TY - JOUR A1 - Török, Tibor A1 - Berger, Mitch A. A1 - Kliem, Bernhard T1 - The writhe of helical structures in the solar corona N2 - Context. Helicity is a fundamental property of magnetic fields, conserved in ideal MHD. In flux rope geometry, it consists of twist and writhe helicity. Despite the common occurrence of helical structures in the solar atmosphere, little is known about how their shape relates to the writhe, which fraction of helicity is contained in writhe, and how much helicity is exchanged between twist and writhe when they erupt. Aims. Here we perform a quantitative investigation of these questions relevant for coronal flux ropes. Methods. The decomposition of the writhe of a curve into local and nonlocal components greatly facilitates its computation. We use it to study the relation between writhe and projected S shape of helical curves and to measure writhe and twist in numerical simulations of flux rope instabilities. The results are discussed with regard to filament eruptions and coronal mass ejections (CMEs). Results. (1) We demonstrate that the relation between writhe and projected S shape is not unique in principle, but that the ambiguity does not affect low- lying structures, thus supporting the established empirical rule which associates stable forward (reverse) S shaped structures low in the corona with positive (negative) helicity. (2) Kink-unstable erupting flux ropes are found to transform a far smaller fraction of their twist helicity into writhe helicity than often assumed. (3) Confined flux rope eruptions tend to show stronger writhe at low heights than ejective eruptions (CMEs). This argues against suggestions that the writhing facilitates the rise of the rope through the overlying field. (4) Erupting filaments which are S shaped already before the eruption and keep the sign of their axis writhe (which is expected if field of one chirality dominates the source volume of the eruption), must reverse their S shape in the course of the rise. Implications for the occurrence of the helical kink instability in such events are discussed. (5) The writhe of rising loops can easily be estimated from the angle of rotation about the direction of ascent, once the apex height exceeds the footpoint separation significantly. Conclusions. Writhe can straightforwardly be computed for numerical data and can often be estimated from observations. It is useful in interpreting S shaped coronal structures and in constraining models of eruptions. Y1 - 2010 UR - http://dispatch.opac.d-nb.de/DB=1.1/SET=4/TTL=1/SHW?FRST=1&PRS=HOL U6 - https://doi.org/10.1051/0004-6361/200913578 SN - 0004-6361 ER - TY - JOUR A1 - Valori, Gherardo A1 - Kliem, Bernhard A1 - Török, Tibor A1 - Titov, Viacheslav S. T1 - Testing magnetofrictional extrapolation with the Titov-Demoulin model of solar active regions N2 - We examine the nonlinear magnetofrictional extrapolation scheme using the solar active region model by Titov and Demoulin as test field. This model consists of an arched, line-tied current channel held in force-free equilibrium by the potential field of a bipolar flux distribution in the bottom boundary. A modified version with a parabolic current density profile is employed here. We find that the equilibrium is reconstructed with very high accuracy in a representative range of parameter space, using only the vector field in the bottom boundary as input. Structural features formed in the interface between the flux rope and the surrounding arcade - "hyperbolic flux tube" and "bald patch separatrix surface" - are reliably reproduced, as are the flux rope twist and the energy and helicity of the configuration. This demonstrates that force-free fields containing these basic structural elements of solar active regions can be obtained by extrapolation. The influence of the chosen initial condition on the accuracy of reconstruction is also addressed, confirming that the initial field that best matches the external potential field of the model quite naturally leads to the best reconstruction. Extrapolating the magnetogram of a Titov-Demoulin equilibrium in the unstable range of parameter space yields a sequence of two opposing evolutionary phases, which clearly indicate the unstable nature of the configuration: a partial buildup of the flux rope with rising free energy is