Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 01/05 Archiv

A parameterization of line-shaped contrails for use within the framework of a general circulation model (ECHAM) was developed for the first time. Contrail coverage, optical properties and radiative forcing are calculated at any model time step depending in a physically based manner on the respective conditions in the ambient air. In addition, possible effects on atmospheric parameters can be simulated, allowing for the determination of a climate sensitivity parameter especially for line-shaped contrails. Regional contrail cover as well as the large range of simulated optical depth values show a fair qualitative and quantitative agreement with observations. Sensitivity studies result in a lower global radiative forcing of line-shaped contrails than estimated by the Intergovernmental Panel on Climate Change (1999). Remaining uncertainties are mainly associated with poor knowledge of microphysical properties such as ice water content, particle shape and size. Considering future changes in air traffic density, and aircraft technology, as well as anthropogenic climate change, an increase of global contrail cover and radiative forcing by roughly a factor of four between 1992 and 2050 is simulated.

In den letzten Jahren wurden 373 ausgedehnte Roentgenquellen in der ROSAT Himmelsdurchmusterung (RASS) als Supernova Ueberreste (SNRs) Kandidaten identifiziert (Busser, 1998). Ein Ziel der vorliegenden Arbeit war die genaue Untersuchung und Identifizierung dieser Galaktischen SNR Kandidaten an Hand ihrer Roentgen- und Radiomorphologie. Diese Analyse erlaubte es fuer die untersuchten Objekte, zwischen extragalaktischen Hintergrundsquellen und SNR Kandidaten zu unterscheiden. Rund 16% der 373 Kandidaten (59) stellten sich als wahrscheinliche Galaxien oder Galaxienhaufen heraus, wohingegen sich 99 Kandidaten als unechte Hintergrundsquellen erwiesen. Nachbeobachtungen der besten Kandidaten wurden im Radioband sowie im Roentgenband durchgefuehrt und G38.7-1.4 und G296.7-0.9 als SNRs identifiziert. Neun Objekte wurden als hervorragende Kandidaten und weitere 90 als moegliche SNRs auf Grund ihrer Radio- und Roentgenmorphologie klassifiert. Die restlichen 114 Quellen zeigen kaum Indizien fuer SNRs and wurden deswegen als SNR Kandidaten verworfen. Ein Vergleich dieser Ergebnisse mit denen einer Simulation von Busser zeigt, dass weniger SNR Kandidaten im RASS gefunden wurden als von der Simulation erwartet. Um eine Uebereinstimmung beider Ergebnisse zu erreichen, muss eine hoehere interstellare Dichte, eine geringe Explosionsenergie und eine geringe galaktische SN Rate angenommen werden. Der zweite Teil dieser Arbeit beschreibt die detailierte Untersuchung dreier galaktischer SNRs. XMM-Newton Beobachtung von RCW 103: RCW 103 ist ein schalenfoermiger SNR mit einer kompakten Roentgenquelle im Zentrum. Es ist allerdings noch unklar, ob RCW 103 von einer Supernova (SN) Ia oder einem Kernkollaps SN stammt. Allerdings konnte gezeigt werden, dass RCW 103 in verschiedenen Linienemissionen die gleiche Ausdehnung hat, sowie eine geringe Expansionsgeschwindigkeit leichter Elemente wie z. Bsp. Magnesium aufweist, was fuer Kernkollaps SN erwartet wird. Schliesslich liefert die Existenz einer zentralen Punktquelle, die wahrscheinlich einem Neutronenstern und seinem Begleitstern zuzuordnen ist, ein ueberzeugendes Argument fuer ein Kernkollaps Szenario. XMM-Newton Beobachtung von G21.5-0.9: G21.5-0.9 ist ein dem Krebsnebel aehnlichen SNR mit einer kompakten Roentgenquelle im Zentrum. XMM-Newton Daten zeigen, dass der diffuse Nebel von G21.5-0.9 am besten durch ein Potenzgesetz beschrieben wird, dessen Spektralindex von 1.72 im Zentrum bis 2.43 am Rande des Halos ansteigt. Weder Linienemission noch Randaufhellung konnte im Halo gefunden werden und auch die spaehrische Symnmetrie legen eine Interpretation des aeusseren Halos als eine Ausdehnung des zentralen Synchrotronnebels nahe. ROSAT Beobachtung von G65.3+5.7: Das Roentgenspektrum von G65.3+5.7 zeigt thermische Roentgenemission, welches durch ein Raymond-Smith Model mit einer Durchschnittstemperatur von 0.20 keV und einer geringen Umgebungsdichte von ~0.019~cm^{-3} beschrieben wird. Unter der Annahme einer Entfernung von 1 kpc und unter der Benutzung der Sedov Gleichungen, erhaehlt man ein Alter von ~ 27500 Jahren, eine Explosionsenergie von ~ 0.18 x 10^{51} erg und eine Leuchtkraft L_x ~ 9.9 x 10^{34} erg. Der Radiopulsar PSR J1931+30 befindet sich in G65.3+5.7. Da keine zeitliche Frequenzaenderung bekannt ist, wurde mit Hilfe einer oberen Schranke der Roentgenzaehlrate und unter Annahme eines Spektrums, das dem des Krebsnebels aehnelt, ein Roentgenfluss f_x = 3.93 x 10^{-13} erg~cm^{-2} s^{-1} bestimmt, das einer Leuchtkraft L_x = 4.32 x 10^{32} erg entspricht und folglich einer unteren Schranke des charakteristischen Alters von 1400 Jahren entspricht.

