TY - JOUR A1 - Raoufi, Meysam A1 - Hörmann, Ulrich A1 - Ligorio, Giovanni A1 - Hildebrandt, Jana A1 - Pätzel, Michael A1 - Schultz, Thorsten A1 - Perdigón-Toro, Lorena A1 - Koch, Norbert A1 - List-Kratochvil, Emil A1 - Hecht, Stefan A1 - Neher, Dieter T1 - Simultaneous effect of ultraviolet radiation and surface modification on the work function and hole injection properties of ZnO thin films JF - Physica Status Solidi. A , Applications and materials science N2 - The combined effect of ultraviolet (UV) light soaking and self-assembled monolayer deposition on the work function (WF) of thin ZnO layers and on the efficiency of hole injection into the prototypical conjugated polymer poly(3-hexylthiophen-2,5-diyl) (P3HT) is systematically investigated. It is shown that the WF and injection efficiency depend strongly on the history of UV light exposure. Proper treatment of the ZnO layer enables ohmic hole injection into P3HT, demonstrating ZnO as a potential anode material for organic optoelectronic devices. The results also suggest that valid conclusions on the energy-level alignment at the ZnO/organic interfaces may only be drawn if the illumination history is precisely known and controlled. This is inherently problematic when comparing electronic data from ultraviolet photoelectron spectroscopy (UPS) measurements carried out under different or ill-defined illumination conditions. KW - charge injection across hybrid interfaces KW - energy-level alignments KW - hybrid metal oxides KW - organic interfaces Y1 - 2020 U6 - https://doi.org/10.1002/pssa.201900876 SN - 1862-6300 SN - 1862-6319 VL - 217 IS - 5 SP - 1 EP - 6 PB - Wiley-VCH CY - Weinheim ER - TY - GEN A1 - Varykhalov, Andrei A1 - Freyse, Friedrich A1 - Aguilera, Irene A1 - Battiato, Marco A1 - Krivenkov, Maxim A1 - Marchenko, Dmitry A1 - Bihlmayer, Gustav A1 - Blugel, Stefan A1 - Rader, Oliver A1 - Sanchez-Barriga, Jaime T1 - Effective mass enhancement and ultrafast electron dynamics of Au(111) surface state coupled to a quantum well T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - We show that, although the equilibrium band dispersion of the Shockley-type surface state of two-dimensional Au(111) quantum films grown on W(110) does not deviate from the expected free-electron-like behavior, its nonequilibrium energy-momentum dispersion probed by time- and angle-resolved photoemission exhibits a remarkable kink above the Fermi level due to a significant enhancement of the effective mass. The kink is pronounced for certain thicknesses of the Au quantum well and vanishes in the very thin limit. We identify the kink as induced by the coupling between the Au(111) surface state and emergent quantum-well states which probe directly the buried gold-tungsten interface. The signatures of the coupling are further revealed by our time-resolved measurements which show that surface state and quantum-well states thermalize together behaving as dynamically locked electron populations. In particular, relaxation of hot carriers following laser excitation is similar for both surface state and quantum-well states and much slower than expected for a bulk metallic system. The influence of quantum confinement on the interplay between elementary scattering processes of the electrons at the surface and ultrafast carrier transport in the direction perpendicular to the surface is shown to be the reason for the slow electron dynamics. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1354 KW - AG KW - films Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-549892 SN - 1866-8372 IS - 1 ER - TY - JOUR A1 - Varykhalov, Andrei A1 - Freyse, Friedrich A1 - Aguilera, Irene A1 - Battiato, Marco A1 - Krivenkov, Maxim A1 - Marchenko, Dmitry A1 - Bihlmayer, Gustav A1 - Blugel, Stefan A1 - Rader, Oliver A1 - Sanchez-Barriga, Jaime T1 - Effective mass enhancement and ultrafast electron dynamics of Au(111) surface state coupled to a quantum well JF - Physical Review Research N2 - We show that, although the equilibrium band dispersion of the Shockley-type surface state of two-dimensional Au(111) quantum films grown on W(110) does not deviate from the expected free-electron-like behavior, its nonequilibrium energy-momentum dispersion probed by time- and angle-resolved photoemission exhibits a remarkable kink above the Fermi level due to a significant enhancement of the effective mass. The kink is pronounced for certain thicknesses of the Au quantum well and vanishes in the very thin limit. We identify the kink as induced by the coupling between the Au(111) surface state and emergent quantum-well states which probe directly the buried gold-tungsten interface. The signatures of the coupling are further revealed by our time-resolved measurements which show that surface state and quantum-well states thermalize together behaving as dynamically locked electron populations. In particular, relaxation of hot carriers following laser excitation is similar for both surface state and quantum-well states and much slower than expected for a bulk metallic system. The influence of quantum confinement on the interplay between elementary scattering processes of the electrons at the surface and ultrafast carrier transport in the direction perpendicular to the surface is shown to be the reason for the slow electron dynamics. KW - AG KW - Flims Y1 - 2020 U6 - https://doi.org/10.1103/PhysRevResearch.2.013343 SN - 0031-9007 VL - 2 IS - 1 SP - 1 EP - 9 PB - American Physical Society CY - Ridge, NY ER - TY - GEN A1 - Schulz, Christian A1 - Lieutenant, Klaus A1 - Xiao, Jie A1 - Hofmann, Tommy A1 - Wong, Deniz A1 - Habicht, Klaus T1 - Characterization of the soft X-ray spectrometer PEAXIS at BESSY II T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The performance of the recently commissioned spectrometer PEAXIS for resonant inelastic soft X-ray scattering (RIXS) and X-ray photoelectron spectroscopy and its hosting beamline U41-PEAXIS at the BESSY II synchrotron are characterized. The beamline provides linearly polarized light from 180 eV to 1600 eV allowing for RIXS measurements in the range 200-1200 eV. The monochromator optics can be operated in different configurations to provide either high flux with up to 10(12) photons s(-1) within the focal spot at the sample or high energy resolution with a full width at half maximum of <40 meV at an incident photon energy of similar to 400 eV. The measured total energy resolution of the RIXS spectrometer is in very good agreement with theoretically predicted values obtained by ray-tracing simulations. PEAXIS features a 5 m-long RIXS spectrometer arm that can be continuously rotated about the sample position by 106 degrees within the horizontal photon scattering plane, thus enabling the study of momentum-transfer-dependent excitations. Selected scientific examples are presented to demonstrate the instrument capabilities, including measurements of excitations in single-crystalline NiO and in liquid acetone employing a fluid cell sample manipulator. Planned upgrades of the beamline and the RIXS spectrometer to further increase the energy resolution to similar to 100 meV at 1000 eV incident photon energy are discussed. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1355 KW - resonant inelastic X-ray scattering; KW - X-ray photoelectron spectroscopy KW - soft X-ray spectroscopy KW - soft X-ray beamline KW - X-ray emission KW - X-ray absorption KW - BESSY II. Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-549928 SN - 1866-8372 ER - TY - GEN A1 - Phuong, Le Quang A1 - Hosseini, Seyed Mehrdad A1 - Sandberg, Oskar J. A1 - Zou, Yingping A1 - Woo, Han Young A1 - Neher, Dieter A1 - Shoaee, Safa T1 - Quantifying quasi-fermi level splitting and open-circuit voltage losses in highly efficient nonfullerene organic solar cells T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The power conversion efficiency (PCE) of state-of-the-art organic solar cells is still limited by significant open-circuit voltage (V-OC) losses, partly due to the excitonic nature of organic materials and partly due to ill-designed architectures. Thus, quantifying different contributions of the V-OC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state-of-the-art systems that demonstrate different V-OC losses in their performance are presented. By evaluating the quasi-Fermi level splitting (QFLS) and the V-OC as a function of the excitation fluence in nonfullerene-based PM6:Y6, PM6:Y11, and fullerene-based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non-radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1384 KW - nonfullerene acceptors KW - organic solar cells KW - quasi-Fermi level KW - splitting KW - quasi-steady-state photoinduced absorptions KW - surface KW - recombinations KW - voltage losses Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-570018 SN - 1866-8372 IS - 1 ER - TY - GEN A1 - Poch, Olivier A1 - Istiqomah, Istiqomah A1 - Quirico, Eric A1 - Beck, Pierre A1 - Schmitt, Bernard A1 - Theulé, Patrice A1 - Faure, Alexandre A1 - Hily-Blant, Pierre A1 - Bonal, Lydie A1 - Kappel, David T1 - Ammonium salts are a reservoir of nitrogen on a cometary nucleus and possibly on some asteroids T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The measured nitrogen-to-carbon ratio in comets is lower than for the Sun, a discrepancy which could be alleviated if there is an unknown reservoir of nitrogen in comets. The nucleus of comet 67P/Churyumov-Gerasimenko exhibits an unidentified broad spectral reflectance feature around 3.2 micrometers, which is ubiquitous across its surface. On the basis of laboratory experiments, we attribute this absorption band to ammonium salts mixed with dust on the surface. The depth of the band indicates that semivolatile ammonium salts are a substantial reservoir of nitrogen in the comet, potentially dominating over refractory organic matter and more volatile species. Similar absorption features appear in the spectra of some asteroids, implying a compositional link between asteroids, comets, and the parent interstellar cloud. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1389 KW - resolution infrared-spectroscopy KW - ice absorption features KW - young stellar objects KW - exposed water ice KW - MU-M KW - bidirectional reflectance KW - murchison meteorite KW - interstellar ice KW - spectra KW - surface Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-513751 SN - 1866-8372 N1 - This secondary publication was withdrawn for copyright reasons. IS - 6483 ER - TY - JOUR A1 - Poch, Olivier A1 - Istiqomah, Istiqomah A1 - Quirico, Eric A1 - Beck, Pierre A1 - Schmitt, Bernard A1 - Theulé, Patrice A1 - Faure, Alexandre A1 - Hily-Blant, Pierre A1 - Bonal, Lydie A1 - Kappel, David T1 - Ammonium salts are a reservoir of nitrogen on a cometary nucleus and possibly on some asteroids JF - Science N2 - The measured nitrogen-to-carbon ratio in comets is lower than for the Sun, a discrepancy which could be alleviated if there is an unknown reservoir of nitrogen in comets. The nucleus of comet 67P/Churyumov-Gerasimenko exhibits an unidentified broad spectral reflectance feature around 3.2 micrometers, which is ubiquitous across its surface. On the basis of laboratory experiments, we attribute this absorption band to ammonium salts mixed with dust on the surface. The depth of the band indicates that semivolatile ammonium salts are a substantial reservoir of nitrogen in the comet, potentially dominating over refractory organic matter and more volatile species. Similar absorption features appear in the spectra of some asteroids, implying a compositional link between asteroids, comets, and the parent interstellar cloud. KW - resolution infrared-spectroscopy KW - ice absorption features KW - young stellar objects KW - exposed water ice KW - MU-M KW - bidirectional reflectance KW - murchison meteorite KW - interstellar ice KW - spectra KW - surface Y1 - 2020 U6 - https://doi.org/10.1126/science.aaw7462 SN - 1095-9203 SN - 0036-8075 VL - 367 IS - 6483 SP - 1 EP - 8 PB - AAAS, American Association for the Advancement of Science CY - Washington, DC ER - TY - GEN A1 - Massolt, Joost Willem A1 - Borowski, Andreas T1 - Perceived relevance of university physics problems by pre-service physics teachers BT - personal constructs T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Pre-service physics teachers often do not recognise the relevance for their future career in their university content knowledge courses. A lower perceived relevance can, however, have a negative effect on their motivation and on their academic success. Several intervention studies have been undertaken with the goal to increase this perceived relevance. A previous study shows that conceptual physics problems used in university physics courses are perceived by pre-service physics teachers as more relevant for their future career than regular, quantitative problems. It is however not clear, what the students' meaning of the construct 'relevance' is: what makes a problem more relevant to them than another problem? To answer this question, N = 7 pre-service teachers were interviewed using the repertory grid technique, based on the personal construct theory. Nine physics problems were discussed with regards to their perceived relevance and with regards to problem properties that distinguish these problems from each other. We are able to identify six problem properties that have a positive influence on the perceived relevance. Physics problems that are based on these properties should therefore potentially have a higher perceived relevance, which can have a positive effect on the motivation of the pre-service teachers who solve these problems. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1396 KW - motivation KW - physics education KW - pre-service teachers KW - repertory grid Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-515838 SN - 1866-8372 VL - 42 IS - 2 SP - 167 EP - 189 ER - TY - GEN A1 - Schué, Emmanuelle A1 - Kopyshev, Alexey A1 - Lutz, Jean-François A1 - Börner, Hans G. T1 - Molecular bottle brushes with positioned selenols BT - Extending the toolbox of oxidative single polymer chain folding with conformation analysis by atomic force microscopy T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - A synthesis route to controlled and dynamic single polymer chain folding is reported. Sequence-controlled macromolecules containing precisely located selenol moieties within a polymer chain are synthesized. Oxidation of selenol functionalities lead to diselenide bridges and induces controlled intramolecular crosslinking to generate single chain collapse. The cyclization process is successfully characterized by SEC as well as by H-1 NMR and 2D HSQC NMR spectroscopies. In order to gain insight on the molecular level to reveal the degree of structural control, the folded polymers are transformed into folded molecular brushes that are known to be visualizable as single molecule structures by AFM. The "grafting onto" approach is performed by using triazolinedione-diene reaction to graft the side chain polymers. A series of folded molecular brushes as well as the corresponding linear controls are synthesized. AFM visualization is proving the cyclization of the folded backbone by showing globular objects, where non-folded brushes show typical worm-like structures. (C) 2019 The Authors. Journal of Polymer Science published by Wiley Periodicals, Inc. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1397 KW - atomic force microscopy (AFM) KW - diselenide KW - grafted polymers KW - molecular bottle brushes KW - sequence-controlled polymers KW - single chain folding Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-516184 SN - 1866-8372 IS - 1 SP - 154 EP - 162 ER - TY - JOUR A1 - Schué, Emmanuelle A1 - Kopyshev, Alexey A1 - Lutz, Jean-François A1 - Börner, Hans G. T1 - Molecular bottle brushes with positioned selenols BT - Extending the toolbox of oxidative single polymer chain folding with conformation analysis by atomic force microscopy JF - Journal of Polymer Science N2 - A synthesis route to controlled and dynamic single polymer chain folding is reported. Sequence-controlled macromolecules containing precisely located selenol moieties within a polymer chain are synthesized. Oxidation of selenol functionalities lead to diselenide bridges and induces controlled intramolecular crosslinking to generate single chain collapse. The cyclization process is successfully characterized by SEC as well as by H-1 NMR and 2D HSQC NMR spectroscopies. In order to gain insight on the molecular level to reveal the degree of structural control, the folded polymers are transformed into folded molecular brushes that are known to be visualizable as single molecule structures by AFM. The "grafting onto" approach is performed by using triazolinedione-diene reaction to graft the side chain polymers. A series of folded molecular brushes as well as the corresponding linear controls are synthesized. AFM visualization is proving the cyclization of the folded backbone by showing globular objects, where non-folded brushes show typical worm-like structures. (C) 2019 The Authors. Journal of Polymer Science published by Wiley Periodicals, Inc. KW - atomic force microscopy (AFM) KW - diselenide KW - grafted polymers KW - molecular bottle brushes KW - sequence-controlled polymers KW - single chain folding Y1 - 2020 U6 - https://doi.org/10.1002/pola.29496 SN - 2642-4169 VL - 58 IS - 1 SP - 154 EP - 162 PB - Wiley CY - Hoboken ER - TY - GEN A1 - Alirezaeizanjani, Zahra A1 - Großmann, Robert A1 - Pfeifer, Veronika A1 - Hintsche, Marius A1 - Beta, Carsten T1 - Chemotaxis strategies of bacteria with multiple run modes T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Bacterial chemotaxis-a fundamental example of directional navigation in the living world-is key to many biological processes, including the spreading of bacterial infections. Many bacterial species were recently reported to exhibit several distinct swimming modes-the flagella may, for example, push the cell body or wrap around it. How do the different run modes shape the chemotaxis strategy of a multimode swimmer? Here, we investigate chemotactic motion of the soil bacterium Pseudomonas putida as a model organism. By simultaneously tracking the position of the cell body and the configuration of its flagella, we demonstrate that individual run modes show different chemotactic responses in nutrition gradients and, thus, constitute distinct behavioral states. On the basis of an active particle model, we demonstrate that switching between multiple run states that differ in their speed and responsiveness provides the basis for robust and efficient chemotaxis in complex natural habitats. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1418 KW - instability KW - flagellum KW - exploit KW - time Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-519098 SN - 1866-8372 IS - 22 ER - TY - GEN A1 - Kirchartz, Thomas A1 - Márquez, José A. A1 - Stolterfoht, Martin A1 - Unold, Thomas T1 - Photoluminescence-based characterization of halide perovskites for photovoltaics T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Photoluminescence spectroscopy is a widely applied characterization technique for semiconductor materials in general and halide perovskite solar cell materials in particular. It can give direct information on the recombination kinetics and processes as well as the internal electrochemical potential of free charge carriers in single semiconductor layers, layer stacks with transport layers, and complete solar cells. The correct evaluation and interpretation of photoluminescence requires the consideration of proper excitation conditions, calibration and application of the appropriate approximations to the rather complex theory, which includes radiative recombination, non-radiative recombination, interface recombination, charge transfer, and photon recycling. In this article, an overview is given of the theory and application to specific halide perovskite compositions, illustrating the variables that should be considered when applying photoluminescence analysis in these materials. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1419 KW - metal halide perovskites KW - numerical simulations KW - photoluminescence KW - photon recycling Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-519702 SN - 1866-8372 IS - 26 ER - TY - JOUR A1 - Kirchartz, Thomas A1 - Márquez, José A. A1 - Stolterfoht, Martin A1 - Unold, Thomas T1 - Photoluminescence-based characterization of halide perovskites for photovoltaics JF - Advanced Energy Materials N2 - Photoluminescence spectroscopy is a widely applied characterization technique for semiconductor materials in general and halide perovskite solar cell materials in particular. It can give direct information on the recombination kinetics and processes as well as the internal electrochemical potential of free charge carriers in single semiconductor layers, layer stacks with transport layers, and complete solar cells. The correct evaluation and interpretation of photoluminescence requires the consideration of proper excitation conditions, calibration and application of the appropriate approximations to the rather complex theory, which includes radiative recombination, non-radiative recombination, interface recombination, charge transfer, and photon recycling. In this article, an overview is given of the theory and application to specific halide perovskite compositions, illustrating the variables that should be considered when applying photoluminescence analysis in these materials. KW - metal halide perovskites KW - numerical simulations KW - photoluminescence KW - photon recycling Y1 - 2020 U6 - https://doi.org/10.1002/aenm.201904134 SN - 1614-6832 SN - 1614-6840 VL - 10 IS - 26 SP - 1 EP - 21 PB - Wiley CY - Weinheim ER - TY - GEN A1 - Cheng, Xin A1 - Zhang, Jie A1 - Kliem, Bernhard A1 - Török, Tibor A1 - Xing, Chen A1 - Zhou, Zhenjun A1 - Inhester, Bernd A1 - Ding, Mingde T1 - Initiation and early kinematic evolution of solar eruptions T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - We investigate the initiation and early evolution of 12 solar eruptions, including six active-region hot channel and six quiescent filament eruptions, which were well observed by the Solar Dynamics Observatory, as well as by the Solar Terrestrial Relations Observatory for the latter. The sample includes one failed eruption and 11 coronal mass ejections, with velocities ranging from 493 to 2140 km s(-1). A detailed analysis of the eruption kinematics yields the following main results. (1) The early evolution of all events consists of a slow-rise phase followed by a main-acceleration phase, the height-time profiles of which differ markedly and can be best fit, respectively, by a linear and an exponential function. This indicates that different physical processes dominate in these phases, which is at variance with models that involve a single process. (2) The kinematic evolution of the eruptions tends to be synchronized with the flare light curve in both phases. The synchronization is often but not always close. A delayed onset of the impulsive flare phase is found in the majority of the filament eruptions (five out of six). This delay and its trend to be larger for slower eruptions favor ideal MHD instability models. (3) The average decay index at the onset heights of the main acceleration is close to the threshold of the torus instability for both groups of events (although, it is based on a tentative coronal field model for the hot channels), suggesting that this instability initiates and possibly drives the main acceleration. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1420 KW - solar coronal mass ejections KW - stellar coronal mass ejections KW - solar storm Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-519720 SN - 1866-8372 IS - 2 ER - TY - JOUR A1 - Cheng, Xin A1 - Zhang, Jie A1 - Kliem, Bernhard A1 - Török, Tibor A1 - Xing, Chen A1 - Zhou, Zhenjun A1 - Inhester, Bernd A1 - Ding, Mingde T1 - Initiation and early kinematic evolution of solar eruptions JF - The Astrophysical Journal N2 - We investigate the initiation and early evolution of 12 solar eruptions, including six active-region hot channel and six quiescent filament eruptions, which were well observed by the Solar Dynamics Observatory, as well as by the Solar Terrestrial Relations Observatory for the latter. The sample includes one failed eruption and 11 coronal mass ejections, with velocities ranging from 493 to 2140 km s(-1). A detailed analysis of the eruption kinematics yields the following main results. (1) The early evolution of all events consists of a slow-rise phase followed by a main-acceleration phase, the height-time profiles of which differ markedly and can be best fit, respectively, by a linear and an exponential function. This indicates that different physical processes dominate in these phases, which is at variance with models that involve a single process. (2) The kinematic evolution of the eruptions tends to be synchronized with the flare light curve in both phases. The synchronization is often but not always close. A delayed onset of the impulsive flare phase is found in the majority of the filament eruptions (five out of six). This delay and its trend to be larger for slower eruptions favor ideal MHD instability models. (3) The average decay index at the onset heights of the main acceleration is close to the threshold of the torus instability for both groups of events (although, it is based on a tentative coronal field model for the hot channels), suggesting that this instability initiates and possibly drives the main acceleration. KW - solar coronal mass ejections KW - stellar coronal mass ejections KW - solar storm Y1 - 2020 U6 - https://doi.org/10.3847/1538-4357/ab886a SN - 1055-6796 SN - 1476-3540 VL - 894 IS - 2 SP - 1 EP - 20 PB - Cambridge Scientific Publishers CY - Cambridge ER - TY - GEN A1 - García-Benito, Inés A1 - Quarti, Claudio A1 - Queloz, Valentin I. E. A1 - Hofstetter, Yvonne J. A1 - Becker-Koch, David A1 - Caprioglio, Pietro A1 - Neher, Dieter A1 - Orlandi, Simonetta A1 - Cavazzini, Marco A1 - Pozzi, Gianluca A1 - Even, Jacky A1 - Nazeeruddin, Mohammad Khaja A1 - Vaynzof, Yana A1 - Grancini, Giulia T1 - Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)(2)PbI4 and (Lf)(2)PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1421 KW - fluorinated organic spacer KW - 2D perovskites KW - phase transition KW - temperature dependence KW - excitonic materials Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-512420 SN - 1866-8372 ER - TY - JOUR A1 - García-Benito, Inés A1 - Quarti, Claudio A1 - Queloz, Valentin I. E. A1 - Hofstetter, Yvonne J. A1 - Becker-Koch, David A1 - Caprioglio, Pietro A1 - Neher, Dieter A1 - Orlandi, Simonetta A1 - Cavazzini, Marco A1 - Pozzi, Gianluca A1 - Even, Jacky A1 - Nazeeruddin, Mohammad Khaja A1 - Vaynzof, Yana A1 - Grancini, Giulia T1 - Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites JF - Frontiers in Chemistry N2 - Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)(2)PbI4 and (Lf)(2)PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors. KW - fluorinated organic spacer KW - 2D perovskites KW - phase transition KW - temperature dependence KW - excitonic materials Y1 - 2020 U6 - https://doi.org/10.3389/fchem.2019.00946 SN - 2296-2646 VL - 7 SP - 1 EP - 11 PB - Frontiers Media CY - Lausanne ER - TY - GEN A1 - Zhong, Yufei A1 - Causa, Martina A1 - Moore, Gareth John A1 - Krauspe, Philipp A1 - Xiao, Bo A1 - Günther, Florian A1 - Kublitski, Jonas A1 - BarOr, Eyal A1 - Zhou, Erjun A1 - Banerji, Natalie T1 - Sub-picosecond charge-transfer at near-zero driving force in polymer:non-fullerene acceptor blends and bilayers T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Organic photovoltaics based on non-fullerene acceptors (NFAs) show record efficiency of 16 to 17% and increased photovoltage owing to the low driving force for interfacial charge-transfer. However, the low driving force potentially slows down charge generation, leading to a tradeoff between voltage and current. Here, we disentangle the intrinsic charge-transfer rates from morphology-dependent exciton diffusion for a series of polymer:NFA systems. Moreover, we establish the influence of the interfacial energetics on the electron and hole transfer rates separately. We demonstrate that charge-transfer timescales remain at a few hundred femtoseconds even at near-zero driving force, which is consistent with the rates predicted by Marcus theory in the normal region, at moderate electronic coupling and at low re-organization energy. Thus, in the design of highly efficient devices, the energy offset at the donor:acceptor interface can be minimized without jeopardizing the charge-transfer rate and without concerns about a current-voltage tradeoff. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1422 KW - organic solar cell KW - electron-transfer KW - Donor-Acceptor (DA) interface KW - transfer dynamics KW - donor KW - seperation KW - efficiency KW - impact KW - energy KW - photovoltaics Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-511936 SN - 1866-8372 IS - 1 ER - TY - JOUR A1 - Zhong, Yufei A1 - Causa, Martina A1 - Moore, Gareth John A1 - Krauspe, Philipp A1 - Xiao, Bo A1 - Günther, Florian A1 - Kublitski, Jonas A1 - BarOr, Eyal A1 - Zhou, Erjun A1 - Banerji, Natalie T1 - Sub-picosecond charge-transfer at near-zero driving force in polymer:non-fullerene acceptor blends and bilayers JF - Nature Communications N2 - Organic photovoltaics based on non-fullerene acceptors (NFAs) show record efficiency of 16 to 17% and increased photovoltage owing to the low driving force for interfacial charge-transfer. However, the low driving force potentially slows down charge generation, leading to a tradeoff between voltage and current. Here, we disentangle the intrinsic charge-transfer rates from morphology-dependent exciton diffusion for a series of polymer:NFA systems. Moreover, we establish the influence of the interfacial energetics on the electron and hole transfer rates separately. We demonstrate that charge-transfer timescales remain at a few hundred femtoseconds even at near-zero driving force, which is consistent with the rates predicted by Marcus theory in the normal region, at moderate electronic coupling and at low re-organization energy. Thus, in the design of highly efficient devices, the energy offset at the donor:acceptor interface can be minimized without jeopardizing the charge-transfer rate and without concerns about a current-voltage tradeoff. KW - organic solar cell KW - electron-transfer KW - Donor-Acceptor (DA) interface KW - transfer dynamics KW - donor KW - seperation KW - efficiency KW - impact KW - energy KW - photovoltaics Y1 - 2020 U6 - https://doi.org/10.1038/s41467-020-14549-w SN - 2041-1723 VL - 11 IS - 1 SP - 1 EP - 10 PB - Nature Publishing Group UK CY - London ER - TY - GEN A1 - Caesar, Levke A1 - Rahmstorf, Stefan A1 - Feulner, Georg T1 - On the relationship between Atlantic meridional overturning circulation slowdown and global surface warming T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - According to established understanding, deep-water formation in the North Atlantic and Southern Ocean keeps the deep ocean cold, counter-acting the downward mixing of heat from the warmer surface waters in the bulk of the world ocean. Therefore, periods of strong Atlantic meridional overturning circulation (AMOC) are expected to coincide with cooling of the deep ocean and warming of the surface waters. It has recently been proposed that this relation may have reversed due to global warming, and that during the past decades a strong AMOC coincides with warming of the deep ocean and relative cooling of the surface, by transporting increasingly warmer waters downward. Here we present multiple lines of evidence, including a statistical evaluation of the observed global mean temperature, ocean heat content, and different AMOC proxies, that lead to the opposite conclusion: even during the current ongoing global temperature rise a strong AMOC warms the surface. The observed weakening of the AMOC has therefore delayed global surface warming rather than enhancing it. Social Media Abstract: The overturning circulation in the Atlantic Ocean has weakened in response to global warming, as predicted by climate models. Since it plays an important role in transporting heat, nutrients and carbon, a slowdown will affect global climate processes and the global mean temperature. Scientists have questioned whether this slowdown has worked to cool or warm global surface temperatures. This study analyses the overturning strength and global mean temperature evolution of the past decades and shows that a slowdown acts to reduce the global mean temperature. This is because a slower overturning means less water sinks into the deep ocean in the subpolar North Atlantic. As the surface waters are cold there, the sinking normally cools the deep ocean and thereby indirectly warms the surface, thus less sinking implies less surface warming and has a cooling effect. For the foreseeable future, this means that the slowing of the overturning will likely continue to slightly reduce the effect of the general warming due to increasing greenhouse gas concentrations. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1426 KW - Atlantic meridional overturning circulation KW - global surface warming KW - ocean heat uptake Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-512382 SN - 1866-8372 IS - 2 ER - TY - GEN A1 - Stolterfoht, Martin A1 - Grischek, Max A1 - Caprioglio, Pietro A1 - Wolff, Christian Michael A1 - Gutierrez-Partida, Emilio A1 - Peña-Camargo, Francisco A1 - Rothhardt, Daniel A1 - Zhang, Shanshan A1 - Raoufi, Meysam A1 - Wolansky, Jakob A1 - Abdi-Jalebi, Mojtaba A1 - Stranks, Samuel D. A1 - Albrecht, Steve A1 - Kirchartz, Thomas A1 - Neher, Dieter T1 - How to quantify the efficiency potential of neat perovskite films BT - Perovskite semiconductors with an implied efficiency exceeding 28% T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Perovskite photovoltaic (PV) cells have demonstrated power conversion efficiencies (PCE) that are close to those of monocrystalline silicon cells; however, in contrast to silicon PV, perovskites are not limited by Auger recombination under 1-sun illumination. Nevertheless, compared to GaAs and monocrystalline silicon PV, perovskite cells have significantly lower fill factors due to a combination of resistive and non-radiative recombination losses. This necessitates a deeper understanding of the underlying loss mechanisms and in particular the ideality factor of the cell. By measuring the intensity dependence of the external open-circuit voltage and the internal quasi-Fermi level splitting (QFLS), the transport resistance-free efficiency of the complete cell as well as the efficiency potential of any neat perovskite film with or without attached transport layers are quantified. Moreover, intensity-dependent QFLS measurements on different perovskite compositions allows for disentangling of the impact of the interfaces and the perovskite surface on the non-radiative fill factor and open-circuit voltage loss. It is found that potassium-passivated triple cation perovskite films stand out by their exceptionally high implied PCEs > 28%, which could be achieved with ideal transport layers. Finally, strategies are presented to reduce both the ideality factor and transport losses to push the efficiency to the thermodynamic limit. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1434 KW - non-radiative interface recombination KW - perovskite solar cells KW - photoluminescence Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-516622 SN - 1866-8372 IS - 17 ER - TY - JOUR A1 - Stolterfoht, Martin A1 - Grischek, Max A1 - Caprioglio, Pietro A1 - Wolff, Christian Michael A1 - Gutierrez-Partida, Emilio A1 - Peña-Camargo, Francisco A1 - Rothhardt, Daniel A1 - Zhang, Shanshan A1 - Raoufi, Meysam A1 - Wolansky, Jakob A1 - Abdi-Jalebi, Mojtaba A1 - Stranks, Samuel D. A1 - Albrecht, Steve A1 - Kirchartz, Thomas A1 - Neher, Dieter T1 - How to quantify the efficiency potential of neat perovskite films BT - Perovskite semiconductors with an implied efficiency exceeding 28% JF - Advanced Materials N2 - Perovskite photovoltaic (PV) cells have demonstrated power conversion efficiencies (PCE) that are close to those of monocrystalline silicon cells; however, in contrast to silicon PV, perovskites are not limited by Auger recombination under 1-sun illumination. Nevertheless, compared to GaAs and monocrystalline silicon PV, perovskite cells have significantly lower fill factors due to a combination of resistive and non-radiative recombination losses. This necessitates a deeper understanding of the underlying loss mechanisms and in particular the ideality factor of the cell. By measuring the intensity dependence of the external open-circuit voltage and the internal quasi-Fermi level splitting (QFLS), the transport resistance-free efficiency of the complete cell as well as the efficiency potential of any neat perovskite film with or without attached transport layers are quantified. Moreover, intensity-dependent QFLS measurements on different perovskite compositions allows for disentangling of the impact of the interfaces and the perovskite surface on the non-radiative fill factor and open-circuit voltage loss. It is found that potassium-passivated triple cation perovskite films stand out by their exceptionally high implied PCEs > 28%, which could be achieved with ideal transport layers. Finally, strategies are presented to reduce both the ideality factor and transport losses to push the efficiency to the thermodynamic limit. KW - non-radiative interface recombination KW - perovskite solar cells KW - photoluminescence Y1 - 2020 U6 - https://doi.org/10.1002/adma.202000080 SN - 0935-9648 SN - 1521-4095 VL - 32 IS - 17 SP - 1 EP - 10 PB - Wiley-VCH CY - Weinheim ER - TY - GEN A1 - Mohammady, M. Hamed A1 - Auffèves, Alexia A1 - Anders, Janet T1 - Energetic footprints of irreversibility in the quantum regime T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - In classical thermodynamic processes the unavoidable presence of irreversibility, quantified by the entropy production, carries two energetic footprints: the reduction of extractable work from the optimal, reversible case, and the generation of a surplus of heat that is irreversibly dissipated to the environment. Recently it has been shown that in the quantum regime an additional quantum irreversibility occurs that is linked to decoherence into the energy basis. Here we employ quantum trajectories to construct distributions for classical heat and quantum heat exchanges, and show that the heat footprint of quantum irreversibility differs markedly from the classical case. We also quantify how quantum irreversibility reduces the amount of work that can be extracted from a state with coherences. Our results show that decoherence leads to both entropic and energetic footprints which both play an important role in the optimization of controlled quantum operations at low temperature. In classical thermodynamics irreversibility occurs whenever a non-thermal system is brought into contact with a thermal environment. Using quantum trajectories the authors here establish two energetic footprints of quantum irreversible processes, and find that while quantum irreversibility leads to the occurrence of a quantum heat and a reduction of work production, the two are not linked in the same manner as the classical laws of thermodynamics would dictate. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1435 KW - entropy production KW - quantum mechanics KW - thermodynamics Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-516766 SN - 1866-8372 IS - 1 ER - TY - JOUR A1 - Mohammady, M. Hamed A1 - Auffèves, Alexia A1 - Anders, Janet T1 - Energetic footprints of irreversibility in the quantum regime JF - Communications Physics N2 - In classical thermodynamic processes the unavoidable presence of irreversibility, quantified by the entropy production, carries two energetic footprints: the reduction of extractable work from the optimal, reversible case, and the generation of a surplus of heat that is irreversibly dissipated to the environment. Recently it has been shown that in the quantum regime an additional quantum irreversibility occurs that is linked to decoherence into the energy basis. Here we employ quantum trajectories to construct distributions for classical heat and quantum heat exchanges, and show that the heat footprint of quantum irreversibility differs markedly from the classical case. We also quantify how quantum irreversibility reduces the amount of work that can be extracted from a state with coherences. Our results show that decoherence leads to both entropic and energetic footprints which both play an important role in the optimization of controlled quantum operations at low temperature. In classical thermodynamics irreversibility occurs whenever a non-thermal system is brought into contact with a thermal environment. Using quantum trajectories the authors here establish two energetic footprints of quantum irreversible processes, and find that while quantum irreversibility leads to the occurrence of a quantum heat and a reduction of work production, the two are not linked in the same manner as the classical laws of thermodynamics would dictate. KW - entropy production KW - quantum mechanics KW - thermodynamics Y1 - 2020 U6 - https://doi.org/10.1038/s42005-020-0356-9 SN - 2399-3650 VL - 3 IS - 1 SP - 1 EP - 14 PB - Springer Nature CY - London ER - TY - GEN A1 - Horton, Benjamin P. A1 - Khan, Nicole S. A1 - Cahill, Niamh A1 - Lee, Janice S. H. A1 - Shaw, Timothy A. A1 - Garner, Andra J. A1 - Kemp, Andrew C. A1 - Engelhart, Simon E. A1 - Rahmstorf, Stefan T1 - Estimating global mean sea-level rise and its uncertainties by 2100 and 2300 from an expert survey T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Sea-level rise projections and knowledge of their uncertainties are vital to make informed mitigation and adaptation decisions. To elicit projections from members of the scientific community regarding future global mean sea-level (GMSL) rise, we repeated a survey originally conducted five years ago. Under Representative Concentration Pathway (RCP) 2.6, 106 experts projected a likely (central 66% probability) GMSL rise of 0.30-0.65 m by 2100, and 0.54-2.15 m by 2300, relative to 1986-2005. Under RCP 8.5, the same experts projected a likely GMSL rise of 0.63-1.32 m by 2100, and 1.67-5.61 m by 2300. Expert projections for 2100 are similar to those from the original survey, although the projection for 2300 has extended tails and is higher than the original survey. Experts give a likelihood of 42% (original survey) and 45% (current survey) that under the high-emissions scenario GMSL rise will exceed the upper bound (0.98 m) of the likely range estimated by the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, which is considered to have an exceedance likelihood of 17%. Responses to open-ended questions suggest that the increases in upper-end estimates and uncertainties arose from recent influential studies about the impact of marine ice cliff instability on the meltwater contribution to GMSL rise from the Antarctic Ice Sheet. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1437 KW - projections KW - Greenland KW - consequences KW - climate Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-516788 SN - 1866-8372 IS - 1 ER - TY - JOUR A1 - Horton, Benjamin P. A1 - Khan, Nicole S. A1 - Cahill, Niamh A1 - Lee, Janice S. H. A1 - Shaw, Timothy A. A1 - Garner, Andra J. A1 - Kemp, Andrew C. A1 - Engelhart, Simon E. A1 - Rahmstorf, Stefan T1 - Estimating global mean sea-level rise and its uncertainties by 2100 and 2300 from an expert survey JF - npj Climate and Atmospheric Science N2 - Sea-level rise projections and knowledge of their uncertainties are vital to make informed mitigation and adaptation decisions. To elicit projections from members of the scientific community regarding future global mean sea-level (GMSL) rise, we repeated a survey originally conducted five years ago. Under Representative Concentration Pathway (RCP) 2.6, 106 experts projected a likely (central 66% probability) GMSL rise of 0.30-0.65 m by 2100, and 0.54-2.15 m by 2300, relative to 1986-2005. Under RCP 8.5, the same experts projected a likely GMSL rise of 0.63-1.32 m by 2100, and 1.67-5.61 m by 2300. Expert projections for 2100 are similar to those from the original survey, although the projection for 2300 has extended tails and is higher than the original survey. Experts give a likelihood of 42% (original survey) and 45% (current survey) that under the high-emissions scenario GMSL rise will exceed the upper bound (0.98 m) of the likely range estimated by the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, which is considered to have an exceedance likelihood of 17%. Responses to open-ended questions suggest that the increases in upper-end estimates and uncertainties arose from recent influential studies about the impact of marine ice cliff instability on the meltwater contribution to GMSL rise from the Antarctic Ice Sheet. KW - projections KW - Greenland KW - consequences KW - climate Y1 - 2020 U6 - https://doi.org/10.1038/s41612-020-0121-5 SN - 2397-3722 VL - 3 IS - 1 SP - 1 EP - 8 PB - Springer Nature CY - London ER - TY - JOUR A1 - Schaffenroth, Veronika A1 - Casewell, Sarah L. A1 - Schneider, D. A1 - Kilkenny, David A1 - Geier, Stephan A1 - Heber, Ulrich A1 - Irrgang, Andreas A1 - Przybilla, Norbert A1 - Marsh, Thomas R. A1 - Littlefair, Stuart P. A1 - Dhillon, Vik S. T1 - A quantitative in-depth analysis of the prototype sdB plus BD system SDSS J08205+0008 revisited in the Gaia era JF - Monthly notices of the Royal Astronomical Society N2 - Subdwarf B stars are core-helium-burning stars located on the extreme horizontal branch (EHB). Extensive mass loss on the red giant branch is necessary to form them. It has been proposed that substellar companions could lead to the required mass loss when they are engulfed in the envelope of the red giant star. J08205+0008 was the first example of a hot subdwarf star with a close, substellar companion candidate to be found. Here, we perform an in-depth re-analysis of this important system with much higher quality data allowing additional analysis methods. From the higher resolution spectra obtained with ESO-VLT/XSHOOTER, we derive the chemical abundances of the hot subdwarf as well as its rotational velocity. Using the Gaia parallax and a fit to the spectral energy distribution in the secondary eclipse, tight constraints to the radius of the hot subdwarf are derived. From a long-term photometric campaign, we detected a significant period decrease of -3.2(8) x 10(-12) dd(-1). This can be explained by the non-synchronized hot subdwarf star being spun up by tidal interactions forcing it to become synchronized. From the rate of period decrease we could derive the synchronization time-scale to be 4 Myr, much smaller than the lifetime on EHB. By combining all different methods, we could constrain the hot subdwarf to a mass of 0.39-0.50 M-circle dot and a radius of R-sdB = 0.194 +/- 0.008 R-circle dot, and the companion to 0.061-0.071 M-circle dot with a radius of R-comp = 0.092 +/- 0.005 R-circle dot, below the hydrogen-burning limit. We therefore confirm that the companion is most likely a massive brown dwarf. KW - stars: abundances KW - stars: atmospheres KW - stars: fundamental parameters KW - stars: horizontal branch KW - stars: low-mass KW - subdwarfs Y1 - 2020 U6 - https://doi.org/10.1093/mnras/staa3661 SN - 0035-8711 SN - 1365-2966 VL - 501 IS - 3 SP - 3847 EP - 3870 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Mansour, Ahmed E. A1 - Lungwitz, Dominique A1 - Schultz, Thorsten A1 - Arvind, Malavika A1 - Valencia, Ana M. A1 - Cocchi, Caterina A1 - Opitz, Andreas A1 - Neher, Dieter A1 - Koch, Norbert T1 - The optical signatures of molecular-doping induced polarons in poly(3-hexylthiophene-2,5-diyl) BT - individual polymer chains versus aggregates JF - Journal of materials chemistry : C, Materials for optical and electronic devices N2 - Optical absorption spectroscopy is a key method to investigate doped conjugated polymers and to characterize the doping-induced charge carriers, i.e., polarons. For prototypical poly(3-hexylthiophene-2,5-diyl) (P3HT), the absorption intensity of molecular dopant induced polarons is widely used to estimate the carrier density and the doping efficiency, i.e., the number of polarons formed per dopant molecule. However, the dependence of the polaron-related absorption features on the structure of doped P3HT, being either aggregates or separated individual chains, is not comprehensively understood in contrast to the optical absorption features of neutral P3HT. In this work, we unambiguously differentiate the optical signatures of polarons on individual P3HT chains and aggregates in solution, notably the latter exhibiting the same shape as aggregates in solid thin films. This is enabled by employing tris(pentafluorophenyl)borane (BCF) as dopant, as this dopant forms only ion pairs with P3HT and no charge transfer complexes, and BCF and its anion have no absorption in the spectral region of P3HT polarons. Polarons on individual chains exhibit absorption peaks at 1.5 eV and 0.6 eV, whereas in aggregates the high-energy peak is split into a doublet 1.3 eV and 1.65 eV, and the low-energy peak is shifted below 0.5 eV. The dependence of the fraction of solvated individual chains versus aggregates on absolute solution concentration, dopant concentration, and temperature is elucidated, and we find that aggregates predominate in solution under commonly used processing conditions. Aggregates in BCF-doped P3HT solution can be effectively removed upon simple filtering. From varying the filter pore size (down to 200 nm) and thin film morphology characterization with scanning force microscopy we reveal the aggregates' size dependence on solution absolute concentration and dopant concentration. Furthermore, X-ray photoelectron spectroscopy shows that the dopant loading in aggregates is higher than for individual P3HT chains. The results of this study help understanding the impact of solution pre-aggregation on thin film properties of molecularly doped P3HT, and highlight the importance of considering such aggregation for other doped conjugated polymers in general. Y1 - 2020 U6 - https://doi.org/10.1039/c9tc06509a SN - 2050-7526 SN - 2050-7534 VL - 8 IS - 8 SP - 2870 EP - 2879 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Zu, Fengshuo A1 - Schultz, Thorsten A1 - Wolff, Christian Michael A1 - Shin, Dongguen A1 - Frohloff, Lennart A1 - Neher, Dieter A1 - Amsalem, Patrick A1 - Koch, Norbert T1 - Position-locking of volatile reaction products by atmosphere and capping layers slows down photodecomposition of methylammonium lead triiodide perovskite JF - RSC Advances N2 - The remarkable progress of metal halide perovskites in photovoltaics has led to the power conversion efficiency approaching 26%. However, practical applications of perovskite-based solar cells are challenged by the stability issues, of which the most critical one is photo-induced degradation. Bare CH3NH3PbI3 perovskite films are known to decompose rapidly, with methylammonium and iodine as volatile species and residual solid PbI2 and metallic Pb, under vacuum under white light illumination, on the timescale of minutes. We find, in agreement with previous work, that the degradation is non-uniform and proceeds predominantly from the surface, and that illumination under N-2 and ambient air (relative humidity 20%) does not induce substantial degradation even after several hours. Yet, in all cases the release of iodine from the perovskite surface is directly identified by X-ray photoelectron spectroscopy. This goes in hand with a loss of organic cations and the formation of metallic Pb. When CH3NH3PbI3 films are covered with a few nm thick organic capping layer, either charge selective or non-selective, the rapid photodecomposition process under ultrahigh vacuum is reduced by more than one order of magnitude, and becomes similar in timescale to that under N-2 or air. We conclude that the light-induced decomposition reaction of CH3NH3PbI3, leading to volatile methylammonium and iodine, is largely reversible as long as these products are restrained from leaving the surface. This is readily achieved by ambient atmospheric pressure, as well as a thin organic capping layer even under ultrahigh vacuum. In addition to explaining the impact of gas pressure on the stability of this perovskite, our results indicate that covalently "locking" the position of perovskite components at the surface or an interface should enhance the overall photostability. Y1 - 2020 U6 - https://doi.org/10.1039/d0ra03572f SN - 2046-2069 VL - 10 IS - 30 SP - 17534 EP - 17542 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Samson, Stephanie A1 - Rech, Jeromy A1 - Perdigón-Toro, Lorena A1 - Peng, Zhengxing A1 - Shoaee, Safa A1 - Ade, Harald A1 - Neher, Dieter A1 - Stolterfoht, Martin A1 - You, Wei T1 - Organic solar cells with large insensitivity to donor polymer molar mass across all acceptor classes JF - ACS applied polymer materials N2 - Donor polymer number-average molar mass (M-n) has long been known to influence organic photovoltaic (OPV) performance via changes in both the polymer properties and the resulting bulk heterojunction morphology. The exact nature of these M-n effects varies from system to system, although there is generally some