followed by destruction of the rope, losing most of the free energy. Y1 - 2010 UR - http://www.aanda.org/ U6 - https://doi.org/10.1051/0004-6361/201014416 SN - 0004-6361 ER - TY - JOUR A1 - Fox, Andrew J. A1 - Wakker, Bart P. A1 - Smoker, Jonathan V. A1 - Richter, Philipp A1 - Savage, Blair D. A1 - Sembach, Kenneth R. T1 - Exploring the origin and fate of the Magellanic stream with ultraviolet and optical absorption N2 - We present an analysis of ionization and metal enrichment in the Magellanic Stream (MS), the nearest gaseous tidal stream, using Hubble Space Telescope/STIS and FUSE ultraviolet spectroscopy of two background active galactic nuclei. The targets are NGC 7469, lying directly behind the MS with log N(H I)(MS) = 18.63 +/- 0.03(stat) +/- 0.08(syst), and Mrk 335, lying 24 degrees.7 away with log N(H I)(MS) = 16.67 +/- 0.05. For NGC 7469, we include optical spectroscopy from VLT/UVES. In both sight lines, the MS is detected in low-ion (O I, C II, C III, Si II, Si III, Al II, Ca II) and high-ion (O VI, C IV, Si IV) absorption. Toward NGC 7469, we measure an MS oxygen abundance [O/H](MS) = [O I/ H I]= -1.00 +/- 0.05(stat) +/- 0.08(syst), supporting the view that the Stream originates in the Small Magellanic Cloud rather than the Large Magellanic Cloud. We use CLOUDY to model the low-ion phase of the Stream as a photoionized plasma using the observed Si III/Si II and C III/C II ratios. Toward Mrk 335, this yields an ionization parameter between log U= -3.45 and -3.15, a gas density log (n(H)/cm(-3)) between-2.51 and -2.21, and a hydrogen ionization fraction of 98.9%- 99.5%. Toward NGC 7469, we derive sub-solar abundance ratios for [Si/O], [Fe/O], and [Al/O], indicating the presence of dust in the MS. The high-ion column densities are too large to be explained by photoionization, but also cannot be explained by a single-temperature collisional ionization model (equilibrium or non-equilibrium). This suggests that the high-ion plasma is multi-phase, with an Si IV region, a hotter O VI region, and C IV potentially contributing to each. Summing over the low-ion and high-ion phases, we derive conservative lower limits on the ratio N(total H II)/N(H I) of greater than or similar to 19 toward NGC 7469 and greater than or similar to 330 toward Mrk 335, showing that along these two directions the vast majority of the Stream has been ionized. The presence of warm-hot plasma together with the small-scale structure observed at 21 cm provides evidence for an evaporative interaction with the hot Galactic corona. This scenario, predicted by hydrodynamical simulations, suggests that the fate of the MS will be to replenish the Galactic corona with new plasma, rather than to bring neutral fuel to the disk. Y1 - 2010 UR - http://iopscience.iop.org/0004-637X/ U6 - https://doi.org/10.1088/0004-637x/718/2/1046 SN - 0004-637X ER - TY - THES A1 - Ksianzou, Viachaslau T1 - Second-order nonlinear optical interactions and cascading effects in thinorganic films T1 - Nichtlineare optische Wechselwirkung zweiter Ordnung und Cascading in dünnen organischen Schichten N2 - The presented work describes new concepts of fast switching elements based on principles of photonics. The waveguides working in visible and infra-red ranges are put in a basis of these elements. And as materials for manufacturing of waveguides the transparent polymers, dopped by molecules of the dyes possessing second order nonlinear-optical properties are proposed. The work shows how nonlinear-optical processes in such structures can be implemented by electro-optical and opto-optical control circuit signals. In this paper we consider the complete cycle of fabrication of several types of integral photonic elements. The theoretical analysis of high-intensity beam propagation in media with second-order optical nonlinearity is performed. Quantitative estimations of necessary conditions of occurrence of the nonlinear-optical phenomena of the second order taking into account properties of used materials are made. The paper describes the various stages of manufacture of the basic structure of the integrated photonics: a planar waveguide. Using the finite element method the structure of the electromagnetic field inside the waveguide in different modes was analysed. A separate part of the work deals with the creation of composite