Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 04/05

Ein analytisches Modell unserer Galaxie wird durch die Kopplung eines chemischen Evolutionsmodells mit analytischen Modellen der Kinematik unserer Galaxie entwickelt. Mit Hilfe dieses Modells wird die umfangreiche radiale Migration von Sternen in der galaktischen Scheibe nachgewiesen. Diese hat umfassende Konsequenzen für die Struktur und Geschichte der Scheibe, einschließlich der Ausbildung einer dicken Scheibe, ohne eine Kollision mit einer kleineren Galaxie voraussetzen zu müssen. Durch die Möglichkeit, die lokal gemessene Metallizitätsverteilung mit Hilfe von Sternen aus anderen Regionen der Scheibe aufzubauen, entfällt die Notwendigkeit starker Veränderungen in der chemischen Zusammensetzung unserer Galaxie in der jüngeren Vergangenheit. Im Gegenteil favorisiert das neue Modell einen nur sehr geringfügigen Anstieg der Metallizität, was in ausgezeichnetem Einklang mit den Beobachtungsdaten steht. Das Modell erklärt ferner auf natürliche Weise die bekannten Zusammenhänge zwischen Chemie und Kinematik in Sterndaten aus der Nachbarschaft unserer Sonne. Einige neue Befunde aus lokalen Beobachtungen werden gezeigt und mit den Modellerwartungen verglichen.

Mit Hilfe des Modells wurde ein grundlegender Fehler in der Bestimmung des Ruhestandards, bzw. der Geschwindigkeit unser Sonne relativ zur idealen Kreisbahn in unserer Galaxie gefunden. Zusammen mit der später erfolgten Messung der Rotationsgeschwindigkeit der Sonne um das Zentrum der Milchstraße konnten wir den galaktozentrischen Radius und die Rotationsgeschwindigkeit der Milchstraße am galaktozentrischen Radius der Sonne neu bestimmen. Diese zweite Messung wurde durch eine neue statistische Methode ermöglicht, die eine höhere Genauigkeit bei der statistischen Korrektur von Sterndistanzen erlaubt als die Ansätze der klassischen statistischen Astronomie. Die neue Methode war auch von großem Nutzen beim Nachweis, dass die jüngsten Behauptungen einer dualen Struktur des galaktischen Halos auf Distanzfehler und die ungerechtfertigte Beschreibung intrinsisch asymmetrischer Daten durch Gaußfunktionen zurückzuführen sind. Aus dem mathematischen Apparat für die Kinematik des Scheibenmodells wird eine einfache analytische Funktion zur Beschreibung der Geschwindigkeitsverteilung in der Scheibe hergeleitet, die bei gleicher Zahl freier Parameter eine physikalisch besser motivierte Alternative zu den häufig genutzten Gaußfunktionen bietet.

One of the key challenges in Cosmology today is to probe both statistical isotropy and Gaussianity of the primordial density perturbations, which are imprinted in the cosmic microwave background (CMB) radiation. While single-field slow-roll inflation predicts the CMB to fulfil these two characteristics, more complex models may give rise to anisotropy and/or non-Gaussianity. A detection or non-detection allows therefore to discriminate between different models of inflation and significantly improves the understanding of basic conditions of the very early Universe.

In this work, a detailed CMB non-Gaussianity and isotropy analysis of the five- and seven-year observations of the WMAP satellite is presented. On the one hand, these investigations are performed by comparing the data set with simulations, which is the usual approach for this kind of analyses. On the other hand, a new model-independent approach is developed and applied in this work. Starting from the random phase hypothesis, so- called surrogate maps are created by shuffling the Fourier phases of the original maps for a chosen scale interval. Any disagreement between the data and these surrogates points towards phase correlations in the original map, and therefore – if systematics and foregrounds can be ruled out – towards a violation of single-field slow roll inflation.

The construction of surrogate maps only works for an orthonormal set of Fourier functions on the sphere, which is provided by the spherical harmonics exclusively on a complete sky. For this reason, the surrogate approach is for the first time combined with a transformation of the full sky spherical harmonics to a cut sky version. Both the single surrogate approach as well as the combination with the cut sky transformation are tested thoroughly to assess and then rule out the effects of systematics. Thus, this work not only represents a detailed CMB analysis, but also provides a completely new method to test for scale- dependent higher order correlations in complete or partial spherical data sets, which can be applied in different fields of research.

