TY - JOUR
A1 - Schulze, Patricia S. C.
A1 - Bett, Alexander J.
A1 - Bivour, Martin
A1 - Caprioglio, Pietro
A1 - Gerspacher, Fabian M.
A1 - Kabaklı, Özde Ş.
A1 - Richter, Armin
A1 - Stolterfoht, Martin
A1 - Zhang, Qinxin
A1 - Neher, Dieter
A1 - Hermle, Martin
A1 - Hillebrecht, Harald
A1 - Glunz, Stefan W.
A1 - Goldschmidt, Jan Christoph
T1 - 25.1% high-efficiency monolithic perovskite silicon tandem solar cell with a high bandgap perovskite absorber
JF - Solar RRL
N2 - 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.
KW - heterojunction silicon solar cells
KW - interfaces
KW - perovskite solar cells
KW - tandem solar cells
KW - thin films
Y1 - 2020
VL - 4
IS - 7
PB - John Wiley & Sons, Inc.
CY - New Jersey
ER -
TY - JOUR
A1 - Risbey, James S.
A1 - Lewandowsky, Stephan
A1 - Cowtan, Kevin
A1 - Oreskes, Naomi
A1 - Rahmstorf, Stefan
A1 - Jokimäki, Ari
A1 - Foster, Grant
T1 - A fluctuation in surface temperature in historical context
BT - reassessment and retrospective on the evidence
JF - Environmental research letters
N2 - 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.
KW - climate variability
KW - climate trends
KW - temperature fluctuation
KW - pause hiatus
Y1 - 2018
U6 - https://doi.org/10.1088/1748-9326/aaf342
SN - 1748-9326
VL - 13
IS - 12
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Hassanin, Alshaimaa
A1 - Kliem, Bernhard
A1 - Seehafer, Norbert
A1 - Török, Tibor
T1 - A model of homologous confined and ejective eruptions involving kink instability and flux cancellation
JF - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2 - 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.
Y1 - 2022
U6 - https://doi.org/10.3847/2041-8213/ac64a9
SN - 2041-8205
SN - 2041-8213
VL - 929
IS - 2
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Grebenkov, Denis S.
A1 - Metzler, Ralf
A1 - Oshanin, Gleb
T1 - A molecular relay race: sequential first-passage events to the terminal reaction centre in a cascade of diffusion controlled processes
JF - New Journal of Physics (NJP)
N2 - 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.
KW - diffusion
KW - reaction cascade
KW - first passage time
Y1 - 2021
U6 - https://doi.org/10.1088/1367-2630/ac1e42
SN - 1367-2630
VL - 23
PB - IOP - Institute of Physics Publishing
CY - Bristol
ER -
TY - JOUR
A1 - Großmann, Robert
A1 - Aranson, Igor S.
A1 - Peruani, Fernando
T1 - A particle-field approach bridges phase separation and collective motion in active matter
JF - Nature Communications
N2 - 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.
Y1 - 2020
U6 - https://doi.org/10.1038/s41467-020-18978-5
SN - 2041-1723
VL - 11
IS - 1
PB - Nature Publishing Group
CY - London
ER -
TY - JOUR
A1 - Hintsche, Marius
A1 - Waljor, Veronika
A1 - Grossmann, Robert
A1 - Kühn, Marco J.
A1 - Thormann, Kai M.
A1 - Peruani, Fernando
A1 - Beta, Carsten
T1 - A polar bundle of flagella can drive bacterial swimming by pushing, pulling, or coiling around the cell body
JF - Scientific reports
N2 - 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.
Y1 - 2017
U6 - https://doi.org/10.1038/s41598-017-16428-9
SN - 2045-2322
VL - 7
PB - Macmillan Publishers Limited, part of Springer Nature
CY - London
ER -
TY - JOUR
A1 - Schlemm, Tanja
A1 - Levermann, Anders
T1 - A simple parametrization of mélange buttressing for calving glaciers
JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2 - 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.
Y1 - 2021
U6 - https://doi.org/10.5194/tc-15-531-2021
SN - 1994-0416
SN - 1994-0424
VL - 15
IS - 2
SP - 531
EP - 545
PB - Copernicus
CY - Göttingen
ER -
TY - JOUR
A1 - Schlemm, Tanja
A1 - Levermann, Anders
T1 - A simple stress-based cliff-calving law
JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2 - 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.
Y1 - 2019
U6 - https://doi.org/10.5194/tc-13-2475-2019
SN - 1994-0416
SN - 1994-0424
VL - 13
IS - 9
SP - 2475
EP - 2488
PB - Copernicus
CY - Göttingen
ER -
TY - JOUR
A1 - Guggenberger, Tobias
A1 - Chechkin, Aleksei
A1 - Metzler, Ralf
T1 - Absence of stationary states and non-Boltzmann distributions of fractional Brownian motion in shallow external potentials
JF - New journal of physics : the open-access journal for physics
N2 - 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.
KW - diffusion
KW - Boltzmann distribution
KW - fractional Brownian motion
Y1 - 2022
U6 - https://doi.org/10.1088/1367-2630/ac7b3c
SN - 1367-2630
VL - 24
IS - 7
PB - Dt. Physikalische Ges.
CY - [Bad Honnef]
ER -
TY - JOUR
A1 - Willner, Sven N.
A1 - Levermann, Anders
A1 - Zhao, Fang
A1 - Frieler, Katja
T1 - Adaptation required to preserve future high-end river flood risk at present levels
JF - Science Advances
N2 - 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.
Y1 - 2018
U6 - https://doi.org/10.1126/sciadv.aao1914
SN - 2375-2548
VL - 4
IS - 1
PB - American Assoc. for the Advancement of Science
CY - Washington
ER -
TY - JOUR
A1 - Smirnov, Artem G.
A1 - Kronberg, Elena A.
A1 - Daly, Patrick W.
A1 - Aseev, Nikita
A1 - Shprits, Yuri
A1 - Kellerman, Adam C.
T1 - Adiabatic Invariants Calculations for Cluster Mission: A Long-Term Product for Radiation Belts Studies
JF - Journal of Geophysical Research: Space Physics
N2 - 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.
KW - L-Asterisk
KW - magnetosphere
KW - electrons
KW - model
Y1 - 2019
VL - 125
IS - 2
PB - John Wiley & Sons, Inc.
CY - New Jersey
ER -
TY - JOUR
A1 - Ciemer, Catrin
A1 - Rehm, Lars
A1 - Kurths, Jürgen
A1 - Donner, Reik Volker
A1 - Winkelmann, Ricarda
A1 - Boers, Niklas
T1 - An early-warning indicator for Amazon droughts exclusively based on tropical Atlantic sea surface temperatures
JF - Environmental Research Letters
N2 - 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.
KW - complex networks
KW - droughts
KW - prediction
KW - Amazon rainforest
Y1 - 2019
VL - 15
IS - 9
PB - IOP - Institute of Physics Publishing
CY - Bristol
ER -
TY - JOUR
A1 - Nakoudi, Konstantina
A1 - Stachlewska, Iwona S.
A1 - Ritter, Christoph
T1 - An extended lidar-based cirrus cloud retrieval scheme
BT - first application over an Arctic site
JF - Optics express : the international electronic journal of optics / Optica
N2 - 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.
Y1 - 2021
U6 - https://doi.org/10.1364/OE.414770
SN - 1094-4087
VL - 29
IS - 6
SP - 8553
EP - 8580
PB - Optical Society of America
CY - Washington
ER -
TY - JOUR
A1 - Schindler, Daniel
A1 - Moldenhawer, Ted
A1 - Stange, Maike
A1 - Lepro, Valentino
A1 - Beta, Carsten
A1 - Holschneider, Matthias
A1 - Huisinga, Wilhelm
T1 - Analysis of protrusion dynamics in amoeboid cell motility by means of regularized contour flows
JF - PLoS Computational Biology : a new community journal
N2 - 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.
Y1 - 2021
U6 - https://doi.org/10.1371/journal.pcbi.1009268
SN - 1553-734X
SN - 1553-7358
VL - 17
IS - 8
PB - PLoS
CY - San Fransisco
ER -
TY - JOUR
A1 - Mattern, Maximilian
A1 - Pudell, Jan-Etienne
A1 - Laskin, Gennadii
A1 - Reppert, Alexander von
A1 - Bargheer, Matias
T1 - Analysis of the temperature- and fluence-dependent magnetic stress in laser-excited SrRuO3
JF - Structural dynamics
N2 - 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 Grüneisen 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.
KW - Thin films
KW - Thermodynamic properties
KW - Bragg peak
KW - Ultrafast X-ray diffraction
KW - Thermal effects
KW - Phonons
KW - Magnetism
KW - Lattice dynamics
KW - Lasers
KW - Perovskites
Y1 - 2020
U6 - https://doi.org/10.1063/4.0000072
SN - 2329-7778
VL - 8
IS - 2
PB - AIP Publishing LLC
CY - Melville, NY
ER -
TY - JOUR
A1 - Munyaev, Vyacheslav O.
A1 - Smirnov, Lev A.
A1 - Kostin, Vasily A.
A1 - Osipov, Grigory V.
A1 - Pikovskij, Arkadij
T1 - Analytical approach to synchronous states of globally coupled noisy rotators
JF - New journal of physics : the open-access journal for physics
N2 - 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.
KW - coupled rotators
KW - synchronization transition
KW - hysteresis
KW - Kuramoto
KW - model
KW - noisy systems
Y1 - 2020
U6 - https://doi.org/10.1088/1367-2630/ab6f93
SN - 1367-2630
VL - 22
IS - 2
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Munyaev, Vyacheslav
A1 - Smirnov, Lev A.
A1 - Kostin, Vasily
A1 - Osipov, Grigory V.
A1 - Pikovskij, Arkadij
T1 - Analytical approach to synchronous states of globally coupled noisy rotators
JF - New Journal of Physics
N2 - 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.
KW - coupled rotators
KW - synchronization transition
KW - hysteresis
KW - Kuramoto model
KW - noisy systems
Y1 - 2019
VL - 22
IS - 2
PB - Springer Science
CY - New York
ER -
TY - JOUR
A1 - Dieterich, Peter
A1 - Lindemann, Otto
A1 - Moskopp, Mats Leif
A1 - Tauzin, Sebastien
A1 - Huttenlocher, Anna
A1 - Klages, Rainer
A1 - Chechkin, Aleksei V.
A1 - Schwab, Albrecht
T1 - Anomalous diffusion and asymmetric tempering memory in neutrophil chemotaxis
JF - PLoS Computational Biology : a new community journal
N2 - 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.
KW - neutrophils
KW - chemotaxis
KW - autocorrelation
KW - zebrafish
KW - cell migration
KW - covariance
KW - brownian motion
KW - stochastic processes
Y1 - 2022
U6 - https://doi.org/10.1371/journal.pcbi.1010089
SN - 1553-734X
SN - 1553-7358
VL - 18
IS - 5
PB - PLoS
CY - San Fransisco
ER -
TY - JOUR
A1 - Reese, Ronja
A1 - Albrecht, Torsten
A1 - Mengel, Matthias
A1 - Asay-Davis, Xylar
A1 - Winkelmann, Ricarda
T1 - Antarctic sub-shelf melt rates via PICO
JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2 - 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.
Y1 - 2018
U6 - https://doi.org/10.5194/tc-12-1969-2018
SN - 1994-0416
SN - 1994-0424
VL - 12
IS - 6
SP - 1969
EP - 1985
PB - Copernicus
CY - Göttingen
ER -
TY - JOUR
A1 - Pranav, Manasi
A1 - Hultzsch, Thomas
A1 - Musiienko, Artem
A1 - Sun, Bowen
A1 - Shukla, Atul
A1 - Jaiser, Frank
A1 - Shoaee, Safa
A1 - Neher, Dieter
T1 - Anticorrelated photoluminescence and free charge generation proves field-assisted exciton dissociation in low-offset PM6:Y5 organic solar cells
JF - APL materials : high impact open access journal in functional materials science
N2 - 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).
Y1 - 2023
U6 - https://doi.org/10.1063/5.0151580
SN - 2166-532X
VL - 11
IS - 6
PB - AIP Publishing
CY - Melville
ER -
TY - JOUR
A1 - Pohl, Martin
A1 - Macias, Oscar
A1 - Coleman, Phaedra
A1 - Gordon, Chris
T1 - Assessing the impact of hydrogen absorption on the characteristics of the Galactic center excess
JF - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2 - 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.
Y1 - 2022
U6 - https://doi.org/10.3847/1538-4357/ac6032
SN - 0004-637X
SN - 1538-4357
VL - 929
IS - 2
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Padash, Amin
A1 - Sandev, Trifce
A1 - Kantz, Holger
A1 - Metzler, Ralf
A1 - Chechkin, Aleksei
T1 - Asymmetric Levy flights are more efficient in random search
JF - Fractal and fractional
N2 - 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.
KW - asymmetric Levy flights
KW - first-arrival density
KW - search efficiency
Y1 - 2022
U6 - https://doi.org/10.3390/fractalfract6050260
SN - 2504-3110
VL - 6
IS - 5
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Seckler, Henrik
A1 - Metzler, Ralf
T1 - Bayesian deep learning for error estimation in the analysis of anomalous diffusion
JF - Nature Communnications
N2 - 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.
KW - random-walk
KW - models
Y1 - 2022
U6 - https://doi.org/10.1038/s41467-022-34305-6
SN - 2041-1723
VL - 13
PB - Nature Publishing Group UK
CY - London
ER -
TY - JOUR
A1 - Seckler, Henrik
A1 - Metzler, Ralf
T1 - Bayesian deep learning for error estimation in the analysis of anomalous diffusion
JF - Nature Communications
N2 - 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.
