TY - JOUR A1 - Cai, Gaochao A1 - Tötzke, Christian A1 - Kaestner, Anders A1 - Ahmed, Mutez Ali T1 - Quantification of root water uptake and redistribution using neutron imaging: a review and future directions JF - The plant journal N2 - Quantifying root water uptake is essential to understanding plant water use and responses to different environmental conditions. However, non-destructive measurement of water transport and related hydraulics in the soil-root system remains a challenge. Neutron imaging, with its high sensitivity to hydrogen, has become an unparalleled tool to visualize and quantify root water uptake in vivo. In combination with isotopes (e.g., deuterated water) and a diffusion-convection model, root water uptake and hydraulic redistribution in root and soil can be quantified. Here, we review recent advances in utilizing neutron imaging to visualize and quantify root water uptake, hydraulic redistribution in roots and soil, and root hydraulic properties of different plant species. Under uniform soil moisture distributions, neutron radiographic studies have shown that water uptake was not uniform along the root and depended on both root type and age. For both tap (e.g., lupine [Lupinus albus L.]) and fibrous (e.g., maize [Zea mays L.]) root systems, water was mainly taken up through lateral roots. In mature maize, the location of water uptake shifted from seminal roots and their laterals to crown/nodal roots and their laterals. Under non-uniform soil moisture distributions, part of the water taken up during the daytime maintained the growth of crown/nodal roots in the upper, drier soil layers. Ultra-fast neutron tomography provides new insights into 3D water movement in soil and roots. We discuss the limitations of using neutron imaging and propose future directions to utilize neutron imaging to advance our understanding of root water uptake and soil-root interactions. KW - attenuation coefficient KW - convection KW - diffusion KW - radiography KW - root hydraulics KW - root water uptake KW - tomography Y1 - 2022 U6 - https://doi.org/10.1111/tpj.15839 SN - 0960-7412 SN - 1365-313X VL - 111 IS - 2 SP - 348 EP - 359 PB - Wiley-Blackwell CY - Oxford [u.a.] 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 - Hennig, Theresa A1 - Kühn, Michael T1 - Potential uranium migration within the geochemical gradient of the opalinus clay system at the Mont Terri JF - Minerals N2 - Transport properties of potential host rocks for nuclear waste disposal are typically determined in laboratory or in-situ experiments under geochemically controlled and constant conditions. Such a homogeneous assumption is no longer applicable on the host rock scale as can be seen from the pore water profiles of the potential host rock Opalinus Clay at Mont Terri (Switzerland). The embedding aquifers are the hydro-geological boundaries, that established gradients in the 210 m thick low permeable section through diffusive exchange over millions of years. Present-day pore water profiles were confirmed by a data-driven as well as by a conceptual scenario. Based on the modelled profiles, the influence of the geochemical gradient on uranium migration was quantified by comparing the distances after one million years with results of common homogeneous models. Considering the heterogeneous system, uranium migrated up to 24 m farther through the formation depending on the source term position within the gradient and on the partial pressure of carbon dioxide pCO2 of the system. Migration lengths were almost equal for single- and multicomponent diffusion. Differences can predominantly be attributed to changes in the sorption capacity, whereby pCO2 governs how strong uranium migration is affected by the geochemical gradient. Thus, the governing parameters for uranium migration in the Opalinus Clay can be ordered in descending priority: pCO2, geochemical gradients, mineralogical heterogeneity.

