TY - THES A1 - Bojahr, Andre T1 - Hypersound interaction studied by time-resolved inelastic light and x-ray scattering T1 - Wechselwirkende Hyperschallwellen untersucht mittels zeitaufgelöster inelastischer Licht- und Röntgenstreuung N2 - This publications-based thesis summarizes my contribution to the scientific field of ultrafast structural dynamics. It consists of 16 publications, about the generation, detection and coupling of coherent gigahertz longitudinal acoustic phonons, also called hypersonic waves. To generate such high frequency phonons, femtosecond near infrared laser pulses were used to heat nanostructures composed of perovskite oxides on an ultrashort timescale. As a consequence the heated regions of such a nanostructure expand and a high frequency acoustic phonon pulse is generated. To detect such coherent acoustic sound pulses I use ultrafast variants of optical Brillouin and x-ray scattering. Here an incident optical or x-ray photon is scattered by the excited sound wave in the sample. The scattered light intensity measures the occupation of the phonon modes. The central part of this work is the investigation of coherent high amplitude phonon wave packets which can behave nonlinearly, quite similar to shallow water waves which show a steepening of wave fronts or solitons well known as tsunamis. Due to the high amplitude of the acoustic wave packets in the solid, the acoustic properties can change significantly in the vicinity of the sound pulse. This may lead to a shape change of the pulse. I have observed by time-resolved Brillouin scattering, that a single cycle hypersound pulse shows a wavefront steepening. I excited hypersound pulses with strain amplitudes until 1% which I have calibrated by ultrafast x-ray diffraction (UXRD). On the basis of this first experiment we developed the idea of the nonlinear mixing of narrowband phonon wave packets which we call "nonlinear phononics" in analogy with the nonlinear optics, which summarizes a kaleidoscope of surprising optical phenomena showing up at very high electric fields. Such phenomena are for instance Second Harmonic Generation, four-wave-mixing or solitons. But in case of excited coherent phonons the wave packets have usually very broad spectra which make it nearly impossible to look at elementary scattering processes between phonons with certain momentum and energy. For that purpose I tested different techniques to excite narrowband phonon wave packets which mainly consist of phonons with a certain momentum and frequency. To this end epitaxially grown metal films on a dielectric substrate were excited with a train of laser pulses. These excitation pulses drive the metal film to oscillate with the frequency given by their inverse temporal displacement and send a hypersonic wave of this frequency into the substrate. The monochromaticity of these wave packets was proven by ultrafast optical Brillouin and x-ray scattering. Using the excitation of such narrowband phonon wave packets I was able to observe the Second Harmonic Generation (SHG) of coherent phonons as a first example of nonlinear wave mixing of nanometric phonon wave packets. N2 - Diese publikationsbasierte Dissertation fasst meinen Beitrag zum Forschungsgebiet der ultraschnellen Strukturdynamik zusammen. Diese Arbeit besteht aus 16 Publikationen aus den Bereichen der Erzeugung, Detektion und Kopplung von kohärenten Gigahertz longitudinal-akustischen Phononen, auch Hyperschallwellen genannt. Um solch hochfrequente Phononen zu erzeugen, werden Femtosekunden nahinfrarot Laserpulse benutzt, um Nanostrukturen auf einer ultraschnellen Zeitskala zu erhitzen. Die aufgeheizten Regionen der Nanostruktur dehnen sich aufgrund der hohen Temperatur aus und ein hochfrequenter Schallpuls wird generiert. Um solche akustischen Pulse zu detektieren benutze ich ultraschnelle Varianten der Brillouin- und Röntgenstreuung. Dabei wird ein einfallendes optisches oder Röntgenphoton an der erzeugten Schallwelle gestreut. Die gemessene Streuintensität ist hierbei ein Maß für die Besetzung einzelner Phononenzustände. Der zentrale Teil dieser Arbeit ist die Untersuchung von kohärenten Phonon-Wellenpaketen mit sehr hoher Amplitude. Diese Wellenpakete können sich nichtlinear verhalten, sehr ähnlich zu Flachwasserwellen bei denen nichtlineare Effekte in Form eines Aufsteilens der Wellenfronten oder der Existenz von Solitonen, bekannt als Tsunamis, äußern. Durch die hohe