intermediate M-n that results in optimal performance. Interestingly, our earlier work with the difluorobenzotriazole (FTAZ)-based donor polymer, paired with either N2200 (polymer acceptor) or PC61BM (fullerene acceptor), PcBm demonstrated <10% variation in power conversion efficiency and a consistent morphology over a large span of M-n (30 kg/mol to over 100 kg/mol). Would such insensitivity to polymer M-n still hold true when prevailing small molecular acceptors were used with FTAZ? To answer this question, we explored the impact of FTAZ on OPVs with ITIC, a high-performance small-molecule fused-ring electron acceptor (FREA). By probing the photovoltaic characteristics of the resulting OPVs, we show that a similar FTAZ mn insensitivity is also found in the FTAZ:ITIC system. This study highlights a single-donor polymer which, when paired with an archetypal fullerene, polymer, and FREA, results in systems that are largely insensitive to donor M. Our results may have implications in polymer batch-to-batch reproducibility, in particular, relaxing the need for tight M-n control during synthesis. KW - polymer solar cells KW - conjugated polymers KW - fullerenes KW - fluorination KW - molecular weight KW - non-fullerene acceptors KW - power conversion efficiency Y1 - 2020 U6 - https://doi.org/10.1021/acsapm.0c01041 SN - 2637-6105 VL - 2 IS - 11 SP - 5300 EP - 5308 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Fulmer, Leah M. A1 - Gallagher, John S. A1 - Hamann, Wolf-Rainer A1 - Oskinova, Lida A1 - Ramachandran, Varsha T1 - Testing massive star evolution, star-formation history, and feedback at low metallicity BT - photometric analysis of OB stars in the SMC Wing JF - Astronomy and astrophysics : an international weekly journal N2 - Context. The supergiant ionized shell SMC-SGS 1 (DEM 167), which is located in the outer Wing of the Small Magellanic Cloud (SMC), resembles structures that originate from an energetic star-formation event and later stimulate star formation as they expand into the ambient medium. However, stellar populations within and surrounding SMC-SGS 1 tell a different story. Aims. We present a photometric study of the stellar population encompassed by SMC-SGS 1 in order to trace the history of such a large structure and its potential influence on star formation within the low-density, low-metallicity environment of the SMC. Methods. For a stellar population that is physically associated with SMC-SGS 1, we combined near-ultraviolet (NUV) photometry from the Galaxy Evolution Explorer with archival optical (V-band) photometry from the ESO Danish 1.54 m Telescope. Given their colors and luminosities, we estimated stellar ages and masses by matching observed photometry to theoretical stellar isochrone models. Results. We find that the investigated region supports an active, extended star-formation event spanning similar to 25-40 Myr ago, as well as continued star formation into the present. Using a standard initial mass function, we infer a lower bound on the stellar mass from this period of similar to 3 x 10(4) M-circle dot, corresponding to a star-formation intensity of similar to 6 x 10(-3) M-circle dot kpc(-2) yr(-1). Conclusions. The spatial and temporal distributions of young stars encompassed by SMC-SGS 1 imply a slow, consistent progression of star formation over millions of years. Ongoing star formation, both along the edge and interior to SMC-SGS 1, suggests a combined stimulated and stochastic mode of star formation within the SMC Wing. We note that a slow expansion of the shell within this low-density environment may preserve molecular clouds within the volume of the shell, leaving them to form stars even after nearby stellar feedback expels local gas and dust. KW - galaxies KW - stellar content KW - stars KW - formation KW - individual KW - Small KW - Magellanic Cloud Y1 - 2020 U6 - https://doi.org/10.1051/0004-6361/201834314 SN - 0004-6361 SN - 1432-0746 VL - 633 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Jay, Raphael M. A1 - Eckert, Sebastian A1 - Mitzner, Rolf A1 - Fondell, Mattis A1 - Föhlisch, Alexander T1 - Quantitative evaluation of transient valence orbital occupations in a 3d transition metal complex as seen from the metal and ligand perspective JF - Chemical physics letters N2 - It is demonstrated for the case of photo-excited ferrocyanide how time-resolved soft X-ray absorption spectroscopy in transmission geometry at the ligand K-edge and metal L-3-edge provides quantitatively equivalent valence electronic structure information, where signatures of photo-oxidation are assessed locally at the metal as well as the ligand. This allows for a direct and independent quantification of the number of photo-oxidized molecules at two soft X-ray absorption edges highlighting the sensitivity of X-ray absorption spectroscopy to the valence orbital occupation of 3d transition metal complexes throughout the soft X-ray range. KW - iron cyanides KW - photochemistry KW - soft X-ray absorption Y1 - 2020 U6 - https://doi.org/10.1016/j.cplett.2020.137681 SN - 0009-2614 SN - 1873-4448 VL - 754 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Albrecht, Torsten A1 - Winkelmann, Ricarda A1 - Levermann, Anders T1 - Glacial-cycle simulations of the Antarctic Ice Sheet with the Parallel Ice Sheet Model (PISM) BT - part 2: parameter ensemble analysis JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union N2 - The Parallel Ice Sheet Model (PISM) is applied to the Antarctic Ice Sheet over the last two glacial cycles (approximate to 210 000 years) with a resolution of 16 km. An ensemble of 256 model runs is analyzed in which four relevant model parameters have been systematically varied using full-factorial parameter sampling. Parameters and plausible parameter ranges have been identified in a companion paper (Albrecht et al., 2020) and are associated with ice dynamics, climatic forcing, basal sliding and bed deformation and represent distinct classes of model uncertainties. The model is scored against both modern and geologic data, including reconstructed grounding-line locations, elevation-age data, ice thickness, surface velocities and uplift rates. An aggregated score is computed for each ensemble member that measures the overall model-data misfit, including measurement uncertainty in terms of a Gaussian error model (Briggs and Tarasov, 2013). The statistical method used to analyze the ensemble simulation results follows closely the simple averaging method described in Pollard et al. (2016). This analysis reveals clusters of best-fit parameter combinations, and hence a likely range of relevant model and boundary parameters, rather than individual best-fit parameters. The ensemble of reconstructed histories of Antarctic Ice Sheet volumes provides a score-weighted likely range of sea-level contributions since the Last Glacial Maximum (LGM) of 9.4 +/- 4.1m (or 6.5 +/- 2.0 x 10(6) km(3)), which is at the upper range of most previous studies. The last deglaciation occurs in all ensemble simulations after around 12 000 years before present and hence after the meltwater pulse 1A (MWP1a). Our ensemble analysis also provides an estimate of parametric uncertainty bounds for the present-day state that can be used for PISM projections of future sea-level contributions from the Antarctic Ice Sheet. Y1 - 2020 U6 - https://doi.org/10.5194/tc-14-633-2020 SN - 1994-0416 SN - 1994-0424 VL - 14 IS - 2 SP - 633 EP - 656 PB - Copernicus Publ. CY - Göttingen 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 - JOUR A1 - Devarapalli, Shanti Priya A1 - Jagirdar, Rukmini A1 - Prasad, Manjunath R. A1 - Thomas, Vineet S. A1 - Ahmed, Syed Aslam A1 - Gralapally, Raghavendra A1 - Das, Jesmin Permala Lohy T1 - Comprehensive study of a neglected contact binary TYC 5532-1333-1 JF - Monthly notices of the Royal Astronomical Society N2 - A comprehensive photometric and spectroscopic analysis of the variable TYC 5532-1333-1 (TYC) along with an investigation of its orbital period variation is presented for the first time. The B- and V-band photometric study indicates that TYC is an intermediate contact binary with degree of contact and mass ratio of 34 per cent and similar to 0.24, respectively. The derived equivalent widths from the spectroscopic study of H alpha and Na-I lines reveal phase-dependent variation and mutual correlation. Using the available times of minimum light, an investigation of orbital period variation shows a long-term decrease at a rate of 3.98 x 10(-6) d yr(-1). Expected causes for such decline in the orbital period could be angular momentum loss and a quasi-sinusoidal variation due to light-time effect probably caused by a third-body companion. The minimum mass of the third body (M-3) was derived to be 0.65 M-circle dot. Our presented study is an attempt to evaluate and understand the evolutionary state of above-mentioned neglected contact binary. KW - line: profiles KW - methods: observational KW - techniques: photometric KW - techniques: spectroscopic KW - stars: activity KW - binaries: eclipsing Y1 - 2019 U6 - https://doi.org/10.1093/mnras/staa031 SN - 0035-8711 SN - 1365-2966 VL - 493 IS - 2 SP - 1565 EP - 1573 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Tokmoldin, Nurlan A1 - Hosseini, Seyed Mehrdad A1 - Raoufi, Meysam A1 - Phuong, Le Quang A1 - Sandberg, Oskar J. A1 - Guan, Huilan A1 - Zou, Yingping A1 - Neher, Dieter A1 - Shoaee, Safa T1 - Extraordinarily long diffusion length in PM6:Y6 organic solar cells JF - Journal of materials chemistry : A, materials for energy and sustainability N2 - The PM6:Y6 bulk-heterojunction (BHJ) blend system achieves high short-circuit current (J(SC)) values in thick photovoltaic junctions. Here we analyse these solar cells to understand the observed independence of the short-circuit current upon photoactive layer thickness. We employ a range of optoelectronic measurements and analyses, including Mott-Schottky analysis, CELIV, photoinduced absorption spectroscopy, mobility measurements and simulations, to conclude that, the invariant photocurrent for the devices with different active layer thicknesses is associated with the Y6's diffusion length exceeding 300 nm in case of a 300 nm thick cell. This is despite unintentional doping that occurs in PM6 and the associated space-charge effect, which is expected to be even more profound upon photogeneration. This extraordinarily long diffusion length - which is an order of magnitude larger than typical values for organics - dominates transport in the flat-band region of thick junctions. Our work suggests that the performance of the doped PM6:Y6 organic solar cells resembles that of inorganic devices with diffusion transport playing a pivotal role. Ultimately, this is expected to be a key