Y1 - 2022
U6 - https://doi.org/10.1038/s41467-022-34305-6
SN - 2041-1723
VL - 13
IS - 1
PB - Nature portfolio
CY - Berlin
ER -
TY - JOUR
A1 - Dai, Xiaolin
A1 - Böker, Alexander
A1 - Glebe, Ulrich
T1 - Broadening the scope of sortagging
JF - RSC Advances
N2 - 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.
Y1 - 2019
U6 - https://doi.org/10.1039/c8ra06705h
SN - 2046-2069
VL - 9
IS - 9
SP - 4700
EP - 4721
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Ulbricht, Alexander
A1 - Mohr, Gunther
A1 - Altenburg, Simon J.
A1 - Oster, Simon
A1 - Maierhofer, Christiane
A1 - Bruno, Giovanni
T1 - Can potential defects in LPBF be healed from the laser exposure of subsequent layers?
BT - A quantitative study
JF - Metals : open access journal
N2 - 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.
KW - selective laser melting (SLM)
KW - additive manufacturing (AM)
KW - process
KW - monitoring
KW - infrared thermography
KW - optical tomography
KW - X-ray computed
KW - tomography (XCT)
KW - healing
KW - in situ monitoring
Y1 - 2021
U6 - https://doi.org/10.3390/met11071012
SN - 2075-4701
VL - 11
IS - 7
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Kretzschmar, Mirjam E.
A1 - Ashby, Ben
A1 - Fearon, Elizabeth
A1 - Overton, Christopher E.
A1 - Panovska-Griffiths, Jasmina
A1 - Pellis, Lorenzo
A1 - Quaife, Matthew
A1 - Rozhnova, Ganna
A1 - Scarabel, Francesca
A1 - Stage, Helena B.
A1 - Swallow, Ben
A1 - Thompson, Robin N.
A1 - Tildesley, Michael J.
A1 - Villela, Daniel Campos
T1 - Challenges for modelling interventions for future pandemics
JF - Epidemics
N2 - 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.
KW - Mathematical models
KW - Pandemics
KW - Pharmaceutical interventions
KW - Non-pharmaceutical interventions
KW - Policy support
Y1 - 2022
U6 - https://doi.org/10.1016/j.epidem.2022.100546
SN - 1755-4365
SN - 1878-0067
VL - 38
PB - Elsevier
CY - Amsterdam
ER -
TY - JOUR
A1 - Kruse, Marlen
A1 - Altattan, Basma
A1 - Laux, Eva-Maria
A1 - Grasse, Nico
A1 - Heinig, Lars
A1 - Möser, Christin
A1 - Smith, David M.
A1 - Hölzel, Ralph
T1 - Characterization of binding interactions of SARS-CoV-2 spike protein and DNA-peptide nanostructures
JF - Scientific reports
N2 - 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.
Y1 - 2022
U6 - https://doi.org/10.1038/s41598-022-16914-9
SN - 2045-2322
VL - 12
IS - 1
PB - Macmillan Publishers Limited, part of Springer Nature
CY - London
ER -
TY - JOUR
A1 - Codutti, Agnese
A1 - Bente, Klaas
A1 - Faivre, Damien
A1 - Klumpp, Stefan
T1 - Chemotaxis in external fields: Simulations for active magnetic biological matter
JF - PLoS Computational Biology : a new community journal
N2 - 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.
Y1 - 2019
U6 - https://doi.org/10.1371/journal.pcbi.1007548
SN - 1553-734X
SN - 1553-7358
VL - 15
IS - 12
PB - PLoS
CY - San Fransisco
ER -
TY - JOUR
A1 - Alirezaeizanjani, Zahra
A1 - Großmann, Robert
A1 - Pfeifer, Veronika
A1 - Hintsche, Marius
A1 - Beta, Carsten
T1 - Chemotaxis strategies of bacteria with multiple run modes
JF - Science advances
N2 - Bacterial chemotaxis-a fundamental example of directional navigation in the living world-is key to many biological processes, including the spreading of bacterial infections. Many bacterial species were recently reported to exhibit several distinct swimming modes-the flagella may, for example, push the cell body or wrap around it. How do the different run modes shape the chemotaxis strategy of a multimode swimmer? Here, we investigate chemotactic motion of the soil bacterium Pseudomonas putida as a model organism. By simultaneously tracking the position of the cell body and the configuration of its flagella, we demonstrate that individual run modes show different chemotactic responses in nutrition gradients and, thus, constitute distinct behavioral states. On the basis of an active particle model, we demonstrate that switching between multiple run states that differ in their speed and responsiveness provides the basis for robust and efficient chemotaxis in complex natural habitats.
KW - exploit
KW - flagellum
KW - instability
KW - time
Y1 - 2020
U6 - https://doi.org/10.1126/sciadv.aaz6153
SN - 2375-2548
VL - 6
IS - 22
PB - American Association for the Advancement of Science
CY - Washington
ER -
TY - JOUR
A1 - Pikovskij, Arkadij
T1 - Chimeras on a social-type network
JF - Mathematical modelling of natural phenomena : MMNP
N2 - 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.
KW - Network
KW - Chimera
KW - correlations
KW - Lyapunov exponent
Y1 - 2021
U6 - https://doi.org/10.1051/mmnp/2021012
SN - 0973-5348
SN - 1760-6101
VL - 16
PB - EDP Sciences
CY - Les Ulis
ER -
TY - JOUR
A1 - Jones, Chris
A1 - Wiesner, Karoline
T1 - Clarifying how degree entropies and degree-degree correlations relate to network robustness
JF - Entropy : an international and interdisciplinary journal of entropy and information studies
N2 - It is often claimed that the entropy of a network's degree distribution is a proxy for its robustness. Here, we clarify the link between degree distribution entropy and giant component robustness to node removal by showing that the former merely sets a lower bound to the latter for randomly configured networks when no other network characteristics are specified. Furthermore, we show that, for networks of fixed expected degree that follow degree distributions of the same form, the degree distribution entropy is not indicative of robustness. By contrast, we show that the remaining degree entropy and robustness have a positive monotonic relationship and give an analytic expression for the remaining degree entropy of the log-normal distribution. We also show that degree-degree correlations are not by themselves indicative of a network's robustness for real networks. We propose an adjustment to how mutual information is measured which better encapsulates structural properties related to robustness.
KW - complex networks
KW - network robustness
KW - degree distribution entropy;
KW - remaining degree entropy
KW - mutual information of networks
Y1 - 2022
U6 - https://doi.org/10.3390/e24091182
SN - 1099-4300
VL - 24
IS - 9
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Tönjes, Ralf
A1 - Fiore, Carlos E.
A1 - Pereira da Silva, Tiago
T1 - Coherence resonance in influencer networks
JF - Nature Communications
N2 - 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.
Y1 - 2021
U6 - https://doi.org/10.1038/s41467-020-20441-4
SN - 2041-1723
VL - 12
IS - 1
PB - Nature Publishing Group UK
CY - London
ER -
TY - JOUR
A1 - Prol, Fabricio S.
A1 - Smirnov, Artem G.
A1 - Hoque, M. Mainul
A1 - Shprits, Yuri
T1 - Combined model of topside ionosphere and plasmasphere derived from radio-occultation and Van Allen Probes data
JF - Scientific reports
N2 - 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.
Y1 - 2022
U6 - https://doi.org/10.1038/s41598-022-13302-1
SN - 2045-2322
VL - 12
IS - 1
PB - Macmillan Publishers Limited, part of Springer Nature
CY - London
ER -
TY - JOUR
A1 - Wiesner, Karoline
A1 - Ladyman, James
T1 - Complex systems are always correlated but rarely information processing
JF - Journal of physics. Complexity
N2 - '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.
KW - correlations
KW - information theory
KW - complex systems
KW - information
KW - processing
KW - self-organisation
Y1 - 2021
U6 - https://doi.org/10.1088/2632-072X/ac371c
SN - 2632-072X
VL - 2
IS - 4
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Mattern, Maximilian
A1 - Reppert, Alexander von
A1 - Zeuschner, Steffen Peer
A1 - Herzog, Marc
A1 - Pudell, Jan-Etienne
A1 - Bargheer, Matias
T1 - Concepts and use cases for picosecond ultrasonics with x-rays
JF - Photoacoustics
N2 - 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.
KW - Picosecond ultrasonics
KW - Ultrafast x-ray diffraction
KW - Ultrafast x-ray
KW - scattering
KW - Ultrafast photoacoustics
KW - Nanoscale heat transfer
KW - Negative
KW - thermal expansion
Y1 - 2023
U6 - https://doi.org/10.1016/j.pacs.2023.100503
SN - 2213-5979
VL - 31
PB - Elsevier
CY - Amsterdam
ER -
TY - JOUR
A1 - Granado, Felipe Le Vot
A1 - Abad, Enrique
A1 - Metzler, Ralf
A1 - Yuste, Santos B.
T1 - Continuous time random walk in a velocity field
BT - role of domain growth, Galilei-invariant advection-diffusion, and kinetics of particle mixing
JF - New Journal of Physics
N2 - 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 Lévy 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 Lévy 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.
KW - diffusion
KW - expanding medium
KW - continuous time random walk
Y1 - 2020
U6 - https://doi.org/10.1088/1367-2630/ab9ae2
SN - 1367-2630
VL - 22
PB - Dt. Physikalische Ges.
CY - Bad Honnef
ER -
TY - JOUR
A1 - Totz, Sonja Juliana
A1 - Löber, Jakob
A1 - Totz, Jan Frederik
A1 - Engel, Harald
T1 - Control of transversal instabilities in reaction-diffusion systems
JF - New journal of physics : the open-access journal for physics
N2 - 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.
KW - traveling waves
KW - control
KW - transversal instabilities
Y1 - 2018
U6 - https://doi.org/10.1088/1367-2630/aabce5
SN - 1367-2630
VL - 20
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Bouchoule, Isabelle
A1 - Schemmer, Max
A1 - Henkel, Carsten
T1 - Cooling phonon modes of a Bose condensate with uniform few body losses
JF - Scipost Physics
N2 - 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.
Y1 - 2018
U6 - https://doi.org/10.21468/SciPostPhys.5.5.043
SN - 2542-4653
VL - 5
IS - 5
PB - Scipost foundation
CY - Amsterdam
ER -
TY - JOUR
A1 - Lever, Fabiano
A1 - Mayer, Dennis
A1 - Metje, Jan
A1 - Alisauskas, Skirmantas
A1 - Calegari, Francesca
A1 - Düsterer, Stefan
A1 - Feifel, Raimund
A1 - Niebuhr, Mario
A1 - Manschwetus, Bastian
A1 - Kuhlmann, Marion
A1 - Mazza, Tommaso
A1 - Robinson, Matthew Scott
A1 - Squibb, Richard J.
A1 - Trabattoni, Andrea
A1 - Wallner, Måns
A1 - Wolf, Thomas J. A.
A1 - Gühr, Markus
T1 - Core-level spectroscopy of 2-thiouracil at the sulfur L1 and L2,3 edges utilizing a SASE free-electron-laser
JF - Molecules
N2 - 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.
KW - X-ray
KW - photoelectron
KW - sulfur
KW - thiouracil
KW - nucleobases
KW - Coster–Kronig
KW - Auger–Meitner
KW - NEXAFS
KW - FLASH
Y1 - 2021
U6 - https://doi.org/10.3390/molecules26216469
SN - 1420-3049
VL - 26
IS - 21
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Vinke, Kira
A1 - Gabrysch, Sabine
A1 - Paoletti, Emanuela
A1 - Rockström, Johan
A1 - Schellnhuber, Hans Joachim
T1 - Corona and the climate
BT - a comparison of two emergencies
JF - Global sustainability
N2 - Lessons from the corona crisis can help manage the even more daunting challenge of anthropogenic global warming.
KW - adaptation and mitigation
KW - ecology and biodiversity
KW - human behaviour
KW - natural resources (biological and non-biological)
KW - policies
KW - politics
KW - and governance
Y1 - 2020
U6 - https://doi.org/10.1017/sus.2020.20
SN - 2059-4798
VL - 3
PB - Cambridge Univ. Press
CY - Cambridge
ER -
TY - JOUR
A1 - Maiti, Snehanshu
A1 - Makwana, Kirit
A1 - Zhang, Heshou
A1 - Yan, Huirong
T1 - Cosmic-ray transport in magnetohydrodynamic turbulence
JF - The astrophysical journal : an international review of spectroscopy and astronomical physics / part 1
N2 - 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.
Y1 - 2022
U6 - https://doi.org/10.3847/1538-4357/ac46c8
SN - 1538-4357
VL - 926
IS - 1
PB - Institute of Physics Publ.
CY - London
ER -
TY - JOUR
A1 - Saha, Sourav
A1 - Owen, Lewis A.
A1 - Orr, Elizabeth N.
A1 - Caffee, Marc W.
T1 - Cosmogenic Be-10 and equilibrium-line altitude dataset of Holocene glacier advances in the Himalayan-Tibetan orogen
JF - Data in brief
N2 - 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).
KW - Cosmogenic nuclides
KW - Equilibrium-line altitudes
KW - Holocene
KW - Central asia
KW - Glaciation
Y1 - 2019
U6 - https://doi.org/10.1016/j.dib.2019.104412
SN - 2352-3409
VL - 26
PB - Elsevier
CY - Amsterdam
ER -
TY - JOUR
A1 - Kreuzer, Moritz
A1 - Reese, Ronja
A1 - Huiskamp, Willem Nicholas
A1 - Petri, Stefan
A1 - Albrecht, Torsten
A1 - Feulner, Georg
A1 - Winkelmann, Ricarda
T1 - 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
JF - Geoscientific model development : an interactive open access journal of the European Geosciences Union
N2 - 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.