Amplitude der akustischen Wellenpakete können sich die akustischen Eigenschaften des Festkörpers in der Umgebung des Schallpulses signifikant ändern, welches sich dann in einer Formänderung des Schallpulses widerspiegelt. Ich konnte mittels zeitaufgelöster Brillouinstreuung das Aufsteilen der Wellenfronten eines Hyperschallpulses bestehend aus einem einzigen Oszillationszyklus beobachten. Hierbei wurden Hyperschallwellen mit einer Dehnungsamplitude von bis zu 1% angeregt, wobei ich diesen Wert mittels ultraschneller Röntgenbeugung kalibrieren konnte. Mit diesem ersten Experiment als Basis entwickelten wir die Idee der nichtlinearen Wellenmischung von schmalbandigen Phonon-Wellenpaketen unter dem Titel "nichtlineare Phononik" in Analogie zur nichtlinearen Optik, welche sich aus einer Reihe von verblüffenden optischen Phänomenen bei sehr hohen elektrischen Feldstärken zusammensetzt. Solche Phänomene sind z. B. die optische Frequenzverdopplung, das Vier-Wellen-Mischen oder Solitone. Nur sind im Falle von kohärenten Phononen die erzeugten Spektren sehr breitbandig, was die Untersuchung von spezifischen Phononen mit festem Impuls und definierter Frequenz fast unmöglich macht. Aus diesem Grund testete ich verschiedene Methoden um schmalbandige Phonon-Wellenpakete anzuregen, welche im Wesentlichen aus Phononen bestimmten Impulses und definierter Frequenz bestehen. Dafür wurden schließ lich epitaktisch auf ein dielektrisches Substrat aufgewachsene Metallfilme mit einen Laserpulszug angeregt. Hier sorgen die Lichtpulse für eine periodische Oszillation des Metalfilms, wobei die Anregefrequenz durch den inversen zeitlichen Abstand der Lichtpulse gegeben ist. Diese periodische Oszillation sendet dann ein Hyperschallwellenpaket eben dieser Frequenz ins Substrat. Die Monochromie dieser Wellenpakete konnte dabei mittels ultraschneller Brillouin- und Röntgenstreuung bestätigt werden. Durch die Benutzung dieser schmalbandigen Phonon-Wellenpakete war es mir möglich, die Frequenzverdopplung (SHG) von kohärenten Phononen zu beobachten, was ein erstes Beispiel für die nichtlineare Wellenmischung von nanometrischen Phonon-Wellenpaketen ist. KW - hypersound KW - nonlinear acoustics KW - ultrafast KW - Brillouin scattering KW - x-ray diffraction KW - self-steepening KW - second-harmonic generation KW - Phononen KW - Wechselwirkung KW - Anharmonizität KW - nichtlineare Wellenmischung KW - zweite Harmonische KW - Phononenstreuung KW - nichlineare Phononik Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-93860 ER - TY - THES A1 - Amaro-Seoane, Pau T1 - Dense stellar systems and massive black holes T1 - Dichte stellare Systeme und massive Schwarze Löcher BT - sources of gravitational radiation and tidal disruptions BT - Quellen von Gravitationsstrahlung und Gezeiten-Sternzerissereignissen N2 - Gravity dictates the structure of the whole Universe and, although it is triumphantly described by the theory of General Relativity, it is the force that we least understand in nature. One of the cardinal predictions of this theory are black holes. Massive, dark objects are found in the majority of galaxies. Our own galactic center very contains such an object with a mass of about four million solar masses. Are these objects supermassive black holes (SMBHs), or do we need alternatives? The answer lies in the event horizon, the characteristic that defines a black hole. The key to probe the horizon is to model the movement of stars around a SMBH, and the interactions between them, and look for deviations from real observations. Nuclear star clusters harboring a massive, dark object with a mass of up to ~ ten million solar masses are good testbeds to probe the event horizon of the potential SMBH with stars. The channel for interactions between stars and the central MBH are the fact that (a) compact stars and stellar-mass black holes can gradually inspiral into the SMBH due to the emission of gravitational radiation, which is known as an “Extreme Mass Ratio Inspiral” (EMRI), and (b) stars can produce gases which will be accreted by the SMBH through normal stellar evolution, or by collisions and disruptions brought about by the strong central tidal field. Such processes can contribute significantly to the mass of the SMBH. These two processes involve different disciplines, which combined will provide us with detailed information about the fabric of space and time. In this habilitation I present nine