TY - JOUR A1 - Meyer, Dominique M.-A. A1 - Petrov, Mykola A1 - Pohl, Martin T1 - Wind nebulae and supernova remnants of very massive stars JF - Monthly notices of the Royal Astronomical Society N2 - 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. KW - shock waves KW - methods: numerical KW - circumstellar matter KW - stars: massive Y1 - 2020 U6 - https://doi.org/10.1093/mnras/staa554 SN - 0035-8711 SN - 1365-2966 VL - 493 IS - 3 SP - 3548 EP - 3564 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Crovetto, Andrea A1 - Hempel, Hannes A1 - Rusu, Marin A1 - Choubrac, Leo A1 - Kojda, Sandrino Danny A1 - Habicht, Klaus A1 - Unold, Thomas T1 - Water adsorption enhances electrical conductivity in transparent p-type CuI JF - ACS applied materials & interfaces N2 - 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. KW - transparent conductors KW - CuI KW - copper iodide KW - conductivity KW - humidity KW - p-type KW - work function Y1 - 2020 U6 - https://doi.org/10.1021/acsami.0c11040 SN - 1944-8244 SN - 1944-8252 VL - 12 IS - 43 SP - 48741 EP - 48747 PB - American Chemical Society CY - Washington, DC ER - TY - JOUR A1 - Abdalla, Hassan E. A1 - Adam, Remi A1 - Aharonian, Felix A. A1 - Benkhali, Faical Ait A1 - Angüner, Ekrem Oǧuzhan A1 - Arakawa, Masanori A1 - Arcaro, C A1 - Armand, Catherine A1 - Armstrong, T. A1 - Egberts, Kathrin T1 - Very high energy γ-ray emission from two blazars of unknown redshift and upper limits on their distance JF - Monthly Notices of the Royal Astronomical Society N2 - 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. KW - BL Lacertae objects: individual KW - galaxies: high-redshift KW - gamma-rays: general KW - Resolved and unresolved sources as a function of wavelength Y1 - 2020 VL - 494 IS - 4 PB - Wiley-Blackwell CY - Oxford ER - TY - GEN A1 - Abdalla, Hassan E. A1 - Adam, Remi A1 - Aharonian, Felix A. A1 - Benkhali, Faical Ait A1 - Angüner, Ekrem Oǧuzhan A1 - Arakawa, Masanori A1 - Arcaro, C A1 - Armand, Catherine A1 - Armstrong, T. A1 - Egberts, Kathrin T1 - Very high energy γ-ray emission from two blazars of unknown redshift and upper limits on their distance T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1202 KW - BL Lacertae objects: individual KW - galaxies: high-redshift KW - gamma-rays: general KW - Resolved and unresolved sources as a function of wavelength Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-526000 SN - 1866-8372 IS - 4 ER - TY - JOUR A1 - Kontro, Inkeri A1 - Buschhüter, David T1 - Validity of Colorado Learning Attitudes about Science Survey for a high-achieving, Finnish population JF - Physical review. Physics education research N2 - 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. Y1 - 2020 U6 - https://doi.org/10.1103/PhysRevPhysEducRes.16.020104 SN - 2469-9896 VL - 16 IS - 2 PB - American Physical Society CY - College Park, MD ER - TY - JOUR A1 - Laquai, Rene A1 - Müller, Bernd R. A1 - Schneider, Judith Ann A1 - Kupsch, Andreas A1 - Bruno, Giovanni T1 - Using SXRR to probe the nature of discontinuities in SLM additive manufactured inconel 718 specimens JF - Metallurgical and Materials Transactions A N2 - 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. Y1 - 2020 U6 - https://doi.org/10.1007/s11661-020-05847-5 SN - 1073-5623 SN - 1543-1940 VL - 51 IS - 8 SP - 4146 EP - 4157 PB - Springer CY - New York ER - TY - THES A1 - Müller, Jirka T1 - Untersuchungen zum flow-Erleben bei Experimenten als physikalische Lerngelegenheit N2 - 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 Glück darstellen. Insbesondere wegen dem oft zitierten Fachkräftemangel in naturwissenschaftlichen und technischen Berufen ist eine Motivationssteigerung in naturwissenschaftlichen Unterrichtsfächern wichtig. Denn trotz Leistungssteigerungen in internationalen Vergleichstests möchten in Deutschland deutlich weniger Schüler*innen einen solchen Beruf ergreifen als in anderen Industriestaaten. Daher gilt es, möglichst früh Schüler*innen für naturwissenschaftlich-technische Fächer 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 Schüler*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 durchgeführte, smartphonebasierte Experimente flow-Erleben erzeugen. Allerdings verursachen die smartphonebasierten Experimente kaum Stressgefühle. Die in dieser Arbeit herausgefundenen Ergebnisse liefern einen ersten Ansatz, der durch Folgestudien erweitert werden sollte. N2 - The present work examines to what extent physical experiments induce a flow-experience in students. Experiencing flow is seen as a source of motivation and should represent the path to joy and happiness. In