Road traffic represents one of the main sources of emissions to the atmosphere. This work determines the impact of road traffic emissions on the chemical composition of the atmosphere by a numerical modelling study with ECHAM4/CBM-IV. For the first time, global impact of non-methane-hydrocarbon-emissions (NMHCs) from road traffic is presented. Annual, global emissions from road traffic following a consumption-based approach amount to (8.8 +/- 1.8) Tg [N] nitrogen oxides, (206 +/- 86) Tg [CO] carbonmonoxide, and (34.4 +/- 18.9) Tg NMHCs. Road traffic emissions cause an increase of ozone, which is an important trace gas for the oxidizing capacity and the radiative budget of the atmosphere. In industrialized regions of the northern hemisphere the increase exceeds more than 20%. In remote regions an increase of more than 10% is calculated. Tropical latitudes show a relative contribution of more than 6% due to road traffic up to 10km. NOx-emissions account for about 70% of this ozone increase. Further, road traffic increases and decreases the concentration of hydroxyl radicals (OH) depending on geographical region and season. This again affects the oxidizing capacity and the lifetime of methane. In summer, road traffic causes in northern extratropics a 3% increase of OH, and in winter a decrease of 10%. These changes in chemical composition cause an indirect radiative forcing to the atmosphere. Ozone increases due to road traffic emissions (NOx, CO, NMHCs) result in an annual and global mean radiative forcing of 0.058 W/m^2. The indirect forcing due to road traffic-induced changes in the lifetime of methane amounts to 0.006 W/m^2. This forcing is temporal and spatial inhomogeneous, and can even possess a positive sign (e.g. in spring). Results show that NMHC-emissions considerably contribute to the global impact of road traffic emissions.

Atomistic theoretical descriptions of thermal chemical recations in complex environments are well achieved by combined quantum and molecular mechanical (QM/MM) methods. The goal of this work is to extend such techniques to enable the description of photochemical reactions and to carry out case studies subsequently. In order to tackle the enormous computational demand due to the involvement of excited electronic states, we (i) largely speed up the individually selecting multi-refernce configuration interaction (IS/MRCI) scheme by Tavan and Schulten (1980) by a new grahical algorithm and (ii) take use of recently developed semimempirical valence shell models (Thiel 1997) which are well suited for excited electronic states. The efficiency and accuracy of the resulting IS/MRCI-algorithm is demonstrated by its application to the first electronic excited states of butadiene. The new QM/MM method is used to calculate absorption energies along a molecular dynamics trajectory of a small Schiff base in isotonic solution.

The shape of a nucleus can be defined in a classical view by a sphere of constant density of positive space-charge in a body-fixed frame of reference. Experimental observations can be interpreted as deviations from spherical symmetry of the nucleus. Static shapes of nuclei in the periodic table near the valley of stability predominantly are rotationally symmetric and mostly quadrupole deformed (American football or lens). For nuclei in time-dependent excited states asymmetric terms are known, like octupole deformation (pear shape). The group of actinides lies in a transition region with possible "static octupole deformation". For a fixed proton number (Z = 91) the impact of changing octupole correlations with neutron number on the configuration of 31Pa and 229Pa was analysed in the present work. A detector optimized for the reaction 231Pa(22 MeV p,t)229Pa at the Munich Universities tandem accelerator laboratory gave experimental clues of the 229Pa ground-state energy. A detailed study of231Pa by Coulomb-excitation with 148 MeV 32S und 255, 260, 261 MeV 58Ni projectiles can answer open questions on octupole correlations and determines a multitude of transition matrix elements as well as their global parameters in an enlarged level scheme. A segmented coincidence detector for backscattered particles with read-out electronics and software for high resolution, combined with Compton-suppressed and background-reduced-gamma spectroscopy following Coulomb-excitation was developed for the NORDBALL gamma-spectrometer of the Niels Bohr Institute Tandem Accelerator Laboratory, Risø (Denmark). An optional extension of the detector system, built by the University of Warsaw (Poland), can be integrated. For some experiments a Si-detector of the College of Industrial Technology Amagasaki (Japan) was used. The 1/2[530] ground-state band 231Pa could be followed up to spin 39/2-, the 1/2[400]+1/2[660] parity-partner band up to 23/2+ and the 3/2[651] side band up to 37/2+. The simulation of Coulomb-excitation with the code GOSIA helped to fit the parameters of a model system consisting of three bands with 47 levels and interconnecting 672 matrix elements of E1, E2, E3, E4 and M1 transitions to experimental data within chi^2/n=1. As far as possible the calculation remained model-independent and led to values for model parameters of multipole moments and deformation. The determination of signs of matrix elements is discussed. Different methods of error analysis were used. The results were related to the experimental known properties of neighbouring nuclei. A comparison of the results with calculations by the Charles University, Prague (Czech Republic) in the one-quasiparticle-plus-phonon model with Coriolis-coupling is given.