articles of my recent work directly related with these topics. N2 - Die Gravitation bestimmt die Struktur des ganzen Universums und ist, obwohl sie mit großem Erfolg durch die Theorie der Allgemeinen Relativitätstheorie beschrieben wird, die am wenigsten verstandene Kraft in der Natur. Eine der grundsätzlichsten Vorhersagen dieser Theorie sind Schwarze Löcher. Massive, dunkle Objekte befinden sich in einem Großteil aller Galaxien. Das Zentrum unserer eigenen Galaxis enthält solch ein Objekt mit einer Masse von etwa vier Millionen Sonnenmassen. Sind diese Objekte supermassive Schwarze Löcher oder brauchen wir Alternativen? Die Antwort liegt im Ereignishorizont, der Eigenschaft, die ein Schwarzes Loch definiert. Der Schlüssel um den Ereignishorizont zu untersuchen ist, die Bewegungen der Sterne um eine Supermassives Schwarzes Loch zu modellieren, sowie deren Interaktionen, und nach Abweichungen von unseren Erwartungen in echten Beobachtungen zu suchen. Zentrale Sternhaufen, die ein massives, dunkles Objekt mit einer Masse bis zu ∼ zehn Millionen Sonnenmassen enthalten, sind gute Laborarien um den Ereignishorizont eines möglichen supermassiven Schwarzen Lochs mit Hilfe von Sternen zu untersuchen. Die Kanäle für mögliche Wechselwirkungen zwischen Sternen und einem zentralen Schwarzen Loch sind: (a) Kompakte Sternreste und stellare Schwarze Löcher können durch die Emission von Gravitationswellen allmählich auf spiralförmigen Orbits in das supermassive Schwarze Loch fallen, was als “Extreme Mass Ratio Inspiral” (EMRI) bezeichent wird. (b) Durch normale Sternentwicklung (Sternwinde) sowie durch Sternkollisionen oder Zerstörung von Sternen im starken zentralen Gezeitenfeld kann Gas freigesetzt werden, welches anschließend vom supermassiven Schwarzen Loch akkretiert werden kann. Solche Prozesse können wesentlich zur Masse eines Supermassiven Schwarzen Lochs beitragen. Die beiden Prozesse (a und b) beinhalten verschiedene astrophysikalische Aspekte, welche uns in ihrer Kombination mit detaillierter Information über die Beschaffenheit der Raumzeit versorgen. In dieser Habilitationsschrift präsentiere ich neun Artikel aus meiner jüngeren Forschungsarbeit, welche direkt Probleme aus diesen Themenbereichen behandeln. KW - stellar dynamics KW - massive black holes KW - gravitational waves KW - general relativity KW - Stellardynamik KW - massive Schwarze Löcher KW - Gravitationswellen KW - allgemeine Relativitätstheorie Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-95439 ER - TY - THES A1 - Dionysopoulou, Kyriaki T1 - General-relativistic magnetohydrodynamics in compact objects BT - a resistive-magnetohydrodynamics approach Y1 - 2016 ER - TY - GEN A1 - Cherstvy, Andrey G. A1 - Metzler, Ralf T1 - Anomalous diffusion in time-fluctuating non-stationary diffusivity landscapes N2 - We investigate the ensemble and time averaged mean squared displacements for particle diffusion in a simple model for disordered media by assuming that the local diffusivity is both fluctuating in time and has a deterministic average growth or decay in time. In this study we compare computer simulations of the stochastic Langevin equation for this random diffusion process with analytical results. We explore the regimes of normal Brownian motion as well as anomalous diffusion in the sub- and superdiffusive regimes. We also consider effects of the inertial term on the particle motion. The investigation of the resulting diffusion is performed for unconfined and confined motion. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 257 Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-95901 SP - 23840 EP - 23852 ER - TY - JOUR A1 - Cherstvy, Andrey G. A1 - Metzler, Ralf T1 - Anomalous diffusion in time-fluctuating non-stationary diffusivity landscapes JF - Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies N2 - We investigate the ensemble and time averaged mean squared displacements for particle diffusion in a simple model for disordered media by assuming that the local diffusivity is both fluctuating in time and has a deterministic average growth or decay in time. In this study we compare computer simulations of the stochastic Langevin equation for this random diffusion process with analytical results. We explore the regimes of normal Brownian motion as well as anomalous diffusion in the sub- and superdiffusive regimes. We also consider effects of the inertial term on the particle motion. The investigation