@misc{AlirezaeizanjaniGrossmannPfeiferetal.2020, author = {Alirezaeizanjani, Zahra and Großmann, Robert and Pfeifer, Veronika and Hintsche, Marius and Beta, Carsten}, title = {Chemotaxis strategies of bacteria with multiple run modes}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {22}, issn = {1866-8372}, doi = {10.25932/publishup-51909}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-519098}, pages = {10}, year = {2020}, abstract = {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.}, language = {en} } @misc{KirchartzMarquezStolterfohtetal.2020, author = {Kirchartz, Thomas and M{\´a}rquez, Jos{\´e} A. and Stolterfoht, Martin and Unold, Thomas}, title = {Photoluminescence-based characterization of halide perovskites for photovoltaics}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {26}, issn = {1866-8372}, doi = {10.25932/publishup-51970}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-519702}, pages = {23}, year = {2020}, abstract = {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.}, language = {en} } @article{KirchartzMarquezStolterfohtetal.2020, author = {Kirchartz, Thomas and M{\´a}rquez, Jos{\´e} A. and Stolterfoht, Martin and Unold, Thomas}, title = {Photoluminescence-based characterization of halide perovskites for photovoltaics}, series = {Advanced Energy Materials}, volume = {10}, journal = {Advanced Energy Materials}, number = {26}, publisher = {Wiley}, address = {Weinheim}, issn = {1614-6832}, doi = {10.1002/aenm.201904134}, pages = {1 -- 21}, year = {2020}, abstract = {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.}, language = {en} } @misc{ChengZhangKliemetal.2020, author = {Cheng, Xin and Zhang, Jie and Kliem, Bernhard and T{\"o}r{\"o}k, Tibor and Xing, Chen and Zhou, Zhenjun and Inhester, Bernd and Ding, Mingde}, title = {Initiation and early kinematic evolution of solar eruptions}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {2}, issn = {1866-8372}, doi = {10.25932/publishup-51972}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-519720}, pages = {22}, year = {2020}, abstract = {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.}, language = {en} } @article{ChengZhangKliemetal.2020, author = {Cheng, Xin and Zhang, Jie and Kliem, Bernhard and T{\"o}r{\"o}k, Tibor and Xing, Chen and Zhou, Zhenjun and Inhester, Bernd and Ding, Mingde}, title = {Initiation and early kinematic evolution of solar eruptions}, series = {The Astrophysical Journal}, volume = {894}, journal = {The Astrophysical Journal}, number = {2}, publisher = {Cambridge Scientific Publishers}, address = {Cambridge}, issn = {1055-6796}, doi = {10.3847/1538-4357/ab886a}, pages = {1 -- 20}, year = {2020}, abstract = {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.}, language = {en} } @misc{GarciaBenitoQuartiQuelozetal.2020, author = {Garc{\´i}a-Benito, In{\´e}s and Quarti, Claudio and Queloz, Valentin I. E. and Hofstetter, Yvonne J. and Becker-Koch, David and Caprioglio, Pietro and Neher, Dieter and Orlandi, Simonetta and Cavazzini, Marco and Pozzi, Gianluca and Even, Jacky and Nazeeruddin, Mohammad Khaja and Vaynzof, Yana and Grancini, Giulia}, title = {Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, issn = {1866-8372}, doi = {10.25932/publishup-51242}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-512420}, pages = {13}, year = {2020}, abstract = {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.}, language = {en} } @article{GarciaBenitoQuartiQuelozetal.2020, author = {Garc{\´i}a-Benito, In{\´e}s and Quarti, Claudio and Queloz, Valentin I. E. and Hofstetter, Yvonne J. and Becker-Koch, David and Caprioglio, Pietro and Neher, Dieter and Orlandi, Simonetta and Cavazzini, Marco and Pozzi, Gianluca and Even, Jacky and Nazeeruddin, Mohammad Khaja and Vaynzof, Yana and Grancini, Giulia}, title = {Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites}, series = {Frontiers in Chemistry}, volume = {7}, journal = {Frontiers in Chemistry}, publisher = {Frontiers Media}, address = {Lausanne}, issn = {2296-2646}, doi = {10.3389/fchem.2019.00946}, pages = {1 -- 11}, year = {2020}, abstract = {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.}, language = {en} } @misc{ZhongCausaMooreetal.2020, author = {Zhong, Yufei and Causa, Martina and Moore, Gareth John and Krauspe, Philipp and Xiao, Bo and G{\"u}nther, Florian and Kublitski, Jonas and BarOr, Eyal and Zhou, Erjun and Banerji, Natalie}, title = {Sub-picosecond charge-transfer at near-zero driving force in polymer:non-fullerene acceptor blends and bilayers}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1}, issn = {1866-8372}, doi = {10.25932/publishup-51193}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-511936}, pages = {12}, year = {2020}, abstract = {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.}, language = {en} } @article{ZhongCausaMooreetal.2020, author = {Zhong, Yufei and Causa, Martina and Moore, Gareth John and Krauspe, Philipp and Xiao, Bo and G{\"u}nther, Florian and Kublitski, Jonas and BarOr, Eyal and Zhou, Erjun and Banerji, Natalie}, title = {Sub-picosecond charge-transfer at near-zero driving force in polymer:non-fullerene acceptor blends and bilayers}, series = {Nature Communications}, volume = {11}, journal = {Nature Communications}, number = {1}, publisher = {Nature Publishing Group UK}, address = {London}, issn = {2041-1723}, doi = {10.1038/s41467-020-14549-w}, pages = {1 -- 10}, year = {2020}, abstract = {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.}, language = {en} } @misc{CaesarRahmstorfFeulner2020, author = {Caesar, Levke and Rahmstorf, Stefan and Feulner, Georg}, title = {On the relationship between Atlantic meridional overturning circulation slowdown and global surface warming}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {2}, issn = {1866-8372}, doi = {10.25932/publishup-51238}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-512382}, pages = {9}, year = {2020}, abstract = {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.}, language = {en} }