organic materials with high optical nonlinearity. Using the methods of quantum chemistry, the dependence of nonlinear properties of dye molecules from its structure were investigated in details. In addition, the paper discusses various methods of inducing of an optical nonlinearity in dye-doping of polymer films. In the work, for the first time is proposed the use of spatial modulation of nonlinear properties of waveguide according Fibonacci law. This allows involving several different nonlinear optical processes simultaneously. The final part of the work describes various designs of integrated optical modulators and switches constructed of organic nonlinear optical waveguides. A practical design of the optical modulator based on Mach-Zehnder interferometer made by a photolithography on polymer film is presented. N2 - Die vorliegende Arbeit beschreibt neue Konzepte für schnelle photonische Schaltelemente. Diese Elemente basieren auf optischer Wellenleitung im sichtbaren und nahen infraroten Spektralbereich. Die Arbeit ist auf organische Wellenleiter aus transparenten, farbstoffdotierten Polymeren fokussiert, welche Chromophore mit besonders großen optischen Nichtlinearitäten zweiter Ordnung enthalten. Insbesondere wird dargestellt, wie nichtlineare optische Prozesse in derartigen Bauelementen genutzt werden können, wenn man elektrische oder optische Steuersignale einsetzt. Es wird der gesamte Her-stellungszyklus verschiedener integrierter photonischer Bauelemente betrachtet. Die Arbeit umfasst weiterhin eine detaillierte theoretische Analyse der Wellenausbreitung in Medien mit großer nichtlinearer optischer Suszeptibilität zweiter Ordnung bei hoher Lichtintensität. Unter Annahme optischer Materialkonstanten, welche den experimentell ermittelten Werten entsprechen, erfolgte eine quantitative Abschätzung für das Auftreten von Szenarien, bei denen messbare Abwei-chungen der Strahlausbreitung vom linearen Regime auftreten, z:B. das Auftreten von zeitlichen, räumlichen und spektralen Satteliten zu den im Material propagierenden Laserpulsen. Es gelang, we-sentliche Aspekte der Strahlpropagationsprozesse durch Anwendung von Jacobi-Integralfunktionen in geschlossener mathematischer Form darzustellen. Darüber hinausgehende theoretische Untersuchungen nutzten die Finite-Elemente-Methode, um die Verteilung des elektromagnetischen Feldes im Inneren optischer Wellenleiter für verschiedene Pro-pagationsmoden zu analysieren. Ein weiterer Teil der Arbeit beschäftigt sich mit organischen Kompositmaterialen, welche große opti-sche Nichtlinearitäten aufweisen. Mittels quantenchemischer Verfahren erfolgte eine detaillierte Un-tersuchung der Zusammenhänge zwischen der molekularen Struktur und den linearen sowie den nichtlinearen optischen Eigenschaften der untersuchten Farbstoffmoleküle und Polymere. In Bezug auf die Probenpräparation sind unterschiedliche Verfahren zur Schichtbildung und zur molekularen Orientierung miteinander verglichen und bewertet worden, da letztere eine Voraussetzung für das Auftreten nichtlinearer optischer Prozesse zweiter Ordnung bildet. Die Untersuchungen erstreckten sich auf Vakuumaufdampfschichten aus niedermolekularen Chromophoren und auf Polymerschich-ten, welche durch Vakuumabscheidung sowie durch Spincoating oder andere Flüssigphasenabschei-dungsverfahren hergestellt worden sind. Auf orientierenden Substraten (z.B. geriebene Schichten aus Polytetrafluoräthylen) konnte eine spontane Orientierung der deponierten Chromophore nachgewie-sen werden. Die Chromophore in Polymerschichten wurden durch Coronapolung orientiert. In der Arbeit ist zum ersten Mal vorgeschlagen worden, eine räumliche Modulation der nichtlinearen optischen Eigenschaften durch gezielte lokale Coronapolung oder andere Orientierungstechniken derart zu generieren, dass die Abfolge gepolter Domänen dem Bildungsgesetz einer modifizierten Fibonacci-Reihe mit gebrochen rationalen Zahlen gehorcht. Der Vorteil von optischen Wellenleitern mit dieser Struktur darin, dass diese mehrere unterschiedli-che nichtlineare optische Prozesse gleichzeitig unterstützen und somit eine Vielzahl neuartiger Phä-nomene auftreten kann, welche man in neuartigen photonischen Bauelementen, z.B. für die optische Informations- und Kommunikationstechnik nutzen kann. Der letzte Teil der Arbeit beschreibt den Aufbau