of the resulting diffusion is performed for unconfined and confined motion. Y1 - 2016 U6 - https://doi.org/10.1039/C6CP03101C SN - 1463-9084 SN - 1463-9076 VL - 18 SP - 23840 EP - 23852 PB - RSC Publ. CY - Cambridge ER - TY - JOUR A1 - Ghosh, Surya K. A1 - Cherstvy, Andrey G. A1 - Petrov, Eugene P. A1 - Metzler, Ralf T1 - Interactions of rod-like particles on responsive elastic sheets JF - Soft matter N2 - What are the physical laws of the mutual interactions of objects bound to cell membranes, such as various membrane proteins or elongated virus particles? To rationalise this, we here investigate by extensive computer simulations mutual interactions of rod-like particles adsorbed on the surface of responsive elastic two-dimensional sheets. Specifically, we quantify sheet deformations as a response to adhesion of such filamentous particles. We demonstrate that tip-to-tip contacts of rods are favoured for relatively soft sheets, while side-by-side contacts are preferred for stiffer elastic substrates. These attractive orientation-dependent substrate-mediated interactions between the rod-like particles on responsive sheets can drive their aggregation and self-assembly. The optimal orientation of the membrane-bound rods is established via responding to the elastic energy profiles created around the particles. We unveil the phase diagramme of attractive–repulsive rod–rod interactions in the plane of their separation and mutual orientation. Applications of our results to other systems featuring membrane-associated particles are also discussed. Y1 - 2016 U6 - https://doi.org/10.1039/C6SM01522K SN - 1744-6848 SN - 1744-683X PB - RSC CY - London ER - TY - GEN A1 - Ghosh, Surya K. A1 - Cherstvy, Andrey G. A1 - Petrov, Eugene P. A1 - Metzler, Ralf T1 - Interactions of rod-like particles on responsive elastic sheets N2 - What are the physical laws of the mutual interactions of objects bound to cell membranes, such as various membrane proteins or elongated virus particles? To rationalise this, we here investigate by extensive computer simulations mutual interactions of rod-like particles adsorbed on the surface of responsive elastic two-dimensional sheets. Specifically, we quantify sheet deformations as a response to adhesion of such filamentous particles. We demonstrate that tip-to-tip contacts of rods are favoured for relatively soft sheets, while side-by-side contacts are preferred for stiffer elastic substrates. These attractive orientation-dependent substrate-mediated interactions between the rod-like particles on responsive sheets can drive their aggregation and self-assembly. The optimal orientation of the membrane-bound rods is established via responding to the elastic energy profiles created around the particles. We unveil the phase diagramme of attractive–repulsive rod–rod interactions in the plane of their separation and mutual orientation. Applications of our results to other systems featuring membrane-associated particles are also discussed. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 256 Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-95882 ER - TY - THES A1 - Lehmann, Jascha In-su T1 - Changes in extratropical storm track activity and their implications for extreme weather events Y1 - 2016 ER - TY - THES A1 - Schröder, Henning T1 - Ultrafast electron dynamics in Fe(CO)5 and Cr(CO)6 T1 - Ultraschnelle Elektronendynamik in Fe(CO)5 und Cr(CO)6 N2 - In this thesis, the two prototype catalysts Fe(CO)₅ and Cr(CO)₆ are investigated with time-resolved photoelectron spectroscopy at a high harmonic setup. In both of these metal carbonyls, a UV photon can induce the dissociation of one or more ligands of the complex. The mechanism of the dissociation has been debated over the last decades. The electronic dynamics of the first dissociation occur on the femtosecond timescale. For the experiment, an existing high harmonic setup was moved to a new location, was extended, and characterized. The modified setup can induce dynamics in gas phase samples with photon energies of 1.55eV, 3.10eV, and 4.65eV. The valence electronic structure of the samples can be probed with photon energies between 20eV and 40eV. The temporal resolution is 111fs to 262fs, depending on the combination of the two photon energies. The electronically excited intermediates of the two complexes, as well as of the reaction product Fe(CO)₄, could be observed with photoelectron spectroscopy in