Y1 - 2021
U6 - https://doi.org/10.5194/gmd-14-3697-2021
SN - 1991-959X
SN - 1991-9603
VL - 14
IS - 6
SP - 3697
EP - 3714
PB - Copernicus
CY - Göttingen
ER -
TY - JOUR
A1 - Petrov, Polina
A1 - Singer, Leo P.
A1 - Coughlin, Michael W.
A1 - Kumar, Vishwesh
A1 - Almualla, Mouza
A1 - Anand, Shreya
A1 - Bulla, Mattia
A1 - Dietrich, Tim
A1 - Foucart, Francois
A1 - Guessoum, Nidhal
T1 - Data-driven expectations for electromagnetic counterpart searches based on LIGO/Virgo public alerts
JF - The astrophysical journal : an international review of spectroscopy and astronomical physics; part 1
N2 - 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.
Y1 - 2022
U6 - https://doi.org/10.3847/1538-4357/ac366d
SN - 1538-4357
VL - 924
IS - 2
PB - Institute of Physics Publ.
CY - London
ER -
TY - JOUR
A1 - Oesch, Tyler
A1 - Weise, Frank
A1 - Bruno, Giovanni
T1 - Detection and quantification of cracking in concrete aggregate through virtual data fusion of X-ray computed tomography images
JF - Materials
N2 - 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.
KW - X-ray computed tomography (CT)
KW - concrete
KW - alkali-silica reaction (ASR)
KW - ASR-sensitive aggregate
KW - solubility test
KW - specific surface area
KW - crack
KW - detection
KW - automated image processing
KW - damage quantification
Y1 - 2020
U6 - https://doi.org/10.3390/ma13183921
SN - 1996-1944
VL - 13
IS - 18
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Park, Jaeheung
A1 - Stolle, Claudia
A1 - Yamazaki, Yosuke
A1 - Rauberg, Jan
A1 - Michaelis, Ingo
A1 - Olsen, Nils
T1 - Diagnosing low-/mid-latitude ionospheric currents using platform magnetometers
BT - CryoSat-2 and GRACE-FO
JF - Earth, planets and space
N2 - 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.
KW - Platform magnetometers
KW - CryoSat-2
KW - GRACE-FO
KW - Inter-hemispheric
KW - field-aligned currents
KW - F-region dynamo currents
Y1 - 2020
U6 - https://doi.org/10.1186/s40623-020-01274-3
SN - 1343-8832
SN - 1880-5981
VL - 72
IS - 1
PB - Springer
CY - New York
ER -
TY - JOUR
A1 - Mani, Deepak
A1 - Kupsch, Andreas
A1 - Müller, Bernd R.
A1 - Bruno, Giovanni
T1 - Diffraction Enhanced Imaging Analysis with Pseudo-Voigt Fit Function
JF - Journal of imaging : open access journal
N2 - 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.
KW - diffraction enhanced imaging
KW - analyzer-based imaging
KW - X-ray refraction;
KW - non-destructive evaluation
KW - Pseudo-Voigt fit function
KW - Python
Y1 - 2022
U6 - https://doi.org/10.3390/jimaging8080206
SN - 2313-433X
VL - 8
IS - 8
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Schröder, Jakob
A1 - Evans, Alexander
A1 - Mishurova, Tatiana
A1 - Ulbricht, Alexander
A1 - Sprengel, Maximilian
A1 - Serrano-Munoz, Itziar
A1 - Fritsch, Tobias
A1 - Kromm, Arne
A1 - Kannengießer, Thomas
A1 - Bruno, Giovanni
T1 - Diffraction-based residual stress characterization in laser additive manufacturing of metals
JF - Metals : open access journal
N2 - 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.
KW - laser-based additive manufacturing
KW - residual stress analysis
KW - X-ray and
KW - neutron diffraction
KW - diffraction-elastic constants
KW - strain-free lattice
KW - spacing
Y1 - 2021
U6 - https://doi.org/10.3390/met11111830
SN - 2075-4701
VL - 11
IS - 11
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - van Marle, Allard Jan
A1 - Bohdan, Artem
A1 - Morris, Paul J.
A1 - Pohl, Martin
A1 - Marcowith, Alexandre
T1 - Diffusive shock acceleration at oblique high mach number shocks
JF - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2 - 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.
Y1 - 2022
U6 - https://doi.org/10.3847/1538-4357/ac5962
SN - 1538-4357
VL - 929
IS - 1
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Haverkamp, Robert
A1 - Sorgenfrei, Nomi
A1 - Giangrisostomi, Erika
A1 - Neppl, Stefan
A1 - Kühn, Danilo
A1 - Föhlisch, Alexander
T1 - Directional charge delocalization dynamics in semiconducting 2H-MoS2 and metallic 1T-LixMoS2
JF - Scientific reports
N2 - 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.
Y1 - 2021
U6 - https://doi.org/10.1038/s41598-021-86364-2
SN - 2045-2322
VL - 11
IS - 1
PB - Macmillan Publishers Limited, part of Springer Nature
CY - London
ER -
TY - JOUR
A1 - Kühn, Danilo
A1 - Müller, Moritz
A1 - Sorgenfrei, Nomi
A1 - Giangrisostomi, Erika
A1 - Jay, Raphael Martin
A1 - Ovsyannikov, Ruslan
A1 - Martensson, Nils
A1 - Sanchez-Portal, Daniel
A1 - Föhlisch, Alexander
T1 - Directional sub-femtosecond charge transfer dynamics and the dimensionality of 1T-TaS2
JF - Scientific reports
N2 - For the layered transition metal dichalcogenide 1T-TaS2, we establish through a unique experimental approach and density functional theory, how ultrafast charge transfer in 1T-TaS2 takes on isotropic three-dimensional character or anisotropic two-dimensional character, depending on the commensurability of the charge density wave phases of 1T-TaS2. The X-ray spectroscopic core-hole-clock method prepares selectively in-and out-of-plane polarized sulfur 3p orbital occupation with respect to the 1T-TaS2 planes and monitors sub-femtosecond wave packet delocalization. Despite being a prototypical two-dimensional material, isotropic three-dimensional charge transfer is found in the commensurate charge density wave phase (CCDW), indicating strong coupling between layers. In contrast, anisotropic two-dimensional charge transfer occurs for the nearly commensurate phase (NCDW). In direct comparison, theory shows that interlayer interaction in the CCDW phase - not layer stacking variations - causes isotropic three-dimensional charge transfer. This is presumably a general mechanism for phase transitions and tailored properties of dichalcogenides with charge density waves.
Y1 - 2019
U6 - https://doi.org/10.1038/s41598-018-36637-0
SN - 2045-2322
VL - 9
IS - 488
PB - Nature Publ. Group
CY - London
ER -
TY - JOUR
A1 - Kupfer, Thomas
A1 - Bauer, Evan B.
A1 - van Roestel, Jan
A1 - Bellm, Eric C.
A1 - Bildsten, Lars
A1 - Fuller, Jim
A1 - Prince, Thomas A.
A1 - Heber, Ulrich
A1 - Geier, Stephan
A1 - Green, Matthew J.
A1 - Kulkarni, Shrinivas R.
A1 - Bloemen, Steven
A1 - Laher, Russ R.
A1 - Rusholme, Ben
A1 - Schneider, David
T1 - Discovery of a Double-detonation Thermonuclear Supernova Progenitor
JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters
N2 - We present the discovery of a new double-detonation progenitor system consisting of a hot subdwarf B (sdB) binary with a white dwarf companion with a P (orb) = 76.34179(2) minutes orbital period. Spectroscopic observations are consistent with an sdB star during helium core burning residing on the extreme horizontal branch. Chimera light curves are dominated by ellipsoidal deformation of the sdB star and a weak eclipse of the companion white dwarf. Combining spectroscopic and light curve fits, we find a low-mass sdB star, M (sdB) = 0.383 +/- 0.028 M (circle dot) with a massive white dwarf companion, M (WD) = 0.725 +/- 0.026 M (circle dot). From the eclipses we find a blackbody temperature for the white dwarf of 26,800 K resulting in a cooling age of approximate to 25 Myr whereas our MESA model predicts an sdB age of approximate to 170 Myr. We conclude that the sdB formed first through stable mass transfer followed by a common envelope which led to the formation of the white dwarf companion approximate to 25 Myr ago. Using the MESA stellar evolutionary code we find that the sdB star will start mass transfer in approximate to 6 Myr and in approximate to 60 Myr the white dwarf will reach a total mass of 0.92 M (circle dot) with a thick helium layer of 0.17 M (circle dot). This will lead to a detonation that will likely destroy the white dwarf in a peculiar thermonuclear supernova. PTF1 J2238+7430 is only the second confirmed candidate for a double-detonation thermonuclear supernova. Using both systems we estimate that at least approximate to 1% of white dwarf thermonuclear supernovae originate from sdB+WD binaries with thick helium layers, consistent with the small number of observed peculiar thermonuclear explosions.
Y1 - 2022
U6 - https://doi.org/10.3847/2041-8213/ac48f1
SN - 2041-8205
SN - 2041-8213
VL - 925
IS - 2
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Grebenkov, Denis S.
A1 - Metzler, Ralf
A1 - Oshanin, Gleb
T1 - Distribution of first-reaction times with target regions on boundaries of shell-like domains
JF - New Journal of Physics (NJP)
N2 - We study the probability density function (PDF) of the first-reaction times between a diffusive ligand and a membrane-bound, immobile imperfect target region in a restricted 'onion-shell' geometry bounded by two nested membranes of arbitrary shapes. For such a setting, encountered in diverse molecular signal transduction pathways or in the narrow escape problem with additional steric constraints, we derive an exact spectral form of the PDF, as well as present its approximate form calculated by help of the so-called self-consistent approximation. For a particular case when the nested domains are concentric spheres, we get a fully explicit form of the approximated PDF, assess the accuracy of this approximation, and discuss various facets of the obtained distributions. Our results can be straightforwardly applied to describe the PDF of the terminal reaction event in multi-stage signal transduction processes.
KW - diffusion
KW - first-passage time
KW - first-reaction time
KW - shell-like geometries
KW - approximate methods
Y1 - 2021
U6 - https://doi.org/10.1088/1367-2630/ac4282
SN - 1367-2630
VL - 2021
SP - 1
EP - 23
PB - IOP Publishing
CY - London
ET - 23
ER -
TY - JOUR
A1 - Sarabadani, Jalal
A1 - Metzler, Ralf
A1 - Ala-Nissila, Tapio
T1 - Driven polymer translocation into a channel: Isoflux tension propagation theory and Langevin dynamics simulations
JF - Physical Review Research
N2 - Isoflux tension propagation (IFTP) theory and Langevin dynamics (LD) simulations are employed to study the dynamics of channel-driven polymer translocation in which a polymer translocates into a narrow channel and the monomers in the channel experience a driving force fc. In the high driving force limit, regardless of the channel width, IFTP theory predicts τ ∝ f βc for the translocation time, where β = −1 is the force scaling exponent. Moreover, LD data show that for a very narrow channel fitting only a single file of monomers, the entropic force due to the subchain inside the channel does not play a significant role in the translocation dynamics and the force exponent β = −1 regardless of the force magnitude. As the channel width increases the number of possible spatial configurations of the subchain inside the channel becomes significant and the resulting entropic force causes the force exponent to drop below unity.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevResearch.4.033003
SN - 2643-1564
VL - 4
SP - 033003-1
EP - 033003-14
PB - American Physical Society
CY - College Park, Maryland, USA
ET - 3
ER -
TY - JOUR
A1 - Zeitz, Maria
A1 - Haacker, Jan M.
A1 - Donges, Jonathan
A1 - Albrecht, Torsten
A1 - Winkelmann, Ricarda
T1 - Dynamic regimes of the Greenland Ice Sheet emerging from interacting melt-elevation and glacial isostatic adjustment feedbacks
JF - Earth system dynamics
N2 - The stability of the Greenland Ice Sheet under global warming is governed by a number of dynamic processes and interacting feedback mechanisms in the ice sheet, atmosphere and solid Earth.
Here we study the long-term effects due to the interplay of the competing melt-elevation and glacial isostatic adjustment (GIA) feedbacks for different temperature step forcing experiments with a coupled ice-sheet and solid-Earth model.
Our model results show that for warming levels above 2 degrees C, Greenland could become essentially ice-free within several millennia, mainly as a result of surface melting and acceleration of ice flow. These ice losses are mitigated, however, in some cases with strong GIA feedback even promoting an incomplete recovery of the Greenland ice volume. We further explore the full-factorial parameter space determining the relative strengths of the two feedbacks: our findings suggest distinct dynamic regimes of the Greenland Ice Sheets on the route to destabilization under global warming - from incomplete recovery, via quasi-periodic oscillations in ice volume to ice-sheet collapse.
In the incomplete recovery regime, the initial ice loss due to warming is essentially reversed within 50 000 years, and the ice volume stabilizes at 61 %-93 % of the present-day volume. For certain combinations of temperature increase, atmospheric lapse rate and mantle viscosity, the interaction of the GIA feedback and the melt-elevation feedback leads to self-sustained, long-term oscillations in ice-sheet volume with oscillation periods between 74 000 and over 300 000 years and oscillation amplitudes between 15 %-70 % of present-day ice volume.
This oscillatory regime reveals a possible mode of internal climatic variability in the Earth system on timescales on the order of 100 000 years that may be excited by or synchronized with orbital forcing or interact with glacial cycles and other slow modes of variability. Our findings are not meant as scenario-based near-term projections of ice losses but rather providing insight into of the feedback loops governing the "deep future" and, thus, long-term resilience of the Greenland Ice Sheet.
Y1 - 2022
U6 - https://doi.org/10.5194/esd-13-1077-2022
SN - 2190-4979
SN - 2190-4987
VL - 13
IS - 3
SP - 1077
EP - 1096
PB - Copernicus Publ.
