@article{SchulzeBettBivouretal.2020,
author = {Schulze, Patricia S. C. and Bett, Alexander J. and Bivour, Martin and Caprioglio, Pietro and Gerspacher, Fabian M. and Kabakl{\i}, {\"O}zde Ş. and Richter, Armin and Stolterfoht, Martin and Zhang, Qinxin and Neher, Dieter and Hermle, Martin and Hillebrecht, Harald and Glunz, Stefan W. and Goldschmidt, Jan Christoph},
title = {25.1\% high-efficiency monolithic perovskite silicon tandem solar cell with a high bandgap perovskite absorber},
series = {Solar RRL},
volume = {4},
journal = {Solar RRL},
number = {7},
publisher = {John Wiley \& Sons, Inc.},
address = {New Jersey},
pages = {10},
year = {2020},
abstract = {Monolithic perovskite silicon tandem solar cells can overcome the theoretical efficiency limit of silicon solar cells. This requires an optimum bandgap, high quantum efficiency, and high stability of the perovskite. Herein, a silicon heterojunction bottom cell is combined with a perovskite top cell, with an optimum bandgap of 1.68 eV in planar p-i-n tandem configuration. A methylammonium-free FA(0.75)Cs(0.25)Pb(I0.8Br0.2)(3) perovskite with high Cs content is investigated for improved stability. A 10\% molarity increase to 1.1 m of the perovskite precursor solution results in approximate to 75 nm thicker absorber layers and 0.7 mA cm(-2) higher short-circuit current density. With the optimized absorber, tandem devices reach a high fill factor of 80\% and up to 25.1\% certified efficiency. The unencapsulated tandem device shows an efficiency improvement of 2.3\% (absolute) over 5 months, showing the robustness of the absorber against degradation. Moreover, a photoluminescence quantum yield analysis reveals that with adapted charge transport materials and surface passivation, along with improved antireflection measures, the high bandgap perovskite absorber has the potential for 30\% tandem efficiency in the near future.},
language = {en}
}
@misc{RisbeyLewandowskyCowtanetal.2018,
author = {Risbey, James S. and Lewandowsky, Stephan and Cowtan, Kevin and Oreskes, Naomi and Rahmstorf, Stefan and Jokim{\"a}ki, Ari and Foster, Grant},
title = {A fluctuation in surface temperature in historical context},
series = {Environmental research letters},
volume = {13},
journal = {Environmental research letters},
number = {12},
publisher = {IOP Publ. Ltd.},
address = {Bristol},
issn = {1748-9326},
doi = {10.1088/1748-9326/aaf342},
pages = {23},
year = {2018},
abstract = {This work reviews the literature on an alleged global warming 'pause' in global mean surface temperature (GMST) to determine how it has been defined, what time intervals are used to characterise it, what data are used to measure it, and what methods used to assess it. We test for 'pauses', both in the normally understood meaning of the term to mean no warming trend, as well as for a 'pause' defined as a substantially slower trend in GMST. The tests are carried out with the historical versions of GMST that existed for each pause-interval tested, and with current versions of each of the GMST datasets. The tests are conducted following the common (but questionable) practice of breaking the linear fit at the start of the trend interval ('broken' trends), and also with trends that are continuous with the data bordering the trend interval. We also compare results when appropriate allowance is made for the selection bias problem. The results show that there is little or no statistical evidence for a lack of trend or slower trend in GMST using either the historical data or the current data. The perception that there was a 'pause' in GMST was bolstered by earlier biases in the data in combination with incomplete statistical testing.},
language = {en}
}
@article{HassaninKliemSeehaferetal.2022,
author = {Hassanin, Alshaimaa and Kliem, Bernhard and Seehafer, Norbert and T{\"o}r{\"o}k, Tibor},
title = {A model of homologous confined and ejective eruptions involving kink instability and flux cancellation},
series = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
volume = {929},
journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
number = {2},
publisher = {IOP Publ. Ltd.},
address = {Bristol},
issn = {2041-8205},
doi = {10.3847/2041-8213/ac64a9},
pages = {7},
year = {2022},
abstract = {In this study, we model a sequence of a confined and a full eruption, employing the relaxed end state of the confined eruption of a kink-unstable flux rope as the initial condition for the ejective one. The full eruption, a model of a coronal mass ejection, develops as a result of converging motions imposed at the photospheric boundary, which drive flux cancellation. In this process, parts of the positive and negative external flux converge toward the polarity inversion line, reconnect, and cancel each other. Flux of the same amount as the canceled flux transfers to a flux rope, increasing the free magnetic energy of the coronal field. With sustained flux cancellation and the associated progressive weakening of the magnetic tension of the overlying flux, we find that a flux reduction of approximate to 11\% initiates the torus instability of the flux rope, which leads to a full eruption. These results demonstrate that a homologous full eruption, following a confined one, can be driven by flux cancellation.},
language = {en}
}
@article{GrebenkovMetzlerOshanin2021,
author = {Grebenkov, Denis S. and Metzler, Ralf and Oshanin, Gleb},
title = {A molecular relay race: sequential first-passage events to the terminal reaction centre in a cascade of diffusion controlled processes},
series = {New Journal of Physics (NJP)},
volume = {23},
journal = {New Journal of Physics (NJP)},
publisher = {IOP - Institute of Physics Publishing},
address = {Bristol},
issn = {1367-2630},
doi = {10.1088/1367-2630/ac1e42},
pages = {18},
year = {2021},
abstract = {We consider a sequential cascade of molecular first-reaction events towards a terminal reaction centre in which each reaction step is controlled by diffusive motion of the particles. The model studied here represents a typical reaction setting encountered in diverse molecular biology systems, in which, e.g. a signal transduction proceeds via a series of consecutive 'messengers': the first messenger has to find its respective immobile target site triggering a launch of the second messenger, the second messenger seeks its own target site and provokes a launch of the third messenger and so on, resembling a relay race in human competitions. For such a molecular relay race taking place in infinite one-, two- and three-dimensional systems, we find exact expressions for the probability density function of the time instant of the terminal reaction event, conditioned on preceding successful reaction events on an ordered array of target sites. The obtained expressions pertain to the most general conditions: number of intermediate stages and the corresponding diffusion coefficients, the sizes of the target sites, the distances between them, as well as their reactivities are arbitrary.},
language = {en}
}
@article{GrossmannAransonPeruani2020,
author = {Großmann, Robert and Aranson, Igor S. and Peruani, Fernando},
title = {A particle-field approach bridges phase separation and collective motion in active matter},
series = {Nature Communications},
volume = {11},
journal = {Nature Communications},
number = {1},
publisher = {Nature Publishing Group},
address = {London},
issn = {2041-1723},
doi = {10.1038/s41467-020-18978-5},
pages = {12},
year = {2020},
abstract = {Whereas self-propelled hard discs undergo motility-induced phase separation, self-propelled rods exhibit a variety of nonequilibrium phenomena, including clustering, collective motion, and spatio-temporal chaos. In this work, we present a theoretical framework representing active particles by continuum fields. This concept combines the simplicity of alignment-based models, enabling analytical studies, and realistic models that incorporate the shape of self-propelled objects explicitly. By varying particle shape from circular to ellipsoidal, we show how nonequilibrium stresses acting among self-propelled rods destabilize motility-induced phase separation and facilitate orientational ordering, thereby connecting the realms of scalar and vectorial active matter. Though the interaction potential is strictly apolar, both, polar and nematic order may emerge and even coexist. Accordingly, the symmetry of ordered states is a dynamical property in active matter. The presented framework may represent various systems including bacterial colonies, cytoskeletal extracts, or shaken granular media. Interacting self-propelled particles exhibit phase separation or collective motion depending on particle shape. A unified theory connecting these paradigms represents a major challenge in active matter, which the authors address here by modeling active particles as continuum fields.},
language = {en}
}
@article{HintscheWaljorGrossmannetal.2017,
author = {Hintsche, Marius and Waljor, Veronika and Grossmann, Robert and K{\"u}hn, Marco J. and Thormann, Kai M. and Peruani, Fernando and Beta, Carsten},
title = {A polar bundle of flagella can drive bacterial swimming by pushing, pulling, or coiling around the cell body},
series = {Scientific reports},
volume = {7},
journal = {Scientific reports},
publisher = {Macmillan Publishers Limited, part of Springer Nature},
address = {London},
issn = {2045-2322},
doi = {10.1038/s41598-017-16428-9},
pages = {10},
year = {2017},
abstract = {Bacteria swim in sequences of straight runs that are interrupted by turning events. They drive their swimming locomotion with the help of rotating helical flagella. Depending on the number of flagella and their arrangement across the cell body, different run-and-turn patterns can be observed. Here, we present fluorescence microscopy recordings showing that cells of the soil bacterium Pseudomonas putida that are decorated with a polar tuft of helical flagella, can alternate between two distinct swimming patterns. On the one hand, they can undergo a classical push-pull-push cycle that is well known from monopolarly flagellated bacteria but has not been reported for species with a polar bundle of multiple flagella. Alternatively, upon leaving the pulling mode, they can enter a third slow swimming phase, where they propel themselves with their helical bundle wrapped around the cell body. A theoretical estimate based on a random-walk model shows that the spreading of a population of swimmers is strongly enhanced when cycling through a sequence of pushing, pulling, and wrapped flagellar configurations as compared to the simple push-pull-push pattern.},
language = {en}
}
@article{SchlemmLevermann2021,
author = {Schlemm, Tanja and Levermann, Anders},
title = {A simple parametrization of m{\´e}lange buttressing for calving glaciers},
series = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union},
volume = {15},
journal = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union},
number = {2},
publisher = {Copernicus},
address = {G{\"o}ttingen},
issn = {1994-0416},
doi = {10.5194/tc-15-531-2021},
pages = {531 -- 545},
year = {2021},
abstract = {Both ice sheets in Greenland and Antarctica are discharging ice into the ocean. In many regions along the coast of the ice sheets, the icebergs calve into a bay. If the addition of icebergs through calving is faster than their transport out of the embayment, the icebergs will be frozen into a melange with surrounding sea ice in winter. In this case, the buttressing effect of the ice melange can be considerably stronger than any buttressing by mere sea ice would be. This in turn stabilizes the glacier terminus and leads to a reduction in calving rates. Here we propose a simple parametrization of ice melange buttressing which leads to an upper bound on calving rates and can be used in numerical and analytical modelling.},
language = {en}
}
@article{SchlemmLevermann2019,
author = {Schlemm, Tanja and Levermann, Anders},
title = {A simple stress-based cliff-calving law},
series = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union},
volume = {13},
journal = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union},
number = {9},
publisher = {Copernicus},
address = {G{\"o}ttingen},
issn = {1994-0416},
doi = {10.5194/tc-13-2475-2019},
pages = {2475 -- 2488},
year = {2019},