the gas phase for the first time. However, photoelectron spectroscopy gives access only to the final ionic states. Corresponding calculations to simulate these spectra are still in development. The peak energies and their evolution in time with respect to the initiation pump pulse have been determined, these peaks have been assigned based on literature data. The spectra of the two complexes show clear differences. The dynamics have been interpreted with the assumption that the motion of peaks in the spectra relates to the movement of the wave packet in the multidimensional energy landscape. The results largely confirm existing models for the reaction pathways. In both metal carbonyls, this pathway involves a direct excitation of the wave packet to a metal-to-ligand charge transfer state and the subsequent crossing to a dissociative ligand field state. The coupling of the electronic dynamics to the nuclear dynamics could explain the slower dissociation in Fe(CO)₅ as compared to Cr(CO)₆. N2 - Diese Dissertation handelt von der Untersuchung der zwei Modell-Katalysatoren Fe(CO)₅ und Cr(CO)₆ mittels zeitaufgelöster Photoelektronen Spektroskopie an einem High Harmonic Setup. In beiden Metallcarbonyl kann die Dissoziation von einem, oder mehreren Liganden durch ein UV Photon ausgelöst werden. Der Dissoziation-Mechanismus wurde in den letzten Jahrzehnten diskutiert. Die Abspaltung des ersten Liganden und die damit verbundenen elektronischen Dynamiken finden auf Zeitskalen von Femtosekunden statt. Für die Durchführung dieses Experiments wurde ein bestehender High Harmonic Setup in ein neues Labor verlegt. Der Aufbau wurde erweitert und charakterisiert. Mit dem modifizierten Aufbau können nun Reaktionen in Gas-Phasen-Proben mit Photonenenergien von 1.55eV, 3.10eV und 4.65eV ausgelöst werden. Dabei kann die Valenz-Elektronen-Struktur mit Photonenenergien zwischen 20eV und 40eV untersucht werden. Die Zeitauflösung liegt im Bereich von 111fs bis 262fs und hängt von der Kombination der zwei Photonenenergien ab. Die beiden Komplexe sowie Fe(CO)₄ konnten in der Gas-Phase zum ersten Mal in elektronisch angeregten Zuständen mittels zeitaufgelöster Photoelektronenspektroskopie beobachtet werden. Im Allgemeinen kann jedoch mit der Photoelektronenspektroskopie nur der ionische Endzustand untersucht werden. Modellrechnungen zu den Spektren und die Entwicklung der dazugehörigen Theorie befinden derzeit noch in der Entwicklungsphase. Die Peaks in den Spektren konnten anhand von Literatur zugeordnet werden. Die Spektren der beiden Komplexe unterscheiden sich deutlich. Zu deren Interpretation wurde die Näherung verwendet, dass die Dynamik der Peaks in den Spektren die Bewegung des Wellenpakets in der multidimensionalen Energielandschaft darstellt. Die neuen Daten bestätigen weitestgehend bestehende Modelle für die Reaktionsmechanismen. Der Reaktionsmechanismus verläuft für beide Metallcarbonyle über eine direkte Anregung des Wellenpakets in einen metal-to-ligand charge transfer Zustand. Von dem angeregten Zustand aus kann das Wellenpaket in den dissoziativen ligand field Zustand wechseln. Dass die Reaktion in Fe(CO)₅ langsamer als in Cr(CO)₆ abläuft, kann durch die Kopplung der Dynamiken von Elektronen und Kernen erklärt werden. KW - dissertation KW - Dissertation KW - photo electron spectroscopy KW - physical chemistry KW - molecular dynamics KW - high harmonic generation KW - iron pentacarbonyl KW - chromium hexacarbonyl KW - metal carbonyls KW - ultrafast KW - dynamics KW - Photoelektronen KW - Spektroskopie KW - Moleküldynamik KW - high harmonic KW - Eisenpentacarbonyl KW - Chromhexacarbonyl KW - Photodissoziation KW - photodissociation KW - ligand KW - bond Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-94589 ER - TY - THES A1 - Gomez, David T1 - Mechanisms of biochemical reactions within crowded environments T1 - Mechanismus der Biochemische Reaktionen im vollgestopfte Umgebungen N2 - The cell interior is a highly packed environment in which biological macromolecules evolve and function. This crowded media has effects in many biological processes such as protein-protein binding, gene regulation, and protein folding. Thus, biochemical reactions that take place in such crowded conditions differ from diluted test tube conditions, and a considerable effort has been invested in order to understand such differences. In this work, we combine different computationally tools to disentangle