In detail, the applications of the above methods involve the following analyses: First, a detailed study of several frequency bands of the WMAP five-year data release is accomplished by means of a scaling index analysis, whereby the data are compared to simulations. Special attention is paid to anomalous local features, and ways to overcome the problem of boundary effects when excluding foreground-influenced parts of the sky. After this, the surrogate approach is for the first time applied to real CMB data sets. In doing so, several foreground-reduced full sky maps from both the five- and seven-year WMAP observations are used. The analysis includes different scale intervals and a huge amount of checks on possible systematics. Then, another step forward is taken by applying the surrogate approach for the first time to incomplete data sets, again from the WMAP five- and seven-year releases. The Galactic Plane, which is responsible for the largest amount of foreground contribution, is removed by means of several cuts of different sizes. In addition, different techniques for the basis transformation are used.

In all of these investigations, remarkable non-Gaussianities and deviations from statistical isotropy are identified. In fact, the surrogate approach shows by far the most significant detection of non-Gaussianity to date. The band-wise analysis shows consistent results for all frequency bands. Despite a thorough search, no candidate for foreground or systematic influences could be found. Therefore, the findings of these analyses have so far to be taken as cosmological, and point on the one hand towards a strong violation of single-field slow-roll inflation, and question on the other hand the concept of statistical isotropy in general. Future analyses of the more precise measurements of the forthcoming PLANCK satellite will yield more information about the

The interactions between biomolecules and their environment can be studied by experiments and simulations. Results from experiments and simulations are often interpretations based on the raw data. For an accurate comparison of both approaches, the interpretation of the raw data from experiments and simulation have to be in compliance.

The design of such simulations and interpretation of raw data is demonstrated in this thesis for two examples; fluorescence resonance energy transfer (FRET) experiments and surface adsorption of biomolecules on inorganic surfaces like gold.

FRET experiments allow to probe molecular distances via the distance-dependent energy transfer efficiency from an excited donor dye to its acceptor counterpart. In single molecule settings, not only average distances, but also distance distributions or even fluctuations can be probed, providing a powerful tool to study flexibilities and structural changes in biomolecules.

However, the measured energy transfer efficiency does not only depend on the distance between the two dyes, but also on their mutual orientation, which is typically inaccessible to experiments. Thus, assumptions on the orientation distributions and averages have to be employed, which severely limit the accuracy of the distance distributions extracted from FRET experiments alone.

In this work, I combined efficiency distributions from FRET experiments with dye orientation statistics from molecular dynamics (MD) simulations to calculate improved estimates of the distance distributions. From the time-dependent mutual dye orientations, the FRET efficiency was calculated and the statistics of individual photo-absorption, FRET, and photo-emission events were determined from subsequent Monte Carlo (MC) simulations. All recorded emission events were then collected to bursts from which efficiencies were calculated in close resemblance to the actual FRET experiment. The feasibility of this approach has been tested by direct comparison to experimental data.

As my test system, I chose a poly-proline chain with Alexa 488 and Alexa 594 dyes attached. Quantitative agreement of calculated efficiency distributions from simulations with the experimental ones was obtained. In addition, the presence of cis-isomers and specific dye conformations were identified as the sources of the experimentally observed heterogeneity.

This agreement of in silico FRET with experiments allows employment of the dye orientation dynamics from simulations in the distance reconstruction. For multiple levels of approximation, the dye orientation dynamics was used in dye orientation models. At each level, fewer assumptions were applied to the dye orientation model. Each model was then used to reconstruct distance distributions from experimental efficiency distributions.

Comparison of reconstructed distance distributions with those from simulations revealed a systematically improved accuracy of the reconstruction in conjunction with a reduction of model assumptions.

This result demonstrates that dye orientations from MD simulations, combined with MC photon generation, can indeed be used to improve the accuracy of distance distribution reconstruction from experimental FRET efficiencies.