The so-called "COMPASS" spectrometer recently put into operation at the European Laboratory for Particle Physics (C.E.R.N.) uses straw drifttubes as space sensitive detectors for tracking purposes. The presented work deals with the specification of these detectors and monitors construction and commissioning up to the investigation of their properties using a testbeam, as well as the installation into the spectrometer. It could be shown that the detectors meet the requirements of the experimental program the COMPASS spectrometer aims for, in particular determined by the necessity of an efficient detection of the D0-meson decay D0 --> K- pi+: Between the first spectrometer magnet and the ring-imaging Cherenkov counter the setup requires a system for the determination of charged-particle tracks. On one hand it has to be compact in the beam direction, on the other it must offer a high time and spatial resolution while covering the relatively large solid angle given by the aperture of the target magnet which amounts to 180 mrad. Due to this the active surface at the foreseen location will be around 10 m^2. The geometrical precision reached during production determines the precision of the information obtained on track coordinates of the decay products and thus - having an impact on the measurement of energies and momenta of the reaction products - influences the precision of the D0-meson mass measurement. Observing rare processes like the one mentioned above with high accuracy means collecting a huge sample of decay events, making it necessary to expose the detectors to high particle fluxes. Thus, particular attention was paid to the experiments concerning spatial resolution and detection efficiency, but also to the aging behaviour. The counters were manufactured at the Joint Institute for Nuclear Research (JINR) at Dubna (Russian Federation), which means that the production was also challenging in terms of logistics. Where necessary not only the production technology but also details concerning the work organization and materials flow are described.

The analysis of the infrared measurements of a number of sophisticated space experiments requires modeling of molecular infrared radiation with accounting for the nonlocal thermodynamic equilibrium (non--LTE). In this dissertation a general formulation is given of the multilevel vibrational-rotational non-LTE problem for a mixture of radiating molecular gases in a planetary atmosphere. The approach for the solution of this problem suggested here utilizes the Accelerated Lambda Iteration (ALI) technique developed in stellar astrophysics for spectrum formation calculations and for the computation of non-LTE model stellar atmospheres. This new for atmospheric science technique is not subject to the limitations of the traditional matrix and conventional lambda iteration methods which dominate the studies dealing with non-LTE in planetary atmospheres. In the case of the CO2 non-LTE problems in the atmospheres of Earth and Mars it is demonstrated that ALI approach is far superior to the other algorithms in minimizing computer time and storage and in converging much more rapidly. While ``atmospheric'' groups concentrated on the development of codes suitable for treatment of limited number of selected non-LTE problems the computer code package ALI-ARMS (for ``Accelerated Lambda Iteration for Atmospheric Radiation and Molecular Spectra'') compiled in framework of this study allows non-LTE treatment of arbitrary number of molecules interacting by collisionally induced exchange of energy and by the band overlaps. It was applied to the analysis of large amount of the infrared limb radiance data obtained both in the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiments on board of the german ASTRO-SPAS satellite and by the Thermal Emission Spectrometer (TES) instrument orbiting Mars on board of the NASA Mars Global Surveyor (MGS) satellite. In case of the Earth's atmosphere first detailed distributions of temperature and trace gas concentrations in the upper mesosphere and lower thermosphere were obtained. The retrieved temperature data confirmed the ``two-level'' structure of the Earth's mesopause which was recently discovered in the lidar and rocket experiments. These results contribute to the studies of the mesosphere, which is considered today to be the tracer of the global climate changes.