KW - PHREEQC KW - reactive transport KW - sorption KW - diffusion KW - repository far-field KW - hydro-geological system Y1 - 2021 U6 - https://doi.org/10.3390/min11101087 SN - 2075-163X VL - 11 IS - 10 PB - MDPI CY - Basel ER - TY - JOUR A1 - Doerries, Timo J. A1 - Chechkin, Aleksei V. A1 - Metzler, Ralf T1 - Apparent anomalous diffusion and non-Gaussian distributions in a simple mobile-immobile transport model with Poissonian switching JF - Interface : journal of the Royal Society N2 - We analyse mobile-immobile transport of particles that switch between the mobile and immobile phases with finite rates. Despite this seemingly simple assumption of Poissonian switching, we unveil a rich transport dynamics including significant transient anomalous diffusion and non-Gaussian displacement distributions. Our discussion is based on experimental parameters for tau proteins in neuronal cells, but the results obtained here are expected to be of relevance for a broad class of processes in complex systems. Specifically, we obtain that, when the mean binding time is significantly longer than the mean mobile time, transient anomalous diffusion is observed at short and intermediate time scales, with a strong dependence on the fraction of initially mobile and immobile particles. We unveil a Laplace distribution of particle displacements at relevant intermediate time scales. For any initial fraction of mobile particles, the respective mean squared displacement (MSD) displays a plateau. Moreover, we demonstrate a short-time cubic time dependence of the MSD for immobile tracers when initially all particles are immobile. KW - diffusion KW - mobile-immobile model KW - tau proteins Y1 - 2022 U6 - https://doi.org/10.1098/rsif.2022.0233 SN - 1742-5689 SN - 1742-5662 VL - 19 IS - 192 PB - Royal Society CY - London 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 - Mutothya, Nicholas Mwilu A1 - Xu, Yong A1 - Li, Yongge A1 - Metzler, Ralf T1 - Characterising stochastic motion in heterogeneous media driven by coloured non-Gaussian noise JF - Journal of physics : A, Mathematical and theoretical N2 - We study the stochastic motion of a test particle in a heterogeneous medium in terms of a position dependent diffusion coefficient mimicking measured deterministic diffusivity gradients in biological cells or the inherent heterogeneity of geophysical systems. Compared to previous studies we here investigate the effect of the interplay of anomalous diffusion effected by position dependent diffusion coefficients and coloured non-Gaussian noise. The latter is chosen to be distributed according to Tsallis' q-distribution, representing a popular example for a non-extensive statistic. We obtain the ensemble and time averaged mean squared displacements for this generalised process and establish its non-ergodic properties as well as analyse the non-Gaussian nature of the associated displacement distribution. We consider both non-stratified and stratified environments. KW - diffusion KW - anomalous diffusion KW - non-extensive statistics KW - coloured KW - noise KW - heterogeneous diffusion process Y1 - 2021 U6 - https://doi.org/10.1088/1751-8121/abfba6 SN - 1751-8113 SN - 1751-8121 VL - 54 IS - 29 PB - IOP Publ. Ltd. CY - Bristol 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 - Singh, Rishu Kumar A1 - Metzler, Ralf A1 - Sandev, Trifce T1 - Resetting dynamics in a confining potential JF - Journal of physics : A, Mathematical and theoretical N2 - We study Brownian motion in a confining potential under a constant-rate resetting to a reset position x(0). The relaxation of this system to the steady-state exhibits a dynamic phase transition, and is achieved in a light cone region which grows linearly with time. When an absorbing boundary is introduced, effecting a symmetry breaking of the system, we find that resetting aids the barrier escape only when the particle starts on the same side as the barrier with respect to the origin. We find that the optimal resetting rate exhibits a