@article{GuliakovaGorokhovatskyGalikhanovetal.2019, author = {Guliakova, A. A. and Gorokhovatsky, Yu. A. and Galikhanov, M. F. and Fr{\"u}bing, Peter}, title = {Thermoactivational spectroscopy of the high impact polystyrene based composite films}, series = {St. Petersburg Polytechnic University Journal : Physics and Mathematics}, volume = {12}, journal = {St. Petersburg Polytechnic University Journal : Physics and Mathematics}, number = {4}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2405-7223}, doi = {10.18721/JPM.12401}, pages = {9 -- 16}, year = {2019}, abstract = {The relaxation processes in the high impact polystyrene (HIPS) films filled with 2, 4, 6 vol.\% of titanium dioxide (TiO2) of the rutile modification have been studied using the thermally stimulated depolarization current (TSDC) technique. Three relaxation processes were observed in the composite HIPS films. The first one (a-relaxation peak) appeared at about 93 degrees C and represented the glass transition. The second peak p was a high-temperature part of the first one and overlapped it. The p peak was caused by the release and subsequent motion of excess charges deposited during the electret preparation or the polarization process. The third peak appeared at about 150 degrees C and occurred only in the spectra of the composite films. The overlapping peaks were separated by the thermal cleaning technique. The subsequent application of the numerical methods (the Tikhonov regularization technique) allowed to determine the activation energy of the second process and to compare the obtained value with the corresponding data on the dielectric relaxation.}, language = {ru} } @misc{Fischer2012, type = {Master Thesis}, author = {Fischer, Jost}, title = {{\"U}ber Synchronisationsph{\"a}nomene nichtlinearer akustischer Oszillatoren}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-63618}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {In dieser Arbeit werden die Effekte der Synchronisation nichtlinearer, akustischer Oszillatoren am Beispiel zweier Orgelpfeifen untersucht. Aus vorhandenen, experimentellen Messdaten werden die typischen Merkmale der Synchronisation extrahiert und dargestellt. Es folgt eine detaillierte Analyse der {\"U}bergangsbereiche in das Synchronisationsplateau, der Ph{\"a}nomene w{\"a}hrend der Synchronisation, als auch das Austreten aus der Synchronisationsregion beider Orgelpfeifen, bei verschiedenen Kopplungsst{\"a}rken. Die experimentellen Befunde werfen Fragestellungen nach der Kopplungsfunktion auf. Dazu wird die Tonentstehung in einer Orgelpfeife untersucht. Mit Hilfe von numerischen Simulationen der Tonentstehung wird der Frage nachgegangen, welche fluiddynamischen und aero-akustischen Ursachen die Tonentstehung in der Orgelpfeife hat und inwiefern sich die Mechanismen auf das Modell eines selbsterregten akustischen Oszillators abbilden l{\"a}sst. Mit der Methode des Coarse Graining wird ein Modellansatz formuliert.}, language = {de} } @phdthesis{Rettig2016, author = {Rettig, Robert}, title = {{\"U}ber die Anisotropie der Kosmischen Strahlung}, school = {Universit{\"a}t Potsdam}, pages = {90, XV}, year = {2016}, language = {de} } @phdthesis{Liepertz2017, author = {Liepertz, Sven Christian}, title = {Zusammenhang zwischen dem Professionswissen von Physiklehrkr{\"a}ften, dem sachstrukturellen Angebot des Unterrichts und der Sch{\"u}lerleistung}, series = {Studien zum Physik- und Chemielernen ; 224}, journal = {Studien zum Physik- und Chemielernen ; 224}, publisher = {Logos}, address = {Berlin}, isbn = {978-3-8325-4480-5}, school = {Universit{\"a}t Potsdam}, pages = {133}, year = {2017}, language = {de} } @phdthesis{Krey2011, author = {Krey, Olaf}, title = {Zur Rolle der Mathematik in der Physik : Wissenschaftstheoretische Aspekte und Vorstellungen Physiklernender}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59412}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Mathematik spielt im Physikunterricht eine nicht unerhebliche Rolle - wenn auch eine zwiesp{\"a}ltige. Oft wird sie sogar zum Hindernis beim Lernen von Physik und kann ihr emanzipatorisches Potenzial nicht entfalten. Die vorliegende Arbeit stellt zwei Bausteine f{\"u}r eine begr{\"u}ndete Konzeption zum Umgang mit Mathematik beim Lernen von Physik zur Verf{\"u}gung. Im Theorieteil der Arbeit werden zum Einen wissenschaftstheoretische Aspekte der Rolle der Mathematik in der Physik aufgearbeitet und der physikdidaktischen Forschungsgemeinschaft im Zusammenhang zug{\"a}nglich gemacht. Zum anderen werden Forschungsergebnisse zu Vorstellungen Lernender {\"u}ber Physik und Mathematik sowie im Bereich der Epistemologie zusammengestellt. Im empirischen Teil der Arbeit werden Vorstellungen zur Rolle der Mathematik in der Physik von Sch{\"u}lerinnen und Sch{\"u}lern der Klassenstufen 10 und 12 sowie Physik-Lehramtstudierenden im Grundstudium mit Hilfe eines Fragebogens erhoben und unter Verwendung inhaltsanalytischer bzw. statistischer Methoden ausgewertet. Die Ergebnisse zeigen unter Anderem, dass Mathematik im Physikunterricht entgegen g{\"a}ngiger Meinungen bei den Lernenden nicht negativ, aber zumindest bei j{\"u}ngeren Lernenden formal und algorithmisch konnotiert ist.}, language = {de} } @article{SchmidtBechmann2014, author = {Schmidt, Joachim and Bechmann, Wolfgang}, title = {Zur Anwendung des Skalarprodukts von Kraft und Weg auf reversible Prozesse (Druck-Volumen-{\"A}nderung, Dehnung, Elektrostatische Wechselwirkung, Hub)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-69732}, year = {2014}, abstract = {Wir schlagen einen allgemein anwendbaren Algorithmus vor, der unter Verwendung des Skalarprodukts von Kraft und Weg zum richtigen Vorzeichen in den Gleichungen f{\"u}r die Arbeit und die Potentielle Energie bei reversiblen Prozessen (Druck-Volumen-{\"A}nderung, Dehnung, Elektrostatische Wechselwirkung, Hub)f{\"u}hrt. Wir zeigen, dass es dabei m{\"o}glich ist, systemimmanente oder externe Kr{\"a}fte zu benutzen. Wir zeigen, dass bei Verwendung von systemimmanenten Kr{\"a}ften das Skalarprodukt mit negativem Vorzeichen anzusetzen ist. Zudem ist es sehr wichtig, n{\"o}tige Vorzeichenwechsel bei den einzelnen Schritten zu beachten. Wir betonen dies, weil gelegentlich {\"u}bersehen wird, dass ein Vorzeichenwechsel n{\"o}tig ist, wenn das Wegdifferential ds durch das H{\"o}hendifferential dh beziehungsweise durch das Abstandsdifferential dx oder dr ersetzt werden muss.}, language = {de} } @phdthesis{Gellert2004, author = {Gellert, Marcus}, title = {Zum Dynamoeffekt in extern getriebenen Str{\"o}mungen}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001705}, school = {Universit{\"a}t Potsdam}, year = {2004}, abstract = {Die Frage nach der Herkunft und der dynamischen Entwicklung langlebiger kosmischer Magnetfelder ist in vielen Details noch unbeantwortet. Es besteht zwar kein Zweifel daran, dass das Magnetfeld der Erde und anderer kosmischer Objekte durch den sogenannten Dynamoeffekt verursacht werden, der genaue Mechanismus als auch die notwendigen Voraussetzungen und Randbedingungen der zugrundeliegenden Str{\"o}mungen sind aber weitgehend unbekannt. Die f{\"u}r einen Dynamo interessanten Str{\"o}mungsmuster, die im Inneren von Himmelsk{\"o}rpern durch Konvektion und differentielle Rotation entstehen, sind Konvektionsrollen parallel zur Rotationsachse. Auf einer Str{\"o}mung mit eben solcher Geometrie, der sogenannten Roberts-Str{\"o}mung, basieren die in der vorliegenden Arbeit untersuchten Dynamomodelle. Mit Methoden der nichtlinearen Dynamik wird versucht, das Systemverhalten bei {\"A}nderung der Systemparamter genauer zu charakterisieren. Die numerischen Untersuchungen beginnen mit einer Analyse der Dynamoaktivit{\"a}t der Roberts-Str{\"o}mung in Abh{\"a}ngigkeit von den zwei freien Parametern in den Modellgleichungen, der magnetischen Prandtl-Zahl und der St{\"a}rke des Energieinputs. Gefunden werden verschiedene L{\"o}sungstypen die von einem station{\"a}ren Magnetfeld {\"u}ber periodische bis zu chaotischen Zust{\"a}nden reichen. Die yugrundeliegenden Symmetrien werden beschrieben und die Bifurkationen, die zum Wechsel der L{\"o}sungstypen f{\"u}hren, charakterisiert. Zus{\"a}tzlich gibt es Bereiche bei sehr kleinen Prandtl-Zahlen, in denen {\"u}berhaupt kein Dynamo existiert. Dieses Verhalten wird in der Literatur auch f{\"u}r viele andere numerisch ausgewertete Modelle beschrieben. Im {\"U}bergangsbereich zwischen dynamoaktivem und dynamoinaktivem Bereich wird das Auftreten einer sogenannten Blowout-Bifurkation gefunden. Desweiteren besch{\"a}ftigt sich die Arbeit mit der Frage, inwiefern Helizit{\"a}t, also eine schraubenf{\"o}rmige Bewegung, der Str{\"o}mung den Dynamoeffekt beeinflusst. Dazu werden {\"a}hnliche Str{\"o}mungstypen verglichen, die sich haupts{\"a}chlich in ihrem Helizit{\"a}tswert unterscheiden. Es wird gefunden, dass ein bestimmter Wert der Helizit{\"a}t nicht unterschritten werden darf, um einen stabilen Roberts-Dynamo zu erhalten.}, language = {de} } @article{LeussuUsoskinValliappanetal.2017, author = {Leussu, R. and Usoskin, IIlya G. and Valliappan, Senthamizh Pavai and Diercke, Andrea and Arlt, Rainer and Denker, Carsten and Mursula, K.}, title = {Wings of the butterfly}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {599}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201629533}, pages = {8}, year = {2017}, abstract = {The spatio-temporal evolution of sunspot activity, the so-called Maunder butterfly diagram, has been continously available since 1874 using data from the Royal Greenwich Observatory, extended by SOON network data after 1976. Here we present a new extended butterfly diagram of sunspot group occurrence since 1826, using the recently digitized data from Schwabe (1826-1867) and Sporer (1866-1880). The wings of the diagram are separated using a recently developed method based on an analysis of long gaps in sunspot group occurrence in different latitude bands. We define characteristic latitudes, corresponding to the start, end, and the largest extent of the wings (the F, L, and H latitudes). The H latitudes (30 degrees-45 degrees) are highly significantly correlated with the strength of the wings (quantified by the total sum of the monthly numbers of sunspot groups). The F latitudes (20 degrees-30 degrees) depict a weak tendency, especially in the southern hemisphere, to follow the wing strength. The L latitudes (2 degrees-10 degrees) show no clear relation to the wing strength. Overall, stronger cycle wings tend to start at higher latitudes and have a greater wing extent. A strong (5-6)-cycle periodic oscillation is found in the start and end times of the wings and in the overlap and gaps between successive wings of one hemisphere. While the average wing overlap is zero in the southern hemisphere, it is two to three months in the north. A marginally significant oscillation of about ten solar cycles is found in the asymmetry of the L latitudes. The new long database of butterfly wings provides new observational constraints to solar dynamo models that discuss the spatio-temporal distribution of sunspot occurrence over the solar cycle and longer.}, language = {en} } @article{MeyerPetrovPohl2020, author = {Meyer, Dominique M.-A. and Petrov, Mykola and Pohl, Martin}, title = {Wind nebulae and supernova remnants of very massive stars}, series = {Monthly notices of the Royal Astronomical Society}, volume = {493}, journal = {Monthly notices of the Royal Astronomical Society}, number = {3}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/staa554}, pages = {3548 -- 3564}, year = {2020}, abstract = {A very small fraction of (runaway) massive stars have masses exceeding 60-70 M-circle dot and are predicted to evolve as luminous blue variable and Wolf-Rayet stars before ending their lives as core-collapse supernovae. Our 2D axisymmetric hydrodynamical simulations explore how a fast wind (2000 km s(-1)) and high mass-loss rate (10(-5)M(circle dot) yr(-1)) can impact the morphology of the circumstellar medium. It is shaped as 100 pc-scale wind nebula that can be pierced by the driving star when it supersonically moves with velocity 20-40 km s(-1) through the interstellar medium (ISM) in the Galactic plane. The motion of such runaway stars displaces the position of the supernova explosion out of their bow shock nebula, imposing asymmetries to the eventual shock wave expansion and engendering Cygnus-loop-like supernova remnants. We conclude that the size (up to more than 200 pc) of the filamentary wind cavity in which the chemically enriched supernova ejecta expand, mixing efficiently the wind and ISM materials by at least 10 per cent in number density, can be used as a tracer of the runaway nature of the very massive progenitors of such 0.1Myr old remnants. Our results motivate further observational campaigns devoted to the bow shock of the very massive stars BD+43 degrees 3654 and to the close surroundings of the synchrotron-emitting Wolf-Rayet shell G2.4+1.4.}, language = {en} } @article{BaushevBarkov2018, author = {Baushev, Anton N. and Barkov, M. V.}, title = {Why does Einasto profile index n similar to 6 occur so frequently?}, series = {Journal of cosmology and astroparticle physics}, journal = {Journal of cosmology and astroparticle physics}, number = {3}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1475-7516}, doi = {10.1088/1475-7516/2018/03/034}, pages = {15}, year = {2018}, abstract = {We consider the behavior of spherically symmetric Einasto halos composed of gravitating particles in the Fokker-Planck approximation. This approach allows us to consider the undesirable influence of close encounters in the N-body simulations more adequately than the generally accepted criteria. The Einasto profile with index n approximate to 6 is a stationary solution of the Fokker-Planck equation in the halo center. There are some reasons to believe that the solution is an attractor. Then the Fokker-Planck diffusion tends to transform a density profile to the equilibrium one with the Einasto index n approximate to 6. We suggest this effect as a possible reason why the Einasto index n approximate to 6 occurs so frequently in the interpretation of N-body simulation results. The results obtained cast doubt on generally accepted criteria of N-body simulation convergence.}, language = {en} } @article{HaasShpritsAllisonetal.2022, author = {Haas, Bernhard and Shprits, Yuri Y. and Allison, Hayley and Wutzig, Michael and Wang, Dedong}, title = {Which parameter controls ring current electron dynamics}, series = {Frontiers in astronomy and space sciences}, volume = {9}, journal = {Frontiers in astronomy and space sciences}, publisher = {Frontiers Media}, address = {Lausanne}, issn = {2296-987X}, doi = {10.3389/fspas.2022.911002}, pages = {11}, year = {2022}, abstract = {Predicting the electron population of Earth's ring current during geomagnetic storms still remains a challenging task. In this work, we investigate the sensitivity of 10 keV ring current electrons to different driving processes, parameterised by the Kp index, during several moderate and intense storms. Results are validated against measurements from the Van Allen Probes satellites. Perturbing the Kp index allows us to identify the most dominant processes for moderate and intense storms respectively. We find that during moderate storms (Kp < 6) the drift velocities mostly control the behaviour of low energy electrons, while loss from wave-particle interactions is the most critical parameter for quantifying the evolution of intense storms (Kp > 6). Perturbations of the Kp index used to drive the boundary conditions at GEO and set the plasmapause location only show a minimal effect on simulation results over a limited L range. It is further shown that the flux at L \& SIM; 3 is more sensitive to changes in the Kp index compared to higher L shells, making it a good proxy for validating the source-loss balance of a ring current model.}, language = {en} } @article{KloseWunderlingWinkelmannetal.2021, author = {Klose, Ann Kristin and Wunderling, Nico and Winkelmann, Ricarda and Donges, Jonathan}, title = {What do we mean, 'tipping cascade'?}, series = {Environmental research letters : ERL}, volume = {16}, journal = {Environmental research letters : ERL}, number = {12}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1748-9326}, doi = {10.1088/1748-9326/ac3955}, pages = {11}, year = {2021}, abstract = {Based on suggested interactions of potential tipping elements in the Earth's climate and in ecological systems, tipping cascades as possible dynamics are increasingly discussed and studied. The activation of such tipping cascades would impose a considerable risk for human societies and biosphere integrity. However, there are ambiguities in the description of tipping cascades within the literature so far. Here we illustrate how different patterns of multiple tipping dynamics emerge from a very simple coupling of two previously studied idealized tipping elements. In particular, we distinguish between a two phase cascade, a domino cascade and a joint cascade. A mitigation of an unfolding two phase cascade may be possible and common early warning indicators are sensitive to upcoming critical transitions to a certain degree. In contrast, a domino cascade may hardly be stopped once initiated and critical slowing down-based indicators fail to indicate tipping of the following element. These different potentials for intervention and anticipation across the distinct patterns of multiple tipping dynamics should be seen as a call to be more precise in future analyses of cascading dynamics arising from tipping element interactions in the Earth system.}, language = {en} } @article{ToetzkeKardjilovLenoiretal.2019, author = {T{\"o}tzke, Christian and Kardjilov, Nikolay and Lenoir, Nicolas and Manke, Ingo and Oswald, Sascha and Tengattini, Alessandro}, title = {What comes NeXT?}, series = {Optics express : the international electronic journal of optics}, volume = {27}, journal = {Optics express : the international electronic journal of optics}, number = {20}, publisher = {Optical Society of America}, address = {Washington}, issn = {1094-4087}, doi = {10.1364/OE.27.028640}, pages = {28640 -- 28648}, year = {2019}, abstract = {Here, we report on a new record in the acquisition time for fast neutron tomography. With an optimized imaging setup, it was possible to acquire single radiographic projection images with 10 ms and full tomographies with 155 projections images and a physical spatial resolution of 200 mu m within 1.5 s. This is about 6.7 times faster than the current record. We used the technique to investigate the water infiltration in the soil with a living lupine root system. The fast imaging setup will be part of the future NeXT instrument at ILL in Grenoble with a great field of possible future applications. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, language = {en} } @article{MuenchLaepple2018, author = {M{\"u}nch, Thomas and Laepple, Thomas}, title = {What climate signal is contained in decadal- to centennial-scale isotope variations from Antarctic ice cores?}, series = {Climate of the past : CP}, volume = {14}, journal = {Climate of the past : CP}, number = {12}, publisher = {Copernicus Gesellschaft mbH}, address = {G{\"o}ttingen}, issn = {1814-9324}, doi = {10.5194/cp-14-2053-2018}, pages = {2053 -- 2070}, year = {2018}, abstract = {Ice-core-based records of isotopic composition are a proxy for past temperatures and can thus provide information on polar climate variability over a large range of timescales. However, individual isotope records are affected by a multitude of processes that may mask the true temperature variability. The relative magnitude of climate and non-climate contributions is expected to vary as a function of timescale, and thus it is crucial to determine those temporal scales on which the actual signal dominates the noise. At present, there are no reliable estimates of this timescale dependence of the signal-to-noise ratio (SNR). Here, we present a simple method that applies spectral analyses to stable-isotope data from multiple cores to estimate the SNR, and the signal and noise variability, as a function of timescale. The method builds on separating the contributions from a common signal and from local variations and includes a correction for the effects of diffusion and time uncertainty. We apply our approach to firn-core arrays from Dronning Maud Land (DML) in East Antarctica and from the West Antarctic Ice Sheet (WAIS). For DML and decadal to multi-centennial timescales, we find an increase in the SNR by nearly 1 order of magnitude (similar to 0.2 at decadal and similar to 1.0 at multi-centennial scales). The estimated spectrum of climate variability also shows increasing variability towards longer timescales, contrary to what is traditionally inferred from single records in this region. In contrast, the inferred variability spectrum for WAIS stays close to constant over decadal to centennial timescales, and the results even suggest a decrease in SNR over this range of timescales. We speculate that these differences between DML and WAIS are related to differences in the spatial and temporal scales of the isotope signal, highlighting the potentially more homogeneous atmospheric conditions on the Antarctic Plateau in contrast to the marine-influenced conditions on WAIS. In general, our approach provides a methodological basis for separating local proxy variability from coherent climate variations, which is applicable to a large set of palaeoclimate records.}, language = {en} } @phdthesis{Maraun2006, author = {Maraun, Douglas}, title = {What can we learn from climate data? : Methods for fluctuation, time/scale and phase analysis}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-9047}, school = {Universit{\"a}t Potsdam}, year = {2006}, abstract = {Since Galileo Galilei invented the first thermometer, researchers have tried to understand the complex dynamics of ocean and atmosphere by means of scientific methods. They observe nature and formulate theories about the climate system. Since some decades powerful computers are capable to simulate the past and future evolution of climate. Time series analysis tries to link the observed data to the computer models: Using statistical methods, one estimates characteristic properties of the underlying climatological processes that in turn can enter the models. The quality of an estimation is evaluated by means of error bars and significance testing. On the one hand, such a test should be capable to detect interesting features, i.e. be sensitive. On the other hand, it should be robust and sort out false positive results, i.e. be specific. This thesis mainly aims to contribute to methodological questions of time series analysis with a focus on sensitivity and specificity and to apply the investigated methods to recent climatological problems. First, the inference of long-range correlations by means of Detrended Fluctuation Analysis (DFA) is studied. It is argued that power-law scaling of the fluctuation function and thus long-memory may not be assumed a priori but have to be established. This requires to investigate the local slopes of the fluctuation function. The variability characteristic for stochastic processes is accounted for by calculating empirical confidence regions. The comparison of a long-memory with a short-memory model shows that the inference of long-range correlations from a finite amount of data by means of DFA is not specific. When aiming to infer short memory by means of DFA, a local slope larger than \$\alpha=0.5\$ for large scales does not necessarily imply long-memory. Also, a finite scaling of the autocorrelation function is shifted to larger scales in the fluctuation function. It turns out that long-range correlations cannot be concluded unambiguously from the DFA results for the Prague temperature data set. In the second part of the thesis, an equivalence class of nonstationary Gaussian stochastic processes is defined in the wavelet domain. These processes are characterized by means of wavelet multipliers and exhibit well defined time dependent spectral properties; they allow one to generate realizations of any nonstationary Gaussian process. The dependency of the realizations on the wavelets used for the generation is studied, bias and variance of the wavelet sample spectrum are calculated. To overcome the difficulties of multiple testing, an areawise significance test is developed and compared to the conventional pointwise test in terms of sensitivity and specificity. Applications to Climatological and Hydrological questions are presented. The thesis at hand mainly aims to contribute to methodological questions of time series analysis and to apply the investigated methods to recent climatological problems. In the last part, the coupling between El Nino/Southern Oscillation (ENSO) and the Indian Monsoon on inter-annual time scales is studied by means of Hilbert transformation and a curvature defined phase. This method allows one to investigate the relation of two oscillating systems with respect to their phases, independently of their amplitudes. The performance of the technique is evaluated using a toy model. From the data, distinct epochs are identified, especially two intervals of phase coherence, 1886-1908 and 1964-1980, confirming earlier findings from a new point of view. A significance test of high specificity corroborates these results. Also so far unknown periods of coupling invisible to linear methods are detected. These findings suggest that the decreasing correlation during the last decades might be partly inherent to the ENSO/Monsoon system. Finally, a possible interpretation of how volcanic radiative forcing could cause the coupling is outlined.