abstract = {Over large coastal regions in Greenland and Antarctica the ice sheet calves directly into the ocean. In contrast to ice-shelf calving, an increase in calving from grounded glaciers contributes directly to sea-level rise. Ice cliffs with a glacier freeboard larger than approximate to 100 m are currently not observed, but it has been shown that such ice cliffs are increasingly unstable with increasing ice thickness. This cliff calving can constitute a self-amplifying ice loss mechanism that may significantly alter sea-level projections both of Greenland and Antarctica. Here we seek to derive a minimalist stress-based parametrization for cliff calving from grounded glaciers whose freeboards exceed the 100m stability limit derived in previous studies. This will be an extension of existing calving laws for tidewater glaciers to higher ice cliffs. To this end we compute the stress field for a glacier with a simplified two-dimensional geometry from the two-dimensional Stokes equation. First we assume a constant yield stress to derive the failure region at the glacier front from the stress field within the glacier. Secondly, we assume a constant response time of ice failure due to exceedance of the yield stress. With this strongly constraining but very simple set of assumptions we propose a cliff-calving law where the calving rate follows a power-law dependence on the freeboard of the ice with exponents between 2 and 3, depending on the relative water depth at the calving front. The critical freeboard below which the ice front is stable decreases with increasing relative water depth of the calving front. For a dry water front it is, for example, 75 m. The purpose of this study is not to provide a comprehensive calving law but to derive a particularly simple equation with a transparent and minimalist set of assumptions.},
language = {en}
}
@article{GuggenbergerChechkinMetzler2022,
author = {Guggenberger, Tobias and Chechkin, Aleksei and Metzler, Ralf},
title = {Absence of stationary states and non-Boltzmann distributions of fractional Brownian motion in shallow external potentials},
series = {New journal of physics : the open-access journal for physics},
volume = {24},
journal = {New journal of physics : the open-access journal for physics},
number = {7},
publisher = {Dt. Physikalische Ges.},
address = {[Bad Honnef]},
issn = {1367-2630},
doi = {10.1088/1367-2630/ac7b3c},
pages = {18},
year = {2022},
abstract = {We study the diffusive motion of a particle in a subharmonic potential of the form U(x) = |x|( c ) (0 < c < 2) driven by long-range correlated, stationary fractional Gaussian noise xi ( alpha )(t) with 0 < alpha <= 2. In the absence of the potential the particle exhibits free fractional Brownian motion with anomalous diffusion exponent alpha. While for an harmonic external potential the dynamics converges to a Gaussian stationary state, from extensive numerical analysis we here demonstrate that stationary states for shallower than harmonic potentials exist only as long as the relation c > 2(1 - 1/alpha) holds. We analyse the motion in terms of the mean squared displacement and (when it exists) the stationary probability density function. Moreover we discuss analogies of non-stationarity of Levy flights in shallow external potentials.},
language = {en}
}
@article{WillnerLevermannZhaoetal.2018,
author = {Willner, Sven N. and Levermann, Anders and Zhao, Fang and Frieler, Katja},
title = {Adaptation required to preserve future high-end river flood risk at present levels},
series = {Science Advances},
volume = {4},
journal = {Science Advances},
number = {1},
publisher = {American Assoc. for the Advancement of Science},
address = {Washington},
issn = {2375-2548},
doi = {10.1126/sciadv.aao1914},
pages = {8},
year = {2018},
abstract = {Earth's surface temperature will continue to rise for another 20 to 30 years even with the strongest carbon emission reduction currently considered. The associated changes in rainfall patterns can result in an increased flood risk worldwide. We compute the required increase in flood protection to keep high-end fluvial flood risk at present levels. The analysis is carried out worldwide for subnational administrative units. Most of the United States, Central Europe, and Northeast and West Africa, as well as large parts of India and Indonesia, require the strongest adaptation effort. More than half of the United States needs to at least double their protection within the next two decades. Thus, the need for adaptation to increased river flood is a global problem affecting industrialized regions as much as developing countries.},
language = {en}
}
@article{SmirnovKronbergDalyetal.2020,
author = {Smirnov, Artem G. and Kronberg, Elena A. and Daly, Patrick W. and Aseev, Nikita and Shprits, Yuri and Kellerman, Adam C.},
title = {Adiabatic Invariants Calculations for Cluster Mission: A Long-Term Product for Radiation Belts Studies},
series = {Journal of Geophysical Research: Space Physics},
volume = {125},
journal = {Journal of Geophysical Research: Space Physics},
number = {2},
publisher = {John Wiley \& Sons, Inc.},
address = {New Jersey},
pages = {12},
year = {2020},
abstract = {The Cluster mission has produced a large data set of electron flux measurements in the Earth's magnetosphere since its launch in late 2000. Electron fluxes are measured using Research with Adaptive Particle Imaging Detector (RAPID)/Imaging Electron Spectrometer (IES) detector as a function of energy, pitch angle, spacecraft position, and time. However, no adiabatic invariants have been calculated for Cluster so far. In this paper we present a step-by-step guide to calculations of adiabatic invariants and conversion of the electron flux to phase space density (PSD) in these coordinates. The electron flux is measured in two RAPID/IES energy channels providing pitch angle distribution at energies 39.2-50.5 and 68.1-94.5 keV in nominal mode since 2004. A fitting method allows to expand the conversion of the differential fluxes to the range from 40 to 150 keV. Best data coverage for phase space density in adiabatic invariant coordinates can be obtained for values of second adiabatic invariant, K, similar to 10(2), and values of the first adiabatic invariant mu in the range approximate to 5-20 MeV/G. Furthermore, we describe the production of a new data product "LSTAR," equivalent to the third adiabatic invariant, available through the Cluster Science Archive for years 2001-2018 with 1-min resolution. The produced data set adds to the availability of observations in Earth's radiation belts region and can be used for long-term statistical purposes.},
language = {en}
}
@article{CiemerRehmKurthsetal.2020,
author = {Ciemer, Catrin and Rehm, Lars and Kurths, J{\"u}rgen and Donner, Reik Volker and Winkelmann, Ricarda and Boers, Niklas},
title = {An early-warning indicator for Amazon droughts exclusively based on tropical Atlantic sea surface temperatures},
series = {Environmental Research Letters},
volume = {15},
journal = {Environmental Research Letters},
number = {9},
publisher = {IOP - Institute of Physics Publishing},
address = {Bristol},
pages = {10},
year = {2020},
abstract = {Droughts in tropical South America have an imminent and severe impact on the Amazon rainforest and affect the livelihoods of millions of people. Extremely dry conditions in Amazonia have been previously linked to sea surface temperature (SST) anomalies in the adjacent tropical oceans. Although the sources and impacts of such droughts have been widely studied, establishing reliable multi-year lead statistical forecasts of their occurrence is still an ongoing challenge. Here, we further investigate the relationship between SST and rainfall anomalies using a complex network approach. We identify four ocean regions which exhibit the strongest overall SST correlations with central Amazon rainfall, including two particularly prominent regions in the northern and southern tropical Atlantic. Based on the time-dependent correlation between SST anomalies in these two regions alone, we establish a new early-warning method for droughts in the central Amazon basin and demonstrate its robustness in hindcasting past major drought events with lead-times up to 18 months.},
language = {en}
}
@article{NakoudiStachlewskaRitter2021,
author = {Nakoudi, Konstantina and Stachlewska, Iwona S. and Ritter, Christoph},
title = {An extended lidar-based cirrus cloud retrieval scheme},
series = {Optics express : the international electronic journal of optics / Optica},
volume = {29},
journal = {Optics express : the international electronic journal of optics / Optica},
number = {6},
publisher = {Optical Society of America},
address = {Washington},
issn = {1094-4087},
doi = {10.1364/OE.414770},
pages = {8553 -- 8580},
year = {2021},
abstract = {Accurate and precise characterization of cirrus cloud geometrical and optical properties is essential for better constraining their radiative footprint. A lidar-based retrieval scheme is proposed here, with its performance assessed on fine spatio-temporal observations over the Arctic site of Ny-Alesund, Svalbard. Two contributions related to cirrus geometrical (dynamic Wavelet Covariance Transform (WCT)) and optical properties (constrained Klett) are reported. The dynamic WCT rendered cirrus detection more robust, especially for thin cirrus layers that frequently remained undetected by the classical WCT method. Regarding optical characterization, we developed an iterative scheme for determining the cirrus lidar ratio (LRci) that is a crucial parameter for aerosol - cloud discrimination. Building upon the Klett-Fernald method, the LRci was constrained by an additional reference value. In established methods, such as the double-ended Klett, an aerosol-free reference value is applied. In the proposed constrained Klett, however, the reference value was approximated from cloud-free or low cloud optical depth (COD up to 0.2) profiles and proved to agree with independent Raman estimates. For optically thin cirrus, the constrained Klett inherent uncertainties reached 50\% (60-74\%) in terms of COD (LRci). However, for opaque cirrus COD (LRci) uncertainties were lower than 10\% (15\%). The detection method discrepancies (dynamic versus static WCT) had a higher impact on the optical properties of low COD layers (up to 90\%) compared to optically thicker ones (less than 10\%). The constrained Klett presented high agreement with two established retrievals. For an exemplary cirrus cloud, the constrained Klett estimated the COD355 (LRci355) at 0.28 +/- 0.17 (29 +/- 4 sr), the double-ended Klett at 0.27 +/- 0.15 (32 +/- 4 sr) and the Raman retrievals at 0.22 +/- 0.12 (26 +/- 11 sr). Our approach to determine the necessary reference value can also be applied in established methods and increase their accuracy. In contrast, the classical aerosol-free assumption led to 44 sr LRci overestimation in optically thin layers and 2-8 sr in thicker ones. The multiple scattering effect was corrected using Eloranta (1998) and accounted for 50-60\% extinction underestimation near the cloud base and 20-30\% within the cirrus layers.},
language = {en}
}
@article{SchindlerMoldenhawerStangeetal.2021,
author = {Schindler, Daniel and Moldenhawer, Ted and Stange, Maike and Lepro, Valentino and Beta, Carsten and Holschneider, Matthias and Huisinga, Wilhelm},
title = {Analysis of protrusion dynamics in amoeboid cell motility by means of regularized contour flows},
series = {PLoS Computational Biology : a new community journal},
volume = {17},
journal = {PLoS Computational Biology : a new community journal},
number = {8},
publisher = {PLoS},
address = {San Fransisco},
issn = {1553-734X},
doi = {10.1371/journal.pcbi.1009268},
pages = {33},
year = {2021},
abstract = {Amoeboid cell motility is essential for a wide range of biological processes including wound healing, embryonic morphogenesis, and cancer metastasis. It relies on complex dynamical patterns of cell shape changes that pose long-standing challenges to mathematical modeling and raise a need for automated and reproducible approaches to extract quantitative morphological features from image sequences. Here, we introduce a theoretical framework and a computational method for obtaining smooth representations of the spatiotemporal contour dynamics from stacks of segmented microscopy images. Based on a Gaussian process regression we propose a one-parameter family of regularized contour flows that allows us to continuously track reference points (virtual markers) between successive cell contours. We use this approach to define a coordinate system on the moving cell boundary and to represent different local geometric quantities in this frame of reference. In particular, we introduce the local marker dispersion as a measure to identify localized membrane expansions and provide a fully automated way to extract the properties of such expansions, including their area and growth time. The methods are available as an open-source software package called AmoePy, a Python-based toolbox for analyzing amoeboid cell motility (based on time-lapse microscopy data), including a graphical user interface and detailed documentation. Due to the mathematical rigor of our framework, we envision it to be of use for the development of novel cell motility models. We mainly use experimental data of the social amoeba Dictyostelium discoideum to illustrate and validate our approach.