continuous phase transition with critical exponent of unity. Exact expressions are derived for the mean escape time, the second moment, and the coefficient of variation (CV). KW - diffusion KW - resetting KW - barrier escape KW - first-passage Y1 - 2020 U6 - https://doi.org/10.1088/1751-8121/abc83a SN - 1751-8113 SN - 1751-8121 VL - 53 IS - 50 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Dunsing, Valentin A1 - Petrich, Annett A1 - Chiantia, Salvatore T1 - Multicolor fluorescence fluctuation spectroscopy in living cells via spectral detection JF - eLife N2 - Signaling pathways in biological systems rely on specific interactions between multiple biomolecules. Fluorescence fluctuation spectroscopy provides a powerful toolbox to quantify such interactions directly in living cells. Cross-correlation analysis of spectrally separated fluctuations provides information about intermolecular interactions but is usually limited to two fluorophore species. Here, we present scanning fluorescence spectral correlation spectroscopy (SFSCS), a versatile approach that can be implemented on commercial confocal microscopes, allowing the investigation of interactions between multiple protein species at the plasma membrane. We demonstrate that SFSCS enables cross-talk-free cross-correlation, diffusion, and oligomerization analysis of up to four protein species labeled with strongly overlapping fluorophores. As an example, we investigate the interactions of influenza A virus (IAV) matrix protein 2 with two cellular host factors simultaneously. We furthermore apply raster spectral image correlation spectroscopy for the simultaneous analysis of up to four species and determine the stoichiometry of ternary IAV polymerase complexes in the cell nucleus. KW - fluorescence KW - optical microscopy KW - virus assembly KW - protein-protein KW - interactions KW - diffusion KW - Viruses Y1 - 2021 U6 - https://doi.org/10.7554/eLife.69687 SN - 2050-084X VL - 10 PB - eLife Sciences Publications CY - Cambridge ER - TY - JOUR A1 - Xu, Pengbo A1 - Zhou, Tian A1 - Metzler, Ralf A1 - Deng, Weihua T1 - Stochastic harmonic trapping of a Lévy walk BT - transport and first-passage dynamics under soft resetting strategies JF - New journal of physics : the open-access journal for physics / Deutsche Physikalische Gesellschaft ; IOP, Institute of Physics N2 - We introduce and study a Lévy walk (LW) model of particle spreading with a finite propagation speed combined with soft resets, stochastically occurring periods in which an harmonic external potential is switched on and forces the particle towards a specific position. Soft resets avoid instantaneous relocation of particles that in certain physical settings may be considered unphysical. Moreover, soft resets do not have a specific resetting point but lead the particle towards a resetting point by a restoring Hookean force. Depending on the exact choice for the LW waiting time density and the probability density of the periods when the harmonic potential is switched on, we demonstrate a rich emerging response behaviour including ballistic motion and superdiffusion. When the confinement periods of the soft-reset events are dominant, we observe a particle localisation with an associated non-equilibrium steady state. In this case the stationary particle probability density function turns out to acquire multimodal states. Our derivations are based on Markov chain ideas and LWs with multiple internal states, an approach that may be useful and flexible for the investigation of other generalised random walks with soft and hard resets. The spreading efficiency of soft-rest LWs is characterised by the first-passage time statistic. KW - diffusion KW - anomalous diffusion KW - stochastic resetting KW - Levy walks Y1 - 2022 U6 - https://doi.org/10.1088/1367-2630/ac5282 SN - 1367-2630 VL - 24 IS - 3 SP - 1 EP - 28 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef 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 - Grätz, Fabio M. A1 - Seiss, Martin A1 - Spahn, Frank T1 - Formation of moon-induced gaps in dense planetary rings BT - application to the rings of saturn JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We develop an axisymmetric diffusion model to describe radial density profiles in the vicinity of tiny moons embedded in planetary rings. Our diffusion model accounts for the gravitational scattering of the ring particles by an embedded moon and for the viscous diffusion of the ring matter back into the gap. With test particle simulations, we show that the scattering of the ring particles passing the moon is larger for small impact parameters than estimated by Goldreich & Tremaine and Namouni. This is significant for modeling the Keeler gap. We apply our model to the gaps of the moons Pan and Daphnis embedded in the outer A ring of Saturn with the aim to estimate the shear viscosity of the ring in the vicinity of the Encke and Keeler gap. In addition, we analyze whether tiny icy moons whose dimensions lie below Cassini's resolution capabilities would be able to explain the gap structure of the C ring and the Cassini division. KW - diffusion KW - planets and satellites: rings KW - scattering Y1 - 2018 U6 - https://doi.org/10.3847/1538-4357/aace00 SN - 0004-637X SN - 1538-4357 VL - 862 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 - Seiß, Martin A1 - Albers, Nicole A1 - Sremčević, Miodrag A1 - Schmidt, Jürgen A1 - Salo, Heikki A1 - Seiler, Michael A1 - Hoffmann, Holger A1 - Spahn, Frank T1 - Hydrodynamic Simulations of Moonlet-induced Propellers in Saturn's Rings BT - Application to Bleriot JF - The astronomical journal N2 - One of the biggest successes of the Cassini mission is the detection of small moons (moonlets) embedded in Saturns rings that cause S-shaped density structures in their close vicinity, called propellers. Here, we present isothermal hydrodynamic simulations of moonlet-induced propellers in Saturn's A ring that denote a further development of the original model. We find excellent agreement between these new hydrodynamic and corresponding N-body simulations. Furthermore, the hydrodynamic simulations confirm the predicted scaling laws and the analytical solution for the density in the propeller gaps. Finally, this mean field approach allows us to simulate the pattern of the giant propeller Blériot, which is too large to be modeled by direct N-body simulations. Our results are compared to two stellar occultation observations by the Cassini Ultraviolet Imaging Spectrometer (UVIS), which intersect the propeller Blériot. Best fits to the UVIS optical depth profiles are achieved for a Hill radius of 590 m, which implies a moonlet diameter of about 860 m. Furthermore, the model favors a kinematic shear viscosity of the surrounding ring material of ν0 = 340 cm2 s−1, a dispersion velocity in the range of 0.3 cm s−1 < c0 < 1.5 cm s−1, and a fairly high bulk viscosity 7 < ξ0/ν0 < 17. These large transport values might be overestimated by our isothermal ring model and should be reviewed by an extended model including thermal fluctuations. KW - diffusion KW - hydrodynamics KW - planets and satellites: rings Y1 - 2018 U6 - https://doi.org/10.3847/1538-3881/aaed44 SN - 0004-6256 SN - 1538-3881 VL - 157 IS - 1 PB - IOP Publishing Ltd. CY - Bristol ER - TY - JOUR A1 - Abdalla, Hassan E. A1 - Aharonian, Felix A. A1 - Benkhali, F. Ait A1 - Angüner, Ekrem Oǧuzhan A1 - Arakawa, M. A1 - Arcaro, C. A1 - Armand, C. A1 - Arrieta, M. A1 - Backes, M. A1 - Barnard, M. A1 - Becherini, Y. A1 - Tjus, J. Becker A1 - Berge, D. A1 - Bernloehr, K. A1 - Blackwell, R. A1 - Bottcher, M. A1 - Boisson, C. A1 - Bolmont, J. A1 - Bonnefoy, S. A1 - Bordas, Pol A1 - Bregeon, J. A1 - Brun, F. A1 - Brun, P. A1 - Bryan, M. A1 - Buechele, M. A1 - Bulik, T. A1 - Bylund, T. A1 - Capasso, M. A1 - Caroff, S. A1 - Carosi, A. A1 - Casanova, Sabrina A1 - Cerruti, M. A1 - Chakraborty, N. A1 - Chand, T. A1 - Chandra, S. A1 - Chaves, R. C. G. A1 - Chen, A. A1 - Colafrancesco, S. A1 - Condon, B. A1 - Davids, I. D. A1 - Deil, C. A1 - Devin, J. A1 - deWilt, P. A1 - Dirson, L. A1 - Djannati-Atai, A. A1 - Dmytriiev, A. A1 - Donath, A. A1 - Doroshenko, V A1 - Dyks, J. A1 - Egberts, Kathrin A1 - Emery, G. A1 - Ernenwein, J-P A1 - Eschbach, S. A1 - Fegan, S. A1 - Fiasson, A. A1 - Fontaine, G. A1 - Funk, S. A1 - Fuessling, M. A1 - Gabici, S. A1 - Gallant, Y. A. A1 - Gate, F. A1 - Giavitto, G. A1 - Glawion, D. A1 - Glicenstein, J. F. A1 - Gottschall, D. A1 - Grondin, M-H A1 - Hahn, J. A1 - Haupt, M. A1 - Heinzelmann, G. A1 - Henri, G. A1 - Hermann, G. A1 - Hinton, James Anthony A1 - Hofmann, W. A1 - Hoischen, Clemens A1 - Holch, Tim Lukas A1 - Holler, M. A1 - Horns, D. A1 - Huber, D. A1 - Iwasaki, H. A1 - Jacholkowska, A. A1 - Jamrozy, M. A1 - Jankowsky, D. A1 - Jankowsky, F. A1 - Jouvin, L. A1 - Jung-Richardt, I A1 - Kastendieck, M. A. A1 - Katarzynski, K. A1 - Katsuragawa, M. A1 - Katz, U. A1 - Kerszberg, D. A1 - Khangulyan, D. A1 - Khelifi, B. A1 - King, J. A1 - Klepser, S. A1 - Kluzniak, W. A1 - Komin, Nu A1 - Kosack, K. A1 - Kraus, M. A1 - Lamanna, G. A1 - Lau, J. A1 - Lefaucheur, J. A1 - Lemiere, A. A1 - Lemoine-Goumard, M. A1 - Lenain, J-P A1 - Leser, Eva A1 - Lohse, T. A1 - Lopez-Coto, R. A1 - Lypova, I A1 - Malyshev, D. A1 - Marandon, V A1 - Marcowith, Alexandre A1 - Mariaud, C. A1 - Marti-Devesa, G. A1 - Marx, R. A1 - Maurin, G. A1 - Meintjes, P. J. A1 - Mitchell, A. M. W. A1 - Moderski, R. A1 - Mohamed, M. A1 - Mohrmann, L. A1 - Moore, C. A1 - Moulin, Emmanuel A1 - Murach, T. A1 - Nakashima, S. A1 - de Naurois, M. A1 - Ndiyavala, H. A1 - Niederwanger, F. A1 - Niemiec, J. A1 - Oakes, L. A1 - Odaka, H. A1 - Ohm, S. A1 - Ostrowski, M. A1 - Oya, I A1 - Panter, M. A1 - Parsons, R. D. A1 - Perennes, C. A1 - Petrucci, P-O A1 - Peyaud, B. A1 - Piel, Q. A1 - Pita, S. A1 - Poireau, V A1 - Noel, A. Priyana A1 - Prokhorov, D. A. A1 - Prokoph, H. A1 - Puehlhofer, G. A1 - Punch, M. A1 - Quirrenbach, A. A1 - Raab, S. A1 - Rauth, R. A1 - Reimer, A. A1 - Reimer, O. A1 - Renaud, M. A1 - Rieger, F. A1 - Rinchiuso, L. A1 - Romoli, C. A1 - Rowell, G. A1 - Rudak, B. A1 - Ruiz-Velasco, E. A1 - Sahakian, V A1 - Saito, S. A1 - Sanchez, David M. A1 - Santangelo, A. A1 - Sasaki, M. A1 - Schlickeiser, R. A1 - Schussler, F. A1 - Schulz, A. A1 - Schutte, H. A1 - Schwanke, U. A1 - Schwemmer, S. A1 - Seglar-Arroyo, M. A1 - Senniappan, M. A1 - Seyffert, A. S. A1 - Shafi, N. A1 - Shilon, I A1 - Shiningayamwe, K. A1 - Simoni, R. A1 - Sinha, A. A1 - Sol, H. A1 - Specovius, A. A1 - Spir-Jacob, M. A1 - Stawarz, L. A1 - Steenkamp, R. A1 - Stegmann, Christian A1 - Steppa, Constantin Beverly A1 - Takahashi, T. A1 - Tavernet, J-P A1 - Tavernier, T. A1 - Taylor, A. M. A1 - Terrier, R. A1 - Tibaldo, L. A1 - Tiziani, D. A1 - Tluczykont, M. A1 - Trichard, C. A1 - Tsirou, M. A1 - Tsuji, N. A1 - Tuffs, R. A1 - Uchiyama, Y. A1 - van der Walt, D. J. A1 - van Eldik, C. A1 - van Rensburg, C. A1 - van Soelen, B. A1 - Vasileiadis, G. A1 - Veh, J. A1 - Venter, C. A1 - Vincent, P. A1 - Vink, J. A1 - Voisin, F. A1 - Voelk, H. J. A1 - Vuillaume, T. A1 - Wadiasingh, Z. A1 - Wagner, S. J. A1 - Wagner, R. M. A1 - White, R. A1 - Wierzcholska, A. A1 - Yang, R. A1 - Yoneda, H. A1 - Zaborov, D. A1 - Zacharias, M. A1 - Zanin, R. A1 - Zdziarski, A. A. A1 - Zech, Alraune A1 - Zefi, F. A1 - Ziegler, A. A1 - Zorn, J. A1 - Zywucka, N. T1 - Particle transport within the pulsar wind nebula HESS J1825-137 JF - Astronomy and astrophysics : an international weekly journal N2 - Context. We present a detailed view of the pulsar wind nebula (PWN) HESS J1825-137. We aim to constrain the mechanisms dominating the particle transport within the nebula, accounting for its anomalously large size and spectral characteristics. Aims. The nebula was studied using a deep exposure from over 12 years of H.E.S.S. I operation, together with data from H.E.S.S. II that improve the low-energy sensitivity. Enhanced