particular, because of the often-cited shortage of employees in the natural sciences and technical professions, increasing motivation in natural sciences subjects is important. Because despite performance increases in international comparative tests, significantly fewer students in Germany want to take up such a profession than in other industrialized countries. It is therefore important to get students enthusiastic about scientific and technical subjects as early as possible and, in particular, to create a flow experience in the downright hated physics class. In the context of this work, the flow-experience of students is examined as a learning environment in classic laboratory experiments and FELS (inquiry-based learning with the smartphone, based on the German term: Forschend-Entdeckendes Lernen mit dem Smartphone). FELS is a learning environment adapted to the students' living environment, in which they use smartphones to experimentally examine their own living environment. It turns out that both classic laboratory experiments and smartphone-based experiments create flow-experiences. However, the smartphone-based experiments hardly cause any feelings of stress. The results found in this work provide a first approach, which should be expanded through follow-up studies. T2 - Examining the flow-experience in experiments as a physical learning opportunity KW - Flow KW - Smartphone KW - Experimente KW - Physikdidaktik KW - FELS KW - Lernumgebung KW - blended learning KW - Forschend Entdeckendes Lernen KW - inquiry based learning KW - physics education KW - learning environment KW - experiment Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-482879 ER - TY - JOUR A1 - Sposini, Vittoria A1 - Grebenkov, Denis S. A1 - Metzler, Ralf A1 - Oshanin, Gleb A1 - Seno, Flavio T1 - Universal spectral features of different classes of random-diffusivity processes JF - New Journal of Physics N2 - 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. KW - diffusion KW - power spectrum KW - random diffusivity KW - single trajectories Y1 - 2020 U6 - https://doi.org/10.1088/1367-2630/ab9200 SN - 1367-2630 VL - 22 IS - 6 PB - Dt. Physikalische Ges. CY - Bad Honnef ER - TY - GEN A1 - Sposini, Vittoria A1 - Grebenkov, Denis S. A1 - Metzler, Ralf A1 - Oshanin, Gleb A1 - Seno, Flavio T1 - Universal spectral features of different classes of random-diffusivity processes T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 999 KW - diffusion KW - power spectrum KW - random diffusivity KW - single trajectories Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-476960 SN - 1866-8372 IS - 999 ER - TY - JOUR A1 - Wang, Wei A1 - Seno, Flavio A1 - Sokolov, Igor M. A1 - Chechkin, Aleksei V. A1 - Metzler, Ralf T1 - Unexpected crossovers in correlated random-diffusivity processes JF - New Journal of Physics N2 - 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. KW - diffusion KW - anomalous diffusion KW - non-Gaussianity KW - fractional Brownian motion Y1 - 2020 U6 - https://doi.org/10.1088/1367-2630/aba390 SN - 1367-2630 VL - 22 PB - Dt. Physikalische Ges. CY - Bad Honnef ER - TY - GEN A1 - Wang, Wei A1 - Seno, Flavio A1 - Sokolov, Igor M. A1 - Chechkin, Aleksei V. A1 - Metzler, Ralf T1 - Unexpected crossovers in correlated random-diffusivity processes N2 - 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1006 KW - diffusion KW - anomalous diffusion KW - non-Gaussianity KW - fractional Brownian motion Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-480049 SN - 1866-8372 IS - 1006 ER - TY - JOUR A1 - Wang, Jingwen A1 - Rychkov, Dmitry A1 - Nguyen, Quyet Doan A1 - Gerhard, Reimund T1 - Unexpected bipolar space-charge polarization across transcrystalline interfaces in polypropylene electret films JF - Journal of applied physics N2 - 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. Y1 - 2020 U6 - https://doi.org/10.1063/5.0022071 SN - 0021-8979 SN - 1089-7550 VL - 128 IS - 13 PB - American Institute of Physics, AIP CY - Melville, NY ER - TY - JOUR A1 - Li, Hua A1 - Xu, Yong A1 - Li, Yongge A1 - Metzler, Ralf T1 - Transition path dynamics across rough inverted parabolic potential barrier JF - The European physical journal : Plus N2 - Transition path dynamics have been widely studied in chemical, physical, and technological systems. Mostly, the transition path dynamics is obtained for smooth barrier potentials, for instance, generic inverse-parabolic shapes. We here present analytical results for the mean transition path time, the distribution of transition path times, the mean transition path velocity, and the mean transition path shape in a rough inverted