}, subject = {Spektralanalyse }, language = {en} } @phdthesis{Kayser2017, author = {Kayser, Markus}, title = {Wechselwirkung der atmosph{\"a}rischen Grenzschicht mit synoptisch-skaligen Prozessen w{\"a}hrend der N-ICE2015 Kampagne}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-411124}, school = {Universit{\"a}t Potsdam}, pages = {147}, year = {2017}, abstract = {Die Arktis erw{\"a}rmt sich schneller als der Rest der Erde. Die Auswirkungen manifestieren sich unter Anderem in einer verst{\"a}rkten Erw{\"a}rmung der arktischen Grenzschicht. Diese Arbeit befasst sich mit Wechselwirkungen zwischen synoptischen Zyklonen und der arktischen Atmosph{\"a}re auf lokalen bis {\"u}berregionalen Skalen. Ausgangspunkt daf{\"u}r sind Messdaten und Modellsimulationen f{\"u}r den Zeitraum der N-ICE2015 Expedition, die von Anfang Januar bis Ende Juni 2015 im arktischen Nordatlantiksektor stattgefunden hat. Anhand von Radiosondenmessungen lassen sich Auswirkungen von synoptischen Zyklonen am deutlichsten im Winter erkennen, da sie durch die Advektion warmer und feuchter Luftmassen in die Arktis den Zustand der Atmosph{\"a}re von einem strahlungs-klaren in einen strahlungs-opaken {\"a}ndern. Obwohl dieser scharfe Kontrast nur im Winter existiert, zeigt die Analyse, dass der integrierte Wasserdampf als Indikator f{\"u}r die Advektion von Luftmassen aus niedrigen Breiten in die Arktis auch im Fr{\"u}hjahr geeignet ist. Neben der Advektion von Luftmassen wird der Einfluss der Zyklonen auf die statische Stabilit{\"a}t charakterisiert. Beim Vergleich der N-ICE2015 Beobachtungen mit der SHEBA Kampagne (1997/1998), die {\"u}ber dickerem Eis stattfand, finden sich trotz der unterschiedlichen Meereisregime {\"A}hnlichkeiten in der statischen Stabilit{\"a}t der Atmosph{\"a}re. Die beobachteten Differenzen in der Stabilit{\"a}t lassen sich auf Unterschiede in der synoptischen Aktivit{\"a}t zur{\"u}ckf{\"u}hren. Dies l{\"a}sst vermuten, dass die d{\"u}nnere Eisdecke auf saisonalen Zeitskalen nur einen geringen Einfluss auf die thermodynamische Struktur der arktischen Troposph{\"a}re besitzt, solange eine dicke Schneeschicht sie bedeckt. Ein weiterer Vergleich mit den parallel zur N-ICE2015 Kampagne gestarteten Radiosonden der AWIPEV Station in Ny-{\AA}esund, Spitzbergen, macht deutlich, dass die synoptischen Zyklonen oberhalb der Orographie auf saisonalen Zeitskalen das Wettergeschehen bestimmen. Des Weiteren werden f{\"u}r Februar 2015 die Auswirkungen von in der Vertikalen variiertem Nudging auf die Entwicklung der Zyklonen am Beispiel des hydrostatischen regionalen Klimamodells HIRHAM5 untersucht. Es zeigt sich, dass die Unterschiede zwischen den acht Modellsimulationen mit abnehmender Anzahl der genudgten Level zunehmen. Die gr{\"o}ßten Differenzen resultieren vornehmlich aus dem zeitlichen Versatz der Entwicklung synoptischer Zyklonen. Zur Korrektur des Zeitversatzes der Zykloneninitiierung gen{\"u}gt es bereits, Nudging in den unterstem 250 m der Troposph{\"a}re anzuwenden. Daneben findet sich zwischen den genudgten HIRHAM5-Simulation und den in situ Messungen der gleiche positive Temperaturbias, den auch ERA-Interim besitzt. Das freie HIRHAM hingegen reproduziert das positive Ende der N-ICE2015 Temperaturverteilung gut, besitzt aber einen starken negativen Bias, der sehr wahrscheinlich aus einer Untersch{\"a}tzung des Feuchtegehalts resultiert. An Beispiel einer Zyklone wird gezeigt, dass Nudging Einfluss auf die Lage der H{\"o}hentiefs besitzt, die ihrerseits die Zyklonenentwicklung am Boden beeinflussen. Im Weiteren wird mittels eines f{\"u}r kleine Ensemblegr{\"o}ßen geeigneten Varianzmaßes eine statistische Einsch{\"a}tzung der Wirkung des Nudgings auf die Vertikale getroffen. Es wird festgestellt, dass die {\"A}hnlichkeit der Modellsimulationen in der unteren Troposph{\"a}re generell h{\"o}her ist als dar{\"u}ber und in 500 hPa ein lokales Minimum besitzt. Im letzten Teil der Analyse wird die Wechselwirkung der oberen und unteren Stratosph{\"a}re anhand zuvor betrachteter Zyklonen mit Daten der ERA-Interim Reanalyse untersucht. Lage und Ausrichtung des Polarwirbels erzeugten ab Anfang Februar 2015 eine ungew{\"o}hnlich große Meridionalkomponente des Tropopausenjets, die Zugbahnen in die zentrale Arktis beg{\"u}nstigte. Am Beispiel einer Zyklone wird die {\"U}bereinstimmung der synoptischen Entwicklung mit den theoretischen Annahmen {\"u}ber den abw{\"a}rts gerichteten Einfluss der Stratosph{\"a}re auf die Troposph{\"a}re hervorgehoben. Dabei spielt die nicht-lineare Wechselwirkung zwischen der Orographie Gr{\"o}nlands, einer Intrusion stratosph{\"a}rischer Luft in die Troposph{\"a}re sowie einer in Richtung Arktis propagierender Rossby-Welle eine tragende Rolle. Als Indikator dieser Wechselwirkung werden horizontale Signaturen aus abwechselnd aufsteigender und absinkender Luft innerhalb der Troposph{\"a}re identifiziert.}, language = {de} } @article{AydinerCherstvyMetzler2018, author = {Aydiner, Ekrem and Cherstvy, Andrey G. and Metzler, Ralf}, title = {Wealth distribution, Pareto law, and stretched exponential decay of money}, series = {Physica : europhysics journal ; A, Statistical mechanics and its applications}, volume = {490}, journal = {Physica : europhysics journal ; A, Statistical mechanics and its applications}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0378-4371}, doi = {10.1016/j.physa.2017.08.017}, pages = {278 -- 288}, year = {2018}, abstract = {We study by Monte Carlo simulations a kinetic exchange trading model for both fixed and distributed saving propensities of the agents and rationalize the person and wealth distributions. We show that the newly introduced wealth distribution - that may be more amenable in certain situations - features a different power-law exponent, particularly for distributed saving propensities of the agents. For open agent-based systems, we analyze the person and wealth distributions and find that the presence of trap agents alters their amplitude, leaving however the scaling exponents nearly unaffected. For an open system, we show that the total wealth - for different trap agent densities and saving propensities of the agents - decreases in time according to the classical Kohlrausch-Williams-Watts stretched exponential law. Interestingly, this decay does not depend on the trap agent density, but rather on saving propensities. The system relaxation for fixed and distributed saving schemes are found to be different.}, language = {en} } @article{RosenauPikovskij2021, author = {Rosenau, Philip and Pikovskij, Arkadij}, title = {Waves in strongly nonlinear Gardner-like equations on a lattice}, series = {Nonlinearity / the Institute of Physics and the London Mathematical Society}, volume = {34}, journal = {Nonlinearity / the Institute of Physics and the London Mathematical Society}, number = {8}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0951-7715}, doi = {10.1088/1361-6544/ac0f51}, pages = {5872 -- 5896}, year = {2021}, abstract = {We introduce and study a family of lattice equations which may be viewed either as a strongly nonlinear discrete extension of the Gardner equation, or a non-convex variant of the Lotka-Volterra chain. Their deceptively simple form supports a very rich family of complex solitary patterns. Some of these patterns are also found in the quasi-continuum rendition, but the more intriguing ones, like interlaced pairs of solitary waves, or waves which may reverse their direction either spontaneously or due a collision, are an intrinsic feature of the discrete realm.}, language = {en} } @unpublished{DickenMaass1995, author = {Dicken, Volker and Maaß, Peter}, title = {Wavelet-Galerkin methods for ill-posed problems}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-13890}, year = {1995}, abstract = {Projection methods based on wavelet functions combine optimal convergence rates with algorithmic efficiency. The proofs in this paper utilize the approximation properties of wavelets and results from the general theory of regularization methods. Moreover, adaptive strategies can be incorporated still leading to optimal convergence rates for the resulting algorithms. The so-called wavelet-vaguelette decompositions enable the realization of especially fast algorithms for certain operators.}, language = {en} } @article{AgarwalMaheswaranMarwanetal.2018, author = {Agarwal, Ankit and Maheswaran, Rathinasamy and Marwan, Norbert and Caesar, Levke and Kurths, J{\"u}rgen}, title = {Wavelet-based multiscale similarity measure for complex networks}, series = {The European physical journal : B, Condensed matter and complex systems}, volume = {91}, journal = {The European physical journal : B, Condensed matter and complex systems}, number = {11}, publisher = {Springer}, address = {New York}, issn = {1434-6028}, doi = {10.1140/epjb/e2018-90460-6}, pages = {12}, year = {2018}, abstract = {In recent years, complex network analysis facilitated the identification of universal and unexpected patterns in complex climate systems. However, the analysis and representation of a multiscale complex relationship that exists in the global climate system are limited. A logical first step in addressing this issue is to construct multiple networks over different timescales. Therefore, we propose to apply the wavelet multiscale correlation (WMC) similarity measure, which is a combination of two state-of-the-art methods, viz. wavelet and Pearson's correlation, for investigating multiscale processes through complex networks. Firstly we decompose the data over different timescales using the wavelet approach and subsequently construct a corresponding network by Pearson's correlation. The proposed approach is illustrated and tested on two synthetics and one real-world example. The first synthetic case study shows the efficacy of the proposed approach to unravel scale-specific connections, which are often undiscovered at a single scale. The second synthetic case study illustrates that by dividing and constructing a separate network for each time window we can detect significant changes in the signal structure. The real-world example investigates the behavior of the global sea surface temperature (SST) network at different timescales. Intriguingly, we notice that spatial dependent structure in SST evolves temporally. Overall, the proposed measure has an immense potential to provide essential insights on understanding and extending complex multivariate process studies at multiple scales.}, language = {en} } @unpublished{MaassRieder1996, author = {Maaß, Peter and Rieder, Andreas}, title = {Wavelet-accelerated Tikhonov-Phillips regularization with applications}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-14104}, year = {1996}, abstract = {Contents: 1 Introduction 1.1 Tikhanov-Phillips Regularization of Ill-Posed Problems 1.2 A Compact Course to Wavelets 2 A Multilevel Iteration for Tikhonov-Phillips Regularization 2.1 Multilevel Splitting 2.2 The Multilevel Iteration 2.3 Multilevel Approach to Cone Beam Reconstuction 3 The use of approximating operators 3.1 Computing approximating families {Ah}}, language = {en} } @article{MaheswaranAgarwalSivakumaretal.2019, author = {Maheswaran, Rathinasamy and Agarwal, Ankit and Sivakumar, Bellie and Marwan, Norbert and Kurths, J{\"u}rgen}, title = {Wavelet analysis of precipitation extremes over India and teleconnections to climate indices}, series = {Stochastic Environmental Research and Risk Assessment}, volume = {33}, journal = {Stochastic Environmental Research and Risk Assessment}, number = {11-12}, publisher = {Springer}, address = {New York}, issn = {1436-3240}, doi = {10.1007/s00477-019-01738-3}, pages = {2053 -- 2069}, year = {2019}, abstract = {Precipitation patterns and extremes are significantly influenced by various climatic factors and large-scale atmospheric circulation patterns. This study uses wavelet coherence analysis to detect significant interannual and interdecadal oscillations in monthly precipitation extremes across India and their teleconnections to three prominent climate indices, namely, Nino 3.4, Pacific Decadal Oscillation, and Indian Ocean Dipole (IOD). Further, partial wavelet coherence analysis is used to estimate the standalone relationship between the climate indices and precipitation after removing the effect of interdependency. The wavelet analysis of monthly precipitation extremes at 30 different locations across India reveals that (a) interannual (2-8 years) and interdecadal (8-32 years) oscillations are statistically significant, and (b) the oscillations vary in both time and space. The results from the partial wavelet coherence analysis reveal that Nino 3.4 and IOD are the significant drivers of Indian precipitation at interannual and interdecadal scales. Intriguingly, the study also confirms that the strength of influence of large-scale atmospheric circulation patterns on Indian precipitation extremes varies with spatial physiography of the region.}, language = {en} } @phdthesis{Solopow2019, author = {Solopow, Sergej}, title = {Wavelength dependent demagnetization dynamics in Co2MnGa Heusler-alloy}, doi = {10.25932/publishup-42786}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-427860}, school = {Universit{\"a}t Potsdam}, pages = {91}, year = {2019}, abstract = {In dieser Arbeit haben wir ultraschnelle Entmagnetisierung an einer Heusler-Legierung untersucht. Es handelt sich um ein Halbmetall, das sich in einer ferromagnetischen Phase befindet. Die Besonderheit dieses Materials besteht im Aufbau einer Bandstruktur. Diese bildet Zustandsdichten, in der die Majorit{\"a}tselektronen eine metallische B{\"a}nderbildung aufweisen und die Minorit{\"a}tselektronen eine Bandl{\"u}cke in der N{\"a}he des Fermi-Niveaus aufweisen, das dem Aufbau eines Halbleiters entspricht. Mit Hilfe der Pump-Probe-Experimente haben wir zeitaufgel{\"o}ste Messungen durchgef{\"u}hrt. F{\"u}r das Pumpen wurden ultrakurze Laserpulse mit einer Pulsdauer von 100 fs benutzt. Wir haben dabei zwei verschiedene Wellenl{\"a}ngen mit 400 nm und 1240 nm benutzt, um den Effekt der Prim{\"a}ranregung und der Bandl{\"u}cke in den Minorit{\"a}tszust{\"a}nden zu untersuchen. Dabei wurde zum ersten Mal OPA (Optical Parametrical Amplifier) f{\"u}r die Erzeugung der langwelligen Pulse an der FEMTOSPEX-Beamline getestet und erfolgreich bei den Experimenten verwendet. Wir haben Wellenl{\"a}ngen bedingte Unterschiede in der Entmagnetisierungszeit gemessen. Mit der Erh{\"o}hung der Photonenenergie ist der Prozess der Entmagnetisierung deutlich schneller als bei einer niedrigeren Photonenenergie. Wir verkn{\"u}pften diese Ergebnisse mit der Existenz der Energiel{\"u}cke f{\"u}r Minorit{\"a}tselektronen. Mit Hilfe lokaler Elliot-Yafet-Streuprozesse k{\"o}nnen die beobachteten Zeiten gut erkl{\"a}rt werden. Wir haben in dieser Arbeit auch eine neue Probe-Methode f{\"u}r die Magnetisierung angewandt und somit experimentell deren Effektivit{\"a}t, n{\"a}mlich XMCD in Refletiongeometry, best{\"a}tigen k{\"o}nnen. Statische Experimente liefern somit deutliche Indizien daf{\"u}r, dass eine magnetische von einer rein elektronischen Antwort des Systems getrennt werden kann. Unter der Voraussetzung, dass die Photonenenergie der R{\"o}ntgenstrahlung auf die L3 Kante des entsprechenden Elements eingestellt, ein geeigneter Einfallswinkel gew{\"a}hlt und die zirkulare Polarisation fixiert wird, ist es m{\"o}glich, diese Methode zur Analyse magnetischer und elektronischer Respons anzuwenden.}, language = {en} } @article{SunSandbergNeheretal.2022, author = {Sun, Bowen and Sandberg, Oskar and Neher, Dieter and Armin, Ardalan and Shoaee, Safa}, title = {Wave optics of differential absorption spectroscopy in thick-junction organic solar cells}, series = {Physical review applied / The American Physical Society}, volume = {17}, journal = {Physical review applied / The American Physical Society}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.17.054016}, pages = {12}, year = {2022}, abstract = {Differential absorption spectroscopy techniques serve as powerful techniques to study the excited species in organic solar cells. However, it has always been challenging to employ these techniques for characterizing thick-junction organic solar cells, especially when a reflective top contact is involved. In this work, we present a detailed and systematic study on how a combination of the presence of the interference effect and a nonuniform charge-distribution profile, severely manipulates experimental spectra and the decay dynamics. Furthermore, we provide a practical methodology to correct these optical artifacts in differential absorption spectroscopies. The results and the proposed correction method generally apply to all kinds of differential absorption spectroscopy techniques and various thin-film systems, such as organics, perovskites, kesterites, and two-dimensional materials. Notably, it is found that the shape of differential absorption spectra can be strongly distorted, starting from 150-nm active-layer thickness; this matches the thickness range of thick-junction organic solar cells and most perovskite solar cells and needs to be carefully considered in experiments. In addition, the decay dynamics of differential absorption spectra is found to be disturbed by optical artifacts under certain conditions. With the help of the proposed correction formalism, differential spectra and the decay dynamics can be characterized on the full device of thin-film solar cells in transmission mode and yield accurate and reliable results to provide design rules for further progress.}, language = {en} } @article{SteigertKojdaIbacetaJanaetal.2022, author = {Steigert, Alexander and Kojda, Sandrino Danny and Ibaceta-Ja{\~n}a, Josefa Fernanda and Abou-Ras, Daniel and Gunder, Ren{\´e} and Alktash, Nivin and Habicht, Klaus and Wagner, Markus Raphael and Klenk, Reiner and Raoux, Simone and Szyszka, Bernd and Lauermann, Iver and Muydinov, Ruslan}, title = {Water-assisted crystallization of amorphous indium zinc oxide films}, series = {Materials today. Communications}, volume = {31}, journal = {Materials today. Communications}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2352-4928}, doi = {10.1016/j.mtcomm.2022.103213}, pages = {10}, year = {2022}, abstract = {Transparent conductive materials based on indium oxide remain yet irreplaceable in various optoelectronic applications. Amorphous oxides appear especially attractive for technology as they are isotropic, demonstrate relatively high electron mobility and can be processed at low temperatures. Among them is indium zinc oxide (IZO) with a large zinc content that is crucial for keeping the amorphous state but redundant for the doping. In this work we investigated water-free and water containing IZO films obtained by radio frequency sputtering. The correlation between temperature driven changes of the chemical state, the optical and electrical properties as well as the progression of crystallization was in focus. Such characterization methods as: scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, temperature dependent Hall-effect measurements and others were applied. Temperature dependent electrical properties of amorphous IZO and IZO:H2O films were found to evolve similarly. Based on our experience in In2O3:H2O (In2O3:H or IOH) we proposed an explanation for the changes observed. Water admixture was found to decrease crystallization temperature of IZO significantly from similar to 550 degrees C to similar to 280 degrees C. Herewith, the presence and concentration of water and/or hydroxyls was found to determine Zn distribution in the film. In particular, Zn enrichment was detected at the film's surface respective to the high water and/or hydroxyl amount. Raman spectra revealed a two-dimensional crystallization of w-ZnO which precedes regardless water presence an extensive In2O3 crystallization. An abrupt loss of electron mobility as a result of crystallization was attributed to the formation of ZnO interlayer on grain boundaries.}, language = {en} } @article{CrovettoHempelRusuetal.2020, author = {Crovetto, Andrea and Hempel, Hannes and Rusu, Marin and Choubrac, Leo and Kojda, Sandrino Danny and Habicht, Klaus and Unold, Thomas}, title = {Water adsorption enhances electrical conductivity in transparent p-type CuI}, series = {ACS applied materials \& interfaces}, volume = {12}, journal = {ACS applied materials \& interfaces}, number = {43}, publisher = {American Chemical Society}, address = {Washington, DC}, issn = {1944-8244}, doi = {10.1021/acsami.0c11040}, pages = {48741 -- 48747}, year = {2020}, abstract = {CuI has been recently rediscovered as a p-type transparent conductor with a high figure of merit. Even though many metal iodides are hygroscopic, the effect of moisture on the electrical properties of CuI has not been clarified. In this work, we observe a 2-fold increase in the conductivity of CuI after exposure to ambient humidity for 5 h, followed by slight long-term degradation. Simultaneously, the work function of CuI decreases by almost 1 eV, which can explain the large spread in the previously reported work function values. The conductivity increase is partially reversible and is maximized at intermediate humidity levels. On the basis of the large intragrain mobility measured by THz spectroscopy, we suggest that hydration of grain boundaries may be beneficial for the overall hole mobility.}, language = {en} } @article{StolterfohtLeCorreFeuersteinetal.2019, author = {Stolterfoht, Martin and Le Corre, Vincent M. and Feuerstein, Markus and Caprioglio, Pietro and Koster, Lambert Jan Anton and Neher, Dieter}, title = {Voltage-Dependent Photoluminescence and How It Correlates with the Fill Factor and Open-Circuit Voltage in Perovskite Solar Cells}, series = {Acs energy letters}, volume = {4}, journal = {Acs energy letters}, number = {12}, publisher = {American Chemical Society}, address = {Washington}, issn = {2380-8195}, doi = {10.1021/acsenergylett.9b02262}, pages = {2887 -- 2892}, year = {2019}, abstract = {Optimizing the photoluminescence (PL) yield of a solar cell has long been recognized as a key principle to maximize the power conversion efficiency. While PL measurements are routinely applied to perovskite films and solar cells under open circuit conditions (V-OC), it remains unclear how the emission depends on the applied voltage. Here, we performed PL(V) measurements on perovskite cells with different hole transport layer thicknesses and doping concentrations, resulting in remarkably different fill factors (FFs). The results reveal that PL(V) mirrors the current-voltage (JV) characteristics in the power-generating regime, which highlights an interesting correlation between radiative and nonradiative recombination losses. In particular, high FF devices show a rapid quenching of PL(V) from open-circuit to the maximum power point. We conclude that, while the PL has to be maximized at V-OC at lower biases < V-OC the PL must be rapidly quenched as charges need to be extracted prior to recombination.}, language = {en} } @article{StolterfohtWolffMarquezetal.2018, author = {Stolterfoht, Martin and Wolff, Christian Michael and Marquez, Jose A. and Zhang, Shanshan and Hages, Charles J. and Rothhardt, Daniel and Albrecht, Steve and Burn, Paul L. and Meredith, Paul and Unold, Thomas and Neher, Dieter}, title = {Visualization and suppression of interfacial recombination for high-efficiency large-area pin perovskite solar cells}, series = {Nature Energy}, volume = {3}, journal = {Nature Energy}, number = {10}, publisher = {Nature Publ. Group}, address = {London}, issn = {2058-7546}, doi = {10.1038/s41560-018-0219-8}, pages = {847 -- 854}, year = {2018}, abstract = {The performance of perovskite solar cells is predominantly limited by non-radiative recombination, either through trap-assisted recombination in the absorber layer or via minority carrier recombination at the perovskite/transport layer interfaces. Here, we use transient and absolute photoluminescence imaging to visualize all non-radiative recombination pathways in planar pintype perovskite solar cells with undoped organic charge transport layers. We find significant quasi-Fermi-level splitting losses (135 meV) in the perovskite bulk, whereas interfacial recombination results in an additional free energy loss of 80 meV at each individual interface, which limits the open-circuit voltage (V-oc) of the complete cell to similar to 1.12 V. Inserting ultrathin interlayers between the perovskite and transport layers leads to a substantial reduction of these interfacial losses at both the p and n contacts. Using this knowledge and approach, we demonstrate reproducible dopant-free 1 cm(2) perovskite solar cells surpassing 20\% efficiency (19.83\% certified) with stabilized power output, a high V-oc (1.17 V) and record fill factor (>81\%).