energy-dependent morphological and spatially resolved spectral analyses probe the very high energy (VHE, E > 0.1 TeV) gamma-ray properties of the nebula. Methods. The nebula emission is revealed to extend out to 1.5 degrees from the pulsar, similar to 1.5 times farther than previously seen, making HESS J1825-137, with an intrinsic diameter of similar to 100 pc, potentially the largest gamma-ray PWN currently known. Characterising the strongly energy-dependent morphology of the nebula enables us to constrain the particle transport mechanisms. A dependence of the nebula extent with energy of R proportional to E alpha with alpha = -0.29 +/- 0.04(stat) +/- 0.05(sys) disfavours a pure diffusion scenario for particle transport within the nebula. The total gamma-ray flux of the nebula above 1 TeV is found to be (1.12 +/- 0.03(stat) +/- 0.25(sys)) +/- 10(-11) cm(-2) s(-1), corresponding to similar to 64% of the flux of the Crab nebula. Results. HESS J1825-137 is a PWN with clearly energy-dependent morphology at VHE gamma-ray energies. This source is used as a laboratory to investigate particle transport within intermediate-age PWNe. Based on deep observations of this highly spatially extended PWN, we produce a spectral map of the region that provides insights into the spectral variation within the nebula. KW - gamma rays: general KW - acceleration of particles KW - convection KW - diffusion KW - pulsars: general Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201834335 SN - 1432-0746 VL - 621 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Sposini, Vittoria A1 - Chechkin, Aleksei V. A1 - Metzler, Ralf T1 - First passage statistics for diffusing diffusivity JF - Journal of physics : A, Mathematical and theoretical N2 - A rapidly increasing number of systems is identified in which the stochastic motion of tracer particles follows the Brownian law < r(2)(t)> similar or equal to Dt yet the distribution of particle displacements is strongly non-Gaussian. A central approach to describe this effect is the diffusing diffusivity (DD) model in which the diffusion coefficient itself is a stochastic quantity, mimicking heterogeneities of the environment encountered by the tracer particle on its path. We here quantify in terms of analytical and numerical approaches the first passage behaviour of the DD model. We observe significant modifications compared to Brownian-Gaussian diffusion, in particular that the DD model may have a faster first passage dynamics. Moreover we find a universal crossover point of the survival probability independent of the initial condition. KW - diffusion KW - superstatistics KW - first passage Y1 - 2018 U6 - https://doi.org/10.1088/1751-8121/aaf6ff SN - 1751-8113 SN - 1751-8121 VL - 52 IS - 4 PB - IOP Publ. Ltd. CY - Bristol 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 - Grätz, Fabio M. A1 - Seiß, Martin A1 - Schmidt, Jürgen A1 - Colwell, Joshua A1 - Spahn, Frank T1 - Sharp Gap Edges in Dense Planetary Rings BT - an Axisymmetric Diffusion Model JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - One of the most intriguing facets of Saturn's rings are the sharp edges of gaps in the rings where the surface density abruptly drops to zero. This is despite of the fact that the range over which a moon transfers angular momentum onto the ring material is much larger. Recent UVIS-scans of the edges of the Encke and Keeler gap show that this drop occurs over a range approximately equal to the rings' thickness. Borderies et al. show that this striking feature is likely related to the local reversal of the usually outward directed viscous transport of angular momentum in strongly perturbed regions. In this article we revise the Borderies et al. model using a granular flow model to define the shear and bulk viscosities, ν and ζ, and incorporate the angular momentum flux reversal effect into the axisymmetric diffusion model we developed for gaps in dense planetary rings. Finally, we apply our