Author summary Amoeboid motion is a crawling-like cell migration that plays an important key role in multiple biological processes such as wound healing and cancer metastasis. This type of cell motility results from expanding and simultaneously contracting parts of the cell membrane. From fluorescence images, we obtain a sequence of points, representing the cell membrane, for each time step. By using regression analysis on these sequences, we derive smooth representations, so-called contours, of the membrane. Since the number of measurements is discrete and often limited, the question is raised of how to link consecutive contours with each other. In this work, we present a novel mathematical framework in which these links are described by regularized flows allowing a certain degree of concentration or stretching of neighboring reference points on the same contour. This stretching rate, the so-called local dispersion, is used to identify expansions and contractions of the cell membrane providing a fully automated way of extracting properties of these cell shape changes. We applied our methods to time-lapse microscopy data of the social amoeba Dictyostelium discoideum.},
language = {en}
}
@article{MatternPudellLaskinetal.2021,
author = {Mattern, Maximilian and Pudell, Jan-Etienne and Laskin, Gennadii and Reppert, Alexander von and Bargheer, Matias},
title = {Analysis of the temperature- and fluence-dependent magnetic stress in laser-excited SrRuO3},
series = {Structural dynamics},
volume = {8},
journal = {Structural dynamics},
number = {2},
publisher = {AIP Publishing LLC},
address = {Melville, NY},
issn = {2329-7778},
doi = {10.1063/4.0000072},
pages = {9},
year = {2021},
abstract = {We use ultrafast x-ray diffraction to investigate the effect of expansive phononic and contractive magnetic stress driving the picosecond strain response of a metallic perovskite SrRuO3 thin film upon femtosecond laser excitation. We exemplify how the anisotropic bulk equilibrium thermal expansion can be used to predict the response of the thin film to ultrafast deposition of energy. It is key to consider that the laterally homogeneous laser excitation changes the strain response compared to the near-equilibrium thermal expansion because the balanced in-plane stresses suppress the Poisson stress on the picosecond timescale. We find a very large negative Gr{\"u}neisen constant describing the large contractive stress imposed by a small amount of energy in the spin system. The temperature and fluence dependence of the strain response for a double-pulse excitation scheme demonstrates the saturation of the magnetic stress in the high-fluence regime.},
language = {en}
}
@article{MunyaevSmirnovKostinetal.2020,
author = {Munyaev, Vyacheslav O. and Smirnov, Lev A. and Kostin, Vasily A. and Osipov, Grigory V. and Pikovskij, Arkadij},
title = {Analytical approach to synchronous states of globally coupled noisy rotators},
series = {New journal of physics : the open-access journal for physics},
volume = {22},
journal = {New journal of physics : the open-access journal for physics},
number = {2},
publisher = {IOP Publ. Ltd.},
address = {Bristol},
issn = {1367-2630},
doi = {10.1088/1367-2630/ab6f93},
pages = {14},
year = {2020},
abstract = {We study populations of globally coupled noisy rotators (oscillators with inertia) allowing a nonequilibrium transition from a desynchronized state to a synchronous one (with the nonvanishing order parameter). The newly developed analytical approaches resulted in solutions describing the synchronous state with constant order parameter for weakly inertial rotators, including the case of zero inertia, when the model is reduced to the Kuramoto model of coupled noise oscillators. These approaches provide also analytical criteria distinguishing supercritical and subcritical transitions to the desynchronized state and indicate the universality of such transitions in rotator ensembles. All the obtained analytical results are confirmed by the numerical ones, both by direct simulations of the large ensembles and by solution of the associated Fokker-Planck equation. We also propose generalizations of the developed approaches for setups where different rotators parameters (natural frequencies, masses, noise intensities, strengths and phase shifts in coupling) are dispersed.},
language = {en}
}
@article{MunyaevSmirnovKostinetal.2020,
author = {Munyaev, Vyacheslav and Smirnov, Lev A. and Kostin, Vasily and Osipov, Grigory V. and Pikovskij, Arkadij},
title = {Analytical approach to synchronous states of globally coupled noisy rotators},
series = {New Journal of Physics},
volume = {22},
journal = {New Journal of Physics},
number = {2},
publisher = {Springer Science},
address = {New York},
pages = {15},
year = {2020},
abstract = {We study populations of globally coupled noisy rotators (oscillators with inertia) allowing a nonequilibrium transition from a desynchronized state to a synchronous one (with the nonvanishing order parameter). The newly developed analytical approaches resulted in solutions describing the synchronous state with constant order parameter for weakly inertial rotators, including the case of zero inertia, when the model is reduced to the Kuramoto model of coupled noise oscillators. These approaches provide also analytical criteria distinguishing supercritical and subcritical transitions to the desynchronized state and indicate the universality of such transitions in rotator ensembles. All the obtained analytical results are confirmed by the numerical ones, both by direct simulations of the large ensembles and by solution of the associated Fokker-Planck equation. We also propose generalizations of the developed approaches for setups where different rotators parameters (natural frequencies, masses, noise intensities, strengths and phase shifts in coupling) are dispersed.},
language = {en}
}
@article{DieterichLindemannMoskoppetal.2022,
author = {Dieterich, Peter and Lindemann, Otto and Moskopp, Mats Leif and Tauzin, Sebastien and Huttenlocher, Anna and Klages, Rainer and Chechkin, Aleksei V. and Schwab, Albrecht},
title = {Anomalous diffusion and asymmetric tempering memory in neutrophil chemotaxis},
series = {PLoS Computational Biology : a new community journal},
volume = {18},
journal = {PLoS Computational Biology : a new community journal},
number = {5},
publisher = {PLoS},
address = {San Fransisco},
issn = {1553-734X},
doi = {10.1371/journal.pcbi.1010089},
pages = {26},
year = {2022},
abstract = {Neutrophil granulocytes are essential for the first host defense. After leaving the blood circulation they migrate efficiently towards sites of inflammation. They are guided by chemoattractants released from cells within the inflammatory foci. On a cellular level, directional migration is a consequence of cellular front-rear asymmetry which is induced by the concentration gradient of the chemoattractants. The generation and maintenance of this asymmetry, however, is not yet fully understood. Here we analyzed the paths of chemotacting neutrophils with different stochastic models to gain further insight into the underlying mechanisms. Wildtype chemotacting neutrophils show an anomalous superdiffusive behavior. CXCR2 blockade and TRPC6-knockout cause the tempering of temporal correlations and a reduction of chemotaxis. Importantly, such tempering is found both in vitro and in vivo. These findings indicate that the maintenance of anomalous dynamics is crucial for chemotactic behavior and the search efficiency of neutrophils. The motility of neutrophils and their ability to sense and to react to chemoattractants in their environment are of central importance for the innate immunity. Neutrophils are guided towards sites of inflammation following the activation of G-protein coupled chemoattractant receptors such as CXCR2 whose signaling strongly depends on the activity of Ca2+ permeable TRPC6 channels. It is the aim of this study to analyze data sets obtained in vitro (murine neutrophils) and in vivo (zebrafish neutrophils) with a stochastic mathematical model to gain deeper insight into the underlying mechanisms. The model is based on the analysis of trajectories of individual neutrophils. Bayesian data analysis, including the covariances of positions for fractional Brownian motion as well as for exponentially and power-law tempered model variants, allows the estimation of parameters and model selection. Our model-based analysis reveals that wildtype neutrophils show pure superdiffusive fractional Brownian motion. This so-called anomalous dynamics is characterized by temporal long-range correlations for the movement into the direction of the chemotactic CXCL1 gradient. Pure superdiffusion is absent vertically to this gradient. This points to an asymmetric 'memory' of the migratory machinery, which is found both in vitro and in vivo. CXCR2 blockade and TRPC6-knockout cause tempering of temporal correlations in the chemotactic gradient. This can be interpreted as a progressive loss of memory, which leads to a marked reduction of chemotaxis and search efficiency of neutrophils. In summary, our findings indicate that spatially differential regulation of anomalous dynamics appears to play a central role in guiding efficient chemotactic behavior.},
language = {en}
}
@article{ReeseAlbrechtMengeletal.2018,
author = {Reese, Ronja and Albrecht, Torsten and Mengel, Matthias and Asay-Davis, Xylar and Winkelmann, Ricarda},
title = {Antarctic sub-shelf melt rates via PICO},
series = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union},
volume = {12},
journal = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union},
number = {6},
publisher = {Copernicus},
address = {G{\"o}ttingen},
issn = {1994-0416},
doi = {10.5194/tc-12-1969-2018},
pages = {1969 -- 1985},
year = {2018},