}, language = {en} } @article{GandhimathiRajasekarKurths2006, author = {Gandhimathi, V. M. and Rajasekar, S. and Kurths, J{\"u}rgen}, title = {Vibrational and stochastic resonances in two coupled overdamped anharmonic oscillators}, series = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics}, volume = {360}, journal = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics}, number = {2}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0375-9601}, doi = {10.1016/j.physleta.2006.08.051}, pages = {279 -- 286}, year = {2006}, abstract = {We study the overdamped version of two coupled anharmonic oscillators under the influence of both low- and high-frequency forces respectively and a Gaussian noise term added to one of the two state variables of the system. The dynamics of the system is first studied in the presence of both forces separately without noise. In the presence of only one of the forces, no resonance behaviour is observed, however, hysteresis happens there. Then the influence of the high-frequency force in the presence of a low-frequency, i.e. biharmonic forcing, is studied. Vibrational resonance is found to occur when the amplitude of the high-frequency force is varied. The resonance curve resembles a stochastic resonance-like curve. It is maximum at the value of g at which the orbit lies in one well during one half of the drive cycle of the low-frequency force and in the other for the remaining half cycle. Vibrational resonance is characterized using the response amplitude and mean residence time. We show the occurrence of stochastic resonance behaviour in the overdamped system by replacing the high-frequency force by Gaussian noise. Similarities and differences between both types of resonance are presented. (c) 2006 Elsevier B.V. All rights reserved.}, language = {en} } @article{AbdallaAdamAharonianetal.2020, author = {Abdalla, Hassan E. and Adam, Remi and Aharonian, Felix A. and Benkhali, Faical Ait and Ang{\"u}ner, Ekrem Oǧuzhan and Arakawa, Masanori and Arcaro, C and Armand, Catherine and Armstrong, T. and Egberts, Kathrin}, title = {Very high energy γ-ray emission from two blazars of unknown redshift and upper limits on their distance}, series = {Monthly Notices of the Royal Astronomical Society}, volume = {494}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {4}, publisher = {Wiley-Blackwell}, address = {Oxford}, pages = {13}, year = {2020}, abstract = {We report on the detection of very high energy (VHE; E > 100 GeV) gamma-ray emission from the BL Lac objects KUV 00311-1938 and PKS 1440-389 with the High Energy Stereoscopic System (H.E.S.S.). H.E.S.S. observations were accompanied or preceded by multiwavelength observations with Fermi/LAT, XRT and UVOT onboard the Swift satellite, and ATOM. Based on an extrapolation of the Fermi/LAT spectrum towards the VHE gamma-ray regime, we deduce a 95 per cent confidence level upper limit on the unknown redshift of KUV 00311-1938 of z < 0.98 and of PKS 1440-389 of z < 0.53. When combined with previous spectroscopy results, the redshift of KUV 00311-1938 is constrained to 0.51 <= z < 0.98 and of PKS 1440-389 to 0.14 (sic) z < 0.53.}, language = {en} } @misc{AbdallaAdamAharonianetal.2020, author = {Abdalla, Hassan E. and Adam, Remi and Aharonian, Felix A. and Benkhali, Faical Ait and Ang{\"u}ner, Ekrem Oǧuzhan and Arakawa, Masanori and Arcaro, C and Armand, Catherine and Armstrong, T. and Egberts, Kathrin}, title = {Very high energy γ-ray emission from two blazars of unknown redshift and upper limits on their distance}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {4}, issn = {1866-8372}, doi = {10.25932/publishup-52600}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-526000}, pages = {15}, year = {2020}, abstract = {We report on the detection of very high energy (VHE; E > 100 GeV) gamma-ray emission from the BL Lac objects KUV 00311-1938 and PKS 1440-389 with the High Energy Stereoscopic System (H.E.S.S.). H.E.S.S. observations were accompanied or preceded by multiwavelength observations with Fermi/LAT, XRT and UVOT onboard the Swift satellite, and ATOM. Based on an extrapolation of the Fermi/LAT spectrum towards the VHE gamma-ray regime, we deduce a 95 per cent confidence level upper limit on the unknown redshift of KUV 00311-1938 of z < 0.98 and of PKS 1440-389 of z < 0.53. When combined with previous spectroscopy results, the redshift of KUV 00311-1938 is constrained to 0.51 <= z < 0.98 and of PKS 1440-389 to 0.14 (sic) z < 0.53.}, language = {en} } @article{KayserMaturilliGrahametal.2017, author = {Kayser, Markus and Maturilli, Marion and Graham, Robert M. and Hudson, Stephen R. and Rinke, Annette and Cohen, Lana and Kim, Joo-Hong and Park, Sang-Jong and Moon, Woosok and Granskog, Mats A.}, title = {Vertical thermodynamic structure of the troposphere during the Norwegian young sea ICE expedition (N-ICE2015)}, series = {Journal of geophysical research-atmosheres}, volume = {122}, journal = {Journal of geophysical research-atmosheres}, number = {20}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-897X}, doi = {10.1002/2016JD026089}, pages = {10855 -- 10872}, year = {2017}, abstract = {The Norwegian young sea ICE (N-ICE2015) expedition was designed to investigate the atmosphere-snow-ice-ocean interactions in the young and thin sea ice regime north of Svalbard. Radiosondes were launched twice daily during the expedition from January to June 2015. Here we use these upper air measurements to study the multiple cyclonic events observed during N-ICE2015 with respect to changes in the vertical thermodynamic structure, moisture content, and boundary layer characteristics. We provide statistics of temperature inversion characteristics, static stability, and boundary layer extent. During winter, when radiative cooling is most effective, we find the strongest impact of synoptic cyclones. Changes to thermodynamic characteristics of the boundary layer are associated with transitions between the radiatively "clear" and "opaque" atmospheric states. In spring, radiative fluxes warm the surface leading to lifted temperature inversions and a statically unstable boundary layer. Further, we compare the N-ICE2015 static stability distributions to corresponding profiles from ERA-Interim reanalysis, from the closest land station in the Arctic North Atlantic sector, Ny-Alesund, and to soundings from the SHEBA expedition (1997/1998). We find similar stability characteristics for N-ICE2015 and SHEBA throughout the troposphere, despite differences in location, sea ice thickness, and snow cover. For Ny-Alesund, we observe similar characteristics above 1000 m, while the topography and ice-free fjord surrounding Ny-Alesund generate great differences below. The long-term radiosonde record (1993-2014) from Ny-Alesund indicates that during the N-ICE2015 spring period, temperatures were close to the climatological mean, while the lowest 3000 m were 1-3 degrees C warmer than the climatology during winter. Plain Language Summary The Norwegian young sea ICE (N-ICE2015) expedition was designed to investigate the atmosphere-snow-ice-ocean interactions in the young and thin sea ice regime north of Svalbard. Radiosondes were launched twice daily during the expedition from January to June 2015. Here we use these upper air measurements to study the multiple cyclonic events observed during N-ICE2015 with respect to changes in the vertical thermodynamic structure, moisture content, and the atmospheric boundary layer characteristics. During winter, we find the strongest impact of synoptic cyclones, which transport warm and moist air into the cold and dry Arctic atmosphere. In spring, incoming solar radiation warms the surface. This leads to very different thermodynamic conditions and higher moisture content, which reduces the contrast between stormy and calm periods. Further, we compare the N-ICE2015 measurements to corresponding profiles from ERA-Interim reanalysis, from the closest land station in the Arctic North Atlantic sector, Ny-Alesund, and to soundings from the SHEBA expedition (1997/1998). We find similar stability characteristics for N-ICE2015 and SHEBA throughout the troposphere, despite differences in location, sea ice thickness, and snow cover. The comparisons highlight the value of the N-ICE2015 observation and show the importance of winter time observations in the Arctic North Atlantic sector.}, language = {en} } @misc{SchickEckertPontiusetal.2016, author = {Schick, Daniel and Eckert, Sebastian and Pontius, Niko and Mitzner, Rolf and F{\"o}hlisch, Alexander and Holldack, Karsten and Sorgenfrei, Nomi}, title = {Versatile soft X-ray-optical cross-correlator for ultrafast applications}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1331}, issn = {1866-8372}, doi = {10.25932/publishup-43696}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436962}, pages = {054304-1 -- 054304-8}, year = {2016}, abstract = {We present an X-ray-optical cross-correlator for the soft (> 150 eV) up to the hard X-ray regime based on a molybdenum-silicon superlattice. The cross-correlation is done by probing intensity and position changes of superlattice Bragg peaks caused by photoexcitation of coherent phonons. This approach is applicable for a wide range of X-ray photon energies as well as for a broad range of excitation wavelengths and requires no external fields or changes of temperature. Moreover, the cross-correlator can be employed on a 10 ps or 100 fs time scale featuring up to 50\% total X-ray reflectivity and transient signal changes of more than 20\%. (C) 2016 Author(s).}, language = {en} } @article{SchickEckertPontiusetal.2016, author = {Schick, Daniel and Eckert, Sebastian and Pontius, Niko and Mitzner, Rolf and F{\"o}hlisch, Alexander and Holldack, Karsten and Sorgenfrei, Nomi}, title = {Versatile soft X-ray-optical cross-correlator for ultrafast applications}, series = {Structural dynamics}, volume = {3}, journal = {Structural dynamics}, publisher = {American Institute of Physics}, address = {Melville}, issn = {2329-7778}, doi = {10.1063/1.4964296}, pages = {054304-1 -- 054304-8}, year = {2016}, abstract = {We present an X-ray-optical cross-correlator for the soft (> 150 eV) up to the hard X-ray regime based on a molybdenum-silicon superlattice. The cross-correlation is done by probing intensity and position changes of superlattice Bragg peaks caused by photoexcitation of coherent phonons. This approach is applicable for a wide range of X-ray photon energies as well as for a broad range of excitation wavelengths and requires no external fields or changes of temperature. Moreover, the cross-correlator can be employed on a 10 ps or 100 fs time scale featuring up to 50\% total X-ray reflectivity and transient signal changes of more than 20\%. (C) 2016 Author(s).}, language = {en} } @article{AbeysekaraArcherBenbowetal.2018, author = {Abeysekara, A. U. and Archer, A. and Benbow, Wystan and Bird, Ralph and Brill, A. and Brose, Robert and Buckley, J. H. and Christiansen, Jessie L. and Chromey, A. J. and Daniel, M. K. and Falcone, A. and Feng, Qi and Finley, John P. and Fortson, L. and Furniss, Amy and Gillanders, Gerard H. and Gueta, O. and Hanna, David and Hervet, O. and Holder, J. and Hughes, G. and Humensky, T. B. and Johnson, Caitlin A. and Kaaret, Philip and Kar, P. and Kelley-Hoskins, N. and Kertzman, M. and Kieda, David and Krause, Maria and Krennrich, F. and Lang, M. J. and Moriarty, P. and Mukherjee, Reshmi and Ong, R. A. and Otte, A. N. and Park, N. and Petrashyk, A. and Pohl, Martin and Pueschel, Elisa and Quinn, J. and Ragan, K. and Reynolds, P. T. and Richards, Gregory T. and Roache, E. and Rulten, C. and Sadeh, I. and Santander, Marcos and Scott, S. S. and Sembroski, G. H. and Shahinyan, Karlen and Tyler, J. and Wakely, S. P. and Weinstein, A. and Wells, R. M. and Wilcox, P. and Wilhelm, Alina and Williams, D. A. and Williamson, T. J. and Zitzer, B. and Kaur, A.}, title = {VERITAS Observations of the BL Lac Object TXS 0506+056}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, volume = {861}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, organization = {VERITAS Collaboration}, issn = {2041-8205}, doi = {10.3847/2041-8213/aad053}, pages = {6}, year = {2018}, abstract = {On 2017 September 22, the IceCube Neutrino Observatory reported the detection of the high-energy neutrino event IC 170922A, of potential astrophysical origin. It was soon determined that the neutrino direction was consistent with the location of the gamma-ray blazar TXS 0506+056. (3FGL J0509.4+ 0541), which was in an elevated gamma-ray emission state as measured by the Fermi satellite. Very Energetic Radiation Imaging Telescope Array System (VERITAS) observations of the neutrino/blazar region started on 2017 September 23 in response to the neutrino alert and continued through 2018 February 6. While no significant very-high-energy (VHE; E > 100 GeV) emission was observed from the blazar by VERITAS in the two-week period immediately following the IceCube alert, TXS 0506+ 056 was detected by VERITAS with a significance of 5.8 standard deviations (sigma) in the full 35 hr data set. The average photon flux of the source during this period was (8.9 +/- 1.6). x. 10(-12) cm(-2) s(-1), or 1.6\% of the Crab Nebula flux, above an energy threshold of 110 GeV, with a soft spectral index of 4.8. +/-. 1.3.}, language = {en} } @article{AbeysekaraArcherBenbowetal.2018, author = {Abeysekara, A. U. and Archer, A. and Benbow, Wystan and Bird, Ralph and Brose, Robert and Buchovecky, M. and Buckley, J. H. and Bugaev, V. and Chromey, A. J. and Connolly, M. P. and Cui, Wei and Daniel, M. K. and Falcone, A. and Feng, Qi and Finley, John P. and Fortson, L. and Furniss, Amy and Huetten, M. and Hanna, David and Hervet, O. and Holder, J. and Hughes, G. and Humensky, T. B. and Johnson, Caitlin A. and Kaaret, Philip and Kar, P. and Kertzman, M. and Kieda, David and Krause, M. and Krennrich, F. and Kumar, S. and Lang, M. J. and Lin, T. T. Y. and McArthur, S. and Moriarty, P. and Mukherjee, Reshmi and Ong, R. A. and Otte, Adam Nepomuk and Park, Nahee and Petrashyk, A. and Pohl, Martin and Pueschel, Elisa and Quinn, J. and Ragan, K. and Reynolds, P. T. and Richards, Gregory T. and Roache, E. and Rulten, C. and Sadeh, I. and Santander, Marcos and Sembroski, G. H. and Shahinyan, Karlen and Sushch, I. and Tyler, J. and Wakely, S. P. and Weinstein, A. and Wells, R. M. and Wilcox, P. and Wilhelm, Alina and Williams, D. A. and Williamson, T. J. and Zitzer, B. and Abdollahi, S. and Ajello, Marco and Baldini, Luca and Barbiellini, G. and Bastieri, Denis and Bellazzini, Ronaldo and Berenji, B. and Bissaldi, Elisabetta and Blandford, R. D. and Bonino, R. and Bottacini, E. and Brandt, Terri J. and Bruel, P. and Buehler, R. and Cameron, R. A. and Caputo, R. and Caraveo, P. A. and Castro, D. and Cavazzuti, E. and Charles, Eric and Chiaro, G. and Ciprini, S. and Cohen-Tanugi, Johann and Costantin, D. and Cutini, S. and de Palma, F. and Di Lalla, N. and Di Mauro, M. and Di Venere, L. and Dominguez, A. and Favuzzi, C. and Fegan, S. J. and Franckowiak, Anna and Fukazawa, Yasushi and Funk, Stefan and Fusco, Piergiorgio and Gargano, Fabio and Gasparrini, Dario and Giglietto, Nicola and Giordano, F. and Giroletti, Marcello and Green, D. and Grenier, I. A. and Guillemot, L. and Guiriec, Sylvain and Hays, Elizabeth and Hewitt, John W. and Horan, D. and Johannesson, G. and Kensei, S. and Kuss, M. and Larsson, Stefan and Latronico, L. and Lemoine-Goumard, Marianne and Li, J. and Longo, Francesco and Loparco, Francesco and Lovellette, M. N. and Lubrano, Pasquale and Magill, Jeffrey D. and Maldera, Simone and Mazziotta, Mario Nicola and McEnery, J. E. and Michelson, P. F. and Mitthumsiri, W. and Mizuno, Tsunefumi and Monzani, Maria Elena and Morselli, Aldo and Moskalenko, Igor V. and Negro, M. and Nuss, E. and Ojha, R. and Omodei, Nicola and Orienti, M. and Orlando, E. and Palatiello, M. and Paliya, Vaidehi S. and Paneque, D. and Perkins, Jeremy S. and Persic, M. and Pesce-Rollins, Melissa and Petrosian, Vahe' and Piron, F. and Porter, Troy A. and Principe, G. and Raino, S. and Rando, Riccardo and Rani, B. and Razzano, Massimilano and Razzaque, Soebur and Reimer, A. and Reimer, Olaf and Reposeur, T. and Sgro, C. and Siskind, E. J. and Spandre, Gloria and Spinelli, P. and Suson, D. J. and Tajima, Hiroyasu and Thayer, J. B. and Thompson, David J. and Torres, Diego F. and Tosti, Gino and Troja, Eleonora and Valverde, J. and Vianello, Giacomo and Vogel, M. and Wood, K. and Yassine, M. and Alfaro, R. and Alvarez, C. and Alvarez, J. D. and Arceo, R. and Arteaga-Velazquez, J. C. and Rojas, D. Avila and Ayala Solares, H. A. and Becerril, A. and Belmont-Moreno, E. and BenZvi, S. Y. and Bernal, A. and Braun, J. and Brisbois, C. and Caballero-Mora, K. S. and Capistran, T. and Carraminana, A. and Casanova, Sabrina and Castillo, M. and Cotti, U. and Cotzomi, J. and Coutino de Leon, S. and De Leon, C. and De la Fuente, E. and Dichiara, S. and Dingus, B. L. and DuVernois, M. A. and Diaz-Velez, J. C. and Engel, K. and Enriquez-Rivera, O. and Fiorino, D. W. and Fleischhack, H. and Fraija, N. and Garcia-Gonzalez, J. A. and Garfias, F. and Gonzalez Munoz, A. and Gonzalez, M. M. and Goodman, J. A. and Hampel-Arias, Z. and Harding, J. P. and Hernandez, S. and Hernandez-Almada, A. and Hona, B. and Hueyotl-Zahuantitla, F. and Hui, C. M. and Huntemeyer, P. and Iriarte, A. and Jardin-Blicq, A. and Joshi, V. and Kaufmann, S. and Lara, A. and Lauer, R. J. and Lee, W. H. and Lennarz, D. and Leon Vargas, H. and Linnemann, J. T. and Longinotti, A. L. and Luis-Raya, G. and Luna-Garcia, R. and Lopez-Coto, R. and Malone, K. and Marinelli, S. S. and Martinez, O. and Martinez-Castellanos, I. and Martinez-Castro, J. and Martinez-Huerta, H. and Matthews, J. A. and Miranda-Romagnoli, P. and Moreno, E. and Mostafa, M. and Nayerhoda, A. and Nellen, L. and Newbold, M. and Nisa, M. U. and Noriega-Papaqui, R. and Pelayo, R. and Pretz, J. and Perez-Perez, E. G. and Ren, Z. and Rho, C. D. and Riviere, C. and Rosa-Gonzalez, D. and Rosenberg, M. and Ruiz-Velasco, E. and Salazar, H. and Greus, F. Salesa and Sandoval, A. and Schneider, M. and Arroyo, M. Seglar and Sinnis, G. and Smith, A. J. and Springer, R. W. and Surajbali, P. and Taboada, Ignacio and Tibolla, O. and Tollefson, K. and Torres, I. and Ukwatta, Tilan N. and Villasenor, L. and Weisgarber, T. and Westerhoff, Stefan and Wisher, I. G. and Wood, J. and Yapici, Tolga and Yodh, G. and Zepeda, A. and Zhou, H.}, title = {VERITAS and Fermi-LAT Observations of TeV Gamma-Ray Sources Discovered by HAWC in the 2HWC Catalog}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {866}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, organization = {VERITAS Collaboration Fermi-LAT Collaboration HAWC Collaboration}, issn = {0004-637X}, doi = {10.3847/1538-4357/aade4e}, pages = {18}, year = {2018}, abstract = {The High Altitude Water Cherenkov (HAWC) collaboration recently published their 2HWC catalog, listing 39 very high energy (VHE; >100 GeV) gamma-ray sources based on 507 days of observation. Among these, 19 sources are not associated with previously known teraelectronvolt (TeV) gamma-ray sources. We have studied 14 of these sources without known counterparts with VERITAS and Fermi-LAT. VERITAS detected weak gamma-ray emission in the 1 TeV-30 TeV band in the region of DA 495, a pulsar wind nebula coinciding with 2HWC J1953+294, confirming the discovery of the source by HAWC. We did not find any counterpart for the selected 14 new HAWC sources from our analysis of Fermi-LAT data for energies higher than 10 GeV. During the search, we detected gigaelectronvolt (GeV) gamma-ray emission coincident with a known TeV pulsar wind nebula, SNR G54.1+0.3 (VER J1930+188), and a 2HWC source, 2HWC J1930+188. The fluxes for isolated, steady sources in the 2HWC catalog are generally in good agreement with those measured by imaging atmospheric Cherenkov telescopes. However, the VERITAS fluxes for SNR G54.1+0.3, DA 495, and TeV J2032+4130 are lower than those measured by HAWC, and several new HAWC sources are not detected by VERITAS. This is likely due to a change in spectral shape, source extension, or the influence of diffuse emission in the source region.}, language = {en} } @phdthesis{Tegtmeier2006, author = {Tegtmeier, Susann}, title = {Variationen der stratosph{\"a}rischen Residualzirkulation und ihr Einfluss auf die Ozonverteilung}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12118}, school = {Universit{\"a}t Potsdam}, year = {2006}, abstract = {Die Residualzirkulation entspricht der mittleren Massenzirkulation und beschreibt die im zonalen Mittel stattfindenden meridionalen Transportprozesse. Die Variationen der Residualzirkulation bestimmen gemeinsam mit dem anthropogen verursachten Ozonabbau die j{\"a}hrlichen Schwankungen der Ozongesamts{\"a}ule im arktischen Fr{\"u}hling. In der vorliegenden Arbeit wird die Geschwindigkeit des arktischen Astes der Residualzirkulation aus atmosph{\"a}rischen Daten gewonnen. Zu diesem Zweck wird das diabatische Absinken im Polarwirbel mit Hilfe von Trajektorienrechnungen bestimmt. Die vertikalen Bewegungen der Luftpakete k{\"o}nnen mit vertikalen Windfeldern oder entsprechend einem neuen Ansatz mit diabatischen Heizraten angetrieben werden. Die Eingabedaten stammen aus dem 45 Jahre langen Reanalyse-Datensatz des "European Centre for Medium Range Weather Forecast" (ECMWF). Außerdem kann f{\"u}r die Jahre ab 1984 die operationelle ECMWF-Analyse verwendet werden. Die Qualit{\"a}t und Robustheit der Heizraten- und Trajektorienrechnungen werden durch Sensitivit{\"a}tsstudien und Vergleiche mit anderen Modellen untermauert. Anschließend werden umfangreiche Trajektorienensemble statistisch ausgewertet, um ein detailliertes, zeit- und h{\"o}henaufgel{\"o}stes Bild des diabatischen Absinkens zu ermitteln. In diesem Zusammenhang werden zwei Methoden entwickelt, um das Absinken gemittelt im Polarwirbel oder als Funktion der {\"a}quivalenten Breite zu bestimmen. Es wird gezeigt, dass es notwendig ist den Lagrangeschen auf Trajektorienrechnungen basierenden Ansatz zu verfolgen, da die einfachen Eulerschen Mittel Abweichungen zu den Lagrangeschen Vertikalgeschwindigkeiten aufweisen. Das wirbelgemittelte Absinken wird f{\"u}r einzelne Winter mit dem beobachteten Absinken langlebiger Spurengase und anderen Modellstudien verglichen. Der Vergleich zeigt, dass das Absinken basierend auf den vertikalen Windfeldern der ECMWF-Datens{\"a}tze den Nettoluftmassentransport durch die Residualzirkulation sehr stark {\"u}bersch{\"a}tzt. Der neue Ansatz basierend auf den Heizraten ergibt hingegen realistische Ergebnisse und wird aus diesem Grund f{\"u}r alle Rechnungen verwendet. Es wird erstmalig eine Klimatologie des diabatischen Absinkens {\"u}ber einen fast f{\"u}nf Jahrzehnte umfassenden Zeitraum erstellt. Die Klimatologie beinhaltet das vertikal und zeitlich aufgel{\"o}ste diabatische Absinken gemittelt {\"u}ber den gesamten Polarwirbel und Informationen {\"u}ber die r{\"a}umliche Struktur des vertikalen Absinkens. Die nat{\"u}rliche Jahr-zu-Jahr Variabilit{\"a}t des diabatischen Absinkens ist sehr stark ausgepr{\"a}gt. Es wird gezeigt, dass zwischen der ECMWF-Zeitreihe des diabatischen Absinkens und der Zeitreihe aus einem unabh{\"a}ngig analysierten Temperaturdatensatz hohe Korrelationen bestehen. Erstmals wird der Einfluss von Transportprozessen auf die Ozongesamts{\"a}ule im arktischen Fr{\"u}hling direkt quantifiziert. Es wird gezeigt, dass die Jahr-zu-Jahr Variabilit{\"a}t der Ozongesamts{\"a}ule im arktischen Fr{\"u}hling zu gleichen Anteilen durch die Variabilit{\"a}t der dynamischen Komponente und durch die Variabilit{\"a}t der chemischen Komponente beeinflusst wird. Die gefundenen Variabilit{\"a}ten von diabatischem Absinken und Ozoneintrag in hohen Breiten werden mit der vertikalen Ausbreitung planetarer Wellen aus der Troposph{\"a}re in die Stratosph{\"a}re in Beziehung gesetzt.}, language = {de} } @article{PulkkinenMetzler2015, author = {Pulkkinen, Otto and Metzler, Ralf}, title = {Variance-corrected Michaelis-Menten equation predicts transient rates of single-enzyme reactions and response times in bacterial gene-regulation}, series = {Scientific reports}, journal = {Scientific reports}, number = {5}, publisher = {Nature Publishing Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/srep17820}, year = {2015}, abstract = {Many chemical reactions in biological cells occur at very low concentrations of constituent molecules. Thus, transcriptional gene-regulation is often controlled by poorly expressed transcription-factors, such as E.coli lac repressor with few tens of copies. Here we study the effects of inherent concentration fluctuations of substrate-molecules on the seminal Michaelis-Menten scheme of biochemical reactions. We present a universal correction to the Michaelis-Menten equation for the reaction-rates. The relevance and validity of this correction for enzymatic reactions and intracellular gene-regulation is demonstrated. Our analytical theory and simulation results confirm that the proposed variance-corrected Michaelis-Menten equation predicts the rate of reactions with remarkable accuracy even in the presence of large non-equilibrium concentration fluctuations. The major advantage of our approach is that it involves only the mean and variance of the substrate-molecule concentration. Our theory is therefore accessible to experiments and not specific to the exact source of the concentration fluctuations.}, language = {en} } @article{KontroBuschhueter2020, author = {Kontro, Inkeri and Buschh{\"u}ter, David}, title = {Validity of Colorado Learning Attitudes about Science Survey for a high-achieving, Finnish population}, series = {Physical review. Physics education research}, volume = {16}, journal = {Physical review. Physics education research}, number = {2}, publisher = {American Physical Society}, address = {College Park, MD}, issn = {2469-9896}, doi = {10.1103/PhysRevPhysEducRes.16.020104}, pages = {11}, year = {2020}, abstract = {The Colorado Learning Attitudes about Science Survey (CLASS) is an instrument which is widely used in physics education to characterize students' attitudes toward physics and learning physics and compare them with those of experts. While CLASS has been extensively validated for use in the context of higher education institutions in the United States, there has been less information about its use with European students. We have studied the structural, content, and substantive aspects of validity of CLASS by first doing a confirmatory factor analysis of N = 642 sets of student answers from the University of Helsinki, Finland. The students represented a culturally and demographically different subset of university physics students than in previous studies. The confirmatory factor analysis used a 3-factor, 15-item factor structure as a starting point and the resulting factor structure was similar to the original. Just minor modifications were needed for fit parameters to be in the acceptable range. We explored the differences by student interviews and consultation of experts. With the exception of one item, they supported the new 14-item, 3-factor structure. The results show that the interpretations made from CLASS results are mostly transferable, and CLASS remains a useful instrument for a wide variety of populations.