verschiedener integrierter optischer Modulatoren und Schalter, die sich mit Hilfe das neu entwickelten Verfahrens herstellen lassen. Zukünftige Entwicklungen in der Photonik, insbesondere der optischen Informations- und Kommuni-kationstechnik werden im abschließenden Teil der Arbeit diskutiert. KW - NLO KW - SHG KW - QPM KW - Cascading KW - NLO KW - SHG KW - QPM KW - Cascading Y1 - 2010 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-49186 ER - TY - THES A1 - Schattauer, Sylvia T1 - Hybride Dünnschicht-Solarzellen aus mesoporösem Titandioxid und konjugierten Polymeren T1 - Hybrid thin solar cells comprising mesoporous titanium dioxide and conjugated polymers N2 - Das Ziel dieser Arbeit ist die Untersuchung der aktiven Komponenten und ihrer Wechselwirkungen in teilorganischen Hybrid-Solarzellen. Diese bestehen aus einer dünnen Titandioxidschicht, kombiniert mit einer dünnen Polymerschicht. Die Effizienz der Hybrid-Solarzellen wird durch die Lichtabsorption im Polymer, die Dissoziation der gebildeten Exzitonen an der aktiven Grenzfläche zwischen TiO2 und Polymer, sowie durch Generation und Extraktion freier Ladungsträger bestimmt. Zur Optimierung der Solarzellen wurden grundlegende physikalische Wechselwirkungen zwischen den verwendeten Materialen sowie der Einfluss verschiedener Herstellungsparameter untersucht. Unter anderem wurden Fragen zum optimalen Materialeinsatz und Präparationsbedingungen beantwortet sowie grundlegende Einflüsse wie Schichtmorphologie und Polymerinfiltration näher betrachtet. Zunächst wurde aus unterschiedlich hergestelltem Titandioxid (Akzeptor-Schicht) eine Auswahl für den Einsatz in Hybrid-Solarzellen getroffen. Kriterium war hierbei die unterschiedliche Morphologie aufgrund der Oberflächenbeschaffenheit, der Film-Struktur, der Kristallinität und die daraus resultierenden Solarzelleneigenschaften. Für die anschließenden Untersuchungen wurden mesoporöse TiO2–Filme aus einer neuen Nanopartikel-Synthese, welche es erlaubt, kristalline Partikel schon während der Synthese herzustellen, als Elektronenakzeptor und konjugierte Polymere auf Poly(p-Phenylen-Vinylen) (PPV)- bzw. Thiophenbasis als Donatormaterial verwendet. Bei der thermischen Behandlung der TiO2-Schichten erfolgt eine temperaturabhängige Änderung der Morphologie, jedoch nicht der Kristallstruktur. Die Auswirkungen auf die Solarzelleneigenschaften wurden dokumentiert und diskutiert. Um die Vorteile der Nanopartikel-Synthese, die Bildung kristalliner TiO2-Partikel bei tiefen Temperaturen, nutzen zu können, wurden erste Versuche zur UV-Vernetzung durchgeführt. Neben der Beschaffenheit der Oxidschicht wurde auch der Einfluss der Polymermorphologie, bedingt durch Lösungsmittelvariation und Tempertemperatur, untersucht. Hierbei konnte gezeigt werden, dass u.a. die Viskosität der Polymerlösung die Infiltration in die TiO2-Schicht und dadurch die Effizienz der Solarzelle beeinflusst. Ein weiterer Ansatz zur Erhöhung der Effizienz ist die Entwicklung neuer lochleitender Polymere, welche möglichst über einen weiten spektralen Bereich Licht absorbieren und an die Bandlücke des TiO2 angepasst sind. Hierzu wurden einige neuartige Konzepte, z.B. die Kombination von Thiophen- und Phenyl-Einheiten näher untersucht. Auch wurde die Sensibilisierung der Titandioxidschicht in Anlehnung an die höheren Effizienzen der Farbstoffzellen in Betracht gezogen. Zusammenfassend konnten im Rahmen dieser Arbeit wichtige Einflussparameter auf die Funktion hybrider Solarzellen identifiziert und z.T. näher diskutiert werden. Für einige limitierende Faktoren wurden Konzepte zur Verbesserung bzw. Vermeidung vorgestellt. N2 - The main objective of this thesis is to study the active components and their interactions in so called organic hybrid solar cells. These consist of a thin inorganic titanium dioxide layer, combined with a polymer layer. In general, the efficiency of these hybrid solar cells is determined by the light absorption in the donor polymer, the dissociation of excitons at the heterojunction between TiO2 and polymer, as well as the generation and extraction of free charge carriers. To optimize the solar cells, the physical interactions between the materials are modified and the influences of various preparation parameters are systematically investigated. Among others, important findings regarding the optimal