requirement for the fabrication of efficient, high-photocurrent, thick organic solar cells. Y1 - 2020 U6 - https://doi.org/10.1039/d0ta03016c SN - 2050-7488 SN - 2050-7496 VL - 8 IS - 16 SP - 7854 EP - 7860 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Hajduk, Marcin A1 - Todt, Helge Tobias A1 - Hamann, Wolf-Rainer A1 - Borek, Karolina A1 - van Hoof, Peter A. M. A1 - Zijlstra, Albert A. T1 - The cooling-down central star of the planetary nebula SwSt 1 BT - a late thermal pulse in a massive post-AGB star? JF - Monthly notices of the Royal Astronomical Society N2 - SwSt 1 (PN G001.5-06.7) is a bright and compact planetary nebula containing a late [WC]-type central star. Previous studies suggested that the nebular and stellar lines are slowly changing with time. We studied new and archival optical and ultraviolet spectra of the object. The [O III] 4959 and 5007 angstrom to H beta line flux ratios decreased between about 1976 and 1997/2015. The stellar spectrum also shows changes between these epochs. We modelled the stellar and nebular spectra observed at different epochs. The analyses indicate a drop of the stellar temperature from about 42 kK to 40.5 kK between 1976 and 1993. We do not detect significant changes between 1993 and 2015. The observations show that the star performed a loop in the H-R diagram. This is possible when a shell source is activated during its post-AGB evolution. We infer that a late thermal pulse (LTP) experienced by a massive post-AGB star can explain the evolution of the central star. Such a star does not expand significantly as the result of the LTP and does not became a born-again red giant. However, the released energy can remove the tiny H envelope of the star. KW - stars: AGB and post-AGB KW - stars: atmospheres KW - stars: evolution KW - planetary KW - nebulae: general KW - planetary nebulae: individual: SwSt1 Y1 - 2020 U6 - https://doi.org/10.1093/mnras/staa2274 SN - 0035-8711 SN - 1365-2966 VL - 498 IS - 1 SP - 1205 EP - 1220 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Dineva, Ekaterina Ivanova A1 - Verma, Meetu A1 - Gonzalez Manrique, Sergio Javier A1 - Schwartz, Pavol A1 - Denker, Carsten T1 - Cloud model inversions of strong chromospheric absorption lines using principal component analysis JF - Astronomische Nachrichten = Astronomical notes N2 - High-resolution spectroscopy of strong chromospheric absorption lines delivers nowadays several millions of spectra per observing day, when using fast scanning devices to cover large regions on the solar surface. Therefore, fast and robust inversion schemes are needed to explore the large data volume. Cloud model (CM) inversions of the chromospheric H alpha line are commonly employed to investigate various solar features including filaments, prominences, surges, jets, mottles, and (macro-) spicules. The choice of the CM was governed by its intuitive description of complex chromospheric structures as clouds suspended above the solar surface by magnetic fields. This study is based on observations of active region NOAA 11126 in H alpha, which were obtained November 18-23, 2010 with the echelle spectrograph of the vacuum tower telescope at the Observatorio del Teide, Spain. Principal component analysis reduces the dimensionality of spectra and conditions noise-stripped spectra for CM inversions. Modeled H alpha intensity and contrast profiles as well as CM parameters are collected in a database, which facilitates efficient processing of the observed spectra. Physical maps are computed representing the line-core and continuum intensity, absolute contrast, equivalent width, and Doppler velocities, among others. Noise-free spectra expedite the analysis of bisectors. The data processing is evaluated in the context of "big data," in particular with respect to automatic classification of spectra. KW - sun KW - activity - sun KW - atmosphere - sun KW - chromosphere - methods KW - data KW - analysis - techniques KW - spectroscopic - astronomical databases KW - miscellaneous Y1 - 2020 U6 - https://doi.org/10.1002/asna.202013652 SN - 0004-6337 SN - 1521-3994 VL - 341 IS - 1 SP - 64 EP - 78 PB - Wiley-VCH Verl. CY - Berlin ER - TY - JOUR A1 - Alexoudi, Xanthippi A1 - Mallonn, Matthias A1 - Keles, Engin A1 - Poppenhäger, Katja A1 - von Essen, Carolina A1 - Strassmeier, Klaus T1 - Role of the impact parameter in exoplanet transmission spectroscopy JF - Astronomy and astrophysics : an international weekly journal N2 - Context Transmission spectroscopy is a promising tool for the atmospheric characterization of transiting exoplanets. Because the planetary signal is faint, discrepancies have been reported regarding individual targets. Aims We investigate the dependence of the estimated transmission spectrum on deviations of the orbital parameters of the star-planet system that are due to the limb-darkening effects of the host star. We describe how the uncertainty on the orbital parameters translates into an uncertainty on the planetary spectral slope. Methods We created synthetic transit light curves in seven different wavelength bands, from the near-ultraviolet to the near-infrared, and fit them with transit models parameterized by fixed deviating values of the impact parameter b. First, we performed a qualitative study to illustrate the effect by presenting the changes in the transmission spectrum slope with different deviations of b. Then, we quantified these variations by creating an error envelope (for centrally transiting, off-center, and grazing systems) based on a derived typical uncertainty on b from the literature. Finally, we compared the variations in the transmission spectra for different spectral types of host stars. Results Our simulations show a wavelength-dependent offset that is more pronounced at the blue wavelengths where the limb-darkening effect is stronger. This offset introduces a slope in the planetary transmission spectrum that becomes steeper with increasing b values. Variations of b by positive or negative values within its uncertainty interval introduce positive or negative slopes, thus the formation of an error envelope. The amplitude from blue optical to near-infrared wavelength for a typical uncertainty on b corresponds to one atmospheric pressure scale height and more. This impact parameter degeneracy is confirmed for different host types; K stars present prominently steeper slopes, while M stars indicate features at the blue wavelengths. Conclusions We demonstrate that transmission spectra can be hard to interpret, basically because of the limitations in defining a precise impact parameter value for a transiting exoplanet. This consequently limits a characterization of its atmosphere. KW - planets and satellites: atmospheres KW - planets and satellites: gaseous KW - planets Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-605378 SN - 0004-6361 SN - 1432-0746 VL - 640 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Yochelis, Arik A1 - Beta, Carsten A1 - Gov, Nir S. T1 - Excitable solitons BT - annihilation, crossover, and nucleation of pulses in mass-conserving activator-inhibitor media JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Excitable pulses are among the most widespread dynamical patterns that occur in many different systems, ranging from biological cells to chemical reactions and ecological populations. Traditionally, the mutual annihilation of two colliding pulses is regarded as their prototypical signature. Here we show that colliding excitable pulses may exhibit solitonlike crossover and pulse nucleation if the system obeys a mass conservation constraint. In contrast to previous observations in systems without mass conservation, these alternative collision scenarios are robustly observed over a wide range of parameters. We demonstrate our findings using a model of intracellular actin waves since, on time scales of wave propagations over the cell scale, cells obey conservation of actin monomers. The results provide a key concept to understand the ubiquitous occurrence of actin waves in cells, suggesting why they are so common, and why their dynamics is robust and long-lived. Y1 - 2020 U6 - https://doi.org/10.1103/PhysRevE.101.022213 SN - 2470-0045 SN - 2470-0053 VL - 101 IS - 2 PB - American Physical Society CY - Melville, NY ER - TY - JOUR A1 - Foster, Mary Grace A1 - Poppenhäger, Katja A1 - Alvarado-Gómez, Julián David A1 - Schmitt, Jürgen T1 - The corona of GJ 1151 in the context of star-planet interaction JF - Monthly notices of the Royal Astronomical Society N2 - The low-mass star GJ 1151 has been reported to display variable low-frequency radio emission, which has been interpreted as a signpost of coronal star-planet interactions with an unseen exoplanet. Here we report the first X-ray detection of GJ 1151's corona based on the XMM-Newton data. We find that the star displays a small flare during the X-ray observation. Averaged over the observation, we detect the star with a low coronal temperature of 1.6 MK and an X-ray luminosity of L-X = 5.5 x 10(26) erg s(-1). During the quiescent time periods excluding the flare, the star remains undetected with an upper limit of L-X,L- qui <= 3.7 x 10(26) erg s(-1). This is compatible with the coronal assumptions used in a recently published model for a star-planet interaction origin of the observed radio signals from this star. KW - planet KW - star interactions KW - stars: coronae KW - X-rays: individual: GJ 1151 Y1 - 2020 U6 - https://doi.org/10.1093/mnras/staa1982 SN - 0035-8711 SN - 1365-2966 VL - 497 IS - 1 SP - 1015 EP - 1019 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Vinke, Kira A1 - Gabrysch, Sabine A1 - Paoletti, Emanuela A1 - Rockström, Johan A1 - Schellnhuber, Hans Joachim T1 - Corona and the climate BT - a comparison of two emergencies JF - Global sustainability N2 - Lessons from the corona crisis can help manage the even more daunting challenge of anthropogenic global warming. KW - adaptation and mitigation KW - ecology and biodiversity KW - human behaviour KW - natural resources (biological and non-biological) KW - policies KW - politics KW - and governance Y1 - 2020 U6 - https://doi.org/10.1017/sus.2020.20 SN - 2059-4798 VL - 3 PB - Cambridge Univ. Press CY - Cambridge ER - TY - JOUR A1 - Emanuel, Marc D. A1 - Cherstvy, Andrey G. A1 - Metzler, Ralf A1 - Gompper, Gerhard T1 - Buckling transitions and soft-phase invasion of two-component icosahedral shells JF - Physical review / publ. by The American Physical Society. E, Statistical, nonlinear, and soft matter physics N2 - What is the optimal distribution of two types of crystalline phases on the surface of icosahedral shells, such as of many viral capsids? We here investigate the distribution of a thin layer of soft material on a crystalline convex