 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 95
    facet.materialart.
    Unknown
    Univ. Berlin
    Publication Date: 2021-03-29
    Description: Comets belong to the most pristine objects in the Solar System. The study of comets therefore allows one to put constraints to the physical and chemical conditions in the pre-planetary disc. In this work, a one-dimensional simplified multi-fluid model for the analysis of the chemistry in cometary comae was constructed. This model was used for the study of the formation of the C3 and C2 radicals. For this purpose, radial profiles of the optical emissions of C3 and C2 in comets C/2001 Q4 NEAT, C/2002 T7 LINEAR, and 9P/Tempel 1 at heliocentric distances between 1.0 AU and 1.5 AU were analysed. These profiles were obtained by means of long-slit spectroscopy. A reaction network for the formation of C3 and C2 at larger heliocentric distances (Helbert 2002) was updated and extended. Molecules and radicals were identified for which photodissociation reaction rates have to be further constrained before the formation of C3 and C2 can be understood. As comets of special interest, the comets 67P/Churyumov-Gerasimenko and 9P/Tempel 1 were studied in more detail. Both comets are targets of space missions...
    Description: thesis
    Keywords: 523 ; TGL 200 ; Kometen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 227 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 96
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 539.7215 ; 550 ; TBN 000 ; TIE 900 ; TCE 500 ; Neutrino-Astronomie ; Sonstige Sternensysteme {Astronomie} ; Sonstige Instrumente {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
    Format: 144 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 97
    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.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 98
    Publication Date: 2021-03-29
    Description: Diese Arbeit beschreibt die Verbesserung der Richtungsstabilisierung des Flugzeugteleskops SOFIA. Das Ziel des Flugzeugteleskops SOFIA sind astronomische Beobachtungen im Infrarotbereich. Da der Wasserdampf der Erdatmosphäre den Großteil der Infrarotstrahlung absorbiert, sind solche Beobachtungen mit herkömmlichen Teleskopen von der Erdoberfläche aus kaum möglich. Um unerwünschte Drehbewegungen des Flugzeugteleskops, z.B. hervorgerufen durch Luftturbulenzen, auszugleichen, ist zuerst eine genaue Messung bzw. Schätzung derselben notwendig. Diese Informationen werden dann mittels Computer in Echtzeit weiterverarbeitet. Anschließend sorgen dann Motoren dafür, das Teleskop wieder in die gewünschte Lage zu drehen. Die Motoren können das Teleskop nur so genau ausrichten, wie es die Genauigkeit des Meßsystems zuläßt. Die Messung der Drehbewegungen geschieht mit drei zueinander senkrecht angeordneten Gyroskopen. Diese weisen jedoch Fehler auf, so daß sich die Ausrichtgenauigkeit verschlechtert. Deshalb werden mit Hilfe einer auf das Teleskop montierten Kamera in regelmäßigen Zeitabständen Bilder des Sternhimmels aufgenommen. Aus diesen Bildern wird dann mit Hilfe der dort sichtbaren Sterne die aktuelle Orientierung des Teleskops bestimmt. Mittels dieser Orientierung werden dann die Fehler der Gyroskope korrigiert und der lineare Fehleranteil für die Zukunft extrapoliert. Dieser Fehler wird dann schon im Voraus vom Teleskoplageregler berücksichtigt. Dadurch wird der quasikonstante Fehleranteil minimiert. Je besser dieser Fehler geschätzt wird, desto geringer ist die Drift des Teleskops um seine Achsen. Dadurch erhöht sich die Richtungsstabilisierung ...
    Description: thesis
    Keywords: 522 ; TCE 200 ; Teleskope {Astronomische Instrumente}
    Language: German
    Type: monograph , publishedVersion
    Format: 125 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 99
    facet.materialart.
    Unknown
    Univ. Siegen
    Publication Date: 2021-03-29
    Description: The CosmoALEPH experiment, located underground at the LEP e+e? storage ring at CERN at a depth of 320 m water equivalent, was used to study the chemical composition of primary cosmic rays up to 10 PeV energies from the measurement of high energy muons, created in extensive air showers by interactions of primary nuclei in the atmosphere. The Time Projection Chamber (TPC) and the Hadron Calorimeter of the ALEPH detector and six scintillator stations located at distances up to 1 km from each other were used to analyse the decoherence curve, multiplicity and transverse momentum distributions of energetic cosmic muons. The experimental data were compared with predictions from different Monte Carlo (MC) models and mass composition approaches. From a comparison between the measured decoherence distribution with CosmoALEPH and the MC predicted decoherence curves for proton, helium and iron, a primary composition of (77±11) % protons and (23±11) % iron nuclei with a ?2 - probability of 84 % was determined, based on the predictions of the VENUS model with the constant mass composition approach. The analysis of the decoherence curve, with consideration of correlations between the measured CosmoALEPH parameters, leads to a composition of (88 ± 8) % protons and (12 ± 8) % iron nuclei for cosmic rays with a ?2 -probability of 53 % ...
    Description: thesis
    Keywords: 523 ; TFE 000 ; Kosmische Elektrodynamik {Astrophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: 191 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 100
    Publication Date: 2021-03-29
    Description: In der vorliegenden Arbeit wird zunächst der Transport von kosmischer Strahlung in der Turbulenz der Heliosphäre untersucht. Dabei werden für verschiedene Turbulenzmodelle aktuelle lineare und nichtlineare Theorien mit Simulationen verglichen. Insbesondere wird das Plasmawellen-Modell der quasilinearen Theorie und die nichtlineare Führungszentrums (NLGC)-Theorie für den Fall isotroper Turbulenz verallgemeinert, wobei sich für die NLC-Theorie eine akzeptable Übereinstimmung mit Simulationen ergibt. Weiterhin werden Mechanismen zur Erzeugung der Turbulenz aus Instabilitäten in anisotropen Teilchenverteilungen diskutiert, darunter insbesondere die Weibel-Instabilität in gegenströmenden Maxwellschen Plasmen und die relativistisch und dreidimensional verallgemeinerte Harris-Instabilität in den Jets von Gamma-ray Bursts (GRB). Für GRB erfolgt darüber hinaus eine Vorhersage über die Zusammensetzung der Jets.
    Description: thesis
    Keywords: 523 ; TFG 000 ; Magnetohydrodynamik und Plasma-Astrophysik
    Language: German
    Type: monograph , publishedVersion
    Format: 211 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...