A second example of simulations and interpretation in compliance with experiments are the studies of protein adsorption on gold surfaces. Interactions between biomolecules and inorganic surfaces, e.g. during the biomineralization of bone, are fundamental for multicellular organisms. Moreover, understanding these interactions is the basis for biotechnological applications such as biochips or nano-sensing.

In the framework of the PROSURF project, a multi-scale approach for the simulation of biomolecular adsorption was implemented. First, parameters for MD simulations were derived from ab initio calculations. These parameters were then applied to simulate the adsorption of single amino acids and to calculate their adsorption free energy profiles. Fo

Aerosol particles are important constituents of the Earth's atmosphere. To quantify effects of aerosol particles, their distribution and properties need to be known.

An important tool for the provision of such information is remote sensing. This thesis covers vertically-resolving remote sensing by lidar and vertically-integrating remote sensing by photometer, and thereby considers desert dust aerosols which cause a major uncertainty in climate forecasts, as well as volcanic ash aerosols which, in addition, are relevant for the flight safety of jet-driven aircrafts. Both aerosol types consist of ensembles of particles of varying size, shape, and chemical composition.

This thesis aims to improve the retrieval of the physical properties of such mixtures from remote sensing observations, in particular by using Bayesian approaches and improved aerosol models.

Three types of retrievals were developed. The first retrieval type applies to lidar observations, assumes spheroidal particle shapes, and is based on a Bayesian Monte-Carlo-approach. It was applied to observations of a pure volcanic ash plume from Iceland on 17 April 2010 over Maisach (Germany) for the retrieval of the mass concentration of the ash particles. The second retrieval type applies to photometer observations in the solar aureole, uses a pre-defined set of ensembles of irregularly-shaped particles, and was applied to observations of the same ash plume. Both methods consistently retrieved a maximum ash mass concentration of about 1.1 milligram per cubic meter over Maisach with an uncertainty range from 0.7 to 1.5 milligram per cubic meter. The third retrieval type searches for ensembles that agree with the observations from both remote sensing techniques; it uses a pre-defined set of ensembles derived from the aerosol database OPAC, but consisting of absorbing and non-absorbing irregularly-shaped particles. This approach was successfully applied to Saharan dust observations, which were performed during the SAMUM field campaigns in Morocco and on the Cape Verde islands.

It turned out that, besides the particle shape, also the presence of non-absorbing components strongly influences the backscattering properties of the aerosols. In contrast, aureole radiances are hardly sensitive to particle shape and chemical composition, thus aureole radiances are well-suited for the retrieval of the size of ash and dust particles. It is expected that the accuracy of the retrievals further improves if all parameters observed by photometer are considered.

Organic photovoltaics is a field of rapidly growing activity in both research and industry. Flexibility, light-weight, and low-cost render this technique an appealing alternative to silicon based devices for solar energy power conversion.

Recently, several donor-acceptor systems have been investigated as active materials for organic photovoltaic devices and it has been shown that the morphology of these heterojunction systems has a severe impact on the device performance.

This work focuses on the correlation of nanoscale morphologies of organic donor-acceptor systems with resulting spectroscopic and electronic properties of organic photovoltaic devices. Discotic molecules are used in the active layer of the devices exhibiting a number of properties highly desired for the application in organic photovoltaic devices: The planar core shape of this class of materials allows an assembly to 1-D molecular wires showing anisotropic and exceptionally high charge carrier mobility.It is the aim to establish supramolecular assemblies of the discotic molecules and to realize nanoscale interface morphologies between donor and acceptor compounds in order to optimize the photovoltaic performance of the resulting devices.

The impact of residue modifications attached to the disc shaped molecules on morphology, current generation and recombination is analyzed and design rules for these solution processable small molecule blend mixtures are derived. Vacuum sublimation is discussed as an alternative processing route facilitating the fabrication of devices with mixed but also bi-layered active material stacking.

Using a dye sensitization method the exciton harvesting and photovoltaic performance can be significantly increased in these thin film devices. A highly ordered nanoscale morphology at the donor-acceptor interface, demonstrated using a template assisted imprinting approach, offers high potential towards photovoltaic devices with interdigitated interfaces and superior power conversion efficiency.