parabolic potential function under the driving of Gaussian white noise. These are validated against extensive simulations using the forward flux sampling scheme in parallel computations. We observe how precisely the potential roughness, the barrier height, and the noise intensity contribute to the particle transition in the rough inverted barrier potential. Y1 - 2020 U6 - https://doi.org/10.1140/epjp/s13360-020-00752-7 SN - 2190-5444 VL - 135 IS - 9 PB - Springer CY - Berlin ; Heidelberg ER - TY - THES A1 - Köhler, Raphael T1 - Towards seasonal prediction: stratosphere-troposphere coupling in the atmospheric model ICON-NWP N2 - Stratospheric variability is one of the main potential sources for sub-seasonal to seasonal predictability in mid-latitudes in winter. Stratospheric pathways play an important role for long-range teleconnections between tropical phenomena, such as the quasi-biennial oscillation (QBO) and El Niño-Southern Oscillation (ENSO), and the mid-latitudes on the one hand, and linkages between Arctic climate change and the mid-latitudes on the other hand. In order to move forward in the field of extratropical seasonal predictions, it is essential that an atmospheric model is able to realistically simulate the stratospheric circulation and variability. The numerical weather prediction (NWP) configuration of the ICOsahedral Non-hydrostatic atmosphere model ICON is currently being used by the German Meteorological Service for the regular weather forecast, and is intended to produce seasonal predictions in future. This thesis represents the first extensive evaluation of Northern Hemisphere stratospheric winter circulation in ICON-NWP by analysing a large set of seasonal ensemble experiments. An ICON control climatology simulated with a default setup is able to reproduce the basic behaviour of the stratospheric polar vortex. However, stratospheric westerlies are significantly too weak and major stratospheric warmings too frequent, especially in January. The weak stratospheric polar vortex in ICON is furthermore connected to a mean sea level pressure (MSLP) bias pattern resembling the negative phase of the Arctic Oscillation (AO). Since a good representation of the drag exerted by gravity waves is crucial for a realistic simulation of the stratosphere, three sensitivity experiments with reduced gravity wave drag are performed. Both a reduction of the non-orographic and orographic gravity wave drag respectively, lead to a strengthening of the stratospheric vortex and thus a bias reduction in winter, in particular in January. However, the effect of the non-orographic gravity wave drag on the stratosphere is stronger. A third experiment, combining a reduced orographic and non-orographic drag, exhibits the largest stratospheric bias reductions. The analysis of stratosphere-troposphere coupling based on an index of the Northern Annular Mode demonstrates that ICON realistically represents downward coupling. This coupling is intensified and more realistic in experiments with a reduced gravity wave drag, in particular with reduced non-orographic drag. Tropospheric circulation is also affected by the reduced gravity wave drag, especially in January, when the strongly improved stratospheric circulation reduces biases in the MSLP patterns. Moreover, a retuning of the subgrid-scale orography parameterisations leads to a significant error reduction in the MSLP in all months. In conclusion, the combination of these adjusted parameterisations is recommended as a current optimal setup for seasonal simulations with ICON. Additionally, this thesis discusses further possible influences on the stratospheric polar vortex, including the influence of tropical phenomena, such as QBO and ENSO, as well as the influence of a rapidly warming Arctic. ICON does not simulate the quasi-oscillatory behaviour of the QBO and favours weak easterlies in the tropical stratosphere. A comparison with a reanalysis composite of the easterly QBO phase reveals, that the shift towards the easterly QBO in ICON further weakens the stratospheric polar vortex. On the other hand, the stratospheric reaction to ENSO events in ICON is realistic. ICON and the reanalysis exhibit a weakened stratospheric vortex in warm ENSO years. Furthermore, in particular in winter, warm ENSO events favour the negative phase of the Arctic Oscillation, whereas cold events favour the positive phase. The ICON simulations also suggest a significant effect of ENSO on the Atlantic-European sector in late winter. To investigate the influence of Arctic climate change on mid-latitude circulation changes, two