}, language = {en} } @article{WulffMientusNowaketal.2022, author = {Wulff, Peter and Mientus, Lukas and Nowak, Anna and Borowski, Andreas}, title = {Utilizing a pretrained language model (BERT) to classify preservice physics teachers' written reflections}, series = {International journal of artificial intelligence in education}, journal = {International journal of artificial intelligence in education}, number = {33}, publisher = {Springer}, address = {New York}, issn = {1560-4292}, doi = {10.1007/s40593-022-00290-6}, pages = {439 -- 466}, year = {2022}, abstract = {Computer-based analysis of preservice teachers' written reflections could enable educational scholars to design personalized and scalable intervention measures to support reflective writing. Algorithms and technologies in the domain of research related to artificial intelligence have been found to be useful in many tasks related to reflective writing analytics such as classification of text segments. However, mostly shallow learning algorithms have been employed so far. This study explores to what extent deep learning approaches can improve classification performance for segments of written reflections. To do so, a pretrained language model (BERT) was utilized to classify segments of preservice physics teachers' written reflections according to elements in a reflection-supporting model. Since BERT has been found to advance performance in many tasks, it was hypothesized to enhance classification performance for written reflections as well. We also compared the performance of BERT with other deep learning architectures and examined conditions for best performance. We found that BERT outperformed the other deep learning architectures and previously reported performances with shallow learning algorithms for classification of segments of reflective writing. BERT starts to outperform the other models when trained on about 20 to 30\% of the training data. Furthermore, attribution analyses for inputs yielded insights into important features for BERT's classification decisions. Our study indicates that pretrained language models such as BERT can boost performance for language-related tasks in educational contexts such as classification.}, language = {en} } @article{LaquaiMuellerSchneideretal.2020, author = {Laquai, Rene and M{\"u}ller, Bernd R. and Schneider, Judith Ann and Kupsch, Andreas and Bruno, Giovanni}, title = {Using SXRR to probe the nature of discontinuities in SLM additive manufactured inconel 718 specimens}, series = {Metallurgical and Materials Transactions A}, volume = {51}, journal = {Metallurgical and Materials Transactions A}, number = {8}, publisher = {Springer}, address = {New York}, issn = {1073-5623}, doi = {10.1007/s11661-020-05847-5}, pages = {4146 -- 4157}, year = {2020}, abstract = {The utilization of additive manufacturing (AM) to fabricate robust structural components relies on understanding the nature of internal anomalies or discontinuities, which can compromise the structural integrity. While some discontinuities in AM microstructures stem from similar mechanisms as observed in more traditional processes such as casting, others are unique to the AM process. Discontinuities in AM are challenging to detect, due to their submicron size and orientation dependency. Toward the goal of improving structural integrity, minimizing discontinuities in an AM build requires an understanding of the mechanisms of formation to mitigate their occurrence. This study utilizes various techniques to evaluate the shape, size, nature and distribution of discontinuities in AM Inconel 718, in a non-hot isostatic pressed (HIPed) as-built, non-HIPed and direct age, and HIPed with two step age samples. Non-destructive synchrotron radiation refraction and transmission radiography (SXRR) provides additional information beyond that obtained with destructive optical microscopy. SXRR was able to distinguish between voids, cracks and lack of melt in, due to its sensitivity to the orientation of the discontinuity.}, language = {en} } @article{Teichmann2021, author = {Teichmann, Erik}, title = {Using phase dynamics to study partial synchrony}, series = {European physical journal special topics}, volume = {230}, journal = {European physical journal special topics}, number = {14-15}, publisher = {Springer}, address = {Heidelberg}, issn = {1951-6355}, doi = {10.1140/epjs/s11734-021-00156-3}, pages = {2833 -- 2842}, year = {2021}, abstract = {Partial synchronous states appear between full synchrony and asynchrony and exhibit many interesting properties. Most frequently, these states are studied within the framework of phase approximation. The latter is used ubiquitously to analyze coupled oscillatory systems. Typically, the phase dynamics description is obtained in the weak coupling limit, i.e., in the first-order in the coupling strength. The extension beyond the first-order represents an unsolved problem and is an active area of research. In this paper, three partially synchronous states are investigated and presented in order of increasing complexity. First, the usage of the phase response curve for the description of macroscopic oscillators is analyzed. To achieve this, the response of the mean-field oscillations in a model of all-to-all coupled limit-cycle oscillators to pulse stimulation is measured. The next part treats a two-group Kuramoto model, where the interaction of one attractive and one repulsive group results in an interesting solitary state, situated between full synchrony and self-consistent partial synchrony. In the last part, the phase dynamics of a relatively simple system of three Stuart-Landau oscillators are extended beyond the weak coupling limit. The resulting model contains triplet terms in the high-order phase approximation, though the structural connections are only pairwise. Finally, the scaling of the new terms with the coupling is analyzed.}, language = {en} } @phdthesis{SvirejevaHopkins2004, author = {Svirejeva-Hopkins, Anastasia}, title = {Urbanised territories as a specific component of the global carbon cycle}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001512}, school = {Universit{\"a}t Potsdam}, year = {2004}, abstract = {Wir betrachten folgende Teile: die zus{\"a}tzlichen Kohlenstoff(C)-emissionen, welche aus der Umwandlung von nat{\"u}rlichem Umland durch Stadtwachstum resultieren, und die {\"A}nderung des C-Flusses durch 'urbanisierte' {\"O}kosysteme, soweit atmosph{\"a}risches C durch diese in umliegende nat{\"u}rliche {\"O}kosysteme entlang der Kette \“Atmosph{\"a}re -> Vegetation -> abgestorbene organische Substanzen\” gepumpt wird: d.h. C-Export; f{\"u}r den Zeitraum von 1980 bis 2050. Als Szenario nutzen wir Prognosen der regionalen Stadtbev{\"o}lkerung, welche durch ein 'Hybridmodell' generiert werden f{\"u}r acht Regionen. Alle Sch{\"a}tzungen der C-Fl{\"u}sse basieren auf zwei Modellen: das Regression Modell und das sogenannte G-Modell. Die Siedlungsfl{\"a}che, welche mit dem Wachstum der Stadtbev{\"o}lkerung zunimmt, wird in 'Gr{\"u}nfl{\"a}chen' (Parks, usw.), Geb{\"a}udefl{\"a}chen und informell st{\"a}dtisch genutzte Fl{\"a}chen (Slums, illegale Lagerpl{\"a}tze, usw.) unterteilt. Es werden j{\"a}hrlich die regionale und globale Dynamik der C-Emissionen und des C-Exports sowie die C-Gesamtbilanz berechnet. Dabei liefern beide Modelle qualitativ {\"a}hnliche Ergebnisse, jedoch gibt es einige quantitative Unterschiede. Im ersten Modell erreicht die globale Jahresemission f{\"u}r die Dekade 2020-2030 resultierend aus der Landnutzungs{\"a}nderung ein Maximum von 205 Mt/a. Die maximalen Beitr{\"a}ge zur globalen Emission werden durch China, die asiatische und die pazifische Region erbracht. Im zweiten Modell erh{\"o}ht sich die j{\"a}hrliche globale Emission von 1.12 GtC/a f{\"u}r 1980 auf 1.25 GtC/a f{\"u}r 2005 (1Gt = 109 t). Danach beginnt eine Reduzierung. Vergleichen wir das Emissionmaximum mit der Emission durch Abholzung im Jahre 1980 (1.36 GtC/a), k{\"o}nnen wir konstatieren, daß die Urbanisierung damit in vergleichbarer Gr{\"o}sse zur Emission beitr{\"a}gt. Bezogen auf die globale Dynamik des j{\"a}hrlichen C-Exports durch Urbanisierung beobachten wir ein monotones Wachstum bis zum nahezu dreifachen Wert von 24 MtC/a f{\"u}r 1980 auf 66 MtC/a f{\"u}r 2050 im ersten Modell, bzw. im zweiten Modell von 249 MtC/a f{\"u}r 1980 auf 505 MtC/a f{\"u}r 2050. Damit ist im zweiten Fall die Transportleistung der Siedlungsgebiete mit dem C-Transport durch Fl{\"u}sse in die Ozeane (196 .. 537 MtC/a) vergleichbar. Bei der Absch{\"a}tzung der Gesamtbilanz finden wir, daß die Urbanisierung die Bilanz in Richtung zu einer 'Senke' verschiebt. Entsprechend dem zweiten Modell beginnt sich die C-Gesamtbilanz (nach ann{\"a}hernder Konstanz) ab dem Jahre 2000 mit einer fast konstanten Rate zu verringern. Wenn das Maximum im Jahre 2000 bei 905MtC/a liegt, f{\"a}llt dieser Wert anschliessend bis zum Jahre 2050 auf 118 MtC/a. Bei Extrapolation dieser Dynamik in die Zukunft k{\"o}nnen wir annehmen, daß am Ende des 21. Jahrhunderts die \“urbane\” C-Gesamtbilanz Null bzw. negative Werte erreicht.}, language = {en} } @article{AbdallaAharonianBenkhalietal.2019, author = {Abdalla, Hassan E. and Aharonian, Felix A. and Benkhali, F. Ait and Anguener, E. O. and Arakawa, M. and Arcaro, C. and Armand, C. and Ashkar, H. and Backes, M. and Martins, V. Barbosa and Barnard, M. and Becherini, Y. and Berge, D. and Bernloehr, K. and Blackwell, R. and Boettcher, M. and Boisson, C. and Bolmont, J. and Bonnefoy, S. and Bregeon, J. and Breuhaus, M. and Brun, F. and Brun, P. and Bryan, M. and Buechele, M. and Bulik, T. and Bylund, T. and Capasso, M. and Caroff, S. and Carosi, A. and Casanova, Sabrina and Cerruti, M. and Chakraborty, N. and Chand, T. and Chandra, S. and Chaves, R. C. G. and Chen, A. and Colafrancesco, S. and Curylo, M. and Davids, I. D. and Deil, C. and Devin, J. and de Wilt, P. and Dirson, L. and Djannati-Atai, A. and Dmytriiev, A. and Donath, A. and Doroshenko, V and Dyks, J. and Egberts, Kathrin and Emery, G. and Ernenwein, J-p and Eschbach, S. and Feijen, K. and Fegan, S. and Fiasson, A. and Fontaine, G. and Funk, S. and Fuessling, M. and Gabici, S. and Gallant, Y. A. and Gate, F. and Giavitto, G. and Glawion, D. and Glicenstein, J. F. and Gottschall, D. and Grondin, M-H and Hahn, J. and Haupt, M. and Heinzelmann, G. and Henri, G. and Hermann, G. and Hinton, James Anthony and Hofmann, W. and Hoischen, Clemens and Holch, Tim Lukas and Holler, M. and Horns, D. and Huber, D. and Iwasaki, H. and Jamrozy, M. and Jankowsky, D. and Jankowsky, F. and Jung-Richardt, I and Kastendieck, M. A. and Katarzynski, K. and Katsuragawa, M. and Katz, U. and Khangulyan, D. and Khelifi, B. and King, J. and Klepser, S. and Kluzniak, W. and Komin, Nu and Kosack, K. and Kostunin, D. and Kraus, M. and Lamanna, G. and Lau, J. and Lemiere, A. and Lemoine-Goumard, M. and Lenain, J-P and Leser, Eva and Levy, C. and Lohse, T. and Lopez-Coto, R. and Lypova, I and Mackey, J. and Majumdar, J. and Malyshev, D. and Marandon, V and Marcowith, Alexandre and Mares, A. and Mariaud, C. and Marti-Devesa, G. and Marx, R. and Maurin, G. and Meintjes, P. J. and Mitchell, A. M. W. and Moderski, R. and Mohamed, M. and Mohrmann, L. and Muller, J. and Moore, C. and Moulin, Emmanuel and Murach, T. and Nakashima, S. and de Naurois, M. and Ndiyavala, H. and Niederwanger, F. and Niemiec, J. and Oakes, L. and Odaka, H. and Ohm, S. and Wilhelmi, E. de Ona and Ostrowski, M. and Oya, I and Panter, M. and Parsons, R. D. and Perennes, C. and Petrucci, P-O and Peyaud, B. and Piel, Q. and Pita, S. and Poireau, V and Noel, A. Priyana and Prokhorov, D. A. and Prokoph, H. and Puehlhofer, G. and Punch, M. and Quirrenbach, A. and Raab, S. and Rauth, R. and Reimer, A. and Reimer, O. and Remy, Q. and Renaud, M. and Rieger, F. and Rinchiuso, L. and Romoli, C. and Rowell, G. and Rudak, B. and Ruiz-Velasco, E. and Sahakian, V and Saito, S. and Sanchez, David M. and Santangelo, A. and Sasaki, M. and Schlickeiser, R. and Schussler, F. and Schulz, A. and Schutte, H. and Schwanke, U. and Schwemmer, S. and Seglar-Arroyo, M. and Senniappan, M. and Seyffert, A. S. and Shafi, N. and Shiningayamwe, K. and Simoni, R. and Sinha, A. and Sol, H. and Specovius, A. and Spir-Jacob, M. and Stawarz, L. and Steenkamp, R. and Stegmann, Christian and Steppa, Constantin Beverly and Takahashi, T. and Tavernier, T. and Taylor, A. M. and Terrier, R. and Tiziani, D. and Tluczykont, M. and Trichard, C. and Tsirou, M. and Tsuji, N. and Tuffs, R. and Uchiyama, Y. and van der Walt, D. J. and van Eldik, C. and van Rensburg, C. and van Soelen, B. and Vasileiadis, G. and Veh, J. and Venter, C. and Vincent, P. and Vink, J. and Voisin, F. and Voelk, H. J. and Vuillaume, T. and Wadiasingh, Z. and Wagner, S. J. and White, R. and Wierzcholska, A. and Yang, R. and Yoneda, H. and Zacharias, M. and Zanin, R. and Zdziarski, A. A. and Zech, Alraune and Ziegler, A. and Zorn, J. and Zywucka, N. and Maxted, N.}, title = {Upper limits on very-high-energy gamma-ray emission from core-collapse supernovae observed with H.E.S.S.}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {626}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, organization = {HESS Collaboration}, issn = {1432-0746}, doi = {10.1051/0004-6361/201935242}, pages = {11}, year = {2019}, abstract = {Young core-collapse supernovae with dense-wind progenitors may be able to accelerate cosmic-ray hadrons beyond the knee of the cosmic-ray spectrum, and this may result in measurable gamma-ray emission. We searched for gamma-ray emission from ten super- novae observed with the High Energy Stereoscopic System (H.E.S.S.) within a year of the supernova event. Nine supernovae were observed serendipitously in the H.E.S.S. data collected between December 2003 and December 2014, with exposure times ranging from 1.4 to 53 h. In addition we observed SN 2016adj as a target of opportunity in February 2016 for 13 h. No significant gamma-ray emission has been detected for any of the objects, and upper limits on the >1 TeV gamma-ray flux of the order of similar to 10(-13) cm(-)(2)s(-1) are established, corresponding to upper limits on the luminosities in the range similar to 2 x 10(39) to similar to 1 x 10(42) erg s(-1). These values are used to place model-dependent constraints on the mass-loss rates of the progenitor stars, implying upper limits between similar to 2 x 10(-5) and similar to 2 x 10(-3) M-circle dot yr(-1) under reasonable assumptions on the particle acceleration parameters.}, language = {en} } @article{DiezTauerSchulz2006, author = {Diez, Isabel and Tauer, Klaus and Schulz, Burkhard}, title = {Unusual polymer dispersions-polypyrrole suspensions made of rings, frames, and platelets}, series = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, volume = {284}, journal = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, publisher = {Springer}, address = {New York}, issn = {0303-402X}, doi = {10.1007/s00396-006-1521-8}, pages = {1431 -- 1442}, year = {2006}, abstract = {Experimental results show that the polymerization of pyrrole in the presence of beta-naphthalenesulfonic acid and different fluorosurfactants like perfluorooctanesulfonic acid, perfluorooctyldiethanolamide, and ammonium perfluorooctanoate leads to polypyrrole with special morphologies, such as rings or disks and rectangular frames or plates. The formation of these unusually shaped particles of polymer dispersions is explained by the chemical and colloidal peculiarities of the oxidative pyrrole polymerization with ammonium peroxodisulfate in aqueous medium.}, language = {en} } @phdthesis{Pruefer2014, author = {Pr{\"u}fer, Nicole}, title = {Untersuchungen zur pro-inflammatorischen Wirkung von Serum-Amyloid A in glatten Gef{\"a}ßmuskelzellen}, pages = {XIII, 98}, year = {2014}, language = {de} } @phdthesis{Kleppek2005, author = {Kleppek, Sabine}, title = {Untersuchungen zur dynamischen Kopplung der Troposph{\"a}re und der Stratosph{\"a}re}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-6421}, school = {Universit{\"a}t Potsdam}, year = {2005}, abstract = {Im Rahmen dieser Arbeit wurde ein besseres Verst{\"a}ndnis der Kopplung der Troposph{\"a}re und der Stratosph{\"a}re in den mittleren und polaren Breiten der Nordhemisph{\"a}re (NH) auf Monatszeitskalen erzielt, die auf die Ausbreitung von quasi-station{\"a}ren Wellen zur{\"u}ckzuf{\"u}hren ist. Der Schwerpunkt lag dabei auf den dynamisch aktiven Wintermonaten, welche die gr{\"o}sste Variabilit{\"a}t aufweisen. Die troposph{\"a}rische Variabilit{\"a}t wird zum Grossteil durch bevorzugte Zirkulationsstrukturen, den Telekonnexionsmustern, bestimmt. Mittels einer rotierten EOF-Analyse der geopotenziellen H{\"o}he in 500 hPa wurden die wichtigsten regionalen troposph{\"a}rischen Telekonnexionsmuster der Nordhemisph{\"a}re berechnet. Diese lassen sich drei grossen geografischen Regionen zuordnen; dem nordatlantisch-europ{\"a}ischen Raum, Eurasien und dem pazifisch-nordamerikanischen Raum. Da es sich um die st{\"a}rksten troposph{\"a}rischen Variabilit{\"a}tsmuster handelt, wurden sie als grundlegende troposph{\"a}rische Gr{\"o}ssen herangezogen, um dynamische Zusammenh{\"a}nge zwischen der troposph{\"a}rischen und der stratosph{\"a}rischen Zirkulation zu untersuchen. Dabei wurde anhand von instantanen und zeitverz{\"o}gerten Korrelationsanalysen der troposph{\"a}rischen Muster mit stratosph{\"a}rischen Variablen erstmalig gezeigt, dass unterschiedliche regionale troposph{\"a}rische Telekonnexionsmuster unterschiedliche Auswirkungen auf die stratosph{\"a}rische Zirkulation haben. Es ergaben sich f{\"u}r die pazifisch-nordamerikanischen Muster signifikante instantane Korrelationen mit quasi-barotropen Musterstrukturen und f{\"u}r die nordatlantisch-europ{\"a}ischen Muster zonalsymmetrische Ringstrukturen ab 1978 mit signifikanten Korrelationswerten {\"u}ber tropischen und subtropischen Breiten und inversen Korrelationswerten {\"u}ber polaren Gebieten. Bei einer Untersuchung des Einflusses der stratosph{\"a}rischen Variabilit{\"a}t wurde gezeigt, dass sich die st{\"a}rkste Kopplung von nordatlantisch-europ{\"a}ischen Telekonnexionsmustern mit der stratosph{\"a}rischen Zirkulation bei einem in Richtung Europa verschobenen Polarwirbel ergibt, wodurch die signifikanten Korrelationen ab 1978 erkl{\"a}rt werden k{\"o}nnen. Eine zonal gemittelte und vor allem lokale Untersuchung der Wellenausbreitungsbedingungen w{\"a}hrend dieser stratosph{\"a}rischen Situation zeigt, dass es zu schw{\"a}cheren Windgeschwindigkeiten in der Stratosph{\"a}re im Bereich von Nordamerika und des westlichen Nordatlantiks kommt und sich dadurch die Wellenausbreitungsbedingungen in diesem geografischen Bereich f{\"u}r planetare Wellen verbessern. Durch die st{\"a}rkere Wellenausbreitung kommt es zu einer st{\"a}rkeren Wechselwirkung mit dem Polarjet, wobei dieser abgebremst wird. Diese Abbremsung f{\"u}hrt zu einer Verst{\"a}rkung der meridionalen Residualzirkulation. D. h., wenn es zu einer verst{\"a}rkten Wellenanregung im Nordatlantik und {\"u}ber Europa kommt, ist die Reaktion der Residualzirkulation bei einem nach Europa verschobenem Polarwirbel besonders stark. Die quasi-barotropen Korrelationsstrukturen, die sich bei den pazifisch-nordamerikanischen Mustern zeigen, weisen aufgrund von abnehmenden St{\"o}rungsamplituden mit zunehmender H{\"o}he, keiner Westw{\"a}rtsneigung und einem negativen Brechungsindex im Pazifik auf verschwindende Wellen hin, die als L{\"o}sung der Wellengleichung bei negativem Brechungsindex auftreten. Dies wird durch den Polarjet, der im Bereich des Pazifiks stets sehr weit in Richtung Norden verlagert ist, verursacht. Abschliessend wurde in dieser Arbeit untersucht, ob die gefundenen Zusammenh{\"a}nge von nordatlantisch-europ{\"a}ischen Telekonnexionsmustern mit der stratosph{\"a}rischen Zirkulation auch von einem Atmosph{\"a}renmodell wiedergegeben werden k{\"o}nnen. Dazu wurde ein transienter 40-Jahre-Klimalauf des ECHAM4.L39(DLR)/CHEM Modells mit m{\"o}glichst realistischen Antrieben erstmalig auf die Kopplung der Troposph{\"a}re und der Stratosph{\"a}re analysiert. Dabei konnten sowohl die troposph{\"a}rischen, als auch die stratosph{\"a}rischen Variabilit{\"a}tsmuster vom Modell simuliert werden. Allerdings zeigen sich in den stratosph{\"a}rischen Mustern Phasenverschiebungen in den Wellenzahl-1-Strukturen und ihre Zeitreihen weisen keinen signifikanten Trend ab 1978 auf. Die Kopplung der nordatlantisch-europ{\"a}ischen Telekonnexionsmuster mit der stratosph{\"a}rischen Zirkulation zeigt eine wesentlich schw{\"a}chere Reaktion der meridionalen Residualzirkulation. Somit stellte sich heraus, dass insbesondere die stratosph{\"a}rische Zirkulation im Modell starke Diskrepanzen zu den Beobachtungen zeigt, die wiederum Einfluss auf die Wellenausbreitungsbedingungen haben. Es wird damit deutlich, dass f{\"u}r eine richtige Wiedergabe der Wellenausbreitung und somit der Kopplung der Troposph{\"a}re und Stratosph{\"a}re die stratosph{\"a}rische Zirkulation eine wichtige Rolle spielt.}, subject = {Wellenausbreitung}, language = {de} } @phdthesis{Mueller2020, author = {M{\"u}ller, Jirka}, title = {Untersuchungen zum flow-Erleben bei Experimenten als physikalische Lerngelegenheit}, doi = {10.25932/publishup-48287}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-482879}, school = {Universit{\"a}t Potsdam}, pages = {150}, year = {2020}, abstract = {In der vorliegenden Arbeit wird untersucht, in wie weit physikalische Experimente ein flow-Erleben bei Lernenden hervorrufen. Flow-Erleben wird als Motivationsursache gesehen und soll den Weg zu Freude und Gl{\"u}ck darstellen. Insbesondere wegen dem oft zitierten Fachkr{\"a}ftemangel in naturwissenschaftlichen und technischen Berufen ist eine Motivationssteigerung in naturwissenschaftlichen Unterrichtsf{\"a}chern wichtig. Denn trotz Leistungssteigerungen in internationalen Vergleichstests m{\"o}chten in Deutschland deutlich weniger Sch{\"u}ler*innen einen solchen Beruf ergreifen als in anderen Industriestaaten. Daher gilt es, m{\"o}glichst fr{\"u}h Sch{\"u}ler*innen f{\"u}r naturwissenschaftlich-technische F{\"a}cher zu begeistern und insbesondere im regelrecht verhassten Physikunterricht flow-Erleben zu erzeugen. Im Rahmen dieser Arbeit wird das flow-Erleben von Studierenden in klassischen Laborexperimenten und FELS (Forschend-Entdeckendes Lernen mit dem Smartphone) als Lernumgebung untersucht. FELS ist eine an die Lebenswelt der Sch{\"u}ler*innen angepasste Lernumgebung, in der sie mit Smartphones ihre eigene Lebenswelt experimentell untersuchen. Es zeigt sich, dass sowohl klassische Laborexperimente als auch in der Lebenswelt durchgef{\"u}hrte, smartphonebasierte Experimente flow-Erleben erzeugen. Allerdings verursachen die smartphonebasierten Experimente kaum Stressgef{\"u}hle. Die in dieser Arbeit herausgefundenen Ergebnisse liefern einen ersten Ansatz, der durch Folgestudien erweitert werden sollte.