model to the Encke and Keeler division in order to estimate the shear and bulk viscosities in the vicinity of both gaps KW - celestial mechanics KW - diffusion KW - hydrodynamics KW - planets and satellites: rings KW - scattering Y1 - 2019 U6 - https://doi.org/10.3847/1538-4357/ab007e SN - 0004-637X SN - 1538-4357 VL - 872 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Thapa, Samudrajit A1 - Wyłomańska, Agnieszka A1 - Sikora, Grzegorz A1 - Wagner, Caroline E. A1 - Krapf, Diego A1 - Kantz, Holger A1 - Chechkin, Aleksei V. A1 - Metzler, Ralf T1 - Leveraging large-deviation statistics to decipher the stochastic properties of measured trajectories JF - New Journal of Physics N2 - Extensive time-series encoding the position of particles such as viruses, vesicles, or individualproteins are routinely garnered insingle-particle tracking experiments or supercomputing studies.They contain vital clues on how viruses spread or drugs may be delivered in biological cells.Similar time-series are being recorded of stock values in financial markets and of climate data.Such time-series are most typically evaluated in terms of time-averaged mean-squareddisplacements (TAMSDs), which remain random variables for finite measurement times. Theirstatistical properties are different for differentphysical stochastic processes, thus allowing us toextract valuable information on the stochastic process itself. To exploit the full potential of thestatistical information encoded in measured time-series we here propose an easy-to-implementand computationally inexpensive new methodology, based on deviations of the TAMSD from itsensemble average counterpart. Specifically, we use the upper bound of these deviations forBrownian motion (BM) to check the applicability of this approach to simulated and real data sets.By comparing the probability of deviations fordifferent data sets, we demonstrate how thetheoretical bound for BM reveals additional information about observed stochastic processes. Weapply the large-deviation method to data sets of tracer beads tracked in aqueous solution, tracerbeads measured in mucin hydrogels, and of geographic surface temperature anomalies. Ouranalysis shows how the large-deviation properties can be efficiently used as a simple yet effectiveroutine test to reject the BM hypothesis and unveil relevant information on statistical propertiessuch as ergodicity breaking and short-time correlations. KW - diffusion KW - anomalous diffusion KW - large-deviation statistic KW - time-averaged mean squared displacement KW - Chebyshev inequality Y1 - 2020 U6 - https://doi.org/10.1088/1367-2630/abd50e SN - 1367-2630 VL - 23 PB - Dt. Physikalische Ges. ; IOP CY - Bad Honnef ; London ER - TY - JOUR A1 - Pohlenz, Philipp A1 - Niedermeier, Frank T1 - The Bologna Process and the harmonisation of higher education systems in other world regions BT - a case from Southeast Asia JF - Innovation : the European journal of social sciences N2 - The Bologna Process has inspired harmonisation strategies for higher education systems in other parts of the world. However, developments in other contexts are not much under review in the European debate. The present article describes the case of Southeast Asia and the attempt to promote harmonisation of its higher education systems. It further compares the processes in ASEAN and the European Higher Education Area to then discuss open questions for future comparative research. To do so the authors re-contextualise data from a study in ASEAN against the background of future research needs in the field of higher education harmonisation. KW - ASEAN KW - Bologna Process KW - European Higher Education Area KW - higher education KW - quality assurance KW - harmonisation KW - regionalisation KW - diffusion KW - mobility Y1 - 2019 U6 - https://doi.org/10.1080/13511610.2019.1637248 SN - 1351-1610 SN - 1469-8412 VL - 32 IS - 4 SP - 481 EP - 494 PB - Routledge, Taylor & Francis Group CY - Abingdon ER -