the effects of molecular crowding on biochemical processes. First, we propose a lattice model to study the implications of molecular crowding on enzymatic reactions. We provide a detailed picture of how crowding affects binding and unbinding events and how the separate effects of crowding on binding equilibrium act together. Then, we implement a lattice model to study the effects of molecular crowding on facilitated diffusion. We find that obstacles on the DNA impair facilitated diffusion. However, the extent of this effect depends on how dynamic obstacles are on the DNA. For the scenario in which crowders are only present in the bulk solution, we find that at some conditions presence of crowding agents can enhance specific-DNA binding. Finally, we make use of structure-based techniques to look at the impact of the presence of crowders on the folding a protein. We find that polymeric crowders have stronger effects on protein stability than spherical crowders. The strength of this effect increases as the polymeric crowders become longer. The methods we propose here are general and can also be applied to more complicated systems. N2 - Innerhalb einer Zelle, im Zytosol, entstehen und arbeiten sehr viele biologische Makromoleküle. Die Dichte dieser Moleküle ist sehr hoch und dieses ‘vollgestopfte’ Zytosol hat vielfältige Auswirkungen auf viele biologische Prozessen wie zum Beispiel Protein-Protein Interaktionen, Genregulation oder die Faltung von Proteinen. Der Ablauf von vielen biochemische Reaktionen in dieser Umgebung weicht von denen unter verdünnte Laborbedingungen ab. Um die Effekte dieses ‘makromolekularen Crowdings’ zu verstehen, wurde in den letzten Jahren bereits viel Mühe investiert. In dieser Arbeit kombinieren wir verschiede Computermethoden, um die Wirkungen des ‘makromolekularen Crowdings’ auf biologische Prozesse besser zu verstehen. Zuerst schlagen wir ein Gittermodell vor, um damit die Effekte des ‘makromolekularen Crowdings’ auf enzymatische Reaktionen zu studieren. Damit stellen wir ein detailliertes Bild zusammen, wie Crowding die Assoziations- und Dissozotationsraten beeinflusst und wie verschiedene crowding-Effekte zusammen auf die Gleichgewichtskonstante wirken. Weiterhin implementieren wir ein Gittermodell der ‘erleichterte Diffusion’. Unsere Ergebnisse zeigen, dass Hindernisse an der DNA die vereinfachte Diffusion beeinträchtigen. Das Ausmass dieser Wirkung hängt dabei von der Dynamik der Hindernisse an der DNA ab. Im dem Fall dass Crowder ausschließlich in der Lösung vorhanden sind, erhöhen sich unter bestimmten Bedingungen DNA-spezifische Bindungen. Schließlich nutzten wir strukturbasierte Techniken um damit die Auswirkungen von Crowding auf die Faltung von Proteinen zu untersuchen. Wir fanden dabei, dass Polymer Crowder stärkere Wirkungen auf die Proteinstabilität haben als kugelförmige Crowder. Dieser Effekt verstärkte sich mit der Länge der untersuchten Polymere. Die Methoden die hier vorgeschlagen werden, sind generell anwendbar und können auch an deutlich komplexeren Systemen angewandt werden. KW - molecular crowding KW - gene expression KW - enzymatic activity KW - protein folding KW - Molecular crowding KW - enzymatische Reaktionen KW - Genregulation KW - Faltung von Proteinen Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-94593 ER - TY - THES A1 - Rettig, Robert T1 - Über die Anisotropie der Kosmischen Strahlung Y1 - 2016 ER - TY - THES A1 - Rezanezhad, Vahid T1 - Inversion of the 2004 M6.0 Parkfield Earthquake Coseismic Offsets by Partition Model Y1 - 2016 ER - TY - GEN A1 - Kurpiers, Jona A1 - Neher, Dieter T1 - Dispersive Non-Geminate Recombination in an Amorphous Polymer:Fullerene Blend N2 - Recombination of free charge is a key process limiting the performance of solar cells. For low mobility materials, such as organic semiconductors, the kinetics of non-geminate recombination (NGR) is strongly linked to the motion of charges. As these materials possess significant disorder, thermalization of photogenerated carriers in the inhomogeneously broadened density of state distribution is an unavoidable process. Despite its general importance, knowledge about the kinetics of NGR in complete organic solar cells is rather limited. We employ time delayed collection field (TDCF) experiments to study the recombination of photogenerated charge in the high-performance polymer:fullerene blend PCDTBT:PCBM. NGR in the bulk of this amorphous