}, language = {de} } @phdthesis{Schulz2016, author = {Schulz, Alexander}, title = {Untersuchung der Wechselwirkung synoptisch-skaliger mit orographisch bedingten Prozessen in der arktischen Grenzschicht {\"u}ber Spitzbergen}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400058}, school = {Universit{\"a}t Potsdam}, pages = {vi, 194}, year = {2016}, abstract = {In der vorliegenden Arbeit wird die planetare Grenzschicht in Ny-{\AA}lesund, Spitzbergen, sowohl bez{\"u}glich kleinskaliger („mikrometeorologischer") Effekte als auch in ihrer Kopplung mit der Synoptik untersucht. Dazu werden verschiedene Beobachtungsdaten aus der S{\"a}ule und in Bodenn{\"a}he zusammengezogen und bewertet. Die so gewonnenen Datens{\"a}tze werden dann zur Validierung eines nicht-hydrostatischen, regionalen Klimamodells genutzt. Weiterhin werden orographisch bedingte Einfl{\"u}sse, die Untergrundbeschaffenheit und die lokale Heterogenit{\"a}t der Unterlage untersucht. Hierzu werden meteorologische Gr{\"o}ßen, wie die Variabilit{\"a}t der Temperatur und insbesondere die j{\"a}hrliche Windverteilung in Bodenn{\"a}he untersucht und es erfolgt ein Vergleich von in-situ gemessenen turbulenten Fl{\"u}ssen von den Eddy-Kovarianz-Messkomplexen bei Ny-{\AA}lesund und im Bayelva-Tal unter demselben Aspekt. Es zeigt sich, dass der Eddy-Kovarianz-Messkomplex im Bayelva-Tal sehr stark durch eine orographisch bedingte Kanalisierung der Str{\"o}mung beeinflusst ist und sich nicht f{\"u}r Vergleiche mit regionalen Klimamodellen mit horizontalen Aufl{\"o}sungen von <1km eignet. Die hohe Bodenfeuchte im Bayelva-Tal f{\"u}hrt zudem zu einem deutlich kleineren Bowen-Verh{\"a}ltnis, als es f{\"u}r diese Region zu erwarten ist. Der Eddy-Kovarianz-Messkomplex bei Ny-{\AA}lesund erweist sich hingegen als geeigneter f{\"u}r solche Modellvergleiche, aufgrund der typischen, k{\"u}stennahen Windverteilung und des repr{\"a}sentativen Footprints. Letzteres wird durch die Bestimmung der Footprint-Klimatologie des Jahres 2013 mit einem aktuellen Footprint-Modell erarbeitet. Weiterhin wird die Auswirkung von (Anti-) Zyklonen {\"u}ber den Archipel auf die zeitliche Variabilit{\"a}t der lokalen Grenzschichteigenschaften untersucht und bewertet. Dazu wird ein Zyklonen-Detektions-Algorithmus auf ERA-Interim-Reanalysedatens{\"a}tze angewendet, wodurch die H{\"a}ufigkeit von nahezu ideal konzentrischen Hoch- und die Tiefdruckgebieten f{\"u}r drei Jahre bestimmt wird. Aus dieser Verteilung werden insgesamt drei interessante Zeitr{\"a}ume zu verschiedenen Jahreszeiten ausgew{\"a}hlt und im Rahmen von Prozessstudien die lokalen bodennahen meteorologischen Messungen, der turbulente Austausch an der Oberfl{\"a}che und die Grenzschichtdynamik in der S{\"a}ule untersucht. Die zeitliche Variabilit{\"a}t der dynamischen Grenzschichtstabilit{\"a}t in der S{\"a}ule wird anhand von zeitlich hoch aufgel{\"o}sten vertikalen Profilen der Bulk-Richardson-Zahl aus Kompositprofilen aus Fernerkundungsinstrumenten (Radiometer, Wind-LIDAR) sowie Mastdaten (BSRN-Mast) untersucht und die Grenzschichth{\"o}he ermittelt. Aus diesen Analysen ergibt sich eine deutliche Abh{\"a}ngigkeit der thermischen Stabilit{\"a}t beim Durchzug von Fronten, eine damit einhergehende erhebliche Abh{\"a}ngigkeit der Grenzschichtdynamik und der Grenzschichth{\"o}he sowie des turbulenten Austauschs von der zeitlichen Variabilit{\"a}t der Windgeschwindigkeit in der S{\"a}ule. Auf Grundlage der Standortanalysen und Prozessstudien erfolgt ein Vergleich der bodennahen Messungen und den Beobachtungen aus der S{\"a}ule, sowohl von den genannten Fernerkundungsinstrumenten als auch von In-situ-Messungen (Radiosonden) f{\"u}r den Zeitraum einer Radiosondierungskampagne mit dem nicht-hydrostatischen, regionalen Klimamodel WRF (ARW). Auf Grundlage der Fragestellung, inwieweit aktuelle Schemata die Grenzschichtcharakteristika in orographisch stark gegliedertem Gel{\"a}nde in der Arktis reproduzieren k{\"o}nnen, werden zwei Grenzschichtparametrisierungsschemata mit verschiedenen Ordnungen der Schließung validiert. Hierzu wird die zeitliche Variabilit{\"a}t der Temperatur, der Feuchte und des Windfeldes in der S{\"a}ule bis 2000m in den Simulationen mit den Beobachtungsdaten vergleichen. Es wird gezeigt, dass durch Modifikation der Initialwertfelder eine sehr gute {\"U}bereinstimmung zwischen den Simulationen und den Beobachtungen bereits bei einer horizontalen Aufl{\"o}sung von 1km erreicht werden kann und die Wahl des Grenzschichtschemas nur untergeordneten Einfluss hat. Hieraus werden Ans{\"a}tze der Weiterentwicklung der Parametrisierungen, aber auch Empfehlungen bez{\"u}glich der Initialwertfelder, wie der Landmaske und der Orographie, vorgeschlagen.}, language = {de} } @article{Nowak2023, author = {Nowak, Anna}, title = {Untersuchung der Qualit{\"a}t von Selbstreflexionstexten zum Physikunterricht}, series = {Studien zum Physik- und Chemielernen}, volume = {371}, journal = {Studien zum Physik- und Chemielernen}, publisher = {Logos}, address = {Berlin}, isbn = {978-3-8325-5739-3}, issn = {1614-8967}, doi = {10.30819/5739}, pages = {419}, year = {2023}, abstract = {Reflexion wird als notwendig f{\"u}r die professionelle Entwicklung von Lehrer:innen und die Verbesserung von Unterricht angesehen, wenngleich aus theoretischer Sicht große Uneinigkeit {\"u}ber den Begriff selbst, den Reflexionsprozess und die damit verbundenen Kompetenzen herrscht. Ziel dieser Arbeit war die Entwicklung, Untersuchung und Weiterentwicklung eines Reflexionsmodells mit einem theoriebasierten, klaren Konzept des Reflexionsprozesses und einem passenden Anspruch an die Reflexionsleistung der Reflektierenden. Grundlage f{\"u}r die empirische Untersuchung waren N = 132 Selbstreflexionstexte von N = 22 Studierenden aus dem Praxissemester Physik. Zur Codierung der Texte wurden vier mittels qualitativer Inhaltsanalyse entwickelte Manuale angewandt. Mit quantitativen Methoden wurden Zusammenh{\"a}nge zwischen strukturellen Elementen, Begr{\"u}ndungen, Inhalten und dem Qualit{\"a}tsmerkmal Reflexionstiefe {\"u}berpr{\"u}ft. Es zeigte sich ein "{\"U}berhang an Negativit{\"a}t": negative Bewertungen, negative Reflexionsausl{\"o}ser und negative Inhalte h{\"a}ngen signifikant positiv mit gr{\"o}ßerer Reflexionstiefe zusammen. Auf Grundlage der empirischen Ergebnisse wurde das Reflexionsmodell mit externaler und internaler Zielorientierung (REIZ) entwickelt. Zudem wurde darauf aufbauend eine Definition f{\"u}r Reflexionstiefe in vier Argumentationsclustern formuliert. F{\"u}r die Lehrkr{\"a}ftebildung wird der in REIZ dargestellte differenzierte Ansatz der Zielorientierung von Reflexion empfohlen.}, language = {de} } @phdthesis{Orgis2014, author = {Orgis, Thomas}, title = {Unstetige Galerkin-Diskretisierung niedriger Ordnung in einem atmosph{\"a}rischen Multiskalenmodell}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-70687}, school = {Universit{\"a}t Potsdam}, year = {2014}, abstract = {Die Dynamik der Atmosph{\"a}re der Erde umfasst einen Bereich von mikrophysikalischer Turbulenz {\"u}ber konvektive Prozesse und Wolkenbildung bis zu planetaren Wellenmustern. F{\"u}r Wettervorhersage und zur Betrachtung des Klimas {\"u}ber Jahrzehnte und Jahrhunderte ist diese Gegenstand der Modellierung mit numerischen Verfahren. Mit voranschreitender Entwicklung der Rechentechnik sind Neuentwicklungen der dynamischen Kerne von Klimamodellen, die mit der feiner werdenden Aufl{\"o}sung auch entsprechende Prozesse aufl{\"o}sen k{\"o}nnen, notwendig. Der dynamische Kern eines Modells besteht in der Umsetzung (Diskretisierung) der grundlegenden dynamischen Gleichungen f{\"u}r die Entwicklung von Masse, Energie und Impuls, so dass sie mit Computern numerisch gel{\"o}st werden k{\"o}nnen. Die vorliegende Arbeit untersucht die Eignung eines unstetigen Galerkin-Verfahrens niedriger Ordnung f{\"u}r atmosph{\"a}rische Anwendungen. Diese Eignung f{\"u}r Gleichungen mit Wirkungen von externen Kr{\"a}ften wie Erdanziehungskraft und Corioliskraft ist aus der Theorie nicht selbstverst{\"a}ndlich. Es werden n{\"o}tige Anpassungen beschrieben, die das Verfahren stabilisieren, ohne sogenannte „slope limiter" einzusetzen. F{\"u}r das unmodifizierte Verfahren wird belegt, dass es nicht geeignet ist, atmosph{\"a}rische Gleichgewichte stabil darzustellen. Das entwickelte stabilisierte Modell reproduziert eine Reihe von Standard-Testf{\"a}llen der atmosph{\"a}rischen Dynamik mit Euler- und Flachwassergleichungen in einem weiten Bereich von r{\"a}umlichen und zeitlichen Skalen. Die L{\"o}sung der thermischen Windgleichung entlang der mit den Isobaren identischen charakteristischen Kurven liefert atmosph{\"a}rische Gleichgewichtszust{\"a}nde mit durch vorgegebenem Grundstrom einstellbarer Neigung zu(barotropen und baroklinen)Instabilit{\"a}ten, die f{\"u}r die Entwicklung von Zyklonen wesentlich sind. Im Gegensatz zu fr{\"u}heren Arbeiten sind diese Zust{\"a}nde direkt im z-System(H{\"o}he in Metern)definiert und m{\"u}ssen nicht aus Druckkoordinaten {\"u}bertragen werden.Mit diesen Zust{\"a}nden, sowohl als Referenzzustand, von dem lediglich die Abweichungen numerisch betrachtet werden, und insbesondere auch als Startzustand, der einer kleinen St{\"o}rung unterliegt, werden verschiedene Studien der Simulation von barotroper und barokliner Instabilit{\"a}t durchgef{\"u}hrt. Hervorzuheben ist dabei die durch die Formulierung von Grundstr{\"o}men mit einstellbarer Baroklinit{\"a}t erm{\"o}glichte simulationsgest{\"u}tzte Studie des Grades der baroklinen Instabilit{\"a}t verschiedener Wellenl{\"a}ngen in Abh{\"a}ngigkeit von statischer Stabilit{\"a}t und vertikalem Windgradient als Entsprechung zu Stabilit{\"a}tskarten aus theoretischen Betrachtungen in der Literatur.}, language = {de} } @article{KurthsAgarwalShuklaetal.2019, author = {Kurths, J{\"u}rgen and Agarwal, Ankit and Shukla, Roopam and Marwan, Norbert and Maheswaran, Rathinasamy and Caesar, Levke and Krishnan, Raghavan and Merz, Bruno}, title = {Unravelling the spatial diversity of Indian precipitation teleconnections via a non-linear multi-scale approach}, series = {Nonlinear processes in geophysics}, volume = {26}, journal = {Nonlinear processes in geophysics}, number = {3}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {1023-5809}, doi = {10.5194/npg-26-251-2019}, pages = {251 -- 266}, year = {2019}, abstract = {A better understanding of precipitation dynamics in the Indian subcontinent is required since India's society depends heavily on reliable monsoon forecasts. We introduce a non-linear, multiscale approach, based on wavelets and event synchronization, for unravelling teleconnection influences on precipitation. We consider those climate patterns with the highest relevance for Indian precipitation. Our results suggest significant influences which are not well captured by only the wavelet coherence analysis, the state-of-the-art method in understanding linkages at multiple timescales. We find substantial variation across India and across timescales. In particular, El Ni{\~n}o-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) mainly influence precipitation in the south-east at interannual and decadal scales, respectively, whereas the North Atlantic Oscillation (NAO) has a strong connection to precipitation, particularly in the northern regions. The effect of the Pacific Decadal Oscillation (PDO) stretches across the whole country, whereas the Atlantic Multidecadal Oscillation (AMO) influences precipitation particularly in the central arid and semi-arid regions. The proposed method provides a powerful approach for capturing the dynamics of precipitation and, hence, helps improve precipitation forecasting.}, language = {en} } @article{VilkAghionAvgaretal.2022, author = {Vilk, Ohad and Aghion, Erez and Avgar, Tal and Beta, Carsten and Nagel, Oliver and Sabri, Adal and Sarfati, Raphael and Schwartz, Daniel K. and Weiß, Matthias and Krapf, Diego and Nathan, Ran and Metzler, Ralf and Assaf, Michael}, title = {Unravelling the origins of anomalous diffusion}, series = {Physical Review Research}, volume = {4}, journal = {Physical Review Research}, number = {3}, publisher = {American Physical Society}, address = {College Park, MD}, issn = {2643-1564}, doi = {10.1103/PhysRevResearch.4.033055}, pages = {033055-1 -- 033055-16}, year = {2022}, abstract = {Anomalous diffusion or, more generally, anomalous transport, with nonlinear dependence of the mean-squared displacement on the measurement time, is ubiquitous in nature. It has been observed in processes ranging from microscopic movement of molecules to macroscopic, large-scale paths of migrating birds. Using data from multiple empirical systems, spanning 12 orders of magnitude in length and 8 orders of magnitude in time, we employ a method to detect the individual underlying origins of anomalous diffusion and transport in the data. This method decomposes anomalous transport into three primary effects: long-range correlations ("Joseph effect"), fat-tailed probability density of increments ("Noah effect"), and nonstationarity ("Moses effect"). We show that such a decomposition of real-life data allows us to infer nontrivial behavioral predictions and to resolve open questions in the fields of single-particle tracking in living cells and movement ecology.}, language = {en} } @misc{VilkAghionAvgaretal.2022, author = {Vilk, Ohad and Aghion, Erez and Avgar, Tal and Beta, Carsten and Nagel, Oliver and Sabri, Adal and Sarfati, Raphael and Schwartz, Daniel K. and Weiß, Matthias and Krapf, Diego and Nathan, Ran and Metzler, Ralf and Assaf, Michael}, title = {Unravelling the origins of anomalous diffusion}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1303}, issn = {1866-8372}, doi = {10.25932/publishup-57764}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-577643}, pages = {16}, year = {2022}, abstract = {Anomalous diffusion or, more generally, anomalous transport, with nonlinear dependence of the mean-squared displacement on the measurement time, is ubiquitous in nature. It has been observed in processes ranging from microscopic movement of molecules to macroscopic, large-scale paths of migrating birds. Using data from multiple empirical systems, spanning 12 orders of magnitude in length and 8 orders of magnitude in time, we employ a method to detect the individual underlying origins of anomalous diffusion and transport in the data. This method decomposes anomalous transport into three primary effects: long-range correlations ("Joseph effect"), fat-tailed probability density of increments ("Noah effect"), and nonstationarity ("Moses effect"). We show that such a decomposition of real-life data allows us to infer nontrivial behavioral predictions and to resolve open questions in the fields of single-particle tracking in living cells and movement ecology.}, language = {en} } @article{ZuWolffRalaiarisoaetal.2019, author = {Zu, Fengshuo and Wolff, Christian Michael and Ralaiarisoa, Maryline and Amsalem, Patrick and Neher, Dieter and Koch, Norbert}, title = {Unraveling the Electronic Properties of Lead Halide Perovskites with Surface Photovoltage in Photoemission Studies}, series = {ACS applied materials \& interfaces}, volume = {11}, journal = {ACS applied materials \& interfaces}, number = {24}, publisher = {American Chemical Society}, address = {Washington}, issn = {1944-8244}, doi = {10.1021/acsami.9b05293}, pages = {21578 -- 21583}, year = {2019}, abstract = {The tremendous success of metal-halide perovskites, especially in the field of photovoltaics, has triggered a substantial number of studies in understanding their optoelectronic properties. However, consensus regarding the electronic properties of these perovskites is lacking due to a huge scatter in the reported key parameters, such as work function (Φ) and valence band maximum (VBM) values. Here, we demonstrate that the surface photovoltage (SPV) is a key phenomenon occurring at the perovskite surfaces that feature a non-negligible density of surface states, which is more the rule than an exception for most materials under study. With ultraviolet photoelectron spectroscopy (UPS) and Kelvin probe, we evidence that even minute UV photon fluxes (500 times lower than that used in typical UPS experiments) are sufficient to induce SPV and shift the perovskite Φ and VBM by several 100 meV compared to dark. By combining UV and visible light, we establish flat band conditions (i.e., compensate the surface-state-induced surface band bending) at the surface of four important perovskites, and find that all are p-type in the bulk, despite a pronounced n-type surface character in the dark. The present findings highlight that SPV effects must be considered in all surface studies to fully understand perovskites' photophysical properties.}, language = {en} } @article{RitschelCherstvyMetzler2021, author = {Ritschel, Stefan and Cherstvy, Andrey G. and Metzler, Ralf}, title = {Universality of delay-time averages for financial time series}, series = {Journal of physics. Complexity}, volume = {2}, journal = {Journal of physics. Complexity}, number = {4}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2632-072X}, doi = {10.1088/2632-072X/ac2220}, pages = {30}, year = {2021}, abstract = {We analyze historical data of stock-market prices for multiple financial indices using the concept of delay-time averaging for the financial time series (FTS). The region of validity of our recent theoretical predictions [Cherstvy A G et al 2017 New J. Phys. 19 063045] for the standard and delayed time-averaged mean-squared 'displacements' (TAMSDs) of the historical FTS is extended to all lag times. As the first novel element, we perform extensive computer simulations of the stochastic differential equation describing geometric Brownian motion (GBM) which demonstrate a quantitative agreement with the analytical long-term price-evolution predictions in terms of the delayed TAMSD (for all stock-market indices in crisis-free times). Secondly, we present a robust procedure of determination of the model parameters of GBM via fitting the features of the price-evolution dynamics in the FTS for stocks and cryptocurrencies. The employed concept of single-trajectory-based time averaging can serve as a predictive tool (proxy) for a mathematically based assessment and rationalization of probabilistic trends in the evolution of stock-market prices.}, language = {en} } @article{SposiniGrebenkovMetzleretal.2020, author = {Sposini, Vittoria and Grebenkov, Denis S. and Metzler, Ralf and Oshanin, Gleb and Seno, Flavio}, title = {Universal spectral features of different classes of random-diffusivity processes}, series = {New Journal of Physics}, volume = {22}, journal = {New Journal of Physics}, number = {6}, publisher = {Dt. Physikalische Ges.}, address = {Bad Honnef}, issn = {1367-2630}, doi = {10.1088/1367-2630/ab9200}, pages = {26}, year = {2020}, abstract = {Stochastic models based on random diffusivities, such as the diffusing-diffusivity approach, are popular concepts for the description of non-Gaussian diffusion in heterogeneous media. Studies of these models typically focus on the moments and the displacement probability density function. Here we develop the complementary power spectral description for a broad class of random-diffusivity processes. In our approach we cater for typical single particle tracking data in which a small number of trajectories with finite duration are garnered. Apart from the diffusing-diffusivity model we study a range of previously unconsidered random-diffusivity processes, for which we obtain exact forms of the probability density function. These new processes are different versions of jump processes as well as functionals of Brownian motion. The resulting behaviour subtly depends on the specific model details. Thus, the central part of the probability density function may be Gaussian or non-Gaussian, and the tails may assume Gaussian, exponential, log-normal, or even power-law forms. For all these models we derive analytically the moment-generating function for the single-trajectory power spectral density. We establish the generic 1/f²-scaling of the power spectral density as function of frequency in all cases. Moreover, we establish the probability density for the amplitudes of the random power spectral density of individual trajectories. The latter functions reflect the very specific properties of the different random-diffusivity models considered here. Our exact results are in excellent agreement with extensive numerical simulations.}, language = {en} } @misc{SposiniGrebenkovMetzleretal.2020, author = {Sposini, Vittoria and Grebenkov, Denis S. and Metzler, Ralf and Oshanin, Gleb and Seno, Flavio}, title = {Universal spectral features of different classes of random-diffusivity processes}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {999}, issn = {1866-8372}, doi = {10.25932/publishup-47696}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-476960}, pages = {27}, year = {2020}, abstract = {Stochastic models based on random diffusivities, such as the diffusing-diffusivity approach, are popular concepts for the description of non-Gaussian diffusion in heterogeneous media. Studies of these models typically focus on the moments and the displacement probability density function. Here we develop the complementary power spectral description for a broad class of random-diffusivity processes. In our approach we cater for typical single particle tracking data in which a small number of trajectories with finite duration are garnered. Apart from the diffusing-diffusivity model we study a range of previously unconsidered random-diffusivity processes, for which we obtain exact forms of the probability density function. These new processes are different versions of jump processes as well as functionals of Brownian motion. The resulting behaviour subtly depends on the specific model details. Thus, the central part of the probability density function may be Gaussian or non-Gaussian, and the tails may assume Gaussian, exponential, log-normal, or even power-law forms. For all these models we derive analytically the moment-generating function for the single-trajectory power spectral density. We establish the generic 1/f²-scaling of the power spectral density as function of frequency in all cases. Moreover, we establish the probability density for the amplitudes of the random power spectral density of individual trajectories. The latter functions reflect the very specific properties of the different random-diffusivity models considered here. Our exact results are in excellent agreement with extensive numerical simulations.}, language = {en} } @article{UolaLeverGuehneetal.2018, author = {Uola, Roope and Lever, Fabiano and G{\"u}hne, Otfried and Pellonpaa, Juha-Pekka}, title = {Unified picture for spatial, temporal, and channel steering}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {97}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {3}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9926}, doi = {10.1103/PhysRevA.97.032301}, pages = {6}, year = {2018}, abstract = {Quantum steering describes how local actions on a quantum system can affect another, spacelike separated, quantum state. Lately, quantum steering has been formulated also for timelike scenarios and for quantum channels. We approach all the three scenarios as one using tools from Stinespring dilations of quantum channels. By applying our technique we link all three steering problems one-to-one with the incompatibility of quantum measurements, a result formerly known only for spatial steering. We exploit this connection by showing how measurement uncertainty relations can be used as tight steering inequalities for all three scenarios. Moreover, we show that certain notions of temporal and spatial steering are fully equivalent and prove a hierarchy between temporal steering and macrorealistic hidden variable models.}, language = {en} } @article{WangSenoSokolovetal.2020, author = {Wang, Wei and Seno, Flavio and Sokolov, Igor M. and Chechkin, Aleksei V. and Metzler, Ralf}, title = {Unexpected crossovers in correlated random-diffusivity processes}, series = {New Journal of Physics}, volume = {22}, journal = {New Journal of Physics}, publisher = {Dt. Physikalische Ges.}, address = {Bad Honnef}, issn = {1367-2630}, doi = {10.1088/1367-2630/aba390}, pages = {17}, year = {2020}, abstract = {The passive and active motion of micron-sized tracer particles in crowded liquids and inside living biological cells is ubiquitously characterised by 'viscoelastic' anomalous diffusion, in which the increments of the motion feature long-ranged negative and positive correlations. While viscoelastic anomalous diffusion is typically modelled by a Gaussian process with correlated increments, so-called fractional Gaussian noise, an increasing number of systems are reported, in which viscoelastic anomalous diffusion is paired with non-Gaussian displacement distributions. Following recent advances in Brownian yet non-Gaussian diffusion we here introduce and discuss several possible versions of random-diffusivity models with long-ranged correlations. While all these models show a crossover from non-Gaussian to Gaussian distributions beyond some correlation time, their mean squared displacements exhibit strikingly different behaviours: depending on the model crossovers from anomalous to normal diffusion are observed, as well as a priori unexpected dependencies of the effective diffusion coefficient on the correlation exponent. Our observations of the non-universality of random-diffusivity viscoelastic anomalous diffusion are important for the analysis of experiments and a better understanding of the physical origins of 'viscoelastic yet non-Gaussian' diffusion.}, language = {en} } @misc{WangSenoSokolovetal.2020, author = {Wang, Wei and Seno, Flavio and Sokolov, Igor M. and Chechkin, Aleksei V. and Metzler, Ralf}, title = {Unexpected crossovers in correlated random-diffusivity processes}, number = {1006}, issn = {1866-8372}, doi = {10.25932/publishup-48004}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-480049}, pages = {18}, year = {2020}, abstract = {The passive and active motion of micron-sized tracer particles in crowded liquids and inside living biological cells is ubiquitously characterised by 'viscoelastic' anomalous diffusion, in which the increments of the motion feature long-ranged negative and positive correlations. While viscoelastic anomalous diffusion is typically modelled by a Gaussian process with correlated increments, so-called fractional Gaussian noise, an increasing number of systems are reported, in which viscoelastic anomalous diffusion is paired with non-Gaussian displacement distributions. Following recent advances in Brownian yet non-Gaussian diffusion we here introduce and discuss several possible versions of random-diffusivity models with long-ranged correlations. While all these models show a crossover from non-Gaussian to Gaussian distributions beyond some correlation time, their mean squared displacements exhibit strikingly different behaviours: depending on the model crossovers from anomalous to normal diffusion are observed, as well as a priori unexpected dependencies of the effective diffusion coefficient on the correlation exponent. Our observations of the non-universality of random-diffusivity viscoelastic anomalous diffusion are important for the analysis of experiments and a better understanding of the physical origins of 'viscoelastic yet non-Gaussian' diffusion.