differing approaches with transient and fixed sea ice conditions are chosen. Neither ICON approach exhibits the mid-latitude tropospheric negative Arctic Oscillation circulation response to amplified Arctic warming, as it is discussed on the basis of observational evidence. Nevertheless, adding a new model to the current and active discussion on Arctic-midlatitude linkages, further contributes to the understanding of divergent conclusions between model and observational studies. N2 - Die stratosphärische Variabilität ist eine der wichtigsten potentiellen Quellen für die Vorhersagbarkeit der atmosphärischen Zirkulation in den mittleren Breiten im Winter auf der Zeitskala von Wochen bis zu Jahreszeiten. Stratosphärische Prozesse spielen eine grundlegende Rolle für die Fernverbindungen (Telekonnektionen) zwischen tropischen Klimaphänomenen, wie der quasi-zweijährigen Schwingung (QBO) oder „El Niño-Südliche Oszillation“ (ENSO), und den mittleren Breiten, sowie den Telekonnektionen zwischen arktischen Klimaänderungen und der atmosphärischen Zirkulation in den mittleren Breiten. Die Fähigkeit eines atmosphärischen Modells, die stratosphärische Zirkulation und deren Variabilität realistisch zu simulieren, ist deshalb von grundlegender Bedeutung, um die Jahreszeitenvorhersage in den mittleren Breiten deutlich zu verbessern. Das nichthydrostatische Atmosphärenmodell ICON (ICOsahedral Non-hydrostatic atmosphere model) wird gegenwärtig beim Deutschen Wetterdienst (DWD) in der numerischen Wettervorhersagekonfiguration (ICON-NWP) für die Wettervorhersage genutzt, und soll zukünftig auch für Jahreszeitenvorhersagen benutzt werden. Darauf basierend, präsentiert die vorliegende Arbeit eine Vielzahl von saisonalen Ensembleexperimenten mit ICON-NWP und liefert damit die erste umfassende Bewertung der stratosphärischen Winterzirkulation der nördlichen Hemisphäre in ICON-NWP. Die Klimatologie eines ICON-Modelllaufs im Standardsetup reproduziert die grundlegenden Eigenschaften des stratosphärischen Polarwirbels. Allerdings sind die stratosphärischen Westwinde deutlich schwächer als in den Beobachtungen, und starke Stratosphärenerwärmungen treten insbesondere im Januar zu häufig auf. Zudem ist der schwache stratosphärische Polarwirbel in ICON mit einem typischen Fehler-Muster des Bodenluftdrucks verknüpft, welches der negativen Phase der Arktischen Oszillation (AO) ähnelt. Da eine gute Darstellung des von Schwerewellen ausgeübten Widerstands für eine realistische Simulation der Stratosphäre entscheidend ist, werden drei Sensitivitätsexperimente mit reduziertem Schwerewellenwiderstand durchgeführt. Sowohl eine Verringerung des nicht-orographischen, als auch eine Verringerung des orographischen Schwerewellenwiderstands führen jeweils zu einer Verstärkung des stratosphärischen Wirbels und damit zu einer Verringerung des Fehlers im Winter, insbesondere im Januar. Die Wirkung des nicht-orographischen Schwerewellenwiderstands auf die Stratosphäre ist hierbei jedoch stärker. Ein drittes Experiment, welches den reduzierten orographischen und nicht-orographischen Widerstand kombiniert, zeigt die größten Verbesserungen in der Stratosphäre. Die auf dem Index des „Northern Annular Mode“ basierende Analyse der Stratosphären-Troposphären-Kopplung zeigt, dass ICON die nach unten gerichtete Kopplung zwischen der Stratosphäre und Troposphäre realistisch darstellt. Diese Kopplung wird in Experimenten mit einem reduzierten Schwerewellenwiderstand verstärkt und realistischer dargestellt, dies gilt insbesondere für den reduzierten nicht-orographischen Widerstand. Auch die troposphärische Zirkulation wird durch den reduzierten Schwerewellenwiderstand beeinflusst, vor allem im Januar, wenn die stark verbesserte stratosphärische Zirkulation den Fehler in den Bodenluftdruckfeldern reduziert. Darüber hinaus führt ein Tuning der Parameterisierung der subgrid-skaligen orographischen Schwerewellen zu einer signifikanten Fehlerreduktion des Bodenluftdrucks in allen Monaten. Die Kombination all dieser angepassten Parametrisierungen wird als derzeit optimales Setup für Jahreszeiten-Simulationen mit ICON vorgeschlagen. Darüber hinaus werden in dieser Arbeit weitere mögliche Einflussfaktoren auf den stratosphärischen Polarwirbel diskutiert, darunter der Einfluss tropischer Phänomene, wie QBO und ENSO, sowie der Einfluss einer sich rasch erwärmenden Arktis. Das quasi-oszillierende Verhalten der QBO wird durch ICON nicht simuliert, sodass schwache Ostwinde in der tropischen Stratosphäre dominieren. Ein Vergleich mit einem Reanalyse-Komposit der östlichen QBO-Phase zeigt, dass die Verschiebung