blend is shown to be highly dispersive, with a continuous reduction of the recombination coefficient throughout the entire time scale, until all charge carriers have either been extracted or recombined. Rapid, contact-mediated recombination is identified as an additional loss channel, which, if not properly taken into account, would erroneously suggest a pronounced field dependence of charge generation. These findings are in stark contrast to the results of TDCF experiments on photovoltaic devices made from ordered blends, such as P3HT:PCBM, where non-dispersive recombination was proven to dominate the charge carrier dynamics under application relevant conditions. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 228 Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-91541 ER - TY - JOUR A1 - Kurpiers, Jona A1 - Neher, Dieter T1 - Dispersive Non-Geminate Recombination in an Amorphous Polymer:Fullerene Blend JF - Scientific reports N2 - Recombination of free charge is a key process limiting the performance of solar cells. For low mobility materials, such as organic semiconductors, the kinetics of non-geminate recombination (NGR) is strongly linked to the motion of charges. As these materials possess significant disorder, thermalization of photogenerated carriers in the inhomogeneously broadened density of state distribution is an unavoidable process. Despite its general importance, knowledge about the kinetics of NGR in complete organic solar cells is rather limited. We employ time delayed collection field (TDCF) experiments to study the recombination of photogenerated charge in the high-performance polymer:fullerene blend PCDTBT:PCBM. NGR in the bulk of this amorphous blend is shown to be highly dispersive, with a continuous reduction of the recombination coefficient throughout the entire time scale, until all charge carriers have either been extracted or recombined. Rapid, contact-mediated recombination is identified as an additional loss channel, which, if not properly taken into account, would erroneously suggest a pronounced field dependence of charge generation. These findings are in stark contrast to the results of TDCF experiments on photovoltaic devices made from ordered blends, such as P3HT:PCBM, where non-dispersive recombination was proven to dominate the charge carrier dynamics under application relevant conditions. Y1 - 2016 U6 - https://doi.org/10.1038/srep26832 SN - 2045-2322 VL - 6 PB - Nature Publishing Group CY - London ER - TY - GEN A1 - Neher, Dieter A1 - Kniepert, Juliane A1 - Elimelech, Arik A1 - Koster, L. Jan Anton T1 - A New Figure of Merit for Organic Solar Cells with Transport-limited Photocurrents N2 - Compared to their inorganic counterparts, organic semiconductors suffer from relatively low charge carrier mobilities. Therefore, expressions derived for inorganic solar cells to correlate characteristic performance parameters to material properties are prone to fail when applied to organic devices. This is especially true for the classical Shockley-equation commonly used to describe current-voltage (JV)-curves, as it assumes a high electrical conductivity of the charge transporting material. Here, an analytical expression for the JV-curves of organic solar cells is derived based on a previously published analytical model. This expression, bearing a similar functional dependence as the Shockley-equation, delivers a new figure of merit α to express the balance between free charge recombination and extraction in low mobility photoactive materials. This figure of merit is shown to determine critical device parameters such as the apparent series resistance and the fill factor. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 225 KW - Electronic and spintronic devices KW - Semiconductors Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-91414 ER - TY - JOUR A1 - Neher, Dieter A1 - Kniepert, Juliane A1 - Elimelech, Arik A1 - Koster, L. Jan Anton T1 - A New Figure of Merit for Organic Solar Cells with Transport-limited Photocurrents JF - Scientific reports N2 - Compared to their inorganic counterparts, organic semiconductors suffer from relatively low charge carrier mobilities. Therefore, expressions derived for inorganic solar cells to correlate characteristic performance parameters to material properties are prone to fail when applied to organic devices. This is especially true for the classical Shockley-equation commonly used to