icosahedral shell. We demonstrate how the shapes of spherical viruses can be understood from the perspective of elasticity theory of thin two-component shells. We develop a theory of shape transformations of an icosahedral shell upon addition of a softer, but still crystalline, material onto its surface. We show how the soft component "invades" the regions with the highest elastic energy and stress imposed by the 12 topological defects on the surface. We explore the phase diagram as a function of the surface fraction of the soft material, the shell size, and the incommensurability of the elastic moduli of the rigid and soft phases. We find that, as expected, progressive filling of the rigid shell by the soft phase starts from the most deformed regions of the icosahedron. With a progressively increasing soft-phase coverage, the spherical segments of domes are filled first (12 vertices of the shell), then the cylindrical segments connecting the domes (30 edges) are invaded, and, ultimately, the 20 flat faces of the icosahedral shell tend to be occupied by the soft material. We present a detailed theoretical investigation of the first two stages of this invasion process and develop a model of morphological changes of the cone structure that permits noncircular cross sections. In conclusion, we discuss the biological relevance of some structures predicted from our calculations, in particular for the shape of viral capsids. Y1 - 2020 U6 - https://doi.org/10.1103/PhysRevE.102.062104 SN - 2470-0045 SN - 2470-0053 SN - 2470-0061 SN - 1538-4519 VL - 102 IS - 6 PB - Woodbury CY - New York ER - TY - JOUR A1 - Mishurova, Tatiana A1 - Bruno, Giovanni A1 - Evsevleev, Sergei A1 - Sevostianov, Igor T1 - Determination of macroscopic stress from diffraction experiments BT - a critical discussion JF - Journal of applied physics N2 - The paper is motivated by some inconsistencies and contradictions present in the literature on the calculation of the so-called diffraction elastic constants. In an attempt at unifying the views that the two communities of Materials Science and Mechanics of Materials have on the subject, we revisit and define the terminology used in the field. We also clarify the limitations of the commonly used approaches and show that a unified methodology is also applicable to textured materials with a nearly arbitrary grain shape. We finally compare the predictions based on this methodology with experimental data obtained by in situ synchrotron radiation diffraction on additively manufactured Ti-6Al-4V alloy. We show that (a) the transverse isotropy of the material yields good agreement between the best-fit isotropy approximation (equivalent to the classic Kroner's model) and the experimental data and (b) the use of a general framework allows the calculation of all components of the tensor of diffraction elastic constants, which are not easily measurable by diffraction methods. This allows us to extend the current state-of-the-art with a predictive tool. Y1 - 2020 U6 - https://doi.org/10.1063/5.0009101 SN - 0021-8979 SN - 1089-7550 VL - 128 IS - 2 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Mejia-Monasterio, Carlos A1 - Metzler, Ralf A1 - Vollmer, Jürgen T1 - Editorial: anomalous transport BT - applications, mathematical perspectives, and big data JF - Frontiers in Physics KW - anomalous (or non-Fickian) diffusion KW - anomalous heat conduction KW - stochastic dynamics KW - molecular overcrowding KW - dynamical systems Y1 - 2020 U6 - https://doi.org/10.3389/fphy.2020.622417 SN - 2296-424X VL - 8 PB - Frontiers Media CY - Lausanne ER - 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 - Sandev, Trifce A1 - Iomin, Alexander A1 - Kocarev, Ljupco T1 - Hitting times in turbulent diffusion due to multiplicative noise JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We study a distribution of times of the first arrivals to absorbing targets in turbulent diffusion, which is due to a multiplicative noise. Two examples of dynamical systems with a multiplicative noise are studied. The first one is a random process according to inhomogeneous diffusion, which is also known as a geometric Brownian motion in the Black-Scholes model. The second model is due to a random processes on a two-dimensional comb, where inhomogeneous advection is possible only along the backbone, while Brownian diffusion takes place inside the branches. It is shown that in both cases turbulent diffusion takes place as the one-dimensional random process with the log-normal distribution in the presence of absorbing targets, which are characterized by the Levy-Smirnov distribution for the first hitting times. Y1 - 2020 U6 - https://doi.org/10.1103/PhysRevE.102.042109 SN - 2470-0045 SN - 2470-0053 VL - 102 IS - 4 PB - American Institute of Physics CY - Woodbury, NY ER - TY - JOUR A1 - Aldiyarov, Abdurakhman A1 - Sokolov, Dmitriy A1 - Akylbayeva, Aigerim A1 - Nurmukan, Assel A1 - Tokmoldin, Nurlan T1 - On thermal stability of cryovacuum deposited CH4+H2O films JF - Low temperature physics N2 - Whereas stable homogenous states of aqueous hydrocarbon solutions are typically observed at high temperatures and pressures far beyond the critical values corresponding to individual components, the stability of such system may be preserved upon transition into the region of metastable states at low temperatures and low pressures. This work is dedicated to the study of the thermal stability of a water-methane mixture formed by cryogenic vapor phase deposition. The obtained thin films were studied using vibrational spectroscopy in the temperature range of 16-180 K. During thermal annealing of the samples, characteristic vibrational C-H modes of methane were monitored alongside the chamber pressure to register both structural changes and desorption of the film material. The obtained results reveal that upon the co-deposition of methane and water, methane molecules appear both in non-bound and trapped states. The observed broadening of the characteristic C-H stretching mode at 3010 cm(-1) upon an increase in temperature of the sample from 16 to 90 K, followed by narrowing of the peak as the temperature is reduced back to 16 K, indicates localization of methane molecules within the water matrix at lower temperatures. KW - molecular crystals KW - water-methane films KW - vibrational spectroscopy KW - low KW - temperature KW - methane localization Y1 - 2020 U6 - https://doi.org/10.1063/10.0002156 SN - 1063-777X SN - 1090-6517 VL - 46 IS - 11 SP - 1121 EP - 1124 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Glanemann, Nicole A1 - Willner, Sven N. A1 - Levermann, Anders T1 - Paris Climate Agreement passes the cost-benefit test JF - Nature Communications N2 - The Paris Climate Agreement aims to keep temperature rise well below 2 degrees C. This implies mitigation costs as well as avoided climate damages. Here we show that independent of the normative assumptions of inequality aversion and time preferences, the agreement constitutes the economically optimal policy pathway for the century. To this end we consistently incorporate a damage-cost curve reproducing the observed relation between temperature and economic growth into the integrated assessment model DICE. We thus provide an intertemporally optimizing cost-benefit analysis of this century's climate problem. We account for uncertainties regarding the damage curve, climate sensitivity, socioeconomic future, and mitigation costs. The resulting optimal temperature is robust as can be understood from the generic temperature-dependence of the mitigation costs and the level of damages inferred from the observed temperature-growth relationship. Our results show that the politically motivated Paris Climate Agreement also represents the economically favourable pathway, if carried out properly. Y1 - 2020 U6 - https://doi.org/10.1038/s41467-019-13961-1 SN - 2041-1723 VL - 11 IS - 1 PB - Nature Publishing Group CY - London ER - TY - JOUR A1 - Wilhelm, Alina A1 - Telezhinsky, Igor A1 - Dwarkadas, Vikram V. A1 - Pohl, Martin T1 - Stochastic re-acceleration and magnetic-field damping in Tycho’s supernova remnant JF - Astronomy and astrophysics N2 - Context. Tycho's supernova remnant (SNR) is associated with the historical supernova (SN) event SN 1572 of Type Ia. The explosion occurred in a relatively clean environment, and was visually observed, providing an age estimate. This SNR therefore represents an ideal astrophysical test-bed for the study of cosmic-ray acceleration and related phenomena. A number of studies suggest that shock acceleration with particle feedback and very efficient magnetic-field amplification combined with Alfvenic drift are needed to explain the rather soft radio spectrum and the narrow rims observed in X-rays. Aims. We show that the broadband spectrum of Tycho's SNR can alternatively be well explained when accounting for stochastic acceleration as a secondary process. The re-acceleration of particles in the turbulent region immediately downstream of the shock should be efficient enough to impact particle spectra over several decades in energy. The so-called Alfvenic drift and particle feedback on the shock structure are not required in this scenario. Additionally, we investigate whether synchrotron losses or magnetic-field damping play a more profound role in the formation of the non-thermal filaments. Methods. We solved the full particle transport equation in test-particle mode using hydrodynamic simulations of the SNR plasma flow. The background magnetic field was either computed from the induction equation or follows analytic profiles, depending on the model considered. Fast-mode waves in the downstream region provide the diffusion of particles in momentum space. Results. We show that the broadband spectrum of Tycho can be well explained if magnetic-field damping and stochastic re-acceleration of particles are taken into account. Although not as efficient as standard diffusive shock acceleration, stochastic acceleration leaves its imprint on the particle spectra, which is especially notable in the emission at radio wavelengths. We find a lower limit for the post-shock magnetic-field strength similar to 330 mu G, implying efficient amplification even for the magnetic-field damping scenario. Magnetic-field damping is necessary for the formation of the filaments in the radio range, while the X-ray filaments are shaped by both the synchrotron losses and magnetic-field damping. KW - acceleration of particles KW - radiation mechanisms: non-thermal KW - ISM: supernova remnants KW - cosmic rays KW - ISM: individual objects: Tycho's SNR KW - shock waves Y1 - 2020 U6 - https://doi.org/10.1051/0004-6361/201936079 SN - 0004-6361 SN - 1432-0746 VL - 639 PB - EDP Sciences CY - Les Ulis ER -