abstract = {Ocean-induced melting below ice shelves is one of the dominant drivers for mass loss from the Antarctic Ice Sheet at present. An appropriate representation of sub-shelf melt rates is therefore essential for model simulations of marine-based ice sheet evolution. Continental-scale ice sheet models often rely on simple melt-parameterizations, in particular for long-term simulations, when fully coupled ice-ocean interaction becomes computationally too expensive. Such parameterizations can account for the influence of the local depth of the ice-shelf draft or its slope on melting. However, they do not capture the effect of ocean circulation underneath the ice shelf. Here we present the Potsdam Ice-shelf Cavity mOdel (PICO), which simulates the vertical overturning circulation in ice-shelf cavities and thus enables the computation of sub-shelf melt rates consistent with this circulation. PICO is based on an ocean box model that coarsely resolves ice shelf cavities and uses a boundary layer melt formulation. We implement it as a module of the Parallel Ice Sheet Model (PISM) and evaluate its performance under present-day conditions of the Southern Ocean. We identify a set of parameters that yield two-dimensional melt rate fields that qualitatively reproduce the typical pattern of comparably high melting near the grounding line and lower melting or refreezing towards the calving front. PICO captures the wide range of melt rates observed for Antarctic ice shelves, with an average of about 0.1 ma(-1) for cold sub-shelf cavities, for example, underneath Ross or Ronne ice shelves, to 16 ma(-1) for warm cavities such as in the Amundsen Sea region. This makes PICO a computationally feasible and more physical alternative to melt parameterizations purely based on ice draft geometry.},
language = {en}
}
@article{PranavHultzschMusiienkoetal.2023,
author = {Pranav, Manasi and Hultzsch, Thomas and Musiienko, Artem and Sun, Bowen and Shukla, Atul and Jaiser, Frank and Shoaee, Safa and Neher, Dieter},
title = {Anticorrelated photoluminescence and free charge generation proves field-assisted exciton dissociation in low-offset PM6:Y5 organic solar cells},
series = {APL materials : high impact open access journal in functional materials science},
volume = {11},
journal = {APL materials : high impact open access journal in functional materials science},
number = {6},
publisher = {AIP Publishing},
address = {Melville},
issn = {2166-532X},
doi = {10.1063/5.0151580},
pages = {8},
year = {2023},
abstract = {Understanding the origin of inefficient photocurrent generation in organic solar cells with low energy offset remains key to realizing high-performance donor-acceptor systems. Here, we probe the origin of field-dependent free-charge generation and photoluminescence in wnon-fullereneacceptor (NFA)-based organic solar cells using the polymer PM6 and the NFA Y5-a non-halogenated sibling to Y6, with a smaller energetic offset to PM6. By performing time-delayed collection field (TDCF) measurements on a variety of samples with different electron transport layers and active layer thickness, we show that the fill factor and photocurrent are limited by field-dependent free charge generation in the bulk of the blend. We also introduce a new method of TDCF called m-TDCF to prove the absence of artifacts from non-geminate recombination of photogenerated and dark charge carriers near the electrodes. We then correlate free charge generation with steady-state photoluminescence intensity and find perfect anticorrelation between these two properties. Through this, we conclude that photocurrent generation in this low-offset system is entirely controlled by the field-dependent dissociation of local excitons into charge-transfer states. (c) 2023 Author(s).},
language = {en}
}
@article{PohlMaciasColemanetal.2022,
author = {Pohl, Martin and Macias, Oscar and Coleman, Phaedra and Gordon, Chris},
title = {Assessing the impact of hydrogen absorption on the characteristics of the Galactic center excess},
series = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
volume = {929},
journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
number = {2},
publisher = {IOP Publ. Ltd.},
address = {Bristol},
issn = {0004-637X},
doi = {10.3847/1538-4357/ac6032},
pages = {13},
year = {2022},
abstract = {We present a new reconstruction of the distribution of atomic hydrogen in the inner Galaxy that is based on explicit radiation transport modeling of line and continuum emission and a gas-flow model in the barred Galaxy that provides distance resolution for lines of sight toward the Galactic center. The main benefits of the new gas model are (a) the ability to reproduce the negative line signals seen with the HI4PI survey and (b) the accounting for gas that primarily manifests itself through absorption. We apply the new model of Galactic atomic hydrogen to an analysis of the diffuse gamma-ray emission from the inner Galaxy, for which an excess at a few GeV was reported that may be related to dark matter. We find with high significance an improved fit to the diffuse gamma-ray emission observed with the Fermi-LAT, if our new H i model is used to estimate the cosmic-ray induced diffuse gamma-ray emission. The fit still requires a nuclear bulge at high significance. Once this is included there is no evidence of a dark-matter signal, be it cuspy or cored. But an additional so-called boxy bulge is still favored by the data. This finding is robust under the variation of various parameters, for example, the excitation temperature of atomic hydrogen, and a number of tests for systematic issues.},
language = {en}
}
@article{PadashSandevKantzetal.2022,
author = {Padash, Amin and Sandev, Trifce and Kantz, Holger and Metzler, Ralf and Chechkin, Aleksei},
title = {Asymmetric Levy flights are more efficient in random search},
series = {Fractal and fractional},
volume = {6},
journal = {Fractal and fractional},
number = {5},
publisher = {MDPI},
address = {Basel},
issn = {2504-3110},
doi = {10.3390/fractalfract6050260},
pages = {23},
year = {2022},
abstract = {We study the first-arrival (first-hitting) dynamics and efficiency of a one-dimensional random search model performing asymmetric Levy flights by leveraging the Fokker-Planck equation with a delta-sink and an asymmetric space-fractional derivative operator with stable index alpha and asymmetry (skewness) parameter beta. We find exact analytical results for the probability density of first-arrival times and the search efficiency, and we analyse their behaviour within the limits of short and long times. We find that when the starting point of the searcher is to the right of the target, random search by Brownian motion is more efficient than Levy flights with beta <= 0 (with a rightward bias) for short initial distances, while for beta>0 (with a leftward bias) Levy flights with alpha -> 1 are more efficient. When increasing the initial distance of the searcher to the target, Levy flight search (except for alpha=1 with beta=0) is more efficient than the Brownian search. Moreover, the asymmetry in jumps leads to essentially higher efficiency of the Levy search compared to symmetric Levy flights at both short and long distances, and the effect is more pronounced for stable indices alpha close to unity.},
language = {en}
}
@article{SecklerMetzler2022,
author = {Seckler, Henrik and Metzler, Ralf},
title = {Bayesian deep learning for error estimation in the analysis of anomalous diffusion},
series = {Nature Communnications},
volume = {13},
journal = {Nature Communnications},
publisher = {Nature Publishing Group UK},
address = {London},
issn = {2041-1723},
doi = {10.1038/s41467-022-34305-6},
pages = {13},
year = {2022},
abstract = {Modern single-particle-tracking techniques produce extensive time-series of diffusive motion in a wide variety of systems, from single-molecule motion in living-cells to movement ecology. The quest is to decipher the physical mechanisms encoded in the data and thus to better understand the probed systems. We here augment recently proposed machine-learning techniques for decoding anomalous-diffusion data to include an uncertainty estimate in addition to the predicted output. To avoid the Black-Box-Problem a Bayesian-Deep-Learning technique named Stochastic-Weight-Averaging-Gaussian is used to train models for both the classification of the diffusionmodel and the regression of the anomalous diffusion exponent of single-particle-trajectories. Evaluating their performance, we find that these models can achieve a wellcalibrated error estimate while maintaining high prediction accuracies. In the analysis of the output uncertainty predictions we relate these to properties of the underlying diffusion models, thus providing insights into the learning process of the machine and the relevance of the output.},
language = {en}
}
@article{SecklerMetzler2022,
author = {Seckler, Henrik and Metzler, Ralf},
title = {Bayesian deep learning for error estimation in the analysis of anomalous diffusion},
series = {Nature Communications},
volume = {13},
journal = {Nature Communications},
number = {1},
publisher = {Nature portfolio},
address = {Berlin},
issn = {2041-1723},
doi = {10.1038/s41467-022-34305-6},
pages = {13},
year = {2022},
abstract = {Modern single-particle-tracking techniques produce extensive time-series of diffusive motion in a wide variety of systems, from single-molecule motion in living-cells to movement ecology. The quest is to decipher the physical mechanisms encoded in the data and thus to better understand the probed systems. We here augment recently proposed machine-learning techniques for decoding anomalous-diffusion data to include an uncertainty estimate in addition to the predicted output. To avoid the Black-Box-Problem a Bayesian-Deep-Learning technique named Stochastic-Weight-Averaging-Gaussian is used to train models for both the classification of the diffusion model and the regression of the anomalous diffusion exponent of single-particle-trajectories. Evaluating their performance, we find that these models can achieve a well-calibrated error estimate while maintaining high prediction accuracies. In the analysis of the output uncertainty predictions we relate these to properties of the underlying diffusion models, thus providing insights into the learning process of the machine and the relevance of the output.