use of materials and preparation conditions as well as detailed investigations of fundamental factors such as film morphology and polymer infiltration are presented in more detail. First, a variety of titanium dioxide layer were produced, from which a selection for use in hybrid solar cells was made. The obtained films show differences in surface structure, film morphology and crystallinity, depending on the way how the TiO2 layer has been prepared. All these properties of the TiO2 films may strongly affect the performance of the hybrid solar cells, by influencing e.g. the exciton diffusion length, the efficiency of exciton dissociation at the hybrid interface, and the carrier transport properties. Detailed investigations were made for mesoporous TiO2 layer following a new nanoparticle synthesis route, which allows to produce crystalline particles during the synthesis. As donor component, conjugated polymers, either derivatives of cyclohexylamino-poly(p-phenylene vinylene) (PPV) or a thiophene are used. The preparation routine also includes a thermal treatment of the TiO2 layers, revealing a temperature-dependent change in morphology, but not of the crystal structure. The effects on the solar cell properties have been documented and discussed. To take advantage of the nanoparticle synthesis, the formation of crystalline TiO2 particles by UV crosslinking and first solar cell measurements are presented. In addition to the nature of the TiO2 layer, the influence of polymer morphology is investigated. Different morphologies are realized by solvent variation and thermal annealing. It is shown that, among other factors, the viscosity of the polymer solution and the infiltration into the TiO2 layer mainly affects the efficiency of the solar cell. Another approach to increase the efficiency is the development of new hole-conducting polymers that absorb over a wide spectral range and which are adjusted to the energy levels of TiO2. Also new concepts, for example, the combination of thiophene- and phenyl-units into a copolymer are investigated in more detail. In summary, important parameters influencing the properties of hybrid solar cells are identified and discussed in more detail. For some limiting factors concepts to overcome these limitations are presented. KW - hybride Solarzellen KW - Titandioxid KW - Sintern KW - Polymer KW - hybrid thin solar cells KW - titanium dioxide KW - thermal treatment KW - polymers Y1 - 2010 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-52619 ER - TY - JOUR A1 - Bange, Sebastian A1 - Schubert, Marcel A1 - Neher, Dieter T1 - Charge mobility determination by current extraction under linear increasing voltages : case of nonequilibrium charges and field-dependent mobilities N2 - The method of current extraction under linear increasing voltages (CELIV) allows for the simultaneous determination of charge mobilities and charge densities directly in thin-film geometries as used in organic photovoltaic (OPV) cells. It has been specifically applied to investigate the interrelation of microstructure and charge-transport properties in such systems. Numerical and analytical calculations presented in this work show that the evaluation of CELIV transients with the commonly used analysis scheme is error prone once charge recombination and, possibly, field- dependent charge mobilities are taken into account. The most important effects are an apparent time dependence of charge mobilities and errors in the determined field dependencies. Our results implicate that reports on time-dependent mobility relaxation in OPV materials obtained by the CELIV technique should be carefully revisited and confirmed by other measurement methods. Y1 - 2010 UR - http://prb.aps.org/ U6 - https://doi.org/10.1103/Physrevb.81.035209 SN - 1098-0121 ER - TY - JOUR A1 - Eichler, David A1 - Guetta, Dafne A1 - Pohl, Martin T1 - The high energy budget allocations in shocks and gamma ray bursts N2 - The statistical distribution of energies among particles responsible for long gamma-ray burst (GRB) emission is analyzed in light of recent results of the Fermi Observatory. The all-sky flux, F., recorded by the Gamma-Ray Burst Monitor (GBM) is shown, despite its larger energy range, to be not significantly larger than that reported by the Burst and Transient Explorer, suggesting a