The aim of this thesis is to characterize the properties of the integrated spectrum of active galactic nuclei(AGNs), such as the ubiquity of the Fe Kα emission in AGNs, the dependence of the spectral parameters(e.g. the power law photon index and the Fe Kα equivalent width etc.) on the X-ray luminosity and redshift, and mean properties (including the line profile) of the Fe Kα line which can be addressed via stacking in the source rest-frame.

I selected 2646 point sources observed with XMM-Newton at high galactic latitude (|BII| > 25 degrees) and with the sum of EPIC-PN and EPIC-MOS 0.2–12 keV counts greater than

1000. Redshifts were obtained for 919 sources from the Nasa’s Extragalactic Database. In order to prepare a clean sample, I retained only reliable sources (those for which the detection and the spectral products do not show obvious problems). I also excluded sources classified as HII

regions, groups/clusters, star-forming/starburst galaxies. The final sample consists of 507 AGNs.

To examine the ubiquity of the Fe Kα emission in AGNs and the dependence of the spectral parameters on the X-ray luminosity and redshift, I employed the observed-frame stacking technique, in which individual source spectra were summed in the observed-frame to compute the integrated spectra in different redshift and luminosity bins over the range 0 < z < 5. Detailed analysis of these spectra used appropriately normalized background spectra and exposure time weighted response and ancillary files. I find that the narrow Fe Kα line at 6.4 keV is significantly detected up to z = 1. The line equivalent width decreases with increasing the X-ray luminosity in the 2–10 keV band (“Iwasawa-Taniguchi effect”). The anticorrelation is characterized by the relation log(EW_Fe) = (1.66 ± 0.09) + (−0.43 ± 0.07) log(LX,44), where EW_Fe is the rest-frame equivalent width of the neutral Fe Kα line in eV and LX,44 is the 2–10 keV X-ray luminosity in units of 10^44 erg/s. The equivalent width is nearly independent of redshift up to z ∼ 0.8 with

an average value of 101 ± 40 (rms dispersion) eV in the luminosity range 43.5 ≤ log LX ≤ 44.5. This analysis also confirms the hardening of the spectral indices at low luminosities, implying a dependence of obscuration on luminosity.

To derive the mean properties of the Fe Kα line in the source rest-frame, I refined the final sample of 507 AGNs and selected 248 AGNs with the EPIC-PN net 2–10 keV rest-frame counts ≥200 and power law photon indices in the range 1.5–2.2. I computed the integrated spectrum of these 248 AGNs in the source rest-frame using two different rest-frame stacking procedures. I carried out a detailed spectral analysis of these integrated spectra using various models comprising simple/complex continuum and Fe Kα line components. I find that the average Fe Kα line profile in our sample is best represented by a combination of a narrow and a broad line. The equivalent widths of the narrow and broad components are ∼30 eV and ∼100 eV, respectively. The broad line parameters such as its shape, equivalent width and its detection significance in the integrated spectrum of the 248 AGNs are observed to be very sensitive to the assumed continuum and adopted stacking method. However, despite having a well-defined sample with reasonable statistics (net counts ∼ 198000) in the integrated spectrum, I do not detect a clear extended red-wing, and the measured equivalent width of the broad feature is always lower than 170 eV, implying that most black holes are not maximally rotating.

Die schnellsten bekannten lichtinduzierten Prozesse in der Natur treten auf einer Zeitskala

von wenigen Femtosekunden (fs) oder sogar auf einigen hundert Attosekunden (as) auf. Um

diese ultraschnellen Licht-Materie-Wechelwirkungen aufzulösen und zu erforschen, sind

Lichtpulse von wenigen optischen Zyklen vom extrem Ultravioletten (XUV) bis hin zum

Infraroten (IR) erforderlich. Deren Erzeugung stellt schon seit Jahren eine Herausforderung

dar und stößt auf breites Interesse für Anwendungen in Physik, Chemie und Medizin.