}, language = {en} } @article{WangRychkovNguyenetal.2020, author = {Wang, Jingwen and Rychkov, Dmitry and Nguyen, Quyet Doan and Gerhard, Reimund}, title = {Unexpected bipolar space-charge polarization across transcrystalline interfaces in polypropylene electret films}, series = {Journal of applied physics}, volume = {128}, journal = {Journal of applied physics}, number = {13}, publisher = {American Institute of Physics, AIP}, address = {Melville, NY}, issn = {0021-8979}, doi = {10.1063/5.0022071}, pages = {7}, year = {2020}, abstract = {A double-layer transcrystalline polypropylene (PP) film with a flat central interface layer between its two transcrystalline layers is obtained by recrystallization from the melt between two polytetrafluoroethylene (PTFE) surfaces on both sides of the PP film. Its electret properties are studied and compared with those of a single-layer transcrystalline PP film re-crystallized in contact with only one PTFE surface. Within experimental uncertainty, the two types of transcrystalline films exhibit the same thermal properties and crystallinities. After thermal poling, however, two hetero-charge layers of opposite polarity are found on the internal interfaces of the double-layer transcrystalline films and may together be considered as micrometer-sized dipoles. The unexpected phenomenon does not occur in single-layer transcrystalline samples without a central interface layer, suggesting that the interfaces between the transcrystalline layers and the micrometer-thick central interface layer may be the origin of deeper traps rather than the crystalline structures in the transcrystallites or the spherulites. The origin of the interfacial charges was also studied by means of an injection-blocking charging method, which revealed that intrinsic charge carriers introduced during recrystallization are most likely responsible for the interfacial charges. It is fascinating that a material as familiar as PP can exhibit such intriguing properties with a special bipolar space-charge polarization across the central interface layer after quasi-epitaxial surface moulding into a double-layer transcrystalline form. In addition to applications in electret (micro-)devices for electro-mechanical transduction, the highly ordered structures may also be employed as a new paradigm for studying charge storage and transport in polymer electrets and in dielectrics for DC electrical insulation.}, language = {en} } @article{LiebigSarhanPrietzeletal.2018, author = {Liebig, Ferenc and Sarhan, Radwan Mohamed and Prietzel, Claudia Christina and Th{\"u}nemann, Andreas F. and Bargheer, Matias and Koetz, Joachim}, title = {Undulated Gold Nanoplatelet Superstructures}, series = {Langmuir}, volume = {34}, journal = {Langmuir}, number = {15}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.7b02898}, pages = {4584 -- 4594}, year = {2018}, abstract = {Negatively charged flat gold nanotriangles, formed in a vesicular template phase and separated by an AOT-micelle-based depletion flocculation, were reloaded by adding a cationic polyelectrolyte, that is, a hyperbranched polyethylenimine (PEI). Heating the system to 100 degrees C in the presence of a gold chloride solution, the reduction process leads to the formation of gold nanoparticles inside the polymer shell surrounding the nanoplatelets. The gold nanoparticle formation is investigated by UV-vis spectroscopy, small-angle X-ray scattering, and dynamic light scattering measurements in combination with transmission electron microscopy. Spontaneously formed gold clusters in the hyperbranched PEI shell with an absorption maximum at 350 nm grow on the surface of the nanotriangles as hemispherical particles with diameters of similar to 6 nm. High-resolution micrographs show that the hemispherical gold particles are crystallized onto the {111} facets on the bottom and top of the platelet as well as on the edges without a grain boundary. Undulated gold nanoplatelet superstructures with special properties become available, which show a significantly modified performance in SERS-detected photocatalysis regarding both reactivity and enhancement factor.}, language = {en} } @article{PerdigonToroLeQuangPhuongElleretal.2022, author = {Perdig{\´o}n-Toro, Lorena and Le Quang Phuong, and Eller, Fabian and Freychet, Guillaume and Saglamkaya, Elifnaz and Khan, Jafar and Wei, Qingya and Zeiske, Stefan and Kroh, Daniel and Wedler, Stefan and Koehler, Anna and Armin, Ardalan and Laquai, Frederic and Herzig, Eva M. and Zou, Yingping and Shoaee, Safa and Neher, Dieter}, title = {Understanding the role of order in Y-series non-fullerene solar cells to realize high open-circuit voltages}, series = {Advanced energy materials}, volume = {12}, journal = {Advanced energy materials}, number = {12}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1614-6832}, doi = {10.1002/aenm.202103422}, pages = {13}, year = {2022}, abstract = {Non-fullerene acceptors (NFAs) as used in state-of-the-art organic solar cells feature highly crystalline layers that go along with low energetic disorder. Here, the crucial role of energetic disorder in blends of the donor polymer PM6 with two Y-series NFAs, Y6, and N4 is studied. By performing temperature-dependent charge transport and recombination studies, a consistent picture of the shape of the density of state distributions for free charges in the two blends is developed, allowing an analytical description of the dependence of the open-circuit voltage V-OC on temperature and illumination intensity. Disorder is found to influence the value of the V-OC at room temperature, but also its progression with temperature. Here, the PM6:Y6 blend benefits substantially from its narrower state distributions. The analysis also shows that the energy of the equilibrated free charge population is well below the energy of the NFA singlet excitons for both blends and possibly below the energy of the populated charge transfer manifold, indicating a down-hill driving force for free charge formation. It is concluded that energetic disorder of charge-separated states has to be considered in the analysis of the photovoltaic properties, even for the more ordered PM6:Y6 blend.}, language = {en} } @article{SchroederEvansPolatidisetal.2022, author = {Schr{\"o}der, Jakob and Evans, Alexander and Polatidis, Efthymios and Mohr, Gunther and Serrano-Munoz, Itziar and Bruno, Giovanni and Čapek, Jan}, title = {Understanding the impact of texture on the micromechanical anisotropy of laser powder bed fused Inconel 718}, series = {Journal of materials science}, volume = {57}, journal = {Journal of materials science}, number = {31}, publisher = {Springer}, address = {New York}, issn = {0022-2461}, doi = {10.1007/s10853-022-07499-9}, pages = {15036 -- 15058}, year = {2022}, abstract = {The manufacturability of metallic alloys using laser-based additive manufacturing methods such as laser powder bed fusion has substantially improved within the last decade. However, local melting and solidification cause hierarchically structured and crystallographically textured microstructures possessing large residual stress. Such microstructures are not only the origin of mechanical anisotropy but also pose metrological challenges for the diffraction-based residual stress determination. Here we demonstrate the influence of the build orientation and the texture on the microstructure and consequently the mechanical anisotropy of as-built Inconel 718. For this purpose, we manufactured specimens with [001]/[011]-, [001]- and [011]/[11 (1) over bar]-type textures along their loading direction. In addition to changes in the Young's moduli, the differences in the crystallographic textures result in variations of the yield and ultimate tensile strengths. With this in mind, we studied the anisotropy on the micromechanical scale by subjecting the specimens to tensile loads along the different texture directions during in situ neutron diffraction experiments. In this context, the response of multiple lattice planes up to a tensile strain of 10\% displayed differences in the load partitioning and the residual strain accumulation for the specimen with [011]/[(1) over bar 11]-type texture. However, the relative behavior of the specimens possessing an [001] /[011]- and [001]-type texture remained qualitatively similar. The consequences on the metrology of residual stress determination methods are discussed.}, language = {en} } @phdthesis{Smirnov2023, author = {Smirnov, Artem}, title = {Understanding the dynamics of the near-earth space environment utilizing long-term satellite observations}, doi = {10.25932/publishup-61371}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-613711}, school = {Universit{\"a}t Potsdam}, pages = {xxxvi, 286}, year = {2023}, abstract = {The near-Earth space environment is a highly complex system comprised of several regions and particle populations hazardous to satellite operations. The trapped particles in the radiation belts and ring current can cause significant damage to satellites during space weather events, due to deep dielectric and surface charging. Closer to Earth is another important region, the ionosphere, which delays the propagation of radio signals and can adversely affect navigation and positioning. In response to fluctuations in solar and geomagnetic activity, both the inner-magnetospheric and ionospheric populations can undergo drastic and sudden changes within minutes to hours, which creates a challenge for predicting their behavior. Given the increasing reliance of our society on satellite technology, improving our understanding and modeling of these populations is a matter of paramount importance. In recent years, numerous spacecraft have been launched to study the dynamics of particle populations in the near-Earth space, transforming it into a data-rich environment. To extract valuable insights from the abundance of available observations, it is crucial to employ advanced modeling techniques, and machine learning methods are among the most powerful approaches available. This dissertation employs long-term satellite observations to analyze the processes that drive particle dynamics, and builds interdisciplinary links between space physics and machine learning by developing new state-of-the-art models of the inner-magnetospheric and ionospheric particle dynamics. The first aim of this thesis is to investigate the behavior of electrons in Earth's radiation belts and ring current. Using ~18 years of electron flux observations from the Global Positioning System (GPS), we developed the first machine learning model of hundreds-of-keV electron flux at Medium Earth Orbit (MEO) that is driven solely by solar wind and geomagnetic indices and does not require auxiliary flux measurements as inputs. We then proceeded to analyze the directional distributions of electrons, and for the first time, used Fourier sine series to fit electron pitch angle distributions (PADs) in Earth's inner magnetosphere. We performed a superposed epoch analysis of 129 geomagnetic storms during the Van Allen Probes era and demonstrated that electron PADs have a strong energy-dependent response to geomagnetic activity. Additionally, we showed that the solar wind dynamic pressure could be used as a good predictor of the PAD dynamics. Using the observed dependencies, we created the first PAD model with a continuous dependence on L, magnetic local time (MLT) and activity, and developed two techniques to reconstruct near-equatorial electron flux observations from low-PA data using this model. The second objective of this thesis is to develop a novel model of the topside ionosphere. To achieve this goal, we collected observations from five of the most widely used ionospheric missions and intercalibrated these data sets. This allowed us to use these data jointly for model development, validation, and comparison with other existing empirical models. We demonstrated, for the first time, that ion density observations by Swarm Langmuir Probes exhibit overestimation (up to ~40-50\%) at low and mid-latitudes on the night side, and suggested that the influence of light ions could be a potential cause of this overestimation. To develop the topside model, we used 19 years of radio occultation (RO) electron density profiles, which were fitted with a Chapman function with a linear dependence of scale height on altitude. This approximation yields 4 parameters, namely the peak density and height of the F2-layer and the slope and intercept of the linear scale height trend, which were modeled using feedforward neural networks (NNs). The model was extensively validated against both RO and in-situ observations and was found to outperform the International Reference Ionosphere (IRI) model by up to an order of magnitude. Our analysis showed that the most substantial deviations of the IRI model from the data occur at altitudes of 100-200 km above the F2-layer peak. The developed NN-based ionospheric model reproduces the effects of various physical mechanisms observed in the topside ionosphere and provides highly accurate electron density predictions. This dissertation provides an extensive study of geospace dynamics, and the main results of this work contribute to the improvement of models of plasma populations in the near-Earth space environment.}, language = {en} } @phdthesis{Buechner2022, author = {B{\"u}chner, Robby}, title = {Understanding local electronic structure variations in bio-inspired aromatic molecules}, doi = {10.25932/publishup-55319}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-553192}, school = {Universit{\"a}t Potsdam}, pages = {viii, 111}, year = {2022}, abstract = {In this thesis, the dependencies of charge localization and itinerance in two classes of aromatic molecules are accessed: pyridones and porphyrins. The focus lies on the effects of isomerism, complexation, solvation, and optical excitation, which are concomitant with different crucial biological applications of specific members of these groups of compounds. Several porphyrins play key roles in the metabolism of plants and animals. The nucleobases, which store the genetic information in the DNA and RNA are pyridone derivatives. Additionally, a number of vitamins are based on these two groups of substances. This thesis aims to answer the question of how the electronic structure of these classes of molecules is modified, enabling the versatile natural functionality. The resulting insights into the effect of constitutional and external factors are expected to facilitate the design of new processes for medicine, light-harvesting, catalysis, and environmental remediation. The common denominator of pyridones and porphyrins is their aromatic character. As aromaticity was an early-on topic in chemical physics, the overview of relevant theoretical models in this work also mirrors the development of this scientific field in the 20th century. The spectroscopic investigation of these compounds has long been centered on their global, optical transition between frontier orbitals. The utilization and advancement of X-ray spectroscopic methods characterizing the local electronic structure of molecular samples form the core of this thesis. The element selectivity of the near-edge X-ray absorption fine structure (NEXAFS) is employed to probe the unoccupied density of states at the nitrogen site, which is key for the chemical reactivity of pyridones and porphyrins. The results contribute to the growing database of NEXAFS features and their interpretation, e.g., by advancing the debate on the porphyrin N K-edge through systematic experimental and theoretical arguments. Further, a state-of-the-art laser pump - NEXAFS probe scheme is used to characterize the relaxation pathway of a photoexcited porphyrin on the atomic level. Resonant inelastic X-ray scattering (RIXS) provides complementary results by accessing the highest occupied valence levels including symmetry information. It is shown that RIXS is an effective experimental tool to gain detailed information on charge densities of individual species in tautomeric mixtures. Additionally, the hRIXS and METRIXS high-resolution RIXS spectrometers, which have been in part commissioned in the course of this thesis, will gain access to the ultra-fast and thermal chemistry of pyridones, porphyrins, and many other compounds. With respect to both classes of bio-inspired aromatic molecules, this thesis establishes that even though pyridones and porphyrins differ largely by their optical absorption bands and hydrogen bonding abilities, they all share a global stabilization of local constitutional changes and relevant external perturbation. It is because of this wide-ranging response that pyridones and porphyrins can be applied in a manifold of biological and technical processes.}, language = {en} } @misc{BodrovaChechkinCherstvyetal.2016, author = {Bodrova, Anna S. and Chechkin, Aleksei V. and Cherstvy, Andrey G. and Safdari, Hadiseh and Sokolov, Igor M. and Metzler, Ralf}, title = {Underdamped scaled Brownian motion}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-97158}, pages = {16}, year = {2016}, abstract = {It is quite generally assumed that the overdamped Langevin equation provides a quantitative description of the dynamics of a classical Brownian particle in the long time limit. We establish and investigate a paradigm anomalous diffusion process governed by an underdamped Langevin equation with an explicit time dependence of the system temperature and thus the diffusion and damping coefficients. We show that for this underdamped scaled Brownian motion (UDSBM) the overdamped limit fails to describe the long time behaviour of the system and may practically even not exist at all for a certain range of the parameter values. Thus persistent inertial effects play a non-negligible role even at significantly long times. From this study a general questions on the applicability of the overdamped limit to describe the long time motion of an anomalously diffusing particle arises, with profound consequences for the relevance of overdamped anomalous diffusion models. We elucidate our results in view of analytical and simulations results for the anomalous diffusion of particles in free cooling granular gases.}, language = {en} } @article{BodrovaChechkinCherstvyetal.2016, author = {Bodrova, Anna S. and Chechkin, Aleksei V. and Cherstvy, Andrey G. and Safdari, Hadiseh and Sokolov, Igor M. and Metzler, Ralf}, title = {Underdamped scaled Brownian motion}, series = {Scientific reports}, volume = {6}, journal = {Scientific reports}, publisher = {Nature Publishing Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/srep30520}, year = {2016}, abstract = {It is quite generally assumed that the overdamped Langevin equation provides a quantitative description of the dynamics of a classical Brownian particle in the long time limit. We establish and investigate a paradigm anomalous diffusion process governed by an underdamped Langevin equation with an explicit time dependence of the system temperature and thus the diffusion and damping coefficients. We show that for this underdamped scaled Brownian motion (UDSBM) the overdamped limit fails to describe the long time behaviour of the system and may practically even not exist at all for a certain range of the parameter values. Thus persistent inertial effects play a non-negligible role even at significantly long times. From this study a general questions on the applicability of the overdamped limit to describe the long time motion of an anomalously diffusing particle arises, with profound consequences for the relevance of overdamped anomalous diffusion models. We elucidate our results in view of analytical and simulations results for the anomalous diffusion of particles in free cooling granular gases.}, language = {en} } @misc{vonReppertMatternPudelletal.2020, author = {von Reppert, Alexander and Mattern, Maximilian and Pudell, Jan-Etienne and Zeuschner, Steffen Peer and Dumesnil, Karine and Bargheer, Matias}, title = {Unconventional picosecond strain pulses resulting from the saturation of magnetic stress within a photoexcited rare earth layer}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, number = {899}, issn = {1866-8372}, doi = {10.25932/publishup-46935}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-469350}, pages = {15}, year = {2020}, abstract = {Optical excitation of spin-ordered rare earth metals triggers a complex response of the crystal lattice since expansive stresses from electron and phonon excitations compete with a contractive stress induced by spin disorder. Using ultrafast x-ray diffraction experiments, we study the layer specific strain response of a dysprosium film within a metallic heterostructure upon femtosecond laser-excitation. The elastic and diffusive transport of energy to an adjacent, non-excited detection layer clearly separates the contributions of strain pulses and thermal excitations in the time domain. We find that energy transfer processes to magnetic excitations significantly modify the observed conventional bipolar strain wave into a unipolar pulse. By modeling the spin system as a saturable energy reservoir that generates substantial contractive stress on ultrafast timescales, we can reproduce the observed strain response and estimate the time- and space dependent magnetic stress. The saturation of the magnetic stress contribution yields a non-monotonous total stress within the nanolayer, which leads to unconventional picosecond strain pulses.}, language = {en} } @article{vonReppertMatternPudelletal.2020, author = {von Reppert, Alexander and Mattern, Maximilian and Pudell, Jan-Etienne and Zeuschner, Steffen Peer and Dumesnil, Karine and Bargheer, Matias}, title = {Unconventional picosecond strain pulses resulting from the saturation of magnetic stress within a photoexcited rare earth layer}, series = {Structural Dynamics}, volume = {7}, journal = {Structural Dynamics}, number = {024303}, publisher = {AIP Publishing LLC}, address = {Melville, NY}, issn = {2329-7778}, doi = {10.1063/1.5145315}, pages = {13}, year = {2020}, abstract = {Optical excitation of spin-ordered rare earth metals triggers a complex response of the crystal lattice since expansive stresses from electron and phonon excitations compete with a contractive stress induced by spin disorder. Using ultrafast x-ray diffraction experiments, we study the layer specific strain response of a dysprosium film within a metallic heterostructure upon femtosecond laser-excitation. The elastic and diffusive transport of energy to an adjacent, non-excited detection layer clearly separates the contributions of strain pulses and thermal excitations in the time domain. We find that energy transfer processes to magnetic excitations significantly modify the observed conventional bipolar strain wave into a unipolar pulse. By modeling the spin system as a saturable energy reservoir that generates substantial contractive stress on ultrafast timescales, we can reproduce the observed strain response and estimate the time- and space dependent magnetic stress. The saturation of the magnetic stress contribution yields a non-monotonous total stress within the nanolayer, which leads to unconventional picosecond strain pulses.}, language = {en} } @phdthesis{Goswami2014, author = {Goswami, Bedartha}, title = {Uncertainties in climate data analysis}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-78312}, school = {Universit{\"a}t Potsdam}, year = {2014}, abstract = {Scientific inquiry requires that we formulate not only what we know, but also what we do not know and by how much. In climate data analysis, this involves an accurate specification of measured quantities and a consequent analysis that consciously propagates the measurement errors at each step. The dissertation presents a thorough analytical method to quantify errors of measurement inherent in paleoclimate data. An additional focus are the uncertainties in assessing the coupling between different factors that influence the global mean temperature (GMT). Paleoclimate studies critically rely on `proxy variables' that record climatic signals in natural archives. However, such proxy records inherently involve uncertainties in determining the age of the signal. We present a generic Bayesian approach to analytically determine the proxy record along with its associated uncertainty, resulting in a time-ordered sequence of correlated probability distributions rather than a precise time series. We further develop a recurrence based method to detect dynamical events from the proxy probability distributions. The methods are validated with synthetic examples and demonstrated with real-world proxy records. The proxy estimation step reveals the interrelations between proxy variability and uncertainty. The recurrence analysis of the East Asian Summer Monsoon during the last 9000 years confirms the well-known `dry' events at 8200 and 4400 BP, plus an additional significantly dry event at 6900 BP. We also analyze the network of dependencies surrounding GMT. We find an intricate, directed network with multiple links between the different factors at multiple time delays. We further uncover a significant feedback from the GMT to the El Ni{\~n}o Southern Oscillation at quasi-biennial timescales. The analysis highlights the need of a more nuanced formulation of influences between different climatic factors, as well as the limitations in trying to estimate such dependencies.