describe current-voltage (JV)-curves, as it assumes a high electrical conductivity of the charge transporting material. Here, an analytical expression for the JV-curves of organic solar cells is derived based on a previously published analytical model. This expression, bearing a similar functional dependence as the Shockley-equation, delivers a new figure of merit α to express the balance between free charge recombination and extraction in low mobility photoactive materials. This figure of merit is shown to determine critical device parameters such as the apparent series resistance and the fill factor. KW - Electronic and spintronic devices KW - Semiconductors Y1 - 2016 U6 - https://doi.org/10.1038/srep24861 SN - 2045-2322 VL - 6 PB - Nature Publishing Group CY - London ER - TY - JOUR A1 - Rätzel, Dennis A1 - Wilkens, Martin A1 - Menzel, Ralf T1 - Gravitational properties of light BT - the gravitational field of a laser pulse JF - New journal of physics : the open-access journal for physics N2 - The gravitational field of a laser pulse of finite lifetime, is investigated in the framework of linearized gravity. Although the effects are very small, they may be of fundamental physical interest. It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization. In general, the gravitational field is independent of the polarization direction. It is shown that all physical effects are confined to spherical shells expanding with the speed of light, and that these shells are imprints of the spacetime events representing emission and absorption of the pulse. Nearby test particles at rest are attracted towards the pulse trajectory by the gravitational field due to the emission of the pulse, and they are repelled from the pulse trajectory by the gravitational field due to its absorption. Examples are given for the size of the attractive effect. It is recovered that massless test particles do not experience any physical effect if they are co-propagating with the pulse, and that the acceleration of massless test particles counter-propagating with respect to the pulse is four times stronger than for massive particles at rest. The similarities between the gravitational effect of a laser pulse and Newtonian gravity in two dimensions are pointed out. The spacetime curvature close to the pulse is compared to that induced by gravitational waves from astronomical sources. KW - gravity KW - general relativity KW - laser pulses KW - electromagnetic radiation KW - linearized gravity KW - pp-wave solutions Y1 - 2016 U6 - https://doi.org/10.1088/1367-2630/18/2/023009 SN - 1367-2630 VL - 18 SP - 1 EP - 16 PB - IOP Science CY - London ER - TY - GEN A1 - Rätzel, Dennis A1 - Wilkens, Martin A1 - Menzel, Ralf T1 - Gravitational properties of light BT - the gravitational field of a laser pulse N2 - The gravitational field of a laser pulse of finite lifetime, is investigated in the framework of linearized gravity. Although the effects are very small, they may be of fundamental physical interest. It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization. In general, the gravitational field is independent of the polarization direction. It is shown that all physical effects are confined to spherical shells expanding with the speed of light, and that these shells are imprints of the spacetime events representing emission and absorption of the pulse. Nearby test particles at rest are attracted towards the pulse trajectory by the gravitational field due to the emission of the pulse, and they are repelled from the pulse trajectory by the gravitational field due to its absorption. Examples are given for the size of the attractive effect. It is recovered that massless test particles do not experience any physical effect if they are co-propagating with the pulse, and that the acceleration of massless test particles counter-propagating with respect to the pulse is four times stronger than for massive particles at rest. The similarities between the gravitational effect of a laser pulse and Newtonian gravity in two dimensions are pointed out. The spacetime curvature close to the pulse is compared to that induced by gravitational waves from astronomical sources. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 222 KW - electromagnetic radiation KW - general relativity KW - gravity KW - laser pulses KW - linearized gravity KW - pp-wave solutions Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-90553 ER -