Diffusive motions in complex environments such as living biological cells or soft matter systems can be analyzed with single-particle-tracking approaches, where accuracy of output may vary. The authors involve a machine-learning technique for decoding anomalous-diffusion data and provide an uncertainty estimate together with predicted output.},
language = {en}
}
@misc{DaiBoekerGlebe2019,
author = {Dai, Xiaolin and B{\"o}ker, Alexander and Glebe, Ulrich},
title = {Broadening the scope of sortagging},
series = {RSC Advances},
volume = {9},
journal = {RSC Advances},
number = {9},
publisher = {Royal Society of Chemistry},
address = {Cambridge},
issn = {2046-2069},
doi = {10.1039/c8ra06705h},
pages = {4700 -- 4721},
year = {2019},
abstract = {Sortases are enzymes occurring in the cell wall of Gram-positive bacteria. Sortase A (SrtA), the best studied sortase class, plays a key role in anchoring surface proteins with the recognition sequence LPXTG covalently to oligoglycine units of the bacterial cell wall. This unique transpeptidase activity renders SrtA attractive for various purposes and motivated researchers to study multiple in vivo and in vitro ligations in the last decades. This ligation technique is known as sortase-mediated ligation (SML) or sortagging and developed to a frequently used method in basic research. The advantages are manifold: extremely high substrate specificity, simple access to substrates and enzyme, robust nature and easy handling of sortase A. In addition to the ligation of two proteins or peptides, early studies already included at least one artificial (peptide equipped) substrate into sortagging reactions - which demonstrates the versatility and broad applicability of SML. Thus, SML is not only a biology-related technique, but has found prominence as a major interdisciplinary research tool. In this review, we provide an overview about the use of sortase A in interdisciplinary research, mainly for protein modification, synthesis of protein-polymer conjugates and immobilization of proteins on surfaces.},
language = {en}
}
@article{UlbrichtMohrAltenburgetal.2021,
author = {Ulbricht, Alexander and Mohr, Gunther and Altenburg, Simon J. and Oster, Simon and Maierhofer, Christiane and Bruno, Giovanni},
title = {Can potential defects in LPBF be healed from the laser exposure of subsequent layers?},
series = {Metals : open access journal},
volume = {11},
journal = {Metals : open access journal},
number = {7},
publisher = {MDPI},
address = {Basel},
issn = {2075-4701},
doi = {10.3390/met11071012},
pages = {14},
year = {2021},
abstract = {Additive manufacturing (AM) of metals and in particular laser powder bed fusion (LPBF) enables a degree of freedom in design unparalleled by conventional subtractive methods. To ensure that the designed precision is matched by the produced LPBF parts, a full understanding of the interaction between the laser and the feedstock powder is needed. It has been shown that the laser also melts subjacent layers of material underneath. This effect plays a key role when designing small cavities or overhanging structures, because, in these cases, the material underneath is feed-stock powder. In this study, we quantify the extension of the melt pool during laser illumination of powder layers and the defect spatial distribution in a cylindrical specimen. During the LPBF process, several layers were intentionally not exposed to the laser beam at various locations, while the build process was monitored by thermography and optical tomography. The cylinder was finally scanned by X-ray computed tomography (XCT). To correlate the positions of the unmolten layers in the part, a staircase was manufactured around the cylinder for easier registration. The results show that healing among layers occurs if a scan strategy is applied, where the orientation of the hatches is changed for each subsequent layer. They also show that small pores and surface roughness of solidified material below a thick layer of unmolten material (>200 mu m) serve as seeding points for larger voids. The orientation of the first two layers fully exposed after a thick layer of unmolten powder shapes the orientation of these voids, created by a lack of fusion.},
language = {en}
}
@article{KretzschmarAshbyFearonetal.2022,
author = {Kretzschmar, Mirjam E. and Ashby, Ben and Fearon, Elizabeth and Overton, Christopher E. and Panovska-Griffiths, Jasmina and Pellis, Lorenzo and Quaife, Matthew and Rozhnova, Ganna and Scarabel, Francesca and Stage, Helena B. and Swallow, Ben and Thompson, Robin N. and Tildesley, Michael J. and Villela, Daniel Campos},
title = {Challenges for modelling interventions for future pandemics},
series = {Epidemics},
volume = {38},
journal = {Epidemics},
publisher = {Elsevier},
address = {Amsterdam},
issn = {1755-4365},
doi = {10.1016/j.epidem.2022.100546},
pages = {13},
year = {2022},
abstract = {Mathematical modelling and statistical inference provide a framework to evaluate different non-pharmaceutical and pharmaceutical interventions for the control of epidemics that has been widely used during the COVID-19 pandemic. In this paper, lessons learned from this and previous epidemics are used to highlight the challenges for future pandemic control. We consider the availability and use of data, as well as the need for correct parameterisation and calibration for different model frameworks. We discuss challenges that arise in describing and distinguishing between different interventions, within different modelling structures, and allowing both within and between host dynamics. We also highlight challenges in modelling the health economic and political aspects of interventions. Given the diversity of these challenges, a broad variety of interdisciplinary expertise is needed to address them, combining mathematical knowledge with biological and social insights, and including health economics and communication skills. Addressing these challenges for the future requires strong cross disciplinary collaboration together with close communication between scientists and policy makers.},
language = {en}
}
@article{KruseAltattanLauxetal.2022,
author = {Kruse, Marlen and Altattan, Basma and Laux, Eva-Maria and Grasse, Nico and Heinig, Lars and M{\"o}ser, Christin and Smith, David M. and H{\"o}lzel, Ralph},
title = {Characterization of binding interactions of SARS-CoV-2 spike protein and DNA-peptide nanostructures},
series = {Scientific reports},
volume = {12},
journal = {Scientific reports},
number = {1},
publisher = {Macmillan Publishers Limited, part of Springer Nature},
address = {London},
issn = {2045-2322},
doi = {10.1038/s41598-022-16914-9},
pages = {12},
year = {2022},
abstract = {Binding interactions of the spike proteins of the severe acute respiratory syndrome corona virus 2 (SARS-CoV-2) to a peptide fragment derived from the human angiotensin converting enzyme 2 (hACE2) receptor are investigated. The peptide is employed as capture moiety in enzyme linked immunosorbent assays (ELISA) and quantitative binding interaction measurements that are based on fluorescence proximity sensing (switchSENSE). In both techniques, the peptide is presented on an oligovalent DNA nanostructure, in order to assess the impact of mono- versus trivalent binding modes. As the analyte, the spike protein and several of its subunits are tested as well as inactivated SARS-CoV-2 and pseudo viruses. While binding of the peptide to the full-length spike protein can be observed, the subunits RBD and S1 do not exhibit binding in the employed concentrations. Variations of the amino acid sequence of the recombinant full-length spike proteins furthermore influence binding behavior. The peptide was coupled to DNA nanostructures that form a geometric complement to the trimeric structure of the spike protein binding sites. An increase in binding strength for trimeric peptide presentation compared to single peptide presentation could be generally observed in ELISA and was quantified in switchSENSE measurements. Binding to inactivated wild type viruses could be shown as well as qualitatively different binding behavior of the Alpha and Beta variants compared to the wild type virus strain in pseudo virus models.},
language = {en}
}
@article{CoduttiBenteFaivreetal.2019,
author = {Codutti, Agnese and Bente, Klaas and Faivre, Damien and Klumpp, Stefan},
title = {Chemotaxis in external fields: Simulations for active magnetic biological matter},
series = {PLoS Computational Biology : a new community journal},
volume = {15},
journal = {PLoS Computational Biology : a new community journal},
number = {12},
publisher = {PLoS},
address = {San Fransisco},
issn = {1553-734X},
doi = {10.1371/journal.pcbi.1007548},
pages = {26},
year = {2019},
abstract = {The movement of microswimmers is often described by active Brownian particle models. Here we introduce a variant of these models with several internal states of the swimmer to describe stochastic strategies for directional swimming such as run and tumble or run and reverse that are used by microorganisms for chemotaxis. The model includes a mechanism to generate a directional bias for chemotaxis and interactions with external fields (e.g., gravity, magnetic field, fluid flow) that impose forces or torques on the swimmer. We show how this modified model can be applied to various scenarios: First, the run and tumble motion of E. coli is used to establish a paradigm for chemotaxis and investigate how it is affected by external forces. Then, we study magneto-aerotaxis in magnetotactic bacteria, which is biased not only by an oxygen gradient towards a preferred concentration, but also by magnetic fields, which exert a torque on an intracellular chain of magnets. We study the competition of magnetic alignment with active reorientation and show that the magnetic orientation can improve chemotaxis and thereby provide an advantage to the bacteria, even at rather large inclination angles of the magnetic field relative to the oxygen gradient, a case reminiscent of what is expected for the bacteria at or close to the equator. The highest gain in chemotactic velocity is obtained for run and tumble with a magnetic field parallel to the gradient, but in general a mechanism for reverse motion is necessary to swim against the magnetic field and a run and reverse strategy is more advantageous in the presence of a magnetic torque. This finding is consistent with observations that the dominant mode of directional changes in magnetotactic bacteria is reversal rather than tumbles. Moreover, it provides guidance for the design of future magnetic biohybrid swimmers. Author summary In this paper, we propose a modified Active Brownian particle model to describe bacterial swimming behavior under the influence of external forces and torques, in particular of a magnetic torque. This type of interaction is particularly important for magnetic biohybrids (i.e. motile bacteria coupled to a synthetic magnetic component) and for magnetotactic bacteria (i.e. bacteria with a natural intracellular magnetic chain), which perform chemotaxis to swim along chemical gradients, but are also directed by an external magnetic field. The model allows us to investigate the benefits and disadvantages of such coupling between two different directionality mechanisms. In particular we show that the magnetic torque can speed chemotaxis up in some conditions, while it can hinder it in other cases. In addition to an understanding of the swimming strategies of naturally magnetotactic organisms, the results may guide the design of future biomedical devices.},
language = {en}
}
@article{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 = {Science advances},
volume = {6},
journal = {Science advances},