}, language = {en} } @article{ChengKliemDing2018, author = {Cheng, Xin and Kliem, Bernhard and Ding, Mingde}, title = {Unambiguous evidence of filament splitting-induced partial eruptions}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {856}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.3847/1538-4357/aab08d}, pages = {15}, year = {2018}, abstract = {Coronal mass ejections are often considered to result from the full eruption of a magnetic flux rope (MFR). However, it is recognized that, in some events, the MFR may release only part of its flux, with the details of the implied splitting not completely established due to limitations in observations. Here, we investigate two partial eruption events including a confined and a successful one. Both partial eruptions are a consequence of the vertical splitting of a filament-hosting MFR involving internal reconnection. A loss of equilibrium in the rising part of the magnetic flux is suggested by the impulsive onset of both events and by the delayed onset of reconnection in the confined event. The remaining part of the flux might be line-tied to the photosphere in a bald patch (BP) separatrix surface, and we confirm the existence of extended BP sections for the successful eruption. The internal reconnection is signified by brightenings in the body of one filament and between the rising and remaining parts of both filaments. It evolves quickly into the standard current sheet reconnection in the wake of the eruption. As a result, regardless of being confined or successful, both eruptions produce hard X-ray sources and flare loops below the erupting but above the surviving flux, as well as a pair of flare ribbons enclosing the latter.}, language = {en} } @article{MetzlerCherstvyChechkinetal.2015, author = {Metzler, Ralf and Cherstvy, Andrey G. and Chechkin, Aleksei V. and Bodrova, Anna S.}, title = {Ultraslow scaled Brownian motion}, series = {New journal of physics : the open-access journal for physics}, volume = {17}, journal = {New journal of physics : the open-access journal for physics}, number = {063038}, publisher = {Dt. Physikalische Ges., IOP}, address = {Bad Honnef, London}, issn = {1367-2630}, doi = {10.1088/1367-2630/17/6/063038}, year = {2015}, abstract = {We define and study in detail utraslow scaled Brownian motion (USBM) characterized by a time dependent diffusion coefficient of the form . For unconfined motion the mean squared displacement (MSD) of USBM exhibits an ultraslow, logarithmic growth as function of time, in contrast to the conventional scaled Brownian motion. In a harmonic potential the MSD of USBM does not saturate but asymptotically decays inverse-proportionally to time, reflecting the highly non-stationary character of the process. We show that the process is weakly non-ergodic in the sense that the time averaged MSD does not converge to the regular MSD even at long times, and for unconfined motion combines a linear lag time dependence with a logarithmic term. The weakly non-ergodic behaviour is quantified in terms of the ergodicity breaking parameter. The USBM process is also shown to be ageing: observables of the system depend on the time gap between initiation of the test particle and start of the measurement of its motion. Our analytical results are shown to agree excellently with extensive computer simulations.}, language = {en} } @misc{MetzlerCherstvyChechkinetal.2015, author = {Metzler, Ralf and Cherstvy, Andrey G. and Chechkin, Aleksei V. and Bodrova, Anna S.}, title = {Ultraslow scaled Brownian motion}, series = {New journal of physics : the open-access journal for physics}, journal = {New journal of physics : the open-access journal for physics}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-78618}, year = {2015}, abstract = {We define and study in detail utraslow scaled Brownian motion (USBM) characterized by a time dependent diffusion coefficient of the form . For unconfined motion the mean squared displacement (MSD) of USBM exhibits an ultraslow, logarithmic growth as function of time, in contrast to the conventional scaled Brownian motion. In a harmonic potential the MSD of USBM does not saturate but asymptotically decays inverse-proportionally to time, reflecting the highly non-stationary character of the process. We show that the process is weakly non-ergodic in the sense that the time averaged MSD does not converge to the regular MSD even at long times, and for unconfined motion combines a linear lag time dependence with a logarithmic term. The weakly non-ergodic behaviour is quantified in terms of the ergodicity breaking parameter. The USBM process is also shown to be ageing: observables of the system depend on the time gap between initiation of the test particle and start of the measurement of its motion. Our analytical results are shown to agree excellently with extensive computer simulations.}, language = {en} } @phdthesis{Koc2018, author = {Ko{\c{c}}, Azize}, title = {Ultrafast x-ray studies on the non-equilibrium of the magnetic and phononic system in heavy rare-earths}, doi = {10.25932/publishup-42328}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-423282}, school = {Universit{\"a}t Potsdam}, pages = {ii, 117}, year = {2018}, abstract = {In this dissertation the lattice and the magnetic recovery dynamics of the two heavy rare-earth metals Dy and Gd after femtosecond photoexcitation are described. For the investigations, thin films of Dy and Gd were measured at low temperatures in the antiferromagnetic phase of Dy and close to room temperature in the ferromagnetic phase of Gd. Two different optical pump-x-ray probe techniques were employed: Ultrafast x-ray diffraction with hard x-rays (UXRD) yields the structural response of heavy rare-earth metals and resonant soft (elastic) x-ray diffraction (RSXD), which allows measuring directly changes in the helical antiferromagnetic order of Dy. The combination of both techniques enables to study the complex interaction between the magnetic and the phononic subsystems.}, language = {en} } @article{ClarkWadgaonkarFreyseetal.2022, author = {Clark, Oliver J. and Wadgaonkar, Indrajit and Freyse, Friedrich and Springholz, Gunther and Battiato, Marco and Sanchez-Barriga, Jaime}, title = {Ultrafast thermalization pathways of excited bulk and surface states in the ferroelectric rashba semiconductor GeTe}, series = {Advanced materials}, volume = {34}, journal = {Advanced materials}, number = {24}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0935-9648}, doi = {10.1002/adma.202200323}, pages = {13}, year = {2022}, abstract = {A large Rashba effect is essential for future applications in spintronics. Particularly attractive is understanding and controlling nonequilibrium properties of ferroelectric Rashba semiconductors. Here, time- and angle-resolved photoemission is utilized to access the ultrafast dynamics of bulk and surface transient Rashba states after femtosecond optical excitation of GeTe. A complex thermalization pathway is observed, wherein three different timescales can be clearly distinguished: intraband thermalization, interband equilibration, and electronic cooling. These dynamics exhibit an unconventional temperature dependence: while the cooling phase speeds up with increasing sample temperature, the opposite happens for interband thermalization. It is demonstrated how, due to the Rashba effect, an interdependence of these timescales on the relative strength of both electron-electron and electron-phonon interactions is responsible for the counterintuitive temperature dependence, with spin-selection constrained interband electron-electron scatterings found both to dominate dynamics away from the Fermi level, and to weaken with increasing temperature. These findings are supported by theoretical calculations within the Boltzmann approach explicitly showing the opposite behavior of all relevant electron-electron and electron-phonon scattering channels with temperature, thus confirming the microscopic mechanism of the experimental findings. The present results are important for future applications of ferroelectric Rashba semiconductors and their excitations in ultrafast spintronics.}, language = {en} } @phdthesis{Sander2018, author = {Sander, Mathias}, title = {Ultrafast tailored strain fields in nanostructures}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-417863}, school = {Universit{\"a}t Potsdam}, pages = {xvii, 119}, year = {2018}, abstract = {This publication based thesis, which consists of seven published articles, summarizes my contributions to the research field of laser excited ultrafast structural dynamics. The coherent and incoherent lattice dynamics on microscopic length scales are detected by ultrashort optical and X-ray pulses. The understanding of the complex physical processes is essential for future improvements of technological applications. For this purpose, tabletop soruces and large scale facilities, e.g. synchrotrons, are employed to study structural dynamics of longitudinal acoustic strain waves and heat transport. The investigated effects cover timescales from hundreds of femtoseconds up to several microseconds. The main part of this thesis is dedicated to the investigation of tailored phonon wave packets propagating in perovskite nanostructures. Tailoring is achieved either by laser excitation of nanostructured bilayer samples or by a temporal series of laser pulses. Due to the propagation of longitudinal acoustic phonons, the out-of-plane lattice spacing of a thin film insulator-metal bilayer sample is modulated on an ultrafast timescale. This leads to an ultrafast modulation of the X-ray diffraction efficiency which is employed as a phonon Bragg switch to shorten hard X-ray pulses emitted from a 3rd generation synchrotron. In addition, we have observed nonlinear mixing of high amplitude phonon wave packets which originates from an anharmonic interatomic potential. A chirped optical pulse sequence excites a narrow band phonon wave packet with specific momentum and energy. The second harmonic generation of these phonon wave packets is followed by ultrafast X-ray diffraction. Phonon upconversion takes place because the high amplitude phonon wave packet modulates the acoustic properties of the crystal which leads to self steepening and to the successive generation of higher harmonics of the phonon wave packet. Furthermore, we have demonstrated ultrafast strain in direction parallel to the sample surface. Two consecutive so-called transient grating excitations displaced in space and time are used to coherently control thermal gradients and surface acoustic modes. The amplitude of the coherent and incoherent surface excursion is disentangled by time resolved X-ray reflectivity measurements. We calibrate the absolute amplitude of thermal and acoustic surface excursion with measurements of longitudinal phonon propagation. In addition, we develop a diffraction model which allows for measuring the surface excursion on an absolute length scale with sub-{\"A}angstr{\"o}m precision. Finally, I demonstrate full coherent control of an excited surface deformation by amplifying and suppressing thermal and coherent excitations at the surface of a laser-excited Yttrium-manganite sample.}, language = {en} } @misc{Guehr2016, author = {G{\"u}hr, Markus}, title = {Ultrafast Soft X-ray Probing of Gas Phase Molecular Dynamics}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-97215}, year = {2016}, abstract = {The molecular ability to selectively and efficiently convert sunlight into other forms of energy like heat, bond change, or charge separation is truly remarkable. The decisive steps in these transformations often happen on a femtosecond timescale and require transitions among different electronic states that violate the Born-Oppenheimer approximation (BOA). Non-BOA transitions pose challenges to both theory and experiment. From a theoretical point of view, excited state dynamics and nonadiabatic transitions both are difficult problems (see Figure 1(a)). However, the theory on non-BOA dynamics has advanced significantly over the last two decades. Full dynamical simulations for molecules of the size of nucleobases have been possible for a couple of years and allow predictions of experimental observables like photoelectron energy or ion yield. The availability of these calculations for isolated molecules has spurred new experimental efforts to develop methods that are sufficiently different from all optical techniques. For determination of transient molecular structure, femtosecond X-ray diffraction and electron diffraction have been implemented on optically excited molecules.}, language = {en} } @phdthesis{Trabant2014, author = {Trabant, Christoph}, title = {Ultrafast photoinduced phase transitions in complex materials probed by time-resolved resonant soft x-ray diffraction}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-71377}, school = {Universit{\"a}t Potsdam}, year = {2014}, abstract = {In processing and data storage mainly ferromagnetic (FM) materials are being used. Approaching physical limits, new concepts have to be found for faster, smaller switches, for higher data densities and more energy efficiency. Some of the discussed new concepts involve the material classes of correlated oxides and materials with antiferromagnetic coupling. Their applicability depends critically on their switching behavior, i.e., how fast and how energy efficient material properties can be manipulated. This thesis presents investigations of ultrafast non-equilibrium phase transitions on such new materials. In transition metal oxides (TMOs) the coupling of different degrees of freedom and resulting low energy excitation spectrum often result in spectacular changes of macroscopic properties (colossal magneto resistance, superconductivity, metal-to-insulator transitions) often accompanied by nanoscale order of spins, charges, orbital occupation and by lattice distortions, which make these material attractive. Magnetite served as a prototype for functional TMOs showing a metal-to-insulator-transition (MIT) at T = 123 K. By probing the charge and orbital order as well as the structure after an optical excitation we found that the electronic order and the structural distortion, characteristics of the insulating phase in thermal equilibrium, are destroyed within the experimental resolution of 300 fs. The MIT itself occurs on a 1.5 ps timescale. It shows that MITs in functional materials are several thousand times faster than switching processes in semiconductors. Recently ferrimagnetic and antiferromagnetic (AFM) materials have become interesting. It was shown in ferrimagnetic GdFeCo, that the transfer of angular momentum between two opposed FM subsystems with different time constants leads to a switching of the magnetization after laser pulse excitation. In addition it was theoretically predicted that demagnetization dynamics in AFM should occur faster than in FM materials as no net angular momentum has to be transferred out of the spin system. We investigated two different AFM materials in order to learn more about their ultrafast dynamics. In Ho, a metallic AFM below T ≈ 130 K, we found that the AFM Ho can not only be faster but also ten times more energy efficiently destroyed as order in FM comparable metals. In EuTe, an AFM semiconductor below T ≈ 10 K, we compared the loss of magnetization and laser-induced structural distortion in one and the same experiment. Our experiment shows that they are effectively disentangled. An exception is an ultrafast release of lattice dynamics, which we assign to the release of magnetostriction. The results presented here were obtained with time-resolved resonant soft x-ray diffraction at the Femtoslicing source of the Helmholtz-Zentrum Berlin and at the free-electron laser in Stanford (LCLS). In addition the development and setup of a new UHV-diffractometer for these experiments will be reported.}, language = {en} } @article{PudellvonReppertSchicketal.2019, author = {Pudell, Jan-Etienne and von Reppert, Alexander and Schick, D. and Zamponi, F. and R{\"o}ssle, Matthias and Herzog, Marc and Zabel, Hartmut and Bargheer, Matias}, title = {Ultrafast negative thermal expansion driven by spin disorder}, series = {Physical review : B, Condensed matter and materials physics}, volume = {99}, journal = {Physical review : B, Condensed matter and materials physics}, number = {9}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.094304}, pages = {7}, year = {2019}, abstract = {We measure the transient strain profile in a nanoscale multilayer system composed of yttrium, holmium, and niobium after laser excitation using ultrafast x-ray diffraction. The strain propagation through each layer is determined by transient changes in the material-specific Bragg angles. We experimentally derive the exponentially decreasing stress profile driving the strain wave and show that it closely matches the optical penetration depth. Below the Neel temperature of Ho, the optical excitation triggers negative thermal expansion, which is induced by a quasi-instantaneous contractive stress and a second contractive stress contribution increasing on a 12-ps timescale. These two timescales were recently measured for the spin disordering in Ho [Rettig et al., Phys. Rev. Lett. 116, 257202 (2016)]. As a consequence, we observe an unconventional bipolar strain pulse with an inverted sign traveling through the heterostructure.}, language = {en} } @phdthesis{Willig2019, author = {Willig, Lisa}, title = {Ultrafast magneto-optical studies of remagnetisation dynamics in transition metals}, doi = {10.25932/publishup-44194}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-441942}, school = {Universit{\"a}t Potsdam}, pages = {XIV, 113, XVII}, year = {2019}, abstract = {Ultrafast magnetisation dynamics have been investigated intensely for two decades. The recovery process after demagnetisation, however, was rarely studied experimentally and discussed in detail. The focus of this work lies on the investigation of the magnetisation on long timescales after laser excitation. It combines two ultrafast time resolved methods to study the relaxation of the magnetic and lattice system after excitation with a high fluence ultrashort laser pulse. The magnetic system is investigated by time resolved measurements of the magneto-optical Kerr effect. The experimental setup has been implemented in the scope of this work. The lattice dynamics were obtained with ultrafast X-ray diffraction. The combination of both techniques leads to a better understanding of the mechanisms involved in magnetisation recovery from a non-equilibrium condition. Three different groups of samples are investigated in this work: Thin Nickel layers capped with nonmagnetic materials, a continuous sample of the ordered L10 phase of Iron Platinum and a sample consisting of Iron Platinum nanoparticles embedded in a carbon matrix. The study of the remagnetisation reveals a general trend for all of the samples: The remagnetisation process can be described by two time dependences. A first exponential recovery that slows down with an increasing amount of energy absorbed in the system until an approximately linear time dependence is observed. This is followed by a second exponential recovery. In case of low fluence excitation, the first recovery is faster than the second. With increasing fluence the first recovery is slowed down and can be described as a linear function. If the pump-induced temperature increase in the sample is sufficiently high, a phase transition to a paramagnetic state is observed. In the remagnetisation process, the transition into the ferromagnetic state is characterised by a distinct transition between the linear and exponential recovery. From the combination of the transient lattice temperature Tp(t) obtained from ultrafast X-ray measurements and magnetisation M(t) gained from magneto-optical measurements we construct the transient magnetisation versus temperature relations M(Tp). If the lattice temperature remains below the Curie temperature the remagnetisation curve M(Tp) is linear and stays below the M(T) curve in equilibrium in the continuous transition metal layers. When the sample is heated above phase transition, the remagnetisation converges towards the static temperature dependence. For the granular Iron Platinum sample the M(Tp) curves for different fluences coincide, i.e. the remagnetisation follows a similar path irrespective of the initial laser-induced temperature jump.}, language = {en} } @phdthesis{Schick2013, author = {Schick, Daniel}, title = {Ultrafast lattice dynamics in photoexcited nanostructures : femtosecond X-ray diffraction with optimized evaluation schemes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-68827}, school = {Universit{\"a}t Potsdam}, year = {2013}, abstract = {Within the course of this thesis, I have investigated the complex interplay between electron and lattice dynamics in nanostructures of perovskite oxides. Femtosecond hard X-ray pulses were utilized to probe the evolution of atomic rearrangement directly, which is driven by ultrafast optical excitation of electrons. The physics of complex materials with a large number of degrees of freedom can be interpreted once the exact fingerprint of ultrafast lattice dynamics in time-resolved X-ray diffraction experiments for a simple model system is well known. The motion of atoms in a crystal can be probed directly and in real-time by femtosecond pulses of hard X-ray radiation in a pump-probe scheme. In order to provide such ultrashort X-ray pulses, I have built up a laser-driven plasma X-ray source. The setup was extended by a stable goniometer, a two-dimensional X-ray detector and a cryogen-free cryostat. The data acquisition routines of the diffractometer for these ultrafast X-ray diffraction experiments were further improved in terms of signal-to-noise ratio and angular resolution. The implementation of a high-speed reciprocal-space mapping technique allowed for a two-dimensional structural analysis with femtosecond temporal resolution. I have studied the ultrafast lattice dynamics, namely the excitation and propagation of coherent phonons, in photoexcited thin films and superlattice structures of the metallic perovskite SrRuO3. Due to the quasi-instantaneous coupling of the lattice to the optically excited electrons in this material a spatially and temporally well-defined thermal stress profile is generated in SrRuO3. This enables understanding the effect of the resulting coherent lattice dynamics in time-resolved X-ray diffraction data in great detail, e.g. the appearance of a transient Bragg peak splitting in both thin films and superlattice structures of SrRuO3. In addition, a comprehensive simulation toolbox to calculate the ultrafast lattice dynamics and the resulting X-ray diffraction response in photoexcited one-dimensional crystalline structures was developed in this thesis work. With the powerful experimental and theoretical framework at hand, I have studied the excitation and propagation of coherent phonons in more complex material systems. In particular, I have revealed strongly localized charge carriers after above-bandgap femtosecond photoexcitation of the prototypical multiferroic BiFeO3, which are the origin of a quasi-instantaneous and spatially inhomogeneous stress that drives coherent phonons in a thin film of the multiferroic. In a structurally imperfect thin film of the ferroelectric Pb(Zr0.2Ti0.8)O3, the ultrafast reciprocal-space mapping technique was applied to follow a purely strain-induced change of mosaicity on a picosecond time scale. These results point to a strong coupling of in- and out-of-plane atomic motion exclusively mediated by structural defects.}, language = {en} } @article{vonReppertWilligPudelletal.2018, author = {von Reppert, Alexander and Willig, Lisa and Pudell, Jan-Etienne and Roessle, M. and Leitenberger, Wolfram and Herzog, Marc and Ganss, F. and Hellwig, O. and Bargheer, Matias}, title = {Ultrafast laser generated strain in granular and continuous FePt thin films}, series = {Applied physics letters}, volume = {113}, journal = {Applied physics letters}, number = {12}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.5050234}, pages = {5}, year = {2018}, abstract = {We employ ultrafast X-ray diffraction to compare the lattice dynamics of laser-excited continuous and granular FePt films on MgO (100) substrates. Contrary to recent results on free-standing granular films, we observe in both cases a pronounced and long-lasting out-of-plane expansion. We attribute this discrepancy to the in-plane expansion, which is suppressed by symmetry in continuous films. Granular films on substrates are less constrained and already show a reduced out-of-plane contraction. Via the Poisson effect, out-of-plane contractions drive in-plane expansion and vice versa. Consistently, the granular film exhibits a short-lived out-of-plane contraction driven by ultrafast demagnetization which is followed by a reduced and delayed expansion. From the acoustic reflections of the observed strain waves at the film-substrate interface, we extract a 13\% reduction of the elastic constants in thin 10 nm FePt films compared to bulk-like samples. (C) 2018 Author(s).}, language = {en} } @phdthesis{Schroeder2016, author = {Schr{\"o}der, Henning}, title = {Ultrafast electron dynamics in Fe(CO)5 and Cr(CO)6}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-94589}, school = {Universit{\"a}t Potsdam}, pages = {v, 87}, year = {2016}, abstract = {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.}, language = {en} } @misc{OPUS4-5024, title = {T{\"a}tigkeitsbericht 1994-2000}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-48483}, year = {2004}, abstract = {Das Interdisziplin{\"a}re Zentrum f{\"u}r Nichtlineare Dynamik an der Universit{\"a}t Potsdam verbindet theoretisch-methodische Untersuchungen in Mathematik und theoretischer Physik mit einer Vielzahl anderer Wissenschaften und zielt auf eine fruchtbare Wechselwirkung zwischen Theorie und Experiment. Unter Einbezug von Instituten und Großforschungseinrichtungen, die insbesondere im Potsdamer Raum angesiedelt sind, soll sich ein {\"u}berregional bedeutender Schwerpunkt entwickeln, wie er an keiner anderen deutschen Universit{\"a}t in gleicher Weise interdisziplin{\"a}r angelegt ist.