CY - Göttingen
ER -
TY - JOUR
A1 - Mejia-Monasterio, Carlos
A1 - Metzler, Ralf
A1 - Vollmer, Jürgen
T1 - Editorial: anomalous transport
BT - applications, mathematical perspectives, and big data
JF - Frontiers in Physics
KW - anomalous (or non-Fickian) diffusion
KW - anomalous heat conduction
KW - stochastic dynamics
KW - molecular overcrowding
KW - dynamical systems
Y1 - 2020
U6 - https://doi.org/10.3389/fphy.2020.622417
SN - 2296-424X
VL - 8
PB - Frontiers Media
CY - Lausanne
ER -
TY - JOUR
A1 - Varykhalov, Andrei
A1 - Freyse, Friedrich
A1 - Aguilera, Irene
A1 - Battiato, Marco
A1 - Krivenkov, Maxim
A1 - Marchenko, Dmitry
A1 - Bihlmayer, Gustav
A1 - Blugel, Stefan
A1 - Rader, Oliver
A1 - Sanchez-Barriga, Jaime
T1 - Effective mass enhancement and ultrafast electron dynamics of Au(111) surface state coupled to a quantum well
JF - Physical Review Research
N2 - We show that, although the equilibrium band dispersion of the Shockley-type surface state of two-dimensional Au(111) quantum films grown on W(110) does not deviate from the expected free-electron-like behavior, its nonequilibrium energy-momentum dispersion probed by time- and angle-resolved photoemission exhibits a remarkable kink above the Fermi level due to a significant enhancement of the effective mass. The kink is pronounced for certain thicknesses of the Au quantum well and vanishes in the very thin limit. We identify the kink as induced by the coupling between the Au(111) surface state and emergent quantum-well states which probe directly the buried gold-tungsten interface. The signatures of the coupling are further revealed by our time-resolved measurements which show that surface state and quantum-well states thermalize together behaving as dynamically locked electron populations. In particular, relaxation of hot carriers following laser excitation is similar for both surface state and quantum-well states and much slower than expected for a bulk metallic system. The influence of quantum confinement on the interplay between elementary scattering processes of the electrons at the surface and ultrafast carrier transport in the direction perpendicular to the surface is shown to be the reason for the slow electron dynamics.
KW - AG
KW - Flims
Y1 - 2020
U6 - https://doi.org/10.1103/PhysRevResearch.2.013343
SN - 0031-9007
VL - 2
IS - 1
SP - 1
EP - 9
PB - American Physical Society
CY - Ridge, NY
ER -
TY - JOUR
A1 - Vollbrecht, Joachim
A1 - Brus, Viktor V.
T1 - Effects of recombination order on open-circuit voltage decay measurements of organic and perovskite solar cells
JF - Energies : open-access journal of related scientific research, technology development and studies in policy and management / Molecular Diversity Preservation International (MDPI)
N2 - Non-geminate recombination, as one of the most relevant loss mechanisms in organic and perovskite solar cells, deserves special attention in research efforts to further increase device performance. It can be subdivided into first, second, and third order processes, which can be elucidated by the effects that they have on the time-dependent open-circuit voltage decay. In this study, analytical expressions for the open-circuit voltage decay exhibiting one of the aforementioned recombination mechanisms were derived. It was possible to support the analytical models with experimental examples of three different solar cells, each of them dominated either by first (PBDBT:CETIC-4F), second (PM6:Y6), or third (irradiated CH3NH3PbI3) order recombination. Furthermore, a simple approach to estimate the dominant recombination process was also introduced and tested on these examples. Moreover, limitations of the analytical models and the measurement technique itself were discussed.
KW - organic solar cells
KW - perovskite solar cells
KW - non-geminate recombination
KW - recombination order
KW - open-circuit voltage decay
Y1 - 2021
U6 - https://doi.org/10.3390/en14164800
SN - 1996-1073
VL - 14
IS - 16
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Heinsohn, Natascha Katharina
A1 - Niedl, Robert Raimund
A1 - Anielski, Alexander
A1 - Lisdat, Fred
A1 - Beta, Carsten
T1 - Electrophoretic mu PAD for purification and analysis of DNA samples
JF - Biosensors : open access journal
N2 - In this work, the fabrication and characterization of a simple, inexpensive, and effective microfluidic paper analytic device (mu PAD) for monitoring DNA samples is reported. The glass microfiber-based chip has been fabricated by a new wax-based transfer-printing technique and an electrode printing process. It is capable of moving DNA effectively in a time-dependent fashion. The nucleic acid sample is not damaged by this process and is accumulated in front of the anode, but not directly on the electrode. Thus, further DNA processing is feasible. The system allows the DNA to be purified by separating it from other components in sample mixtures such as proteins. Furthermore, it is demonstrated that DNA can be moved through several layers of the glass fiber material. This proof of concept will provide the basis for the development of rapid test systems, e.g., for the detection of pathogens in water samples.
KW - microfluidic paper analytic device (mu PAD)
KW - patterning glass microfiber
KW - fiber-electrophoresis chip
KW - DNA
KW - imprinted electrodes
KW - cross layer chip
KW - polymerase chain reaction (PCR)
KW - purification
Y1 - 2022
U6 - https://doi.org/10.3390/bios12020062
SN - 2079-6374
VL - 12
IS - 2
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Shoaee, Safa
A1 - Sanna, Anna Laura
A1 - Sforazzini, Giuseppe
T1 - Elucidating charge generation in green-solvent processed organic solar cells
JF - Molecules : a journal of synthetic chemistry and natural product chemistry / Molecular Diversity Preservation International
N2 - Organic solar cells have the potential to become the cheapest form of electricity. Rapid increase in the power conversion efficiency of organic solar cells (OSCs) has been achieved with the development of non-fullerene small-molecule acceptors. Next generation photovoltaics based upon environmentally benign "green solvent" processing of organic semiconductors promise a step-change in the adaptability and versatility of solar technologies and promote sustainable development. However, high-performing OSCs are still processed by halogenated (non-environmentally friendly) solvents, so hindering their large-scale manufacture. In this perspective, we discuss the recent progress in developing highly efficient OSCs processed from eco-compatible solvents, and highlight research challenges that should be addressed for the future development of high power conversion efficiencies devices.
KW - organic solar cells
KW - green solvents
KW - non-halogenated solvents
KW - exaction
KW - diffusion
KW - photoluminescence quenching
Y1 - 2021
U6 - https://doi.org/10.3390/molecules26247439
SN - 1420-3049
VL - 26
IS - 24
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Mohammady, M. Hamed
A1 - Auffèves, Alexia
A1 - Anders, Janet
T1 - Energetic footprints of irreversibility in the quantum regime
JF - Communications Physics
N2 - In classical thermodynamic processes the unavoidable presence of irreversibility, quantified by the entropy production, carries two energetic footprints: the reduction of extractable work from the optimal, reversible case, and the generation of a surplus of heat that is irreversibly dissipated to the environment. Recently it has been shown that in the quantum regime an additional quantum irreversibility occurs that is linked to decoherence into the energy basis. Here we employ quantum trajectories to construct distributions for classical heat and quantum heat exchanges, and show that the heat footprint of quantum irreversibility differs markedly from the classical case. We also quantify how quantum irreversibility reduces the amount of work that can be extracted from a state with coherences. Our results show that decoherence leads to both entropic and energetic footprints which both play an important role in the optimization of controlled quantum operations at low temperature.
In classical thermodynamics irreversibility occurs whenever a non-thermal system is brought into contact with a thermal environment. Using quantum trajectories the authors here establish two energetic footprints of quantum irreversible processes, and find that while quantum irreversibility leads to the occurrence of a quantum heat and a reduction of work production, the two are not linked in the same manner as the classical laws of thermodynamics would dictate.
KW - entropy production
KW - quantum mechanics
KW - thermodynamics
Y1 - 2020
U6 - https://doi.org/10.1038/s42005-020-0356-9
SN - 2399-3650
VL - 3
IS - 1
SP - 1
EP - 14
PB - Springer Nature
CY - London
ER -
TY - JOUR
A1 - Mei, Shilin
A1 - Kochovski, Zdravko
A1 - Roa, Rafael
A1 - Gu, Sasa
A1 - Xu, Xiaohui
A1 - Yu, Hongtao
A1 - Dzubiella, Joachim
A1 - Ballauff, Matthias
A1 - Lu, Yan
T1 - Enhanced Catalytic Activity of Gold@Polydopamine Nanoreactors with Multi-compartment Structure Under NIR Irradiation
JF - Nano-Micro Letters
N2 - Photothermal conversion (PTC) nanostructures have great potential for applications in many fields, and therefore, they have attracted tremendous attention. However, the construction of a PTC nanoreactor with multi-compartment structure to achieve the combination of unique chemical properties and structural feature is still challenging due to the synthetic difficulties. Herein, we designed and synthesized a catalytically active, PTC gold (Au)@polydopamine (PDA) nanoreactor driven by infrared irradiation using assembled PS-b-P2VP nanosphere as soft template. The particles exhibit multi-compartment structure which is revealed by 3D electron tomography characterization technique. They feature permeable shells with tunable shell thickness. Full kinetics for the reduction reaction of 4-nitrophenol has been investigated using these particles as nanoreactors and compared with other reported systems. Notably, a remarkable acceleration of the catalytic reaction upon near-infrared irradiation is demonstrated, which reveals for the first time the importance of the synergistic effect of photothermal conversion and complex inner structure to the kinetics of the catalytic reduction. The ease of synthesis and fresh insights into catalysis will promote a new platform for novel nanoreactor studies.
KW - Gold@polydopamine
KW - 3D tomography
KW - Nanoreactor
KW - Catalysis
KW - Photothermal conversion
Y1 - 2019
U6 - https://doi.org/10.1007/s40820-019-0314-9
SN - 2311-6706
SN - 2150-5551
VL - 11
IS - 1
PB - Shanghai JIAO TONG univ press
CY - Shanghai
ER -
TY - JOUR
A1 - Menzel, Ralf
A1 - Heuer, Axel
A1 - Milonni, Peter W.
T1 - Entanglement, Complementarity, and Vacuum Fields in Spontaneous Parametric Down-Conversion
JF - Atoms
N2 - Using two crystals for spontaneous parametric down-conversion in a parallel setup, we observe two-photon interference with high visibility. The high visibility is consistent with complementarity and the absence of which-path information. The observations are explained as the effects of entanglement or equivalently in terms of interfering probability amplitudes and also by the calculation of a second-order field correlation function in the Heisenberg picture. The latter approach brings out explicitly the role of the vacuum fields in the down-conversion at the crystals and in the photon coincidence counting. For comparison, we show that the Hong-Ou-Mandel dip can be explained by the same approach in which the role of the vacuum signal and idler fields, as opposed to entanglement involving vacuum states, is emphasized. We discuss the fundamental limitations of a theory in which these vacuum fields are treated as classical, stochastic fields.
KW - complementarity
KW - vacuum fields
KW - entanglement
KW - Hong-Ou-Mandel effect
KW - spontaneous parametric down-conversion
Y1 - 2019
U6 - https://doi.org/10.3390/atoms7010027
SN - 2218-2004
VL - 7
IS - 1
PB - MDPI
CY - Basel
ER -
TY - GEN
A1 - Lewandowsky, Stephan
A1 - Cowtan, Kevin
A1 - Risbey, James S.
A1 - Mann, Michael E.
A1 - Steinman, Byron A.
A1 - Oreskes, Naomi
A1 - Rahmstorf, Stefan
T1 - Erratum: The 'pause' in global warming in historical context: II. Comparing models to observations (Environmental research letters. - Vol 13, (2018) 123007)
T2 - Environmental research letters
N2 - We review the evidence for a putative early 21st-century divergence between global mean surface temperature (GMST) and Coupled Model Intercomparison Project Phase 5 (CMIP5) projections. We provide a systematic comparison between temperatures and projections using historical versions of GMST products and historical versions of model projections that existed at the times when claims about a divergence were made. The comparisons are conducted with a variety of statistical techniques that correct for problems in previous work, including using continuous trends and a Monte Carlo approach to simulate internal variability. The results show that there is no robust statistical evidence for a divergence between models and observations. The impression of a divergence early in the 21st century was caused by various biases in model interpretation and in the observations, and was unsupported by robust statistics.
Y1 - 2019
U6 - https://doi.org/10.1088/1748-9326/aafbb7
SN - 1748-9326
VL - 14
IS - 4
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Horton, Benjamin P.
A1 - Khan, Nicole S.
A1 - Cahill, Niamh
A1 - Lee, Janice S. H.
A1 - Shaw, Timothy A.
A1 - Garner, Andra J.
A1 - Kemp, Andrew C.
A1 - Engelhart, Simon E.
A1 - Rahmstorf, Stefan
T1 - Estimating global mean sea-level rise and its uncertainties by 2100 and 2300 from an expert survey
JF - npj Climate and Atmospheric Science
N2 - Sea-level rise projections and knowledge of their uncertainties are vital to make informed mitigation and adaptation decisions. To elicit projections from members of the scientific community regarding future global mean sea-level (GMSL) rise, we repeated a survey originally conducted five years ago. Under Representative Concentration Pathway (RCP) 2.6, 106 experts projected a likely (central 66% probability) GMSL rise of 0.30-0.65 m by 2100, and 0.54-2.15 m by 2300, relative to 1986-2005. Under RCP 8.5, the same experts projected a likely GMSL rise of 0.63-1.32 m by 2100, and 1.67-5.61 m by 2300. Expert projections for 2100 are similar to those from the original survey, although the projection for 2300 has extended tails and is higher than the original survey. Experts give a likelihood of 42% (original survey) and 45% (current survey) that under the high-emissions scenario GMSL rise will exceed the upper bound (0.98 m) of the likely range estimated by the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, which is considered to have an exceedance likelihood of 17%. Responses to open-ended questions suggest that the increases in upper-end estimates and uncertainties arose from recent influential studies about the impact of marine ice cliff instability on the meltwater contribution to GMSL rise from the Antarctic Ice Sheet.