Das CRESST Experiment im Gran Sasso Untergrundlabor sucht nach Dunkler Materie in Form von schwach wechselwirkenden massiven Teilchen (WIMPs) ueber elastische Streuung an Kernen. Die erste Phase von CRESST benutzte 262 g Saphir Kristalle als Absorber. Ein niedriger Untergrund, eine Langzeitstabilitaet des kryogenen Aufbaus, sowie eine niedrige Schwelle und eine hohe Sensitivitaet fuer leichte WIMPs wurden damit erreicht. In einer sehr stabilen Messung von 1.5 kg Tagen wurden ein Untergrund besser als 1 Ereignis/kg/Tag/keV ueber 20 keV und eine Schwelle von 580 eV erreicht. Saphir Detektoren sind besonders geeignet, um leichte WIMPs mit spin-abhaengiger Wechselwirkung zu messen. Die Ergebnisse verbessern existierende Limits in diesem Bereich. Die zweite Phase von CRESST benutzt szintillierende Kristalle als Absorber. In einem Szintillator wird nach einer Energiedeposition neben Phononen auch Licht erzeugt. Kernrueckstoesse erzeugen weniger Licht als voll ionisierende Wechselwirkungen. Die gleichzeitige Messung des Phononen- und Lichtsignals ermoeglicht eine Identifizierung der Wechselwirkung. Erste Messungen mit 300 g CaWO4 Detektoren wurden im Aufbau am Gran Sasso durchgefuehrt. Trotz einiger technischer Probleme war eine Charakterisierung der Detektoren moeglich, die das grosse Potential der Ereignisdiskriminierung aufzeigt.

HI observations of high-velocity clouds (HVCs) indicate that they are interacting with their ambient medium. In this thesis, the question on the dynamical and thermal stabilization of a cold dense neutral cloud in a hot, thin, and magnetized ambient halo plasma is addressed. The results of two-dimensional plasma-neutral gas simulations showing the dynamical evolution of neutral gas clouds in a plasma flow are presented. The simulations show the formation of a comet-like head-tail structure combined with a magnetic barrier which exerts a stabilizing pressure on the cloud and hinders hot plasma from diffusing into the cloud. Furthermore, the magnetic barrier significantly reduces the heat conduction between the plasma and the neutral gas. It is demonstrated that a sufficiently large (but small compared to typical halo B-field strengths) component of the halo B-field perpendicular to the cloud's motion effectively stabilizes HVCs against disruption by Kelvin-Helmholtz- or Rayleigh-Taylor-instabilities and against evaporation by heat transfer for periods comparable with typical observed lifetimes of HVCs. The question on the stability of the clouds is addressed in terms of the stripping of cloud material, the temperature profile of the cloud, the dependence of the cloud's stability on the infall angle of the cloud, two-component clouds, and the cloud's morphology. The results are compared with observations of a compact HVC. In addition, the observed strong H/alpha fluxes from cloud edges can be explained by applying the critical velocity effect to the magnetic barrier. In a second part, the thesis addresses the phenomenon of cometary ion-tail disconnection events (DE) in terms of the theory of magnetic reconnection and by means of two-dimensional plasma-neutral gas simulations. The simulations show that either dayside magnetic diffusion and reconnection (when crossing the heliospheric current sheet) and nightside reconnection (without a switch in the magnetic polarity of the solar wind) lead to the disconnection of the plasma tail on the time scale of days, thus reproducing typical observed disconnection events.

In this thesis I report on experiments that enter a new regime in the many body physics of ultracold atomic gases. A Bose-Einstein condensate is loaded into a three-dimensional optical lattice potential formed by a standing wave laser light field. In this novel quantum system we have been able to both realize a quantum phase transition from a superfluid to a Mott insulator, and to observe the collapse and revival of a macroscopic matter wave field. Quantum phase transitions are driven by quantum fluctuations and occur, even at zero temperature, as the relative strength of two competing energy terms in the underlying Hamiltonian is varied across a critical value. In the first part of this work I report on the observation of such a quantum phase transition in a Bose-Einstein condensate with repulsive interactions, held in a three-dimensional optical lattice potential. In the superfluid ground state, each atom is spread-out over the entire lattice, whereas in the Mott insulating state, exact numbers of atoms are localized at individual lattice sites. We observed the reversible transition between those states and detected the gap in the excitation spectrum of the Mott insulator. A Bose-Einstein condensate is usually described by a macroscopic matter wave field. However, a quantized field underlies such a "classical" matter wave field of a Bose-Einstein condensate. The striking behavior of ultracold matter due to the field quantization and the nonlinear interactions between the atoms is the focus of the second part of this work. The matter wave field of a Bose-Einstein condensate is observed to undergo a series of collapses and revivals as time evolves. Furthermore, we show that the collisions between individual pairs of atoms lead to a fully coherent collisional phase shift in the corresponding many-particle state, which is a crucial cornerstone of proposed novel quantum computation schemes with neutral atoms. With these experiments we enter a new field of physics with ultracold quantum gases. In this strongly correlated regime, interactions between atoms dominate the behavior of the many-body system such that it can no longer be described by the usual theories for weakly interacting Bose gases. This novel quantum system offers the unique possibility to experimentally address fundamental questions of modern solid state physics, atomic physics, quantum optics, and quantum information.