}, language = {de} } @misc{FraschettiPohl2017, author = {Fraschetti, Federico and Pohl, Martin}, title = {Two-zone model for the broadband crab nebula spectrum}, series = {The European physical journal : Web of Conferences : proceedings}, volume = {136}, journal = {The European physical journal : Web of Conferences : proceedings}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {2100-014X}, doi = {10.1051/epjconf/201713602009}, pages = {5}, year = {2017}, abstract = {We develop a simple two-zone interpretation of the broadband baseline Crab nebula spectrum between 10(-5) eV and similar to 100 TeV by using two distinct log-parabola energetic electrons distributions. We determine analytically the very-high energy photon spectrum as originated by inverse-Compton scattering of the far-infrared soft ambient photons within the nebula off a first population of electrons energized at the nebula termination shock. The broad and flat 200 GeV peak jointly observed by Fermi/LAT and MAGIC is naturally reproduced. The synchrotron radiation from a second energetic electron population explains the spectrum from the radio range up to similar to 10 keV. We infer from observations the energy dependence of the microscopic probability of remaining in proximity of the shock of the accelerating electrons.}, language = {en} } @article{BetkeLokstein2019, author = {Betke, Alexander and Lokstein, Heiko}, title = {Two-photon excitation spectroscopy of photosynthetic light-harvesting complexes and pigments}, series = {Faraday discussions}, volume = {216}, journal = {Faraday discussions}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1359-6640}, doi = {10.1039/c8fd00198g}, pages = {494 -- 506}, year = {2019}, abstract = {In addition to (bacterio)chlorophylls, (B)Chls, light-harvesting complexes (LHCs) bind carotenoids, and/or their oxygen derivatives, xanthophylls. Xanthophylls/carotenoids have pivotal functions in LHCs: in stabilization of the structure, as accessory light-harvesting pigments and, probably most importantly, in photoprotection. Xanthophylls are assumed to be involved in the not yet fully understood mechanism of energy-dependent (qE) non-photochemical quenching of Chl fluorescence (NPQ) in higher plants and algae. The so called "xanthophyll cycle" appears to be crucial in this regard. The molecular mechanism(s) of xanthophyll involvement in qE/NPQ have not been established, yet. Moreover, excitation energy transfer (EET) processes involving carotenoids are also difficult to study, due to the fact that transitions between the ground state (S-0, 1(1)A(g)(-)) and the lowest excited singlet state (S-1, 2(1)A(g)(-)) of carotenoids are optically one-photon forbidden ("dark"). Two-photon excitation spectroscopic techniques have been used for more than two decades to study one-photon forbidden states of carotenoids. In the current study, two-photon excitation profiles of LHCII samples containing different xanthophyll complements were measured in the presumed 1(1)A(g)(-) -> 2(1)A(g)(-) (S-0 -> S-1) transition spectral region of the xanthophylls, as well as for isolated chlorophylls a and b in solution. The results indicate that direct two-photon excitation of Chls in this spectral region is dominant over that by xanthophylls. Implications of the results for proposed mechanism(s) of qE/NPQ will be discussed.}, language = {en} } @article{TyulkinaGoldobinKlimenkoetal.2019, author = {Tyulkina, Irina V. and Goldobin, Denis S. and Klimenko, Lyudmila S. and Pikovskij, Arkadij}, title = {Two-Bunch Solutions for the Dynamics of Ott-Antonsen Phase Ensembles}, series = {Radiophysics and Quantum Electronics}, volume = {61}, journal = {Radiophysics and Quantum Electronics}, number = {8-9}, publisher = {Springer}, address = {New York}, issn = {0033-8443}, doi = {10.1007/s11141-019-09924-7}, pages = {640 -- 649}, year = {2019}, abstract = {We have developed a method for deriving systems of closed equations for the dynamics of order parameters in the ensembles of phase oscillators. The Ott-Antonsen equation for the complex order parameter is a particular case of such equations. The simplest nontrivial extension of the Ott-Antonsen equation corresponds to two-bunch states of the ensemble. Based on the equations obtained, we study the dynamics of multi-bunch chimera states in coupled Kuramoto-Sakaguchi ensembles. We show an increase in the dimensionality of the system dynamics for two-bunch chimeras in the case of identical phase elements and a transition to one-bunch "Abrams chimeras" for imperfect identity (in the latter case, the one-bunch chimeras become attractive).}, language = {en} } @article{KumarRosenblum2021, author = {Kumar, Mohit and Rosenblum, Michael}, title = {Two mechanisms of remote synchronization in a chain of Stuart-Landau oscillators}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {104}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {2470-0045}, doi = {10.1103/PhysRevE.104.054202}, pages = {6}, year = {2021}, abstract = {Remote synchronization implies that oscillators interacting not directly but via an additional unit (hub) adjust their frequencies and exhibit frequency locking while the hub remains asynchronous. In this paper, we analyze the mechanisms of remote synchrony in a small network of three coupled Stuart-Landau oscillators using recent results on higher-order phase reduction. We analytically demonstrate the role of two factors promoting remote synchrony. These factors are the nonisochronicity of oscillators and the coupling terms appearing in the secondorder phase approximation. We show a good correspondence between our theory and numerical results for small and moderate coupling strengths.}, language = {en} } @article{BolotovBolotovSmirnovetal.2019, author = {Bolotov, Dmitry and Bolotov, Maxim I. and Smirnov, Lev A. and Osipov, Grigory V. and Pikovskij, Arkadij}, title = {Twisted States in a System of Nonlinearly Coupled Phase Oscillators}, series = {Regular and chaotic dynamics : international scientific journal}, volume = {24}, journal = {Regular and chaotic dynamics : international scientific journal}, number = {6}, publisher = {Pleiades publishing inc}, address = {Moscow}, issn = {1560-3547}, doi = {10.1134/S1560354719060091}, pages = {717 -- 724}, year = {2019}, abstract = {We study the dynamics of the ring of identical phase oscillators with nonlinear nonlocal coupling. Using the Ott - Antonsen approach, the problem is formulated as a system of partial derivative equations for the local complex order parameter. In this framework, we investigate the existence and stability of twisted states. Both fully coherent and partially coherent stable twisted states were found (the latter ones for the first time for identical oscillators). We show that twisted states can be stable starting from a certain critical value of the medium length, or on a length segment. The analytical results are confirmed with direct numerical simulations in finite ensembles.}, language = {en} } @article{ManassenJbaraAverbukhetal.2022, author = {Manassen, Yishay and Jbara, Moamen and Averbukh, Michael and Hazan, Zion and Henkel, Carsten and Horovitz, Baruch}, title = {Tunnel current noise spectra of spins in individual dimers of molecular radicals}, series = {Physical review : B, Condensed matter and materials physics}, volume = {105}, journal = {Physical review : B, Condensed matter and materials physics}, number = {23}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9950}, doi = {10.1103/PhysRevB.105.235438}, pages = {9}, year = {2022}, abstract = {We report the detection of electron spin resonance (ESR) in individual dimers of the stable free radical 2,2,6,6tetramethyl-piperidine-1-oxyl (TEMPO). ESR is measured by the current fluctuations in a scanning tunneling microscope (ESR-STM method). The multipeak power spectra, distinct from macroscopic data, are assigned to dimers having exchange and Dzyaloshinskii-Moriya interactions in the presence of spin-orbit coupling. These interactions are generated in our model by interfering electronic tunneling pathways from tip to sample via the dimer???s two molecules. This is the first demonstration that tunneling via two spins is a valid mechanism of the ESR-STM method.}, language = {en} } @article{RamanVenkatesanSmykallaPlossetal.2022, author = {Raman Venkatesan, Thulasinath and Smykalla, David and Ploss, Bernd and W{\"u}bbenhorst, Michael and Gerhard, Reimund}, title = {Tuning the relaxor-ferroelectric properties of Poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) Terpolymer films by means of thermally induced micro- and nanostructures}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {55}, journal = {Macromolecules : a publication of the American Chemical Society}, number = {13}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/acs.macromol.2c00302}, pages = {5621 -- 5635}, year = {2022}, abstract = {The effects of thermal processing on the micro- and nanostructural features and thus also on the relaxor-ferroelectric properties of a P(VDF-TrFE-CFE) terpolymer were investigated in detail by means of dielectric experiments, such as dielectric relaxation spectroscopy (DRS), dielectric hysteresis loops, and thermally stimulated depolarization currents (TSDCs). The results were correlated with those obtained from differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and Fourier-transform infrared spectroscopy (FTIR). The results from DRS and DSC show that annealing reduces the Curie transition temperature of the terpolymer, whereas the results from WAXD scans and FTIR spectra help to understand the shift in the Curie transition temperatures as a result of reducing the ferroelectric phase fraction, which by default exists even in terpolymers with relatively high CFE contents. In addition, the TSDC traces reveal that annealing has a similar effect on the midtemperature transition by altering the fraction of constrained amorphous phase at the interphase between the crystalline and the amorphous regions. Changes in the transition temperatures are in turn related to the behavior of the hysteresis curves on differently heat-treated samples. During heating, evolution of the hysteresis curves from ferroelectric to relaxor-ferroelectric, first exhibiting single hysteresis loops and then double hysteresis loops near the Curie transition of the sample, is observed. When comparing the dielectric-hysteresis loops obtained at various temperatures, we find that annealed terpolymer films show higher electric-displacement values and lower coercive fields than the nonannealed sample, irrespective of the measurement temperature, and also exhibit ideal relaxor- ferroelectric behavior at ambient temperatures, which makes them excellent candidates for applications at or near room temperature. By tailoring the annealing conditions, it has been shown that the application temperature could be increased by fine tuning the induced micro- and nanostructures.}, language = {en} } @article{SchubertFrischAllardetal.2017, author = {Schubert, Marcel and Frisch, Johannes and Allard, Sybille and Preis, Eduard and Scherf, Ullrich and Koch, Norbert and Neher, Dieter}, title = {Tuning side chain and main chain order in a prototypical donor-acceptor copolymer}, series = {Elementary Processes in Organic Photovoltaics}, volume = {272}, journal = {Elementary Processes in Organic Photovoltaics}, publisher = {Springer}, address = {Berlin}, isbn = {978-3-319-28338-8}, issn = {0065-3195}, doi = {10.1007/978-3-319-28338-8_10}, pages = {243 -- 265}, year = {2017}, abstract = {The recent development of donor-acceptor copolymers has led to an enormous improvement in the performance of organic solar cells and organic field-effect transistors. Here we describe the synthesis, detailed characterisation, and application of a series of structurally modified copolymers to investigate fundamental structure-property relationships in this class of conjugated polymers. The interplay between chemical structure and optoelectronic properties is investigated. These are further correlated to the charge transport and solar cell performance, which allows us to link their chemical structure to the observed physical properties.}, language = {en} } @article{PetreskaPejovSandevetal.2022, author = {Petreska, Irina and Pejov, Ljupco and Sandev, Trifce and Kocarev, Ljupčo and Metzler, Ralf}, title = {Tuning of the dielectric relaxation and complex susceptibility in a system of polar molecules: a generalised model based on rotational diffusion with resetting}, series = {Fractal and fractional}, volume = {6}, journal = {Fractal and fractional}, number = {2}, publisher = {MDPI AG, Fractal Fract Editorial Office}, address = {Basel}, issn = {2504-3110}, doi = {10.3390/fractalfract6020088}, pages = {23}, year = {2022}, abstract = {The application of the fractional calculus in the mathematical modelling of relaxation processes in complex heterogeneous media has attracted a considerable amount of interest lately. The reason for this is the successful implementation of fractional stochastic and kinetic equations in the studies of non-Debye relaxation. In this work, we consider the rotational diffusion equation with a generalised memory kernel in the context of dielectric relaxation processes in a medium composed of polar molecules. We give an overview of existing models on non-exponential relaxation and introduce an exponential resetting dynamic in the corresponding process. The autocorrelation function and complex susceptibility are analysed in detail. We show that stochastic resetting leads to a saturation of the autocorrelation function to a constant value, in contrast to the case without resetting, for which it decays to zero. The behaviour of the autocorrelation function, as well as the complex susceptibility in the presence of resetting, confirms that the dielectric relaxation dynamics can be tuned by an appropriate choice of the resetting rate. The presented results are general and flexible, and they will be of interest for the theoretical description of non-trivial relaxation dynamics in heterogeneous systems composed of polar molecules.}, language = {en} } @phdthesis{Canil2021, author = {Canil, Laura}, title = {Tuning Interfacial Properties in Perovskite Solar Cells through Defined Molecular Assemblies}, doi = {10.25932/publishup-54633}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-546333}, school = {Universit{\"a}t Potsdam}, pages = {vii, 157}, year = {2021}, abstract = {In the frame of a world fighting a dramatic global warming caused by human-related activities, research towards the development of renewable energies plays a crucial role. Solar energy is one of the most important clean energy sources and its role in the satisfaction of the global energy demand is set to increase. In this context, a particular class of materials captured the attention of the scientific community for its attractive properties: halide perovskites. Devices with perovskite as light-absorber saw an impressive development within the last decade, reaching nowadays efficiencies comparable to mature photovoltaic technologies like silicon solar cells. Yet, there are still several roadblocks to overcome before a wide-spread commercialization of this kind of devices is enabled. One of the critical points lies at the interfaces: perovskite solar cells (PSCs) are made of several layers with different chemical and physical features. In order for the device to function properly, these properties have to be well-matched. This dissertation deals with some of the challenges related to interfaces in PSCs, with a focus on the interface between the perovskite material itself and the subsequent charge transport layer. In particular, molecular assemblies with specific properties are deposited on the perovskite surface to functionalize it. The functionalization results in energy level alignment adjustment, interfacial losses reduction, and stability improvement. First, a strategy to tune the perovskite's energy levels is introduced: self-assembled monolayers of dipolar molecules are used to functionalize the surface, obtaining simultaneously a shift in the vacuum level position and a saturation of the dangling bonds at the surface. A shift in the vacuum level corresponds to an equal change in work function, ionization energy, and electron affinity. The direction of the shift depends on the direction of the collective interfacial dipole. The magnitude of the shift can be tailored by controlling the deposition parameters, such as the concentration of the solution used for the deposition. The shift for different molecules is characterized by several non-invasive techniques, including in particular Kelvin probe. Overall, it is shown that it is possible to shift the perovskite energy levels in both directions by several hundreds of meV. Moreover, interesting insights on the molecules deposition dynamics are revealed. Secondly, the application of this strategy in perovskite solar cells is explored. Devices with different perovskite compositions ("triple cation perovskite" and MAPbBr3) are prepared. The two resulting model systems present different energetic offsets at the perovskite/hole-transport layer interface. Upon tailored perovskite surface functionalization, the devices show a stabilized open circuit voltage (Voc) enhancement of approximately 60 meV on average for devices with MAPbBr3, while the impact is limited on triple-cation solar cells. This suggests that the proposed energy level tuning method is valid, but its effectiveness depends on factors such as the significance of the energetic offset compared to the other losses in the devices. Finally, the above presented method is further developed by incorporating the ability to interact with the perovskite surface directly into a novel hole-transport material (HTM), named PFI. The HTM can anchor to the perovskite halide ions via halogen bonding (XB). Its behaviour is compared to that of another HTM (PF) with same chemical structure and properties, except for the ability of forming XB. The interaction of perovskite with PFI and PF is characterized through UV-Vis, atomic force microscopy and Kelvin probe measurements combined with simulations. Compared to PF, PFI exhibits enhanced resilience against solvent exposure and improved energy level alignment with the perovskite layer. As a consequence, devices comprising PFI show enhanced Voc and operational stability during maximum-power-point tracking, in addition to hysteresis reduction. XB promotes the formation of a high-quality interface by anchoring to the halide ions and forming a stable and ordered interfacial layer, showing to be a particularly interesting candidate for the development of tailored charge transport materials in PSCs. Overall, the results exposed in this dissertation introduce and discuss a versatile tool to functionalize the perovskite surface and tune its energy levels. The application of this method in devices is explored and insights on its challenges and advantages are given. Within this frame, the results shed light on XB as ideal interaction for enhancing stability and efficiency in perovskite-based devices.}, language = {en} } @article{DebMolhoBarbara2021, author = {Deb, Marwan and Molho, Pierre and Barbara, Bernard}, title = {Tunable exchange-bias-like effect in bi-substituted Gadolinium iron garnet film}, series = {Physical review applied}, volume = {15}, journal = {Physical review applied}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.15.054064}, pages = {7}, year = {2021}, abstract = {Using magneto-optical Faraday and Kerr measurements, we investigate the magnetic and magnetooptical properties of a thick Bi-substituted gadolinium iron garnet film over a broad range of wavelengths (250-850 nm) and temperatures (150-300 K), including the magnetization compensation point, TM. We observe an exchange-bias-like effect in the vicinity of TM. By slightly changing the sample temperature, we can precisely tune the bias field, which reaches a magnitude 6 times higher than the coercive field. We explain this phenomenon by considering the short-range superexchange interaction and a change in the magnetic behavior when moving from the surface to the bulk of the film. This finding may lead to the development of single-film magneto-optical devices based on the exchange-bias effect.}, language = {en} } @misc{Omel'chenko2019, author = {Omel'chenko, Oleh}, title = {Travelling chimera states in systems of phase oscillators with asymmetric nonlocal coupling}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {2}, issn = {1866-8372}, doi = {10.25932/publishup-51814}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-518141}, pages = {611 -- 642}, year = {2019}, abstract = {We study travelling chimera states in a ring of nonlocally coupled heterogeneous (with Lorentzian distribution of natural frequencies) phase oscillators. These states are coherence-incoherence patterns moving in the lateral direction because of the broken reflection symmetry of the coupling topology. To explain the results of direct numerical simulations we consider the continuum limit of the system. In this case travelling chimera states correspond to smooth travelling wave solutions of some integro-differential equation, called the Ott-Antonsen equation, which describes the long time coarse-grained dynamics of the oscillators. Using the Lyapunov-Schmidt reduction technique we suggest a numerical approach for the continuation of these travelling waves. Moreover, we perform their linear stability analysis and show that travelling chimera states can lose their stability via fold and Hopf bifurcations. Some of the Hopf bifurcations turn out to be supercritical resulting in the observation of modulated travelling chimera states.}, language = {en} } @article{GrebenkovMetzlerOshaninetal.2019, author = {Grebenkov, Denis S. and Metzler, Ralf and Oshanin, Gleb and Dagdug, Leonardo and Berezhkovskii, Alexander M. and Skvortsov, Alexei T.}, title = {Trapping of diffusing particles by periodic absorbing rings on a cylindrical tube}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {150}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {20}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.5098390}, pages = {2}, year = {2019}, language = {en} } @phdthesis{Lazar2005, author = {Lazar, Paul}, title = {Transport mechanisms and wetting dynamics in molecularly thin films of long-chain alkanes at solid/vapour interface : relation to the solid-liquid phase transition}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-5275}, school = {Universit{\"a}t Potsdam}, year = {2005}, abstract = {Wetting and phase transitions play a very important role our daily life. Molecularly thin films of long-chain alkanes at solid/vapour interfaces (e.g. C30H62 on silicon wafers) are very good model systems for studying the relation between wetting behaviour and (bulk) phase transitions. Immediately above the bulk melting temperature the alkanes wet partially the surface (drops). In this temperature range the substrate surface is covered with a molecularly thin ordered, solid-like alkane film ("surface freezing"). Thus, the alkane melt wets its own solid only partially which is a quite rare phenomenon in nature. The thesis treats about how the alkane melt wets its own solid surface above and below the bulk melting temperature and about the corresponding melting and solidification processes. Liquid alkane drops can be undercooled to few degrees below the bulk melting temperature without immediate solidification. This undercooling behaviour is quite frequent and theoretical quite well understood. In some cases, slightly undercooled drops start to build two-dimensional solid terraces without bulk solidification. The terraces grow radially from the liquid drops on the substrate surface. They consist of few molecular layers with the thickness multiple of all-trans length of the molecule. By analyzing the terrace growth process one can find that, both below and above the melting point, the entire substrate surface is covered with a thin film of mobile alkane molecules. The presence of this film explains how the solid terrace growth is feeded: the alkane molecules flow through it from the undercooled drops to the periphery of the terrace. The study shows for the first time the coexistence of a molecularly thin film ("precursor") with partially wetting bulk phase. The formation and growth of the terraces is observed only in a small temperature interval in which the 2D nucleation of terraces is more likely than the bulk solidification. The nucleation mechanisms for 2D solidification are also analyzed in this work. More surprising is the terrace behaviour above bulk the melting temperature. The terraces can be slightly overheated before they melt. The melting does not occur all over the surface as a single event; instead small drops form at the terrace edge. Subsequently these drops move on the surface "eating" the solid terraces on their way. By this they grow in size leaving behind paths from were the material was collected. Both overheating and droplet movement can be explained by the fact that the alkane melt wets only partially its own solid. For the first time, these results explicitly confirm the supposed connection between the absence of overheating in solid and "surface melting": the solids usually start to melt without an energetic barrier from the surface at temperatures below the bulk melting point. Accordingly, the surface freezing of alkanes give rise of an energetic barrier which leads to overheating.}, subject = {Benetzung}, language = {en} }