KW - projections
KW - Greenland
KW - consequences
KW - climate
Y1 - 2020
U6 - https://doi.org/10.1038/s41612-020-0121-5
SN - 2397-3722
VL - 3
IS - 1
SP - 1
EP - 8
PB - Springer Nature
CY - London
ER -
TY - JOUR
A1 - Laquai, Rene
A1 - Gouraud, Fanny
A1 - Müller, Bernd Randolf
A1 - Huger, Marc
A1 - Chotard, Thierry
A1 - Antou, Guy
A1 - Bruno, Giovanni
T1 - Evolution of Thermal Microcracking in Refractory ZrO2-SiO2 after Application of External Loads at High Temperatures
JF - Materials
N2 - Zirconia-based cast refractories are widely used for glass furnace applications. Since they have to withstand harsh chemical as well as thermo-mechanical environments, internal stresses and microcracking are often present in such materials under operating conditions (sometimes in excess of 1700 °C). We studied the evolution of thermal (CTE) and mechanical (Young’s modulus) properties as a function of temperature in a fused-cast refractory containing 94 wt.% of monoclinic ZrO2 and 6 wt.% of a silicate glassy phase. With the aid of X-ray refraction techniques (yielding the internal specific surface in materials), we also monitored the evolution of microcracking as a function of thermal cycles (crossing the martensitic phase transformation around 1000 °C) under externally applied stress. We found that external compressive stress leads to a strong decrease of the internal surface per unit volume, but a tensile load has a similar (though not so strong) effect. In agreement with existing literature on β-eucryptite microcracked ceramics, we could explain these phenomena by microcrack closure in the load direction in the compression case, and by microcrack propagation (rather than microcrack nucleation) under tensile conditions.
KW - electro-fused zirconia
KW - microcracking
KW - synchrotron x-ray refraction radiography (SXRR)
KW - thermal expansion
Y1 - 2019
U6 - https://doi.org/10.3390/ma12071017
SN - 1996-1944
VL - 12
IS - 7
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Grebenkov, Denis S.
A1 - Sposini, Vittoria
A1 - Metzler, Ralf
A1 - Oshanin, Gleb
A1 - Seno, Flavio
T1 - Exact distributions of the maximum and range of random diffusivity processes
JF - New Journal of Physics
N2 - We study the extremal properties of a stochastic process xt defined by the Langevin equation ẋₜ =√2Dₜ ξₜ, in which ξt is a Gaussian white noise with zero mean and Dₜ is a stochastic‘diffusivity’, defined as a functional of independent Brownian motion Bₜ.We focus on threechoices for the random diffusivity Dₜ: cut-off Brownian motion, Dₜt ∼ Θ(Bₜ), where Θ(x) is the Heaviside step function; geometric Brownian motion, Dₜ ∼ exp(−Bₜ); and a superdiffusive process based on squared Brownian motion, Dₜ ∼ B²ₜ. For these cases we derive exact expressions for the probability density functions of the maximal positive displacement and of the range of the process xₜ on the time interval ₜ ∈ (0, T).We discuss the asymptotic behaviours of the associated probability density functions, compare these against the behaviour of the corresponding properties of standard Brownian motion with constant diffusivity (Dₜ = D0) and also analyse the typical behaviour of the probability density functions which is observed for a majority of realisations of the stochastic diffusivity process.
KW - random diffusivity
KW - extremal values
KW - maximum and range
KW - diffusion
KW - Brownian motion
Y1 - 2021
U6 - https://doi.org/10.1088/1367-2630/abd313
SN - 1367-2630
VL - 23
PB - Dt. Physikalische Ges.
CY - Bad Honnef
ER -
TY - JOUR
A1 - Mishurova, Tatiana
A1 - Artzt, Katia
A1 - Haubrich, Jan
A1 - Requena, Guillermo
A1 - Bruno, Giovanni
T1 - Exploring the correlation between subsurface residual stresses and manufacturing parameters in laser powder bed fused Ti-6Al-4V
JF - Metals
N2 - Subsurface residual stresses (RS) were investigated in Ti-6Al-4V cuboid samples by means of X-ray synchrotron diffraction. The samples were manufactured by laser powder bed fusion (LPBF) applying different processing parameters, not commonly considered in open literature, in order to assess their influence on RS state. While investigating the effect of process parameters used for the calculation of volumetric energy density (such as laser velocity, laser power and hatch distance), we observed that an increase of energy density led to a decrease of RS, although not to the same extent for every parameter variation. Additionally, the effect of support structure, sample roughness and LPBF machine effects potentially coming from Ar flow were studied. We observed no influence of support structure on subsurface RS while the orientation with respect to Ar flow showed to have an impact on RS. We conclude recommending monitoring such parameters to improve part reliability and reproducibility.
KW - residual stress
KW - synchrotron X-ray diffraction
KW - additive manufacturing
KW - Ti-6Al-4V
Y1 - 2019
U6 - https://doi.org/10.3390/met9020261
SN - 2075-4701
VL - 9
IS - 2
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Yan, Xiaoli
A1 - Xue, Zhike
A1 - Jiang, Chaowei
A1 - Priest, E. R.
A1 - Kliem, Bernhard
A1 - Yang, Liheng
A1 - Wang, Jincheng
A1 - Kong, Defang
A1 - Song, Yongliang
A1 - Feng, Xueshang
A1 - Liu, Zhong
T1 - Fast plasmoid-mediated reconnection in a solar flare
JF - Nature Communications
N2 - Magnetic reconnection is a multi-faceted process of energy conversion in astrophysical, space and laboratory plasmas that operates at microscopic scales but has macroscopic drivers and consequences.
Solar flares present a key laboratory for its study, leaving imprints of the microscopic physics in radiation spectra and allowing the macroscopic evolution to be imaged, yet a full observational characterization remains elusive.
Here we combine high resolution imaging and spectral observations of a confined solar flare at multiple wavelengths with data-constrained magnetohydrodynamic modeling to study the dynamics of the flare plasma from the current sheet to the plasmoid scale. The analysis suggests that the flare resulted from the interaction of a twisted magnetic flux rope surrounding a filament with nearby magnetic loops whose feet are anchored in chromospheric fibrils. Bright cusp-shaped structures represent the region around a reconnecting separator or quasi-separator (hyperbolic flux tube).
The fast reconnection, which is relevant for other astrophysical environments, revealed plasmoids in the current sheet and separatrices and associated unresolved turbulent motions.
Solar flares provide wide range of observational details about fundamental processes involved. Here, the authors show evidence for magnetic reconnection in a strong confined solar flare displaying all four reconnection flows with plasmoids in the current sheet and the separatrices.
Y1 - 2022
U6 - https://doi.org/10.1038/s41467-022-28269-w
SN - 2041-1723
VL - 13
IS - 1
PB - Nature Publishing Group UK
CY - London
ER -
TY - JOUR
A1 - Smirnov, Lev A.
A1 - Bolotov, Maxim
A1 - Bolotov, Dmitri
A1 - Osipov, Grigory V.
A1 - Pikovsky, Arkady
T1 - Finite-density-induced motility and turbulence of chimera solitons
JF - New Journal of Physics
N2 - We consider a one-dimensional oscillatory medium with a coupling through a diffusive linear field. In the limit of fast diffusion this setup reduces to the classical Kuramoto–Battogtokh model. We demonstrate that for a finite diffusion stable chimera solitons, namely localized synchronous domain in an infinite asynchronous environment, are possible. The solitons are stable also for finite density of oscillators, but in this case they sway with a nearly constant speed. This finite-density-induced motility disappears in the continuum limit, as the velocity of the solitons is inverse proportional to the density. A long-wave instability of the homogeneous asynchronous state causes soliton turbulence, which appears as a sequence of soliton mergings and creations. As the instability of the asynchronous state becomes stronger, this turbulence develops into a spatio-temporal intermittency.
KW - chimera
KW - soliton
KW - finite-size effects
Y1 - 2022
U6 - https://doi.org/10.1088/1367-2630/ac63d9
SN - 1367-2630
VL - 24
PB - IOP
CY - London
ER -
TY - JOUR
A1 - Palyulin, Vladimir V.
A1 - Blackburn, George
A1 - Lomholt, Michael A.
A1 - Watkins, Nicholas W.
A1 - Metzler, Ralf
A1 - Klages, Rainer
A1 - Chechkin, Aleksei V.
T1 - First passage and first hitting times of Levy flights and Levy walks
JF - New journal of physics : the open-access journal for physics
N2 - For both Lévy flight and Lévy walk search processes we analyse the full distribution of first-passage and first-hitting (or first-arrival) times. These are, respectively, the times when the particle moves across a point at some given distance from its initial position for the first time, or when it lands at a given point for the first time. For Lévy motions with their propensity for long relocation events and thus the possibility to jump across a given point in space without actually hitting it ('leapovers'), these two definitions lead to significantly different results. We study the first-passage and first-hitting time distributions as functions of the Lévy stable index, highlighting the different behaviour for the cases when the first absolute moment of the jump length distribution is finite or infinite. In particular we examine the limits of short and long times. Our results will find their application in the mathematical modelling of random search processes as well as computer algorithms.
KW - Levy flights
KW - Levy walks
KW - first-passage time
KW - first-hitting time
Y1 - 2019
U6 - https://doi.org/10.1088/1367-2630/ab41bb
SN - 1367-2630
VL - 21
IS - 10
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Mutothya, Nicholas Mwilu
A1 - Xu, Yong
A1 - Li, Yongge
A1 - Metzler, Ralf
A1 - Mutua, Nicholas Muthama
T1 - First passage dynamics of stochastic motion in heterogeneous media driven by correlated white Gaussian and coloured non-Gaussian noises
JF - Journal of physics. Complexity
N2 - We study the first passage dynamics for a diffusing particle experiencing a spatially varying diffusion coefficient while driven by correlated additive Gaussian white noise and multiplicative coloured non-Gaussian noise. We consider three functional forms for position dependence of the diffusion coefficient: power-law, exponential, and logarithmic. The coloured non-Gaussian noise is distributed according to Tsallis' q-distribution. Tracks of the non-Markovian systems are numerically simulated by using the fourth-order Runge-Kutta algorithm and the first passage times (FPTs) are recorded. The FPT density is determined along with the mean FPT (MFPT). Effects of the noise intensity and self-correlation of the multiplicative noise, the intensity of the additive noise, the cross-correlation strength, and the non-extensivity parameter on the MFPT are discussed.
KW - first passage
KW - diffusion
KW - non-Gaussian
KW - correlated noise
Y1 - 2021
U6 - https://doi.org/10.1088/2632-072X/ac35b5
SN - 2632-072X
VL - 2
PB - IOP Publishing
CY - Bristol
ER -
TY - JOUR
A1 - García-Benito, Inés
A1 - Quarti, Claudio
A1 - Queloz, Valentin I. E.
A1 - Hofstetter, Yvonne J.
A1 - Becker-Koch, David
A1 - Caprioglio, Pietro
A1 - Neher, Dieter
A1 - Orlandi, Simonetta
A1 - Cavazzini, Marco
A1 - Pozzi, Gianluca
A1 - Even, Jacky
A1 - Nazeeruddin, Mohammad Khaja
A1 - Vaynzof, Yana
A1 - Grancini, Giulia
T1 - Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites
JF - Frontiers in Chemistry
N2 - Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)(2)PbI4 and (Lf)(2)PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors.
KW - fluorinated organic spacer
KW - 2D perovskites
KW - phase transition
KW - temperature dependence
KW - excitonic materials
Y1 - 2020
U6 - https://doi.org/10.3389/fchem.2019.00946
SN - 2296-2646
VL - 7
SP - 1
EP - 11
PB - Frontiers Media
CY - Lausanne
ER -
TY - JOUR
A1 - Omel'chenko, Oleh
A1 - Tél, Tamás
T1 - Focusing on transient chaos
JF - Journal of Physics: Complexity
N2 - Recent advances in the field of complex, transiently chaotic dynamics are reviewed, based on the results published in the focus issue of J. Phys. Complex. on this topic. One group of achievements concerns network dynamics where transient features are intimately related to the degree and stability of synchronization, as well as to the network topology. A plethora of various applications of transient chaos are described, ranging from the collective motion of active particles, through the operation of power grids, cardiac arrhythmias, and magnetohydrodynamical dynamos, to the use of machine learning to predict time evolutions. Nontraditional forms of transient chaos are also explored, such as the temporal change of the chaoticity in the transients (called doubly transient chaos), as well as transients in systems subjected to parameter drift, the paradigm of which is climate change.
KW - transient chaos
KW - network dynamics
KW - applications
KW - doubly transient chaos
KW - systems subjected to parameter drift
Y1 - 2022
U6 - https://doi.org/10.1088/2632-072X/ac5566
SN - 2632-072X
VL - 3
IS - 1
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Mayer, Dennis
A1 - Lever, Fabiano
A1 - Picconi, David
A1 - Metje, Jan
A1 - Ališauskas, Skirmantas
A1 - Calegari, Francesca
A1 - Düsterer, Stefan
A1 - Ehlert, Christopher
A1 - Feifel, Raimund
A1 - Niebuhr, Mario
A1 - Manschwetus, Bastian
A1 - Kuhlmann, Marion
A1 - Mazza, Tommaso
A1 - Robinson, Matthew Scott
A1 - Squibb, Richard James
A1 - Trabattoni, Andrea
A1 - Wallner, Måns
A1 - Saalfrank, Peter
A1 - Wolf, Thomas J. A.