relatively small flux in the 3-30MeV energy range. The present-day energy input rate in gamma-rays recorded by the GBM from long GRBs is found, assuming star formation rates in the literature, to be W(0) = 0.5F gamma H/c = 5x10(42) erg Mpc(-3) yr(-1). The Large Area Telescope fluence, when observed, is about 5%-10% per decade of the total, in good agreement with the predictions of saturated, nonlinear shock acceleration. The high- energy component of long GRBs, as measured by Fermi, is found to contain only similar to 10-2.5 of the energy needed to produce ultrahigh-energy cosmic rays (UHECRs) above 4 EeV, assuming the latter to be extragalactic, when various numerical factors are carefully included, if the cosmic-ray source spectrum has a spectral index of -2. The observed. - ray fraction of the required UHECR energy is even smaller if the source spectrum is softer than E-2. The AMANDA II limits rule out such a GRB origin for UHECRs if much more than 10(-2) of the cosmic-ray energy goes into neutrinos that are within, and simultaneous with, the gamma-ray beam. It is suggested that "orphan" neutrinos out of the gamma-ray beam might be identifiable via orphan afterglow or other wide angle signatures of GRBs in lieu of coincidence with prompt gamma-rays, and it is recommended that feasible single neutrino trigger criteria be established to search for such coincidences. Y1 - 2010 UR - http://iopscience.iop.org/0004-637X/ U6 - https://doi.org/10.1088/0004-637x/722/1/543 SN - 0004-637X ER - TY - JOUR A1 - Steyrleuthner, Robert A1 - Schubert, Marcel A1 - Jaiser, Frank A1 - Blakesley, James C. A1 - Chen, Zhihua A1 - Facchetti, Antonio A1 - Neher, Dieter T1 - Bulk electron transport and charge injection in a high mobility n-type semiconducting polymer N2 - Bulk electron transport in a high mobility n-type polymer is studied by time-of-flight photocurrent measurements and electron-only devices. Bulk electron mobilities of similar to 5 x 10(-3) cm(2)/Vs are obtained. The analysis of the electron currents suggests the presence of an injection barrier for all conventionally used low workfunction cathodes. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/jhome/10008336 U6 - https://doi.org/10.1002/adma.201000232 SN - 0935-9648 ER - TY - JOUR A1 - Herzog, Marc A1 - Leitenberger, Wolfram A1 - Shayduk, Roman A1 - van der Veen, Renske Marjan A1 - Milne, Chris J. A1 - Johnson, Steven Lee A1 - Vrejoiu, Ionela A1 - Alexe, Marin A1 - Hesse, Dietrich A1 - Bargheer, Matias T1 - Ultrafast manipulation of hard x-rays by efficient Bragg switches N2 - We experimentally demonstrate efficient switching of the hard x-ray Bragg reflectivity of a SrRuO3 /SrTiO3 superlattice by optical excitation of large-amplitude coherent acoustic superlattice phonons. The rocking curve changes drastically on a 1 ps timescale. The (0 0 116) reflection is almost extinguished (Delta R/R-0=-0.91), while the (0 0 118) reflection increases by more than an order of magnitude (Delta R/R-0=24.1). The change of the x-ray structure factor depends nonlinearly on the phonon amplitude, allowing manipulation of the x-ray response on a timescale considerably shorter than the phonon period. Numerical simulations for a superlattice with slightly changed geometry and realistic parameters predict a switching-contrast ratio Delta R/R-0 of 700 with high reflectivity. Y1 - 2010 UR - http://apl.aip.org/ U6 - https://doi.org/10.1063/1.3402773 SN - 0003-6951 ER - TY - JOUR A1 - Enquist, Henrik A1 - Navirian, Hengameh A1 - Nueske, Ralf A1 - von Korff Schmising, Clemens A1 - Jurgilaitis, Andrius A1 - Herzog, Marc A1 - Bargheer, Matias A1 - Sondhauss, Peter A1 - Larsson, Joergen T1 - Subpicosecond hard x-ray streak camera using single-photon counting N2 - We have developed and characterized a hard x-ray accumulating streak camera that achieves subpicosecond time resolution by using single-photon counting. A high repetition rate of 2 kHz was achieved by use of a readout camera with built-in image processing capabilities. The effects of sweep jitter were removed by using a UV timing reference. The use of single-photon counting allows the camera to reach a high quantum efficiency by not limiting the divergence of the photoelectrons. Y1 - 2010 UR - http://www.opticsinfobase.org/ U6 - https://doi.org/10.1364/OL.35.003219 SN - 0146-9592 ER -