number = {22},
publisher = {American Association for the Advancement of Science},
address = {Washington},
issn = {2375-2548},
doi = {10.1126/sciadv.aaz6153},
pages = {8},
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}
}
@article{Pikovskij2021,
author = {Pikovskij, Arkadij},
title = {Chimeras on a social-type network},
series = {Mathematical modelling of natural phenomena : MMNP},
volume = {16},
journal = {Mathematical modelling of natural phenomena : MMNP},
publisher = {EDP Sciences},
address = {Les Ulis},
issn = {0973-5348},
doi = {10.1051/mmnp/2021012},
pages = {9},
year = {2021},
abstract = {We consider a social-type network of coupled phase oscillators. Such a network consists of an active core of mutually interacting elements, and of a flock of passive units, which follow the driving from the active elements, but otherwise are not interacting. We consider a ring geometry with a long-range coupling, where active oscillators form a fluctuating chimera pattern. We show that the passive elements are strongly correlated. This is explained by negative transversal Lyapunov exponents.},
language = {en}
}
@article{ToenjesFiorePereiradaSilva2021,
author = {T{\"o}njes, Ralf and Fiore, Carlos E. and Pereira da Silva, Tiago},
title = {Coherence resonance in influencer networks},
series = {Nature Communications},
volume = {12},
journal = {Nature Communications},
number = {1},
publisher = {Nature Publishing Group UK},
address = {London},
issn = {2041-1723},
doi = {10.1038/s41467-020-20441-4},
pages = {8},
year = {2021},
abstract = {Complex networks are abundant in nature and many share an important structural property: they contain a few nodes that are abnormally highly connected (hubs). Some of these hubs are called influencers because they couple strongly to the network and play fundamental dynamical and structural roles. Strikingly, despite the abundance of networks with influencers, little is known about their response to stochastic forcing. Here, for oscillatory dynamics on influencer networks, we show that subjecting influencers to an optimal intensity of noise can result in enhanced network synchronization. This new network dynamical effect, which we call coherence resonance in influencer networks, emerges from a synergy between network structure and stochasticity and is highly nonlinear, vanishing when the noise is too weak or too strong. Our results reveal that the influencer backbone can sharply increase the dynamical response in complex systems of coupled oscillators. Influencer networks include a small set of highly-connected nodes and can reach synchrony only via strong node interaction. Tonjes et al. show that introducing an optimal amount of noise enhances synchronization of such networks, which may be relevant for neuroscience or opinion dynamics applications.},
language = {en}
}
@article{ProlSmirnovHoqueetal.2022,
author = {Prol, Fabricio S. and Smirnov, Artem G. and Hoque, M. Mainul and Shprits, Yuri},
title = {Combined model of topside ionosphere and plasmasphere derived from radio-occultation and Van Allen Probes data},
series = {Scientific reports},
volume = {12},
journal = {Scientific reports},
number = {1},
publisher = {Macmillan Publishers Limited, part of Springer Nature},
address = {London},
issn = {2045-2322},
doi = {10.1038/s41598-022-13302-1},
pages = {11},
year = {2022},
abstract = {In the last years, electron density profile functions characterized by a linear dependence on the scale height showed good results when approximating the topside ionosphere. The performance above 800 km, however, is not yet well investigated. This study investigates the capability of the semi-Epstein functions to represent electron density profiles from the peak height up to 20,000 km. Electron density observations recorded by the Van Allen Probes were used to resolve the scale height dependence in the plasmasphere. It was found that the linear dependence of the scale height in the topside ionosphere cannot be directly used to extrapolate profiles above 800 km. We find that the dependence of scale heights on altitude is quadratic in the plasmasphere. A statistical model of the scale heights is therefore proposed. After combining the topside ionosphere and plasmasphere by a unified model, we have obtained good estimations not only in the profile shapes, but also in the Total Electron Content magnitude and distributions when compared to actual measurements from 2013, 2014, 2016 and 2017. Our investigation shows that Van Allen Probes can be merged to radio-occultation data to properly represent the upper ionosphere and plasmasphere by means of a semi-Epstein function.},
language = {en}
}
@article{WiesnerLadyman2021,
author = {Wiesner, Karoline and Ladyman, James},
title = {Complex systems are always correlated but rarely information processing},
series = {Journal of physics. Complexity},
volume = {2},
journal = {Journal of physics. Complexity},
number = {4},
publisher = {IOP Publ. Ltd.},
address = {Bristol},
issn = {2632-072X},
doi = {10.1088/2632-072X/ac371c},
pages = {4},
year = {2021},
abstract = {'Complex systems are information processors' is a statement that is frequently made. Here we argue for the distinction between information processing-in the sense of encoding and transmitting a symbolic representation-and the formation of correlations (pattern formation/self-organisation). The study of both uses tools from information theory, but the purpose is very different in each case: explaining the mechanisms and understanding the purpose or function in the first case, versus data analysis and correlation extraction in the latter. We give examples of both and discuss some open questions. The distinction helps focus research efforts on the relevant questions in each case.},
language = {en}
}
@article{MatternReppertZeuschneretal.2023,
author = {Mattern, Maximilian and Reppert, Alexander von and Zeuschner, Steffen Peer and Herzog, Marc and Pudell, Jan-Etienne and Bargheer, Matias},
title = {Concepts and use cases for picosecond ultrasonics with x-rays},
series = {Photoacoustics},
volume = {31},
journal = {Photoacoustics},
publisher = {Elsevier},
address = {Amsterdam},
issn = {2213-5979},
doi = {10.1016/j.pacs.2023.100503},
pages = {22},
year = {2023},
abstract = {This review discusses picosecond ultrasonics experiments using ultrashort hard x-ray probe pulses to extract the transient strain response of laser-excited nanoscopic structures from Bragg-peak shifts. This method provides direct, layer-specific, and quantitative information on the picosecond strain response for structures down to few-nm thickness. We model the transient strain using the elastic wave equation and express the driving stress using Gruneisen parameters stating that the laser-induced stress is proportional to energy density changes in the microscopic subsystems of the solid, i.e., electrons, phonons and spins. The laser-driven strain response can thus serve as an ultrafast proxy for local energy-density and temperature changes, but we emphasize the importance of the nanoscale morphology for an accurate interpretation due to the Poisson effect. The presented experimental use cases encompass ultrathin and opaque metal-heterostructures, continuous and granular nanolayers as well as negative thermal expansion materials, that each pose a challenge to established all-optical techniques.},
language = {en}
}
@article{GranadoAbadMetzleretal.2020,
author = {Granado, Felipe Le Vot and Abad, Enrique and Metzler, Ralf and Yuste, Santos B.},
title = {Continuous time random walk in a velocity field},
series = {New Journal of Physics},
volume = {22},
journal = {New Journal of Physics},
publisher = {Dt. Physikalische Ges.},
address = {Bad Honnef},
issn = {1367-2630},
doi = {10.1088/1367-2630/ab9ae2},
pages = {27},
year = {2020},
abstract = {We consider the emerging dynamics of a separable continuous time random walk (CTRW) in the case when the random walker is biased by a velocity field in a uniformly growing domain. Concrete examples for such domains include growing biological cells or lipid vesicles, biofilms and tissues, but also macroscopic systems such as expanding aquifers during rainy periods, or the expanding Universe. The CTRW in this study can be subdiffusive, normal diffusive or superdiffusive, including the particular case of a L{\´e}vy flight. We first consider the case when the velocity field is absent. In the subdiffusive case, we reveal an interesting time dependence of the kurtosis of the particle probability density function. In particular, for a suitable parameter choice, we find that the propagator, which is fat tailed at short times, may cross over to a Gaussian-like propagator. We subsequently incorporate the effect of the velocity field and derive a bi-fractional diffusion-advection equation encoding the time evolution of the particle distribution. We apply this equation to study the mixing kinetics of two diffusing pulses, whose peaks move towards each other under the action of velocity fields acting in opposite directions. This deterministic motion of the peaks, together with the diffusive spreading of each pulse, tends to increase particle mixing, thereby counteracting the peak separation induced by the domain growth. As a result of this competition, different regimes of mixing arise. In the case of L{\´e}vy flights, apart from the non-mixing regime, one has two different mixing regimes in the long-time limit, depending on the exact parameter choice: in one of these regimes, mixing is mainly driven by diffusive spreading, while in the other mixing is controlled by the velocity fields acting on each pulse. Possible implications for encounter-controlled reactions in real systems are discussed.},
language = {en}
}
@article{TotzLoeberTotzetal.2018,
author = {Totz, Sonja Juliana and L{\"o}ber, Jakob and Totz, Jan Frederik and Engel, Harald},
title = {Control of transversal instabilities in reaction-diffusion systems},
series = {New journal of physics : the open-access journal for physics},
volume = {20},
journal = {New journal of physics : the open-access journal for physics},
publisher = {IOP Publ. Ltd.},
address = {Bristol},
issn = {1367-2630},
doi = {10.1088/1367-2630/aabce5},
pages = {16},
year = {2018},
abstract = {In two-dimensional reaction-diffusion systems, local curvature perturbations on traveling waves are typically damped out and vanish. However, if the inhibitor diffuses much faster than the activator, transversal instabilities can arise, leading from flat to folded, spatio-temporally modulated waves and to spreading spiral turbulence. Here, we propose a scheme to induce or inhibit these instabilities via a spatio-temporal feedback loop. In a piecewise-linear version of the FitzHugh-Nagumo model, transversal instabilities and spiral turbulence in the uncontrolled system are shown to be suppressed in the presence of control, thereby stabilizing plane wave propagation. Conversely, in numerical simulations with the modified Oregonator model for the photosensitive Belousov-Zhabotinsky reaction, which does not exhibit transversal instabilities on its own, we demonstrate the feasibility of inducing transversal instabilities and study the emerging wave patterns in a well-controlled manner.},
language = {en}
}
@article{BouchouleSchemmerHenkel2018,
author = {Bouchoule, Isabelle and Schemmer, Max and Henkel, Carsten},
title = {Cooling phonon modes of a Bose condensate with uniform few body losses},
series = {Scipost Physics},
volume = {5},
journal = {Scipost Physics},
number = {5},
publisher = {Scipost foundation},
address = {Amsterdam},
issn = {2542-4653},
doi = {10.21468/SciPostPhys.5.5.043},
pages = {18},
year = {2018},