A1 - Gühr, Markus
T1 - Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy
JF - Nature Communications
N2 - The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220–250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states.
Y1 - 2022
U6 - https://doi.org/10.1038/s41467-021-27908-y
SN - 2041-1723
VL - 13
PB - Springer Nature
CY - Berlin
ER -
TY - JOUR
A1 - Woodfield, Emma E.
A1 - Horne, Richard B.
A1 - Glauert, S. A.
A1 - Menietti, J. D.
A1 - Shprits, Yuri
A1 - Kurth, William S.
T1 - Formation of electron radiation belts at Saturn by Z-mode wave acceleration
JF - Nature Communications
N2 - At Saturn electrons are trapped in the planet’s magnetic field and accelerated to relativistic energies to form the radiation belts, but how this dramatic increase in electron energy occurs is still unknown. Until now the mechanism of radial diffusion has been assumed but we show here that in-situ acceleration through wave particle interactions, which initial studies dismissed as ineffectual at Saturn, is in fact a vital part of the energetic particle dynamics there. We present evidence from numerical simulations based on Cassini spacecraft data that a particular plasma wave, known as Z-mode, accelerates electrons to MeV energies inside 4 RS (1 RS = 60,330 km) through a Doppler shifted cyclotron resonant interaction. Our results show that the Z-mode waves observed are not oblique as previously assumed and are much better accelerators than O-mode waves, resulting in an electron energy spectrum that closely approaches observed values without any transport effects included.
Y1 - 2018
U6 - https://doi.org/10.1038/s41467-018-07549-4
SN - 2041-1723
VL - 9
PB - Nature Publ. Group
CY - London
ER -
TY - JOUR
A1 - Moreno, Eduardo
A1 - Großmann, Robert
A1 - Beta, Carsten
A1 - Alonso, Sergio
T1 - From single to collective motion of social amoebae
BT - a computational study of interacting cells
JF - Frontiers in physics
N2 - The coupling of the internal mechanisms of cell polarization to cell shape deformations and subsequent cell crawling poses many interdisciplinary scientific challenges. Several mathematical approaches have been proposed to model the coupling of both processes, where one of the most successful methods relies on a phase field that encodes the morphology of the cell, together with the integration of partial differential equations that account for the polarization mechanism inside the cell domain as defined by the phase field. This approach has been previously employed to model the motion of single cells of the social amoeba Dictyostelium discoideum, a widely used model organism to study actin-driven motility and chemotaxis of eukaryotic cells. Besides single cell motility, Dictyostelium discoideum is also well-known for its collective behavior. Here, we extend the previously introduced model for single cell motility to describe the collective motion of large populations of interacting amoebae by including repulsive interactions between the cells. We performed numerical simulations of this model, first characterizing the motion of single cells in terms of their polarity and velocity vectors. We then systematically studied the collisions between two cells that provided the basic interaction scenarios also observed in larger ensembles of interacting amoebae. Finally, the relevance of the cell density was analyzed, revealing a systematic decrease of the motility with density, associated with the formation of transient cell clusters that emerge in this system even though our model does not include any attractive interactions between cells. This model is a prototypical active matter system for the investigation of the emergent collective dynamics of deformable, self-driven cells with a highly complex, nonlinear coupling of cell shape deformations, self-propulsion and repulsive cell-cell interactions. Understanding these self-organization processes of cells like their autonomous aggregation is of high relevance as collective amoeboid motility is part of wound healing, embryonic morphogenesis or pathological processes like the spreading of metastatic cancer cells.
KW - cell motility
KW - cell polarity
KW - reaction-diffusion models
KW - cell-cell
KW - interactions
KW - phase field model
KW - collective motion
KW - active matter
Y1 - 2022
U6 - https://doi.org/10.3389/fphy.2021.750187
SN - 2296-424X
VL - 9
PB - Frontiers Media
CY - Lausanne
ER -
TY - JOUR
A1 - Grebenkov, Denis S.
A1 - Metzler, Ralf
A1 - Oshanin, Gleb
T1 - From single-particle stochastic kinetics to macroscopic reaction rates
BT - fastest first-passage time of N random walkers
JF - New Journal of Physics
N2 - We consider the first-passage problem for N identical independent particles that are initially released uniformly in a finite domain Ω and then diffuse toward a reactive area Γ, which can be part of the outer boundary of Ω or a reaction centre in the interior of Ω. For both cases of perfect and partial reactions, we obtain the explicit formulas for the first two moments of the fastest first-passage time (fFPT), i.e., the time when the first out of the N particles reacts with Γ. Moreover, we investigate the full probability density of the fFPT. We discuss a significant role of the initial condition in the scaling of the average fFPT with the particle number N, namely, a much stronger dependence (1/N and 1/N² for partially and perfectly reactive targets, respectively), in contrast to the well known inverse-logarithmic behaviour found when all particles are released from the same fixed point. We combine analytic solutions with scaling arguments and stochastic simulations to rationalise our results, which open new perspectives for studying the relevance of multiple searchers in various situations of molecular reactions, in particular, in living cells.
KW - diffusion
KW - first-passage
KW - fastest first-passage time of N walkers
Y1 - 2020
U6 - https://doi.org/10.1088/1367-2630/abb1de
SN - 1367-2630
VL - 22
PB - Dt. Physikalische Ges.
CY - Bad Honnef
ER -
TY - JOUR
A1 - Stojkoski, Viktor
A1 - Sandev, Trifce
A1 - Basnarkov, Lasko
A1 - Kocarev, Ljupco
A1 - Metzler, Ralf
T1 - Generalised geometric Brownian motion
BT - theory and applications to option pricing
JF - Entropy
N2 - Classical option pricing schemes assume that the value of a financial asset follows a geometric Brownian motion (GBM). However, a growing body of studies suggest that a simple GBM trajectory is not an adequate representation for asset dynamics, due to irregularities found when comparing its properties with empirical distributions. As a solution, we investigate a generalisation of GBM where the introduction of a memory kernel critically determines the behaviour of the stochastic process. We find the general expressions for the moments, log-moments, and the expectation of the periodic log returns, and then obtain the corresponding probability density functions using the subordination approach. Particularly, we consider subdiffusive GBM (sGBM), tempered sGBM, a mix of GBM and sGBM, and a mix of sGBMs. We utilise the resulting generalised GBM (gGBM) in order to examine the empirical performance of a selected group of kernels in the pricing of European call options. Our results indicate that the performance of a kernel ultimately depends on the maturity of the option and its moneyness.
KW - geometric Brownian motion
KW - Fokker– Planck equation
KW - Black– Scholes model
KW - option pricing
Y1 - 2020
U6 - https://doi.org/10.3390/e22121432
SN - 1099-4300
VL - 22
IS - 12
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Albrecht, Torsten
A1 - Winkelmann, Ricarda
A1 - Levermann, Anders
T1 - Glacial-cycle simulations of the Antarctic Ice Sheet with the Parallel Ice Sheet Model (PISM)
BT - part 2: parameter ensemble analysis
JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2 - The Parallel Ice Sheet Model (PISM) is applied to the Antarctic Ice Sheet over the last two glacial cycles (approximate to 210 000 years) with a resolution of 16 km. An ensemble of 256 model runs is analyzed in which four relevant model parameters have been systematically varied using full-factorial parameter sampling. Parameters and plausible parameter ranges have been identified in a companion paper (Albrecht et al., 2020) and are associated with ice dynamics, climatic forcing, basal sliding and bed deformation and represent distinct classes of model uncertainties. The model is scored against both modern and geologic data, including reconstructed grounding-line locations, elevation-age data, ice thickness, surface velocities and uplift rates. An aggregated score is computed for each ensemble member that measures the overall model-data misfit, including measurement uncertainty in terms of a Gaussian error model (Briggs and Tarasov, 2013). The statistical method used to analyze the ensemble simulation results follows closely the simple averaging method described in Pollard et al. (2016).
This analysis reveals clusters of best-fit parameter combinations, and hence a likely range of relevant model and boundary parameters, rather than individual best-fit parameters. The ensemble of reconstructed histories of Antarctic Ice Sheet volumes provides a score-weighted likely range of sea-level contributions since the Last Glacial Maximum (LGM) of 9.4 +/- 4.1m (or 6.5 +/- 2.0 x 10(6) km(3)), which is at the upper range of most previous studies. The last deglaciation occurs in all ensemble simulations after around 12 000 years before present and hence after the meltwater pulse 1A (MWP1a). Our ensemble analysis also provides an estimate of parametric uncertainty bounds for the present-day state that can be used for PISM projections of future sea-level contributions from the Antarctic Ice Sheet.
Y1 - 2020
U6 - https://doi.org/10.5194/tc-14-633-2020
SN - 1994-0416
SN - 1994-0424
VL - 14
IS - 2
SP - 633
EP - 656
PB - Copernicus Publ.
CY - Göttingen
ER -
TY - JOUR
A1 - Rikani, Albano
A1 - Schewe, Jacob
T1 - Global bilateral migration projections accounting for diasporas, transit and return flows, and poverty constraints
JF - Demographic research
N2 - BACKGROUND
Anticipating changes in international migration patterns is useful for demographic studies and for designing policies that support the well-being of those involved. Existing forecasting methods do not account for a number of stylized facts that emerge from large-scale migration observations and theories: existing migrant communities - diasporas - act to lower migration costs and thereby provide a mechanism of self-amplification; return migration and transit migration are important components of global migration flows; and poverty constrains emigration.
OBJECTIVE
Here we present hindcasts and future projections of international migration that explicitly account for these nonlinear features.
METHODS
We develop a dynamic model that simulates migration flows by origin, destination, and place of birth. We calibrate the model using recently constructed global datasets of bilateral migration.
RESULTS
We show that the model reproduces past patterns and trends well based only on initial migrant stocks and changes in national incomes. We then project migration flows under future scenarios of global socioeconomic development.
CONCLUSIONS
Different assumptions about income levels and between-country inequality lead to markedly different migration trajectories, with migration flows either converging towards net zero if incomes in presently poor countries catch up with the rest of the world; or remaining high or even rising throughout the 21st century if economic development is slower and more unequal. Importantly, diasporas induce significant inertia and sizable return migration flows.
KW - diaspora
KW - international migration
KW - migration transition
KW - return migration
KW - simulation model
KW - transit migration
Y1 - 2021
U6 - https://doi.org/10.4054/DemRes.2021.45.4
SN - 2363-7064
VL - 45
SP - 87
EP - 140
PB - Max Planck Inst. for Demographic Research
CY - Rostock
ER -
TY - JOUR
A1 - Wunderling, Nico
A1 - Willeit, Matteo
A1 - Donges, Jonathan
A1 - Winkelmann, Ricarda
T1 - Global warming due to loss of large ice masses and Arctic summer sea ice
JF - Nature Communications
N2 - Several large-scale cryosphere elements such as the Arctic summer sea ice, the mountain glaciers, the Greenland and West Antarctic Ice Sheet have changed substantially during the last century due to anthropogenic global warming. However, the impacts of their possible future disintegration on global mean temperature (GMT) and climate feedbacks have not yet been comprehensively evaluated. Here, we quantify this response using an Earth system model of intermediate complexity. Overall, we find a median additional global warming of 0.43 degrees C (interquartile range: 0.39-0.46 degrees C) at a CO2 concentration of 400 ppm. Most of this response (55%) is caused by albedo changes, but lapse rate together with water vapour (30%) and cloud feedbacks (15%) also contribute significantly. While a decay of the ice sheets would occur on centennial to millennial time scales, the Arctic might become ice-free during summer within the 21st century. Our findings imply an additional increase of the GMT on intermediate to long time scales. The disintegration of cryosphere elements such as the Arctic summer sea ice, mountain glaciers, Greenland and West Antarctica is associated with temperature and radiative feedbacks. In this work, the authors quantify these feedbacks and find an additional global warming of 0.43 degrees C.
Y1 - 2020
U6 - https://doi.org/10.1038/s41467-020-18934-3
SN - 2041-1723
VL - 11
IS - 1
PB - Nature Publishing Group
CY - Berlin
ER -
TY - JOUR
A1 - Reese, Ronja
A1 - Winkelmann, Ricarda
A1 - Gudmundsson, Gudmundur Hilmar
T1 - Grounding-line flux formula applied as a flux condition in numerical simulations fails for buttressed Antarctic ice streams
JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2 - Currently, several large-scale ice-flow models impose a condition on ice flux across grounding lines using an analytically motivated parameterisation of grounding-line flux. It has been suggested that employing this analytical expression alleviates the need for highly resolved computational domains around grounding lines of marine ice sheets. While the analytical flux formula is expected to be accurate in an unbuttressed flow-line setting, its validity has hitherto not been assessed for complex and realistic geometries such as those of the Antarctic Ice Sheet. Here the accuracy of this analytical flux formula is tested against an optimised ice flow model that uses a highly resolved computational mesh around the Antarctic grounding lines. We find that when applied to the Antarctic Ice Sheet the analytical expression provides inaccurate estimates of ice fluxes for almost all grounding lines. Furthermore, in many instances direct application of the analytical formula gives rise to unphysical complex-valued ice fluxes. We conclude that grounding lines of the Antarctic Ice Sheet are, in general, too highly buttressed for the analytical parameterisation to be of practical value for the calculation of grounding-line fluxes.