in Richtung der östlichen QBO in ICON den stratosphärischen Polarwirbel weiter abschwächt. Die stratosphärische Reaktion auf ENSO-Ereignisse in ICON ist jedoch realistisch. ICON und Reanalysedaten zeigen einen abgeschwächten Stratosphärenwirbel in warmen ENSO-Jahren. Darüber hinaus begünstigen insbesondere im Winter warme ENSO-Ereignisse die negative Phase der Arktischen Oszillation, während kalte Ereignisse die positive Phase begünstigen. Die ICON-Simulationen deuten auch auf einen signifikanten Effekt von ENSO auf den atlantisch-europäischen Sektor im Spätwinter hin. Um den Einfluss des arktischen Klimawandels auf Änderungen der Zirkulation in mittleren Breiten zu untersuchen, werden zwei unterschiedliche Ansätze mit transienten und festen Meereisgrenzen gewählt. Keiner der beiden ICON-Ansätze zeigt eine Tendenz zur negativen Phase der Arktische Oszillation als Reaktion auf die verstärkte Erwärmung der Arktis, wie sie in der Literatur anhand von Beobachtungsdaten häufig diskutiert wird. Jedoch wird somit der aktuellen und aktiven Diskussion zu den Auswirkungen des arktischen Klimawandels auf die Zirkulation der mittleren Breiten ein neues Modell hinzugefügt. T2 - Im Hinblick auf die Jahreszeitenvorhersage: Stratosphären-Troposphären-Kopplung in dem Atmosphärenmodell ICON-NWP KW - Seasonal prediction KW - Stratosphere-troposphere coupling KW - ICON KW - Stratospheric polar vortex KW - Jahreszeitenvorhersage KW - Stratosphären-Troposphären-Kopplung KW - ICON KW - Stratosphärischer Polarwirbel KW - El Niño-Southern Oscillation (ENSO) KW - El Niño-Südliche Oszillation KW - Arctic-midlatitude linkages KW - Verbindungspfade zwischen der Arktis und den mittleren Breiten Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-487231 ER - TY - JOUR A1 - Fernandez, Ricardo A1 - Gonzalez-Doncel, Gaspar A1 - Garces, Gerardo A1 - Bruno, Giovanni T1 - Towards a comprehensive understanding of creep BT - microstructural dependence of the pre-exponential term in Al JF - Materials science & engineering. A, Structural materials: properties, microstructure and processing N2 - We show that the equation proposed by Takeuchi and Argon to explain the creep behavior of Al-Mg solid solution can be used to describe also the creep behavior of pure aluminum. In this frame, it is possible to avoid the use of the classic pre-exponential fitting parameter in the power law equation to predict the minimum creep strain rate. The effect of the fractal arrangement of dislocations, developed at the mesoscale, must be considered to fully explain the experimental data. These ideas allow improving the recently introduced SSTC model, fully describing the primary and secondary creep regimes of aluminum alloys without the need for fitting. Creep data from commercially pure A199.8% and Al-Mg alloys tested at different temperatures and stresses are used to validate the proposed ideas. KW - creep KW - Aluminum alloys KW - dislocations KW - fractal KW - stress exponent Y1 - 2020 U6 - https://doi.org/10.1016/j.msea.2020.139036 SN - 0921-5093 SN - 1873-4936 VL - 776 PB - Elsevier CY - Lausanne ER - TY - JOUR A1 - Spelzhausen, Simon A1 - Ionian, Mario-Rafael A1 - Gerhard, Reimund A1 - Plath, Ronald T1 - Time-resolved measurement of space-charge evolution in dielectric films or slabs by means of repeatable laser-induced pressure pulses JF - Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques N2 - A new variant of the Laser-Induced Pressure-Pulse (LIPP) method for repeatable, time-resolved space-charge profile measurements is proposed and demonstrated. Automated deposition of a fresh laser-target film before each illumination leads to good repeatability of the LIPP and thus allows for the detection of time-resolved changes in the space-charge distribution over many hours. We describe and discuss the experimental setup and its features, compare the repeatability of the LIPP measurements on the same sample without and with re-preparation of the test cell, and present the time-resolved evolution of the space-charge profile in a two-layer arrangement of a silicone-grease and a silicone-elastomer film as an example. Finally, the temperature dependence of the space-charge evolution during polarization under high voltage and during depolarization in short circuit is shown. Possible uses and future developments of the new LIPP approach are also discussed. Y1 - 2020 U6 - https://doi.org/10.1063/1.5142443 SN - 0034-6748 SN - 1089-7623 VL - 91 IS - 5 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Henkel, Carsten T1 - Thermally excited quasiparticles in metals, dispersion forces, and the