abstract = {We present a general analysis of the cooling produced by losses on condensates or quasi-condensates. We study how the occupations of the collective phonon modes evolve in time, assuming that the loss process is slow enough so that each mode adiabatically follows the decrease of the mean density. The theory is valid for any loss process whose rate is proportional to the jth power of the density, but otherwise spatially uniform. We cover both homogeneous gases and systems confined in a smooth potential. For a low-dimensional gas, we can take into account the modified equation of state due to the broadening of the cloud width along the tightly confined directions, which occurs for large interactions. We find that at large times, the temperature decreases proportionally to the energy scale mc(2), where m is the mass of the particles and c the sound velocity. We compute the asymptotic ratio of these two quantities for different limiting cases: a homogeneous gas in any dimension and a one-dimensional gas in a harmonic trap.},
language = {en}
}
@article{LeverMayerMetjeetal.2021,
author = {Lever, Fabiano and Mayer, Dennis and Metje, Jan and Alisauskas, Skirmantas and Calegari, Francesca and D{\"u}sterer, Stefan and Feifel, Raimund and Niebuhr, Mario and Manschwetus, Bastian and Kuhlmann, Marion and Mazza, Tommaso and Robinson, Matthew Scott and Squibb, Richard J. and Trabattoni, Andrea and Wallner, M{\aa}ns and Wolf, Thomas J. A. and G{\"u}hr, Markus},
title = {Core-level spectroscopy of 2-thiouracil at the sulfur L1 and L2,3 edges utilizing a SASE free-electron-laser},
series = {Molecules},
volume = {26},
journal = {Molecules},
number = {21},
publisher = {MDPI},
address = {Basel},
issn = {1420-3049},
pages = {11},
year = {2021},
abstract = {In this paper, we report X-ray absorption and core-level electron spectra of the nucleobase derivative 2-thiouracil at the sulfur L1- and L2,3-edges. We used soft X-rays from the free-electron laser FLASH2 for the excitation of isolated molecules and dispersed the outgoing electrons with a magnetic bottle spectrometer. We identified photoelectrons from the 2p core orbital, accompanied by an electron correlation satellite, as well as resonant and non-resonant Coster-Kronig and Auger-Meitner emission at the L1- and L2,3-edges, respectively. We used the electron yield to construct X-ray absorption spectra at the two edges. The experimental data obtained are put in the context of the literature currently available on sulfur core-level and 2-thiouracil spectroscopy.},
language = {en}
}
@article{VinkeGabryschPaolettietal.2020,
author = {Vinke, Kira and Gabrysch, Sabine and Paoletti, Emanuela and Rockstr{\"o}m, Johan and Schellnhuber, Hans Joachim},
title = {Corona and the climate},
series = {Global sustainability},
volume = {3},
journal = {Global sustainability},
publisher = {Cambridge Univ. Press},
address = {Cambridge},
issn = {2059-4798},
doi = {10.1017/sus.2020.20},
pages = {7},
year = {2020},
abstract = {Lessons from the corona crisis can help manage the even more daunting challenge of anthropogenic global warming.},
language = {en}
}
@article{MaitiMakwanaZhangetal.2022,
author = {Maiti, Snehanshu and Makwana, Kirit and Zhang, Heshou and Yan, Huirong},
title = {Cosmic-ray transport in magnetohydrodynamic turbulence},
series = {The astrophysical journal : an international review of spectroscopy and astronomical physics / part 1},
volume = {926},
journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics / part 1},
number = {1},
publisher = {Institute of Physics Publ.},
address = {London},
issn = {1538-4357},
doi = {10.3847/1538-4357/ac46c8},
pages = {8},
year = {2022},
abstract = {This paper studies cosmic-ray (CR) transport in magnetohydrodynamic (MHD) turbulence. CR transport is strongly dependent on the properties of the magnetic turbulence. We perform test particle simulations to study the interactions of CR with both total MHD turbulence and decomposed MHD modes. The spatial diffusion coefficients and the pitch angle scattering diffusion coefficients are calculated from the test particle trajectories in turbulence. Our results confirm that the fast modes dominate the CR propagation, whereas Alfven and slow modes are much less efficient and have shown similar pitch-angle scattering rates. We investigate the cross field transport on large and small scales. On large/global scales, normal diffusion is observed and the diffusion coefficient is suppressed by M-A(zeta) compared to the parallel diffusion coefficients, with zeta closer to 4 in Alfven modes than that in total turbulence, as theoretically expected. For the CR transport on scales smaller than the turbulence injection scale, both the local and global magnetic reference frames are adopted. Superdiffusion is observed on such small scales in all the cases. Particularly, CR transport in Alfven modes show clear Richardson diffusion in the local reference frame. The diffusion transitions smoothly from the Richardson's one with index 1.5 to normal diffusion as the particle mean free path decreases from lambda(parallel to) >> L to lambda(parallel to) << L, where L is the injection/coherence length of turbulence. Our results have broad applications to CRs in various astrophysical environments.},
language = {en}
}
@article{SahaOwenOrretal.2019,
author = {Saha, Sourav and Owen, Lewis A. and Orr, Elizabeth N. and Caffee, Marc W.},
title = {Cosmogenic Be-10 and equilibrium-line altitude dataset of Holocene glacier advances in the Himalayan-Tibetan orogen},
series = {Data in brief},
volume = {26},
journal = {Data in brief},
publisher = {Elsevier},
address = {Amsterdam},
issn = {2352-3409},
doi = {10.1016/j.dib.2019.104412},
pages = {13},
year = {2019},
abstract = {A comprehensive analysis of the variable temporal and spatial responses of tropical-subtropical high-altitude glaciers to climate change is critical for successful model predictions and environmental risk assessment in the Himalayan-Tibetan orogen. High-frequency Holocene glacier chronostratigraphies are therefore reconstructed in 79 glaciated valleys across the orogen using 519 published and 16 new terrestrial cosmogenic 10Be exposure age dataset. Published 10Be ages are compiled only for moraine boulders (excluding bedrock ages). These ages are recalculated using the latest ICE-D production rate calibration database and the scaling scheme models. Outliers for the individual moraine are detected using the Chauvenet's criterion. In addition, past equilibrium-line altitudes (ELAs) are determined using the area-altitude (AA), area accumulation ratio (AAR), and toe-headwall accumulation ratio (THAR) methods for each glacier advance. The modern maximum elevations of lateral moraines (MELM) are also used to estimate modern ELAs and as an independent check on mean ELAs derived using the above three methods. These data may serve as an essential archive for future studies focusing on the cryospheric and environmental changes in the Himalayan-Tibetan orogen. A more comprehensive analysis of the published and new 10Be ages and ELA results and a list of references are presented in Saha et al. (2019, High-frequency Holocene glacier fluctuations in the Himalayan-Tibetan orogen. Quaternary Science Reviews, 220, 372-400).},
language = {en}
}
@article{KreuzerReeseHuiskampetal.2021,
author = {Kreuzer, Moritz and Reese, Ronja and Huiskamp, Willem Nicholas and Petri, Stefan and Albrecht, Torsten and Feulner, Georg and Winkelmann, Ricarda},
title = {Coupling framework (1.0) for the PISM (1.1.4) ice sheet model and the MOMS (5.1.0) ocean model via the PICO ice shelf cavity model in an Antarctic domain},
series = {Geoscientific model development : an interactive open access journal of the European Geosciences Union},
volume = {14},
journal = {Geoscientific model development : an interactive open access journal of the European Geosciences Union},
number = {6},
publisher = {Copernicus},
address = {G{\"o}ttingen},
issn = {1991-959X},
doi = {10.5194/gmd-14-3697-2021},
pages = {3697 -- 3714},
year = {2021},
abstract = {The past and future evolution of the Antarctic Ice Sheet is largely controlled by interactions between the ocean and floating ice shelves. To investigate these interactions, coupled ocean and ice sheet model configurations are required. Previous modelling studies have mostly relied on high-resolution configurations, limiting these studies to individual glaciers or regions over short timescales of decades to a few centuries. We present a framework to couple the dynamic ice sheet model PISM (Parallel Ice Sheet Model) with the global ocean general circulation model MOM5 (Modular Ocean Model) via the ice shelf cavity model PICO (Pots-dam Ice-shelf Cavity mOdel). As ice shelf cavities are not resolved by MOM5 but are parameterized with the PICO box model, the framework allows the ice sheet and ocean components to be run at resolutions of 16 km and 3 degrees respectively. This approach makes the coupled configuration a useful tool for the analysis of interactions between the Antarctic Ice Sheet and the global ocean over time spans of the order of centuries to millennia. In this study, we describe the technical implementation of this coupling framework: sub-shelf melting in the ice sheet component is calculated by PICO from modelled ocean temperatures and salinities at the depth of the continental shelf, and, vice versa, the resulting mass and energy fluxes from melting at the ice-ocean interface are transferred to the ocean component. Mass and energy fluxes are shown to be conserved to machine precision across the considered component domains. The implementation is computationally efficient as it introduces only minimal overhead. Furthermore, the coupled model is evaluated in a 4000 year simulation under constant present-day climate forcing and is found to be stable with respect to the ocean and ice sheet spin-up states. The framework deals with heterogeneous spatial grid geometries, varying grid resolutions, and timescales between the ice and ocean component in a generic way; thus, it can be adopted to a wide range of model set-ups.},
language = {en}
}
@article{PetrovSingerCoughlinetal.2022,
author = {Petrov, Polina and Singer, Leo P. and Coughlin, Michael W. and Kumar, Vishwesh and Almualla, Mouza and Anand, Shreya and Bulla, Mattia and Dietrich, Tim and Foucart, Francois and Guessoum, Nidhal},
title = {Data-driven expectations for electromagnetic counterpart searches based on LIGO/Virgo public alerts},
series = {The astrophysical journal : an international review of spectroscopy and astronomical physics; part 1},
volume = {924},
journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics; part 1},
number = {2},
publisher = {Institute of Physics Publ.},
address = {London},
issn = {1538-4357},
doi = {10.3847/1538-4357/ac366d},
pages = {10},
year = {2022},
abstract = {Searches for electromagnetic counterparts of gravitational-wave signals have redoubled since the first detection in 2017 of a binary neutron star merger with a gamma-ray burst, optical/infrared kilonova, and panchromatic afterglow. Yet, one LIGO/Virgo observing run later, there has not yet been a second, secure identification of an electromagnetic counterpart. This is not surprising given that the localization uncertainties of events in LIGO and Virgo's third observing run, O3, were much larger than predicted. We explain this by showing that improvements in data analysis that now allow LIGO/Virgo to detect weaker and hence more poorly localized events have increased the overall number of detections, of which well-localized, gold-plated events make up a smaller proportion overall. We present simulations of the next two LIGO/Virgo/KAGRA observing runs, O4 and O5, that are grounded in the statistics of O3 public alerts. To illustrate the significant impact that the updated predictions can have, we study the follow-up strategy for the Zwicky Transient Facility. Realistic and timely forecasting of gravitational-wave localization accuracy is paramount given the large commitments of telescope time and the need to prioritize which events are followed up. We include a data release of our simulated localizations as a public proposal planning resource for astronomers.},