Y1 - 2018
U6 - https://doi.org/10.5194/tc-12-3229-2018
SN - 1994-0416
SN - 1994-0424
VL - 12
IS - 10
SP - 3229
EP - 3242
PB - Copernicus
CY - Göttingen
ER -
TY - JOUR
A1 - Nagel, Oliver
A1 - Frey, Manuel
A1 - Gerhardt, Matthias
A1 - Beta, Carsten
T1 - Harnessing Motile Amoeboid Cells as Trucks for Microtransport and -Assembly
JF - Advanced science
N2 - Cell-driven microtransport is one of the most prominent applications in the emerging field of biohybrid systems. While bacterial cells have been successfully employed to drive the swimming motion of micrometer-sized cargo particles, the transport capacities of motile adherent cells remain largely unexplored. Here, it is demonstrated that motile amoeboid cells can act as efficient and versatile trucks to transport microcargo. When incubated together with microparticles, cells of the social amoeba Dictyostelium discoideum readily pick up and move the cargo particles. Relying on the unspecific adhesive properties of the amoeba, a wide range of different cargo materials can be used. The cell-driven transport can be directionally guided based on the chemotactic responses of amoeba to chemoattractant gradients. On the one hand, the cargo can be assembled into clusters in a self-organized fashion, relying on the developmentally induced chemotactic aggregation of cells. On the other hand, chemoattractant gradients can be externally imposed to guide the cellular microtrucks to a desired location. Finally, larger cargo particles of different shapes that exceed the size of a single cell by more than an order of magnitude, can also be transported by the collective effort of large numbers of motile cells.
KW - biohybrid microsystems
KW - chemotaxis
KW - Dictyostelium discoideum
KW - microtransport and -assembly
Y1 - 2018
U6 - https://doi.org/10.1002/advs.201801242
SN - 2198-3844
VL - 6
IS - 3
PB - Wiley
CY - Hoboken
ER -
TY - JOUR
A1 - Kliem, Bernhard
A1 - Seehafer, Norbert
T1 - Helicity shedding by flux rope ejection
JF - Astronomy and astrophysics : an international weekly journal
N2 - We quantitatively address the conjecture that magnetic helicity must be shed from the Sun by eruptions launching coronal mass ejections in order to limit its accumulation in each hemisphere. By varying the ratio of guide and strapping field and the flux rope twist in a parametric simulation study of flux rope ejection from approximately marginally stable force-free equilibria, different ratios of self- and mutual helicity are set and the onset of the torus or helical kink instability is obtained. The helicity shed is found to vary over a broad range from a minor to a major part of the initial helicity, with self helicity being largely or completely shed and mutual helicity, which makes up the larger part of the initial helicity, being shed only partly. Torus-unstable configurations with subcritical twist and without a guide field shed up to about two-thirds of the initial helicity, while a highly twisted, kink-unstable configuration sheds only about one-quarter. The parametric study also yields stable force-free flux rope equilibria up to a total flux-normalized helicity of 0.25, with a ratio of self- to total helicity of 0.32 and a ratio of flux rope to external poloidal flux of 0.94. These results numerically demonstrate the conjecture of helicity shedding by coronal mass ejections and provide a first account of its parametric dependence. Both self- and mutual helicity are shed significantly; this reduces the total initial helicity by a fraction of ∼0.4--0.65 for typical source region parameters.
KW - instabilities
KW - magnetic fields
KW - magnetohydrodynamics (MHD)
KW - Sun
KW - corona
KW - coronal mass ejections (CMEs)
KW - flares
Y1 - 2022
U6 - https://doi.org/10.1051/0004-6361/202142422
SN - 0004-6361
SN - 1432-0746
VL - 659
PB - EDP Sciences
CY - Les Ulis
ER -
TY - JOUR
A1 - Steppa, Constantin Beverly
A1 - Holch, Tim Lukas
T1 - HexagDLy-Processing hexagonally sampled data with CNNs in PyTorch
JF - SoftwareX
N2 - HexagDLy is a Python-library extending the PyTorch deep learning framework with convolution and pooling operations on hexagonal grids. It aims to ease the access to convolutional neural networks for applications that rely on hexagonally sampled data as, for example, commonly found in ground-based astroparticle physics experiments.
KW - Convolutional neural networks
KW - Hexagonal grid
KW - PyTorch
KW - Astroparticle physics
Y1 - 2019
U6 - https://doi.org/10.1016/j.softx.2019.02.010
SN - 2352-7110
VL - 9
SP - 193
EP - 198
PB - Elsevier
CY - Amsterdam
ER -
TY - JOUR
A1 - Pauzon, Camille
A1 - Mishurova, Tatiana
A1 - Fischer, Marie
A1 - Ahlström, Johan
A1 - Fritsch, Tilman
A1 - Bruno, Giovanni
A1 - Hryha, Eduard
T1 - Impact of contour scanning and helium-rich process gas on performances of Alloy 718 lattices produced by laser powder bed fusion
JF - Materials & Design
N2 - Contour scanning and process gas type are process parameters typically considered achieving second order effects compared to first order factors such as laser power and scanning speed.
The present work highlights that contour scanning is crucial to ensure geometrical accuracy and thereby the high performance under uniaxial compression of complex Alloy 718 lattice structures.
Studies of X-ray computed tomography visualizations of as-built and compression-strained structures reveal the continuous and smooth bending and compression of the walls, and the earlier onset of internal contact appearance in the denser lattices printed with contour. In contrast, the effect of addition of He to the Ar process gas appears to have limited influence on the mechanical response of the lattices and their microstructure as characterized by electron backscattered diffraction.
However, the addition of He proved to significantly enhance the cooling rate and to reduce the amount of the generated spatters as evidenced by in situ monitoring of the process emissions, which is very promising for the process stability and powder reusability during laser powder bed fusion.
KW - additive manufacturing
KW - laser powder bed fusion
KW - gyroid lattice
KW - process atmosphere
KW - Alloy 718
KW - spatters
Y1 - 2022
U6 - https://doi.org/10.1016/j.matdes.2022.110501
SN - 0264-1275
SN - 1873-4197
VL - 215
PB - Elsevier
CY - Oxford
ER -
TY - JOUR
A1 - Schwarze, Martin
A1 - Schellhammer, Karl Sebastian
A1 - Ortstein, Katrin
A1 - Benduhn, Johannes
A1 - Gaul, Christopher
A1 - Hinderhofer, Alexander
A1 - Perdigón-Toro, Lorena
A1 - Scholz, Reinhard
A1 - Kublitski, Jonas
A1 - Roland, Steffen
A1 - Lau, Matthias
A1 - Poelking, Carl
A1 - Andrienko, Denis
A1 - Cuniberti, Gianaurelio
A1 - Schreiber, Frank
A1 - Neher, Dieter
A1 - Vandewal, Koen
A1 - Ortmann, Frank
A1 - Leo, Karl
T1 - Impact of molecular quadrupole moments on the energy levels at organic heterojunctions
JF - Nature Communications
N2 - The functionality of organic semiconductor devices crucially depends on molecular energies, namely the ionisation energy and the electron affinity. Ionisation energy and electron affinity values of thin films are, however, sensitive to film morphology and composition, making their prediction challenging. In a combined experimental and simulation study on zinc-phthalocyanine and its fluorinated derivatives, we show that changes in ionisation energy as a function of molecular orientation in neat films or mixing ratio in blends are proportional to the molecular quadrupole component along the p-p-stacking direction. We apply these findings to organic solar cells and demonstrate how the electrostatic interactions can be tuned to optimise the energy of the charge-transfer state at the donor-acceptor interface and the dissociation barrier for free charge carrier generation. The confirmation of the correlation between interfacial energies and quadrupole moments for other materials indicates its relevance for small molecules and polymers.
Y1 - 2019
U6 - https://doi.org/10.1038/s41467-019-10435-2
SN - 2041-1723
VL - 10
PB - Nature Publ. Group
CY - London
ER -
TY - JOUR
A1 - Zeitz, Maria
A1 - Reese, Ronja
A1 - Beckmann, Johanna
A1 - Krebs-Kanzow, Uta
A1 - Winkelmann, Ricarda
T1 - Impact of the melt-albedo feedback on the future evolution of the Greenland Ice Sheet with PISM-dEBM-simple
JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2 - Surface melting of the Greenland Ice Sheet contributes a large amount to current and future sea level rise. Increased surface melt may lower the reflectivity of the ice sheet surface and thereby increase melt rates: the so-called melt-albedo feedback describes this self-sustaining increase in surface melting. In order to test the effect of the melt-albedo feedback in a prognostic ice sheet model, we implement dEBM-simple, a simplified version of the diurnal Energy Balance Model dEBM, in the Parallel Ice Sheet Model (PISM). The implementation includes a simple representation of the melt-albedo feedback and can thereby replace the positive-degree-day melt scheme. Using PISM-dEBM-simple, we find that this feedback increases ice loss through surface warming by 60 % until 2300 for the high-emission scenario RCP8.5 when compared to a scenario in which the albedo remains constant at its present-day values. With an increase of 90 % compared to a fixed-albedo scenario, the effect is more pronounced for lower surface warming under RCP2.6. Furthermore, assuming an immediate darkening of the ice surface over all summer months, we estimate an upper bound for this effect to be 70 % in the RCP8.5 scenario and a more than 4-fold increase under RCP2.6. With dEBM-simple implemented in PISM, we find that the melt-albedo feedback is an essential contributor to mass loss in dynamic simulations of the Greenland Ice Sheet under future warming.
Y1 - 2021
U6 - https://doi.org/10.5194/tc-15-5739-2021
SN - 1994-0416
SN - 1994-0424
VL - 15
IS - 12
SP - 5739
EP - 5764
PB - Copernicus
CY - Katlenburg-Lindau
ER -
TY - JOUR
A1 - Köhler, Raphael H.
A1 - Handorf, Dörthe
A1 - Jaiser, Ralf
A1 - Dethloff, Klaus
A1 - Zängl, Günther
A1 - Majewski, Detlev
A1 - Rex, Markus
T1 - Improved circulation in the Northern hemisphere by adjusting gravity wave drag parameterizations in seasonal experiments with ICON-NWP
JF - Earth and Space Science : ESS
N2 - The stratosphere is one of the main potential sources for subseasonal to seasonal predictability in midlatitudes in winter. The ability of an atmospheric model to realistically simulate the stratospheric dynamics is essential in order to move forward in the field of seasonal predictions in midlatitudes. Earlier studies with the ICOsahedral Nonhydrostatic atmospheric model (ICON) point out that stratospheric westerlies in ICON are underestimated. This is the first extensive study on the evaluation of Northern Hemisphere stratospheric winter circulation with ICON in numerical weather prediction (NWP) mode. Seasonal experiments with the default setup are able to reproduce the basic climatology of the stratospheric polar vortex. However, westerlies are too weak and major stratospheric warmings too frequent in ICON. Both a reduction of the nonorographic, and a reduction of the orographic gravity wave and wake drag lead to a strengthening of the stratospheric vortex and a bias reduction, in particular in January. However, the effect of the nonorographic gravity wave drag scheme on the stratosphere is stronger. Stratosphere-troposphere coupling is intensified and more realistic due to a reduced gravity wave drag. Furthermore, an adjustment of the subgrid-scale orographic drag parameterization leads to a significant error reduction in the mean sea level pressure. As a result of these findings, we present our current suggested improved setup for seasonal experiments with ICON-NWP.
Plain Language Summary Although seasonal forecasts for midlatitudes have the potential to be highly beneficial to the public sector, they are still characterized by a large amount of uncertainty. Exact simulations of the circulation in the stratosphere can help to improve tropospheric predictability on seasonal time scales. For this reason, we investigate how well the new German atmospheric model is able to simulate the stratospheric circulation. The model reproduces the basic behavior of the Northern Hemisphere stratospheric polar vortex, but the westerly circulation in winter is underestimated. The stratospheric circulation is influenced by gravity waves that exert drag on the flow. These processes are only partly physically represented in the model, but are very important and are hence parameterized. By adjusting the parameterizations for the gravity wave drag, the stratospheric polar vortex is strengthened, thereby yielding a more realistic stratospheric circulation. In addition, the altered parameterizations improve the simulated surface pressure pattern. Based upon this, we present our current suggested improved model setup for seasonal experiments.
Y1 - 2021
U6 - https://doi.org/10.1029/2021EA001676
SN - 2333-5084
VL - 8
IS - 3
PB - American Geophysical Union
CY - Malden, Mass.
ER -
TY - JOUR
A1 - Omarova, Zhansaya
A1 - Yerezhep, Darkhan
A1 - Aldiyarov, Abdurakhman
A1 - Tokmoldin, Nurlan
T1 - In Silico Investigation of the Impact of Hole-Transport Layers on the Performance of CH3NH3SnI3 Perovskite Photovoltaic Cells
JF - Crystals
N2 - Perovskite solar cells represent one of the recent success stories in photovoltaics. The device efficiency has been steadily increasing over the past years, but further work is needed to enhance the performance, for example, through the reduction of defects to prevent carrier recombination. SCAPS-1D simulations were performed to assess efficiency limits and identify approaches to decrease the impact of defects, through the selection of an optimal hole-transport material and a hole-collecting electrode. Particular attention was given to evaluation of the influence of bulk defects within light-absorbing CH3NH3SnI3 layers. In addition, the study demonstrates the influence of interface defects at the TiO2/CH3NH3SnI3 (IL1) and CH3NH3SnI3/HTL (IL2) interfaces across the similar range of defect densities. Finally, the optimal device architecture TiO2/CH3NH3SnI3/Cu2O is proposed for the given absorber layer using the readily available Cu2O hole-transporting material with PCE = 27.95%, FF = 84.05%, V-OC = 1.02 V and J(SC) = 32.60 mA/cm(2), providing optimal performance and enhanced resistance to defects.