thermal anomaly JF - Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics N2 - We provide a brief review of the contribution of thermally excited carriers to dispersion forces. In a metal, these carriers generate charge and current fluctuations whose spectral frequencies are comparable to k(B)T/(h) over bar. They are very likely responsible for the "plasma vs. Drude" anomaly. KW - Dispersion force KW - quasi-particles Y1 - 2020 U6 - https://doi.org/10.1142/S021773232040009X SN - 0217-7323 SN - 1793-6632 VL - 35 IS - 3 PB - World Scientific CY - Singapore ER - TY - JOUR A1 - Petreska, Irina A1 - de Castro, Antonio S. M. A1 - Sandev, Trifce A1 - Lenzi, Ervin K. T1 - The time-dependent Schrödinger equation in non-integer dimensions for constrained quantum motion JF - Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics N2 - We propose a theoretical model, based on a generalized Schroedinger equation, to study the behavior of a constrained quantum system in non-integer, lower than two-dimensional space. The non-integer dimensional space is formed as a product space X x Y, comprising x-coordinate with a Hausdorff measure of dimension alpha(1) = D -1 (1 < D < 2) and y-coordinate with the Lebesgue measure of dimension of length (alpha(2) = 1). Geometric constraints are set at y = 0. Two different approaches to find the Green's function are employed, both giving the same form in terms of the Fox H-function. For D = 2, the solution for two-dimensional quantum motion on a comb is recovered. (C) 2020 Elsevier B.V. All rights reserved. KW - Schrödinger equation KW - non-integer dimension KW - Green's function KW - Bessel functions KW - Fox H-function Y1 - 2020 U6 - https://doi.org/10.1016/j.physleta.2020.126866 SN - 0375-9601 SN - 1873-2429 VL - 384 IS - 34 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Reese, Ronja A1 - Levermann, Anders A1 - Albrecht, Torsten A1 - Seroussi, Helene A1 - Winkelmann, Ricarda T1 - The role of history and strength of the oceanic forcing in sea level projections from Antarctica with the Parallel Ice Sheet Model JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union N2 - Mass loss from the Antarctic Ice Sheet constitutes the largest uncertainty in projections of future sea level rise. Ocean-driven melting underneath the floating ice shelves and subsequent acceleration of the inland ice streams are the major reasons for currently observed mass loss from Antarctica and are expected to become more important in the future. Here we show that for projections of future mass loss from the Antarctic Ice Sheet, it is essential (1) to better constrain the sensitivity of sub-shelf melt rates to ocean warming and (2) to include the historic trajectory of the ice sheet. In particular, we find that while the ice sheet response in simulations using the Parallel Ice Sheet Model is comparable to the median response of models in three Antarctic Ice Sheet Intercomparison projects - initMIP, LARMIP-2 and ISMIP6 - conducted with a range of ice sheet models, the projected 21st century sea level contribution differs significantly depending on these two factors. For the highest emission scenario RCP8.5, this leads to projected ice loss ranging from 1:4 to 4:0 cm of sea level equivalent in simulations in which ISMIP6 ocean forcing drives the PICO ocean box model where parameter tuning leads to a comparably low sub-shelf melt sensitivity and in which no surface forcing is applied. This is opposed to a likely range of 9:1 to 35:8 cm using the exact same initial setup, but emulated from the LARMIP-2 experiments with a higher melt sensitivity, even though both projects use forcing from climate models and melt rates are calibrated with previous oceanographic studies. Furthermore, using two initial states, one with a previous historic simulation from 1850 to 2014 and one starting from a steady state, we show that while differences between the ice sheet configurations in 2015 seem marginal at first sight, the historic simulation increases the susceptibility of the ice sheet to ocean warming, thereby increasing mass loss from 2015 to 2100 by 5% to 50 %. Hindcasting past ice sheet changes with numerical models would thus provide valuable tools to better constrain projections. Our results emphasize that the uncertainty that arises from the forcing is of the same order of magnitude as the ice dynamic response for future sea level projections. Y1 - 2020 U6 - https://doi.org/10.5194/tc-14-3097-2020 SN - 1994-0416 SN - 1994-0424 VL - 14 IS - 9 SP - 3097 EP - 3110 PB - Copernicus CY - Göttingen ER - TY - THES A1 - Sposini, Vittoria T1 - The random