Im ersten Teil dieser Dissertation wird die vielversprechende Methodik der nichtkollinearen

optisch parametrischen Verstärkung gestreckter Lichtpulse (NOPCPA) für die Generierung

von „few-cycle“ Lichtpulsen im Sichtbaren (Vis) und nahen IR (NIR) mit Pulsdauern von 5-

8 fs Halbwertsbreite erheblich weiterentwickelt. Grundlegende parametrische Einflüsse, wie

die Existenz einer parametrisch induzierten Phase und die Generierung von optisch

parametrischer Fluoreszenz (OPF), werden sowohl durch theoretische Analysen und

numerische Simulationen, als auch durch konkrete Experimente erforscht. Experimentell

werden im Rahmen dieser Arbeit „few-cycle“ Lichtpulse mit einer Pulsdauer von 7.9 fs,

130 mJ Energie, bei 805 nm Zentralwellenlänge und einem sehr hohen, „seed“-Puls

limitierten Vorpuls-Kontrast von 11 und 8 Größenordnungen bei 30 ps und ca. 3 ps erzielt.

Diese stellen derzeit die leistungsstärksten „few-cycle“ Lichtpulse weltweit dar und es werden

durch diese Arbeit und Kooperationen neue Experimente in der Hochfeld-Physik realisiert.

Zum Einen, ist es mit dem hier beschriebenen Breitbandpulsverstärker gelungen, "quasimonoenergetische"

Elektronen mit Energien mit bis zu 50 MeV zu beschleunigen. Dazu wird

der Lichtpuls zu relativistischen Intensitäten von mehreren 1019 W/cm2 in einen Helium-

Gasjet fokussiert. Die Elektronen zeigen einen stark reduzierten niederenergetischen

Elektronenhintergrund, verglichen mit Beschleunigung durch längere Lichtpulse. Zum

Anderen, wurde XUV-Licht bis zur 20. Harmonischen des generierten Lichtpulses aus dem

Breitbandpulsverstärker durch dessen „sub-cycle“ Wechselwirkung mit Festkörperoberflächen

erzeugt. Die Erzeugung von solchen kohärenten hohen Harmonischen verspricht den Bau von

kompakteren XUV-Strahlungsquellen, die as-Pulsdauern mit hohen Photonenflüssen XUVAnrege/

XUV-Abfrage Experimente kombinieren würden.

Im Rahmen dieser Arbeit werden darüber hinaus neue, erweiterte Konzepte für noch

breitbandigeres NOPCPA über eine Oktave entwickelt und charakterisiert, die die

Verwendung von zwei Pumppulsen in einer NOPCPA Stufe und die Verwendung von zwei

verschiedenen Pumpwellenlängen in zwei aufeinanderfolgenden NOPCPA Stufen beinhalten.

Im zweiten Teil dieser Dissertation werden breitbandige Weißlicht-Spektren und mittels

NOPCPA spektral abstimmbare, ultrakurze Lichtpulse verwendet um ein weltweit

einzigartiges transientes Absorptionsspektrometer mit Vielkanaldetektion zu realisieren.

Dieser neue Anrege-Abfrage Aufbau kombiniert eine sehr breitbandige UV-Vis-NIR Abfrage

mit einer hohen Zeitauflösung von 40 fs und hoher Sensitivität für die transiente Änderung

der optischen Dichte von weniger als 10-4. Damit ist es in dieser Dissertation zum ersten Mal

gelungen den photoinduzierten Ladungstransfer im konjugierten Polymer Polythiophen und in

hybriden Polythiophen/Silizium Solarzellen in Echtzeit aufzulösen. Dabei wird eine seit

mehreren Dekaden geführte kontroverse Debatte über die Natur der primären Photoanregung

in organischen Halbleitern aufgelöst: Exzitonen dissoziieren mit 140 fs Zeitkonstante zu

Polaronen (Ladungsträger). Entscheidende Parameter (z.B. strukturelle Ordnung,

Ladungsträgermobilität) für die Effizienz der Generierung und Extraktion von freien

Ladungsträgern können bestimmt werden, was fundamentales Verständnis für die

Optimierung von organischer und hybrider Photovoltaik für zukünftige nachhaltige

Energiequellen beisteuert. Weitere Ultrakurzzeit-Experimente an neuartig