KW - perovskite solar cells
KW - CH3NH3SnI3
KW - SCAPS-1D
KW - modeling
KW - HTL
Y1 - 2022
U6 - https://doi.org/10.3390/cryst12050699
SN - 2073-4352
VL - 12
IS - 5
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Gieg, Henrique
A1 - Schianchi, Federico
A1 - Dietrich, Tim
A1 - Ujevic, Maximiliano
T1 - Incorporating a Radiative Hydrodynamics Scheme in the Numerical-Relativity Code BAM
JF - Universe : open access journal
N2 - To study binary neutron star systems and to interpret observational data such as gravitational-wave and kilonova signals, one needs an accurate description of the processes that take place during the final stages of the coalescence, for example, through numerical-relativity simulations. In this work, we present an updated version of the numerical-relativity code BAM in order to incorporate nuclear-theory-based equations of state and a simple description of neutrino interactions through a neutrino leakage scheme. Different test simulations, for stars undergoing a neutrino-induced gravitational collapse and for binary neutron stars systems, validate our new implementation. For the binary neutron stars systems, we show that we can evolve stably and accurately distinct microphysical models employing the different equations of state: SFHo, DD2, and the hyperonic BHB Lambda phi. Overall, our test simulations have good agreement with those reported in the literature.
KW - numerical relativity
KW - binary neutron stars
KW - neutrinos
KW - leakage scheme
Y1 - 2022
U6 - https://doi.org/10.3390/universe8070370
SN - 2218-1997
VL - 8
IS - 7
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Rosenblum, Michael
A1 - Pikovsky, Arkady
T1 - Inferring connectivity of an oscillatory network via the phase dynamics reconstruction
JF - Frontiers in network physiology
N2 - We review an approach for reconstructing oscillatory networks’ undirected and directed connectivity from data. The technique relies on inferring the phase dynamics model. The central assumption is that we observe the outputs of all network nodes. We distinguish between two cases. In the first one, the observed signals represent smooth oscillations, while in the second one, the data are pulse-like and can be viewed as point processes. For the first case, we discuss estimating the true phase from a scalar signal, exploiting the protophase-to-phase transformation. With the phases at hand, pairwise and triplet synchronization indices can characterize the undirected connectivity. Next, we demonstrate how to infer the general form of the coupling functions for two or three oscillators and how to use these functions to quantify the directional links. We proceed with a different treatment of networks with more than three nodes. We discuss the difference between the structural and effective phase connectivity that emerges due to high-order terms in the coupling functions. For the second case of point-process data, we use the instants of spikes to infer the phase dynamics model in the Winfree form directly. This way, we obtain the network’s coupling matrix in the first approximation in the coupling strength.
KW - oscillations
KW - network
KW - connectivity
KW - data analysis
KW - phase reduction
Y1 - 2023
U6 - https://doi.org/10.3389/fnetp.2023.1298228
SN - 2674-0109
VL - 3
PB - Frontiers Media
CY - Lausanne
ER -
TY - JOUR
A1 - Cestnik, Rok
A1 - Mau, Erik T. K.
A1 - Rosenblum, Michael
T1 - Inferring oscillator's phase and amplitude response from a scalar signal exploiting test stimulation
JF - New journal of physics : the open-access journal for physics
N2 - The phase sensitivity curve or phase response curve (PRC) quantifies the oscillator's reaction to stimulation at a specific phase and is a primary characteristic of a self-sustained oscillatory unit.
Knowledge of this curve yields a phase dynamics description of the oscillator for arbitrary weak forcing. Similar, though much less studied characteristic, is the amplitude response that can be defined either using an ad hoc approach to amplitude estimation or via the isostable variables.
Here, we discuss the problem of the phase and amplitude response inference from observations using test stimulation. Although PRC determination for noise-free neuronal-like oscillators perturbed by narrow pulses is a well-known task, the general case remains a challenging problem. Even more challenging is the inference of the amplitude response. This characteristic is crucial, e.g. for controlling the amplitude of the collective mode in a network of interacting units-a task relevant to neuroscience. Here, we compare the performance of different techniques suitable for inferring the phase and amplitude response, particularly with application to macroscopic oscillators. We suggest improvements to these techniques, e.g. demonstrating how to obtain the PRC in case of stimuli of arbitrary shape. Our main result is a novel technique denoted by IPID-1, based on the direct reconstruction of the Winfree equation and the analogous first-order equation for isostable dynamics. The technique works for signals with or without well-pronounced marker events and pulses of arbitrary shape; in particular, we consider charge-balanced pulses typical in neuroscience applications. Moreover, this technique is superior for noisy and high-dimensional systems. Additionally, we describe an error measure that can be computed solely from data and complements any inference technique.
KW - phase response
KW - amplitude response
KW - phase-isostable reduction
KW - inference
Y1 - 2022
U6 - https://doi.org/10.1088/1367-2630/aca70a
SN - 1367-2630
VL - 24
IS - 12
PB - Dt. Physikalische Ges., IOP
CY - Bad Honnef, London
ER -
TY - JOUR
A1 - Cestnik, Rok
A1 - Rosenblum, Michael
T1 - Inferring the phase response curve from observation of a continuously perturbed oscillator
JF - Scientific reports
N2 - Phase response curves are important for analysis and modeling of oscillatory dynamics in various applications, particularly in neuroscience. Standard experimental technique for determining them requires isolation of the system and application of a specifically designed input. However, isolation is not always feasible and we are compelled to observe the system in its natural environment under free-running conditions. To that end we propose an approach relying only on passive observations of the system and its input. We illustrate it with simulation results of an oscillator driven by a stochastic force.
Y1 - 2018
U6 - https://doi.org/10.1038/s41598-018-32069-y
SN - 2045-2322
VL - 8
PB - Nature Publ. Group
CY - London
ER -
TY - JOUR
A1 - Raman Venkatesan, Thulasinath
A1 - Gulyakova, Anna A.
A1 - Gerhard, Reimund
T1 - Influence of film stretching on crystalline phases and dielectric properties of a 70/30 mol% poly(vinylidenefluoride-tetrafluoroethylene) copolymer
JF - Journal of advanced dielectrics
N2 - Polyvinylidene fluoride (PVDF)-based copolymers with tetrafluoroethylene (P(VDF-TFE)), trifluoroethylene (P(VDF-TrFE)) or hexafluoropropylene (P(VDF-HFP)) are of strong interest due to the underlying fundamental mechanisms and the potential ferro-, pyro- and piezo-electrical applications. Their flexibility and their adaptability to various shapes are advantageous in comparison to inorganic ferroelectrics. Here, we study the influence of stretching temperature on the crystalline phases and the dielectric properties in P(VDF-TFE) films by means of Dielectric Relaxation Spectroscopy (DRS), Fourier-Transform InfraRed spectroscopy (FTIR), Wide-Angle X-ray Diffraction (WAXD), Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). Especially, the effect of stretching and the influence of the temperature of stretching on the mid-temperature (T-mid) transition are studied in detail. The results show that stretching has a similar effect as that on PVDF, and we observe an increase in the fraction of ferroelectric beta-phase with a simultaneous increment in both melting point (T-m) and crystallinity (chi(c)) of the copolymer. While an increase in the stretching temperature does not have a profound impact on the amount of ferroelectric phase, the stability of the ferroelectric phase seems to improve - as seen in the reduction of the Full Width at Half Maximum (FWHM) of the WAXD peaks in both parallel and perpendicular directions to the molecular chain axis. The observation is also supported by the reduction of dissipation losses with an increase in stretching temperature - as seen in DRS measurements. Finally, both stretching itself and the temperature of stretching affect the various molecular processes taking place in the temperature range of the T-mid transition.
KW - P(VDF-TFE) copolymer
KW - dielectric properties
KW - crystalline phases
KW - film
KW - stretching
KW - mid-temperature transition
Y1 - 2020
U6 - https://doi.org/10.1142/S2010135X2050023X
SN - 2010-135X
SN - 2010-1368
VL - 10
IS - 5
PB - World Scientific
CY - Singapore
ER -
TY - JOUR
A1 - Seroussi, Helene
A1 - Nowicki, Sophie
A1 - Simon, Erika
A1 - Abe-Ouchi, Ayako
A1 - Albrecht, Torsten
A1 - Brondex, Julien
A1 - Cornford, Stephen
A1 - Dumas, Christophe
A1 - Gillet-Chaulet, Fabien
A1 - Goelzer, Heiko
A1 - Golledge, Nicholas R.
A1 - Gregory, Jonathan M.
A1 - Greve, Ralf
A1 - Hoffman, Matthew J.
A1 - Humbert, Angelika
A1 - Huybrechts, Philippe
A1 - Kleiner, Thomas
A1 - Larourl, Eric
A1 - Leguy, Gunter
A1 - Lipscomb, William H.
A1 - Lowry, Daniel
A1 - Mengel, Matthias
A1 - Morlighem, Mathieu
A1 - Pattyn, Frank
A1 - Payne, Anthony J.
A1 - Pollard, David
A1 - Price, Stephen F.
A1 - Quiquet, Aurelien
A1 - Reerink, Thomas J.
A1 - Reese, Ronja
A1 - Rodehacke, Christian B.
A1 - Schlegel, Nicole-Jeanne
A1 - Shepherd, Andrew
A1 - Sun, Sainan
A1 - Sutter, Johannes
A1 - Van Breedam, Jonas
A1 - van de Wal, Roderik S. W.
A1 - Winkelmann, Ricarda
A1 - Zhang, Tong
T1 - initMIP-Antarctica
BT - an ice sheet model initialization experiment of ISMIP6
JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2 - Ice sheet numerical modeling is an important tool to estimate the dynamic contribution of the Antarctic ice sheet to sea level rise over the coming centuries. The influence of initial conditions on ice sheet model simulations, however, is still unclear. To better understand this influence, an initial state intercomparison exercise (initMIP) has been developed to compare, evaluate, and improve initialization procedures and estimate their impact on century-scale simulations. initMlP is the first set of experiments of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), which is the primary Coupled Model Intercomparison Project Phase 6 (CMIP6) activity focusing on the Greenland and Antarctic ice sheets. Following initMlP-Greenland, initMlP-Antarctica has been designed to explore uncertainties associated with model initialization and spin-up and to evaluate the impact of changes in external forcings. Starting from the state of the Antarctic ice sheet at the end of the initialization procedure, three forward experiments are each run for 100 years: a control run, a run with a surface mass balance anomaly, and a run with a basal melting anomaly beneath floating ice. This study presents the results of initMlP-Antarctica from 25 simulations performed by 16 international modeling groups. The submitted results use different initial conditions and initialization methods, as well as ice flow model parameters and reference external forcings. We find a good agreement among model responses to the surface mass balance anomaly but large variations in responses to the basal melting anomaly. These variations can be attributed to differences in the extent of ice shelves and their upstream tributaries, the numerical treatment of grounding line, and the initial ocean conditions applied, suggesting that ongoing efforts to better represent ice shelves in continental-scale models should continue.
Y1 - 2019
U6 - https://doi.org/10.5194/tc-13-1441-2019
SN - 1994-0416
SN - 1994-0424
VL - 13
IS - 5
SP - 1441
EP - 1471
PB - Copernicus
CY - Göttingen
ER -
TY - JOUR
A1 - Hsu, H. F.
A1 - Krekhov, Andrey
A1 - Tarantola, Marco
A1 - Beta, Carsten
A1 - Bodenschatz, Eberhardt
T1 - Interplay between myosin II and actin dynamics in chemotactic amoeba
JF - New journal of physics : the open-access journal for physics
N2 - The actin cytoskeleton and its response to external chemical stimuli is fundamental to the mechano-biology of eukaryotic cells and their functions. One of the key players that governs the dynamics of the actin network is the motor protein myosin II. Based on a phase space embedding we have identified from experiments three phases in the cytoskeletal dynamics of starved Dictyostelium discoideum in response to a precisely controlled chemotactic stimulation. In the first two phases the dynamics of actin and myosin II in the cortex is uncoupled, while in the third phase the time scale for the recovery of cortical actin is determined by the myosin II dynamics. We report a theoretical model that captures the experimental observations quantitatively. The model predicts an increase in the optimal response time of actin with decreasing myosin II-actin coupling strength highlighting the role of myosin II in the robust control of cell contraction.
KW - actin
KW - myosin II
KW - chemotaxis
KW - oscillations
KW - coupling
KW - delay differential equation
KW - contraction
Y1 - 2019
U6 - https://doi.org/10.1088/1367-2630/ab5822
SN - 1367-2630
VL - 21
IS - 11
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Teichmann, Erik
A1 - Lewandowski, Heather J.
A1 - Alemani, Micol
T1 - Investigating students’ views of experimental physics in German laboratory classes
JF - Physical Review Physics Education Research
N2 - There is a large variety of goals instructors have for laboratory courses, with different courses focusing on different subsets of goals. An often implicit, but crucial, goal is to develop students’ attitudes, views, and expectations about experimental physics to align with practicing experimental physicists. The assessment of laboratory courses upon this one dimension of learning has been intensively studied in U.S. institutions using the Colorado Learning Attitudes about Science Survey for Experimental Physics (E-CLASS). However, there is no such an instrument available to use in Germany, and the influence of laboratory courses on students views about the nature of experimental physics is still unexplored at German-speaking institutions. Motivated by the lack of an assessment tool to investigate this goal in laboratory courses at German-speaking institutions, we present a translated version of the E-CLASS adapted to the context at German-speaking institutions. We call the German version of the E-CLASS, the GE-CLASS. We describe the translation process and the creation of an automated web-based system for instructors to assess their laboratory courses. We also present first results using GE-CLASS obtained at the University of Potsdam. A first comparison between E-CLASS and GE-CLASS results shows clear differences between University of Potsdam and U.S. students’ views and beliefs about experimental physics.
Y1 - 2022
U6 - https://doi.org/10.1103/PhysRevPhysEducRes.18.010135
SN - 1554-9178
VL - 18
SP - 010135-1
EP - 010135-17
PB - APS
CY - College Park, Maryland, United States
ET - 1
ER -