diffusivity approach for diffusion in heterogeneous systems N2 - The two hallmark features of Brownian motion are the linear growth < x2(t)> = 2Ddt of the mean squared displacement (MSD) with diffusion coefficient D in d spatial dimensions, and the Gaussian distribution of displacements. With the increasing complexity of the studied systems deviations from these two central properties have been unveiled over the years. Recently, a large variety of systems have been reported in which the MSD exhibits the linear growth in time of Brownian (Fickian) transport, however, the distribution of displacements is pronouncedly non-Gaussian (Brownian yet non-Gaussian, BNG). A similar behaviour is also observed for viscoelastic-type motion where an anomalous trend of the MSD, i.e., ~ ta, is combined with a priori unexpected non-Gaussian distributions (anomalous yet non-Gaussian, ANG). This kind of behaviour observed in BNG and ANG diffusions has been related to the presence of heterogeneities in the systems and a common approach has been established to address it, that is, the random diffusivity approach. This dissertation explores extensively the field of random diffusivity models. Starting from a chronological description of all the main approaches used as an attempt of describing BNG and ANG diffusion, different mathematical methodologies are defined for the resolution and study of these models. The processes that are reported in this work can be classified in three subcategories, i) randomly-scaled Gaussian processes, ii) superstatistical models and iii) diffusing diffusivity models, all belonging to the more general class of random diffusivity models. Eventually, the study focuses more on BNG diffusion, which is by now well-established and relatively well-understood. Nevertheless, many examples are discussed for the description of ANG diffusion, in order to highlight the possible scenarios which are known so far for the study of this class of processes. The second part of the dissertation deals with the statistical analysis of random diffusivity processes. A general description based on the concept of moment-generating function is initially provided to obtain standard statistical properties of the models. Then, the discussion moves to the study of the power spectral analysis and the first passage statistics for some particular random diffusivity models. A comparison between the results coming from the random diffusivity approach and the ones for standard Brownian motion is discussed. In this way, a deeper physical understanding of the systems described by random diffusivity models is also outlined. To conclude, a discussion based on the possible origins of the heterogeneity is sketched, with the main goal of inferring which kind of systems can actually be described by the random diffusivity approach. N2 - Die zwei grundlegenden Eigenschaften der Brownschen Molekularbewegung sind das lineare Wachstum < x2(t)> = 2Ddt der mittleren quadratischen Verschiebung (mean squared displacement, MSD) mit dem Diffusionskoeffizienten D in Dimension d und die Gauß Verteilung der räumlichen Verschiebung. Durch die zunehmende Komplexität der untersuchten Systeme wurden in den letzten Jahren Abweichungen von diesen zwei grundlegenden Eigenschaften gefunden. Hierbei, wurde über eine große Anzahl von Systemen berichtet, in welchen die MSD das lineare Wachstum der Brownschen Bewegung (Ficksches Gesetzt) zeigt, jedoch die Verteilung der Verschiebung nicht einer Gaußverteilung folgt (Brownian yet non-Gaussian, BNG). Auch in viskoelastischen Systemen Bewegung wurde ein analoges Verhalten beobachtet. Hier ist ein anomales Verhalten des MSD, ~ ta, in Verbindung mit einer a priori unerwarteten nicht gaußchen Verteilung (anomalous yet non-Gaussian, ANG). Dieses Verhalten, welches sowohl in BNG- als auch in ANG-Diffusion beobachtet wird, ist auf eine Heterogenität in den Systemen zurückzuführen. Um diese Systeme zu beschreiben, wurde ein einheitlicher Ansatz, basierend auf den Konzept der zufälligen Diffusivität, entwickelt. Die vorliegende Dissertation widmet sich ausführlich Modellen mit zufälligen Diffusivität. Ausgehend von einem chronologischen Überblick der grundlegenden Ansätze der Beschreibung der BNG- und ANG-Diffusion werden mathematische Methoden entwickelt, um die verschiedenen Modelle zu untersuchen. Die in dieser Arbeit diskutierten Prozesse können in drei Kategorien unterteil werden: i) randomly-scaled Gaussian processes, ii) superstatistical models und iii) diffusing diffusivity models, welche alle zu den allgemeinen Modellen mit zufälligen Diffusivität gehören. Der