language = {en}
}
@article{OeschWeiseBruno2020,
author = {Oesch, Tyler and Weise, Frank and Bruno, Giovanni},
title = {Detection and quantification of cracking in concrete aggregate through virtual data fusion of X-ray computed tomography images},
series = {Materials},
volume = {13},
journal = {Materials},
number = {18},
publisher = {MDPI},
address = {Basel},
issn = {1996-1944},
doi = {10.3390/ma13183921},
pages = {27},
year = {2020},
abstract = {In this work, which is part of a larger research program, a framework called "virtual data fusion" was developed to provide an automated and consistent crack detection method that allows for the cross-comparison of results from large quantities of X-ray computed tomography (CT) data. A partial implementation of this method in a custom program was developed for use in research focused on crack quantification in alkali-silica reaction (ASR)-sensitive concrete aggregates. During the CT image processing, a series of image analyses tailored for detecting specific, individual crack-like characteristics were completed. The results of these analyses were then "fused" in order to identify crack-like objects within the images with much higher accuracy than that yielded by any individual image analysis procedure. The results of this strategy demonstrated the success of the program in effectively identifying crack-like structures and quantifying characteristics, such as surface area and volume. The results demonstrated that the source of aggregate has a very significant impact on the amount of internal cracking, even when the mineralogical characteristics remain very similar. River gravels, for instance, were found to contain significantly higher levels of internal cracking than quarried stone aggregates of the same mineralogical type.},
language = {en}
}
@article{ParkStolleYamazakietal.2020,
author = {Park, Jaeheung and Stolle, Claudia and Yamazaki, Yosuke and Rauberg, Jan and Michaelis, Ingo and Olsen, Nils},
title = {Diagnosing low-/mid-latitude ionospheric currents using platform magnetometers},
series = {Earth, planets and space},
volume = {72},
journal = {Earth, planets and space},
number = {1},
publisher = {Springer},
address = {New York},
issn = {1343-8832},
doi = {10.1186/s40623-020-01274-3},
pages = {18},
year = {2020},
abstract = {Electric currents flowing in the terrestrial ionosphere have conventionally been diagnosed by low-earth-orbit (LEO) satellites equipped with science-grade magnetometers and long booms on magnetically clean satellites. In recent years, there are a variety of endeavors to incorporate platform magnetometers, which are initially designed for navigation purposes, to study ionospheric currents. Because of the suboptimal resolution and significant noise of the platform magnetometers, however, most of the studies were confined to high-latitude auroral regions, where magnetic field deflections from ionospheric currents easily exceed 100 nT. This study aims to demonstrate the possibility of diagnosing weak low-/mid-latitude ionospheric currents based on platform magnetometers. We use navigation magnetometer data from two satellites, CryoSat-2 and the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO), both of which have been intensively calibrated based on housekeeping data and a high-precision geomagnetic field model. Analyses based on 8 years of CryoSat-2 data as well as similar to 1.5 years of GRACE-FO data reproduce well-known climatology of inter-hemispheric field-aligned currents (IHFACs), as reported by previous satellite missions dedicated to precise magnetic observations. Also, our results show that C-shaped structures appearing in noontime IHFAC distributions conform to the shape of the South Atlantic Anomaly. The F-region dynamo currents are only partially identified in the platform magnetometer data, possibly because the currents are weaker than IHFACs in general and depend significantly on altitude and solar activity. Still, this study evidences noontime F-region dynamo currents at the highest altitude (717 km) ever reported. We expect that further data accumulation from continuously operating missions may reveal the dynamo currents more clearly during the next solar maximum.},
language = {en}
}
@article{ManiKupschMuelleretal.2022,
author = {Mani, Deepak and Kupsch, Andreas and M{\"u}ller, Bernd R. and Bruno, Giovanni},
title = {Diffraction Enhanced Imaging Analysis with Pseudo-Voigt Fit Function},
series = {Journal of imaging : open access journal},
volume = {8},
journal = {Journal of imaging : open access journal},
number = {8},
publisher = {MDPI},
address = {Basel},
issn = {2313-433X},
doi = {10.3390/jimaging8080206},
pages = {13},
year = {2022},
abstract = {Diffraction enhanced imaging (DEI) is an advanced digital radiographic imaging technique employing the refraction of X-rays to contrast internal interfaces. This study aims to qualitatively and quantitatively evaluate images acquired using this technique and to assess how different fitting functions to the typical rocking curves (RCs) influence the quality of the images. RCs are obtained for every image pixel. This allows the separate determination of the absorption and the refraction properties of the material in a position-sensitive manner. Comparison of various types of fitting functions reveals that the Pseudo-Voigt (PsdV) function is best suited to fit typical RCs. A robust algorithm was developed in the Python programming language, which reliably extracts the physically meaningful information from each pixel of the image. We demonstrate the potential of the algorithm with two specimens: a silicone gel specimen that has well-defined interfaces, and an additively manufactured polycarbonate specimen.},
language = {en}
}
@article{SchroederEvansMishurovaetal.2021,
author = {Schr{\"o}der, Jakob and Evans, Alexander and Mishurova, Tatiana and Ulbricht, Alexander and Sprengel, Maximilian and Serrano-Munoz, Itziar and Fritsch, Tobias and Kromm, Arne and Kannengießer, Thomas and Bruno, Giovanni},
title = {Diffraction-based residual stress characterization in laser additive manufacturing of metals},
series = {Metals : open access journal},
volume = {11},
journal = {Metals : open access journal},
number = {11},
publisher = {MDPI},
address = {Basel},
issn = {2075-4701},
doi = {10.3390/met11111830},
pages = {34},
year = {2021},
abstract = {Laser-based additive manufacturing methods allow the production of complex metal structures within a single manufacturing step. However, the localized heat input and the layer-wise manufacturing manner give rise to large thermal gradients. Therefore, large internal stress (IS) during the process (and consequently residual stress (RS) at the end of production) is generated within the parts. This IS or RS can either lead to distortion or cracking during fabrication or in-service part failure, respectively. With this in view, the knowledge on the magnitude and spatial distribution of RS is important to develop strategies for its mitigation. Specifically, diffraction-based methods allow the spatial resolved determination of RS in a non-destructive fashion. In this review, common diffraction-based methods to determine RS in laser-based additive manufactured parts are presented. In fact, the unique microstructures and textures associated to laser-based additive manufacturing processes pose metrological challenges. Based on the literature review, it is recommended to (a) use mechanically relaxed samples measured in several orientations as appropriate strain-free lattice spacing, instead of powder, (b) consider that an appropriate grain-interaction model to calculate diffraction-elastic constants is both material- and texture-dependent and may differ from the conventionally manufactured variant. Further metrological challenges are critically reviewed and future demands in this research field are discussed.},
language = {en}
}
@article{vanMarleBohdanMorrisetal.2022,
author = {van Marle, Allard Jan and Bohdan, Artem and Morris, Paul J. and Pohl, Martin and Marcowith, Alexandre},
title = {Diffusive shock acceleration at oblique high mach number shocks},
series = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
volume = {929},
journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
number = {1},
publisher = {IOP Publ. Ltd.},
address = {Bristol},
issn = {1538-4357},
doi = {10.3847/1538-4357/ac5962},
pages = {10},
year = {2022},
abstract = {The current paradigm of cosmic-ray (CR) origin states that the greater part of galactic CRs is produced by supernova remnants. The interaction of supernova ejecta with the interstellar medium after a supernova's explosions results in shocks responsible for CR acceleration via diffusive shock acceleration (DSA). We use particle-in-cell (PIC) simulations and a combined PIC-magnetohydrodynamic (PIC-MHD) technique to investigate whether DSA can occur in oblique high Mach number shocks. Using the PIC method, we follow the formation of the shock and determine the fraction of the particles that gets involved in DSA. With this result, we use PIC-MHD simulations to model the large-scale structure of the plasma and the magnetic field surrounding the shock and find out whether or not the reflected particles can generate upstream turbulence and trigger DSA. We find that the feasibility of this process in oblique shocks depends strongly on the Alfvenic Mach number, and the DSA process is more likely to be triggered at high Mach number shocks.},
language = {en}
}
@article{HaverkampSorgenfreiGiangrisostomietal.2021,
author = {Haverkamp, Robert and Sorgenfrei, Nomi and Giangrisostomi, Erika and Neppl, Stefan and K{\"u}hn, Danilo and F{\"o}hlisch, Alexander},
title = {Directional charge delocalization dynamics in semiconducting 2H-MoS2 and metallic 1T-LixMoS2},
series = {Scientific reports},
volume = {11},
journal = {Scientific reports},
number = {1},
publisher = {Macmillan Publishers Limited, part of Springer Nature},
address = {London},
issn = {2045-2322},
doi = {10.1038/s41598-021-86364-2},
pages = {7},
year = {2021},
abstract = {The layered dichalcogenide MoS2 is relevant for electrochemical Li adsorption/intercalation, in the course of which the material undergoes a concomitant structural phase transition from semiconducting 2H-MoS2 to metallic 1T-LixMoS2. With the core hole clock approach at the S L1 X-ray absorption edge we quantify the ultrafast directional charge transfer of excited S3p electrons in-plane () and out-of-plane (perpendicular to) for 2H-MoS2 as tau 2H,=0.38 +/- 0.08 fs and tau 2H,perpendicular to =0.33 +/- 0.06 fs and for 1T-LixMoS2 as tau 1T,=0.32 +/- 0.12 fs and tau 1T,perpendicular to =0.09 +/- 0.07 fs. The isotropic charge delocalization of S3p electrons in the semiconducting 2H phase within the S-Mo-S sheets is assigned to the specific symmetry of the Mo-S bonding arrangement. Formation of 1T-LixMoS2 by lithiation accelerates the in-plane charge transfer by a factor of similar to 1.2 due to electron injection to the Mo-S covalent bonds and concomitant structural repositioning of S atoms within the S-Mo-S sheets. For excitation into out-of-plane orbitals, an accelerated charge transfer by a factor of similar to 3.7 upon lithiation occurs due to S-Li coupling.},
language = {en}
}