Hauptteil dieser Arbeit ist die Untersuchung auf die BNG Diffusion, welche inzwischen relativ gut verstanden ist. Dennoch werden auch viele Beispiele für die Beschreibung von ANG-Diffusion diskutiert, um die Möglichkeiten der Analyse solcher Prozesse aufzuzeigen. Der zweite Teil der Dissertation widmet sich der statistischen Analyse von Modellen mit zufälligen Diffusivität. Eine allgemeine Beschreibung basierend auf dem Konzept der momenterzeugenden Funktion wurde zuerst herangezogen, um grundsätzliche statistische Eigenschaften der Modelle zu erhalten. Anschließend konzentriert sich die Diskussion auf die Analyse der spektralen Leistungsdichte und der first passage Statistik für einige spezielle Modelle mit zufälligen Diffusivität. Diese Ergebnisse werden mit jenen der normalen Brownschen Molekularbewegung verglichen. Dadurch wird ein tiefergehendes physikalisches Verständnis über die Systeme erlangt, welche durch ein Modell mit zufälligen Diffusivität beschrieben werden. Abschließend, zeigt eine Diskussion mögliche Ursachen für die Heterogenität auf, mit dem Ziel darzustellen, welche Arten von Systemen durch den Zufalls-Diffusivitäts-Ansatz beschrieben werden können. N2 - Las dos características distintivas del movimiento Browniano son el crecimiento lineal < x2(t)> = 2Ddt del desplazamiento cuadrático medio (mean squared displacement}, MSD) con el coeficiente de difusión D en dimensiones espaciales d, y la distribución Gaussiana de los desplazamientos. Con los continuos avances en tecnologías experimentales y potencia de cálculo, se logra estudiar con mayor detalle sistemas cada vez más complejos y algunos sistemas revelan desviaciones de estas dos propiedades centrales. En los últimos años se ha observado una gran variedad de sistemas en los que el MSD presenta un crecimiento lineal en el tiempo (típico del transporte Browniano), no obstante, la distribución de los desplazamientos es pronunciadamente no Gaussiana (Brownian yet non-Gaussian diffusion}, BNG). Un comportamiento similar se observa asimismo en el caso del movimiento de tipo viscoelástico, en el que se combina una tendencia anómala del MSD, es decir, ~ ta, con a, con distribuciones inesperadamente no Gaussianas (Anomalous yet non-Gaussian diffusion, ANG). Este tipo de comportamiento observado en las difusiones BNG y ANG se ha relacionado con la presencia de heterogeneidades en los sistemas y se ha establecido un enfoque común para abordarlo: el enfoque de difusividad aleatoria. En la primera parte de esta disertación se explora extensamente el área de los modelos de difusividad aleatoria. A través de una descripción cronológica de los principales enfoques utilizados para caracterizar las difusiones BNG y ANG, se definen diferentes metodologías matemáticas para la resolución y el estudio de estos modelos. Los procesos expuestos en este trabajo, pertenecientes a la clase más general de modelos de difusividad aleatoria, pueden clasificarse en tres subcategorías: i) randomly-scaled Gaussian processes, ii) superstatistical models y iii) diffusing diffusivity models. Fundamentalmente el enfoque de este trabajo se centra en la difusión BNG, bien establecida y ampliamente estudiada en los últimos años. No obstante, múltiples ejemplos son examinados para la descripción de la difusión ANG, a fin de remarcar los diferentes modelos de estudio disponibles hasta el momento. En la segunda parte de la disertación se desarolla el análisis estadístico de los procesos de difusividad aleatoria. Inicialmente se expone una descripción general basada en el concepto de la función generadora de momentos para obtener las propiedades estadísticas estándar de los modelos. A continuación, la discusión aborda el estudio de la densidad espectral de potencia y la estadística del tiempo de primer paso para algunos modelos de difusividad aleatoria. Adicionalmente, los resultados del método de difusividad aleatoria se comparan junto a los de movimiento browniano estándar. Como resultado, se obtiene una mayor comprensión física de los sistemas descritos por los modelos de difusividad aleatoria. Para concluir, se presenta una discusión acerca de los posibles orígenes de la heterogeneidad, con el objetivo principal de inferir qué tipo de sistemas pueden describirse apropiadamente según el enfoque de la difusividad aleatoria. KW - diffusion KW - non-gaussianity KW - random diffusivity KW - power spectral analysis KW - first passage KW - Diffusion KW - zufälligen Diffusivität KW - spektrale Leistungsdichte KW - first passage KW - Heterogenität Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-487808 ER -